Patent Publication Number: US-6703164-B2

Title: Hydrogen-absorbing alloy, secondary battery, hybrid car and electromobile

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Division of Ser. No. 09/475,037 filed Dec. 30, 1999 now U.S. Pat. No. 6,268,084 which is a Continuation-in-Part application of U.S. patent application Ser. No. 09/200,464, filed Nov. 27, 1998, now U.S. Pat. No. 6,248,475 the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a hydrogen-absorbing alloy, a secondary battery comprising a negative electrode containing the hydrogen-absorbing alloy, a hybrid car equipped with a secondary battery comprising a negative electrode containing the hydrogen-absorbing alloy, and an electromobile equipped with the aforementioned secondary battery. 
     Hydrogen-absorbing alloy has been noticed as being capable of safely and easily storing hydrogen as an energy source, and also as being useful as an energy exchange material or an energy storage material. Therefore, there have being proposed various applications of hydrogen-absorbing alloy as a new functional material. For example, hydrogen-absorbing alloy has been proposed to employ for the storage and transport of hydrogen, the storage and transport of heat, the conversion of heat energy to mechanical energy, the separation and purification of hydrogen, the separation of hydrogen isotope, a battery employing hydrogen as an active material, a catalyst in synthetic chemistry, and a temperature sensor. 
     Particularly, the application of a secondary battery which is capable of reversibly absorbing and desorbing hydrogen to the negative electrode of a secondary battery is extensively studied. In fact, some of secondary batteries of this kind are put to practical use. By the way, a secondary battery has been employed as a power source for various kinds of portable electronic apparatus of small size and light weight. These portable electronic apparatuses are now being increasingly enhanced in the performance, function and miniaturization thereof, so that in order to enable these portable electronic apparatuses to be operable for a long period of time, the discharge capacity per unit volume of the secondary battery is required to be increased. Additionally, it is also desired in recent years to make the secondary battery more light in weight, i.e. to increase the discharge capacity per unit weight of the secondary battery in addition to increasing the discharge capacity per unit volume thereof. 
     A rare earth element-based hydrogen-absorbing alloy of AB 5  type is capable of reacting with hydrogen at the normal temperature and pressure, and is relatively excellent in chemical stability, so that this rare earth element-based hydrogen-absorbing alloy of AB 5  type is now extensively studied as a prospective hydrogen-absorbing alloy for the secondary battery, and is actually put to practical use for a negative electrode of the secondary battery available on the market. However, the discharge capacity of this secondary battery placed on the market and provided with the negative electrode containing this AB 5  type rare earth element-based hydrogen-absorbing alloy now reaches to as high as 80% or more of the theoretical capacity, so that any further increase in discharge capacity would be difficult. 
     By the way, there are a large number of the rare earth element-Ni based intermetallic compounds other than the aforementioned AB 5  type rare earth element-based intermetallic compound. For example, Mat. Res. Bull., 11, (1976) 1241 describes that an intermetallic compound containing a larger quantity of rare earth element as compared with the AB 5  type compound is capable of absorbing a larger quantity of hydrogen in the vicinity of room temperature as compared with the AB 5  type compound. Further, with respect to the system wherein the A-site is constituted by a mixture comprising a rare earth element and Mg, there are known a couple of publications as explained below. 
     Namely, J. Less-Common Metals, 73, (1980) 339 discloses a hydrogen-absorbing alloy having a composition represented by La 1-x Mg x Ni 2 . However, this hydrogen-absorbing alloy is accompanied with a problem that due to its high stability in relative to hydrogen, hydrogen can be hardly released therefrom, thus making it difficult to fully desorb hydrogen at the occasion of discharging the secondary battery. On the other hand, there is also a report on a hydrogen-absorbing alloy having a composition of LaMg 2 Ni 9  (a summary of lecture in the 120th Spring Meeting of Japan Institute of Metals, p.289 (1997). However, this hydrogen-absorbing alloy is accompanied with a problem that the degree of hydrogen absorption is relatively low. 
     Japanese Patent Unexamined Publication S/62-271348 discloses a hydrogen absorption electrode comprising a hydrogen-absorbing alloy represented by a general formula Mm 1-x A x Ni a Co b M c , while Japanese Patent Unexamined Publication S/62-271349 discloses a hydrogen absorption electrode comprising a hydrogen-absorbing alloy represented by a general formula La 1-x A x Ni a Co b M c . 
     However, a metal oxide-hydrogen secondary battery provided with any one of these hydrogen absorption electrodes is accompanied with a problem that it is low in discharge capacity and short in charge/discharge cycle life. 
     Further, International Re-publication No. WO97/03213 and U.S. Pat. No. 5,840,166 disclose a hydrogen-absorbing electrode comprising a hydrogen-absorbing alloy having a specific antiphase boundary and a composition represented by the following general formula (i). This hydrogen-absorbing alloy is said as having a crystal structure consisting of LaNi 5 , i.e. CaCu 5  type single-phase. 
     
       
         (R 1-x L x )(Ni 1-y L y ) z   (i) 
       
     
     wherein R is at least one element selected from La, Ce, Pr and Nd; L is at least one element selected from Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, Mg and Ca; M is at least one element selected from Co, Al, Mn, Fe, Cu, Zr, Ti, Mo, Si, V, Cr, Nb, Hf, Ta, W, B and C; and x, y and z are respectively a number satisfying the conditions of: 0.05≦x≦0.4, 0≦y≦0.5, 0≦z&lt;4.5. 
     This hydrogen-absorbing alloy is manufactured by allowing a melt of the alloy represented by the general formula (i) to drop on the surface of a roll having a surface roughness of 30 to 150 μm in mean maximum height Rmax, whereby cooling and solidifying the melt under cooling conditions: 50 to 500° C. in supercooling degree and 1,000 to 10,000° C./sec. in cooling rate, thus obtaining flakes having a thickness of 0.1 to 2.0 mm, which is then heat-treated. This publication also mentions that if the aforementioned manufacturing conditions are not met, the resultant alloy may have two phases, i.e. a LaNi 5  type phase and a Ce 2 Ni 7  type phase, and hence it is impossible to obtain an alloy constituted by LaNi 5  type single phase. 
     However, a secondary battery equipped with a negative electrode comprising a hydrogen-absorbing alloy having a CaCu 5  type crystal structure, a specific antiphase boundary and a composition represented by the aforementioned general formula (i) is accompanied with problems that it is low in discharge capacity and short in charge/discharge cycle life. 
     Additionally, Japanese Patent Unexamined Publication H/11-29832 discloses a hydrogen-absorbing material represented by the following general formula (ii) and having a hexagonal system wherein a space group is P6  3 /mmc, i.e. a Ce 2 Ni 7  type crystal structure. 
     
       
         (R 1-X A X ) 2 (Ni 7-Y-Z-α-β Mn Y Nb Z B α C β ) n   (ii) 
       
     
     wherein R is a rare earth element or a misch metal (Mm); A is at least one element selected from Mg, Ti, Zr, Th, Hf, Si and Ca; B is at least one element selected from Al and Cu; C is at least one element selected from Ga, Ge, In, Sn, Sb, Tl, Pb and Bi; and X, Y, Z, α, β and n are respectively a number satisfying the conditions of: 0&lt;X≦0.3, 0.3≦Y≦1.5, 0&lt;Z≦0.3, 0≦α≦1.0, 0≦β≦1.0, and 0.9≦n≦1.1. 
     In this hydrogen-absorbing alloy having a composition represented by the above formula (ii), the atomic ratio of Mn/(R+A) is in the range of 0.135 to 0.825. 
     However, since this hydrogen-absorbing alloy is poor in the reversibility of absorption/desorption reaction, the degree of hydrogen absorption and desorption is relatively low. Accordingly, a secondary battery equipped with a negative electrode comprising this hydrogen-absorbing alloy is accompanied with problems that the reversibility of absorption/desorption reaction is poor and the discharge voltage is also low, so that the discharge capacity thereof would be reduced. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a hydrogen-absorbing alloy, which is capable of overcoming the problem of prior art that the desorption of hydrogen is suppressed due to an excessively high stability in relative to hydrogen in a hydrogen-absorbing alloy having a composition wherein the A-site is included in a relatively large ratio as compared with the composition of the AB 5  type hydrogen-absorbing alloy; also capable of overcoming the problem of prior art that the hydrogen-absorbing alloy is vulnerable to corrosion and oxidation by the effect of an alkaline electrolyte; and capable of exhibiting an improved hydrogen absorption/desorption property. 
     Another object of the present invention is to provide a secondary battery which is large in capacity and excellent in charge/discharge cycles. 
     A further object of this invention is to provide a hybrid car and an electromobile, which are excellent in traveling performance such as fuel consumption, etc. 
     Namely, according to the present invention, there is provided a hydrogen-absorbing alloy comprising, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu 5  type crystal structure) and a second phase having a rhombohedral crystal system, the hydrogen-absorbing alloy having a composition represented by the following general formula (1): 
     
       
         R 1-a-b Mg a T b Ni Z-X-Y-α M1 X M2 Y Mn α   (1) 
       
     
     wherein R is at least one kind of element selected from rare earth elements (which include Y); T is at least one element selected from the group consisting of Ca, Ti, Zr and Hf; M1 is at least one element selectedfrom the group consisting of Co and Fe; M2 is at least one element selected from the group consisting of Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, Li, P and S; and the atomic ratios of a, b, X, Y, α and Z are respectively a number satisfying the conditions of: 0.15≦a≦0.37, 0≦b≦0.3, 0≦X≦1.3, 0≦Y≦0.5, 0≦α≦0.135, and 2.5≦Z≦4.2. 
     According to the present invention, there is also provided a secondary battery which comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; 
     wherein the hydrogen-absorbing alloy comprises, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu 5  type crystal structure) and a second phase having a rhombohedral crystal system; and the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (1). 
     According to the present invention, there is also provided a hybrid car comprising an electric driving means, and a power source for the electric driving means; 
     wherein the power source comprises a secondary battery which comprises a positive electrode, a negative electrode containing a hydrogen-absorbing alloy, and an alkaline electrolyte; and 
     wherein the hydrogen-absorbing alloy comprises, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu 5  type crystal structure) and a second phase having a rhombohedral crystal system; and the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (1). 
     According to the present invention, there is also provided an electromobile comprising a secondary battery as a driving power source; 
     wherein the secondary battery comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; and 
     wherein the hydrogen-absorbing alloy comprises, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu 5  type crystal structure) and a second phase having a rhombohedral crystal system; and the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (1). 
     Further, according to the present invention, there is provided a hydrogen-absorbing alloy exhibiting less than 0.15 (including 0) in intensity ratio to be calculated according to the following formula (2) and having a composition represented by the following general formula (3): 
     
       
         I 1 /I 2   (2) 
       
     
     wherein I 2  is an intensity of a peak exhibiting a highest intensity in an X-ray diffraction using CuKα-ray; and I 1  is an intensity of a peak exhibiting a highest intensity within 2θ of 8 to 13°, θ being Bragg angle, in the X-ray diffraction; 
     
       
         R 1-a-b Mg a T b Ni Z-X M3 X   (3) 
       
     
     wherein R is at least one kind of element selected from rare earth elements (which include Y); T is at least one element selected from the group consisting of Ca, Ti, Zr and Hf; M3 is at least one element selected from the group consisting of Co, Mn, Fe, Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, Li, P and S; and the atomic ratios of a, b, X and Z are respectively a number satisfying the conditions of: 0.1≦a≦0.6, 0≦b≦0.3, 0≦X≦2, and 2.5≦Z≦4. 
     According to the present invention, there is also provided a secondary battery which comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; 
     wherein the hydrogen-absorbing alloy exhibits less than 0.15 (including 0) in intensity ratio to be calculated according to the aforementioned formula (2) and has a composition represented by the aforementioned general formula (3). 
     According to the present invention, there is also provided a hybrid car comprising an electric driving means, and a power source for the electric driving means; 
     wherein the power source comprises a secondary battery which comprises a positive electrode, a negative electrode containing a hydrogen-absorbing alloy, and an alkaline electrolyte; and 
     wherein the hydrogen-absorbing alloy exhibits less than 0.15 (including 0) in intensity ratio to be calculated according to the aforementioned formula (2) and has a composition represented by the aforementioned general formula (3). 
     According to the present invention, there is also provided an electromobile comprising a secondary battery as a driving power source; 
     wherein the secondary battery comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; and 
     wherein the hydrogen-absorbing alloy exhibits less than 0.15 (including 0) in intensity ratio to be calculated according to the aforementioned formula (2) and has a composition represented by the aforementioned general formula (3). 
     Furthermore, according to the present invention, there is provided a hydrogen-absorbing alloy having a composition represented by the following general formula (4): 
     
       
         R 1-a Mg a Ni Z-X-Y Al X Co Y M4 α   (4) 
       
     
     wherein R is at least one kind of element selected from rare earth elements (which include Y) with a proviso that the content of Ce in the R is less than 20% by weight (including 0% by weight); M4 is at least one element selected from the group consisting of Mn, Fe, Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Ti, Zr, In, Mo, V, Cr, P and S; and the atomic ratios of a, X, Y, Z and α are respectively a number satisfying the conditions of: 0.15≦a≦0.33, 0.06≦X≦0.15, 0≦Y≦0.2, 3.15&lt;Z≦3.55, and 0≦α&lt;0.135. 
     According to the present invention, there is also provided a secondary battery which comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; 
     wherein the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (4). 
     According to the present invention, there is also provided a hybrid car comprising an electric driving means, and a power source for the electric driving means; 
     wherein the power source comprises a secondary battery which comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; and 
     wherein the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (4). 
     According to the present invention, there is also provided an electromobile comprising a secondary battery as a driving power source; 
     wherein the secondary battery comprises a positive electrode, a negative electrode comprising a hydrogen-absorbing alloy, and an alkaline electrolyte; and 
     wherein the hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (4). 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a partially sectioned perspective view showing a cylindrical nickel-hydrogen secondary battery representing one embodiment of an alkaline secondary battery of this invention; 
     FIG. 2 is a cross-sectional view showing a spiral type electrode group; 
     FIG. 3 is a chart as obtained in an X-ray diffraction analysis using CuKα-ray on the hydrogen-absorbing alloy contained in the negative electrode of nickel-hydrogen secondary battery according to Example 1; 
     FIG. 4 is a cross-sectional view of a battery internal pressure-measuring apparatus employed in Examples of this invention; 
     FIG. 5 is a graph illustrating a relationship between the quantity P(g) of the hydrogen-absorbing alloy per theoretical capacity 1 Ah of the positive electrode and the quantity Q(mL) of the alkaline electrolyte per theoretical capacity lAh of the positive electrode in the nickel-hydrogen secondary batteries according to Examples 1 to 25 and Comparative Examples 1 to 12; 
     FIG. 6 is a chart showing an X-ray diffraction pattern which was obtained using CuKα-ray on the examples of the hydrogen-absorbing alloy according to this invention; and 
     FIG. 7 is a schematic diagram showing a temperature scanning type hydrogen absorption/desorption characteristics evaluating apparatus to be employed for evaluating a hydrogen-absorbing alloy. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     (1) A First Nickel-hydrogen Secondary Battery 
     This invention will be explained further with reference to FIG. 1 showing a cylindrical nickel-hydrogen secondary battery representing one embodiment of the nickel-hydrogen secondary battery of this invention. 
     Referring to FIG. 1, a bottomed cylindrical case  1  is accommodated therein with an electrode group  5  which has been manufactured by stacking a positive electrode  2 , a separator  3  and a negative electrode  4 , and then by spirally winding the stacked body. The negative electrode  4  is disposed at the outermost periphery of the electrode group  5  so as to electrically contact with the cylindrical case  1 . The cylindrical case  1  contains an alkaline electrolyte. A sealing plate  7  formed of a disk having an opening  6  at the center is disposed on the upper opening of the cylindrical case  1 . An insulating gasket  8  having a ring-like shape is interposed between the periphery of the first sealing plate  7  and the upper inner wall surface of the opening of the cylindrical case  1 . The peripheral fringe portion of the opening of the cylindrical case  1  is caulked inward so that the first sealing plate  7  is hermetically fixed via the gasket  8  to cylindrical case  1 . The positive electrode lead  9  is connected through its one end to the positive electrode  2  and through its other end to the lower surface of the first sealing plate  7 . A positive electrode terminal  10  having a hat-like shape is mounted over the first sealing plate  7  in such a manner as to cover the opening  6 . A rubber safety valve  11  is disposed in a space surrounded by the first sealing plate  7  and the positive electrode terminal  10  in such a manner as to seal the opening  6 . A holding plate  12  formed of an insulating disk having an opening at the center is disposed over the positive electrode terminal  10  in such a manner that the projected portion of the positive electrode terminal  10  is protruded out through the opening of the holding plate  12 . An envelope tube  13  is disposed to cover all of the periphery of the holding plate  12 , the side wall of the cylindrical case  1  and the periphery of the bottom of the cylindrical case  1 . 
     Next, the details of the positive electrode  2 , the negative electrode  4 , the separator  3  and the electrolyte will be explained. 
     (1) The Positive Electrode  2   
     This positive electrode  2  contains nickel hydroxide, and can be manufactured by a process wherein a conductive material is added at first to an active material, i.e. nickel hydroxide powder to obtain a mixture, which is then kneaded together with a binder and water to prepare a paste, which is then stuffed into a conductive substrate and, after being dried, molded into a predetermined shape. 
     Although there is not any particular limitation regarding the nickel hydroxide powder to be employed in this invention as far as the nickel hydroxide is capable of normally charging and discharging, it is preferable in view of obtaining desired properties as a battery to contain a transition metal such as zinc and cobalt. 
     As for the conductive material, cobalt oxide, cobalt hydroxide can be used. 
     Examples of the binder are carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene and polyvinyl alcohol (PVA). 
     The conductive substrate may be formed of a mesh-like, sponge-like, fibrous or metallic porous body which is made of a metal such as nickel, stainless steel or a nickel-plated metal. 
     (2) The Negative Electrode  4   
     This negative electrode comprises a hydrogen-absorbing alloy represented by the following general formula (A); 
     
       
         (R 1-x Mg x )Ni y A z   (A) 
       
     
     wherein R is at least one element selected from rare earth elements (including yttrium), Ca, Zr and Ti; A is at least one element selected from Co, Mn, Fe, V, Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P and B; and x, y and z are atomic ratio individually defined as 0&lt;x&lt;1, 0≦z≦1.5, 2.5≦y+z&lt;4.5; 
     This negative electrode 4 can be manufactured for example by a method wherein a conductive material is added at first to a hydrogen-absorbing alloy powder and then kneaded together with a binder and water to prepare a paste, which is then stuffed into a conductive substrate and, after being dried, press-molded into a predetermined shape, thereby forming the negative electrode. 
     As for the R to be incorporated into the hydrogen-absorbing alloy, it is preferable to employ a rare earth element (including yttrium). Further, if a rare earth element is to be employed as the R, it is more preferable in view of saving the manufacturing cost of a hydrogen-absorbing electrode to employ at least one kind of rare earth elements selected from the group consisting of La, Ce, Pr, Nd and Y. One example of such a preferable example of the R is a misch-metal (Mm) which is a mixture of rare earth elements such as Ce-rich Mm and La-rich Lm. 
     It is also possible to employ, as the R, a mixture containing at least one element selected from Ca, Zr and Ti, in addition to the aforementioned rare earth elements. In this case, the former elements may be incorporated therein substituting for 30 atom. % or less of the rare earth elements. 
     When the range of the x in the general formula (A) is confined to the aforementioned limitation, it is possible to overcome the problem of difficulty in releasing hydrogen and hence to realize a large discharge capacity. In particular, the range of the x should more preferably be confined to the range of 0.1≦x≦0.6. Because if the x is less than 0.1, the problem of difficulty in releasing hydrogen from the hydrogen-absorbing alloy may not be sufficiently overcome, thus making it difficult to obtain a secondary battery of large discharge capacity. On the other hand, if the x exceeds over 0.6, the reversible absorption/desorption quantity of the alloy would be deteriorated, thus making it difficult to obtain a secondary battery of large discharge capacity. A most preferable range of the x is 0.15≦x≦0.45. 
     When the range of the z in the general formula (A) absorbing alloy is confined to the aforementioned limitation, it is possible not only to enhance the hydrogen absorption/desorption property such as the hydrogen absorption/desorption rate of the alloy, but also to prominently improve the charge/discharge cycle property of the nickel-hydrogen secondary battery. However, if the z exceeds over 1.5, the discharge capacity of the secondary battery would be deteriorated. Therefore, a most preferable range of the z is 0.1≦z≦1.0. 
     The A in the general formula (A) should preferably be at least one element selected from Co and Mn. Namely, the inclusion of these elements as A for a hydrogen-absorbing alloy to be incorporated in a negative electrode of secondary battery would lead to an improvement of the charge/discharge cycle property of the battery. In particular, when Co is included as A, the discharge capacity of the battery can be also enhanced. 
     When the value of the y+z in the general formula (A) is confined to 2.5 or more, it is possible to prominently improve the hydrogen absorption/desorption property such as the hydrogen absorption/desorption rate of the alloy, and hence to enhance the discharge capacity and charge/discharge cycle property of the nickel-hydrogen secondary battery. However, if the y+z exceeds over 4.5, the hydrogen site of the alloy would be decreased, thus reducing the hydrogen absorption capacity of the alloy and hence deteriorating the discharge capacity of the secondary battery. Therefore, a more preferable range of the y+z is 3.0≦y+z≦3.8. 
     The hydrogen-absorbing alloy should preferably be such that, when the alloy is analyzed by an X-ray diffraction method using CuKα-ray, the alloy exhibits a highest peak in the range of 42.1°±1° and does not exhibit a peak having an intensity of more than 15% of the aforementioned highest peak in the range of 30.2°±1°. In other words, the hydrogen-absorbing alloy is analyzed by an X-ray diffraction method using CuK α-ray, a highest peak appears in the range of 42.1°±1°, and a peak does not appear in the range of 30.2°±1°, or even if a peak appears in the range of 30.2°±1°, the peak should be of not more than 15% in intensity of the aforementioned highest peak. It should be noted that the intensity of each peak is one obtained by subtracting the intensity of the background from the intensity of the peak actually measured. 
     If the hydrogen-absorbing alloy is constructed as mentioned above, the alloy contains as a principal phase a phase having an AB 3  type crystal structure such as CeNi 3  type crystal structure and PuNi 3  type crystal structure; an A 2 B 7  type crystal structure such as Ce 2 Ni 7  type crystal structure and Gd 2 Co 7  type crystal structure; or a crystal structure which is similar to these types. In this case, the term “principal phase” noted above denotes a phase in the alloy which is highest in existing ratio. 
     If the hydrogen-absorbing alloy represented by the aforementioned general formula is such that, when the alloy is analyzed by an X-ray diffraction method using CuK α-ray, the alloy exhibits a highest peak in the range of 42.1°±10 and a peak having an intensity of more than 15% of the aforementioned highest peak in the range of 30.2°±1°, the alloy contains as a principal phase a phase having a CaCu 5  type crystal structure such as LaNi 5  type crystal structure, or otherwise the alloy contains such a high ratio of the phase having the CaCu 5  type crystal structure that cannot be disregarded just like a principal phase. 
     If the hydrogen-absorbing alloy contains as a principal phase a phase having a CaCu 5  type crystal structure such as LaNi 5  type crystal structure, or contains the phase having the CaCu 5  type crystal structure at such a high ratio that cannot be disregarded just like a principal phase, it may be impossible to obtain a secondary battery having a sufficient charge/discharge cycle life. A more preferable hydrogen-absorbing alloy among these preferable hydrogen-absorbing alloys is the one where a peak having an intensity of more than 10% of the aforementioned highest peak does not appear in the range of 30.2°±1°. 
     A most preferable alloy among the hydrogen-absorbing alloys represented by the aforementioned general formula (A) is such that, when the alloy is analyzed by an X-ray diffraction method using CuKα-ray, the alloy exhibits a highest peak in the range of 42.1°±1° and a peak having an intensity greater than 5% of that of the highest peak in the range of 32.5°±1° and does not exhibit a peak having an intensity greater than 15% of that of the highest peak in the range of 30.2°±1°. In particular, it is far more preferable to employ an alloy where a peak having an intensity of more than 10% of the aforementioned highest peak appears in the range of 32.5°±1°. 
     The hydrogen-absorbing alloy represented by the aforementioned general formula (A) can be manufactured by means of a casting method, a sintering method, an ultra-quenching method such as a single rolling method, a double rolling method, a disc-atomizing method or a gas-atomizing method. 
     The alloy thus obtained is then preferably heat-treated in vacuum or in an inert atmosphere at a temperature ranging from 300° C. to less than melting point thereof for a time period ranging from 0.1 to 500 hours. It is possible through this heat treatment to alleviate the distortion in lattice of the alloy, so that the hydrogen absorption/desorption characteristics such as the hydrogen absorption/desorption rate of the alloy can be improved. The heat treatment temperature should preferably be in the range from 750 to 1,050° C., more preferably in the range from 800 to 1,000° C. Further, the heat treatment period should preferably be in the range from 0.5 to 100 hours, more preferably in the range from 1 to 20 hours. 
     As for the binder, the same kinds of material as employed for the positive electrode can be employed. 
     As for the conductive material, carbon black, conductive metallic pieces, etc. can be used. 
     As for the conductive metal for the conductive metallic pieces, Ni, Cu, etc. can be employed. The conductive metallic pieces may be in the form of granule or flake having an average diameter of 1 to 100 μm. The conductive metallic pieces should preferably be employed at a ratio of 0.3 to 20 parts by weight per 100 parts by weight of a hydrogen-absorbing alloy. 
     The conductive substrate may be formed of a two-dimensional substrate such as a punched metal, an expanded metal and a nickel net; or a three-dimensional substrate such as a felt-shaped metallic porous body or a sponge-shaped metallic porous body. 
     (3) The Separator  3   
     There is not any particular limitation regarding the material and configuration of the separator  3  as long as the separator  3  is formed of an insulating material having a sufficient hydrophilicity and gas-permeability. However, in view of enhancing the properties of nickel-hydrogen secondary battery, it should preferably be formed of a sheet containing a polyolefin type resin fiber. 
     As for the polyolefin type resin fiber, a fiber consisting of only one kind of polyolefin; a composite fiber of core-sheath structure where a core material consisting of a polyolefin fiber is covered by a different kind of polyolefin fiber; or a composite fiber of split structure where polyolefin fibers which are different in kind from each other are connected with each other to form a ring-like structure may be employed. As for the polyolefin, it is possible to employ polyethylene, polypropylene, etc. 
     As for the sheet containing a polyolefin type resin fiber, it is possible to employ a non-woven fabric or woven fabric comprising the aforementioned polyolefin type resin fibers, or a composite sheet composed of these non-woven fabric and woven fabric. This non-woven fabric can be manufactured by means of a dry process, a wet process, a spun-bonding method, melt-blow method, etc. The average thickness of the fiber constituting the separator should preferably be in the range of 1 to 20 μm in view of the mechanical strength and of preventing a short circuit between the positive and negative electrodes. 
     For the purpose of providing the separator  3  with hydrophilicity, the surface of the polyolefin type resin fiber to be included in the sheet should preferably be covered with a copolymer having a hydrophilic group (such as ethylene vinyl alcohol copolymer), or the sheet should preferably be graft-copolymerized with a vinyl monomer having a hydrophilic group. Examples of vinyl monomer having a hydrophilic group are acrylic acid, methacrylic acid, acrylate, methacrylate, vinylpyridine, vinylpyrrolidone, styrene sulfonic acid, a monomer having a functional group which is capable of forming a salt through a reaction thereof with an acid or base such as styrene, or a monomer having a functional group which is capable of forming a salt through hydrolysis after being graft-copolymerized. Among these vinyl monomers, acrylic acid is most preferable. 
     (4) Alkaline Electrolyte 
     Examples of the alkaline electrolyte which are useful in this invention include an aqueous solution of potassium hydroxide (KOH), a mixed solution of potassium hydroxide (KOH) and sodium hydroxide (NaOH), a mixed solution of potassium hydroxide (KOH) and lithium hydroxide (LiOH), and a mixed solution of NaOH, KOH and LiOH. In particular, the alkaline electrolyte should preferably be the aqueous mixed solution of NaOH and KOH or the aqueous mixed solution of LiOH and KOH. The concentration of KOH in this alkaline electrolyte should preferably be 2.0 to 9.0 N, more preferably 3.0 to 8.5 N. Likewise, the concentration of NaOH in this alkaline electrolyte should preferably be 1.0 to 6.0 N, more preferably 2.0 to 5.0 N. Further, the concentration of LiOH in this alkaline electrolyte should preferably be 0.3 to 2.0 N, more preferably 0.5 to 1.5 N. 
     Although this invention has been explained about a cylindrical alkaline secondary battery, it is also possible according to this invention to apply it to a rectangular alkaline secondary battery, wherein a closed-end rectangular case is accommodated therein with an electrode group consisting of a laminated body that positive electrodes and negative electrodes which are alternately superimposed one upon another with a separator being interposed therebetween, and with an alkali electrolyte. 
     (2) A Second Nickel-hydrogen Secondary Battery 
     The second nickel-hydrogen secondary battery comprises an electrode group comprising a positive electrode, a negative electrode and a separator being interposed positive and negative electrodes. The secondary battery further comprises an alkali electrolyte and a case accommodating therein the aforementioned electrode group and alkali electrolyte. 
     This second nickel-hydrogen secondary battery is applicable to the cylindrical alkaline secondary battery shown for instance in FIG.  1 . Further, this second nickel-hydrogen secondary battery is also applicable to a rectangular alkaline secondary battery, wherein a closed-end rectangular case is accommodated therein with an electrode group consisting of a laminated body that positive electrodes and negative electrodes which are alternately superimposed one upon another with a separator being interposed therebetween, and with an alkali electrolyte. 
     As for the positive electrode, the negative electrode, the separator and the electrolyte, the same kinds of materials as employed in the aforementioned first nickel-hydrogen secondary battery can be employed. 
     Followings are explanations on the case (battery case). 
     This case has a tensile strength of 65 to 80 kgf/mm 2 , a yield point of 30 to 55 kgf/mm 2  and an elastic modulus of 20,000 to 30,000 kgf/mm 2 . 
     The measurement of these mechanical properties of the case can be performed based on the method described in JIS Z 2241. The elastic modulus of the case can be calculated based on the data to be obtained from the method described in JIS Z 2241. Further, the test pieces to be employed are those of No. 5 which is described in JIS Z 2201. 
     Next, the reasons for limiting the mechanical properties of the case to the aforementioned ranges will be explained. 
     (1) Tensile Strength 
     If the tensile strength of the case is less than 65 kgf/mm 2 , not only the strength of the case becomes insufficient, but also a plastic deformation such as swelling of the case due to the stress resulting from the volumetric expansion of the negative electrode would be caused. On the other hand, since it is more or less difficult to manufacture the case having a tensile strength exceeding over 80 kgf/mm 2  by means of deep draw forming, there is a possibility that cracking or a great magnitude of strain which may be generated in the working of the case. Therefore, a preferable range of the tensile strength of the case is 68 to 75 kgf/mm 2 . 
     (2) Yield Point 
     If the yield point of the case is less than 30 kgf/mm 2 , not only the strength of the case becomes insufficient, but also a plastic deformation such as swelling of the case due to the stress resulting from the volumetric expansion of the negative electrode would be caused. On the other hand, since it is more or less difficult to manufacture the case having a yield point exceeding over 55 kgf/mm 2  by means of deep draw forming, there is a possibility that cracking or a great magnitude of strain which may be generated in the working of the case. Therefore, a preferable range of the yield point of the case is 35 to 50 kgf/mm 2 . 
     (3) Elastic Modulus 
     As the elastic modulus is increased, a higher stress is required for generating an elastic deformation of the case. Namely, if the elastic modulus of the case exceeds over 30,000 kgf/mm 2 , the magnitude of elastic deformation of the case in relative to the stress originating from a volumetric expansion of the negative electrode at the occasion of charging would become smaller, thus causing an internal short-circuit to be easily generated. Therefore, a preferable range of the elastic modulus of the case is 21000 to 26000 kgf/mm 2 . 
     This case should preferably be formed of a steel plate containing not more than 0.13% (including 0%) of carbon, not more than 0.5% (including 0%) of manganese, not more than 0.05% (including 0%) of phosphorus, and not more than 0.05% (including 0%) of sulfur, at least a part of the surface of the steel plate being preferably plated with nickel. However, it should be noted that all of carbon, manganese, phosphorus and sulfur should not be simultaneously zero. When the composition of the steel plate is controlled as mentioned above, it becomes possible to obtain a steel plate which is suited for a deep draw forming, and at the same time, the mechanical property of the case can be controlled to a desired range. On the other hand, if the composition of the steel plate falls outside the aforementioned range, it may become difficult to perform the deep draw forming of the case due to an increase in mechanical strength of the steel plate, or the mechanical property of the case may fall outside the aforementioned desired ranges due to a strain originating from the molding of the case. 
     This case can be manufactured by cold-working such as deep draw forming a plate material having a tensile strength of 25 to 40 kgf/mm 2 , a yield point of 10 to 30 kgf/mm 2  and an elastic modulus of 20,000 to 26,000 kgf/mm 2  thereby to form a closed-end cylindrical or square tubular configuration, which is then plated with nickel. This plate material may be formed of a metal such as steel. The purpose of nickel-plating is to enhance the alkali-resistance of the case, and hence this nickel-plating can be performed by any desired method as long as the method does not induce a deterioration of the mechanical and electric properties of the case. 
     For example, it is possible to adopt a method wherein an electroplating is performed after the plating material is molded into a desired configuration, or a method wherein a plating is performed after the plating material is molded into a desired configuration, subsequently a heat treatment is performed at a temperature lower than the melting point of the plated layer so as to enhance the strength of the plating. Although it is possible to perform a heat treatment during the deep draw forming so as to workability of the plate material, this heat treatment would lead to an increase in manufacturing cost of the case. 
     (3) A Third Nickel-hydrogen Secondary Battery 
     The third nickel-hydrogen secondary battery comprises an electrode group consisting of a positive electrode, a negative electrode and a separator being interposed positive and negative electrodes. The secondary battery further comprises an alkali electrolyte and a case accommodating therein the aforementioned electrode group and alkali electrolyte. 
     This third nickel-hydrogen secondary battery is applicable to the cylindrical alkaline secondary battery shown for instance in FIG.  1 . Further, this second nickel-hydrogen secondary battery is also applicable to a rectangular alkaline secondary battery, wherein a closed-end rectangular case is accommodated therein with an electrode group consisting of a laminated body that positive electrodes and negative electrodes which are alternately superimposed one upon another with a separator being interposed therebetween, and with an alkali electrolyte. 
     As for the positive electrode, the separator and the electrolyte, the same kinds of materials as employed in the aforementioned first nickel-hydrogen secondary battery can be employed. 
     Followings are explanations on the negative electrode. 
     This negative electrode comprises a mixture containing a hydrogen-absorbing alloy represented by the aforementioned general formula (A), and a conductive substrate carrying this mixture. 
     This negative electrode can be manufactured by a process wherein a conductive material is added to the powder of the aforementioned hydrogen-absorbing alloy, and the resultant mixture is kneaded together with a binder and water to obtain a paste. The paste is then stuffed into the conductive substrate and, after being dried, press-molded to obtain the negative electrode. 
     As for the hydrogen-absorbing alloy, the conductive material, the binder and the conductive substrate, the same kinds of materials as employed in the aforementioned first nickel-hydrogen secondary battery can be employed. 
     In view of inhibiting the self-discharge at the initial stage of the charge/discharge cycle of the battery, the density of the mixture in the negative electrode should be set to 5.1 g/cc to 5.8 g/cc. The reason for the improvement in self-discharge by this density range of the mixture may be ascribed to the fact that this density of the mixture is almost the same as that of hydrogen-absorbing alloy in the negative electrode, thereby giving a great influence to the compression degree of the separator and to the distribution of the electrolyte. More preferable range of the density of the mixture is from 5.2 to 5.7 g/cc. 
     Next, details of the electrode group will be explained as follows. 
     In view of inhibiting the self-discharge at the initial stage of the charge/discharge cycle of the battery, the tightness of the electrode group is confined to the range of 98 to 110%. By the way, even if the tightness of the electrode group exceeds over 100%, it is possible to house the electrode group in the case, since the separator can be compressed at the occasion of housing the electrode group in the case. More preferable range of the tightness of the electrode group is from 99 to 105%. 
     This tightness of the electrode group can be calculated as follows. 
     (a) Cylindrical Nickel-hydrogen Secondary Battery 
     First of all, the designed diameter R 0  of the electrode group is calculated according to the following formula (I). 
     
       
           R   0   =T   p   ×N   p   +T   n   ×N   n   +T   s   ×N   s   +r   (I) 
       
     
     wherein T p  is the thickness (mm) of the positive electrode before making of the electrode group; T n  is the thickness (mm) of the negative electrode before making of the electrode group; T s  is the thickness (mm) of the separator before making of the electrode group; N p  is the number of segments of the positive electrode which exist in a longitudinal section of the electrode group, taken along a longest diameter thereof; Nn is the number of segments of the negative electrode which exist in the longitudinal section; N s  is the number of segments of the separator which exist in the longitudinal section; and r is the diameter (mm) of the core to be employed in the manufacture of the electrode group. 
     The number of segments of the positive electrode, the negative electrode and the separator will be explained as follows. FIG. 2 is a cross-sectional view illustrating one example of spiral type electrode group. A longest diameter means a diameter that passing across the end portion of the positive electrode  2  and across a portion of the negative electrode  4  which is superimposed on the aforementioned end portion. In the case of the electrode group shown in FIG. 2, the number of segments of the positive electrode  2  which exit in the longitudinal section is  8 , the number of segments of the negative electrode  4  which exit in the longitudinal section is  8 , and the number of segments of the separator  3  which exit in the longitudinal section is  20 . 
     By making use of this designed diameter Ro thus obtained, the tightness X(%) is calculated according to the following formula (II). 
     
       
           X =( R   0   /R   c )×100  (II) 
       
     
     wherein R c  is the inner diameter of the closed-end cylindrical case. 
     (b) Rectangular Nickel-hydrogen Secondary Battery 
     First of all, the designed thickness H 0  of the electrode group is calculated according to the following formula (III). 
     
       
           H   0   =T   p   ×M   p   +T   n   ×M   n   +T   s   ×M   s   (III) 
       
     
     wherein T p  is the thickness (mm) of the positive electrode before making of the electrode group; T n  is the thickness (mm) of the negative electrode before making of the electrode group; T s  is the thickness (mm) of the separator before making of the electrode group; M p  is the number of laminated layers of the positive electrode; M n  is the number of laminated layers of the negative electrode; and M s  is the number of laminated layers of the separator. 
     The number of laminated layers of the positive electrode, the negative electrode and the separator means the number of layers of the positive electrode, the negative electrode and the separator, respectively, each constituting a laminate type electrode group that has been actually manufactured. 
     By making use of this designed thickness Ho thus obtained, the tightness X(%) is calculated according to the following formula (IV). 
     
       
           X =( H   0   /H   c )×100  (IV) 
       
     
     wherein H c  is the inner width of the closed-end box-like case as measured taking along the laminated direction of the electrode group. 
     The width of the electrode group having the aforementioned specific tightness should preferably be set to 98 to 100% of the inner width of the case as measured taking along the laminated direction of the electrode group. The reason for limiting the width of the electrode group in this manner is as follows. Namely, if the width of the electrode group in the laminated direction thereof is less than 98%, it may become difficult to inhibit the self-discharge of the nickel-hydrogen secondary battery comprising a negative electrode comprising a hydrogen-absorbing alloy of the aforementioned specific composition. On the other hand, if the width of the electrode group in the laminated direction thereof exceeds over 100%, it may become difficult to house&#39;the electrode group in the case. The expression of “the width of the electrode group in the laminated direction” means herein the aforementioned longest diameter of the electrode group in the case of the cylindrical nickel-hydrogen secondary battery, or the thickness of the electrode group in the laminated direction in the case of the rectangular nickel-hydrogen secondary battery. Further, the expression of “the inner width of the case as measured taking along the laminated direction of the electrode group” means, in the case of the cylindrical nickel-hydrogen secondary battery, the inner diameter of the case. 
     The case housing an electrode group having the aforementioned specific tightness should preferably have a tensile strength of 65 to 80 kgf/mm 2 , a yield point of 30 to 55 kgf/mm 2  and an elastic modulus of 20,000 to 30,000 kgf/mm 2 . 
     The first nickel-hydrogen secondary battery according to this invention comprises a negative electrode comprising a hydrogen-absorbing alloy represented by the aforementioned general formula (A). Since the hydrogen absorption capacity per unit volume of this hydrogen-absorbing alloy is about 20% larger than that of LaNi 5  type hydrogen-absorbing alloy, it is possible to fabricate a secondary battery of high capacity even if the quantity of this hydrogen-absorbing alloy per theoretical capacity of the positive electrode is reduced. However, the negative electrode containing this hydrogen-absorbing alloy differs from the negative electrode containing the LaNi 5  type hydrogen-absorbing alloy in the pulverization rate and in the reactivity with the electrolyte. 
     Therefore, in order to achieve a high battery capacity while ensuring other desired properties of the battery, the battery is required to satisfy the conditions represented by the following formulas (1) and (2). 
     
       
         3.2≦P≦5.0  (1) 
       
     
     
       
         0.9≦Q≦0.2 P+0.7  (2) 
       
     
     wherein P is a quantity (g) of the hydrogen-absorbing alloy per theoretical capacity 1 Ah of the positive electrode; and Q is a quantity (mL) of the alkaline electrolyte per theoretical capacity 1 Ah of the positive electrode. 
     In the case of the closed-type nickel-hydrogen secondary battery where capacity of the positive electrode regulates the battery capacity, it is imperative, for the purpose of enhancing the battery capacity, to increase the quantity of active material of the positive electrode and to reduce the quantity of the active material of the negative electrode. Since the hydrogen absorption capacity per unit volume of this hydrogen-absorbing alloy represented by the aforementioned general formula (A) is larger than that of LaNi 5  type hydrogen-absorbing alloy, it is possible to provide a negative electrode having a sufficient capacity even if the quantity of this hydrogen-absorbing alloy is smaller than the quantity of LaNi 5  type hydrogen-absorbing alloy. By the way, the properties desired of the nickel-hydrogen secondary battery are not limited to a high battery capacity, but include those which are closely related to the quantity of electrolyte, such as the low temperature discharge property and the internal pressure at the occasion of over-charging. Only when these properties are well-balanced, a secondary battery which is practical and large in capacity can be obtained. 
     In order to obtain a nickel-hydrogen secondary battery which comprises a negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A), and which is capable of exhibiting a large capacity, the quantity P(g) of the hydrogen-absorbing alloy per theoretical capacity 1 Ah of the positive electrode should be the range of 3.2 to 5.0 g. Because if the quantity P(g) of the hydrogen-absorbing alloy is less than 3.2 g, a difference in capacity between the negative electrode and the positive electrode becomes too small, so that the electric potential of the negative electrode may become lowered at the terminal period of discharging of the positive electrode regulating the discharge capacity, thus rendering the capacity at low temperatures in particular in the vicinity of −20° C. to become lower than that of the LaNi 5  type hydrogen-absorbing alloy. On the other hand, if the quantity P(g) of the hydrogen-absorbing alloy is more than 5.0 g,the advantage that the hydrogen absorption quantity of the alloy represented by the aforementioned general formula (A) is higher than that of the LaNi 5  type hydrogen-absorbing alloy would be dissipated. More preferable range of the quantity P(g) of the hydrogen-absorbing alloy is 3.6≦P≦4.5. By the way, the quantity P(g) can be adjusted by modifying the density of alloy of the negative electrode. 
     The quantity Q(mL) of the alkaline electrolyte per theoretical capacity 1 Ah of the positive electrode in the nickel-hydrogen secondary battery comprising a negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A) should be selected so as to meet the condition represented by the aforementioned formula (2). 
     The reason for limiting the quantity Q(mL) of the alkaline electrolyte to the range defined by the aforementioned formula (2) is as follows. Namely, if the quantity Q(mL) of the alkaline electrolyte is less than 0.9 mL, it would be impossible to uniformly disperse the electrolyte in the negative electrode. As a result, the capacity at low temperatures in particular in the vicinity of −20° C. would be prominently deteriorated. On the other hand, if the quantity Q(mL) of the alkaline electrolyte is more than the value calculated from 0.2 P+0.7 (P is a quantity (g) of the hydrogen-absorbing alloy per theoretical capacity 1 Ah of the positive electrode), the internal pressure of the battery would be increased, thus making it impossible to obtain a sufficient charge/discharge cycle life. This quantity of electrolyte is closely related to the quantity of the alloy as seen from the formula (2). 
     In order to suppress any increase in internal pressure of the battery, the oxygen gas generated at the occasion of over-charging is required to be quickly diffused over the surface of the alloy existing in the negative electrode, so that it is required to secure a space between the alloy particles for a gas passageway where no electrolyte is existed therein. Therefore, the quantity of electrolyte per weight of the alloy becomes approximately constant, thus assumably allowing the aforementioned relational expression to be established. Therefore, this relational expression indicates the upper limit in quantity of the electrolyte which obviates the increase of internal pressure in the nickel-hydrogen secondary battery comprising a negative electrode containing the alloy in a quantity meeting the aforementioned formula (1). More preferable range of the quantity Q(mL) of the electrolyte is 0.95≦Q≦0.2 P+0.6. 
     According to the first nickel-hydrogen secondary battery of this invention, since the battery comprises a negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A), and since the quantity of the hydrogen-absorbing alloy in relative to the theoretical capacity of the _positive electrode as well as the quantity of the alkaline electrolyte in relative to theoretical capacity of the positive electrode are both controlled according to the formulas (1) and (2), it is now possible to enhance the battery capacity while ensuring the properties desired of the battery such as the low temperature discharge property, the internal pressure, the charge/discharge cycle, etc. 
     In particular, when the hydrogen-absorbing alloy exhibits a highest peak in the range of 42.1°±1° and does not exhibit a peak having an intensity greater than 15% of that of the highest peak in the range of 30.2°±1° as measured by X-ray diffraction using CuK α-ray, it is possible not only to enhance the capacity of the secondary battery without damaging other desired properties, but also to improve the charge/discharge cycle life of the secondary battery. Further, when the hydrogen-absorbing alloy further exhibits a peak having an intensity of more than 5% of the highest peak in the range of 32.5°±1°, it is possible to further improve the charge/discharge cycle life of the secondary battery. 
     According to the second nickel-hydrogen secondary battery of this invention, any volumetric changes due to the expansion and shrinkage of the negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A) at the occasion of charging and discharging can be absorbed by an elastic deformation of the case. As a result, the electrode group including the negative electrode can be inhibited from being oppressed by the case at the occasion of the expansion of the negative electrode, so that the space balance inside the electrode group can be maintained in a desired condition. Accordingly, the secondary battery can be prevented, at a relatively early stage of charge/discharge cycle, from generating an internal short-circuit, from decreasing quantity of electrolyte due to the actuation of safety valve due to an increase of internal pressure, or from decreasing effective quantity of electrolyte due to an irreversible expansion of the case. Therefore, it is possible to prevent the deterioration of discharge capacity at a relatively early stage of charge/discharge cycle and also to enhance the charge/discharge cycle life of the battery. 
     In particular, when the hydrogen-absorbing alloy exhibits a highest peak in the range of 42.1°±1° and does not exhibit a peak having an intensity greater than 15% of that of the highest peak in the range of 30.2°±1° as measured by X-ray diffraction using CuK α-ray, it is possible not only to prevent the battery from generating an internal short-circuit or increasing internal pressure at a relatively early stage of charge/discharge cycle, but also to enhance the charge/discharge cycle life of the battery. Further, when the hydrogen-absorbing alloy further exhibits a peak having an intensity of more than 5% of the highest peak in the range of 32.5°±1°, it is possible to further improve the charge/discharge cycle life of the secondary battery. 
     According to the third nickel-hydrogen secondary battery of this invention, since not only the density of the mixture containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A) but also the tightness of the electrode group fall within specific ranges respectively, it is possible to suppress the self-discharging at the initial stage of the charge/discharge cycle of the nickel-hydrogen secondary battery comprising a negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A). The reason for this may be explained as follows. 
     In the case of a nickel-hydrogen secondary battery, a hydrogen partial pressure corresponding to the equilibrium pressure of the hydrogen-absorbing alloy contained in a negative electrode is retained in the case during the storage thereof. This phenomenon occurs inevitably in the case of the nickel-hydrogen secondary battery comprising the negative electrode containing the hydrogen-absorbing alloy. In the case of a closed type secondary battery, when this hydrogen is contacted with a positive electrode, the charge-reaction product of the positive electrode such as nickel oxyhydroxide is reduced, thus allowing a self-discharging reaction to proceed. This self-discharging reaction is further promoted as the ambient temperature of storage becomes higher. This self-discharging reaction can be effectively suppressed by reducing the chance of reaction between the charged positive electrode and the gaseous hydrogen. As one of the methods to reduce this chance of contact between them, there is known a method wherein the hydrophilicity of the separator is enhanced, thereby increasing the electrolyte retention quantity of the separator and hence filling the voids of the separator with the electrolyte, and at the same time, the wettability of the surface of the positive electrode is enhanced, thus inhibiting the diffusion of the hydrogen gas. 
     It has been found as a result of intensive study made by the present inventors that the hydrogen-absorbing alloy represented by the aforementioned general formula (A) indicates more prominent volumetric change at the occasion of charging/discharging as compared with the known alloys, and hence the magnitude of self-discharging reaction is more changeable at the initial period of the charge/discharge cycle. Based on this findings, the present inventors have further found that the self-discharging reaction can be suppressed by optimizing not only the density of the mixture of the negative electrode but also the construction of the electrode group. Thus, it has been found that the self-discharging reaction at the initial period of the charge/discharge cycle can be suppressed by taking into account the volumetric change accompanying the charging/discharging of the negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A) at the occasion of designing the negative electrode and the electrode group. 
     Namely, when the negative electrode is expanded due to the charging of the secondary battery, the separator is compressed. As a result of this compression of the separator, the voids inside the separator and the quantity of electrolyte are caused to change, and hence the magnitude in proceeding of the self-discharging reaction is also altered. The magnitude of expansion and shrinkage of the negative electrode is greatly influenced by the ratio in volumetric change of a hydrogen-absorbing alloy to be employed, and this ratio in volumetric change differs depending on the kinds of the hydrogen-absorbing alloy. In other words, the composition of the hydrogen-absorbing alloy, the density of the mixture of the negative electrode and the tightness of the electrode group are closely interrelated with each other. Accordingly, it is possible, in the nickel-hydrogen secondary battery comprising an negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A), to suppress the self-discharging by confining the density of the mixture in the negative electrode to 5.1 g/cc to 5.8 g/cc, and also confining the tightness of the electrode group to the range of 98 to 110%. 
     Namely, if the density of the mixture in the negative electrode is less than 5.1 g/cc, the compression of the separator becomes insufficient, thus making it difficult to minimize the void in the separator. On the other hand, if the density of the mixture in the negative electrode is more than 5.8 g/cc, even though it may be possible to reduce the void in the separator due to the expansion of the alloy as a result of charging, the gap between the particles of alloy in the negative electrode is enlarged, thus allowing the electrolyte in the separator to move into the gap. As a result, the retention of the electrolyte by the separator would be reduced, thus making it impossible to sufficiently fill the void in the separator with the electrolyte, and hence the magnitude of self-discharging would be increased. 
     On the other hand, if the tightness of the electrode group is less than 98%, the compression of the separator by the expansion of the negative electrode resulting from charging would become insufficient, thus enlarging the void in the separator. As a result, it becomes impossible to suppress the diffusion of hydrogen gas, and hence the self-discharging may be prominently proceed. On the other hand, if the tightness of the electrode group is more than 110%, even though it may be possible to strongly compress the separator thereby to minimize the void in the separator, the quantity of electrolyte in the separator would be reduced, thus promoting the process of self-discharge. 
     Therefore, it is now possible according to this invention to inhibit the self-discharge of the nickel-hydrogen secondary battery comprising a negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A). 
     Since the width of the electrode group along the laminated direction thereof is set to 98 to 100% of the inner width of the case as taken along the laminated direction of the electrode group, it is now possible to smoothly house the electrode group into the case and, at the same time, to further inhibit the self-discharge of the nickel-hydrogen secondary battery. 
     Further, when the hydrogen-absorbing alloy exhibits a highest peak in the range of 42.1°±1° and does not exhibit a peak having an intensity greater than 15% of that of the highest peak in the range of 30.2°±1° as measured by X-ray diffraction using CuK α-ray, it is now possible not only to improve the self-discharge-inhibiting property of the secondary battery, but also to improve the charge/discharge cycle life of the secondary battery. Further, when the hydrogen-absorbing alloy further exhibits a peak having an intensity of more than 5% of the aforementioned highest peak in the range of 32.5°±1°, it is now possible to further improve the charge/discharge cycle life of the secondary battery. 
     Next, a hydrogen-absorbing alloy according to the present invention, a secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy, a hybrid car comprising such a secondary battery, and an electromobile comprising such a secondary battery will be explained as follows. 
     A First Hydrogen-absorbing Alloy 
     This first hydrogen-absorbing alloy contains, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu 5  type crystal structure) and a second phase having a rhombohedral crystal system. Further, this hydrogen-absorbing alloy has a composition represented by the following general formula (1): 
     
       
         R 1-a-b Mg a T b Ni Z-X-Y-α M1 X M2 Y Mn α   (1) 
       
     
     wherein R is at least one kind of element selected from rare earth elements (which include Y); T is at least one element selected from the group consisting of Ca, Ti, Zr and Hf; M1 is at least one element selected from the group consisting of Co and Fe; M2 is at least one element selected from the group consisting of Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, Li, P and S; and the atomic ratios of a, b, X, Y, α and Z are respectively a number satisfying the conditions of: 0.15≦a≦0.37, 0≦b≦0.3, 0≦X≦1.3, 0≦Y≦0.5, 0≦α&lt;0.135, and 2.5≦Z≦4.2. 
     The aforementioned first phase should preferably be constituted by a phase having Ce 2 Ni 7  type crystal structure, a phase having CeNi 3  type crystal structure and a phase having a crystal structure which is similar to Ce 2 Ni 7  or CeNi 3  type structure. On the other hand, the aforementioned second phase should preferably be constituted by a phase having Gd 2 Co 7  type crystal structure, a phase having PuNi 3  type crystal structure and a phase having a crystal structure which is similar to Gd 2 Co 7  or PuNi 3  type structure. 
     In this case, by the expressions of “a phase having a crystal structure which is similar to Ce 2 Ni 7  type structure, CeNi 3  type structure, Gd 2 Co 7  type structure or PuNi 3  type structure (hereinafter, referred to as an analogous crystal phase)”, it is meant a phase whose main peak in the X-ray diffraction pattern thereof is similar to the main peak in the X-ray diffraction pattern of the normal structure. This analogous crystal phase should preferably have a crystal structure which can be defined by the Miller index of the Ce 2 Ni 7  type crystal structure, CeNi 3  type crystal structure, Gd 2 Co 7  type crystal structure or PuNi 3  type crystal structure. It is more preferable that this analogous crystal phase has such a crystal structure as explained with reference to the following items (1) or (2). 
     (1) A crystal structure wherein a peak exhibiting a highest intensity in an X-ray diffraction using CuKα-ray appears within 2θ of 42.1±1°, θ being Bragg angle, and the intensity ratio represented by the following formula (I) is not more than 80%: 
      I 3 /I 4   (I) 
     wherein I 4  is an intensity of a peak exhibiting a highest intensity in an X-ray diffraction using CuKα-ray; and I 3  is an intensity of a peak appearing within 2θ of 31 to 34°, θ being Bragg angle, in the X-ray diffraction. 
     (2) A crystal structure wherein a peak exhibiting a highest intensity in an X-ray diffraction using CuKα-ray appears within 2θ of 42.1±1°, and the peak appearing within 2θ of 31 to 34° in the X-ray diffraction is split into a plurality of peaks. θ is Bragg angle. 
     FIG. 6 shows an X-ray diffraction pattern which a was obtained using CuKα-ray on the hydrogen-absorbing alloy containing as a principal phase a phase having the Ce 2 Ni 7  type crystal structure, and on the hydrogen-absorbing alloy containing as a principal phase a phase having a crystal structure which is similar to the Ce 2 Ni 7  type crystal structure. The diffraction pattern of (a) in FIG. 6 is of the hydrogen-absorbing alloy containing as a principal phase a phase having the Ce 2 Ni 7  type crystal structure. In this hydrogen-absorbing alloy, the main peaks P, P1 thereof appear within 2θ of 42.1±1° and within 20 of 31 to 34° in the X-ray diffraction. Further, the peak P appearing within 2θ of 42.1±1° is the highest in intensity. 
     The diffraction patterns of (b) and (c) in FIG. 6 are of the hydrogen-absorbing alloys containing as a principal phase a phase having a crystal structure which is similar to the Ce 2 Ni 7  type structure. In the diffraction pattern of (b) of FIG. 6, a peak P 2  exhibiting the highest intensity appears within 2θ of 42.1±1°, and the peak P 3  appearing within 2θ of 31 to 34° is split into two. The intensity of this peak P3 which is split into two is lower in intensity than that of the peak P1 appearing within 2θ of 31 to 34° in the diffraction pattern of aforementioned (a). On the other hand, in the diffraction pattern of (c) of FIG. 6, a peak P4 exhibiting the highest intensity appears within of 2θ of 42.1±1°, and the peak P 5  appearing within 2θ of 31 to 34° is lower in intensity than that of the peak P 1  appearing within 2θ of 31 to 34° in the diffraction pattern of aforementioned (a). When the intensity ratio is calculated in this case according to the aforementioned formula (I) based on the diffraction pattern of (c), it would become not more than 20%. A hydrogen-absorbing alloy containing as a principal phase a phase having a crystal structure which is similar to the Ce 2 Ni 7  structure can be obtained by adjusting the temperature of heat treatment of the alloy. 
     The principal phase of the hydrogen-absorbing alloy should preferably be formed of at least one kind of phase selected from the group consisting of a phase having PuNi 3  type crystal structure, a phase having a crystal structure which is similar to the PuNi 3  type structure, a phase having Ce 2 Ni 7  type crystal structure, and a phase having a crystal structure which is similar to the Ce 2 Ni 7  type structure. It is more preferable that the aforementioned principal phase is formed of at least one kind of phase selected from the group consisting of a phase having Ce 2 Ni 7  type crystal structure and a phase having a crystal structure which is similar to the Ce 2 Ni 7  type structure. 
     In this case, by the expression of “principal phase”, it is meant a situation where at least one kind of phase selected from the group consisting of the aforementioned first phase and second phase occupies the largest volume ratio in the hydrogen-absorbing alloy, or occupies the largest area in a cross-section of the hydrogen-absorbing alloy. It is more preferable that at least one kind of phase selected from the group consisting of the aforementioned first phase and second phase occupies 50% or more in areal ratio in the hydrogen-absorbing alloy. Because, if this areal ratio is less than 50%, the hydrogen storage capacity would be undesirably reduced, thereby deteriorating the discharge capacity of the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy, or deteriorating the charge/discharge cycle life of the battery. A more preferable range of the areal ratio is not less than 60%, most preferably not less than 70%. 
     In addition to the aforementioned at least one kind of phase selected from the group consisting of the aforementioned first phase and second phase, the hydrogen-absorbing alloy may further contain a phase having an AB5 type crystal structure such as a CaCu 5  type crystal structure, a phase having an AB 2  type crystal structure such as a MgCu 2  type crystal structure, or a phase containing both of these AB 5  type and AB 2  type crystal structures. 
     As for the R, it is more preferable in view of saving the manufacturing cost of the electrode containing a hydrogen-absorbing alloy to employ at least one kind of rare earth elements selected from the group consisting of La, Ce, Pr, Nd and Y. Among them, a most preferable example of the R is a misch metal which is a mixture of rare earth elements. As for the misch metal, it is possible to employ a Ce-rich misch metal (Mm) or a La-rich misch metal (Lm). 
     It is also preferable that the R includes La, the preferable content of which being at a ratio of 60 at % or more. Because, if the content of La is less than 60 at %, the pulverization of the alloy that may be brought about repeating the hydrogen absorption/desorption reaction may occur. As a result, the cycle life of the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy may be deteriorated. More preferable content of La is 70 at % or more. However, the upper limit of La should preferably be set to 99 at %. Because, if the content of La is more than 99 at %; the reversibility of the hydrogen absorption/desorption reaction of the hydrogen-absorbing alloy would be more likely to be deteriorated. 
     It is possible, through the limitation of atomic ratio “a” to the aforementioned range, to enhance the hydrogen storage capacity, and to facilitate the release of hydrogen, thereby improving the discharge capacity of the resultant secondary battery. If the atomic ratio “a” is less than 0.15, the hydrogen-desorption property of the alloy would be deteriorated. On the other hand, if the atomic ratio “a” is more than 0.37, the hydrogen storage capacity would be greatly lowered, thus making it impossible to obtain a secondary battery having a large discharge capacity. The atomic ratio “a” should more preferably be in the range of 0.15 to 0.35, further preferably in the range of 0.15 to 0.32, most preferably in the range of 0.17 to 0.3. 
     When the aforementioned “T” is included in the hydrogen-absorbing alloy, it becomes possible to improve the characteristics of the alloy such as hydrogen-desorption rate without greatly deteriorating the hydrogen storage capacity of the alloy, or to suppress the pulverization of the alloy that may be brought about repeating the absorption and desorption of hydrogen. 
     If the atomic ratio “b” is more than 0.3, it would become impossible to expect any improvement in the hydrogen desorption property of the alloy and to suppress the pulverization of the alloy. As a result, the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy would become deteriorated in discharge capacity. Therefore, the atomic ratio “b” should more preferably be in the range of 0 to 0.2, most preferably in the range of 0 to 0.1. 
     When the aforementioned “M1” is included in the hydrogen-absorbing alloy, it becomes possible to improve the hydrogen absorption and desorption characteristics of the alloy such as hydrogen-absorption/desorption rate. This may be ascribed to the facts that when M1 is added to the hydrogen-absorbing alloy, the diffusion of hydrogen that has entered into the alloy can be facilitated, and at the same time, the absorption and desorption of hydrogen in the hydrogen-absorbing alloy can be facilitated. As aresult, the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy would be improved in initial activity. 
     If the atomic ratio X exceeds over 1.3, the charge/discharge cycle life of the secondary battery would be deteriorated. Therefore, the atomic ratio X should more preferably be in the range of 0 to 0.3. 
     When the aforementioned “M2” is included in the hydrogen-absorbing alloy, it becomes possible to improve the hydrogen absorption and desorption characteristics of the alloy such as hydrogen-absorption/desorption rate. This may be ascribed to the facts that when M2 is added to the hydrogen-absorbing alloy, the diffusion of hydrogen that has entered into the alloy can be facilitated, and at the same time, the absorption and desorption of hydrogen in the hydrogen-absorbing alloy can be facilitated. As a result, the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy would be greatly improved in charge/discharge cycle life. 
     If the atomic ratio Y exceeds over 0.5, the discharge capacity of the secondary battery would be deteriorated. Therefore, the atomic ratio Y should more preferably be in the range of 0.01 to 0.2. 
     Next, the reasons for limiting the atomic ratio α to the aforementioned range will be explained. When the atomic ratio α is 0.135 or more, the hydrogen equilibrium pressure would be deteriorated, and at the same time, the reversibility of the hydrogen absorption/desorption reaction would be deteriorated. The secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy would be deteriorated in terms of discharge voltage, thereby lowering the discharge capacity. The atomic ratio α should more preferably be in the range of 0 to 0.13, most preferably in the range of 0 to 0.1. 
     Then, the reasons for limiting the atomic ratio Z to the aforementioned range will be explained. When the atomic ratio Z becomes less than 2.5, a phase having an AB 2  type crystal structure such as an MgCu 2  type crystal structure would become a principal phase. On the other hand, when the atomic ratio Z exceeds over 4.2, a phase having an AB 5  type crystal structure such as a CaCu 5  type crystal structure would become a principal phase. Therefore, a secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy where the atomic ratio Z is less than 2.5 or more than 4.2 would be deteriorated in terms of discharge capacity and charge/discharge cycle life. Therefore, the atomic ratio Z should more preferably be in the range of 2.5 to 4, further preferably in the range of 3 to 3.8, most preferably in the range of 3 to 3.7. 
     It is particularly preferable that the atomic ratios of a, X, Y and Z are respectively satisfy the conditions of: 0.15≦a≦0.35, 0≦X≦0.3, 0≦Y≦0.3, and 2.5≦Z≦4. The secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy can be greatly improved in discharge capacity as well as in charge/discharge cycle life. 
     The hydrogen-absorbing alloy according to this invention may contain other kinds of elements such as C, N, O, F, etc. more or less as an impurity as long as it would not substantially obstruct the property of the hydrogen-absorbing alloy of this invention. By the way, it is preferable that the inclusion of these impurities should be limited to not more than 1 wt %, respectively. 
     Next, the method of manufacturing this first hydrogen-absorbing alloy will be explained. 
     First of all, each element was weighed to obtain a predetermined mixture, which was then subjected to a high frequency induction melting in an inert gas atmosphere such as an argon atmosphere for instance to obtain an alloy ingot having a composition represented by the aforementioned general formula (1). By the way, if an aimed alloy is produced by making use of a rapid solidification such as a single rolling method, a double rolling method, a disc-atomizing method or a gas-atomizing method, it is possible to enhance the homogeneity of the alloy. However, in view of reducing the manufacturing cost, the employment of a casting method as represented by the aforementioned high frequency induction melting is more preferable in obtaining the alloy having an aimed composition. 
     The aforementioned at least one kind of phase selected from the group consisting of the first phase and the second phase is assumed to be produced through a peritectic reaction between the AB 2  phase and the AB 5  phase. Therefore, the resultant alloy having a composition represented by the formula (1) should desirably be heat-treated in vacuum or in an inert atmosphere at a temperature ranging from 300° C. to less than melting point thereof for a time period ranging from 0.1 to 500 hours. More preferable temperature for this heat treatment is in the range of 600 to 1,100° C., though the optimum temperature for this heat treatment may depend on the specific composition of the alloy. Because, if the temperature for this heat treatment is less than 600° C., the peritectic reaction would not sufficiently take place, thereby possibly leaving a large quantity of a phase having the AB 2  type crystal structure as well as a large quantity of a phase having the AB 5  type crystal structure in the alloy. On the other hand, if the temperature for this heat treatment is higher than 1,100° C., a portion of the hydrogen-absorbing alloy may be melted, thereby deteriorating the characteristics of the alloy. 
     A Second Hydrogen-absorbing Alloy 
     This second hydrogen-absorbing alloy exhibits less than 0.15 (including 0) in intensity ratio to be calculated according to the following formula (2): 
     
       
         I 1 /I 2   (2)  
       
     
     wherein I 2  is an intensity of a peak exhibiting a highest intensity in an X-ray diffraction pattern using CuKα-ray; and I, is an intensity of a peak exhibiting a highest intensity within 2θ of 8 to 13°, θ being Bragg angle, in the X-ray diffraction pattern. 
     By the way, a situation where this intensity ratio (I 1 /I 2 ) is zero means a case where no peak can be detected in 2θ of 8 to 13°. Meanwhile, if there is only one peak within 2θ of 8 to 13°, the intensity of the peak is determined as I 1 . On the other hand, if a plurality of peaks all exhibiting the same intensity with each other are appeared within 2θ of 8 to 13°, the intensity of any one of the peaks is determined as I 1 . 
     Further, the composition of this hydrogen-absorbing alloy is represented by the following general formula (3): 
     
       
         R 1-a-b Mg a T b Ni Z-X M3 X   (3) 
       
     
     wherein R is at least one kind of element selected from rare earth-elements (which include Y); T is at least one element selected from the group consisting of Ca, Ti, Zr and Hf; M3 is at least one element selected from the group consisting of Co, Mn, Fe, Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, Li, P and S; and the atomic ratios of a, b, X and Z are respectively a number satisfying the conditions of: 0.1≦a≦0.6, 0≦b≦0.3, 0≦X≦2, and 2.5≦Z≦4. 
     When the intensity ratio, I 1 /I 2  becomes more than 0.15, the hydrogen-absorbing property of the alloy would be deteriorated. Therefore, a secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy would be deteriorated in terms of discharge capacity and charge/discharge cycle life. Therefore, the intensity ratio should more preferably be not more than 0.1, most preferably not more than 0.05. 
     As for the R, it is more preferable in view of saving the manufacturing cost of the electrode containing a hydrogen-absorbing alloy to employ at least one kind of rare earth elements selected from the group consisting of La, Ce, Pr, Nd and Y. Among them, a most preferable example of the R is a misch metal which is a mixture of rare earth elements. As for the misch metal, it is possible to employ a Ce-rich misch metal (Mm) or a La-rich misch metal (Lm). 
     It is also preferable that the R includes La, the preferable content of which being at a ratio of 60 at % or more. Because, if the content of La is less than 60 at %, the pulverization of the alloy that may be brought about repeating the hydrogen absorption/desorption reaction may occur. As a result, the cycle life of the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy may be deteriorated. More preferable content of La is 70 at % or more. However, the upper limit of La should preferably be set to 99 at %. Because, if the content of La is more than 99 at %; the reversibility of the hydrogen absorption/desorption reaction of the hydrogen-absorbing alloy would be more likely to be deteriorated. 
     It is possible, through the limitation of atomic ratio “a” to the aforementioned range, to enhance the hydrogen storage capacity, and to facilitate the release of hydrogen, thereby improving the discharge capacity of the resultant secondary battery. If the atomic ratio “a” is less than 0.1, the hydrogen-desorption property of the alloy would be deteriorated. On the other hand, if the atomic ratio “a” is more than 0.6, the hydrogen storage capacity would be greatly lowered, thus making it impossible to obtain a secondary battery having a large discharge capacity. As the atomic ratio “a” is increased, the intensity of peak appearing within 2θ of 8 to 13° of the X-ray diffraction pattern would be proportionately increased, thereby increasing the intensity ratio, I 1 /I 2 . Therefore, the atomic ratio “a” should more preferably be confined within the range of 0.15 to 0.35, further preferably in the range of 0.15 to 0.32, most preferably in the range of 0.17 to 0.3. 
     When the aforementioned “T” is included in the hydrogen-absorbing alloy, it becomes possible to improve the characteristics of the alloy such as hydrogen-desorption rate without greatly deteriorating the hydrogen storage capacity of the alloy, or to suppress the pulverization of the alloy that may be brought about repeating the absorption and desorption of hydrogen. 
     If the atomic ratio “b” is more than 0.3, it would become impossible to expect any improvement in the hydrogen desorption property of the alloy and to suppress the pulverization of the alloy. As a result, the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy would become deteriorated in discharge capacity. Therefore, the atomic ratio “b” should more preferably be in the range of 0 to 0.2, most preferably in the range of 0 to 0.1. 
     When the aforementioned M3 is included in the hydrogen-absorbing alloy, it becomes possible to improve the hydrogen absorption and desorption characteristics of the alloy such as hydrogen-absorption/desorption rate. This may be ascribed to the facts that when M3 is added to the hydrogen-absorbing alloy, the diffusion of hydrogen that has entered into the alloy can be facilitated, and at the same time, the absorption and desorption of hydrogen in the hydrogen-absorbing alloy can be facilitated. As a result, the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy would be improved in charge/discharge cycle property. 
     If the atomic ratio X exceeds over 2.0, the discharge capacity of the secondary battery would be deteriorated. Therefore, the atomic ratio X should more preferably be in the range of 0 to 0.5. 
     Then, the reasons for limiting the atomic ratio Z to the aforementioned range are as follows. When the atomic ratio Z becomes less than 2.5, a large quantity of hydrogen would be accumulated in the alloy, thereby deteriorating the desorption rate of hydrogen. On the other hand, when the atomic ratio Z exceeds over 4, a phase having an AB 5  type crystal structure would generated in large quantity, so that a secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy would be deteriorated in terms of discharge capacity. Therefore, the atomic ratio Z should more preferably be in the range of 3.0 to 4.0. 
     It is particularly preferable that the atomic ratios of “a” and X are respectively satisfy the conditions of: 0.15≦a≦0.35, and 0≦X≦0.5. The secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy can be greatly improved in discharge capacity as well as in charge/discharge cycle life. 
     The hydrogen-absorbing alloy according to this invention may contain other kinds of elements such as C, N, O, F, etc. more or less as an impurity as long as it would not substantially obstruct the property of the hydrogen-absorbing alloy of this invention. By the way, it is preferable that the inclusion of these impurities should be limited to not more than 1 wt %, respectively. 
     Next, the method of manufacturing this second hydrogen-absorbing alloy will be explained. 
     First of all, each element was weighed to obtain a predetermined mixture, which was then subjected to a high frequency induction melting in an inert gas atmosphere such as an argon atmosphere for instance to obtain an alloy ingot having a composition represented by the aforementioned general formula (3). By the way, if an aimed alloy is produced by making use of a rapid solidification such as a single rolling method, a double rolling method, a disc-atomizing method or a gas-atomizing method, it is possible to enhance the homogeneity of the alloy. However, in view of reducing the manufacturing cost, the employment of a casting method as represented by the aforementioned high frequency induction melting is more preferable in obtaining the alloy having an aimed composition. The aforementioned crystal structure where the intensity ratio, I 1 /I 2  is not more than 0.15 is assumed to be produced through a peritectic reaction between the AB 2  phase and the AB 5  phase. 
     Therefore, the resultant alloy having a composition represented by the formula (3) should desirably be heat-treated in vacuum or in an inert atmosphere at a temperature ranging from 300° C. to less than melting point thereof for a time period ranging from 0.1 to 500 hours. More preferable temperature for this heat treatment is in the range of 600 to 1,100° C., though the optimum temperature for this heat treatment may depend on the specific composition of the alloy. Because, if the temperature for this heat treatment is less than 600° C., the peritectic reaction would not sufficiently take place, thereby possibly leaving a large quantity of a phase having the AB 2  type crystal structure as well as a large quantity of a phase having the AB 5  type crystal structure in the alloy. On the other hand, if the temperature for this heat treatment is higher than 1,100° C., a portion of the hydrogen-absorbing alloy may be melted, thereby deteriorating the characteristics of the alloy. 
     A Third Hydrogen-absorbing Alloy 
     This third hydrogen-absorbing alloy has a composition represented by the following general formula (4): 
     
       
         R 1-a Mg a Ni Z-X-y Al X Co Y M4 α   (4) 
       
     
     wherein R is at least one kind of element selected from rare earth elements (which include Y) with a proviso that the content of Ce in said R is less than 20% by weight (including 0% by weight); M4 is at least one element selected from&#39;the group consisting of Mn, Fe, Al, Ga, Zn, Sn, Cu, Si, B, Nb, W, Ti, Zr, In, Mo, V, Cr, P and S; and the atomic ratios of a, X, Y, Z and α are respectively a number satisfying the conditions of: 0.15≦a≦0.33, 0.06≦X≦0.15, 0≦Y≦0.2, 3.15&lt;Z≦3.55, and 0≦α&lt;0.135. 
     The reasons for limiting the atomic ratio “a” to the aforementioned range are as follows. Namely, if the atomic ratio “a” is less than 0.15, the hydrogen absorbed in the hydrogen-absorbing alloy is stabilized, thereby making it difficult to release the hydrogen from the hydrogen-absorbing alloy. On the other hand, if the atomic ratio “a” is more than 0.33, a phase (for example, CaCu 5  type crystal phase) which differs from the aimed phase is more likely to be precipitated, thereby possibly deteriorating the hydrogen storage capacity. Therefore, more preferable range of the atomic ratio “a” is: 0.17≦a≦0.31, most preferably 0.18≦a≦0.3. 
     As for the R, it is more preferable in view of saving the manufacturing cost of the electrode containing a hydrogen-absorbing alloy to employ at least one kind of rare earth elements selected from the group consisting of La, Ce, Pr, Nd and Y. Among them, a most preferable example of the R is a misch metal which is a mixture of rare earth elements. 
     Next, the reasons for limiting the content of Ce in the R will be explained. If the content of Ce is 20% by weight or more, a phase (for example, CaCu 5  type crystal phase) which differs from the aimed phase is more likely to be precipitated, thereby possibly deteriorating the hydrogen storage capacity. Therefore, a preferable range of Ce content is less than 18% by weight, more preferably less than 16% by weight. 
     It is also preferable that the R includes La, the preferable content of which being at a ratio of 60 at % or more. Because, if the content of La is less than 60 at %, the pulverization of the alloy that may be brought about repeating the hydrogen absorption/desorption reaction may occur. As a result, the cycle life of the secondary battery comprising a negative electrode containing such a hydrogen-absorbing alloy may be deteriorated. More preferable content of La is 70 at % or more. However, the upper limit of La should preferably be set to 99 at %. Because, if the content of La is more than 99 at %, the reversibility of the hydrogen absorption/desorption reaction of the hydrogen-absorbing alloy would be more likely to be deteriorated. 
     Next, the reasons for limiting the atomic ratio X to the aforementioned range will be explained. Namely, if the atomic ratio X is less than 0.06, the deterioration of characteristics to be induced by the oxidation of the alloy under a high temperature environment would be especially accelerated. On the other hand, if the atomic ratio X exceeds over 0.15, a phase (for example, CaCu 5  type crystal phase) which differs from the aimed phase may be precipitated. Therefore, more preferable range of the atomic ratio X is in the range of 0.07≦X≦0.13, most preferably 0.08≦X≦0.12. 
     Next, the reasons for limiting the atomic ratio Y to the aforementioned range will be explained. Even if the atomic ratio Y of Co is increased more than 0.2 in the alloy where the atomic ratio X of Al is confined within the aforementioned range, not only it is impossible to improve the corrosion resistance of the alloy, but also it will become disadvantageous in terms of manufacturing cost. Therefore, the atomic ratio Y should more preferably be in the range of 0≦Y≦0.18, most preferably 0≦Y≦0.15. 
     Next, the reasons for limiting the atomic ratio α to the aforementioned range will be explained. When the atomic ratio α is 0.135 or more, a phase (for example, CaCu 5  type crystal phase) which differs from the aimed phase may be precipitated, thereby possibly deteriorating the hydrogen storage capacity. Therefore, the atomic ratio α should more preferably be in the range of 0≦α≦0.13, more preferably 0≦α≦0.12, most preferable 0≦α≦0.1. 
     Then, the reasons for limiting the atomic ratio Z to the aforementioned range will be explained. When the atomic ratio Z becomes 3.15 or less, a Laves type phase (an AB 2  type crystal phase) is more likely to be precipitated, thereby increasing the residual hydrogen in concurrent with the repetition of hydrogen absorption/desorption. On the other hand, when the atomic ratio Z exceeds over 3.55, a phase (for example, CaCu 5  type crystal phase) which differs from the aimed phase is more likely to be precipitated, thereby deteriorating the hydrogen storage capacity. Therefore, the atomic ratio Z should more preferably be in the range of 3.17≦Z≦3.53, most preferably 3.18≦Z≦3.52. 
     This third hydrogen-absorbing alloy should preferably contains, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu 5  type crystal structure) and a second phase having a rhombohedral crystal system. The definition of “principal phase” is the same as explained with reference to the first hydrogen-absorbing alloy. 
     As for the specific examples of the first phase and the second phase, the same crystal phases as explained with reference to the first hydrogen-absorbing alloy will be employed. 
     The principal phase of this hydrogen-absorbing alloy should preferably be formed of at least one kind of phase selected from the group consisting of a phase having PuNi 3  type crystal structure, a phase having a crystal structure which is similar to the PuNi 3  type structure, a phase having Ce 2 Ni 7  type crystal structure, and a phase having a crystal structure which is similar to the Ce 2 Ni 7  type structure. It is more preferable that the aforementioned principal phase is formed of at least one kind of phase selected from the group consisting of a phase having Ce 2 Ni 7  type crystal structure and a phase having a crystal structure which is similar to the Ce 2 Ni 7  type structure. 
     It is more preferable, by the same reasons as explained with reference to the first hydrogen-absorbing alloy, that at least one kind of phase selected from the group consisting of the aforementioned first phase and second phase occupies 50% or more in areal ratio in the hydrogen-absorbing alloy. A more preferable range of the areal ratio is not less than 60%, most preferably not less than 70%. 
     In addition to the aforementioned at least one kind of phase selected from the group consisting of the aforementioned first phase and second phase, the hydrogen-absorbing alloy may further contain a phase having an AB 5  type crystal structure such as a CaCu 5  type crystal structure, a phase having an AB 2  type crystal structure such as a MgCu 2  type crystal structure, or a phase containing both of these AB 5  type and AB 2  type crystal structures. 
     The hydrogen-absorbing alloy according to this invention may contain other kinds of elements such as C, N, O, F, etc. more or less as an impurity as long as it would not substantially obstruct the property of the hydrogen-absorbing alloy of this invention. By the way, it is preferable that the inclusion of these impurities should be limited to not more than 1 wt %, respectively. 
     Next, the method of manufacturing this third hydrogen-absorbing alloy will be explained. 
     First of all, each element was weighed to obtain a predetermined mixture, which was then subjected to a high frequency induction melting in an inert gas atmosphere such as an argon atmosphere for instance to obtain an alloy ingot having a composition represented by the aforementioned general formula (4). By the way, if an aimed alloy is produced by making use of a rapid solidification such as a single rolling method, a double rolling method, a disc-atomizing method or a gas-atomizing method, it is possible to enhance the homogeneity of the alloy. However, in view of reducing the manufacturing cost, the employment of a casting method as represented by the aforementioned high frequency induction melting is more preferable in obtaining the alloy having an aimed composition. 
     The aforementioned at least one kind of phase selected from the group consisting of the first phase group and the second phase is assumed to be produced through a peritectic reaction between the AB 2  phase and the AB 5  phase. Therefore, the resultant alloy having a composition represented by the formula (4) should desirably be heat-treated in vacuum or in an inert atmosphere at a temperature ranging from 300° C. to less than melting point thereof for a time period ranging from 0.1 to 500 hours. More preferable temperature for this heat treatment is in the range of 600 to 1,100° C., though the optimum temperature for this heat treatment may depend on the specific composition of the alloy. Because, if the temperature for this heat treatment is less than 600° C., the peritectic reaction would not sufficiently take place, thereby possibly leaving a large quantity of a phase having the AB 2  type crystal structure as well as a large quantity of a phase having the AB 5  type crystal structure in the alloy. On the other hand, if the temperature for this heat treatment is higher than 1,100° C., a portion of the hydrogen-absorbing alloy may be melted, thereby deteriorating the characteristics of the alloy. 
     Next, the secondary battery according to this invention will be explained. 
     This secondary battery comprises an electrode group essentially consisting of a positive electrode, a negative electrode containing a hydrogen-absorbing alloy, and a separator interposed between the positive electrode and the negative electrode; and an electrolyte impregnated in the electrode group. As for the hydrogen-absorbing alloy, at least one kind of hydrogen-absorbing alloy selected from the aforementioned first, second and third hydrogen-absorbing alloys can be employed. 
     In the followings, the details of the positive electrode, the negative electrode, the separator and the electrolyte will be explained. 
     (1) The Positive Electrode 
     This positive electrode can be manufactured by a process wherein a conductive material is added at first to an active material, e.g. nickel hydroxide powder to obtain a mixture, which is then kneaded together with a binder and water to prepare a paste, which is then stuffed into a conductive substrate and, after being dried, pressed and punched into a predetermined shape. 
     The nickel hydroxide powder may contain at least one kind of compound selected from the group consisting of zinc oxide, cobalt oxide, zinc hydroxide and cobalt hydroxide. 
     As for the conductive material, cobalt oxide, cobalt hydroxide, metallic cobalt, metallic nickel and carbon can be used. 
     Examples of the binder are carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene. 
     The electroconductive substrate may be formed of a mesh-shape, sponge-shape, fibrous or felt-shape metallic porous body which is made of a metal such as nickel, stainless steel or a nickel-plated metal. 
     (2) The Negative Electrode 
     This negative electrode can be manufactured for example by a method wherein a conductive material is added at first to a hydrogen-absorbing alloy powder and then kneaded together with a binder and water to prepare a paste, which is then stuffed into an electroconductive substrate and, after being dried, pressed and punched into a predetermined shape, thereby forming the negative electrode. 
     As for the binder, the same materials as explained with reference to the positive electrode can be employed. 
     As for the conductive material, carbon black for example can be used. 
     An oxide such as Y 2 O 3 , Er 2 O 3 , Yb 2 O 3 , Sm 2 O 3 , Mn 3 O 4 , LiMn 2 O 4 , Nb 2 O 5  or SnO 2  may be added to the aforementioned paste. It is possible, through the addition of these oxide to the negative electrode, to improve the charge/discharge cycle life of the battery at high temperatures. These oxides may be added singly or in combination of two or more kinds. The content of the oxide to be added should preferably be limited to the range of 0.2 to 5 wt %, more preferably 0.4 to 2 wt % based on the hydrogen-absorbing alloy. 
     The electroconductive substrate may be formed from a two-dimensional substrate such as a punched metal, an expanded metal and a nickel net; or a three-dimensional substrate such as a felt-shape metallic porous body or a sponge-shape metallic substrate. 
     (3) The Separator 
     The separator may be formed of a nonwoven polymer fabric such as a polypropylene nonwoven fabric, a nylon nonwoven fabric or a nonwoven fabric comprising polypropylene fiber and nylon fiber. In particular, a polypropylene nonwoven fabric treated to have a hydrophilic surface is preferable as a separator. 
     (4) Alkaline Electrolyte 
     Examples of the alkaline electrolyte which are useful in this invention include an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of lithium hydroxide (LiOH), an aqueous solution of potassium hydroxide (KOH), a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH), a mixed solution of potassium hydroxide (KOH) and lithium hydroxide (LiOH), and a mixed solution of NaOH, KOH and LiOH. 
     The secondary battery according to this invention can be applied to such a cylindrical alkaline secondary battery as shown in FIG.  1 . Alternatively, it is also possible to apply the secondary battery to a rectangular alkaline secondary battery, wherein a closed-end rectangular case is accommodated therein with an electrode group consisting of a laminated body comprising positive electrodes and negative electrodes which are alternately superimposed one upon another with a separator being interposed therebetween, and with an alkali electrolyte. 
     As for the hydrogen-absorbing alloy for the negative electrode of the aforementioned first, second and third nickel-hydrogen secondary batteries, at least one kind of hydrogen-absorbing alloy selected from the aforementioned first, second and third hydrogen-absorbing alloys can be employed. 
     Next, the hybrid car and electromobile according to this invention will be explained as follows. 
     The hybrid car according to this invention includes an external or internal combustion engine, an electric driving means such as a motor, and a power source for actuating the electric driving means. This power source comprises a secondary battery comprising a positive electrode, a negative electrode containing a hydrogen-absorbing alloy, and an alkaline electrolyte. As for the hydrogen-absorbing alloy, at least one kind of alloy selected from the aforementioned first, second and third hydrogen-absorbing alloys can be employed. By the way, with regard to the secondary battery, the aforementioned first, second and third nickel-hydrogen secondary batteries can be employed. 
     The “hybrid car” in this specification includes a car wherein an external or internal combustion engine is employed for actuating a generator, and the power generated by the generator and the power from the aforementioned secondary batteries are used for actuating the electric driving means to drive the wheels of the car; as well as a car wherein an external or internal combustion engine and the electric driving means are individually and properly selected in driving the wheels of the car. 
     The electromobile according to this invention includes a secondary battery as a driving power source. This secondary battery comprises a positive electrode, a negative electrode containing a hydrogen-absorbing alloy, and an alkaline electrolyte. As for the hydrogen-absorbing alloy, at least one kind of alloy selected from the aforementioned first, second and third hydrogen-absorbing alloys can be employed. By the way, with regard to the secondary battery, the aforementioned first, second and third nickel-hydrogen secondary batteries can be employed. 
     The aforementioned first hydrogen-absorbing alloy according to the present invention comprises, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu 5  type crystal structure) and a second phase having a rhombohedral crystal system. This hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (1). According to this hydrogen-absorbing alloy, it becomes possible to enhance the hydrogen equilibrium pressure and to improve the reversibility of the hydrogen absorption/desorption reaction. Further, a secondary battery comprising a negative electrode containing this hydrogen-absorbing alloy is capable of enhancing the discharge voltage, so that the discharge capacity and charge/discharge cycle life thereof can be improved. Therefore, a hybrid car as well as an electromobile comprising such a secondary battery will exhibit an improved traveling performance such as fuel consumption. 
     The aforementioned second hydrogen-absorbing alloy according to the present invention exhibits an intensity ratio of less than 0.15 (including 0) as it is calculated according to the following formula (2). Further, this hydrogen-absorbing alloy has a composition represented by the aforementioned general formula (3). This hydrogen-absorbing alloy is excellent in hydrogen absorption property and exhibits an improved hydrogen desorption property in the vicinity of normal temperature. Further, a secondary battery comprising a negative electrode containing this hydrogen-absorbing alloy is of high capacity, exhibiting an excellent charge/discharge cycle property. Therefore, a hybrid car as well as an electromobile comprising such a secondary battery will exhibit an improved traveling performance such as fuel consumption. 
     The aforementioned third hydrogen-absorbing alloy according to the present invention has a composition represented by the aforementioned general formula (4). Since the atomic ratio X of Al in this hydrogen-absorbing alloy is in the range of 0.06 to 0.15, the equilibrium pressure thereof can be enhanced and the corrosion resistance thereof can be improved. Additionally, since the atomic ratio Y of Co in this hydrogen-absorbing alloy is in the range of 0 to 0.2, the pulverization of the alloy can be inhibited. Therefore, since a secondary battery comprising a negative electrode containing this hydrogen-absorbing alloy is capable of enhancing the discharge voltage, the discharge capacity thereof can be improved. Additionally, since a secondary battery comprising a negative electrode containing this hydrogen-absorbing alloy is capable of inhibiting the corrosion of hydrogen-absorbing alloy, the degree of consumption of alkaline electrolyte due to the corrosion of hydrogen-absorbing alloy can be minimized, thus making it possible to improve the charge/discharge cycle life thereof. As a result, a hybrid car as well as an electromobile comprising such a secondary battery will exhibit an improved traveling performance such as fuel consumption. 
     Since this third hydrogen-absorbing alloy comprises, as a principal phase, at least one kind of phase selected from the group consisting of a first phase having a hexagonal crystal system (excluding a phase having a CaCu 5  type crystal structure) and a second phase having a rhombohedral crystal system, the rechargeable hydrogen storage capacity can be greatly improved. As a result, a secondary battery comprising a negative electrode containing this hydrogen-absorbing alloy would be enabled to greatly improve the discharge capacity and charge/discharge cycle life thereof. 
     Next, the examples of this invention will be explained in detail as follows with reference to drawings. 
     EXAMPLES 1-25 AND COMPARATIVE EXAMPLES 1-12 
     Preparation of a Negative Electrode 
     By making use of a high frequency furnace, a hydrogen-absorbing alloy having a composition of (La 0.7 Mg 0.3 )Ni 2.5 Co 0.5  was obtained. The alloy thus obtained was then homogenized in an argon atmosphere by heat-treating it at a temperature of 900° C. This hydrogen-absorbing alloy was then subjected to an X-ray diffraction analysis using CuKα-ray to obtain a diffraction chart shown in FIG.  3 . 
     As seen from FIG. 3, the hydrogen-absorbing alloy thus obtained indicated a highest peak in the range of 42.1°±1°, a peak having an intensity of 8.8% of the aforementioned highest peak in the range of 30.2°±1° and a peak having an intensity of 56% of the aforementioned highest peak in the range of 32.5°±1°. It should be noted that the intensity of each peak is one obtained by subtracting the intensity of the background from the intensity of the peak actually measured. 
     This hydrogen-absorbing alloy was then pulverized in an inert atmosphere, and subsequently sieved to select alloy powder having particle sizes ranging from 400 mesh to 200 mesh. Then, 100 parts by weight of the hydrogen-absorbing alloy powder was mixed with 0.5 part by weight of nickel powder which was prepared by means of carbonyl process and available in the market thereby to obtain a mixture. Thereafter, to 100 parts by weight of this mixture was added 25 parts by weight of a 4% aqueous solution of polyvinyl alcohol thereby to obtain a paste. The paste was then stuffed into a nickel foamed substrate employed as a conductive substrate, and the resultant substrate was then press-molded to obtain a paste type negative electrode. 
     Preparation of Positive Electrode 
     First of all, 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt oxide powder were mixed together to obtain a mixture, which was then mixed with 0.15 part by weight of carboxymethyl cellulose, 0.15 part by weight of sodium polyacrylate and 0.5 part by weight (reduced to solid matter) of a dispersion of polytetrafluoroethylene (1.5 in specific gravity and 60 wt % in solid matter) to obtain a mixed solution. Subsequently, 45% by weight of water was further added to the above mixed solution and the resultant mixture was kneaded to prepare a paste. Then, this paste was filled in a nickel-plated fibrous substrate and, after being dried, the substrate was rolled by making use of a roller press to manufacture a paste-type nickel positive electrode. 
     Preparation of Separator 
     A polypropylene non-woven fabric was manufactured from polypropylene resin by means of a spun-bonding method. Then, the resultant non-woven fabric was dipped into an aqueous solution of acrylic acid and then irradiated with ultraviolet rays to graft-polymerize the non-woven fabric with acrylic monomer. Thereafter, the resultant non-woven fabric was washed to remove any unreacted acrylic acid and then dried to obtain a separator having a weight per unit area of 50 g/m 2 . 
     The negative electrode and the positive electrode thus prepared was spirally wound with the aforementioned separator being interposed therebetween thereby to obtain an electrode group. In this case, the volumetric ratio between the positive electrode and the negative electrode was set such that the capacity of the positive electrode regulates the discharge capacity. Then, this electrode group and an electrolyte consisting of 2.75 N of KOH, 4.75 N of NaOH and 1 N of LiOH were placed in a closed-end cylindrical case thereby to assembling an AA size cylindrical nickel-hydrogen secondary battery having a structure as shown in FIG.  1 . 
     The quantity P(g) of the hydrogen-absorbing alloy per theoretical capacity 1 Ah of the positive electrode and the quantity Q(mL) of the alkaline electrolyte per theoretical capacity 1 Ah of the positive electrode in the secondary battery thus obtained are shown in the following Tables 1 to 3. 
     COMPARATIVE EXAMPLE 13 
     By making use of a high frequency furnace, a hydrogen-absorbing alloy represented by a composition of Mm 1.0 Ni 4.0 Co 0.4 Mn 0.3 Al 0.3  (Mm is a lanthanum-rich misch-metal) was obtained. The alloy thus obtained was then homogenized in an argon atmosphere by heat-treating it at a temperature of 1000° C. This hydrogen-absorbing alloy was then subjected to an X-ray diffraction analysis using CuKα-ray to find that the hydrogen-absorbing alloy thus obtained indicated a highest peak in the range of 42.1°±1°, a peak having an intensity of 52% of the aforementioned highest peak in the range of 30.2°±1°. However, a peak having an intensity of more than 5% of the aforementioned highest peak was not recognized in the range of 32.5°±1°. It should be noted that the intensity of each peak is one obtained by subtracting the intensity of the background from the intensity of the peak actually measured. As a result, this hydrogen-absorbing alloy was admitted as containing a phase having a LaNi 5  type crystal structure as a principle phase. 
     Then, a cylindrical nickel-hydrogen secondary battery was assembled in the same manner as that of Example 13 except that the aforementioned hydrogen-absorbing alloy was employed herein. 
     COMPARATIVE EXAMPLE 14 
     A cylindrical nickel-hydrogen secondary battery was assembled in the same manner as that of Comparative Example 11 except that the same hydrogen-absorbing alloy as explained in Comparative Example 13 was also employed herein. 
     Each of the secondary batteries obtained from Examples 1 to 25 and Comparative Examples 1 to 14 was activated and then subjected to a charge/discharge cycle at a temperature of 20° C. wherein each battery was charged to a depth of 150% with a current of 1 C, and, after 30 minutes of cut-off, discharged with 1 C until the voltage was lowered down to 1.1V. In this case, a discharge capacity was measured at the 20th cycle. The discharge capacity of each sample was indicated in comparison with the value of discharge capacity of Example 13 which was defined as 100, the results being shown in Tables 1 to 3. 
     Further, each of the secondary batteries obtained from Examples 1 to 25 and Comparative Examples 1 to 14 was charged to a depth of 150% with a current of 1 C, and, after being sufficiently cooled in a thermostat of −20° C., discharged with 0.3 C under the condition of −20° C. until the voltage of battery was lowered down to 1.1V, upon which the discharge capacity of the battery was measured. The discharge capacity of each sample was indicated in comparison with the value of discharge capacity of Example 13 which was defined as 100, the results being shown in Tables 1 to 3. 
     Further, each of the secondary batteries obtained from Examples 1 to 25 and Comparative Examples 1 to 14 was measured with regard to the internal pressure thereof. The measurement of internal pressure of these secondary batteries was performed by placing respectively the secondary batteries of Examples 1 to 25 and Comparative Examples 1 to 14 in the case of a pressure-measuring apparatus shown in FIG.  4 . 
     As shown in FIG. 4, each pressure-measuring apparatus is provided with a main case body  21  and a cap  22 , both being made of acrylic resin. The main case body  21  is provided at the center thereof with a space  23  having the same inner diameter and the same height as those of the metallic case of the AA size battery, so as to allow each of these batteries  24  to be placed in the interior of this space  23 . This battery  24  is placed in this space  23  in a state that the top of the closed-end cylindrical case is left open without being attached with a sealing plate. The top surface of the main case body  21  is hermetically closed with the cap  22 , which is fixed, via a packing  25  and an O-ring  26 , to the main case body  21  by making use of bolts  27  and nuts  28 . A pressure detector  29  is attached to the cap  22 . The lead  30  extending from the negative electrode and the lead  31  extending from the positive electrode are lead out through a space between the packing  25  and the O-ring  26 . 
     By making use of this internal pressure-measuring apparatus, a maximum internal pressure of battery at the moment where each of the secondary batteries of Examples 1 to 25 and Comparative Examples 1 to 14 was charged to a depth of 480% with a current of 0.5 C was measured, the results being shown in the following Tables 1 to 3. 
     Further, a relationship between the quantity P(g) of the hydrogen-absorbing alloy per theoretical capacity 1 Ah of the positive electrode and the quantity Q(mL) of the electrolyte per theoretical capacity 1 Ah of the positive electrode was plotted on each of the nickel-hydrogen secondary batteries of Examples 1 to 25 and Comparative Examples 1 to 12, the results being shown in FIG.  5 . 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 0.90 
                 91 
                 89 
                 1.0 
               
               
                 Example 2 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.10 
                 92 
                 91 
                 2.0 
               
               
                 Example 3 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.20 
                 92 
                 92 
                 3.0 
               
               
                 Example 4 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.34 
                 92 
                 93 
                 4.7 
               
               
                 Example 5 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 0.90 
                 94 
                 92 
                 1.1 
               
               
                 Example 6 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 0.95 
                 98 
                 96 
                 1.5 
               
               
                 Example 7 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.10 
                 98 
                 98 
                 2.0 
               
               
                 Example 8 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.20 
                 99 
                 99 
                 3.1 
               
               
                 Example 9 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.32 
                 99 
                 98 
                 4.0 
               
               
                 Example 10 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.42 
                 99 
                 100 
                 5.5 
               
               
                 Example 11 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 0.90 
                 94 
                 93 
                 2.0 
               
               
                 Example 12 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.10 
                 100 
                 99 
                 2.5 
               
               
                 Example 13 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.20 
                 100 
                 100 
                 3.5 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 14 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.30 
                 100 
                 100 
                 4.5 
               
               
                 Example 15 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.50 
                 100 
                 101 
                 5.8 
               
               
                 Example 16 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 0.90 
                 94 
                 93 
                 2.0 
               
               
                 Example 17 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 0.95 
                 98 
                 97 
                 2.5 
               
               
                 Example 18 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.10 
                 99 
                 99 
                 2.8 
               
               
                 Example 19 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.20 
                 100 
                 100 
                 3.6 
               
               
                 Example 20 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.50 
                 99 
                 100 
                 4.9 
               
               
                 Example 21 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.60 
                 99 
                 101 
                 6.0 
               
               
                 Example 22 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 0.90 
                 93 
                 91 
                 2.8 
               
               
                 Example 23 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.20 
                 93 
                 93 
                 4.6 
               
               
                 Example 24 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.30 
                 93 
                 94 
                 5.2 
               
               
                 Example 25 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.70 
                 93 
                 95 
                 6.5 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 0.90 
                 70 
                 55 
                 0.8 
               
               
                 Example 1 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 1.10 
                 75 
                 60 
                 4.5 
               
               
                 Example 2 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 1.20 
                 75 
                 65 
                 6.5 
               
               
                 Example 3 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 0.85 
                 80 
                 72 
                 1.0 
               
               
                 Example 4 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.50 
                 100 
                 97 
                 12.2 
               
               
                 Example 5 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 0.85 
                 80 
                 72 
                 0.9 
               
               
                 Example 6 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.65 
                 100 
                 100 
                 12.5 
               
               
                 Example 7 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 0.85 
                 80 
                 74 
                 1.7 
               
               
                 Example 8 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.80 
                 100 
                 99 
                 13.0 
               
               
                 Example 9 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 0.90 
                 80 
                 70 
                 1.2 
               
               
                 Example 10 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 1.30 
                 80 
                 75 
                 6.2 
               
               
                 Example 11 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 1.80 
                 82 
                 78 
                 16.0 
               
               
                 Example 12 
               
               
                 Comparative 
                 MmNi 5  type 
                 4.0 
                 1.50 
                 1.20 
                 80 
                 75 
                 4.5 
               
               
                 Example 13 
               
               
                 Comparative 
                 MmNi 5  type 
                 5.5 
                 — 
                 1.30 
                 82 
                 76 
                 11.0 
               
               
                 Example 14 
               
               
                   
               
            
           
         
       
     
     As seen from Tables 1 to 3 and FIG. 5, the secondary batteries of Examples 1 to 25 each having a suitable quantity P(g) of the hydrogen-absorbing alloy and a suitable quantity Q(mL) of the electrolyte, i.e. both quantities falling within the region encircled by four straight lines; Q=0.9, Q=0.2 P+0.7, P=3.2, P=5.0, were found satisfactory in all of discharge capacity, low temperature discharge property and internal pressure property. 
     Whereas in the case of the secondary batteries of Comparative Examples 1 to 12 wherein both of the quantity P(g) of the hydrogen-absorbing alloy and the quantity Q(mL) of the electrolyte fall out of the aforementioned region were found unsatisfactory in at least one of the aforementioned three properties, i.e. discharge capacity, low temperature discharge property and internal pressure property. 
     On the other hand, in the case of the secondary battery of Comparative Example 13 which comprised a negative electrode containing a hydrogen-absorbing alloy having a MmNi 5  type composition and containing a phase having a LaNi 5  type crystal structure as a principle phase, even though the quantity P(g) and the quantity Q(mL) were both existed within the aforementioned region, the discharge capacity and low temperature discharge property thereof were found as being almost the same as those of the secondary battery of Comparative Example 14 where the quantity P(g) and the quantity Q(mL) were both existed outside the aforementioned region. 
     Therefore, it will be understood that as long as a hydrogen-absorbing alloy to be employed has a MmNi 5  type composition and contains a phase having a LaNi 5  type crystal structure as a principle phase, it would be impossible, even if the quantity P(g) and quantity Q(mL) are suitably regulated, to obtain a secondary battery which is satisfactory in all of discharge capacity, low temperature discharge property and internal pressure property. 
     Each of the secondary batteries obtained from Examples 3, 13, 23 and Comparative Example 13 was subjected to a charge/discharge cycle at a temperature of 20° C. wherein each battery was charged to a depth of 150% with a current of 1 C, and, after 30 minutes of cut-off, discharged with 1 C until the voltage was lowered down to 1.1V. In this case, the number of cycle when the discharge capacity was lowered to 80% of the discharge capacity at moment of the first cycle was measured, the results being shown in Table 4. 
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Cycle life 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Example 3 
                 780 
               
               
                   
                 Example 13 
                 810 
               
               
                   
                 Example 23 
                 680 
               
               
                   
                 Comparative Example 13 
                 490 
               
               
                   
                   
               
            
           
         
       
     
     As seen from Table 4, the secondary batteries of Examples 3, 13 and 23 were found superior in charge/discharge cycle life as compared with the secondary battery of Comparative Example 13. 
     EXAMPLES 26-50 AND COMPARATIVE EXAMPLES 15-28 
     The batteries of Examples 26-50 and Comparative Examples 15-28 were prepared in the same manner as those of Examples 1-25 and Comparative Examples 1-14 except that the weight per unit area of the separator was altered to 40 g/m 2 . 
     In the same manner as described above, the discharge capacity at the normal temperature, the discharge capacity at a low temperature and the maximum internal pressure were measured using the batteries of Examples 26-50 and Comparative Examples 15-28, the results being shown in the following Tables 5 to 7. By the way, the discharge capacity of each secondary battery at normal temperature was indicated in comparison with the discharge capacity measured at normal temperature of the secondary battery of Example 13, which was defined as 100. Further, the discharge capacity of each secondary battery at the low temperature was indicated in comparison with the discharge capacity measured at the low temperature of the secondary battery of Example 13, which was defined as 100. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 26 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 0.90 
                 92 
                 90 
                 0.7 
               
               
                 Example 27 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.10 
                 93 
                 92 
                 1.8 
               
               
                 Example 28 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.20 
                 93 
                 93 
                 2.7 
               
               
                 Example 29 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.34 
                 93 
                 95 
                 4.5 
               
               
                 Example 30 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 0.90 
                 95 
                 96 
                 0.8 
               
               
                 Example 31 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 0.95 
                 99 
                 97 
                 1.2 
               
               
                 Example 32 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.10 
                 99 
                 99 
                 1.7 
               
               
                 Example 33 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.20 
                 100 
                 100 
                 2.8 
               
               
                 Example 34 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.32 
                 100 
                 99 
                 3.6 
               
               
                 Example 35 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.42 
                 101 
                 102 
                 5.0 
               
               
                 Example 36 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 0.90 
                 95 
                 94 
                 1.8 
               
               
                 Example 37 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.10 
                 101 
                 99 
                 2.2 
               
               
                 Example 38 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.20 
                 101 
                 101 
                 3.1 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 39 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.30 
                 101 
                 101 
                 4.0 
               
               
                 Example 40 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.50 
                 101 
                 102 
                 5.5 
               
               
                 Example 41 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 0.90 
                 95 
                 94 
                 1.8 
               
               
                 Example 42 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 0.95 
                 99 
                 98 
                 2.3 
               
               
                 Example 43 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.10 
                 100 
                 100 
                 2.5 
               
               
                 Example 44 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.20 
                 101 
                 102 
                 3.3 
               
               
                 Example 45 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.50 
                 100 
                 102 
                 4.7 
               
               
                 Example 46 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.60 
                 100 
                 102 
                 5.8 
               
               
                 Example 47 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 0.90 
                 94 
                 92 
                 2.6 
               
               
                 Example 48 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.20 
                 94 
                 94 
                 4.4 
               
               
                 Example 49 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.30 
                 94 
                 95 
                 5.0 
               
               
                 Example 50 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.70 
                 94 
                 96 
                 6.2 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 0.90 
                 72 
                 57 
                 0.6 
               
               
                 Example 15 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 1.10 
                 75 
                 61 
                 4.0 
               
               
                 Example 16 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 1.20 
                 76 
                 67 
                 6.1 
               
               
                 Example 17 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 0.85 
                 81 
                 74 
                 0.9 
               
               
                 Example 18 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.50 
                 101 
                 98 
                 11.5 
               
               
                 Example 19 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 0.85 
                 80 
                 74 
                 0.8 
               
               
                 Example 20 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.65 
                 100 
                 101 
                 11.6 
               
               
                 Example 21 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 0.85 
                 80 
                 76 
                 0.8 
               
               
                 Example 22 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.80 
                 101 
                 100 
                 12.2 
               
               
                 Example 23 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 0.90 
                 81 
                 72 
                 1.1 
               
               
                 Example 24 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 1.30 
                 81 
                 75 
                 5.7 
               
               
                 Example 25 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 1.80 
                 82 
                 79 
                 15.4 
               
               
                 Example 26 
               
               
                 Comparative 
                 MmNi 5  type 
                 4.0 
                 1.50 
                 1.20 
                 81 
                 77 
                 3.8 
               
               
                 Example 27 
               
               
                 Comparative 
                 MmNi 5  type 
                 5.5 
                 — 
                 1.30 
                 82 
                 77 
                 9.8 
               
               
                 Example 28 
               
               
                   
               
            
           
         
       
     
     EXAMPLES 51-75 AND COMPARATIVE EXAMPLES 29-42 
     The batteries of Examples 51-75 and Comparative Examples 29-42 were prepared in the same manner as those of Examples 1-25 and Comparative Examples 1-14 except that the conductive substrate of the negative electrode was changed to a punched metal. 
     In the same manner as described above, the discharge capacity at the normal temperature, the discharge capacity at a low temperature and the maximum internal pressure were measured using the batteries of Examples 51-75 and Comparative Examples 29-42, the results being shown in the following Tables 8 to 10. By the way, the discharge capacity of each secondary battery at normal temperature was indicated in comparison with the discharge capacity measured at normal temperature of the secondary battery of Example 13, which was defined as 100. Further, the discharge capacity of each secondary battery at the low temperature was indicated in comparison with the discharge capacity measured at the low temperature of the secondary battery of Example 13, which was defined as 100. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 51 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 0.90 
                 90 
                 89 
                 0.9 
               
               
                 Example 52 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.10 
                 92 
                 91 
                 1.9 
               
               
                 Example 53 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.20 
                 92 
                 92 
                 3.0 
               
               
                 Example 54 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.34 
                 92 
                 93 
                 4.7 
               
               
                 Example 55 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 0.90 
                 94 
                 92 
                 1.1 
               
               
                 Example 56 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 0.95 
                 98 
                 96 
                 1.5 
               
               
                 Example 57 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.10 
                 97 
                 98 
                 2.0 
               
               
                 Example 58 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.20 
                 99 
                 99 
                 3.1 
               
               
                 Example 59 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.32 
                 99 
                 98 
                 3.7 
               
               
                 Example 60 
                 La—Mg—Ni type 
                 3.6 
                 1.42 
                 1.42 
                 98 
                 99 
                 5.5 
               
               
                 Example 61 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 0.90 
                 94 
                 93 
                 2.0 
               
               
                 Example 62 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.10 
                 100 
                 99 
                 2.4 
               
               
                 Example 63 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.20 
                 99 
                 100 
                 3.5 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 9 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 64 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.30 
                 99 
                 100 
                 4.5 
               
               
                 Example 65 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.50 
                 99 
                 100 
                 5.8 
               
               
                 Example 66 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 0.90 
                 94 
                 93 
                 2.0 
               
               
                 Example 67 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 0.95 
                 99 
                 98 
                 2.4 
               
               
                 Example 68 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.10 
                 99 
                 99 
                 2.9 
               
               
                 Example 69 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.20 
                 100 
                 100 
                 3.6 
               
               
                 Example 70 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.50 
                 98 
                 100 
                 4.9 
               
               
                 Example 71 
                 La—Mg—Ni type 
                 4.5 
                 1.60 
                 1.60 
                 99 
                 100 
                 6.0 
               
               
                 Example 72 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 0.90 
                 93 
                 91 
                 2.8 
               
               
                 Example 73 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.20 
                 92 
                 93 
                 4.6 
               
               
                 Example 74 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.30 
                 93 
                 94 
                 5.2 
               
               
                 Example 75 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.70 
                 92 
                 95 
                 6.4 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Normal 
                 Low 
                   
               
               
                   
                   
                   
                   
                   
                 Temperature 
                 temperature 
               
               
                   
                 Hydrogen- 
                   
                   
                   
                 (20° C.) 
                 (−20° C.) 
                 Internal 
               
               
                   
                 absorbing 
                 Alloy 
                 0.2 P + 0.7 
                 Electrolyte 
                 Discharge 
                 Discharge 
                 pressure 
               
               
                   
                 alloy 
                 P (g) 
                 (mL) 
                 Q (mL) 
                 capacity 
                 capacity 
                 (kgf/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 0.90 
                 68 
                 52 
                 0.8 
               
               
                 Example 29  
               
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 1.10 
                 73 
                 58 
                 4.6 
               
               
                 Example 30 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 2.5 
                 — 
                 1.20 
                 73 
                 63 
                 6.5 
               
               
                 Example 31 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 0.85 
                 79 
                 70 
                 0.9 
               
               
                 Example 32 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 3.2 
                 1.34 
                 1.50 
                 98 
                 95 
                 12.5 
               
               
                 Example 33 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 0.85 
                 78 
                 69 
                 1.0 
               
               
                 Example 34 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 4.0 
                 1.50 
                 1.65 
                 97 
                 98 
                 12.4 
               
               
                 Example 35 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 0.85 
                 78 
                 71 
                 1.0 
               
               
                 Example 36 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.0 
                 1.70 
                 1.80 
                 99 
                 97 
                 13.3 
               
               
                 Example 37 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 0.90 
                 78 
                 68 
                 1.4 
               
               
                 Example 38 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 1.30 
                 79 
                 74 
                 6.1 
               
               
                 Example 39 
               
               
                 Comparative 
                 La—Mg—Ni type 
                 5.5 
                 — 
                 1.80 
                 81 
                 76 
                 16.2 
               
               
                 Example 40 
               
               
                 Comparative 
                 MmNi 5  type 
                 4.0 
                 1.50 
                 1.20 
                 78 
                 73 
                 4.4 
               
               
                 Example 41 
               
               
                 Comparative 
                 MmNi 5  type 
                 5.5 
                 — 
                 1.30 
                 80 
                 74 
                 10.5 
               
               
                 Example 42 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 76 
     Preparation of a Paste-type Negative Electrode 
     Each element was weighed so as to obtain a composition of La 0.63 Mg 0.37 (Ni 0.75 Co 0.1 Al 0.05 ) 3.2 , and the resultant mixture was melted in an argon atmosphere by making use of a high frequency furnace thereby to obtain an alloy ingot having the aforementioned composition. 
     Then, this hydrogen-absorbing alloy was then subjected to an X-ray diffraction analysis using CuKα-ray. As a result, the hydrogen-absorbing alloy thus obtained indicated a highest peak in the range of 42.1°±1°, a peak having an intensity of 9.2% of the aforementioned highest peak in the range of 30.2°±1°, and a peak having an intensity of 27% of the aforementioned highest peak in the range of 32.5°±1°. It should be noted that the intensity of each peak is one obtained by subtracting the intensity of the background from the intensity of the peak actually measured. 
     Then, this alloy ingot was pulverized to obtain hydrogen-absorbing alloy powder. After 100 parts by weight of the hydrogen-absorbing alloy powder thus obtained was mixed with 0.5 part by weight of carbon black, 100 parts by weight of the resultant mixture was mixed with 25 parts by weight of a 4% aqueous solution of polyvinyl alcohol thereby to obtain a paste. The paste was coated on the surface of a punched metal and then dried to obtain a negative electrode. 
     Preparation of Positive Electrode 
     First of all, 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt oxide powder were mixed together to obtain a mixture, which was then mixed with 0.15 part by weight of carboxymethyl cellulose, 0.15 part by weight of sodium polyacrylate and 0.5 part by weight (reduced to solid matter) of a dispersion of polytetrafluoroethylene (1.5 in specific gravity and 60 wt % in solid matter) to obtain a mixed solution. Subsequently, 45% by weight of pure water was further added to the above mixed solution and the resultant mixture was kneaded to prepare a paste. Then, this paste was filled in a nickel-plated fibrous substrate and, after being dried, the substrate was rolled by making use of a roller press to manufacture a paste-type nickel positive electrode. 
     The negative electrode and the positive electrode thus prepared was spirally wound with a separator consisting of a polymer unwoven fabric being interposed therebetween thereby to obtain an electrode group. 
     Preparation of a Case 
     A steel plate having a composition shown in the following Table 11 and exhibiting a tensile strength of 35 kgf/mm 2 , a yield point of 20 kgf/mm 2  and an elastic modulus of 22,900 kgf/mm 2  was cold-worked thereby to form a closed-end cylindrical, which was then plated with nickel. As a result, a case (battery case) having a tensile strength, a yield point and an elastic modulus shown in the following Table 11 was obtained. By the way, the tensile strength, yield point and elastic modulus of the case were measured by the methods explained above. 
     Then, the aforementioned electrode group was placed in this case, and then a 8 N KOH electrolyte was poured into the case. Thereafter, the case was sealed to obtain a cylindrical nickel-hydrogen secondary battery having a 4/3 A size and a capacity of 4,500 mAh. By repeating the same procedures as described above, 100 pieces of the same kind of cylindrical nickel-hydrogen secondary batteries were prepared. 
     EXAMPLE 77 
     Preparation of a Case 
     A steel plate having a composition shown in the following Table 11 and exhibiting a tensile strength of 33 kgf/mm 2 , a yield point of 19 kgf/mm 2  and an elastic modulus of 22,100 kgf/mm 2  was cold-worked thereby to form a closed-end cylindrical, which was then plated with nickel. As a result, a case (battery case) having a tensile strength, a yield point and an elastic modulus shown in the following Table 11 was obtained. 
     The same procedures as explained in Example 76 were repeated except that the case prepared in this example was employed, thereby manufacturing 100 pieces of the same kind of cylindrical nickel-hydrogen secondary batteries. 
     COMPARATIVE EXAMPLE 43 
     Preparation of a Case 
     A steel plate having a composition shown in the following Table 11 and exhibiting a tensile strength of 46 kgf/mm 2 , a yield point of 36 kgf/mm 2  and an elastic modulus of 27,000 kgf/mm 2  was cold-worked, while applying a heat treatment, thereby to form a closed-end cylindrical, which was then plated with nickel. As a result, a case (battery case) having a tensile strength, a yield point and an elastic modulus shown in the following Table 11 was obtained. 
     The same procedures as explained in Example 76 were repeated except that the case prepared in this example was employed, thereby manufacturing 100 pieces of the same kind of cylindrical nickel-hydrogen secondary batteries. 
     The secondary batteries of Examples 76 and 77 and Comparative Example 43 (100 pieces in each example) were subjected to a charge/discharge cycle under the conditions shown below thereby to investigate percent defective in capacity that has been generated up to the ends of 10th cycle, 50th cycle, 100th cycle and 200th cycle. The results are shown in Table 12. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Charge/discharge condition 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Charge current 
                 4,500 
                 mA 
               
               
                   
                 Charging time 
                 1.3 
                 hours 
               
               
                   
                 Discharge current 
                 4,500 
                 mA 
               
               
                   
                 Discharge-terminating voltage 
                 1 
                 V 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 11 
               
             
            
               
                   
                   
               
               
                   
                   
                 Tensile 
                 Yield 
                 Elastic 
               
               
                   
                 Components of case (%) 
                 strength 
                 point 
                 modulus 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 C 
                 Mn 
                 P 
                 S 
                 (kgf/mm 2 ) 
                 (kgf/mm 2 ) 
                 (kgf/mm 2 ) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Exam- 
                 0.09 
                 0.43 
                 0.020 
                 0.031 
                 71 
                 43 
                 24100 
               
               
                 ple 76 
               
               
                 Exam- 
                 0.07 
                 0.37 
                 0.028 
                 0.025 
                 69 
                 40 
                 23800 
               
               
                 ple 77 
               
               
                 Com- 
                 0.19 
                 0.60 
                 0.031 
                 0.036 
                 83 
                 59 
                 31000 
               
               
                 parative 
               
               
                 Exam- 
               
               
                 ple 43 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 12 
               
             
            
               
                   
                   
               
               
                   
                 Percent lowering capacity (%) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 After 
                 After 
                 After 
                 After 
               
               
                   
                 10 cycles 
                 50 cycles 
                 100 cycles 
                 200 cycles 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Example 76 
                 0 
                 0 
                 0 
                 0 
               
               
                 Example 77 
                 0 
                 0 
                 0 
                 0 
               
               
                 Comparative 
                 9 
                 18 
                 24 
                 35 
               
               
                 Example 43 
               
               
                   
               
            
           
         
       
     
     As seen from Tables 11 and 12, the secondary batteries of Examples 76 and 77 each comprising a negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A) and a case having a tensile strength falling within the range of 65 to 80 kgf/mm 2 , a yield point falling within the range of 30 to 55 kgf/mm 2  and an elastic modulus falling within the range of 20,000 to 30,000 kgf/mm 2  were free from any percent defective in capacity during the charge/discharge cycle. Whereas the secondary battery of Comparative Example 43 comprising the aforementioned negative electrode and a case which does not meet the aforementioned conditions with respect to the tensile strength, yield point and elastic modulus was subject to percent defective in capacity at the initial stage of the charge/discharge cycle. 
     EXAMPLE 78 
     Preparation of a Case 
     A steel plate having a composition shown in the following Table 13 and exhibiting a tensile strength of 33 kgf/mm 2 , a yield point of 19 kgf/mm 2  and an elastic modulus of 21,500 kgf/mm 2  was cold-worked thereby to form a closed-end cylindrical, which was then plated with nickel. As a result, a case (battery case) having a tensile strength, a yield point and an elastic modulus shown in the following Table 13 was obtained. 
     The same procedures as explained in Example 76 were repeated except that the case prepared in this example was employed, thereby manufacturing 100 pieces of the same kind of cylindrical nickel-hydrogen secondary batteries. 
     EXAMPLE 79 
     Preparation of a Case 
     A steel plate having a composition shown in the following Table 13 and exhibiting a tensile strength of 34 kgf/mm 2 , a yield point of 23 kgf/mm 2  and an elastic modulus of 22,600 kgf/mm 2  was cold-worked thereby to form a closed-end cylindrical, which was then plated with nickel. As a result, a case (battery case) having a tensile strength, a yield point and an elastic modulus shown in the following Table 13 was obtained. 
     The same procedures as explained in Example 76 were repeated except that the case prepared in this example was employed, thereby manufacturing 100 pieces of the same kind of cylindrical nickel-hydrogen secondary batteries. 
     COMPARATIVE EXAMPLE 44 
     Preparation of a Case 
     A steel plate having a composition shown in the following Table 13 and exhibiting a tensile strength of 49 kgf/mm 2 , a yield point of 38 kgf/mm 2  and an elastic modulus of 26,500 kgf/mm 2  was cold-worked thereby to form a closed-end cylindrical, which was then plated with nickel. As a result, a case (battery case) having a tensile strength, a yield point and an elastic modulus shown in the following Table 13 was obtained. 
     The same procedures as explained in Example 76 were repeated except that the case prepared in this example was employed, thereby manufacturing 100 pieces of the same kind of cylindrical nickel-hydrogen secondary batteries. 
     The secondary batteries of Examples 78 and 79 and Comparative Example 44 (100 pieces in each example) were subjected to a charge/discharge cycle under the same conditions as mentioned above thereby to investigate percent defective in capacity that has been generated up to the ends of 10th cycle, 50th cycle, 100th cycle and 200th cycle. The results are shown in Table 14. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 13 
               
             
            
               
                   
                   
               
               
                   
                   
                 Tensile 
                 Yield 
                 Elastic 
               
               
                   
                 Components of case (%) 
                 strength 
                 point 
                 modulus 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 C 
                 Mn 
                 P 
                 S 
                 (kgf/mm 2 ) 
                 (kgf/mm 2 ) 
                 (kgf/mm 2 ) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Exam- 
                 0.06 
                 0.40 
                 0.037 
                 0.030 
                 68 
                 42 
                 22000 
               
               
                 ple 78 
               
               
                 Exam- 
                 0.07 
                 0.35 
                 0.040 
                 0.023 
                 70 
                 45 
                 22800 
               
               
                 ple 79 
               
               
                 Com- 
                 0.20 
                 0.57 
                 0.036 
                 0.034 
                 85 
                 60 
                 30500 
               
               
                 parative 
               
               
                 Exam- 
               
               
                 ple 44 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 14 
               
             
            
               
                   
                   
               
               
                   
                 Percent lowering capacity (%) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 After 
                 After 
                 After 
                 After 
               
               
                   
                 10 cycles 
                 50 cycles 
                 100 cycles 
                 200 cycles 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Example 78 
                 0 
                 0 
                 0 
                 0 
               
               
                 Example 79 
                 0 
                 0 
                 0 
                 0 
               
               
                 Comparative 
                 8 
                 21 
                 26 
                 34 
               
               
                 Example 44 
               
               
                   
               
            
           
         
       
     
     As seen from Tables 13 and 14, the secondary batteries of Examples 78 and 79 each comprising a negative electrode containing the hydrogen-absorbing alloy represented by the aforementioned general formula (A) and a case having a tensile strength falling within the range of 65 to 80 kgf/mm 2 , a yield point falling within the range of 30 to 55 kgf/mm 2  and an elastic modulus falling within the range of 20,000 to 30,000 kgf/mm 2  were free from any percent defective in capacity during the charge/discharge cycle. Whereas the secondary battery of Comparative Example 44 comprising the aforementioned negative electrode and a case which does not meet the aforementioned conditions with respect to the tensile strength, yield point and elastic modulus was subject to percent defective in capacity at the initial stage of the charge/discharge cycle. 
     EXAMPLES 80-95 AND COMPARATIVE EXAMPLES 45-60 
     Preparation of a Negative Electrode 
     100 parts by weight of the hydrogen-absorbing alloy powder of the same kind as employed in Example 1 was mixed with 25 parts by weight of a 4% aqueous solution of polyvinyl alcohol thereby to obtain a paste. The paste was then stuffed into a nickel foamed substrate employed as a conductive substrate, and the resultant substrate was then press-molded to obtain a paste type negative electrode where a mixture containing the hydrogen-absorbing alloy was carried on the conductive substrate. 
     Preparation of Positive Electrode 
     First of all, 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt oxide powder were mixed together to obtain a mixture, which was then mixed with 0.15 part by weight of carboxymethyl cellulose, 0.15 part by weight of sodium polyacrylate and 0.5 part by weight (reduced to solid matter) of a dispersion of polytetrafluoroethylene (1.5 in specific gravity and 60 wt % in solid matter) to obtain a mixed solution. Subsequently, 45% by weight of water was further added to the above mixed solution and the resultant mixture was kneaded to prepare a paste. Then, this paste was filled in a nickel-plated fibrous substrate and, after being dried, the substrate was rolled by making use of a roller press to manufacture a paste-type nickel positive electrode. 
     Preparation of Separator 
     A polypropylene non-woven fabric was manufactured from polypropylene resin by means of a spun-bonding method. Then, the resultant non-woven fabric was dipped into an aqueous solution of acrylic acid and then irradiated with ultraviolet rays to graft-polymerize the non-woven fabric with acrylic monomer. Thereafter, the resultant non-woven fabric was washed to remove any unreacted acrylic acid and then dried to obtain a separator. 
     The negative electrode and the positive electrode thus prepared was spirally wound with the aforementioned separator being interposed therebetween thereby to obtain an electrode group. The density of the mixture in the negative electrode, the tightness of the electrode group to be calculated from the aforementioned formula (II) and the ratio of longest diameter of electrode group in relative to the inner diameter of the case are shown in the following Tables 15 to 16. In this case, the density of the mixture in the negative electrode was varied by altering the filling quantity of the paste. Further, the tightness was varied by altering the thickness of the negative electrode. 
     Then, each electrode group and an electrolyte consisting of 3.5 N of KOH, 4 N of NaOH and 1 N of LiOH were placed in a closed-end cylindrical case thereby to assembling a 4/3 A size cylindrical nickel-hydrogen secondary battery having a structure as shown in FIG.  1 . 
     COMPARATIVE EXAMPLES 61-65 
     A cylindrical nickel-hydrogen secondary battery where the density of the mixture in the negative electrode and the tightness of the electrode group were those as indicated in the following Table 17 was assembled in the same manner as that of Examples 80-95 except that the same kind of hydrogen-absorbing alloy as employed in Comparative Example 13 was employed herein. 
     The secondary batteries obtained from Examples 80 to 95 were subjected to one charge/discharge cycle wherein these batteries were charged to a depth of 150% with a current of 0.1 C, and then discharged with 1 C until the voltage was lowered down to 0.8V, and then further subjected to ten charge/discharge cycles wherein these batteries were charged to a depth of 150% with a current of 0.3 C, and then discharged with 1 C until the voltage was lowered down to 1.0V in each cycle, thus rendering the discharge capacity of each battery to become constant. After this constant discharge capacity was confirmed, the self-discharge property of the batteries was measured. 
     First of all, these secondary batteries were charged to a depth of 150% with a current of 0.3 C at the normal temperature, and then stored for seven days in a thermostat which was kept at a temperature of 50° C. Thereafter, the temperature of these secondary batteries was returned to the normal temperature. Then, these secondary batteries were discharged with an electric quantity of 1 C until the battery voltage was decreased down to 1.0V, and the discharge capacity at this moment (residual capacity) was measured. Then, the ratio of residual capacity “R” was calculated from the following formula, and the self-discharge property of the secondary battery was determined based on this ratio of residual capacity “R”. The results are shown in Tables 15 to 17. 
     
       
           R (%)=( C   2   /C   1 )×100 
       
     
     wherein C 1  denotes a discharge capacity which was measured after a charge/discharge cycle wherein a secondary battery was charged to a depth of 150% with a current of 0.3 C, and then discharged with an electric quantity of 1 C until the battery voltage was decreased down to 1.0V before it was stored in a thermostat kept at a temperature of 50° C. for seven days; and C 2  denotes a residual capacity, i.e. a discharge capacity which was measured after a secondary battery was stored in a thermostat kept at a temperature of 50° C. for seven days. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 15 
               
               
                   
                   
               
               
                   
                   
                 Density 
                   
                 Ratio of longest 
                 Ratio of 
               
               
                   
                   
                 of 
                   
                 diameter of electrode 
                 residual 
               
               
                   
                 Hydrogen-absorbing 
                 mixture 
                 Tightness 
                 group to inner diameter 
                 capacity 
               
               
                   
                 alloy 
                 (g/cc) 
                 (%) 
                 of case (%) 
                 (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 80 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.1 
                  98 
                 99 
                 75 
               
               
                 Example 81 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.3 
                  98 
                 99 
                 77 
               
               
                 Example 82 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.5 
                  98 
                 99 
                 78 
               
               
                 Example 83 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.8 
                  98 
                 99 
                 76 
               
               
                 Example 84 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.1 
                 100 
                 99 
                 78 
               
               
                 Example 85 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.3 
                 100 
                 99 
                 80 
               
               
                 Example 86 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.5 
                 100 
                 99 
                 81 
               
               
                 Example 87 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.8 
                 100 
                 99 
                 79 
               
               
                 Example 88 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.1 
                 105 
                 100 
                 80 
               
               
                 Example 89 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.3 
                 105 
                 100 
                 82 
               
               
                 Example 90 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.5 
                 105 
                 100 
                 83 
               
               
                 Example 91 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.8 
                 105 
                 100 
                 81 
               
               
                 Example 92 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.1 
                 110 
                 100 
                 76 
               
               
                 Example 93 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.3 
                 110 
                 100 
                 78 
               
               
                 Example 94 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.5 
                 110 
                 100 
                 80 
               
               
                 Example 95 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.8 
                 110 
                 100 
                 77 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 16 
               
               
                   
                   
               
               
                   
                   
                 Density 
                   
                 Ratio of longest 
                 Ratio of 
               
               
                   
                   
                 of 
                   
                 diameter of electrode 
                 residual 
               
               
                   
                 Hydrogen-absorbing 
                 mixture 
                 Tightness 
                 group to inner diameter 
                 capacity 
               
               
                   
                 alloy 
                 (g/cc) 
                 (%) 
                 of case (%) 
                 (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.0 
                  98 
                 98 
                 61 
               
               
                 Example 45 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.0 
                 100 
                 98 
                 62 
               
               
                 Example 46 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.0 
                 105 
                 100 
                 64 
               
               
                 Example 47 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.0 
                 110 
                 100 
                 65 
               
               
                 Example 48 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 6.0 
                  98 
                 99 
                 64 
               
               
                 Example 49 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 6.0 
                 100 
                 100 
                 63 
               
               
                 Example 50 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 6.0 
                 105 
                 100 
                 60 
               
               
                 Example 51 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 6.0 
                 110 
                 100 
                 58 
               
               
                 Example 52 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.1 
                  95 
                 95 
                 55 
               
               
                 Example 53 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.3 
                  95 
                 95 
                 58 
               
               
                 Example 54 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.5 
                  95 
                 96 
                 60 
               
               
                 Example 55 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.8 
                  95 
                 96 
                 63 
               
               
                 Example 56 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.1 
                 112 
                 100 
                 66 
               
               
                 Example 57 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.3 
                 112 
                 100 
                 65 
               
               
                 Example 58 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.5 
                 112 
                 100 
                 64 
               
               
                 Example 59 
               
               
                 Comparative 
                 La 0.7 Mg 0.3 Ni 2.5 Co 0.5   
                 5.8 
                 112 
                 100 
                 62 
               
               
                 Example 60 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 17 
               
               
                   
                   
               
               
                   
                   
                 Density 
                   
                 Ratio of longest 
                 Ratio of 
               
               
                   
                   
                 of 
                   
                 diameter of electrode 
                 residual 
               
               
                   
                 Hydrogen-absorbing 
                 mixture 
                 Tightness 
                 group to inner diameter 
                 capacity 
               
               
                   
                 alloy 
                 (g/cc) 
                 (%) 
                 of case (%) 
                 (%)  
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Comparative 
                 Mm 1.0 Ni 4.0 Co 0.4 Mn 0.3 Al 0.3   
                 5.1 
                 100 
                 98 
                 65 
               
               
                 Example 61 
               
               
                 Comparative 
                 Mm 1.0 Ni 4.0 Co 0.4 Mn 0.3 Al 0.3   
                 5.3 
                 100 
                 98 
                 65 
               
               
                 Example 62 
               
               
                 Comparative 
                 Mm 1.0 Ni 4.0 Co 0.4 Mn 0.3 Al 0.3   
                 5.5 
                 100 
                 99 
                 65 
               
               
                 Example 63 
               
               
                 Comparative 
                 Mm 1.0 Ni 4.0 Co 0.4 Mn 0.3 Al 0.3   
                 5.8 
                 100 
                 100 
                 66 
               
               
                 Example 64 
               
               
                 Comparative 
                 Mm 1.0 Ni 4.0 Co 0.4 Mn 0.3 Al 0.3   
                 6.0 
                 112 
                 100 
                 65 
               
               
                 Example 65  
               
               
                   
               
            
           
         
       
     
     It is clear from Tables 15 to 17 that the secondary batteries of Examples 80 to 95, which comprising a hydrogen-absorbing alloy represented by the aforementioned general formula (A) and where the density of the mixture in the negative electrode was set to fall within the range of 5.1 to 5.8 g/cc and the tightness of the electrode group was set to fall within the range of 98 to 110%, were capable of improving the ratio of residual capacity in the situation where the batteries were stored at high temperatures. 
     By contrast, although the aforementioned hydrogen-absorbing alloy was being employed, the secondary batteries of Comparative Examples 45 to 60 where the density of the mixture in the negative electrode or the tightness of the electrode group fell outside aforementioned ranges were found poor in the ratio of residual capacity in the situation where the batteries were stored at high temperatures. Further, the secondary batteries of Comparative Examples 61 to 64 which comprised a negative electrode containing a MmNi 5  type hydrogen-absorbing alloy, and where the density of the mixture in the negative electrode and the tightness of the electrode group fell within the aforementioned ranges were found almost equivalent in the ratio of residual capacity to the secondary battery of Comparative Example 65 which comprised a negative electrode containing a MmNi 5  type hydrogen-absorbing alloy, and where the density of the mixture in the negative electrode and the tightness of the electrode group fell outside the aforementioned ranges. 
     Each of the secondary batteries obtained from Examples 85, 89, 93 and Comparative Example 62 was subjected to a repetition of charge/discharge cycle wherein each battery was charged to a depth of 150% with a current of 0.3 C, and then discharged with 1 C until the voltage was lowered down to 1.0V in each cycle. In this case, the number of cycle when the discharge capacity was lowered to 80% of the discharge capacity at moment of the first cycle was measured, the results being shown in Table 18. 
     
       
         
           
               
               
             
               
                   
                 TABLE 18 
               
               
                   
                   
               
               
                   
                 Cycle life 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Example 85 
                 650 
               
               
                   
                 Example 89 
                 740 
               
               
                   
                 Example 93 
                 800 
               
               
                   
                 Example 62 
                 480 
               
               
                   
                   
               
            
           
         
       
     
     As seen from Table 18, the secondary batteries of Examples 85, 89 and 93 were found superior in charge/discharge cycle life as compared with the secondary battery of Comparative Example 62. 
     EXAMPLES 94-100 AND COMPARATIVE EXAMPLES 63-64 
     Each element was weighed so as to obtain the compositions shown in Tables 19 and 20 shown below, and the resultant compositions were melted in a high frequency induction furnace filled with an argon gas atmosphere, thereby preparing various kinds of hydrogen-absorbing alloy ingot. These alloy ingots were then heat-treated at a temperature of 970° C. in an argon gas atmosphere for 6 hours. By the way, the Lm in these Tables 19 and 20 was formed of a composition of: La=94 at. %, Ce=2 at. %, Pr=1 at. %, and Nd=3 at. %. Likewise, the Mm was formed of a composition of: La=35 at. %, Ce=50.3 at. %, Pr=5.5 at. %, Nd=9 at. %, and Sm=0.2 at. %. 
     Each of the hydrogen-absorbing alloys thus obtained was subjected to measurements to investigate the characteristics as illustrated in the following items (a) to (c). 
     (a) The crystal system of the principal phase in each hydrogen-absorbing alloys was determined by observing the crystal structure obtained from an X-ray diffraction pattern formed using CuKα-ray as an X-ray source. 
     (b) The areal ratio of the principal phase in each of the hydrogen-absorbing alloys was measured by making use of a scanning electron microscope (SEM). By the way, in the calculation of this areal ratio, SEM photographs of five view fields were employed wherein the areal ratio of the principal phase in relative to the entire area of the alloy in the view field of each SEM photograph was determined at first, and then, an average value of these areal ratios obtained was calculated to determine the areal ratio. 
     (c) Each hydrogen-absorbing alloys was tested to measure, as one of the hydrogen absorption characteristics, a rechargeable hydrogen storage capacity (JIS H7003: Term for Hydrogen Absorbing Alloy) from the iso-thermal line of pressure-composition which was measured under a hydrogen pressure of less than 10 atm. at a temperature of 60° C. by making use of Sievert&#39;s method (JIS H7201). 
     The results of these measurements are shown in the following Tables 19 and 20. 
     Subsequently, the alloy ingots thus obtained were pulverized to a particle diameter of 150 μm or less to prepare hydrogen absorbing alloy powder of 9 kinds. 
     Each hydrogen absorbing alloy powder was then mixed with electrolytic copper powder at a ratio of 1:2 (weight ratio), and 1 g of the resultant mixture was pressed for 5 minutes with a pressure of 10,000 kg/cm 2 , thus obtaining 9 kinds of pellet each having a diameter of 12 mm. These pellets were sandwiched between Ni wire nettings, and the peripheral portion thereof was spot-welded to achieve the press-bonding thereof. Subsequently, to this press-bonded body was connected Ni lead wires by means of spot-welding thereby preparing 9 kinds of hydrogen absorbing alloy electrode (a negative electrode). 
     Each of the negative electrodes thus obtained was dipped together with a counter electrode (sintered nickel electrode) into an aqueous solution of 8 N-KOH, whereby assembling test. 
     Then, the test cells thus prepared were subjected to a charge/discharge cycle test at a temperature of 20° C. The charge/discharge conditions in this test were as follows. Namely, the cell was subjected at first to a charging for 5 hours with a current of 100 mA per 1 g of the hydrogen-absorbing alloy, and, after 10 minute cessation, discharged with a current of 100 mA per 1 g of the hydrogen-absorbing alloy until the voltage (with respect to a mercury oxide electrode) was decreased down to −0.6V. This charge/discharge cycle was repeated so as to measure the maximum discharge capacity and the cycle life. The cycle life is the number of cycle when the discharge capacity was lowered to 80% of the maximum discharge capacity. The results of this test are shown in the following Tables 19 and 20. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 19 
               
               
                   
                   
               
               
                   
                   
                   
                 Areal 
                 Rechargeable 
                 Discharge 
                   
               
               
                   
                   
                 Crystal 
                 ratio of 
                 hydrogen storage 
                 capacity 
               
               
                   
                 Composition 
                 structure 
                 principal phase 
                 capacity (H/M) 
                 (mAh/g) 
                 Cycle life 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Example 94 
                 La 0.73 Mg 0.27 (Ni 0.85 Co 0.14 Al 0.01 ) 3.4   
                 Ce 2 Ni 7   
                 85% 
                 1.09 
                 400 
                 380 
               
               
                 Example 95 
                 Lm 0.68 Mg 0.32 (Ni 0.98 Al 0.02 ) 3.15   
                 PuNi 3   
                 90% 
                 1.05 
                 365 
                 290 
               
               
                 Example 96 
                 Lm 0.78 Mg 0.22 (Ni 0.85 Co 0.1 Fe 0.05 ) 3.7   
                 Ce 2 Ni 7   
                 88% 
                 1.07 
                 380 
                 325 
               
               
                 Example 97 
                 La 0.8 Y 0.05 Mg 0.15 (Ni 0.7 Co 0.28 Sn 0.02 ) 4.08   
                 Ce 2 Ni 7   
                 74% 
                 0.92 
                 290 
                 325 
               
               
                 Example 98 
                 Lm 0.64 Mg 0.36 (Ni 0.85 Co 0.1 Cu 0.05 ) 3.2   
                 PuNi 3   
                 87% 
                 1.08 
                 388 
                 270 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 20 
               
               
                   
                   
               
               
                   
                   
                   
                 Areal 
                 Rechargeable 
                 Discharge 
                   
               
               
                   
                   
                 Crystal 
                 ratio of 
                 hydrogen storage 
                 capacity 
               
               
                   
                 Composition 
                 structure 
                 principal phase 
                 capacity (H/M) 
                 (mAh/g) 
                 Cycle life 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Example 99 
                 Lm 0.74 Mg 0.26 (Ni 0.85 Co 0.1 Nb 0.04 B 0.01 ) 3.8   
                 Ce 2 Ni 7   
                 90% 
                 1.05 
                 365 
                 275 
               
               
                 Example 100 
                 Lm 0.6 Mg 0.3 Ca 0.1 (Ni 0.8 Co 0.05 Cr 0.05 ) 3.12   
                 PuNi 3   
                 94% 
                 1.08 
                 385 
                 220 
               
               
                 Comparative 
                 La 0.3 Mg 0.7 Ni 4.7   
                 CaCu 5   
                 78% 
                 0.1 
                  50 
                 120 
               
               
                 Example 63 
               
               
                 Comparative 
                 La 0.55 Mg 0.45 Ni 2.12   
                 MgCu 2   
                 92% 
                 0.2 
                  80 
                  40 
               
               
                 Example 64 
               
               
                   
               
            
           
         
       
     
     As apparent from Tables 19 and 20, the hydrogen-absorbing alloys according to Examples 94 to 100 which had a composition represented by the general formula (1) and contained, as a principal phase, at least one kind of phase selected from the group consisting of the aforementioned first phase and the aforementioned second phase indicated a higher rechargeable hydrogen storage capacity as compared with the hydrogen-absorbing alloy of Comparative Example 63 containing, as a principal phase, an AB 5  type phase such as a CaCu 5  type phase, as well as with the hydrogen-absorbing alloy of Comparative Example 64 containing, as a principal phase, an AB 2  type phase such as a MgCu 2  type phase. 
     Further, the metal oxide/hydrogen secondary batteries of Examples 94 to 100 indicated more excellent properties in both discharge capacity per unit weight and charge/discharge cycle life as compared with the secondary batteries of Comparative Examples 63 and 64. 
     EXAMPLES 101-119 AND COMPARATIVE EXAMPLES 65-69 
     High Frequency Induction Melting 
     Each element was weighed so as to obtain the compositions shown in the following Tables 21 and 23, and the resultant compositions were melted in a high frequency induction furnace filled with an argon gas atmosphere, thereby preparing the ingots of hydrogen-absorbing alloys. 
     Rapidly Solidification 
     Each element was weighed so as to obtain the compositions shown in the following Tables 21 and 23, and the resultant compositions were melted in a high frequency induction furnace filled with an argon gas atmosphere, thereby preparing the ingots of hydrogen-absorbing alloys. Then, each of these ingots was melted, and the resultant melt was dropped in an argon gas atmosphere on the surface of a copper single roll rotating at a peripheral velocity of 15 m/sec to solidify the melt, thereby obtaining a thin hydrogen-absorbing alloy flake. 
     Subsequently, each hydrogen-absorbing alloy ingot and each hydrogen-absorbing alloy flake were heat-treated under the conditions (temperature and time) shown in Tables 22 and 24. By the way, the Lm in these Tables 21 and 23 was formed of a composition of: La=94 at. %, Ce=2 at. %, Pr=1 at. %, and Nd=3 at. %. Likewise, the Mm was formed of a composition of: La=35 at. %, Ce=50.3 at. %, Pr=5.5 at. %, Nd=9 at. %, and Sm=0.2 at. %. 
     Each of the hydrogen-absorbing alloys thus obtained was subjected to measurements to investigate the characteristics as illustrated in the aforementioned items (a) to (b), the results being shown in the following Tables 21 and 23. 
     Subsequently, each of the alloy ingots and flakes thus obtained were mechanically pulverized and sieved to prepare hydrogen absorbing alloy powders having a particle diameter of 20 to 150 μm. 
     Each hydrogen absorbing alloy powder was then mixed with electrolytic copper powder at a ratio of 1:3 (weight ratio), and 1 g of the resultant mixture was pressed for 5 minutes with a pressure of 1,000 kg/cm 2 , thus obtaining pellets each having a diameter of 12 mm. These pellets were then sandwiched between Ni wire nettings, and the peripheral portion thereof was spot-welded to achieve the press-bonding thereof. Subsequently, to this press-bonded body was connected Ni lead wires by means of spot-welding thereby preparing 24 kinds of hydrogen absorbing alloy electrode (a negative electrode). 
     Each of the negative electrodes thus obtained was dipped together with a counter electrode (sintered nickel electrode) into an aqueous solution of 8 N-KOH, whereby assembling test. 
     Then, the test cells thus prepared were subjected to a charge/discharge cycle test at a temperature of 25° C. The charge/discharge conditions in this test were as follows. Namely, the cell was subjected at first to a charging for 5 hours with a current of 100 mA per 1 g of the hydrogen-absorbing alloy, and, after 10 minute cessation, discharged with a current of 50 mA per 1 g of the hydrogen-absorbing alloy until the voltage (with respect to a mercury oxide electrode) was decreased down to −0.6V. This charge/discharge cycle was repeated so as to measure the maximum discharge capacity. Further, the electric potential at the middle point of the third discharge cycle was also measured. Additionally, the cycle life was also measured. The results of this test are shown in the following Tables 22 and 24. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 21 
               
               
                   
                   
               
               
                   
                   
                   
                 Areal 
               
               
                   
                   
                 Crystal 
                 ratio of 
               
               
                   
                   
                 struc- 
                 principal 
               
               
                   
                 Composition 
                 ture 
                 phase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Exam- 
                 La 0.69 Mg 0.31 (Ni 0.73 Co 0.27 ) 3.1   
                 PuNi 3   
                 92 
               
               
                 ple 101 
               
               
                 Exam- 
                 Lm 0.72 Mg 0.28 (Ni 0.92 Fe 0.08 ) 3.2   
                 PuNi 3   
                 89 
               
               
                 ple 102 
               
               
                 Exam- 
                 La 0.53 Nd 0.24 Mg 0.23 (Ni 0.85 Cr 0.12 Al 0.03 ) 3.3   
                 Ce 2 Ni 7   
                 88 
               
               
                 ple 103 
               
               
                 Exam- 
                 La 0.5 Mm 0.16 Mg 0.34 (Ni 0.97 V 0.01 Ga 0.02 ) 2.85   
                 PuNi 3   
                 85 
               
               
                 ple 104 
               
               
                 Exam- 
                 Lm 0.67 Mg 0.33 (Ni 0.95 Al 0.03 Cu 0.02 ) 3.1   
                 PuNi 3   
                 91 
               
               
                 ple 105 
               
               
                 Exam- 
                 La 0.76 Mg 0.24 (Ni 0.97 Sn 0.03 ) 3.3   
                 Ce 2 Ni 7   
                 90 
               
               
                 ple 106 
               
               
                 Exam- 
                 Lm 0.75 Mg 0.25 (Ni 0.82 Co 0.1 Si 0.08 ) 3.4   
                 Ce 2 Ni 7   
                 92 
               
               
                 ple 107 
               
               
                 Exam- 
                 La 0.45 Pr 0.26 Mg 0.29 (Ni 0.88 Co 0.1 P 0.02 ) 3.2   
                 PuNi 3   
                 93 
               
               
                 ple 108 
               
               
                 Exam- 
                 La 0.67 Y 0.1 Mg 0.23 (Ni 0.7 Co 0.2 Cu 0.1 ) 3.9   
                 Ce 2 Ni 7   
                 89 
               
               
                 ple 109 
               
               
                 Exam- 
                 La 0.76 Mg 0.24 (Ni 0.89 V 0.04 Nb 0.07 ) 3.5   
                 Ce 2 Ni 7   
                 97 
               
               
                 ple 110 
               
               
                 Exam- 
                 La 0.6 Mm 0.13 Mg 0.27 (Ni 0.9 Zn 0.02 Sn 0.06 ) 3.6   
                 Ce 2 Ni 7   
                 95 
               
               
                 ple 111 
               
               
                 Exam- 
                 Lm 0.71 Mg 0.29 (Ni 0.96 Si 0.01 Nb 0.03 ) 3.55   
                 Ce 2 Ni 7   
                 96 
               
               
                 ple 112 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 22 
               
             
            
               
                   
                   
               
               
                   
                 Conditions for 
                   
                 Potential 
                   
               
               
                   
                 heat treatment 
                   
                 at middle 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 Tem- 
                   
                 Discharge 
                 point of 
                   
               
               
                   
                   
                 perature 
                 Time 
                 Capacity 
                 discharging 
                 Cycle 
               
               
                   
                 Methods 
                 (° C.) 
                 (H) 
                 (mAh/g) 
                 (V) 
                 life 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Example 
                 rf 
                 980 
                  2 
                 417 
                 0.92 
                 386 
               
               
                 101 
               
               
                 Example 
                 mq 
                 950 
                 40 
                 366 
                 0.88 
                 354 
               
               
                 102 
               
               
                 Example 
                 rf 
                 1000 
                 10 
                 382 
                 0.87 
                 375 
               
               
                 103 
               
               
                 Example 
                 rf 
                 950 
                 300 
                 349 
                 0.86 
                 332 
               
               
                 104 
               
               
                 Example 
                 rf 
                 1000 
                 5 
                 368 
                 0.89 
                 310 
               
               
                 105 
               
               
                 Example 
                 rf 
                 950 
                 1 
                 379 
                 0.89 
                 368 
               
               
                 106 
               
               
                 Example 
                 rf 
                 1000 
                 10 
                 398 
                 0.89 
                 379 
               
               
                 107 
               
               
                 Example 
                 mq 
                 1020 
                 3.5 
                 394 
                 0.88 
                 354 
               
               
                 108 
               
               
                 Example 
                 rf 
                 1050 
                 5 
                 346 
                 0.92 
                 305 
               
               
                 109 
               
               
                 Example 
                 rf 
                 1030 
                 20 
                 376 
                 0.91 
                 347 
               
               
                 110 
               
               
                 Example 
                 rf 
                 1040 
                 50 
                 382 
                 0.9 
                 365 
               
               
                 111 
               
               
                 Example 
                 mq 
                 1050 
                 0.5 
                 392 
                 0.91 
                 329 
               
               
                 112 
               
               
                   
               
               
                 (Note)  
               
               
                 In the manufacturing method, rf represents a high frequency induction melting, and mq represents a rapidly solidification.  
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 23 
               
               
                   
                   
               
               
                   
                   
                 Crystal 
                 Areal ratio of 
               
               
                   
                 Composition 
                 structure 
                 principal phase 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Example 113 
                 La 0.74 Mg 0.24 Ca 0.02 (Ni 0.92 Cr 0.08 ) 3.5   
                 Ce 2 Ni 7   
                 95 
               
               
                 Example 114 
                 Lm 0.40 Mm 0.20 Mg 0.32 Zr 0.08 (Ni 0.96 Ga 0.02 Cu 0.02 ) 3.05   
                 PuNi 3   
                 91 
               
               
                 Example 115 
                 La 0.64 Ce 0.10 Mg 0.22 Ca 0.04 (Ni 0.65 Co 0.34 Si 0.01 ) 3.8   
                 Ce 2 Ni 7   
                 85 
               
               
                 Example 116 
                 La 0.76 Mg 0.22 Zr 0.02 (Ni 0.99 Al 0.01 ) 3.65   
                 Ce 2 Ni 7   
                 89 
               
               
                 Example 117 
                 La 0.59 Mg 0.34 Zr 0.07 (Ni 0.96 Si 0.01 Nb 0.03 ) 3.02   
                 PuNi 3   
                 95 
               
               
                 Example 118 
                 Lm 0.73 Mg 0.24 Ca 0.03 (Ni 0.89 V 0.04 Cu 0.07 ) 3.45   
                 Ce 2 Ni 7   
                 92 
               
               
                 Example 119 
                 La 0.59 Y 0.04 Mg 0.31 Ti 0.06 (Ni 0.98 Sn 0.02 ) 3.2   
                 PuNi 3   
                 88 
               
               
                 Comparative 
                 La 0.36 Mg 0.62 Zr 0.12 (Ni 0.35 Al 0.65 ) 4.1   
                 CaCu 5   
                 65 
               
               
                 Example 65 
               
               
                 Comparative 
                 Lm 0.10 Mg 0.32 Ti 0.58 (Ni 0.95 Sn 0.05 ) 3.1   
                 TiNi 3   
                 55 
               
               
                 Example 66 
               
               
                 Comparative 
                 Ce 0.47 Mg 0.48 Zr 0.05 (Ni 0.65 Zn 0.35 ) 4.1   
                 CaCu 5   
                 70 
               
               
                 Example 67 
               
               
                 Comparative 
                 Mm 0.45 Mg 0.32 Ca 0.23 (Ni 0.95 Si 0.05 ) 3.5   
                 CaCu 5   
                 65 
               
               
                 Example 68 
               
               
                 Comparative 
                 Lm 0.62 Mg 0.24 Zr 0.14 (Ni 0.96 Al 0.03 B 0.01 ) 2.1   
                 MgCu 2   
                 90 
               
               
                 Example 69 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 24 
               
             
            
               
                   
                   
               
               
                   
                 Conditions for 
                   
                 Potential 
                   
               
               
                   
                 heat treatment 
                   
                 at middle 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 Tem- 
                   
                 Discharge 
                 point of 
                   
               
               
                   
                   
                 perature 
                 Time 
                 Capacity 
                 discharging 
                 Cycle 
               
               
                   
                 Methods 
                 (° C.) 
                 (H) 
                 (mAh/g) 
                 (V) 
                 life 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Example 
                 rf 
                 920 
                 2 
                 343 
                 0.87 
                 275 
               
               
                 113 
               
               
                 Example 
                 rf 
                 950 
                 2.5 
                 369 
                 0.91 
                 376 
               
               
                 114 
               
               
                 Example 
                 mq 
                 910 
                 10 
                 374 
                 0.88 
                 298 
               
               
                 115 
               
               
                 Example 
                 mq 
                 930 
                 15 
                 341 
                 0.91 
                 380 
               
               
                 116 
               
               
                 Example 
                 rf 
                 900 
                 4 
                 382 
                 0.89 
                 395 
               
               
                 117 
               
               
                 Example 
                 rf 
                 920 
                 10 
                 377 
                 0.88 
                 305 
               
               
                 118 
               
               
                 Example 
                 mq 
                 950 
                 4 
                 345 
                 0.88 
                 355 
               
               
                 119 
               
               
                 Compara- 
                 rf 
                 1200 
                 4 
                 100 
                 0.80 
                 120 
               
               
                 tive Ex- 
               
               
                 ample 65 
               
               
                 Compara- 
                 rf 
                 1250 
                 20 
                 30 
                 0.72 
                 40 
               
               
                 tive Ex- 
               
               
                 ample 66 
               
               
                 Compara- 
                 mq 
                 900 
                 0.01 
                 80 
                 0.75 
                 78 
               
               
                 tive Ex- 
               
               
                 ample 67 
               
               
                 Compara- 
                 rf 
                 600 
                 10 
                 154 
                 0.71 
                 107 
               
               
                 tive Ex- 
               
               
                 ample  68 
               
               
                 Compara- 
                 mq 
                 950 
                 10 
                 55 
                 0.70 
                 67 
               
               
                 tive Ex- 
               
               
                 ample 69 
               
               
                   
               
               
                 (Note)  
               
               
                 In the manufacturing method, rf represents a high frequency induction melting, and mq represents a rapidly solidification.  
               
            
           
         
       
     
     As apparent from Tables 21 to 24, the metal oxide-hydrogen secondary batteries of Examples 101 to 119 which comprised a negative electrode containing the hydrogen-absorbing alloys having a composition represented by the general formula (1) and containing, as a principal phase, at least one kind of phase selected from the group consisting of the aforementioned first phase and the aforementioned second phase indicated more excellent discharge capacity per unit weight and charge/discharge cycle life as compared with the secondary batteries of Comparative Examples 65 to 69. 
     EXAMPLES 120-137 AND COMPARATIVE EXAMPLES 70-73 
     Each element was weighed so as to obtain the compositions shown in the following Table 25, and the resultant compositions were melted in a high frequency induction furnace filled with an argon gas atmosphere, thereby preparing the ingots of hydrogen-absorbing alloys. Then, each of these ingots was heat-treated in an argon gas atmosphere at a temperature of 940° C. for 6 hours, thereby obtaining the hydrogen-absorbing alloys of Examples 120-133 and Comparative Examples 70-73. 
     On the other hand, each element was weighed so as to obtain the compositions shown in the following Table 25, and the resultant compositions were melted in a high frequency induction furnace filled with an argon gas atmosphere, thereby preparing the ingots of hydrogen-absorbing alloys. Then, each of these ingots was heat-treated in an argon gas atmosphere under the conditions shown below, thereby obtaining the hydrogen-absorbing alloys of Examples 134-137. 
     Conditions for the Heat Treatment 
     In Example 134, the treatment temperature was set to 980° C., and the treatment time was set to 6 hours. 
     In Example 135, the treatment temperature was set to 975° C., and the treatment time was set to 8 hours. 
     In Example 136, the treatment temperature was set to 1,000° C., and the treatment time was set to 5 hours. 
     In Example 137, the treatment temperature was set to 1,020° C., and the treatment time was set to 4 hours. 
     By the way, the Lm in the Table 25 was formed of a composition of: La=80 at. %, Ce=4 at. %, Pr=4 at. %, and Nd=12 at. %. Likewise, the Mm was formed of a composition of: La=35 at. %, Ce=50.3 at. %, Pr=5.5 at. %, Nd=9 at. %, and Sm=0.2 at. %. 
     The hydrogen-absorbing alloy ingot was pulverized in an argon gas atmosphere so as to obtain powders having an average particle diameter of 45 μm. Then, 100 parts by weight of the hydrogen-absorbing alloy powder was mixed with 0.5 part by weight of nickel powder which was prepared by means of carbonyl process and available in the market and with 0.5 part by weight of Ketjen Black, thereby to obtain a mixture. Thereafter, to 100 parts by weight of this mixture was added 1 part by weight of polytetrafluoroethylene (PTFE), 0.2 part by weight of sodium polyacrylate, 0.2 part by weight of carboxymethylcellulose and 50 parts by weight of water to obtain a mixture which was then agitated, thereby to obtain a paste. The paste was then coated on an iron porous thin plate covered with a nickel plating, and dried to obtain a coated plate. The thickness of this coated layer on the plate was adjusted by roll pressing, the resultant plate being cut into a predetermined size thereby to obtain a negative electrode containing 7 g of the hydrogen-absorbing alloy. 
     This negative electrode and a pasted nickel positive electrode having a nominal capacity of 1500 mAh and manufactured according to known technique were spirally wound with a separator being interposed therebetween thereby to obtain an electrode group. By the way, as for the separator, a polyolefin non-woven fabric graft-copolymerized with acrylic monomer was employed. 
     Then, this electrode group and 2.4 mL of an electrolyte containing 7 mol/cm 3  of KOH, 0.5 mol/cm 3  of NaOH and 0.5 mol/cm 3  of LiOH were placed and sealed in a closed-end cylindrical case thereby assembling an AA size cylindrical nickel-hydrogen secondary battery having a nominal capacity of 1500 mAh. 
     Then, the secondary batteries of Examples 120-137 and Comparative Examples 70 and 73 were subjected to a charge/discharge test after being left to stand at room temperature for 24 hours as follows. Namely, each of the secondary batteries was subjected to the charge/discharge cycle four times wherein these batteries were charged with a current of 150 mA for 15 hours, followed by the discharging thereof with 150 mA until the voltage was lowered down to 0.8V. 
     Thereafter, the charge/discharge cycle was repeated in an environment of 40° C. until the discharge capacity thereof was lowered to 80% or less of the discharge capacity of the first charge/discharge cycle, at which moment the number of the charge/discharge cycle was measured. The number of the charge/discharge cycle and the discharge capacity of the first charge/discharge cycle are shown in the following Table 25. By the way, the charging step in this charge/discharge cycle was performed by way of −ΔV method wherein the charging current was set to 1500 mA and the charging was terminated when the voltage was lowered by 10 mV from the maximum charge voltage. On the other hand, the discharging in this charge/discharge cycle was continued using a current of 3000 mA until the voltage of the battery was reduced to 1.0V. 
     Table 26 shows the results of measurement on the characteristics of the hydrogen-absorbing alloys of Examples 120 to 137 and Comparative Examples 70 to 73, which are performed as explained in the following paragraphs (1) to (3). 
     (1) The crystal system of the principal phase in each hydrogen-absorbing alloys was determined by observing the crystal structure obtained from an X-ray diffraction pattern formed using CuKα-ray as an X-ray source. The crystal structure of the principal phase are also shown in Table 26. 
     By the way, the hydrogen-absorbing alloys of Examples 134 and 137 contained, as a principal phase, a phase having a crystal structure which was similar to the Ce 2 Ni 7  type structure. Specifically, the alloy of Example 134 indicated a highest peak in 2θ of 42.1°±1°, in an X-ray diffraction using CuKα-ray, and the intensity ratio thereof as represented by the following formula (I) was 25%. On the other hand, the alloy of Example 135 indicated a highest peak in 2θ of 42.1°±1°, in an X-ray diffraction using CuKα-ray, and the peak appeared in 2θ of 31° to 34° was found as being split into two. 
     
       
         I 3 /I 4   (I) 
       
     
     wherein I 4  is an intensity of a peak exhibiting a highest intensity in the X-ray diffraction; and I 3  is an intensity of a peak appearing within 2θ of 31 to 34° in the X-ray diffraction. 
     On the other hand, the hydrogen-absorbing alloys of Examples 136 and 137 contained, as a principal phase, a phase having a crystal structure which was similar to the PuNi 3  type structure. Specifically, the alloy of Example 136 indicated a highest peak in 2θ of 42.1°±1°, in an X-ray diffraction using CuKα-ray, and the intensity ratio thereof as represented by the above formula (I) was 22%. On the other hand, the alloy of Example 137 indicated a highest peak in 2θ of 42.1°±1°, in an X-ray diffraction using CuKα-ray, and the peak appeared in 20 of 31° to 34° was found as being split into two. 
     (2) In the same manner as explained above with reference to Example 94, the areal ratio of the principal phase of each of the hydrogen-absorbing alloys was measured, the results being shown in Table 26. 
     (3) Each hydrogen-absorbing alloys was tested to measure, as one of the hydrogen absorption characteristics, a rechargeable hydrogen storage capacity (JIS H7003: Term for Hydrogen Absorbing Alloy) from the iso-thermal line of pressure-composition which was measured under a hydrogen pressure of less than 10 atm. at a temperature of 60° C. by making use of Sievert&#39;s method (JIS H7201). The results are shown in Table 26. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 25 
               
               
                   
                   
               
               
                   
                   
                 Capacity 
                 Cycle 
               
               
                   
                 Composition 
                 (mAh/g) 
                 life 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Example 120 
                 La 0.76 Mg 0.24 Ni 3.32 Al 0.08   
                 1350 
                 325 
               
               
                 Example 121 
                 La 0.6 Pr 0.14 Mg 0.26 Ni 3.18 Mn 0.02 Si 0.01   
                 1335 
                 220 
               
               
                 Example 122 
                 La 0.52 Nd 0.2 Mg 0.28 Ni 3.1 Co 0.1 Fe 0.01 Al 0.08   
                 1360 
                 265 
               
               
                 Example 123 
                 Lm 0.77 Mg 0.23 Ni 3.35 Al 0.1 Mo 0.01   
                 1355 
                 315 
               
               
                 Example 124 
                 Lm 0.8 Mg 0.2 Ni 3.4 Co 0.05 Mn 0.02 Al 0.1 Ta 0.01   
                 1350 
                 245 
               
               
                 Example 125 
                 La 0.75 Ce 0.05 Mg 0.2 Ni 3.5 Zn 0.02 Al 0.12 Li 0.01   
                 1320 
                 270 
               
               
                 Example 126 
                 La 0.74 Y 0.08 Mg 0.18 Ni 3.45 Co 0.08 Sn 0.02   
                 1330 
                 265 
               
               
                 Example 127 
                 Lm 0.7 Mg 0.3 Ni 3.15 Cu 0.05 Al 0.06   
                 1368 
                 250 
               
               
                 Example 128 
                 Lm 0.74 Mg 0.26 Ni 3.35 Co 0.02 W 0.01 B 0.01 Al 0.05   
                 1365 
                 275 
               
               
                 Example 129 
                 Lm 0.68 Mm 0.11 Mg 0.21 Ni 3.4 Al 0.12 Ga 0.03   
                 1335 
                 295 
               
               
                 Example 130 
                 Lm 0.66 Mm 0.1 Mg 0.24 Ni 3.3 Co 0.06 Mn 0.03 V 0.02 Al 0.07   
                 1345 
                 230 
               
               
                 Example 131 
                 Lm 0.76 Ca 0.01 Mg 0.23 Ni 3.3 Cr 0.01 Al 0.05   
                 1385 
                 295 
               
               
                 Example 132 
                 Lm 0.75 Zr 0.02 Mg 0.23 Ni 3.28 P 0.01 Al 0.1   
                 1355 
                 300 
               
               
                 Example 133 
                 Lm 0.78 Ti 0.01 Mg 0.21 Ni 3.4 Al 0.15 S 0.01   
                 1345 
                 310 
               
               
                 Example 134 
                 Lm 0.77 Mg 0.23 Ni 3.23 Al 0.12   
                 1335 
                 305 
               
               
                 Example 135 
                 Lm 0.72 Mm 0.06 Mg 0.22 Ni 3.3 Co 0.02 Mn 0.01 Sn 0.02 Al 0.07   
                 1340 
                 285 
               
               
                 Example 136 
                 Lm 0.77 Mg 0.23 Ni 3.13 Co 0.2 Mn 0.02 Al 0.12   
                 1330 
                 230 
               
               
                 Example 137 
                 Lm 0.72 Mm 0.06 Mg 0.22 Ni 3.1 Co 0.2 Mn 0.03 Nb 0.02 Al 0.07   
                 1325 
                 220 
               
               
                 Comparative 
                 La 0.3 Mg 0.7 Ni 4.7   
                  500 
                  25 
               
               
                 Example 70 
               
               
                 Comparative 
                 La 0.55 Mg 0.45 Ni 2.12   
                 1100 
                  35 
               
               
                 Example 71 
               
               
                 Comparative 
                 (La 0.32 Ce 0.48 Pr 0.05 Nd 0.13 Sm 0.02 ) 0.975 Mg 0.025 Ni 2.925 Mn 0.35 Cu 0.1 Nb 0.075   
                 1020 
                  25 
               
               
                 Example 72 
               
               
                 Comparative 
                 (La 0.3 Ce 0.49 Pr 0.05 Nd 0.14 Sm 0.02 ) 0.975 Mg 0.025 Ni 3 Mn 0.35 Cu 0.1 Ga 0.05   
                 1230 
                  30 
               
               
                 Example 73 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 26 
               
               
                   
                   
               
               
                   
                   
                 Areal ratio 
                 Rechargeable 
               
               
                   
                 Crystal structure of 
                 of principal 
                 hydrogen storage 
               
               
                   
                 principal phase 
                 phase 
                 capacity (H/M) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Example 120 
                 Ce 2 Ni 7  type 
                 97% 
                 1.09 
               
               
                 Example 121 
                 Ce 2 Ni 7  type + PuNi 3  type 
                 94% 
                 1.08 
               
               
                 Example 122 
                 Ce 2 Ni 7  type + CeNi 3  type 
                 92% 
                 1.06 
               
               
                 Example 123 
                 Ce 2 Ni 7  type + PuNi 3  type 
                 91% 
                 1.05 
               
               
                 Example 124 
                 Ce 2 Ni 7  type 
                 94% 
                 1.07 
               
               
                 Example 125 
                 Ce 2 Ni 7  type 
                 89% 
                 1.03 
               
               
                 Example 126 
                 Ce 2 Ni 7  type 
                 88% 
                 0.92 
               
               
                 Example 127 
                 Ce 2 Ni 7  type + PuNi 3  type 
                 95% 
                 1.08 
               
               
                 Example 128 
                 Ce 2 Ni 7  type 
                 92% 
                 1.05 
               
               
                 Example 129 
                 Ce 2 Ni 7  type 
                 96% 
                 1.08 
               
               
                 Example 130 
                 Ce 2 Ni 7  type + CeNi 3  type 
                 92% 
                 1.05 
               
               
                 Example 131 
                 Ce 2 Ni 7  type 
                 94% 
                 1.08 
               
               
                 Example 132 
                 Ce 2 Ni 7  type + PuNi 3  type 
                 90% 
                 0.99 
               
               
                 Example 133 
                 Ce 2 Ni 7  type 
                 89% 
                 0.97 
               
               
                 Example 134 
                 Similar to Ce 2 Ni 7  type 
                 82% 
                 0.89 
               
               
                 Example 135 
                 Similar to Ce 2 Ni 7  type 
                 83% 
                 0.87 
               
               
                 Example 136 
                 Similar to PuNi 3  type 
                 72% 
                 0.86 
               
               
                 Example 137 
                 Similar to PuNi 3  type 
                 74% 
                 0.85 
               
               
                 Comparative 
                 CaCu 5  type 
                 78% 
                 0.3 
               
               
                 Example 70 
               
               
                 Comparative 
                 MgCu 2  type 
                 79% 
                 0.2 
               
               
                 Example 71 
               
               
                 Comparative 
                 Ce 2 Ni 7  type 
                 83% 
                 0.52 
               
               
                 Example 72 
               
               
                 Comparative 
                 Ce 2 Ni 7  type 
                 85% 
                 0.51 
               
               
                 Example 73 
               
               
                   
               
            
           
         
       
     
     As apparent from Tables 25 and 26, the hydrogen-absorbing alloys according to Examples 120 to 137 which had a composition represented by the general formula (1) and contained, as a principal phase, at least one kind of phase selected from the group consisting of the aforementioned first phase and the aforementioned second phase indicated a higher rechargeable hydrogen storage capacity as compared with the hydrogen-absorbing alloys of Comparative Examples 70 to 73. By the way, the hydrogen-absorbing alloy of Comparative Example 70 contained, as a principal phase, an AB 5  type crystal phase such as a CaCu 5  type crystal phase, while the hydrogen-absorbing alloy of Comparative Example 71 contained, as a principal phase, an AB 2  type crystal phase such as a MgCu 2  type crystal phase. Further, the hydrogen-absorbing alloy of Comparative Examples 72 and 73 were of the kind where the atomic ratio of Mn was 0.135 or more, which correspond to the hydrogen-absorbing alloy disclosed in the aforementioned Japanese Patent Unexamined Publication H11-29832. 
     It will be also seen that the secondary batteries of Examples 120 to 137 are more excellent in both discharge capacity per unit weight and charge/discharge cycle life as compared with the secondary batteries of Comparative Examples 70 and 73. 
     EXAMPLES 138-153 AND COMPARATIVE EXAMPLES 74-79 
     Each element was weighed so as to obtain predetermined compositions, and the resultant compositions were melted in a high frequency induction furnace filled with an argon gas atmosphere, thereby preparing the hydrogen-absorbing alloy ingots of Examples 138-145 and Comparative Examples 74-76. On the other hand, the alloys of RNi 5  type, R 2 Ni 7  type, RNi 3  type, RNi 2  type and MgNi type, which are relatively high in melting point, were manufactured by high frequency induction furnace, and then, the resultant alloys were mixed together to obtain mixtures, which were then melted to prepare the hydrogen-absorbing alloys of Examples 146-153 and Comparative Examples 77-79. 
     Out of these alloys thus obtained, the alloys of Comparative Examples 74, 75 and 78, and the alloys of all of Examples 138-153 were heat-treated at a temperature of 900° C. for 7 hours. After being further heat-treated at a temperature of 700° C. for 40 hours, the alloys were pulverized to prepare alloy powders having a particle diameter of 25 μm or less. On the other hand, the alloys of Comparative Examples 76, 77 and 79 were pulverized, without performing the heat treatment thereof, to prepare alloy powders having a particle diameter of 125 μm or less. 
     Evaluation of Hydrogen Absorption Rate 
     The hydrogen absorption rate of the hydrogen-absorbing alloys of Examples 138-153 and Comparative Examples 74-79 was measured by making use of the temperature scanning type hydrogen absorption/desorption characteristics evaluating apparatus shown in FIG.  7 . 
     Referring to FIG. 7, a hydrogen gas cylinder  31  is connected via a pipe  32  to a test sample vessel  33 . The middle portion of the pipe  32  is branched, and a distal end of the branched pipe  34  is connected to a vacuum pump  35 . A manometer  36  is mounted on a pipe portion  34   a  branched from the branched pipe  34 . On the pipe  32  interposed between the hydrogen gas cylinder  31  and the test sample vessel  33 , there are mounted a first valve  37   1  and a second valve  37   2  in the mentioned order starting from the hydrogen gas cylinder  31 . A pressure accumulator  38  is attached to a portion of the pipe  32  which is located between the first valve  37   1  and the second valve  37   2 . Further, the vacuum pump  35  is connected via a third valve  37   3  with the branched pipe  34   a.    
     The test sample vessel  33  is provided with a heater  39 . A thermocouple  40  is disposed inside the test sample vessel  33 . A temperature controller  42  to be controlled by a computer  41  is connected to the thermocouple  40  as well as to the heater  39  so as to control the temperature of the heater  39  on the basis of a temperature detected from the thermocouple  40 . A recorder  43  to be controlled by the computer  41  is connected to the manometer  36  as well as to the temperature controller  42 . 
     Then, each of these hydrogen-absorbing alloys according to Examples  138 - 153  and Comparative Examples  74 - 79  was charged into the test sample vessel  33  (ambient temperature: 80° C.) shown in FIG.  7 . Thereafter, the first valve  37   1  was closed, and both of the second valve  37   2  and the third valve  37   3  were opened. Under this condition, the vacuum pump  35  was actuated to exhaust the air in each of the pipe  32 , the branched pipe  34  and the pressure accumulator  38 . Then, after the second valve  37   2  and the third valve  37   3  were closed, the first valve  37   1  was opened to supply hydrogen from the hydrogen gas cylinder  31  to each of the pipe  32 , the branched pipe  34  and the pressure accumulator  38  thereby carrying out a hydrogen displacement of them. Subsequently, the first valve  37   1  was closed and at the same time, the quantity of hydrogen introduced was calculated from the pressures of the system indicated by the manometer  36 . Thereafter, the second valve  37   2  was opened thereby feeding hydrogen to the test sample vessel  33 , and the temperature thereof was monitored by the thermocouple  40 . Then, the temperature of the test sample vessel  33  was controlled to rise at a constant rate by making use of the computer  41  and the temperature controller  42 . The temperature of the test sample vessel  33  was scanned by making use of a heater  39  which was designed to receive the control signals. At the same time, a change in pressure if any within the test sample vessel  33  was detected by means of the manometer  36  and recorded in the recorder  43 . 
     As described above, a constant volume of hydrogen was introduced into the test sample vessel  33  at a temperature of 80° C., and the quantity of hydrogen absorbed in each of the hydrogen-absorbing alloys during the period of five hours starting from the initiation of introducing hydrogen was detected from the changes in pressure inside the test sample vessel  33 , and at the same time, the hydrogen absorption rate was determined by calculating the quantity of hydrogen absorption per unit time (H/M·h −1 ). The results are shown in the following Tables 27 and 28. 
     In the following Tables 27 and 28, the compositions of the hydrogen-absorbing alloys as well as the intensity ratios (I 1 /I 2 ) are shown. By the way, I 2  is an intensity of a peak exhibiting a highest intensity in the X-ray diffraction pattern using CuKα-ray; and I 1  is an intensity of a peak exhibiting a highest intensity within 2θ of 8 to 13° in the X-ray diffraction pattern. 
     Evaluation of Secondary Battery Comprising a Negative Electrode Containing a Hydrogen-absorbing Alloy 
     The powder of each hydrogen absorbing alloy which was pulverized in advance to 75 μm or less was mixed with electrolytic copper powder at a ratio of 1:1 (weight ratio), and 1 g of the resultant mixture was pressed for 5 minutes with a pressure of 10,000 kg/cm 2  by making use of a tablet-molding machine (10 mm in inner diameter), thus obtaining pellets. These pellets were then sandwiched between Ni wire nettings, and the peripheral portion thereof was spot-welded to achieve the press-bonding thereof. Subsequently, to this press-bonded body was connected Ni lead wires by means of spot-welding thereby preparing 22 kinds of hydrogen absorbing alloy electrode (a negative electrode). 
     Each of the negative electrodes thus obtained was dipped together with a counter electrode (sintered nickel electrode) into an aqueous solution of 8 N-KOH, whereby assembling test. 
     Then, the test cells thus prepared were subjected to a charge/discharge cycle test at a temperature of 25° C. to obtain a maximum discharge capacity. By the way, the charge/discharge conditions in this test were as follows. Namely, the cell was subjected at first to a charging for 10 hours with a current of 100 mA per 1 g of the hydrogen-absorbing alloy, and, after 10 minute cessation, discharged with a current of 20 mA per 1 g of the hydrogen-absorbing alloy until the voltage (with respect to a mercury oxide electrode) was decreased down to −0.5V. This charge/discharge cycle was repeated so as to measure the maximum discharge capacity during this charge/discharge cycle. At the same time, the charge/discharge cycle life thereof was measured. The results of this test are shown in the following Tables 27 and 28. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 27 
               
               
                   
                   
               
               
                   
                   
                   
                   
                 Dis- 
               
               
                   
                   
                 Inten- 
                 Hydrogen 
                 charge 
               
               
                   
                   
                 sity 
                 absorption 
                 capacity 
               
               
                   
                   
                 ratio 
                 rate 
                 (mAh/ 
               
               
                   
                 Hydrogen absorbing alloy 
                 (I 1 /I 2 ) 
                 (H/M · h −1 ) 
                 g) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Compara- 
                 Ma 0.6 La 0.4 Ni 3   
                 0.28 
                 0.21 
                 100 
               
               
                 tive Ex- 
               
               
                 ample 74 
               
               
                 Compara 
                 Mg 0.5 La 0.5 Ni 3   
                 0.23 
                 0.35 
                 150 
               
               
                 tive Ex- 
               
               
                 ample 75 
               
               
                 Compara- 
                 Mg 0.45 La 0.55 Ni 3  (As cast) 
                 0.32 
                 0.15 
                  95 
               
               
                 tive Ex- 
               
               
                 ample 76 
               
               
                 Compara- 
                 Mg 0.4 La 0.6 Ni 3.1  (As cast) 
                 0.28 
                 0.23 
                 105 
               
               
                 tive Ex- 
               
               
                 ample 77 
               
               
                 Compara- 
                 Mg 0.65 La 0.15 Al 0.25 Ni 3.2   
                 0.31 
                 0.17 
                 101 
               
               
                 tive Ex- 
               
               
                 ample 78 
               
               
                 Compara- 
                 Mg 0.35 La 0.55 Ag 0.1 Ni 3.1   
                 0.25 
                 0.33 
                 122 
               
               
                 tive Ex- 
                 (As cast) 
               
               
                 ample 79 
               
               
                 Example 
                 Mg 0.45 La 0.55 Ni 3   
                 0.14 
                 0.75 
                 250 
               
               
                 138 
               
               
                 Example 
                 Mg 0.4 La 0.6 Ni 3.1   
                 0.10 
                 0.85 
                 299 
               
               
                 139 
               
               
                 Example 
                 Mg 0.3 La 0.7 Ni 3.3   
                 0.05 
                 1.10 
                 405 
               
               
                 140 
               
               
                 Example 
                 Mg 0.25 La 0.7 Al 0.05 Ni 3.2   
                 0.03 
                 1.10 
                 437 
               
               
                 141 
               
               
                 Example 
                 Mg 0.35 La 0.55 Ag 0.1 Ni 3.1   
                 0.10 
                 1.00 
                 405 
               
               
                 142 
               
               
                 Example 
                 Mg 0.25 Y 0.65 V 0.05 Mo 0.05 Ni 3.3   
                 0.09 
                 1.00 
                 411 
               
               
                 143 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 28 
               
               
                   
                   
               
               
                   
                   
                 Intensity 
                 Hydrogen 
                 Discharge 
               
               
                   
                   
                 ratio 
                 absorption 
                 capacity 
               
               
                   
                 Hydrogen absorbing alloy 
                 (I 1 /I 2 ) 
                 rate (H/M · h −1 ) 
                 (mAh/g) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Example 144 
                 Ma 0.34 La 0.5 Mm 0.06 Nb 0.05 Sn 0.05 Ni 2.8   
                 0.13 
                 0.90 
                 367 
               
               
                 Example 145 
                 Mg 0.2 Lm 0.7 Si 0.05 Ga 0.05 Ni 3.5   
                 0.13 
                 0.80 
                 371 
               
               
                 Example 146 
                 Mg 0.3 La 0.7 Ni 2.5 Co 0.6   
                 0.06 
                 1.10 
                 410 
               
               
                 Example 147 
                 Mg 0.2 La 0.8 Ni 2.5 Cu 1.5   
                 0.13 
                 0.80 
                 370 
               
               
                 Example 148 
                 Mg 0.35 Lm 0.5 Gd 0.15 Ni 2.6 Fe 0.6   
                 0.11 
                 0.90 
                 388 
               
               
                 Example 149 
                 Mg 0.4 La 0.4 Ce 0.2 Ni 2.9 Cr 0.3 Zn 0.1   
                 0.12 
                 0.80 
                 275 
               
               
                 Example 150 
                 Mg 0.3 La 0.6 Al 0.1 Ni 2.5 Co 0.7   
                 0.13 
                 0.80 
                 374 
               
               
                 Example 151 
                 Mg 0.15 La 0.4 Sm 0.35 Pb 0.05 C 0.05 Ni 2.9 Cr 0.9   
                 0.10 
                 0.80 
                 257 
               
               
                 Example 152 
                 Mg 0.15 Lm 0.6 Nd 0.1 Ta 0.05 Ge 0.07 B 0.03 Ni 2.5 Fe 1.5   
                 0.11 
                 0.70 
                 221 
               
               
                 Example 153 
                 Mg 0.25 Ca 0.65 In 0.05 P 0.05 Ni 2.9 Cu 1.1 Zn 0.3   
                 0.09 
                 1.00 
                 419 
               
               
                   
               
            
           
         
       
     
     As apparent from Tables 27 and 28, the hydrogen-absorbing alloys of Examples 138 to 153 having a composition represented by the aforementioned general formula (3) and exhibiting less than 0.15 in intensity ratio (I 1 /I 2 ) indicated more excellent hydrogen absorption property as compared with the hydrogen-absorbing alloys of Comparative Examples 74 to 78. 
     It will be also seen that the secondary batteries of Examples 138 to 153 each comprising a negative electrode containing these hydrogen-absorbing alloys are greatly excellent in both discharge capacity per unit weight and charge/discharge property as compared with the secondary batteries of Comparative Examples 74 to 79. 
     In particular, it will be seen that the hydrogen-absorbing alloy of Example 142 is more excellent in hydrogen absorption rate as well as in the discharge capacity per unit weight as compared with the hydrogen-absorbing alloy of Comparative Example 79 having the same composition as that of Example 275. 
     EXAMPLES 154 TO 171 AND COMPARATIVE EXAMPLES 80 AND 81 
     Each element was weighed so as to obtain the compositions shown in the following Table 29, and the resultant compositions were melted in a high frequency induction furnace filled with an argon gas atmosphere, thereby preparing the ingots of hydrogen-absorbing alloys. Then, each of these ingots was heat-treated in an argon gas atmosphere at a temperature of 950° C. for 5 hours, which was further followed by an additional heat treatment at a temperature of 800° C. for 20 hours, thereby obtaining the hydrogen-absorbing alloys of Examples 154 to 171 and Comparative Examples 80 and 81. 
     By the way, the Lm in the Table 29 was formed of a composition of: La=90 at. %, Ce=2 at. %, Pr=2 at. %, and Nd=6 at. %. Likewise, the Mm was formed of a composition of: La=45 at. %, Ce=50.3 at. %, Pr=1 at. %, Nd=3.5 at. %, and Sm=0.2 at. %. 
     The hydrogen-absorbing alloy ingot was pulverized in an argon gas atmosphere so as to obtain powders having an average particle diameter of 45 μm. Then, 100 parts by weight of the hydrogen-absorbing alloy powder was mixed with 0.5 part by weight of nickel powder which was prepared by means of carbonyl process and available in the market and with 0.5 part by weight of Ketjen Black, thereby to obtain a mixture. Thereafter, to 100 parts by weight of this mixture was added 1 part by weight of styrene-butadiene rubber (SBR), 0.2 part by weight of sodium polyacrylate, 0.2 part by weight of carboxymethylcellulose and 50 parts by weight of water to obtain a mixture which was then agitated, thereby to obtain a paste. The paste was then coated on an iron porous thin plate covered with a nickel plating, and dried to obtain a coated plate. The thickness of this coated layer on the plate was adjusted by roll pressing, the resultant plate being cut into a predetermined size thereby to obtain a negative electrode containing 3.2 g of the hydrogen-absorbing alloy. 
     This negative electrode and a pasted nickel positive electrode having a nominal capacity of 650 mAh and manufactured according to known technique were spirally wound with a separator being interposed therebetween thereby to obtain an electrode group. By the way, as for the separator, a polyolefin non-woven fabric graft-copolymerized with acrylic monomer was employed. 
     Then, this electrode group and 1.5 mL of an electrolyte containing 7 mol/cm 3  of KOH and 1.0 mol/cm 3  of LiOH were placed and sealed in a closed-end cylindrical case thereby assembling an AAA size cylindrical nickel-hydrogen secondary battery having a nominal capacity of 650 mAh. 
     Then, the secondary batteries of Examples 154-171 and Comparative Examples 80 and 81 were subjected to a charge/discharge test after being left to stand at room temperature for 24 hours as follows. Namely, each of the secondary batteries was subjected to the charge/discharge cycle four times wherein these batteries were charged with a current of 65 mA for 15 hours, followed by the discharging thereof with 65 mA until the voltage was lowered down to 0.7V. 
     Thereafter, the charge/discharge cycle was repeated in an environment of 45° C. until the discharge capacity thereof was lowered to 80% or less of the discharge capacity of the first charge/discharge cycle, at which moment the number of the charge/discharge cycle was measured. The number of the charge/discharge cycle and the discharge capacity of the first charge/discharge cycle are shown in the following Table 29. By the way, the charging step in this charge/discharge cycle was performed by way of −ΔV method wherein the charging current was set to 650 mA and the charging was terminated when the voltage was lowered by 10 mV from the maximum charge voltage. On the other hand, the discharging in this charge/discharge cycle was continued using a current of 1300 mA until the voltage of the battery was reduced to 1.0V. 
     Further, the intensity ratio (I 1 /I 2 ) of each of the hydrogen-absorbing alloys of Examples 154 to 171 and Comparative Examples 80 and 81 was measured in the same manner as explained with reference to Example 138, the results being shown in the following Table 30. Additionally, each hydrogen-absorbing alloys was tested to measure a rechargeable hydrogen storage capacity (JIS H7003: Term for Hydrogen Absorbing Alloy) from the iso-thermal line of pressure-composition which was measured under a hydrogen pressure of less than 10 atm. at a temperature of 60° C. by making use of Sievert&#39;s method (JIS H7201). The results are shown in Table 30. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 29 
               
               
                   
                   
               
               
                   
                   
                 Capacity 
                   
               
               
                   
                 Composition 
                 (mAh/g) 
                 Cycle life 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Example 154 
                 Lm 0.77 Mg 0.23 Ni 3.32 Al 0.09   
                 381 
                 322 
               
               
                 Example 155 
                 La 0.63 Nd 0.14 Mg 0.23 Ni 3.28 Mn 0.02 Si 0.01   
                 374 
                 218 
               
               
                 Example 156 
                 La 0.55 Pr 0.2 Mg 0.23 Ni 3.21 Co 0.1 Fe 0.01 Al 0.08   
                 385 
                 262 
               
               
                 Example 157 
                 Lm 0.77 Mg 0.23 Ni 3.29 Al 0.11 W 0.01   
                 383 
                 312 
               
               
                 Example 158 
                 Lm 0.8 Mg 0.2 Ni 3.38 Co 0.05 Mn 0.02 Al 0.11 Mo 0.01   
                 381 
                 243 
               
               
                 Example 159 
                 La 0.77 Ce 0.03 Mg 0.2 Ni 3.5 Zn 0.02 Al 0.12   
                 368 
                 267 
               
               
                 Example 160 
                 La 0.74 Y 0.08 Mg 0.18 Ni 3.45 Co 0.08 Sn 0.02   
                 372 
                 262 
               
               
                 Example 161 
                 Lm 0.7 Mg 0.3 Ni 3.15 Cu 0.05 Al 0.06 Li 0.01   
                 388 
                 248 
               
               
                 Example 162 
                 Lm 0.74 Mg 0.26 Ni 3.25 Co 0.05 Ta 0.01 B 0.01 Al 0.08   
                 387 
                 272 
               
               
                 Example 163 
                 Lm 0.69 Mm 0.07 Mg 0.24 Ni 3.2 Al 0.12 Ga 0.02   
                 374 
                 292 
               
               
                 Example 164 
                 Lm 0.66 Mm 0.11 Mg 0.23 Ni 3.3 Co 0.03 Mn 0.01 V 0.02 Al 0.1   
                 378 
                 228 
               
               
                 Example 165 
                 Lm 0.74 Ca 0.01 Mg 0.25 Ni 3.3 Cr 0.01 Al 0.07   
                 396 
                 292 
               
               
                 Example 166 
                 Lm 0.76 Zr 0.02 Mg 0.22 Ni 3.28 P 0.01 Al 0.11   
                 383 
                 297 
               
               
                 Example 167 
                 Lm 0.77 Ti 0.01 Mg 0.22 Ni 3.3 Al 0.12 S 0.01   
                 378 
                 307 
               
               
                 Example 168 
                 Lm 0.77 Mg 0.23 Ni 3.23 Al 0.12   
                 374 
                 302 
               
               
                 Example 169 
                 Lm 0.72 Mm 0.06 Mg 0.22 Ni 3.3 Co 0.02 Mn 0.01 Sn 0.02 Al 0.07   
                 376 
                 282 
               
               
                 Example 170 
                 Lm 0.77 Mg 0.23 Ni 3.13 Co 0.2 Mn 0.02 Al 0.12   
                 372 
                 228 
               
               
                 Example 171 
                 Lm 0.72 Mm 0.06 Mg 0.22 Ni 3.1 Co 0.2 Mn 0.03 Nb 0.02 Al 0.07   
                 370 
                 218 
               
               
                 Comparative 
                 La 0.5 Mg 0.5 Ni 4.7   
                 250 
                  25 
               
               
                 Example 80 
               
               
                 Comparative 
                 La 0.35 Mg 0.65 Ni 3.1   
                 200 
                  20 
               
               
                 Example 81 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 30 
               
               
                   
                   
               
               
                   
                   
                 Rechargeable hydrogen 
               
               
                   
                 Intensity ratio 
                 storage capacity 
               
               
                   
                 (I 1 /I 2 ) 
                 (H/M) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Example 154 
                 0.002 
                 1.02 
               
               
                 Example 155 
                 0 
                 0.95 
               
               
                 Example 156 
                 0.004 
                 1.01 
               
               
                 Example 157 
                 0.01 
                 0.97 
               
               
                 Example 158 
                 0 
                 0.99 
               
               
                 Example 159 
                 0.006 
                 0.95 
               
               
                 Example 160 
                 0.009 
                 1.03 
               
               
                 Example 161 
                 0.013 
                 1.01 
               
               
                 Example 162 
                 0.01 
                 0.98 
               
               
                 Example 163 
                 0.002 
                 0.93 
               
               
                 Example 164 
                 0.008 
                 0.94 
               
               
                 Example 165 
                 0.002 
                 0.92 
               
               
                 Example 166 
                 0.01 
                 0.96 
               
               
                 Example 167 
                 0 
                 0.94 
               
               
                 Example 168 
                 0.003 
                 0.97 
               
               
                 Example 169 
                 0.007 
                 0.98 
               
               
                 Example 170 
                 0.002 
                 0.93 
               
               
                 Example 171 
                 0.01 
                 0.91 
               
               
                 Comparative Example 80 
                 0.27 
                 0.13 
               
               
                 Comparative Example 81 
                 0.32 
                 0.14 
               
               
                   
               
            
           
         
       
     
     As apparent from Tables 29 and 30, the hydrogen-absorbing alloys of Examples 154 to 171 having a composition represented by the aforementioned general formula (3) and exhibiting less than 0.15 in intensity ratio (I 1 /I 2 ) indicated more excellent rechargeable hydrogen storage capacity as compared with the hydrogen-absorbing alloys of Comparative Examples 80 and 81. 
     It will be also seen that the nickel-hydrogen secondary batteries of Examples 154 to 171 are greatly excellent in both initial discharge capacity per unit weight and charge/discharge cycle life as compared with the secondary batteries of Comparative Examples 80 and 81. 
     EXAMPLES 172 TO 182 AND COMPARATIVE EXAMPLES 82 TO 87 
     Each element was weighed so as to obtain the compositions shown in the following Tables 31 and 33, and the resultant compositions were melted in a high frequency induction furnace filled with an argon gas atmosphere, thereby preparing the ingots of hydrogen-absorbing alloys. Then, each of these ingots was heat-treated in an argon gas atmosphere under the conditions shown below, thereby obtaining the hydrogen-absorbing alloys of Examples 172 to 82 and Comparative Examples 82 to 87. 
     Conditions for the Heat Treatment 
     In Examples 172 to 178 and Comparative Examples 82 to 87, the treatment temperature was set to 945° C., and the treatment time was set to 8 hours. 
     In Example 179, the treatment temperature was set to 985° C., and the treatment time was set to 5 hours. 
     In Example 180, the treatment temperature was set to 990° C., and the treatment time was set to 4 hours. 
     In Example 181, the treatment temperature was set to 970° C., and the treatment time was set to 6 hours. 
     In Example 182, the treatment temperature was set to 1020° C., and the treatment time was set to 3 hours. 
     The hydrogen-absorbing alloy ingot was pulverized in an argon gas atmosphere so as to obtain powders having an average particle diameter of 65 μm. Then, 100 parts by weight of the hydrogen-absorbing alloy powder was mixed with 0.5 part by weight of nickel powder which was prepared by means of carbonyl process and available in the market and with 0.5 part by weight of Ketjen Black, thereby to obtain a mixture. Thereafter, to 100 parts by weight of this mixture was added 1 part by weight of polytetrafluoroethylene (PTFE), 0.2 part by weight of sodium polyacrylate, 0.2 part by weight of carboxymethylcellulose and 50 parts by weight of water to obtain a mixture which was then agitated, thereby to obtain a paste. The paste was then coated on an iron porous thin plate covered with a nickel plating, and dried to obtain a coated plate. The thickness of this coated layer on the plate was adjusted by roll pressing, the resultant plate being cut into a predetermined size thereby to obtain a negative electrode containing 7 g of the hydrogen-absorbing alloy. 
     This negative electrode and a pasted nickel positive electrode having a nominal capacity of 1500 mAh and manufactured according to known technique were spirally wound with a separator being interposed therebetween thereby to obtain an electrode group. By the way, as for the separator, a polyolefin non-woven fabric graft-copolymerized with acrylic monomer was employed. 
     Then, this electrode group and 2.4 mL of an electrolyte containing 7 mol/cm 3  of KOH and 1.0 mol/cm 3  of LiOH were placed and sealed in a closed-end cylindrical case thereby assembling an AAA size cylindrical nickel-hydrogen secondary battery having a nominal capacity of 1500 mAh. 
     Then, the secondary batteries of Examples 172 to 182 and Comparative Examples 82 to 87 were subjected to a charge/discharge test after being left to stand at room temperature for 24 hours as follows. Namely, each of the secondary batteries was subjected to the charge/discharge cycle four times wherein these batteries were charged with a current of 150 mA for 15 hours, followed by the discharging thereof with 150 mA until the voltage was lowered down to 0.8V. 
     Thereafter, the charge/discharge cycle was repeated 50 times in an environment of 25° C. Then, the internal impedance was measured, the results being shown in the following Table 31. By the way, the charging step in this charge/discharge cycle was performed by way of −ΔV method wherein the charging current was set to 1500 mA and the charging was terminated when the voltage was lowered by 10 mV from the maximum charge voltage. On the other hand, the discharging in this charge/discharge cycle was continued using a current of 3000 mA until the voltage of the battery was reduced to 1.0V. Thereafter, the battery was stored for two days at a temperature of 80° C., and then, the charge/discharge cycle was again repeated 50 times at a temperature of 25° C. and at the same conditions as mentioned above. Upon finishing this 50 times of repetition of charge/discharge cycle, the internal impedance was measured, the results being shown in the following Table 31. Furthermore, the battery was again stored for two days at a temperature of 80° C., and then, the charge/discharge cycle was again repeated 50 times at a temperature of 25° C. and at the same conditions as mentioned above. 
     Upon finishing this 50 times of repetition of charge/discharge cycle, the internal impedance was measured, the results being shown in the following Table 31. Additionally, the battery was again stored for two days at a temperature of 80° C., and then, the charge/discharge cycle was again repeated 50 times at a temperature of 25° C. and at the same conditions as mentioned above. Upon finishing this 50 times of repetition of charge/discharge cycle, the internal impedance was measured, the results being shown in the following Table 31. 
     Further, the crystal system of the principal phase, the areal ratio of the principal phase and the rechargeable hydrogen storage capacity of the hydrogen-absorbing alloys of Examples 172 to 182 and Comparative Examples 82 to 87 were measured in the same manner as in Example 94, the results being shown in the following Table 32. 
     By the way, the hydrogen-absorbing alloys of Examples 179 and 180 contained, as a principal phase, a phase having a crystal structure which was similar to the Ce 2 Ni 7  type structure. Specifically, the alloy of Example 179 indicated a highest peak in 2θ of 42.1°±1°, in an X-ray diffraction using CuKα-ray, and the intensity ratio thereof as represented by the following formula (I) was 21%. On the other hand, the alloy of Example 180 indicated a highest peak in 2θ of =42.1°±1°, in an X-ray diffraction using CuKα-ray, and the peak appeared in 2θ of 31° to 34° was found as being split into two. 
     On the other hand, the hydrogen-absorbing alloys of Examples 181 and 182 contained, as a principal phase, a phase having a crystal structure which was similar to the PuNi 3  type structure. Specifically, the alloy of Example 181 indicated a highest peak in 2θ of 42.1°±1°, in an X-ray diffraction using CuKα-ray, and the intensity ratio thereof as represented by the above formula (I) was 16%. On the other hand, the alloy of Example 182 indicated a highest peak in 2θ of 42.1°±1°, in an X-ray diffraction using CuKα-ray, and the peak appeared in 2θ of 31° to 34° was found as being split into three. 
     
       
         
           
               
               
             
               
                   
                 TABLE 31 
               
             
            
               
                   
                   
               
               
                   
                 Internal impedance (mΩ) 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 50 
                 100 
                 150 
                 200 
               
               
                   
                 Composition 
                 cycles 
                 cycles 
                 cycles 
                 cycles 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 172 
                 (La 0.97 Ce 0.01 Pr 0.01 Nd 0.01 ) 0.77 Mg 0.23 Ni 3.19 Al 0.09 Co 0.02 P 0.01   
                 22 
                 21 
                 25 
                 31 
               
               
                 Example 173 
                 (La 0.47 Ce 0.03 Pr 0.12 Nd 0.38 ) 0.8 Mg 0.2 Ni 3.2 Al 0.1 Co 0.03 Fe 0.01 Ti 0.01   
                 25 
                 23 
                 24 
                 41 
               
               
                 Example 174 
                 (La 0.97 Ce 0.01 Pr 0.01 Nd 0.01 ) 0.78 Mg 0.22 Ni 3.31 Al 0.11   
                 22 
                 21 
                 22 
                 35 
               
               
                 Example 175 
                 (La 0.47 Ce 0.03 Pr 0.12 Nd 0.38 ) 0.76 Mg 0.24 Ni 3.25 Al 0.08 Cu 0.01 B 0.01   
                 24 
                 24 
                 25 
                 38 
               
               
                 Example 176 
                 (La 0.49 Ce 0.01 Pr 0.10 Nd 0.40 ) 0.74 Mg 0.26 Ni 3.17 Al 0.07 No 0.01 Zn 0.01   
                 25 
                 25 
                 27 
                 47 
               
               
                 Example 177 
                 (La 0.89 Ce 0.01 Pr 0.01 Nd 0.09 ) 0.78 Mg 0.22 Ni 3.19 Al 0.14 Co 0.19 Sn 0.01 Cu 0.01   
                 26 
                 25 
                 26 
                 63 
               
               
                 Example 178 
                 (La 0.88 Ce 0.01 Pr 0.08 Nd 0.03 ) 0.79 Mg 0.21 Ni 3.35 Al 0.1 Cr 0.01 S 0.01   
                 22 
                 22 
                 24 
                 43 
               
               
                 Example 179 
                 (La 0.48 Ce 0.03 Pr 0.10 Nd 0.39 ) 0.76 Mg 0.24 Ni 3.05 Al 0.07 Co 0.05 W 0.01 Si 0.01 Mo 0.01   
                 25 
                 24 
                 24 
                 55 
               
               
                 Example 180 
                 (La 0.93 Ce 0.01 Pr 0.01 Nd 0.05 ) 0.75 Mg 0.25 Ni 3.28 Al 0.08 Co 0.02 In 0.01 V 0.01   
                 25 
                 22 
                 23 
                 43 
               
               
                 Example 181 
                 (La 0.49 Ce 0.02 Pr 0.15 Nd 0.34 ) 0.82 Mg 0.18 Ni 3.38 Al 0.09 Ga 0.02 Zr 0.01   
                 24 
                 21 
                 25 
                 49 
               
               
                 Example 182 
                 (La 0.98 Nd 0.01 Y 0.01 ) 0.77 Mg 0.23 Ni 3.15 Al 0.08 Mn 0.01 No 0.01   
                 26 
                 24 
                 24 
                 40 
               
               
                 Comparative 
                 (La 0.97 Ce 0.01 Pr 0.01 Nd 0.01 ) 0.70 Mg 0.30 Ni 2.53 Al 0.4 Co 0.20   
                 48 
                 130 
                 290 
                 — 
               
               
                 Example 82 
               
               
                 Comparative 
                 (La 0.47 Ce 0.03 Pr 0.12 Nd 0.38 ) 0.72 Mg 0.28 Ni 3.7 Al 0.25 Co 0.3 Cu 0.01 Fe 0.01   
                 37 
                 96 
                 230 
                 — 
               
               
                 Example 83 
               
               
                 Comparative 
                 (La 0.47 Ce 0.13 Pr 0.01 Nd 0.20 ) 0.9 Mg 0.1 Ni 2.75 Co 0.25 Cr 0.20   
                 42 
                 110 
                 245 
                 — 
               
               
                 Example 84 
               
               
                 Comparative 
                 (La 0.88 Ce 0.03 Pr 0.01 Nd 0.08 ) 0.45 Mg 0.55 Ni 3.1 Al 0.15 Cu 0.01 Si 0.01   
                 78 
                 23 
                 — 
                 — 
               
               
                 Example 85 
               
               
                 Comparative 
                 (La 0.94 Ce 0.01 Pr 0.05 Nd 0.04 ) 0.78 Mg 0.22 Ni 1.6 Mn 0.05 Co 1.5 Al 0.01   
                 64 
                 190 
                 — 
                 — 
               
               
                 Example 86 
               
               
                 Comparative 
                 (La 0.3 Ce 0.5 Pr 0.01 Nd 0.13 Sm 0.02 ) 0.975 Mg 0.025 Ni 2.925 Mn 0.35 Cu 0.1 No 0.075   
                 50 
                 130 
                 270 
                 — 
               
               
                 Example 87 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 32 
               
               
                   
                   
               
               
                   
                 Crystal structure of 
                 Areal ratio of 
                 Rechargeable hydrogen 
               
               
                   
                 principal phase 
                 principal phase 
                 storage capacity (H/M) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Example 172 
                 Ce 2 Ni 7  type 
                 92% 
                 1.03 
               
               
                 Example 173 
                 Ce 2 Ni 7  type + PuNi 3  type 
                 84% 
                 1.02 
               
               
                 Example 174 
                 Ce 2 Ni 7  type + CeNi 3  type 
                 88% 
                 1.06 
               
               
                 Example 175 
                 Ce 2 Ni 7  type 
                 91% 
                 1.05 
               
               
                 Example 176 
                 Ce 2 Ni 7  type 
                 94% 
                 0.98 
               
               
                 Example 177 
                 Ce 2 Ni 7  type + PuNi 3  type 
                 89% 
                 1.03 
               
               
                 Example 178 
                 Ce 2 Ni 7   type 
                 88% 
                 0.92 
               
               
                 Example 179 
                 Similar to Ce 2 Ni 7  type 
                 90% 
                 1.01 
               
               
                 Example 180 
                 Similar to Ce 2 Ni 7  type 
                 92% 
                 1.05 
               
               
                 Example 181 
                 Similar to PuNi 3  type 
                 86% 
                 1.03 
               
               
                 Example 182 
                 Similar to PuNi 3  type 
                 84% 
                 1.05 
               
               
                 Comparative 
                 CaCu 5  type 
                 63% 
                 0.52 
               
               
                 Example 82 
               
               
                 Comparative 
                 CaCu 5  type 
                 61% 
                 0.47 
               
               
                 Example 83 
               
               
                 Comparative 
                 PuNi 3  type 
                 67% 
                 0.35 
               
               
                 Example 84 
               
               
                 Comparative 
                 CaCu 5  type 
                 55% 
                 0.24 
               
               
                 Example 85 
               
               
                 Comparative 
                 MgCu 2  type 
                 52% 
                 0.22 
               
               
                 Example 86 
               
               
                 Comparative 
                 Ce 2 Ni 7  type 
                 83% 
                 0.53 
               
               
                 Example 87 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 33 
               
               
                   
                   
               
               
                   
                 Ce content in the 
                 La content in the 
               
               
                   
                 R of the alloy 
                 R of the alloy 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Example 172 
                 1 wt% 
                 97 at % 
               
               
                 Example 173 
                 3 wt % 
                 47 at % 
               
               
                 Example 174 
                 1 wt % 
                 97 at % 
               
               
                 Example 175 
                 3 wt % 
                 47 at % 
               
               
                 Example 176 
                 1 wt % 
                 49 at % 
               
               
                 Example 177 
                 1 wt % 
                 89 at % 
               
               
                 Example 178 
                 1 wt % 
                 88 at % 
               
               
                 Example 179 
                 3 wt % 
                 48 at % 
               
               
                 Example 180 
                 1 wt % 
                 93 at % 
               
               
                 Example 181 
                 2 wt % 
                 49 at % 
               
               
                 Example 182 
                 0 wt % 
                 98 at % 
               
               
                 Comparative 
                 1 wt % 
                 97 at % 
               
               
                 Example 82 
               
               
                 Comparative 
                 3 wt % 
                 47 at % 
               
               
                 Example 83 
               
               
                 Comparative 
                 13 wt %  
                 47 at % 
               
               
                 Example 84 
               
               
                 Comparative 
                 3 wt % 
                 88 at % 
               
               
                 Example 85 
               
               
                 Comparative 
                 1 wt % 
                 94 at % 
               
               
                 Example 86 
               
               
                 Comparative 
                 50 wt %  
                 30 at % 
               
               
                 Example 87 
               
               
                   
               
            
           
         
       
     
     As apparent from Tables 31 to 33, the hydrogen-absorbing alloys of Examples 172 to 182 which had a composition represented by the general formula (4) indicated a higher rechargeable hydrogen storage capacity as compared with the hydrogen-absorbing alloys of Comparative Examples 82 to 87. By the way, the hydrogen-absorbing alloy of Comparative Example 87 was of the kind where the atomic ratio of Mn was 0.135 or more, which corresponds to the hydrogen-absorbing alloy disclosed in the aforementioned Japanese Patent Unexamined Publication H11-29832. 
     It will be also seen that the secondary batteries of Examples 172 to 182 are smaller in internal impedance as compared with the secondary batteries of Comparative Examples 82 to 87. 
     As explained above, it is possible according to this invention to provide a hydrogen-absorbing alloy, which is capable of inhibiting the corrosion that might be caused due to the effect of an alkaline aqueous solution such as an alkaline electrolyte, and capable of improving the hydrogen storage capacity. 
     It is possible according to this invention to provide a secondary battery which is large in capacity and excellent in charge/discharge life. 
     It is possible according to this invention to provide a hybrid car and an electromobile, which are excellent in traveling performance such as fuel consumption, etc. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.