Battery

Abstract: To present a battery having a stable internal resistance small in deviation of internal resistance, and capable of suppressing change or elevation of internal resistance due to external impact. The battery of the invention comprises a battery can having a conductivity, serving also as a negative terminal, and including an opening, a spiral electrode group disposed in the battery can, winding a positive plate and a negative plate around a separator, an electrolyte member disposed in the battery can, and a sealing member serving also as a positive terminal, disposed in the opening of the battery can through an electric insulating member. In the inner wall of the battery can contacting with the negative electrode positioned on the outermost circumference of the plate group, plural linear bumps vertical to the bottom of the battery can are formed, and the height of each linear bump of the plural linear bumps ranges from 0.05 mm to 0.25 mm, and the pitch of the linear bumps ranges from 0.5 mm to 10 mm. The negative electrode member comprises a metal core and a negative electrode material covering the surface of the metal core, and linear bumps are formed on the inner surface of the battery can, and the bumps are formed in a state of biting into the surface of the negative electrode material.

Description: FIELD OF THE INVENTION The present invention relates to a battery can for storing a spiral plate group of a battery, in particular, an enclosed type alkaline storage battery. BACKGROUND OF THE INVENTION Recently, in the rapid progress in portable and cordless appliances, there is a mounting demand for the secondary battery of small size and light weight and having a high energy density as the power source of these appliances. In particular, the lithium secondary battery and nickel-hydrogen storage battery are highly expected, and many new products are developed. Besides, in the nickel-cadmium storage battery which is low in cost and high in reliability, a further enhancement of characteristic is desired. A conventional nickel-cadmium battery is composed of a battery can, a plate group contained in the battery can, and an electrolytic member. The inner wall of the battery can is a smooth surface, so that the spiral plate group can be inserted easily. The plate group comprises a positive plate, a negative plate, and a separator. The plate group is spiral, and the negative plate is positioned on the outermost circumference, and this negative plate contacts with the inner wall of the battery can. That is, the battery can serves also as the negative terminal. The plate group is only wound, and the lead of the negative plate is not spot-welded or bonded to the bottom of the battery can. In this structure, therefore, since the inner wall of the battery can confronting the outermost circumference of the negative plate is a smooth surface, the negative plate and battery can only contact with each other, and the contact pressure is small, and hence the internal resistance of the battery is often heightened. Besides, the plate group is likely to be moved by an external impact, and the internal resistance is not stabilized, and, as a result, when the internal resistance is large, sufficient charging or discharging cannot be conducted. To reduce the internal resistance of an alkaline manganese battery, in Japanese Patent Publication No. 7-99686, it is proposed to form fine vertical stripes on the inner surface of the can. However, in the case of the alkaline manganese battery in which the positive electrode compound directly contacts with the inner surface of the can, it is effective to form vertical stripes at protrusion height of 0.005 to 0.02 mm and stripe pitch of 0.002 to 0.4 mm as disclosed therein, but in the case of the battery in which contact between the negative plate and the inner wall of the battery can must be maintained only by inserting a spiral plate group composed by winding a positive plate and a negative plate around a separator into the battery can, a negative compound material of high resistance value is interposed between the negative plate on the outermost circumference of the spiral plate group and the inner surface of the battery can. Accordingly, if the vertical stripe pitch is less than 0.4 mm, the contact surface area of the battery can and negative electrode material is increased, but the material resistance of the negative electrode material is high, and hence the effect for reducing the internal resistance of the battery and the effect for suppressing changes of internal resistance due to external impact are small. SUMMARY OF THE INVENTION The present invention provides an enclosed type alkaline storage battery comprising: a battery can having a conductivity, serving also as a negative terminal, and including an opening, an electrode group disposed in said battery can, an electrolyte member disposed in said battery can, and a sealing member serving also as a positive terminal, disposed in said opening of said battery can together with an electric insulating member, wherein said electrode group includes a positive electrode member, a negative electrode member, and a separator disposed between said positive electrode member and said negative electrode member, said negative electrode member including a metal core material and a negative electrode material covering the surface of said metal core material, said electrode group is spirally wound so that said negative electrode member is positioned at the outside and that said positive electrode member is positioned at the inside, part of said positive electrode member electrically conducts with said sealing member, a plurality of linear bumps having heights in the range 0.05 to 0.25mm are formed inside of said battery can extending vertically from the bottom of said battery can to locations spaced from said opening at a pitch in the range 0.5 to 10mm, said plurality of bumps are disposed in a contacting state while pressurizing said negative electrode member positioned on the outermost circumference of said spirally wound electrode group, and each of said plural bumps is disposed in electrical contact with and bites into the surface of said negative electrode material. In this constitution, preferably, the battery can is a cylindrical battery can. Preferably, the conductivity of the negative electrode material is smaller than the conductivity of the metal core. The present invention also provides a method of fabricating a closed alkaline storage battery comprising the steps of: (a) forming a battery can having an opening to serve also as a negative terminal, (b) forming a positive member, (c) forming a negative member comprising a negative electrode material covering a metal core, (d) forming an electrode group by placing a separator between said positive member and negative member, (e) putting said electrode group into said battery can, (f) placing an electrolyte member in said battery can, and (g) placing a sealing member serving also as a positive terminal into said opening together with an electric insulating material, wherein the step of forming said battery can includes: (1) preliminarily forming a metal material into a cup shape, (2) drawing and forming a battery can in a desired shape, by pressing a punch against an inside of said metal material having the cup shape, and passing said metal material having the cup shape against which said punch is pressed sequentially through a plurality of outer pattern drawing dies, said punch having a plurality of grooves formed parallel to the axis, and (3) forming a plurality of linear bumps in an inside of said battery can extending from the bottom of the battery can to locations spaced from said opening, by pressurizing said punch to a final outer pattern drawing die out of the plurality of outer pattern drawing dies by a pressurizing force of said die, said bumps having heights in the range 0.05 to 0.25mm and being formed at a pitch in the range 0.5 to 10mm, wherein at the step of putting said electrode group into said battery can, said electrode group is spirally wound so that the negative member is positioned at the outside while the positive member is positioned at the inside, and put into said battery can with each of said bumps being in electrical contact with and biting into a surface of the negative electrode material. In batteries of the present invention, since the bumps strongly pressurize the surface of the negative electrode member, and the negative electrode member is firmly fixed to the bumps of the battery can, if an external impact is given, the plate group is not deviated and moved, so that change or elevation of internal resistance may be suppressed. Moreover, the bumps strongly pressurize the surface of the negative electrode member. By this pressurizing force, the bumps deeply bite into the negative electrode material having a conductivity covering the surface of the negative electrode member. Accordingly, the deviation of the internal resistance value is small, and a stable internal resistance is obtained. Besides, the distance between the metal core and the bumps composed inside of the negative electrode member is shortened. As a result, the resistance between the negative electrode member and the bumps as negative terminals is reduced, and the internal resistance becomes smaller. Moreover, when the thickness of the material plate of the battery can and the outside diameter of the battery can are constant, the above effects are obtained without lowering the effective capacity in the battery can. Thus, while maintaining a high capacity in a limited outer shape of small internal resistance, a battery having an excellent reliability hardly changing in the resistance against external impact is obtained. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a horizontal sectional view of a battery can according to an embodiment of the invention. Fig. 2 is a vertical sectional view of a battery can according to an embodiment of the invention. Fig. 3 is a sectional view explaining the processing method of a battery can used in a battery according to an embodiment of the invention. Fig. 4 is a perspective view showing a structure of a battery according to an embodiment of the invention. Reference Numerals 1 Battery can 2 Positive member 3 Negative member 4 Separator 5 Punch 6 Punch groove 7 Cup-shaped metal material 8 Drawing and ironing die 9 Linear bump DETAILED DESCRIPTION OF THE INVENTION A perspective view of a battery according to an embodiment of the invention is shown in Fig. 4. In Fig. 4, the battery is composed of a battery can 1, an electrode group 20 contained in the battery can 1, an electrolyte member 21 immersed in the electrode group, and a metal sealing plate 23 disposed to seal the opening of the battery can 1. The plate group 20 includes a positive electrode member 2, a negative electrode member 2, and a separator 4 disposed between the positive electrode member 2 and negative electrode member 3. The plate group 20 is wound in a spiral form, and the negative electrode member 3 is disposed on the outer circumferential side and the positive electrode member 2 on the inner circumference side thereof. The negative electrode member 3 is composed of a metal core and a negative electrode material covering the surface of the core. That is, the positive electrode member 2, negative electrode member 3, and separator 4 are band-shaped sheets or plates, and they are wound spirally. At the opening of the battery can 1, a metal sealing plate 23 is disposed through an electrical insulating packing 22. The metal sealing plate 23 also serves as a positive terminal. Of the electrode group 20 wound spirally, part of the positive electrode member 2 is electrically connected to the inside of the metal sealing plate 23. Plural linear bumps are formed inside of the battery can 1. Of the electrode group 20 wound spirally, the outermost surface of the negative electrode member 3 contacts with the linear bumps of the battery can 1, and an electrical conduction is achieved by this contact. Examples of the battery can being used are shown in Fig. 1 and Fig. 2. Fig. 1 is a horizontal sectional view of the battery can, and Fig. 2 is a vertical sectional view of the battery can. In Fig. 1 and Fig. 2, the battery can 1 is cylindrical in shape, and plural linear bumps 9 are formed inside of the battery can 1. In the inner wall of the battery can 1, linear bumps are formed vertically at a height of 0.05 to 0.25 mm from the bottom of the battery can and at a pitch of 0.5 to 10 mm. Such battery can was fabricated by the drawing and ironing (DI) technology shown in Fig. 3. In Fig. 3, a groove 6 in a depth corresponding to the required height of bumps is formed at the leading end of a punch 5 parallel to the axial line of the punch. This punch 5 is abutted against a metal material 7 preliminarily formed in a cup shape by nickel plated iron plate, and the drawing and ironing dies 8a to 8n of outer pattern are passed sequentially. The die of which drawing and ironing diameter of the final stage 8n is the desired outside diameter of the can is pressurized by the punch 5. At this time, the can inside is strongly pressed against the punch peripheral surface by the pressurizing force from the die, and vertical stripes are transferred. In this way, the battery can forming linear bumps on the inner surface of the can was fabricated. In this case, the linear bumps are set in the length of the groove also in the punch so as not to reach the vicinity of the opening of the battery can. The fabricated nickel-cadmium storage battery is 16.3 mm in outside diameter of battery can, and 42.5 mm in height of battery. As a nickel plated iron plate for fabricating the battery can, a 0.45 mm thick plate was used. In the DI process, the can bottom is nearly same as the thickness of the plated iron plate being used, but the side surface may be made thinner. In this embodiment, the side thickness was 0.19 mm. The positive electrode member is composed of a core material of foamed nickel board, and an active substance mainly composed of nickel hydroxide filled in the core material. The negative electrode material is composed of a metal core having a conductivity, and a cadmium compound covering the surface of the core. In the battery can shown in Fig. 1, a positive plate as a positive electrode member and a negative plate as a negative electrode member were put in a plate group wound spirally through a separator, and an electrolyte mainly composed of KOH was injected as the electrode member, and the opening was sealed. Thus, an enclosed nickel-cadmium storage battery of capacity of 1200 mAh was fabricated. The linear bumps of the battery can were defined in the height, pitch and length. In this method, various nickel-cadmium storage batteries were fabricated. Then the initial internal resistance was measured. Afterwards, the storage battery was dropped on an oak board of 10 mm or more in thickness, from a height of 20 cm, five times in the battery axial direction and five times in the direction vertical to the axial line. The internal resistance after dropping was also measured. Comparing the internal resistance before dropping and after dropping, it was confirmed that the elevation of the internal resistance was suppressed within 5 mohms or less. Various battery cans and various batteries were manufactured by forming linear bumps in various lengths, heights and pitches. In 50 cells each of the manufactured batteries, the internal resistance was measured after initial charging and discharging, and the internal resistance was measured after the drop test, and the difference of the internal resistance before and after dropping was calculated. The initial internal resistance before dropping was about 21 mohms to about 25 mohms. On the other hand, after the dropping test, the internal resistance was as follows. The internal resistance after dropping test of the battery using the battery can with the linear bump length of 37 mm, bump pitch of 2.08 mm and bump height of 0.14 mm was 21 mohms to 26 mohms, or 23 mohms in average. The internal resistance after dropping test of the battery using the battery can with the linear bump length of 37 mm, bump pitch of 0.33 mm and bump height of 0.03 mm was 21 mohms to 31 mohms, or 25 mohms in average. The internal resistance after dropping test of the battery using the battery can with the linear bump length of 37 mm, bump pitch of 16.7 mm and bump height of 0.03 mm was 23 mohms to 40 mohms, or 27 mohms in average. The internal resistance after dropping test of the battery using the battery can with the linear bump length of 37 mm, bump pitch of 16.7 mm and bump height of 0.14 mm was 21 mohms to 29 mohms, or 25 mohms in average. The internal resistance after dropping test of the battery using the battery can with the linear bump length of 37 mm, bump pitch of 2.08 mm and bump height of 0.03 mm was 22 mohms to 36 mohms, or 26 mohms in average. The internal resistance after dropping test of the battery using the battery can with the linear bump length of 37 mm, bump pitch of 0.33 mm and bump height of 0.14 mm was 21 mohms to 29 mohms, or 25 mohms in average. Thus, when the linear bump pitch was 0.5 mm or less or 10 mm or more, or the linear bump height was 0.05 mm or less, the internal resistance value was not stable, and the deviation tended to be larger. Results of measurement of difference of internal resistance before and after dropping in various batteries are shown in Table 1, Table 2, and Table 3. In the batteries in Table 1, the linear bump length in the battery can is 37 mm, and the bump height is shown in horizontal lines and the pitch is given in the vertical columns. The "-" mark refers to an item that is not measured, including a case in which the punch could not be manufactured. The "O" mark shows the elevation of internal resistance was within 5 mohms in all of 50 cells. The figure shows the number of cells of which internal resistance exceeded 5 mohms. In Table 1, since the thickness of the nickel plated iron plate is 0.45 mm, and the thickness of the formed battery can is 0.19 mm, the bump height does not exceed 0.26 mm. In the case of the pitch in a range of 0.5 mm to 10.0 mm and bump height of 0.09 mm or more, all are "O" marked. If the bump height is 0.05 mm, it is "O" depending on the pitch condition. In Table 2, the length of the linear bumps in the battery can is 30 mm, and in Table 3, it is 20 mm. As clear from Table 1, Table 2, and Table 3, in the constitution of forming the linear bumps on the surface in the battery can and forming the bumps so as to bite into or compress the surface of the negative electrode member, it is effective to suppress elevation of internal resistance due to external impact. In particular, an excellent effect is obtained when the linear bumps have a specified pitch and height. Also as known from Table 1, Table 2, and Table 3, when the height of the linear bumps is in a range of 0.05 mm to 0.25 mm, and the pitch of linear bumps is in a range of 0.5 mm to 10 mm, the effect of suppressing elevation of internal resistance due to dropping is obtained. When the linear bump height is less than 0.05 mm and the pitch is less than 0.5 mm, the force of pressurizing the negative plate by the linear bumps is weak, and the contact force between the negative plate and linear bumps is weak and the contact resistance is high, so that the effect for suppressing elevation of internal resistance due to dropping is smaller. When the pitch is 10 mm or more, the contact surface area of the negative plate and linear bumps is small, and the amount of change of contact resistance due to impact from outside is larger, so that the effect of suppressing the elevation of internal resistance due to dropping is smaller. Besides, by controlling the thickness of the battery can and the thickness of the nickel plated pole plate, the height of the linear bumps may be 0.25 mm or more. When the thickness of the battery can is about 0.45 mm, the height of linear bumps is preferred to be 0.26 mm or less. If more than 0.26 mm, the pressurizing force of the negative plate and linear bumps increases, and the effect for suppressing elevation of internal resistance due to dropping also becomes larger, but as the effect for suppressing elevation of internal loss is saturated, to the contrary, the volume for installing the plate group is decreased. The shape of the linear bumps is not particularly limited, but the shape likely to bite into the negative electrode material is preferred, or the shape easy to compress is desired, and, for example, the sectional shape of the bumps may be an acute triangle, an obtuse triangle, a circle, a semi-circle, a trapezoid, or a quadrangle. The conductivity of the negative electrode material for composing the negative electrode member is desired to be smaller than the conductivity of the metal core. In this constitution, the effect for decreasing the internal resistance is further enhanced. In this embodiment, the DI can is presented, but same effects are obtained in other battery cans such as drawn cans. Also in the embodiment, the nickel-cadmium storage battery is shown, but same effects are obtained in other spiral batteries such as nickel-hydrogen battery and lithium secondary battery. As the negative electrode material, an example of cadmium compound is shown, but not limited to this, for example, hydrogen occluded alloy, lithium metal of lithium secondary battery, lithium alloy, or carbon material capable of intercalating lithium may be used. As the positive electrode material, an example of nickel compound is presented, but not limited to this, for example, lithium transition metal of lithium secondary battery (such as LiMO 2 , M=Co, Ni, or CoMn) and spinel LiMo204 may be also used. Thus, according to the constitution of the invention, it is possible to obtain a battery simultaneously having various characteristics including small internal resistance, high capacity in a limited external volume, and excellent reliability against external impact.

Claims: An enclosed type alkaline storage battery comprising: a battery can (1) having a conductivity, serving also as a negative terminal, and including an opening, an electrode group (20) disposed in said battery can (1), an electrolyte member (21) disposed in said battery can (1), and a sealing member (23) serving also as a positive terminal, disposed in said opening of said battery can (1) together with an electric insulating member, wherein said electrode group (20) includes a positive electrode member (2), a negative electrode member (3), and a separator (4) disposed between said positive electrode member and said negative electrode member, said negative electrode member including a metal core material and a negative electrode material covering the surface of said metal core material, said electrode group (20) is spirally wound so that said negative electrode member is positioned at the outside and that said positive electrode member is positioned at the inside, part of said positive electrode member electrically conducts with said sealing member (23), a plurality of linear bumps (9) having heights in the range 0.05 to 0.25mm are formed inside of said battery can extending vertically from the bottom of said battery can to locations spaced from said opening at a pitch in the range 0.5 to 10mm, said plurality of bumps are disposed in a contacting state while pressurizing said negative electrode member positioned on the outermost circumference of said spirally wound electrode group, and each of said plural bumps is disposed in electrical contact with and bites into the surface of said negative electrode material. A battery of claim 1, wherein each of said plurality of bumps compresses the surface of said negative electrode material. A battery of claim 1, wherein said battery can (1) is a cylindrical battery can. A battery of claim 1, wherein said battery can abutting said electric insulating member is a nearly smooth surface. A battery of claim 1, wherein said metal core member has a conductivity smaller than that of the negative electrode material. A battery of claim 1 being an alkaline nickel cadmium battery having a capacity of approximately 1200mAh. A battery of claim 1 being an alkaline nickel cadmium battery having an external diameter of approximately 16mm and a height of approximately 43mm. A method of fabricating a closed alkaline storage battery comprising the steps of: (a) forming a battery can having an opening to serve also as a negative terminal, (b) forming a positive member, (c) forming a negative member comprising a negative electrode material covering a metal core, (d) forming an electrode group by placing a separator between said positive member and negative member, (e) putting said electrode group into said battery can, (f) placing an electrolyte member in said battery can, and (g) placing a sealing member serving also as a positive terminal into said opening together with an electric insulating material, wherein the step of forming said battery can includes: (1) preliminarily forming a metal material into a cup shape, (2) drawing and forming a battery can in a desired shape, by pressing a punch against an inside of said metal material having the cup shape, and passing said metal material having the cup shape against which said punch is pressed sequentially through a plurality of outer pattern drawing dies, said punch having a plurality of grooves formed parallel to the axis, and (3) forming a plurality of linear bumps in an inside of said battery can extending from the bottom of the battery can to locations spaced from said opening, by pressurizing said punch to a final outer pattern drawing die out of the plurality of outer pattern drawing dies by a pressurizing force of said die, said bumps having heights in the range 0.05 to 0.25mm and being formed at a pitch in the range 0.5 to 10mm, wherein at the step of putting said electrode group into said battery can, said electrode group is spirally wound so that the negative member is positioned at the outside while the positive member is positioned at the inside, and put into said battery can with each of said bumps being in electrical contact with and biting into a surface of the negative electrode material.

Inventors: AOKI KENICHI, ASANO GOTA, IWASE AKIRA, SUZUKI NORIO, TOKUMOTO TADAHIRO, AOKI, KENICHI, ASANO, GOTA, IWASE, AKIRA, SUZUKI, NORIO, TOKUMOTO, TADAHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: H01M10
IPC codes: H01M10, H01M2