Nickel positive electrode for use in alkaline storage battery.

Abstract: A nickel positive electrode for use in alkaline storage batteries which is improved in the rate of utilization of the nickel hydroxide in a wide temperature range with an oxygen evolving overvoltage being increased by incorporating at least one selected from the group consisting of compounds of yttrium, indium, antimony, and at least one selected from the group consisting of compounds of cobalt and calcium into the nickel positive electrode (2), and a nickel-hydrogen storage battery using the same. The nickel positive electrode (2) contains at least one selected from the group consisting of compounds of yttrium, indium, antimony. The nickel positive electrode contains at least one of cobalt and calcium compounds.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a nickel positive electrode having improved characteristics for use in alkaline storage batteries using the positive electrodes of nickel oxide and the negative electrodes of a hydrogen storage alloy capable of electrochemically absorbing and desorbing hydrogen, cadmium, or zinc, and to a nickel-hydrogen storage battery having improved characteristics. Description of the Related Art Recently, there has been an intensive need for high energy density secondary batteries associated with portable appliances which are made much more valuable, compact and lighter in weight. Similarly, such new high energy density secondary cells are also vigorously sought for power supplies for electric automobiles. To cope with these needs, in the technical field of nickel-cadmium cell (referred to as Ni/Cd cell hereunder), there have been developed a Ni/Cd cell having a higher capacity using conventional sintered nickel positive electrodes and further a much higher energy density Ni/Cd cell having a capacity of 30 to 60 % greater than that of the former using foamed metal type nickel positive electrodes. Moreover, there has been developed a nickel-hydrogen storage battery with negative electrodes of a hydrogen storage alloy having a higher capacity than those of Ni/Cd cells, i.e., a capacity two times or more as great as those of Ni/Cd cells using sintered nickel positive electrodes. These high capacity alkaline storage batteries include positive electrodes composed of a sintered porous nickel body, a bulk foamed porous nickel body, or a porous fibrous nickel body of a high porosity (90 % or more) which are filled with nickel hydroxide powder to a high density in order to achieve an improvement in energy density of the positive electrodes. Consequently, modern sintered nickel positive electrodes have an improved energy density of 450 to 500 mAh/cm 3 , and foamed metal type nickel positive electrodes have an energy density of 550 to 650 mAh/cm 3 , as opposed to conventional sintered nickel positive electrodes having an energy density of 400 to 500 mAh/cm 3 . Those positive electrodes composed of a sintered porous nickel body, a foamed porous nickel body, or a porous fibrous nickel body which are filled with nickel hydroxide powder to a high density have a problem that their energy density can be maintained at higher levels about at normal temperature, but reduced at high temperature atmosphere. Therefore, it is difficult to take advantages of the characteristics of high energy density in a wider temperature range. This is attributed to the fact that a charge reaction accompanied by a conversion from nickel hydroxide to nickel oxyhydroxide and an oxygen evolving reaction are liable to simultaneously occur under a high temperature atmosphere. That is, an oxygen evolving overvoltage at positive electrodes is reduced leading to an insufficient charge reaction of the conversion of nickel hydroxide to nickel oxyhydroxide with a reduced rate of utilization of the nickel hydroxide. In order to overcome this problem, the following methods have been proposed: (1) a method where cadmium oxide powder or cadmium hydroxide powder is added into positive electrodes, and (2) a method where cadmium oxide is incorporated into the nickel hydroxide powder (Japanese Patent KOKAI (Laid-open) No. 61-104565). In the conventionally proposed methods (1) and (2) as above, the presence of cadmium oxide inside or with the nickel hydroxide powder improves the rate of utilization of the nickel hydroxide under a high temperature atmosphere. However, even when the addition of cadmium oxide is made, the rate of utilization of the nickel hydroxide under a high temperature atmosphere is only on the order of 80 %. In order to improve the rate of utilization of the nickel hydroxide under a high temperature atmosphere, the amount of cadmium oxide to be added into inside the nickel hydroxide or into the nickel positive electrodes must be increased. However, the increase of the amount of cadmium oxide to be added causes a problem of adversely diminishing the rate of utilization of the nickel hydroxide about at normal temperature though the rate of utilization of the nickel hydroxide under a high temperature atmosphere may be improved up to about 90 %. In recent years, attention has been directed to a nickel-hydrogen storage battery containing no cadmium, heavy metal, from the point of environmental hazards. The removal of cadmium oxide from the nickel hydroxide or the positive electrodes, however, produces problems that the rate of utilization of the nickel hydroxide under a high temperature atmosphere is reduced to a range in the order of from 50 to 60 % and that when a sealed nickel-hydrogen storage battery with a positive electrode capacity controlled is arranged under less electrolyte conditions, the cycle life is shortened. The present invention is to overcome these problems by providing a nickel positive electrode for use in alkaline storage batteries having an excellent rate of utilization of the nickel hydroxide in an atmosphere in a wide range of temperature. Moreover, an object of the present invention is to provide a nickel-hydrogen storage battery being excellent in the cell capacity and in the cycle life in an atmosphere in a wide range of temperature. JP-B-51036465 discloses Ni-Cd alkaline batteries, in which a material such as Cd, Pb, Al, Zn, Sb or their compounds having higher oxygen over-voltage than that of the cathode active material is added to the cathode, and metaborate is added to the electrolyte. DE-A-20 07 987 discloses a material for positive electrodes for use in alkaline storage batteries, an active material thereof including a sulfate of Ba, Sr, Hg or Sb. JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Volume 136, No. 3, March 1989, "Effect of Coprecipitated Metal Ions on the Electrochemistry of Nickel Hydroxide Thin Films: Cyclic Voltammetry in 1M KOH", pages 723 - 728, teaches that the oxygen evolution overpotential of yttrium is 402 mV, and that of cadmium and nickel is 442 mV and 420 mV, respectively. SUMMARY OF THE INVENTION For overcoming the foregoing problems, the present invention provides a paste type nickel positive electrode (2) comprising a major component of nickel oxide and a bulk porous body, porous plate, or plate supporting the nickel oxide and imparting electroconductivity thereto, where the positive electrode contains at least one of compounds of yttrium and indium. Preferred embodiments are claimed in the subclaims. This constitution, i.e., the inclusion of at least one of compounds of yttrium and indium into the nickel positive electrode (2) allows these compounds to be absorbed on the surfaces of the active material, the nickel oxide resulting in an increase in the overvoltage of evolving oxygen due to a competitive reaction (2) at charging under a high temperature atmosphere. As a result, the charge reaction of the conversion of the nickel hydroxide to nickel oxyhydroxide according to the equation (1) is sufficiently effected with an improvement in the rate of utilization under a high temperature atmosphere. Ni(OH) 2 + OH - → NiOOH + H 2 O + e 2OH - → 1 / 2 O 2 + H 2 O + e Therefore, the inclusion of the compounds according to the present invention permits the attainment of a positive electrode being excellent in the rate of utilization of the active material in a wide range of temperature. For practical nickel-hydrogen storage batteries, the charging efficiency according to the above equation (1) may be enhanced by adding cobalt and the calcium compounds to the positive electrode so as to have a specific gravity of 1.2 to 1.3, thereby achieving an excellent discharge capacity in a wide temperature range. Moreover, under the conditions that at least one of zinc oxide or zinc hydroxide is incorporated in the positive electrode and that the specific gravity and the amount of the alkaline electrolyte range from 1.2 to 1.3 and from 1.0 to 2.5 cm 3 /Ah, respectively, and that the negative capacity is not less than 1.1 times the positive electrode capacity, localized presence and leakage of the electrolyte inside the cells owing to the repetition of a charge-discharge cycle are inhibited so that the cycle life is improved. These results are recognized to be attributed to the synergetic effect of the conditions of cell design such as the specific gravity and the amount of the electrolyte and the ratio of the negative electrode capacity to the positive electrode capacity and the mixture of at least one of zinc oxide or zinc hydroxide and calcium compounds. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of the nickel-hydrogen storage battery structured according to the present invention, Figure 2 is a graphical illustration showing the relationship between the environmental temperature when charging the nickel positive electrode produced according to the present invention and the rate of utilization of the nickel hydroxide, and Figure 3 is a graphical illustration showing the relationship between the amount of the additive to the nickel positive electrode produced according to the present invention and the rate of utilization. In Figure 1, 1 designates a negative electrode, 2 does a positive electrode, 3 does a separator, 4 does a case, 6 is a relief valve, and 7 does a seal plate. 8 designates an insulating gasket and 9 designates a positive current collector. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT The present invention is illustrated with reference to Examples under. Example 1 Nickel positive electrodes containing no cadmium to be used in the present invention were produced in the following procedure: A spherical nickel hydroxide powder, a cobalt powder, a cobalt hydroxide powder and various additives were mixed in a proportion by weight of 100 : 7 : 5 : X with X being varied to produce compositions as shown in Table 1. To each mixture there was added water to form a paste which was filled into a porous support of foamed nickel having a porosity of 95 % and a facial density of 300 g/cm 2 , dried, pressed, and thereafter, immersed in an aqueous dispersion of fluorinated resin powder. Thereafter, the impregnated support was redried and cut into predetermined dimensions to produce various nickel positive electrodes having a theoretical capacity of 1000 mAh. For Comparative Examples, nickel positive electrodes containing no cadmium and none of the various additives were prepared. The thus produced nickel positive electrodes were designated as shown in Table 1, in which the compositions thereof and the amounts cf the additives incorporated therein are also indicated. Designations and compositions of produced nickel positive electrodes, and amounts of additives incorporated therein. Amount X 0.2 0.5 1.0 3.0 5.0 6.0 Y 2 O 3 A1 A2 A3 A4 A5 A6 Y(OH) 3 B In 2 O 3 C1 C2 C3 C4 C5 C6 Sb 2 O 3 D Ba(OH) 2 E BeO F Be(OH) 2 G Examples D, E, F and G are Comparative Examples. Next, the positive electrode 2 produced as above and a hydrogen storage alloy negative electrode 1 (the hydrogen storage alloy had a composition of MmNi 3,6 Co 0.7 Mn 0.4 Al 0.3 ) were rolled in a spiral form with a separator being interposed therebetween, and inserted in a case 4 which also acts as a negative terminal. Thereafter, in the resultant assembly, there were injected 2.0 cm 3 of an alkaline electrolyte which was a solution of lithium hydroxide dissolved in an aqueous solution of potassium hydroxide having a concentration of 20 g/l and having a specific gravity of 1.3, followed by sealing the case 4 with a seal plate 7 equipped with a relief valve 6 to constitute a sealed nickel-hydrogen storage battery of a AA size having a theoretical capacity of 1000 mAh with the cell capacity being controlled by the positive electrode. The arrangement of the resultant battery is shown in Figure 1, in which 8 designates an insulating gasket, and 9 designates a positive current collector electrically connecting the positive electrode 2 and the seal plate 7. In this way, various cells were made using positive electrodes A to G and evaluated for the rate of utilization of the positive electrode. The cells were charged at a charge rate of 0.1 C for 15 hours at a temperature of 20, 30, 40 and 50 °C in ambient atmosphere, and then left to stand for three hours 5 at 20 °C in ambient atmosphere, and thereafter, discharged at a discharge rate of 0.2 C in ambient atmosphere at 20 °C until reaching 1.0 V. After performing the charge and discharge cycles under the aforementioned conditions, the rate of utilization of the positive active material, nickel hydroxide, was determined by calculation according to the following equation: Rate of utilization of positive electrode (%) = (Discharge capacity/1000 mAh) × 100 The results of the evaluation for the rate of utilization of the positive active material, nickel hydroxide, using A4, B, C4, D, E, F, G are shown in Figure 2. Further Comparative Examples indicated a rate of utilization of 95 % in ambient atmosphere at 20 °C, but 79 % at 30 °C, 57 % at 40 °C, and 35 % at 50 °C. It can clearly be seen that when the positive electrode containing no cadmium was used in the further Comparative Examples, the rate of utilization of the nickel hydroxide was lowered with charging in a higher temperature atmosphere. In contrast, the use of the positive electrodes, A4, B, C4 according to the present invention achieved a rate of utilization of the nickel hydroxide of 94 to 95 %, 90 to 93 %, 78 to 85 %, and 66 to 78 % at 20 °C, 30 °C, 40 °C, and 50 °C, respectively, indicating the attainment of excellent rate of utilization in a wider temperature range. This may be attributed to an increase in oxygen evolving overvoltage owing to absorption or adsorption of Y 2 O 3 , Y(OH) 3 , In 2 O 3 on the surfaces of the nickel hydroxide powder, whereby even when the charging is conducted in an atmosphere at temperatures of 30 °C or higher, the oxygen evolving reaction is suppressed to facilitate the oxidation reaction of the nickel hydroxide to nickel oxyhydroxide. Next, the positive electrodes, A1 to A6 and C1 to C6 were evaluated for the rate of utilization of the nickel hydroxide to yield the results as shown in Figure 3. The addition amount by weight of 0.2 (Al, A2) resulted in a rate of utilization of about 60 % at 40 °C, i.e., the same level as in Comparative Examples shown in Figure 2 indicating no effect attained by the addition. The effects of the addition of Y 2 O 3 and In 2 O 3 can be perceived in a ratio by weight from 0.5 or more allowing for attainment of an excellent rate of utilization no less than 70 %. If the addition amount is in a ratio of 6, however, the rate of utilization at 20 °C is lowered to 86 %, though the rate of utilization at 40 °C is not less than 85 %. From the foregoing, the amount of Y 2 O 3 and In 2 O 3 to be added is preferably in a ratio by weight of 0.5 to 5. Although description has been made only for the amount of Y 2 O 3 and In 2 O 3 to be added in this Example, the identical tendency has been exhibited when further additives were added. Moreover, although a foamed nickel having a nominal weight of 300 g/m 2 has been used for supports to retain the positive electrode active materials, those having a nominal weight ranging from 200 to 700 g/cm 2 are preferred from the point of view of energy density. Furthermore, the identical effects could be obtained by using other supports such as a porous fibrous nickel body, a sintered porous nickel body, punched metal, expanded metal, nets, or foils. Similarly, other cells or batteries such as Ni/Cd cells, nickel-zinc storage batteries, and the like than the nickel-hydrogen storage batteries can attain the same effects so long as they are of the cell type using the nickel positive electrode. The addition of powdery carbon and nickel to the positive electrode has an effect of improving discharge characteristics at the time of discharging at a great current. As above, according to the present invention there is provided a paste type nickel positive electrode comprising a major component of nickel oxide and a bulk porous body, porous plate, or plate supporting the nickel oxide and imparting electroconductivity thereto, where the positive electrode contains at least one of compounds of yttrium and indium. By employing a simple constitution as above, there can be provided a positive electrode for use in alkaline storage batteries which is excellent in the rate of utilization of the nickel hydroxide in ambient atmosphere in a wide range of temperature. Moreover, there can be povided a nickel-hydrogen storage battery which has an excellent cell capacity in an atmosphere in a wide temperature range and an excellent cycle life.

Claims: A paste type nickel positive electrode for use in alkaline storage batteries comprising an active material containing a major component of nickel oxide and a support selected from the group consisting of a bulk porous body, porous plate and a plate supporting said active material and imparting electroconductivity thereto, wherein said active material contains at least one selected from the group consisting of compounds of yttrium and indium. The nickel positive electrode according to claim 1, wherein said compounds of yttrium and indium are Y 2 O 3 , Y(OH) 3 , In 2 O 3 , In 2 O and In 2 O 3 ·H 2 O. The nickel positive electrode according to claim 1 or 2, wherein said compounds of yttrium and indium are included in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of said nickel oxide. The nickel positive electrode according to any preceding claim, wherein said active material contains at least one selected from the group consisting of cobalt, cobalt hydroxide and cobalt oxide. The nickel positive electrode according to any preceding claim, wherein said active material contains at least one selected from the group consisting of zinc oxide and zinc hydroxide. The nickel positive electrode according to any preceding claim, wherein said bulk porous body is one selected from the group consisting of foamed porous nickel body, fibrous porous nickel body, sintered porous nickel body, porous plate, perforated metal and expanded metal. The nickel positive electrode according to claim 6, wherein said foamed porous nickel body has a facial density of 200 to 700 g/m 2 . The nickel positive electrode according to any of claims 1 to 6, wherein said plate is a nickel or nickel plated iron foil. The nickel positive electrode according to any preceding claim, wherein said nickel oxide is like spherical nickel hydroxide particles. The nickel positive electrode according to claim 1, wherein said active material is of a paste type and contains at least one selected from the group consisting of carbon and nickel.

Inventors: AKUTSU NORIKATSU, IKOMA MUNEHISA, MATSUDA HIROMU, MATSUMOTO ISAO, MURAMATSU KIMIE, AKUTSU, NORIKATSU, IKOMA, MUNEHISA, MATSUDA, HIROMU, MATSUMOTO, ISAO, MURAMATSU, KIMIE
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: H01M4
IPC codes: H01M4, H01M10, H01M6