JPH0773048B2 - Method for manufacturing sintered cadmium cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for producing a sintered cadmium cathode used in an alkaline storage battery or the like.

(B) Conventional technology In a method of manufacturing an electrode generally used in an alkaline storage battery, as shown in JP-A-56-82573, a binder is added to an active material powder and kneaded to form a paste. A non-sintering method in which a paste is applied to a conductive substrate or the like and dried to produce a paste, and a salt of an active material such as cadmium nitrate is added to a porous nickel sintered substrate as shown in JP-A-51-18834. There is a sintering type manufacturing method in which a substrate is filled with a desired amount of an active material by performing an active material impregnating step of impregnating a solution, followed by alkali treatment, washing with water, and drying several times.

The former electrode disclosed in JP-A-56-82573 uses polyvinyl alcohol as a binder and is heat treated at a temperature of 120 to 220 ° C. to prevent its dissolution. Since the electrode fixes the active material with a binder, there is a binder between the active material particles, and this binder reduces the conductivity between the active material particles and between the active material and the conductive substrate. ,
It cannot be said that sufficient electrode characteristics can be obtained.

On the other hand, in the latter sintered electrode, since the active material is in direct contact with the substrate without a binder or the like, there is no decrease in conductivity as in the non-sintered electrode described above, Furthermore, since the conductive matrix of the porous nickel sintered substrate is present in the electrode, the conductivity in the electrode is high and the electrode characteristics are superior to those of the non-sintered electrode.

However, in this highly conductive sintered electrode, when a cadmium active material such as cadmium hydroxide or cadmium oxide was used as the active material, the active material became inactive as the charge and discharge cycles were repeated. However, there is a problem that the capacity of the electrode plate is reduced due to the accumulation of non-dischargeable metal cadmium. This is peculiar to the sintered electrode with high conductivity, and in the non-sintered electrode with low conductivity, the cycle life is increased by other factors before the phenomenon of accumulation of undischarged metal cadmium described above occurs. turn into.

(C) Problems to be Solved by the Invention The present invention is intended to prevent accumulation of non-dischargeable metal cadmium in a sintered cadmium cathode caused by stacking charge / discharge cycles, and prevent reduction in electrode plate capacity. It is what

(D) Means for solving the problem A sintered cadmium cathode filled with a cadmium active material such as cadmium hydroxide or cadmium oxide was impregnated with a polyvinyl alcohol solution, and then subjected to a chemical conversion treatment, and then 10
Dry at a temperature of 0-220 ° C.

(E) Action As described above, the electrode plate capacity of the sintered cadmium cathode decreases with repeated charge and discharge cycles because the discharge product of cadmium hydroxide on the surface of the active material metal cadmium during discharge. It is considered that a film is formed, and this film of cadmium hydroxide prevents contact between the metal cadmium present inside and the electrolytic solution, thereby leaving undischarged metal cadmium. By impregnating polyvinyl alcohol and suppressing the film formation of the cadmium hydroxide by covering the surface of the active material with a film of polyvinyl alcohol, cadmium hydroxide is generated nonuniformly on the surface of the metal cadmium which is the active material during discharge, In order to prevent the contact between the metal cadmium of
It is considered that the increase of non-dischargeable metal cadmium can be suppressed, and thus the reduction of the electrode plate capacity can be suppressed.

However, the polyvinyl alcohol shows a water-soluble physical property when it is dried at a temperature of less than 100 ° C. after impregnating the electrode plate as a solution, and thus the polyvinyl alcohol coating film is dissolved in the alkaline aqueous solution of the electrolytic solution in the battery. , The effect of suppressing the increase of non-dischargeable metal cadmium cannot be maintained, but when dried at a temperature of 100 ° C or higher,
Since polyvinyl coal causes a cross-linking reaction and does not exhibit water solubility and is able to maintain the above effect, it is necessary to dry after the impregnation of the electrode plate with polyvinyl alcohol at a temperature of 100 ° C or higher.

Further, when the temperature is higher than 220 ° C., the nickel sintered substrate of the active material holder is oxidized and nickel oxide is generated on the surface of the substrate to lower the conductivity of the electrode plate. Therefore, the upper limit of the drying temperature is 220 ° C. And need to.

Further, the sintering type cadmium cathode generally includes a chemical conversion treatment step in the production process of the electrode plate, and if impregnation and drying of polyvinyl alcohol are performed before the chemical conversion treatment, the electrode is generated from the electrode plate during the charge and discharge of the chemical conversion. The generated gas may cause peeling of the polyvinyl alcohol film. Therefore,
Impregnation and drying of polyvinyl alcohol must be performed after the chemical conversion treatment. Also, cadmium hydroxide as an active material changes to cadmium oxide at about 180 ° C, and when incorporated into a battery in the state of this cadmium oxide, it immediately returns to cadmium hydroxide in the alkaline aqueous solution of the electrolytic solution, which changes the concentration of the electrolytic solution. Therefore, when the polyvinyl alcohol is impregnated and dried after the chemical conversion step to be incorporated in the battery, the drying temperature is preferably 170 ° C. or lower.

(F) Example A porous nickel sintered substrate was impregnated with an aqueous cadmium nitrate solution, and an active material impregnation process of alkali treatment, water washing and drying was repeated 6 times to fill the substrate with a desired amount of cadmium hydroxide, and then an electrode plate. After this, the electrode plate is subjected to a chemical conversion treatment by charging and discharging in an alkaline aqueous solution, washed with water and dried, and then the electrode plate after the chemical conversion treatment is immersed in a 3% aqueous solution of polyvinyl alcohol, The cathode A of the present invention is obtained by drying at a temperature. For comparison, the drying temperature after immersion in the polyvinyl alcohol aqueous solution in the above example was set to 80
Instead of C, the other conditions were the same, and comparative cathode B was obtained, and the electrode plate washed with water and dried after the chemical conversion treatment in the above example was used as a completed electrode plate without adding polyvinyl alcohol. Get C.

The cathodes A to C were repeatedly charged and discharged in an alkaline aqueous solution with a nickel plate as a counter electrode. FIG. 1 shows the change in the electrode plate capacity with the progress of this charge / discharge cycle, and
Further, FIG. 2 shows a change in the amount of undischarged metal cadmium with the progress of the charge / discharge cycle. In FIG. 1, the capacity of the first cycle of each battery is 100, and in FIG. 2, the amount of undischarged metal cadmium of the first cycle of each battery is 1.

As is apparent from these drawings, the cathode of the present invention impregnated with polyvinyl alcohol and dried at a temperature of 120 ° C. has a small increase in the amount of undischarged undischarged metal cadmium, which is suppressed as compared with Comparative cathodes B and C. It can be seen that this is an excellent cathode with little reduction in plate capacity.

(G) Effect of the invention The present invention impregnates a polyvinyl alcohol solution into a sintered cadmium cathode having a porous nickel sintered substrate as an active material holder, and then performs a chemical conversion treatment, and then dry at a temperature of 100 to 200 ° C. The cathode thus added with polyvinyl alcohol does not peel off the polyvinyl alcohol coating film during the chemical conversion treatment, and can suppress an increase in the amount of metal cadmium that cannot be discharged as the charge-discharge cycle progresses. It is possible to suppress a decrease in plate capacity.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between charge / discharge cycle and electrode plate capacity ratio,
FIG. 2 is a diagram showing the relationship between the charge / discharge cycle and the amount ratio of undischarged metal cadmium. A: Inventive battery, B, C: Comparative battery.

Claims (1)

[Claims] 1. After impregnating a porous nickel sintered substrate filled with a cadmium active material with a polyvinyl alcohol solution,
A method for producing a sintered cadmium cathode, which comprises subjecting to a chemical conversion treatment and then drying at a temperature of 100 to 220 ° C.