JP3272009B2 - Method for producing nickel electrode for alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a nickel electrode used in an alkaline storage battery such as a nickel-cadmium battery.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a nickel electrode for an alkaline storage battery, a porous nickel sintered substrate as an active material holder is immersed in an acidic nickel salt impregnating solution such as nickel nitrate to form nickel in a hole of the substrate. It is generally known to perform an active material filling operation in which an acidic nickel salt is converted into nickel hydroxide as an active material in an alkaline solution after salt impregnation. However, in such an active material filling operation, the amount of active material charged per operation is small, and a sufficient amount of active material cannot be obtained by one operation. Therefore, the above operation is repeated a plurality of times to obtain a desired amount of active material. The substance needs to be filled. Therefore, there has been a problem that a large amount of time is required for manufacturing the nickel electrode, and the manufacturing cost increases.

[0003] Therefore, as disclosed in Japanese Patent Application Laid-Open No. 62-58566, a high-temperature and high-concentration molten salt impregnating solution such as nickel nitrate aqueous solution is used as an impregnating solution to improve the active material filling efficiency. A method for simplifying the manufacturing process has been proposed.

[0004]

However, in such a method, the substrate is eroded (that is, the nickel constituting the substrate is dissolved) because the impregnating solution becomes more corrosive. As a result, there has been a problem that the substrate becomes brittle and the cycle characteristics of a battery using such an electrode plate deteriorate.

[0005] The present invention has been made in view of the above problems, and by reducing the number of active material filling operations,
It is an object of the present invention to provide a method of manufacturing a nickel electrode for an alkaline storage battery, which can improve the cycle characteristics of a battery using a sintered nickel electrode and improve the productivity of the sintered nickel electrode to reduce the manufacturing cost.

[0006]

In order to achieve the above object, the present invention provides a first step in which a porous nickel substrate is immersed in an acidic nickel salt impregnated aqueous solution; The second to make salt active material
And the alkaline aqueous solution held on the substrate in the second step.
The active material filling operation including the third step of drying while holding the material as it is is performed a plurality of times.

[0007]

Generally, when the active material filling operation for generating nickel hydroxide by the neutralization reaction between an acidic nickel salt and an aqueous alkali solution in the pores of a nickel sintered substrate is repeated, the active material filling amount gradually increases. It was confirmed by experiments that the concentration decreased. This is considered to be because the ratio of the volume of the active material to the volume of the pores of the nickel sintered substrate increases with the active material filling operation.

In view of the above, in order to efficiently fill the nickel sintered substrate with the active material, nickel hydroxide is generated from the deep part of the hole of the nickel sintered substrate, and the volume density of the generated nickel is increased. Must be large. Therefore, as in the above method, when the substrate is dried without removing the alkaline aqueous solution used to make the acidic nickel salt an active material, the substrate is immersed in the acidic nickel salt aqueous solution in the second and subsequent active material filling operations. Is
The acidic nickel salt aqueous solution reacts with the solid alkali to form nickel hydroxide. Thus, according to experiments performed by the present inventors, it has been confirmed that nickel hydroxide produced by reaction with solid-state alkali has a higher bulk density than nickel hydroxide produced by reaction with liquid-state alkali. Was. As described above, when nickel hydroxide having a large bulk density is generated, the nickel sintered substrate can be efficiently filled with the active material, so that productivity is improved. still,
According to another experiment, it was confirmed that the increase in the bulk density of nickel hydroxide as described above was caused by an increase in the true density of nickel hydroxide.

In addition, with the above method, in the second and subsequent active material filling operations, an active material generation reaction occurs when immersed in an acidic nickel salt aqueous solution and when immersed in an alkaline aqueous solution. That is, two active material generation reactions occur in one active material filling operation. Therefore, the number of times of the active material filling operation can be reduced, so that the productivity can be improved, and the number of times of immersing the nickel sintered substrate in the acidic nickel salt impregnating liquid can be reduced. Corrosion of the substrate is suppressed, and as a result, it is possible to improve the cycle characteristics of the battery using the electrode according to the manufacturing method of the present invention.

Further, according to the method of the present invention, nickel hydroxide can be generated from the deep portion of the hole of the nickel sintered substrate, and the active material filling operation can be performed efficiently from this point as well.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. EXAMPLE First, a nickel sintered substrate having a porosity of 80% obtained by drying in a reducing atmosphere is immersed in a molten salt of nickel nitrate (temperature: 80 ° C., specific gravity: 1.75). Next, the nickel nitrate is converted into nickel hydroxide, which is an active material, by immersing the nickel sintered substrate in a 25% aqueous solution of caustic soda. Next, the substrate is dried while the alkali is held on the nickel sintered substrate. By repeating such a series of active material filling operations five times, a nickel electrode was produced.

The electrode fabricated in this manner is hereinafter referred to as (A) electrode. [Comparative Example 1] Instead of a step of drying a nickel sintered substrate while holding an alkali, a step of generating nickel hydroxide as an active material and then removing the alkali by washing with water was performed. An electrode was produced in the same manner as in the above example. Note that such an active material filling operation is repeated five times as in the above-described embodiment.

The electrode fabricated in this manner is referred to as (X
₁ ) Called electrodes. [Comparative Example 2] Except for not performing the step of drying the nickel sintered substrate while holding the alkali (that is, performing the next active material filling operation while holding the alkali in the liquid state on the substrate), An electrode was produced in the same manner as in the above example. Note that such an active material filling operation is repeated five times as in the above-described embodiment.

The electrode fabricated in this manner is referred to as (X
₂ ) Called electrodes. [Experiment 1] The electrode (A) produced by the production method of the present invention and the electrode (X ₁ ) produced by the production method of the comparative example, (X)
₂ ) As to the electrodes, the active material filling amounts in the first to fifth active material filling operations were examined, and the results are shown in FIG. In FIG. 1, the active material filling amount after the fifth active material filling operation in the (X ₁ ) battery of the comparative example was 10
It is represented as 0. Further, the active material filling amount at each time is obtained by immersing the nickel substrate in an alkali to convert the active material into an active material, rinsing with water, drying, and then measuring.

As is apparent from FIG. 1, the electrode (A) manufactured by the manufacturing method of the present invention is ₂ times smaller than the electrodes (X ₁ ) and (X ₂ ) manufactured by the manufacturing method of the comparative example. It is recognized that the active material filling amount after the first time has increased dramatically. This is considered to be due to the following reason. That is, in the (A) electrode of the present invention, in the second and subsequent active material filling operations, the nickel nitrate molten salt reacts with solid caustic soda to produce nickel hydroxide. As described above, nickel hydroxide produced by the reaction with the alkali in the solid state has a larger bulk density than nickel hydroxide produced by the reaction with the alkali in the liquid state. As a result, the active material filling operation can proceed smoothly. In addition, 2
In the active material filling operation after the first time, an active material generation reaction occurs when immersed in molten nickel nitrate and when immersed in caustic soda. That is, two active material generation reactions occur in one active material filling operation. From these facts, it is considered that the filling amount of the active material after the second time has increased dramatically as described above.

On the other hand, in the (X ₁ ) electrode of the comparative example, the alkali was removed after the active material was turned into an active material. Since only active substances are generated by the reaction, the bulk density of the active material is reduced. In addition, in one active material filling operation, only one active material generation reaction occurs. Further, in the (X ₂ ) electrode of the comparative example, the active material generation reaction occurs twice in the second and subsequent active material filling operations.
The generated active material is an active material having a small bulk density due to the reaction with the liquid alkali. In addition, an active material generation reaction occurs on the surface, not on the deep part of the substrate. From these facts, it is considered that the amount of the active material charged after the second time is reduced as described above. [Experiment 2] The electrode (A) produced by the production method of the present invention and the electrode (X ₁ ) and (X ₂ ) produced by the production method of the comparative example
The utilization rate of the active material was measured for the electrodes. In the experiment, the active material filling amounts of all the electrode plates were set to be the same. The experimental conditions are such that the battery is charged in an aqueous solution of potassium hydroxide at a theoretical capacity of 5 hours and then discharged at a rate of 3 hours.

As a result, although not shown, it was confirmed that the (A) electrode, the (X ₁ ) electrode, and the (X ₂ ) electrode had the same active material utilization rate. Therefore, it is understood that the utilization rate of the active material is the same regardless of the magnitude of the bulk density.

[0018]

As described above, according to the present invention, the reaction between the solid-state alkali and the aqueous acidic nickel salt solution produces nickel hydroxide, which is an active material, so that the bulk density of nickel hydroxide increases. . In addition, nickel hydroxide can be generated from the deep part of the hole of the nickel sintered substrate. From these, the active material filling operation can be performed efficiently.

Further, in the second and subsequent active material filling operations, two active material generation reactions occur in one active material filling operation, so that the number of active material filling operations can be reduced. As a result, productivity can be improved. In addition, since the number of times the nickel sintered substrate is immersed in the acidic nickel salt impregnation liquid can be reduced, the corrosion of the nickel sintered substrate is suppressed, and as a result, the cycle of the battery using the electrode according to the manufacturing method of the present invention is reduced. Excellent effects such as improvement of characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 shows the first to fifth active material filling operations for the (A) electrode manufactured by the manufacturing method of the present invention and the (X ₁ ) electrode and (X ₂ ) electrode manufactured by the manufacturing method of the comparative example. 4 is a graph showing the amount of active material charged in FIG.

────────────────────────────────────────────────── (5) References JP-A-64-648 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4 / 32

Claims (1)

(57) [Claims] 1. A first step in which a porous nickel substrate is immersed in an acidic nickel salt impregnated aqueous solution, a second step in which the substrate is immersed in an alkaline aqueous solution to convert the acidic nickel salt into an active material, and the second step. Alkaline water held on substrate by
3. A method for producing a nickel electrode for an alkaline storage battery, comprising performing a plurality of times of an active material filling operation including a third step of drying while keeping the solution as it is.