JP2999878B2 - Manufacturing method of non-sintered cadmium electrode - 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 non-sintered cadmium electrode used in an alkaline storage battery such as a nickel-cadmium storage battery.

[0002]

2. Description of the Related Art Cadmium electrodes used in alkaline storage batteries such as the above-mentioned nickel-cadmium storage batteries include:
Paste-type ones whose processes are relatively simple and whose production costs are low are widely used. A method for producing such a paste-type cadmium electrode is disclosed in JP-B-58-4899.
As disclosed in Japanese Patent Publication No. 0, a so-called active material paste is prepared by mixing an active material powder such as cadmium oxide, a reinforcing fiber, a binder, and the like, and applying the paste to a conductive core and drying the paste. A method for manufacturing an unformed electrode plate is known.

However, in the above manufacturing method, when the electrode plate is wound using a pressure roller or the like, due to the softness of the active material paste, the degree of pressurization is higher at the end than at the start of the winding. Increase. Therefore, the electrode thickness decreases as the winding ends, and accordingly, the electrode porosity decreases as the winding ends. As a result, when a battery is manufactured using an unformed electrode plate manufactured by such a manufacturing method, the amount of electrolyte held by the electrode plate is smaller than that of the electrode plate already formed, and the battery Since the reaction cannot be performed uniformly, the battery performance decreases.

Therefore, a production method has been proposed in which the electrode plate (cadmium oxide) is pre-hydrated in an alkaline aqueous solution. When the hydration treatment of cadmium oxide is performed in this manner, a large cadmium hydroxide having a crystal grain size grown is formed, so that relatively large pores are uniformly formed inside the paste-like active material, and extremely large cavities are formed. The mechanical strength of the plate is improved. As a result, at the time of winding the electrode plate, the active material is hardly rolled, and the porosity becomes uniform in the winding direction, and the porosity is maintained high.

[0005]

However, it takes a long time to complete the hydration reaction. Therefore, in order to reduce the cost in the hydration treatment step, it is necessary to raise the temperature of the alkaline aqueous solution and terminate the reaction in a short time. However, when hydrated at high temperature,
The crystal form of the generated active material changes, or the active material is partially detached from the core due to a rapid chemical reaction, so that blisters are generated. As a result, there was a problem that the battery characteristics deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above situation, and has as its object to provide a method of manufacturing a non-sintered cadmium electrode which can reduce the manufacturing cost without lowering the battery performance. .

[0007]

In order to achieve the above object, the present invention provides a first step in which a paste mainly composed of cadmium oxide as a main active material is applied to a conductive core to produce an electrode plate; A second step of immersing the electrode plate in an alkaline aqueous solution at 10 to 50 ° C. and partially prehydrating the cadmium oxide, and immersing the electrode plate in an alkaline aqueous solution at 60 to 90 ° C. to remove the cadmium oxide; And a third step of hydration.

[0008]

Generally, when cadmium oxide, which is the main active material, is hydrated in sodium hydroxide, γ-type cadmium hydroxide is produced. However, if the temperature of the alkali treatment is increased in order to complete the hydration treatment quickly, β-type cadmium hydroxide is generated preferentially over γ-type.

Here, since the γ-type cadmium hydroxide is a needle-like crystal having a small particle size, the specific surface area is large. However, since the β-type cadmium hydroxide is a hexagonal system having a large particle size, , The specific surface area becomes smaller. Therefore, the β-type cadmium hydroxide has a lower charge acceptability than the γ-type cadmium hydroxide, has a smaller charge depth of the active material, and has a faster hydrogen gas generation.

[0010] In addition, since γ-type cadmium hydroxide is a needle-like crystal having a small particle size, it can be densely packed, and as a result, blister generation can be suppressed. In contrast, β-cadmium hydroxide grows as larger crystals,
Cannot be filled densely. Therefore, blisters are easily generated under a sudden chemical reaction such as when the temperature of the alkali treatment is increased. Considering these facts, the form of the active material generated by hydration is preferably γ-type cadmium hydroxide.

In consideration of the above, the present inventors conducted an experiment. When the alkali treatment temperature was increased to accelerate the hydration reaction, β-type cadmium hydroxide was formed. It has been found that the crystal morphology is determined by the processing temperature when cadmium oxide is first immersed in an alkaline processing solution. For example, if the temperature at the time of first immersion is low, γ-type crystal nuclei are generated, and even if the reaction speed is increased by treating at a higher temperature, the crystal form does not become β-type, but γ-type It was found to grow as crystals. As a specific alkali treatment temperature, it was confirmed by an experiment that it was necessary to be in the range of 10 to 50 ° C. at the time of immersion first and to be in the range of 60 to 90 ° C. at the time of subsequent immersion. .

From these facts, if a non-sintered cadmium electrode is produced by the above-described method, γ-type cadmium hydroxide is generated, so that it is possible to improve the charge acceptability and suppress the generation of hydrogen gas, Blistering can be prevented. In addition, the alkali treatment is performed at a low temperature only at the beginning, and thereafter the alkali treatment can be performed at a high temperature, so that the hydration step can be completed in a short time.

[0013]

【Example】

[Preliminary experiment] An active material powder comprising 80% by weight of cadmium oxide powder and 20% by weight of metal cadmium powder, a methylcellulose solution, and a nylon fiber were kneaded to prepare a paste, which was then applied to a conductive core. Dry and make the plates. Next, after manufacturing many such plates,
Each electrode plate was treated with a 25% aqueous sodium hydroxide solution (solution temperature varied from 0 to 90 ° C.) for 5 minutes and 1 hour.
Hydration was performed for 5 minutes, and finally each electrode plate was washed with water and dried.

FIG. 1 shows the hydration rate of each electrode plate in this case, and FIG. 2 shows the ratio between γ-type cadmium hydroxide and β-type cadmium hydroxide formed by hydration for 15 minutes.
As is clear from FIG. 1, it can be seen that as the temperature of sodium hydroxide increases, the hydration rate also increases, and the speed of the hydration reaction increases. Specifically, to reach a satisfactory level of hydration in a short time,
A hydration temperature of 60 ° C. or higher is required. However, at 90 ° C. or higher, blisters are generated and decomposition of nylon fibers and the like is caused regardless of the crystal form because the reaction speed is too rapid. In consideration of these, the temperature of sodium hydroxide needs to be 60 to 90 ° C.

On the other hand, as is apparent from FIG. 2, cadmium hydroxide produced during hydration is γ at 10 to 50 ° C.
There are many types, but when the temperature exceeds 50 ° C., the ratio of β-type gradually increases. Therefore, in order to generate γ-type cadmium hydroxide, the temperature of sodium hydroxide must be 1
It is necessary to perform in the range of 0 to 50 ° C. From these experimental results, the temperature at the first immersion in the alkaline solution is 10 to
The temperature must be in the range of 50 ° C., and the temperature when subsequently immersed in the alkaline solution must be in the range of 60 to 90 ° C. [Example] First, an electrode plate coated with an active material was prepared in the same manner as in the above-mentioned preliminary experiment, and this electrode plate was partially applied to a sodium hydroxide aqueous solution (25%) at 20 ° C for only 5 minutes. After pre-hydration, the solution was placed in an aqueous sodium hydroxide solution at 70 ° C for 15
Hydrate for a minute. Thereafter, the electrode plate was washed with water and dried to produce an electrode.

The electrode fabricated in this manner is hereinafter referred to as (A) electrode. Thereafter, the electrode was cut into a predetermined size, and further combined with a known sintered nickel anode to produce a sealed alkaline storage battery having a nominal capacity of 1.3 AH. The battery fabricated in this manner is hereinafter referred to as (a) battery. [Comparative Example] No partial prehydration was performed (that is, 70 ° C
Only hydrate for 15 minutes in aqueous sodium hydroxide solution)
Otherwise, an electrode and a battery were manufactured in the same manner as in the above example.

The electrode and the battery thus produced are
Hereinafter, they are referred to as (X) electrode and (x) battery, respectively. [Experiment 1] The structures of the electrode (A) of the present invention and the electrode (X) of the comparative example were examined by an X-ray diffraction method, and the results are shown in FIG.

As is clear from FIG. 3, (X) of the comparative example
In the electrode, β-type cadmium hydroxide is preferentially generated, whereas in the electrode (A) of the present invention, the temperature of the alkali treatment depends on the crystal form generated at 20 ° C., so that the γ-type water It is recognized that cadmium oxide is mainly produced. [Experiment 2] Blister generation rate between the electrode (A) of the present invention and the electrode (X) of the comparative example, and (a) the battery using the electrode of the present invention and the electrode of the comparative example (x) The amount of hydrogen gas generated in the battery was examined. The results are shown in Table 1. The hydrogen gas generation amount is the amount of hydrogen gas after charging (temperature: 0 ° C.) at a nominal capacity of 0.1 C for one week.

[0019]

[Table 1]

As is clear from Table 1, (X) of Comparative Example
It is recognized that a large number of blisters are generated in the electrode, whereas no blister is recognized in the electrode (A) of the present invention. This is because the electrode (X) of the comparative example is immersed in an alkaline solution having a high temperature from the beginning of the hydration treatment.
In contrast to the formation of β-type cadmium hydroxide, the electrode (A) of the present invention is immersed in a low-temperature alkaline solution at the beginning of the hydration treatment, so that γ-type cadmium hydroxide is generated. This is probably due to the reason.

From Table 1, it can be seen that the (x) battery using the electrode of the comparative example produced an extremely large amount of hydrogen gas, whereas the (a) battery using the electrode of the present invention produced a hydrogen gas. It is recognized that the amount of generation is extremely small. this is,
In the (x) battery using the electrode of the comparative example, β generated at the electrode
On the other hand, in the battery (a) using the electrode of the present invention, the charge acceptability of γ-type cadmium hydroxide generated in the electrode is improved, while the charge acceptability of the cadmium hydroxide of the type is poor. Conceivable. [Experiment 3] The relationship between the number of charge / discharge cycles and the utilization rate of the active material was examined for the electrode (A) of the present invention and the electrode (X) of the comparative example. The results are shown in FIG. The experimental conditions were as follows: after charging to 160% of the capacity with an electric current of 0.3 C in an excessive amount of 25 wt% potassium hydroxide aqueous solution,
The condition is that the battery is discharged at a current of 0.5 C until it reaches -1.0 V with respect to the metal nickel counter electrode.

As is apparent from FIG. 4, (X) of the comparative example
It can be seen that the electrode has lower active material utilization in all cycles than the electrode (A) of the present invention. This is because, in the (X) electrode of the comparative example, the adhesion between the core and the active material is reduced due to the generation of blisters. Therefore, 1
From the cycle, the utilization rate of the active material becomes low, and the deterioration increases with the cycle. On the other hand, in the electrode (A) of the present invention, since no blister is generated, the adhesion between the core and the active material is improved. Therefore, it is considered that the reason is that the utilization rate of the active material is high from the first cycle, and the deterioration decreases with each cycle.

[0023]

As described above, according to the present invention, γ
Since cadmium hydroxide of the type is generated, it is possible to improve the charge acceptability, suppress the generation of hydrogen gas, and prevent the generation of blisters. In addition, the alkali treatment is performed at a low temperature only at the beginning, and thereafter the alkali treatment is performed at a high temperature, so that the hydration step can be completed in a short time. From these facts, there is an excellent effect that the time of the hydration step can be reduced without lowering the electrode performance.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an alkali treatment temperature and a hydration rate.

FIG. 2 is a graph showing the alkali treatment temperature and the ratio of γ-type cadmium hydroxide / β-type cadmium hydroxide of a hydrated electrode plate.

FIG. 3 is an X-ray diffraction diagram of an electrode (A) of the present invention and an electrode (X) of a comparative example.

FIG. 4 is a graph showing the relationship between the number of cycles and the active material utilization in the electrode (A) of the present invention and the electrode (X) of the comparative example.

Claims (1)

(57) [Claims] A first method for producing an electrode plate by applying a paste mainly composed of cadmium oxide as a main active material to a conductive core.
A step of immersing the electrode plate in an alkaline aqueous solution at 10 to 50 ° C. and partially pre-hydrating the cadmium oxide; and immersing the electrode plate in an alkaline aqueous solution at 60 to 90 ° C. A third step of hydrating cadmium oxide; and a method for producing a non-sintered cadmium electrode.