JP2562669B2 - Alkaline storage battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a zinc electrode and an alkaline storage battery using a zinc active material as a negative electrode of a nickel-zinc storage battery, a silver-zinc storage battery or the like.

(B) Conventional technology Zinc used as an active material for a negative electrode has been researched and developed because it has a large energy density per unit weight, is inexpensive, and is non-polluting. However, it has not been put to practical use yet. This is because the zinc electrode is a soluble electrode. That is, zinc is dissolved as zincate ions in the alkaline electrolyte at the time of discharge, and at the time of the next charge, the zincate ions are electrodeposited on the surface of the zinc electrode. The acid ion electrodeposition reaction becomes non-uniform, the active material undergoes shape deformation, and the electrode reaction area decreases. As a result, the battery capacity decreases. In order to maintain the battery capacity even if the shape deformation of the active material progresses, it is effective to include metallic zinc as a dischargeable substance in the negative electrode active material. This is because metallic zinc added as an active material can be discharged together with metallic zinc charged from zinc oxide, so if metallic zinc is contained as a dischargeable substance in the negative electrode active material before the start of the charge / discharge cycle,
This is because the discharge capacity of the negative electrode will be maintained at a high level. Further, since the metallic zinc powder also acts as a conductive material, the current collecting effect is increased and the high rate discharge characteristic is also improved.

However, since the starting material metal zinc has a much larger particle size than zinc oxide, it tends to become the nucleus of dendritic zinc crystal growth during charging, and when performing rapid charging or charging at high temperature, Internal short circuit occurs and charge / discharge cycle characteristics deteriorate. Therefore, when the present inventor uses a zinc powder in which the surface of zinc oxide is coated with metallic zinc as a negative electrode active material, metallic zinc as a dischargeable substance is retained and metallic zinc with a large particle size is present. Therefore, it was found that internal short circuit due to the growth of dendritic zinc is unlikely to occur and the charge-discharge cycle characteristics can be improved.

However, if the surface of the zinc oxide powder is coated only with active metallic zinc, the distribution of the electrode reaction tends to be non-uniform at the beginning of the cycle when the additive is not sufficiently distributed, which causes the shape deformation of the zinc electrode. There was a problem that it was not sufficiently suppressed.

(C) Problems to be Solved by the Invention If a zinc active material powder in which the surface of zinc oxide is coated with metallic zinc as a dischargeable substance is used, the battery capacity can be prevented from decreasing and quick charging or charging at high temperature can be performed. Although the effect of suppressing the growth of dendritic zinc crystals is recognized, it cannot be completely prevented. The present invention has been made in view of such problems, preventing the growth of dendritic zinc crystals in the zinc electrode,
It is intended to provide an alkaline storage battery having excellent cycle characteristics.

(D) Means for Solving the Problems The zinc electrode for an alkaline storage battery of the present invention is one in which zinc oxide is coated with metallic zinc, and a part of the metallic zinc is at least indium, thallium, lead, cadmium, bismuth. The main component is a zinc active material substituted with one kind of element selected from gallium.

Further, the alkaline storage battery of the present invention is a zinc active material in which zinc oxide is coated with metallic zinc and at least a part of the metallic zinc is replaced with at least one element selected from indium, thallium, lead, cadmium, bismuth and gallium. It is composed of a zinc electrode containing a substance as a main component, a positive electrode, and an alkaline electrolyte.

(E) Operation Usually, the particle size of zinc metal powder used as a starting material for a zinc active material is about 10 times larger than that of zinc oxide, even if it is small. As described above, the zinc metal particles having larger particles than the zinc oxide particles tend to become nuclei for dendritic zinc crystal growth more easily than the particles in which zinc oxide is changed to zinc metal during charging. When a material capable of discharging is retained by the method of coating the surface of zinc oxide with metallic zinc, the capacity reduction of the battery is suppressed, and since there is no metallic zinc having a larger particle size, dendritic zinc crystals are formed. It becomes difficult to grow. However, the above-mentioned powder has a non-spherical shape and is non-uniform, and since the surface is only active metal zinc, the distribution of the electrode reaction becomes non-uniform at the beginning of the cycle when the additive is not sufficiently distributed. It is easy, and as a result, dendritic zinc crystals may grow.

On the other hand, as in the present invention, the surface of zinc oxide is coated with metallic zinc, and at least indium, thallium, lead, cadmium, bismuth, gallium, etc., which have a larger hydrogen overvoltage and a redox potential more noble than that of metallic zinc. When a part of metallic zinc is replaced with one or more additive elements selected from metals, microscopically, the overvoltage of the zincate ion electrodeposition reaction is increased by the action of the additive elements. As a result, the zincate ion can be gently and uniformly deposited on the surface of the active material particles. Therefore, the growth of dendritic zinc crystals from the zinc active material is effectively prevented. Furthermore, when viewed macroscopically, zinc oxide, metallic zinc as a dischargeable substance, and an additive element as an additive can be completely integrated, so that the dispersibility of the additive in the zinc electrode is improved, Even if the charge / discharge cycle progresses, the effect as an additive is effectively exhibited, the current distribution in the entire electrode becomes uniform, and the active material is effectively used. As a result, even if such a zinc electrode is charged rapidly or at high temperature,
The cycle characteristics of the alkaline storage battery can be improved without deterioration of the cycle characteristics.

(F) Example First, preparation of zinc powder in which zinc oxide is coated with metallic zinc will be described.

Zinc oxide powder having an average particle size of 0.4 μm was held in a hydrogen atmosphere at 3 atm at 1100 ° C. for 3 hours. By this treatment, the zinc oxide surface was reduced with hydrogen to obtain a zinc active material powder in which the surface coated with metallic zinc was modified. The surface-modified zinc active material had an average particle size of 0.6 μm.

When this powder was dissolved in an aqueous solution of ammonia and ammonium chloride and the ratio of metallic zinc to zinc oxide was quantified, it was confirmed that about 20 wt% of the zinc oxide powder was reduced to metallic zinc.

This surface-modified zinc active material was used in the following Example 1,
Used in Example 2 and Comparative Example 2.

Example 1 The surface-modified zinc active material powder was immersed in a 0.3 mol / indium chloride aqueous solution and stirred for 30 minutes.
A 1 mol / potassium hydroxide aqueous solution was added, and then thoroughly washed with water to obtain an integrated active material according to the present invention in which a part of metallic zinc on the surface was replaced with indium. The weight of the substituted indium at this time was about 3% by weight of the weight of the zinc active material having the surface modified.

Next, 95% by weight of the integrated active material and 5% by weight of fluororesin
To the mixed powder consisting of, kneading, to obtain a paste,
A zinc electrode was obtained by pressing on the current collector. By combining this with a known sintered nickel electrode of zinc electrode, a cylindrical sealed nickel-zinc battery with a nominal capacity of 500 mAh was obtained, which was designated as Battery A of the present invention.

Example 2 An aqueous solution of thallium chloride was used in place of the aqueous solution of indium chloride used in Example 1 to prepare an integrated active material in which a part of the metallic zinc on the surface was replaced with thallium, and the others were the same as in Example 1. Battery B of the present invention was obtained in the same manner.

Comparative Example 1 Zinc oxide, metallic zinc, and indium hydroxide were powder mixed so that the molar ratio of zinc oxide, metallic zinc, and indium in the integrated active material of the present invention was the same, and this mixture was mixed. Comparative battery C was obtained in the same manner as in Example 1 except that the active material was used.

[Comparative Example 2] The surface-modified zinc active material (zinc oxide is coated with metallic zinc so that the molar ratio of zinc oxide, metallic zinc, and indium in the integrated active material of the present invention is the same. Comparative battery D was obtained in the same manner as in Example 1 below, except that the zinc powder) was mixed with indium hydroxide and the mixture was used as the active material.

Using the batteries A and B of the present invention thus obtained and the comparative batteries C and D, a charging / discharging cycle test of charging for 15 hours at a charging current of 500 mA and discharging to a final voltage of 1.4 V at a discharging current of 500 mA was performed. . The charge / discharge cycle test was repeated until the battery capacity reached 350 mAh.

The figure shows a comparison of the charge / discharge cycle characteristics of the batteries A and B having the zinc electrode of the present invention and the batteries C and D having the zinc electrode of the comparative example.

As is clear from the figure, in the batteries A and B of the present invention, the initial failure rate is drastically reduced, and the charge / discharge cycle characteristics are greatly improved.

In this example, a method of reducing the surface of the zinc oxide powder in a high temperature hydrogen atmosphere was used as the method of coating with the metallic zinc, but the method of coating the surface of the zinc oxide powder by electroless plating with metallic zinc is also the same. The effect of is obtained. Further, while the chloride aqueous solution was used when substituting the additive element as the additive, the same effect can be obtained with a nitrate or sulfate aqueous solution.

(G) Effect of the Invention According to the present invention, there is almost no initial failure due to an internal short circuit based on the growth of dendritic zinc crystals even when performing rapid charging,
It is possible to obtain a zinc electrode with a small decrease in capacity over a long cycle. By using such a zinc electrode, an alkaline storage battery having excellent cycle characteristics can be provided and its industrial value is extremely large.

[Brief description of drawings]

The figure is a comparison diagram of the cycle characteristics of the batteries A and B of the present invention and the comparative batteries C and D. A, B ... Inventive battery, C, D ... Comparative battery.

Claims (2)

(57) [Claims] 1. A zinc activity obtained by coating zinc oxide with zinc metal, wherein a part of the zinc metal is replaced with at least one element selected from indium, thallium, lead, cadmium, bismuth and gallium. Zinc electrode for alkaline storage batteries whose main component is a substance. 2. Zinc oxide is coated with metallic zinc, and a part of said metallic zinc is at least indium, thallium,
1 selected from lead, cadmium, bismuth and gallium
An alkaline storage battery comprising a zinc electrode having a zinc active material as a main component substituted with certain elements, a positive electrode, and an alkaline electrolyte.