JPS63158749A - Zinc electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To retard the growth of dendritic zinc from metallic zinc particles in the initial charge-discharge stage in a zinc electrode to obtain good cycle performance by covering metallic zinc in a zinc electrode mainly comprising zinc oxide and metallic zinc with indium or indium compound. CONSTITUTION:A specified amount of zinc powder is immersed in three normal hydroxide aqueous solution for a given time to dissolve a zinc oxide film on the surface of the zinc powder. A specified amount of indium hydroxide is added to this aqueous solution and a mixture is stirred, then the filtered, and the zinc powder is dried at a given temperature to obtain the zinc powder covered with indium. The weight of indium film is limited to 1 wt% of the metallic zinc. 15 wtpts metallic zinc, 100 wtpts zinc oxide, and 2 wtpts mercuric oxide are mixed, then water and polytetrafluoroethylene are added to and kneaded with the mixture to obtain paste. The paste is pressed against a current collector to manufacture a zinc electrode.

Description

[Detailed description of the invention] (a) Field of industrial application The present invention relates to a zinc electrode for an alkaline storage battery using zinc as an active material, which is used in nickel-zinc storage batteries and silver-zinc storage ponds. .

(b) Conventional technology Zinc, which is used as a negative electrode active material, has the advantage of having a high energy density per unit of energy and being inexpensive.
Alkaline zinc storage batteries having such zinc electrodes have high expectations as batteries with features such as high energy density and high operating voltage.

However, in this type of alkaline zinc storage battery, the zincate ions produced when zinc is eluted into the alkaline electrolyte during discharge are deposited and grow in a dendritic form on the surface of the zinc electrode during charging. Electrodeposited zinc may penetrate the separator and come into contact with the positive electrode, causing an internal short circuit in the battery.
Another disadvantage is that the surface of the zinc electrode becomes highly dense and the battery discharge capacity decreases, resulting in a very short cycle life of the battery.

As a conventional technique for addressing this drawback and improving battery cycle characteristics, for example, Japanese Patent Application Laid-Open No. 189562/1989 discloses that thallium oxide or hydroxide and indium oxide or hydroxide are used as zinc active materials. On the other hand, it is disclosed that when 11 to 15% by weight of total additives are added, the cycle characteristics can be significantly improved. However, simply adding these does not effectively inhibit the growth of dendritic zinc, and the effect cannot be fully exhibited.

This is because these additives are reduced and cover the metal zinc surface as the number of cycles progresses, but at the beginning of the charge/discharge cycle, these additives do not cover the metal zinc surface, and at this time the dendritic This is because once metallic zinc, which becomes the core of zinc production, appears, the growth of dendritic zinc cannot be effectively inhibited as the number of cycles progresses, even if the additive is present. Further, the additive covers the surface of metallic zinc only after charge/discharge cycles have been repeated several 10 times, and at this point, metallic zinc that will become the nucleus for the formation of dendritic zinc has already appeared. Furthermore, the formation of dendritic zinc becomes particularly noticeable during rapid charging and overcharging.

(c) Problems to be Solved by the Invention The present invention has been made in view of the above-mentioned problems, and it suppresses the generation of dendritic zinc from metal zinc particles at the beginning of the charge/discharge cycle in the zinc electrode, thereby improving the cycle characteristics. The aim is to provide an excellent alkaline storage battery.

(d) Means for solving the problem The gist of the present invention is that in a zinc electrode whose main active materials are zinc oxide and metallic zinc, the metallic zinc is covered with indium or an indium compound. .

(E) Effect During rapid charging or overcharging, the electrode potential of the zinc electrode shifts to the more base side than during normal charging, and a reaction in which zincate ions are reduced and electrodeposited on metal zinc becomes more likely to occur. That is, the electrode reaction at the zinc electrode during rapid charging or overcharging is a competitive reaction between a reaction in which zinc oxide is reduced and a reaction in which zincate ions are reduced and electrodeposited on metal zinc.

However, when the surface of metallic zinc is covered with indium or an indium compound, the overvoltage of the electrodeposition reaction increases, and only the reduction of zinc oxide occurs preferentially. Therefore, even if rapid charging or overcharging is performed at the beginning of one cycle, the growth of dendritic zinc from the zinc electrode can be effectively prevented, and short circuits within the battery circle can be suppressed.

(To) Example 3 Specified sodium hydroxide aqueous solution 1! zinc powder 500
g was added and immersed for 30 minutes to dissolve the zinc oxide film that had formed on the surface of the zinc powder.

Next, 1.0 g of indium hydroxide was added to this solution, and 1.0 g of indium hydroxide was added to the solution.
After stirring for 0 minutes, this solution was filtered, washed 10 times with 500 m2 of pure water, and dried at 70°C to produce metallic zinc whose surface was covered with indium.

The weight of the indium coating at this time was 1% by weight based on the metal zinc.Next, 151 parts of this metal zinc, 100 parts by weight of zinc oxide, and 2 parts by weight of mercury oxide to increase the hydrogen overvoltage were added. After powder mixing, water and polytetrafluoroethylene (PTFE) were added and kneaded to obtain a paste, which was pressed onto a current collector to form a zinc electrode. By combining the zinc electrode of the present invention and the sintered nickel electrode, 10 cells of a cylindrical sealed nickel-zinc battery A according to the present invention having a nominal capacity of 1i700 mAh were fabricated.

In addition, as a comparison battery, a zinc electrode similar to the zinc electrode of the present invention was obtained, except that metal zinc whose surface was not indium-treated was used and 2 parts by weight of indium hydroxide was added, and a comparison battery B was prepared in the same manner. 10 cells were created.

Using these batteries, charging 150% with a single current of 1c and discharging 100% with a current of 1c, the battery capacity was 500mA.
A charge/discharge cycle test was conducted under cycle conditions in which the battery life is defined as the point at which the battery life drops below h (final voltage 1.OV). The results are shown in the figure.

From the results shown in the figure, it can be seen that the battery A of the present invention is superior. This is because the surface of the metallic zinc particles, which serve as the nucleus for the generation of dendritic zinc, is covered with indium, so that even as the number of cycles progresses, the growth of dendritic zinc is effectively suppressed.

The inventor has discovered that the amount of indium added is preferably 0.5 to 2.0% by weight based on the weight of metal zinc.

Further, in the examples, the surface of metal zinc particles is covered with metal indium, but the same effect can be obtained even if the surface is covered with an indium compound such as indium oxide.

(G) Effects of the Invention The zinc electrode for alkaline storage batteries of the present invention can effectively suppress the growth of dendritic zinc by covering the surface of the metal zinc particles to be added with indium or an indium compound. The alkaline storage batteries used in this study have extremely excellent cycle characteristics and are of great industrial value.

[Brief explanation of the drawing]

The figure is a comparison diagram of cycle characteristics of batteries. A... Uninvented battery, B... Comparison! pond.

Claims (1)

[Claims] (1) A zinc electrode for an alkaline storage battery using zinc oxide and metallic zinc as main active materials, characterized in that the metallic zinc is covered with indium or an indium compound.