JPS63158750A - Zink 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 cycle stage in a zinc electrode to increase the cycle performance of an alkaline storage battery by covering metallic zinc in a zinc electrode mainly comprising zinc oxide and metallic zinc with thallium or thallium compound. CONSTITUTION:A specified amount of zinc powder is immersed in three normal sodium hydroxide solution for a given time, and filtered, then washed with water several times. The zinc powder obtained is immersed in a thallous nitrate solution, stirred, filtered, and dried to obtain metallic zinc covered with thallium. The weight of thallium film is limited to 1 wt% of the metallic zinc. 15 wtpts metallic zinc, 100 wtpts zinc oxide, and 2 wtpts mercuric oxide for raising hydrogen overvoltage 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 that uses zinc as an active material for use in nickel-zinc storage batteries, silver-zinc storage batteries, and the like.

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

However, in this type of alkaline zinc storage battery, zinc leaches into the alkaline electrolyte during discharge and produces zincate ions, which are then deposited and grown in the form of branches on the surface of the zinc electrode during charging. Electrodeposited zinc may penetrate the separator and come into contact with the positive electrode, causing a short circuit in the inward direction of 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 Laid-Open No. 189562 discloses that thallium oxide or hydroxide and indium oxide or hydroxide are used as zinc active materials. However, it has been disclosed that the cycle characteristics can be significantly improved by adding a total amount of 1 to 15% by weight. However, simply adding these substances cannot effectively inhibit the growth of dendritic zinc. and cannot fully demonstrate its effects.

This is because these additives are reduced and cover the surface of the metal zinc as the number of cycles progresses, but at the beginning of the charge/discharge cycle, these additives do not cover the surface of the metal zinc, 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 the charge/discharge cycle has been repeated several dozen 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 initial stage of charge/discharge cycles in a zinc electrode, and improves cycle characteristics. The aim is to provide an excellent alkaline storage battery.

(d) Means to solve the problem The gist of the present invention is that in a zinc electrode whose seven active materials are zinc oxide and metallic lead, the metallic zinc is covered with thallium or a thallium compound. be.

(e) Effect: During rapid charging or overcharging, the electrode potential of the zinc electrode shifts more arbitrarily than during normal charging, and a reaction in which zincate ions are completely reduced and electrodeposited on metal zinc becomes more likely to occur. In other words, the electrode reaction at the zinc electrode during rapid charging or overcharging is a reaction in which zinc oxide is reduced and a reaction in which zinc oxide is reduced.
・is reduced to metal zinc! It becomes a competitive reaction with the reaction that occurs.

However, when the surface of metallic zinc is covered with thallium or a thallium 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 the cycle, the growth of dendritic zinc from the zinc electrode can be effectively prevented, and short circuits within the battery circle can be suppressed.

(f) Example 3 Add 500% zinc powder to the specified sodium hydroxide aqueous solution IP.
g, soaked for 30 minutes, filtered, 500m2
It was washed 10 times with pure water. This zinc powder was poured into 50 ml of 0.5% thallium nitrate aqueous solution, stirred, filtered, washed with water, and dried at 70°C to produce metallic zinc whose surface was removed by thallium. The weight of the thallium coating at this time was 1Fijt% based on the metal zinc.Next, 15 parts by weight 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 mixing the powders, water and polytetrafluoroethylene (PTFE) were added and kneaded to obtain a paste, which was pressed onto a current collector to form a zinc electrode.The zinc electrode of the present invention and the sintered nickel electrode In combination, the nominal capacity of the cylindrical sealed type is 70
Ten cells of 0 mAh nickel-zinc battery A according to the present invention were prepared.

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 treated with thallium was used and 2 parts by weight of thallium oxide was added, and a comparative battery B was prepared in the same manner. Created a cell.

Next, use these batteries and charge them at 150% with the IC current.
, the discharge is performed 100% with the IC current, and the battery capacity is 500%.
mAh (end t) El, OV ) or less? , : A charge/discharge cycle test was conducted under cycle conditions that set the battery life at the end of the battery life. The results are shown in the figure.

From the results shown in the figure, it can be seen that the first cell 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 thallium, so that even as the number of cycles progresses, the growth of dendritic zinc is effectively suppressed.

The amount of thallium added is 0 based on the weight of metal zinc.
．． It has been confirmed through experiments that the content is preferably 5 to 2.0% by weight.

Further, in the examples, the surface of metal zinc particles is coated with metal thallium, but coating with a thallium compound such as thallium oxide also has a coexistence effect.

(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 thallium or a thallium 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: Battery of the present invention, B: Comparative battery.

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 thallium or a thallium compound.