JPS6177264A - Zinc powder for alkaline battery - Google Patents

Abstract

PURPOSE:To obtain zinc powder, whose hydrogen gas evolution is retarded, for an alkaline battery by treating the surface of zinc powder with an organic compound which forms a chelate compound with zinc, washing, then drying. CONSTITUTION:Zinc powder is treated in a solution in which an organic compound which forms a chelate compound with zinc, such as tannic acid or imidazole is dissolved. By this surface treatment, hydrogen gas evolution from the zinc powder is retarded compared with nontreated zinc powder. Before this surface treatment, if the surface of zinc powder is treated with acid such as potassium hydroxide or sodium hydroxide, hydrogen gas evolution from zinc powder is remarkably retarded.

Description

Detailed Description of the Invention (Field of the Invention) The present invention relates to zinc powder for alkaline batteries, and more particularly to treating the surface of the zinc powder with an organic compound that forms a chelate compound with zinc to form a chelate film. The present invention relates to zinc powder for use in alkaline batteries, which significantly suppresses hydrogen gas generation compared to untreated zinc powder.

(Night of the invention) Atomized zinc powder is used exclusively as the cathode active material of alkaline batteries because it is a large electrical product per ψ position, is relatively chemically stable, has good processability, and is inexpensive. It is used for awards.

However, in an alkaline electrolyte, chemical dissolution of zinc causes gas to build up inside the battery, creating a buildup of pressure, which can cause leakage of the electrolyte, deformation of the battery, and in extreme cases, destruction of the battery. As a countermeasure against this problem, frozen zinc powder, which utilizes the hydrogen overvoltage of mercury, has conventionally been used as a negative electrode active material.

For this reason, the negative electrode active materials of alkaline batteries commercially available today contain a large amount of mercury, approximately 5 to 10% by weight.
As a social need, there are strong expectations for the development of low-mercury or mercury-free batteries.

Therefore, in order to avoid reducing the mercury content in batteries, various zinc powders containing elements that suppress hydrogen gas generation from zinc other than mercury have been proposed, but none of them suppress the hydrogen gas generation rate. There is still no way to avoid the use of mercury.

(Objective of the Invention) In view of the above-mentioned situations, the present invention aims to further increase the hydrogen gas generation suppressing effect of these zinc powders. The purpose is to provide zinc powder.

(Details of the Invention) The present inventors have conducted various studies to achieve object 1-1, and found that various zinc powders can be used with zinc to form organic compounds τ, certain tannic acids, and imidazole. In comparison with lead powder, hydrogen gas generation (structure of the invention) (J, that is, the present invention 4) Zinc and 4
Zinc powder for alkaline batteries obtained by surface treatment with an organic compound that forms a lithium compound.

The zinc powder used in the present invention is not only zinc powder, but also zinc alloy powder alloyed with lead or indium, frozen zinc powder made by freezing these zinc powders, zinc alloy powder, and frozen zinc alloy powder. is also included.

In the present invention, the surface of zinc powder is treated with an organic compound that forms a chelate compound with zinc to form a film on Kire-1. The organic compound used here is not particularly limited, but tannic acid and imidazole are preferred. . In addition, as a pretreatment for the surface treatment of zinc powder with this organic compound, the surface of the zinc powder is treated with an acid such as hydrochloric acid or acetic acid, or with potassium hydroxide.
By treating with an alkali solution such as sodium hydroxide, the effect of suppressing hydrogen gas generation is further promoted.

Although the reason why the present invention has the effect of suppressing hydrogen gas generation is not clear, there are several possible reasons.

Zinc powder is usually produced by the atomization method, but this method generally results in a rough surface, which tends to cause scratches and fine irregularities on the surface. From a corrosion perspective, these parts act as active sites and promote corrosion. In other words, hydrogen gas should be easily generated, but by surface treatment with tannic acid or imidazole, the extreme surface layer of zinc powder can be cleaned.
1. It dissolves due to the formation reaction, forming a new surface with high smoothness, and at the same time, the film of the formed chelate compound becomes [
It is thought that it brings about monotony and suppresses hydrogen gas generation as a result.

The chelate compound film formed on the surface of the zinc powder can sometimes be confirmed by the generation of interference colors;
It is estimated that the film is extremely thin, less than 1 μm in thickness, and it has been confirmed that the zinc powder's waste electrical properties have no effect whatsoever. As mentioned above, the present invention is also applicable to zinc alloy powder, glazed zinc powder, and glazed zinc alloy powder. It is thought that these reactions to oxidation are also caused by the formation of a film due to the oxidation reaction of the surface layer of zinc, similar to the battery reaction.

(Examples of the Invention) Hereinafter, the present invention will be specifically explained based on zinc powder preparation examples, examples and comparative examples, but the processing conditions, zinc powder used, etc. are not limited thereto.

Tsui 13ji L- Zinc ingot with a purity of 99.997% or higher is melted at approximately 500°C, and elements (Pb, In, TJ) are added to achieve the composition and content shown in Table 1. Create an alloy and infuse it with high pressure air gas (injection pressure 5'J/ctl)
Atomized powder was created using then 50-150
The mixture was sieved into mesh to prepare zinc powder (a) and zinc powder (b).

Further, the zinc powder (a) was frozen in an alkaline aqueous solution to prepare zinc powder (C), which is frozen zinc powder with a mercury content of 1.0% by weight.

Example 1 Tannic acid was dissolved in pure water to prepare a 10o/J tannic acid solution 1j. Add 1kg of zinc powder (a) to this solution.
The surface treatment was carried out while stirring at 50° C. for 30 minutes. Next, washing with water was repeated five times, and after filtration, it was dried at 45° C. for a day and night to obtain zinc powder of the present invention (Example 1).

This J uses zinc powder obtained by sea urchin to produce hydrogen gas light.
I started testing. The test method is 1! as an electrolyte!
F40 Ichio% potassium hydroxide aqueous solution saturated with zinc oxide 5me, using 10g of zinc powder, 3o at 45℃
The gas generation of rlfil was measured (one hanger was measured. This result was used as the first
Shown in the table.

To Tomato Example 2・4 1: 101 Pour zinc powder (a), zinc powder (11) J5 and zinc powder (C) into CJ melt J for 1 hour each, bring to room temperature - (1 q stroke for 10 minutes) Next, wash the diluted HCJ containing zinc powder with l'l)l of about 2.
The solution was 0.5J. Next, the pre-made 10g/l
Add the tannic acid solution and stir at room temperature for 60 minutes.
Surface treatment was performed. Thereafter, washing with water was repeated five times, and after filtration, it was dried at 45° C. for a day and night to obtain zinc powder of the present invention (Examples 2 to 4).

Using the zinc powder thus obtained, a hydrogen gas generation test was conducted in the same manner as in Example 1. The results are shown in Table 1. The method of the present invention was carried out in the same manner as in Example 1 except that zinc powder (a) and zinc powder (C) were used on the top of the 4° h1 row, and imidazole was used instead of tannic acid. Zinc powder (Examples 5) to 6) was obtained.

Using the zinc powder thus obtained, a hydrogen gas generation test was conducted in the same manner as in Example 1. The results are shown in Table 1.

Comparative Examples 1-2 Zinc powder (a), zinc powder (b) and zinc powder (C) were subjected to a hydrogen gas generation test in the same manner as in Example 1 without any treatment. The results are shown in Table 1.

= 7- As shown in Table 1, zinc powder (a), -111i lead powder (b) and zinc powder (C) were surface-treated with tannic acid j: or imidazole in Examples 1 to 6. In the zinc powder, hydrogen gas generation is significantly suppressed compared to Comparative Examples 1 to 3 in which zinc powder (a), zinc powder (1)), and zinc powder (C) were not subjected to any treatment.

(Effects of the Invention) As explained above, the zinc powder for alkaline batteries of the present invention, which is produced by treating the surface of zinc powder with an organic compound that forms a chelate film with zinc and forming a chelate film on the surface, can be treated with hydrogen gas. Since it significantly suppresses generation, it is suitably used as the negative electrode of alkaline batteries, and its industrial value is great.

Claims (1)

[Claims] 1. Zinc powder for alkaline batteries, which is obtained by surface-treating zinc powder for negative electrodes of alkaline batteries using an aqueous caustic solution as an electrolyte with an organic compound that forms a chelate compound with zinc. 2. The zinc powder for alkaline batteries according to claim 1, wherein the zinc powder is treated with acid or alkali as a pretreatment for the surface treatment of the zinc powder with the organic compound. 3. Zinc powder for alkaline batteries according to claim 1 or 2, wherein the organic compound is tannic acid or imidazole.