JPH0425670B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to zinc powder for alkaline batteries, and more specifically, by treating the surface of zinc powder with tannic acid or imidazole to form a chelate film, it has a higher hydrogen resistance than untreated zinc powder. This invention relates to zinc powder for alkaline batteries that significantly suppresses gas generation. [Prior art] Atomized zinc powder has been used exclusively as a cathode active material for alkaline batteries because it has a large amount of electricity per unit weight, is relatively stable chemically, has good processability, and is inexpensive. ing. However, in an alkaline electrolyte, chemical dissolution of zinc causes gas to accumulate inside the battery and increase 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, conventionally, zinc chloride powder, which utilizes the hydrogen overvoltage of mercury, has 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, and social needs call for the development of lower mercury or mercury-free batteries. It has become highly anticipated. Therefore, in order to reduce the mercury content in batteries,
Various zinc powders have been proposed that contain elements other than mercury that suppress hydrogen gas generation from zinc, but none of them are sufficient to suppress the hydrogen gas generation rate, and the use of mercury is still unavoidable. be. [Problems to be Solved by the Invention] In view of the above-mentioned circumstances, an object of the present invention is to provide zinc powder that further increases the hydrogen gas generation suppressing effect of these zinc powders. [Means for Solving the Problems] In order to achieve the above object, the present inventors conducted various studies and found that various zinc powders were dissolved in a solution containing tannic acid and imidazole, which are organic compounds that form chelate compounds with zinc. The present invention was based on the finding that hydrogen gas generation is significantly suppressed by surface treatment in zinc powder compared to untreated zinc powder. That is, the present invention provides zinc powder for negative electrodes of alkaline batteries using an aqueous caustic solution as an electrolyte.
Zinc powder for alkaline batteries obtained by surface treatment with tannic acid or imidazole. The zinc powder used in the present invention is not only zinc powder, but also zinc alloy powder alloyed with lead or indium, zinc alloy powder made of these zinc powders, zinc alloy powder made of zinc alloy powder, and zinc alloy powder made of zinc alloy powder. is also included. In the present invention, the surface of zinc powder is treated with tannic acid or imidazole to form a chelate film. In addition, as a pretreatment for the surface treatment of zinc powder with tannic acid, etc., the surface of the zinc powder is treated with hydrochloric acid.
The effect of suppressing hydrogen gas generation is further promoted by treatment with an acid such as acetic acid or an alkali solution such as potassium hydroxide or sodium hydroxide. Although it is not clear why the present invention has the effect of suppressing hydrogen gas generation, the following reasons can be considered. 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 the zinc powder is dissolved by a chelate formation reaction, creating a new highly smooth surface condition. It is thought that the resulting chelate compound film provides corrosion resistance and, as a result, suppresses hydrogen gas generation. The chelate compound film formed on the surface of the zinc powder can sometimes be confirmed by the generation of interference colors, but it is estimated to be an extremely thin film with a thickness of less than 1μ, and has no effect on the discharge characteristics of the zinc powder. It has also been confirmed that it does not. As mentioned above, the present invention is also applicable to zinc alloy powder, zinc chloride powder, and zinc chloride alloy powder. It is thought that these chelate reactions also produce a film due to the oxidation reaction of the surface layer of zinc, similar to the battery reaction. [Example] The present invention will be specifically described below based on zinc powder preparation examples, examples, and comparative examples, but the processing conditions, zinc powder used, etc. are not limited thereto. Zinc powder preparation example Zinc alloy is created by melting zinc ingot with a purity of 99.997% or higher at approximately 500℃ and adding elements (Pb, In, Tl) to the composition and content shown in Table 1. This powder was atomized using high-pressure air gas (ejection pressure: 5 kg/cm ² ). Next, the powder was sieved to a size of 50 to 150 meshes to prepare zinc powder (a) and zinc powder (b). Further, the zinc powder (a) was aqueous in an alkaline aqueous solution to prepare zinc powder (c), which is a aqueous zinc powder with a mercury content of 1.0% by weight. Example 1 Tannic acid was dissolved in pure water to prepare 10 g/tannic acid solution 1. Zinc powder (a) in this solution
1 kg of was added, and the surface treatment was carried out at 50°C while stirring for 30 minutes. Next, the water washing was repeated 5 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). A hydrogen gas generation test was conducted using the zinc powder thus obtained. The test method was to use 5 ml of a potassium hydroxide aqueous solution with a concentration of 40% by weight saturated with zinc oxide and 10 g of zinc powder as the electrolyte.
The amount of gas generated was measured at 45°C for 30 days. The results are shown in Table 1. Examples 2 to 4 1 kg of zinc powder (a), zinc powder (b), and zinc powder (c) were each added to 1:10 HCI solution 1, and the mixture was heated to 1 kg at room temperature.
Stirring was performed for a minute. Next, perform tilting water washing,
A dilute HCI solution containing zinc powder with a pH of about 2 was used. Next, 10 g/tannic acid solution prepared in advance was added, and the surface treatment was performed while stirring at room temperature for 60 minutes. 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. Examples 5-6 Zinc powder of the present invention (Examples 5-6) was prepared in the same manner as in Example 1 except that zinc powder (a) and zinc powder (c) were used and imidazole was used instead of tannic acid. 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 to 3 A hydrogen gas generation test was conducted in the same manner as in Example 1, without subjecting zinc powder (a), zinc powder (b), and zinc powder (c) to any treatment. The results are shown in Table 1. Comparative Example 4 Zinc powder (Comparative Example 4) was obtained in the same manner as in Example 1 except that zinc powder (a) was used and sodium oxalate was used instead of tannic acid. Using the zinc powder thus obtained, a hydrogen gas generation test was conducted in the same manner as in Example 1. This result is shown in the first vote. Comparative Example 5 Zinc powder (Comparative Example 5) was obtained in the same manner as in Example 2 except that zinc powder (a) was used and sodium oxalate was used instead of tannic acid. 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.

[Table] As shown in Table 1, zinc powder (a), zinc powder (b)
The zinc powders of Examples 1 to 6, in which the zinc powder (c) was surface-treated with tannic acid or imidazole, were
Hydrogen gas generation is significantly suppressed compared to Comparative Examples 1 to 3 in which zinc powder (a), zinc powder (b), and zinc powder (c) were not subjected to any treatment. Furthermore, in Comparative Examples 4 and 5, sodium oxalate was used in place of tannic acid in Examples 1 and 2, but the effect of suppressing hydrogen gas generation was that of Examples 1 and 2.
inferior to. [Effects of the Invention] As explained above, the zinc powder for alkaline batteries of the present invention, in which the surface of the zinc powder is treated with tannic acid or imidazole to form a chelate film on the surface, significantly suppresses hydrogen gas generation. It is suitably used as a negative electrode for alkaline batteries and has great industrial value.

Claims (1)

[Scope of Claims] 1. Zinc powder for alkaline batteries obtained by surface-treating zinc powder for negative electrodes of alkaline batteries using an aqueous caustic alkali solution as an electrolyte with tannic acid or imidazole. 2. Claim 1, wherein the zinc powder is treated with acid or alkali as a pretreatment for the surface treatment.
Zinc powder for alkaline batteries as described in .