JPS61221311A - Production of zinc powder for negative electrode of alkaline cell - Google Patents

Abstract

PURPOSE:To produce zinc or zinc alloy powder for a negative electrode of an alkaline cell having a large surface area and excellent heavy load discharge characteristic by spraying molten zinc or molten zinc alloy into an atmosphere in which the oxygen concn. is higher than the oxygen concn. in air. CONSTITUTION:High-purity Zn or Zn alloy formed by adding positively a prescribed ratio each of Al, Mn, Pb, Sn, Cd, Tl, Bi, etc. thereto is melted. The molten Zn or molten Zn alloy is then sprayed into the atmosphere in which the oxygen concn. is higher than the oxygen concn. of the air. The zinc oxide is formed on the surface of the molten drops formed in the above-mentioned manner and at the same time the molten drops are cooled and solidified, by which the Zn or Zn alloy powder having he large surface area is obtd. The negative electrode of the alkaline cell having the excellent heavy load discharge characteristic is formed by using such powder.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for producing zinc or zinc alloy powder used as a negative electrode for alkaline batteries, and more specifically, to a method for producing zinc or zinc alloy powder that has excellent heavy load discharge characteristics. Regarding the manufacturing method.

[Technical background of the invention and its problems]

Zinc powder or zinc alloy powder used as the negative electrode of an alkaline battery whose electrolyte is an alkaline aqueous solution such as caustic potash or caustic powder is generally produced as follows. That is, molten zinc or molten zinc alloy is trap-sprayed into a fine powder in air or in a reducing atmosphere where the oxygen concentration is lower than air, and then this fine powder is immersed in water or a zinc-soluble aqueous solution. This method involves freezing the surface of the sample with metallic mercury or a soluble mercury salt such as mercuric chloride while stirring.

However, when producing negative electrode powder using the above method,
Since the oxygen concentration during melt spraying is low, there is an advantage that the amount of zinc oxide on the surface of the obtained fine powder is reduced, but on the other hand, there is a problem that the surface area of the fine powder is reduced. Moreover, during the above-mentioned hydration treatment, the surface area of the zinc is further reduced due to mutual abrasion between the fine powders due to the dissolution reaction on the zinc surface and stirring.

This reduction in surface area means that the overall reaction area of the zinc or zinc alloy powder as a negative electrode is reduced, which is the cause of the deterioration of heavy load discharge characteristics in the battery characteristics.

[Purpose of the invention]

The present invention solves the above-mentioned problems and provides a method for manufacturing zinc or zinc alloy powder that reduces the surface area of negative electrode zinc or zinc alloy powder that contributes to electrode reactions, thereby making heavy load discharge possible. purpose.

[Summary of the invention]

As a result of intensive research to achieve the above object, the present inventors found that when zinc or zinc alloy is melted and sprayed, the specific surface area (surface area per unit weight) of the powder obtained depends on the oxygen concentration of the surrounding atmosphere. Based on the findings that the specific surface area increases as the oxygen concentration increases, the method of the present invention was developed.

That is, the method for producing negative electrode zinc powder for alkaline batteries of the present invention is characterized by spraying molten zinc or molten zinc alloy into an atmosphere in which the oxygen concentration is higher than the oxygen concentration in the air.

In the method of the present invention, first, high-purity zinc or a zinc alloy formed by actively adding a predetermined amount of elements such as aluminum, manganese, lead, tin, cadmium, thallium, and bismuth to the zinc is melted. This molten zinc or molten zinc alloy is then sprayed into an atmosphere described below to form a powder. The method of melt spraying at this time is, for example, Japanese Patent Application Laid-Open No. 50-484
It is preferable to use the apparatus disclosed in Publication No. 27, and by appropriately selecting conditions such as the diameter of the pouring crucible hole and the intersection angle of the spray nozzle, the desired particle size,
It is possible to produce powders in the following shapes.

The applied atmosphere is one in which the oxygen concentration is higher than that in air. Specifically, the oxygen concentration in the air is approximately 20
．． Since it is 9 vo/chi, the oxygen concentration is 20.9 vod
The atmosphere is higher than %.

When zinc or zinc alloy is molten and sprayed into an atmosphere with such a high oxygen concentration, the d-specific surface area of the formed powder increases, although the reasoning is not necessarily clear. It is assumed that this is probably based on the following reasons. That is, when spraying molten zinc or molten zinc alloy,
Zinc oxide is formed on the surface of the powder of the nine melt droplets, which is formed by the oxygen in the atmosphere. The formed molten droplet powder is simultaneously cooled, and at this time the surface of the powder condenses. In this condensation process, it is thought that the degree of condensation varies depending on the amount of oxide produced on the surface, which in turn causes a difference in surface area.

In any case, if the oxygen concentration in the atmosphere is lower than that in air, the specific surface area of the obtained powder will decrease, resulting in a decrease in the reaction area that contributes to electrode reactions, and heavy load discharge characteristics will not be improved. .

[Embodiments of the invention]

Zinc with a purity of 99.99% was placed in a quartz glass and the whole was melted at a temperature of 600°C in an argon atmosphere. After thoroughly stirring the melt, it was pulverized by a gas atomization method using an apparatus disclosed in Japanese Patent Application Laid-Open No. 50-48427. At this time, various zinc powders were prepared by changing the oxygen concentration of the atmosphere during spraying, and their specific surface areas were measured.

The specific surface area was measured by the method described on page 129 of the abstracts of the 24th Battery Symposium (1981) sponsored by the Electrochemical Society of Japan.

The results are shown in air (oxygen concentration 20.9 vol%).
) It is expressed as the ratio (So/SA) of the specific surface area (S□) when spraying in each oxygen concentration atmosphere to the specific surface area (SA) when spraying.

Table 1 Next, each zinc powder was immersed in a weakly acidic mercuric chloride aqueous solution and stirred to obtain zinc hydrate powder having a mercury freezing rate of 5% by weight. A half cell was fabricated using a 40% potassium hydroxide aqueous solution saturated with zinc oxide as the electrolyte, a nickel plate as the counter electrode, mercury as the reference electrode, and a mercury oxide electrode.

This half cell was discharged at the constant current shown in Table 2. The discharge duration (hr) at that time was measured, and the value divided by the theoretical capacity, that is, the zinc utilization rate (9)) was calculated. The results are shown in Table 2.

Table 2 [Effects of the Invention] As is clear from the above explanation, according to the method of the present invention, powder having a larger surface area than zinc or zinc alloy powder produced by the conventional method can be produced. Therefore, an alkaline battery using the same has excellent heavy load discharge characteristics.

Claims (1)

[Claims] A method for producing negative electrode zinc powder for alkaline batteries, which comprises spraying molten zinc or molten zinc alloy into an atmosphere in which the oxygen concentration is higher than that of air.