JPS6123707A - Production of zinc alloy powder for negative electrode of alkali battery without addition of mercury - Google Patents

Abstract

PURPOSE:To produce a negative electrode having an excellent effect of suppressing the generation of hydrogen by using the Zn alloy powders obtd. by electrolyzing a Zn electrolyte which dissolves specific amts. of Pb, In, Ga, etc. as a raw material for the negative electrode of an alkali battery. CONSTITUTION:The powder of Zn alloy consisting of 0.01-0.10wt% Pb, 0.005- 0.05wt% In and the balance Zn or the Zn alloy consisting of 0.01-0.10wt% Pb, 0.01-0.10wt% Ga and the balance Zn or the Zn alloy consisting of 0.01- 0.10wt% Pb, 0.005-0.05wt% In, 0.01-0.10wt% Ga and the balance zn is used as a raw material the negative electrode for the alkali battery using NaOH liquid which dissolves ZnO as the electrolyte. The Zn-contg. electrolyte dissolved with Pb, In, Ga, etc. so as to obtain three kinds of the above-mentioned compsn. is electrolyzed and after the Zn alloy electrodepositing on the cathode is rinsed, the alloy is pressed and compacted and is further pulverized and sized, by which the above-mentioned Zn alloy powder for the negative electrode of the alkali battery is produced.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for producing a zinc alloy powder used for a negative electrode of a mercury-free alkaline battery, and more specifically, to a method for producing a zinc alloy powder for use in a negative electrode of a mercury-free alkaline battery, and more specifically, a method for producing hydrogen gas during storage before and after discharge. The present invention relates to a method for producing zinc alloy powder that is effective in suppressing.

[Technical background of the invention and its problems 1 The negative electrode of an alkaline battery whose electrolyte is an aqueous caustic alkaline solution in which zinc oxide is dissolved is made by adding several layers of zinc powder produced by melting and spraying high-purity zinc. A compound containing 1% of mercury is used. This is 1. when the negative electrode is only zinc powder. Because zinc has an extremely base electrochemical potential, this is to prevent hydrogen gas from being generated at the contact interface between the zinc powder and the electrolyte as the zinc dissolves, increasing the internal pressure of the battery. .

However, since mercury is a harmful substance, research has recently been progressing on negative electrode materials that can suppress the generation of hydrogen gas without adding mercury.

As a material for such a negative electrode, a mercury-free zinc alloy powder, which is a mixture of zinc, lead, and further indium and gallium in a predetermined ratio, has been developed and is being used.

This zinc alloy powder is usually made by adding a predetermined amount of other ingredients such as lead to high-purity zinc produced by applying an electrolytic method, melting the whole to form an alloy, and then melting and spraying this alloy. It is manufactured by turning it into powder with a predetermined particle size.

However, in the case of this manufacturing method, a problem arises in that the added components, particularly lead, are not uniformly dispersed with zinc, and lead is partially unevenly distributed in the resulting alloy. That is,
Even if the overall lead content is appropriate,
This means that when observed from a partial or microscopic perspective, the lead content varies.

In such a state, the effectiveness of the lead-containing zinc alloy powder in suppressing hydrogen gas generation is diminished, resulting in an increase in battery internal pressure.

Therefore, among those skilled in the art, there is an extremely high demand for zinc alloy powder for negative electrodes, in which the above-mentioned components, especially lead, are uniformly alloyed with zinc, and local variations in a certain set content are small. strong.

[Objective of the Invention 1] The present invention, in response to the above-mentioned needs, provides a method for producing zinc alloy powder L powder for negative electrodes, which has small variations in the set content of lead and therefore has a large suppressive effect on hydrogen gas generation.
The purpose is to provide.

[Summary of the Invention] The method for producing a zinc alloy powder of the present invention is a method for producing a zinc alloy powder for a negative electrode of a mercury-free alkaline battery, comprising:
The electrolytic solution containing each component element of the alloy powder is electrolyzed to electrodeposit each component element on the cathode surface, and the resulting electrodeposit is washed with water and then pressure molded to form a thin layer or The method is characterized in that it is formed into a scale-like molded body, and then the molded body is crushed and sized.6 First, an electrolytic solution containing each component element constituting a zinc alloy having the desired composition is prepared in a bath. do.

In this case, the component contained in zinc is preferably mackerel, indium, or gallium, or both.

If the lead content is too low, the resulting zinc alloy powder will not have a sufficient hydrogen gas generation suppressing effect, and if it is too high, problems such as heavy load characteristics and poor utilization of the battery will occur. , is usually set within the range of 0.01 to 0.10% by weight, preferably 0.03 to 0.08% by weight.

In addition, both indium and gallium are effective components for increasing the effect of suppressing hydrogen gas generation, and in the case of indium, it is 0.005 to 0.05% by weight, and in the case of gallium, it is 0.01 to 0.05% by weight. The content is preferably 10% by weight.

The bath composition and concentration of the electrolytic solution are determined in relation to the types of each component described above and the amounts to be included in the intended zinc alloy powder.

A sulfuric acid bath is usually used as a zinc source, but a hydrochloride bath is preferable because lead becomes lead sulfate and cannot be melted, such as zinc chloride; lead chloride as a lead source; indium chloride as an indium source; and gallium source as a gallium source. Gallium chloride: is preferred. A uniform electrolytic solution containing each component at a predetermined concentration is prepared by appropriately selecting each of the above-mentioned component sources according to the intended composition and dissolving a predetermined amount of these in water.

Next, the bath temperature is maintained at an appropriate temperature and electrolysis is carried out at a predetermined current density to electrodeposit the above-mentioned components on the surface of the cathode. During this electrolysis, a carbon electrode is usually used as the anode, and an aluminum electrode with a smooth surface is used as the cathode. Electrolytic conditions such as bath temperature and current density at this time cannot be uniquely determined because they need to be changed depending on the type of each component, their combination, concentration, etc. Through such electrodeposition treatment, each component is electrodeposited on the surface of the cathode in a uniformly mixed state.

That is, each component is precipitated as a homogeneous alloy precursor without being locally unevenly distributed.

Next, the electrodeposit is carefully scraped up from the cathode, and the resulting cake is thoroughly washed with water and then pressure molded. As the pressure molding method, methods such as roll press and mold press may be applied. Especially the roll press
This is effective because the obtained molded product is in the form of a thin layer or scales, which facilitates the subsequent pulverization process.

Pressure molding is preferably carried out in a state where the aggregate cake to be molded contains some moisture.

This is because moisture functions like a binder and facilitates molding. Further, the molding pressure at this time is preferably controlled so that the bulk specific gravity of the obtained molded product is 3.0 to 4.0. If the compacting pressure is too high, the compact will become too dense, making the subsequent pulverization process somewhat difficult, and when the resulting powder is used as an actual negative electrode, it will be difficult for the electrolyte to be impregnated into the powder. Reactivity decreases. The obtained molded body is composed of irregularly shaped scale pieces that overlap each other. Furthermore, in order to prevent contamination from the outside during pressure molding, it is preferable that the rollers be made of ceramics, for example.

This compact is pulverized using, for example, a ceramic acid medium, dried, and then classified (sized) to obtain the alloy powder of the present invention. When used in the negative electrode, the particle size of the alloy powder is 10
It is preferably within the range of 5 to 500 μm.

[Embodiments of the invention] Examples 1-3 Three types of electrolytes having the bath compositions shown in Table 1 were prepared.

Table 1 Next, an LRfi type alkaline manganese battery was assembled as follows.

Each of the above zinc alloy powders with a particle size of 105 to 50 (lILm) was mixed with an electrolytic solution of 40% by weight potassium hydroxide aqueous solution in which zinc oxide was dissolved, and a gelling agent of sodium polyacrylate. A gel-like negative electrode mixture was prepared.A positive electrode mixture was prepared by mixing manganese dioxide with graphite as a conductive material, and an LR8 type alkaline manganese battery was manufactured according to a conventional method.

30 batteries of each type, undischarged and 10Ω load
was connected and discharged for 5 hours, and then stored at a temperature of 60°C.

The amount of hydrogen gas (layer 1) generated within the battery was measured every time the 10th, 20th, and 30th days passed. The average value (1
) and the difference (R) between the maximum value and the minimum value are shown in Table 3.

Table 3: Similar tests were conducted on LR44 type alkali manganese.
I battery, 5R44 type silver oxide button battery l, %
However, results similar to those of LReRe sialkali manganese batteries were obtained.

[Effects of the invention] As is clear from the above explanation, the zinc alloy powder produced by the method of the present invention has a variation in lead content that is about one order of magnitude smaller than that of conventional powders, and is very uniformly dispersed in zinc. are doing(
Therefore, when used as the negative electrode of an alkaline battery, the amount of hydrogen gas generated is small even during long-term storage, regardless of whether the battery is undischarged or discharged (data in Table 2). data in the table), it has great industrial value as a negative electrode material for mercury-free alkaline batteries, and its contribution to pollution prevention is extremely large.

Claims (1)

[Claims] 1. A method for producing a zinc alloy powder for a negative electrode of a mercury-free alkaline battery, which comprises electrolyzing an electrolytic solution containing each component element of the alloy powder to coat each component on the surface of the cathode. The method is characterized in that the component elements are electrodeposited, the resulting electrodeposited material is washed with water, and then pressure molded to form a thin layer-like or scale-like molded product, and then the molded product is pulverized and then sized. A method for producing zinc alloy powder for negative electrodes of mercury-free alkaline batteries. 2. Adjust the concentration of each component element of the electrolytic solution so that the composition of the zinc alloy powder is 0.01 to 0.10% by weight of lead, 0.005 to 0.05% by weight of indium, and the balance is zinc. A method according to claim 1. 3. Adjust the concentration of each component element of the electrolytic solution so that the composition of the zinc alloy powder is 0.01 to 0.10% by weight of lead, 0.01 to 0.10% by weight of gallium, and the balance is zinc. A method according to claim 1. 4. The composition of the zinc alloy powder is 0.01 to 0.10% by weight of lead, 0.005 to 0.05% by weight of indium, 0.01 to 0.10% by weight of gallium, and the balance is zinc. The method according to claim 1, wherein the concentration of each component element of the electrolytic solution is adjusted. 5. The method according to claim 1, wherein the molded product is pressure-molded so as to have a bulk specific gravity of 3.0 to 4.0.