JPS6164074A - Zinc alloy powder for the negative electrode of a mercury-free alkaline battery and its manufacture - Google Patents

Abstract

PURPOSE:To reduce the amount of corrosion of the negative electrode and reduce the amount of hydrogen gas generation by preparing the negative electrode from a zinc alloy powder which contains zinc, tin and an alkali metal as essential components and at least a specified percentage of which consists of a powder with specific configurational characteristics. CONSTITUTION:A zinc alloy containing zinc, tin and an alkali metal as essential components is molten and atomized in an atmosphere containing at most 0.4vol% of oxygen. It is preferable to use sodium, potassium or lithium as the alkali metal. It is preferable to adjust the contents of the alkali metal and tin to within the ranges of 0.001-2.0wt% and 0.0.5-0.8wt% respectively. At least 50wt% of the thus prepared zinc alloy powder consists of ellipsoidal, cocoon-like or teardrop-like particles having a long axis length of at most 0.3mm and a short axis length of at least 0.05mm. By the means mentioned above, a short circuit current can be abundantly produced. Additionally, because there are no projections on the surface of the particles, hydrogen gas generation is suppressed.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a zinc alloy powder useful as a negative electrode of a mercury-free alkaline battery and a method for producing the same.
The present invention relates to an anhydrous zinc alloy powder that, when used as a negative electrode, can produce a battery with small corrosion loss and variation, little hydrogen gas generation, and excellent discharge characteristics, and a method for producing the same.

[Technical background of the invention and its problems]

Conventionally, the negative electrode of a sealed alkaline battery is usually made of fine zinc powder produced by melting and spraying in the air.
Powders with added weight percent mercury have been used. The reason for adding mercury here is to prevent self-dissolution by amalgamating the surface of the zinc powder to increase its hydrogen overvoltage and suppressing the generation of hydrogen gas. This suppresses gas generation and the accompanying increase in battery internal pressure during battery storage or use, and improves battery storage stability.

However, since mercury is a harmful substance, mercury in anal ponds has recently come to be seen as a new source of pollution.

For this reason, research into batteries without the addition of mercury (mercury-free batteries) is actively underway, and some of them are already being put into practical use.

The negative electrodes used in such batteries include thallium, indilim, gallium, lead, tin, and cadmium.
Anhydrous zinc alloy powder containing one or more species is known (see JP-A-58-218760). This is a negative electrode with properties comparable to those of amalgamated zinc powder.

However, conventionally known anhydrous zinc alloy powders are affected by impurities or surface oxidation during the alloying process or melt spraying process, making it difficult for each added element to perform its original function. First, the amount of hydrogen gas generated is increased, and the surface oxidation layer acts as a diffusion inhibiting layer during rapid discharge, resulting in an inconvenient situation in which the discharge characteristics are deteriorated.

Furthermore, during the production of this ice-free zinc alloy powder, the solid solubility of additive components such as lead dissolved in the base zinc in zinc is extremely low, so these additive components are not uniformly dispersed in the zinc. Therefore, local corrosion inevitably occurs in the obtained zinc alloy powder. Additionally, when gallium or indium is added to zinc, there is a slight discrepancy between the amount added and the content when alloyed, resulting in variations in the corrosion behavior of the resulting zinc alloy powder. and lack stability in terms of quality.

[Purpose of the invention]

The present invention solves the above-mentioned problems regarding anhydrous zinc alloy powder, and when used as a negative electrode, the corrosion loss and its variation are small, and the amount of hydrogen gas generated is small.
The purpose of the present invention is to provide a zinc alloy powder for a negative electrode and a method for producing the same, which contributes to the production of a battery that can extract a large short-circuit current and has improved discharge characteristics.

[Summary of the invention]

The zinc alloy powder for a negative electrode of a mercury thermothermal alkaline battery of the present invention is a zinc alloy powder containing zinc, tin, and an alkali metal as essential components, and the powder has a minor axis length of 0.
05111111 or more, major axis length 0.31! It is characterized by containing 50% by weight or more of powder having a shape characteristic of less than 4 volumes! It is characterized by melting and spraying in an atmosphere of R% or less.

The alkali metals contained as one of the essential components of the alloy powder of the present invention include sodium, potassium, lithium,
Examples include rubidium and cesium. In particular, sodium, potassium, and lithium are preferred because they are easily available, inexpensive, and easy to add, that is, have high industrial applicability.

These alkali metals are components that reduce the corrosion weight loss of zinc alloy powder and its dispersion, thereby suppressing hydrogen gas generation, but the theoretical basis thereof is not necessarily clear. Probably the alkali metals contained in
Creating an intermetallic compound with minute amounts of impurities such as iron and cobalt that are contained in the base zinc and reducing its corrosion resistance, and sealing off the effects of these impurities, increasing the hydrogen overvoltage on the surface of zinc, or lead. It is presumed that this is because when elements such as , gallium, and indium are added to base zinc, they promote uniform dispersion and suppress local corrosion.

These alkali metals may be contained alone or in combination of two or more.

The content of alkali metal is preferably set within the range of 0.001 to 2.0% by weight. If this content is out of the above range, the corrosion loss of the zinc alloy powder increases when the obtained zinc alloy powder is brought into contact with an alkaline aqueous solution. In other words, the amount of hydrogen gas generated increases rapidly, which is inconvenient.

When two or more types of alkali metals are contained, the content thereof is adjusted to satisfy the above range.

Tin, which is the second essential component, is a component that contributes to reducing the accumulated stress of the obtained zinc alloy powder in the manufacturing method described below, thereby reducing corrosion loss, and thus reducing the amount of hydrogen gas generated. It is preferable that the tin content is set within the range of 0.005 to 0.8% by weight. If the content is less than o, oos weight%, the above effects cannot be obtained, and O, S
If the amount is greater than % by weight, the reactivity between the zinc grains decreases, causing problems such as the discharge characteristics as a negative electrode beginning to deteriorate, which is disadvantageous.

The third component is zinc or the aforementioned JP-A-58-21876
This is a zinc alloy consisting of base zinc and other additive elements as disclosed in No. 0. In the latter case, the disclosed additive elements may contain at least one of these elements, but each content may be at most 0.1% by weight.
It is preferable that the content of these elements is 1. It is preferable to limit the O weight to fjk% or less.

If this content becomes too large, the amount of zinc becomes relatively small, and the discharge characteristics as a negative electrode begin to deteriorate.

The zinc alloy powder for negative electrodes of the present invention has all the above alloy compositions, but the powder having the shape described below is 50M
Contains 96 or more.

That is, the shape is an elongated spherical shape with a major axis length of 0.3 or less and a minor axis length of 0.05 or more.
It has a cocoon-like or teardrop-like shape, and there are no sharp protrusions on the surface that are thought to be due to surface oxidation.

Since the powder having such a shape occupies 50% or more of the total weight, the negative electrode powder of the present invention has many opportunities for mutual contact as a whole, and as a result, it is possible to extract a large amount of short circuit current. It becomes possible. Furthermore, since there are no protrusions on the surface, hydrogen gas generation is also suppressed.

Powder that does not meet the above-mentioned limitations regarding shape characteristics has a shape that approximates a linear shape, so the chances of mutual contact are reduced and the discharge characteristics are unavoidably deteriorated.

Furthermore, a negative electrode mixture is prepared from these zinc alloy powders,
When it is injected into a battery can through a nozzle, accidents such as nozzle clogging are likely to occur, which adversely affects the battery manufacturing process.

Furthermore, if the occupancy is less than 50% by weight, the short circuit current is halved and the discharge characteristics deteriorate, although the reason is not clear.

The zinc alloy powder of the present invention as described above is manufactured as follows. First, a zinc alloy of a predetermined composition is prepared, for example, by a conventional melting method. What is important at this time is to control the atmosphere to an oxygen concentration of 0.4% by volume or less. Specifically, an inert gas atmosphere such as nitrogen or argon is suitable. When lithium is used as the alkali metal, the use of nitrogen should then be eliminated, since lithium easily forms nitrides with nitrogen. Moreover, the temperature applied to alloying may generally be 410 to 650°C.

The tin contained at this time helps lower the melting point of the melt. Therefore, it is considered that when the melt is sprayed, surface aggregation progresses sufficiently while the spray droplets are scattered in the inert gas and cooled and solidified, so that the above-mentioned tin addition effect is exhibited.

Next, the molten zinc alloy was heated to the same oxygen concentration of 0.4% by volume.
Finely powder by spraying and cooling in the following atmosphere.

The reason why the atmosphere during alloying and melt spraying was set to an oxygen concentration of 0.4% by volume or less is that when the oxygen concentration of the atmosphere cake increases beyond 0.4% by volume, oxidation of the powder surface progresses and the surface roughness increases. The surface area of the powder also increases, reducing the corrosion of zinc alloy powder4.
This is because this results in an increase in Fk and thus an increase in hydrogen gas generation Fk.

The melting and spraying at this time is preferably carried out using the apparatus disclosed in JP-A-50-48427.

The conditions of this apparatus, such as the diameter of the pouring crucible hole and the intersection angle of the injection nozzle, are set appropriately, and the conditions such as the spray gas pressure are appropriately selected to produce powder having the above-described shape characteristics.

[Practice of the invention]

Example 1 (1) Preparation of zinc alloy powder Zinc with a purity of 99.99% was placed in a crucible made of high-purity graphite, and 0.08 weight x amount of tin and 0.06 weight percent of lead were added thereto. The whole body was heated in argon gas with different oxygen concentrations.
The mixture was melted and heated to 00°C. 0.1 weight of lithium Xi was added to each of the obtained melts in the same atmosphere, the whole was stirred with a quartz glass rod, and then heated to 600° C. again.

After thorough stirring, various zinc alloy powders were melted and sprayed in the same atmosphere using the apparatus disclosed in JP-A-50-48427. The obtained powder has a minor axis length of 0.05
Those with shape characteristics of 111111 or more and major axis length of 0.3 or less account for 60 to 80% by weight, respectively.

The amount of hydrogen gas generated was measured when the sample was immersed in an aqueous potassium hydroxide solution and left at 45°C for 3 days. The result is the first
Nine shown in the figure. In the figure, the vertical axis shows the hydrogen gas generation of powder 12.1 per day! -(μl).

As is clear from the figure, the zinc alloy powder produced under the oxygen concentration of the present invention has a low hydrogen gas generation rate.

(3) Battery discharge characteristics Among these zinc alloy powders, the oxygen concentration was 0.2X.

LR6 type manganese alkaline batteries were manufactured with the following specifications using the negative electrodes manufactured with 0.4%, 0.5%, and 0.6%.

Masaya mixture: manganese dioxide and graphite powder, separator: polypropylene nonwoven fabric, current collector: zinc rod, negative electrode mixture 2 above fraction 60 Ti't% and sodium salt of carboxymethyl lullose (thickener) 0.4 weight % and 30 aqueous caustic potassium solution (electrolytic g) 39. A gel body consisting of s weight % (in addition,
What is the viscosity of the electrolyte? , Q O0cps , zinc concentration is 5%
, the carbon dioxide concentration was 0.8 N (9).

The amount of hydrogen gas generated when the obtained battery was stored at 60° C. for 20 days and the continuous discharge duration under a 10Ω load at 20° C. after storage were measured.

The results obtained are shown in Table 1.

Table 1 Batteries using the zinc alloy powder of the present invention generate less gas and last longer when left unused.

(4) Influence of the occupancy of powder with a major axis length of 03 m or less and a minor axis length of 0.05 WIn or more by changing the operating conditions of the device in (1),
A variety of zinc alloy powders having different proportions of powder having a short axis length of 005 rrrIn or more under bleaching were manufactured by A, and using these powders, an L-6 type alkaline manganese battery was manufactured in the same manner as in (3). The short circuit current at 20° C. was initially measured. The results are shown in Table 2.

As is clear from Table 2, when it is less than 50%, the short circuit current is halved and the discharge characteristics of the battery are drastically reduced.

Example 2 Same as Example 1 except that the amount of tin added was changed as shown in Table 3 and the atmosphere was fixed to an argon atmosphere with an oxygen concentration of 0.2 valley product. Zinc alloy powder was produced. Using these powders, Example 1-
Fifty LR6 type manganese alkaline batteries were manufactured as described in (3), and hydrogen gas generation 'J1 was measured when these batteries were stored at 60°C for 50 days. The results are shown in Table 3.

Table 3 Example 3 Lithium was selected as the alkali metal, and zinc alloys with different lithium contents were prepared according to the method of Example 1. By melting and spraying this alloy, the powder of the present invention can be obtained.

Five pellets with the same surface area were cut out from each zinc alloy with different lithium content, and after surface polishing, each pellet was immersed in a 40% potassium hydroxide aqueous solution for 10 minutes at 60°C.
I left it for days. Measure the weight loss of each pellet at that time, measure its dispersion (unit: q), and divide the average value by the pellet surface area to calculate the corrosion weight loss (unit: q).
/cffl) was calculated. The above results are shown in Figure 2. The horizontal axis is a logarithmic scale.

As is clear from the figure, 1 lithium is o, oot~2.
It was found that the corrosion loss was small when the content was 0% by weight.

〔Effect of the invention〕

As is clear from the above explanation, when the zinc alloy powder produced by the method of the present invention is used for a negative electrode, it has a small corrosion loss, a small amount of hydrogen gas generation, and a large short circuit current. It is possible to obtain a battery that has a long discharge duration. Since this zinc alloy powder is ice-free, the problem of environmental pollution caused by pollution is also solved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the amount of hydrogen gas generated from various zinc alloy powders produced by changing the oxygen concentration during melt spraying. FIG. 2 is a diagram showing the relationship between corrosion loss and lithium content of the zinc alloy of the present invention. Figure 1 Figure 2

Claims (1)

[Claims] 1. A zinc alloy powder containing zinc, tin, and an alkali metal as essential components, the powder having a minor axis length of 0.05 mm or more and a major axis length of 0.3 m.
A zinc alloy powder for a negative electrode of a mercury-free alkaline battery, characterized in that it contains 50% by weight or more of a powder having a shape characteristic of m or less. 2. Zinc alloy powder for a negative electrode of a mercury-free alkaline battery according to claim 1, wherein the tin content is 0.005 to 0.8% by weight. 3. Alkali metal content is 0.001-2.0% by weight
A zinc alloy powder for a negative electrode of a mercury-free alkaline battery according to claim 1. 4. Zinc for negative electrode of mercury-free alkaline battery, characterized in that a zinc alloy containing zinc, tin, and alkali metal as essential components is melted and sprayed in an atmosphere with an oxygen concentration of 0.4% by volume or less. Method for producing alloy powder.