JPH05166507A - Zinc alloy powder for alkaline battery and its manufacture - Google Patents

Abstract

PURPOSE:To provide an alkaline battery with zinc alloy powder which suppresses the generation of hydrogen gas substantially when the powder is processed to be unmercurial and unleaded, and can retain discharge performance at a practical level, and to provide its manufacture. CONSTITUTION:Zinc alloy powder contains components selected from (1) 0.001-0.5 percentage by weight of aluminum, 0.01-0.5 percentage by weight of bismuth, (2) 0.001-0.5 percentage by weight of aluminum, 0.1-0.5 percentage by weight of bismuth, 1.0 percentage by weight or less of indium, (3) 0.001-0.5 percentage by weight of aluminum, 0.01-0.5 percentage by weight of bismuth, 0.5 percentage by weight or less of lithium, (4) 0.001-0.5 percentage by weight of aluminum, 0.01-0.5 percentage by weight of bismuth, 1.0 percentage by weight or less of indium, 0.5 percentage by weight or less of calcium or 0.5 percentage by weight or less of lithium. The rest portion is formed of zinc containing 1ppm or less of iron as accompanying impurity.

Description

Detailed Description of the Invention

[0001]

[Industrial applications]

The present invention relates to a zinc alloy powder for alkaline batteries and a method for producing the same. More specifically, the content of iron as a concomitant impurity in zinc is 1 ppm or less, and a specific additive element is contained, so that it is a harmful element. The present invention relates to a zinc alloy powder for an alkaline battery, which suppresses hydrogen gas generation and improves battery leakage resistance without using mercury and lead, and a method for producing the same.

[0003]

2. Description of the Related Art Mercury in zinc fluoride powder used as a negative electrode active material of alkaline batteries suppresses generation of hydrogen gas due to corrosion of zinc and prevents leakage of batteries due to this. It was considered to be an essential component for the negative electrode active material of alkaline batteries.

However, there is a demand for reduction of mercury from the viewpoint of environmental measures. Therefore, by adding lead, aluminum, bismuth, indium and the like as additive elements to zinc, the content of mercury is reduced from 10% by weight. Even if the amount was drastically reduced to around 1% by weight, it became possible to suppress the generation of hydrogen gas.

[0005] However, as a further social demand, it has been recently demanded that the content of mercury in the negative electrode active material be 0% by weight, in other words, it should be constant. As described above, the situation is significantly different when the negative electrode active material is made unconstrained, and it is difficult to suppress the hydrogen gas generation amount to a predetermined level even if the above-mentioned additional elements are added. That is, conventionally, a zinc alloy powder as a negative electrode active material to which various additive elements have been added has been proposed (for example, Japanese Patent Publication No. 2-2298).
No. 4, JP-A-61-153950), these can achieve the desired suppression of hydrogen gas generation even when the mercury content is 1% by weight or less, but they could not be realized by the unconstrained. ..

Further, with the reduction of the content of mercury, the zinc corrosion inhibiting effect of lead has become the most important in recent years. Negative electrode active materials for low-mercury alkaline batteries currently on the market are generally composed of alloy compositions such as zinc-lead, zinc-aluminum-lead, zinc-aluminum-indium-lead, and zinc-bismuth-lead. Is. That is, the reduction of the mercury content was largely achieved by the effect of adding lead, and it was considered that the mercury-free conversion in the negative electrode active material could not be achieved without using lead.

Lead, like mercury, is known to adversely affect the human body. Considering the social needs for a clean environment, artificial addition of lead is not preferable. However, as described above, up to now, lead-free lead in the negative electrode active material has not been easily achieved even in the case of reducing mercury.

On the other hand, attempts have been made to suppress the generation of hydrogen gas and improve the discharge performance by reducing the content of impurities in zinc. For example, JP-A-62-1
Japanese Patent No. 123653 describes reducing impurities such as iron and chromium. In Table 1 on page 4 of the same publication, it contains a certain amount of lead, indium and aluminum, and contains 1% by weight of mercury. In the negative electrode active material using the contained zinc hydride alloy powder, the discharge performance is improved while suppressing generation of hydrogen gas by reducing iron to about 10 ppm.

However, in a zinc alloy powder having a mercury content of 0% by weight, the desired hydrogen content is reduced even if the content of iron as an impurity is reduced to about 10 ppm as described above and an additive element such as lead is contained. The effect of suppressing the generation of gas was not obtained.

As described above, making the negative electrode active material free from lead and lead-free has fundamentally different difficulties from the case of low lead having a mercury content of 0.6 to 1.0% by weight. No alkaline battery has been obtained in which a lead-free and lead-free zinc alloy powder is used as a negative electrode active material to suppress the generation of hydrogen gas and thus improve the leakage resistance.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above problems of the prior art, and it is a zinc alloy powder for an alkaline battery, which greatly suppresses the generation of hydrogen gas in a lead-free and lead-free manner. And to provide a method for producing the same, and to finally improve the leakage resistance of a mercury-free alkaline battery.

[0012]

Means for Solving the Problems The inventors of the present invention have earnestly studied in accordance with this object, and as a result, by using zinc having an extremely small content of iron as an impurity, and by adding a specific additive element thereto, The inventors have found that the above objects can be achieved by the synergistic effect of the two, and have reached the present invention.

That is, the zinc alloy powder for a smooth alkaline battery of the present invention comprises the following (1) to (4): (1) 0.001 to 0.5% by weight of aluminum and 0.01 to 0.5 of bismuth. % By weight, (2) aluminum 0.0
01-0.5 wt%, bismuth 0.01-0.5 wt%, indium 1.0 wt% or less, (3) aluminum 0.001-0.5 wt%, bismuth 0.01-0.5
Wt%, lithium 0.5 wt% or less, (4) aluminum 0.001-0.5 wt%, bismuth 0.01-0.
Zinc containing a component selected from 5 wt%, indium 1.0 wt% or less, calcium 0.5 wt% or less or lithium 0.5 wt% or less, and the balance containing 1 ppm or less of iron as an accompanying impurity. It is characterized by consisting of.

In the present invention, it is necessary that the content of iron as an accompanying impurity in zinc is 1 ppm or less. When the iron content exceeds 1 ppm, the effect of suppressing the generation of hydrogen gas is small. Iron content 1 here
The term "ppm or less" means an analytical limit value or less when using ICP or atomic absorption spectrophotometry, which is a usual analytical means, without using a separation operation of zinc and iron. Conventionally, such zinc or zinc alloy powder having a low iron content has not been used as a negative electrode active material, and no such report has been known. High-purity zinc metal can be made for special applications, for example, for semiconductors using a special method such as the zone melting method, but it is also expensive in price and cannot be used as a raw material for dry batteries. Absent. Moreover, the example used as an alloy powder is not found, either. Among the zinc ingots obtained as industrial products, the highest purity rectified zinc has an iron concentration of 20 pp according to Japanese Industrial Standards.
The iron concentration is generally 2 ppm or more, even if the impurity level is particularly low. In addition, electric zinc is at the same level.

Further, the present invention contains a component selected from the above (1) to (4). If the content of each component element deviates from the above range, there is a problem that the desired effect of suppressing the generation of hydrogen gas cannot be obtained, or that practical discharge performance cannot be maintained. Even if the additive elements other than these components, such as aluminum, bismuth, and calcium contained in the zinc alloy powder conventionally used as the negative electrode active material, are contained alone, the above-described effects of the present invention cannot be obtained.

Next, the manufacturing method of the present invention will be described. In the present invention, the content of iron as an accompanying impurity is 1 p
Zinc of pm or less is used. Examples of such zinc having a low iron content include zinc deposited by electrolysis and zinc ingot produced by vacuum distillation. Conventionally, fused zinc is melted with a flux such as ammonium chloride,
A zinc ingot cast in a mold was used as a zinc raw material for the negative electrode active material. In such a zinc ingot, the iron content cannot be 1 ppm or less. The reason is that the dross part floating in the melting step of zinc is removed, but zinc partially recovered in the removal step is returned to the melting part. This is because the iron content from the separator is usually mixed in this dross removal step. In addition, iron content from the melt pump, mold, and environment is also predicted.

In the molten zinc having a low iron content, each of the additive elements shown in the above (1) to (4) is dissolved so as to have a content within a predetermined range. Then, it is pulverized by an atomizing method and further sieved to obtain a zinc alloy powder. At this time, the iron content in the melting and atomizing atmosphere is preferably set to 0.009 mg / m ³ or less from the viewpoint of further improving the effect of suppressing hydrogen gas generation. It is also desirable to magnetically sort the obtained zinc alloy powder from the same viewpoint.

FIG. 1 shows a flow sheet showing the difference between the conventional method and the method for producing the zinc alloy powder of the present invention.
The iron content in the zinc alloy powder thus obtained is 1 ppm or less as described above, and the zinc alloy powder has an allowable upper limit of leakage resistance of about 300 μl / day.
-Hydrogen gas generation can be controlled below cell (AA type).

Conventionally, the generation mechanism of hydrogen gas due to corrosion of zinc is clarified by actually going into the gas generation site only by discussing the relationship of the crystal structure by macroscopically measuring and estimating the gas amount. I've never been there. The inventors of the present invention, who thought that this might be the reason why the various applications were not practically applicable to the mercury-free battery, did not perform zinc observation by careful microscopic observation and EPMA analysis of the gas generation site. It has been found that when fine particles of iron or its oxides, alloys, etc. as unavoidable impurities contained in the powder exist between zinc particles and / or on the surface, the fine particles serve as a source of hydrogen gas generation.

That is, the zinc powder was immersed in an aqueous potassium hydroxide solution similar to the electrolytic solution of an alkaline battery, and it was observed with an optical microscope that there were specific sites where gas was continuously generated. Next, the state of gas generation was similarly observed using relatively large particles, thin rod-shaped or plate-shaped zinc. And
It was confirmed that there was a place where gas would be generated from the same place for a long time, and the point where continuous gas was generated was marked using a sharp instrument. Next, the zinc was subjected to compositional analysis by EMPA.

As a result, the continuous gas generation point is always 0.
It was found that fine particles of 5 to 5 μm mainly containing iron were unevenly distributed. In some cases, chromium, nickel, silver, sulfur, and oxygen were detected as components other than iron. From this, it was found that the gas generation was mainly caused by a very small amount of iron or iron oxide particles being mixed.

As shown in Table 1, various particles having an average particle diameter of 0.1 to several mm are added to zinc powder or a zinc plate so as to have a concentration of about 1 to several ppm, and potassium hydroxide is added. The situation of gas generation was observed in the aqueous solution. The results are shown in Table 1.

[0023]

[Table 1]

From the results shown in Table 1, it was found that particles of iron, iron oxide and stainless steel were the center of gas generation. Thus, it was found that the gas generation source was fine particles, which were also mainly iron-based particles.

Furthermore, the present inventors have found that the effect of adding lead is not the effect of suppressing the simple corrosion that occurs between zinc and the electrolytic solution, but the effect of local cell reaction caused by the unevenly distributed iron content in zinc. When the content of iron as an impurity in zinc is extremely reduced, the hydrogen gas generation amount falls below the permissible upper limit of leakage resistance without the addition of lead. I also found out.

Therefore, in the present invention, the content of iron as an accompanying impurity in zinc is made extremely small and a specific amount of a specific additive element other than mercury and lead is contained. This suppresses the generation of hydrogen gas due to the synergistic effect of the two.

[0027]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples.

Examples 1 to 15 and Comparative Examples 1 to 8 In a room with an iron content of 0.005 mg / m ^{3 in} the atmosphere, about 0.1 ppm of ionized zinc having an iron content of 1 ppm or less as an accompanying impurity was used. It was melted at 500 ° C., and a predetermined amount of each element shown in Table 2 was added thereto to prepare a molten zinc alloy.

Next, this was directly pulverized in the same atmosphere using high pressure argon gas (jet pressure 5 kg / cm ² ), and the obtained zinc alloy powder was sieved to a particle size of 50 to 150 mesh.

Further, a magnetic force was used to select magnetic force to remove free iron powder. The iron contents of the obtained zinc alloy powders were all 1 ppm or less.

Here, in a 40% aqueous potassium hydroxide solution saturated with zinc oxide, carboxymethyl cellulose and sodium polyacrylate as gelling agents were added to 1.
About 0% was added to prepare an electrolytic solution.

The above zinc alloy powder was used as the negative electrode active material, and 3.0 g of this zinc alloy powder was mixed with 1.5 g of the electrolytic solution to form a gel, which was directly used as the negative electrode material, and the alkaline manganese battery shown in FIG. Created.

After the alkaline manganese battery was partially discharged by 25%, the amount of hydrogen gas generated by the corrosion of the zinc alloy powder was measured, and the obtained results are shown in Table 2. The 25% partial discharge is because the hydrogen gas generation rate is maximum per 25% partial discharge when a mercury-free alkaline manganese battery is configured and the discharge time up to 0.9 V is 100%. Yes, a 25% partial discharge was performed under the discharge conditions of 1Ω and 11 minutes.

The alkaline manganese battery of FIG. 2 has a positive electrode can 1, a positive electrode 2, a negative electrode (gelled zinc alloy powder) 3, a separator 4, a sealing body 5, a negative electrode bottom plate 6, a negative electrode current collector 7,
Cap 8, heat-shrinkable resin tube 9, insulating ring 1
It is composed of 0, 11 and an outer can 12.

Comparative Examples 9 to 11 Starting from a zinc ingot in which ion-analyzed zinc having an iron content of 1 ppm or less was cast as usual, the starting material was about 500 mg in an atmosphere having an iron content of 5 mg / m ^3. Melt at ℃,
A predetermined amount of each element shown in Table 2 was added to this to prepare a zinc alloy melt.

Next, this was pulverized in the same atmosphere using high-pressure argon gas (jet pressure 5 kg / cm ² ), and the obtained zinc-zinc alloy powder was sieved to a particle size of 50 to 150 mesh.

The iron content of each of the obtained zinc alloy powders was 3 ppm. Note that no magnetic force selection was performed here.

Using this zinc alloy powder, an alkaline battery shown in FIG. 2 was prepared in the same manner as in Example 1, 25% partial discharge was performed, and the hydrogen gas generation amount was measured. The results are shown in Table 2.

[0039]

[Table 2]

As shown in Table 2, the iron content is 1 p
Examples 1 to 15 having a specific composition of not more than pm
In all of the zinc alloy powders, the hydrogen gas generation amount is about 300 μ1 / day · cell (L
R6 type) or less. On the other hand, the zinc alloy powders of Comparative Examples 1 to 8 have a composition that deviates from the range defined by the present invention, even though the iron content is 1 ppm or less.
No effect of suppressing hydrogen gas generation is observed. further,
The zinc alloy powders of Comparative Examples 9 to 11 had an iron content of 3 pp.
Since it is m, the effect of suppressing the generation of hydrogen gas is not recognized regardless of whether the composition falls within the range specified in the present invention.

Examples 16 to 19 Zinc alloy powders were obtained under the same composition and conditions as in Example 2 except that the magnetic force selection was not carried out (Example 16).
Also, the content of iron in the melting and atomizing atmosphere is 5 mg / m
^A zinc alloy powder was obtained with the same composition and conditions as in Example 2 except that the operation was performed in the atmosphere of Example 3 (Example 17).

Similarly, a zinc alloy powder was obtained with the same composition and conditions as in Example 6 except that magnetic force selection was not carried out (Example 18). Further, a zinc alloy powder was obtained under the same composition and conditions as in Example 6, except that the melting and atomizing atmosphere was performed in an atmosphere in which the iron content was 5 mg / m ³ (Example 19).

The iron contents of the zinc alloy powders thus obtained were all 1 ppm or less. Using this zinc alloy powder, an alkaline battery shown in FIG. 2 was prepared in the same manner as in Example 1, 25% partial discharge was performed, and the hydrogen gas generation amount was measured. The results are shown in Table 3.

[0044]

[Table 3]

As can be seen from Table 3, Examples 16-1
7 has almost the same results as in Example 2, and Examples 18 to 1
In No. 9, almost the same results as in Example 6 were obtained.

Experimental Example 1 The zinc alloy powders of Example 2 and Comparative Example 9 were screened so as to contain 1% by weight and 10% by weight of mercury to obtain a zinc halide alloy powder.

Using this zinc hydride alloy powder, an alkaline battery shown in FIG. 2 was prepared in the same manner as in Example 1, 25% partial discharge was performed, and the amount of hydrogen gas generated was measured. The results are plotted in FIG. 3 together with the values of Example 2 and Comparative Example 9.

As shown in FIG. 3, when the iron content is 3 ppm, the mercury content is less than the allowable upper limit of the liquid leakage resistance at 1 wt% or more, whereas the iron content is 1 pp
If it is m or less, the upper limit of the liquid leakage resistance is below the upper limit regardless of the presence or absence of mercury.

Experimental Example 2 (1) 0.01% by weight of aluminum and 0.05 of bismuth
Wt%, balance zinc, (2) aluminum 0.01 wt%, bismuth 0.05 wt%, lead 0.05 wt%, balance zinc, (3) aluminum 0.01 wt%, bismuth 0.05 wt%, A zinc alloy powder was obtained in the same manner as in Example 2 so that the lead content was 0.05% by weight, the mercury content was 0.15% by weight, and the balance was zinc. The content of iron in the zinc alloy powder at this time was varied.

Example 1 using these zinc alloy powders
The alkaline battery shown in FIG. 2 was prepared in the same manner as above, 25% partial discharge was performed, and the hydrogen gas generation amount was measured. The results are plotted and shown in FIG.

As shown in FIG. 4, when the content of iron as an accompanying impurity is 2 ppm or more, the permissible upper limit of the liquid leakage resistance is exceeded regardless of the presence or absence of mercury or lead. It can be seen that the iron content must be 1 ppm or less in any case in order to fall below the upper limit of liquid leakage resistance.

[0052]

As described above, zinc having an iron content of 1 ppm or less as an accompanying impurity and a specific additive element are dissolved in a molten metal, and the molten metal is directly atomized to obtain an iron content of 1 ppm. The following zinc alloy powder for alkaline batteries is obtained.

By using this zinc alloy powder as a negative electrode active material for alkaline batteries, it is possible to significantly suppress the generation of hydrogen gas and maintain the discharge performance at a practical level, even though it is lead-free and lead-free. You can Further, since it contains neither mercury nor lead, an alkaline battery using this zinc alloy powder as a negative electrode active material meets social needs.

[Brief description of drawings]

FIG. 1 is a flow sheet showing a conventional method and a method for producing a zinc alloy powder according to the present invention.

FIG. 2 shows a side sectional view of an alkaline manganese battery according to the present invention.

FIG. 3 is a graph showing a relationship between a mercury content in a zinc alloy powder and a hydrogen gas generation amount.

FIG. 4 is a graph showing the relationship between the iron content in zinc alloy powder and the hydrogen gas generation rate.

[Explanation of symbols]

1: Positive electrode can, 2: Positive electrode, 3: Negative electrode, 4: Separator, 5: Sealing body, 6: Negative electrode bottom plate, 7: Negative electrode current collector,
8: Cap, 9: Heat-shrinkable resin tube, 1
0, 11: Insulating ring, 12: Outer can.

Claims (8)

[Claims] 1. An unconstrained product comprising 0.001 to 0.5% by weight of aluminum, 0.01 to 0.5% by weight of bismuth, and the balance being zinc containing 1 ppm or less of iron as an accompanying impurity. Zinc alloy powder for alkaline batteries. 2. Aluminum 0.001 to 0.5% by weight, bismuth 0.01 to 0.5% by weight, indium 1.
0 wt% or less, the balance is 1 ppm of iron as an accompanying impurity
A zinc alloy powder for a non-alkaline alkaline battery, characterized by comprising zinc contained below. 3. Aluminum 0.001 to 0.5% by weight, bismuth 0.01 to 0.5% by weight, lithium 0.5.
A zinc alloy powder for a non-alkaline alkaline battery, characterized in that it is made of zinc containing 1 wt% or less by weight and the balance of 1 ppm or less of iron as an accompanying impurity. 4. Aluminum 0.001 to 0.5% by weight, bismuth 0.01 to 0.5% by weight, indium 1.
A zinc alloy powder for use in a non-alkaline alkaline battery, comprising 0% by weight or less, 0.5% by weight or less of calcium or 0.5% by weight or less of lithium, and the balance of zinc containing 1 ppm or less of iron as an accompanying impurity. 5. The following (1), (2), (3) or (4) in (1), (2), (3) or (4): (1) 0.001 to 0.5 weight of aluminium, in ionized zinc containing 1 ppm or less of iron as an accompanying impurity %, Bismuth 0.01 to 0.5 wt%, (2) aluminum 0.001 to 0.5 wt%, bismuth 0.01 to 0.5 wt%, indium 1.0 wt% or less, (3) aluminum 0.001 to 0.5% by weight, bismuth 0.01 to 0.5% by weight, lithium 0.5% by weight or less, (4) Aluminum 0.001 to 0.5% by weight, bismuth 0.01 to 0. 5 wt%, indium 1.0 wt% or less, calcium 0.5 wt% or less, or lithium 0.5
Zinc for a non-alkaline battery containing 1 ppm or less of iron as an accompanying impurity, characterized in that the additive element is melted so as to have a content ratio of any one of wt% or less and the molten metal is directly atomized. Method for manufacturing alloy powder. 6. The method for producing a zinc alloy powder for a smooth alkaline battery according to claim 5, wherein the iron content in the melting and atomizing atmosphere is 0.009 mg / m ³ or less. 7. The method for producing a zinc alloy powder for a smooth alkaline battery according to claim 5, wherein the atomized powder obtained is magnetically selected. 8. An alkaline battery using the zinc alloy powder according to claim 1, 2, 3 or 4 as a negative electrode active material.