JPH05299082A - Zinc alloy powder for alkaline battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To substantially restrain the occurrence of hydrogen gas and improve the resistance of a mercury-less alkaline battery against liquid leakage by using zinc with an extremely small content of iron as an impurity, and adding the predetermined element thereto. CONSTITUTION:Each additional element represented by the following (1) or (2) is dissolved in the hot melt of zinc containing 1ppm or less of iron as an associated impurity to obtain the content thereof within the prescribed range; (1) 0.001 to 0.5wt.% of aluminum, and bismuth less than 0.001 to 0.01wt.%, and (2) 0.001 to 0.5wt% of aluminum, bismuth less than 0.001 to 0.01wt.% and indium equal to or less than 0.5wt.%. The product so obtained is pulverized by the atomizing method and sieved. Zinc alloy powder is thereby obtained. The occurrence of hydrogen gas can be restrained at approximately 300mul/day.cell or below as an upper allowable limit for leakage liquid resistance, using the zinc alloy powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 an accompanying impurity in zinc is 1 ppm or less and the addition of a specific additive element. The present invention relates to a zinc alloy powder for alkaline batteries, which suppresses hydrogen gas generation and improves the leak resistance of batteries without using mercury and lead, which are harmful elements, and a method for producing the same.

[0002]

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.

[0004] 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 unconstrained. 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. In other words, reduction of the mercury content is largely achieved by the effect of adding lead, and it was considered that silver-free conversion in the negative electrode active material could not be achieved without using lead.

It is known that lead, like mercury, also has an adverse effect on the human body. Considering the social needs for a clean environment, artificial addition of lead is not preferable. However, as described above, up to the present, 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.
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 can be obtained even if the content of iron as an impurity is reduced to about 10 ppm 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 involves 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 the use of non-selective and lead-free zinc alloy powder as the negative electrode active material suppresses the generation of hydrogen gas and, in turn, improves the leakage resistance.

[0010]

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.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in accordance with this object, and as a result, use zinc containing an extremely small amount of iron as an impurity, and add a specific additive element to the zinc. 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 non-alkaline alkaline battery of the present invention has the following (1) or (2): (1) 0.001 to 0.5% by weight of aluminum and 0.001 to 0.01 of bismuth. Less than 1% by weight, (2) 0.001 to 0.5% by weight of aluminum, 0.001 to bismuth
It is characterized in that it contains a component selected from less than 0.01% by weight and indium 0.5% by weight or less, and the balance is zinc containing 1 ppm or less of iron as an accompanying impurity.

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.

The present invention also contains a component selected from the above (1) or (2). 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 with a low iron content include zinc deposited by electrolysis and zinc ingot produced by vacuum distillation. Conventionally, a zinc ingot obtained by melting dissociated zinc with a flux such as ammonium chloride and casting it in a mold has been used as a zinc raw material for a 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 this molten zinc containing iron having a low iron content, each of the additive elements shown in the above (1) or (2) 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 zinc alloy powder manufacturing method of the present invention.

The content of iron 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 μm.
It is possible to suppress the generation of hydrogen gas below 1 / day · 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, it was found that 0.5 to 5 μm of fine particles mainly containing iron were unevenly distributed at the continuous gas generation points. 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, Reference Examples and Comparative Examples.

Examples 1-2, Reference Examples 1-8 and Comparative Examples
In a room with an iron content of 0.005 mg / m ^{3 in} an atmosphere of 1 to 7, ionically-analyzed zinc having an iron content of 1 ppm or less was melted at about 500 ° C. A predetermined amount was added to prepare a molten zinc alloy. In Comparative Example 1, no element was added.

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 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 8 to 9 Starting from a zinc ingot in which electroanalyzed zinc having an iron content of 1 ppm or less was cast as usual, in an atmosphere having an iron content of 5 mg / m ³ , about 500 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
In each of the zinc alloy powders of Examples 1 and 2 and Reference Examples 1 to 8 having a specific composition of pm or less, the hydrogen gas generation amount is about 300 μl / da which is the upper limit of the leakage resistance.
It is less than or equal to y · cell (AA type). On the other hand, in the zinc alloy powders of Comparative Examples 1 to 7, the composition deviates from the range specified by the present invention, even though the iron content is 1 ppm or less. Is not recognized. Furthermore, since the zinc alloy powders of Comparative Examples 8 to 9 have an iron content of 3 ppm, the effect of suppressing hydrogen gas generation is recognized regardless of whether or not the composition falls within the range defined by the present invention. I can't.

Experimental Example The zinc alloy powders of Example 1 and Comparative Example 8 were blunted 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. 1 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 1 and Comparative Example 8.

As shown in FIG. 3, when the iron content is 3 ppm, the mercury content is less than the upper limit of the leakage resistance at 1 wt% or more, while 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.

Further, similar tests were conducted on the zinc alloy powders of Example 2 and Comparative Example 9, but almost similar results were obtained.

[0045]

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.

Although this zinc alloy powder is both lead-free and lead-free, it can be used as a negative electrode active material in alkaline batteries to significantly suppress hydrogen gas generation and to have a discharge performance at a practical level. Can hold. 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.

[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,
10, 11: insulating ring, 12: outer can.

Claims (6)

[Claims] 1. A stable container comprising 0.001 to 0.5% by weight of aluminum, 0.001 to less than 0.01% 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 alkaline batteries. 2. Zinc containing 0.001 to 0.5% by weight of aluminum, 0.001 to less than 0.01% by weight of bismuth, 0.5% by weight or less of indium, and the balance of 1 ppm or less of iron as an accompanying impurity. A zinc alloy powder for a non-alkaline alkaline battery, characterized in that 3. An electroanalyzed zinc containing 1 ppm or less of iron as an accompanying impurity, and the following (1) or (2): (1) 0.001 to 0.5% by weight of aluminum and 0.001 to 0 of bismuth. Less than 0.01% by weight, (2) 0.001 to 0.5% by weight of aluminum, 0.001 to bismuth
Iron as a concomitant impurity, characterized in that the additive element is dissolved and the molten metal is directly atomized so as to have a content ratio of less than 0.01% by weight and indium 0.5% by weight or less. Of 1 ppm or less of zinc alloy powder for a non-alkaline alkaline battery. 4. The method for producing a zinc alloy powder for an alkaline battery according to claim 3, wherein the iron content in the melting and atomizing atmosphere is 0.009 mg / m ³ or less. 5. The method for producing a zinc alloy powder for an alkaline battery according to claim 3, wherein the atomized powder thus obtained is magnetically selected. 6. An alkaline battery using the zinc alloy powder according to claim 1 or 2 as a negative electrode active material.