JPH0143429B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention is an improvement of the negative electrode of a zinc-alkaline battery that uses zinc as the negative electrode active material, an alkaline aqueous solution as the electrolyte, and manganese dioxide, silver oxide, mercury oxide, oxygen, nickel hydroxide, etc. as the positive electrode active material. It is related to. Prior Art A common problem with zinc-alkaline batteries is corrosion of the negative electrode zinc by electrolyte during storage. Conventionally, it has been widely used as an industrial method to add 5 to 10% by weight of mercury to zinc to suppress corrosion to a level that causes no practical problems. However, in recent years, there has been an increasing social need to reduce the amount of mercury contained in batteries in order to reduce pollution, and various studies have been conducted. For example, a method has been proposed in which the corrosion resistance is improved by using an alloy powder in which lead, cadmium, indium, gallium, etc. are added to zinc, and the amount of mercury used for oxidation, the so-called oxidation rate, is reduced. These corrosion-inhibiting effects are not only due to the single additive element, but also due to the combined effect of multiple additive elements, such as indium and lead, or the combination of indium and lead with the addition of gallium, and even zinc alloys with the addition of gallium and lead. has been proposed as a promising system. Although all of these can be expected to have a certain degree of corrosion resistance and to reduce the degree of corrosion to some extent, it is necessary to search for an alloy system with even better corrosion resistance. In addition, we mainly aim to improve manganese dry batteries.
There is a proposal that using a zinc alloy with indium added to the zinc alloy for the negative electrode has a great anticorrosion effect (Japanese Patent Publication No. 33-3204). Problems to be solved by the invention Among the above proposals, as an element in zinc alloy,
In addition to indium, Fe, Cd, Cr, Pb, Ca, Hg,
The description includes cases in which one or more of Bi, Sb, Al, Ag, Mg, Si, Ni, Mn, etc. are included as impurities or additives, but when indium and lead are used together as additive elements. Other than the effectiveness of corrosion prevention, there is no clear distinction as to whether each of the miscellaneous elements listed above is added as an impurity or as an effective element, and it is not even clear which elements are effective for corrosion prevention. There is no description of the amount of addition other than indium and lead. It remains a matter of future research to study the effects of these element combinations in zinc-alkaline batteries and to find effective alloy compositions. The present invention aims to provide a zinc-alkaline battery with low pollution and excellent overall performance such as discharge performance, storage performance, and leakage resistance, by reducing the corrosion resistance and discharge performance of the negative electrode zinc. purpose. Means for Solving the Problems The present invention includes an electrolyte containing an alkaline aqueous solution containing caustic potassium or caustic soda as a main component, zinc as a negative electrode active material, and manganese dioxide, silver oxide, oxygen, or mercury oxide as a positive electrode active material. For the negative electrode of a so-called zinc-alkaline battery, which uses zinc as the main component, 0.01 to 0.5% by weight of nickel, 0.01 to 0.5% by weight of at least one of indium, lead, and cadmium, aluminum, magnesium, and calcium. ,
It is characterized by using a zinc alloy containing 0.005 to 0.2% by weight of at least one member of the group consisting of strontium, and the balance being zinc. The present invention conducted experiments focusing on Ni and Co among the additive elements, impurities, and other elements in the zinc alloy.
Zinc alloys containing Ni or Co alone have poor corrosion resistance, but the combined effect with other additive elements is significant.In particular, the above-mentioned Ni is cheaper than Co and can improve corrosion resistance when alloyed. This work was completed after discovering that an extremely remarkable composite anticorrosion effect can be obtained when the appropriate amount is contained in combination with the following elements. Effect The mechanism of action of the anticorrosive effect of adding each element and the combined effect of these elements is unclear, but it is inferred as follows. First, although the solubility of Ni in zinc is small, the cooling rate when pulverizing molten zinc alloy by the injection method is on the order of 10 ² °C/sec, which is extremely high, so the appropriate content in the examples described later is There is a possibility that Ni may become a solution with zinc in the zinc alloy powder. Therefore, when a zinc alloy is made into a starch from the surface, Ni, which has a low affinity for mercury,
It is thought that this contributes to suppressing the diffusion of mercury into the crystal and maintaining a high concentration of mercury on the surface of the zinc alloy. However, on the other hand, there is also a concern that the adhesion of mercury to the surface of the zinc alloy may become worse. Also,
Pb and Cd tend to segregate near the grain boundaries of zinc alloys,
It is thought that this suppresses the diffusion of mercury in the surface layer of the zinc chloride alloy into the interior through grain boundaries, thereby contributing to maintaining a high mercury concentration on the surface. In addition, In increases the hydrogen overvoltage of zinc alloys, and since it is easily compatible with mercury, it is effective in making the surface condition uniform when a zinc alloy is oxidized. It is also expected to play a role in fixing mercury in the world. Also, Al,
Like Ni, Mg, Ca, and Sr all have a low affinity for mercury, so they suppress the diffusion of mercury into the zinc alloy. It is thought that this method eliminates the wrinkles on the surface of the zinc alloy powder that occur when it is oxidized, making it smoother, reducing the surface area, and increasing the anticorrosion effect. However, since these elements are base metals than zinc, they are more likely to corrode than zinc in the electrolyte.
It is necessary to consider the balance with the expected anticorrosion effect, and excessive addition will actually impair the anticorrosion property. As mentioned above, each additive element is expected to have a different effect. However, each element alone may have a poor anticorrosive effect. The present invention was completed by experimentally determining the appropriate combination and content of elements that complement the strengths and weaknesses of these additive elements, and it is possible to reduce the hydrogen overvoltage on the surface of zinc alloy powder by adding a small amount of mercury. By maintaining a high level over a long period of time, making the surface uniform, and further reducing the surface area,
This significantly improves the corrosion resistance of the zinc alloy used in the negative electrode. As a result, a corrosion-resistant zinc negative electrode with a low rate of decay was realized, and a low-pollution zinc-alkaline battery with excellent discharge performance and storage performance was provided. Hereinafter, it will be explained in detail using examples. Example: Various zinc alloys were created by adding various elements shown in the following table to zinc ingot with a purity of 99.997%.
Melt it at ℃ and inject it with compressed air to powder it.
It was sieved to a particle size range of 50 to 150 mesh.
Next, the above powder was put into a 10% by weight aqueous solution of caustic potash, and a predetermined amount of mercury was added dropwise to the solution while stirring. Thereafter, it was washed with water, substituted with acetone, and dried to produce a zinc chloride alloy powder. Furthermore, zinc chloride powder or zinc chloride alloy powder other than the examples of the present invention were also prepared in the same manner as comparative examples. A button-shaped silver oxide battery shown in FIG. 1 was manufactured using these oxidized powders. In the figure, reference numeral 1 denotes a sealing plate made of stainless steel, the inner surface of which is plated with copper 1'. 2 is a zinc negative electrode prepared by gelling an electrolytic solution of a 40% by weight aqueous solution of caustic potassium saturated with zinc oxide with carboxymethylcellulose, and dispersing zinc oxide alloy powder in this gel.
3 is a cellulose-based liquid retaining material, 4 is a separator made of porous polypropylene, 5 is a positive electrode made of a mixture of silver oxide and graphite and pressure molded, 6 is a positive electrode ring made of nickel-plated iron, and 7 is made of stainless steel. The positive electrode can has nickel plating (not shown) on its inner and outer surfaces. A polypropylene gasket 8 is compressed between the positive electrode can and the sealing plate by bending the positive electrode can. The prototype battery has a diameter of 11.6 mm and a height of 5.4 mm.
The weight of the oxidized powder of the negative electrode was unified to 193 mg, and the amount of mercury added (the oxidized ratio) was 0.5% by weight based on the zinc alloy powder. The following table shows the composition of the zinc alloy of the prototype battery, and the changes in discharge performance and total battery height after storage at 60°C for one month. The discharge performance is 510Ω at 20℃.
It is expressed as the average discharge duration of three batteries when discharged with a final voltage of 0.9V, and the change in total battery height is the average height of 20 batteries after storage compared to the standard value (5.4mm). An increase is indicated by +, and a decrease is indicated by -. Regarding this change in total battery height, after sealing the battery,
It is normal for the total height of the battery to decrease over time until the stress relationship between the battery components becomes stable. However, in a battery in which a large amount of hydrogen gas is generated due to corrosion of the zinc negative electrode, there is a strong tendency to increase the total battery height due to an increase in battery internal pressure that counteracts the above-described force for decreasing the total battery height. Therefore, the corrosion resistance of the zinc negative electrode can be evaluated based on the change in total battery height from the standard value due to storage. In addition, after 20 batteries were left at a temperature of 60°C and humidity of 90% for one month, the state of leakage was visually determined, and the number of batteries leaking was also indicated.

【table】

【table】

[Table] As is clear from the table, in batteries with insufficient corrosion resistance, the total height of the battery increases, the leakage resistance deteriorates due to an increase in battery internal pressure, zinc is consumed due to corrosion, and an oxide film on the surface of the zinc increases. The discharge performance is significantly deteriorated due to the formation of hydrogen gas and the inhibition of the discharge reaction due to the internal pressure of hydrogen gas, and the discharge duration also largely depends on the corrosion resistance of the zinc negative electrode. In the above table, the following are listed as comparative examples of the present invention.
Among Nos. 1 to 8, cases in which only one additional element was added (Nos. 1 to 2), cases in which two elements were added (Nos. 3 and 4), and cases in which three additional elements were added (Nos. 1 to 2) .5, 6, 7, 8) have better corrosion resistance of zinc negative electrode,
Both discharge performance has been improved somewhat. However, In, Cd, Pb, Ni, Al, Mg, Ca, Sr
No. 10, 11, 12, 15, 16, 19, 21, 22, 23,
Samples Nos. 24, 25, 26, 27, 28, 29, 30, 31, 32, and 33 have even better corrosion resistance and discharge performance than the above-mentioned comparative examples, and the combined effects of the added elements are clearly exhibited. On the other hand, even when three elements are present together, in cases where there is an excess or deficiency in the content (Nos. 9, 13, 14, 17, 18, 20), there is no significant difference from the comparative example, and the combined effect is poor. Figures 2 to 4 show the above-mentioned In, Pb, Al or
Among the four elements Mg and Ni, three elements are fixed at appropriate addition amounts (0.05% or 0.02% by weight each), and the addition amount of the other element is changed to adjust the zinc alloy powder, and the amount of mercury is adjusted. The corrosion resistance of the alloy was evaluated from the rate of hydrogen gas generation upon contact with an alkaline electrolyte at 45° C. after hydrogenation at 1% by weight, and the preferred content was determined. In order to keep the hydrogen gas generation rate to a level of 2 to 2.5 μ/g/day or less, which is practically acceptable, that is, the same level as the conventional zinc chloride powder containing about 10% by weight of mercury, we have improved the corrosion resistance. added to aim for
As is clear from FIG. 2, Ni is preferably contained in an amount of 0.01 to 0.5% by weight. Similarly, as shown in Figure 3, the amount of Al added is 0.005 to 0.2% by weight, while Mg
As shown in FIG. 4, 0.005 to 0.2% by weight was also suitable. Further, although not shown in the drawings, even when calcium or strontium is contained, the preferable addition amount is the same as that for aluminum. Furthermore, In and
Not only when Pb is used in combination, but also when these are used alone, or when Cd is used alone or in combination with In etc., the preferable addition amount is 0.01 to
It was 0.5% by weight. Figure 5 shows the relationship between the number of days elapsed and the amount of hydrogen gas generated for various zinc alloy powders. In the figure, A is pure zinc powder with no added mercury, and B is pure zinc powder with 9 wt% Added mercury, C is In and
Contains 0.05% by weight each of Pb and 3% by weight of mercury, D contains 0.05% by weight each of In, Pb, and Al, and Ni
E shows the characteristics of a material containing 0.02% by weight of mercury and 1% by weight of mercury, and E shows the characteristics of D with an increased amount of mercury added to 1.5% by weight. As described above, the present invention has discovered that the corrosion resistance of the zinc alloy used for the negative electrode is improved due to the synergistic effect of the combination of the above-mentioned additive elements, and has determined the appropriate content to create a zinc-alkaline alloy with low pollution and excellent practical performance. This is the realization of a battery. In addition, in the examples, a battery using a zinc chloride negative electrode was explained, but in an open air battery or a sealed zinc alkaline battery equipped with a hydrogen absorption mechanism,
Since the permissible amount of hydrogen gas to be generated is relatively large, when the present invention is applied to such a case, it is possible to further reduce the rate of hydrogenation, or in some cases, it can be carried out with no rate of hydrogenation. Effects of the Invention As described above, the present invention can reduce the oxidation rate of negative electrode zinc, and is extremely effective in obtaining a low-pollution zinc-alkaline battery.

[Brief explanation of drawings]

FIG. 1 is a side view of a button-shaped silver oxide battery used in an example of the present invention, with a part cut away, and FIGS. 2 to 4 show the content of alloy components in zinc alloy powder and the rate of hydrogen gas generation. FIG. 5 is a diagram showing the relationship between the number of days elapsed and the amount of hydrogen gas generated for various zinc alloy powders. 2... Alloy negative electrode, 4... Separator, 5... Silver oxide positive electrode.

Claims (1)

[Claims] 1 a positive electrode, an electrolyte consisting of an alkaline aqueous solution,
Equipped with a negative electrode, 0.01 to 0.5% by weight of nickel, 0.01 to 0.5% by weight of at least one of the group consisting of indium, lead, and cadmium, and 0.005% of at least one of the group consisting of aluminum, magnesium, calcium, and strontium. ~0.2
A zinc-alkaline battery using a zinc alloy as a negative electrode active material, with the balance being zinc with a low concentration ratio.