JPH0365622B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to improvement of the negative electrode of a zinc-alkaline battery using 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 something. Prior Art A common problem with zinc-alkaline batteries is corrosion of the negative electrode zinc by electrolyte during storage. Conventionally, an industrial method has been used to increase the hydrogen overvoltage by using zinc chloride powder containing 5 to 10% by weight of mercury to suppress corrosion to a level that poses no practical problems. . However, in recent years,
In order to reduce pollution, there is a growing social need to reduce the amount of mercury contained in batteries, and various studies are being conducted. For example, a method has been proposed that uses an alloy powder in which lead, cadmium, indium, gallium, etc. are added to zinc to improve corrosion resistance and reduce the rate of corrosion. These corrosion-inhibiting effects are not only due to the single additive element, but also due to the combined effect of multiple additive elements. Conventionally,
It 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.
It has been proposed that the use of zinc or a zinc alloy prepared by adding indium to a zinc alloy for the negative electrode has a great anticorrosive 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 challenge for the future to study the effects of the combination of these elements in zinc-alkaline batteries and to find an effective alloy composition. 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 uses an aqueous alkaline solution containing caustic potash, caustic soda, etc. as the main components in the electrolyte, zinc as the negative electrode active material, manganese dioxide, silver oxide, mercury oxide, etc. as the positive electrode active material, The negative electrode of a so-called zinc-alkaline battery that uses oxygen etc. has zinc as its main component, with 0.001 to 0.5% by weight of indium and lead as essential additive elements.
0.01-0.5% by weight, 0.001-0.3% by weight of gallium,
At least one of nickel and cobalt at 0.01
It is characterized by using a zinc alloy containing ~0.5% by weight. In the present invention, among the additive elements and other elements in the conventional zinc alloy mentioned above, the anticorrosion effect is poor when added alone, but it is added in combination with elements such as In, Ga, and Pb that have a relatively large anticorrosion effect. They discovered Ni and Co as elements that exert a complex anti-corrosion effect, and completed an experimental study of their addition rates. Effects Although the mechanism of action of the additive elements of the present invention is not clear, it is thought that the effects of each additive element exert a synergistic effect to significantly improve corrosion resistance.
It is inferred as follows. In is known as one of the most effective additive elements for corrosion prevention among all elements, and in addition to having the effect of increasing hydrogen overvoltage, it has a high affinity with mercury, so it is The mercury added for this purpose is fixed on the surface and grain boundaries of the zinc alloy,
It is thought that a great anticorrosion effect can be obtained by suppressing diffusion into the crystals and inside the zinc alloy and maintaining a high mercury concentration on the surface and grain boundaries by adding a small amount of mercury. Pb tends to segregate near the grain boundaries of zinc alloys, and when it becomes a layer from the surface of zinc alloys, it suppresses the diffusion of mercury in the surface layer into the interior of the zinc alloys through the grain boundaries. This is thought to contribute to maintaining high mercury concentrations.
In addition, Ga has a relatively high affinity with mercury, so
In, the effect of Ga existing in the grain boundaries fixing mercury that has become aqueous from the surface of the zinc alloy at the grain boundaries, suppressing its diffusion from the surface layer into the crystals, and maintaining a high surface concentration of mercury. It is thought that this effect is synergistic with the action of Pb. In addition, although Ni and Co have low solubility in zinc, the cooling rate when pulverizing molten zinc alloy by injection method is extremely high, on the order of approximately 10 ² °C/sec. content (0.01~0.5
% by weight), it may be dissolved with zinc. Therefore, Ni or Co, which originally has a low affinity for mercury, is dissolved in the crystal, suppresses the diffusion of mercury into the crystal, and contributes to maintaining a high concentration of mercury on the surface of the zinc alloy. it is conceivable that. The present invention uses the synergistic effect of the coexistence of In, Pb, and Ga to increase the hydrogen overvoltage of the zinc alloy itself, fix mercury on the surface layer of the zinc alloy that has become oxidized from the surface, and transfer mercury to the grain boundaries. The diffusion is suppressed, the mercury that has diffused without being suppressed is fixed at the grain boundaries, and further, by the action of solutionized Ni or Co,
This prevents mercury that cannot be fixed at the grain boundaries from diffusing into the crystal grains, and due to the combined effect of each additive element, the mercury on the surface of the zinc alloy is kept at a high concentration by the oxidation of a small amount of mercury, and the surface The inventors invented a zinc alloy that has extremely excellent corrosion resistance by making the hydrogen overvoltage more uniform and increasing the hydrogen overvoltage. As described above, the present invention has experimentally investigated the combination of additive elements and their content in the zinc alloy used for the negative electrode, and has developed a low-pollution zinc-alkaline battery having a zinc negative electrode with a low rate of deterioration that combines discharge performance and corrosion resistance. This provides an effective means to achieve this goal. Hereinafter, the present invention will be explained in detail with reference to 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 while stirring to form a solution. 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. The button-shaped silver oxide battery shown in the figure 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. With the positive electrode can,
Although not shown, the inner and outer surfaces are decorated with nickel plating. A polypropylene gasket 8 is compressed between the positive electrode can 7 and the sealing plate 1 by bending the positive electrode can 7. 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, the discharge performance after storage at 60°C for one month, the number of leaking batteries as determined by visual inspection, and the changes in the total battery height.
The discharge performance was expressed as the discharge duration when discharged at 20°C with a resistance of 510Ω and a final voltage of 0.9V.

【table】

【table】

[Table] Regarding changes in total battery height in this table,
After the battery is sealed, the total height of the battery typically decreases during the period until the stress relationship between the battery components becomes stable over time. However, in a battery where 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 counters the above-mentioned 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 due to storage. In addition, 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, and the zinc is consumed due to corrosion, the formation of an oxide film on the zinc surface, and the presence of hydrogen gas. The discharge performance is significantly deteriorated due to inhibition of the discharge reaction, and the leakage resistance and discharge duration are also largely dependent on the corrosion resistance of the zinc negative electrode. As seen in this table, among Nos. 1, 2, 3, 5, and 6, in which a single element was added, the effect of In was the largest, followed by Ga and Pb. , Ni, and Co have the worst corrosion resistance and discharge performance compared to the others. In addition, No. 4, which coexists with In, Pb, and Ga, which has traditionally attracted attention as one of the most corrosion-resistant zinc alloys, is No. 1 to No.
Although it has the best performance among No. 6, it cannot be said to have sufficient practical performance in terms of discharge performance and leakage resistance with a low rate of reduction of 0.5% by weight. In contrast to these conventional examples, among Nos. 7 to 24, in which Ni coexists with In, Pb, Ga, and Ni, those with appropriate contents of each additive element show superior performance than No. 4. ,
It has been confirmed that the addition of Ni has a complex anticorrosion effect. That is, 0.001-0.5 wt% In, Pb
0.01~0.5 wt%, Ga 0.001~0.3 wt%, Ni
In the range of 0.01 to 0.5% by weight, the zinc alloy containing each is effective, and if the content of each added element is excessive or insufficient than the above, it will not be much different from No. 4 or the performance value will have the opposite effect. It shows. In addition, Nos. 25 and 26 were added with Co instead of Ni, and Ni and Co coexisted.
Similar effects were also observed in Nos. 27 and 28. As described above, the present invention uses a zinc alloy containing In, Pb, and Ga as essential additive elements and one or both of Ni and Co as essential additive elements, and containing appropriate amounts of each, for the negative electrode. As a result, we have completed a zinc-alkaline battery with a low rate of depletion and excellent practical performance such as discharge performance, storage performance, and leakage resistance. In the above example, In, Pb, Ga, and
Although only Ni or Co, which is an essential additive element in the present invention, has been described, additional non-essential additive elements such as Tl, Cd, Sn, Bi, Ag, Al,
Mg, Ca, Ba, Sr, Hi, Na, K, Rb, Cu,
Add 0.1 of Te, Ta, Si, or Ti to No. 12 in the previous table.
Even when it was contained in a weight percent, almost the same performance value as No. 12 was obtained. Therefore, even if the essential additive elements of the present invention are contained in a predetermined amount and the above-mentioned non-essential additive elements are added within the limits, the essential The same effects can be obtained. 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, the hydrogen gas generation capacity is relatively low. Therefore, the present invention can be carried out with a lower rate of change, or even with no rate of change as the case may be. Furthermore, in this example, a case was explained in which additive elements were added to a molten zinc alloy, alloyed, and then powdered. However, as an alternative method, among the additive elements, In, Ga, etc., which are easy to form into amalgam, There are methods in which additive metals are added in advance to the mercury used for forming zinc alloys and added at the same time as forming zinc alloys, and Pb,
It is also possible to adopt a method in which the above elements are precipitated on the surface of a zinc alloy through a substitution reaction with zinc in a solution containing a hydroxide or salt of In or Ga to form an alloy. 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]

The figure is a partially sectional side view of a button-shaped silver oxide battery used in an example of the present invention. 2... Zinc negative electrode, 4... Separator, 5... Silver oxide positive electrode.

Claims (1)

[Claims] 1 Indium 0.001~0.5% by weight, lead 0.01~0.01% by weight
0.5% by weight, 0.001 to 0.3% by weight of gallium, and 0.01 to 0.5% of at least one of nickel and cobalt.
A zinc alkaline battery using a zinc alloy containing % by weight as a negative electrode active material.