JPS61253764A - Zinc alkaline battery - Google Patents

Abstract

PURPOSE:To increase the corrosion resistance of a zinc alloy used as the negative electrode by adding a combination of specific elements to produce a synergistic effect. CONSTITUTION:The negative electrode of the zinc alkaline battery of this invention is made of a zinc alloy which principally consists of zinc and contains 0.01-0.5wt% of nickel and 0.005-0.3wt% of either an element selected from magnesium, calcium and strontium or a mixture composed of at least two elements selected from magnesium calcium and strontium. The surfaces of atomized zinc particles are generally full of wrinkles produced during solidification. But, adding Mg, Ca or Sr results in production of atomized particles with smooth surfaces which have reduced specific surface area thereby reducing the amount of mercury necessary for preventing corrosion. In this battery, nickel which is almost homogeneously distributed in the atomized particles inhibits the diffusion of mercury from the surface to the core.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention uses zinc as a negative electrode active material, an alkaline aqueous solution as an electrolyte, and manganese dioxide, silver oxide, or silver oxide as a positive electrode active material.
This invention relates to improvements in negative electrodes for zinc-alkaline batteries using mercury oxide, oxygen, nickel hydroxide, etc.

A common problem with conventional zinc-alkaline batteries is corrosion of the negative electrode zinc by the electrolyte during storage.

Conventionally, it has been adopted as an industrial method to increase the hydrogen overvoltage by using unchlorinated zinc powder, which is made by adding 5 to 10% by weight of mercury to zinc, and to suppress corrosion to the extent that there is no practical problem. . However, in recent years, in order to reduce pollution, there has been an increasing social need to reduce the amount of mercury contained in batteries, and various studies have been conducted. For example, lead and cadmium in zinc.

A method has been proposed to improve corrosion resistance and reduce the lignification rate by using alloy powder to which indium, gallium, etc. are added. This means that the corrosion inhibiting effect is not only due to the effect of a single additive element, but also the combined effect of multiple additive elements. It has been proposed as a promising system.

Although all of these can be expected to have a certain degree of corrosion resistance and a reduction in the lignification rate to some extent, it is necessary to search for an alloy system with even better corrosion resistance.

In addition, with the aim of improving manganese dry batteries, the use of zinc or a zinc alloy with indium added to the zinc alloy for the negative electrode has a great anti-corrosion effect./'1. X'l 0
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:49 n A? jrl-Problems to be solved by the invention Among the above proposals, in addition to indium, Fe, Cd, Cr, Pb, Ca, and H are used as elements in the zinc alloy.
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Bi, Sb, A1. Although it is described including the case where one or more types of Ag, Mg, Si, Ni, Mn, etc. are included as impurities or additives, there is no effect other than when indium and lead are used together as additive elements. However, it is not clearly stated whether each of the miscellaneous elements mentioned above is added as an impurity or as an effective element, and it is not even clear which elements are effective for corrosion prevention, and the appropriate amount of addition is unknown.

There is no mention of anything other than 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 reduces the molten metal ratio without deteriorating the corrosion resistance and discharge performance of negative electrode zinc, and improves discharge performance, storage performance, and storage performance with low pollution.
The purpose is to provide a zinc-alkaline battery with excellent overall performance such as leakage resistance.

Means for Solving the Problems The present invention uses an alkaline aqueous solution containing caustic potash, caustic soda, etc. as the main components for the electrolyte, zinc for the negative electrode active material, and manganese dioxide, silver oxide, mercury oxide, etc. for 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, 0.01 to 0.5% by weight of nickel (Ni), and magnesium (Mg>).

It is characterized by using a zinc alloy containing o, oos to 0.3% by weight of one or more of calcium (Ca) and strontium (Sr).

action The effect of the additive elements here can be considered as follows.

Usually, the zinc powder used in alkaline batteries is so-called atomized powder, which is made by spraying and solidifying molten metal with high-pressure gas. The surface of atomized zinc powder is generally covered with wrinkles that form during solidification. However, M
When G, Ca, Sr, etc. are added, the wrinkles are removed and the surface is smoothed, and the specific surface area is reduced, so the amount of mercury required for corrosion prevention can be reduced. Further, Ni is distributed almost uniformly in the atomized powder, and it is thought that it suppresses the diffusion of mercury from the surface to the inside. In addition, the standard potential of Mg, Ca, and Sr is very low, and sufficient corrosion resistance cannot be obtained by adding them alone. However, Ni keeps the surface concentration of mercury high, and the Mg
, Ca, and Sr are not in contact with each other, and Mg, C
It is thought that a combined effect can be obtained by simultaneously adding one or more of Sr and Ni.

The potential is very low, and adding strontium alone does not provide sufficient corrosion protection. Indium has a high hydrogen overvoltage and a high affinity for mercury. lead.

Cadmium also has a relatively high hydrogen overvoltage and is likely to segregate at zinc grain boundaries, and is thought to have the effect of suppressing mercury diffusion through grain boundaries.

Indium covers the negative effects of adding strontium to zinc, and is thought to have a synergistic anti-corrosion effect when added at the same time as lead and cadmium.

Based on the above speculation, the present invention uses Ni and Mg.

We investigated the synergistic anti-corrosion effect of zinc alloys and succeeded in significantly improving the corrosion resistance and lowering the corrosion resistance of the zinc alloy used in the negative electrode.
This provides a low-pollution zinc-alkaline battery with excellent discharge performance and storage performance.

Examples Various zinc alloys were prepared by adding the various elements shown in the following table to zinc ingot with a purity of 99.997%, melted at about 500°C, and powdered by spraying with compressed air. 150
It was sieved into a mesh particle size range. 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 hydrate it. Then wash with water,
The mixture was replaced with acetone and dried to produce zinc hydrate alloy powder.

Furthermore, hydrated zinc powder or zinc hydrated alloy powder other than the examples of the present invention were also prepared in the same manner as comparative examples.

Using these hydrated powders, the button-shaped silver oxide battery shown in the figure was manufactured. In the figure, l is a sealing plate made of stainless steel, the inner surface of which is coated with copper plating 1'. 2 is a zinc negative electrode prepared by gelling an electrolytic solution in which a 40% by weight aqueous solution of caustic potassium is saturated with zinc oxide with carboxymethylcellulose, and dispersing zinc hydrate 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 stainless steel. This is a positive electrode can with nickel plating on the inside and outside surfaces. Reference numeral 8 denotes a P gasket made of polypropylene, which 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 hydrated powder of the negative electrode is unified to 193n+g, and the amount of mercury added (hydration rate) is 3% to the zinc alloy powder. It was bound in weight%.

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.

Note that the discharge performance was expressed as the discharge duration when discharge was performed at 20° C. at 510Ω with a final voltage of 0.9V.

□−□□□−會□ Regarding changes in the total battery height in this table, the total battery height decreases during the period after the battery is sealed until the stress relationship between each battery component stabilizes over time. It is customary to do so.

However, in batteries where a large amount of hydrogen gas is generated due to corrosion of the zinc negative electrode, there is a strong tendency for the total battery height to increase 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 by the increase or decrease in the total height of the battery due to storage. In addition, batteries with insufficient corrosion resistance will not only increase the total height of the battery, but also deteriorate leakage resistance due to an increase in battery internal pressure, as well as depletion of zinc due to corrosion, formation of an oxide film on the surface of zinc, and the presence of hydrogen gas. The discharge performance will be significantly deteriorated due to inhibition of the discharge reaction by the zinc negative electrode, and the discharge duration also largely depends on the corrosion resistance of the zinc negative electrode.

Now, in the table, Mg listed as a comparative example of the present invention,
When Ca and Sr were added alone to zinc (No, 2.3
．． In case 4), the total height of the battery is quite high, and the discharge performance is also significantly low. In addition, when Ni is added alone (No. 1), when Mg, Ca, and Sr are added alone (No. 2.3. 4
) Although it is not bad, the discharge performance and battery swelling are also not good. However, Mg, Ca.

Example of the present invention (No, 6.7.8°11,
12.13.16.1? , 18.21.22.23.
In the case of No. 25 and 26), both the corrosion resistance and the discharge performance are superior to those of the comparative example, and the combined effect of the added elements is remarkable. On the other hand, even if additive elements are present together, there is an excess or deficiency in the content (No, 5.9.10.14. is
.

19, 20.24) are not much different from the comparative example, and the composite effect is poor. As mentioned above, by using a zinc alloy in the negative electrode, which is a combination of one or more of Mg, Ca, and Sr and Ni in an appropriate content, we have succeeded in reducing the wood reduction rate. The content of each element is 0°005 to 0.3% by weight of one or more of Mg, Ca, and Sr, and N
It is appropriate that i is 0.01 to 0.5% 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 hydrate 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 carry out the process with the reduction of shrubs and, in some cases, anhydrous state.

Effects of the Invention As described above, the present invention can reduce the hydration rate of negative electrode zinc,
It is extremely effective in obtaining low-pollution zinc-alkaline batteries.

[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] 0.01 to 0.5% by weight of nickel, and 0.01% to 0.5% by weight of one or more of magnesium, calcium, and strontium.
A zinc alkaline battery using a zinc alloy containing 05 to 0.3% by weight as a negative electrode active material.