JPS63133450A - Zinc alkaline battery - Google Patents

Abstract

PURPOSE:To reduce public pollution and to improve discharging, storage and leakage resisting properties, by adding In, Ba and an element selected from Al, Ca, and Mg. CONSTITUTION:A negative electrode of a zinc alkaline battery is composed mainly of zinc, and zinc alloy as an additive element containing indium of 0.001-0.5 wt%, one or more of aluminum, calcium and magnesium of 0.001-0.3 wt% and barium of 0.001-0.5 wt%. The indium has an action for increasing a hydrogen over-voltage and an action for fixing mercury added for to the surface and particle boundary of the zinc alloy to keep a mercury concentration at the surface and the particle boundary of the zinc alloy at a high level by the addition of a small amount of mercury for providing a large corrosion prevention effect. The addition of the Al, Ca and Mg has an effect to reduce a surface area of zinc alloy powder used to the negative electrode to restrict corrosion of the zinc alloy. With the arrangement, a zinc alkaline battery of low public pollution can be provided which has a lower amalgamation ratio and excellent discharging, storage and leakage prevention properties.

Description

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

2. Prior Art Conventionally, a common problem with this type of zinc-alkaline battery is corrosion of the negative electrode zinc by the electrolyte during storage. Up until now, an industrial method has been adopted to increase the hydrogen overvoltage by using zinc hydrate powder containing 6 to 10% by weight of mercury and to suppress corrosion to a level that poses 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 to improve corrosion resistance and reduce the hydration rate by using an alloy powder in which lead, cadmium, indium, gallium, etc. are added to zinc. These corrosion inhibition effects are not only due to the effect of a single additive element but also the combined effect of multiple additive elements. Conventionally, indium and lead, or gallium added to these, and zinc alloys with gallium and lead added are used. , has been proposed as a promising system.

Also, a zinc alloy in which gallium and silver are added to lead and cadmium (Japanese Unexamined Patent Publication No. 78062/1983).

A zinc alloy in which aluminum is added to gallium and thallium (Japanese Unexamined Patent Publication No. 78061/1983).

Zinc alloy made by adding one or more of silver, gallium, thallium, and cadmium to aluminum and lead (Japanese Patent Laid-Open No. 6
1-78059), etc.

Problems to be Solved by the Invention All of the zinc alloys proposed above can be expected to have a certain degree of corrosion resistance and to reduce the hydration rate to a certain extent, but the effect of the combination of these elements is currently insufficient. However, it remains a future challenge to elucidate alloy compositions based on effective combinations.

The present invention solves these problems, and reduces the hydration rate without deteriorating the corrosion resistance of negative electrode zinc, resulting in low pollution and excellent overall performance such as discharge performance, storage performance, and leakage resistance. The purpose of this invention is to provide a zinc negative electrode.

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 and 0.001 to 0.00% of indium as an additional element.
5% by weight, 0.0% of one or more of the group consisting of aluminum, calcium, and magnesium. Oo1-0.3% by weight,
It is characterized by using a zinc alloy containing 0.001 to 0.5% by weight of barium.

The present invention uses In in combination with In, which is known as an element with a relatively large anticorrosion effect.
We discovered that by adding elements selected from Al, Ca, and Mg and Ba, we could obtain a zinc alloy that was much better than the zinc alloy that added In alone. This was completed after experimental study.

Function Although the mechanism of action of each additive element in the zinc alloy according to the present invention is unclear, the synergistic effect regarding corrosion prevention is inferred as follows.

First, since In has the effect of increasing hydrogen overvoltage and has a high affinity for mercury, the mercury added for hydration is fixed on the surface and grain boundaries of the zinc alloy, and by adding a small amount of mercury, the surface of the zinc alloy is It is thought that this has a large anti-corrosion effect due to the action of maintaining a high mercury concentration at the grain boundaries. Also, Al, Ca,
The effect of adding Mg is to reduce the surface area of the zinc alloy powder that is pulverized and used for the negative electrode, thereby suppressing corrosion of the zinc alloy.

In other words, the zinc alloy powder normally used for the negative electrode is an atomized powder made by spraying and solidifying molten zinc alloy with high-pressure gas, and the surface of the atomized zinc or zinc alloy powder has fine wrinkles that occur during solidification. However, when Al, Ca, and Mg are added, the wrinkles are reduced.
The surface of the particles can be smoothed, reducing the surface area where corrosion reactions occur upon contact with the electrolytic solution, and increasing corrosion resistance.

Furthermore, since Ba has a high affinity with mercury, it is expected to have a similar effect to the anticorrosion effect of In, and is presumed to play a role in supplementing the effect of In. As mentioned above, by hydrating the zinc alloy used in the present invention with a small amount of mercury, the mercury concentration on the surface of the zinc alloy can be maintained high, and the surface area of the zinc alloy powder can be reduced, so it has extremely excellent corrosion resistance. considered to be a thing. The present invention has experimentally investigated the combination of additive elements and their contents in the zinc alloy, and
.

This work has completed an effective means for realizing a low-pollution, highly practical zinc-alkaline battery that has both sufficient corrosion resistance and discharge performance at a low corrosion rate. Hereinafter, it will be explained in detail using examples.

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%.
Melt at c and sprayed with compressed air to powder, 50~
It was sieved to a particle size range of 150 mesh. Then,
The above powder was put into a 10M aqueous solution of caustic potash, and a predetermined amount of mercury was added dropwise while stirring to hydrate it. after that,
It was washed with water, replaced with acetone, and dried to produce a zinc hydrate alloy powder.

Furthermore, hydrated zinc powder or glazed zinc 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 frozen powders. In the figure, reference numeral 1 denotes a sealing plate made of stainless steel, the inner surface of which is coated with copper plating 1'. 2 is a zinc negative electrode in which an electrolytic solution in which a 40% by weight aqueous solution of caustic potassium is saturated with zinc oxide is gelled with carboxymethylcellulose, and zinc hydrate alloy powder is dispersed in this gel. 3 is a cellulose-based liquid retaining material, 4 is a porous polypropylene ring separator, 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 iron plated with nickel, and 7 is nickel plated. This is a positive electrode can made of stainless steel. Reference numeral 8 denotes a polypropylene ring gasket, which is compressed between the positive electrode can 7 and the sealing plate 1 by bending the opening of the positive electrode can 7 . The prototype battery has a diameter of 11.6++
m, the height of 5.4 m, the weight of the negative electrode frozen powder was unified to 193 m, and the amount of mercury added (frozen rate) to the zinc alloy powder was
Both amounts were 1.0% by weight.

The following table shows the composition of the zinc alloy of the prototype battery, the change in discharge performance and total battery height after storage at 6C)°C for one month, and the number of leaking batteries as determined by visual inspection. The discharge performance was expressed by the discharge duration when discharging at 510Ω at 20° C. with a final voltage of 0.9V.

In this table, the total battery height generally decreases over time after the battery is sealed until the stress relationship between each battery component 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-mentioned decrease in the total battery height. Therefore, the corrosion resistance of the zinc negative electrode can be evaluated based on changes in the total battery height due to storage. In addition, in batteries with insufficient corrosion resistance, the total height of the battery increases, and leakage resistance deteriorates due to an increase in battery internal pressure. At the same time, zinc is consumed due to corrosion, an oxide film is formed on the zinc surface, and discharge occurs due to the presence of hydrogen gas. Due to reaction inhibition, etc.
The discharge performance will be significantly deteriorated, and both the leakage resistance and the discharge duration will largely depend on the corrosion resistance of the zinc negative electrode.

As can be seen in this table, in contrast to the flat 1 battery in which In was added alone, the 42 and 3.4 batteries in which AJ, Ca, or Mg were added together had better corrosion resistance than the 7fL1 battery. In particular, the combined effect of Ca and Al is large.

However, these materials do not have practically satisfactory properties at a water conversion rate as low as 1.0% by weight, and cannot be said to have sufficient corrosion resistance.

In contrast to these conventional examples, In, Al, Ca, Mg
Of the cases 5 to 27 in which one or more of the following elements coexisted together with Ba, those with an appropriate content of each additive element showed even better characteristics. For example, 42 and A10
, A3 and A 15 , and A4 and Haruka 18 make this clear. In addition, the appropriate content of each element is as follows: In is 0.
001 to 0.5% by weight, and the sum of the contents of one or more elements selected from Al, Ca, and Mq is 0.001 to 0.5% by weight.
Zinc alloy containing 3% by weight and Ba in the range of 0.001 to 0.6% by weight is effective, and if the content of each additional element is excessive or insufficient than the above, it is not much different from the conventional example. Or, it shows characteristic values that have the opposite effect. As described above, the present invention uses In and Ba as essential additive elements, and furthermore, Al.

By using a zinc alloy in the negative electrode containing one or more of Ca and Mg as essential additive elements and containing appropriate amounts of each, discharge performance and storage stability can be achieved with a low hydration rate.

This is a low-pollution zinc-alkaline battery with excellent practical performance such as leak resistance.

In addition, in the examples, as a method of adding additional elements,
Although the method of adding the elements to the molten zinc ingot was adopted, when adding In or Ba, which easily forms into amalgam, it is also possible to dissolve the additional elements in advance and add them simultaneously with hydration. In addition, when adding In, which has a smaller ionization tendency than zinc, for example, in a solution of indium chloride, Z
It is also possible to precipitate on the surface of the zinc alloy and alloy it by a substitution reaction with n, and either method can obtain the same effect as the present invention and is not included in the embodiments of the present invention. Ru.

In addition, in the example, a battery using a 1.0% by weight zinc hydrate negative electrode was described, but if very strict storage performance or leakage resistance is required, the upper limit is about 3% by weight, and 1.0% by weight is used. In some cases, it may be appropriate to apply a freezing rate of 0.0 weight - or more, and conversely, in air batteries equipped with an exhaust system or sealed zinc-alkaline batteries equipped with a hydrogen absorption mechanism, hydrogen gas Since the allowable amount of generation is relatively large, it is possible to carry out the process with a freezing rate of less than 1.0% by weight, and in some cases with anhydrous state.

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

[Brief explanation of the drawing]

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,
6...Silver oxide positive electrode.

Claims (1)

[Claims] 0.001 to 0.5% by weight of indium, 0.001 to 0.3% by weight of one or more of the group consisting of aluminum, calcium, and magnesium, and 0.001 to 0.001% of barium.
A zinc alkaline battery using a zinc alloy containing 0.5% by weight as a negative electrode active material.