JPS6084766A - Zinc alkaline battery - Google Patents

Abstract

PURPOSE:To increase discharge performance of zinc electrode in alkaline electrolyte by using zinc alloy prepared by adding Mg as negative active material. CONSTITUTION:A zinc alkaline battery is formed by using alkaline solution as electrolite, zinc as negative active material, and manganese dioxide, silver oxide, mercuric oxide, or oxygen as positive active material. In this battery, zinc alloy obtained by adding 0.02-0.5wt% of Mg is used in a negative electrode. By using this negative active material, utilization rate of zinc in high rate discharge is increased, and large capacity is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Field The present invention uses an alkaline aqueous solution as an electrolyte, zinc as a negative electrode active material, and manganese dioxide and silver oxide as a positive electrode active material.

This invention relates to the improvement of negative electrodes for zinc alkaline batteries that use mercury oxide, oxygen, etc.

The structure of conventional examples and their problems Zinc electrodes in alkaline electrolytes have been commonly used as negative electrodes in various alkaline battery systems in combination with various active materials such as the above-mentioned positive electrode active materials. There is. In order to suppress the self-depletion of zinc in alkaline electrolytes and the generation of hydrogen scum, zinc hydrate is commonly used, and it has also been proposed to alloy zinc with lead, cadmium, indium, etc. Using these methods, corrosion prevention technology that is sufficient for practical use has been established. On the other hand, in order to improve the discharge characteristics of zinc electrodes, methods have been adopted in which powdered zinc is molded or dispersed in a gel electrolyte to increase the reaction surface area. Usually, the particle size of the zinc powder used is 50 to 150 menonyu. As a discharge reaction product of zinc in an alkaline electrolyte, zinc hydroxide or zinc oxide is first generated on the surface of particles, which becomes zincate ions and is dissolved in the electrolyte. However, the problem that essentially needs to be improved is that the layer of reaction products formed on the surface of the zinc particles dissolves in the electrolyte, or even if it does not dissolve, the hydroxide ions in the electrolyte sufficiently diffuse through the layer. However, the discharge reaction proceeds smoothly when hydroxide ions easily reach the reaction surface of zinc, but as the discharge reaction progresses or the discharge reaction rate increases, the reaction products become difficult to dissolve and the reaction slows down. Since the product layer becomes dense and a so-called passivation film is formed on the zinc surface and inhibits the discharge reaction, there is a problem in that sufficient capacity cannot be obtained for large current discharge.

OBJECTS OF THE INVENTION The present invention relates to the discharge performance of a zinc electrode in an alkaline electrolyte,
In particular, the purpose is to improve performance in large current discharge.

Structure of the Invention The present invention uses an alkaline aqueous solution containing caustic potash, caustic acid, etc. as the main components for electrolysis, zinc as a negative electrode active material, and manganese dioxide and silver oxide as positive electrode active materials.

A zinc alloy to which magnesium is added is used for the negative electrode of a so-called zinc alkaline battery, which is equipped with mercury oxide, oxygen, etc., and preferably the content of magnesium in this zinc alloy is 0.02 to 0.5 wt%. It is characterized by this.

As shown in the examples below, the present invention has experimentally demonstrated that by using a zinc alloy to which magnesium is added for the negative electrode, it is possible to increase the discharge utilization rate of zinc in a large current discharge and obtain a large capacity. It has been made clear. Although the mechanism of its action is not fully understood, magnesium, which is contained as an alloy in the negative electrode zinc and has a potential lower than that of zinc, is discharged together with zinc, and the discharge products are the discharge products of zinc. This is thought to play a role in promoting the dissolution of zinc into the electrolytic solution, or by densifying the layer of undissolved discharge products, thereby alleviating the effect of passivating the zinc surface. As a result, a state in which hydroxide ions are abundantly supplied to the active surface of the zinc powder is ensured continuously from the initial stage of discharge until the zinc is completely exhausted, and the utilization rate of the zinc discharge reaction is increased. The effects of the present invention are particularly remarkable in high current discharge where the supply of hydroxide ions to the active surface of zinc dominates the discharge performance. Naturally, the effect will vary depending on the content of magnesium in the zinc alloy, and if it exceeds the appropriate amount, there will be damage such as oxidation of the magnesium component and generation of hydrogen gas due to reaction with the electrolyte during storage. From experiments shown in Examples below, it was confirmed that the appropriate content is 0.02 to 0.6 wt%, more preferably O, O5-0.25 wt%.

Description of Examples Various alloys were created by adding varying amounts of magnesium as an alloying element to zinc base metal with a purity of 99.997% and containing trace amounts of lead, cadmium, and iron as impurities, and melted at approximately 500"C. Blow out compressed air to make powder, and reduce to 50-15
Sorted by sieve into particle size range of 0 mesh, 10 of caustic potash
% concentration of aqueous solution, and while stirring, mercury with a weight ratio of 5 to 100 parts of zinc alloy powder was added dropwise, and the powder was washed with water and dried to prepare a hydrated zinc alloy powder.

Furthermore, as comparative examples, zinc alloys containing no added magnesium and zinc alloys containing calcium as an alloying element, which has a more base potential than zinc and magnesium, were prepared in the same manner as described above and made into permanent powders. The button-shaped silver oxide battery shown in the figure was manufactured using each of these phosphorized powders. In the figure, 1 is a sealing plate made of stainless steel, and the inner surface is coated with copper plating 1. 2 is a negative electrode made of a 40% caustic acid aqueous solution saturated with zinc oxide to form a carpoxymethyl cellulose gel, and zinc hydride powder is dispersed in this gel; 3 is a cellulose-based liquid retaining material. , 4 is a porous polypropylene ring separator, 6 is a pressure-molded electrode made by mixing graphite with silver oxide powder, 6' is a positive electrode link made of nickel-plated iron, and 6 is a stainless steel positive electrode can. , nickel plating 6' is applied to both the inside and outside surfaces. Reference numeral 7 denotes a polypropylene ring scraper, which seals between the positive electrode can 6 and the sealing plate 1' by bending the opening of the positive electrode can 6. All of the prototype batteries had a diameter of 11.
61171j, height 5.4 mice, and the negative electrode zinc hydrate (or alloy) powder weight was unified to 193 mg.

The following table shows the details of the prototype battery, the discharge test after storage at 60°C for one month (20°C, 61oΩ, 0.9V termination), and the results of measuring the amount of increase in total battery height due to storage.

As seen in the table, the most effective magnesium content is 0.1 to 0.25 wt%, and the range judged to be effective is 0.02 to Q, 5 wt%. In case i in the table, since the magnesium content was too high, expansion of the battery due to hydrogen gas generation and deterioration of battery performance were observed.

Furthermore, in cases j and k in which calcium was added, battery expansion and deterioration of battery performance were observed despite the addition amount matching the optimum content of magnesium, which had the opposite effect. The cause is unknown, but magnesium and calcium are more base than zinc and are alkaline earth metals in common, but calcium is even more base than magnesium, which is a factor that promotes hydrogen gas generation. It seems that it is. Even when 1 liter of calcium and magnesium were added at the same time, the calcium was unlikely to have an adverse effect and had the opposite effect. It is presumed that the effect of adding magnesium within an appropriate range is due to the reasons mentioned above.

Effects of the Invention As described above, by using a zinc alloy prepared by adding an appropriate amount of magnesium as an alloying element to zinc for the negative electrode of an alkaline battery, a battery with excellent discharge performance can be obtained.

[Brief explanation of drawings]

Claims (2)

[Claims] (1) A zinc-alkaline battery characterized in that a zinc alloy containing zinc as a main component and magnesium added as an alloying element is used as a negative electrode active material. (2) Magnesium content is 0.02 to 0.5wt
% of the zinc alloy according to claim 1.