JPS59186256A - Zinc negative electrode for alkali battery - Google Patents

Abstract

PURPOSE:To largely reduce the amalgamation rate of the zinc powder thereby to attain cost reduction and provide a battery substantially free from environmental nuisance, by using the mixture of amalgamated zinc powder, electrolyte soluble indium compound powder and powder of a water soluble high molecular compound serving as a gelling agent in which an alkali electrolyte is injected. CONSTITUTION:The gel negative electrode 5 is provided by injecting an alkali electrolyte in the mixture of amalgamated zinc powder, an indium compound such as indium oxide and indium hydroxide soluble in the electrolyte, and a water soluble high molecular compound serving as a gelling agent. And, for example, a water solution of 10mol/l of KOH free from ZnO is used as the electrolyte. The positive electrode 2, the negative electrode 5, the separator 3, and the electrolyte carrier for negative electrode 4 are impregnated with the electrolyte and no free electrolyte is allowed to be present. Since the indium hydroxide mixed in the negative electrode 5 is soluble in the alkali electrolyte, the indium ions are adsorbed to the surfaces of the particles of the amalgamated zinc powder and elevate the hydrogen overvoltage and thereby suppress the generation of hydrogen gas by self-discharge of the zinc electrode.

Description

[Detailed description of the invention] Regarding good.

Conventional Structures and Problems Generally, zinc negative electrodes for alkaline batteries are subject to severe corrosion and dissolution by the alkaline electrolyte of zinc, resulting in increased self-discharge due to hydrogen gas generation. As a measure to prevent this, it is necessary to maintain a high hydrogen overvoltage, and methods such as freezing with mercury or dissolving the electrolytic solution KZn○ near saturation have been adopted so far. This freezing rate is generally around 10%. Therefore, the cost is high, and -1 is not preferable from the viewpoint of safety. In particular, when discharged batteries are disposed of, there is a risk that the mercury in zinc will contaminate the environment and cause pollution problems.

Addition of nearly saturated ZnO to the electrolytic solution inhibits the discharge response of the zinc negative electrode, increases the viscosity of the electrolytic solution, lowers the electrical conductivity, and causes particularly poor rapid discharge characteristics. Become.

OBJECTS OF THE INVENTION The present invention reduces the risk of pollution caused by mercury, and provides an electrical structure using flexible and conventional frozen zinc electrodes. An alkaline electrolyte is injected into a mixture of an electrolyte-soluble indium compound such as indium oxide and a water-soluble polymer gelling agent to form a gel negative electrode.

Description of examples Hereinafter, the present invention will be explained with reference to examples thereof.

The drawing shows a button-shaped silver oxide battery according to an example. 1 is a nickel-plated iron container, 2 is a positive electrode made of a pressure-molded mixture of silver oxide, phosphorous graphite, and manganese dioxide in a weight ratio of 90 = 5:5, which is closely attached to container 1. .

Separator 3 consists of two layers: a polyethylene film graft-polymerized with methacrylic acid and a cellophane semipermeable membrane laminated together. 4 is a liquid-containing material on the negative electrode side, which is made of nylon nonwoven fabric. 5 is a mixture of zinc powder with a hydration rate of 2%, indium hydroxide in a ratio of 1 weight to frozen zinc powder, and crosslinked sodium polyacrylate powder in a ratio of 3 weight to frozen zinc powder, injecting the electrolytic solution described below. This is a gel negative electrode. 6 is a sealing plate that also serves as a negative electrode terminal, 7 is a nylon gasket, 8
is the positive current collecting ring.

A 10 mol/g KOH aqueous solution containing no ZnO was used as the electrolytic solution, and was absorbed and impregnated into the positive electrode, negative electrode, separator, and negative electrode liquid-containing material so that no free liquid remained.

The size of this battery is JIS designation 5R44 and the capacity is 1so.
It is mAh.

The above battery is referred to as A. For comparison, a battery with a configuration in which indium hydroxide is not added to the negative electrode, zinc powder with a freezing rate of 10 cm is used, and an electrolyte in which Zn○ is dissolved near saturation is applied is designated as B. .

Furthermore, zinc powder with a hydration rate of 2% was used without adding indium hydroxide, and the electrolyte was 10 mol/l without ZnO.
C is a battery using a KOH aqueous solution.

6oΩ when 50 of these battery cans are stored at 60℃ for 40 days.
The battery voltage when discharged is 1. A comparison with the discharge time until the discharge time decreased to o■ is shown in the following table.

The results in this table clearly show the differences in the negative electrode configuration conditions. Tamashi, Zn in electrolyte with conventional hydration rate of 10%
Battery B, which is saturated with O, has excellent leakage resistance but poor rapid discharge characteristics. This is because it is affected by the amount of ZxO in the electrolyte. In general, the discharge reaction of a zinc electrode involves the supply of OH- and the reaction product Z, as is clear from the formula %.
n (OH) 4− dissipation is dominant. For these reasons, in the case of battery B, adding ZnO to near saturation in the electrolytic solution increases the viscosity of the electrolytic solution, lowering the electrical conductivity and inhibiting rapid discharge.

Battery C has extremely poor leakage resistance. This is because at a hydration rate of 2%, the amount of mercury remaining on the surface of the zinc particles is small, making it impossible to maintain a sufficiently high hydrogen overvoltage in a stable state. In other words, the mercury on the surface of the zinc particles diffused to the grain boundaries of the zinc during storage, reducing the mercury concentration on the surface and lowering the hydrogen overvoltage, generating hydrogen gas and causing leakage. be. Although the rapid discharge characteristics of Battery C are better than Battery B, a small amount of gas is generated inside the battery immediately after prototype production, which deteriorates the balance of the electrolyte and the contact between zinc particles, so the discharge time is longer than that of Battery B. is soluble in an alkaline electrolyte, indium ions are adsorbed on the particle surface of the zinc hydride powder and act to increase the hydrogen overvoltage, suppressing hydrogen gas generation due to self-discharge of the zinc electrode.

However, when indium hydroxide or indium oxide is added to ice-free zinc powder, the hydrogen overvoltage increases due to adsorption of indium ions to the surface of the ice-free zinc particles, but this alone cannot completely suppress hydrogen gas generation. There is a problem that cannot be solved.

About 2% mercury is required on the surface of the zinc particles, and the synergistic effect between this and the adsorption of indium ions improves the stability during storage.

On the other hand, the rapid discharge characteristics of Battery A are superior to Battery C because of the stability of the zinc negative electrode in the electrolyte.

It should be noted that if the icing rate of the negative electrode is less than 2%, the mercury concentration on the surface of the zinc particles tends to become uneven, and if the hydration rate is 2% or more, the effect of suppressing hydrogen gas during storage tends not to change. Therefore, it can be said that a hydration rate of 2% is sufficient.

On the other hand, the cross-linked branched sodium polyacrylate used as a gelling agent has excellent alkali resistance, miscibility with zinc hydrate powder, absorption rate of electrolyte, and ability to maintain uniform dispersion of zinc particles when stored for a long period of time. Are better.

Linear sodium polyacrylate has a disadvantage that the ability to maintain uniform dispersion of the zinc particles is low, and the active material zinc aggregates after storage, reducing the reaction surface area. Furthermore, since the gel state obtained by injecting an electrolytic solution and forming a gel has strong stringiness and becomes difficult to handle, a cross-linked and branched type is preferable because this phenomenon is less likely to occur. There are various other natural polymer pastes, but they all have the disadvantage of poor alkali resistance and a decrease in viscosity during storage. As a result, the use of natural systems is not preferable because a problem arises in which the retention of uniform dispersion of zinc particles is significantly reduced.

As a soluble indium compound, indium hydroxide (
I n (OH,) s) and indium oxide (OH,) s)
203) Powders can be used and these have good miscibility with zinc hydrate powder and gelling agent powder.

In the examples, a button-type silver oxide battery was used as an example, but the present invention can also be applied as a gel zinc electrode for a secondary alkaline battery using other alkaline electrolytes.

Effects of the Invention As described above, according to the present invention, the hydration rate of zinc powder can be significantly reduced, resulting in cost reduction and 1. It is possible to reduce pollution.

[Brief explanation of the drawing]

The figure is a longitudinal cross-sectional view of a button-shaped silver oxide battery according to an example. 2...Positive electrode, 3...Separator, 4...
...Liquid-containing material, 5...Negative electrode.

Claims (1)

[Claims] A zinc negative electrode for alkaline batteries made by injecting alkaline electrolyte into a mixture of frozen zinc powder, electrolyte-soluble indium compound powder, and water-soluble polymer gelling agent powder.