JPH0441469B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention relates to the improvement of the negative electrode of a zinc-alkaline primary battery that uses zinc as the negative electrode active material, an alkaline aqueous solution as the electrolyte, and manganese dioxide, silver oxide, mercury oxide, oxygen, etc. as the positive electrode active material. be. Structure of conventional example and its problems A common problem with the above-mentioned 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 zinc hydroxide powder containing about 5 to 10% mercury added to zinc, and to suppress corrosion to a level that causes 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 in which an alloy powder in which lead, cadmium, indium, etc. are added to zinc is used to improve corrosion resistance and reduce the degree of corrosion. Although this is effective in suppressing corrosion, it has the opposite effect of deteriorating strong discharge performance by reducing the rate of corrosion. In these proposals, the cause of the deterioration of strong discharge performance when the rate of discharge is lowered is unclear, but the discharge products cover the surface of active zinc, and the zinc hydroxide ions necessary for the discharge reaction are This is thought to be because the degree of obstruction to the supply to the surface is greater than when the mercury content is high.
Establishing a zinc negative electrode with a low oxidation rate that combines corrosion resistance and strong discharge performance is considered to be an important issue in the future. Purpose of the Invention The present invention provides a zinc-alkaline primary battery in which the corrosion resistance of the negative electrode zinc and the corrosion rate are reduced without deteriorating the discharge performance, and the battery is low in pollution and has excellent performance such as discharge performance, storage performance, and leakage resistance. The purpose is to Structure of the Invention The present invention uses an alkaline aqueous solution containing caustic potash, caustic soda, etc. as the main components as an electrolyte, zinc as a negative electrode active material, and manganese dioxide, silver oxide, mercury oxide, oxygen, etc. as a positive electrode active material. At least one element of aluminum or magnesium and one or more elements selected from the group consisting of gallium, thallium, silver, and indium are added to the negative electrode of the so-called zinc-alkaline battery type, and the surface layer is formed with a concentration of 3% or less. This is characterized by the use of a zinc alloy that has been oxidized. The present invention first addresses the problem that when using zinc with a low oxidation rate, there is a tendency that discharge reaction products cover the active zinc surface, inhibiting the supply of hydroxide ions, and preventing the discharge reaction from proceeding smoothly at large currents. This problem is solved by alloying zinc with an element selected from aluminum and magnesium, and by alloying it with an element selected from gallium, thallium, silver, and indium. This increases the anti-corrosion properties of zinc and creates a zinc negative electrode with a low rate of corrosion. Although the effects of aluminum and magnesium mentioned above are clear in the examples described below, the mechanism of action is not fully understood. It is estimated that aluminum and magnesium, which are contained as an alloy in the negative electrode zinc and have a more base potential than zinc, are discharged together with zinc, and the discharge products promote the dissolution of the zinc discharge products into the electrolyte. In addition, by playing a role in alleviating the effect that the layer of undissolved discharge products becomes dense and the zinc surface becomes passivated, a state in which hydroxide ions are abundantly supplied to the active surface of zinc is created. It is thought that this will continue to be secured until it is exhausted, increasing the discharge utilization rate of zinc. or,
As mentioned earlier, adding an element selected from the group consisting of gallium, thallium, silver, and indium to zinc as an alloying element has the effect of increasing the hydrogen overvoltage of the zinc chloride alloy and improving its corrosion resistance. It is. Although there is no established theory regarding its mechanism of action, each of the above additive elements has a strong affinity with mercury, so the presence of these additive elements at grain boundaries causes the addition of mercury present at the grain boundaries and the zinc surface. It is thought that it has an affinity with the elements and is fixed at the grain boundaries, suppressing diffusion into the crystal grains. In addition, corrosion of zinc or zinc alloys generally progresses preferentially from the grain boundaries, but as mercury is fixed at the grain boundaries due to the above action, the hydrogen overvoltage at the grain boundaries increases, and corrosion from the grain boundaries increases. It is estimated that corrosion can be effectively suppressed and that corrosion prevention can be achieved with a small amount of mercury. As described above, the present invention has realized a zinc negative electrode that has a low rate of corrosion, good corrosion resistance, and excellent discharge performance due to the synergistic effect of adding an additive element that improves discharge performance and an additive element that prevents corrosion. This will be explained in detail below using examples. Description of Examples Various alloys are prepared by adding at least one element of aluminum or magnesium and one or more elements from the group consisting of gallium, thallium, silver, and indium to a zinc base metal with a purity of 99.997%. It was prepared, melted at about 500°C, pulverized by spraying with compressed air, and sieved into particle sizes ranging from 50 to 150 mesh. Next, the powder was put into a 10% caustic potassium aqueous solution, and a predetermined amount of mercury was added dropwise while stirring to form a solution. Then wash with water,
The mixture was replaced with acetone and dried to produce a zinc chloride alloy powder. Furthermore, as a comparative example, a zinc alloy containing only an element selected from gallium, thallium, silver, and indium, and a zinc alloy containing only an element selected from aluminum and magnesium were melt-injected and powdered. A powder was prepared using the same method. The button-shaped silver oxide battery shown in the figure was manufactured using these oxidized powders. In the figure, 1 is a stainless steel sealing plate, and the inner surface is copper plated 1'.
is applied. 2 is a zinc negative electrode made by gelling an electrolytic solution of a 40% concentration caustic potassium aqueous solution saturated with zinc oxide with carboxymethyl cellulose and dispersing aqueous powder in this gel, 3 is a cellulose-based liquid retaining material, and 4 is a A separator made of porous polypropylene, 5 a positive electrode made of a mixture of silver oxide and graphite and pressure molded, 5' a positive electrode ring made of iron with nickel plating, and 6 a positive electrode can made of stainless steel with nickel plating on the inner and outer surfaces. It has been subjected. 7 is a gasket made of polypropylene, which is sealed by bending the positive electrode can. The prototype battery has a diameter of 11.6
mm, height 5.4 mm, and the weight of the anode powder is
The dosage has been standardized to 193mg. We measured the details of the prototype battery, the results of the discharge test (20℃, 510Ω, 0.9V termination) after storing it at 60℃ for one month (average value of n = 3), and the change in total battery height due to storage. The results (average value of n=20) are shown in the following table. In addition, the amount of mercury added (corrosion rate) was 3% with respect to the zinc alloy powder.

[Table] As seen in this table, in all cases (g to r) to which the present invention was applied, the discharge performance was good and the battery expansion due to gas generation was small. On the other hand, among the conventional examples, when only the elements for corrosion prevention are added (a~
In case d), the expansion of the battery is small and gas generation is suppressed, but the duration under heavy load discharge of 510Ω load is shorter than that of the product of the present invention. Furthermore, when only elements for smoothing the discharge reaction of the negative electrode (e, f) are added, the corrosion protection is insufficient and the battery expands significantly, and furthermore, self-depletion during storage and discharge reaction due to built-in hydrogen gas occur. Due to inhibition, the discharge performance after storage is also significantly degraded. As mentioned above, in the conventional methods a to f, a water extraction rate of 3% is insufficient, and it is considered that it is necessary to further increase the water extraction rate in order to provide practicality. On the other hand, in the case of gr to r, a highly practical zinc-alkaline battery with a low water content of 3% or less and excellent storage stability and discharge performance has been obtained. The present invention complements the drawbacks of methods a to d and methods e and f, and solves them very effectively due to their synergistic effect. Effects of the Invention As described above, the present invention is extremely effective in reducing the water retention rate of negative electrode zinc and obtaining a low-pollution zinc-alkaline primary battery.

[Brief explanation of drawings]

The figure is a cross-sectional view of a button silver oxide battery manufactured to examine the effects of the present invention. DESCRIPTION OF SYMBOLS 1... Sealing plate, 2... Zinc negative electrode, 3... Liquid retaining material, 4... Separator, 5... Silver oxide positive electrode, 6...
...Positive electrode can, 5'...Positive electrode ring, 7...Gasket.

Claims (1)

[Claims] 1 The main component is zinc, at least one element of aluminum or magnesium, and gallium,
A zinc-alkaline primary battery characterized by using, as a negative electrode active material, a zinc alloy which has been added with one or more elements selected from the group consisting of thallium, silver, and indium and whose surface has become grainy with a graining rate of 3% or less. .