JPH079806B2 - Zinc electrode for alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a zinc electrode for an alkaline storage battery, which uses zinc as an active material used in a nickel / zinc storage battery, a silver / zinc storage battery or the like.

(B) Conventional technology Zinc used as a negative electrode active material has the advantages that it has a large energy density per unit weight and is inexpensive,
The alkaline zinc storage battery having such a zinc electrode is highly expected as a battery having features such as high energy density and high operating voltage.

However, in this type of alkaline zinc storage battery, zinc acid ions generated by elution of zinc in the alkaline electrolyte during discharge are deposited on the surface of the zinc electrode in a dendritic manner during charging, and therefore, due to repeated charging and discharging, Electrodeposited zinc penetrates the separator and contacts the positive electrode to cause an internal short circuit in the battery, or the zinc electrode surface densifies and the battery discharge capacity decreases, resulting in a very short cycle life of the battery. .

As a conventional technique for dealing with this drawback and improving the cycle characteristics of the battery, for example, JP-A-59-189562 discloses that thallium oxide or hydroxide and indium oxide or hydroxide are used as zinc active materials. On the other hand, it is disclosed that the addition of a total amount of 1 to 15% by weight makes it possible to significantly improve the cycle characteristics. However, merely adding these cannot effectively prevent the growth of dendritic zinc, and the effect cannot be sufficiently exerted. This is because these additives are reduced and cover the metal zinc surface as the number of cycles progresses, but at the beginning of the charge / discharge cycle, these additives do not cover the metal zinc surface, and at this time the dendritic This is because once the metallic zinc that becomes the nucleus of zinc generation appears, the dendritic zinc growth cannot be effectively prevented even if the above additives are added as the number of cycles progresses. Further, the surface of the metallic zinc is covered with the additive only after the charge / discharge cycle is repeated several tens of times, and metallic zinc that has become a nucleus for the formation of dendritic zinc has already appeared at this point. Furthermore, the generation of dendritic zinc becomes particularly remarkable during rapid charging and overcharging.

(C) Problems to be Solved by the Invention The present invention has been made in view of the above problems, and suppresses generation of dendritic zinc from metal zinc particles at the initial stage of charge / discharge cycles in a zinc electrode, thereby improving cycle characteristics It is intended to provide an excellent alkaline storage battery.

(D) Means for Solving Problems The present invention is characterized in that, in a zinc electrode containing zinc oxide and metallic zinc as main active materials, the metallic zinc is covered with indium or indium oxide. .

(E) Action The electrode potential of the zinc electrode during rapid charging or overcharging shifts to the base side as compared with during normal charging, and the zincate ion is reduced to facilitate the reaction of electrodeposition on metallic zinc. That is, the electrode reaction at the zinc electrode during rapid charging or overcharging is a competitive reaction between a reaction in which zinc oxide is reduced and a reaction in which zincate ions are reduced and electrodeposited on metallic zinc. However, covering the surface of metallic zinc with indium or indium oxide increases the overvoltage of the electrodeposition reaction,
Only the reduction of zinc oxide will occur preferentially. Therefore, even if rapid charging or overcharging is performed at the beginning of the cycle, dendritic zinc growth from the zinc electrode can be effectively prevented, and internal short circuit in the battery can be suppressed.

(F) Example 3 500 g of zinc powder was added to 3 N aqueous sodium hydroxide solution 1 and immersed for 30 minutes to dissolve the zinc oxide film formed on the surface of the zinc powder. Next, add indium hydroxide 5.0 to this solution, stir for 10 minutes, then filter this solution, wash with 500 ml of pure water 10 times, and dry at 70 ° C to dry the metallic zinc surface-coated with indium. It was created.
The weight of the indium coating film at this time was 1% by weight with respect to metallic zinc. Next, 15 parts by weight of this metallic zinc, 100 parts by weight of zinc oxide, and 2 parts by weight of mercury oxide for increasing the hydrogen overvoltage are powder-mixed, and then water and polytetrafluoroethylene (PTFE) are added and kneaded, A paste was obtained and pressure-bonded onto a current collector to form a zinc electrode. By combining this zinc electrode of the present invention and a sintered nickel electrode, a cylindrical closed type nominal capacity
Ten cells of 700 mAh nickel-zinc battery A according to the present invention were prepared.

Further, as a comparative battery, a zinc electrode similar to the zinc electrode of the present invention was obtained except that 2 parts by weight of indium hydroxide was added using metallic zinc whose surface was not treated with indium. I made 10 cells.

Using these batteries, charge at 150% at a current of 1c and discharge at 1
100% with the current of c, the battery capacity is 500mAh (final voltage 1.0
A charging / discharging cycle test was conducted under the cycle condition in which the battery life was defined as V) or less. The results are shown in the figure.

From the results shown in the figure, it is understood that the battery A of the present invention is excellent. This is based on the fact that the surface of the metallic zinc particles, which serves as the nucleus for the generation of dendritic zinc, is covered with indium, so that the growth of dendritic zinc is effectively suppressed even if the number of cycles progresses.

The amount of the indium coating is based on the weight of metallic zinc.
It was found by the present inventor that 0.5 to 2.0% by weight is preferable.

In addition, although the examples in which the surface of the metallic zinc particles is covered with metallic indium have been disclosed, the same effect can be obtained by covering with indium oxide.

(G) Effect of the Invention Since the zinc electrode for an alkaline storage battery of the present invention can effectively suppress dendritic zinc growth by covering the surface of the metallic zinc particles to be added with indium or indium oxide,
The alkaline storage battery using such a zinc electrode is extremely excellent in cycle characteristics, and its industrial value is great.

[Brief description of drawings]

 The figure is a comparison diagram of battery cycle characteristics. A: battery of the present invention, B: comparative battery.

Claims (1)

[Claims] 1. A zinc electrode for an alkaline storage battery, wherein zinc oxide and zinc metal are used as main active materials, and the zinc metal is covered with indium or indium oxide.