JPH079807B2 - 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 the 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 thallium or thallium 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, if the surface of metallic zinc is covered with thallium or thallium oxide, the overvoltage of the electrodeposition reaction increases, and only reduction of zinc oxide occurs 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 3N aqueous sodium hydroxide solution 1, immersed for 30 minutes, filtered, and washed with 500 ml of pure water 10 times. This zinc powder was added to 500 ml of 2.0% aqueous solution of thallium nitrate, stirred, filtered, washed with water, and heated to 70 ° C.
And dried to prepare metallic zinc whose surface was covered with thallium. The weight of the thallium coating 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 on a current collector to form a zinc electrode. By combining this zinc electrode of the present invention and a sintered nickel electrode, a nickel-zinc battery A of the present invention having a nominal capacity of 700 mAh in a cylindrical sealed type.
10 cells were created.

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 thallium oxide was used using metallic zinc whose surface was not treated with thallium. I made a cell.

Next, using these batteries, charging is performed at a current of 1c for 150% and discharging is performed at a current of 1c for 100%, and when the battery capacity reaches 500 mAh (end voltage 1.0 V) or less, the cycle condition is defined as the battery life. Then, a charge / discharge cycle test was performed. 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 is the nucleus for the generation of dendritic zinc, is covered with thallium, so that the growth of dendritic zinc is effectively suppressed even if the number of cycles is increased.

The amount of thallium coating was 0.
It was confirmed by experiments that it is preferable to set the content to 5 to 2.0% by weight.

Further, in the examples, the one in which the surface of the metallic zinc particles is covered with metallic thallium is disclosed, but the same effect can be obtained by covering with thallium oxide.

(G) Effect of the Invention The zinc electrode for alkaline storage batteries of the present invention can effectively suppress dendritic zinc growth by covering the surface of the metal zinc particles to be added with thallium or thallium oxide. The alkaline storage battery used is extremely excellent in cycle characteristics and has a great industrial value.

[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 metallic zinc are used as main active materials, and the metallic zinc is covered with thallium or thallium oxide.