JPS58137966A - Zinc electrode - Google Patents

Abstract

PURPOSE:To prevent any immobilization of a cadmium compound by means of an indium compound by mixing both the cadmium compound and the indium compound into a zinc active material. CONSTITUTION:After zinc oxide powder is sufficiently mixed with zinc metal powder, and cadmium oxide and indium hydroxide which are used as additives, a fluorine resin (PTFE) dispersion (60% concentration) and water are added to the mixture powder, and thus obtained mixture is kneaded into a paste. Next, the paste is applied to a porous metallic current-collecting member, and dried so as to make a zinc electrode. After that, a nickel-zinc storage battery (A) is constituted by using thus made zinc electrode. In the battery (A), a sintered nickel electrode is used as a positive electrode, and a member prepared by stacking together a cellophane and a porous nonwoven nylon fabric is used as a separator.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in zinc electrodes for alkaline zinc storage batteries, such as nickel-zinc batteries and wrought-zinc batteries.

In the seed battery, zinc as the negative electrode active material has the advantages of high energy density per unit weight and low cost, but has the following disadvantages. That is, zincate ions, which are the discharge products of the zinc electrode, are liberated in the electrolytic solution, and during charging, the metal zinc is electrodeposited in a dendritic or spongy form, and after repeated charging and discharging, the electrodeposited zinc is grows through the separator and contacts the opposite electrode, removing the internal short circuit. Zinc electrodes are usually made by adding a binder to the zinc active material, applying the kneaded paste to the core (current collector), and drying it. As a result, when charging and discharging are repeated, a difference in zinc concentration occurs between the surface of the zinc electrode and the inside of the zinc electrode, and the proportion of binder on the surface of the zinc electrode increases, resulting in a decrease in electrical conductivity and liquid impregnation. As a result, a reaction occurs inside the zinc electrode, causing damage and reducing battery capacity.

ξIf we consider in detail the cause of these phenomena, the zinc electrode undergoes a fertilizing reaction during discharge.

Zn + 20H-4ZnO+H20+ 2e , -
−−−■Zn + 4 QH−−* Zn(OH)i−
+ 21L" Formula 00 occurs as the main reaction, but the reaction of Formula 0 occurs simultaneously and dissolves in the electrolyte as zincate ions. These zincate ions are electrodeposited in a dendritic or spongy form during charging. Moreover, since zinc is dissolved as zincate ions, the zinc concentration on the surface of the zinc electrode decreases.

Therefore, it can be seen that the cycle characteristics of this type of battery can be improved by suppressing the elution of zincate ions generated during discharge into the electrolytic solution. In that ζ, A1EIIIi Takusei Domiu ^ Sumikin Monomono Tsubo 轡加 上 ζ4 has been proposed. According to this proposal, the cadmium compound in the zinc electrode forms metallic cadmium upon initial charging, and the electrical conductivity of this metallic cadmium is high (and if the active surface area of zinc is increased by the addition of cadmium, then the zinc active material is more active than K). This prevents melting and falling off, shrinkage, and crystallization, thereby improving the cycle life of alkaline zinc storage batteries.

However, according to subsequent research, cadmium compounds
It was found that as the cycle progressed, a passivation phenomenon was observed, and the passive film cadmium layer became resistive, degrading the battery performance.

The present invention was invented in view of the above points, and it is an object of the present invention to provide a zinc electrode in which a cadmium compound and an indium compound are mixed in a zinc active material. This prevents cadmium from becoming passivated.

An embodiment of the present invention will be described below.

Example 80% by weight of zinc oxide powder, 8% by weight of metal zinc powder, 5% by weight of cadmium oxide and 2% by weight of indium hydroxide as additives were thoroughly mixed, and this mixed powder was added with fluororesin (F).
5 parts by weight of TIFK) Despurdine 3 (concentration 6011) and 50 parts by weight of water are added, kneaded to form a paste, and this paste is applied to a porous metal current collector and dried to form a zinc electrode.

Next, a nickel-zinc storage battery (4) was prepared using this zinc electrode. A sintered nickel electrode was used as the anode, and a layer of cellophane and porous nylon nonwoven fabric was used as the separator.

For comparison, a zinc electrode was formed using only one type of cadmium oxide as an additive in the example, and this zinc electrode was used to construct a nickel-zinc storage battery (with other conditions being the same as in the example).
) was created. Further, a zinc electrode was formed using only one type of indium hydroxide as an additive in the example, and a nickel-zinc storage battery (C) was created using this zinc electrode under the same conditions as in the example.

The drawing is a comparison diagram of the cycle characteristics of these storage batteries, and the characteristics (^ to (C)) are the cycle characteristics of the storage batteries with the same symbols.The charging and discharging conditions were a storage battery with a capacity of 800 mAH at 150 mA for 76 hours. After charging, the battery is discharged at 150mm, and the discharge is stopped when the storage battery voltage reaches 1.0'VK.From this comparison diagram, it can be seen that the zinc electrode according to the present invention has a cadmium compound and an indium compound in the zinc electrode. It can be seen that the cycle characteristics of the storage battery using (8) are superior to those using only one of the additives in the zinc electrode (ONIC) and (ONIC).

The reason for this is thought to be the following points.

First, cadmium compounds are used as conductive materials in electrodes, and have a higher redox potential than zinc. Therefore, during charging, it is charged before zinc oxide and reduced to metal cadmium, and this metal cadmium acts as a conductive material for the electrode.

Second, cadmium and indium compounds have higher hydrogen overvoltage than zinc, so they prevent zinc from self-discharging.
Prevents hydrogen gas generation from zinc electrodes.

Fifth, the indium compound prevents the additive cadmium compound from becoming passivated, and during charging, indium is deposited in the metal lattice of zinc, which becomes the nucleus for the next zinc deposition.
Uniform zinc electrodeposition is achieved.

Fourthly, the indium compound has good affinity with the electrolyte, and since this indium compound is uniformly dispersed in the zinc electrode, the electrolyte can be easily diffused uniformly into the zinc electrode.
Electrodeposition of zinc on both sides becomes uniform and the effective area of zinc increases, improving discharge characteristics.

As described above, the present invention is a zinc electrode characterized by a mixture of a cadmium compound and an indium compound in a zinc active material. It can improve cycle life, which is its industrial value.

[Brief explanation of drawings]

The drawing is a comparison diagram of cycle characteristics of a zinc electrode according to the present invention and a nickel-zinc storage battery using a zinc electrode, which is a premise of the present invention.

Claims (1)

[Claims] (1) A zinc electrode characterized in that a cadmium compound and an indium compound are mixed in a zinc active material.