JPH0687417B2 - Alkaline zinc storage battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alkaline zinc storage battery using zinc as a negative electrode active material such as a nickel-zinc storage battery and a silver-zinc storage battery.

Zinc as a negative electrode active material has the advantages that it has a large energy density per unit weight and is inexpensive, but on the other hand, zinc is eluted into the alkaline electrolyte during discharge to become zincate ions, and during charging, the zincate ions form the zinc electrode surface. In addition, since it is electrodeposited in the form of dendritic or sponge-like, when charging and discharging are repeated, the electrodeposited zinc penetrates the separator to come into contact with the counter electrode and causes an internal short circuit, which causes a short cycle life.

In order to improve the cycle life, it has been proposed to add various metals or oxides to the active material or the electrolytic solution. One of them is tin. Since tin has a high hydrogen overvoltage and is nobler than the oxidation-reduction potential of zinc, it not only suppresses the formation of dendrites of zinc, but also acts as a conductive material and there is no fear of pollution. Promising.

However, as a result of a long-term charging / discharging cycle, not only the zinc active material but also tin participates in the charging / discharging reaction and becomes highly densified and electrodeposited. As a result, the porosity of the zinc electrode was reduced, the effective area of the zinc electrode was gradually reduced, and it became difficult to diffuse the electrolytic solution into the electrode, which significantly reduced the discharge capacity of the alkaline zinc storage battery.

The present invention has been made in view of the above points, and is a zinc electrode containing zinc and zinc oxide as main components, and indium oxide or hydroxide is added in addition to tin oxide or hydroxide. By doing so, the defects of tin as an additive can be reduced, and the optimum ratio of the additive in the zinc electrode can be found to prolong the cycle life of the alkaline zinc storage battery.

Therefore, the present inventor created a large number of prototype batteries (a) to (h) in the following manner. That is, water was added to a mixed powder of zinc oxide powder X% by weight, zinc powder 10% by weight, tin oxide Y% by weight and indium oxide Z% by weight as an additive, and fluororesin powder 5% by weight as a binder, and kneading. After that, the sheet-shaped ones made by rollers are attached to both sides of a current collector made of copper or the like, pressure-molded and dried to form a zinc electrode.

A nickel-zinc storage battery (A) was assembled by combining the zinc electrode thus prepared and a known sintered nickel electrode. A cross-sectional view of this storage battery is shown in FIG. In this drawing,
(1) is a zinc electrode, (2) is a nickel electrode, (3) is a separator, (4) is a liquid retaining layer, (5) is a battery case, (6) is a battery case lid, and (7) and (8) are Positive and negative terminals.

Thus, zinc oxide powder X% by weight, tin oxide Y as an additive
The specific proportions of the total weight% and indium oxide Z weight% were set to the values shown in Table 1 for each of the prototype batteries (A) to (K). Table 1 also shows a comparative battery in which only 5% by weight of tin oxide was added as an additive.

These prototype batteries (a) to (h) and comparative battery (h)
5 were prepared for each of them, the cycle characteristics of each battery were tested, and the average value of each battery is shown in FIG. In this drawing, the horizontal axis is the weight% of tin oxide and indium oxide as additives, and the vertical axis is the number of cycles. As is clear from FIG. 2, all the prototype batteries (A) to (K) in which indium oxide was added in addition to tin oxide as an additive for the zinc electrode were improved in cycle characteristics of the comparative battery (H). .
In particular, the cycle characteristics of the prototype batteries (A) to (K) in which the total amount of tin oxide and indium oxide is 2 to 15% by weight are good.
In each of the trial electric devices shown in Table 1, the compounding ratio of tin oxide to indium oxide was set to 4. Regarding cycle conditions, after charging at 150 mA for 6 hours, discharging was stopped at 150 mA and the discharge was stopped when the battery voltage reached 1.0 V, and the cycle test was stopped when the discharge capacity reached 50% of the initial capacity.

In each of the prototype batteries (a) to (h), the compounding ratio of tin oxide to indium oxide was 4, but the zinc oxide powder X in the zinc electrode was 80% by weight, and tin oxide was used as an additive. Prototype batteries (X) to (X) were prepared in which the total weight% of indium oxide was 5% and the compounding ratio was changed as shown in Table 2.

Five prototype batteries (K) to (T) were prepared, and the cycle characteristics of each battery (the cycle conditions were the same as those described above) were tested. The average value of each battery is shown in FIG.
In this figure, the horizontal axis represents the compounding ratio (Y / Z) of the weight% of tin oxide to the weight% of indium oxide, and the vertical axis represents the number of cycles. As is clear from this drawing, the cycle characteristics are improved when the compounding ratio is from 9 times to 1/6 times, but if it deviates from this range, the cycle characteristics are not preferable.

Considering the reason for this, since indium oxide has a good wettability with the electrolytic solution, the electrolytic solution is uniformly held in the zinc electrode, which makes the electrodeposition of zinc uniform and increases the effective surface area of zinc. It is considered that this is for suppressing the densification of tin during charging. It is considered that these effects cannot be obtained when the amount of indium is small, that is, when the compounding ratio is larger than 9. Further, when the amount of indium is large, that is, when the compounding ratio is less than 1/4, the conductivity of indium is poor, so that the charge / discharge efficiency is reduced and the cycle characteristics are deteriorated, and the tin addition amount is sufficiently reduced to sufficiently improve the tin addition effect. It is thought that it is not exerting.

In the above prototype battery, oxides of tin and indium were used, but hydroxides may be used instead of oxides.

As described above, the present invention provides a zinc electrode containing zinc and zinc oxide as main components, the zinc electrode containing 2 to 15% by weight of an additive made of an oxide or hydroxide of tin and indium. Therefore, the additive effect of the additive can be enhanced and the cycle characteristics of the alkaline zinc storage battery can be improved as compared with the conventional comparative battery, which is of great industrial value.

[Brief description of drawings]

FIG. 1 is a sectional view of an alkaline zinc storage battery according to the present invention, FIG. 2 is a cycle characteristic comparison diagram of alkaline zinc storage batteries when the total weight% of tin oxide and indium oxide in the zinc electrode is changed, and FIG. 3 is tin oxide. FIG. 4 is a comparison diagram of cycle characteristics of alkaline zinc storage batteries in which the compounding ratios of In and In are different. (1) …… Zinc pole.

Claims (2)

[Claims] 1. An alkaline zinc storage battery comprising a zinc electrode containing zinc and zinc oxide as main components, the zinc electrode containing 2 to 15% by weight of an additive composed of an oxide or hydroxide of tin and indium. . 2. The alkaline zinc storage battery according to claim 1, wherein the compounding ratio of tin oxide or hydroxide to indium oxide or hydroxide is 1/6 to 10. .