JPH0927341A - Electrolyte for alkaline zinc storage battery and alkaline zinc storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline zinc storage battery with a long cycle life without disadvantages of the shape change of an electrode or the growth of a dendrite by retarding elution of zinc during discharging and provide an electrolyte using in this storage battery. SOLUTION: An electrolyte for an alkaline zinc storage battery contains potassium fluoride as an alkali metal fluoride, and also can contain an alkali metal hydroxide. The alkaline zinc storage batter is constituted by facing a zinc negative electrode 1 containing zinc and a positive electrode 2 made of a material having a noble electrode potential than zinc in an alkaline solution through a separating part 2. The zinc negative electrode 1, the positive electrode 2, and the separating part 3 are electrically, connected through the electrolyte for the alkaline zinc storage battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline zinc storage battery and an electrolytic solution used for the same, and more specifically, it uses zinc as a negative electrode active material, nickel hydroxide, silver oxide, manganese dioxide as a positive electrode active material, and the like as an electrolytic solution. The present invention relates to an alkaline zinc storage battery using an alkaline solution and an electrolytic solution used therefor.

[0002]

2. Description of the Related Art In recent years, the demand for high energy density storage batteries has been increasing as mobile devices have become smaller and lighter. Zinc as the negative electrode active material of such a storage battery has the advantages of high energy density and output density per unit weight, low cost, and excellent safety.

[0003]

However, zinc has a drawback that its cycle life is short because it deteriorates rapidly with repeated charging and discharging. This is because zincate, which is a discharge product of zinc, has a property of being easily dissolved in an aqueous solution of a concentrated alkali metal hydroxide which is an electrolytic solution. Therefore, when the storage battery is discharged, zinc is likely to be eluted at the negative electrode, but the original shape is not restored during zinc deposition during charging, the porosity of the zinc electrode is gradually lost, and zinc utilization efficiency is reduced. Markedly reduced. Another problem is that when zincate ions are reduced to zinc during charging, the deposited zinc grows as dendrites, causing a short circuit between the positive and negative electrodes.

Therefore, attempts have been made to reduce the amount of the electrolytic solution as much as possible in order to suppress the elution of zinc and to control the electrode reaction by adding various metals and metal oxides to the zinc electrode and the electrolytic solution. Has not achieved sufficient results.

Therefore, a technical problem of the present invention is to provide an alkaline zinc storage battery having a long cycle life and an electrolytic solution used therefor, which is free from the problem of electrode shape change and dendrite growth by suppressing the elution of zinc during discharge. To provide.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and instead of an aqueous solution of an alkali metal hydroxide, which is a conventional electrolytic solution, an aqueous solution of an alkali metal fluoride, such as a fluorine solution, is used. A storage battery having excellent charge-discharge cycle characteristics of zinc is provided by using an aqueous solution of potassium fluoride (KF).

That is, according to the present invention, there is obtained an electrolytic solution for an alkaline zinc storage battery, which is an aqueous solution containing an alkali metal fluoride.

Further, according to the present invention, in the electrolytic solution, there is obtained an electrolytic solution for an alkaline zinc storage battery, wherein the alkali metal fluoride is potassium fluoride.

Further, according to the present invention, there is obtained an electrolytic solution for an alkaline zinc storage battery, which is characterized in that an alkaline metal hydroxide is added to the electrolytic solution.

Further, according to the present invention, a zinc negative electrode containing zinc and a positive electrode made of a substance having an electrode potential nobler than zinc in an alkaline solution are opposed to each other via a partition wall,
An alkaline zinc storage battery is obtained in which the zinc negative electrode, the positive electrode, and the partition wall are electrically contacted via the electrolytic solution for the alkaline zinc storage battery.

[0011]

In the present invention, by using an aqueous solution of an alkali metal fluoride such as potassium fluoride as the electrolytic solution, the zinc discharge product is not a zincate ion soluble in the alkaline solution but an insoluble hydroxide. It becomes a compound containing zinc, zinc oxide or fluorine. Therefore, it is considered that the electrode morphology does not change and the cycle life of zinc is improved.

Further, in the present invention, since the utilization efficiency of the positive electrode is low only with potassium fluoride, an alkali metal hydroxide such as potassium hydroxide is added in an amount of 1 to 10 g / 1. As the amount of potassium hydroxide added increases, the amount of soluble zincate ions produced increases. Therefore, it is desirable to use the minimum amount of potassium hydroxide necessary for not lowering the utilization efficiency of nickel.

[0013]

Embodiments of the present invention will be described below.

FIG. 1 is a sectional view showing a schematic structure of a nickel-zinc storage battery according to an embodiment of the present invention. Referring to FIG. 1, a nickel-zinc storage battery 10 includes a zinc negative electrode 1 and a sintered nickel electrode 2 forming a positive electrode, which are opposed to each other through a separator 3 and inserted into a negative electrode terminal 4 in a container shape. A positive electrode terminal 5 is provided on the nickel electrode 2 side, and an insulator 6 is provided between the inner wall of the negative electrode terminal 4 and the sintered nickel electrode 2.

As the electrolytic solution of the zinc storage battery according to the embodiment of the present invention, a solution obtained by adding potassium hydroxide (KOH) to an aqueous solution of potassium fluoride (KF) was used. As a result of investigating the solubility of zinc oxide in these electrolytes, it was found that zinc oxide was hardly dissolved. The cycle characteristics were also good, and the lower the potassium hydroxide concentration, the better the cycle characteristics. Furthermore, the higher the potassium hydroxide concentration, the higher the utilization efficiency of the sintered nickel electrode.

[0016]

Embodiments of the present invention will be described below.

A nickel-zinc storage battery having the same structure as that shown in FIG. 1 was constructed. Here, the zinc negative electrode 1 was formed into a sheet after diluting a mixed powder of 90% by weight of zinc oxide powder, 5% by weight of mercury oxide powder and 5% by weight of polytetrafluoroethylene dispersion liquid as a binder with water and kneading. The obtained product was pressed onto both sides of a current collector made of copper. As the sintered nickel electrode 2, a known nickel grid for a substrate was used, in which nickel powder was sintered and impregnated with a positive electrode active material. As the separator 3, an alkali resistant porous plate made of polypropylene was used. The electrolytic solution is used by impregnating the positive and negative electrodes 1 and 2 and the separator 3 respectively. Moreover, polytetrafluoroethylene was used as the insulator 6.

Next, as an electrolytic solution for a nickel-zinc storage battery according to an embodiment of the present invention, as shown in Table 1 below, 350 g was used.
Solution of potassium hydroxide (KOH) added to an aqueous solution of potassium fluoride (KF) in an amount of 0 to 10 g / 1 (Sample N
o. 1 to 5) were used. As a comparative example, 400 g /
An aqueous solution of potassium monohydroxide was used as an electrolytic solution (Sample No. 6).

[0019]

[Table 1]

As shown in Table 1 above, the solubility of zinc oxide in these electrolytes was determined by the comparative sample No. In the case of Sample No. 6, dissolution of 30 g / 1 was observed by heating, whereas Sample No. In the case of 1, it hardly dissolved.

In order to confirm the characteristics of these electrolytic solutions,
Using metallic zinc as the working electrode and platinum as the counter electrode, the sample No. 1 of the example and the sample no. When constant current oxidation was performed in each of the electrolyte solutions of Example 6, the weight of the zinc electrode increased in the electrolyte solution of Example 1, while in the electrolyte solution of Comparative Example 1, the amount calculated from the energization amount. Only the oxidative dissolution reaction of zinc was occurring.

FIG. 2 shows the sample No. of the electrolytic solution. It is a comparison figure of the cycle characteristic when the battery of FIG. 1 is comprised using 1-6. The cycle condition is that the battery is charged at 100 mA for 4 hours and then discharged at a final voltage of 1.2 V at 150 mA.

As is apparent from FIG. 2, the sample No. of the electrolytic solution according to the embodiment of the present invention was used. By using 1-5,
Sample No. of Comparative Example 6 that the cycle characteristics are remarkably improved, and it is understood that the cycle characteristics are better as the concentration of potassium hydroxide is lower.

FIG. 3 shows the electrolyte sample No. 1 according to the embodiment of the present invention. It is a change figure of the utilization efficiency of the sintering type nickel electrode of a positive electrode with respect to the density | concentration of potassium hydroxide when 1-5 is used. As shown in FIG. 3, it can be seen that the higher the concentration of potassium hydroxide, the higher the utilization efficiency of nickel, and that it is desirable to add potassium hydroxide to some extent in order to prevent the reduction in utilization efficiency. The use efficiency of nickel in the electrolytic solution of Comparative Example 1 was 100%. However, in Comparative Example 1, the KOH concentration is high and the solubility of zinc oxide is large, which is not suitable.

[0025]

As described above, according to the present invention, by using an alkali metal fluoride that suppresses elution of zinc, for example, an alkaline aqueous solution containing potassium fluoride as an electrolytic solution in an alkaline zinc battery, cycle characteristics are improved. It is possible to provide an excellent alkaline zinc storage battery and an electrolytic solution used therein.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an alkaline zinc storage battery using an electrolytic solution according to an embodiment of the present invention.

FIG. 2 is a cycle characteristic diagram of an alkaline zinc storage battery using an electrolytic solution according to an example of the present invention and a comparative example.

FIG. 3 is a diagram showing utilization efficiency of a nickel positive electrode of an alkaline zinc storage battery according to an embodiment of the present invention. In addition, the utilization efficiency of the nickel positive electrode of the comparative electrolyte is also shown.

[Explanation of symbols]

 1 Zinc negative electrode 2 Nickel electrode 3 Separator 4 Negative electrode terminal 5 Positive electrode terminal 6 Insulator

Claims (4)

[Claims] 1. An electrolytic solution for an alkaline zinc storage battery, which is used as an electrolytic solution for an alkaline zinc storage battery and is an aqueous solution containing an alkali metal fluoride. 2. The electrolytic solution for an alkaline zinc storage battery according to claim 1, wherein the alkali metal fluoride is potassium fluoride. 3. The electrolyte solution for an alkaline zinc storage battery according to claim 1, further comprising an alkali metal hydroxide. 4. A zinc negative electrode containing zinc and a positive electrode made of a substance having an electrode potential nobler than zinc in an alkaline solution are opposed to each other via a partition wall portion to form the zinc negative electrode, the positive electrode, and the partition wall. An alkaline zinc storage battery, characterized in that the parts are brought into electrical contact with each other through the electrolytic solution for an alkaline zinc storage battery according to any one of claims 1 to 3.