JPH071733Y2 - Zinc electrode for alkaline zinc storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is directed to a zinc electrode for an alkaline zinc storage battery, such as a nickel-zinc storage battery or a silver-zinc storage battery, which uses zinc oxide or metallic zinc as a cathode active material. It is about.

<Prior Art> Zinc used as a cathode active material of a zinc electrode in an alkaline zinc storage battery as described above has advantages such as high energy density per unit weight and low cost, but zinc is not The zincate ion Zn (0H) ₄ ^2- eluting from the alkaline electrolyte is deposited and grows as dendrites or spongy crystals (hereinafter referred to as "dendrites") on the zinc electrode surface during charging. When charge and discharge are repeated, the electrodeposited zinc penetrates the separator and contacts the counter electrode to cause an internal short circuit, which disadvantageously shortens the cycle life of the battery.

In order to eliminate the above-mentioned inconveniences caused by electrodeposited zinc and improve the cycle life of the zinc electrode and the battery, the amount of electrolytic solution in the battery is regulated to a level where there is substantially no zinc oxide. Suppresses the growth of zinc dendrites that prevent the diffusion of ions (for example, disclosed in Japanese Patent Publication No. 56-19710), and stacks or integrates a plurality of organic separators or inorganic separators. It has been proposed to increase the strength of the separator by using one as a battery separator, and such a structure can be expected to significantly improve the cycle life.

<Problems to be solved by the device> However, zinc that is eluted as zincate ions during discharge hardly deposits at the original position during charging, and the electrode plate of the zinc electrode is not deformed by repeated charging and discharging. It will be noticeable. Therefore, even when the above-mentioned configuration is adopted, there is a problem that the capacity of the zinc electrode after a long-term cycle is greatly reduced, and it becomes impossible to endure long-term charge / discharge.

Such electrode plate deformation is most remarkable at the periphery of the electrode plate.
This is because an electric current easily flows to the peripheral edge of the electrode plate due to the so-called edge effect, and excess electrolytic solution easily accumulates on the peripheral edge of the electrode plate.Therefore, the amount of zinc eluted during discharging and the amount of electrodeposited zinc during charging are large. Due to. Further, since the amount of eluted zinc and the amount of electrodeposited zinc are large in this way, the growth of zinc dendrites in the peripheral portion of the electrode plate is larger than in other portions,
There is also a problem that zinc dendrites grown along the outer circumference of the separator come into contact with the peripheral edge of the counter electrode to cause an internal short circuit. In particular, in the case of a cylindrical battery having a structure in which a power generation element formed by winding an anode and a cathode through a separator is housed in a battery can, the central portion of the power generation element of the electrolyte solution contained in the electrode and the separator. The electrolytic solution tends to be present in a large amount in the peripheral portion of the electrode plate due to insufficient diffusion into the electrode plate, and the degree of the above-mentioned problem is correspondingly large.

<Means for Solving Problems> The inventors of the present invention have studied to improve the cycle life of the zinc electrode and the battery by suppressing the deformation in the zinc electrode peripheral portion and the growth of zinc dendrite as described above. As a result of consideration, they realized that the intended purpose could be achieved by using the following means, and completed the present invention.

That is, the zinc electrode for an alkaline zinc storage battery of the present invention has an active material containing at least one of zinc oxide and metallic zinc as a main component attached to a current collector, and at least a part of a peripheral portion of the current collector is burned. The gist is that it is covered with a bonded fluororesin.

<Function> Like the above-mentioned means, by sintering the fluorocarbon resin, which is an electrical insulator and is rich in water repellency, and firmly covering the peripheral portion of the current collector, the peripheral portion of the zinc electrode is extended over a long cycle. The edge effect is eliminated, and the elution of the zinc active material into the electrolytic solution at the peripheral portion is suppressed.

<Embodiment> An embodiment of the present invention will be described below with reference to the accompanying drawings.

5 parts by weight of mercury oxide as an additive was added to 45 parts by weight of zinc oxide powder and 45 parts by weight of zinc powder, and after thoroughly mixing them, 5 parts by weight of polytetrafluoroethylene (PTFE) dispersion was added, and then This was diluted with water and kneaded to prepare a paste-like active material, and this paste-like active material was made into a calendar sheet having a predetermined thickness with a rolling roller.

On the other hand, the surface of a punching plate having a large number of openings formed in an iron plate was plated with nickel and cut into a predetermined size to obtain a cathode current collector. Apply unsintered fluororesin dispersion such as PTFE dispersion or FEP dispersion to the peripheral portion of this cathode current collector, and after applying at a temperature of 60 to 80 ° C.
Water was removed from the dispersion by drying for 10 hours.
Then, the cathode current collector having the unsintered fluororesin layer formed on the peripheral portion in this manner is heat-treated in a mixed gas atmosphere of nitrogen-hydrogen (320 ° C. for 30 minutes in the case of PTFE coating, 28 in the case of FEP).
(0 ° C. for 30 minutes) to transform the unsintered fluororesin into a sintered fluororesin to form a strong sintered fluororesin coating on the peripheral edge of the cathode current collector. The calendered sheet obtained as described above is attached to both surfaces of the thus-formed current collector treated with the fluorocarbon resin coating, and then pressure-bonded with a pressure-bonding roller, as shown in FIGS. The zinc electrode according to the present invention shown in FIG. In these drawings, 1 is a cathode current collector, 2
Is a sintered fluororesin coating, and 3 is a zinc active material formed by pressing a calendar sheet onto the cathode current collector 1.

Then, the zinc electrode 4 formed as described above is combined with the known sintered nickel electrode 6 via the separator 5,
An alkaline zinc storage battery (product A of the present invention) according to the present invention as shown in the figure was produced. In the figure, 7 to 10 are battery cases,
The battery case lid, cathode terminal, and anode terminal are shown.

Also, as shown in FIG. 4, a conventional zinc electrode made by pressing calender sheet-shaped zinc active material 3 on both surfaces of the same cathode current collector 1 except that the peripheral portion is not treated with sintered fluororesin is used. A conventional alkaline zinc storage battery (conventional product B) was manufactured in the same manner except that it was used.

A cycle change in battery capacity (%) was examined when a series of charge and discharge cycles were repeated, in which the above two alkaline zinc batteries were charged at 150 mA for 6 hours and then discharged until the 150 mA battery voltage became 1.0 V. The results are as shown in Fig. 3. For example, when the battery life is 50% or less of the initial capacity, the cycle life of the device A is significantly higher than that of the conventional product B. It turns out to be excellent.

The reason for this is as follows. That is, in the case of the conventional product B, in addition to the state in which the excess electrolytic solution is likely to exist at the zinc electrode peripheral portion, the dissolution reaction of zinc as the active material is more likely to occur in the zinc electrode peripheral portion than in the zinc electrode central portion, Since the electric current in the peripheral portion of the cathode current collector easily flows due to the edge effect, the deformation of the peripheral portion of the cathode in the charge / discharge cycle is large, and the dendrite of zinc grows from the peripheral portion of the cathode as the cycle progresses, This is likely to come into contact with the nickel electrode and cause an internal short circuit, which is one of the factors that significantly deteriorate the battery characteristics. On the other hand, in the product A of the present invention, since the peripheral portion of the cathode current collector is firmly coated with the sintered fluororesin, the sintered fluororesin will not be removed even if excess electrolyte is present in the peripheral portion of the zinc electrode. Since it is rich in water repellency and is an electric insulator, the edge effect is suppressed over a long period of time, and substantially no current flows at the periphery of the zinc electrode, and the dissolution reaction of zinc is also suppressed. Therefore, it is considered that the deformation of the zinc electrode peripheral edge portion and the growth of zinc dendrites were prevented, and as a result, excellent cycle characteristics were obtained.

It is possible to form the sintered fluororesin so as to cover the zinc electrode surface, that is, the peripheral edge of the zinc active material layer surface, but it is necessary to apply the unsintered fluororesin to the zinc electrode surface and then sinter it. However, there is a possibility that the temperature of the zinc active material may change during sintering and the zinc active material may be deteriorated. It is also possible to use unsintered fluororesin, but the coating strength is lower than that of sintered fluororesin, and the fluororesin dispersion is provided with a surfactant, so that the surfactant may adhere to the coating. Since the water repellency becomes small, a sufficient effect cannot be obtained.

<Effect of device> According to the zinc electrode for alkaline zinc storage battery of the present invention configured as described above, it is possible to effectively prevent deformation of the peripheral portion of the zinc electrode and also prevent growth of dendrite of zinc from the peripheral portion. It is possible to provide a zinc electrode that can withstand a longer-term charge / discharge cycle, and it is possible to extend the life of the alkaline zinc storage battery.

[Brief description of drawings]

1 (A) is a partial sectional view showing an embodiment of the present invention, FIG. 1 (B) is a sectional view taken along the line II of FIG. 1 (A), and FIG. FIG. 4 is a sectional view showing an alkaline zinc storage battery, FIG. 3 is a graph showing cycle characteristics of alkaline zinc storage batteries using the embodiment and the conventional example, and FIG. 4 is a partial sectional view showing the conventional example. 1 ... Cathode current collector, 2 ... Sintered fluororesin coating, 3 ...
Zinc active material, 4 ... Zinc electrode.

Claims (1)

[Scope of utility model registration request] 1. An active material containing at least one of zinc oxide and metallic zinc as a main component is attached to a current collector, and at least a part of a peripheral portion of the current collector is covered with a sintered fluororesin. A zinc electrode for an alkaline zinc storage battery, which is characterized in that