JPH0679481B2 - Alkaline zinc storage battery - Google Patents

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.

(B) Prior art Zinc as a negative electrode active material has the advantage 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 solution during discharge to become zincate ions, and during charging, the zinc Since acid ions are electrodeposited on the surface of the zinc electrode in a dendritic or spongy fashion, repeated charging and discharging causes the electrodeposited zinc to penetrate the separator and come into contact with the counter electrode to cause an internal short circuit, resulting in a short cycle life. .

In order to improve this cycle life, the amount of electrolyte is regulated to prevent the diffusion of zincate ions, and a plurality of organic separators or inorganic separators are piled up, or the integrated product is used to improve the cycle life. Considerably improved. However, zinc, which has been once dissolved as zincate ions during discharge, hardly deposits at the original position during charging, and therefore, when the charge and discharge are further repeated, the electrode plate of the zinc electrode becomes noticeably deformed, resulting in a decrease in capacity. In addition, it could not withstand long-term charge and discharge.

The area where the electrode plate deformation of the zinc electrode is most remarkable is the electrode plate periphery,
This is due to the edge effect and also to the fact that the electrolytic solution easily accumulates on the periphery of the electrode plate. Generally, in a battery composed of a positive electrode, a separator and a negative electrode, a pressure is applied between the positive electrode and the negative electrode, and the electrolytic solution contained in the electrode and the separator tends to be pushed out to the peripheral portion of the electrode.
For this reason, an electrolytic solution that is basically unnecessary for the battery reaction also exists in the peripheral portion of the zinc electrode, and the elution of the zinc active material into the electrolytic solution is promoted.

Although various methods have been proposed for this problem,
As one of them, there is a proposal that the periphery of the zinc electrode is coated with an alkali-resistant synthetic resin or rubber so as to have water repellency. The method according to this proposal enhances the water repellency at the periphery of the zinc electrode and suppresses the above problems, thus contributing to the improvement of the cycle life.

However, this method also cannot endure a longer-term charge / discharge cycle. The reason for this is that the adhesion between the zinc active material and the alkali-resistant synthetic resin or rubber deteriorates, so that the two gradually begin to separate and the electrolyte begins to penetrate between them, resulting in the elution of the zinc active material. It is thought that it cannot be suppressed.

(C) Object of the invention The present invention has been made in view of the above point, and changes in the binder concentration in the central part of the zinc electrode, focusing on the fact that the electrode plate deformation of the zinc electrode starts from the peripheral part. It is intended to provide an alkaline zinc storage battery which can further reduce the electrode plate deformation of the zinc electrode and withstand a longer cycle life.

(D) Structure of the Invention In order to achieve the above object, the alkaline zinc storage battery according to the present invention contains a binder composed mainly of metallic zinc and zinc oxide, and composed of an alkali-resistant and water-repellent fibrous synthetic resin. In addition, the zinc electrode is configured so that the concentration of the binder in the peripheral portion of the electrode plate is higher than that in the central portion of the electrode plate.

(E) Example Hereinafter, one example of the present invention will be described to refer to comparison with a comparative example.

〔Example〕

80% by weight of zinc oxide powder, 10% by weight of metallic zinc powder, 5% by weight of cadmium oxide as an additive, and alkali resistant and water-repellent fibrous fluororesin powder (PTFE) as a binder.
After adding water to the mixed powder of 5% by weight and kneading,
A first sheet having a length of 45 mm and a width of 36 mm was prepared by pressing with a roller. By the above kneading, the fluororesin is made into fibers.

Fluorine resin powder in this first sheet was set to 15% by weight, and the amount of zinc oxide powder was reduced by an increase amount of, and in the same manner as in the first sheet, a vertical bar with a width of 4 mm and a horizontal bar with a width of 5 mm were formed into a frame shape. Two sheets were created.

The first sheet is placed in the center and the second sheet is placed on the periphery of both sides of a current collector made of copper or the like having a length of 50 mm and a width of 40 mm. Created.

A rectangular nickel-zinc storage battery (A) was prepared by combining the zinc electrode thus obtained with a known sintered nickel electrode. FIG. 1 is a front view of the zinc electrode, wherein (1) is a zinc electrode, and has a central first sheet (2) and a peripheral second sheet (3). (4) is a lead portion provided on the current collector.

[Comparative Example 1] For comparison, a sheet having the same composition ratio as that of the first sheet of the example and having a size corresponding to the size of the current collector of the example was prepared, and the sheet having the same size as that of the example was prepared. Both sides of the current collector were pressure-molded and dried to prepare a zinc electrode. Comparative battery (B) which is the same as the embodiment except that this zinc electrode is used.
It was created.

[Comparative Example 2] The peripheral portion of the zinc electrode obtained in Comparative Example 1, that is, the second electrode of Example.
A comparative battery which is the same as that of the example except that a zinc electrode prepared by applying a fluororesin dispersion (60% by weight) 5 times to a position corresponding to the sheet (3) and then drying the same ( C) was created.

[Comparison]

FIG. 2 shows a storage battery (A) and a comparative battery (B) according to the present invention.
It is a cycle characteristic diagram of (C), the initial capacity of the storage battery is 10
Shown as 0%. The cycle condition is that the battery is charged at 150 mA for 5 hours, then discharged at 150 mA and stopped when the battery voltage reaches 1.2 V. As is clear from this figure, it is understood that the storage battery (A) according to the present invention has improved cycle life as compared with the comparative batteries (B) and (C).

The reason for this is that in the comparative batteries (B) and (C), the zinc active material cannot be suppressed from eluting into the electrolytic solution, the electrode plate of the zinc electrode is deformed, and the capacity is decreased. In the storage battery (A) according to the above, the fibrous binders are entangled with each other to form a strong skeleton, and since the concentration of the binder in the periphery of the electrode plate of the zinc electrode is higher than that in the central part of the electrode plate, The zinc active material in the peripheral portion of the plate is firmly held in the mesh of fibers,
Further, the high concentration of the binder contained in the peripheral portion of the electrode plate increases the water repellency of the peripheral portion of the electrode plate and makes it difficult for excess electrolytic solution to exist in the peripheral portion of the electrode plate. Therefore, it is considered that the cycle life of the storage battery (A) according to the example is significantly improved.

In the examples, a fluororesin is used as the synthetic resin having alkali resistance and water repellency, which is fiberized, but a dispersion liquid of fiberized polyethylene fiber, polypropylene fiber, nylon fiber or the like can be used. In the embodiment, the width of the second sheet is set to 1/10 of the electrode plate size, but it may be set to 1/20 to 1/5 depending on the electrode plate shape. Further, the present invention is not limited to the square electrode plate. However, it is obvious that it can also be applied to spiral electrodes.

(F) Effect of the Invention As described above, the present invention contains a binder composed mainly of metallic zinc and zinc oxide, and made of a synthetic resin in the form of fibers, which is alkali-resistant and water-repellent. Since there is a zinc electrode whose content concentration in the periphery of the electrode plate is higher than that in the center of the electrode plate, there is a fibrous binder having a higher content concentration in the periphery of the electrode plate of the zinc electrode than in the center of the electrode plate. Therefore, the zinc active material in the peripheral portion of the electrode plate is more firmly trapped than in the central portion of the electrode plate, and the elution into the electrolytic solution is suppressed. In addition, since the content concentration of the water-repellent binder in the peripheral portion of the electrode plate is high, the electrolyte solution is reduced in the peripheral portion of the electrode plate due to the water repellency, so that the elution of the zinc active material is suppressed. It is possible to provide an alkaline zinc storage battery that can withstand a longer cycle life by suppressing electrode plate deformation in the electrode plate peripheral portion.

[Brief description of drawings]

FIG. 1 is a front view of a zinc electrode according to an embodiment of the present invention, and FIG. 2 is a cycle characteristic diagram of a storage battery according to the embodiment and a comparative battery.

Claims (1)

[Claims] 1. A binder containing, as a main component, metallic zinc and zinc oxide, a synthetic resin having alkali resistance and water repellency and made into fibers, and the concentration of the binder in the periphery of the electrode plate is An alkaline zinc storage battery having a zinc electrode having a concentration higher than that of the central portion of the electrode plate.