JPS58165250A - Alkali-zinc storage battery - Google Patents

Abstract

PURPOSE:To improve the repetition lifetime through charging and discharge and the efficiency thereof, by causing a zinc electrode to contain expanded graphite and by providing an electrolyte whose quantity is limited to such an extent that no free electrolyte exists. CONSTITUTION:Water is added to mixed powder comprising powder of zinc oxide, powder of metal zinc, cadmium oxide as an additive, expanded graphite and powder of fluorine resin as a binder. The mixture of the water and the mixed powder is kneaded and then made into a paste sheet. The sheet is put on both the sides of a current collector of copper or the like and press-formed and dried, thereby providing a zinc electrode. The zinc electrode is combined with a sintered nickel electrode to manufacture a nickel-zinc battery in which the quantity of an alkaline electrolyte is limited to such an extent that no free electrolyte exists. The battery is excellent is charging and discharge repetition properties and in capacity because the porosity of the zinc electrode is heightened by the mixed expanded graphite to enhance the electrolyte holding property and uniformly distribute the electrolyte and the electric conductivity is also heightened by the expanded graphite.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to alkaline zinc storage batteries that use zinc as a negative electrode active material, such as nickel-zinc storage batteries and silver-zinc storage batteries.

Zinc as a negative electrode active material has the advantage of having a high energy density per unit weight and being inexpensive, but on the other hand, since zinc is deposited in a dendritic or spongy form during charging, repeated charging and discharging will cause the deposited zinc to has the disadvantage that it penetrates the separator and comes into contact with the opposite electrode, causing an internal short circuit.

In order to deal with this problem, a method has been proposed in which multiple types of separators are combined and the amount of electrolyte is regulated.

This method alleviated the deterioration caused by internal short circuits caused by deposited zinc.

However, since the amount of electrolyte is regulated, the electrolyte is unevenly distributed in the zinc electrode, resulting in a reduction in the reaction surface area, making it impossible to obtain satisfactory discharge capacity and cycle life, and also having the disadvantage that charging and discharging efficiency is reduced.

The present invention has been devised in view of the above points, and includes a zinc electrode containing expanded graphite and an electrolyte whose amount is regulated to such an extent that no free electrolyte exists. By containing carbonized graphite, the porosity of the zinc electrode is increased and the effective surface area is increased, thereby making the active material within the zinc electrode more active.

The expanded graphite referred to herein is obtained by the following treatment.

As shown in Figure 1, graphite is a hexagonal hexagonal plate-like flat crystal with a layered structure formed by a series of cataclysmic rings. This graphite is wet-oxidized using a mixed acid of concentrated sulfuric acid and concentrated nitric acid, and a strong oxidizing agent such as potassium chlorate, potassium dichromate, potassium permanganate, etc., and the wet-oxidized graphite is heated to a high temperature of 900°C or more. When rapidly heated, the interlayers in the crystal structure of graphite expand 50 to 600 times in the C-axis direction.

Expanded graphite subjected to such treatment forms porous particles that are thermally and chemically stable and highly conductive, and has extremely good pressure moldability.

Therefore, if expanded graphite is used as a conductive agent, when mixed with the active material of the zinc electrode, it becomes fine and uniformly dispersed in the zinc electrode, increasing the contact area with the active material and improving the conductivity of the zinc electrode. This will improve your sexuality.

An embodiment of the present invention will be described below.

After adding water to a mixed powder consisting of 777% by weight zinc oxide powder, 100% by weight metallic zinc powder, 5% by weight cadmium oxide as additives, 5% by weight expanded graphite, and 5% by weight fluororesin powder as a binder, and kneading. , create a paced snoring sheet by Laura. This sheet is attached to both sides of a sound electric body made of copper or the like, molded under pressure, and dried to create a zinc electrode.

In the examples, the amount of expanded graphite was limited to 3% by weight, but a range of 0.1 to 5% by weight is appropriate.

A nickel-zinc storage battery (8) was created by combining the zinc electrode thus obtained and a known sintered nickel electrode, in which the amount of alkaline electrolyte was regulated to such an extent that no free electrolyte was present. FIG. 2 is a sectional view of this storage battery body. 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, (71 (81 is a positive and negative electrode terminal).

For comparison, a comparative battery 03) was created which was the same as in Example except that it did not contain expanded graphite and the amount of zinc oxide powder was increased by the amount of expanded graphite in Example. .

FIG. 5 is a cycle characteristic diagram of a storage battery according to the present invention (41) and a comparative battery (B).The charging/discharging cycle conditions are as follows:
After being charged at 50 mA for 5 hours, it is discharged at 150 mA and the discharge is stopped when the battery voltage reaches 1.2 4'□. “As is clear from Figure 3, the storage battery (8) according to the present invention has superior cycle characteristics and capacity characteristics compared to the comparative battery.The reason for this is that the expanded graphite mixed in the zinc electrode This is thought to be due to the fact that the porosity of the zinc electrode is increased and the electrolyte holding capacity is increased, the electrolyte is uniformly distributed in the zinc electrode, and the expanded graphite increases the conductivity of the zinc electrode.

As described above, the present invention contains expanded graphite together with a zinc active material in a zinc electrode, and is provided with an electrolytic solution whose amount is regulated to a fine powder that does not contain any free electrolytic solution, so that it has excellent cycle characteristics. It is possible to obtain an alkaline zinc storage battery exhibiting capacity characteristics, and its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the crystal structure of graphite, FIG. 2 is a sectional view of an embodiment of an alkaline zinc storage battery according to the invention, and FIG. 6 is a cycle characteristic diagram of the storage battery according to the invention and a comparative battery. (1)...Zinc electrode.

Claims (1)

[Claims] (1) An alkaline zinc storage battery comprising a zinc electrode containing expanded graphite and an electrolyte whose amount is regulated to such an extent that no free electrolyte exists.