JPS59134565A - Plastic electrode for zinc-bromine battery - Google Patents

Abstract

PURPOSE:To increase the effective surface area required for reacting electrochemically with an active material on the surface of a plastic electrode and improve the potential of the plastic electrode by heat-contacting conductive fluororesin and conductivity sheets on the surface of the plastic electrode. CONSTITUTION:Especially the abnormal rise of activated overvoltage at the end of discharge is suppressed and the sudden drop of discharge potential is prevented by laminating and heat-contacting conductive fluororesin and conductivity sheets on the surface of a plastic electrode. The conductivity sheets use paper type ones such as conductive carbon fiber or cotton stuff type such as felt, knit, and cloth. When cotton stuff is used as the conductivity sheet, commercial cotton stuff with the thickness of approximately 1-30mm. is used and it is recommended that a layer of approximately 40-95g/m<2> should be provided on the surface of the plastic electrode. When this electrode is used, the voltage efficiency and coulon efficiency of a battery can be increased and at the same time stable discharge potential can be obtained even when the concentration of bromine in an electrolyte is exceedingly low and current density is high.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to bromine-zinc batteries, and in particular, the activation overvoltage at the end of discharge can be reduced by para-kinking a specific material on the surface of a carbon plastic electrode used in zinc-bromine batteries. The purpose is to suppress the abnormal rise and prevent a sudden drop in the discharge level.

Plastic electrodes used as electrode materials for bromine-zinc secondary batteries are practical because they are cheaper and lighter than metal electrodes or carbon electrodes.

However, the properties of these plastic electrodes are such that the specific resistance of the electrode itself is high, so unless some surface treatment is performed, it is not possible to approach the performance of metal or carbon electrodes.

Under these circumstances, the effective surface area necessary for electrochemical reaction with the active material on the surface of the plastic electrode is increased, and the electrode potential is increased, resulting in a reduction in the voltage efficiency and coulomb of a battery incorporating this electrode. As a result of research aimed at significantly improving efficiency, we have come to the point where we have obtained an extremely efficient plastic electrode.

In other words, in carrying out conductivity improvement treatment on the surface of a plastic electrode, the present invention requires that a conductive sheet is further thermocompression bonded to the surface of the plastic electrode on which a conductive fluororesin sheet has been thermocompression bonded in advance, or that a conductive sheet is bonded to the surface of the branched electrode. The present invention relates to a plastic electrode characterized in that a fluororesin sheet and a conductive sheet are bonded together by thermocompression.

A conductive sheet is, for example, a material made of conductive carbon fiber that maintains the form of a fabric such as felt, knit, or cloth, and is used to form a layer on the surface of a plastic electrode. It is easy to handle.

When using this conductive sheet as a cloth, one of the commercially available ones with a thickness of about 1 to 6 mm is used,
Also, on the surface of the plastic electrode, approximately 40 to 95
It is preferable to provide a layer so that the amount of water is approximately g/silence.

An electrode with a layer of a conductive sheet and a conductive fluororesin sheet on the surface of the plastic electrode increases the effective surface area of the active material against fluorine, improves the electrode potential characteristics on the bromine side, and reduces the voltage when looking at the battery as a whole. It has the effect of sufficiently reducing the efficiency and Coulombic efficiency, and the bromine concentration in the electrolyte is extremely low (for example, in the region of about 1.Q mat/L or lower) when the tIL flow density is large. A stable discharge level 4 can also be obtained.

The present invention will be further explained below with reference to Examples.

When hot-pressing a tetraelectric fluororesin sheet onto the surface of the plastic electrode, a double-backed plastic electrode (hereinafter referred to as WB main electrode) was formed by overlapping knitted carbon fibers at the same time. An electrode obtained by thermocompression bonding only a conductive fluororesin sheet without using fibers (hereinafter referred to as F
B electrode) and an electrode obtained by thermocompression bonding only knitted carbon fiber to a plastic electrode (hereinafter referred to as CBt electrode),
Specific resistance ρ (Ω・CIrL), ten-point average surface roughness RZ (μ
mrL) and specific surface area 5 (rr?/g by Bett method)
) were measured, and the results shown in the table below were obtained.

From the results in the table, when compared with the WB main electrode and the FB electrode, although a slight increase in the specific resistance value is observed due to the influence of contact resistance, the values of the ten-point average surface roughness R2 and specific surface area S have both improved, and the electrode It can be seen that a significant improvement in the reaction area has been achieved.

Also, in comparison with conventional CB electrodes, the values of ten-point average surface roughness R2 and specific surface area S are similarly improved, and the carbon fiber layer on the surface of the plastic electrode can sufficiently produce the desired effect. It can be seen that they are bonded under heat.

When the discharge characteristic E(V) at the anode was determined for the six types of electrodes mentioned above, the behavior shown in FIG. 1 was obtained. In addition, the electrolyte at this time was 3 mot/L ZnBr
Measurements were made using an Ag-Ag Cl electrode under an atmosphere of □10 Brz, current density of 20-A/i, and 25°C.

As is clear from the figure, in the early stage of discharge, all six types of electrodes show similar potentials, but at the end of discharge, when the bromine concentration is low, the FB electrode shows a rapid decrease, and the C
In the case of the B electrode, a decrease is also observed, although the degree is somewhat smaller.

On the other hand, in the case of the WB main electrode, the bromine concentration (Br2(
It is clear that a high discharge level is maintained over the entire range of mot/l)), and it can be seen that the effect of the double-backed plastic electrode is remarkable.

Separately, a zinc-bromine battery was constructed using a conventional plastic electrode as the cathode and the three types of plastic electrodes mentioned above as the anode, with a distance of 1 inch between the electrodes and a charging depth of 80%.
, charging and discharging under conditions of current density 20-A/, ffl8. When we calculated the voltage efficiency, coulomb efficiency, and energy efficiency, we obtained the results shown in the following table. The table results show that the double-backed plastic electrode outperforms the other two in both efficiencies.

[Brief explanation of drawings]

FIG. 1 is a graph showing the tracking results of the discharge level fluctuation when using each army/plan. Agent Patent Attorney Sanro Kimura

Claims (1)

[Claims] 1. A plastic electrode for a zinc-bromine battery, comprising: a conductive fluororesin sheet on the surface of the plastic electrode; and a conductive sheet thermocompressed onto the surface of the fluororesin sheet.