JP3028595B2 - Positive electrode of metal-halogen battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of the Invention The present invention relates to a positive electrode of a metal-halogen battery, and more particularly, to a metal having a low-cost positive electrode active layer and having almost the same performance as a conventional positive electrode. The present invention relates to a positive electrode of a halogen battery.

B. Summary of the Invention In the present invention, in a positive electrode of a metal-halogen battery, an inexpensive positive electrode active layer can be formed by fixing short fibers of activated carbon fibers to a polyolefin-based nonwoven fabric, and a conventional carbon cloth is used. It is possible to maintain almost the same performance as the positive electrode.

C. Prior Art In recent years, the development of battery power storage systems has been promoted, and as part of this, zinc-bromine batteries have been developed.

This battery is a compact liquid circulation type laminated battery composed of an aqueous solution of zinc bromide as an electrolytic solution, a carbon plastic sheet as a bipolar electrode plate, and a plurality of single cells electrically laminated in series. Zn ²⁺ during charging at the negative electrode + 2e ^- → Zn
Zinc is deposited on the negative electrode plate by the reaction of (1), and 2B
^{r - + Q + · Br -} → Q + · Br 3 - + 2e - at the same time bromine complex compound when bromine is generated by the reaction of ^{(2) (Q + · Br} -) combine with bromine complex compound (Q ⁺ · Br ₃ ^- ) Generate.

On the other hand, at the time of discharging, zinc is oxidized by the reverse reaction of the above (1) at the negative electrode to become zinc ions and dissolved in the electrolytic solution, and at the positive electrode, the bromine complex compound is converted into a bromine ion and a bromine complex by the reverse reaction of the above (2). Separation into compounds.

In this way, the zinc-bromine battery performs the binding and dissociation of bromine by the bromine complexing agent on the positive electrode, and on the negative electrode,
High electrical energy can be released through the deposition and dissolution of zinc.

By the way, the positive electrode of this battery is composed of carbon plastic formed by mixing polyethylene as a binder and carbon black and graphite at a ratio of 6: 3: 1, respectively, to give conductivity, and forming the mixture into a sheet shape. When molding this carbon plastic, the activated carbon fiber is thermocompression-bonded to one side by lamination to reduce the bromine generation overvoltage at the positive electrode. At present, this activated carbon fiber has good characteristics in terms of the basis weight and specific surface by using a cross-shaped one, and it can achieve the target battery performance and its life is long. It can be said that it is promising as a raw material for a positive electrode material.

On the other hand, the lamination method is adopted as a simple method because the process can be shortened as compared with the thermocompression bonding using a press.

D. Problems to be Solved by the Invention However, since the activated carbon fibers are used in the form of a cloth, wrinkles are likely to occur during thermocompression bonding by the lamination method, resulting in a decrease in the yield, and therefore, in addition to the raw materials, a cloth form is used. In addition to increasing the cost of finishing parts, it also increases costs due to lower yield,
This hindered the commercialization of this battery. Therefore, the present invention was conceived to solve this problem, and by fixing short fibers of activated carbon fibers to a polyolefin-based nonwoven fabric, there is no need to use activated carbon fibers in a cloth form as a raw material. Therefore, the amount of raw material used can be reduced, wrinkles due to lamination can be prevented by the strength of the nonwoven fabric, and the performance of a positive electrode of a metal-halogen battery that can maintain almost the same performance as a conventional positive electrode using carbon cloth. The purpose is to provide.

E. Means and Action for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, by fixing short fibers of activated carbon fibers to a polyolefin-based nonwoven fabric, a conventional carbon cloth was obtained. The cost of active carbon fiber was successfully reduced as a raw material while maintaining almost the same performance as the used positive electrode, and the positive electrode of the metal-halogen battery according to the present invention was completed.

That is, the positive electrode of the metal-halogen battery according to the present invention is obtained by fixing short fibers of activated carbon fibers to a polyolefin-based nonwoven fabric to obtain a positive electrode active layer, mixing a conductive material with a polyolefin-based resin, and forming a sheet. The solution is to form the formed electrode integrally with the positive electrode active layer by thermocompression bonding.

 Hereinafter, the present invention will be described in more detail.

First, examples of the short fibers of the activated carbon fibers used as a raw material of the positive electrode according to the present invention include, for example, phenol-based, acrylic, PAN-based and pitch-based fibers, preferably pitch-based activated carbon fibers, more preferably fiber length. 120-150μ
m (specific surface area: 1500 m ² , 2 × 10 ⁻³ Ω · cm). As a result, the micropores of the activated carbon can be effectively used as a reaction active point in the electrolytic solution to reduce overvoltage.

Next, the activated carbon fiber short fibers are fixed to a polyolefin-based nonwoven fabric to obtain a positive electrode active layer.

Here, examples of the "polyolefin-based nonwoven fabric" include polyethylene-based and polypropylene-based nonwoven fabrics. Preferably, the polyethylene-based nonwoven fabric is used as a binder for fixing the activated carbon fibers.

Further, “fixed” refers to, for example, polyvinyl alcohol (hereinafter, referred to as polyvinyl alcohol).
This is performed by dissolving short fibers of activated carbon fibers together with a nonwoven fabric in a solution (PVA).

Further, examples of the conductive substance used in the present invention include carbon black and graphite.

The above-mentioned nonwoven fabric to which carbon fibers are fixed is polyolefin,
50-6 each for carbon black and graphite
A carbon plastic electrode mixed in a ratio of 0,20 to 40,20 to 40% by weight, preferably 50,15,35% by weight and formed into a sheet-like carbon plastic electrode by thermocompression bonding or the like, and integrally molded. Obtain a positive electrode of a halogen battery.

The metal-halogen battery that can use the positive electrode according to the present invention includes, for example, a zinc-bromine battery.

F. Examples Hereinafter, detailed description of the positive electrode of the metal-halogen battery according to the present invention will be described based on examples.

Example 1 Method for producing positive electrode of metal-halogen battery Pitch-based carbon fiber as raw material 120 to 150 μm (specific surface area)
1500m ² , 2 × 10 ^-3 Ω · cm, manufactured by Nippon Kainol, trade name ACC
Series), polyethylene nonwoven fabric (FT series, manufactured by Nippon Vilene Co., Ltd.), PVA, carbon black (manufactured by Lion Akzo Co., Ketjen Black EC) and graphite (Kish graphite manufactured by Kowa Seiko Co., Ltd.) Thus, a positive electrode of a zinc-bromine battery was manufactured.

(1) First, put water 1 into a beaker and put PVA10g in it.
And warmed to 60 ° C. with a burner to dissolve the PVA.

(2) then it was transferred to dissolved PVA in a plastic container vertical 11cm × horizontal 11cm × height 2 cm, the pitch-based carbon fiber 1 m ² per
Approximately 1 g, which was converted to 100 cm ² , was added to the container as 100 g, followed by stirring. Next, a non-woven fabric with a basis weight of 17.0 g / m ² was placed in the
It was cut into pieces of 10 cm in size, soaked well in the PVA solution, and left for a while. Furthermore, place the plastic container in a thermostat for 10 minutes.
The mixture was left at 0 ° C. for 30 minutes to evaporate water.

(3) Further, the non-woven fabric on which the dried carbon fibers are fixed is made of polyethylene 50 wt%, carbon 15 wt%, graphite 35
is hardly subjected to pressure using a heat press machine to the carbon plastic electrode 1mm thick constituted by a mixing ratio of ^{wt% (0~5kg / m 2)} , about 120 ° C., and is held for 3 minutes and thermally bonding , Then cooled and removed.

(4) Next, the removed electrode was immersed in warm water at 60 ° C. for 30 minutes to remove PVA from the nonwoven fabric, thereby obtaining a positive electrode for a zinc-bromine battery.

Example 2 Zinc - an electrical characteristics test in Example 1 positive electrode obtained in the positive electrode bromine battery into small pieces of 1 cm × 10 cm, using a 3MolZnBr ² and 0.1MolBr ² as the electrolyte, ± by cyclic voltammetry the behavior of 50mA / cm ² 5m
The test was performed at a running speed of A / sec. Similarly, a carbon cloth (specific surface area of 1500 m ² , 2 × 10 ⁻³ ) conventionally used as a comparative example
Ω · cm) was also examined. FIG. 1 shows the results.

As shown in FIG. 1, the positive electrode according to the present invention has an overvoltage increase of about 5 mV in the range of 10 to 20 mA / cm ² actually used in the present battery as compared with the conventional positive electrode using carbon cloth. This means that even if short fibers of activated carbon fibers fixed to a polyethylene-based nonwoven fabric are used instead of the conventional carbon cloth, the electrical characteristics of the positive electrode of the zinc-bromine battery are not significantly changed and can be used sufficiently. are doing.

Example 3 Battery test of a positive electrode of a zinc-bromine battery In the same manner as in Example 1, a nonwoven fabric in which carbon fibers of about 40 cm × 5 cm were immobilized was formed and laminated with a carbon plastic electrode to form an 800 cm ² size electrode. 3 mol / ZnBr ₂ , 2 mol / NH ₄ Cl, 1 mol / bromine complexing agent and dendrite inhibitor (Pb, Sn, quaternary ammonium salt) as electrolyte
Charge at a liquid temperature of 30 ° C. and 15 mA / cm ² for 8 hours using
^{The battery} was discharged at ² and a charge / discharge test was performed. Similarly, a positive electrode using a conventional carbon cloth was examined. Table 1 shows the results. As shown in Table 1, the positive electrode according to the present invention has substantially the same values for voltage efficiency (%), coulomb efficiency (%), and energy efficiency (%) as compared to the conventional positive electrode using carbon cloth. It can be seen that it is.

This means that the positive electrode according to the present invention has almost the same battery characteristics as the conventional positive electrode using carbon cloth, and is sufficiently usable.

G. Effects of the Invention The present invention can form an inexpensive positive electrode active layer by fixing short fibers of activated carbon fibers to a polyolefin-based nonwoven fabric, and has almost the same performance as a conventional positive electrode using carbon cloth. Can be retained. Therefore, according to the positive electrode of the present invention, it is possible to manufacture an inexpensive metal-halogen battery, which can greatly contribute to commercialization of the metal-halogen battery.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of an overvoltage evaluation test of a positive electrode battery using the activated carbon fiber and the nonwoven fabric according to the present invention and a positive electrode using a conventional carbon cloth.

Claims (1)

(57) [Claims] 1. A positive electrode active layer is obtained by fixing short fibers of activated carbon fibers to a polyolefin-based nonwoven fabric, and an electrode formed into a sheet by mixing a conductive material with a polyolefin-based resin is used as the positive electrode active layer. A positive electrode of a metal-halogen battery, which is integrally formed by thermocompression bonding.