JPS62128452A - Glassy carbon composite electrode - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a vitrus carbonaceous electrode suitable for use as an electrode, particularly as an anode electrode, for use in zinc-bromine batteries.

B. Summary of the Invention The present invention uses glassy carbon (hereinafter referred to as vitrus carbon) as an electrode material for a lead-bromine battery, and coats the surface with a carbon-based adhesive to impart surface activity as an electrode. Vitrous carbon not only has bromine resistance and discharge characteristics, but also has bromine impermeability as a bipolar electrode. It concerns a degree electrode.

C. Prior Art One of the conductive carbon-based materials is vitrus carbon.

This vitrus carbon was developed as a material for electrodes in electric furnaces and the like, and is commercially available from carbon manufacturers, steel manufacturers, non-metal material manufacturers, and the like.

Since vitrus carbon has poor bromine resistance and good air conductivity, attempts have been made to form it into a plate-like material and use it as the m-pole of a zinc-bromine battery.

D Problems to be Solved by the Invention However, when using this Pitrus carbon as an electrode for a zinc-bromine battery, especially when it is used as an anode, that is, a bromine electrode, the activation overvoltage on the electrode surface is large when using Pitrus carbon alone. Currently, it is almost impossible to use it as it is due to problems with its reactivity.

Therefore, when using vitrus carbon for electrodes, its usefulness is not fully utilized unless some kind of preliminary treatment is performed.

So 1. As a surface treatment measure for this vitrus carbon electrode, for example, a method of making vitrus carbon itself porous,
Possible methods include increasing the surface roughness of the electrode by means such as electroplating to increase the reaction area, or applying a surface treatment material made of other materials, but none of these methods has been perfected to the point where it can be put to practical use. At present, a method has not yet been developed.

E F,'i Means for solving the 8 points The present invention was made to solve the problems of the conventional vitrus carbon electrode as described above. Using the prepared Vitrus carbon as an electrode substrate, a sheet of carbon fiber is pasted on the surface of B with conductive carbon paste interposed as an adhesive, and then fired at high temperature 1 to cover the surface with carbon fiber. The present invention relates to obtaining a vitrus carbon electrode.

Since the present invention, which has the above-described configuration, is a composite electrode made by bonding carbon fibers to a vitrus carbon plate,
Due to its bromine resistance and the electrochemical activation effect of the carbon fibers covering the surface of the fJ electrode, it has superior properties over conventional Pitrus carbon electrodes, and is impermeable to bromine. It can be made into a composite electrode that can also be used as a bipolar electrode.

Vitrous carbon here is made by uniformly mixing graphite with a synthetic resin (for example, phenolic), molding it into a plate shape, gradually heating it in a non-oxidizing atmosphere, and carbonizing it at 1000℃ or higher. It is slowly cooled and used as a substrate for bipolar electrodes in zinc-bromine batteries.

The sheet-like carbon fiber as used in the present invention refers to carbon fiber formed into a sheet, and includes a woven fabric made of carbon fiber, such as a cloth-like, felt-like, or knit-like material, or carbon paper made from carbon fiber. means.

When porous carbon fibers are used as the carbon fibers constituting the sheet-like carbon fibers, activation of the electrode surface can be further improved.

Next, an example of a specific configuration of the carbon fiber-bonded Pitrus carbon electrode of the present invention will be explained based on the first rIA.

In FIG. 1, 1 is a vitrus carbon plate as an electrode substrate, 2 is a conductive carbon paste serving as an adhesive, and 3 is a sheet-like carbon fiber for imparting activity to the electrode surface.

Examples of G-Design Example 1 After laminating the electrode forming materials as described above, they were fired for 1 hour in a nitrogen atmosphere width of about 1000° C. to obtain a carbon fiber-bonded vitrus carbon electrode W of the present invention.

Vitrus Carbon is GCR-101 manufactured by Kobe Steel Corporation.
As the carbon fiber, Bermatsu IV-205E carbon fiber paper manufactured by Kenbetsu Kagaku was used.

This electrode W of the present invention and the electrode X1 made only of Pitrus carbon GCR-101 prepared for characteristic comparison. Carbon plastic commonly used (weight ratio polyethylene/carbon black/graphite = 50/30/
20) Electrode Y1 This carbon plastic electrode INFIa
; To the surface carbon 1a fiber paper (Pale Pine 1.V-20
Electrode Z (7) 41f1 type electrode with backing 5E)? ftm (V), m air resistance ρ (Ω-am), and bromine permeation tests were conducted.

The test method for the discharge potential (V) is to configure a half cell using each of the electrodes W-Z as a working electrode and the same carbon plastic electrode as above as a counter electrode,
3 mol/I ZnBr20Br2(0
, 4 to 1.0 mol/l) using an Ag-AgCl electrode as a reference.

In this case, the difference in potential at each current density from the state where no electricity is conducted (open potential) is the overvoltage ΔV, and those with a small value have a large activation effect with bromine and can be said to be good electrodes.

Electrical resistance is a measure of electrical conductivity, and is a measure of volume resistivity ρ (rho-) using the four-probe method.

Further, the bromine permeation test used the apparatus shown in FIG. 2, in which numeral 4 represents a working electrode, and each of the electrodes W-Z was used.

In Figure 2, 5 is 3+eol/l ZnBrt aqueous solution,
6 is 3 n+ol/l ZnBr2 aqueous solution +3a
+o! /lBrg, and these 5.6 both liquids are
Working electrode 4 provided approximately at the bottom of the shape tube
Fill the aqueous solution 6 in equal amounts with
This is to measure the bromine concentration that permeates from the bromine through the working electrode 4 to the opposite aqueous solution 5, and to evaluate the bromine resistance and impermeability of the electrode.

The results of this characteristic test are shown in the following table and FIGS. 3 and 4.

FIG. 3 shows the discharge electrode potential characteristics at 25° C. of electrodes W to Z, and FIG. 4 shows the temporal change in the amount of bromine permeated through electrodes W to Z.

From the above table and Figure 3, there is a remarkable difference in the electrochemical properties of electrodes W-Z, and compared to carbon plastic electrode IIY, electrode Z, which is simply backed with carbon fiber, has a higher discharge potential due to its surface active effect. Potential characteristics are improved.

On the other hand, since the vitrus carbon electrode X itself has a good electrical conductivity of 1O-3Ω, it has properties substantially equivalent to those of the electrode Z even without surface activation treatment.

The electrode W of the present invention, in which carbon fibers are bonded to this vitrus carbon electrode, has a high conductivity of the vitrus carbon used as an electrode substrate and a surface activity due to the carbon fibers baked and coated on the surface. In terms of effectiveness, it shows the best characteristics among the four types of electrodes.

Furthermore, from FIG. 4, electrodes Z and Y have a large permeation amount of bromine of 0.1 s+ol/1 or more in 500 hours, whereas electrode W of the present invention has a permeation amount of 0.02 mol in 2000 hours.
Electrode W is excellent in terms of impermeability to bromine, which is 1/l, indicating that it can be used as a bipolar electrode.

Example 2 Toyobo Co., Ltd.'s loss-form activated carbon fiber, liKF-M-303, was used as the carbon fiber to be joined, and Kobe Steel's GCR-101 was used as the vitrus carbon, and carbon black and phenolic resin were used. Using an adhesive mixed with activated carbon, several electrodes were made by firing and bonding.

The mixing ratio of carbon black and activated carbon in the adhesive was 40-60:60-40% by weight, and phenol formaldehyde was used as the phenol resin.

Electrodes were fabricated by bonding under various conditions, and the conditions and conditions after fabrication are shown in the table below.

In both cases, the heat treatment conditions were 1 hour.

Regarding the carbon fiber-bonded pitrus carbon composite electrodes A-E obtained in this way, when each was used as an electrode, the discharge position 4 with respect to a silver-chloride if electrode was measured, and the results were as shown in Fig. 5. I got the behavior.

The electrolyte used at this time was 3-Otori 01/IZ
n B r2 + B r, (0.33 mol/l)
, and was measured at 25°C.

From the behavior shown in Figure 5, it can be seen that there are differences in electrode characteristics depending on the amount of adhesive applied and the firing temperature, and that electrode E, which has a large amount of adhesive applied and a relatively high firing temperature, is superior to other electrodes. It was observed that it exhibited good discharge characteristics.

Example 3 Using the bonding conditions of Electron$1iE in Example 2, different types of activated carbon fibers were bonded to Vitrus Carbon GCR-101.
The properties were measured and compared using the same conditions as in Example 1.

The materials used were a total of 5 fibers selected from 381 types of activated carbon fibers including PAN type, rayon type, and phenol type.

KF-M-303: Toyobo AC series: Nippon Kynol FE-200: 7 finger F EF-200, Toho Peslon m: Novolac type m fiber The results are shown in Figure 6, but rayon-based and PAN
Compared to m-electrodes E and I obtained by bonding activated carbon fibers of the phenolic novolac type, electrodes F, G, and H of phenolic novolak type have extremely good characteristics, and among them, the electrodes F, G, and H of the phenolic novolak type have extremely good characteristics, and among them, the electrodes F, G, and H of the phenolic novolac type have extremely good characteristics, and among them, the electrodes F, G, and H of the phenolic novolac type have extremely good characteristics. Electrode H showed the most excellent discharge 4th position curve.

In addition, electrodes F and G, which are made of the same kynol system, have the same cross-shaped activated carbon fibers, but perhaps because electrode G has a larger specific surface area than F, the characteristics of electrode G are better than those of F. The results were shown.

The specific surface area of the activated carbon fibers is that G and H are almost the same, about 2000 m'/g, E and F are about the same, about 1500 m'/g, and I is about 1000 m'/g.
It was g.

The reason why phenolic activated carbon fibers have better properties than activated carbon fibers made from other resins is thought to be due to the heat resistance and flame retardant properties of m-fibers, which prevent the fibers from being destroyed by re-firing. This is thought to be due to the fact that it adhered well to the Vitrus carbon of the substrate.

Example 4 Selecting the typical three electrodes E, F, and H from Example 3, six of each were fabricated and used as intermediate electrodes, and one anode and one cathode end plate were fabricated separately. A 7-cell stacked battery was constructed and a charge/discharge test was conducted.

In addition, the separator is a porous membrane RAS with a thickness of 0.6 mm.
(manufactured by Asahi Kasei Corporation) and 3 mol/l Z in the electrolyte.
A bromine complexing agent was mixed with nBr2, and 4 mat/I N H4CI was used to further improve the conductivity.

A battery using electrode E is r, a battery using fWiF is ■,
Furthermore, the voltage efficiency, coulombic efficiency, and energy efficiency when a battery using m-pole H is charged as ■ for 8 hours at a current density of 15 tsA/crl, and discharged at the same current density and the discharge voltage is cut off at IOV. The results of the comparison are shown in the table below.

Figure 7 shows the curves of their charging and discharging characteristics.Batteries ■ and Battery■, in which two types of activated carbon fibers with similar specific surface areas are bonded to the anode surface treatment material, show that the battery operation during charging and discharging is The results were similar to the results of the discharge characteristics shown in FIG. 6, and it was found that the battery H using phenolic novolac type activated carbon fiber as the starting material showed better results.

Furthermore, even though the same phenol-based activated carbon fibers were used, it was found that battery (2), which uses felt-type fibers with a large specific surface area, has even better charge and discharge characteristics.

The following table summarizes these results.

From the table above, comparing Ws Pond LII and ■, ■
It can be seen that each efficiency increases in the order of , ■, and ■, and that the increase in Coulomb efficiency is especially large.

This seems to be due to the difference in the bromine retention ability of the anode surface treatment materials, but this data also shows that the method and conditions for bonding carbon fibers to Pitrus carbon affect the characteristics of the activated carbon m, it. It is recognized that the system makes good use of the

Effects of H-device As explained above, dense vitrus carbon is used as an electrode substrate, strong carbon fibers are laminated on top of it with conductive carbon paste interposed as an adhesive, and then fired. It can be seen that the electrode of the present invention not only has good resistance and impermeability to bromine, but also has the electrochemical activation effect of carbon fibers, so it is superior to an electrode made only of vitrus carbon.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing one embodiment of the carbon fiber-bonded vitrus carbon electrode of the present invention, Fig. 2 is a cross-sectional view of an electrode bromine permeability test device, and Fig. 3 is a cross-sectional view of the electrode of the present invention and a comparative example electrode. Graph showing the relationship between discharge current density and discharge potential V, 4th
The figure is a graph showing the relationship between the elapsed time and permeation rate of bromine in the bromine permeation test for the electrode of the present invention and the comparative electrode. Figure 5 is a graph showing preliminary evaluation of various electrode materials. A graph showing evaluations made on specific electrode materials using the results in FIG. 5, and FIG. 7 is a graph showing evaluations when used as an electrode in a cell close to the actual electrode. 1 is vitrus carbon, 2 is carbon paste, 3 is carbon fiber, 4 is working electrode, 5 is zinc bromide aqueous solution,
6 is an aqueous solution of zinc bromide.

Claims (2)

[Claims] (1) A vitrus carbon composite electrode formed by using a densely formed vitrus carbon plate as an electrode substrate, laminating sheet-like carbon fibers on the surface of the plate via a conductive carbon paste, and then firing the layer. (2) The vitrus carbon composite electrode according to claim 1, which uses a conductive carbon paste consisting of phenol resin and carbon black in approximately the same weight ratio.