JP3196417B2 - Glassy carbon electrode for metal-halogen batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glassy carbon electrode used as a positive electrode of a metal-halogen battery, particularly a zinc-bromine battery which is a laminated electrolyte secondary battery for storing electric power. .

[0002]

2. Description of the Related Art A zinc-bromine battery as a metal-halogen electrode is a secondary battery in which bromine is used as a positive electrode active material and zinc is used as a negative electrode active material. In order to solve the problem, it is used for storing electric power at night when power demand is small and releasing it during the day.

[0003] The bromine generated on the positive electrode side during charging reacts with the bromine complexing agent added to the electrolytic solution and is returned to the positive electrode side storage tank as an oily precipitate. It is sent inside and reduced. The component of the electrolyte is ZnBr
_{(2) an} aqueous solution, a salt such as NH ₄ Cl for lowering resistance, Pb, Sn, and quaternary ammonium salts for preventing dendrite on the negative electrode zinc side and promoting uniform electrodeposition, and a bromine complexing agent. It is. A separator is interposed between the positive electrode and the negative electrode to prevent self-discharge caused by bromine generated at the positive electrode diffusing into the negative electrode and reacting with zinc.

This zinc-bromine battery mainly has a bipolar type electrode, a battery body in which a plurality of unit cells (single cells) are electrically stacked in series, an electrolytic solution storage tank, and an electrolytic solution between these. It is composed of a pump and a piping system for circulating the liquid.

FIG. 3 is an exploded perspective view showing an example of a battery main body constituting the zinc-bromine battery. An insulating frame 1b is arranged on the outer periphery of an electrode portion 1a of a bipolar intermediate electrode 1 having a rectangular flat plate shape. Similarly, the rectangular flat separator plate 2
Has a frame 2 a formed on the outer periphery of the separator 3.
The separator plate 2 and, if necessary, the packing 4 and the spacer mesh 5 are stacked on the intermediate electrode 1 to form a single cell, and a plurality of the single cells are laminated to form a battery body.

[0006] At both ends of the stacked battery body, a collecting electrode 7 having a collecting mesh 6, a pair of fastening end plates 8,
A holding laminated end plate 9 located on the inside thereof is arranged. Then, a bolt (not shown) for tightening is passed between the two tightening end plates 8 and 8, and the bolts are tightened to form a battery body integrally laminated and fixed.

In each unit cell of the battery body configured as described above, each intermediate electrode 1 and the frame 2a of the separator plate 2 are provided.
Positive electrode manifold 10 formed at the upper and lower two corners of
Then, the electrolyte flows in and out of the negative electrode manifold 11 through the channel 12 and the micro channel 13 provided in the frame 2a of the separator plate 2, respectively.

As an electrode material for the zinc-bromine battery, glassy carbon having excellent bromine resistance and good conductivity is used. This glassy carbon is, for example, after uniformly mixing graphite with a phenolic synthetic resin, forming it into a plate shape, gradually heating and raising the temperature in a non-oxidizing atmosphere, carbonizing at 1000 ° C. or more, and then gradually cooling. It was done. However, this glassy carbon alone has a large activation overvoltage on the electrode surface and has a problem in reactivity, so that it cannot be used as an electrode as it is.

Therefore, in order to impart the activity of the electrode to the glassy carbon, a sheet made of carbon fibers is laminated on the surface of the dense glassy carbon via a carbon-based adhesive, and the fired composite electrode is formed into a plate-like shape. The material formed on the body is used as the electrode material. By using a porous carbon fiber, the activity of the electrode surface can be increased.

Regarding the above, Japanese Patent Application No. 60-267412 proposed by the present applicant discloses a conductive carbon paste having a function as an adhesive on a glassy carbon 15 as an electrode substrate as shown in FIG. A composite electrode structure in which a sheet-like carbon fiber 17 is adhered via a support 16 is disclosed.

According to such a composite electrode, in addition to the resistance and impermeability to bromine, the electrochemical activity of the carbon fiber is added, so that the electrode characteristics using the glassy carbon 15 are enhanced.

[0012]

However, in such a composite electrode using glassy carbon, when the amount of the adhesive for bonding the sheet-like carbon fiber to the glassy carbon is large, this adhesive is used. There is a problem that the electrode area deteriorates due to permeation into the positive electrode active layer to reduce the reaction area, and conversely, when the amount of the adhesive is small, the bonding strength of the sheet-like carbon fiber decreases, There is a problem that the stagnation of the electrolytic solution causes the corrosion of the sheet-like carbon fibers to proceed, thereby increasing the contact resistance and deteriorating the battery characteristics.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is intended to prevent a decrease in electrode characteristics due to the above-mentioned adhesive and to increase the bonding strength to reduce contact resistance and improve conductivity. It is intended to obtain a vitreous carbon electrode.

[0014]

According to the present invention, in order to achieve the above object, a densely formed glassy carbon is used as an electrode substrate, and a liquid phenol resin is added to cellulose fibers in which activated carbon is dispersed. A glassy carbon electrode is formed by laminating and fixing porous sheet-like carbon fibers using the impregnated bonding layer.

According to a second aspect of the present invention, there is provided a glassy carbon electrode of a metal-halogen battery fired under appropriate conditions with the bonding layer interposed between glassy carbon and a porous sheet carbon fiber. I do.

[0016]

According to this glassy carbon electrode, the cellulose fibers are carbonized in the firing process to form carbon fibers, and the carbon fibers adhere to the activated carbon and act as a binder for the phenolic resin, thereby forming the glassy carbon into a sheet. An electrode having a strong bonding structure as a whole can be obtained by strongly bonding the carbon fibers. With the improvement of bonding strength, the electrical resistance at the bonding interface between glassy carbon and carbon fiber decreases, the conductivity increases, and the porous sheet-like carbon fiber laminated and fixed provides electrochemical reactivity. The present invention provides a glassy carbon electrode rich in carbon.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, an embodiment of a glass-like carbon electrode of a metal-halogen battery according to the present invention will be described in detail by assigning the same reference numerals to the same components as the conventional components. I do.

FIG. 1 is a cross-sectional view of an essential part showing an electrode structure according to the present embodiment, wherein 15 is a glassy carbon formed densely as an electrode substrate, 20 is a bonding layer to which the present embodiment is applied, and 17 is a sheet. Carbon fiber. The bonding layer 20
Uses a material obtained by impregnating a liquid phenol resin into a material obtained by dispersing activated carbon in cellulose fibers, instead of a conventional conductive carbon paste. In manufacturing the electrode, the bonding layer 20 is sandwiched between the glassy carbon 15 and the porous sheet-like carbon fiber 17 and fired under the conditions described later.

In the firing process, the cellulose fibers are carbonized into carbon fibers. The carbon fibers adhere well to the activated carbon and act as a binder for the phenol resin, and strongly adhere to the glassy carbon 15 and the sheet-like carbon fibers. As a result, the bonding effect between the two is enhanced, and an electrode having a strong bonding structure as a whole can be obtained.

Hereinafter, specific embodiments of the present invention will be described. The composition ratio of activated carbon and cellulose fibers constituting the bonding layer 20 is activated carbon / cellulose fibers = 30/70 (% by weight). After sufficiently mixing both, the mixture is impregnated with a liquid phenol resin.

In order to verify the electrode characteristics using the bonding layer 20, the structure of the bonding layer 20 is sandwiched between the glassy carbon 15 and the porous sheet-like carbon fiber 17, and an appropriate load is applied. Heating rate 10 in the electric furnace
1000 ° C, 1500 ° C, 3000 ° C at 0 ° C / Hr
Baking is performed under the following three conditions, and the temperature is lowered at a rate of 300 ° C. /
The composite electrode was gradually cooled with Hr.

In order to compare the electrode characteristics of the obtained three types of composite electrodes and the conventional composite electrode (see FIG. 4), Zn
Charging / discharging was performed using an electrolyte of Br ₂ (3 mol / l) + Br ₂ (0.3 mol / l), and the overvoltage was measured. The result is shown in FIG. FIG. 2 shows a heating rate of 100 ° C./H.
When firing at 1000 ° C at maximum,
The case of baking at 00 ° C. indicates the case of baking at 3000 ° C., and the case of a conventional composite electrode. The vertical axis in the figure is the overvoltage (mv), and the horizontal axis is the current density (mA / cm ² ).

In the composite electrode according to the present embodiment, the maximum firing temperatures in the firing process are different from each other, so that the degree of graphitization is different and the overvoltage as an electrode characteristic is different. The overvoltage for the same current density was smaller than that of the conventional composite electrode, and it was confirmed that the electrode characteristics were improved.

Further, as the bonding strength of the obtained electrode is improved, the electric resistance at the bonding interface is reduced, the conductivity is increased, and the bonded porous sheet-like carbon fiber 17 is further improved.
As a result, an effect of rich electrochemical reactivity is obtained.

[0025]

As described in detail above, the glassy carbon electrode of the metal-halogen battery according to the present invention has a strong bonding structure between the glassy carbon and the porous sheet carbon fiber. It is possible to obtain an electrode, especially by firing with a bonding layer between them,
During the firing process, the cellulose fibers are carbonized into carbon fibers,
This carbon fiber adheres well to the activated carbon and acts as a binder for the phenolic resin, so that the glassy carbon and the sheet-like carbon fiber can be strongly bonded.

In addition, a phenomenon of adhesive penetration or a decrease in bonding strength due to the amount of the adhesive is prevented, and an increase in contact resistance due to stagnation of the electrolyte and progress of corrosion of the sheet-like carbon fiber is eliminated. In addition, the effect that the electrical resistance of the bonding interface is reduced and the conductivity is increased with the improvement in the bonding strength of the electrodes is exhibited.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing an electrode structure according to an embodiment.

FIG. 2 is a graph comparing the electrode characteristics of a composite electrode obtained according to the present embodiment and a conventional composite electrode.

FIG. 3 is an exploded perspective view showing the structure of a zinc-bromine battery.

FIG. 4 is a sectional view of a main part showing an example of a conventional composite electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Intermediate electrode 1b ... Frame 2 ... Separator plate 3 ... Separator 8 ... Tightened end plate 9 ... Laminated end plate 10 ... Positive electrode manifold 11 ... Negative electrode manifold 12 ... Channel 13 ... Microchannel 15 ... Glassy carbon 17 ... Sheet-like Carbon fiber 20: bonding layer

Claims (2)

(57) [Claims] 1. A porous sheet-like material formed by using a densely formed glassy carbon as an electrode substrate, and using a bonding layer obtained by impregnating a cellulose fiber in which activated carbon is dispersed with a liquid phenol resin on the electrode substrate. A glassy carbon electrode for a metal-halogen battery, wherein carbon fibers are laminated and fixed. 2. The glass-like carbon electrode of a metal-halogen battery according to claim 1, wherein said bonding layer is sandwiched between glass-like carbon and porous sheet-like carbon fibers and fired under appropriate conditions.