JPS6293867A - Vitreous carbon composite electrode - Google Patents

Abstract

PURPOSE:To aim at improvements in bromine resistance and a discharge potential characteristic, by setting dense vitreous carbon down to an electrode substrate, and layering a C-C composite on the surface via a bonding agent before burning. CONSTITUTION:Dense, bromine unpenetrative vitreous carbon is used as an electrode substrate and, after a C-C composite is layered on this surface with carbon paste having conductivity as a bonding agent, burned at a high temperature of 800-1,000 deg.C in an inert gas ambience inside an electric furnace or the like. In case of a vitreous carbon composite electrode where a porous C-C composite is joined on a surface of the dense vitreous carbon to be obtained in this way, there is bromine resistance, and an electrochemical active action of the C-C composite covering the electrode surface at the bromine side is added, so that it has an excellent characteristic exceeding the conventional vitreous carbon electrode, and additionally, owing to its inherent dense quality, it is utilizable even as a bipolar electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Application Field The present invention relates to an electrode that is particularly applied as a positive electrode in zinc-bromine batteries and the like.

B Summary of the invention The present invention uses vitrus carbon as a substrate for the M pole of a zinc-bromine battery, etc., and in order to impart surface activity as an electrode to the carbon, a C-C composite is bonded to the surface via a carbon-based adhesive. (carbon fiber and synthetic JI4 resin are laminated and fired at high temperature in an inert gas atmosphere) and then fired in an inert gas atmosphere, for example in an electric furnace. This relates to an electrode with deteriorated discharge potential characteristics.

C. Conventional technology As an electrode for zinc-bromine batteries, Japanese Patent Application Laid-Open No. 59-96662
As shown in the publication, the carbon fiber bonded IF electrode, in which carbon plastic or the like is used as an electrode substrate and carbon fibers are bonded to the surface by heat press or the like, is endowed with the electrochemical activity that carbon fibers have. It has been known.

Vitrous carbon can also be used as this type of electric cap, but its main use was as an electrode material in electric furnaces, etc., and it has been widely used by carbon manufacturers, steel manufacturers, non-metal material manufacturers, etc. It is commercially available.

When this vitrus carbon is used as an electrode for a leaded-bromine battery, it has poor bromine resistance and good electrical conductivity, so it is convenient from these points of view, but as a positive electrode, that is, a bromine electrode, vitrus carbon is used as an electrode. Carbon alone has a problem with reactivity, and it is necessary to take some kind of surface treatment or other countermeasures.

D invention solves the problem (7) Therefore, as a countermeasure for surface treatment of the positive electrode side of this Vitrus Carbon Hm, for example, by making Vitrus Carbon itself porous or by means such as electroplating, the unevenness of the electrode surface is increased. Possible methods include expanding the reaction area by using a wafer, and applying surface treatment materials made of other substances, but none of these methods have yet been developed to be effective enough to put them into practical use.

In addition, in the electrode described above in which carbon plastic is used as the electrode substrate and carbon fibers are bonded to the surface of the positive electrode side, the carbon'ta fibers as the active layer are formed in the electrode frame by the beat press method or the indie excisine mold method. It is difficult to withstand the pressure when the mold is opened and closed, and the fiber itself may be destroyed, or the carbon fiber may fall off the electrode surface during long charging and discharging.
- There is a problem.

E I! Means for Solving the Problem The present invention has been made to solve the problems in the prior art described above, and uses dense bromine-impermeable vitrus carbon as an electrode substrate. A dense material obtained by laminating a C-C composite using carbon paste I, which has conductivity on the surface, as an adhesive, and then firing it at a high temperature of 800 to 1000°C in an inert gas atmosphere in an electric furnace or other furnace. This is a vitrus carbon composite electrode in which a porous C-C composite is bonded to the surface of quality vitrus carbon.

The C-C composite used in this case is typified by Nippon Light Metal's prototype PP"444, and is made of polyolefin, polyvinyl, etc., which are advantageous for conducting materials for zinc-bromine batteries and for firing during carbonization. A sheet made of a polymer, graphite powder or carbon black (Ketjen, Furnace, etc.) for imparting conductivity, and carbon fiber is arranged in a layered manner, and the thermoplastic polymer is heated and melted to impregnate or impregnate the carbon product. 500-30 for carbonization of the polymer in an inert gas after the bonding and integration process.
This is a porous carbonaceous composite material obtained by firing at 00°C for several hours to day and night.

This C-C composite is made from the types of carbon fibers used as raw materials (PAN type, activated carbonaceous.

It is possible to change the degree of porosity by changing the texture (such as those spun with P I CH system), the texture, the weaving method (cross-shaped, two-knit shape, etc.), etc. In particular, the form of the C-C composite that is effective for electrodes of zinc-bromine batteries, which is the object of the present invention, has a specific surface area of 3 m' by the BET method.
/g or more, the porosity is 0.3c+ with a pore diameter of 0.1 to 10'nm by Xi small-angle scattering method and Irg intrusion method.
I wish there was more than n'/g.

For example, activated carbon fibers (KF-M series manufactured by Toyobo, ACF manufactured by Nippon Kynor Co., Ltd.).

ACC, ACN, ACPC Linds, etc.), stacked in layers with mixed molded thin plates of carbon black with polyolefin resin powder or crushed products thereof, and heated from 10℃ to 7m1n to 500 to 2500℃ in an inert gas atmosphere furnace. 1
When the resin is heated and melted and impregnated and fired at a temperature increase range of 0°C/h, not only the voids due to the basis weight of the carbon fibers but also the fine pores inherent in activated carbon are left behind.
-C combore) is formed.

The vitrus carbon composite electrode bonded with the C-C combo 1- of the present invention having the above structure has bromine resistance, and the C-C composite electrode covering the bromine side electrode surface has bromine resistance. Because of the addition of electrochemical activation, it has superior properties over conventional vitrus carbon electrodes, and due to its inherently dense nature, it can also be used as a bipolar electrode.

Examples of the G invention (a) Example 1 Machi charcoal λ manufactured by Tohoku Kyowa Carbon Co., Ltd. as an electrode substrate
! F-306-3 and GCR- manufactured by Kobe Steel, Ltd.
101, and the surface active layer was made of Kuchigaru Giken's C-C composite PM-1 and activated carbon fiber-containing CC-507-15 manufactured by Nippon Kynol Co., Ltd., respectively.
(Machitan MF-308-3+PM-1", Electrode ■ (Machitan MF-306-318 CC-507-15), Electrode 1
[(GCR-101+PM-1) and electrode 111/ (
GCR-101 Junin CC-507-15) was fired under the same conditions (1000° C. for 1 hour in an Ar gas atmosphere).

Note that carbon paste was used as the adhesive.

10 dumbbells were taken from each electrode of these r-main electrodes, 5 were used to measure the initial bending strength and specific resistance, and the remaining 5 were 3 mol/l ZnBr2+3+o.
After being immersed in a high Br2 concentration electrolyte of l/I Br2 for 30 days, the bending strength and specific resistance were measured.

Next, take two 10 cm square pieces of each of the above electrodes iI to ■ to form a half cell, and use an electrolytic solution with the same composition as above to supply a constant current at a high current density of 50 a+A/cIj from an external power source. , after 30 days, electrode 1 on the oxidized side
-■ were taken out and their bending strength and specific resistance were measured in the same manner as above, and the results are shown in Table 1.

As is clear from Table 1, the bending strength of electrodes ■ and electrodes to which 'tc-c composites are bonded does not change much even after immersion and energization experiments, but electrodes to which carbon fibers are bonded and electrodes ■The change is relatively large. This difference is thought to depend on the strength of the surface-treated materials being joined. On the other hand, although the specific resistance value is slightly lower in the case where carbon fibers are bonded, it is advantageous because when electricity is applied, the value also decreases in the case where the C-C composite is bonded.

(b) Example 2 In order to examine the positive electrode characteristics (bromine side) as an electrode for a zinc-bromine battery, electrode A of a comparative example (B-I-Ruscarbon G
CR-101 only) and Comparative Example Electric 1B (C-C
Composite Kuchikaru Giken PP-444 only) and Example of the present invention (Vitrus Carbon 0CR- used for the electrode A)
101 and the C-C composite PP- used for the electrode B
3 mol/l ZnBr2+
The charge/discharge overvoltage was measured in an electrolytic solution of 0.3 mol/l Br2 at 25°C. The results are shown in the figure.

As is clear from the figure, electrode A of the comparative example has a low specific resistance value and good conductivity, but the overvoltage is large in both charging and discharging because the surface activity is small. In contrast, electrode (B) of comparative example
Since electrode A is porous, its surface activity is large, and its overvoltage is considerably smaller than that of electrode A. On the other hand, electrode C of the embodiment of the present invention
1, has the respective advantages of the electrodes A and B, and the overvoltage is smaller than that of electrodes A and B.

Table 1 ■ (As described in detail, according to the present invention, vitrus carbon is used as an electrode substrate, and a C-C composite is formed on the surface thereof)
By bonding -, even if an electrochemical reaction is performed in a liquid for a long period of time, the electrode becomes strong and has a long life. Furthermore, the electrical conductivity is improved by sufficient aging with an electrolytic solution. Furthermore, since the electrochemical activity is greater than that of an electrode composed of a single component, the overvoltage of the battery can be reduced.

Furthermore, since bonding is performed by firing in an electric furnace or the like at 800 to 1000° C. in an inert gas atmosphere, it can be performed stably and easily.

[Brief explanation of drawings]

The figure is a diagram showing the charging/discharging overvoltages of the electrode of the example of the present invention and the electrode of the comparative example.

Claims (1)

[Claims] A vitrus carbon composite electrode is made by using dense vitrus carbon as an electrode substrate, laminating a C-C composite on the surface of the electrode substrate via an adhesive, and then firing it.