JPH0358149B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a carbon plastic electrode used in a bromine-zinc battery, in which a conductive sheet made of high temperature treated carbon fiber is back-treated on the surface of a conventional carbon plastic member. In particular, the present invention relates to a carbon plastic electrode capable of improving the efficiency of electrochemical reactions and stably maintaining the efficiency. [Prior art] The electrodes conventionally used in bromine-zinc secondary batteries can be broadly classified from the material standpoint: metal electrodes using metal, carbon electrodes using carbon itself, and conductive materials such as plastics. There are plastic electrodes made by kneading carbon, silver, etc.) to give them conductivity. Among these, the material of the metal electrode is limited to noble metals such as platinum, considering the corrosive effect of bromine molecules generated when charging the battery. These precious metals generally have the advantage of having very low electrical resistance, good battery voltage efficiency, long discharging time, and excellent coulombic efficiency, but their biggest drawback is their It is expensive and ultimately unsuitable for practical use. Furthermore, although carbon electrodes have the lowest electrical resistance next to metal electrodes, they have low mechanical strength and are particularly susceptible to cracking due to impact, which poses a problem in their reliability. In addition, carbon electrodes have the disadvantage that, because they are generally porous, they cannot be used in bibolar series stacked battery systems in which the electrode itself functions as a separator. Finally, although plastic electrodes have sufficient mechanical strength, their electrical resistance is high, and their coulombic efficiency is low in reactivity with the active material, resulting in the problem of having to settle for low efficiency. remains. As described above, each material has its advantages and disadvantages in terms of economy, lifespan, efficiency, etc., and an electrode material that can be safely used in bromine-zinc secondary batteries has not yet been found. The inventors of the present application previously proposed in Japanese Patent Laid-Open No. 57-197772 an electrode to solve the above problems, in which a conductive electrode was made of carbon fiber with or without an adhesive layer on the surface of the plastic member, and was made of felt or knit. We also proposed a plastic electrode formed by forming a layer of conductive sheets selected from cross-type or cross-type conductive sheets. However, it is still insufficient. [Object of the Invention] Under these circumstances, the present invention provides high efficiency, long life,
The purpose of this study is to conduct various studies to obtain inexpensive electrode materials, and to obtain electrodes that can relatively easily improve the voltage efficiency and Coulombic efficiency of a battery. [Summary of the Invention] The present invention was obtained by further improving the above-mentioned research, and includes backing a conductive sheet selected from the above-mentioned felt, knit, or cloth forms not made of carbon fibers on the surface of a conductive plastic member. The carbon plastic electrode is characterized by being subjected to high-temperature treatment beforehand. Polyolefin is used as the paste polymer of the conductive plastic member constituting the electrode base because it is required to be resistant to deterioration even when in contact with free bromine or ionic bromine for a long time. The conductive plastic member (CP) is made of, for example, 100 parts by weight of high-density polyethylene and carbon black.
It can be made by kneading 50 parts by weight and press molding. Furthermore, the method of high-temperature treatment of a conductive sheet in the present invention involves heating a sheet made of carbon fiber in the form of felt, knit, cloth, etc. in a trace oxygen atmosphere, generally in an electric furnace, to a temperature of 1000 to 2000 ml.
℃ for 10 minutes to 2 hours. An electrode obtained by backing a high-temperature-treated conductive sheet onto the surface of a conventional conductive plastic member (CP) using a conventional method (referred to as HT.CC-CP electrode).
No matter which form of conductive sheet is used, the characteristics are improved compared to conventional electrodes (CC-CP electrodes) that are backed by conductive sheets that are not subjected to high-temperature treatment. When measuring the specific resistance (p) of the treated surface, that is, the HT.CC-CP electrode, it was lower than that of the conventional CC-CP electrode, and this is because the carbon fiber graphitizes due to the high temperature treatment. The conductivity of HT increases.
This contributes to lowering the specific resistance of the CC-CP electrode. The characteristics of carbon plastic electrodes vary depending on the heat treatment time and temperature, and this is due to the degree of graphitization of the carbon fibers due to the high temperature treatment. The layer of high temperature treated conductive sheet (HT.CC) is formed on the conductive plastic component (CP) by thermocompression bonding. This crimping work is
This is done when the plastic electrode member has sufficiently softened due to heating, but by providing a layer of HT.CC on the surface of the plastic member, the surface is activated while exerting a secondary effect of protecting the electrode surface. form a layer. If the HT.CC used is one made of porous carbon fiber, the specific resistance of the electrode backed with a conductive sheet (HT.CC-CP electrode) can be further reduced. There are no restrictions on the porosity, thickness, or basis weight of the sheet, but the thickness should be 1/2 to 3 of the CP thickness, regardless of bipolar or polar type, to avoid increasing the voltage when connected in series (laminated) to increase the voltage. /2 is desirable, and the treatment temperature and time in high temperature treatment is 1500℃.
It took about 1 hour before and after, and it was more economical than Example 2, which will be described later, and was constructed with these HT.CC-CP electrodes.
The discharge characteristics of Zn-Br ₂ cells are more voltage efficient and therefore more energy efficient than those of Zn-Br ₂ cells constructed with conventionally treated CP electrodes. HT.CC made of carbon fiber which is then treated at high temperature
Regarding the morphology of HT.CC, the cross morphology or nitrite morphology is an electrode made using HT.CC obtained by high-temperature treatment of a porous material with a higher porosity (HT.CC-CP).
It was confirmed by the Examples described later that the electrode) exhibited improved characteristics over conventional electrodes. The configuration and effects of the present invention will be explained in more detail below using Examples. [Examples of the Invention] Example 1 A cross-shaped conductive sheet was subjected to high-temperature treatment in an electric furnace in a trace oxygen atmosphere at 1000°C, 1400°C, 1600°C, and 2000°C for 30 minutes each. On the other hand, a conventional cross-shaped conductive sheet that is not subjected to high temperature treatment and the four types of high temperature treated conductive sheets are thermocompression bonded to the CP. Obtained electrode (): CC−CP electrode: HT ₁₀₀₀ CC−
CP electrode: HT ₁₄₀₀ CC−CP electrode:
HT ₁₆₀₀ CC-CP electrode, :HT ₂₀₀₀ CC-CP electrode These are used as the bromine side electrode, and a conventional plastic electrode (CP electrode) is used as the zinc side electrode.
Distance between the anode and cathode is 2mm, and Asahi Kasei is used as the diaphragm.
A bromine-zinc battery was constructed using RAS0.6 manufactured by Co., Ltd., and discharged at room temperature (25°C) with an electrolyte concentration of 3 mol/ZnBr ₂ +Br ₂ and a current density of 20 mA/cm ² . -Electrode potential (V) compared to AgCl electrode
As a result, Figure 1 was obtained. As shown in Figure 1, the high temperature treated HT.CC-CP electrode has better discharge characteristics than the non-high temperature treated CC-CP electrode, and the higher the treatment temperature, the better the characteristics. .
However, the degree of improvement in the properties is only gradual at temperatures above 1500 to 1600°C. Example 2 In the same atmosphere as in Example 1, only the high temperature treatment temperature was kept constant at 1600°C, and the treatment time was 10 minutes () 30 minutes () 1 hour () 1 hour 30 minutes ()
CP the HT.CC prepared after changing for 2 hours ()
A discharge test was performed on the HT.CC-CP electrode obtained by bombarding the HT. As a result, Figure 2 was obtained. As shown in FIG. 2, those treated at a high temperature of 1600° C. for more than 1 hour show almost the same excellent properties. Example 3 A carbon plastic electrode (A) (HT.CC-CP electrode) in which a conductive sheet that has been subjected to high temperature treatment for 1 hour at 1500°C is backed with CP is used as an anode, and a carbon plastic electrode (CP electrode) is used as a cathode. did
For comparison with Zn-Br ₂ batteries, conventional CC-CP was used as the anode.
Characteristic tests were carried out on Zn-Br ₂ batteries using the electrode (B), the untreated CP electrode (C), and the CP electrode as the cathode.
The operation was carried out under the following operating conditions: RAS 0.6, 20 mA/cm ² constant current charging and discharging (charging for 3 hours, discharge cutoff at 0 V). The results are shown in Table 1.

[Table] As shown in the table above, plastic electrodes (HT.
CC-CP) A shows an increased value especially in terms of voltage efficiency compared to the other B (CC-CP electrode) and C(CP electrode), and therefore the energy efficiency is improved. Example 4 A conductive sheet (P.CC) made of cross-shaped porous carbon fibers is heated in an electric furnace at 1500°C in an inert atmosphere with a trace oxygen concentration for 30 minutes.The resulting high-temperature-treated porous conductive sheet The sheet is thermocompression bonded to a conductive plastic member at the same time as the frame is formed on the member.The cross-shaped high temperature treated porous conductive sheet thus obtained is called a backing carbon plastic electrode (hereinafter referred to as HT.P.CC-CP). (electrode), the porosity is calculated from the thickness of the cloth, the basis weight, and the amount of pores.
It became 12.8%. Next, the above HT.P.CC-CP electrode, a conventional cross-form porous conductive sheet that has not been subjected to high temperature treatment, a backing carbon plastic electrode (hereinafter referred to as P.CC.-CP electrode, porosity 12.8%) and an untreated A discharge potential characteristic test of treated carbon plastic electrodes (CP electrodes) was carried out using ZnBr 2 with an electrolyte concentration of 3 mol/ZnBr _2.
A discharge test was conducted at 25° C. with +Br ₂ and a current density of 40 mA/cm ² , and the electrode potential (V) was determined in the same manner as in Example 1, and the results shown in FIG. 3 were obtained. In Figure 3, the curve is
HT.P.CC-CP electrode, the curve is P.CC.-CP electrode,
The curve is a characteristic curve when using a CP electrode,
It is clear that despite the same porosity, HT.P.CC-CP maintains a higher discharge potential than conventional P.CC.-CP, especially in the low Br ₂ concentration range. Furthermore, the characteristic values of the above three types of electrodes are shown in Table 2.

[Table] As shown in Table 2, the HT.P.CC-CP electrode is
It is clear that the specific resistance value is particularly small compared to the P.CC.-CP electrode. Example 5 Three types of cross-shaped conductive sheets CC _6.0 , CC 13.2 , with different porosity (P) of 6.0%, 13.2%, and _19.2 %, respectively.
CC _19.2 (the number of saphix indicates P%) was selected and heated in an electric furnace in the same atmosphere as in Example 4.
High temperature treatment was carried out by heating at 1100°C for 30 minutes. Thereafter, a conductive plastic member was heat-pressed in the same manner as shown in Example 4 to form high-temperature-treated porous conductive sheet backing CP electrodes (three types of
HT.P.CC _6.0 −CP, electrode HT.P.CC _13.7 −CP electrode,
and HT.P.CC _19.2 −CP electrode. ) was obtained. Next, each of these was assembled into a cell and the electrode potential during discharge was measured using a conventional method. In addition, the electrolyte contains 3 mol/
A ZnBr ₂ +Br ₂ solution was used, and an untreated CP electrode was used as the counter electrode. The average discharge potential (V ₄₀ ) at an electrolytic solution Br ₂ concentration of 0.4 to 1.0 mol/was determined from the obtained discharge potential curve at 40 mA/cm ² discharge. The result is the third
Shown in the table.

[Table] From the results in Table 3, HT.P obtained by high temperature treatment.
It can be seen that all the CC-CP electrodes have improved characteristic values compared to the conventional P.CC.-CP electrode. Example 6 The high temperature treated porous conductive sheet-backed carbon plastic electrode (HT.P.
CC-CP electrode) and a porous conductive sheet-backed carbon plastic electrode (P.CC.-CP electrode) were used as the anode (bromine electrode), respectively, and an untreated carbon plastic electrode diaphragm was used as the cathode as in Example 1.
Using RAS0.6, the electrode spacing is approximately 2mm, and the charging and discharging current density is 20m.
Voltage efficiency (Veff%) ^and coulombic efficiency (Ceff
%) and energy efficiency (Eeff%)
Shown in the table.

[Table] As shown in Table 4, HT.P.CC− as an anode
Batteries using CP electrodes had particularly improved voltage efficiency and, as a result, increased energy efficiency. Example 7 A porous conductive sheet in the form of a nitrate was prepared in an electric furnace.
Heat at 1100℃ for 30 minutes in an inert atmosphere with trace oxygen concentration. The obtained porous conductive sheet in the form of a high-temperature treated knit is thermocompression bonded to a carbon plastic member when the member is framed. Carbon plastic (CP) electrodes have a density of 0.94g/ ^cm3 , for example.
Carbon black (surface area 1000m ² /g, average particle size 30n) is added to 100 parts by weight of high-density polyethylene
m) Knead 50 parts by weight and make a thin plate electrode by hot press molding. High-temperature-treated porous conductive sheet backing in the form of a knit formed in this way
CP electrode (hereinafter referred to as HT.NPCC-CP electrode) and conventional knitted conductive sheet backing CP
Table 5 was obtained by comparing the characteristics of electrodes (hereinafter referred to as NPCC-CP electrodes) with a porosity P of 14.1%.

[Table] As is clear from Table 5, although the specific surface area of the HT.NPCC-CP electrode has hardly changed, the overall resistivity has decreased and the potential characteristics (average potential) have improved. Example 8 HT.NPCC-CP() and NPCC-CP() obtained in Example 7 were used as a bromine electrode, and 3 mol/ZnBr ₂ +Br ₂ was used as the electrolyte, and discharged at 25°C at a current density of 40 mA/cm ² The electrode potential (V) was determined and the results shown in Figure 4 were obtained. It is clear that the characteristics of the HT.NPCC-CP electrode are improved even at this current density. Example 9 Nit-form porous conductive sheets with different porosity P as in Example 7, A (P=0%), B (P=
Three types, 14.1%) and C (P=16.0%), were selected and subjected to high-temperature treatment by heating each in an electric furnace at 1000° C. for 40 minutes in the atmosphere of Example 7. Then, it was treated at high temperature
Surface-treated electrodes were fabricated by thermocompression bonding AB and C to CP using conventional methods. These are designated as the A-HT.CC-CP electrode, the B-HT.CC-CP electrode, and the C-HT.CC-CP electrode. For these, the average discharge potential V ₂₀ at a constant current discharge of 20 mA/cm ² at a Br ₂ concentration in the electrolyte in the range of 0.4 to 1.0 mol/was compared with that of a conventional one not subjected to high temperature treatment, and Table 6 was obtained.

[Table] As is clear from Table 6, the higher the porosity, the better the characteristics of the electrode treated at high temperature. Example 10 The C-HT.CC-CP electrode obtained in Example 9 and the conventional C-CC-CP electrode were respectively used as the anode (bromine electrode) of a Zn-Br ₂ battery, and the negative electrode (zinc electrode) was Using the same RAS0.6 as used in Example 1 for the treated CP electrode and the diaphragm between the anode chamber and the cathode chamber, the battery was assembled with a distance between electrodes of 2 mm and a charge/discharge current density of 20 mA/cm ³
Battery characteristics (voltage efficiency Veff%, coulombic efficiency Ceff
%, and energy efficiency Eeff%). The results are shown in Table 7 below.

〔Effect of the invention〕

Electroconductive sheet made of carbon fiber which is an electrode for Zn-Br ₂ battery Anode The conductive sheet which is the backing material in the CP electrode, especially the porous conductive sheet with fine pores formed therein, is heated in an electric furnace before backing. A high-temperature-treated conductive sheet-backed CP electrode (HT.CC-CP
The conductivity of the sheet increases due to the graphitization of carbon fibers caused by high-temperature treatment, and therefore the discharge potential characteristics of the electrode itself are improved compared to untreated CC-CP electrodes. .The Zn-Br ₂ battery with the CC-CP electrode as the anode has increased voltage efficiency and therefore energy efficiency compared to the conventional battery with the CC-CP electrode as the anode. The above characteristics are the same when the porous conductive sheet in the form of cloth or knit is subjected to high temperature treatment. In addition, the porosity of porous conductive sheet backing CP electrodes differs depending on the amount of pores in the sheet, and therefore the potential characteristics also differ depending on the surface area. The properties of the electrodes that were exposed to heat were improved compared to those that were not subjected to high-temperature treatment. As mentioned above, when the carbon plastic electrode according to the present invention is applied as an anode of a Zn-Br ₂ battery,
This has the effect of significantly improving the voltage efficiency, Coulomb efficiency, and energy efficiency of the battery compared to when electrodes made of conventional materials are used.

[Brief explanation of drawings]

Figures 1 to 4 are for showing the effects of the present invention.
It is a graph of Br ₂ concentration vs. electrode potential.

Claims (1)

[Scope of Claims] 1. A carbon plastic electrode characterized in that it is made by backing a sheet made of high temperature treated carbon fiber on the surface of a conductive plastic member. 2 The sheet made of carbon fiber is felt,
2. A carbon plastic electrode according to claim 1, characterized in that a conductive sheet selected from the above is used. 3. The sheet made of the carbon fiber is heated in an inert atmosphere with a trace oxygen concentration at a temperature of 1000 to 2000°C for 10 minutes.
The carbon plastic electrode according to claim 1, characterized in that it is heated at high temperature for 2 hours. 4. The carbon plastic electrode according to claims 1 and 2, wherein the sheet is made of porous carbon fiber.