JPH06290796A - Bipolar plate with reaction electrode layer for secondary battery - Google Patents

Abstract

PURPOSE:To reduce contact resistance between a bipolar plate and a reaction electrode layer so as to improve the energy efficiency of a bipolar plate with the reaction electrode layer for a secondary battery and to attain a thin and small size by joining the reaction electrode layer to the carbon conductive bipolar plate in a body. CONSTITUTION:A solution of polyvinyl chloride conductive resin prepared by kneading and conditioning polyvinyl chloride and a carbon filler or the like with each other is impregnately applied to nonwoven carbon fiber cloth, and then specific treatment is given to the nonwoven cloth to form a carbon conductive resin plate. A solution of vinyl chloride conductive resin is applied to the one or two faces of the resin plate, and then nonwoven ACF cloth is placed on the resin plate and the ACF cloth is compressively pressed to be joined to the resin plate in a body. The resultant resin plate is used for a bipolar plate 7. Then a diaphragm 5 is arranged in a middle part between the two bipolar plates 7 while collecting electrodes 8 are arranged respectively on the external faces of the plates 7, and the resultant unit is pressurized from the outside thereof to form a cell 4. A reaction electrode layer 6 is joined to a bipolar plate in a body in such a manner like this, so that contact resistance between the bipolar plate and the layer 6 can be reduced to improve the energy efficiency of the resultant bipolar plate 7, and the bipolar plate 7 is made to thin so that the thickness and size of the whole of a redox flow type secondary battery can be reduced.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a bipolar plate with a reaction electrode layer used in a secondary battery for an electric power storage system, and particularly useful for a redox flow type secondary battery, which has high energy efficiency during charging and discharging. The present invention relates to a bipolar plate with a reaction electrode layer that is easy to assemble.

[0002]

2. Description of the Related Art Power generation facilities are required to have the capacity to meet peak demand, but during non-peak hours such as at night, the power generation capacity is excessive and the operating rate of equipment is reduced, which is uneconomical. . Therefore, it would be very convenient to be able to store power during non-peak times and discharge it during peak times. Currently, pumped storage power generation is used as one method of power storage, but the installation location is generally remote and there is a problem of transmission loss, and it is becoming difficult to locate. Therefore, as an efficient alternative to this, a power storage system using a secondary battery is currently being developed.

For example, the Ministry of International Trade and Industry Institute of Industry and Technology has launched a large-scale project (one of the moonlight projects) from 1980 to 2011, and research targets include sodium-sulfur secondary batteries, zinc-chlorine secondary batteries, and zinc. -Four types of bromine rechargeable batteries and redox flow type rechargeable batteries are taken up, and concrete targets are output 1000 kW class, 8
Hourly charge / 8 hour discharge, total energy efficiency 70%
As mentioned above, under the condition that the life is 1500 cycles or more of charge and discharge, we have commissioned the designated company to carry out research and development.

Among the secondary batteries, the features of the redox flow battery are (a) easy design because the output part (battery cell part) and the capacity part (tank part) are independent, and (b) each battery cell. Since the state of charge of all parts is the same, it is not necessary to check the state of charge of all batteries and maintenance is easy. It is expected to be the most promising in the future because it can be expected to have a long life without any problems such as dropouts and growth of dendrites.

The technical contents of the redox flow secondary battery will be briefly described below. As shown in FIG. 2, this battery circulates a hydrochloric acid aqueous solution (hereinafter referred to as an electrolytic solution) containing two kinds of metal ions having different valences, which are stored in a positive electrode electrolytic solution tank 1 and a negative electrode electrolytic solution tank 2. The pump 3 supplies the flow-type battery cell 4 for charging and discharging.

That is, in this battery cell 4, a reaction electrode layer 6 is symmetrically arranged around a diaphragm 5 made of a cation exchange membrane.
A bipolar plate (bipolar plate) 7 and a collecting electrode (metal electrode) 8 are arranged, and the electrolytic solution circulates and circulates in the reaction electrode layer 6. The electrolytic solution of the positive electrode is an aqueous hydrochloric acid solution in which Fe ions are dissolved, and the electrolytic solution of the negative electrode is an aqueous hydrochloric acid solution in which Cr ions are dissolved, which are stored in the positive and negative electrode electrolytic solution tanks 1 and 2, respectively. The equilibrium reaction occurring in the battery cell during charge / discharge is represented by the following equation. Positive electrode Fe ³⁺ + e → Fe 2 ⁺ … Reduction reaction (discharge) Positive electrode Fe ³⁺ + e ← Fe 2 ⁺ … Oxidation reaction (charge) Negative electrode Cr ²⁺ → Cr ³⁺ + e… Oxidation reaction (discharge) Negative electrode Cr ²⁺ ← Cr ³⁺ + e ... Reduction reaction (charging) The diaphragm 5 separates positive and negative ions and permeates electron carriers, that is, hydrogen ions, and is generally a cation exchange membrane.

FIG. 2 shows a single battery cell, but in order to obtain a desired battery output (kW), the positive electrode reaction electrode layer 6 / bipolar plate 7 / negative electrode reaction electrode layer 6 / diaphragm 5 are actually formed as one unit. They are stacked as a unit, and the collective electrode 8 is provided on this outermost layer. This collective electrode 8 is connected to an external energy source (or external load) 9 to transfer energy.
A multi-layered body of single battery cells is called a cell stack. In the 60 kW class pilot plant currently undergoing verification test, the cell stack has 60 single cells (output capacity of 0.1
kW) multi-layered structure. In the battery cell of the present invention, the concentration of hydrochloric acid in the electrolytic solution is about 10%, and the temperature is up to 50 ° C.

The bipolar plate is required to have a property of efficiently passing electrons of the redox reaction shown in the above formula, that is, a low resistance property, a function of isolating the positive and negative electrode liquids, and a property of protecting the collecting electrode from the acidic electrolytic solution, that is, a hydrochloric acid aqueous solution. To be done. That is, (a) is not corroded by an aqueous hydrochloric acid solution containing Fe ions or Cr ions, (b) has a low resistance of 0.1 Ω or less for the through layer per cm ² between the front and back surfaces, and (c) has no liquid leakage. d) Excellent gas impermeability, (e) Large size, that is, about 100 kW or more, about 1 m square is required.

In the 60 kW class demonstration test plant, a bipolar plate is made to shrink while reacting with a special thermosetting resin at 1000 to 3000 ° C. to form an amorphous glassy carbon-based conductive plate called glassy carbon. This glassy carbon is (a) generally expensive, (b) hard and brittle, so it is easy to crack due to a slight twist during handling, (c) a bipolar plate support ( There is a difference in the coefficient of thermal expansion from that of a normal resin frame, which may lead to distortion and destruction due to the temperature difference, and it is difficult to increase the area. In order to solve this, it has been proposed to use a carbon-based conductive resin plate made of a composite conductive material in which a vinyl resin-based matrix is filled with a carbon-based filler.

In the case of a cell stack, positive electrode and negative electrode reaction electrode layers are arranged on both sides of a bipolar plate, and an activated carbon fiber nonwoven fabric (hereinafter referred to as ACF) having a thickness of about 3 mm is arranged on the reaction electrode layers. A thick steel plate is applied as a pressing jig to the outside of the cell stack so that the thickness is about 70% of the initial thickness, and the bolt is tightened and compressed at a pressure of 1 to ² kg per cm ² . ACF
Is a carbon fiber-based woven or non-woven fabric whose surface is activated in a microporous state.

[0011]

The electrical contact state between the bipolar plate and the reaction electrode layer is very important because it is involved in the transfer of electrons in the redox reaction, and as shown in FIG. The separate bipolar plate and the reaction electrode layer are mechanically compressed, but there are the following problems in reducing the contact resistance in this way. The current flowing through the contact boundary surface is naturally narrowed at the minute contact portion, and is easily unstable due to the influence of foreign matter, dust, fine irregularities on the surface of the bipolar plate, so that the contact resistance between solids is large. It becomes stable and it is difficult to increase energy conversion efficiency above a certain level. Since the bipolar plate and the diaphragm are required to have a mechanical strength sufficient to withstand a pressure of 1 to ² kgf / cm ² , a certain thickness or more is required. Also, the pressing jig is required to be thick and strong. This reduces the total thickness of the cell stack,
It goes against the demand to downsize the entire secondary battery system. From the viewpoint of assembling work, incorporating separate individual parts requires more steps and more assembly cost than incorporating integrated parts.

[0012] The present invention solves the above-mentioned conventional problems. The contact resistance between the bipolar plate and the reaction electrode layer is low, the energy conversion efficiency is high, and no excessive pressing force is required. It is an object of the present invention to provide a bipolar plate with a reaction electrode layer for a secondary battery, which can reduce the assembly cost because the diaphragm and the diaphragm can be thinned, the entire system can be thinned and downsized, and the number of parts can be reduced.

[0013]

As a result of various studies, the inventors of the present invention achieved the above-mentioned object, which is composed of a carbon-based conductive plate and has a carbon fiber-based woven fabric or a carbon fiber-based woven fabric on at least one surface. A bipolar plate with a reaction electrode layer for a secondary battery is characterized in that a reaction electrode layer made of a non-woven fabric is integrally bonded.

As an embodiment of the present invention, as shown in FIG. 1 (a), when the reaction electrode layers 6 are integrally bonded to both surfaces of the bipolar plate 7, as shown in FIG. When the reaction electrode layer 6 is integrally bonded to one surface of the plate 7, and further on the outermost side of the cell stack, as shown in FIG. 1C, the collective electrode (metal electrode) 8 is connected to one surface of the bipolar plate 7. In some cases, and the reaction electrode layer 6 is joined and integrated in the other surface.

As a material used for the bipolar plate of the present invention, the above-mentioned glassy carbon or a carbon-based conductive resin plate made of a composite conductive material including a vinyl resin-based matrix and a carbon-based filler is used, and more specifically, Is
(A) is composed of a composite material in which a carbon resin filler such as graphite or carbon black is filled in a vinyl resin matrix,
(B) or a carbon-based conductive resin plate made of a conductive resin in which a vinyl-based matrix is filled with a carbon-based filler and a carbon fiber-based base cloth.

While glassy carbon is expensive and has the drawback of being easily broken during handling, the carbon-based conductive resin plate is easy to integrate with the reaction electrode layer, and has a higher thermal conductivity than glassy carbon. In the present invention, the carbon-based conductivity is low because the rate is low, the heat insulation is excellent, the temperature of the electrolytic solution is easy to control, and it is strong against external force in the bending direction during handling, drop, impact, etc. Use of resin plate is desirable.

The vinyl resin matrix used for the carbon conductive resin plate is obtained by addition polymerization of monomers having a vinyl group (CH ² ═CH—X and CH ² ═C (X) —Y). Including all high molecular compounds,
Polyethylene, polypropylene, poly-n-butylene,
Polyisobutylene, polybutene, poly-4-methylpentene-1, polyvinyl chloride, polyvinyl alcohol, polystyrene, polyvinyl acetate, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, polyacrylic Acid, polymethacrylic acid, polymethylmethacrylate, polymethylmethacrylate, polyacrylic acid higher ester, polyacrylonitrile, chlorinated polyethylene, chlorosulfonated polyethylene, epichlorohydrin rubber, acrylic rubber, ethylene propylene rubber, ethylene propylene diene rubber, styrene -Ethylene butylene-styrene block copolymer, carboxylated styrene-ethylene butylene-styrene block copolymer and the like can be mentioned, but hydrochloric acid resistance, easy blending of carbonaceous filler, extrusion It is desirable to select chlorine-containing polymers such as polyvinyl chloride, chlorinated polyethylene, vinyl chloride-vinyl acetate copolymer, etc. .

Further, since these vinyl resin-based matrices have a low melting point or softening point and melt at a relatively low temperature, the carbon-based conductive resin plate using this as a matrix and the reaction electrode layer can be integrally bonded. It can be easily achieved by a simple means such as heat fusion bonding such as a) thermocompression bonding method, (b) ultrasonic welder method, and (c) high frequency welder method.

[0019] the carbon-based filler, flakes of natural graphite, amorphous natural graphite, artificial graphite, expanded graphite, acetylene black, Ketjen black ^R EC, conductive oil furnace black include alone or combined formulations, such as carbon fiber. Examples of the method of directly kneading the carbon-based filler into the vinyl resin-based matrix include a two-roll with heating device, a Banbury mixer, a Henschel mixer, and a cokneader (biaxial extruder).

The carbon-based conductive plate (A) mentioned in the above "0015" is a slit-shaped die (commonly referred to as a T-die) of an extruder for thermoplastic resin after kneading a vinyl resin-based matrix and a carbon-based filler. ) And extruding into a sheet shape, and if necessary, press molding can be carried out for production. In this case, if the filling amount of the carbon-based filler is too small, the resistance value becomes high, and if it is too large, the molding process becomes difficult. Therefore, it is 10 to 80% by weight, preferably 20 to 60% by weight.
It is good to say

The carbon conductive plate (B) mentioned in the above "0015" is a base cloth such as a woven or non-woven fabric of acrylic fiber (PAN) carbon fiber, petroleum pitch carbon fiber, coal pitch carbon fiber. In addition, the vinyl resin matrix is impregnated with a conductive resin solution filled with a carbon-based filler and cured, and further, a method of press-molding the same, or a conductive resin layer is laminated on a carbon fiber-based base cloth. It can be manufactured by a method of pressing together. The role of this carbon fiber-based fabric is the mechanical strength of the carbon-based conductive plate,
Dimensional stability, low resistance, etc.

The conductive resin solution impregnated into the carbon fiber base cloth is prepared by dissolving the selected resin matrix in a suitable solvent,
It can be obtained by mixing the above-mentioned conductive filler, kneading with a blade type high speed stirrer such as a dissolver, and then finely crushing and kneading meat with a sand grinder or the like. When polyvinyl chloride is used as the vinyl resin matrix, the solvent includes tetrahydrofuran, cyclohexanone, nitrobenzene, methyl ethyl ketone, dioxane and the like. If the viscosity of this solution is too low, it is necessary to repeat the impregnation several times because the voids of the base cloth cannot be filled with one time impregnation, and if it is too high, impregnation becomes difficult.
10,000P range, preferably 100-1000P
It is good to select from the range. The thickness of the carbon-based conductive plate is
The thickness may be equivalent to that of conventional glassy carbon (0.5 to 2 mm), but in the present invention, mechanical compression is not required and the bipolar plate is not required to have mechanical strength. It can be selected from a range of up to 1 mm.

The reaction electrode layer used in the present invention may be a conventionally known one, and the above ACF can be used. As a method of joining and integrating the reaction electrode layer to the carbon-based conductive plate, a method of applying a conductive adhesive to one or both surfaces of the reaction electrode layer and the carbon-based conductive plate, and bonding and curing, or carbon. When the system conductive plate is a conductive resin plate, it is passed through a heating laminator roll or a hot plate press to heat-melt the surface layer of the conductive resin plate and join it, applying a conductive adhesive The method of heat and pressure bonding, the ultrasonic welding method using the frictional heat of ultrasonic vibration of several tens of kHz, the microwave (1.
A high-frequency welder joining method using 25 GHz) is exemplified, but the simplest method is to apply a conductive adhesive to the surface of the conductive resin plate and bond it by ACF compression bonding.

As the conductive adhesive used here,
Since it is necessary not to be attacked by the hydrochloric acid-based electrolytic solution and not to adversely affect the electrolytic solution, it is sufficient to include a carbon-based filler as a conductivity-imparting component in the resin-based adhesive. As the adhesive, in addition to the vinyl resin type represented by polyvinyl chloride, epoxy resin type, urethane resin type, acrylic resin type, synthetic rubber type, etc. are exemplified, but when using a conductive resin plate In order to obtain adhesive strength, it is preferable to use a vinyl resin adhesive of the same type as the resin component used for the conductive resin plate described above.

[0025]

In the present invention, the contact resistance between the bipolar plate and the reaction electrode layer is reduced in the bipolar plate composed of the carbon-based conductive plate,
This is because the reaction electrode layers are bonded and integrated, and because they are integrated, the assembly process is simplified.

[0026]

Example: Polyvinyl chloride having a degree of polymerization of 700, TK700
(Shin-Etsu Chemical Co., Ltd., trade name) 100 parts by weight and stabilizer, octyl tin mercapto 3 parts by weight, are dissolved in a solvent, cyclohexanone, 600 parts by weight using a blade type high speed stirrer, and flakes therein. Natural graphite, CPB-30
(Co., Ltd. Chuetsu Graphite Industries, Ltd., trade name) and 75 parts by weight, Ketchen black ^R EC (Lion Corporation, trade name) 2
5 parts by weight was added, and the mixture was kneaded by dispersion with the same high-speed stirrer to prepare a polyvinyl chloride conductive resin solution having a solid content of 25% by weight.

Next, using a comma coater as an impregnating device, a basis weight of 100 gf / m ² (apparent thickness of 1.7 mm),
PAN-based carbon fiber non-woven fabric with an area resistance of 0.3Ω / □, Best Fight Paper BP-1100A-EP (trade name, manufactured by Toho Rayon Co., Ltd.) is impregnated and applied, and passed through a hot air drying oven at 100 ° C. for 90 seconds. After touch and dry
A heating / cooling press was performed under the conditions of 0 ° C. × 30 kgf / cm ² , 10 minutes of preliminary heating, 15 minutes of main heating press, and 20 minutes of cooling press to obtain a carbon-based conductive resin plate having a thickness of 0.6 mm.
The volume resistivity of this carbon-based conductive resin plate is calculated by Loresta A
When measured using a P.MCP-T400 (trade name, manufactured by Mitsubishi Petrochemical Co., Ltd.), it was 3 × 10 ⁻² Ω · cm, and the actual measured value of the penetration resistance per 1 cm ^{2 of} the front and back surfaces was about 8 mΩ. It was

Next, on one surface of the carbon-based conductive resin plate,
The polyvinyl chloride conductive resin solution mentioned in the above “0026” is applied, an ACF non-woven fabric having a thickness of 3.1 mm × 150 mm □ is applied thereon, and the ACF is compressed by about 10% at 120 ° C. for 60 minutes. Bonding and integration were performed under the conditions. This A
A carbon-based conductive resin plate laminated with a CF nonwoven fabric on one side is used as a bipolar plate, a diaphragm is arranged at the center, and a Cu electrode plate as a collective electrode is arranged on the outer surface as shown in FIG.
5kgf / cm ² is added to make ACF nonwoven fabric 2.2
By pressing so as to have a size of mm, a redox flow type small battery cell A for evaluation was formed.

[0029]

[Comparative example] ACF non-woven fabric is 0.6mm thick
× 150mm □ carbon-based conductive resin plate, thickness 3.1m
Using an ACF non-woven fabric of m × 150 mm □, a diaphragm is placed in the center and a Cu electrode plate as a collective electrode is placed on the outer surface, and a surface pressure of 1.5 kgf / cm ² is applied from the outside as in FIG.
The CF non-woven fabric was pressed so as to have a thickness of 2.2 mm to form a redox flow type small battery cell B for evaluation.

After all, the difference between the small battery cell A and the small battery cell B is whether or not the bipolar plate and the reaction electrode layer are integrally bonded. The reason why the ACF having the same thickness was used and compressed to the same thickness is to make the flow passage cross-sectional area of the electrolytic solution and the flow passage resistance constant. Table 1 shows small battery cells A and B
The evaluation results when charging and discharging are shown.

[0031]

[Table 1]

[0032]

In the present invention, since the reaction electrode layer is joined and integrated with the bipolar plate made of the carbon-based conductive plate, the contact resistance between the bipolar plate and the reaction electrode layer is reduced, and as a result, energy is reduced. The efficiency can be improved.
Further, since a thin bipolar plate can be used, the redox flow type secondary battery as a whole can be made thin and compact.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a bipolar plate with a reaction electrode layer for a secondary battery of the present invention, (a) is a bipolar plate in which reaction electrode layers are joined and integrated on both sides, and (b) is a reaction electrode on one side. A bipolar plate obtained by joining and integrating layers is shown. (C) is a bipolar plate obtained by joining and integrating a collective electrode (metal electrode) on one surface and a reaction electrode layer on the other surface.

FIG. 2 is a conceptual diagram of a redox flow secondary battery.

FIG. 3 is a vertical sectional view of a conventional bipolar plate in which a reaction electrode layer and a bipolar plate are separated.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrolyte tank for positive electrodes 2 ... Electrolyte tank for negative electrodes 3 ... Circulation pump 4 ... Battery cell 5 ... Diaphragm 6 ... Reaction electrode layer 7 ... Bipolar plate 8 ... Collective electrode 9 ... External energy source

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Isono, 1-406-1 Yoshino-cho, Omiya-shi, Saitama, Shin-Etsu Polymer Co., Ltd. Product Research Laboratory (72) Tetsuji Ito 1-3-1, Shimaya, Konohana-ku, Osaka No. Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Toshio Shigematsu 1-3-3 Shimaya, Konohana-ku, Osaka City Sumitomo Electric Industries, Ltd. Osaka Works

Claims (3)

[Claims] 1. A bipolar plate with a reaction electrode layer for a secondary battery, comprising a carbon-based conductive plate, and a reaction electrode layer made of a carbon fiber-based woven or non-woven fabric bonded and integrated on at least one surface. . 2. The bipolar plate according to claim 1, wherein the carbon-based conductive plate is made of a composite conductive material in which a vinyl resin-based matrix is filled with a carbon-based filler. 3. The bipolar plate according to claim 1, wherein the carbon-based conductive plate comprises a conductive resin in which a vinyl-based matrix is filled with a carbon-based filler and a carbon fiber-based base fabric.