JP2012221775A - Bipolar plate for redox flow battery and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bipolar plate for redox flow battery having high conductivity in which mixing of a resin and a conductive carbon and sheeting of the mixture are facilitated during manufacture, and elution of a plasticizer into an electrolytic solution is suppressed, and to provide a manufacturing method therefor.SOLUTION: The bipolar plate for redox flow battery consists of a sheet of a composite conductive material containing a thermoplastic resin, a conductive carbon and a plasticizer, and is manufactured by irradiating the sheet with ionizing radiation thereby bonding the thermoplastic resin and the plasticizer. A manufacturing method therefor is also provided.

Description

  The present invention relates to a bipolar plate (bipolar plate) for partitioning cells of a redox flow battery (also referred to as a redox flow secondary battery) and a method for manufacturing the same.

  A redox flow battery is a battery that utilizes changes in the valence (oxidation-reduction reaction) of ions (such as vanadium) in an electrolytic solution (a positive electrode solution, a negative electrode solution). This battery is composed of a plurality of cells. In each cell, a frame having a porous electrode (positive electrode and negative electrode) and a bipolar plate is disposed on both sides of the diaphragm. Then, the positive electrode solution is circulated in the positive electrode chamber in which the positive electrode is disposed, and the negative electrode solution is circulated in the negative electrode chamber in which the negative electrode is disposed to cause the battery reaction. In a redox flow battery, in order to obtain a high voltage, a plurality of the above cells are stacked (cell stack).

  In order to reduce the internal resistance of the redox flow battery, the bipolar plate is required to have high conductivity. Therefore, it is desirable that the bipolar plate is made of a conductive plate that allows current to pass but not electrolyte, and has a high mechanical strength. For example, a conductive filler is dispersed in a resin to provide conductivity. What consists of the composite electrically-conductive material used is used.

  Here, the conductive filler is referred to as a conductive filler made of a chemically stable carbonaceous material (hereinafter referred to as “conductive carbon”) rather than a metal filler that may be ionized by the electrolytic solution and impair the battery characteristics. ), For example, graphite and carbon black are considered preferable. Therefore, as a preferable bipolar plate, plastic carbon obtained by kneading conductive carbon into a resin is widely used. For example, Patent Document 1 discloses a bipolar plate made of chlorinated polyethylene containing graphite. .

JP 2002-367660 A

  A bipolar plate made of plastic carbon is formed by processing a compound obtained by mixing conductive carbon into resin into a sheet shape. On the other hand, it is desirable that the bipolar plate has higher conductivity, but in order to achieve higher conductivity, it is necessary to add a larger amount of conductive carbon to the resin. However, when a large amount of conductive carbon is added to the resin, there is a problem that the compound becomes hard and its fluidity is lowered, and mixing and sheet processing become extremely difficult.

  The fluidity of the compound can be improved by adding a plasticizer to improve processability. However, from the bipolar plate produced by adding a plasticizer, elution of the plasticizer into the electrolytic solution during battery operation can be considered. If the electrolytic solution is contaminated by elution of the plasticizer, the plasticizer may adhere to the surface of another battery member and adversely affect battery performance. For example, when the electrolytic solution adheres to the electrode, the resistance may increase significantly. In addition, the electrolyte may enter the plasticizer elution portion of the bipolar plate, which may adversely affect the mechanical properties and resistance of the bipolar plate.

  The present invention has a high conductivity, and the bipolar plate for a redox flow battery in which the above-mentioned problems of the prior art are solved, that is, it is easy to mix and sheet a resin and conductive carbon at the time of production, It is another object of the present invention to provide a bipolar plate for a redox flow battery in which elution of a plasticizer into an electrolyte solution is suppressed, and a method for manufacturing the same.

  As a result of intensive studies to achieve the above-mentioned problems, the inventor has blended a plasticizer with a compound composed of a resin and conductive carbon to process it (ease of mixing of resin and conductive carbon, sheet processing, etc.). ), It was found that by irradiating the resin with ionizing radiation after processing, elution of the plasticizer into the electrolyte solution can be suppressed while maintaining high conductivity, and the present invention has been completed. . That is, said subject is solved by the invention which consists of a structure shown below.

  The invention according to claim 1 is a bipolar plate comprising a sheet of a composite conductive material containing a thermoplastic resin, conductive carbon and a plasticizer, and the sheet is irradiated with ionizing radiation, and the thermoplastic resin and plastic A bipolar plate for a redox flow battery, wherein the agent is bonded.

  The bipolar plate of the present invention is obtained by processing a composite conductive material into a sheet, and this composite conductive material is mixed with a thermoplastic resin so as to obtain high conductivity, and, A plasticizer is mixed so that the compound containing conductive carbon has excellent processability. Therefore, both high conductivity and excellent workability are achieved. The composite conductive material forming the bipolar plate of the present invention may contain components other than the thermoplastic resin, conductive carbon, and plasticizer as long as the gist of the present invention is not impaired.

  The bipolar plate of the present invention is also characterized in that after the composite conductive material is processed into a sheet shape, the obtained sheet is irradiated with ionizing radiation, and as a result, the thermoplastic resin and the plasticizer are bonded. Accordingly, the plasticizer used in the present invention is selected from those having the function of improving the processability of the compound and the property of being bonded to the thermoplastic resin by irradiation with ionizing radiation.

  In this bipolar plate, since the thermoplastic resin and the plasticizer are bonded, elution of the plasticizer into the electrolyte during battery operation is suppressed. Therefore, the contamination of the electrolytic solution due to the elution of the plasticizer, the adverse effect on the battery performance, the mechanical characteristics of the bipolar plate, and the like are prevented. In general, the mechanical strength of the bipolar plate is improved by the irradiation of ionizing radiation.

  The thermoplastic resin used for forming the bipolar plate of the present invention is selected from resins that can be molded into a sheet that does not allow electrolyte solution to pass through, and that are not corroded by the electrolyte solution and give a sheet having high mechanical strength. Conductive carbon refers to a filler made of a carbonaceous material having high conductivity. Specific examples include graphite and carbon black. Moreover, the carbon nanotube which consists of carbon fiber whose fiber diameter is about 0.5-150 nm can also be mentioned.

  The invention according to claim 2 is the bipolar plate for a redox flow battery according to claim 1, wherein the plasticizer is a compound having an unsaturated bond. The unsaturated bond referred to here includes a carbon-carbon double bond, a triple bond, a double bond containing an element other than carbon, and the like.

  The plasticizer is not particularly limited as long as it improves the processability of the compound, has a functional group that causes a crosslinking reaction with the thermoplastic resin, and has a property of binding to the thermoplastic resin. A compound having a saturated bond is preferably used because it is excellent in the reactivity of the crosslinking reaction by irradiation with ionizing radiation. Examples of the compound having an unsaturated bond include acrylic acid esters and methacrylic acid esters.

  The invention according to claim 3 is characterized in that the thermoplastic resin comprises one or more selected from the group consisting of chlorinated polyethylene, polyethylene, polypropylene, polyvinyl chloride and polycarbonate. 2. A bipolar plate for redox flow battery as described in 1. above. Specific examples of thermoplastic resins that can be molded into sheets that do not allow electrolyte to pass through, and that are not corroded by the electrolyte and give a sheet with high mechanical strength include chlorinated polyethylene, polyethylene, polypropylene, and polyvinyl chloride. Or a polycarbonate etc. can be mentioned, 1 type, or 2 or more types of mixed resin chosen from these are used preferably.

  In the invention of claim 4, the conductive carbon is selected from the group consisting of graphite, carbon black and carbon nanotubes. In the composite conductive material, the conductive carbon is contained in 100 parts by weight of the thermoplastic resin. The bipolar plate for a redox flow battery according to any one of claims 1 to 3, wherein the bipolar plate is contained in an amount of 20 to 150 parts by weight. When the conductive carbon selected from graphite, carbon black, and carbon nanotubes is used, sufficient conductivity can be obtained when the conductive carbon content is less than 20 parts by weight with respect to 100 parts by weight of the thermoplastic resin. On the other hand, if the content exceeds 150 parts by weight, molding may be difficult, which is not preferable.

  The content of the plasticizer varies depending on the desired degree of workability and the content of conductive carbon, and is not particularly limited. That is, when the degree of workability desired is low, or when the content of conductive carbon is low, the content of plasticizer may be low. On the other hand, if the plasticizer content is too large, it will not be settled as a compound, so the plasticizer content is selected within the range where this problem does not occur.

  The invention of claim 5 includes a mixing step of preparing a compound of a composite conductive material by mixing a thermoplastic resin, conductive carbon and a plasticizer, a forming step of forming the compound of the composite conductive material into a sheet, and the forming step A method for producing a bipolar plate for a redox flow battery, comprising an irradiation step of irradiating the sheet obtained in the above with ionizing radiation to bond the thermoplastic resin and the plasticizer.

  The bipolar plate for a redox flow battery of the present invention can be produced by a method having the mixing step, the forming step, and the irradiation step. In the mixing step, for example, a pressure kneader is used. Examples of the processing method into a sheet shape in the forming step include a method using an extruder, a method using a combination of an extruder and a rolling roll, and a method of supplying a powdered material to a roll.

  The irradiation amount of the ionizing radiation in the irradiation step is determined so that the bonding between the plasticizer and the thermoplastic resin is sufficiently achieved and the plasticizer can be sufficiently prevented from being eluted into the electrolytic solution. The irradiation amount that can sufficiently prevent the elution of the plasticizer varies depending on the type of the plasticizer and the thermoplastic resin, the thickness of the sheet, and the like, and is not specifically specified. In addition, the present inventor does not affect the mechanical strength such as the electrical conductivity of the sheet and the maximum tensile strength even if the ionizing radiation dose is sufficient to prevent the plasticizer from eluting into the electrolyte. I found out. Therefore, the bipolar plate of the present invention manufactured by the above method has excellent mechanical strength as well as high conductivity.

  Examples of the ionizing radiation include high-energy electromagnetic waves such as gamma rays and X-rays, charged particle beams, neutron beams, and electron beams, but electron beams that are easy to handle and inexpensive in terms of equipment are preferably used.

  The sheet produced as described above has high conductivity, excellent mechanical strength, and the elution of the plasticizer into the electrolyte solution is also suppressed. Therefore, it is suitable as a bipolar plate constituting a redox flow battery. Used.

  The bipolar plate for a redox flow battery of the present invention has high conductivity and excellent mechanical strength, and it is easy to mix a resin and conductive carbon and to process a sheet at the time of production. Elution was also suppressed. This bipolar plate for a redox flow battery can be produced by the method for producing a bipolar plate for a redox flow battery of the present invention.

It is a schematic exploded perspective view of a redox flow battery cell. It is an external view of the principal part of a redox flow battery.

  Next, although the form for implementing this invention is demonstrated, the range of this invention is not limited to this form, A various change can be made in the range which does not impair the meaning of this invention. First, each component which comprises the composite electrically-conductive material which forms the bipolar plate for redox flow batteries of this invention is demonstrated.

[Conductive carbon (carbonaceous material)]
Graphite is a hexagonal plate-like crystal of carbon. In the present invention, any of natural graphite such as earthy graphite, massive graphite, and scaly graphite, and artificial graphite can be used. In addition, exfoliated graphite, exfoliated graphite with improved moldability and conductivity by flaking, spheroidized graphite with reduced orientation by spheroidizing and pulverization, and melted pig iron, the temperature of which decreases during hot metal pretreatment, etc. Along with this, quiche graphite, which is crystallized in a plane, is used.

  Among them, expanded graphite, exfoliated graphite or spheroidized graphite is preferable because it can impart high conductivity to the bipolar plate. In addition, expanded graphite refers to, for example, immersing natural graphite or the like in a strong oxidizing solution of a mixture of concentrated sulfuric acid and nitric acid, or a mixture of concentrated sulfuric acid and hydrogen peroxide to form a graphite intercalation compound. It is a powder obtained by washing with water and then rapidly heating to expand the C-axis direction of the graphite crystal, or a powder obtained by pulverizing it once rolled into a sheet.

  Carbon black is a fine particle of carbon having a diameter of about 3 to 500 nm. The carbon black is mainly composed of a single carbon, but includes carbon having a complicated composition in which various functional groups remain on the surface. Also, it can be obtained by pyrolysis of furnace black, acetylene gas produced by incomplete combustion of hydrocarbon oil and natural gas (furnace method), ketjen black obtained by pyrolyzing acetylene gas, channel black, and natural gas. Thermal black or the like can also be used. Among them, acetylene black or ketjen black is preferable because it can impart high conductivity to the bipolar plate. As the conductive carbon, one kind selected from the above exemplified graphite, carbon black, carbon nanotube and the like may be used alone, or two or more kinds may be used in combination.

[About thermoplastic resin]
Examples of the thermoplastic resin forming the bipolar plate of the present invention include polyolefins such as chlorinated polyethylene, polyethylene, and polypropylene, acrylonitrile butadiene styrene copolymer, polystyrene, acrylic resin, polyvinyl chloride, polyimide, liquid crystal polymer, and polyether ether ketone. , Fluororesin, polyacetal, polyamide, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polycycloolefin, polyphenylene sulfide, polyether sulfone, polyphenylene oxide, polyphenylene sulfone, and the like.

  In the thermoplastic resin, in order to make the bipolar plate difficult to break, a polymer (elastomer) having rubber-like elasticity near normal temperature can be contained. Examples of the elastomer include acrylonitrile butadiene rubber, hydrogenated nitrile rubber, styrene butadiene rubber, ethylene propylene copolymer, ethylene-octene copolymer, ethylene-butene copolymer, propylene-butene copolymer, ethylene propylene diene. One or a plurality of combinations selected from terpolymer rubber, ethylene butadiene rubber, fluorine rubber, isoprene rubber, silicone rubber, acrylic rubber, butadiene rubber and the like can be used.

[About plasticizers]
The plasticizer used in the present invention has a function of improving the workability of the compound, and has a property of reacting with and binding to a thermoplastic resin by irradiation with ionizing radiation. Such plasticizers include paraffinic oils, aromatic oils, naphthenic oils, mineral oil plasticizers such as coumarone-indene resin, fatty acids (stearic acid, etc.), fatty oils (rapeseed oil, etc.), rosin, etc. There may be mentioned synthetic plasticizers such as vegetable oil plasticizers, chlorinated paraffins, phthalic acid esters (DOP, etc.), acrylic acid esters, and methacrylic acid esters.

  Among these, acrylic acid esters and methacrylic acid esters are preferable because they are excellent in reactivity by irradiation with ionizing radiation. More specifically, as an acrylic ester or methacrylic ester, trimethylolpropane acrylate, 1,6-hexanediol diacrylate, 1,10-decanediol diacrylate, polyethylene glycol diacrylate, 1,6-hexanediol diacrylate Those having two or more unsaturated bonds in the molecule, such as methacrylate, 1,10-decanediol dimethacrylate, and polyethylene glycol dimethacrylate, can be mentioned, and can be preferably used as a plasticizer in the present invention.

  Other components (components other than thermoplastic resin, conductive carbon and plasticizer) that may be included in the composite conductive material forming the bipolar plate of the present invention include stabilizers, antioxidants, dispersants, A lubricant etc. can be mentioned.

  Next, the example of the specific form of the manufacturing method of the bipolar plate for redox flow batteries of this invention is demonstrated.

[Production of bipolar plates]
The bipolar plate of the present invention is manufactured by molding a molding material (composite conductive material) containing the conductive carbon, a thermoplastic resin and a plasticizer. Preferably, it is manufactured by melt-mixing conductive carbon and a plasticizer in a thermoplastic resin to prepare a mixture, and pressing the mixture while heating to form a sheet (plate).

  Examples of the molding machine used for processing into a sheet form include a calendar roll and an extruder. Also, a method of obtaining a sheet-like bipolar plate by mixing using a ball mill or the like, filling the mixture in a mold, and performing pressure molding while heating with a hot press machine can be employed. The bipolar plate thus obtained is mounted on a frame (frame body) and used for a redox flow battery, as will be described below.

  Next, a specific form of a redox flow battery in which the bipolar plate of the present invention is used will be described. FIG. 1 is a schematic exploded perspective view showing an example of a redox flow battery cell in which the bipolar plate of the present invention is used.

  As shown in FIG. 1, a redox flow battery cell 51 includes a rectangular diaphragm 1 that is an ion exchange membrane, rectangular bipolar plates 2a and 2b that are respectively disposed on both sides of the diaphragm 1, and the outer periphery of each bipolar plate. Frame 3a, 3b for fixing and holding the part, and rectangular liquid-permeable porous electrodes 4a, 4b respectively disposed between the diaphragm 1 and the bipolar plates 2a, 2b. The electrode 4a is a positive electrode disposed in the positive electrode chamber between the diaphragm 1 and the bipolar plate 3a, and the electrode 4b is a negative electrode disposed in the negative electrode chamber between the diaphragm 1 and the bipolar plate 3b.

  The frames 3a and 3b are made of an acid resistant material such as polyvinyl chloride resin, and the electrodes 4a and 4b are made of carbon fiber felt. 2a and 2b are bipolar plates of the present invention. The outer peripheral portions of the bipolar plates 2a and 2b are accommodated in and sandwiched in grooves formed on the inner peripheral walls of the frames 3a and 3b, and are integrated with the frame. The region between the bipolar plates 2a and 2b disposed on the frames 3a and 3b forms an electrode chamber 12. In the electrode chamber 12, electrodes 4a and 4b are accommodated.

  The overlapping surface of the frame 3a faces the right side in FIG. Further, the overlapping surface of the frame 3b faces the left side in FIG.

  Notch step portions 5a and 5b are formed on the inner edge of the electrode chamber 12 (5a is not shown). The notch depth of the notch step portions 5a and 5b is equal to the thickness of the protective plates 6a and 6b and shallower than the thickness of the electrode chamber 12. Therefore, the frame portion in which the notch step portion is formed is a two-step concave portion. This notch step is a locking portion for positioning the protection plates 6a and 6b and extends over the overlapping surface of the frame beyond the inner edge of the recess. The electrode 4a is accommodated in the electrode chamber 12 which is a recess of the frame 3a.

  9a is a liquid supply port which is a liquid distribution port provided in the frame 3a. Reference numeral 10a denotes a drainage port provided as a liquid distribution port in the frame 3a. The liquid supply port 9a and the liquid discharge port 10a are through-holes opened in the overlapping surface of the frame. In addition, the holes 8a and 8b arrange | positioned coaxially with the liquid supply port 9a and the drainage port 10a are opened in one edge part of the protection plates 6a and 6b. The protection plates 6a and 6b are narrow and long plates made of an acid resistant material such as polyvinyl chloride resin.

  The diaphragm 1 is slightly larger than the electrode chamber 12, and the outer periphery of the diaphragm 1 reaches the overlapping surface of the frame. In the state shown in the drawing, the frame 3b is superimposed on the frame 3a. The outer peripheral portion of the diaphragm 1 is sandwiched between the overlapping surface of the frame 3a and the overlapping surface of the frame 3b. The diaphragm 1 can be an ion exchange membrane based on an organic polymer. Either an cation exchange membrane or an anion exchange membrane can be used.

  Annular grooves 11a and 11b are formed outside the outer peripheral end portions of the diaphragms on the overlapping surfaces of the frames 3a and 3b (in the drawing, the annular grooves are formed only on the overlapping surface forming a cell composed of a pair of positive and negative electrode chambers. ), An O-ring serving as a sealing means is installed in each annular groove. When the frames 3a and 3b are overlapped and tightened, liquid leakage is prevented by the O-ring.

  In order to prevent leakage of the electrolyte from the liquid supply ports 9a and 9b and the drainage ports 10a and 10b, an O-ring (not shown) is provided around each of the liquid supply ports 9a and 9b and the drainage ports 10a and 10b. An annular recess (not shown) to which can be mounted is formed. The electrolyte is supplied into the electrode chamber 12 from the liquid supply port 9a, and is discharged through the liquid discharge port 10a.

  When the frames 3a and 3b are overlapped, the liquid supply ports 9a and 9b are connected to form a liquid supply conduit. At the same time, the drainage ports 10a and 10b communicate to form a drainage conduit. A part of the positive electrode solution that has flowed into the liquid supply conduit is divided, reaches the positive electrode 4a, and is guided to the drainage conduit. Similarly, a part of the remaining positive electrode solution reaching the liquid supply conduit of the adjacent cell is diverted. The subsequent flow of the positive electrode solution is the same as the flow of the positive electrode solution described above.

  A plurality of redox flow battery cells having the above structure are stacked to constitute a redox flow battery cell stack. Also, a redox flow battery cell stack is positioned between a pair of end plates, tightened with a fastener such as a bolt and nut, and a redox flow battery is mounted by installing a distribution member having an electrolyte supply pipe and a drain pipe. The main part is composed.

  FIG. 2 is an external view of the main part of the redox flow battery. In FIG. 2, 52 is a main part of the redox flow battery. A redox flow battery is configured by adding a positive electrode liquid tank, a negative electrode liquid tank, a circulation pump for each of the positive electrode liquid and the negative electrode liquid, piping, and the like to the main part.

  As the electrolytic solution used in the redox flow battery in which the bipolar plate of the present invention is used, various electrolytic solutions capable of ion redox reaction can be used. For example, an electrolytic solution containing vanadium ions (vanadium sulfate aqueous solution) or an electrolytic solution constituting an iron-chromium battery (combination of an electrolytic solution containing iron ions and ions containing chromium ions) can be used.

[Preparation of composite conductive material sample]
Using a pressure kneader (MIX-LABO ML500 manufactured by Moriyama Co., Ltd.), chlorinated polyethylene, various conductive carbons, additives and plasticizers shown in the column of [Used raw material] below are shown in Tables 1 to 3 (weights). The composite conductive material sample was prepared by mixing at 160 ° C. for 5 minutes with the composition shown in FIG. About each adjusted sample, the melt flow rate and the Brabender torque were measured by the method shown below.

[Melt flow rate (MFR)]
Using a melt indexer (manufactured by Toyo Seiki Co., Ltd.), the load was measured at 21.6 kg and 180 ° C. according to JIS K7210. The measurement was performed twice for each sample (n = 2), and the average value was taken as the measurement value.

[Brabender Torque]
Using Laboplast mill 30C150 (manufactured by Toyo Seiki Co., Ltd.), the entire amount of the composite conductive material sample prepared above was put into a 180 ° C. tank (filling amount: 100 vol%), and then mixed for 10 minutes at a rotor rotation speed of 5 rpm. Torque values were measured. The results are shown in Table 1.

The composite conductive material sample prepared in [Preparation of Composite Conductive Material Sample] was formed into a sheet by roll processing, then pressed with a heating / cooling press at 160 ° C. and 100 kg / cm ² for 5 minutes, and then cooled to a thickness. An approximately 0.6 mm sheet was obtained. This sheet was irradiated with an electron beam using an electron beam irradiation apparatus. About the sheet before electron beam irradiation, the sheet after 6 Mrad irradiation of the electron beam and the sheet after 12 Mrad irradiation of the electron beam, the volume resistivity in the plane direction and the layer direction, the maximum tensile strength and the tensile breaking elongation are as follows. Was measured. Further, for each sheet, the degree of elution of the plasticizer into the electrolytic solution was evaluated, and it was confirmed by a viscoelastic spectrometer (DMS) that the plasticizer and the thermoplastic resin (chlorinated polyethylene) were bonded. The results are shown in Table 1.

[Raw materials used]
1) Thermoplastic resin:
-Chlorinated polyethylene: Eraslen 303A (made by Showa Denko KK, chlorine content: 32%, melt index = 120)
2) Conductive carbon / graphite: BSP-10AK (manufactured by Chuetsu Graphite Industries Co., Ltd., expanded graphite, average particle size 10 μm)
Carbon black: EC300J (manufactured by Lion, Ketjen Black, primary particle size 40 μm)
Carbon nanotube (CNT): VGCF-X (Showa Denko, 15 nmφ × 3 μm)

3) Plasticizer-Polyethylene glycol dimethacrylate with n = 4

[Measurement method of volume resistivity]
The volume resistivity was measured by a four-probe method using a Loresta resistivity meter (Mitsubishi Chemical Corporation). The measurement was performed twice for each sheet (n = 2), and the average value was taken as the measurement value.

[Measurement method of maximum tensile strength and tensile elongation at break]
The sheet (sample) was punched into a JIS K6251 No. 3 dumbbell test piece, and a tensile test was performed using Autograph AG-I (manufactured by Shimadzu Corporation) (tensile speed: 50 mm / min). The measurement was performed three times (n = 3) for each sheet at room temperature, and the average value was taken as the measured value.

[Evaluation of ease of elution of plasticizer into electrolyte]
A sample piece of about 20 mm × 10 mm × 0.6 mm was immersed in methyl ethyl ketone (MEK) in a test tube. The immersion conditions were two conditions of 25 ° C. × 24 hours and 50 ° C. × 5 hours. After immersion, the sample piece is removed from the test tube, dried in a thermostat at 80 ° C for 24 hours, the weight of the sample piece is measured, and the ease of elution of the plasticizer into the electrolyte is evaluated by the weight reduction rate. did. In this experiment, MEK having a high elution property was used instead of the electrolyte solution in order to accelerate the elution of the plasticizer.

  As shown in Table 1 above, the torque value of the Brabender torque is 24 N · m in Experimental Example 1 in which no plasticizer is added, but the torque value in Experimental Example 2 in which the plasticizer is added is 24 N · m. , 20 N · m, it is confirmed that Brabender torque is reduced by adding a plasticizer, that is, fluidity of a compound is improved by adding a plasticizer, and excellent workability is obtained. .

  As is clear from comparison of the results shown in the row of “ease of elution” in Example 2 in which electron beam irradiation was not performed and Example 4 in which electron beam irradiation was performed, When irradiated, the amount of plasticizer eluted into the electrolyte is greatly reduced.

  Furthermore, as is clear from the measured values of volume resistivity, maximum tensile strength, and elongation at break shown in the table, even when electron beam irradiation is performed, the increase in volume resistivity or the maximum tensile strength, elongation at break The maximum tensile strength is rather improved by electron beam irradiation. In particular, when the electron beam irradiation amount is 6 Mrad, the maximum tensile strength is remarkably improved.

  In other words, it is clear from the results shown in the table that the electron beam irradiation suppresses the elution of the plasticizer without adversely affecting the electrical conductivity and mechanical strength of the sheet (rather than having a favorable effect). is there.

DESCRIPTION OF SYMBOLS 1 Diaphragm 2a, 2b Bipolar plate 3a, 3b Frame 4a, 4b Electrode 9a, 9b Liquid supply port 10a, 10b Drainage port 11a, 11b Annular groove 12 Electrode chamber

Claims (5)

  A bipolar plate made of a composite conductive material sheet containing a thermoplastic resin, conductive carbon and a plasticizer, wherein the sheet is irradiated with ionizing radiation, and the thermoplastic resin and the plasticizer are combined. A bipolar plate for redox flow batteries.   The bipolar plate for a redox flow battery according to claim 1, wherein the plasticizer is a compound having an unsaturated bond.   3. The redox flow battery according to claim 1, wherein the thermoplastic resin is at least one selected from the group consisting of chlorinated polyethylene, polyethylene, polypropylene, polyvinyl chloride, and polycarbonate. 4. Bipolar plate.   The conductive carbon is selected from the group consisting of graphite, carbon black and carbon nanotubes, and the composite conductive material contains 20 to 150 parts by weight of conductive carbon with respect to 100 parts by weight of the thermoplastic resin. The bipolar plate for a redox flow battery according to any one of claims 1 to 3, wherein the bipolar plate is for a redox flow battery.   A mixing process for producing a compound of a composite conductive material by mixing a thermoplastic resin, conductive carbon and a plasticizer, a molding process for forming the compound of the composite conductive material into a sheet, and a sheet obtained in the molding process is ionized. The manufacturing method of the bipolar plate for redox flow batteries characterized by including the irradiation process which irradiates a radiation and couple | bonds the said thermoplastic resin and a plasticizer.

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