JP2021125385A - Electrode for redox flow battery and redox flow cell - Google Patents

Abstract

To provide an electrode for a redox flow battery with reduced conductive resistance and diffusion resistance.SOLUTION: In an electrode for a redox flow battery includes a layer 1 and a layer 2, the layer 1 and the layer 2 include a carbon fiber (A), carbonaceous (B), and graphite particles (C), and the flexural modulus when bent toward the layer 1 is 130 to 180 MPa, the flexural modulus when bent toward the layer 2 is 1.2 to 1.4 times the flexural modulus when bent toward the layer 1, the thickness of the layer 1 is 560 to 1900 μm, the thickness of the layer 2 is 110 to 420 μm, and the basis weight of the electrode is 300 to 680 g/m2.SELECTED DRAWING: None

Description

The present invention relates to electrodes for redox flow batteries and redox flow batteries.

A redox flow battery is mainly composed of two bipolar plates facing an external tank for storing an electrolytic solution, a diaphragm (ion exchange membrane), and two electrodes. In a redox flow battery, an electrolytic solution containing an active material is supplied to at least one of the positive electrode and the negative electrode of the electrode, and charging and discharging are performed by a redox reaction. Examples of the active material include ions such as vanadium, halogen, iron, zinc, sulfur, titanium, copper, chromium, manganese, cerium, cobalt and lithium, compound ions thereof, non-metallic quinone compound ions and aromatics. Compound ions are used. Further, as the electrode, paper, felt, woven fabric, knitted fabric, etc. using carbon fiber are used in order to increase the reaction area with the active material.

Redox flow batteries are safe because their energy capacity can be increased relatively easily by adding a solution tank, their cycle life is long, they can be operated at room temperature, and they can be charged and discharged without using flammable materials. It has features such as high performance, and is expected to be widely used as a storage battery for adjusting output fluctuations due to weather in wind power generation and solar power generation and leveling the output, and the energy conversion efficiency of redox flow batteries. It is required to reduce the internal resistance of the battery in order to increase the energy. The internal resistance of the battery is mainly derived from the resistance at the diaphragm and electrodes. Resistance at the diaphragm can be reduced by thinning the diaphragm. On the other hand, the resistance at the electrode is generated from the conductivity inside the electrode, the conductive resistance due to the contact resistance between the electrode and the current collector plate, the diffusion resistance due to the liquid permeability of the electrolytic solution in the electrode, the reaction resistance with the electrolytic solution, and the like.

As a method for reducing the resistance of an electrode in a redox flow battery, for example, the electrode has catalytic activity with respect to an electrolytic solution, and a compressive strain of less than 20% and a range of 60 to 85% by volume with a compressive stress of 0.8 MPa are used. A redox flow battery containing carbon paper (see, for example, Patent Document 1) that defines the uncompressed pore ratio of the above has been proposed.

Japanese Patent Application Laid-Open No. 2015-505148

According to the invention described in Patent Document 1, it is possible to prevent the electrode from bending into the flow path of the electrolytic solution supply formed on the bipolar plate by setting the compressive strain to less than 20% with a compressive stress of 0.8 MPa. Although the conductive resistance inside the electrode can be reduced, in order to obtain such an electrode, it is necessary to increase the density and attach a large amount of binder, so that the permeability of the electrolytic solution in the electrode is lowered. There is a problem that it is not possible to achieve both reduction of diffusion resistance.

Therefore, an object of the present invention is to provide an electrode for a redox flow battery with reduced conductive resistance and diffusion resistance.

As a result of diligent studies to achieve the above problems, the present inventors have reached the following inventions.

An electrode composed of layers 1 and 2
The layer 1 and the layer 2 contain carbon fibers (A), carbonaceous (B), and graphite particles (C).
The flexural modulus when bent toward the layer 1 is 130 to 180 MPa.
The flexural modulus when bent toward the layer 2 is 1.2 to 1.4 times the flexural modulus when bent toward the layer 1.
The thickness of the layer 1 is 560 to 1900 μm.
The thickness of the layer 2 is 110 to 420 μm.
An electrode for a redox flow battery having a basis weight of the electrode of 300 to 680 g / m ^2.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an electrode for a redox flow battery with reduced conductive resistance and diffusion resistance.

The present invention is an electrode composed of a layer 1 and a layer 2, wherein the layer 1 and the layer 2 include carbon fibers (A), a carbonaceous material (B), and graphite particles (C), and the layer 1 has a carbon fiber (A), a carbonaceous material (B), and a graphite particle (C). The flexural modulus when bent to the side is 130 to 180 MPa, and the flexural modulus when bent to the side of the layer 2 is 1.2 to the flexural modulus when bent to the side of the layer 1. Redox flow, which is 1.4 times, the thickness of the layer 1 is 560 to 1900 μm, the thickness of the layer 2 is 110 to 420 μm, and the grain size of the electrode is 300 to 680 g / m ^2. Electrodes for batteries. Such an electrode for a redox flow battery of the present invention contains carbon fibers (A), carbonaceous materials (B), and graphite particles (C), and has a layer 1 on one surface of the electrode and a flexural modulus different from that of the layer 1. Layers 2 with different layers are arranged on opposite surfaces. By separating the diffusion resistance reduction function into the layer 1 and the conduction resistance reduction function into the layer 2, it is possible to obtain an electrode having both conductivity resistance and diffusion resistance reduction, which is difficult to achieve with an electrode composed of a uniform layer. can.

Examples of the carbon fiber (A) contained in the layer 1 and the layer 2 include polyacrylonitrile (hereinafter, may be abbreviated as “PAN”) carbon fiber, pitch carbon fiber, rayon carbon fiber, and phenol resin carbon fiber. And so on. Two or more of these may be contained. Among these, it is preferable to use PAN-based carbon fiber because it is excellent in strength and residual carbon ratio at the time of carbon fiber formation.

The carbonaceous substance (B) contained in the layer 1 and the layer 2 is a resin carbide obtained by carbonizing the resin binder. By binding the carbon fibers (A) with the carbon material (B), the contact area between the carbon fibers can be increased, so that the conductivity of the electrodes can be improved and the mechanical properties such as flexural rigidity can be improved. Examples of the resin binder used to obtain the carbonaceous material (B) include thermosetting resins such as phenol resin, epoxy resin, melamine resin, and furan resin. Among these, phenol resin is particularly preferable because it has a high carbonization yield.

When the layer 1 and the layer 2 contain the graphite particles (C), the reactivity of redox of the electrolytic solution can be improved and the reaction resistance can be reduced. As the graphite particles (C), it is preferable to use scaly graphite, scaly graphite, flaky graphite or the like having many electrochemically active edge surfaces.

The electrode for a redox flow battery of the present invention has a flexural modulus of 130 to 180 MPa when bent toward the layer 1, and a flexural modulus when bent toward the layer 2 is bent toward the layer 1. It is 1.2 to 1.4 times the flexural modulus at the time of bending. The flexural modulus here means the elastic modulus obtained by the three-point bending test. That is, the electrode of the present invention has a flexural rigidity of 130 to 180 MPa when the side of layer 1 is pushed by an indenter and bent toward the side of layer 1 in the three-point bending test, and the electrode of the present invention has a flexural rigidity of 130 to 180 MPa in the three-point bending test. The flexural rigidity when the side is pushed with an indenter and bent toward the layer 2 side is 1.2 to 1.4 times the flexural modulus when bent toward the layer 1. The flexural modulus when bent toward the layer 2 is more preferably 1.3 to 1.4 times the flexural modulus when bent toward the layer 1.

When the electrode of the present invention is incorporated into a redox flow battery, by arranging the layer 1 on the ion exchange membrane side of the battery, the diffusivity of the electrolytic solution can be kept good, and the bending rigidity is set to the bipolar plate side of the battery. By arranging the high layer 2, it is possible to prevent the electrode from bending into the supply flow path of the electrolytic solution formed on the bipolar plate at the time of cell fastening.

When the flexural modulus when bent toward the layer 1 side of the electrode is less than 130 MPa, the electrode bends into the flow path of the bipolar plate, and the density of the electrode on the flow path decreases, so that the conductive resistance tends to deteriorate. If it exceeds 180 MPa, the diffusibility of the electrolytic solution into the electrode tends to decrease, and the diffusion resistance tends to deteriorate. Further, if the flexural rigidity when the electrode is bent toward the layer 2 side is less than 1.2 times the flexural modulus when bent toward the layer 1, the electrode is likely to bend into the flow path of the bipolar plate. There is a tendency, and if it exceeds 1.4 times, the diffusibility of the electrolytic solution into the electrode tends to decrease.

Basis weight of the redox flow battery electrode of the present invention is a 300~680g / ^{m 2,} preferably 350~650g / ^{m 2,} more preferably 400-600 g / ^{m 2.} Basis weight tend to internal resistance is increased by the surface area insufficient as a reaction field is less than 300 g / m ^2, diffusion of the electrolytic solution is lowered by the substrate becomes thick exceeds 680 g / m ^2, the internal Resistance tends to be high. From the viewpoint of the surface area of the electrode and the diffusivity of the electrolytic solution, the basis weight occupied by the layer 1 in the electrode is 260 to 580 g / m ² , preferably 300 to 550 g / m ² , and more preferably 350 to 550 g / m. It is ^2. The basis weight occupied by the layer 2 is 40 to 100 g / m ² , preferably 50 to 90 g / m ² , and more preferably 50 to 80 g / m ² .

From the viewpoint of diffusivity of the electrolytic solution, the thickness of the layer 1 constituting the electrode is 560 to 1900 μm, preferably 670 to 1700 μm, and more preferably 850 μm to 1600 μm. If the thickness of layer 1 is less than 560 μm, the voids in the layer become smaller and the diffusibility of the electrolytic solution tends to decrease. If it exceeds 1900 μm, the carbon fibers broken by compression during cell assembly tend to undergo ion exchange. It tends to make it easier to make pinholes in the membrane.

The thickness of the layer 2 is 110 to 420 μm, preferably 140 to 370 μm, and more preferably 150 to 320 μm. If the thickness of the layer 2 is less than 110 μm, the voids in the layer become smaller and the diffusibility of the electrolytic solution tends to decrease. It tends to bend easily.

The configuration of the electrode for the redox flow battery of the present invention is not particularly limited, but as a base material containing carbon fibers (A), carbonaceous materials (B), and graphite particles (C), a carbon fiber woven fabric or carbon fiber felt is formed on the layer 1. One preferred configuration is to use carbon fiber paper for the layer 2 using the above. As described above, by using different base materials for the layer 1 and the layer 2, it is possible to easily respond to the change in the electrode specifications by changing the combination.

As another suitable configuration, as a base material containing carbon fibers (A), carbonaceous materials (B), and graphite particles (C), carbon fiber felt is used for layers 1 and 2, and layer 1 is 100% by mass. The aspect in which the content of carbon (B) in layer 2 is higher than the content of carbon (B) in layer 1 when the ratio is 100% by mass is given. Can be done. By using carbon fiber felt as the base material of the layer 1 and the layer 2 in this way, the manufacturing cost can be suppressed because there is no manufacturing process for manufacturing the base material of other kinds.

In 100% by mass of the electrode for a redox flow battery of the present invention, it is preferable that the carbonaceous material (B) and the graphite particles (C) are contained in a total amount of 20 to 45% by mass, more preferably 25 to 40% by mass, and 25 to 50% by mass. It is more preferable to contain 35% by mass. When the total content of carbonaceous (B) and graphite particles (C) is in this range, the diffusivity of the electrolytic solution and the effect of suppressing the deflection of the bipolar plate into the flow path can be easily obtained, and the redox flow battery Cell resistance can be reduced.

As a ratio of carbonaceous material (B) and graphite particles (C) in each layer of layer 1 and layer 2 in the electrode for a redox flow battery of the present invention, layer 1 is electrolyzed by adding graphite particles (C). In order to improve the redox reactivity of the liquid, the mass ratio of carbonaceous material (B) / graphite particles (C) is preferably 0.15 to 0.30. On the other hand, the layer 2 has a mass ratio of carbonaceous (B) / graphite particles (C) of 0.40 to 0.75 in order to increase the flexural rigidity and suppress the deflection of the bipolar plate into the flow path. Is preferable. Further, from the viewpoint of maintaining the diffusivity of the electrode, the content of carbon fibers (A) in the layers 1 and 2 when each layer is 100% by mass is 55 to 85% by mass in the layer 1. Is preferable, and in layer 2, it is more preferably 50 to 70% by mass.

Next, a method for manufacturing the electrode for a redox flow battery of the present invention will be described.

The electrode for a redox flow battery using a carbon fiber woven fabric for layer 1 of the present invention is, for example, a spun yarn having a twist number of 150 to 1000 times / m by spinning using a PAN-based flame-resistant yarn as a precursor fiber of the carbon fiber. Is produced, and woven fabrics such as plain weave, twill weave, and red weave are woven by weaving, and strands of carbon fibers are woven to produce woven fabrics. Next, a thermosetting resin binder such as phenol resin and a solution containing graphite particles are impregnated or sprayed and dried, and then carbon fiber paper obtained by a method described later or the like is layered and heat-pressed to form a resin. It can be obtained by a method of performing thermosetting and integration of the binder and firing at 1200 ° C. or higher in an inert atmosphere.

Further, in the electrode for a redox flow battery using carbon fiber felt for layer 1, PAN-based flame-resistant yarn having a fiber length of 30 to 100 mm with crimp is processed into a web shape, and the fibers are further processed by needle punching or water jet processing. Is made into felt by entwining. Next, a solution containing a thermosetting resin binder such as phenol resin and graphite particles is impregnated or sprayed to dry, and then heat-pressed to heat-cure the resin binder at 1200 ° C. in an inert atmosphere. Carbon fiber felt is obtained by carbonizing as described above. After applying a thermosetting resin binder to the carbon fiber felt, carbon fiber paper is layered as a layer 2, and the carbon fiber paper is integrated by heat pressing, and can be obtained by a method of carbonizing at 1200 ° C. or higher in an inert atmosphere. A method of producing carbon fiber woven fabric or carbon fiber felt and carbon fiber paper without integrating them and stacking them in a cell of a redox flow battery may be used.

The carbon fiber paper used for the layer 2 of the electrode for a redox flow battery of the present invention is prepared by dispersing carbon fibers having a fiber length of 3 to 20 mm in a liquid, making a paper by a wet paper making method, and applying an aqueous polyvinyl alcohol solution as a binder to the paper. , Dry. Next, the resin binder is heat-cured by impregnating or spraying a solution containing a thermosetting resin binder such as phenol resin and graphite particles and heat-pressing, and then firing at 1200 ° C. or higher in an inert atmosphere. It can be obtained by the method of

The redox flow battery electrode, in which the layers 1 and 2 are made of carbon fiber felt, is made by processing a crimped PAN-based flame-resistant yarn having a fiber length of 30 to 100 mm into a web shape, and further processing the fibers with each other by needle punching or water jet processing. Is made into felt by entwining. Next, a solution containing a thermosetting resin binder such as phenol resin and graphite particles is impregnated or sprayed to dry, and then further impregnated or sprayed so that the thermosetting resin binder adheres to only one side, and then heat-pressed. A method in which a resin binder is thermoset and then fired at 1200 ° C. or higher in an inert atmosphere. Alternatively, a crimped PAN-based flame-resistant yarn having a fiber length of 30 to 100 mm is processed into a web shape, and the fibers are entangled with each other by needle punching or water jet processing to produce high basis weight and low basis weight. Make the felt. Next, a solution containing a thermosetting resin binder such as phenol resin and graphite particles is impregnated or sprayed and dried, and the mass% of the resin binder in the low-grained felt is higher than the mass% of the resin binder in the high-grained felt. After adhering the resin binder so that it becomes It can be obtained by the method of

The redox flow battery of the present invention is a redox flow battery in which the above-mentioned electrodes for the redox flow battery of the present invention are used for the positive electrode and / or the negative electrode, and the layer 1 is on the ion exchange membrane side and the layer 2 is on the bipolar plate side. It is placed facing. This will be specifically described below.

The electrode for a redox flow battery of the present invention can be used in any of the flow-through type and flow-by type cells, and the layer 1 is placed on the ion exchange membrane side and the layer 2 on either or both of the positive electrode and the negative electrode. The electrode of the present invention can obtain a great effect in a flow-by type cell in which the electrodes are arranged toward the bipolar plate side. The flow-by type is a method in which an electrolytic solution is supplied from the groove of the bipolar plate to the electrode sandwiched between the ion exchange membrane and the bipolar plate having a groove, and the electrode is passed through the groove of the bipolar plate. Since the internal resistance increases due to the deterioration of the conductive resistance due to the bending, the internal resistance can be reduced by arranging the layer 2 having high flexural rigidity toward the bipolar plate side in the electrode of the present invention. As the groove shape of the flow-by type bipolar plate, a shape known as a redox flow battery or a polymer electrolyte fuel cell such as parallel, column, serpentine, and comb tooth type can be used.

Hereinafter, the present invention will be described in more detail with reference to Examples. First, the evaluation method in each Example and Comparative Example will be described.

(1) Electrode thickness (μm)
The electrodes obtained in each Example and Comparative Example were cut into 5 test pieces having a size of 50 mm length × 10 mm width. Using a dial thickness gauge G-2.4N (manufactured by Ozaki Seisakusho Co., Ltd.), the thickness (μm) at four points per sheet was measured, and the first decimal place was rounded off. The thickness (μm) of each of the five test pieces was measured, the number average value was calculated, and the value rounded to the first decimal place was taken as the electrode thickness.

(2) Electrode flexural modulus (MPa)
The electrodes obtained in each Example and Comparative Example were cut into test pieces with dimensions of 50 mm length × 10 mm width, and based on JIS K6911 (1995), the test pieces were set to have an indenter radius of 5 mm, a fulcrum radius of 5 mm, and a distance between fulcrums of 32 mm. The value measured by 3-point bending using a small desktop tester EZ-LX (manufactured by Shimadzu Corporation) was used as the flexural modulus of the electrode. The thickness of the electrode used in the calculation of the flexural modulus was a value obtained according to the "thickness of the electrode" in (1).

(3) Electrode basis weight (g / m ² )
A test piece was cut from five randomly selected electrodes obtained in each of the examples and comparative examples to a size of 50 mm length × 50 mm width, and the mass W (g) was measured. The basis weight (g / m ² ) was calculated. The average value was calculated from the basis weight (g / m ² ) of 5 test pieces, and the value rounded to the first decimal place was used as the basis weight of the electrode.

Electrode basis weight [g / m ² ] = W [g] / (length 50 [mm] x width 50 [mm] / 100) x 10000
(4) Thickness (μm) of layer 1 and layer 2 in the electrode
Electrodes obtained in each Example and Comparative Example were randomly selected at 10 locations, and a cross section perpendicular to the plane direction was cut out with a cutting tool and magnified and observed at a magnification of 100 times using an electron microscope (VHX-D500 manufactured by KEYENCE). .. The interface between the layer 1 and the layer 2 was discriminated from the orientation state of the carbon fiber (A) and the adhesion state of the carbon substance (B) in the cross section. The thickness (μm) from the interface of the layers 1 and 2 to the surface was measured at 10 points, the average value was calculated, and the value rounded off to the first decimal place was taken as the thickness of the layers 1 and 2.

(5) Thickness of electrode when pressurized (μm)
Specimens were cut to a length of 40 mm and a width of 40 mm from five randomly selected electrodes obtained in each of the examples and comparative examples. Using a small desktop tester EZ-LX (manufactured by Shimadzu Corporation), the test type was a compression test, and the upper compression jig was lowered without sandwiching the test piece to contact the lower jig. The point was set to the zero point of thickness. Next, the test piece was placed in the center of the jig, compressed at a speed of 2 mm / min, the thickness (μm) under a 1 MPa load was measured, and the first decimal place was rounded off. An average value was calculated for the thickness (μm) of five test pieces under a load of 1 MPa, and the value rounded to the first decimal place was taken as the thickness (μm) of the electrode when pressed.

(6) Cell resistance (Ωcm ² )
The electrodes are cut into a square of 50 mm x 50 mm, and a cation exchange membrane (Nafion NRE-212, manufactured by DuPont) is placed between these electrodes, and a single-row serpentine type (groove width 1 mm, groove depth 1 mm, ribs) is placed. A single cell was formed by sandwiching it between bipolar plates having a groove having a width of 1 mm). Further, when the electrode was sandwiched between the bipolar plates, a spacer was inserted to obtain the thickness of the electrode at the time of pressurization measured by the above method, and the thickness of the electrode at the time of cell fastening was adjusted.

As a positive electrode electrolyte, pentavalent and tetravalent vanadium 1M (sulfuric acid 5M) is mixed at a mass ratio of 1: 1 to obtain an electrolytic solution having a charge rate of 50%, and as a negative electrode electrolyte, divalent and trivalent vanadium 1M (sulfuric acid 5M). ) Was mixed at a mass ratio of 1: 1 and circulated at 90 ml / min using an electrolytic solution having a charge rate of 50%, and the discharge IV curve up ^{to a current density of 1.0 A / cm 2 was measured.} For the obtained IV curve, the cell resistance (Ωcm ² ) was calculated from the voltage V0 at a current density of 0 A / cm ^{2 and the voltage V1 at 0.40 A / cm 2 by the following equation.}
Cell resistance [Ωcm ² ] = (voltage V0-voltage V1) /0.4 (A / cm ² )
(7) Conductive resistance of the electrode (Ωcm ² )
After measuring the IV curve, a Core-Cole plot was performed by the AC impedance method using a commercially available measuring device, and the conductive resistance (Ωcm ² ) was obtained from the resistance portion until the arc was drawn. The measurement was performed with a voltage amplitude of 10 mV and a measurement frequency range of 10 kHz to 10 MHz.

(Manufacturing Example 1 Carbon Fiber Felt 1)
The PAN-based flame-resistant yarn was made into a crimped yarn by a push-in crimper. After cutting this flame-resistant yarn to a number average fiber length of 76 mm, a web sheet is made using a card and a cloth wrapper, and then needle punching is performed to perform a PAN-based flame resistance ^{having a basis weight of 350 g / m 2} and an apparent density of 0.13 ^{g / cm 3.} Obtained thread felt. This is 1.6% by mass of phenol resin (mass residue when calcined at 1300 ° C. in an inert atmosphere is 46%), 2.9% by mass of flaky graphite having an average particle size of 5 μm, and 95.5% by mass of methanol. The felt was immersed in a mixed solution of%, squeezed with a mangle, and dried at 100 ° C. for 10 minutes to obtain a felt to which phenol resin and graphite were attached. After adjusting the density of the felt at 200 ° C. with a press pressure of 5 MPa and a compression time of 3 minutes, the temperature was raised to 1300 ° C. in nitrogen gas for carbonization, and carbon (B) in 100% by mass of carbon fiber felt. A carbon fiber felt 1 having a grain size of ^{282 g / m 2} and a thickness of 881 μm was obtained in which the content of the graphite particles (C) was 20% by mass.

(Manufacturing Example 2 Carbon Fiber Felt 2)
The PAN-based flame-resistant yarn was made into a crimped yarn by a push-in crimper. After cutting the flame yarn number average fiber length of 76 mm, cards, and a web sheet with a cross-wrapper, then subjected to needle punching, PAN-based flame having a basis weight of 540 g / ^{m 2,} an apparent density of 0.13 g / cm ³ Obtained thread felt. Then, using the same phenol resin and flaky graphite as in Production Example 1, the felt was immersed in a solution in which 1.8% by mass of phenol resin, 3.3% by mass of flaky graphite, and 94.9% by mass of methanol were mixed. The mixture was squeezed with a mangle and dried at 100 ° C. for 10 minutes to obtain a felt to which phenol resin and graphite were attached. After adjusting the density of the felt at 200 ° C. with a press pressure of 5 MPa and a compression time of 3 minutes, the temperature was raised to 1300 ° C. in nitrogen gas for carbonization, and carbon (B) in 100% by mass of carbon fiber felt. A carbon fiber felt 2 having a grain size of ^{442 g / m 2} and a thickness of 1421 μm was obtained, which contained 22% by mass of the graphite particles (C).

(Manufacturing Example 3 Carbon Fiber Felt 3)
The carbon fiber felt was carried out in the same manner as in Example 1 except that the mixed concentration of the phenol resin and the flaky graphite was changed to 2.6% by mass of the phenol resin, 4.7% by mass of the flaky graphite, and 92.7% by mass of the methanol. A carbon fiber felt 3 having a grain size of ^{354 g / m 2} and a thickness of 1049 μm having a carbon content (B) and graphite particles (C) of 37% by mass at 100% by mass was obtained.

(Production Example 4 Carbon Fiber Felt 4)
The carbon fiber felt was carried out in the same manner as in Example 1 except that the mixed concentration of the phenol resin and the flaky graphite was changed to 3.9% by mass of the phenol resin, 7.1% by mass of the flaky graphite, and 89.0% by mass of the methanol. A carbon fiber felt 4 having a grain size of ^{590 g / m 2} and a thickness of 1306 μm having a carbon content (B) and graphite particles (C) of 62% by mass at 100% by mass was obtained.

(Production Example 5 Carbon Fiber Felt 5)
Using the same phenol resin and flaky graphite as in Production Example 1, the PAN-based flame-resistant yarn felt used in Production Example 1 was 1.6% by mass of phenol resin, 2.9% by mass of flaky graphite, and 95.5% by mass of methanol. Was immersed in the mixed solution, squeezed with a mangle, and dried at 100 ° C. for 10 minutes to obtain a felt to which phenol resin and graphite were attached. Next, of the thickness of the felt, only the portion 210 μm from the surface was immersed in a solution containing 10% by mass of phenol resin and 90% by mass of methanol, squeezed with a mangle, dried at 100 ° C. for 10 minutes, and the surface layer on one side. A felt having a phenol resin further attached to the side was obtained. After adjusting the density of the felt at 200 ° C. with a press pressure of 5 MPa and a compression time of 3 minutes, the temperature was raised to 1300 ° C. in nitrogen gas for carbonization, and carbon (B) in 100% by mass of carbon fiber felt. ^{A carbon fiber felt 4 having a grain size of 384 g / m 2} and a thickness of 1000 μm was obtained in which the content of the graphite particles (C) was 43% by mass.

(Production Example 6 Carbon Fiber Paper 1)
PAN-based carbon fibers are cut to a fiber length of 6 mm, made into carbon fiber paper by a wet papermaking method, an aqueous solution of polyvinyl alcohol is applied as a binder, and then dried and heat-pressed. A carbon fiber papermaking of m ^{2 was obtained.} Using the same phenol resin and flaky graphite as in Production Example 1, dip this in a mixed solution of 2.2% by mass of phenol resin, 2.3% by mass of flaky graphite, and 95.5% by mass of methanol with a mangle. It was squeezed and dried at 100 ° C. for 10 minutes to obtain a carbon fiber paper with phenol resin and graphite attached. After adjusting the density of this carbon fiber paper by setting a press pressure of 5 MPa at 200 ° C. and a compression time of 3 minutes, the temperature is raised to 1500 ° C. in nitrogen gas to carbonize the carbon fiber (carbon fiber paper) in 100% by mass of the carbon fiber paper. A carbon fiber paper 1 having a grain size of ^{50 g / m 2} and a thickness of 191 μm having a content of B) and graphite particles (C) of 47% by mass was obtained.

(Manufacturing Example 7 Carbon Fiber Paper 2)
PAN-based carbon fibers are cut to a fiber length of 6 mm, made into carbon fiber paper by a wet papermaking method, an aqueous solution of polyvinyl alcohol is applied as a binder, and then dried and heat-pressed. A carbon fiber papermaking of m ^{2 was obtained.} Using the same phenol resin and flaky graphite as in Production Example 1, dip this in a mixed solution of 2.2% by mass of phenol resin, 2.3% by mass of flaky graphite, and 95.5% by mass of methanol with a mangle. It was squeezed and dried at 100 ° C. for 10 minutes to obtain a carbon fiber paper with phenol resin and graphite attached. After adjusting the density of this carbon fiber paper by setting a press pressure of 5 MPa at 200 ° C. and a compression time of 3 minutes, the temperature is raised to 1500 ° C. in nitrogen gas to carbonize the carbon fiber (carbon fiber paper) in 100% by mass of the carbon fiber paper. A carbon fiber paper 2 having a ^{grain size of 84 g / m 2} and a thickness of 320 μm having a content of B) and graphite particles (C) of 45% by mass was obtained.

(Production Example 8 Carbon Fiber Paper 3)
The carbon fiber paper 100 was carried out in the same manner as in Production Example 6 except that the concentrations of the phenol resin and the flaky graphite were changed to 1.0% by mass of the phenol resin, 1.1% by mass of the flaky graphite, and 97.9% by mass of the methanol. A carbon fiber paper 3 having a ^{grain size of 34 g / m 2} and a thickness of 190 μm having a content of carbonaceous material (B) and graphite particles (C) in mass% of 20% by mass was obtained.

(Manufacturing Example 9 Carbon Fiber Paper 4)
PAN-based carbon fibers are cut to a fiber length of 6 mm, made into carbon fiber paper by a wet papermaking method, an aqueous solution of polyvinyl alcohol is applied as a binder, and then dried and heat-pressed. A carbon fiber papermaking of m ^{2 was obtained.} Using the same phenol resin and flaky graphite as in Production Example 1, this is immersed in a mixed solution of 3.0% by mass of phenol resin, 3.1% by mass of flaky graphite, and 93.9% by mass of methanol with a mangle. It was squeezed and dried at 100 ° C. for 10 minutes to obtain a carbon fiber paper with phenol resin and graphite attached. After adjusting the density of this carbon fiber paper by setting a press pressure of 5 MPa at 200 ° C. and a compression time of 3 minutes, the temperature is raised to 1500 ° C. in nitrogen gas to carbonize the carbon fiber (carbon fiber paper) in 100% by mass of the carbon fiber paper. A carbon fiber paper 4 having a ^{grain size of 158 g / m 2} and a thickness of 460 μm having a content of B) and graphite particles (C) of 66 mass% was obtained.

(Manufacturing Example 10 Negative electrode)
The PAN-based flame-resistant yarn was made into a crimped yarn by a push-in crimper. After cutting this flame-resistant yarn to a number average fiber length of 76 mm, a web sheet was formed using a card and a cross wrapper, and then needle punching was performed to obtain a PAN-based flame-resistant yarn felt having ^{an apparent density of 0.13 g / cm 3.} Next, the material was carbonized by raising the temperature to a temperature of 1,300 ° C. in a nitrogen atmosphere to obtain ^{a carbon fiber felt having a grain size of 280 g / m 2} and a density of 0.08 g / cm 3. Then, it was heated at 700 ° C. for 20 minutes in an air atmosphere to obtain an electrode material for a negative electrode ^{having a basis weight of 240 g / m 2.}

(Example 1)
After applying a phenol resin to one side of the carbon fiber felt 1 obtained in Production Example 1, the carbon fiber paper 1 obtained in Production Example 6 was laminated, pressed at 200 ° C. at 5 MPa, and the compression time was 3 minutes for integration. Then, the temperature was raised to 1300 ° C. again in nitrogen gas and carbonization was performed to prepare an electrode. A single-cell redox flow battery is assembled in a cell using the carbon fiber felt side of this electrode as the ion exchange membrane side as the positive electrode and the negative electrode obtained in Production Example 10 as the negative electrode, and the cell resistance and the conductivity of the electrode are conductive. The resistance was measured. In the cell of this combination, the conductive resistance and the diffusion resistance were reduced, and a redox flow battery having a low cell resistance was obtained. The characteristics of the obtained electrodes are shown in Table 1.

(Example 2)
After applying a phenol resin to one side of the carbon fiber felt 2 obtained in Production Example 2, the carbon fiber paper 2 obtained in Production Example 7 was laminated, pressed at 200 ° C. at 5 MPa, and the compression time was 3 minutes for integration. Then, the temperature was raised to 1300 ° C. again in nitrogen gas and carbonization was performed to prepare an electrode. A single-cell redox flow battery is assembled in a cell using the carbon fiber felt side of this electrode as the ion exchange membrane side as the positive electrode and the negative electrode obtained in Production Example 10 as the negative electrode, and the cell resistance and the conductivity of the electrode are conductive. The resistance was measured. In the cell of this combination, the conductive resistance and the diffusion resistance were reduced, and a redox flow battery having a low cell resistance was obtained. The characteristics of the obtained electrodes are shown in Table 1.

(Example 3)
After applying a phenol resin to one side of the carbon fiber felt 3 obtained in Production Example 3, the carbon fiber paper 1 obtained in Production Example 6 was laminated, pressed at 200 ° C. at 5 MPa, and the compression time was 3 minutes for integration. Then, the temperature was raised to 1300 ° C. again in nitrogen gas and carbonization was performed to prepare an electrode. A single-cell redox flow battery is assembled in a cell using the carbon fiber felt side of this electrode as the ion exchange membrane side as the positive electrode and the negative electrode obtained in Production Example 10 as the negative electrode, and the cell resistance and the conductivity of the electrode are conductive. The resistance was measured. In the cell of this combination, the conductive resistance and the diffusion resistance were reduced, and a redox flow battery having a low cell resistance was obtained. The characteristics of the obtained electrodes are shown in Table 1.

(Example 4)
A single cell redox is used in a cell in which the surface of the carbon fiber felt 5 obtained in Production Example 5 having a small amount of phenol resin adhered is used as the ion exchange membrane side for the positive electrode and the negative electrode obtained in Production Example 10 is used as the negative electrode. A flow battery was assembled and the cell resistance and the conductive resistance of the electrodes were measured. In the cell of this combination, the conductive resistance and the diffusion resistance were reduced, and a redox flow battery having a low cell resistance was obtained. The characteristics of the obtained electrodes are shown in Table 1.

(Example 5)
A single-cell redox flow battery was assembled in a cell used for the positive electrode and the negative electrode with the carbon fiber felt side of the electrode of Example 1 as the ion exchange membrane side, and the cell resistance and the conductive resistance of the electrode were measured. In the cell of this combination, the conductive resistance and the diffusion resistance were reduced, and a redox flow battery having a low cell resistance was obtained. The characteristics of the obtained electrodes are shown in Table 1.

(Comparative Example 1)
A single-cell redox flow battery was assembled in a cell using the carbon fiber felt 1 obtained in Production Example 1 as the positive electrode and the negative electrode obtained in Production Example 10 as the negative electrode, and the cell resistance and the conductive resistance of the electrode were measured. went. In the cell of this combination, the conductive resistance was high due to the bending of the electrode into the flow path of the bipolar plate, and the result was that the cell resistance was high due to the influence. The characteristics of the obtained electrodes are shown in Table 1.

(Comparative Example 2)
A single-cell redox flow battery was assembled in a cell using the carbon fiber felt 4 obtained in Production Example 4 as the positive electrode and the negative electrode obtained in Production Example 10 as the negative electrode, and the cell resistance and the conductive resistance of the electrode were measured. went. In the cell of this combination, the electrode did not bend into the flow path of the bipolar plate and the conductive resistance was low, but the diffusivity of the electrode was low, so that the cell resistance was high. The characteristics of the obtained electrodes are shown in Table 1.

(Comparative Example 3)
After applying a phenol resin to one side of the carbon fiber felt 1 obtained in Production Example 1, the carbon fiber paper 3 obtained in Production Example 8 is laminated, and the press pressure is 5 MPa at 200 ° C. and the compression time is 3 minutes. Then, the temperature was raised to 1300 ° C. again in nitrogen gas and carbonization was performed to prepare an electrode. A single-cell redox flow battery is assembled in a cell using the carbon fiber felt side of this electrode as the ion exchange membrane side as the positive electrode and the negative electrode obtained in Production Example 10 as the negative electrode, and the cell resistance and the conductivity of the electrode are conductive. The resistance was measured. In the cell of this combination, the conductive resistance was high due to the bending of the electrode into the flow path of the bipolar plate, and the result was that the cell resistance was high due to the influence. The characteristics of the obtained electrodes are shown in Table 1.

(Comparative Example 4)
After applying a phenol resin to one side of the carbon fiber felt 1 obtained in Production Example 1, the carbon fiber paper 4 obtained in Production Example 9 was laminated, and the press pressure was 5 MPa at 200 ° C. and the compression time was 3 minutes for integration. Then, the temperature was raised to 1300 ° C. again in nitrogen gas and carbonization was performed to prepare an electrode. A single-cell redox flow battery is assembled in a cell using the carbon fiber felt side of this electrode as the ion exchange membrane side as the positive electrode and the negative electrode obtained in Production Example 10 as the negative electrode, and the cell resistance and the conductivity of the electrode are conductive. The resistance was measured. In the cell of this combination, the electrode did not bend into the flow path of the bipolar plate and the conductive resistance was low, but the diffusivity of the electrode was low, so that the cell resistance was high. The characteristics of the obtained electrodes are shown in Table 1.

Claims (5)

An electrode composed of layers 1 and 2
The layer 1 and the layer 2 contain carbon fibers (A), carbonaceous (B), and graphite particles (C).
The flexural modulus when bent toward the layer 1 is 130 to 180 MPa.
The flexural modulus when bent toward the layer 2 is 1.2 to 1.4 times the flexural modulus when bent toward the layer 1.
The thickness of the layer 1 is 560 to 1900 μm.
The thickness of the layer 2 is 110 to 420 μm.
An electrode for a redox flow battery having a basis weight of the electrode of 300 to 680 g / m ^2. The layer 1 is a carbon fiber woven fabric or a carbon fiber felt.
The electrode for a redox flow battery according to claim 1, wherein the layer 2 is a carbon fiber paper. The layer 1 and the layer 2 are carbon fiber felts, and the layer 1 and the layer 2 are carbon fiber felts.
The content of carbonaceous material (B) in the layer 2 when the layer 2 is 100% by mass is higher than the content of carbonaceous material (B) in the layer 1 when the layer 1 is 100% by mass. The electrode for a redox flow battery according to claim 1, which has a higher rate. The electrode for a redox flow battery according to any one of claims 1 to 3, wherein the electrode contains 100% by mass of carbonaceous material (B) and graphite particles (C) in a total amount of 20 to 45% by mass. A redox flow battery in which the electrode for a redox flow battery according to any one of claims 1 to 4 is used for a positive electrode and / or a negative electrode.
A redox flow battery in which the layer 1 is arranged toward the ion exchange membrane side and the layer 2 is arranged toward the bipolar plate side.