WO2020158797A1 - Electrode, method for producing same and battery - Google Patents

Electrode, method for producing same and battery Download PDF

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Publication number
WO2020158797A1
WO2020158797A1 PCT/JP2020/003162 JP2020003162W WO2020158797A1 WO 2020158797 A1 WO2020158797 A1 WO 2020158797A1 JP 2020003162 W JP2020003162 W JP 2020003162W WO 2020158797 A1 WO2020158797 A1 WO 2020158797A1
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Prior art keywords
electrode
carbon
battery
positive electrode
redox flow
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PCT/JP2020/003162
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French (fr)
Japanese (ja)
Inventor
義史 横山
丈智 西方
ティンティン シュウ
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昭和電工株式会社
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Publication of WO2020158797A1 publication Critical patent/WO2020158797A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/96—Carbon-based electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates to an electrode, a method for manufacturing the electrode, and a battery including the electrode.
  • a redox flow battery supplies and circulates a positive electrode electrolytic solution and a negative electrode electrolytic solution to and from a battery cell having a positive electrode, a negative electrode, and a diaphragm interposed between both electrodes, and a power converter (for example, an AC/DC converter or the like). ) Is used to charge and discharge.
  • a power converter for example, an AC/DC converter or the like.
  • the electrolytic solution an aqueous solution containing a metal ion (active material) whose valence changes by redox is usually used.
  • a vanadium redox flow battery using vanadium (V) as an active material of a positive electrode and a negative electrode is well known.
  • Carbon materials such as carbon nanotubes and carbon fibers are used as the material of the electrodes used in such a redox flow battery.
  • Patent Document 1 describes the use of vapor grown carbon fiber as an electrode material of a redox flow battery.
  • Patent Document 2 a carbon fiber felt having voids inside the felt is used as a material of the electrode which has a small pressure loss when an electrolytic solution is passed through the electrode and has good conductivity in the thickness direction. Is described.
  • the redox flow battery described in Patent Documents 1 and 2 is a redox flow battery using a vanadium-based electrolyte solution, which has a low cell resistivity and a small pressure loss when the electrolyte solution is passed through the electrodes. It was done.
  • electrolytes other than vanadium-based electrolytes that contain ions with a high oxidizing power such as manganese-titanium-based electrolytes.
  • an electrode for a redox flow battery which is less likely to cause deterioration of the electrode due to oxidation, more specifically, increase in cell resistivity and breakage.
  • An object of the present invention is to provide an electrode, a manufacturing method thereof, and a battery, which are less likely to be deteriorated by oxidation.
  • the present inventors have found that the carbon electrode material constituting the electrode, appearing in the Raman spectrum measured by Raman spectroscopy, the peak intensity of D-band (I D) and the peak intensity of G-band peak intensity ratio (I G) ( By including a carbon material having a small I D /I G ratio), it was found that the increase in cell resistivity due to oxidation is unlikely to occur even when the battery is repeatedly used, and the present invention has been completed. More specifically, the present invention provides the following.
  • the present invention is an electrode having a carbon electrode material, wherein the carbon electrode material has a G band peak intensity of a D band peak intensity (I D ) that appears in a Raman spectrum measured by Raman spectroscopy.
  • I D D band peak intensity
  • I G peak intensity ratio
  • the content of oxygen element is an electrode containing a carbon material is less than 0.50 wt%.
  • the present invention is the electrode according to (1), wherein the carbon electrode material contains 50% by mass or more of the carbon material.
  • the present invention is the electrode according to (1) or (2), wherein the carbon material includes carbon fiber.
  • the present invention is the electrode according to (3), wherein the carbon fiber has an average fiber diameter of 1 ⁇ m or more.
  • the present invention also provides the electrode according to (3) or (4), wherein the carbon electrode material is composed of a sheet material of carbon felt or carbon paper formed using the carbon fiber.
  • the present invention is the electrode according to any one of (1) to (5), wherein the electrode is used as a positive electrode of a redox flow battery.
  • the present invention is a battery including a positive electrode and a negative electrode, wherein the positive electrode is the electrode according to any one of (1) to (6).
  • the battery is a redox flow battery, and further comprises a positive electrode electrolytic solution supplied to the positive electrode and a negative electrode electrolytic solution supplied to the negative electrode, wherein the positive electrode electrolytic solution is:
  • the battery according to (7) which contains one or more ions selected from manganese ions, cerium ions, and chlorine ions.
  • the present invention is the method for manufacturing an electrode according to any one of (1) to (6), wherein the molded body containing a carbon material is treated in an inert gas atmosphere at 2300° C. or higher and 3500° C. or lower.
  • a method for manufacturing an electrode which includes a high-temperature firing step of firing to obtain a carbon electrode material.
  • a low temperature firing step of firing the molded body in an atmosphere containing oxygen gas at 700° C. or lower is performed before performing the high temperature firing step. It is a manufacturing method.
  • the present invention it is possible to obtain a battery electrode that is less likely to be deteriorated by oxidation, a manufacturing method thereof, and a battery.
  • FIG. 5 is an SEM (scanning electron microscope) image of the surface of carbon fiber that constitutes the same carbon paper as in Example 1.
  • FIG. 2A is a SEM image of the carbon fiber surface before the low temperature firing step
  • FIG. 2B is a SEM image of the carbon fiber surface after the low temperature firing step and before the high temperature firing step. It is a statue.
  • the electrode of the present embodiment is an electrode having a carbon electrode material, and the carbon electrode material has a G-band peak intensity (I D ) of the D-band peak intensity ( ID ) that appears in a Raman spectrum measured by Raman spectroscopy.
  • I G peak intensity ratio) (I D / I G ratio) is 0.50 or less, and the content of oxygen element comprises a carbon material is less than 0.50 wt%.
  • the electrode (hereinafter, also referred to as “battery electrode”) according to the present embodiment mainly includes a carbon electrode material containing a carbon material.
  • the carbon material contained in the carbon electrode material (hereinafter sometimes referred to as “carbon material A”) is the G band of the peak intensity ( ID ) of the D band that appears in the Raman spectrum measured by Raman spectroscopy.
  • peak intensity peak intensity ratio (I G) (I D / I G ratio) is 0.50 or less, and the content of oxygen element is less than 0.50 wt%.
  • the carbon electrode material containing the carbon material A is mainly used, and the I D /I G ratio of the carbon material A is reduced so that the electrode is placed in an environment with high oxidizing power.
  • the I D /I G ratio of the carbon material A is reduced so that the electrode is placed in an environment with high oxidizing power.
  • Carbon material A The carbon material A contained in the carbon electrode material, appearing in the Raman spectrum measured by Raman spectroscopy, the peak intensity of D-band (I D), the peak intensity ratio to the peak intensity of G-band (I G) (I D / I G ratio) is 0.50 or less.
  • the ratio ( ID / IG ratio) of the peak intensity ( ID ) of the D band appearing due to the disorder and the defect of the carbon material structure to the peak intensity ( IG ) of the G band derived from the graphite structure of the carbon material. ) Is set to 0.50 or less, the electrode is less likely to be oxidized by oxygen (O 2 ) or an electrolytic solution containing ions having high oxidizing power.
  • the I D /I G ratio of the carbon material A is preferably 0.45 or less, and more preferably 0.40 or less.
  • the content of oxygen element in this carbon material A is 0.50 mass% or less.
  • the oxygen element in the carbon material A is preferably 0.40 mass% or less, and more preferably 0.30 mass% or less.
  • Examples of the carbon material A include carbon fibers, graphene, carbon black, etc., which have an I D /I G ratio of 0.50 or less and an oxygen element content of 0.50 mass% or less. One of these materials may be used, or two or more of them may be used. When using two or more kinds of materials as the carbon material A, D peak intensity of band (I D), the peak intensity ratio to the peak intensity of G-band (I G) (I D / I G ratio), various carbon materials The weighted average value obtained from the sum of the values obtained by multiplying the I D /I G ratio by the mass ratio.
  • the carbon material A preferably contains carbon fibers.
  • examples of the carbon fiber include a fibrous (including tubular) carbon material having an average fiber diameter of 10 nm or more.
  • the upper limit of the average fiber diameter of the carbon fibers is preferably set from the viewpoint of ease of processing into a carbon electrode material, and can be set to, for example, 200 ⁇ m or less.
  • a plurality of types of carbon fibers having different average fiber diameters and average fiber lengths may be included as the carbon material A.
  • the carbon fibers include those having an average fiber diameter of 1 ⁇ m or more and those having an average fiber diameter of less than 1 ⁇ m (for example, carbon nanofibers and carbon nanotubes).
  • the average fiber diameter of the carbon fibers is preferably in the range of 1 ⁇ m to 200 ⁇ m, more preferably 2 ⁇ m to 100 ⁇ m, and further preferably 5 ⁇ m to 30 ⁇ m.
  • the average fiber length of the carbon fibers is preferably 0.01 mm to 20 mm, more preferably 0.05 mm to 10 mm, still more preferably 0.1 mm to 8 mm.
  • the average fiber diameter of the carbon nanofibers or carbon nanotubes is preferably 1 nm to 300 nm, more preferably 10 nm to 200 nm, More preferably, it is in the range of 15 nm to 150 nm.
  • the average fiber length of the carbon nanotubes is preferably in the range of 0.1 ⁇ m to 30 ⁇ m, more preferably 0.5 ⁇ m to 25 ⁇ m, still more preferably 0.5 ⁇ m to 20 ⁇ m.
  • the average fiber diameter and the average fiber length of the carbon fibers are obtained by randomly measuring the diameters (fiber diameters) of 100 or more carbon fibers using a transmission electron microscope (TEM), and calculating the arithmetic average value thereof. You can ask.
  • TEM transmission electron microscope
  • Carbon fiber can be molded into carbon felt when the fiber length is relatively long, and can be molded into carbon paper when the fiber length is relatively short. At this time, as the average fiber length of the carbon fibers, it is preferable to adopt a dimension suitable for each shape.
  • the carbon electrode material is configured using the above-mentioned carbon material A, for example, carbon fiber. Since the electrode according to the present embodiment includes such a carbon electrode material, the oxidation resistance of the electrode is improved, so that the deterioration due to the oxidation of the electrode can be made difficult to occur.
  • the carbon electrode material in addition to the carbon material A described above, the carbon material B I D / I G ratio of 0.50 than, the I D / I G ratio is 0.50 or less, and oxygen element
  • the carbon material C having a content of 0.50% by mass or more, or a conductive polymer may be further included.
  • the content of the above carbon material A in the carbon electrode material is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass or more with respect to the mass of the carbon electrode material.
  • the shape of the carbon electrode material can be appropriately set according to the type and the form of the battery in which the electrode is used. Among them, it is preferable to have a sheet shape from the viewpoint of improving productivity and handleability.
  • the thickness of the carbon electrode material in the dry state can be appropriately set according to the type of battery in which the electrode is used, etc., and is preferably 0.1 mm to 1.0 mm, more preferably 0 mm.
  • the range is 0.2 mm to 0.9 mm, more preferably 0.3 mm to 0.7 mm.
  • the electrode according to the present embodiment is mainly composed of a carbon electrode material containing the above-mentioned carbon material A and can be used as at least a positive electrode in various batteries.
  • the electrode according to the present embodiment has high durability because it is unlikely to be deteriorated by oxidation caused by oxygen (O 2 ) or ions having high oxidizing power in the electrolytic solution. Therefore, the electrode according to the present embodiment can be suitably used as an electrode of a redox flow battery, in particular, as a positive electrode of a redox flow battery using an electrolytic solution containing highly oxidizing ions as a positive electrode electrolytic solution. The increase in cell resistivity due to repeated use of the battery can be suppressed.
  • the battery according to the present embodiment includes at least a positive electrode and a negative electrode, and uses the above-mentioned electrode as at least the positive electrode. As a result, deterioration of the electrode due to oxidation is less likely to occur, so that durability of the electrode can be improved.
  • FIG. 1 is a schematic configuration diagram showing a configuration of a redox flow battery as an example of the configuration of the battery according to the present embodiment.
  • a manganese compound is used as the active material of the positive electrode side electrolytic solution (positive electrode electrolytic solution) and a titanium compound is used as the negative electrode side electrolytic solution (negative electrode electrolytic solution) is shown as an example.
  • the redox flow battery 1 includes a positive electrode 111 and a negative electrode 121, and includes a positive electrode cell 11 including the positive electrode 111, a negative electrode cell 12 including the negative electrode 121, a positive electrode 111, and
  • the battery cell 10 mainly has a battery cell 10 that is interposed between the negative electrodes 121 to separate the two cells and has an ion exchange membrane 13 that allows predetermined ions to pass therethrough.
  • the redox flow battery 1 according to the present embodiment includes a positive electrode electrolytic solution supplied to the positive electrode 111 and a negative electrode electrolytic solution supplied to the negative electrode 121.
  • the redox flow battery 1 is used alone or in a form called a battery cell stack in which a plurality of battery cells 10 are stacked with the battery cell 10 as a minimum unit, and the battery cell 10 is charged by circulating an electrolytic solution. Discharge.
  • the above-mentioned electrode is used as at least the positive electrode 111.
  • the positive electrode electrolyte contains ions having a high oxidizing power
  • the positive electrode 111 is less likely to be oxidized, and therefore, even if the redox flow battery 1 is repeatedly used, the deterioration of the positive electrode 111 can be less likely to occur. it can.
  • one of the two surfaces of the redox flow battery electrode may be held by an electrode plate (not shown).
  • the redox flow battery electrode should be arranged between the ion exchange membrane 13 and the electrode plate. Is preferred.
  • the redox flow battery electrode is provided so that one of the two surfaces, which does not face the electrode plate, faces the ion exchange membrane 13.
  • the positive electrode electrolyte and the negative electrode electrolyte of the redox flow battery 1 each contain an active material, and the types thereof are not particularly limited.
  • the ions generated from the active material contained in the positive electrode electrolyte include ions having high oxidizing power, for example, one or more ions selected from manganese ion, cerium ion and chlorine ion. It may be.
  • the ions generated from the active material on the negative electrode side included in the negative electrode electrolyte those that are combined with the ions on the positive electrode side described above are used.
  • the positive electrode electrolytic solution contains a manganese compound as an active material
  • the negative electrode electrolytic solution can contain a titanium compound as an active material.
  • a known cation exchange membrane can be used as the ion exchange membrane 13 used in the redox flow battery 1.
  • a perfluorocarbon polymer having a sulfonic acid group a hydrocarbon-based polymer compound having a sulfonic acid group, a polymer compound doped with an inorganic acid such as phosphoric acid, a part of which is a proton-conductive functional group.
  • examples include organic/inorganic hybrid polymers substituted with, and a proton conductor obtained by impregnating a polymer matrix with a phosphoric acid solution or a sulfuric acid solution.
  • perfluorocarbon polymers having a sulfonic acid group are preferable, and Nafion (registered trademark) is more preferable.
  • the redox flow battery 1 includes a positive electrode electrolytic solution tank 112 that stores a positive electrode electrolytic solution that is circulated and supplied to the positive electrode cell 11, a positive electrode outward pipe 115 that sends the positive electrode electrolytic solution from the positive electrode electrolytic solution tank 112 to the positive electrode cell 11, and a positive electrode electrolytic solution. And a positive electrode return pipe 114 for returning from the positive electrode cell 11 to the positive electrode electrolyte tank 112. Of these, a pump 113 for circulating the positive electrode electrolytic solution is arranged in the positive electrode outward pipe 114.
  • the redox flow battery 1 includes a negative electrode electrolyte tank 122 that stores a negative electrode electrolyte solution that is circulated and supplied to the negative electrode cell 12, and a negative electrode outward pipe 124 that sends the negative electrode electrolyte solution from the negative electrode electrolyte solution tank 122 to the negative electrode cell 12.
  • a negative electrode return pipe 125 for returning the negative electrode electrolytic solution from the negative electrode cell 12 to the negative electrode electrolytic solution tank 122 is provided.
  • a pump 123 for circulating the negative electrode electrolyte is arranged in the negative electrode outward pipe 124.
  • the electrolytic solution in the positive electrode electrolytic solution tank 112 is sent to the battery cell 10 (more strictly, the positive electrode cell 11) through the positive electrode outward pipe 114 by operating the pump 113. ..
  • the positive electrode electrolytic solution sent to the battery cell 10 is discharged upward through the inside of the battery cell 10 and returned to the positive electrode electrolytic solution tank 112 through the positive electrode return pipe 115 and circulates in the direction of arrow A in the figure. ..
  • the electrolytic solution in the negative electrode electrolytic solution tank 122 is sent to the battery cell 10 (more strictly, the negative electrode cell 12) through the negative electrode outward pipe 124 by operating the pump 123.
  • the electrolytic solution sent to the battery cell 10 is discharged upward through the inside of the battery cell 10 and returned to the negative electrode electrolytic solution tank 112 through the negative electrode return pipe 125 and circulates in the direction of arrow B in the figure.
  • the redox reaction of the active material contained in the electrolytic solution is carried out in the battery cell 10, and it becomes possible to store or take out the electric power. That is, it becomes possible to charge the electric power supplied from the power supply 31 such as a power plant via the AC/DC converter 2. Further, it becomes possible to discharge the charged power to the load 32 via the AC/DC converter 2.
  • the battery cell 10 of the redox flow battery 1 is described as a single cell, but may be formed in a form called a cell stack in which a plurality of single cells are stacked (not shown). ).
  • the electrode manufacturing method according to the present embodiment is performed by firing a molded body containing a carbon material (carbon material molded body) such as carbon felt or carbon paper in an inert gas atmosphere of 2300° C. or higher and 3500° C. or lower. It has a high temperature firing step of obtaining an electrode material. If necessary, a low temperature firing step may be performed on the carbon material compact before the high temperature firing step.
  • a carbon material carbon material molded body
  • carbon felt or carbon paper containing carbon fiber can be used, and carbon felt made of carbon fiber or carbon paper is preferable.
  • a carbon material molded body may be produced from carbon fiber by a known means, or commercially available carbon felt or carbon paper may be processed into a predetermined size and used as a carbon material molded body. ..
  • Low temperature firing process In the present embodiment, it is preferable to perform a low temperature firing step of firing the carbon material molded body in an atmosphere containing oxygen gas at 700° C. or lower before performing a high temperature firing step described later.
  • the surface area of the carbon material forming the carbon material molded body is increased by performing the low temperature firing step on the carbon material molded body in an atmosphere containing oxygen gas.
  • an atmosphere containing oxygen gas can be used as an atmosphere for performing the low temperature firing step.
  • the firing temperature in the low-temperature firing process shall be 700°C or lower.
  • the firing temperature in the low temperature firing step is preferably 600° C. or lower, and more preferably 500° C. or lower.
  • the lower limit of the firing temperature may be, for example, 300° C. or higher, or 400° C. or higher.
  • the firing time in the low temperature firing process is set according to the firing temperature and the oxygen gas concentration in the atmosphere. More specifically, it is preferably 0.5 hours to 10 hours, more preferably 1 hour to 5 hours, and further preferably 2 hours to 4 hours.
  • the temperature rising rate up to the predetermined firing temperature is 0.5° C./minute or more from the viewpoint of increasing the productivity in the low temperature firing step and reducing the cost.
  • the heating rate is preferably 100° C./minute or less, more preferably 1° C./minute or more and 25° C./minute or less.
  • the cooling after the elapse of a predetermined firing time is preferably performed at a cooling rate of 0.5° C./minute or more and 100° C./minute or less, and is preferably performed at a cooling rate of 1° C./minute or more and 25° C./minute or less. Is more preferable.
  • the carbon material molded body fired in the low temperature firing step is fired in an inert gas atmosphere of 2300° C. or higher and 3500° C. or lower as necessary to obtain a carbon electrode material.
  • the proportion of carbon in the carbon material occupied by the graphite structure increases, and the proportion of other phases and defects or edges in the graphite structure and other phases are increased. The ratio of will decrease.
  • the oxygen atoms attached to the carbon material are removed, the content of oxygen element contained in the carbon material is reduced. With these, when the obtained electrode is used in a battery, it is possible to obtain a low cell resistivity in the initial state and to prevent deterioration of the electrode due to oxidation or the like.
  • Examples of the inert gas that constitutes the atmosphere in which the high temperature firing step is performed include noble gases such as argon (Ar) gas and nitrogen (N 2 ) gas.
  • the temperature (firing temperature) for firing in the high-temperature firing process should be 2300°C or higher and 3500°C or lower.
  • the firing temperature in the high temperature firing step is preferably 2400° C. or higher, and more preferably 2500° C. or higher.
  • the upper limit of the firing temperature is preferably 3300°C or lower, more preferably 3100°C or lower.
  • the time for performing the firing in the high temperature firing step can be appropriately established within the range where the above-mentioned I D /I G ratio is 0.5 or less.
  • the firing time in the high temperature firing step may be, for example, 15 minutes to 4 hours.
  • the rate of temperature increase until reaching a predetermined firing temperature is 0.5° C./minute or more and 100° C./minute or more from the viewpoint of making deterioration of electrode performance less likely to occur.
  • the heating rate is preferably the following, and more preferably 1° C./minute or more and 25° C./minute or less.
  • the cooling after the elapse of a predetermined firing time is preferably performed at a cooling rate of 0.5° C./minute or more and 100° C./minute or less, and is preferably performed at a cooling rate of 1° C./minute or more and 25° C./minute or less. Is more preferable.
  • the electrode manufacturing method includes a high temperature firing step of firing a carbon material in an inert gas atmosphere of 2300° C. or higher and 3500° C. or lower, and a carbon electrode formed by molding the carbon material fired in the high temperature firing step. Forming step of obtaining a material. If necessary, the low temperature firing step may be performed on the carbon material before the high temperature firing step.
  • the low temperature firing step and the high temperature firing step can be performed in the same manner as in the first embodiment, except that an unformed carbon material is used instead of the carbon material molded body.
  • the forming step is a step of forming the carbon material fired in the high temperature firing step to obtain a carbon electrode material.
  • a known method for obtaining a carbon material molded body such as carbon felt or carbon paper from carbon fiber can be used.
  • the carbon material can be formed into a sheet using this dispersion liquid.
  • the dispersion medium for dispersing the carbon material is not particularly limited, and for example, water can be used.
  • a dispersant When dispersing the carbon material in the dispersion medium, it is preferable to add a dispersant to the dispersion medium, which can facilitate the uniform dispersion of the carbon material.
  • a dispersant a known dispersant can be used, and for example, a water-soluble conductive polymer can be used.
  • the method for dispersing the carbon material to prepare the dispersion liquid is not particularly limited, and examples thereof include a method using ultrasonic waves, a ball mill, and a magnetic stirrer.
  • a method of forming a carbon material into a sheet from the obtained dispersion liquid for example, a method of drying the dispersion medium after applying the dispersion liquid to a substrate, or filtering the dispersion liquid to remove the dispersion medium. Any method can be used.
  • an electrode having a carbon electrode material containing a carbon material having an I D /I G ratio by Raman spectroscopy of 0.50 or less and an oxygen element content of 0.50 mass% or less can be obtained.
  • the carbon material is subjected to the low temperature firing step and the high temperature firing step, and in the molding step, the carbon material after firing is molded to obtain the carbon electrode material.
  • You may perform a shaping
  • the electrode thus obtained can be incorporated into a battery by a conventional method, for example, the redox flow battery 1 shown in FIG.
  • this electrode is provided on one side of the ion exchange membrane 13, and the negative electrode 121 is separately provided on the other side of the ion exchange membrane 13.
  • Example 1 Preparation of carbon material molded body
  • carbon paper of size (length 100 mm, width 100 mm, thickness 0.19 mm) (manufactured by SGL Carbon Co., model number GDL-39AA) is used. I was there.
  • This carbon paper is made of carbon fiber which is a carbon material, and the average fiber diameter of the carbon fibers constituting the carbon paper is 1 ⁇ m.
  • Low temperature firing step for carbon material molded body As a low temperature firing step, the carbon paper was fired at a firing temperature of 480° C. in air for a firing time of 3 hours (3 h). Here, the temperature was raised to the firing temperature at a rate of 10° C./min, and after firing, it was cooled to room temperature at a cooling rate of 10° C./min.
  • High temperature firing step for carbon material molded body As a high temperature firing step, the carbon paper after low temperature firing is fired at a firing temperature of 3000° C. in an argon (Ar) gas for a firing time of 1 hour (1 h). A carbon electrode material was produced. Here, the temperature was raised to the firing temperature at a heating rate of 10° C./min, and after firing, the temperature was cooled to room temperature at a cooling rate of 10° C./min to obtain a carbon electrode material.
  • Ar argon
  • the carbon electrode material has the following 4. 4. The number of sheets necessary for evaluating the I D /I G ratio and the content of oxygen element, and 5. Then, the total number of sheets required for use in the positive electrode of the battery was prepared. In addition, regarding the carbon material molded body after the above-mentioned low temperature firing step, the following 5. Then, the number of sheets required for use as the negative electrode of the battery was prepared.
  • I D /I G ratio D band peak appearing in Raman spectrum measured by Raman spectroscopy of the obtained carbon electrode material
  • the intensity (I D ) and the peak intensity (I G ) of the G band are determined, and the peak intensity ratio (I D /is the ratio of the peak intensity (I D ) of the D band to the peak intensity (I G ) of the G band.
  • IG ratio was determined.
  • a laser Raman spectrophotometer manufactured by JASCO Corporation, model number: NRS-5100 was used as the spectrophotometer, and the excitation wavelength was 532.36 nm, the laser intensity was 1.6 mW, the incident slit width was 50 ⁇ m, and the exposure time was 15 seconds.
  • Raman spectroscopic spectra were measured twice under a condition of 600 diffraction gratings/mm, and the peak intensity ( ID ) of the D band near 1360 cm -1 and the peak intensity of the G band near 1580 cm -1. The ratio to ( IG ) was determined.
  • the positive electrode electrolytic solution and the negative electrode electrolytic solution are obtained by dissolving manganese sulfate (MnSO 4 ) and titanium oxide sulfate (TiOSO 4 ) in an aqueous sulfuric acid solution, respectively.
  • the manganese ion concentration is 1M
  • the titanium ion concentration is 1M
  • the sulfuric acid is 1M.
  • An electrolytic solution having an ion concentration of 5M was used. 50 mL of this electrolytic solution was introduced into each of the positive electrode side and the negative electrode side of the redox flow battery to form a single cell of the redox flow battery.
  • the initial resistivity of the redox flow battery was the cell resistivity obtained after repeating the charge/discharge cycle 5 times.
  • the charge average voltage and the discharge average voltage were obtained, and the values were obtained based on the following calculation formula.
  • Cell resistivity [ ⁇ cm 2 ] (charge average voltage [V] ⁇ discharge average voltage [V]) ⁇ electrode area [cm 2 ] ⁇ (2 ⁇ charge current [A])
  • Example 2 In "3. High-temperature firing step for molded carbon material", a carbon electrode material was produced in the same manner as in Example 1 except that the firing temperature was 2500°C, and a single cell of a redox flow battery was constructed. The obtained carbon electrode material was similarly evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
  • Example 3 A carbon electrode material was produced in the same manner as in Example 2 except that the carbon paper was not subjected to the "2. Low temperature firing step for the carbon material molded body", but was subjected to the high temperature firing step, and also the redox flow battery. The single cell of The obtained carbon electrode material was similarly evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
  • Example 1 The carbon paper was used as it is as a carbon electrode material without performing “2. Low temperature firing step for carbon material compact” and “3. High temperature firing step for carbon material compact,” as in Example 1. A single cell of a redox flow battery was constructed. Similarly, the unburned carbon paper used as the carbon electrode material was evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
  • Example 3 In "3. High-temperature firing step for carbon material molded body", a carbon electrode material was produced in the same manner as in Example 1 except that the firing temperature was set to 2000°C, and a single cell of a redox flow battery was constructed. The obtained carbon electrode material was similarly evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
  • Table 1 shows various conditions in Examples 1 to 3 and Comparative Examples 1 to 3, I D /I G ratio, oxygen element content, cell resistivity in the initial state, cell resistivity after repeated use, and resistance. The rate of deterioration is shown below.
  • the carbon electrode material has an I D /I G ratio of 0.50 or less and an oxygen element content of 0.50 mass% or less, so that I D / compared to the electrodes of I G ratio is larger Comparative examples 1 to 3, also include a high oxidizing power manganese ions in the electrolyte of the positive electrode side, the cell resistivity of redox flow batteries, hardly deteriorated by repeated use I understood it.
  • the positive electrode of Examples 1 and 2 since the positive electrode of Examples 1 and 2 has a lower I D /I G ratio in the carbon electrode material, it has a lower cell resistivity in the initial state, and also has a cell resistivity with repeated use. I found it harder to get worse.
  • the positive electrodes of Examples 1 to 3 were manufactured by a method including a high temperature firing step of firing carbon paper at 2300° C. or higher and 3500° C. or lower to obtain a carbon electrode material.
  • the carbon electrode material obtained has a lower I D /I G ratio, and thus has a higher oxidizing power. It was found that even if manganese ions were included in the electrolyte solution on the positive electrode side, the cell resistivity of the redox flow battery was unlikely to deteriorate with repeated use.
  • FIG. 2A is a SEM image of the surface of the carbon fiber before the low temperature firing step
  • FIG. 2B is a carbon fiber before the high temperature firing step after the low temperature firing step. It is a SEM image of the surface. From the comparison of the SEM images of FIG. 2(a) and FIG.
  • the content of the oxygen element contained in the carbon electrode material depends on whether the low temperature firing step is performed in Examples 1 to 3 and Comparative Examples 2 and 3 in which the high temperature firing step was performed at a firing temperature of 2000° C. or higher. Regardless of the relationship, both were low at 0.20% by mass to 0.22% by mass, but in Comparative Example 1 in which the high temperature firing step was not performed, it was remarkably high at 1.00% by mass. From this, the carbon electrode material forming the positive electrode can be suppressed to a low content without increasing the content of oxygen element by performing the high temperature firing step regardless of whether or not the low temperature firing step is performed. all right.

Abstract

The present invention provides: an electrode which is not susceptible to deterioration due to oxidation; a method for producing this electrode; and a battery.　An electrode according to the present invention comprises a carbon electrode material; and the carbon electrode material has a peak intensity ratio of the peak intensity of the D band (ID) to the peak intensity of the G band (IG), namely ID/IG of 0.50 or less in the Raman spectrum as determined by Raman spectroscopy, while having an elemental oxygen content of 0.50% by mass or less. It is preferable that this electrode is used as a positive electrode 111 of a redox flow battery 1.

Description

電極及びその製造方法、並びに電池Electrode, manufacturing method thereof, and battery
　本発明は、電極及びその製造方法、並びにこの電極を備えた電池に関する。 The present invention relates to an electrode, a method for manufacturing the electrode, and a battery including the electrode.
　電力貯蔵用の電池として、種々の電池の開発が進められており、電解液流通型の電池として、レドックスフロー電池が挙げられる。レドックスフロー電池は、正極と負極と両電極の間に介在される隔膜とを有する電池セルに、正極電解液及び負極電解液をそれぞれ供給循環し、電力変換器（例えば、交流／直流変換器等）を介して充放電を行なう。電解液には、酸化還元により価数が変化する金属イオン（活物質）を含有する水溶液が通常使用されている。レドックスフロー電池としては、例えば正極及び負極の活物質にバナジウム（Ｖ）を用いたバナジウム系レドックスフロー電池がよく知られている。 Various types of batteries are being developed as batteries for storing electric power, and redox flow batteries can be mentioned as electrolyte flow batteries. A redox flow battery supplies and circulates a positive electrode electrolytic solution and a negative electrode electrolytic solution to and from a battery cell having a positive electrode, a negative electrode, and a diaphragm interposed between both electrodes, and a power converter (for example, an AC/DC converter or the like). ) Is used to charge and discharge. As the electrolytic solution, an aqueous solution containing a metal ion (active material) whose valence changes by redox is usually used. As a redox flow battery, for example, a vanadium redox flow battery using vanadium (V) as an active material of a positive electrode and a negative electrode is well known.
　このようなレドックスフロー電池に用いられる電極の材料としては、カーボンナノチューブやカーボンファイバー等の炭素材料が用いられる。例えば、特許文献１には、レドックスフロー電池の電極材料に気相法炭素繊維を用いることが記載されている。また、特許文献２には、電解液を電極に通液させた時の圧力損失が小さく、厚さ方向への導電性の良い電極の材料として、フェルト内部に空隙部を有する炭素繊維フェルトを用いることが記載されている。 Carbon materials such as carbon nanotubes and carbon fibers are used as the material of the electrodes used in such a redox flow battery. For example, Patent Document 1 describes the use of vapor grown carbon fiber as an electrode material of a redox flow battery. Further, in Patent Document 2, a carbon fiber felt having voids inside the felt is used as a material of the electrode which has a small pressure loss when an electrolytic solution is passed through the electrode and has good conductivity in the thickness direction. Is described.
特開２００６－１５６０２９号公報JP, 2006-156029, A 特開２０１３－１４４８５７号公報JP, 2013-144857, A
　特許文献１、２に記載のレドックスフロー電池は、バナジウム系の電解液を用いたレドックスフロー電池において、セル抵抗率を低くし、また、電解液を電極に通液させた時の圧力損失を小さくしたものである。しかしながら、バナジウム系以外の電解液には、例えばマンガン－チタン系のように酸化力の高いイオンを含むものもあるため、このような酸化力の高いイオンを含んだ電解液を含んだ場合であっても、酸化による電極の劣化、より具体的にはセル抵抗率の上昇や破損が起こり難い、レドックスフロー電池の電極が求められていた。 The redox flow battery described in Patent Documents 1 and 2 is a redox flow battery using a vanadium-based electrolyte solution, which has a low cell resistivity and a small pressure loss when the electrolyte solution is passed through the electrodes. It was done. However, there are electrolytes other than vanadium-based electrolytes that contain ions with a high oxidizing power, such as manganese-titanium-based electrolytes. However, there has been a demand for an electrode for a redox flow battery, which is less likely to cause deterioration of the electrode due to oxidation, more specifically, increase in cell resistivity and breakage.
　また、レドックスフロー電池以外の電池においても、酸化によるセル抵抗率の上昇や破損による劣化が起こり難い電極が求められていた。 Also, for batteries other than redox flow batteries, there was a demand for electrodes that are unlikely to cause cell resistance increase due to oxidation and deterioration due to damage.
　本発明の目的は、酸化による劣化が起こり難い電極及びその製造方法、並びに電池を提供することである。 An object of the present invention is to provide an electrode, a manufacturing method thereof, and a battery, which are less likely to be deteriorated by oxidation.
　本発明者らは、電極を構成するカーボン電極材に、ラマン分光法によって測定したラマンスペクトルに現れる、Ｄバンドのピーク強度（ＩＤ）とＧバンドのピーク強度（ＩＧ）のピーク強度比（ＩＤ／ＩＧ比）が小さい炭素材料を含めることで、例えば電池の繰り返しの使用によっても、酸化によるセル抵抗率の上昇が起こり難くなることを見出し、本発明を完成するに至った。より具体的には、本発明は、以下のものを提供する。 The present inventors have found that the carbon electrode material constituting the electrode, appearing in the Raman spectrum measured by Raman spectroscopy, the peak intensity of D-band (I D) and the peak intensity of G-band peak intensity ratio (I G) ( By including a carbon material having a small I D /I G ratio), it was found that the increase in cell resistivity due to oxidation is unlikely to occur even when the battery is repeatedly used, and the present invention has been completed. More specifically, the present invention provides the following.
　（１）本発明は、カーボン電極材を有する電極であって、前記カーボン電極材は、ラマン分光法によって測定したラマンスペクトルに現れる、Ｄバンドのピーク強度（ＩＤ）の、Ｇバンドのピーク強度（ＩＧ）に対するピーク強度比（ＩＤ／ＩＧ比）が０．５０以下であり、かつ、酸素元素の含有量が０．５０質量％以下である炭素材料を含む電極である。 (1) The present invention is an electrode having a carbon electrode material, wherein the carbon electrode material has a G band peak intensity of a D band peak intensity (I D ) that appears in a Raman spectrum measured by Raman spectroscopy. (I G) peak intensity ratio (I D / I G ratio) is 0.50 or less, and the content of oxygen element is an electrode containing a carbon material is less than 0.50 wt%.
　（２）また、本発明は、前記カーボン電極材は、前記炭素材料を５０質量％以上含有する、（１）に記載の電極である。 (2) Further, the present invention is the electrode according to (1), wherein the carbon electrode material contains 50% by mass or more of the carbon material.
　（３）また、本発明は、前記炭素材料は、カーボンファイバーを含む、（１）または（２）に記載の電極である。 (3) Further, the present invention is the electrode according to (1) or (2), wherein the carbon material includes carbon fiber.
　（４）また、本発明は、前記カーボンファイバーの平均繊維径が１μｍ以上である、（３）に記載の電極である。 (4) Further, the present invention is the electrode according to (3), wherein the carbon fiber has an average fiber diameter of 1 μm or more.
　（５）また、本発明は、前記カーボン電極材は、前記カーボンファイバーを用いて形成されたカーボンフェルトまたはカーボンペーパーのシート材料で構成される、（３）または（４）に記載の電極。 (5) The present invention also provides the electrode according to (3) or (4), wherein the carbon electrode material is composed of a sheet material of carbon felt or carbon paper formed using the carbon fiber.
　（６）また、本発明は、前記電極が、レドックスフロー電池の正極電極として用いられる、（１）～（５）のいずれかに記載の電極である。 (6) Further, the present invention is the electrode according to any one of (1) to (5), wherein the electrode is used as a positive electrode of a redox flow battery.
　（７）また、本発明は、正極電極および負極電極を備える電池であって、前記正極電極が、（１）～（６）のいずれかに記載の電極である、電池である。 (7) Further, the present invention is a battery including a positive electrode and a negative electrode, wherein the positive electrode is the electrode according to any one of (1) to (6).
　（８）また、本発明は、前記電池がレドックスフロー電池であり、前記正極電極に供給される正極電解液、および前記負極電極に供給される負極電解液をさらに備え、前記正極電解液が、マンガンイオン、セリウムイオンおよび塩素イオンから選択される１種又は２種以上のイオンを含む、（７）に記載の電池である。 (8) Further, in the present invention, the battery is a redox flow battery, and further comprises a positive electrode electrolytic solution supplied to the positive electrode and a negative electrode electrolytic solution supplied to the negative electrode, wherein the positive electrode electrolytic solution is: The battery according to (7), which contains one or more ions selected from manganese ions, cerium ions, and chlorine ions.
　（９）また、本発明は、（１）～（６）のいずれかに記載の電極の製造方法であって、炭素材料を含む成形体を、不活性ガス雰囲気中、２３００℃以上３５００℃以下で焼成してカーボン電極材を得る高温焼成工程を有する、電極の製造方法である。 (9) Further, the present invention is the method for manufacturing an electrode according to any one of (1) to (6), wherein the molded body containing a carbon material is treated in an inert gas atmosphere at 2300° C. or higher and 3500° C. or lower. Is a method for manufacturing an electrode, which includes a high-temperature firing step of firing to obtain a carbon electrode material.
　（１０）また、本発明は、前記高温焼成工程を行なう前に、前記成形体を、７００℃以下の酸素ガスを含む雰囲気中で焼成する低温焼成工程を行なう、（９）に記載の電極の製造方法である。 (10) Further, according to the present invention, before performing the high temperature firing step, a low temperature firing step of firing the molded body in an atmosphere containing oxygen gas at 700° C. or lower is performed. It is a manufacturing method.
　本発明によれば、酸化による劣化が起こり難い電池の電極及びその製造方法、並びに電池を得ることができる。 According to the present invention, it is possible to obtain a battery electrode that is less likely to be deteriorated by oxidation, a manufacturing method thereof, and a battery.
本実施形態に係る電極を備えたレドックスフロー電池システムの構成の一例を示す構成図である。It is a block diagram which shows an example of a structure of the redox flow battery system provided with the electrode which concerns on this embodiment. 実施例１と同じカーボンペーパーを構成する、カーボンファイバー表面のＳＥＭ（走査型電子顕微鏡）像である。図２（ａ）は、低温焼成工程を行なう前のカーボンファイバー表面のＳＥＭ像であり、図２（ｂ）は、低温焼成工程を行なった後で高温焼成工程を行なう前のカーボンファイバー表面のＳＥＭ像である。5 is an SEM (scanning electron microscope) image of the surface of carbon fiber that constitutes the same carbon paper as in Example 1. FIG. 2A is a SEM image of the carbon fiber surface before the low temperature firing step, and FIG. 2B is a SEM image of the carbon fiber surface after the low temperature firing step and before the high temperature firing step. It is a statue.
　以下、本発明の具体的な実施形態について、図面を参照しながら詳細に説明する。なお、本発明は、以下の実施形態に限定されるものではなく、本発明の要旨を変更しない範囲で種々の変更が可能である。 Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention.
　本実施形態の電極は、カーボン電極材を有する電極であって、カーボン電極材は、ラマン分光法によって測定したラマンスペクトルに現れる、Ｄバンドのピーク強度（ＩＤ）の、Ｇバンドのピーク強度（ＩＧ）に対するピーク強度比（ＩＤ／ＩＧ比）が０．５０以下であり、かつ、酸素元素の含有量が０．５０質量％以下である炭素材料を含む。 The electrode of the present embodiment is an electrode having a carbon electrode material, and the carbon electrode material has a G-band peak intensity (I D ) of the D-band peak intensity ( ID ) that appears in a Raman spectrum measured by Raman spectroscopy. I G peak intensity ratio) (I D / I G ratio) is 0.50 or less, and the content of oxygen element comprises a carbon material is less than 0.50 wt%.
＜電極＞
　本実施形態に係る電極（以下、「電池電極」という場合がある。）は、炭素材料を含んだカーボン電極材を主構成とする。ここで、カーボン電極材に含まれる炭素材料（以下「炭素材料Ａ」という場合がある。）は、ラマン分光法によって測定したラマンスペクトルに現れる、Ｄバンドのピーク強度（ＩＤ）の、Ｇバンドのピーク強度（ＩＧ）に対するピーク強度比（ＩＤ／ＩＧ比）が０．５０以下であり、かつ、酸素元素の含有量が０．５０質量％以下である。 <Electrode>
The electrode (hereinafter, also referred to as “battery electrode”) according to the present embodiment mainly includes a carbon electrode material containing a carbon material. Here, the carbon material contained in the carbon electrode material (hereinafter sometimes referred to as “carbon material A”) is the G band of the peak intensity ( ID ) of the D band that appears in the Raman spectrum measured by Raman spectroscopy. peak intensity peak intensity ratio (I G) (I D / I G ratio) is 0.50 or less, and the content of oxygen element is less than 0.50 wt%.
　本実施形態に係る電極では、炭素材料Ａを含んだカーボン電極材を主構成とし、且つ炭素材料ＡのＩＤ／ＩＧ比を小さくすることで、電極が酸化力の高い環境に置かれていても、酸化による電極の劣化を起こり難くすることができる。 In the electrode according to the present embodiment, the carbon electrode material containing the carbon material A is mainly used, and the I D /I G ratio of the carbon material A is reduced so that the electrode is placed in an environment with high oxidizing power. However, it is possible to prevent deterioration of the electrode due to oxidation.
　以下、本発明の電極を構成する、炭素材料Ａおよびカーボン電極材について、詳細に説明する。 Hereinafter, the carbon material A and the carbon electrode material that compose the electrode of the present invention will be described in detail.
　（炭素材料Ａ）
　カーボン電極材に含まれる炭素材料Ａは、ラマン分光法によって測定したラマンスペクトルに現れる、Ｄバンドのピーク強度（ＩＤ）の、Ｇバンドのピーク強度（ＩＧ）に対するピーク強度比（ＩＤ／ＩＧ比）が０．５０以下である。炭素材料の構造の乱れや欠陥に起因して現れるＤバンドのピーク強度（ＩＤ）の、炭素材料のグラファイト構造に由来するＧバンドのピーク強度（ＩＧ）に対する比（ＩＤ／ＩＧ比）を０．５０以下にすることで、酸素（Ｏ２）や、酸化力の高いイオンを含んだ電解液等によっても電極が酸化され難くなる。そのため、電池を繰り返し使用しても、電極の破損を起こり難くすることができ、また、セル抵抗率の上昇を起こり難くすることができる。ここで、炭素材料ＡのＩＤ／ＩＧ比は、０．４５以下であることが好ましく、０．４０以下であることがより好ましい。 (Carbon material A)
The carbon material A contained in the carbon electrode material, appearing in the Raman spectrum measured by Raman spectroscopy, the peak intensity of D-band (I D), the peak intensity ratio to the peak intensity of G-band (I G) (I D / I G ratio) is 0.50 or less. The ratio ( ID / IG ratio) of the peak intensity ( ID ) of the D band appearing due to the disorder and the defect of the carbon material structure to the peak intensity ( IG ) of the G band derived from the graphite structure of the carbon material. ) Is set to 0.50 or less, the electrode is less likely to be oxidized by oxygen (O 2 ) or an electrolytic solution containing ions having high oxidizing power. Therefore, even if the battery is repeatedly used, it is possible to make the electrodes less likely to be damaged and to make it difficult to increase the cell resistivity. Here, the I D /I G ratio of the carbon material A is preferably 0.45 or less, and more preferably 0.40 or less.
　また、この炭素材料Ａにおける酸素元素の含有量は、０．５０質量％以下である。炭素材料Ａにおける酸素元素の含有量が０．５０質量％以下であることで、炭素材料に含まれる酸素原子による電極反応の阻害が起こり難くなるため、電池のセル抵抗率をより低くすることができる。ここで、炭素材料Ａにおける酸素元素は、０．４０質量％以下であることが好ましく、０．３０質量％以下であることがより好ましい。 Also, the content of oxygen element in this carbon material A is 0.50 mass% or less. When the content of the oxygen element in the carbon material A is 0.50% by mass or less, it becomes difficult for the oxygen atoms contained in the carbon material to inhibit the electrode reaction, so that the cell resistivity of the battery can be further lowered. it can. Here, the oxygen element in the carbon material A is preferably 0.40 mass% or less, and more preferably 0.30 mass% or less.
　炭素材料Ａとしては、例えば、ＩＤ／ＩＧ比が０．５０以下であり、酸素元素の含有量が０．５０質量％以下である、カーボンファイバー、グラフェン、カーボンブラック等が挙げられる。これらの材料を１種用いてもよく、２種類以上を用いてもよい。炭素材料Ａとして２種類以上の材料を用いる場合、Ｄバンドのピーク強度（ＩＤ）の、Ｇバンドのピーク強度（ＩＧ）に対するピーク強度比（ＩＤ／ＩＧ比）は、各種炭素材料のＩＤ／ＩＧ比に質量割合を乗じた値の合計より得られる加重平均値とする。なお、炭素材料Ａは、特にカーボンファイバーを含んでいることが好ましい。ここで、カーボンファイバーとしては、平均繊維径が１０ｎｍ以上の繊維状（管状を含む）のカーボン材料を挙げることができる。他方で、カーボンファイバーの平均繊維径の上限は、カーボン電極材への加工のし易さの観点から設定されることが好ましく、例えば２００μｍ以下にすることができる。ここで、平均繊維径や平均繊維長が異なる、複数の種類のカーボンファイバーを炭素材料Ａとして含んでいてもよい。 Examples of the carbon material A include carbon fibers, graphene, carbon black, etc., which have an I D /I G ratio of 0.50 or less and an oxygen element content of 0.50 mass% or less. One of these materials may be used, or two or more of them may be used. When using two or more kinds of materials as the carbon material A, D peak intensity of band (I D), the peak intensity ratio to the peak intensity of G-band (I G) (I D / I G ratio), various carbon materials The weighted average value obtained from the sum of the values obtained by multiplying the I D /I G ratio by the mass ratio. The carbon material A preferably contains carbon fibers. Here, examples of the carbon fiber include a fibrous (including tubular) carbon material having an average fiber diameter of 10 nm or more. On the other hand, the upper limit of the average fiber diameter of the carbon fibers is preferably set from the viewpoint of ease of processing into a carbon electrode material, and can be set to, for example, 200 μm or less. Here, a plurality of types of carbon fibers having different average fiber diameters and average fiber lengths may be included as the carbon material A.
　カーボンファイバーとしては、平均繊維径が１μｍ以上のものと、平均繊維径が１μｍ未満のもの（例えばカーボンナノファイバーやカーボンナノチューブ）が挙げられる。 The carbon fibers include those having an average fiber diameter of 1 μm or more and those having an average fiber diameter of less than 1 μm (for example, carbon nanofibers and carbon nanotubes).
　このうち、平均繊維径が１μｍ以上のカーボンファイバーを含有することで、カーボン電極材を用いた電極の導電性や強度の向上の効果を期待できる。また、より大きな空隙がカーボン電極材の内部に形成されるため、特に電極をレドックスフロー電池の電極に用いた場合、電解液を電極に通液させる際の圧力損失を小さくすることができる。したがって、カーボンファイバーの平均繊維径は、好ましくは１μｍ～２００μｍ、より好ましくは２μｍ～１００μｍ、さらに好ましくは５μｍ～３０μｍの範囲である。また、カーボンファイバーの平均繊維長は、好ましくは０．０１ｍｍ～２０ｍｍ、より好ましくは０．０５ｍｍ～１０ｍｍ、さらに好ましくは０．１ｍｍ～８ｍｍの範囲である。 Among these, by containing carbon fibers having an average fiber diameter of 1 μm or more, the effect of improving the conductivity and strength of the electrode using the carbon electrode material can be expected. Further, since a larger void is formed inside the carbon electrode material, it is possible to reduce the pressure loss when the electrolytic solution is passed through the electrode, particularly when the electrode is used as an electrode of a redox flow battery. Therefore, the average fiber diameter of the carbon fibers is preferably in the range of 1 μm to 200 μm, more preferably 2 μm to 100 μm, and further preferably 5 μm to 30 μm. The average fiber length of the carbon fibers is preferably 0.01 mm to 20 mm, more preferably 0.05 mm to 10 mm, still more preferably 0.1 mm to 8 mm.
　また、平均繊維径が１μｍ未満のカーボンナノファイバーやカーボンナノチューブを含有してもよく、この場合、カーボンナノファイバーやカーボンナノチューブの平均繊維径は、好ましくは１ｎｍ～３００ｎｍ、より好ましくは１０ｎｍ～２００ｎｍ、さらに好ましくは１５ｎｍ～１５０ｎｍの範囲である。また、カーボンナノチューブの平均繊維長は、好ましくは０．１μｍ～３０μｍ、より好ましくは０．５μｍ～２５μｍ、さらに好ましくは０．５μｍ～２０μｍの範囲である。 Further, it may contain carbon nanofibers or carbon nanotubes having an average fiber diameter of less than 1 μm. In this case, the average fiber diameter of the carbon nanofibers or carbon nanotubes is preferably 1 nm to 300 nm, more preferably 10 nm to 200 nm, More preferably, it is in the range of 15 nm to 150 nm. The average fiber length of the carbon nanotubes is preferably in the range of 0.1 μm to 30 μm, more preferably 0.5 μm to 25 μm, still more preferably 0.5 μm to 20 μm.
　ここで、カーボンファイバーの平均繊維径及び平均繊維長は、透過型電子顕微鏡（ＴＥＭ）を用いて、無作為に１００本以上のカーボンファイバーの直径（繊維径）を測定し、その算術平均値として求めることができる。 Here, the average fiber diameter and the average fiber length of the carbon fibers are obtained by randomly measuring the diameters (fiber diameters) of 100 or more carbon fibers using a transmission electron microscope (TEM), and calculating the arithmetic average value thereof. You can ask.
　カーボンファイバーは、繊維長が比較的長い場合には、カーボンフェルトに成形することができ、また、繊維長が比較的短い場合には、カーボンペーパーに成形することができる。このとき、カーボンファイバーの平均繊維長としては、それぞれの形状にするのに適した寸法が採用されることが好ましい。 Carbon fiber can be molded into carbon felt when the fiber length is relatively long, and can be molded into carbon paper when the fiber length is relatively short. At this time, as the average fiber length of the carbon fibers, it is preferable to adopt a dimension suitable for each shape.
　（カーボン電極材）
　カーボン電極材は、上述の炭素材料Ａ、例えばカーボンファイバーを用いて構成されるものである。本実施形態に係る電極は、このようなカーボン電極材を含むことにより、電極の耐酸化性が向上するため、電極の酸化による劣化を起こり難くすることができる。 (Carbon electrode material)
The carbon electrode material is configured using the above-mentioned carbon material A, for example, carbon fiber. Since the electrode according to the present embodiment includes such a carbon electrode material, the oxidation resistance of the electrode is improved, so that the deterioration due to the oxidation of the electrode can be made difficult to occur.
　また、カーボン電極材は、上述の炭素材料Ａの他に、ＩＤ／ＩＧ比が０．５０超である炭素材料Ｂ、ＩＤ／ＩＧ比が０．５０以下であり、かつ酸素元素の含有量が０．５０質量％超である炭素材料Ｃ、または導電性高分子をさらに含んでもよい。カーボン電極材における上述の炭素材料Ａの含有量は、カーボン電極材の質量に対して、好ましくは５０質量％以上、より好ましくは６０質量％以上、さらに好ましくは７０質量％以上である。カーボン電極材における上述の炭素材料Ａの含有量を多くすることで、電極の酸化による劣化をより起こり難くすることができ、かつセル抵抗率を小さくすることができる。 The carbon electrode material, in addition to the carbon material A described above, the carbon material B I D / I G ratio of 0.50 than, the I D / I G ratio is 0.50 or less, and oxygen element The carbon material C having a content of 0.50% by mass or more, or a conductive polymer may be further included. The content of the above carbon material A in the carbon electrode material is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass or more with respect to the mass of the carbon electrode material. By increasing the content of the above-mentioned carbon material A in the carbon electrode material, the deterioration due to the oxidation of the electrode can be made more difficult to occur, and the cell resistivity can be reduced.
　カーボン電極材の形状は、電極が用いられる電池の種類やその形態に応じて適宜設定することができる。その中でも、生産性および取扱い性を高める観点から、シートの形状を有することが好ましい。 The shape of the carbon electrode material can be appropriately set according to the type and the form of the battery in which the electrode is used. Among them, it is preferable to have a sheet shape from the viewpoint of improving productivity and handleability.
　カーボン電極材の乾燥状態での厚み（厚さ寸法）は、電極が用いられる電池の種類等に応じて、適宜に設定することができ、好ましくは０．１ｍｍ～１．０ｍｍ、より好ましくは０．２ｍｍ～０．９ｍｍ、さらに好ましくは０．３ｍｍ～０．７ｍｍの範囲である。カーボン電極材の厚みを０．１ｍｍ以上にすることで、カーボン電極材を取り扱える程度の強度を確保することができる。また、カーボン電極材の厚みを１．０ｍｍ以下にすることで、特に電極をレドックスフロー電池の電極に用いた場合に、圧力損失を小さくすることができることができる。 The thickness of the carbon electrode material in the dry state (thickness dimension) can be appropriately set according to the type of battery in which the electrode is used, etc., and is preferably 0.1 mm to 1.0 mm, more preferably 0 mm. The range is 0.2 mm to 0.9 mm, more preferably 0.3 mm to 0.7 mm. By setting the thickness of the carbon electrode material to be 0.1 mm or more, it is possible to secure strength enough to handle the carbon electrode material. In addition, by setting the thickness of the carbon electrode material to 1.0 mm or less, it is possible to reduce the pressure loss, especially when the electrode is used as an electrode of a redox flow battery.
　本実施形態に係る電極は、上述の炭素材料Ａを含んだカーボン電極材を主構成とし、種々の電池に、少なくとも正極電極として用いることが可能である。本実施形態に係る電極は、酸素（Ｏ２）や、電解液中の酸化力が高いイオン等によって引き起こされる、酸化による劣化が起こり難いため、電極の耐久性が高い。したがって、本実施形態に係る電極は、レドックスフロー電池の電極、特に、酸化力の高いイオンを含む電解液を正極電解液として用いたレドックスフロー電池の正極電極として好適に用いることができ、これにより、電池の繰り返しの使用によるセル抵抗率の上昇を抑えることができる。 The electrode according to the present embodiment is mainly composed of a carbon electrode material containing the above-mentioned carbon material A and can be used as at least a positive electrode in various batteries. The electrode according to the present embodiment has high durability because it is unlikely to be deteriorated by oxidation caused by oxygen (O 2 ) or ions having high oxidizing power in the electrolytic solution. Therefore, the electrode according to the present embodiment can be suitably used as an electrode of a redox flow battery, in particular, as a positive electrode of a redox flow battery using an electrolytic solution containing highly oxidizing ions as a positive electrode electrolytic solution. The increase in cell resistivity due to repeated use of the battery can be suppressed.
＜電池＞
　本実施形態に係る電池は、少なくとも正極電極および負極電極を備えるものであり、少なくとも正極電極として上述の電極を用いる。これにより、電極の酸化による劣化が起こり難くなるため、電極の耐久性を高めることができる。 <Battery>
The battery according to the present embodiment includes at least a positive electrode and a negative electrode, and uses the above-mentioned electrode as at least the positive electrode. As a result, deterioration of the electrode due to oxidation is less likely to occur, so that durability of the electrode can be improved.
＜レドックスフロー電池＞
　次に、本実施形態に係る電極を備えるレドックスフロー電池について説明する。 <Redox flow battery>
Next, a redox flow battery including the electrode according to the present embodiment will be described.
　図１は、本実施形態に係る電池の構成の一例として、レドックスフロー電池の構成を示す概略構成図である。図１では、正極側の電解液（正極電解液）の活物質としてマンガン化合物を用い、負極側の電解液（負極電解液）の活物質としてチタン化合物を用いた場合を例として示す。 FIG. 1 is a schematic configuration diagram showing a configuration of a redox flow battery as an example of the configuration of the battery according to the present embodiment. In FIG. 1, a case where a manganese compound is used as the active material of the positive electrode side electrolytic solution (positive electrode electrolytic solution) and a titanium compound is used as the negative electrode side electrolytic solution (negative electrode electrolytic solution) is shown as an example.
　本実施形態に係るレドックスフロー電池１は、正極電極１１１および負極電極１２１を備えるものであり、正極電極１１１を内蔵する正極セル１１と、負極電極１２１を内蔵する負極セル１２と、正極電極１１１及び負極電極１２１の間に介在されて両セルを分離するとともに、所定のイオンを透過するイオン交換膜１３とを有する電池セル１０を主構成とする。また、本実施形態に係るレドックスフロー電池１は、正極電極１１１に供給される正極電解液と、負極電極１２１に供給される負極電解液とを備える。ここで、レドックスフロー電池１は、電池セル１０を最小単位として、これを単独で、又は複数枚積層した電池セルスタックと称される形態で使用され、電池セル１０に電解液を循環させて充放電を行なう。 The redox flow battery 1 according to the present embodiment includes a positive electrode 111 and a negative electrode 121, and includes a positive electrode cell 11 including the positive electrode 111, a negative electrode cell 12 including the negative electrode 121, a positive electrode 111, and The battery cell 10 mainly has a battery cell 10 that is interposed between the negative electrodes 121 to separate the two cells and has an ion exchange membrane 13 that allows predetermined ions to pass therethrough. Further, the redox flow battery 1 according to the present embodiment includes a positive electrode electrolytic solution supplied to the positive electrode 111 and a negative electrode electrolytic solution supplied to the negative electrode 121. Here, the redox flow battery 1 is used alone or in a form called a battery cell stack in which a plurality of battery cells 10 are stacked with the battery cell 10 as a minimum unit, and the battery cell 10 is charged by circulating an electrolytic solution. Discharge.
　本実施形態に係るレドックスフロー電池１では、少なくとも正極電極１１１として、上述の電極を用いる。これにより、正極電解液が酸化力の高いイオンを含有しても、正極電極１１１が酸化され難くなるため、レドックスフロー電池１を繰り返し使用しても、正極電極１１１の劣化を起こり難くすることができる。 In the redox flow battery 1 according to the present embodiment, the above-mentioned electrode is used as at least the positive electrode 111. As a result, even if the positive electrode electrolyte contains ions having a high oxidizing power, the positive electrode 111 is less likely to be oxidized, and therefore, even if the redox flow battery 1 is repeatedly used, the deterioration of the positive electrode 111 can be less likely to occur. it can.
　ここで、レドックスフロー電池電極の両面のうち一方の面を図示しない極板で保持してもよく、この場合、レドックスフロー電池電極は、イオン交換膜１３と極板との間に配置されることが好ましい。このとき、レドックスフロー電池電極は、両面のうち極板に面していない面が、イオン交換膜１３と対向するように設けられる。 Here, one of the two surfaces of the redox flow battery electrode may be held by an electrode plate (not shown). In this case, the redox flow battery electrode should be arranged between the ion exchange membrane 13 and the electrode plate. Is preferred. At this time, the redox flow battery electrode is provided so that one of the two surfaces, which does not face the electrode plate, faces the ion exchange membrane 13.
　レドックスフロー電池１の正極電解液および負極電解液は、それぞれ活物質を含有しており、その種類は特に限定されない。本実施形態では、正極電解液に含まれる活物質から生成されるイオンとして、酸化力の高いイオン、例えば、マンガンイオン、セリウムイオンおよび塩素イオンから選択される１種又は２種以上のイオンが含まれていてもよい。上述の電極を少なくとも正極電極１１１に用いることで、これらの酸化力の高いイオンを正極電解液に含んでいても、正極電極１１１の酸化等による劣化や、それによる破損を起こり難くすることができる。 The positive electrode electrolyte and the negative electrode electrolyte of the redox flow battery 1 each contain an active material, and the types thereof are not particularly limited. In the present embodiment, the ions generated from the active material contained in the positive electrode electrolyte include ions having high oxidizing power, for example, one or more ions selected from manganese ion, cerium ion and chlorine ion. It may be. By using the above-mentioned electrode for at least the positive electrode 111, it is possible to prevent deterioration of the positive electrode 111 due to oxidation or the like and damage thereof due to oxidation, even if the positive electrolyte contains these highly oxidizing ions. ..
　他方で、負極電解液に含まれる負極側の活物質から生成されるイオンとしては、上述の正極側のイオンと組み合わせられるものを用いる。例えば、正極電解液にマンガン化合物を活物質として含む場合、負極電解液にチタン化合物を活物質として含むことができる。 On the other hand, as the ions generated from the active material on the negative electrode side included in the negative electrode electrolyte, those that are combined with the ions on the positive electrode side described above are used. For example, when the positive electrode electrolytic solution contains a manganese compound as an active material, the negative electrode electrolytic solution can contain a titanium compound as an active material.
　レドックスフロー電池１に用いられるイオン交換膜１３としては、公知の陽イオン交換膜を用いることができる。具体的には、スルホン酸基を有するパーフルオロカーボン重合体、スルホン酸基を有する炭化水素系高分子化合物、リン酸等の無機酸をドープさせた高分子化合物、一部がプロトン伝導性の官能基で置換された有機／無機ハイブリッドポリマー、高分子マトリックスにリン酸溶液や硫酸溶液を含浸させたプロトン伝導体が挙げられる。これらのうち、スルホン酸基を有するパーフルオロカーボン重合体が好ましく、ナフィオン（登録商標）がより好ましい。 As the ion exchange membrane 13 used in the redox flow battery 1, a known cation exchange membrane can be used. Specifically, a perfluorocarbon polymer having a sulfonic acid group, a hydrocarbon-based polymer compound having a sulfonic acid group, a polymer compound doped with an inorganic acid such as phosphoric acid, a part of which is a proton-conductive functional group. Examples include organic/inorganic hybrid polymers substituted with, and a proton conductor obtained by impregnating a polymer matrix with a phosphoric acid solution or a sulfuric acid solution. Among these, perfluorocarbon polymers having a sulfonic acid group are preferable, and Nafion (registered trademark) is more preferable.
　レドックスフロー電池１は、正極セル１１に循環供給する正極電解液を貯蔵する正極電解液タンク１１２と、正極電解液を正極電解液タンク１１２から正極セル１１に送る正極往路配管１１５と、正極電解液を正極セル１１から正極電解液タンク１１２に戻す正極復路配管１１４とを備える。このうち、正極往路配管１１４には、正極電解液を循環させるためのポンプ１１３が配置される。 The redox flow battery 1 includes a positive electrode electrolytic solution tank 112 that stores a positive electrode electrolytic solution that is circulated and supplied to the positive electrode cell 11, a positive electrode outward pipe 115 that sends the positive electrode electrolytic solution from the positive electrode electrolytic solution tank 112 to the positive electrode cell 11, and a positive electrode electrolytic solution. And a positive electrode return pipe 114 for returning from the positive electrode cell 11 to the positive electrode electrolyte tank 112. Of these, a pump 113 for circulating the positive electrode electrolytic solution is arranged in the positive electrode outward pipe 114.
　同様に、レドックスフロー電池１は、負極セル１２に循環供給する負極電解液を貯蔵する負極電解液タンク１２２と、負極電解液を負極電解液タンク１２２から負極セル１２に送る負極往路配管１２４と、負極電解液を負極セル１２から負極電解液タンク１２２に戻す負極復路配管１２５とを備える。このうち、負極往路配管１２４には、負極電解液を循環させるためのポンプ１２３が配置される。 Similarly, the redox flow battery 1 includes a negative electrode electrolyte tank 122 that stores a negative electrode electrolyte solution that is circulated and supplied to the negative electrode cell 12, and a negative electrode outward pipe 124 that sends the negative electrode electrolyte solution from the negative electrode electrolyte solution tank 122 to the negative electrode cell 12. A negative electrode return pipe 125 for returning the negative electrode electrolytic solution from the negative electrode cell 12 to the negative electrode electrolytic solution tank 122 is provided. Of these, a pump 123 for circulating the negative electrode electrolyte is arranged in the negative electrode outward pipe 124.
　上記構成のレドックスフロー電池１において、正極電解液タンク１１２内の電解液は、ポンプ１１３を作動させることにより、正極往路配管１１４を通って電池セル１０（より厳密には正極セル１１）に送られる。電池セル１０に送られた正極電解液は、電池セル１０の下方から内部を通って上方に排出され、正極復路配管１１５を通して正極電解液タンク１１２に戻されて、図中矢印Ａ方向に循環する。同様に、負極電解液タンク１２２内の電解液は、ポンプ１２３を作動させることにより、負極往路配管１２４を通って電池セル１０（より厳密には負極セル１２）に送られる。電池セル１０に送られた電解液は、電池セル１０の下方から内部を通って上方に排出され、負極復路配管１２５を通して負極電解液タンク１１２に戻されて、図中矢印Ｂ方向に循環する。 In the redox flow battery 1 having the above configuration, the electrolytic solution in the positive electrode electrolytic solution tank 112 is sent to the battery cell 10 (more strictly, the positive electrode cell 11) through the positive electrode outward pipe 114 by operating the pump 113. .. The positive electrode electrolytic solution sent to the battery cell 10 is discharged upward through the inside of the battery cell 10 and returned to the positive electrode electrolytic solution tank 112 through the positive electrode return pipe 115 and circulates in the direction of arrow A in the figure. .. Similarly, the electrolytic solution in the negative electrode electrolytic solution tank 122 is sent to the battery cell 10 (more strictly, the negative electrode cell 12) through the negative electrode outward pipe 124 by operating the pump 123. The electrolytic solution sent to the battery cell 10 is discharged upward through the inside of the battery cell 10 and returned to the negative electrode electrolytic solution tank 112 through the negative electrode return pipe 125 and circulates in the direction of arrow B in the figure.
　これにより、電池セル１０の中で電解液に含まれる活物質の酸化還元反応が行なわれ、電力の貯蔵又は取出しが可能となる。すなわち、交流／直流変換器２を介して、発電所等の電源３１から供給される電力を充電することが可能となる。また、充電した電力を、交流／直流変換器２を介して負荷３２に放電することも可能となる。 By this, the redox reaction of the active material contained in the electrolytic solution is carried out in the battery cell 10, and it becomes possible to store or take out the electric power. That is, it becomes possible to charge the electric power supplied from the power supply 31 such as a power plant via the AC/DC converter 2. Further, it becomes possible to discharge the charged power to the load 32 via the AC/DC converter 2.
　なお、本実施形態では、レドックスフロー電池１の電池セル１０を、単セルで構成した場合で説明したが、複数の単セルを積層したセルスタックと呼ばれる形態で構成してもよい（図示せず）。 In the present embodiment, the battery cell 10 of the redox flow battery 1 is described as a single cell, but may be formed in a form called a cell stack in which a plurality of single cells are stacked (not shown). ).
＜電極の製造方法についての第一実施形態＞
　本実施形態に係る電極の製造方法は、カーボンフェルトやカーボンペーパー等の、炭素材料を含む成形体（炭素材料成形体）を、２３００℃以上３５００℃以下の不活性ガス雰囲気中で焼成してカーボン電極材を得る高温焼成工程を有する。なお、必要に応じて、高温焼成工程を行なう前に、炭素材料成形体に対して低温焼成工程を行なってもよい。 <First Embodiment of Manufacturing Method of Electrode>
The electrode manufacturing method according to the present embodiment is performed by firing a molded body containing a carbon material (carbon material molded body) such as carbon felt or carbon paper in an inert gas atmosphere of 2300° C. or higher and 3500° C. or lower. It has a high temperature firing step of obtaining an electrode material. If necessary, a low temperature firing step may be performed on the carbon material compact before the high temperature firing step.
　炭素材料成形体について、２３００℃以上３５００℃以下の不活性ガス雰囲気中で焼成する高温焼成工程を行なうことで、成形体に含まれる炭素の結晶構造の中で、グラファイト構造が占める割合が増加するため、得られる電極を電池に用いたときに、酸化による電極の劣化を起こり難くすることできる。 By performing a high temperature firing step of firing the carbon material compact in an inert gas atmosphere at 2300° C. or higher and 3500° C. or lower, the proportion of the graphite structure in the crystal structure of carbon contained in the compact increases. Therefore, when the obtained electrode is used in a battery, it is possible to prevent deterioration of the electrode due to oxidation.
　以下、本実施形態に係る電極の製造方法について、詳細に説明する。 Hereinafter, the method of manufacturing the electrode according to the present embodiment will be described in detail.
　（炭素材料成形体の準備）
　本実施形態で用いられる炭素材料成形体としては、カーボンファイバーを含んだカーボンフェルトやカーボンペーパーを用いることができ、カーボンファイバーからなるカーボンフェルト、またはカーボンペーパーであることが好ましい。ここで、カーボンファイバーから公知の手段を用いて炭素材料成形体を作製してもよく、また、市販のカーボンフェルトやカーボンペーパーを所定の大きさに加工し、炭素材料成形体として用いてもよい。 (Preparation of carbon material compact)
As the carbon material molded body used in the present embodiment, carbon felt or carbon paper containing carbon fiber can be used, and carbon felt made of carbon fiber or carbon paper is preferable. Here, a carbon material molded body may be produced from carbon fiber by a known means, or commercially available carbon felt or carbon paper may be processed into a predetermined size and used as a carbon material molded body. ..
　（低温焼成工程）
　本実施形態では、後述する高温焼成工程を行なう前に、炭素材料成形体を７００℃以下の酸素ガスを含む雰囲気中で焼成する、低温焼成工程を行なうことが好ましい。炭素材料成形体について、酸素ガスを含む雰囲気中で低温焼成工程を行なうことで、炭素材料成形体を構成している炭素材料の表面積が高められる。これにより、得られる電極をレドックスフロー電池などの電池に用いたときに、電極表面の活性点が増加するため、初期状態でのセル抵抗率を低くすることができる。 (Low temperature firing process)
In the present embodiment, it is preferable to perform a low temperature firing step of firing the carbon material molded body in an atmosphere containing oxygen gas at 700° C. or lower before performing a high temperature firing step described later. The surface area of the carbon material forming the carbon material molded body is increased by performing the low temperature firing step on the carbon material molded body in an atmosphere containing oxygen gas. As a result, when the obtained electrode is used in a battery such as a redox flow battery, the number of active sites on the electrode surface is increased, so that the cell resistivity in the initial state can be lowered.
　低温焼成工程を行なう雰囲気としては、酸素ガスを含む雰囲気を用いることができる。特に、安価に得られる点で、空気を焼成炉内に供給して用いることが好ましい。 As an atmosphere for performing the low temperature firing step, an atmosphere containing oxygen gas can be used. In particular, it is preferable to supply air into the firing furnace for use because it can be obtained at a low cost.
　低温焼成工程において焼成を行なう温度（焼成温度）は、７００℃以下とする。酸素ガスを含む雰囲気中で７００℃以下の焼成温度で焼成することで、炭素材料の表面の凹凸が増えることによって表面積が高められる。そのため、得られる電極をレドックスフロー電池に用いたときに、酸化還元反応を促進してセル抵抗率を低くすることができる。ここで、低温焼成工程における焼成温度は、６００℃以下であることが好ましく、５００℃以下であることがより好ましい。他方で、焼成温度の下限については、例えば３００℃以上にしてもよく、また、４００℃以上にしてもよい。 -The firing temperature in the low-temperature firing process (firing temperature) shall be 700°C or lower. By firing at a firing temperature of 700° C. or lower in an atmosphere containing oxygen gas, the surface area of the carbon material is increased by increasing the unevenness of the surface. Therefore, when the obtained electrode is used in a redox flow battery, it is possible to promote the redox reaction and reduce the cell resistivity. Here, the firing temperature in the low temperature firing step is preferably 600° C. or lower, and more preferably 500° C. or lower. On the other hand, the lower limit of the firing temperature may be, for example, 300° C. or higher, or 400° C. or higher.
　低温焼成工程における焼成時間は、焼成温度と、雰囲気中の酸素ガス濃度に応じて設定される。より具体的には、０．５時間～１０時間とすることが好ましく、１時間～５時間とすることがより好ましく、２時間～４時間とすることがさらに好ましい。 The firing time in the low temperature firing process is set according to the firing temperature and the oxygen gas concentration in the atmosphere. More specifically, it is preferably 0.5 hours to 10 hours, more preferably 1 hour to 5 hours, and further preferably 2 hours to 4 hours.
　低温焼成工程において、所定の焼成温度になるまでの昇温速度は、低温焼成工程における生産性を高める観点及びコストを低減する観点から、焼成温度までの昇温を、０．５℃／分以上１００℃／分以下の昇温速度で行なうことが好ましく、１℃／分以上２５℃／分以下の昇温速度で行なうことがより好ましい。また、所定の焼成時間が経過した後の冷却は、０．５℃／分以上１００℃／分以下の冷却速度で行なうことが好ましく、１℃／分以上２５℃／分以下の冷却速度で行なうことがより好ましい。 In the low temperature firing step, the temperature rising rate up to the predetermined firing temperature is 0.5° C./minute or more from the viewpoint of increasing the productivity in the low temperature firing step and reducing the cost. The heating rate is preferably 100° C./minute or less, more preferably 1° C./minute or more and 25° C./minute or less. Further, the cooling after the elapse of a predetermined firing time is preferably performed at a cooling rate of 0.5° C./minute or more and 100° C./minute or less, and is preferably performed at a cooling rate of 1° C./minute or more and 25° C./minute or less. Is more preferable.
　（高温焼成工程）
　高温焼成工程では、必要に応じて低温焼成工程で焼成された炭素材料成形体を、２３００℃以上３５００℃以下の不活性ガス雰囲気中で焼成してカーボン電極材を得る。炭素材料成形体に対して高温焼成工程を行なうことで、炭素材料に含まれる炭素のグラファイト構造が占める割合が増加し、他の相の割合や、グラファイト構造や他の相に含まれる欠陥やエッジの割合が減少する。また、炭素材料に付着していた酸素原子が取り除かれるため、炭素材料に含まれる酸素元素の含有量が減少する。これらによって、得られる電極を電池に用いたときに、初期状態で低いセル抵抗率を得ることができるとともに、酸化等による電極の劣化を起こり難くすることできる。 (High temperature firing process)
In the high temperature firing step, the carbon material molded body fired in the low temperature firing step is fired in an inert gas atmosphere of 2300° C. or higher and 3500° C. or lower as necessary to obtain a carbon electrode material. By subjecting the carbon material compact to a high temperature firing step, the proportion of carbon in the carbon material occupied by the graphite structure increases, and the proportion of other phases and defects or edges in the graphite structure and other phases are increased. The ratio of will decrease. Further, since the oxygen atoms attached to the carbon material are removed, the content of oxygen element contained in the carbon material is reduced. With these, when the obtained electrode is used in a battery, it is possible to obtain a low cell resistivity in the initial state and to prevent deterioration of the electrode due to oxidation or the like.
　高温焼成工程を行なう雰囲気を構成する不活性ガスとしては、アルゴン（Ａｒ）ガスなどの希ガスや、窒素（Ｎ２）ガスを挙げることができる。 Examples of the inert gas that constitutes the atmosphere in which the high temperature firing step is performed include noble gases such as argon (Ar) gas and nitrogen (N 2 ) gas.
　高温焼成工程において焼成を行なう温度（焼成温度）は、２３００℃以上３５００℃以下とする。２３００℃以上の焼成温度で焼成することで、炭素材料に含まれる炭素の結晶構造のグラファイトへの変化が促進される。そのため、繰り返しの使用によっても、酸化によるセル抵抗率の上昇が起こり難い電極を得ることができる。ここで、高温焼成工程における焼成温度は、２４００℃以上であることが好ましく、２５００℃以上であることがより好ましい。他方で、焼成温度の上限については、３３００℃以下にすることが好ましく、３１００℃以下にすることがより好ましい。 -The temperature (firing temperature) for firing in the high-temperature firing process should be 2300°C or higher and 3500°C or lower. By firing at a firing temperature of 2300° C. or higher, the change of the crystal structure of carbon contained in the carbon material to graphite is promoted. Therefore, even with repeated use, it is possible to obtain an electrode in which increase in cell resistivity due to oxidation does not easily occur. Here, the firing temperature in the high temperature firing step is preferably 2400° C. or higher, and more preferably 2500° C. or higher. On the other hand, the upper limit of the firing temperature is preferably 3300°C or lower, more preferably 3100°C or lower.
　高温焼成工程において焼成を行なう時間（焼成時間）は、上述のＩＤ／ＩＧ比が０．５以下になる範囲で適宜に制定することができる。高温焼成工程における焼成時間は、例えば１５分～４時間としてもよい。 The time for performing the firing in the high temperature firing step (firing time) can be appropriately established within the range where the above-mentioned I D /I G ratio is 0.5 or less. The firing time in the high temperature firing step may be, for example, 15 minutes to 4 hours.
　高温焼成工程において、所定の焼成温度になるまでの昇温速度は、電極の性能の劣化をより起こり難くする観点から、焼成温度までの昇温を、０．５℃／分以上１００℃／分以下の昇温速度で行なうことが好ましく、１℃／分以上２５℃／分以下の昇温速度で行なうことがより好ましい。また、所定の焼成時間が経過した後の冷却は、０．５℃／分以上１００℃／分以下の冷却速度で行なうことが好ましく、１℃／分以上２５℃／分以下の冷却速度で行なうことがより好ましい。 In the high temperature firing step, the rate of temperature increase until reaching a predetermined firing temperature is 0.5° C./minute or more and 100° C./minute or more from the viewpoint of making deterioration of electrode performance less likely to occur. The heating rate is preferably the following, and more preferably 1° C./minute or more and 25° C./minute or less. Further, the cooling after the elapse of a predetermined firing time is preferably performed at a cooling rate of 0.5° C./minute or more and 100° C./minute or less, and is preferably performed at a cooling rate of 1° C./minute or more and 25° C./minute or less. Is more preferable.
＜電極の製造方法についての第二実施形態＞
　本実施形態に係る電極の製造方法は、炭素材料を２３００℃以上３５００℃以下の不活性ガス雰囲気中で焼成する高温焼成工程と、前記高温焼成工程で焼成された炭素材料を成形してカーボン電極材を得る成形工程と、を有する。なお、必要に応じて、高温焼成工程を行なう前に、炭素材料に対して低温焼成工程を行なってもよい。 <Second Embodiment for Manufacturing Method of Electrode>
The electrode manufacturing method according to the present embodiment includes a high temperature firing step of firing a carbon material in an inert gas atmosphere of 2300° C. or higher and 3500° C. or lower, and a carbon electrode formed by molding the carbon material fired in the high temperature firing step. Forming step of obtaining a material. If necessary, the low temperature firing step may be performed on the carbon material before the high temperature firing step.
　（低温焼成工程・高温焼成工程）
　このうち、低温焼成工程と高温焼成工程については、炭素材料成形体の代わりに未成形の炭素材料を用いる点を除いて、第一実施形態と同様に行なうことができる。 (Low temperature firing process/High temperature firing process)
Of these, the low temperature firing step and the high temperature firing step can be performed in the same manner as in the first embodiment, except that an unformed carbon material is used instead of the carbon material molded body.
　（成形工程）
　成形工程は、高温焼成工程で焼成された炭素材料を成形してカーボン電極材を得る工程である。 (Molding process)
The forming step is a step of forming the carbon material fired in the high temperature firing step to obtain a carbon electrode material.
　成形工程で炭素材料を成形する方法としては、カーボンファイバーから、カーボンフェルトやカーボンペーパー等の炭素材料成形体を得るための公知の方法を用いることができる。例えば、炭素材料を含む分散液を調製した後、この分散液を用いて炭素材料をシート状に成形することができる。 As a method of molding a carbon material in the molding step, a known method for obtaining a carbon material molded body such as carbon felt or carbon paper from carbon fiber can be used. For example, after preparing a dispersion liquid containing a carbon material, the carbon material can be formed into a sheet using this dispersion liquid.
　ここで、炭素材料を分散させる分散媒としては、特に限定されず、例えば水を用いることができる。 Here, the dispersion medium for dispersing the carbon material is not particularly limited, and for example, water can be used.
　炭素材料を分散媒に分散させる際、分散媒に分散剤を加えることが好ましく、これにより炭素材料を均一に分散させ易くすることができる。ここで、分散剤としては、公知のものを用いることができ、例えば水溶性導電性高分子を用いることができる。 When dispersing the carbon material in the dispersion medium, it is preferable to add a dispersant to the dispersion medium, which can facilitate the uniform dispersion of the carbon material. Here, as the dispersant, a known dispersant can be used, and for example, a water-soluble conductive polymer can be used.
　炭素材料を分散させて分散液を調製する方法としては、特に限定されないが、例えば、超音波、ボールミル、マグネティックスターラーを用いる方法を挙げることができる。 The method for dispersing the carbon material to prepare the dispersion liquid is not particularly limited, and examples thereof include a method using ultrasonic waves, a ball mill, and a magnetic stirrer.
　また、得られた分散液から炭素材料をシート状に成形する方法としては、例えば、分散液を基材に塗布した後に分散媒を乾燥させる方法や、分散液を濾過して分散媒を除去する方法を用いることができる。 Further, as a method of forming a carbon material into a sheet from the obtained dispersion liquid, for example, a method of drying the dispersion medium after applying the dispersion liquid to a substrate, or filtering the dispersion liquid to remove the dispersion medium. Any method can be used.
　このような方法により、ラマン分光法によるＩＤ／ＩＧ比が０．５０以下であり、かつ酸素元素の含有量が０．５０質量％以下である炭素材料を含んだカーボン電極材を有する電極を得ることができる。 By such a method, an electrode having a carbon electrode material containing a carbon material having an I D /I G ratio by Raman spectroscopy of 0.50 or less and an oxygen element content of 0.50 mass% or less Can be obtained.
　なお、本実施形態では、炭素材料に対して低温焼成工程および高温焼成工程を行ない、成形工程では焼成後の炭素材料を成形してカーボン電極材を得ているが、低温焼成工程による焼成後の炭素材料に対して成形工程を行ない、得られた成形体に対して高温焼成工程を行なってもよい。 In the present embodiment, the carbon material is subjected to the low temperature firing step and the high temperature firing step, and in the molding step, the carbon material after firing is molded to obtain the carbon electrode material. You may perform a shaping|molding process with respect to a carbon material, and may perform a high temperature baking process with respect to the obtained molded object.
［レドックスフロー電池の作製］
　このようにして得られる電極は、常法により電池に組み込むことができ、例えば図１に記載されるレドックスフロー電池１に組み込むことができる。例えば、得られた電極を正極電極１１１として用いる場合、この電極をイオン交換膜１３の一方の側に設け、これとは別に負極電極１２１をイオン交換膜１３の他方の側に設ける。 [Preparation of redox flow battery]
The electrode thus obtained can be incorporated into a battery by a conventional method, for example, the redox flow battery 1 shown in FIG. For example, when the obtained electrode is used as the positive electrode 111, this electrode is provided on one side of the ion exchange membrane 13, and the negative electrode 121 is separately provided on the other side of the ion exchange membrane 13.
　以下、本発明を実施例によりさらに詳細に説明するが、本発明はこれらの実施例に何ら限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
［実施例１］
１．炭素材料成形体の準備
　炭素材料を含む成形体（炭素材料成形体）として、サイズ（長さ１００ｍｍ、幅１００ｍｍ、厚み０．１９ｍｍ）のカーボンペーパー（ＳＧＬカーボン社製、型番ＧＤＬ－３９ＡＡ）を用いた。このカーボンペーパーは、炭素材料であるカーボンファイバーからなり、カーボンペーパーを構成しているカーボンファイバーの平均繊維径は１μｍである。 [Example 1]
1. Preparation of carbon material molded body As a molded body containing a carbon material (carbon material molded body), carbon paper of size (length 100 mm, width 100 mm, thickness 0.19 mm) (manufactured by SGL Carbon Co., model number GDL-39AA) is used. I was there. This carbon paper is made of carbon fiber which is a carbon material, and the average fiber diameter of the carbon fibers constituting the carbon paper is 1 μm.
２．炭素材料成形体についての低温焼成工程
　このカーボンペーパーに対して、低温焼成工程として、４８０℃の焼成温度で、空気中で３時間（３ｈ）の焼成時間にわたり焼成を行なった。ここで、焼成温度までの昇温は１０℃／分の昇温速度で行ない、焼成後は１０℃／分の冷却速度で室温まで冷却した。 2. Low temperature firing step for carbon material molded body As a low temperature firing step, the carbon paper was fired at a firing temperature of 480° C. in air for a firing time of 3 hours (3 h). Here, the temperature was raised to the firing temperature at a rate of 10° C./min, and after firing, it was cooled to room temperature at a cooling rate of 10° C./min.
３．炭素材料成形体についての高温焼成工程
　低温焼成後のカーボンペーパーに対して、高温焼成工程として、３０００℃の焼成温度で、アルゴン（Ａｒ）ガス中で１時間（１ｈ）の焼成時間にわたり焼成を行ない、カーボン電極材を作製した。ここで、焼成温度までの昇温は１０℃／分の昇温速度で行ない、焼成後は１０℃／分の冷却速度で室温まで冷却し、カーボン電極材を得た。 3. High temperature firing step for carbon material molded body As a high temperature firing step, the carbon paper after low temperature firing is fired at a firing temperature of 3000° C. in an argon (Ar) gas for a firing time of 1 hour (1 h). A carbon electrode material was produced. Here, the temperature was raised to the firing temperature at a heating rate of 10° C./min, and after firing, the temperature was cooled to room temperature at a cooling rate of 10° C./min to obtain a carbon electrode material.
　ここで、カーボン電極材は、以下の４．でＩＤ／ＩＧ比および酸素元素の含有量を評価するのに必要な枚数と、５．で電池の正極に用いるのに必要な枚数を合計した枚数を準備した。このほか、上記低温焼成工程を行った後の炭素材料成形体について、以下の５．で電池の負極に用いるのに必要な枚数を準備した。 Here, the carbon electrode material has the following 4. 4. The number of sheets necessary for evaluating the I D /I G ratio and the content of oxygen element, and 5. Then, the total number of sheets required for use in the positive electrode of the battery was prepared. In addition, regarding the carbon material molded body after the above-mentioned low temperature firing step, the following 5. Then, the number of sheets required for use as the negative electrode of the battery was prepared.
４．カーボン電極材のＩＤ／ＩＧ比および酸素元素の含有量の評価
（１）ＩＤ／ＩＧ比
　得られたカーボン電極材について、ラマン分光法によって測定したラマンスペクトルに現れる、Ｄバンドのピーク強度（ＩＤ）と、Ｇバンドのピーク強度（ＩＧ）を求め、Ｄバンドのピーク強度（ＩＤ）の、Ｇバンドのピーク強度（ＩＧ）に対する比であるピーク強度比（ＩＤ／ＩＧ比）を求めた。ここで、分光光度計としてはレーザラマン分光光度計（日本分光株式会社製、型番：ＮＲＳ－５１００）を用い、励起波長５３２．３６ｎｍ、レーザ強度１．６ｍＷ、入射スリット幅５０μｍ、露光時間１５秒、積算２回、回折格子６００本／ｍｍの条件でラマン分光スペクトルを測定し、１３６０ｃｍ－１の付近にあるＤバンドのピーク強度（ＩＤ）の、１５８０ｃｍ－１の付近にあるＧバンドのピーク強度（ＩＧ）に対する比を求めた。 4. Evaluation of I D /I G ratio and content of oxygen element of carbon electrode material (1) I D /I G ratio D band peak appearing in Raman spectrum measured by Raman spectroscopy of the obtained carbon electrode material The intensity (I D ) and the peak intensity (I G ) of the G band are determined, and the peak intensity ratio (I D /is the ratio of the peak intensity (I D ) of the D band to the peak intensity (I G ) of the G band. IG ratio) was determined. Here, a laser Raman spectrophotometer (manufactured by JASCO Corporation, model number: NRS-5100) was used as the spectrophotometer, and the excitation wavelength was 532.36 nm, the laser intensity was 1.6 mW, the incident slit width was 50 μm, and the exposure time was 15 seconds. Raman spectroscopic spectra were measured twice under a condition of 600 diffraction gratings/mm, and the peak intensity ( ID ) of the D band near 1360 cm -1 and the peak intensity of the G band near 1580 cm -1. The ratio to ( IG ) was determined.
（２）酸素元素の含有量
　また、得られたカーボン電極材を削り取って得られた試料約１０ｍｇをニッケルカプセルに秤量し、酸素・窒素分析装置（ＬＥＣＯ社製、型番：ＴＣ６００）を用い、５０００Ｗの出力で、不活性ガス融解－熱伝導度法により、酸素元素の含有量（質量％）を測定した。 (2) Content of oxygen element Further, about 10 mg of a sample obtained by scraping off the obtained carbon electrode material was weighed into a nickel capsule, and an oxygen/nitrogen analyzer (LECO, model number: TC600) was used to measure 5000 W. The content of elemental oxygen (% by mass) was measured by the inert gas fusion-thermal conductivity method at the output of.
５．レドックスフロー電池の作製およびその評価
（１）電池の作製
　本実施例では、得られたカーボン電極材を５０ｍｍ×１００ｍｍの大きさに切り出して２枚ずつ重ね、レドックスフロー電池の正極電極として用いた。また、負極電極としては、前記「２．炭素材料成形体についての低温焼成工程」で得られる低温焼成後のカーボンペーパーを５０ｍｍ×１００ｍｍの大きさに切り出し、これを２枚ずつ重ねて用いた。ここで、両電極間のイオン交換膜としては、Ｎａｆｉｏｎ（登録商標）ＮＲ２１２（型番）を用いた。また、正極および負極の外側（イオン交換膜に面しない側）に、集電板（極板）として金メッキを施した真鍮板を載置した。 5. Production of Redox Flow Battery and Its Evaluation (1) Production of Battery In this example, the obtained carbon electrode material was cut into a size of 50 mm×100 mm, and two pieces were stacked and used as a positive electrode of a redox flow battery. Further, as the negative electrode, the carbon paper after low temperature firing obtained in the above-mentioned “2. Low temperature firing step for carbon material molded body” was cut into a size of 50 mm×100 mm, and two sheets of this were stacked and used. Here, Nafion (registered trademark) NR212 (model number) was used as the ion exchange membrane between both electrodes. Further, a brass plate plated with gold was placed as a current collector (electrode plate) on the outside of the positive electrode and the negative electrode (the side not facing the ion exchange membrane).
　正極電解液及び負極電解液としては、それぞれ、硫酸マンガン（ＭｎＳＯ４）と酸化硫酸チタン（ＴｉＯＳＯ４）を硫酸水溶液に溶解することで得られる、マンガンイオン濃度が１Ｍ、チタンイオン濃度が１Ｍ、硫酸イオン濃度が５Ｍの電解液を用いた。この電解液をレドックスフロー電池の正極側と負極側にそれぞれ５０ｍＬ導入し、レドックスフロー電池の単セルを構成した。 The positive electrode electrolytic solution and the negative electrode electrolytic solution are obtained by dissolving manganese sulfate (MnSO 4 ) and titanium oxide sulfate (TiOSO 4 ) in an aqueous sulfuric acid solution, respectively. The manganese ion concentration is 1M, the titanium ion concentration is 1M, and the sulfuric acid is 1M. An electrolytic solution having an ion concentration of 5M was used. 50 mL of this electrolytic solution was introduced into each of the positive electrode side and the negative electrode side of the redox flow battery to form a single cell of the redox flow battery.
（２）初期状態でのセル抵抗率および抵抗率悪化率の評価
　得られたレドックスフロー電池について、電解液をチューブポンプで循環させて運転を行なった。このとき、電解液の流量は６０ｍＬ／ｍｉｎに設定した。また、充放電時の電流は５．０Ａ（１００ｍＡ／ｃｍ２）とし、充電停止電圧を１．６Ｖ、放電停止電圧を０．８Ｖとした。 (2) Evaluation of Cell Resistivity and Resistivity Deterioration Rate in Initial State The obtained redox flow battery was operated by circulating the electrolytic solution with a tube pump. At this time, the flow rate of the electrolytic solution was set to 60 mL/min. The current during charging/discharging was 5.0 A (100 mA/cm 2 ), the charge stop voltage was 1.6 V, and the discharge stop voltage was 0.8 V.
　レドックスフロー電池の初期抵抗率（初期状態でのセル抵抗率）は、充放電サイクルを５回繰り返した後に求めたセル抵抗率とした。ここで、セル抵抗率については、充電平均電圧及び放電平均電圧を求め、次の計算式に基づいて得られる値とした。
　セル抵抗率[Ω・ｃｍ２]＝（充電平均電圧[Ｖ]－放電平均電圧[Ｖ]）×電極面積[ｃｍ２]÷（２×充電電流[Ａ]） The initial resistivity of the redox flow battery (cell resistivity in the initial state) was the cell resistivity obtained after repeating the charge/discharge cycle 5 times. Here, with respect to the cell resistivity, the charge average voltage and the discharge average voltage were obtained, and the values were obtained based on the following calculation formula.
Cell resistivity [Ω·cm 2 ]=(charge average voltage [V]−discharge average voltage [V])×electrode area [cm 2 ]÷(2×charge current [A])
　また、充放電サイクルを１００回繰り返した後のセル抵抗率（１００回繰り返し使用後のセル抵抗率）を求め、上述の初期状態でのセル抵抗率に対する、繰り返し使用によるセル抵抗率の増加量の比から、抵抗率悪化率（％）を求めた。
　抵抗率悪化率（％）＝（１００回繰り返し使用後のセル抵抗率[Ω・ｃｍ２]－初期状態でのセル抵抗率[Ω・ｃｍ２]）／初期状態でのセル抵抗率[Ω・ｃｍ２]×１００ In addition, the cell resistivity after repeating the charge/discharge cycle 100 times (the cell resistivity after 100 times of repeated use) was calculated, and the increase in the cell resistivity due to repeated use with respect to the cell resistivity in the initial state described above was calculated. From the ratio, the resistivity deterioration rate (%) was obtained.
Deterioration rate of resistivity (%)=(cell resistivity after 100 times repeated use [Ω·cm 2 ]-cell resistivity in initial state [Ω·cm 2 ])/cell resistivity in initial state [Ω· cm 2 ]×100
　［実施例２］
　「３．炭素材料成形体についての高温焼成工程」において、焼成温度を２５００℃にした以外は、実施例１と同様にカーボン電極材を作製し、また、レドックスフロー電池の単セルを構成した。得られたカーボン電極材について、同様にＩＤ／ＩＧ比および酸素元素の含有量を評価した。また、得られたレドックスフロー電池について、同様に初期状態でのセル抵抗率、繰り返し使用後のセル抵抗率および抵抗率悪化率を確認した。 [Example 2]
In "3. High-temperature firing step for molded carbon material", a carbon electrode material was produced in the same manner as in Example 1 except that the firing temperature was 2500°C, and a single cell of a redox flow battery was constructed. The obtained carbon electrode material was similarly evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
　［実施例３］
　カーボンペーパーに対して、「２．炭素材料成形体についての低温焼成工程」を行なわずに高温焼成工程を行なった以外は、実施例２と同様にカーボン電極材を作製し、また、レドックスフロー電池の単セルを構成した。得られたカーボン電極材について、同様にＩＤ／ＩＧ比および酸素元素の含有量を評価した。また、得られたレドックスフロー電池について、同様に、初期状態でのセル抵抗率、繰り返し使用後のセル抵抗率および抵抗率悪化率を確認した。 [Example 3]
A carbon electrode material was produced in the same manner as in Example 2 except that the carbon paper was not subjected to the "2. Low temperature firing step for the carbon material molded body", but was subjected to the high temperature firing step, and also the redox flow battery. The single cell of The obtained carbon electrode material was similarly evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
　［比較例１］
　カーボンペーパーに対して「２．炭素材料成形体についての低温焼成工程」および「３．炭素材料成形体についての高温焼成工程」を行なわずに、そのままカーボン電極材として用い、実施例１と同様にレドックスフロー電池の単セルを構成した。カーボン電極材として用いた未焼成のカーボンペーパーについて、同様にＩＤ／ＩＧ比および酸素元素の含有量を評価した。また、得られたレドックスフロー電池について、同様に、初期状態でのセル抵抗率、繰り返し使用後のセル抵抗率および抵抗率悪化率を確認した。 [Comparative Example 1]
The carbon paper was used as it is as a carbon electrode material without performing “2. Low temperature firing step for carbon material compact” and “3. High temperature firing step for carbon material compact,” as in Example 1. A single cell of a redox flow battery was constructed. Similarly, the unburned carbon paper used as the carbon electrode material was evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
　［比較例２］
　「３．炭素材料成形体についての高温焼成工程」において、焼成温度を２０００℃にした以外は、実施例３と同様にカーボン電極材を作製し、また、レドックスフロー電池の単セルを構成した。得られたカーボン電極材について、同様にＩＤ／ＩＧ比および酸素元素の含有量を評価した。また、得られたレドックスフロー電池について、同様に、初期状態でのセル抵抗率、繰り返し使用後のセル抵抗率および抵抗率悪化率を確認した。 [Comparative example 2]
In "3. High-temperature firing step for molded carbon material", a carbon electrode material was produced in the same manner as in Example 3 except that the firing temperature was set to 2000°C, and a single cell of a redox flow battery was constructed. The obtained carbon electrode material was similarly evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
　［比較例３］
　「３．炭素材料成形体についての高温焼成工程」において、焼成温度を２０００℃にした以外は、実施例１と同様にカーボン電極材を作製し、また、レドックスフロー電池の単セルを構成した。得られたカーボン電極材について、同様にＩＤ／ＩＧ比および酸素元素の含有量を評価した。また、得られたレドックスフロー電池について、同様に、初期状態でのセル抵抗率、繰り返し使用後のセル抵抗率および抵抗率悪化率を確認した。 [Comparative Example 3]
In "3. High-temperature firing step for carbon material molded body", a carbon electrode material was produced in the same manner as in Example 1 except that the firing temperature was set to 2000°C, and a single cell of a redox flow battery was constructed. The obtained carbon electrode material was similarly evaluated for the I D /I G ratio and the oxygen element content. Further, regarding the obtained redox flow battery, similarly, the cell resistivity in the initial state, the cell resistivity after repeated use, and the resistivity deterioration rate were confirmed.
　表１に、実施例１～３、比較例１～３における各種条件と、ＩＤ／ＩＧ比、酸素元素の含有量、初期状態でのセル抵抗率、繰り返し使用後のセル抵抗率、抵抗率悪化率について示す。
Table 1 shows various conditions in Examples 1 to 3 and Comparative Examples 1 to 3, I D /I G ratio, oxygen element content, cell resistivity in the initial state, cell resistivity after repeated use, and resistance. The rate of deterioration is shown below.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　実施例１～３の正極電極は、カーボン電極材におけるＩＤ／ＩＧ比が０．５０以下であり、かつ、酸素元素の含有量が０．５０質量％以下であることで、ＩＤ／ＩＧ比が大きい比較例１～３の電極に比べて、酸化力の高いマンガンイオンを正極側の電解液に含んでいても、レドックスフロー電池のセル抵抗率が、繰り返しの使用によって悪化し難いことがわかった。 In the positive electrode of each of Examples 1 to 3, the carbon electrode material has an I D /I G ratio of 0.50 or less and an oxygen element content of 0.50 mass% or less, so that I D / compared to the electrodes of I G ratio is larger Comparative examples 1 to 3, also include a high oxidizing power manganese ions in the electrolyte of the positive electrode side, the cell resistivity of redox flow batteries, hardly deteriorated by repeated use I understood it.
　特に、実施例１～２の正極電極は、カーボン電極材におけるＩＤ／ＩＧ比がより低いため、初期状態でのセル抵抗率がより低く、また、繰り返しの使用によっても、セル抵抗率がより悪化し難いことがわかった。 In particular, since the positive electrode of Examples 1 and 2 has a lower I D /I G ratio in the carbon electrode material, it has a lower cell resistivity in the initial state, and also has a cell resistivity with repeated use. I found it harder to get worse.
　実施例１～３の正極電極は、カーボンペーパーを２３００℃以上３５００℃以下で焼成してカーボン電極材を得る高温焼成工程を含む方法で製造していることで、高温焼成工程を行なっていない比較例１の正極電極や、高温焼成工程における焼成温度が２０００℃の比較例２～３の正極電極と比べて、得られるカーボン電極材におけるＩＤ／ＩＧ比が低くなるため、酸化力の高いマンガンイオンを正極側の電解液に含んでいても、レドックスフロー電池のセル抵抗率が、繰り返しの使用によって悪化し難いことがわかった。 The positive electrodes of Examples 1 to 3 were manufactured by a method including a high temperature firing step of firing carbon paper at 2300° C. or higher and 3500° C. or lower to obtain a carbon electrode material. Compared with the positive electrode of Example 1 and the positive electrodes of Comparative Examples 2 to 3 in which the firing temperature in the high temperature firing step is 2000° C., the carbon electrode material obtained has a lower I D /I G ratio, and thus has a higher oxidizing power. It was found that even if manganese ions were included in the electrolyte solution on the positive electrode side, the cell resistivity of the redox flow battery was unlikely to deteriorate with repeated use.
　特に、実施例１～２の正極電極は、レドックスフロー電池の初期状態でのセル抵抗率がより低くなることがわかった。その理由は、図２に示される、実施例１のカーボンペーパー（ＧＤＬ－３９ＡＡ）を構成するカーボンファイバーの低温焼成工程前後の表面のＳＥＭ（走査型電子顕微鏡）像より推察することができる。ここで、図２（ａ）は、低温焼成工程を行なう前のカーボンファイバー表面のＳＥＭ像であり、図２（ｂ）は、低温焼成工程を行なった後で高温焼成工程を行なう前のカーボンファイバー表面のＳＥＭ像である。図２（ａ）と図２（ｂ）のＳＥＭ像の比較から、高温焼成工程の前に、酸素ガスを含む雰囲気中で低温焼成工程をさらに行なうことによって、カーボンファイバーの表面に凹凸がより多く形成されることで表面積が高められ、表面積が高まることで電極表面の活性点が多くなり、それにより、レドックスフロー電池の初期状態でのセル抵抗率が低くなっていることが推察される。 In particular, it was found that the positive electrodes of Examples 1 and 2 have a lower cell resistivity in the initial state of the redox flow battery. The reason can be inferred from the SEM (scanning electron microscope) images of the surface of the carbon fiber constituting the carbon paper (GDL-39AA) of Example 1 before and after the low temperature firing step shown in FIG. Here, FIG. 2A is a SEM image of the surface of the carbon fiber before the low temperature firing step, and FIG. 2B is a carbon fiber before the high temperature firing step after the low temperature firing step. It is a SEM image of the surface. From the comparison of the SEM images of FIG. 2(a) and FIG. 2(b), it can be seen that by further performing the low temperature firing step in an atmosphere containing oxygen gas before the high temperature firing step, the surface of the carbon fiber has more irregularities. It is presumed that the formation increases the surface area, and the increased surface area increases the number of active sites on the electrode surface, thereby lowering the cell resistivity in the initial state of the redox flow battery.
　さらに、カーボン電極材に含まれる酸素元素の含有量は、２０００℃以上の焼成温度で高温焼成工程を行なった実施例１～３ならびに比較例２および３では、低温焼成工程を行なうか否かに関係なく、いずれも０．２０質量％～０．２２質量％と低かったが、高温焼成工程を行なわなかった比較例１では、１．００質量％と顕著に高かった。
　このことから、正極電極を構成するカーボン電極材は、低温焼成工程を行なうか否かに関係なく、高温焼成工程を行なうことによって、酸素元素の含有量を増加させずに低く抑えることができることもわかった。 Further, the content of the oxygen element contained in the carbon electrode material depends on whether the low temperature firing step is performed in Examples 1 to 3 and Comparative Examples 2 and 3 in which the high temperature firing step was performed at a firing temperature of 2000° C. or higher. Regardless of the relationship, both were low at 0.20% by mass to 0.22% by mass, but in Comparative Example 1 in which the high temperature firing step was not performed, it was remarkably high at 1.00% by mass.
From this, the carbon electrode material forming the positive electrode can be suppressed to a low content without increasing the content of oxygen element by performing the high temperature firing step regardless of whether or not the low temperature firing step is performed. all right.
　１　　　レドックスフロー電池
　１０　　　電池セル
　１１　　正極セル
　１１１　　正極電極
　１１２　　正極電解液タンク
　１１４　　正極往路配管
　１１５　　正極復路配管
　１１３、１２３　ポンプ
　１２　　負極セル
　１２１　　負極電極
　１２２　　負極電解液タンク
　１２４　　負極往路配管
　１２５　　負極復路配管
　１３　　イオン交換膜
　２　　　交流／直流変換器
　３１　　電源
　３２　　負荷 1 Redox Flow Battery 10 Battery Cell 11 Positive Cell 111 111 Positive Electrode 112 Positive Electrolyte Tank 114 Positive Electrode Forward Piping 115 Positive Return Pipe 113, 123 Pump 12 Negative Cell 121 Negative Electrode 122 Negative Electrolyte Tank 124 Negative Forward Pipe 125 Negative Return Piping 13 Ion exchange membrane 2 AC/DC converter 31 Power supply 32 Load

Claims (10)

  1. 　カーボン電極材を有する電極であって、
    　前記カーボン電極材は、ラマン分光法によって測定したラマンスペクトルに現れる、Ｄバンドのピーク強度（ＩＤ）の、Ｇバンドのピーク強度（ＩＧ）に対するピーク強度比（ＩＤ／ＩＧ比）が０．５０以下であり、かつ、酸素元素の含有量が０．５０質量％以下である炭素材料を含む電極。     An electrode having a carbon electrode material,
    The carbon electrode material has a peak intensity ratio (I D /I G ratio) of the D band peak intensity (I D ) to the G band peak intensity (I G ) that appears in the Raman spectrum measured by Raman spectroscopy. An electrode containing a carbon material having an oxygen element content of 0.50% by mass or less and 0.50 or less.
  2. 　前記カーボン電極材は、前記炭素材料を５０質量％以上含有する、請求項１に記載の電極。 The electrode according to claim 1, wherein the carbon electrode material contains 50% by mass or more of the carbon material.
  3. 　前記炭素材料は、カーボンファイバーを含む、請求項１または２に記載の電極。 The electrode according to claim 1 or 2, wherein the carbon material includes carbon fiber.
  4. 　前記カーボンファイバーの平均繊維径が１μｍ以上である、請求項３に記載の電極。 The electrode according to claim 3, wherein the carbon fiber has an average fiber diameter of 1 μm or more.
  5. 　前記カーボン電極材は、前記カーボンファイバーを用いて形成された、カーボンフェルトまたはカーボンペーパーのシート材料で構成される、請求項３または４に記載の電極。 The electrode according to claim 3 or 4, wherein the carbon electrode material is composed of a sheet material of carbon felt or carbon paper formed using the carbon fiber.
  6. 　前記電極が、レドックスフロー電池の正極電極として用いられる、請求項１～５のいずれか１項に記載の電極。 The electrode according to any one of claims 1 to 5, wherein the electrode is used as a positive electrode of a redox flow battery.
  7. 　正極電極および負極電極を備える電池であって、
    　前記正極電極が、請求項１～６のいずれか１項に記載の電極である、電池。     A battery comprising a positive electrode and a negative electrode,
    The battery, wherein the positive electrode is the electrode according to any one of claims 1 to 6.
  8. 　前記電池がレドックスフロー電池であり、
    　前記正極電極に供給される正極電解液、および前記負極電極に供給される負極電解液をさらに備え、
    　前記正極電解液が、マンガンイオン、セリウムイオンおよび塩素イオンから選択される１種又は２種以上のイオンを含む、請求項７に記載の電池。     The battery is a redox flow battery,
    Further comprising a positive electrode electrolytic solution supplied to the positive electrode, and a negative electrode electrolytic solution supplied to the negative electrode,
    The battery according to claim 7, wherein the positive electrode electrolyte contains one or more ions selected from manganese ions, cerium ions, and chlorine ions.
  9. 　請求項１～６のいずれか１項に記載の電極の製造方法であって、
    　炭素材料を含む成形体を、不活性ガス雰囲気中、２３００℃以上３５００℃以下で焼成してカーボン電極材を得る高温焼成工程を有する、電極の製造方法。     A method for manufacturing the electrode according to any one of claims 1 to 6,
    A method for producing an electrode, comprising a high temperature firing step of firing a molded body containing a carbon material at 2300° C. or higher and 3500° C. or lower in an inert gas atmosphere to obtain a carbon electrode material.
  10. 　前記高温焼成工程を行なう前に、前記成形体を、７００℃以下の酸素ガスを含む雰囲気中で焼成する低温焼成工程を行なう、請求項９に記載の電極の製造方法。 The method for manufacturing an electrode according to claim 9, wherein a low temperature firing step of firing the molded body in an atmosphere containing oxygen gas at 700° C. or lower is performed before the high temperature firing step.
PCT/JP2020/003162 2019-01-29 2020-01-29 Electrode, method for producing same and battery WO2020158797A1 (en)

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