WO2018142716A1 - レドックスフロー電池用電極、及びレドックスフロー電池 - Google Patents
レドックスフロー電池用電極、及びレドックスフロー電池 Download PDFInfo
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- WO2018142716A1 WO2018142716A1 PCT/JP2017/041021 JP2017041021W WO2018142716A1 WO 2018142716 A1 WO2018142716 A1 WO 2018142716A1 JP 2017041021 W JP2017041021 W JP 2017041021W WO 2018142716 A1 WO2018142716 A1 WO 2018142716A1
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- electrode
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- redox flow
- flow battery
- battery
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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
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
- H01M8/184—Regeneration by electrochemical means
- H01M8/188—Regeneration by electrochemical means by recharging of redox couples containing fluids; Redox flow type batteries
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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
- H01M4/8605—Porous electrodes
- H01M4/8626—Porous electrodes characterised by the form
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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
- H01M4/96—Carbon-based electrodes
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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
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
-
- 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
- H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
- H01M2004/8689—Positive electrodes
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- 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 for a redox flow battery and a redox flow battery.
- an electrolyte solution (a positive electrode electrolyte solution and a negative electrode electrolyte solution) is supplied to a pair of electrodes (a positive electrode electrode and a negative electrode electrode) disposed on both sides of a diaphragm, respectively, and an electrochemical reaction (battery reaction) on the electrodes is performed.
- a redox flow battery that charges and discharges.
- An aggregate of carbon fibers is used for the electrode.
- An electrode for a redox flow battery is: An electrode for a redox flow battery composed of an aggregate of base materials containing carbon, In the cross section of the base material, centered on the center of gravity of the base material, and a circle having a diameter of 95% of the equivalent area circle equivalent diameter of the base material as a reference circle,
- the base material includes a plurality of perforations extending from the surface toward the inside and having a part of a locus along the extending direction in the reference circle.
- the redox flow battery according to the present disclosure is: A redox flow battery for supplying and discharging a positive electrode electrolyte and a negative electrode electrolyte to a battery cell comprising a positive electrode, a negative electrode, and a diaphragm interposed between the positive electrode and the negative electrode.
- the positive electrode is a redox flow battery electrode according to the present disclosure.
- Sample No. in Test Example 1 is a scanning electron micrograph showing the substrate surface of an electrode of 1-1.
- 3B is a scanning electron micrograph showing a cross section taken along line 3B-3B in FIG. 3A.
- Sample No. in Test Example It is a scanning electron micrograph showing the substrate surface of the electrode 1-11.
- 4B is a scanning electron micrograph showing a cross section taken along line 4B-4B of FIG. 4A.
- an object of the present invention is to provide a redox flow battery electrode capable of constructing a redox flow battery having a low internal resistance over a long period of time. Another object is to provide a redox flow battery with low internal resistance over a long period of time.
- the above redox flow battery electrode can construct a redox flow battery having a small internal resistance over a long period of time.
- the redox flow battery has a low internal resistance over a long period of time.
- the surface of the substrate constituting the electrode (or carbon fiber when the electrode is an aggregate of carbon fibers) is roughened. It was considered to provide a concavo-convex structure by performing treatment or the like. This is because if the surface of the base material has a concavo-convex structure, the surface area becomes large, and the reaction field for performing the battery reaction becomes large.
- the present inventors examined a configuration that can suppress the surface area of the base material from decreasing with time in the operation of the RF battery over a long period of time.
- the recess is made up of perforations that reach the center region of the base material (if the base material is carbon fiber, the vicinity region centered on the axis of the carbon fiber). It has been found that even if erosion occurs, the rate of surface area decrease is small and the internal resistance can be reduced over a long period of time.
- the present invention has been made based on the above findings. The contents of the embodiments of the present invention will be listed and described below.
- An electrode for a redox flow battery composed of an aggregate of base materials containing carbon, In the cross section of the base material, centered on the center of gravity of the base material, and a circle having a diameter of 95% of the equivalent area circle equivalent diameter of the base material as a reference circle,
- the base material includes a plurality of perforations extending from the surface toward the inside and having a part of a locus along the extending direction in the reference circle.
- the surface area can be increased as compared with the case where the perforations are not provided on the surface of the base material, so that the initial internal resistance can be reduced. Since a part of the trajectory along the extending direction from the surface of the base material to the inside exists in the base material, even if the surface is eroded with the aging of the base material, The part which exists in the inside of remains. The remaining portion of the perforations can reduce the reduction rate of the surface area of the substrate. Therefore, by providing the substrate with a plurality of perforations extending from the surface toward the inside, it is possible to construct a redox flow battery having a low internal resistance over a long period from the initial operation of the RF battery.
- the cross section of a base material means a cross section perpendicular
- the base material may include a carbon fiber having a cross section with an equivalent area equivalent circle diameter of 3 ⁇ m to 100 ⁇ m.
- the electrode Since the electrode is composed of an aggregate of carbon fibers, it is easy to increase the conductivity by increasing the number of carbon fiber contacts, and it is easy to increase the flowability of the electrolyte by ensuring voids in the electrodes.
- the equivalent area circle equivalent diameter of the carbon fiber When the equivalent area circle equivalent diameter of the carbon fiber is 3 ⁇ m or more, it is easy to ensure the strength of the carbon fiber aggregate.
- the equivalent area circle equivalent diameter of the carbon fibers is 100 ⁇ m or less, the surface area of the carbon fibers per unit weight in the aggregate of carbon fibers can be increased, and a sufficient battery reaction can be performed.
- At least a part of the plurality of perforations has an equivalent area circle equivalent diameter of an opening on the surface of the substrate of 50 nm or more and 2000 nm or less. .
- the equivalent area equivalent circle diameter of the opening of the perforation is 50 nm or more, it is easy to maintain the durability when the basis weight is reduced. On the other hand, it is easy to ensure the strength of the substrate because the equivalent area equivalent diameter of the opening of the perforation is 2000 nm or less.
- a BET specific surface area is 0.1 m 2 / g or more.
- the BET specific surface area is a specific surface area determined by a gas adsorption method (BET method: specific surface area measurement method using BET equation derived from Brunauer, Emmett and Teller). Sufficient battery reaction can be performed because the BET specific surface area is 0.1 m 2 / g or more.
- the capacitance is 0.05 F / g or more.
- the redox flow battery having a high electromotive force can be constructed by increasing the redox potential of the active material.
- the positive electrode is likely to be oxidized and deteriorated due to a side reaction accompanying charge / discharge, and therefore, the effect of using the redox flow battery electrode of the present embodiment for the positive electrode is easily exhibited.
- At least a part of the plurality of perforations has a metal oxide at the bottom.
- the perforation can be formed by a metal oxide deposited on the surface of the substrate in the electrode manufacturing process (detailed in the electrode manufacturing method described later). For this reason, the metal oxide having the perforations may remain at the bottom of the perforations. Depending on the metal species that make up the metal oxide and the type of electrode used (type of electrolyte, etc.), even if the metal oxide remains at the bottom of the perforations, it does not affect the performance of the redox flow battery There is. In this case, the step of removing the metal oxide can be omitted, and the electrode productivity is excellent.
- the redox flow battery according to the embodiment of the present invention A redox flow battery for supplying and discharging a positive electrode electrolyte and a negative electrode electrolyte to a battery cell comprising a positive electrode, a negative electrode, and a diaphragm interposed between the positive electrode and the negative electrode.
- the positive electrode is the redox flow battery electrode according to any one of (1) to (6) above.
- the redox flow battery uses the redox flow battery electrode according to the embodiment of the present invention as the positive electrode, the internal resistance is small for a long period from the initial operation of the RF battery.
- the RF battery 1 includes a battery cell 100 and a circulation mechanism that circulates and supplies an electrolytic solution to the battery cell 100.
- the RF battery 1 is typically connected to a power generation unit and a load such as an electric power system or a consumer via an AC / DC converter, a substation facility, etc., and is charged by using the power generation unit as a power supply source. , Discharging the load as a power consumption target.
- the power generation unit include a solar power generator, a wind power generator, and other general power plants.
- the battery cell 100 includes a positive electrode 12 to which a positive electrode electrolyte is supplied, a negative electrode 14 to which a negative electrode electrolyte is supplied, and a diaphragm 11 interposed between the positive electrode 12 and the negative electrode 14.
- the positive electrode 12 and the negative electrode 14 are reaction fields in which active material ions contained in the supplied electrolyte solution perform a battery reaction.
- the diaphragm 11 is a separation member that separates the positive electrode 12 and the negative electrode 14 and transmits predetermined ions.
- the positive electrode electrolyte circulation mechanism is provided in a positive electrode tank 140 that stores the positive electrode electrolyte, pipes 142 and 144 that connect the positive electrode tank 140 and the battery cell 100, and a pipe 142 on the upstream side (supply side). And a pump 146.
- the negative electrode electrolyte circulation mechanism is provided in the negative electrode tank 150 that stores the negative electrode electrolyte, pipes 152 and 154 that connect the negative electrode tank 150 and the battery cell 100, and the pipe 152 on the upstream side (supply side). And a pump 156.
- the positive electrode electrolyte is supplied from the positive electrode tank 140 to the positive electrode 12 via the upstream pipe 142 and returned from the positive electrode 12 to the positive electrode tank 140 via the downstream (discharge side) pipe 144. Further, the negative electrode electrolyte is supplied from the negative electrode tank 150 to the negative electrode 14 via the upstream pipe 152, and is returned from the negative electrode 14 to the negative electrode tank 150 via the downstream (discharge side) pipe 154.
- the active material ions in the electrolyte solution of each electrode Charge / discharge is performed with the valence change reaction.
- manganese ions and titanium ions shown in the positive electrode tank 140 and the negative electrode tank 150 are examples of ionic species included as active materials in the positive electrode electrolyte and the negative electrode electrolyte.
- a solid line arrow means charging, and a broken line arrow means discharging.
- the RF battery 1 is typically used in a form called a cell stack in which a plurality of battery cells 100 are stacked.
- the battery cell 100 includes a bipolar plate (not shown) in which the positive electrode 12 is disposed on one surface and the negative electrode 14 is disposed on the other surface, and a frame (not illustrated) formed on the outer periphery of the bipolar plate. It is configured using a frame.
- the frame body has a liquid supply hole for supplying an electrolytic solution and a liquid discharge hole for discharging the electrolytic solution. By stacking a plurality of cell frames, the liquid supply hole and the liquid discharge hole can be connected to the flow of the electrolytic solution.
- a path is configured, and pipes 142, 144, 152, and 154 are connected to the flow path.
- the cell stack is configured by repeatedly stacking a cell frame, a positive electrode 12, a diaphragm 11, a negative electrode 14, a cell frame,.
- One of the features of the RF battery 1 of the embodiment is that an electrode capable of constructing the RF battery 1 having a small internal resistance over a long period of time is used.
- the electrode is composed of an aggregate of carbon-containing base materials, and the base material includes a plurality of perforations extending from the surface toward the inside.
- This electrode is the positive electrode 12 or the negative electrode 14 described above, and will be described below as the electrode 10 (FIG. 1).
- the electrode 10 is composed of an aggregate of a plurality of carbon fibers (base materials 110).
- FIG. 1 shows an electrode 10, a middle view is a partially enlarged view of the electrode 10, and a lower view is an enlarged cross-sectional view of each substrate 110 constituting the electrode 10.
- the base 110 includes a plurality of perforations 112 extending from the surface toward the inside as shown in the lower diagram of FIG. In the lower diagram of FIG. 1, for convenience of explanation, the shape and size of the locus along the extending direction of the perforation 112 are exaggerated.
- the base material 110 is carbon fiber, and comprises the fiber assembly (electrode 10) in which several carbon fiber becomes mutually entangled.
- the base material 110 has different proportions of fibers in the fiber assembly depending on its structure (fiber combination form).
- the ratio for which it accounts to a fiber assembly (electrode 10) is 30 mass% or more, Furthermore, it is mentioned that it is 50 mass% or more.
- a fiber assembly is comprised only by carbon fiber, or carbon fiber and things other than carbon fiber are contained and comprised. Examples of materials other than carbon fibers include carbonized binders.
- Examples of the fiber aggregate include carbon felt, carbon cloth (made of only carbon fibers), carbon paper (made of carbon fibers solidified by a carbonized binder), and the like. As these fiber assemblies, commercially available products or those manufactured by a known manufacturing method can be used.
- the graphitization degree R value of the carbon fiber is 1.4 or less, the base material 110 is hardly oxidized and deteriorated. It is mentioned that the graphitization degree R value of the carbon fiber is 1.0 or less, particularly 0.5 or less.
- the carbon fibers constituting the substrate 110 may have a cross section with an equivalent area equivalent circle diameter of 3 ⁇ m to 100 ⁇ m.
- the equivalent area circle equivalent diameter of the carbon fiber is a diameter of a circle having the same area as the cross-sectional area in the cross section of the carbon fiber. It is easy to ensure the strength of the fiber assembly when the equivalent area equivalent diameter of the carbon fiber is 3 ⁇ m or more.
- the equivalent area circle equivalent diameter of the carbon fiber is 100 ⁇ m or less, the surface area of the fiber per unit weight of the electrode 10 can be increased, and the battery reaction is easily performed.
- the equivalent area equivalent circle diameter of the carbon fiber is further 5 ⁇ m or more and 50 ⁇ m or less, particularly 7 ⁇ m or more and 20 ⁇ m or less.
- the equivalent circular equivalent diameter of the cross section of the carbon fiber constituting the substrate 110 is such that the electrode 10 is cut to expose the cross section of the carbon fiber, and at least 5 fields of view under a microscope are 3 or more carbon fibers per field of view. It is obtained by averaging the results measured for.
- Examples of the cross-sectional shape of the carbon fiber (base material 110) include a circular shape, a polygonal shape such as a rectangular shape, a triangular shape, and a star shape.
- the porosity of the fiber assembly by the base material 110 is more than 40% by volume and less than 98% by volume.
- the porosity of the fiber assembly is more than 40% by volume, it is easy to improve the flowability of the electrolytic solution.
- the porosity of the fiber assembly is less than 98% by volume, the density of the fiber assembly can be increased, the conductivity can be improved, and a sufficient battery reaction can be performed.
- the porosity of the fiber aggregate due to the substrate 110 is further 60% to 95% by volume, particularly 70% to 93% by volume.
- the base material 110 is provided with a plurality of perforations 112 extending from the surface toward the inside as shown in the lower diagram of FIG.
- the electrode 10 used in the RF battery 1 of the embodiment is characterized in that the perforation 112 has a part of the locus along the extending direction in the central region of the substrate 110.
- the central region of the base material 110 is a circle having a diameter of 95% of the equivalent area circle diameter of the base material 110 in the cross section of the base material 110 with the center of gravity of the base material 110 as the center C (in the lower diagram of FIG. (Hereinafter, this circle is referred to as a reference circle).
- the center of gravity of the region surrounded by the outline of the cross section of the base material 110 is obtained, for example, by performing image processing on a cross-sectional photograph of the base material 110.
- the perforation 112 has an opening 112o on the surface of the base 110, and extends continuously from the opening 112o toward the inside, and is like a so-called wormhole.
- the extending direction of the perforations 112 is not particularly limited, and there are those that extend in a straight line and those that extend while making a detour. Therefore, the perforation 112 has a perforation 112a extending in a direction approaching the center C of the base 110 when the cross section of the base 110 is viewed, and the center C of the base 110 in the middle of the extension as shown in the lower diagram of FIG.
- perforation 112b extending in a direction away from the perforation 112
- a perforation 112c that is folded back in the middle of the extension and extends outward.
- the perforations 112 also make a detour in the longitudinal direction of the substrate 110. In that case, when the cross section of the base material 110 is viewed, the perforations 112 are cut in a direction crossing the extending direction, and thus appear to be hollow (a cavity indicated by 112d in the lower diagram of FIG. 1).
- the drill 112 has a part of the trajectory along the distraction direction in the reference circle. That is, the trajectory from the middle of the extending direction of the perforation 112 to the bottom may exist in the reference circle (perforations 112a and 112b), and a part of the trajectory in the extending direction of the perforation 112 is within the reference circle. It may be present (perforation 112c). Further, in the case of a perforation that extends while making a detour in the longitudinal direction of the base material 110, a perforation 112d that looks like a cavity when the cross section of the base material 110 is viewed may exist in the reference circle.
- the perforations 112 are preferably present in a direction in which a part of the trajectory approaches the center C of the substrate 110. That is, it is preferable that the perforations 112 exist in a reference circle having a diameter of 90%, 80%, particularly 70% of the equivalent area circle equivalent diameter of the substrate 110. By doing so, even if the surface of the base material 110 is greatly eroded due to aging, the disappearance of the perforations 112 can be suppressed, and the reduction ratio of the surface area of the base material 110 can be made smaller.
- the plurality of perforations 112 may exist independently of each other, may exist in communication with each other, or may be mixed. Further, the perforations 112 may exist through the base material 110.
- the hole 112 in the case of a hole that does not penetrate the substrate 110, the hole 112 has an opening 112o on the surface of the substrate 110, a bottom, and a side wall connecting the opening 112o and the bottom, In the case of a hole penetrating the base material 110, it has an opening portion 112o on one end side and an opening portion 112o on the other end side formed on the surface of the base material 110, and a side wall portion connecting the both opening portions 112o.
- the equivalent area equivalent diameter of the opening part 112o on the surface of the base material 110 is 50 nm or more and 2000 nm or less.
- the equivalent area equivalent circle diameter of the opening 112o is the diameter of a circle having the same area as the opening 112o in the opening 112o on the surface of the substrate 110. Since the equivalent area equivalent diameter of the opening 112o of the perforation 112 is 50 nm or more, it is easy to maintain the durability when the basis weight is reduced. On the other hand, since the equivalent area equivalent diameter of the opening 112o of the perforation 112 is 2000 nm or less, it is easy to ensure the strength of the substrate 110.
- the equivalent area equivalent circle diameter of the opening 112o of the perforation 112 is further 100 nm or more, particularly 300 nm or more.
- the equivalent area equivalent circle diameter of the opening 112o on the surface of the substrate 110 should be the average of the results of measurements for three or more fields of view and 20 or more openings for one field of view by surface observation using a scanning electron microscope (SEM). Is required.
- SEM scanning electron microscope
- Examples of the opening shape of the opening 112o of the perforation 112 include a circular shape, a polygonal shape such as a rectangular shape, a triangular shape, and a star shape.
- a metal oxide 120 may be provided at the bottom of the perforation 112 of the substrate 110.
- the perforations 112 of the substrate 110 can be formed by the metal oxide 120 deposited on the surface of the substrate 110 during the manufacturing process of the electrode 10 (described in detail in the electrode manufacturing method described later). Therefore, the metal oxide 120 in which the perforations 112 are formed may remain at the bottom of the perforations 112.
- the metal element constituting the metal oxide 120 include iron (Fe), zirconium (Zr), cobalt (Co), tungsten (W), nickel (Ni), and the like.
- the metal oxide 120 contains one or more metal elements selected from the above metal elements.
- oxides of each metal element Fe 2 O 3 , ZrO 2, etc.
- composite oxides containing a plurality of kinds of metal elements ((Fe, Zr ) O etc.).
- the absence of the metal oxide 120 may be preferable. If the electrode 10 with the metal oxide 120 remaining is used in the RF battery 1, the metal oxide 120 may be dissolved in the electrolytic solution and react with the electrolytic solution components to generate a deposit, which may cause problems. Because there is. In that case, the metal oxide 120 can be removed after the perforations 112 are formed (detailed in the electrode manufacturing method described later). That is, the electrode 10 can be in a state where the metal oxide 120 does not exist. On the other hand, it is preferable that the metal oxide 120 is present, and even if the metal oxide 120 is present, there may be no problem. The presence or absence of the metal oxide 120 can be appropriately selected according to the metal species constituting the metal oxide 120, the type of the electrolytic solution, and the like.
- the above-described electrode 10 for an RF battery includes, for example, a preparation process for preparing a base 110 and a coating liquid containing a specific metal, a coating process for coating the coating liquid on the surface of the base 110, and a coating liquid. It is obtained by performing a heat treatment step of performing a heat treatment on the coated substrate 110. By applying a coating solution to the substrate 110 and performing a heat treatment, the substrate 110 can be formed with perforations 112 extending from the surface toward the inside. When the absence of a metal component (metal oxide 120) is preferable as the electrode 10, a removal step of removing the metal oxide 120 attached to the substrate 110 may be performed.
- a metal component metal oxide 120
- the base material 110 As the base material 110, a fiber assembly in which a plurality of carbon fibers are entangled with each other is prepared. What is necessary is just to select suitably the magnitude
- FIG. As one of the conditions for forming the perforations 112 extending from the surface toward the inside of the base material 110, the base material 110 is a carbon fiber having a graphitization degree with an R value determined by Raman spectroscopy analysis of 1.4 or less. It is mentioned to use what is comprised.
- the metal oxide 120 is formed on the base material 110 while suppressing the oxidative deterioration at the portion where the metal oxide 120 is not attached.
- the perforation 112 can be formed only at the adhered portion.
- the graphitization degree R value of the carbon fiber is further preferably 1.0 or less, particularly preferably 0.5 or less.
- a coating solution containing a raw material of a specific metal element such as Fe, Zr, Co, W, Ni and a solvent is prepared.
- a specific metal element such as Fe, Zr, Co, W, Ni and a solvent
- Various metal chlorides such as tetrahydrate, zirconium tetrachloride, tungsten hexachloride, cobalt chloride (II) hexahydrate, nickel (II) hexahydrate, metals such as NiSO 4 and CoSO 4 Examples thereof include sulfates and various organometallic complexes.
- the solvent used for the coating solution include water, ethanol, methanol, propyl alcohol, isopropanol, butanol, pentanol, and hexanol.
- concentration of the specific metal element in the coating solution is 0.005 mass% or more and 3 mass% or less.
- concentration of the metal element in the coating solution can be measured by ICP (inductively coupled plasma emission analysis).
- concentration of the specific metal element tends to affect the particle size of the metal oxide 120 generated in the heat treatment step described later. Therefore, by setting the concentration of the specific metal in the coating solution in the above range, a metal oxide 120 having a desired size can be generated on the substrate 110 in the heat treatment step described later.
- Perforations 112 can be formed according to the size.
- the higher the concentration of the specific metal in the coating solution the more easily the metal oxide 120 that is produced is aggregated in the heat treatment step described later.
- the base material 110 is eroded in the aggregated state, so that the perforations 112 can be easily enlarged.
- the concentration of the specific metal element in the coating solution is further 0.01% by mass or more and 2.5% by mass or less, 0.05% by mass or more and 2.3% by mass or less, 0.07% by mass or more and 2% by mass or less, particularly It is preferable to set it to 0.1 mass% or more and 1.5 mass% or less.
- the coating liquid may contain a silicon-based surfactant, a fluorine-based surfactant, a cationic surfactant, an anionic surfactant, or the like as the surfactant.
- the surfactant is contained, it is preferably contained in the coating solution in an amount of 0.05% by mass to 3% by mass.
- a coating solution containing metal nanoparticles (the metal species is the same as that of the specific metal element) and water or an organic solvent may be used.
- a coating liquid is apply
- the coating method include a dip coating method, a brush coating method, a spraying method, a flow coating method, and a roll coating method.
- One of the conditions for forming the perforations 112 extending from the surface toward the inside of the substrate 110 is that the coating amount is 0.1 g / m 2 or more and 30 g / m 2 or less. The coating amount of the coating liquid tends to affect the number of metal oxides 120 generated in the heat treatment step described later.
- the coating amount of the coating solution is further preferably 0.5 g / m 2 or more and 10 g / m 2 or less, particularly preferably 1 g / m 2 or more and 5 g / m 2 or less.
- the solvent is dried (for example, about 150 ° C.).
- coated the coating liquid is heat-processed in the atmosphere containing oxygen.
- the metal oxide 120 is generated on the base 110, and the metal oxide 120 is eroded toward the inside of the base 110, so that the surface of the base 110 can be eroded.
- a perforation 112 can be formed extending inward.
- the atmosphere containing oxygen preferably has an oxygen concentration of 1% by volume or more, more preferably 5% by volume or more, and particularly preferably 10% by volume or more.
- atmosphere is an air atmosphere, atmosphere control is easy and workability is excellent.
- the atmosphere may contain more oxygen than the atmosphere.
- the heat treatment temperature is set to 400 ° C. or higher and 800 ° C. or lower.
- the heat treatment temperature tends to affect the extending direction of the perforations 112 and the length (depth) in the extending direction. Therefore, by setting the heat treatment temperature in the above range, the metal oxide 120 can be eroded to the central region of the base material 110 (within the reference circle in the cross section of the base material 110). That is, the perforations 112 that reach the center region of the substrate 110 can be formed.
- the heat treatment temperature is preferably 450 ° C. or higher and 750 ° C. or lower, more preferably 500 ° C. or higher and 700 ° C. or lower.
- the heat treatment time is 30 minutes or more and 10 hours or less.
- the heat treatment time tends to affect the extending direction of the perforations 112 and the length (depth) in the extending direction, similarly to the heat treatment temperature. Therefore, by setting the heat treatment time in the above range, the metal oxide 120 can be eroded to the central region of the substrate 110 (within the reference circle in the cross section of the substrate 110). That is, the perforations 112 that reach the center region of the substrate 110 can be formed.
- the heat treatment time is preferably 1 hour or more and 7 hours or less, particularly preferably 1 hour or more and 5 hours or less.
- the heat treatment temperature and the heat treatment time be a long time at a low temperature within the above range.
- the metal oxide 120 may remain at the bottom of the perforations 112 in the electrode 10 obtained in the heat treatment process.
- the metal oxide 120 can be removed by dissolving it or subjecting the electrode 10 to an acid cleaning treatment.
- the acid cleaning treatment include immersing in a cleaning liquid (for example, hydrochloric acid or hydrofluoric acid) for about 0.1 hour or more and 2 hours or less. After removing the metal oxide with the cleaning solution, the substrate is cleaned with ultrapure water and dried.
- the above-described electrode 10 for an RF battery can also be obtained by previously forming a hole in a PAN-based (polyacrylonitrile-based) fiber before carbonization and then carbonizing.
- a hole can be formed by dissolving two types of polymers that are not mixed in a compatible solvent to form a fiber and then dissolving one polymer in the fiber with the solvent. For example, after forming a fiber in which PVP (polyvinylpyrrolidone) is dispersed so that PAN becomes the fiber base, only PVP is dissolved in a solvent to obtain a PAN fiber having a hole.
- PVP polyvinylpyrrolidone
- the electrode 10 for an RF battery extends to the base 110 from the surface thereof toward the inside, and a part of the trajectory along the extension direction exists in the central region (reference circle) of the base 110. Since the perforation 112 is provided, the BET specific surface area of the electrode 10 can be set to 0.1 m 2 / g or more. Sufficient battery reaction can be performed because the BET specific surface area is 0.1 m 2 / g or more. Since a part of the trajectory along the extending direction of the perforation 112 exists in the central region (reference circle) of the base material 110, even if the base material 110 deteriorates over time, the reduction rate of the surface area of the base material 110 is reduced. it can. Therefore, by using this electrode 10, it is possible to construct the RF battery 1 having a small internal resistance for a long period from the initial operation and to construct a stable RF battery 1.
- the electrode 10 for an RF battery of the embodiment can be suitably used particularly for the positive electrode 12 (FIG. 2).
- the positive electrode carbon fiber
- the positive electrode is caused by side reactions associated with charge and discharge in the operation of the RF battery 1 over a long period of time. Tends to cause oxidative degradation and increase in internal resistance.
- the electrode 10 for an RF battery of the embodiment as a positive electrode, even if the carbon fiber is oxidized and deteriorated, an increase in internal resistance can be suppressed because the reduction ratio of the surface area is small. Therefore, the capacitance of the electrode 10 can be increased to 0.05 F / g or more.
- the capacitance is 0.05 F / g or more
- the redox potential of the active material can be increased, and the RF battery 1 having a high electromotive force can be constructed.
- the positive electrode is likely to be oxidized and deteriorated due to a side reaction accompanying charging and discharging, and thus the effect obtained by using the RF battery electrode 10 of the embodiment as a positive electrode is easily exhibited.
- Electrolyte used for the RF battery 1 contains active material ions such as metal ions and nonmetal ions.
- active material ions such as metal ions and nonmetal ions.
- a manganese-titanium-based electrolytic solution containing manganese (Mn) ions as a positive electrode active material and titanium (Ti) ions as a negative electrode active material can be given (see FIG. 2).
- an aqueous solution containing at least one acid or acid salt selected from sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid can be used.
- the positive electrode electrolyte and the negative electrode electrolyte preferably contain an active material having a redox potential of 0.9 V or higher. If the redox potential of the active material is 0.9 V or higher, the RF battery 1 having a high electromotive force can be constructed. In the RF battery 1 having a high electromotive force, the positive electrode 12 (FIG. 2) is liable to be oxidized and deteriorated due to a side reaction accompanying charging and discharging. Therefore, the effect obtained by using the RF battery electrode 10 of the present embodiment for the positive electrode 12. Is easier to demonstrate.
- the electrode 10 for an RF battery according to the embodiment can be suitably used as an electrode of the RF battery 1.
- the RF battery 1 according to the embodiment has a large capacity for the purpose of stabilizing fluctuations in power generation output, storing electricity when surplus generated power, leveling load, etc., with respect to natural power generation such as solar power generation and wind power generation. It can be used for storage batteries.
- the RF battery 1 of the embodiment can be suitably used as a large-capacity storage battery that is provided in a general power plant and is used for the purpose of instantaneous voltage drop / power failure countermeasures and load leveling.
- Test Example 1 An electrode having perforations in a carbon-containing substrate was prepared, and the cell resistivity was examined as a change over time.
- Sample preparation ⁇ Sample No. 1-1 to 1-6 A carbon paper made of carbon fibers having a graphitization degree R value of 0.35 was prepared as a base material containing carbon. This carbon paper has a fiber diameter (equivalent area equivalent circle diameter): 8 ⁇ m, size: 30 mm ⁇ 30 mm, thickness: 0.2 mm, porosity: 65% by volume, basis weight: 120 g / m 2 .
- As a coating solution iron (II) chloride tetrahydrate was used. 1-1, 1-3 to 1-6, 1% by mass; In 1-2, a solution dissolved in ethanol so as to be 0.1% by mass was prepared. Sample No.
- Sample No. 1-7 Sample No. After iron oxide nanoparticles (average particle size 6 nm) were coated on the same substrate as 1-1, firing was performed at 650 ° C. for 1 hour in the air.
- Sample No. 1-11 A coating solution prepared by dissolving zirconium chloride in ethanol so that the concentration of zirconium was 1% by mass was prepared. This coating solution was added to Sample No. It was applied to the same substrate as 1-1 by dip coating, dried at 150 ° C. until the organic solvent was removed, and then baked at 650 ° C. for 1 hour in the air.
- Sample No. 1-21 As a coating solution, CoSO 4 was dissolved in water so that the concentration of cobalt was 1% by mass, and 0.5% by mass of a fluorosurfactant was further prepared. This coating solution was added to Sample No. It was applied to the same substrate as 1-1 by the dip coating method, dried at 150 ° C. until the solvent was removed, and then baked at 650 ° C. for 1 hour in the air.
- Sample No. 1-31 As a coating solution, a solution prepared by dissolving tungsten chloride in ethanol so that the concentration of tungsten was 1% by mass was prepared. This coating solution was added to Sample No. It was applied to the same substrate as 1-1 by dip coating, dried at 150 ° C. until the organic solvent was removed, and then baked at 650 ° C. for 1 hour in the air.
- Sample No. 1-100 As a substrate, Sample No. A substrate similar to 1-1 was prepared. Sample No. In No. 1-100, the base material is not applied with the coating liquid and fired after the coating.
- Sample No. 1-111 As a substrate, Sample No. A substrate similar to 1-1 was prepared. Sample No. In 1-11, carbon nanotubes were grown on carbon fibers by chemical vapor deposition (CVD) (size 50 nm).
- CVD chemical vapor deposition
- Sample No. 1-112 As a substrate, Sample No. A substrate similar to 1-1 was prepared. Sample No. In 1-112, carbon black particles (35 nm in size) were dispersed in ethanol, a fluororesin dispersion was mixed as a binder, applied onto the substrate and dried to adhere.
- Sample No. 1-113 Sample No. The surface of the base material similar to 1-1 was subjected to plasma hydrophilization treatment.
- FIG. 1-1 is an SEM photograph of the surface of the carbon fiber constituting the electrode 1-1 (magnification: 12,000 times), and FIG. 3B shows the perforation observed on the surface of the carbon fiber, almost the center of the opening (SEM photograph of the surface of FIG. 3A).
- the cross section of the carbon fiber is obtained by processing the carbon fiber with a focused ion beam (FIB). In this example, when FIB processing is performed, the carbon fiber is coated with platinum (Pt).
- FIB focused ion beam
- Electrodes 1-2 to 1-7, 1-21, and 1-31 also have perforations extending from the surface toward the inside in the carbon fiber (base material), and the perforations having the metal oxide at the bottom. It could be confirmed.
- the equivalent area circle equivalent diameter of the opening on the surface of the carbon fiber was examined.
- the perforations are formed by the metal oxide generated on the surface of the base material eroding into the base material by heat treatment in the manufacturing process of the electrode. Therefore, it is considered that the diameter of the perforations is maintained substantially along the extending direction of the opening on the surface of the carbon fiber.
- the equivalent area equivalent circle diameter of the opening on the surface of the carbon fiber was obtained by surface observation with an SEM photograph. If multiple perforations are in contact, use the value of the diameter if the diameter of the perforation can be distinguished, or use the value calculated by adding both perforations if the boundary between the perforations cannot be distinguished. .
- Table 1 shows the equivalent area equivalent diameter of the opening on the surface of the carbon fiber as the diameter of the perforation.
- the center of gravity of the carbon fiber is the center C
- the portion closest to the center C of the trajectory along the extending direction of the drilling is the depth point A.
- a length D from the surface of the carbon fiber to the depth point A on the straight line connecting the center C and the depth point A is set (see the lower diagram in FIG. 1).
- the depth of the perforations was obtained by taking a cross section near the perforations by FIB processing and observing the surface with an SEM photograph.
- the deepest length D was adopted (for example, in FIGS. 3B and 4B, the perforations with double arrows shown in the SEM photographs of the cross section were adopted).
- Table 1 shows the length D as the perforation depth.
- the RF battery of the single cell structure was produced using the positive electrode, the negative electrode, and the diaphragm.
- the positive electrode one in which two electrodes of each sample described above were stacked was used.
- the negative electrode a laminate of two carbon papers made of carbon fibers having a graphitization degree R value of 1.5 was used.
- the carbon paper used for the negative electrode has a fiber diameter (equal area equivalent circle diameter): 10 ⁇ m, size: 30 mm ⁇ 30 mm, thickness: 0.1 mm, porosity: 70% by volume, basis weight: 56 g / m 2 . .
- a manganese-titanium-based electrolytic solution containing manganese ions as an active material and a titanium ion as an active material was used as a negative electrode electrolytic solution. Since each sample was an RF battery having a single cell structure, the internal resistance of the RF battery is expressed as cell resistivity. For each sample, the battery cell was charged and discharged at a constant current of 70 mA / cm 2 current density. In this test, when a predetermined switching voltage set in advance was reached, switching from charging to discharging was performed, and charging and discharging were performed for a plurality of cycles. After charge / discharge of each cycle, the cell resistivity ( ⁇ ⁇ cm 2 ) was determined for each sample.
- the cell resistivity is obtained by calculating an average voltage during charging and an average voltage during discharging in any one of a plurality of cycles, and ⁇ (difference between average voltage during charging and average voltage during discharging) / (average current / 2) ⁇ ⁇
- the cell effective area was determined.
- Table 1 shows the cell resistivity of the electrode immediately after the start of immersion in the electrolyte (0 days of immersion) as the initial cell resistivity.
- Sample No. 1 was obtained by applying a specific metal element (Fe, Zr, Co, W) to carbon fiber and performing heat treatment.
- 1-1 to 1-7, 1-11, 1-21, 1-31 have perforations with an opening diameter of 60 nm to 1500 nm and a depth (length D) of 200 nm to 3500 nm on the surface of the carbon fiber.
- Nos. 1-1 to 1-7, 1-11, 1-21, and 1-31 indicate that the increase rate of the cell resistivity is a sample No. 1 with no carbon fiber perforation. Low compared to 1-111, 1-112, 1-113. This is because, even when the carbon fiber deteriorates over time and the surface is eroded in the operation of the RF battery over a long period of time, the portion of the perforation exists in a region close to the center C of the carbon fiber, and the surface area reduction rate This is thought to be due to the reduction of On the other hand, sample No.
- 1-111, 1-112, 1-113 are the reaction of carbon nanotubes and carbon black particles adhering to the surface of the carbon fiber that have dropped off or disappeared due to oxidative decomposition during long-term operation of the RF battery. It is thought that the cell resistivity increased due to the decrease in area.
- the present invention is not limited to these exemplifications, is shown by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.
- the shape and size of the trajectory along the extending direction of the perforation can be changed as appropriate by changing the metal type in the coating solution, its concentration, the coating amount, or changing the heat treatment conditions. Can be changed.
- the kind of electrolyte solution can be changed suitably.
- Redox flow battery (RF battery) DESCRIPTION OF SYMBOLS 100 Battery cell 11 Diaphragm 10 Electrode 110 Base material 112,112a, 112b, 112c, 112d Drilling 112o Opening 120 Metal oxide 12 Positive electrode 14 Negative electrode 140 Positive electrode tank 150 Negative electrode tank 142,144,152,154 Piping 146,156 pump
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Abstract
Description
本出願は、2017年1月31日出願の日本出願第2017-15046号に基づく優先権を主張し、上記日本出願に記載された全ての記載内容を援用するものである。
炭素を含有する基材の集合体で構成されるレドックスフロー電池用電極であって、
前記基材の横断面において、前記基材の重心を中心とし、前記基材の等面積円相当径の95%の直径を有する円を基準円とするとき、
前記基材は、表面から内部に向かって延びると共に、その伸延方向に沿った軌跡の一部が前記基準円内に存在する複数の穿孔を備える。
正極電極と、負極電極と、前記正極電極と前記負極電極との間に介在される隔膜とを備える電池セルに正極電解液及び負極電解液を供給して充放電を行うレドックスフロー電池であって、
前記正極電極は、上記本開示に係るレドックスフロー電池用電極である。
レドックスフロー電池に対して、長期的に安定な性能を達成することが望まれる。長期に亘るレドックスフロー電池の運転では、正極電極に炭素繊維の集合体を用いると、電解液中で炭素繊維が酸化劣化し、内部抵抗の増加を招く虞がある。
上記レドックスフロー電池用電極は、長期に亘り内部抵抗が小さいレドックスフロー電池を構築できる。また、上記レドックスフロー電池は、長期に亘り内部抵抗が小さい。
レドックスフロー電池(以下、RF電池と呼ぶことがある)の反応活性の向上のために、電極を構成する基材(電極が炭素繊維の集合体の場合、炭素繊維)の表面に、粗面化処理等を行うことで凹凸構造を設けることを検討した。基材表面が凹凸構造であると、表面積が大きくなるため、電池反応を行う反応場が大きくなるからである。しかし、基材表面に単純な凹凸構造を設けるだけでは、長期に亘るRF電池の運転において、基材の経年劣化に伴い表面が侵食されて凹凸構造が消失し、表面積が小さくなることで、内部抵抗が増加することがわかった。
炭素を含有する基材の集合体で構成されるレドックスフロー電池用電極であって、
前記基材の横断面において、前記基材の重心を中心とし、前記基材の等面積円相当径の95%の直径を有する円を基準円とするとき、
前記基材は、表面から内部に向かって延びると共に、その伸延方向に沿った軌跡の一部が前記基準円内に存在する複数の穿孔を備える。
正極電極と、負極電極と、前記正極電極と前記負極電極との間に介在される隔膜とを備える電池セルに正極電解液及び負極電解液を供給して充放電を行うレドックスフロー電池であって、
前記正極電極は、上記(1)から(6)のいずれか1つに記載のレドックスフロー電池用電極である。
以下、図面を参照して、本発明の実施形態に係るレドックスフロー電池(RF電池)に備わる電極、及びその電極を備えるRF電池を詳細に説明する。
RF電池1は、図2に示すように、電池セル100と、電池セル100に電解液を循環供給する循環機構とを備える。RF電池1は、代表的には、交流/直流変換器や変電設備等を介して、発電部と、電力系統や需要家等の負荷とに接続され、発電部を電力供給源として充電を行い、負荷を電力消費対象として放電を行う。発電部は、例えば、太陽光発電機、風力発電機、その他一般の発電所等が挙げられる。
電池セル100は、正極電解液が供給される正極電極12と、負極電解液が供給される負極電極14と、正極電極12と負極電極14との間に介在される隔膜11とを備える。正極電極12及び負極電極14は、供給された電解液に含まれる活物質イオンが電池反応を行う反応場である。隔膜11は、正極電極12と負極電極14とを分離すると共に、所定のイオンを透過する分離部材である。
実施形態のRF電池1は、長期に亘り内部抵抗が小さいRF電池1を構築できる電極を用いる点を特徴の一つとする。具体的には、電極は、炭素を含有する基材の集合体で構成されており、基材は、表面から内部に向かって延びる複数の穿孔を備える。この電極とは、上述した正極電極12や負極電極14のことであり、以下では電極10(図1)として説明する。
電極10は、図1に示すように、複数本の炭素繊維(基材110)の集合体で構成される。図1は、電極10を示し、中図は電極10の一部拡大図であり、下図は電極10を構成する各基材110の拡大横断面図である。基材110は、図1の下図に示すように、表面から内部に向かって延びる複数の穿孔112を備える。なお、図1の下図では、説明の便宜上、穿孔112の伸延方向に沿った軌跡の形状・大きさ等を誇張して示す。
基材110は、炭素繊維であり、複数本の炭素繊維が互いに絡み合う繊維集合体(電極10)を構成する。基材110は、その構造(繊維の組み合わせ形態)によって繊維集合体に占める繊維の割合が異なる。基材110は、繊維集合体(電極10)に占める割合が30質量%以上、更に50質量%以上であることが挙げられる。繊維集合体は、炭素繊維のみで構成されたり、炭素繊維と炭素繊維以外のものとが含まれて構成されたりする。炭素繊維以外のものとして、炭化したバインダー等が挙げられる。繊維集合体は、カーボンフェルトやカーボンクロス(炭素繊維のみで構成されたもの)、カーボンペーパー(炭素繊維が炭化バインダーにより固められたもの)等が挙げられる。これらの繊維集合体は、市販品や公知の製造方法によって製造されたものを利用できる。
基材110は、図1の下図に示すように、表面から内部に向かって延びる複数の穿孔112を備える。実施形態のRF電池1に用いる電極10は、穿孔112が、その伸延方向に沿った軌跡の一部が基材110の中心領域に存在する点を特徴の一つとする。基材110の中心領域とは、基材110の横断面において、基材110の重心を中心Cとし、基材110の等面積円相当径の95%の直径を有する円(図1の下図にて点線で示す円)の内側領域のことである(以下、この円のことを基準円と呼ぶ)。基材110の横断面の輪郭で囲まれる領域の重心は、例えば、基材110の断面写真を画像処理することで求められる。
基材110の穿孔112の底部には、金属酸化物120を有していてもよい。基材110の穿孔112は、電極10の製造過程において、基材110の表面上に付着された金属酸化物120によって形成できる(後述の電極の製造方法にて詳述する)。そのため、穿孔112を形成した金属酸化物120が、その穿孔112の底部に残存することがある。金属酸化物120を構成する金属元素としては、鉄(Fe)、ジルコニウム(Zr)、コバルト(Co)、タングステン(W)、ニッケル(Ni)等が挙げられる。金属酸化物120は、上記金属元素から選択される一種以上の金属元素を含有する。上記金属元素から選択される複数種の金属元素を含有する場合、各金属元素の酸化物(Fe2O3、ZrO2等)や、複数種の金属元素を含む複合酸化物((Fe,Zr)O等)の形態で存在する。
上述したRF電池用の電極10は、例えば、基材110と、特定金属を含有する塗布液とを準備する準備工程と、塗布液を基材110の表面に塗布する塗布工程と、塗布液を塗布した基材110に熱処理を施す熱処理工程と、を行うことで得られる。基材110に塗布液を塗布して熱処理を施すことで、基材110に表面から内部に向かって延びる穿孔112を形成できる。電極10として金属成分(金属酸化物120)の不存在が好ましい場合には、基材110に付着した金属酸化物120を除去する除去工程を行えばよい。以下、RF電池用の電極10の製造方法を詳細に説明する。
基材110として、複数本の炭素繊維が互いに絡み合った繊維集合体を準備する。この繊維集合体の大きさや形状は、所望の電極10の大きさや形状となるように適宜選択すればよい。基材110に表面から内部に向かって延びる穿孔112を形成する条件の一つとして、基材110として、ラマン分光法解析により求めたR値が1.4以下である黒鉛化度を有する炭素繊維で構成されるものを用いることが挙げられる。黒鉛化度R値が1.4以下であることで、後述する熱処理工程において、基材110上で金属酸化物120が付着していない箇所での酸化劣化を抑制しつつ、金属酸化物120が付着した箇所のみに穿孔112を形成できる。炭素繊維の黒鉛化度R値は、更に1.0以下、特に0.5以下とすることが好ましい。
塗布液として、Fe,Zr,Co,W,Ni等の特定金属元素の原料と、溶媒とを含有する塗布液を準備する、上記特定金属元素の原料としては、塩化鉄(II)四水和物、四塩化ジルコニウム、六塩化タングステン、塩化コバルト(II)六水和物、塩化ニッケル(II)六水和物等の各種金属塩化物、NiSO4、CoSO4等の金属硫酸塩、各種有機金属錯体等が挙げられる。塗布液に用いる溶媒としては、水、エタノール、メタノール、プロピルアルコール、イソプロパノール、ブタノール、ペンタノール、ヘキサノール等が挙げられる。
繊維集合体(基材110)の表面に塗布液を塗布する。塗布方法としては、ディップコーティング法、刷毛塗法、噴霧法、フローコート法、ロールコート法等が挙げられる。基材110に表面から内部に向かって延びる穿孔112を形成する条件の一つとして、塗布量を0.1g/m2以上30g/m2以下とすることが挙げられる。塗布液の塗布量は、後述する熱処理工程において生成される金属酸化物120の数に影響を及ぼす傾向にある。そのため、塗布液の塗布量を上記範囲とすることで、後述する熱処理工程において、基材110上に所望の個数の金属酸化物120を生成することができ、その金属酸化物120の個数に応じた穿孔112を形成できる。特に、塗布量が多いほど、後述する熱処理工程において、基材110の表面に均一的に金属酸化物120を生成し易く、基材110の全体に亘って均一的に穿孔112を形成し易い。塗布液の塗布量は、更に0.5g/m2以上10g/m2以下、特に1g/m2以上5g/m2以下とすることが好ましい。
塗布液を塗布した繊維集合体に、酸素を含む雰囲気中で熱処理を施す。酸素を含む雰囲気中で熱処理を行うことで、基材110上に金属酸化物120を生成し、その金属酸化物120を基材110の内部に向かって侵食させることで、基材110の表面から内部に向かって延びる穿孔112を形成できる。酸素を含む雰囲気は、酸素濃度が1体積%以上、更に5体積%以上、特に10体積%以上が好ましく、大気雰囲気とすると雰囲気制御が容易であり作業性に優れる。勿論、大気よりも多くの酸素が含まれる雰囲気であっても構わない。
上記熱処理工程で得られた電極10は、図1の下図に示すように、穿孔112の底部に金属酸化物120が残存することがある。金属酸化物120は、溶解させたり、電極10を酸洗浄処理したりすることで除去できる。酸洗浄処理としては、洗浄液(例えば、塩酸やフッ酸等)に、0.1時間以上2時間以下程度浸漬することが挙げられる。洗浄液にて金属酸化物を除去した後は、超純水による洗浄を行い、乾燥する。
実施形態のRF電池用の電極10は、基材110に、その表面から内部に向かって延びると共に、その伸延方向に沿った軌跡の一部が基材110の中心領域(基準円)内に存在する穿孔112を備えるため、電極10のBET比表面積を0.1m2/g以上とすることができる。BET比表面積が0.1m2/g以上であることで、十分な電池反応を行うことができる。穿孔112は、伸延方向に沿った軌跡の一部が基材110の中心領域(基準円)内に存在するため、基材110が経年劣化したとしても、基材110の表面積の減少割合を小さくできる。よって、この電極10を用いることで、初期運転時から長期に亘り内部抵抗が小さいRF電池1を構築できると共に、安定したRF電池1を構築できる。
・電解液
RF電池1に利用する電解液は、金属イオンや非金属イオン等の活物質イオンを含む。例えば、正極活物質としてマンガン(Mn)イオン、負極活物質としてチタン(Ti)イオンを含むマンガン-チタン系電解液が挙げられる(図2を参照)。その他、正極活物質及び負極活物質として、価数の異なるバナジウムイオンを含むバナジウム系電解液、正極活物質として鉄(Fe)イオン、負極活物質としてクロム(Cr)イオンを含む鉄-クロム系電解液等が挙げられる。電解液は、活物質に加えて、硫酸、リン酸、硝酸、塩酸から選択される少なくとも1種の酸又は酸塩を含む水溶液等を利用できる。正極電解液及び負極電解液は、酸化還元電位が0.9V以上の活物質を含有することが好ましい。活物質の酸化還元電位が0.9V以上であれば、高い起電力を有するRF電池1を構築することができる。高い起電力を有するRF電池1では、充放電に伴う副反応によって正極電極12(図2)が酸化劣化し易いため、本実施形態のRF電池用の電極10を正極電極12に用いることによる効果をより発揮し易い。
実施形態のRF電池用の電極10は、RF電池1の電極に好適に利用できる。実施形態のRF電池1は、太陽光発電、風力発電等の自然エネルギーの発電に対して、発電出力の変動の安定化、発電電力の余剰時の蓄電、負荷平準化等を目的とした大容量の蓄電池に利用できる。また、実施形態のRF電池1は、一般的な発電所に併設されて、瞬低・停電対策や負荷平準化を目的とした大容量の蓄電池としても好適に利用できる。
炭素を含有する基材に穿孔を有する電極を作製し、経時的な変化としてセル抵抗率を調べた。
・試料No.1-1~1-6
炭素を含有する基材として、黒鉛化度R値が0.35の炭素繊維からなるカーボンペーパーを準備した。このカーボンペーパーは、繊維径(等面積円相当径):8μm、大きさ:30mm×30mm、厚み:0.2mm、空隙率:65体積%、目付量:120g/m2である。塗布液として、塩化鉄(II)四水和物を、鉄の濃度が試料No.1-1,1-3~1-6では1質量%、試料No.1-2では0.1質量%となるようにエタノールに溶解させたものを準備した。試料No.1-3~1-6に関しては、塗布液に表1に示す界面活性剤を0.5質量%添加した。この塗布液を上記基材にディップコーティング法にて塗布し、その後150℃で有機溶媒が除去されるまで乾燥した。その後、大気中で表1に示す熱処理条件にて焼成を施した。
試料No.1-1と同様の基材に酸化鉄ナノ粒子(平均粒径6nm)を塗布した後、大気中で650℃×1時間の焼成を施した。
塗布液として、塩化ジルコニウムを、ジルコニウムの濃度が1質量%となるようにエタノールに溶解させたものを準備した。この塗布液を試料No.1-1と同様の基材にディップコーティング法にて塗布し、150℃で有機溶媒が除去されるまで乾燥した後、大気中で650℃×1時間の焼成を施した。
塗布液として、CoSO4を、コバルトの濃度が1質量%となるように水に溶解させ、更にフッ素系界面活性剤を0.5質量%添加したものを準備した。この塗布液を試料No.1-1と同様の基材にディップコーティング法にて塗布し、150℃で溶媒が除去されるまで乾燥した後、大気中で650℃×1時間の焼成を施した。
塗布液として、塩化タングステンを、タングステンの濃度が1質量%となるようにエタノールに溶解させたものを準備した。この塗布液を試料No.1-1と同様の基材にディップコーティング法にて塗布し、150℃で有機溶媒が除去されるまで乾燥した後、大気中で650℃×1時間の焼成を施した。
基材として、試料No.1-1と同様の基材を準備した。試料No.1-100では、この基材に対して、塗布液の塗布及び塗布後の焼成は施していない。
基材として、試料No.1-1と同様の基材を準備した。試料No.1-111では、化学蒸着法(CVD法)により炭素繊維上にカーボンナノチューブを成長させた(大きさ50nm)。
基材として、試料No.1-1と同様の基材を準備した。試料No.1-112では、カーボンブラック粒子(大きさ35nm)をエタノール中に分散しバインダーとしてフッ素系樹脂の分散液を混合し、基材上に塗布・乾燥して付着させた。
試料No.1-1と同様の基材の表面にプラズマ親水化処理を施した。
得られた各試料の電極について、電極を構成する炭素繊維を、走査型電子顕微鏡(SEM)によって観察した。図3Aに、試料No.1-1の電極を構成する炭素繊維の表面のSEM写真(倍率12000倍)、及び図3Bに、炭素繊維の表面に観察された穿孔をその開口部のほぼ中心(図3Aの表面のSEM写真に示す一点鎖線部分)にて切断した横断面のSEM写真(倍率10000倍)を示す。炭素繊維の横断面は、炭素繊維を集束イオンビーム(FIB)加工して得られる。本例では、FIB加工する際に、炭素繊維上に白金(Pt)を被覆してから行っている。そのため、図3Bの横断面のSEM写真において、上側にPtの被膜が残存している。同様に、図4Aに、試料No.1-11の電極を構成する炭素繊維の表面のSEM写真(倍率12000倍)、及び図4Bに、炭素繊維の表面に観察された穿孔をその開口部のほぼ中心(図4Aの表面のSEM写真に示す一点鎖線部分)にて切断した横断面のSEM写真(倍率10000倍)を示す。図3A、図3B、図4A及び図4Bにより、いずれの試料の電極も、炭素繊維(基材)に表面から内部に向かって延びる穿孔を有することが確認できた。また、図3Bでは、穿孔の底部に金属酸化物を有することも確認できた。なお、試料No.1-2~1-7,1-21,1-31の電極も、炭素繊維(基材)に表面から内部に向かって延びる穿孔を有することが確認でき、底部に金属酸化物を有する穿孔も確認できた。
穿孔の径について、炭素繊維の表面上における開口部の等面積円相当径を調べた。穿孔は、電極の製造過程において、基材の表面上に生成された金属酸化物が熱処理によって基材の内部に侵食することで形成されたものである。そのため、穿孔の径は、炭素繊維の表面上における開口部の径が伸延方向に沿ってほぼ維持されると考えられる。本例では、炭素繊維の表面上における開口部の等面積円相当径は、SEM写真による表面観察によって求めた。複数の穿孔が接触している場合は、穿孔の径が判別できるのであればその径の値を採用し、穿孔同士の境界が区別できないのであれば両穿孔を合算して算出した値を採用した。炭素繊維の表面上における開口部の等面積円相当径をその穿孔の径として、表1に示す。
穿孔の深さについては、炭素繊維の横断面において、炭素繊維の重心を中心Cとし、穿孔の伸延方向に沿った軌跡のうち中心Cに最も近い部分を深さ点Aとして、中心Cと深さ点Aとを結ぶ直線上における炭素繊維の表面から深さ点Aまでの長さDとする(図1の下図を参照)。本例では、穿孔の深さは、FIB加工により穿孔付近の横断面を採取し、SEM写真による表面観察によって求めた。横断面内に複数の穿孔を有する場合、最も深い長さDを採用した(例えば、図3B及び図4Bでは、断面のSEM写真に示す両矢印を付した穿孔を採用した)。上記長さDをその穿孔の深さとして、表1に示す。
・静電容量
上述した各試料の電極について、イオン溶液として6M(モル濃度)の硫酸水溶液を準備し、構築したRF電池の電池セルに上記イオン溶液を供給し、電極がイオン溶液に浸漬された状態を維持して、サイクリックボルタンメトリーによって電極の静電容量(F/g)を測定した。静電容量の測定は、市販の測定装置を利用し、作用電極と対電極との間で-0.2Vから0.2Vの範囲を20mV/sで繰り返し電子走査を行い、電極重量から静電容量を算出した。その結果を表1に示す。
正極電極と、負極電極と、隔膜とを用いて、単セル構造のRF電池を作製した。正極電極には、上述した各試料の電極を2枚積層したものを用いた。負極電極には、黒鉛化度R値が1.5の炭素繊維からなるカーボンペーパーを2枚積層したものを用いた。負極電極に用いたカーボンペーパーは、繊維径(等面積円相当径):10μm、大きさ:30mm×30mm、厚み:0.1mm、空隙率:70体積%、目付量:56g/m2である。電解液は、正極電解液として活物質にマンガンイオン、負極電解液として活物質にチタンイオンを含むマンガン-チタン系電解液を用いた。各試料は、単セル構造のRF電池としたため、RF電池の内部抵抗は、セル抵抗率として表す。各試料について、電池セルに電流密度:70mA/cm2の定電流で充放電を行った。この試験では、予め設定した所定の切替電圧に達したら、充電から放電に切り替え、複数サイクルの充放電を行った。各サイクルの充放電後、各試料についてセル抵抗率(Ω・cm2)を求めた。セル抵抗率は、複数サイクルのうち、任意の1サイクルにおける充電時平均電圧及び放電時平均電圧を求め、{(充電時平均電圧と放電時平均電圧の差)/(平均電流/2)}×セル有効面積とした。電解液に浸漬開始直後(浸漬日数0日)の電極におけるセル抵抗率を初期セル抵抗率として、表1に示す。
RF電池のセル抵抗率の経時的な増加率を調べた。表2に、各試料について、表1に示す初期のセル抵抗率を基準(1.00)とし、7日後及び14日後における各セル抵抗率の増加率を示す。
100 電池セル
11 隔膜
10 電極
110 基材
112,112a,112b,112c,112d 穿孔
112o 開口部
120 金属酸化物
12 正極電極 14 負極電極
140 正極タンク 150 負極タンク
142,144,152,154 配管
146,156 ポンプ
Claims (7)
- 炭素を含有する基材の集合体で構成されるレドックスフロー電池用電極であって、
前記基材の横断面において、前記基材の重心を中心とし、前記基材の等面積円相当径の95%の直径を有する円を基準円とするとき、
前記基材は、表面から内部に向かって延びると共に、その伸延方向に沿った軌跡の一部が前記基準円内に存在する複数の穿孔を備えるレドックスフロー電池用電極。 - 前記基材は、等面積円相当径が3μm以上100μm以下の前記横断面を有する炭素繊維を含む請求項1に記載のレドックスフロー電池用電極。
- 前記複数の穿孔の少なくとも一部は、前記基材の表面上における開口部の等面積円相当径が50nm以上2000nm以下である請求項1又は請求項2に記載のレドックスフロー電池用電極。
- BET比表面積が0.1m2/g以上である請求項1から請求項3のいずれか1項に記載のレドックスフロー電池用電極。
- 静電容量が0.05F/g以上である請求項1から請求項4のいずれか1項に記載のレドックスフロー電池用電極。
- 前記複数の穿孔の少なくとも一部は、その底部に金属酸化物を有する請求項1から請求項5のいずれか1項に記載のレドックスフロー電池用電極。
- 正極電極と、負極電極と、前記正極電極と前記負極電極との間に介在される隔膜とを備える電池セルに正極電解液及び負極電解液を供給して充放電を行うレドックスフロー電池であって、
前記正極電極は、請求項1から請求項6のいずれか1項に記載のレドックスフロー電池用電極であるレドックスフロー電池。
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WO2024075439A1 (ja) * | 2022-10-06 | 2024-04-11 | 住友電気工業株式会社 | レドックスフロー電池用電極、レドックスフロー電池セル、およびレドックスフロー電池システム |
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- 2017-11-15 US US16/482,521 patent/US11139481B2/en active Active
- 2017-11-15 AU AU2017396673A patent/AU2017396673A1/en not_active Abandoned
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See also references of EP3579316A4 |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2021108241A1 (en) * | 2019-11-26 | 2021-06-03 | The Government Of The United States Of America, As Represented By The Secretary Of The Navy | Borosulfate proton conducting materials |
US11296346B2 (en) | 2019-11-26 | 2022-04-05 | The Government Of The United States Of America, As Represented By The Secretary Of The Navy | Borosulfate proton conducting materials |
WO2021177137A1 (ja) * | 2020-03-02 | 2021-09-10 | 住友電気工業株式会社 | 電極、レドックスフロー電池、及び電極の製造方法 |
WO2024075439A1 (ja) * | 2022-10-06 | 2024-04-11 | 住友電気工業株式会社 | レドックスフロー電池用電極、レドックスフロー電池セル、およびレドックスフロー電池システム |
Also Published As
Publication number | Publication date |
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JP6955708B2 (ja) | 2021-10-27 |
US20200403248A1 (en) | 2020-12-24 |
JPWO2018142716A1 (ja) | 2019-11-14 |
KR20190111926A (ko) | 2019-10-02 |
AU2017396673A1 (en) | 2019-08-22 |
CN110199423A (zh) | 2019-09-03 |
EP3579316A4 (en) | 2020-02-19 |
CN110199423B (zh) | 2022-06-14 |
EP3579316A1 (en) | 2019-12-11 |
TW201830759A (zh) | 2018-08-16 |
US11139481B2 (en) | 2021-10-05 |
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