Electrode, battery cell, and redox flow battery

Abstract

This electrode for a redox flow battery comprises a sheet-like base material and a catalyst supported on the base material, wherein: the base material is composed of a sintered body in which a plurality of particles containing titanium are bonded to each other; the catalyst contains a first oxide provided so as to cover at least some of the plurality of particles; the first oxide contains ruthenium and at least one first element selected from the group consisting of tungsten, molybdenum, cerium, neodymium, and vanadium; and the contents of iridium and palladium contained in the catalyst per 1 m2 of the area of the electrode are each at most 1 g.

Description

Electrodes, battery cells, and redox flow batteries

[0001] The present disclosure relates to an electrode, a battery cell, and a redox flow battery. This application claims priority to Japanese Patent Application No. 2022-093332, filed on June 8, 2022. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] Patent Documents 1 and 2 disclose electrodes for redox flow batteries. These electrodes have a catalyst supported on a substrate. The catalyst is a metal oxide. The metal oxide that functions as a catalyst contains a metal element such as ruthenium, iridium, or palladium.

[0003] JP 2017-143002 A JP 2019-164882 A

[0004] The electrode of the present disclosure is an electrode for a redox flow battery, comprising: a sheet-like substrate; and a catalyst supported on the substrate; the substrate is made of a sintered body in which a plurality of particles containing titanium are bonded to one another; the catalyst includes a first oxide provided so as to cover at least a portion of the plurality of particles; the first oxide is an oxide containing ruthenium and at least one first element selected from the group consisting of tungsten, molybdenum, cerium, neodymium, and vanadium; and the electrode has an area of ​​1 m ２ The content of iridium and the content of palladium contained in the catalyst are each 1 g or less per unit area.

[0005] The battery cell of the present disclosure is a redox flow battery cell including a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode is an electrode of the present disclosure.

[0006] The redox flow battery of the present disclosure comprises the battery cell of the present disclosure.

[0007] Fig. 1 is a schematic diagram showing an electrode according to an embodiment. Fig. 2 is a schematic cross-sectional view showing an enlarged view of the inside of a portion surrounded by a dashed line in Fig. 1. Fig. 3 is an enlarged cross-sectional view showing a further enlarged view of Fig. 2. Fig. 4 is a schematic diagram showing the configuration of a redox flow battery according to an embodiment.

[0008] [Problem to be Solved by the Present Disclosure] In redox flow batteries, an electrode carrying a catalyst can activate the oxidation-reduction reaction at the electrode and improve the battery reactivity with the electrolyte. There is a demand for reducing the cost of electrodes for redox flow batteries. Electrodes containing iridium oxide or palladium oxide as a catalyst promote charge and discharge reactions at the electrode. However, using iridium oxide or palladium oxide as an electrode catalyst increases the cost of the electrode. It is necessary to increase the battery reactivity of the catalyst while minimizing the amount of iridium and palladium used.

[0009] An object of the present disclosure is to provide an electrode having high battery reactivity at low cost. Another object of the present disclosure is to provide a battery cell and a redox flow battery having low cell resistivity. [Advantages of the present disclosure]

[0010] The electrodes disclosed herein have low cost and high battery reactivity. The battery cells and redox flow batteries disclosed herein have low cell resistivity.

[0011] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0012] (1) An electrode according to an embodiment of the present disclosure is an electrode for a redox flow battery, comprising: a sheet-like substrate; and a catalyst supported on the substrate; the substrate is made of a sintered body in which a plurality of particles containing titanium are bonded to each other; the catalyst includes a first oxide provided so as to cover at least a portion of the plurality of particles; the first oxide is an oxide containing ruthenium and at least one first element selected from the group consisting of tungsten, molybdenum, cerium, neodymium, and vanadium; and the electrode has an area of ​​1 m ２The content of iridium and the content of palladium contained in the catalyst are each 1 g or less per unit area.

[0013] The electrode of the present disclosure has a catalyst supported on the substrate, thereby improving the battery reactivity with the electrolyte compared to an electrode without the catalyst. The catalyst can function as both an oxidation catalyst and a reduction catalyst by including a first oxide. An electrode with such a catalyst has high battery reactivity because charge and discharge reactions in the electrode are promoted. Therefore, the electrode of the present disclosure can reduce cell resistivity.

[0014] In the electrode of the present disclosure, the catalyst contains a low content of iridium and palladium, or the catalyst does not contain iridium or palladium, and therefore the electrode of the present disclosure is low in cost.

[0015] (2) In the electrode of (1) above, the first oxide may contain at least one element selected from the group consisting of tin, antimony, and titanium.

[0016] According to the above configuration (2), it may be possible to enhance the catalytic function and to prevent the catalyst from falling off the substrate.

[0017] (3) The electrode of (1) or (2) may further include an intermediate layer between the particle and the catalyst, the intermediate layer including a second oxide, the second oxide including at least one element selected from the group consisting of ruthenium, tin, antimony, titanium, tungsten, and molybdenum, and the number of types of metal elements included in the second oxide being smaller than the number of types of metal elements included in the first oxide.

[0018] The electrode having the intermediate layer can prevent the catalyst from falling off the substrate and can provide good electrical connection between the substrate and the catalyst.

[0019] (4) In the electrode according to any one of (1) to (3), the first oxide may have a larger number of moles of ruthenium than the total number of moles of the first element.

[0020] According to the above configuration (4), the catalyst can have both the functions of an oxidation catalyst and a reduction catalyst in a balanced manner.

[0021] (5) In the electrode of any one of (1) to (4) above, the porosity of the electrode may be 40% by volume or more and 75% by volume or less.

[0022] An electrode having a porosity of 40% by volume or more allows the electrolyte to flow easily through the electrode, and an electrode having a porosity of 75% by volume or less has a large true volume excluding the voids, allowing for sufficient battery reaction.

[0023] (6) In any of the electrodes (1) to (5), the area of ​​the electrode is 1 m ２ the content of ruthenium contained in the catalyst is 0.1 g or more and 90.0 g or less per 1 m of the area of ​​the electrode; ２ The total content of the first element contained in the catalyst per unit area may be 0.1 g or more and 50.0 g or less.

[0024] According to the above configuration (6), the effect of improving the cell reactivity by the catalyst is enhanced.

[0025] (7) In the electrode of any one of (1) to (6) above, the electrode may have a tensile strength of 4.0 MPa or more and 16.0 MPa or less.

[0026] When the tensile strength of the electrode satisfies the above range, the electrode is less likely to deform excessively or break, has high handleability, and is less likely to be damaged when incorporated into a battery cell due to moderate deformation.

[0027] (8) In the electrode of any one of (1) to (7) above, the electrode may have a flexural modulus of elasticity of 0.25 GPa or more and 3.0 GPa or less.

[0028] When the flexural modulus of the electrode satisfies the above range, the electrode is less likely to deform excessively or break, has high handleability, and is less likely to be damaged when incorporated into a battery cell due to moderate deformation.

[0029] (9) A battery cell according to an embodiment of the present disclosure is a battery cell of a redox flow battery including a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode according to any one of (1) to (8) above.

[0030] The battery cell of the present disclosure has a low cell resistivity, which can improve the charge and discharge efficiency of the redox flow battery.

[0031] (10) Furthermore, a battery cell according to another embodiment of the present disclosure is a battery cell of a redox flow battery including a positive electrode and a negative electrode, wherein one of the positive electrode and the negative electrode is the electrode described in any one of (1) to (8) above, and the other of the positive electrode and the negative electrode includes a substrate made of an aggregate of a plurality of carbon fibers.

[0032] The configuration (10) above provides excellent battery cell assembly. An electrode having a substrate made of an aggregate of carbon fibers has higher flexibility than the electrode of the present disclosure having a substrate made of the sintered body. Therefore, when the positive electrode and the negative electrode are assembled into a battery cell, the other electrode undergoes compressive deformation, facilitating assembly of the battery cell.

[0033] (11) A redox flow battery according to an embodiment of the present disclosure includes the battery cell according to (9) or (10) above.

[0034] The redox flow battery has a low cell resistivity and, since it includes the battery cell, has high charge efficiency and discharge efficiency.

[0035] [Details of the embodiments of the present disclosure] Specific examples of electrodes, battery cells, and redox flow batteries according to embodiments of the present disclosure will be described below with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts. Hereinafter, redox flow batteries may be referred to as "RF batteries." Note that the present invention is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0036] First, the basic configuration of the RF battery 1 of the embodiment will be described with reference to Fig. 4. Next, the electrode 10 of the embodiment will be described in detail with reference to Figs.

[0037] <RF Battery> The RF battery 1 is a storage battery that is charged and discharged by utilizing the oxidation-reduction reaction of ions in an electrolyte solution circulated through the battery cell 100. In the RF battery 1, the positive electrode electrolyte solution and the negative electrode electrolyte solution contain, as active materials, ions whose valence changes due to oxidation-reduction. The electrolyte solution is, for example, a vanadium-based electrolyte solution or a titanium-manganese-based electrolyte solution. In the vanadium-based electrolyte solution, both the positive electrode electrolyte solution and the negative electrode electrolyte solution contain vanadium (V) ions. In the titanium-manganese-based electrolyte solution, the positive electrode electrolyte solution contains manganese (Mn) ions, and the negative electrode electrolyte solution contains titanium (Ti) ions.

[0038] The RF battery 1 is typically connected to a power generation unit 8 and a load 9 via an AC / DC converter 7 and a transformer 71. The RF battery 1 can be charged with power generated by the power generation unit 8 and can discharge the charged power to the load 9. The power generation unit 8 is a power generation facility that uses natural energy such as solar power generation or wind power generation, or other general power plants. The RF battery 1 is used, for example, for load leveling, momentary sag compensation, emergency power supply, and output smoothing of natural energy power generation.

[0039] The RF battery 1 includes a battery cell 100, tanks 106 and 107 that store electrolyte, and a circulation flow path that circulates the electrolyte between each of the tanks 106 and 107 and the battery cell 100. A positive electrode electrolyte is stored in the tank 106. A negative electrode electrolyte is stored in the tank 107. The RF battery 1 can be configured in any known manner as appropriate.

[0040] <Battery Cell> The battery cell 100 includes a positive electrode 104, a negative electrode 105, and a diaphragm 101. The diaphragm 101 is disposed between the positive electrode 104 and the negative electrode 105. The battery cell 100 is separated into a positive electrode cell 102 and a negative electrode cell 103 by the diaphragm 101. The positive electrode 104 is disposed in the positive electrode cell 102. The negative electrode 105 is disposed in the negative electrode cell 103. A positive electrode electrolyte is supplied to the positive electrode cell 102. A negative electrode electrolyte is supplied to the negative electrode cell 103. The positive electrode 104 and the negative electrode 105 are reaction fields where ions contained in the supplied electrolytes undergo a battery reaction. The positive electrode 104 and the negative electrode 105 are formed, for example, from a sheet-like porous body.

[0041] In this example, a circulation flow path for the positive electrode electrolyte is formed by pipes 108 and 110 connecting the battery cell 100 and the tank 106. A pump 112 is provided in the pipe 108. The positive electrode electrolyte is supplied from the tank 106 to the positive electrode cell 102 through the pipe 108 by the pump 112. The positive electrode electrolyte, which has passed through the positive electrode cell 102 and is discharged from the positive electrode cell 102, is returned to the tank 106 through the pipe 110. In this example, a circulation flow path for the negative electrode electrolyte is formed by pipes 109 and 111 connecting the battery cell 100 and the tank 107. A pump 113 is provided in the pipe 109. The negative electrode electrolyte is supplied from the tank 107 through the pipe 109 by the pump 113 to the negative electrode cell 103. The negative electrode electrolyte, which has passed through the negative electrode cell 103 and is discharged from the negative electrode cell 103, is returned to the tank 107 through the pipe 111.

[0042] The RF battery 1 may be configured to include a single battery cell 100 or multiple battery cells 100. As shown in FIG. 4 , the RF battery 1 of this example includes a cell stack 200 in which multiple battery cells 100 are stacked. The cell stack 200 is configured by repeatedly stacking a cell frame 120, a positive electrode 104, a diaphragm 101, and a negative electrode 105 in this order. End plates 210 are arranged on both ends of the cell stack 200. The cell stack 200 is integrated by clamping the end plates 210 together with clamping members 230. The cell stack 200 can be configured in a known manner as appropriate.

[0043] The cell frame 120 has a bipolar plate 121 and a frame body 122. The bipolar plate 121 is disposed between the positive electrode 104 and the negative electrode 105. The frame body 122 is provided around the bipolar plate 121. Inside the frame body 122, a recess is formed by the bipolar plate 121 and the frame body 122. The recesses are provided on both sides of the bipolar plate 121. The positive electrode 104 and the negative electrode 105 are housed in each recess, with the bipolar plate 121 sandwiched between them.

[0044] As shown in Figure 4, a single battery cell 100 is formed by arranging a positive electrode 104 and a negative electrode 105 between the bipolar plates 121 of adjacent cell frames 120 with a diaphragm 101 sandwiched between them. An annular sealing member 127, for example, is arranged between the frames 122 of each cell frame 120. The number of stacked battery cells 100 in the cell stack 200 can be selected as appropriate.

[0045] Although not shown, the frame 122 has a liquid supply manifold for supplying each electrolyte solution and a liquid discharge manifold for discharging each electrolyte solution. Each manifold is provided to penetrate the frame 122, and a flow path for each electrolyte solution is formed by stacking the cell frames 120. Each of these flow paths is connected to each of the pipes 108, 109, 110, and 111.

[0046] <Electrode> An electrode 10 for an RF battery according to an embodiment includes a substrate 20, as shown in FIG. 1. The substrate 20 is made of a sintered body. This sintered body is an aggregate of a plurality of particles 21, as shown in FIG. 2. The electrode 10 includes a catalyst 30 supported on the substrate 20, as shown in FIG. 3. FIG. 1 is an overall view of the electrode 10. FIG. 2 is an enlarged cross-sectional view schematically showing the area surrounded by the dashed dotted line in FIG. 1. FIG. 3 is an enlarged cross-sectional view schematically showing a further enlargement of FIG. 2. The electrode 10 has improved battery reactivity due to the catalyst 30 being supported on the substrate 20. The electrode 10 according to this embodiment has a specific oxide in the catalyst 30, thereby enabling increased battery reactivity at low cost.

[0047] <Thickness> The electrode 10 is a sheet-like porous body. The thickness of the electrode 10 is, for example, 0.1 mm or more and 5.0 mm or less. When the thickness of the electrode 10 is 0.1 mm or more, it is easy to ensure a contact area with the electrolyte, i.e., a reaction area, and sufficient battery reaction can occur. When the thickness of the electrode 10 is 5.0 mm or less, the battery cell can be made thin. The thickness here refers to the thickness of the electrode 10 in its natural state when no external force is acting on it. The thickness of the electrode 10 may further be 0.2 mm or more and 2.5 mm or less, or 0.3 mm or more and 2.0 mm or less.

[0048] <Porosity> The porosity of the electrode 10 is, for example, 40% by volume or more and 75% by volume or less. When the porosity of the electrode 10 is 40% by volume or more, the electrolyte can easily flow through the electrode 10. When the porosity of the electrode 10 is 75% by volume or less, the true volume of the electrode 10 is large, enabling current collection with low electrical resistance. Therefore, if the porosity of the electrode 10 is 75% by volume or less, a sufficient battery reaction can be performed. Furthermore, if the porosity of the electrode 10 is 75% by volume or less, the mechanical properties of the electrode 10 can be easily ensured. The porosity of the electrode 10 may further be 50% by volume or more and 70% by volume or less, particularly 55% by volume or more and 65% by volume or less. The porosity is a value expressed as a percentage, calculated by [1 - {W / (ρ × Va)}]. ρ is the true density of the material constituting the electrode 10. W is the mass of the electrode 10. Va is the apparent volume of the electrode 10. The apparent volume includes voids.

[0049] <Mechanical Properties> The electrode 10 preferably has high mechanical properties such as strength and rigidity. An electrode 10 with high mechanical properties is less likely to deform or crack excessively, and therefore has high handleability. Examples of mechanical properties include tensile strength, tensile modulus, flexural strength, and flexural modulus.

[0050] The tensile strength of the electrode 10 is, for example, 4.0 MPa or more and 16.0 MPa or less. When the tensile strength of the electrode 10 is 4.0 MPa or more, the electrode 10 has high mechanical properties. When the tensile strength of the electrode 10 is 16.0 MPa or less, the electrode 10 undergoes moderate deformation when incorporated into the battery cell 100 (see FIG. 4 ), making the electrode 10 less likely to be damaged. The tensile strength of the electrode 10 may further be 5.0 MPa or more and 13.0 MPa or less. The tensile modulus of the electrode 10 is, for example, 1.0 GPa or more and 4.0 GPa or less. When the tensile modulus of the electrode 10 is 1.0 GPa or more, the electrode 10 has high mechanical properties. When the tensile modulus of the electrode 10 is 4.0 GPa or less, the electrode 10 undergoes moderate deformation when incorporated into the battery cell 100, making the electrode 10 less likely to be damaged. The tensile modulus of the electrode 10 may further be 1.5 GPa or more and 3.5 GPa or less.

[0051] The bending strength of the electrode 10 is, for example, 3.0 MPa or more and 30.0 MPa or less. When the bending strength of the electrode 10 is 3.0 MPa or more, the electrode 10 has high mechanical properties. When the bending strength of the electrode 10 is 30.0 MPa or less, the electrode 10 deforms appropriately when incorporated into the battery cell 100, making the electrode 10 less likely to be damaged. The bending strength of the electrode 10 may further be 10.0 MPa or more and 20.0 MPa or less. The bending modulus of the electrode 10 is, for example, 0.25 GPa or more and 3.0 GPa or less. When the bending modulus of the electrode 10 is 0.25 GPa or more, the electrode 10 has high mechanical properties. When the bending modulus of the electrode 10 is 3.0 GPa or less, the electrode 10 deforms appropriately when incorporated into the battery cell 100, making the electrode 10 less likely to be damaged. The bending modulus of the electrode 10 may further be 1.0 GPa or more and 2.5 GPa or less.

[0052] (Substrate) The substrate 20 is a porous body that serves as the skeleton of the electrode 10. The substrate 20 has the electrical conductivity required for the electrode 10. In this embodiment, the substrate 20 is made of a sintered body of titanium (Ti). As shown in FIG. 2, the Ti sintered body that constitutes the substrate 20 is composed of a plurality of Ti-containing particles 21 bonded to one another. The sintered body has a three-dimensional network-like skeleton structure due to the plurality of particles 21 being bonded to one another. There are voids between the particles 21. The Ti-containing particles 21 are made of pure Ti or a Ti alloy. Pure Ti contains 99% by mass or more of Ti, with the remainder consisting of unavoidable impurities. Examples of Ti alloys include α-type Ti alloys, α+β-type Ti alloys, β-type Ti alloys, and corrosion-resistant Ti alloys.

[0053] <Thickness> The substrate 20 is in a sheet form. The thickness of the substrate 20 is substantially equal to the thickness of the electrode 10 described above.

[0054] <Porosity> The porosity of the substrate 20 is substantially equal to the porosity of the electrode 10 described above. Because the catalyst 30 is supported on the substrate 20 as shown in Fig. 3, strictly speaking, the porosity of the substrate 20 is slightly greater than the porosity of the electrode 10. Because the amount of catalyst 30 supported on the substrate 20 is small, the difference in porosity due to the presence or absence of the catalyst 30 can be ignored.

[0055] Area of ​​electrode 10: 1 m ２ The mass of the substrate 20 per unit area is, for example, 300 g or more and 3000 g or less. Here, the area of ​​the electrode 10 is the area when the electrode 10 is viewed in plan, that is, the projected area onto the electrode 10. When the mass of the substrate 20 per unit area is 300 g / m ２ When the mass of the substrate 20 per unit area is 3000 g / m or more, the true volume of the substrate 20 excluding the voids is increased, and it is easy to ensure electrical conductivity and mechanical properties. ２ By setting the thickness of the base material 20 to 400 g / m or less, it is possible to prevent the voids from becoming excessively small, and it is easy to ensure the flow of the electrolyte solution. ２ More than 2000g / m ２ The true volume of the substrate 20 is the mass of the substrate 20 divided by the density of the material that makes up the substrate 20.

[0056] <Average particle size of particles> The average particle size of the particles 21 is, for example, 3 μm or more and 500 μm or less. When the average particle size of the particles 21 is 3 μm or more, the particles 21 are easy to handle. When the average particle size of the particles 21 is 500 μm or less, the surface area of ​​the sintered body constituting the base material 20 can be increased, making it easy to ensure a reaction area. The average particle size of the particles 21 may further be 4 μm or more and 300 μm or less, or 5 μm or more and 50 μm or less. Note that the particle size of the particles 21 is determined by the following equation: [2×(3Vp / 4π) １／３ The average value of these values ​​is the average particle size of the particles 21.

[0057] The average particle size of the particles 21 can be determined as follows: The cross section of the substrate 20 is observed with a scanning electron microscope (SEM). The size of the observation field is preferably set so that 50 or more particles 21 are included within the observation field. The particle sizes of all particles 21 within the observation field are measured. The particle size of a particle 21 is defined as the diameter of a circle having an area equal to the cross-sectional area of ​​the particle 21. The cross-sectional area of ​​the particle 21 can be determined by image processing. The average value of the measured particle sizes of the particles 21 is considered to be the average particle size of the particles 21.

[0058] (Catalyst) The catalyst 30 is supported on the substrate 20. As shown in FIG. 3, the catalyst 30 is formed in a layer on the surface of the particles 21 so as to cover the particles 21 constituting the substrate 20. The catalyst 30 may be provided on at least some of the particles 21 shown in FIG. 2. The catalyst 30 may be provided on 80% or more of all the particles 21, or may be provided on all the particles 21. This ratio refers to the ratio of the number of particles 21 provided with the catalyst 30 to the total number of particles. In this embodiment, the catalyst 30 is provided on substantially all the particles 21. The catalyst 30 may be in direct contact with the surface of the particles 21, or may be provided on the surface of the particles 21 via an intermediate layer 40. The catalyst 30 has the function of activating the oxidation-reduction reaction in the electrode 10 and enhancing the battery reactivity with the electrolyte.

[0059] <Material> The catalyst 30 has a first oxide. The first oxide is an oxide containing ruthenium (Ru) and a first element. The first element is at least one selected from the group consisting of tungsten (W), molybdenum (Mo), cerium (Ce), neodymium (Nd), and vanadium (V). The first oxide is, for example, a composite oxide containing Ru and W, a composite oxide containing Ru and Mo, a composite oxide containing Ru and Ce, a composite oxide containing Ru and Nd, or a composite oxide containing Ru and V. The first oxide may contain multiple types of the first element. As a result of extensive research, the inventors have found that a composite oxide of Ru and the first element has excellent functionality as the catalyst 30. Such a composite oxide functions as both an oxidation catalyst and a reduction catalyst. The catalyst 30 functions as both an oxidation catalyst and a reduction catalyst, thereby accelerating the charge and discharge reactions at the electrode 10. Generally, an oxide containing Ru but not the first element functions as an oxidation catalyst but is inferior in function as a reduction catalyst. It is believed that the composite of Ru and the first element improves the function as a reduction catalyst.

[0060] The first oxide may further contain at least one element selected from the group consisting of tin (Sn), antimony (Sb), and titanium (Ti). When the first oxide contains at least one element selected from Sn, Sb, and Ti, it may be possible to enhance the catalytic function and to prevent the catalyst from falling off the substrate.

[0061] <Molar Ratio of Ru> The first oxide may have a larger number of moles of Ru than the total number of moles of the first elements. That is, the molar ratio of Ru to the total number of first elements may be greater than 1. A large molar ratio of Ru to the total number of first elements can provide a balanced combination of both oxidation catalyst and reduction catalyst functions. The molar ratio of Ru to the total number of first elements may be, for example, 5 to 40, or even 10 to 25. When the total of all metal elements contained in the first oxide is 100 mol%, the Ru content is, for example, 50 mol% to 80 mol%, or even 55 mol% to 75 mol%. The total content of the first elements is, for example, 2 mol% to 40 mol%, or even 2 mol% to 10 mol%.

[0062] <Ru content> Area of ​​electrode 10 1 m ２ The content of Ru contained in the catalyst 30 per unit area may be 0.1 g or more and 90.0 g or less, and the total content of the first elements contained in the catalyst 30 may be 0.1 g or more and 50.0 g or less. When the content of Ru per unit area and the total content of the first elements each satisfy the above ranges, the effect of improving the cell reactivity by the catalyst 30 is enhanced. When the content of Ru and the total content of the first elements each satisfy the above ranges, an increase in the cost of the electrode 10 can be suppressed. The content of Ru per unit area may be further reduced to 0.1 g / m or less. ２ 40.0g / m or more ２ Below, 0.1g / m ２ 30.0g / m or more ２ The total content of the first element per unit area may be 0.1 g / m or less. ２ 10.0g / m or more ２ It may be the following:

[0063] Area of ​​electrode 10: 1 m ２ The mass of the catalyst 30 per unit area may be 1 g or more and 100 g or less. ２ When the mass of the catalyst 30 per unit area is 100 g / m or more, the catalyst 30 can fully function. ２By setting the mass of the catalyst 30 per unit area to 2 g / m or less, the content of the catalyst 30 is small, and the cost of the electrode 10 is reduced. ２ 80g / m or more ２ Below, 2g / m ２ 60g / m or more ２ It may be the following:

[0064] The catalyst 30 may contain an oxide other than the first oxide described above, and a metal element such as gold (Au) or platinum (Pt). The oxide other than the first oxide is, for example, an oxide containing Sn, Sb, Ti, or the like alone. The total content of Au and Pt per unit area is 1 g / m. ２ Au and Pt are expensive metals. The lower the Au content and Pt content, the more cost-effective the result. The Au content and Pt content per unit area are each 0.5 g / m or less. ２ Below that, further 0.1 g / m ２ Hereinafter, it may be zero, in particular. In other words, the electrode 10 may not contain Au and Pt. The proportion of the first oxide contained in the catalyst 30 may be 60 mass % or more, or even 80 mass % or more. The proportion of the first oxide may be 100 mass %. In other words, the catalyst 30 may be composed only of the first oxide.

[0065] <Ir content, Pd content> Area of ​​electrode 10 1 m ２ The content of iridium (Ir) and the content of palladium (Pd) contained in the catalyst 30 per unit area are each 1 g or less. ２ The cost of the electrode 10 is reduced by making the total content of Ir and Pd per unit area equal to or less than 1 g / m. ２ The lower the Ir content and Pd content per unit area, the greater the cost reduction effect. The Ir content and Pd content per unit area are each 0.5 g / m or less. ２ Below that, further 0.1 g / m ２ Hereinafter, it may be zero, in particular. In other words, the electrode 10 may not contain Ir and Pd.

[0066] (Intermediate Layer) As shown in Fig. 3, the electrode 10 may include an intermediate layer 40 between the particles 21 constituting the substrate 20 and the catalyst 30. The intermediate layer 40 is provided so as to cover the particles 21. The intermediate layer 40 is in direct contact with the surfaces of the particles 21. The catalyst 30 is supported on the particles 21 via the intermediate layer 40. The intermediate layer 40 has the function of preventing the catalyst 30 from falling off the particles 21 and electrically connecting the particles 21 and the catalyst 30.

[0067] <Material> The intermediate layer 40 includes a second oxide. The second oxide is an oxide containing at least one element selected from the group consisting of Ru, Sn, Sb, Ti, W, and Mo. The second oxide containing such a specific metal element can function as the intermediate layer 40.

[0068] The metal element contained in the second oxide may contain one or more elements of the same type as the metal element contained in the first oxide constituting the catalyst 30. When the second oxide and the first oxide contain the same type of metal element, the metal elements of the same type are bonded to each other at the interface between the intermediate layer 40 and the catalyst 30. This improves adhesion between the intermediate layer 40 and the catalyst 30 and also improves electrical conductivity between the intermediate layer 40 and the catalyst 30. Furthermore, at the interface between the particles 21 and the intermediate layer 40, oxygen (O) in the second oxide diffuses into and bonds with Ti constituting the particles 21. This improves adhesion between the particles 21 and the intermediate layer 40 and improves electrical conductivity between the particles 21 and the intermediate layer 40. Therefore, when the second oxide and the first oxide contain the same type of metal element, the catalyst 30 is less likely to fall off the particles 21 and good electrical connection can be achieved between the particles 21 and the catalyst 30. The second oxide may contain at least one of Ru, Sn, and Ti from the above-mentioned group of elements, and may particularly contain Ru. When the second oxide contains Ru, the first oxide also contains Ru, which effectively improves the adhesion between the intermediate layer 40 and the catalyst 30. When the second oxide contains Sn, Sn easily diffuses into Ti constituting the particles 21, which effectively improves the adhesion between the particles 21 and the intermediate layer 40. When the second oxide contains Ti, Ti in the second oxide bonds with Ti constituting the particles 21, which effectively improves the adhesion between the particles 21 and the intermediate layer 40.

[0069] Since the intermediate layer 40 electrically connects the particles 21 and the catalyst 30, it is required that the intermediate layer 40 have higher conductivity than the catalyst 30. In other words, the electrical resistivity of the intermediate layer 40 may be lower than that of the catalyst 30. To increase the conductivity of the intermediate layer 40, the number of types of metal elements contained in the second oxide may be smaller than the number of types of metal elements contained in the first oxide constituting the catalyst 30. The fewer the number of types of metal elements contained in the second oxide, the higher the conductivity of the second oxide. Therefore, the electrical resistivity of the intermediate layer 40 is reduced. Furthermore, if the metal element contained in the second oxide has high conductivity among the above group of elements, the electrical resistivity of the intermediate layer 40 is reduced. The lower the electrical resistivity of the intermediate layer 40, the lower the resistance with which the particles 21 and the catalyst 30 can be connected. The number of types of metal elements contained in the second oxide may be three or less, or even two or less. The number of types of metal elements contained in the second oxide may be one.

[0070] The thickness of the intermediate layer 40 may be thinner than the thickness of the catalyst 30. ２ The mass of the intermediate layer 40 per unit area may be 1 g or more and 40 g or less. ２ When the mass of the intermediate layer 40 per unit area is 40 g / m or more, the intermediate layer 40 can fully exhibit its function. ２ By setting the mass of the intermediate layer 40 to 1.5 g / m or less, the content of the intermediate layer 40 is small, and the cost of the electrode 10 is reduced. ２ 35g / m or more ２ It may be the following:

[0071] As a result of intensive research, the inventors have found that by providing the catalyst 30 on the intermediate layer 40, the effect of improving the cell reactivity can be sufficiently exhibited even with a small amount of catalyst 30. Therefore, when the electrode 10 includes the intermediate layer 40, the content of the catalyst 30 can be reduced compared to when the electrode 10 does not include the intermediate layer 40. For example, when the mass of the catalyst 30 per unit area is 60 g / m, ２ Below, 50 g / m ２ It may be the following:

[0072] The electrode 10 for an RF battery of this embodiment can be used for both the positive electrode 104 and the negative electrode 105 of the RF battery 1. The electrode 10 is particularly preferably used for the positive electrode 104. If the electrode 10 is used for the negative electrode 105, the Ti sintered body constituting the substrate 20 may be deteriorated by contact with the negative electrode electrolyte. Furthermore, in the battery cell 100, when one of the positive electrode 104 and the negative electrode 105 is the electrode 10 of this embodiment, the other may be an electrode having a substrate made of an aggregate of multiple carbon fibers. The carbon fiber aggregate is formed by multiple carbon fibers entangled with each other. The carbon fiber aggregate is typically carbon felt. An electrode having a substrate made of an aggregate of carbon fibers has higher flexibility than an electrode 10 having a substrate 20 made of a sintered Ti body. Therefore, when the positive electrode 104 and the negative electrode 105 are assembled into the battery cell 100, the electrodes having a base material made of an aggregate of carbon fibers undergo compressive deformation, making it easy to assemble the battery cell 100.

[0073] <Method for Manufacturing Electrode> The above-described electrode 10 can be manufactured as follows. A substrate 20, a first solution, and a second solution are prepared. The first solution contains metal elements that constitute a first oxide that will become the catalyst 30. The second solution contains metal elements that constitute a second oxide that will become the intermediate layer 40. The second solution is applied to the substrate 20 and a heat treatment is performed, thereby forming the intermediate layer 40 on the substrate 20. After forming the intermediate layer 40, the first solution is applied to the substrate 20 and a heat treatment is performed, thereby forming the catalyst 30 on the substrate 20. The method for manufacturing the electrode 10 will be described in detail below.

[0074] (Preparation of the substrate) A sintered body of Ti is prepared as the substrate 20. The size and shape of this sintered body may be selected appropriately to obtain the size and shape of the desired electrode 10. The substrate 20 can be produced as follows. Ti powder is filled into a mold to produce a compact. The Ti powder is composed of particles 21 containing Ti. By sintering this compact, the substrate 20 is produced as a sintered body in which multiple particles 21 are bonded to each other. The sintering temperature is, for example, 800°C or higher and 1500°C or lower. The holding time at the sintering temperature is, for example, 30 minutes or higher and 3 hours or lower. The higher the sintering temperature, the stronger the sintered body tends to be.

[0075] (Preparation of Solutions) The first solution contains raw materials of metal elements constituting the first oxide and an organic solvent. The second solution contains raw materials of metal elements constituting the second oxide and an organic solvent. The raw materials of the metal elements include organic compounds, chlorides, metal alkoxides, acetates, etc.

[0076] Examples of Ru raw materials include ruthenium(III) chloride hydrate, ruthenium(III) nitrate, ruthenium(IV) oxide hydrate, ruthenium(III) acetate, tris(acetylacetonato)ruthenium(III), and hexaammineruthenium(III) chloride. Examples of W raw materials include tungsten(VI) ethoxide, tungsten(VI) phenoxide, bis(cyclopentadienyl)tungsten(IV) dichloride, hexacarbonyltungsten, and tungsten chloride. Examples of Mo raw materials include molybdenum(V) ethoxide, bis(acetylacetonato)molybdenum(IV) oxide, molybdenum(II) acetate, molybdenum(II) acetate dimer, carbonylmolybdenum, molybdenum 2-ethylhexanoate, and molybdenum(V) chloride. Examples of Ce raw materials include cerium(III) nitrate, cerium(III) chloride, cerium(III) chloride heptahydrate, cerium(IV)-i-propoxide, cerium(IV)-methoxyethoxide, cerium(III)-t-butoxide, and cerium(III) 2-ethylhexanoate. Examples of Nd raw materials include neodymium(III) isopropoxide, neodymium(III) 2,4-pentanedionate, neodymium(III) trifluoroacetylacetonate, neodymium nitrate hexahydrate, neodymium acetate monohydrate, neodymium chloride monohydrate, neodymium chloride hexahydrate, neodymium fluoride, and neodymium(III) 2-ethylhexanoate. Examples of V raw materials include acetylacetonato vanadium(III), vanadium(IV) bis(acetylacetonate) oxide, vanadium(V) oxide trichloride, vanadium(IV) oxide bis(2,4-pentanedionate), vanadium(V) oxide trifluoride, vanadium(III) chloride, vanadium(V) triisopropoxy oxide, vanadium(III) fluoride, vanadium(III) bromide, vanadyl(V) chloride, vanadyl oxalate n-hydrate, bis(cyclopentadienyl)vanadium dichloride, cyclopentadienylvanadium tetracarbonyl, and vanadium 2-ethylhexanoate.

[0077] Examples of Sn raw materials include tin tetrachloride, tin(IV) chloride pentahydrate, tin(II) chloride, tin(II) chloride dihydrate, tin(II) bis(2-ethylhexanoate), tin(II) bis(neodecanoate), n-butyltin(IV) trichloride, dibutyltin bis(acetylacetonate), di-n-butyl-di-n-butoxidetin(IV), tin(IV)-n-butoxide, tin(IV)-t-butoxide, tetramethyltin, tin(II) acetate, and tin(IV) acetate. Examples of Sb raw materials include tri-i-propoxyantimony, tri-n-propoxyantimony, tri-n-butoxyantimony, tri-i-butoxyantimony, trimethoxyantimony, antimony (III) acetate, antimony trichloride, antimony pentachloride, antimony (III) methoxide, antimony (III) ethoxide, and antimony (III) butoxide. Examples of Ti raw materials include titanium tetrachloride, titanium(IV) ethoxide, titanium(IV)-n-butoxide, titanium(IV)-t-butoxide, titanium(IV)-i-propoxide, titanium(IV)-n-propoxide, titanium(IV) monochloride-i-tripropoxide, titanium(IV) methoxide, (bis-2,4-neodecanoic acid)-titanium(IV)-n-dibutoxide, titanium(IV) dichloride-diethoxide, (bis-2,4-pentanedionate)-titanium(IV)-i-dipropoxide, titanium(IV) 2-ethylhexanoate, titanium(IV) methylphenoxide, and titanium(IV)-n-stearylside.

[0078] Examples of organic solvents include trifluoroethanol, pentafluoropropanol, 2,2,3,3,4,4,4-heptafluoro-1-butanol, methanol, ethanol, propyl alcohol, isopropanol, butanol, pentanol, hexanol, 3-methoxy-3-methyl-1-butanol, acetonitrile, propylene carbonate, and ethylene carbonate. The organic solvent may be present in an amount of 70% by mass or more and 95% by mass or less relative to the entire solution. The solution may also contain a stabilizer, if necessary. Examples of the stabilizer include acetylacetone. The stabilizer may be present in an amount of 1% by mass or more and 10% by mass or less relative to the entire solution. A first solution and a second solution are prepared by stirring a liquid containing the above-described metal element raw materials, an organic solvent, and a stabilizer in an inert gas atmosphere. Examples of the inert gas include nitrogen and argon. The metal element raw materials are blended so that the metal element concentrations are in the desired ratio. The stirring time is, for example, approximately 1 hour to 5 hours.

[0079] (Coating and Heat Treatment) By coating the substrate 20 made of a sintered body with a solution, the solution penetrates into the substrate 20. The solution is coated so as to cover the particles 21 that make up the substrate 20. Methods for coating the solution include, for example, brush coating, spraying, immersion, flow coating, roll coating, and dipping. The substrate 20 coated with the solution is dried. The substrate 20 coated with the solution is then subjected to a heat treatment. This heat treatment includes a first heat treatment, a second heat treatment, and a final heat treatment. The heat treatment temperature is, for example, 300°C or higher and 600°C or lower. The heat treatment time is, for example, 10 minutes or higher and 5 hours or lower. The heat treatment atmosphere is an atmosphere containing an oxidizing gas. The oxidizing gas is, for example, air. The heat treatment oxidizes the metal elements contained in the solution to form oxides. When the first solution is used, a first oxide is formed. When the second solution is used, a second oxide is formed.

[0080] When manufacturing an electrode 10 including a catalyst 30 and an intermediate layer 40, a step of forming the catalyst 30 is performed after a step of forming the intermediate layer 40. In the step of forming the intermediate layer 40, a second solution is applied to the substrate 20, followed by a second heat treatment. This step forms an intermediate layer 40 having a second oxide, and the intermediate layer 40 is supported on the substrate 20. Specifically, a series of operations, including application of the second solution, drying, and second heat treatment, is repeated until a desired amount of intermediate layer 40 is supported on the substrate 20. The second heat treatment facilitates the diffusion of constituent elements in the second oxide from the intermediate layer 40 to the particles 21. The conditions for this second heat treatment are, for example, 300°C to 500°C for 10 minutes to 2 hours. The more times the above operation is repeated, the thicker the intermediate layer 40 becomes and the greater its weight becomes. The number of times this operation is repeated is appropriately selected so that the desired mass of the intermediate layer 40 per unit area of ​​the electrode 10 is achieved. In the step of forming the intermediate layer 40, the above operation may be repeated, for example, once or more and five or less times, or even once or more and four or less times.

[0081] In the process of forming the catalyst 30, a first solution is applied to the substrate 20 on which the intermediate layer 40 has been formed, followed by a first heat treatment. This process forms the catalyst 30 having a first oxide on the intermediate layer 40, and the catalyst 30 is supported on the substrate 20 via the intermediate layer 40. Specifically, a series of operations, including application of the first solution, drying, and first heat treatment, is repeated until a desired amount of catalyst 30 is supported on the substrate 20. The first heat treatment facilitates interdiffusion of constituent elements in the second oxide and those in the first oxide between the intermediate layer 40 and the catalyst 30, facilitating bonding of metal elements of the same kind. The conditions for the first heat treatment in this process are, for example, 300°C to 500°C for 10 minutes to 2 hours. The more times the above process is repeated, the thicker the catalyst 30 becomes and the heavier the catalyst 30 becomes. The number of times this process is repeated is appropriately selected so that the desired mass of catalyst 30 per unit area of ​​the electrode 10 is achieved. In the step of forming the catalyst 30, the above operation may be repeated, for example, once or more and ten or less times, or even twice or more and eight or less times.

[0082] In both the step of forming the intermediate layer 40 and the step of forming the catalyst 30, if the above operations are repeated many times, the number of heat treatments increases, which may result in a deterioration in the mechanical properties of the substrate 20. From the viewpoint of maintaining the mechanical properties of the substrate 20, the total number of heat treatments in both steps may be, for example, 10 times or less, further 8 times or less, and particularly 6 times or less.

[0083] After the step of forming the catalyst 30, the substrate 20 on which the catalyst 30 and the intermediate layer 40 have been formed may be subjected to a final heat treatment. The conditions for the final heat treatment are, for example, 400°C or higher and 600°C or lower for 1 hour or higher and 5 hours or lower. The temperature and time of the final heat treatment may be higher than those of the first heat treatment and the second heat treatment, and may be longer than those of the first heat treatment and the second heat treatment. This makes it easier for the metal elements in the first oxide and the second oxide to be sufficiently oxidized.

[0084] Test Example 1 An electrode including a substrate, an intermediate layer, and a catalyst was fabricated and evaluated.

[0085] The substrate prepared was a sintered body of Ti. The Ti sintered body was produced as follows. Ti powder was filled into a mold to produce a compact. The particle size of the Ti particles constituting the Ti powder was 45 μm or less. The size of the compact was 30 mm × 30 mm in area and 0.5 mm in thickness. This compact was sintered in an argon gas atmosphere to produce a sintered body of Ti. The porosity of the substrate made of this sintered Ti body was approximately 60% by volume. The mass of the substrate per unit area was approximately 1,300 g / m ２ In this example, three types of sintered bodies A to C were produced by changing the sintering temperature. Sintered body A was sintered at 1000°C for 1 hour. Sintered body B was sintered at 950°C for 2 hours. Sintered body C was sintered at 900°C for 3 hours. Of the samples shown in Tables 1 and 2, the base material of sample No. 12 was sintered body B. The base material of sample No. 13 was sintered body C. The base material of all samples except for samples No. 12 and No. 13 was sintered body A.

[0086] The solution was applied to the substrate and subjected to heat treatment to form the intermediate layer and catalyst shown in Tables 1 and 2. The mass (g / m) in the "Intermediate layer" column in Tables 1 and 2 ２ The column for "Mass (g / m)" indicates the mass of the intermediate layer per unit area of ​​the electrode. ２ The column labeled "(I)" indicates the mass of catalyst per unit area of ​​the electrode. Two solutions were prepared: a first solution for forming the catalyst and a second solution for forming the intermediate layer. The first solution was a mixture of the raw materials for the metal elements constituting the first oxide shown in Tables 1 and 2 with an organic solvent. The second solution was a mixture of the raw materials for the metal elements constituting the second oxide shown in Tables 1 and 2 with an organic solvent. Butanol containing 1% by mass of acetylacetone as a stabilizer was used as the organic solvent. The raw materials for the metal elements were dibutyltin bisacetylacetonate, ruthenium(IV) oxide hydrate, antimony(III) ethoxide, tungsten(VI) ethoxide, molybdenum chloride, tri-i-propoxycerium, neodymium(III) chloride hexahydrate, vanadium(III) chloride, iridium trichloride, and palladium dichloride. Each solution was prepared by stirring the raw materials for the metal elements in an organic solvent containing a stabilizer in a nitrogen atmosphere for 5 hours.

[0087] First solutions were prepared by selecting raw materials for the metal elements so that the metal elements in the first solutions would be the metal elements constituting the first oxides shown in Tables 1 and 2. The raw materials for the metal elements were prepared so that the molar concentrations of the metal elements in the first solutions would be the molar ratios shown in Tables 1 and 2. The first solutions were also prepared so that the total amount of the metal elements in the first solutions would be 10 mass%. For example, in the case of catalyst Sample No. 1 shown in Table 1, dibutyltin bisacetylacetonate, ruthenium (IV) oxide hydrate, and tungsten (VI) ethoxide were used as raw materials for the metal elements constituting the first oxide. These raw materials for the metal elements were prepared so that the molar concentrations of the metal elements in the first solutions would be the molar ratios shown in Table 1. In the "Catalyst" section of Tables 1 and 2, for example, if the "First Oxide" column is [Sn / Ru / W] and the "Molar Ratio" column is [30:65:5], this means that the first oxide contains Sn, Ru, and W, and the molar ratio of Sn, Ru, and W is 30:65:5. Note that a trace amount of antimony (III) ethoxide was mixed into the first solution. Although not shown in Tables 1 and 2, the first oxide of each sample contained less than 3 mol% Sb.

[0088] The second solutions were prepared by selecting raw materials for the metal elements so that the metal elements in the second solutions would be the metal elements that constitute the second oxides shown in Tables 1 and 2. The second solutions were prepared so that the total amount of metal elements in the second solutions was 5 mass%. For example, in the case of the intermediate layer of Sample No. 1 shown in Table 1, ruthenium (IV) oxide hydrate was used as the raw material for the metal element that constitutes the second oxide. In the "Intermediate Layer" section of Tables 1 and 2, for example, when [Ru] is entered in the "Second Oxide" column, this means that the second oxide contains Ru.

[0089] First, to form an intermediate layer, the second solution was applied to the substrate by a brush coating method. After the second solution was applied, the substrate was dried. Then, the substrate to which the second solution had been applied was subjected to a second heat treatment. Specifically, the steps of [application of the second solution] → [drying] → [second heat treatment] were repeated until the mass of the intermediate layer per unit area reached the mass shown in Tables 1 and 2. The second heat treatment was performed at 400°C for 10 minutes.

[0090] Next, to form a catalyst, a first solution was applied to the substrate on which the intermediate layer had been formed by a brush coating method. After the first solution was applied, the substrate was dried. Thereafter, the substrate to which the first solution had been applied was subjected to a first heat treatment. Specifically, the cycle of [application of the first solution] → [drying] → [first heat treatment] was repeated until the mass of the catalyst per unit area reached the mass shown in Tables 1 and 2. The conditions for the first heat treatment were 400°C x 10 minutes.

[0091] Finally, the substrate on which the intermediate layer and catalyst were formed was subjected to a final heat treatment at 500°C for 1 hour. In this manner, electrodes of Samples No. 1 to No. 17 shown in Table 1 and electrodes of Samples No. 101 to No. 118 shown in Table 2 were produced. The electrode of Sample No. 109 did not have an intermediate layer formed thereon.

[0092] (Composition Analysis) The cross section of the electrode of each obtained sample was subjected to composition analysis using SEM and EDX. In all samples except sample No. 109, the metal elements contained in the second oxide constituting the intermediate layer were confirmed as shown in Tables 1 and 2. In all samples, the metal elements contained in the first oxide constituting the catalyst were confirmed as shown in Tables 1 and 2. Furthermore, the crystal structure was analyzed using an X-ray diffraction device (XRD) and the element composition was measured using an X-ray microanalyzer (EPMA) to investigate the state of the intermediate layer and the catalyst, confirming that they were oxides containing metal elements. It was found that the intermediate layer was composed of the second oxide shown in Tables 1 and 2. It was found that the catalyst was composed of the first oxide shown in Tables 1 and 2.

[0093] From the results of the composition analysis of each sample, the contents of Ru and the first element per unit area of ​​the electrode (g / m ２The content of each element of Ir and Pd per unit area of ​​the electrode (g / m) was also determined. ２ The results are shown in Tables 1 and 2. The content of the first element is shown as the total content of W, Mo, Ce, Nd, and V.

[0094] (Cell Resistivity) The electrode of each sample was used as the positive electrode of an RF battery to fabricate a single battery cell. Carbon felt was used as the negative electrode. The area of ​​each of the positive and negative electrodes was 9 cm. ２ The electrolyte used was a sulfuric acid solution containing 1M each of Ti and Mn. A charge-discharge test was carried out on this battery cell to examine the cell resistivity. The test conditions were a current density of 140 mA / cm ２ The battery was charged and discharged at a constant current of 1.6 V. In this test, four cycles of charging and discharging were performed, switching from charging to discharging when the upper limit voltage of 1.6 V was reached, and from discharging to charging when the lower limit voltage of 0.9 V was reached. The cell resistivity was determined as follows: the difference between the average voltage during charging and the average voltage during discharging in each of the second to fourth cycles was measured. This difference was taken as the average voltage difference. [Average voltage difference / (average current × 2) × electrode area] in each cycle was calculated as the cell resistivity (Ω cm) in that cycle. ２ ) is defined as the average value of the cell resistivity from the second to fourth cycles. The average voltage during charging is defined as the battery voltage at which the charge capacity in the charge curve obtained by the charge-discharge test is 1 / 2. The average voltage during discharging is defined as the battery voltage at which the charge capacity in the discharge curve obtained by the charge-discharge test is 1 / 2. The charge curve shows the relationship between the voltage and capacity during charging. The discharge curve shows the relationship between the voltage and capacity during discharging. The charge curve and discharge curve are graphs with the battery capacity (Ah) on the horizontal axis and the battery voltage (V) on the vertical axis, showing the progress of charge and discharge at the same current. The average current is the average value of the current during charge and discharge. In the charge-discharge test, charging and discharging were performed in constant current mode, so the current during charge and discharge was constant. The cell resistivity of each sample is shown in Tables 1 and 2.

[0095] (Mechanical Properties) The mechanical properties of each sample were evaluated, and the mechanical properties of the electrode were measured, including tensile strength, tensile modulus, flexural strength, and flexural modulus.

[0096] The tensile strength and tensile modulus were measured using a tensile tester. The test specimens were in the shape of strips with a length of approximately 150 mm and a width of approximately 5 mm. The test specimens were prepared as follows. A sintered body of Ti with a thickness of 5 mm and an area larger than the test specimen was prepared. This sintered body of Ti was used as a substrate, and an intermediate layer and catalyst were formed on the substrate using the method described above. The electrodes of each obtained sample were processed to the size of the test specimens. The tensile tester used was a Tensilon UCT-30T model manufactured by Orientec Co., Ltd. The tensile test conditions were as follows:

[0097] Strain measurement: Crosshead movement method Distance between grips: 10 mm Test speed: 1 mm / min Test temperature: 23°C ± 2°C

[0098] The tensile modulus was calculated from the maximum gradient at 0.1% strain intervals. The tensile strength and tensile modulus were calculated by averaging the values ​​obtained by performing the tensile test three times. The tensile strength and tensile modulus of each sample are shown in Tables 1 and 2.

[0099] The bending strength and bending modulus were measured by a three-point bending test. The three-point bending test was performed in accordance with JIS Z 2248:2014. The test specimens were approximately 150 mm long, 30 mm wide, and 0.5 mm thick. The test specimens were prepared as follows: A 0.5 mm thick Ti sintered body with an area larger than the test specimen was prepared. This Ti sintered body was used as a substrate, and an intermediate layer and catalyst were formed on the substrate using the above-mentioned formation method. The resulting electrodes of each sample were processed to the size of the test specimen. An Instron 5966 composite material testing machine was used for the bending test. The maximum load of this testing machine was 10 kN. The bending test conditions were as follows:

[0100] Test speed: 2 mm / min Distance between supports: 26.5 mm Indenter radius: 5 mm Support radius: 5 mm Test temperature: 23°C ± 2°C

[0101] The bending strength and bending modulus of each sample are shown in Tables 1 and 2.

[0102]

[0103]

[0104] In each of Samples No. 1 to No. 17 shown in Table 1, the first oxide constituting the catalyst is an oxide containing Ru and a first element. In Samples No. 1 to No. 13, the first oxide is a composite oxide of Sn, Ru, and W. In Sample No. 14, the first oxide is a composite oxide of Sn, Ru, and Mo. In Sample No. 15, the first oxide is a composite oxide of Sn, Ru, and Ce. In Sample No. 16, the first oxide is a composite oxide of Sn, Ru, and Nd. In Sample No. 17, the first oxide is a composite oxide of Sn, Ru, and V. In none of these samples, the first oxide contains Ir or Pd. Furthermore, in each of Samples No. 1 to No. 17, the second oxide constituting the intermediate layer does not contain Ir or Pd. Therefore, each of Samples No. 1 to No. 17 can be manufactured at low cost.

[0105] In each of the electrodes of Samples No. 101 to No. 118 shown in Table 2, the first oxide constituting the catalyst contains Ru but does not contain the first element. In Samples No. 101 to No. 117, the first oxide constituting the catalyst is an oxide containing Ru and at least one of Ir and Pd. Therefore, the electrodes of Samples No. 101 to No. 117 are expensive. Of these samples, in Samples No. 101 to No. 108, the second oxide constituting the intermediate layer contains at least one of Ir and Pd. Therefore, the electrodes of Samples No. 101 to No. 108 are more expensive. In Sample No. 118, the first oxide is a composite oxide of Sn and Ru.

[0106] The cell resistivity of each of Samples No. 1 to No. 17 and the cell resistivity of each of Samples No. 101 to No. 118 were all 1.2 Ω cm ２ Because the cell resistivity is low, the electrodes of these samples have a relatively high cell reactivity. ２Cells No. 1 and No. 14, which have a resistivity of 0.5 Ω cm, are compared with cells No. 101 to No. 117. The resistivity of each of cells No. 1 and No. 14 is equal to or lower than the resistivity of each of cells No. 101 to No. 117. Cells No. 1 and No. 14 to No. 17, which have different compositions of the first oxide constituting the catalyst, each have a resistivity of 0.5 Ω cm. ２ That's about it.

[0107] Although the first oxide constituting the catalyst of each of the electrodes of Samples No. 1 and No. 14 to No. 17 does not contain Ir or Pd, the electrodes have battery reactivity equal to or greater than that of each of Samples No. 101 to No. 117. This indicates that the first oxide containing Ru and the first element has excellent catalytic function.

[0108] Furthermore, the cell resistivity of each of Samples No. 1 and No. 14 to No. 17 is lower than the cell resistivity of Sample No. 118. Therefore, each of the electrodes of Samples No. 1 and No. 14 to No. 17 has higher battery reactivity than the electrode of Sample No. 118. This shows that the first oxide containing Ru and the first element has improved catalytic function due to the Ru and the first element being composited.

[0109] From the results of cell resistivity of No. 5 to No. 11, it was found that the mass of catalyst per unit area was 80 g / m ２ It can be seen that even if the temperature is less than this, the catalyst function can be fully exerted.

[0110] Comparing Samples No. 1 to No. 11, it can be seen that the smaller the catalyst mass per unit area, the higher the mechanical properties of the electrode. The smaller the amount of catalyst supported on the substrate, the fewer heat treatments are required in the catalyst formation process during electrode manufacturing. Electrodes with a smaller catalyst mass per unit area are more likely to ensure high mechanical properties because the deterioration of the mechanical properties of the substrate due to heat treatment is suppressed. Furthermore, electrodes that require fewer heat treatments are more elastic and easier to handle, which is expected to improve yield when incorporated into battery cells.

[0111] Samples No. 9, No. 12, and No. 13, which have the same catalyst and intermediate layer configurations, are compared. The cell resistivity of No. 9 is lower than those of Nos. 12 and 13. The tensile strength of No. 9 is 4.0 MPa or more and 16.0 MPa or less. The tensile modulus of No. 9 is 1.0 GPa or more and 4.0 GPa or less. Furthermore, the bending strength of No. 9 is 3.0 MPa or more and 30.0 MPa or less. The bending modulus of No. 9 is 0.25 GPa or more and 3.0 GPa or less. The tensile strengths and tensile moduli of No. 12 and No. 13 are outside the above ranges. Furthermore, the bending modulus of No. 13 is outside the above ranges. From these findings, it is believed that electrodes with mechanical properties within the specified ranges are more likely to suppress an increase in cell resistivity. Electrodes in which a large amount of catalyst is supported on a substrate and which have been subjected to a large number of heat treatments tend to have high bending strength and / or bending modulus, but are prone to microcracks and high cell resistivity.

[0112] 1 Redox flow battery (RF battery), 7 AC / DC converter, 71 Substation equipment, 8 Power generation unit, 9 Load, 10 Electrode, 20 Substrate, 21 Particles, 30 Catalyst, 40 Intermediate layer, 100 Battery cell, 101 Diaphragm, 102 Positive electrode cell, 103 Negative electrode cell, 104 Positive electrode, 105 Negative electrode, 106, 107 Tank, 108, 109, 110, 111 Piping, 112, 113 Pump, 120 Cell frame, 121 Bipolar plate, 122 Frame, 127 Sealing member, 200 Cell stack 210 End plate, 230 Fastening member.

Claims

1. An electrode for a redox flow battery, The present invention comprises a sheet-like substrate and a catalyst supported on the substrate, The substrate is made of a sintered body in which a plurality of particles containing titanium are bonded to each other, the catalyst includes a first oxide provided so as to cover at least a portion of the plurality of particles; the first oxide is an oxide containing ruthenium and at least one first element selected from the group consisting of tungsten, molybdenum, cerium, neodymium, and vanadium, The area of ​​the electrode is 1 m ２ The iridium content and the palladium content contained in the catalyst are each 1 g or less per unit area. electrode.

2. 2. The electrode of claim 1, wherein the first oxide comprises at least one element selected from the group consisting of tin, antimony, and titanium.

3. an intermediate layer between the particles and the catalyst; the intermediate layer comprises a second oxide; the second oxide is an oxide containing at least one element selected from the group consisting of ruthenium, tin, antimony, titanium, tungsten, and molybdenum; 3. The electrode according to claim 1, wherein the number of types of metal elements contained in the second oxide is smaller than the number of types of metal elements contained in the first oxide.

4. 3. The electrode of claim 1, wherein the first oxide has a greater number of moles of ruthenium than the total number of moles of the first element.

5. The electrode according to claim 1 or 2, wherein the porosity of the electrode is 40 volume % or more and 75 volume % or less.

6. The area of ​​the electrode is 1 m ２ The content of ruthenium contained in the catalyst is 0.1 g or more and 90.0 g or less per unit weight, The area of ​​the electrode is 1 m ２ 3. The electrode according to claim 1, wherein a total content of the first element contained in the catalyst per unit area is 0.1 g or more and 50.0 g or less.

7. The electrode according to claim 1 or 2, wherein the electrode has a tensile strength of 4.0 MPa or more and 16.0 MPa or less.

8. The electrode according to claim 1 or 2, wherein the electrode has a flexural modulus of elasticity of 0.25 GPa or more and 3.0 GPa or less.

9. A battery cell of a redox flow battery comprising a positive electrode and a negative electrode, At least one of the positive electrode and the negative electrode is the electrode according to claim 1. Battery cell.

10. A battery cell of a redox flow battery comprising a positive electrode and a negative electrode, One of the positive electrode and the negative electrode is the electrode according to claim 1 , The other of the positive electrode and the negative electrode has a base material made of an aggregate of a plurality of carbon fibers. Battery cell.

11. A battery cell according to claim 9 or 10, Redox flow battery.