Battery cell and redox flow battery system

Abstract

A battery cell according to the present disclosure comprises a positive electrode, a negative electrode, a diaphragm, and a porous body. The porous body is disposed either one between the positive electrode and the diaphragm or between the negative electrode and the diaphragm, or each one between the positive electrode and the diaphragm and between the negative electrode and the diaphragm. The porous body includes a porous substrate made of an insulating material, and a coating part formed on at least a portion of the substrate. The coating part includes at least one of a cation exchange material and an anion exchange material.

Description

Battery cells and redox flow battery systems

[0001] This disclosure relates to a battery cell and a redox flow battery system. This application claims priority to Japanese Patent Application No. 2023-203975, filed December 1, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Literature 1 discloses a redox flow battery system as a type of storage battery. The redox flow battery system includes a battery cell. The battery cell includes a positive electrode cell and a negative electrode cell separated by a membrane. In the redox flow battery system, charging and discharging are performed by circulating a positive electrode electrolyte through the positive electrode cell and a negative electrode electrolyte through the negative electrode cell. These electrolytes contain active material ions that change valence to perform charging and discharging.

[0003] During operation of a redox flow battery system, active material ions may migrate from the positive electrode cell to the negative electrode cell or from the negative electrode cell to the positive electrode cell. The migration of active material ions changes the balance between the concentration of positive electrode active material ions in the positive electrode electrolyte and the concentration of negative electrode active material ions in the negative electrode electrolyte, resulting in a deterioration in the battery characteristics of the redox flow battery system. In the redox flow battery system of Patent Document 1, the positive electrode electrolyte and the negative electrode electrolyte are mixed to correct the change in the balance.

[0004] Japanese Patent Application Laid-Open No. 2020-187939

[0005] The battery cell of the present disclosure includes a positive electrode, a negative electrode, a diaphragm, and a porous body. The porous body is disposed between the positive electrode and the diaphragm, between the negative electrode and the diaphragm, or between the positive electrode and the diaphragm and between the negative electrode and the diaphragm. The porous body includes a porous substrate made of an insulating material and a covering portion formed on at least a portion of the substrate. The covering portion includes at least one of a cation exchange material and an anion exchange material.

[0006] Fig. 1 is a schematic diagram of a redox flow battery system including a battery cell according to an embodiment. Fig. 2 is a schematic diagram showing the arrangement of each component in a battery cell. Fig. 3 is a schematic diagram showing the arrangement of each component in a battery cell different from that shown in Fig. 2. Fig. 4 is a partially enlarged view of a porous body provided in a battery cell according to an embodiment. Fig. 5 is a partially enlarged view of an electrode provided in a battery cell according to an embodiment.

[0007] When the positive electrode electrolyte and the negative electrode electrolyte are mixed in a battery cell, a portion of the stored power is wasted due to self-discharge. Therefore, there is a need to reduce the active material ions that migrate from the positive electrode cell to the negative electrode cell or from the negative electrode cell to the positive electrode cell, that is, to reduce the active material ions that permeate the diaphragm. Furthermore, there is a need to reduce the frequency of mixing the positive electrode electrolyte and the negative electrode electrolyte.

[0008] An object of the present disclosure is to provide a battery cell and a redox flow battery system that can reduce active material ions that permeate a diaphragm.

[0009] The battery cell of the present disclosure can reduce the amount of active material ions that permeate the membrane.

[0010] First, embodiments of the present disclosure will be listed and described. In this specification, positive and negative electrodes will not be distinguished from each other and may be simply referred to as electrodes. Cation and anion exchange materials will not be distinguished from each other and may be simply referred to as ion exchange materials.

[0011] <1> A battery cell according to one aspect of the present disclosure includes a positive electrode, a negative electrode, a diaphragm, and a porous body. The porous body is disposed between the positive electrode and the diaphragm, between the negative electrode and the diaphragm, or between the positive electrode and the diaphragm and between the negative electrode and the diaphragm. The porous body includes a porous substrate made of an insulating material and a covering portion formed on at least a portion of the substrate. The covering portion includes at least one of a cation exchange material and an anion exchange material.

[0012] The membrane is proton permeable. That is, ions, typically protons, that maintain the electrical neutrality of the battery can pass through the membrane. The cation exchange material is a material that has the property of selectively exchanging specific cations. The anion exchange material is a material that has the property of selectively exchanging specific anions.

[0013] By disposing a porous body containing an ion exchange material between the diaphragm and the electrode, the amount of active material ions that permeate the diaphragm can be reduced. For example, if a porous body is disposed between the diaphragm and the negative electrode, negative electrode active material ions are less likely to reach the diaphragm and therefore less likely to migrate into the positive electrode electrolyte. This is thought to be because the ion exchange material makes it difficult for the active material ions to migrate.

[0014] When the number of active material ions that permeate the membrane is reduced, the current efficiency of the redox flow battery system including the battery cell is likely to improve. Furthermore, the frequency of mixing the positive electrode electrolyte and the negative electrode electrolyte can be reduced. Therefore, the power stored in the redox flow battery system is less likely to be wasted. Therefore, the current efficiency of the battery cell of the present disclosure is improved.

[0015] The substrate has a skeleton with a three-dimensional network structure. The coating portion is formed on at least a portion of the surface of this skeleton. The porous body has a plurality of pores. Because the electrolyte can pass through the pores of the porous body, the flow of the electrolyte in the battery cell is not easily obstructed. Therefore, even if the porous body is disposed, the cell resistivity of the battery cell is not likely to increase.

[0016] The provision of the porous body reduces the likelihood of contact between the electrode and the diaphragm, making the diaphragm less likely to be damaged. For example, even if the electrode is made of a fiber assembly containing a plurality of carbon fibers, if a porous body is provided between the electrode and the diaphragm, the carbon fibers are less likely to pierce the diaphragm, making the diaphragm less likely to be damaged.

[0017] <2> In the battery cell described in <1> above, the porous body may be disposed between the positive electrode and the diaphragm and between the negative electrode and the diaphragm.

[0018] If a porous body is disposed between the positive electrode and the diaphragm and between the negative electrode and the diaphragm, respectively, the current efficiency of the battery cell is improved and the diaphragm is less likely to be damaged.

[0019] <3> In the battery cell described in <1> above, the porous body may be disposed only between the negative electrode and the diaphragm.

[0020] In some cases, negative electrode active material ions may permeate the diaphragm more easily than positive electrode active material ions. For example, in a vanadium-based redox flow battery system, divalent vanadium ions permeate the diaphragm more easily. If a porous body is disposed between the negative electrode and the diaphragm, the negative electrode active material ions are less likely to reach the diaphragm and therefore less likely to migrate into the positive electrode electrolyte.

[0021] If the porous body is disposed only between the negative electrode and the diaphragm, the cell resistivity of the battery cell is unlikely to increase even if the porous body is disposed therein, and the number of parts in the battery cell can be minimized.

[0022] <4> In the battery cell according to any one of <1> to <3> above, the anion exchange material may be one or more materials selected from the group consisting of materials containing primary to tertiary amino groups, materials containing quaternary ammonium groups, and materials containing nitrogen-containing heterocyclic molecules.

[0023] These anion exchange materials reduce the amount of active material ions that permeate the membrane.

[0024] <5> In the battery cell according to any one of the above items <1> to <4>, the covering portion may contain both the cation exchange material and the anion exchange material.

[0025] When the coating portion contains both a cation exchange material and an anion exchange material, the number of active material ions that permeate the membrane is further reduced, which makes it easier to improve the current efficiency of a redox flow battery system including the battery cell.

[0026] <6> In the battery cell according to any one of the above items <1> to <4>, the covering portion may contain only the anion exchange material, without containing the cation exchange material.

[0027] Even if the ion exchange material contained in the coating portion is only an anion exchange material, the number of active material ions that permeate the diaphragm is reduced, and the current efficiency of the redox flow battery system including the battery cell is likely to improve.

[0028] <7> In the battery cell described in any one of <1> to <5> above, the cation exchange material may be one or more materials selected from the group consisting of a material containing a sulfonic acid group, a material containing a carboxylic acid group, and a material containing a phosphate group.

[0029] The cation exchange material reduces the amount of active material ions that permeate the membrane.

[0030] <8> In the battery cell according to any one of the above items <1> to <7>, at least one of the cation exchange material and the anion exchange material may contain a hydrocarbon-based ion exchange material.

[0031] The hydrocarbon-based ion exchange material reduces the amount of active material ions that permeate the membrane.

[0032] <9> In the battery cell described in any one of <1> to <8> above, the insulating material may be polyethylene, polypropylene, an ethylene-α-olefin copolymer, a vinyl copolymer resin, an engineering plastic, a super engineering resin, or a halogen-containing resin.

[0033] The substrate made of the insulating material has excellent flexibility, so that the diaphragm is less likely to be damaged even if the porous body comes into contact with the diaphragm.

[0034] <10> In the battery cell according to any one of the above items <1> to <9>, the thickness of the diaphragm may be 60 μm or less.

[0035] If the thickness of the diaphragm is 60 μm (micrometers) or less, protons can easily pass through the diaphragm. Therefore, if the diaphragm is proton permeable, the resistivity of the battery cell can be easily reduced. The thinner the diaphragm, the more easily active material ions can pass through the diaphragm. In the battery cell of the present disclosure, even if the diaphragm is thin, the porous body can reduce the amount of active material ions that pass through the diaphragm, so the current efficiency of the redox flow battery system is less likely to decrease.

[0036] <11> In the battery cell described in <10> above, the thickness of the diaphragm may be 5 μm or more.

[0037] A membrane with a thickness of 5 μm or more is less likely to be damaged.

[0038] <12> In the battery cell according to any one of the above items <1> to <11>, the base may include a plurality of resin fibers, and the resin fibers may have an average diameter of 0.1 μm or more and 20 μm or less.

[0039] Resin fibers with an average diameter of 0.1 μm or more are less likely to pierce the diaphragm. Resin fibers with an average diameter of 20 μm or less are less likely to get caught on the diaphragm. Therefore, in the battery cell of the present disclosure, even if the porous body comes into contact with the diaphragm, the diaphragm is less likely to be damaged. Therefore, the positive electrode electrolyte and the negative electrode electrolyte are less likely to mix, and the battery is less likely to short-circuit.

[0040] <13> In the battery cell according to any one of the above items <1> to <12>, the porosity of the substrate may be 60% or more and 99% or less.

[0041] A porous body including a substrate with a porosity of 60% or more is less likely to obstruct the flow of electrolyte in a battery cell. Therefore, even if a porous body is disposed, the cell resistivity of the battery cell is less likely to increase. A substrate with a porosity of 99% or less has excellent mechanical strength. Therefore, even if the porous body is compressed between the diaphragm and the electrode, the diaphragm and the electrode are less likely to come into contact with each other.

[0042] <14> In the battery cell according to any one of <1> to <13> above, the weight of the substrate is 2 g / m ２ 40g / m or more ２ It may be the following:

[0043] Weight per unit area: 2g / m ２ In the porous body containing the above substrate, the electrode and the diaphragm are less likely to come into contact with each other, and the diaphragm is less likely to be damaged. ２ A porous body including the following substrate is less likely to obstruct the flow of electrolyte inside a battery cell.

[0044] <15> In the battery cell according to any one of the above items <1> to <14>, the porous body may have a thickness of 0.5 μm or more and 200 μm or less.

[0045] A porous body with a thickness of 0.5 μm or more is less likely to cause contact between the electrodes and the diaphragm, making the diaphragm less likely to be damaged.A porous body with a thickness of 200 μm or less is less likely to increase the cell resistivity of the battery cell and to inhibit the flow of electrolyte within the battery cell.

[0046] <16> In the battery cell according to any one of the above items <1> to <15>, at least one of the positive electrode and the negative electrode may be a fiber aggregate having a plurality of carbon fibers. The fiber aggregate may be a nonwoven fabric, a woven fabric, or a paper.

[0047] Carbon fibers have excellent electrical conductivity and excellent resistance to electrolytes.

[0048] <17> A redox flow battery system according to an aspect of the present disclosure includes the battery cell according to any one of <1> to <16> above, a first circulation mechanism for circulating a positive electrode electrolyte through the battery cell, and a second circulation mechanism for circulating a negative electrode electrolyte through the battery cell. The positive electrode electrolyte contains vanadium ions as a positive electrode active material. The negative electrode electrolyte contains vanadium ions as a negative electrode active material.

[0049] The redox flow battery system of the present disclosure includes the battery cell, and therefore has improved current efficiency. The redox flow battery system of the present disclosure can reduce the frequency of mixing the positive electrode electrolyte and the negative electrode electrolyte.

[0050] <Details of the embodiments of the present disclosure> Specific examples of battery cells and redox flow battery systems according to embodiments of the present disclosure will be described below with reference to the drawings. In the embodiments, the redox flow battery is referred to as an RF battery. The same reference numerals in the drawings indicate the same or equivalent parts. The sizes of components shown in the drawings are expressed for the purpose of clarity of explanation and do not necessarily represent the actual sizes. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0051] 1 includes a battery cell 10, a first circulation mechanism 10P, and a second circulation mechanism 10N. The battery cell 10 has a positive electrode 14, a negative electrode 15, a diaphragm 11, and a porous body 17. The diaphragm 11 is disposed between the positive electrode 14 and the negative electrode 15. The first circulation mechanism 10P and the second circulation mechanism 10N circulate the electrolyte through the battery cell 10. One of the features of the RF battery system 1 is that a porous body 17 is disposed between the positive electrode 14 and the diaphragm 11, between the negative electrode 15 and the diaphragm 11, or between the positive electrode 14 and the diaphragm 11 and between the negative electrode 15 and the diaphragm 11. In FIG. 1 , the porous body 17 is disposed between the positive electrode 14 and the diaphragm 11 and between the negative electrode 15 and the diaphragm 11.

[0052] [Overview of RF Battery System] The RF battery system 1 shown in FIG. 1 charges and discharges power. The charging power is power generated by a power generation unit 510. The discharging power is supplied to a load 530. The power generation unit 510 is, for example, a solar power generation system, a wind power generation system, or other power generation equipment installed in a general power plant. The load 530 is, for example, a power consumer. Typically, the RF battery system 1 is connected to an AC / DC converter 500, which is connected to a substation 520, which is connected to the power generation unit 510 and the load 530. In FIG. 1, the solid arrow between the AC / DC converter 500 and the substation 520 indicates charging, and the dashed arrow indicates discharging. The RF battery system 1 is used, for example, for load leveling, instantaneous voltage drop compensation, or output smoothing of natural energy power generation. Natural energy power generation is, for example, solar power generation or wind power generation, which are being introduced on a large scale. The RF battery system 1 can also be used as an emergency power source. The RF battery system 1 uses a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte and the negative electrode electrolyte typically contain metal ions whose valence changes through oxidation-reduction as active material ions. The RF battery system 1 is charged and discharged by utilizing the difference between the oxidation-reduction potential of the active material ions contained in the positive electrode electrolyte and the oxidation-reduction potential of the active material ions contained in the negative electrode electrolyte.

[0053] [Basic Configuration of RF Battery] The RF battery system 1 includes a battery cell 10. The battery cell 10 includes a positive electrode cell and a negative electrode cell. The positive electrode cell and the negative electrode cell are separated by a diaphragm 11, which will be described later.

[0054] The cathode cell contains a cathode electrode 14, which will be described later. A cathode electrolyte is circulated through the cathode cell by a first circulation mechanism 10P. The first circulation mechanism 10P includes a cathode electrolyte tank 18, a supply pipe 20, a discharge pipe 22, and a pump 24. The cathode electrolyte tank 18 stores the cathode electrolyte. The cathode electrolyte flows through the supply pipe 20 and the discharge pipe 22. The supply pipe 20 connects the cathode electrolyte tank 18 and the cathode cell. The discharge pipe 22 connects the cathode cell and the cathode electrolyte tank 18. The pump 24 pressure-feeds the cathode electrolyte in the cathode electrolyte tank 18. The pump 24 is provided midway through the supply pipe 20.

[0055] The anode cell contains a negative electrode 15, which will be described later. Anode electrolyte is circulated through the anode cell by a second circulation mechanism 10N. The second circulation mechanism 10N includes an anode electrolyte tank 19, a supply pipe 21, a discharge pipe 23, and a pump 25. The anode electrolyte tank 19 stores the anode electrolyte. The anode electrolyte flows through the supply pipe 21 and the discharge pipe 23. The supply pipe 21 connects the anode electrolyte tank 19 and the anode cell. The discharge pipe 23 connects the anode cell and the anode electrolyte tank 19. The pump 25 pressure-feeds the anode electrolyte in the anode electrolyte tank 19. The pump 25 is provided midway through the supply pipe 21.

[0056] When the RF battery system 1 is in operation, the positive electrode electrolyte and the negative electrode electrolyte pumped by the pump 24 and the pump 25 flow as follows: The positive electrode electrolyte flows through the supply pipe 20 and is supplied from the positive electrode electrolyte tank 18 to the positive electrode cells. The positive electrode electrolyte flows through the discharge pipe 22 and is discharged from the positive electrode cells to the positive electrode electrolyte tank 18. The negative electrode electrolyte flows through the supply pipe 21 and is supplied from the negative electrode electrolyte tank 19 to the negative electrode cells. The negative electrode electrolyte flows through the discharge pipe 23 and is discharged from the negative electrode cells to the negative electrode electrolyte tank 19. During standby when no charging or discharging is performed, the pumps 24 and 25 are stopped, and the positive electrode electrolyte and the negative electrode electrolyte do not flow.

[0057] The battery cells 10 are typically provided inside a cell stack 200. The cell stack 200 includes a stack of multiple battery cells 10, two end plates 220, and a clamping mechanism 230. In the stack of this embodiment, a cell frame 16, a positive electrode 14, a porous body 17, a diaphragm 11, a porous body 17, and a negative electrode 15 are stacked in this order. The two end plates 220 sandwich the stack from the outside. The clamping mechanism 230 clamps both end plates 220. The cell stack 200 may include multiple sub-cell stacks. The main body of each sub-cell stack is the above-mentioned stack.

[0058] The cell frame 16 includes a bipolar plate 161 and a frame body 162. The cell frame 16 includes a recess in which the positive electrode 14 or negative electrode 15 is disposed. The recess is formed by the surface of the bipolar plate 161 and the inner peripheral surface of the frame body 162. One battery cell 10 is disposed between the bipolar plates 161 of two adjacent cell frames 16. One bipolar plate 161 is disposed between the positive electrode cell and the negative electrode cell of the adjacent battery cell 10. The bipolar plate 161 and the frame body 162 may have a known configuration. An annular sealing member 167 is disposed between the frame bodies 162. The sealing member 167 makes it difficult for electrolyte to leak from the battery cell 10.

[0059] The positive electrode active material ions contained in the positive electrode electrolyte are, for example, one or more selected from the group consisting of vanadium ions, manganese ions, iron ions, polyacids, quinone derivatives, amines, organic compounds, and organometallic complexes. The negative electrode active material ions contained in the negative electrode electrolyte are, for example, one or more selected from the group consisting of vanadium ions, titanium ions, chromium ions, polyacids, quinone derivatives, amines, and organometallic complexes. Charging and discharging occur in association with a valence change reaction of the active material ions. The solvent for the electrolyte is, for example, an aqueous solution containing one or more acids or acid salts selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid.

[0060] When the positive electrode active material ions and the negative electrode active material ions are vanadium (V) ions, the V ions constituting the positive electrode active material ions are V ４＋ and V ５＋ During charging, V ４＋ is oxidized, and V ５＋ When discharging, V ５＋ is reduced, and V ４＋ The negative electrode active material is V ２＋ and V ３＋ During charging, V ３＋ is reduced, and V ２＋ When discharging, V ２＋ is oxidized, and V ３＋The membrane 11 has proton permeability. In addition to protons permeating the membrane 11, metal ions, for example, V ions, which are cations, may also permeate the membrane 11. When the membrane 11 has proton permeability, V ２＋ Compared to other V ions, V ２＋ are likely to permeate through the diaphragm 11. If positive electrode active material ions pass through the diaphragm 11 and move to the negative electrode electrolyte, or if negative electrode active material ions pass through the diaphragm 11 and move to the positive electrode electrolyte, a difference in the amount of active material ions between the positive electrode electrolyte and the negative electrode electrolyte may occur, which may result in a decrease in battery capacity.

[0061] The RF battery system 1 includes the porous body 17, which makes it difficult for the active material ions to move between the positive electrode electrolyte and the negative electrode electrolyte. The RF battery system 1, mainly the porous body 17, will be described below.

[0062] [Porous Body] As shown in Fig. 2 , in the battery cell 10, the positive electrode 14, porous body 17, diaphragm 11, porous body 17, and negative electrode 15 are arranged in contact with each other in this order. The porous body 17 reduces the amount of active material ions that permeate the diaphragm 11. Specifically, the porous body 17 arranged in the negative electrode cell reduces the amount of negative electrode active material ions that permeate the diaphragm 11 and move from the negative electrode cell to the positive electrode cell. The porous body 17 arranged in the positive electrode cell reduces the amount of positive electrode active material ions that permeate the diaphragm 11 and move from the positive electrode cell to the negative electrode cell. It is believed that this effect is brought about by the porous body 17.

[0063] As shown in Fig. 3, the porous body 17 may be disposed only between the diaphragm 11 and the negative electrode 15. For example, when the positive electrode active material ions and the negative electrode active material ions are V ions, the negative electrode active material ions permeate the diaphragm 11 more easily than the positive electrode active material ions. The porous body 17 may be disposed only in the negative electrode cell, and may not be disposed in the positive electrode cell. In the following description, the positive electrode 14 and the negative electrode 15 may not be distinguished from each other and may be simply referred to as electrodes 100.

[0064] The porous body 17 is a member independent of the electrode 100. An example of the planar shape of the porous body 17 is a rectangle. The planar shape refers to the outline shape of the first or second surface of the porous body 17 when the first or second surface is viewed from above. The first surface is the surface facing the electrode 100. The second surface is the surface facing the diaphragm 11. The term "rectangle" here includes a square. The same meaning applies to the planar shape of the electrode 100 and the planar shape of the diaphragm 11.

[0065] When the porous body 17 is disposed, the electrode 100 is less likely to come into contact with the diaphragm 11. If the electrode 100 and the diaphragm 11 are less likely to come into contact with each other, the diaphragm 11 is less likely to be damaged. Therefore, the positive electrode electrolyte and the negative electrode electrolyte are less likely to mix, and the battery is less likely to short-circuit. As a result, high current efficiency is maintained.

[0066] The thickness of the porous body 17 is, for example, 0.1 μm or more and 200 μm or less. The thickness of the porous body 17 is the thickness of the porous body 17 in a compressed state. A porous body 17 with a thickness of 0.1 μm or more can reduce active material ions that permeate the diaphragm 11 and can reduce damage to the diaphragm 11 due to contact between the electrode 100 and the diaphragm 11. A porous body 17 with a thickness of 200 μm or less is less likely to obstruct the flow of electrolyte within the battery cell 10. The thickness of the porous body 17 may be 5 μm or more and 200 μm or less, 30 μm or more and 200 μm or less, or 50 μm or more and 150 μm or less.

[0067] As shown in FIG. 4, the porous body 17 includes a porous base 171 made of an insulating material, such as an insulating resin, and a covering portion 172 formed on at least a part of the base 171 .

[0068] (Base) The base 171 is made of an insulating material. The base 171 has multiple pores through which the electrolyte can flow. The base 171 is, for example, a fiber aggregate containing resin fibers, a resin foam, or a resin mesh member. The fiber aggregate is, for example, a nonwoven fabric or a woven fabric. In a nonwoven fabric, independent resin fibers are intertwined. In a woven fabric, warp and weft threads of resin fibers are alternately woven. The resin is, for example, polyethylene, polypropylene, ethylene-α-olefin copolymer, vinyl copolymer resin, engineering plastic, super-engineering resin, or halogen-containing resin. Examples of the engineering plastic or super-engineering resin include polyphenylene sulfide (PPS) or polystyrene. Examples of the halogen-containing resin include polytetrafluoroethylene, polyvinyl chloride, or polyvinylidene fluoride. These resins have excellent resistance to the electrolyte solution and are therefore less likely to damage the base 171. The material of the base 171 can be determined by identifying its molecular structure using at least one of the following analytical methods: infrared absorption spectroscopy, Raman spectroscopy, pyrolysis gas chromatography mass spectrometry, time-of-flight secondary ion mass spectrometry, and nuclear magnetic resonance analysis.

[0069] The base 171 is made of a fiber aggregate including a plurality of resin fibers 171a. The base 171 has a plurality of pores formed by being surrounded by the resin fibers 171a. The larger the average diameter of the resin fibers 171a, the easier it is to form a porous body 17 that is less likely to obstruct the flow of electrolyte within the battery cell 10. The average diameter of the resin fibers 171a is, for example, 0.1 μm or more. The average diameter of the resin fibers 171a may be 0.5 μm or more, 1 μm or more, 2 μm or more, or 5 μm or more.

[0070] The average diameter of the resin fibers 171a is, for example, 20 μm or less. The smaller the average diameter of the resin fibers 171a, the less likely the diaphragm 11 is to be damaged even when the porous body 17 comes into contact with the diaphragm 11. Resin fibers 171a with an average diameter of 20 μm or less have low rigidity, and therefore the diaphragm 11 is less likely to be damaged even when the porous body 17 comes into contact with the diaphragm 11. The average diameter of the resin fibers 171a may be 18 μm or less, or 15 μm or less.

[0071] The average diameter of the resin fibers 171a may be 0.1 μm or more and 20 μm or less, 0.5 μm or more and 18 μm or less, or 1 μm or more and 15 μm or less.

[0072] The resin fibers 171a that make up the base 171 may be softer than the carbon fibers 111a (see FIG. 5 ) that make up the electrode 100. The base 171 made of the resin fibers 171a has excellent flexibility. Therefore, even if the porous body 17 comes into contact with the diaphragm 11, the diaphragm 11 is unlikely to be damaged.

[0073] The average diameter of the resin fibers 171a is determined as follows: The porous body 17 is cut to expose the cross section of the resin fibers 171a. The porous body 17 is cut along a plane perpendicular to the surface of the porous body 17 facing the electrode. The cross section is enlarged using a microscope. The magnification is, for example, 1000 times. The diameter of each of five or more resin fibers 171a is determined. The diameter is the diameter of a circle having the same area as the cross section of the resin fiber 171a. The average of all the determined diameters is the average diameter of the resin fibers 171a.

[0074] The base 171 may be made of an insulating material other than resin, such as an inorganic material such as ceramic or glass, or may be a nonwoven fabric containing ceramic fiber or glass fiber.

[0075] The porosity of the substrate 171 is, for example, 60% or more and 99% or less. In this specification, the porosity of the substrate 171 refers to the porosity of the uncompressed substrate 171. A porous body 17 formed from a substrate 171 with a porosity of 60% or more is less likely to impede the flow of electrolyte within the battery cell 10. Therefore, the cell resistivity of the battery cell 10 in which the porous body 17 is disposed is less likely to increase. A substrate 171 with a porosity of 99% or less has excellent mechanical strength. Therefore, even if the porous body 17 is compressed between the diaphragm 11 and the electrode 100, the diaphragm 11 and the electrode 100 are less likely to come into contact with each other. The porosity of the substrate 171 may be 70% or more and 95% or less, or 75% or more and 90% or less. The porosity of the porous body 17 may be less than or greater than the porosity of the electrode 100. When the porosity of the base 171 is equal to or less than the porosity of the electrode 100, the presence of the porous body 17 makes it difficult for the electrode 100 to come into contact with the diaphragm 11 and therefore the diaphragm 11 to be damaged. Even if the porosity of the base 171 is greater than the porosity of the electrode 100, as long as the thickness of the porous body 17 is sufficient, the electrode 100 is unlikely to come into contact with the diaphragm 11 and the diaphragm 11 is unlikely to be damaged.

[0076] After removing the covering portion 172 from the base 171 using a solvent, the porosity of the base 171 can be determined by measuring the volume, mass, and true density of the base 171. The true density of the base 171 can be determined by identifying the material of the base 171. The porosity of the base 171 constituting the porous body 17 is often substantially the same as the porosity of the base 171 prepared during the manufacturing process.

[0077] The weight of the base 171 is, for example, 2 g / m ２ 40g / m or more ２ The basis weight is 2 g / m or less. ２ The above-described base 171 can hold an appropriate amount of the covering portion 172. This reduces the amount of active material ions that permeate the diaphragm 11, reducing damage to the diaphragm 11 due to contact between the electrode 100 and the diaphragm 11. ２ In the porous body 17 formed from the substrate 171 described below, the cell resistivity of the battery cell 10 is less likely to increase, and the flow of the electrolyte in the battery cell 10 is less likely to be obstructed. The weight of the substrate 171 is 5 g / m ２ 40g / m or more ２It may be less than 8 g / m ２ 35g / m or more ２ or less, or 10 g / m ２ 30g / m or more ２ The following is also acceptable.

[0078] (Coating portion) The covering portion 172 is formed so as to cover at least a portion of the surface of the skeleton of the base body 171. When the covering portion 172 is formed, the volume of the pores in the base body 171 can be reduced. Pores may be formed in the covering portion 172 so that the electrolyte can flow through the porous body 17. As long as the electrolyte can flow through the porous body 17, the porous body 17 may include pores blocked by the covering portion 172.

[0079] The covering portion 172 is formed on at least a part of the surface of the resin fiber 171 a. The covering portion 172 may be formed on the entire surface of the resin fiber 171 a. In this case, the resin fiber 171 a is coated with the covering portion 172.

[0080] The coating portion 172 contains an ion exchange material. Ion exchange materials include an anion exchange material and a cation exchange material. The coating portion 172 may contain a single ion exchange material or multiple different ion exchange materials. The coating portion 172 may contain only an anion exchange material without containing a cation exchange material. The coating portion 172 may contain only a cation exchange material without containing an anion exchange material. The coating portion 172 may contain both an anion exchange material and a cation exchange material. When the active material ions are cations such as metal ions, the coating portion 172 may contain an anion exchange material or a cation exchange material with excellent ion selectivity. A cation exchange material with excellent ion selectivity selects ions, such as protons, to maintain the battery's electrical neutrality, but does not select active material ions. Therefore, protons permeate the porous body 17 containing a cation exchange material with excellent ion selectivity, while active material ions have a low permeability through the porous body 17 containing a cation exchange material with excellent ion selectivity.

[0081] Examples of anion exchange materials include materials containing primary to tertiary amino groups, materials containing quaternary ammonium groups, or materials containing nitrogen-containing heterocyclic molecules. When the coating 172 includes multiple anion exchange materials, the coating 172 may include one or more materials selected from the group consisting of the above three materials. Examples of materials containing primary to tertiary amino groups include polyethyleneimine or its salts, polyaniline or its salts, polyallylamine or its salts, polystyrene-based tertiary amines, and polyphenol-based tertiary amines. Examples of materials containing quaternary ammonium groups include diallyldimethylammonium chloride polymers, diallylamine hydrochloride-sulfur dioxide copolymers, tetrabutylammonium, benzyltriethylammonium, polystyrene-based quaternary ammonium, and benzethonium. Examples of materials containing nitrogen-containing heterocyclic molecules include polypyrrole or a salt thereof, diallylamine polymer or a salt thereof, poly(4-vinylpyridine) or a salt thereof, vinylpyridine / divinylbenzene copolymer or a salt thereof, vinylpyridine / styrene copolymer or a salt thereof, polybenzimidazole or a salt thereof, poly(diallyldimethylammonium) or a salt thereof, and cetylpyridinium. The anion exchange material may include a hydrocarbon-based ion exchange material. The anion exchange material may also be a known anion exchange resin other than those mentioned above.

[0082] The cation exchange material may be, for example, a material containing sulfonic acid groups, a material containing carboxylic acid groups, or a material containing phosphate groups. When the covering portion 172 includes multiple cation exchange materials, it may include one or more materials selected from the group consisting of the above three materials. Examples of the material containing sulfonic acid groups include sulfonated polymers, perfluorocarbon sulfonic acid resins, polystyrene sulfonic acid resins, sulfonated polyether sulfones, sulfonated polyether ether ketones, sulfonated polyimides, sulfonated polyethers, sulfonated polybenzimidazoles, and sulfonated polyarylenes. Examples of the material containing carboxylic acid groups include methacrylic acid-based weakly acidic cation exchange resins or acrylic acid-based weakly acidic cation exchange resins. The material containing phosphate groups is, for example, a phosphate ester polymer, or polyphosphate. The cation exchange material may include a hydrocarbon-based ion exchange material.

[0083] When the ion exchange material is at least one selected from the group consisting of the anion exchange material and the cation exchange material described above, the amount of active material ions that permeate the membrane 11 in the battery cell 10 can be reduced.

[0084] The mass of the covering portion 172 is obtained by subtracting the mass of the substrate 171 from the mass of the produced porous body 17 .

[0085] The coating portion 172 may be formed, for example, by the following method: A raw material solution containing an ion exchange material is prepared. The raw material solution is applied to the substrate 171, or the substrate 171 is immersed in the raw material solution. The amount of ion exchange material contained in the raw material solution is adjusted so that the ratio of the coating portion 172 to the porous body 17 is appropriate. The ion exchange material contained in the raw material solution may be in the form of particles dispersed in the raw material solution or dissolved in the raw material solution. The raw material solution may also contain a crosslinking agent. Depending on the type of raw material solution, the substrate 171 may be pretreated. The pretreatment may be, for example, a corona treatment, a plasma treatment, or an ozone treatment. This pretreatment may improve the adhesion between the substrate 171 and the coating portion 172. The substrate 171, with the raw material solution adhering to the surface of the resin fibers 171a, is dried to evaporate the liquid components of the raw material solution, thereby forming the coating portion 172. Drying may be performed in an atmosphere at a temperature below the melting point of the resin fibers 171a. If the raw material liquid contains a cross-linking agent, the ion exchange material is cross-linked by a cross-linking treatment, such as a heat treatment. When the ion exchange material is cross-linked, the coating portion 172 becomes less likely to peel off from the surface of the resin fiber 171 a.

[0086] [Positive Electrode and Negative Electrode] The configuration of the positive electrode 14 may be the same as or different from the configuration of the negative electrode 15. An example of the planar shape of the electrode 100 is rectangular.

[0087] The electrode 100 is made of a porous material. In this embodiment, the porous material is a fiber aggregate 111, as shown in FIG. 5 . The fiber aggregate 111 has a plurality of carbon fibers 111a. The carbon fibers 111a are electrically conductive. In the fiber aggregate 111, the carbon fibers 111a are likely to have many contact points with each other. Therefore, the electrode 100 made of the fiber aggregate 111 is likely to have improved electrical conductivity. Pores are likely to be formed in the fiber aggregate 111. Therefore, the electrode 100 made of the fiber aggregate 111 is likely to have improved electrolyte flow. The fiber aggregate 111 may be in the form of, for example, a nonwoven fabric, a woven fabric, or paper. In a nonwoven fabric, independent carbon fibers 111a are entangled. In a woven fabric, the warp and weft of the carbon fibers 111a are alternately woven. The paper is, for example, carbon paper having a plurality of carbon fibers 111a and a binder that binds the carbon fibers 111a. The nonwoven fabric includes felt, spunlace, and Marifleece. Known carbon fibers can be used for the carbon fiber 111a.

[0088] [Diaphragm] The diaphragm 11 is disposed between the positive electrode 14 and the negative electrode 15. The diaphragm 11 separates the positive electrode cell from the negative electrode cell. The diaphragm 11 has proton permeability, i.e., hydrogen ion permeability. A known diaphragm can be used as the diaphragm 11. An example of the planar shape of the diaphragm 11 is rectangular.

[0089] The thickness of the diaphragm 11 is, for example, 60 μm or less. A diaphragm 11 with a thickness of 60 μm or less is likely to reduce cell resistivity. This is because such a diaphragm 11 is likely to allow hydrogen ions to permeate. The thickness of the diaphragm 11 may be 40 μm or less, or 30 μm or less. The lower limit of the thickness of the diaphragm 11 is, for example, 5 μm. A diaphragm 11 with a thickness of 5 μm or more is less likely to be damaged. The thickness of the diaphragm 11 may be 8 μm or more, or 10 μm or more. The thickness of the diaphragm 11 is, for example, 5 μm or more and 60 μm or less, 8 μm or more and 40 μm or less, or 10 μm or more and 30 μm or less.

[0090] <Test Example> In the test example, we investigated the effect of the porous body on the battery performance of the RF battery system 1. Specifically, we fabricated a single-cell battery including one positive electrode 14 and one negative electrode 15, and measured the cell resistivity and current efficiency of the single-cell battery.

[0091] <<Sample No. 1 to Sample No. 12>> In each of the single-cell batteries of Sample No. 1 to Sample No. 12, the first cell frame 16, positive electrode 14, porous body 17, diaphragm 11, porous body 17, negative electrode 15, and second cell frame 16 were stacked in contact with each other in this order. In these samples, the porous body 17 was disposed in each of the positive and negative cells. That is, the porous body 17 was disposed between the positive electrode 14 and diaphragm 11 and between the negative electrode 15 and diaphragm 11. The main configuration of the battery cell 10 is as follows:

[0092] Diaphragm 11: proton-permeable diaphragm made of perfluorocarbon sulfonic acid resin Thickness of diaphragm 11: 20 μm Thickness of uncompressed porous body 17: 80 μm Base 171: PPS resin nonwoven fabric Porosity of uncompressed base 171: 81% Weight of base 171: 20 g / m ２- Method for forming the coating portion 172: A coating method in which a raw material solution containing an ion exchange material is applied to the substrate 171 and then dried. - Material for the coating portion 172: Shown in Table 1. "Both electrodes" in Table 1 means that the porous body 17 is disposed in each of the positive and negative electrodes, i.e., between the positive electrode 14 and the diaphragm 11 and between the negative electrode 15 and the diaphragm 11. "Negative electrode" means that the porous body 17 is disposed only in the negative electrode cell, i.e., only between the negative electrode 15 and the diaphragm 11. In Table 1, "pC-based" means an anion exchange material, and "pA-based" means a cation exchange material. "Poly(sodium 4-styrenesulfonate)" in Sample No. 6 is a type of polystyrene sulfonate resin. Also, "+" means that multiple types of ion exchange materials are formed sequentially. For example, "polydiallyldimethylammonium + perfluorocarbon sulfonic acid resin" means that the coating portion 172 is formed by applying polydiallyldimethylammonium to the base 171 and then applying perfluorocarbon sulfonic acid resin.

[0093] <<Sample No. 13>> In the single-cell battery of Sample No. 13, the first cell frame 16, the positive electrode 14, the diaphragm 11, the porous body 17, the negative electrode 15, and the second cell frame 16 were stacked in this order so as to be in contact with each other. In the single-cell battery of Sample No. 13, the porous body 17 was disposed only in the negative cell. In other words, the porous body 17 was disposed only between the negative electrode 15 and the diaphragm 11. The configuration of the single-cell battery of Sample No. 13 was the same as the configuration of the single-cell battery of Sample No. 2, except that the porous body 17 was disposed only in the negative cell.

[0094] <Sample No. 101> In the single-cell battery of Sample No. 101, a porous body without a covering portion 172 was disposed in each of the positive and negative cells. That is, a porous body without a covering portion 172 was disposed between the positive electrode 14 and the diaphragm 11 and between the negative electrode 15 and the diaphragm 11. The porous body without a covering portion 172 was a porous body consisting only of the substrate 171. The configuration of the single-cell battery of Sample No. 101 was the same as the configuration of the single-cell batteries of Sample No. 1 to Sample No. 12, except that it did not have a covering portion 172.

[0095] <<Sample No. 102>> In the single-cell battery of Sample No. 102, the first cell frame 16, the positive electrode 14, the diaphragm 11, the negative electrode 15, and the second cell frame 16 were stacked in this order so as to be in contact with each other. The configuration of the single-cell battery of Sample No. 102 was the same as the configuration of the single-cell batteries of Sample No. 1 to Sample No. 13, except that the porous body 17 was not included.

[0096] <Battery Characteristics Test> A vanadium sulfate aqueous solution was used for each of the positive electrode electrolyte and the negative electrode electrolyte. The vanadium concentration was 1.7 mol / L. The vanadium ions act as active material ions. The charge-discharge test was performed at a current density of 70 mA / cm. ２ When the battery voltage reached a preset switching voltage, charging and discharging were switched. In this battery characteristic test, five cycles of charging and discharging were performed.

[0097] Based on the data obtained by the test, the cell resistivity (Ω cm ２ The cell resistance (%) and current efficiency (%) were calculated. The results are shown in Table 1. The cell resistivity was calculated by multiplying the cell resistance value by the area of ​​the electrode 100. The cell resistance value is calculated by dividing the difference between the intermediate voltage of charge and the intermediate voltage of discharge by 2, and then dividing that value by the current value. The "intermediate voltage" is the voltage value at the point when half the time from the start to the end of charge or discharge has elapsed since the start of charge or discharge. The current efficiency is the ratio of the discharge time to the charge time in the fifth cycle. Specifically, the current efficiency is (total discharge time / total charge time) × 100.

[0098]

[0099] Samples No. 1 to No. 13 are compared with Sample No. 101. The inclusion of an ion exchange material in the porous body improved the current efficiency. Samples No. 1 to No. 3, Sample No. 6, and Sample No. 7 had current efficiencies of 98% or higher. In Samples No. 1 to No. 3, the porous body contained only a specific anion exchange material. In Samples No. 6 and No. 7, the porous body contained both a cation exchange material and an anion exchange material. Therefore, it is presumed that the current efficiency improved due to a reduction in the amount of active material ions that permeated the diaphragm.

[0100] Samples No. 1 to No. 12 are compared with Sample No. 102. Even when a porous body is placed in each of the positive electrode cell and the negative electrode cell, the increase in cell resistivity is only 0.1 Ω cm ２ It is presumed that the porous body does not significantly increase the cell resistivity because the porous body does not obstruct the flow of the electrolyte.

[0101] The current efficiency of Sample No. 13 was lower than those of Samples No. 1 to 12. This is thought to be because Sample No. 13 did not have a porous body between the positive electrode and the diaphragm, causing damage to a portion of the diaphragm. Although damage to a portion of the diaphragm is thought to have occurred, the current efficiency of Sample No. 13 was higher than that of Sample No. 101. Even if a porous body is disposed only in the negative electrode cell, it is thought that the current efficiency can be improved by thickening the diaphragm 11 or by forming the positive electrode 14 from a soft material. However, it is thought that thickening the diaphragm increases the cell resistivity.

[0102] REFERENCE SIGNS LIST 1 RF battery system (redox flow battery system) 10 Battery cell 11 Diaphragm 14 Positive electrode 15 Negative electrode 16 Cell frame 161 Bipolar plate 162 Frame 167 Sealing member 17 Porous body 171 Base body 171a Resin fiber 172 Covering portion 10P First circulation mechanism 10N Second circulation mechanism 18 Positive electrode electrolyte tank 19 Negative electrode electrolyte tank 20, 21 Supply pipe 22, 23 Discharge pipe 24, 25 Pump 100 Electrode 111 Fiber assembly 111a Carbon fiber 200 Cell stack 220 End plate 230 Fastening mechanism 500 AC / DC converter 510 Power generation unit 520 Substation equipment 530 Load

Claims

1. A battery cell comprising: a positive electrode, a negative electrode, a diaphragm, and a porous body, wherein the porous body is disposed between the positive electrode and the diaphragm, between the negative electrode and the diaphragm, or between the positive electrode and the diaphragm and between the negative electrode and the diaphragm, respectively, and the porous body comprises a porous base made of an insulating material and a covering portion formed on at least a part of the base, and the covering portion includes at least one of a cation exchange material and an anion exchange material.

2. The battery cell according to claim 1, wherein the porous body is disposed between the positive electrode and the diaphragm and between the negative electrode and the diaphragm.

3. The battery cell according to claim 1, wherein the porous body is disposed only between the negative electrode and the diaphragm.

4. A battery cell according to any one of claims 1 to 3, wherein the anion exchange material is one or more materials selected from the group consisting of materials containing primary to tertiary amino groups, materials containing quaternary ammonium groups, and materials containing nitrogen-containing heterocyclic molecules.

5. A battery cell according to any one of claims 1 to 4, wherein the covering portion contains both the cation exchange material and the anion exchange material.

6. A battery cell according to any one of claims 1 to 4, wherein the covering portion does not contain the cation exchange material and contains only the anion exchange material.

7. The battery cell of any one of claims 1 to 5, wherein the cation exchange material is one or more materials selected from the group consisting of materials containing sulfonic acid groups, materials containing carboxylic acid groups, and materials containing phosphate groups.

8. The battery cell of any one of claims 1 to 7, wherein at least one of the cation exchange material and the anion exchange material comprises a hydrocarbon-based ion exchange material.

9. The battery cell of any one of claims 1 to 8, wherein the insulating material is polyethylene, polypropylene, ethylene-alpha olefin copolymer, vinyl copolymer resin, engineering plastic, super engineering resin, or halogen-containing resin.

10. A battery cell as described in any one of claims 1 to 9, wherein the thickness of the diaphragm is 60 μm or less.

11. The battery cell according to claim 10, wherein the thickness of the diaphragm is 5 μm or more.

12. A battery cell according to any one of claims 1 to 11, wherein the base includes a plurality of resin fibers, and the average diameter of the resin fibers is 0.1 μm or more and 20 μm or less.

13. A battery cell according to any one of claims 1 to 12, wherein the porosity of the substrate is 60% or more and 99% or less.

14. The basis weight of the substrate is 2 g / m ２ 40g / m or more ２ 14. The battery cell according to claim 1 , wherein:

15. A battery cell as described in any one of claims 1 to 14, wherein the thickness of the porous body is 0.5 μm or more and 200 μm or less.

16. A battery cell as described in any one of claims 1 to 15, wherein at least one of the positive electrode and the negative electrode is a fiber aggregate having a plurality of carbon fibers, and the fiber aggregate is a nonwoven fabric, a woven fabric, or a paper.

17. A redox flow battery system comprising: a battery cell according to any one of claims 1 to 16; a first circulation mechanism for circulating a positive electrode electrolyte through the battery cell; and a second circulation mechanism for circulating a negative electrode electrolyte through the battery cell, wherein the positive electrode electrolyte contains vanadium ions as a positive electrode active material, and the negative electrode electrolyte contains vanadium ions as a negative electrode active material.

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