Redox flow battery separator, method for producing redox flow battery separator, redox flow battery separator electrode assembly, redox flow battery cell, and redox flow battery

Abstract

An object of the present invention is to provide a redox flow battery separator, a redox flow battery separator-electrode assembly, a redox flow battery cell, and a redox flow battery that suppress curling and exhibit high power efficiency. The aforementioned object can be achieved by a redox flow battery separator comprising, in order, a first ion exchange resin layer, an anion exchange resin layer containing an anion exchange compound, and a second ion exchange resin layer, wherein the value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer is 0.7 to 1.3, and the thickness of the anion exchange resin layer is 0.02 μm to 3 μm.

Description

Technical Field

[0001] The present invention relates to a redox flow battery separator, a method for producing a redox flow battery separator, a redox flow battery separator-electrode assembly, a redox flow battery cell, and a redox flow battery. Background Art

[0002] Redox flow batteries are secondary batteries that store and discharge electricity, and are suitable for use as large, stationary batteries to balance power consumption. Redox flow batteries use a structure in which a diaphragm separates a positive electrolyte (positive electrode unit) containing a positive electrode and positive active material from a negative electrolyte (negative electrode unit) containing a negative electrode and negative active material. Charging and discharging occur through the redox reaction of these two active materials. By flowing the electrolyte containing these two active materials from a storage tank to an electrolytic cell, a larger capacity can be achieved.

[0003] Active materials used in the electrolyte include iron-chromium, chromium-bromine, zinc-bromine, and vanadium-based materials that utilize different charges. Vanadium-based secondary batteries, in particular, have made significant progress due to their advantages, such as high electromotive force, rapid electrode reactions of vanadium ions, low hydrogen production as a side reaction, and high output power.

[0004] In vanadium redox flow batteries, the divalent vanadium (V 2+ ) / 3 valence (V 3+ ), and the tetravalent vanadium (V 4+ ) / 5 valence (V 5+ ) redox reaction. In this way, the electrolytes of the positive and negative electrode units are composed of the same metal ion species. Even if the electrolytes mix through the separator, they can be regenerated through the electrical process, which is less likely to cause major problems than with other metal species. However, if the active material penetrates, the stored charge is wasted and the current efficiency is reduced. Therefore, it is preferred that the active material does not penetrate. On the other hand, it is preferred that the protons that transport the charge can easily penetrate sufficiently, and a separator that achieves both high current efficiency and high voltage efficiency, that is, high power efficiency, is sought.

[0005] To suppress the permeation of electrolyte ions and achieve high power efficiency, ion exchange membranes are sometimes processed. Patent Document 1 discloses an example of a vanadium-based redox flow battery in which the outermost surface of the membrane is modified to improve the suppression of vanadium ion permeation. Furthermore, Patent Document 2 discloses an example of achieving high power efficiency by alternating cation exchange substrates and anion exchange substrates.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application No. 2019-507006

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 11-260390 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] However, in redox flow batteries, processing of the separator to improve current efficiency can impair proton conductivity and degrade voltage efficiency. Using the processing described in Patent Document 1 increases membrane resistance, which poses a problem in improving power efficiency.

[0012] In addition, when a cation exchange layer is stacked with an anion exchange layer, the membrane may curl due to the difference in swelling between the cation exchange layer and the anion exchange layer. When evaluating redox flow batteries, the membrane is immersed in sulfuric acid and an electrolyte and then assembled into a battery cell. However, a membrane that easily curls creates space when assembled into the cell, which may cause leakage. For example, Patent Document 2 discloses improvements in battery characteristics achieved by alternating cation exchange layers and anion exchange layers, but does not describe membrane curling.

[0013] An object of the present invention is to provide a redox flow battery separator, a redox flow battery separator-electrode assembly, a redox flow battery cell, and a redox flow battery that are prevented from curling and exhibit high power efficiency.

[0014] Another object of the present invention is to provide a redox flow battery separator, a redox flow battery separator-electrode assembly, a redox flow battery cell, and a redox flow battery that maintain high power efficiency for a long period of time.

[0015] Solutions for solving problems

[0016] The present inventors conducted intensive research to address the above-mentioned issues and discovered that by forming ion exchange resin layers so as to sandwich anion exchange resin layers containing an anion exchange compound, curling can be suppressed and high power efficiency can be achieved. Furthermore, they discovered that by arranging the anion exchange resin layer so as to sandwich the ion exchange resin layers, permeation of electrolyte ions can be suppressed, and the device is less susceptible to direct oxidation from the electrolyte ions, thereby achieving high long-term durability.

[0017] That is, embodiments of the present invention are as follows.

[0018] [1] A redox flow battery separator comprising, in this order, a first ion exchange resin layer, an anion exchange resin layer containing an anion exchange compound, and a second ion exchange resin layer.

[0019] The value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer is 0.7 or more and 1.3 or less,

[0020] The thickness of the anion exchange resin layer is 0.02 μm or more and 3 μm or less.

[0021] [2] The redox flow battery separator according to [1], wherein the thickness of the first ion exchange resin layer and the second ion exchange resin layer are each 5 μm or more and 50 μm or less.

[0022] [3] The redox flow battery separator according to [1] or [2], wherein the first ion exchange resin layer is a first ion exchange resin layer containing a cation exchange resin.

[0023] [4] The redox flow battery separator according to any one of [1] to [3], wherein the second ion exchange resin layer is a second ion exchange resin layer containing a cation exchange resin.

[0024] [5] The redox flow battery separator according to [3] or [4], wherein the cation exchange resin contains a fluorine-based polymer electrolyte polymer.

[0025] [6] The redox flow battery separator according to any one of [1] to [5], wherein the anion exchange compound has a tertiary amino group or a quaternary ammonium group.

[0026] [7] A method for producing a redox flow battery separator, comprising: a first ion exchange resin layer, an anion exchange resin layer, and a second ion exchange resin layer in this order;

[0027] The manufacturing method includes the steps of forming an anion exchange resin layer on a first ion exchange resin layer to obtain a first ion exchange resin layer / anion exchange resin layer structure;

[0028] A step of forming a second ion exchange resin layer on the anion exchange resin layer of the structure.

[0029] [8] A method for producing a redox flow battery separator, comprising: a first ion exchange resin layer, an anion exchange resin layer, and a second ion exchange resin layer in this order;

[0030] The manufacturing method includes the steps of forming an anion exchange resin layer on a first ion exchange resin layer to obtain a first ion exchange resin layer / anion exchange resin layer structure;

[0031] forming an anion exchange resin layer on the second ion exchange resin layer to obtain a second ion exchange resin layer / anion exchange resin layer structure;

[0032] A step of attaching the first ion exchange resin layer / anion exchange resin layer structure and the second ion exchange resin layer / anion exchange resin layer structure to each other with the surfaces of the respective anion exchange resin layers, and bonding them by heat pressing.

[0033] [9] A redox flow battery separator electrode assembly comprising the redox flow battery separator according to any one of [1] to [6], and a carbon electrode bonded to the redox flow battery separator.

[0034]

[10] A redox flow battery cell comprising the membrane electrode assembly described in [9].

[0035]

[11] A redox flow battery comprising an electrolytic cell comprising: a positive electrode cell chamber including a positive electrode formed of a carbon electrode, a negative electrode cell chamber including a negative electrode formed of a carbon electrode, and a separator separating the positive electrode cell chamber from the negative electrode cell chamber.

[0036] The positive electrode unit cell contains a positive electrode electrolyte containing an active material.

[0037] The negative electrode unit cell contains a negative electrode electrolyte containing an active material.

[0038] The separator is the separator for a redox flow battery according to any one of [1] to [6].

[0039] Effects of the Invention

[0040] According to the present invention, a redox flow battery separator, a redox flow battery separator-electrode assembly, a redox flow battery cell, and a redox flow battery can be provided, which are suppressed from curling and exhibit high power efficiency.

[0041] Furthermore, according to the present invention, a redox flow battery separator, a redox flow battery separator-electrode assembly, a redox flow battery cell, and a redox flow battery can be provided, which maintain high power efficiency for a long period of time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1An example of a schematic diagram of a redox flow battery using the redox flow battery separator according to the present embodiment is shown.

[0043] Figure 2 Schematic diagram of the curl evaluation method. DETAILED DESCRIPTION

[0044] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. However, the present invention is not limited to the following description and can be carried out with various modifications within the scope of the gist of the invention.

[0045] [Separator for redox flow batteries]

[0046] The redox flow battery separator (hereinafter simply referred to as the "separator") of this embodiment includes, in this order, a first ion exchange resin layer, an anion exchange resin layer containing an anion exchange compound, and a second ion exchange resin layer. The value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer is 0.7 to 1.3. The thickness of the anion exchange resin layer is 0.02 μm to 3 μm.

[0047] By controlling the thickness of the anion exchange resin layer within the above range, the movement of protons between the positive and negative electrodes will not be significantly impaired, and the movement of active materials (such as vanadium ions) can be greatly suppressed. As a result, the current efficiency can be improved while maintaining the voltage efficiency, so that high power efficiency can be obtained. In addition, by forming a three-layer structure in which the first and second ion exchange resin layers sandwich the anion exchange resin layer, direct contact between the anion exchange resin layer and the highly corrosive electrolyte can be avoided. As a result, even in long-term operation, the deterioration of the anion exchange resin layer can be suppressed and high power efficiency can be maintained. In addition, by controlling the value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer within the above range, the distribution of the internal stress generated in the diaphragm in the thickness direction can be reduced. As a result, the curling of the diaphragm can be suppressed.

[0048] The value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer is preferably 0.8 to 1.2, more preferably 0.85 to 1.15, and even more preferably 0.9 to 1.1.

[0049] Examples of methods for adjusting the value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer to 0.7 or more and 1.3 or less include adjusting the coating amount during membrane formation.

[0050] The thickness of each layer in the separator of this embodiment and the thickness of the separator can be measured by the method described in Examples.

[0051] The ion exchange resin layer in this embodiment refers to a layer having a function of suppressing the passage of active material ions and allowing protons and anions to pass therethrough.

[0052] The separator of this embodiment may have other layers other than the above layers. The other layers are not particularly limited, and examples thereof include porous layers that enhance the strength of the separator.

[0053] The diaphragm of this embodiment includes at least a first ion exchange resin layer, an anion exchange resin layer, and a second ion exchange resin layer. The diaphragm of one embodiment may include, in this order, a first ion exchange resin layer, a first anion exchange resin layer, a second ion exchange resin layer, a second anion exchange resin layer, and a third ion exchange resin layer.

[0054] <First ion exchange resin layer>

[0055] The first ion exchange resin layer is not particularly limited, and examples thereof include cation exchange resins.

[0056] The cation exchange resin is not particularly limited, and examples thereof include fluorine-based polyelectrolyte polymers. Examples of the fluorine-based polyelectrolyte polymer include perfluorocarbon polymers having ion exchange groups.

[0057] The ion exchange group is not particularly limited, and examples thereof include -COOH, -SO3H, -PO3H2, or salts thereof. The salt is not particularly limited, and examples thereof include alkali metal salts, alkaline earth metal salts, and amine salts.

[0058] The perfluorocarbon polymer preferably includes a structure represented by the following formula (1).

[0059] -[CF2-CX 1 X 2 ] a -[CF2-CF(-O-(CF2-CF(CF2X 3 )) b -O c -(CFR 1 ) d -(CFR 2 ) e -(CF2) f -X 4 )] g -(1)

[0060] X in formula (1) 1 、X 2 、X 3 、X 4 、R 1、R 2 and a to g are defined as follows, respectively.

[0061] X 1 、X 2 and X 3 Each independently represents a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms.

[0062] The halogen atom is not particularly limited, and examples thereof include fluorine, chlorine, bromine, and iodine. The perfluoroalkyl group having 1 to 3 carbon atoms is not particularly limited, and examples thereof include trifluoromethyl, pentafluoroethyl, perfluoro-n-propyl, and perfluoro-isopropyl.

[0063] From the perspective of chemical stability such as resistance to oxidative degradation of the polymer, X 1 、X 2 and X 3 Each independently is preferably a fluorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms, and more preferably a fluorine atom.

[0064] X 4 It is a -COOZ group, a -SO3Z group, a -PO3Z2 group or a -PO3HZ group.

[0065] Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, NH4, NH3R 11 NH2R 11 R 12 、NHR 11 R 12 R 13 NR 11 R 12 R 13 R 14 .

[0066] Here, R 11 、R 12 、R 13 and R 14 Each is independently an alkyl group or an aryl group. 11 、R 12 、R 13 and R 14 The alkyl group is preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, or an n-hexyl group. The aryl group is not particularly limited, and examples thereof include a phenyl group and a naphthyl group.

[0067] It should be noted that X 4 In the case of -PO3Z2 group, Z may be the same or different. As the above-mentioned alkali metal atom, there is no particular limitation, and examples thereof include lithium atom, sodium atom, potassium atom. As the alkaline earth metal atom, there is no particular limitation, and examples thereof include calcium atom, magnesium atom.4 , from the viewpoint of chemical stability such as oxidation degradation resistance of the polymer, SO3Z is preferred.

[0068] R 1 and R 2 are each independently a halogen atom, a perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group. Here, as the halogen atom of R 1 and R 2 , there is no particular limitation, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among them, a fluorine atom is preferred.

[0069] a and g are numbers satisfying 0 ≤ a < 1, 0 < g ≤ 1, and a + g = 1. b is an integer from 0 to 8. c is 0 or 1. d, e, and f are each independently integers from 0 to 6. Among them, d, e, and f are not simultaneously 0.

[0070] It should be noted that for the structural unit of [CF2 - CX 1 X 2 , and the structural unit of [CF2 - CF(-O-(CF2 - CF(CF2X 3 )) b -O c -(CFR 1 ) d -(CFR 2 ) e -(CF2) f -X 4 )], the arrangement order is not particularly limited and can be a random or block form.

[0071] As the perfluorocarbon polymer in the present embodiment, since there is a tendency for the effects of the present embodiment to become more significant, a perfluorocarbon sulfonic acid resin (hereinafter also referred to as "PFSA resin") is preferred. The PFSA resin in the present embodiment is a resin formed by bonding a perfluorocarbon as a side chain to the main chain containing a PTFE backbone chain, and one or more sulfonic acid groups (a part of which can form a salt form as needed) on each side chain.

[0072] The PFSA resin preferably contains a repeating unit represented by -[CF2CF2]-, and a repeating unit derived from a compound represented by the following formula (3), (4-1), or (4-2).

[0073] CF2 = CF(-O-(CF2CFXO) n -[A]) (3)

[0074] (In formula (3), X is F or a perfluoroalkyl group having 1 to 3 carbon atoms, and n is an integer from 0 to 5. [A] is (CF2) m-SO3H, m represents an integer from 0 to 6. n and m cannot be 0 at the same time.

[0075] CF2=CF-O-(CF2) P -CFX(-O-(CF2) K -SO3H) (4-1)

[0076] CF2=CF-O-(CF2) P -CFX(-(CF2) L -O-(CF2) m -SO3H) (4-2)

[0077] (In formulas (4-1) and (4-2), X is a perfluoroalkyl group having 1 to 3 carbon atoms, P is an integer of 0 to 12, K is an integer of 1 to 5, L is an integer of 1 to 5, and m is an integer of 0 to 6. K and L may be the same or different, and P, K, and L may not all be 0.)

[0078] Furthermore, the PFSA resin is more preferably a resin comprising a repeating unit represented by -[CF2CF2]- and -[CF2-CF(-O-(CF2CFXO) n -(CF2) m -SO3H)]- (wherein X is F or CF3, n is an integer from 0 to 5, and m is an integer from 0 to 12. However, n and m are not both 0.) The repeating unit comprises -[CF2-CF(-O-(CF2CFXO) n -(CF2) m -SO3H)]- (wherein X is CF3, n is 0 or 1, and m is an integer from 0 to 12. However, n and m cannot be 0 at the same time.) A copolymer having at least one repeating unit. When the PFSA resin is a copolymer having the above structure and having a predetermined equivalent weight EW, the resulting separator tends to have sufficient hydrophilicity and enhanced resistance to electrolyte active materials, such as pentavalent vanadium.

[0079] Furthermore, the aforementioned -[CF2-CF(-O-(CF2CFXO) n -(CF2) m -SO3H)]- (wherein X is CF3, n is 0, and m is an integer from 1 to 6), or -[CF2-CF(-O-(CF2)] derived from the compound represented by formula (4-1) and the compound represented by formula (4-2) P -CFX(-O-(CF2) K -SO3H))]- and -[CF2-CFX(-O-(CF2) P -CFX(-(CF2)L -O-(CF2) m -SO3H))] - In the case of these two repeating units, the equivalent weight (EW) decreases, and there is a tendency for the hydrophilicity of the obtained separator to increase.

[0080] The perfluorocarbon polymer represented by the formula (1) in the present embodiment has a tendency for the effects of the present embodiment to become more significant, and thus preferably has a structure represented by the following formula (2).

[0081] -[CF2CF2] a -[CF2-CF(-O-(CF2) m -SO3H)] g -(2)

[0082] In the formula (2), a and g are numbers satisfying 0 ≤ a < 1, 0 < g ≤ 1, and a + g = 1, and m is an integer from 1 to 6.

[0083] The perfluorocarbon polymer in the present embodiment is not particularly limited if it has a structure represented by the formula (1) or the formula (2), and may also contain other structures.

[0084] From the viewpoint of controlling solubility or swelling property, the perfluorocarbon polymer in the present embodiment may be formed by a partial crosslinking reaction between molecules directly or indirectly through ion exchange groups. By performing partial crosslinking, for example, even when the equivalent weight EW of the perfluorocarbon polymer is about 500 g / eq, the water solubility of the perfluorocarbon polymer can be reduced (water resistance is improved).

[0085] In addition, even when the perfluorocarbon polymer has a low melt flow value (has a high molecular weight), through the aforementioned partial crosslinking, the entanglement between molecules is increased, and the solubility and excessive swelling property can also be reduced.

[0086] As the aforementioned partial crosslinking reaction, for example, the reaction of an ion exchange group with a functional group or the main chain of other molecules, or the reaction between ion exchange groups, a crosslinking reaction (covalent bonding) by an oxidation-resistant low molecular compound, oligomer or polymer substance, etc. can be cited. According to needs, it may also be a reaction with a substance forming a salt (ionic bonding with the -SO3H group). As the oxidation-resistant low molecular compound, oligomer or polymer substance, for example, polyols and organic diamines can be cited.

[0087] The molecular weight of the perfluorocarbon polymer in this embodiment is not particularly limited, but is preferably 0.05 g / 10 min or more and 50 g / 10 min or less, more preferably 0.1 g / 10 min or more and 30 g / 10 min or less, and further preferably 0.5 g / 10 min or more and 20 g / 10 min or less, based on the melt flow index (MFI) value measured in accordance with ASTM: D1238 (measurement conditions: temperature 270°C, load 2160 g).

[0088] (Equivalent mass EW)

[0089] From the viewpoint of suppressing the permeation of active material ions and improving power efficiency, and from the viewpoint of improving proton conductivity and reducing resistance, the cation exchange resin preferably has an ion exchange group equivalent weight EW of 450 g / eq or more and 2000 g / eq or less.

[0090] From the perspective of suppressing the permeation of active material ions and improving power efficiency, the equivalent weight (EW) of the cation exchange resin used in this embodiment is more preferably 500 g / eq or greater, further preferably 600 g / eq or greater, and even more preferably 700 g / eq or greater. From the perspective of improving proton conductivity and reducing electrical resistance, the equivalent weight (EW) of the cation exchange resin used in this embodiment is more preferably 1700 g / eq or less, further preferably 1500 g / eq or less, and even more preferably 1200 g / eq or less.

[0091] The equivalent weight EW of the cation exchange resin is preferably 450 g / eq to 2000 g / eq, more preferably 500 g / eq to 1700 g / eq, further preferably 600 g / eq to 1500 g / eq, and still further preferably 700 g / eq to 1200 g / eq.

[0092] In addition, the equivalent mass EW means the dry mass (g) of the cation exchange resin per 1 equivalent of ion exchange groups.

[0093] The equivalent weight EW of the cation exchange resin can be measured by subjecting a perfluorocarbon polymer to salt substitution and back-titrating the resulting solution with an alkaline solution.

[0094] The equivalent weight EW can be adjusted by, for example, the copolymerization ratio of monomers serving as raw materials for the cation exchange resin, the selection of monomer types, and the like.

[0095] Of the dimensional changes of the first ion exchange resin layer due to immersion in a 2 M sulfuric acid aqueous solution described below, at least one of the dimensional changes in the X direction and the Y direction is preferably 100% or more.

[0096] <Dimensional change rate due to immersion in 2M sulfuric acid aqueous solution>

[0097] A test membrane having the same composition as the first ion exchange resin layer and a water content of 1% or less was prepared. The test membrane was immersed in a 2M aqueous sulfuric acid solution at 25°C for 30 minutes. The dimensional change rates in the X direction and in the Y direction perpendicular to the X direction on the surface of the test membrane were calculated using the following formula.

[0098] Dimensional change rate (%) = {(dimension in a specific direction after immersion) / (dimension in a specific direction before immersion)}×100

[0099] It is preferred that the first ion exchange resin layer have a dimensional change rate of 100% or more in at least one of the X and Y directions and a dimensional change rate of less than 115% in the Z direction among the dimensional changes due to immersion in distilled water described below.

[0100] <Dimensional change rate due to distilled water immersion>

[0101] A test membrane having the same composition as the first ion exchange resin layer and a water content of 1% or less was manufactured. The test membrane was immersed in distilled water at 25°C for 30 minutes. The dimensional change rates in the X direction, the Y direction orthogonal to the X direction, and the Z direction orthogonal to the X and Y directions on the surface of the test electrolyte membrane were calculated using the following formula.

[0102] Dimensional change rate (%) = {(dimension in a specific direction after immersion) / (dimension in a specific direction before immersion)}×100

[0103] (Method for producing cation exchange resin)

[0104] The cation exchange resin in the present embodiment is not particularly limited, and can be obtained, for example, by producing a precursor of a cation exchange resin having an ion exchange group (hereinafter also referred to as a "resin precursor") and then subjecting the resulting precursor to a hydrolysis treatment.

[0105] In the case of a PFSA resin, for example, it can be obtained by hydrolyzing a PFSA resin precursor comprising a copolymer of a fluorinated vinyl ether compound represented by the following formula (6) or (7) and a fluorinated olefin monomer represented by the following formula (8).

[0106] CF2=CF-O-(CF2CFXO) n -A (6)

[0107] (In formula (6), X is F or a perfluoroalkyl group having 1 to 3 carbon atoms, n is an integer from 0 to 5, and A is (CF2) m-W, where m is an integer of 0 to 6, n and m cannot be 0 at the same time, and W is a functional group that can be converted into a -SO3H group by hydrolysis.

[0108] CF2=CF-O-(CF2) P -CFX(-O-(CF2) K -W) or

[0109] CF2=CF-O-(CF2) P -CFX(-(CF2) L -O-(CF2) m -W) (7)

[0110] (In formula (7), X is a perfluoroalkyl group having 1 to 3 carbon atoms, P is an integer of 0 to 12, K is an integer of 1 to 5, and L is an integer of 1 to 5. Here, L, K, and m are not simultaneously 0, m is an integer of 0 to 6, and W is a functional group that can be converted into a -SO3H group by hydrolysis.)

[0111] CF2=CFZ (8)

[0112] (In formula (8), Z is H, Cl, F, a perfluoroalkyl group having 1 to 3 carbon atoms, or a cyclic perfluoroalkyl group which may contain oxygen as a ring atom.)

[0113] W in formula (6) and formula (7) is not particularly limited, and examples thereof include -SO2F group, -SO2Cl group, and -SO2Br group. Furthermore, preferably, in formula (6) and formula (7), X is CF3, W is a -SO2F group, and in formula (8), Z is F. Among these, n = 0, m = an integer from 1 to 6, X is CF3, W is a -SO2F group, and Z is F, which tends to result in a solution with high hydrophilicity and a high resin concentration.

[0114] The resin precursor in this embodiment can be synthesized by known means. For example, in the presence of a free radical generator such as a peroxide, a resin having a structure that can be converted into an ion exchange group (X in formula (1)) by hydrolysis or the like can be synthesized by a known means. 4) group (ion exchange group precursor group) and tetrafluoroethylene (hereinafter also referred to as "TFE") and other fluorinated olefins polymerized to produce the resin precursor in this embodiment. The aforementioned polymerization method is not particularly limited, and for example, a method in which the aforementioned fluorinated vinyl compound and fluorinated olefin gas is filled and dissolved in a polymerization solvent such as a fluorinated hydrocarbon to react, thereby performing polymerization (solution polymerization); a method in which the fluorinated vinyl compound itself is used as a polymerization solvent without using a fluorinated hydrocarbon solvent (bulk polymerization); a method in which an aqueous solution of a surfactant is used as a medium and the gas of the fluorinated vinyl compound and the fluorinated olefin is filled and reacted to perform polymerization (emulsion polymerization); a method in which an aqueous solution of a surfactant and an emulsifier such as an alcohol is filled with the gas of the fluorinated vinyl compound and the fluorinated olefin, emulsified, and reacted to perform polymerization (emulsion polymerization); and a method in which the gas of the fluorinated vinyl compound and the fluorinated olefin is filled and suspended in an aqueous solution of a suspension stabilizer to react to perform polymerization (suspension polymerization).

[0115] The resin precursor in this embodiment may be any resin precursor produced by any of the above-mentioned polymerization methods. Alternatively, a block-shaped or tapered polymer obtained by adjusting polymerization conditions such as the supply amount of TFE gas may be used as the resin precursor.

[0116] The resin precursor may be one obtained by treating impure terminals or easily oxidized portions (CO groups, H-bonded portions, etc.) generated in the resin molecular structure during the polymerization reaction under fluorine gas by a known method to fluorinate the portions.

[0117] In the resin precursor, a portion of the ion exchange group precursor group (eg, -SO2F group) may be partially (including between molecules) imidized (eg, alkyl imidized).

[0118] The molecular weight of the resin precursor is not particularly limited, but is preferably 0.05 g / 10 min or more and 50 g / 10 min or less, more preferably 0.1 g / 10 min or more and 30 g / 10 min or less, and further preferably 0.5 g / 10 min or more and 20 g / 10 min or less, based on the melt flow index (MFI) value obtained by measuring the precursor in accordance with ASTM: D1238 (measurement conditions: temperature 270°C, load 2160 g).

[0119] The shape of the resin precursor is not particularly limited, but is preferably 0.5 cm 3 The following granular form, or dispersed liquid form, powder granular form. Among them, the use of a resin precursor in a powder form after polymerization is more preferred. From the perspective of cost, a film-shaped resin precursor formed by extrusion molding can be used.

[0120] The method for producing the perfluorocarbon polymer in this embodiment from a resin precursor is not particularly limited. For example, there is the following method: after the resin precursor is extruded into shape using an extruder using a nozzle or a die, a hydrolysis treatment is performed, or directly the output during polymerization, that is, a dispersed liquid or a powder obtained by precipitation and filtration, is hydrolyzed.

[0121] Specifically, the resin precursor obtained as described above and formed as needed can then be immersed in an alkaline reaction liquid and provided for hydrolysis treatment. As the alkaline reaction liquid used in the hydrolysis treatment, there is no particular limitation, and examples include aqueous solutions of amine compounds such as dimethylamine, diethylamine, monomethylamine and monoethylamine, and aqueous solutions of hydroxides of alkali metals or alkaline earth metals. Among them, an aqueous solution of sodium hydroxide or potassium hydroxide is preferred. In the case of using hydroxides of alkali metals or alkaline earth metals, its content is not particularly limited, and is preferably 10% by mass or more and 30% by mass or less relative to the total reaction solution. More preferably, the above-mentioned reaction solution also contains swelling organic compounds such as methanol, ethanol, acetone and dimethyl sulfoxide (DMSO). The content of the swelling organic compound is preferably 1% by mass or more and 30% by mass or less relative to the total reaction solution.

[0122] The resin precursor is subjected to a hydrolysis treatment in an alkaline reaction liquid, then thoroughly washed with warm water, and then subjected to an acid treatment. The acid used in the acid treatment is not particularly limited, and examples thereof include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid. A mixture of these acids and water is preferred. The above acids may be used alone or in combination of two or more. Furthermore, the alkaline reaction liquid used in the hydrolysis treatment may be removed prior to the acid treatment by, for example, treating it with a cation exchange resin.

[0123] The acid treatment protonates the ion-exchange groups of the resin precursor to form ion-exchange groups. For example, when using the resin precursor produced by the aforementioned formula (6), W in the formula (6) is protonated by the acid treatment to form a -SO3H group. The perfluorocarbon polymer obtained by hydrolysis and acid treatment can be dispersed or dissolved in a protic organic solvent, water, or a mixed solvent of the two, and can form a suspension or solution.

[0124] The perfluorocarbon polymer may contain an alkali metal, an alkaline earth metal, or other radically decomposable transition metal (such as a Ce compound or a Mn compound) in the form of a partial salt thereof (about 0.01 to 5 equivalent % of the total ion exchange group equivalents), or used alone or in combination with a basic polymer described below.

[0125] From the viewpoint of improving electrical resistance and mechanical strength, the separator of the present embodiment preferably contains a mixture of two or more types of perfluorocarbon polymers having ion exchange groups and having different monomer structures.

[0126] By mixing two or more perfluorocarbon polymers, excellent properties can be exhibited by combining their functions.

[0127] Furthermore, from the perspective of achieving better mechanical strength, when two or more perfluorocarbon polymers are mixed, the ratio of the polymer having a higher equivalent weight (EW) is preferably greater than 50% by mass, more preferably greater than 55% by mass, and even more preferably greater than 60% by mass. Polymers having a higher equivalent weight (EW) tend to have higher crystallinity, and thus, when the ratio is set to this level, higher mechanical strength tends to be exhibited.

[0128] (Method for producing raw material membrane of perfluorocarbon polymer)

[0129] The raw material film used in the manufacture of the diaphragm of this embodiment is obtained by processing a precursor resin or perfluorocarbon polymer into a thin film using known methods. For example, the following method can be used: melt-kneading the perfluorocarbon polymer precursor, forming a thin film using an extruder, and then hydrolyzing it to form ion exchange groups. Alternatively, a film can be formed by dispersing the perfluorocarbon polymer in a solvent at one time and then casting the film onto a substrate.

[0130] The content of the cation exchange resin in the first ion exchange resin layer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The content of the cation exchange resin in the first ion exchange resin layer is, for example, 100% by mass or less.

[0131] The thickness of the first ion exchange resin layer is preferably 5 μm or more, more preferably 8 μm or more, and further preferably 10 μm or more. When the thickness of the first ion exchange resin layer is 5 μm or more, high proton conductivity can be maintained and high power efficiency can be achieved. In addition, short circuits caused by electrode penetration can be prevented. The thickness is preferably 50 μm or less, more preferably 30 μm or less, and further preferably 20 μm or less. When the thickness of the first ion exchange resin layer is 50 μm or less, a thinner diaphragm can be formed, thereby reducing the size of the device. The thickness of the above-mentioned first ion exchange resin layer is preferably 5 μm or more and 50 μm or less, more preferably 8 μm or more and 30 μm or less, and further preferably 10 μm or more and 20 μm or less.

[0132] <Anion exchange resin layer>

[0133] The separator of this embodiment includes an anion exchange resin layer containing an anion exchange compound. The presence of the anion exchange resin layer can improve initial power efficiency and other aspects of battery performance. The anion exchange compound referred to herein is a compound that has a basic functional group, such as a primary or tertiary amino group or a quaternary ammonium group, in its molecular structure and is positively charged under acidic conditions of at least pH 1.

[0134] The anion exchange resin layer provides electrostatic repulsion to electrolyte ions within the membrane, excludes metal ions with high charge density from the membrane, and selectively allows protons with low charge density to permeate the membrane, thereby improving power efficiency.

[0135] From the viewpoint of maintaining high power efficiency, the anion exchange compound preferably has a tertiary amino group or a quaternary ammonium group.

[0136] The anion exchange compound is not particularly limited, and examples thereof include polyvinylpyridine polymers or salts thereof, vinylpyridine / divinylbenzene copolymers or salts thereof, vinylpyridine / styrene copolymers or salts thereof, polyethyleneimine or salts thereof, vinylbenzyltrimethylammonium chloride polymers, vinylbenzyltrimethylammonium chloride / divinylbenzene copolymers, vinylbenzyltrimethylammonium chloride / styrene copolymers, polybenzimidazole or salts thereof, polymers having a benzimidazole structure or salts thereof, polypyrrole or salts thereof, and other anion exchange polymers; tetrabutylammonium, octyltrimethylammonium, decyltrimethylammonium, tetradecyltrimethylammonium, dodecyltrimethylammonium, dodecyldimethylbenzylammonium, cetyltrimethylammonium, stearyltrimethylammonium, butylpyridinium, dodecylpyridinium, cetylpyridinium, trimethylamine or salts thereof, triethylamine or salts thereof, tripropylamine or salts thereof, trioctylamine or salts thereof, triethanolamine or salts thereof, and N,N,N',N'-tetramethylbutanediamine or salts thereof. The anion exchange polymer may be obtained by coating a monomer such as pyrrole on the first ion exchange resin layer and polymerizing the resulting polymer by heat treatment, etc. The anion exchange compound is preferably an anion exchange polymer and preferably does not have a cation exchange group such as a sulfonic acid group or a carboxylic acid group.

[0137] The weight average molecular weight of the anion exchange polymer is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 30,000 or more. The weight average molecular weight of the anion exchange polymer is preferably 300,000 or less, more preferably 200,000 or less, and even more preferably 100,000 or less. The weight average molecular weight of the anion exchange polymer is preferably 10,000 or more and 300,000 or less, more preferably 20,000 or more and 200,000 or less, and even more preferably 30,000 or more and 100,000 or less. The weight average molecular weight is a value measured by gel permeation chromatography.

[0138] (Method for Forming Anion Exchange Resin Layer)

[0139] The method for forming the anion exchange resin layer is not particularly limited, and examples thereof include a method of applying an anion exchange compound or a liquid containing a monomer for forming an anionic polymer dissolved or melted to the first ion exchange resin layer; or a method of thermocompression bonding an anion exchange resin membrane containing an anion exchange compound to the first ion exchange resin layer.

[0140] The content of the anion exchange compound in the anion exchange resin layer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. For example, the content of the anion exchange compound in the anion exchange resin layer is 100% by mass or less.

[0141] The thickness of the anion exchange resin layer is 0.02 μm or more, preferably 0.05 μm or more, and more preferably 0.1 μm or more. When the thickness of the anion exchange resin layer is 0.02 μm or more, the permeation of active substances (such as vanadium ions) can be suppressed, the initial power efficiency can be improved, and as a result, the power efficiency is improved. When the thickness of the anion exchange resin layer is 0.05 μm or more, the power efficiency during long-term operation can be further improved. The thickness of the anion exchange resin layer is 3.0 μm or less, preferably 2.5 μm or less, more preferably 2.0 μm or less, and further preferably 1.0 μm or less. When the thickness of the anion exchange resin layer is 3.0 μm or less, high power efficiency can be obtained. In addition, when the thickness of the anion exchange resin layer is 3.0 μm or less, proton conductivity will not be significantly impaired, and high power efficiency can be maintained during long-term operation. When the thickness of the anion exchange resin layer is 2.5 μm or less, proton conductivity will not be impaired, and the permeation of active substances (such as vanadium ions) can be suppressed. Furthermore, when the thickness of the anion exchange resin layer is from 0.02 μm to 3.0 μm, curling of the membrane tends to be suppressed. The thickness of the anion exchange resin layer is from 0.02 μm to 3.0 μm, preferably from 0.05 μm to 2.5 μm, more preferably from 0.1 μm to 2.0 μm, and even more preferably from 0.1 μm to 1.0 μm.

[0142] <Second ion exchange resin layer>

[0143] The second ion exchange resin layer is not particularly limited, but a cation exchange resin may be used.

[0144] The type and content of the cation exchange resin contained in the second ion exchange resin layer are the same as those exemplified and preferred in the first ion exchange resin layer. The thickness of the second ion exchange resin layer is the same as the preferred range in the first ion exchange resin layer.

[0145] The thickness of the diaphragm of this embodiment is preferably 10 μm or more, more preferably 15 μm or more, and further preferably 20 μm or more. By having a thickness of 10 μm or more, the corrosion of the diaphragm due to the electrolyte can be suppressed, and the power efficiency in long-term operation can be further improved. In addition, short circuits caused by electrode penetration can be prevented. The thickness of the diaphragm is preferably 100 μm or less, more preferably 60 μm or less, and further preferably 40 μm or less. By having a thickness of 100 μm or less, a thinner diaphragm can be formed, thereby reducing the size of the device. The thickness of the above-mentioned diaphragm is preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more and 60 μm or less, and further preferably 20 μm or more and 40 μm or less.

[0146] The diaphragm of this embodiment comprises a first ion exchange resin layer, an anion exchange resin layer, and a second ion exchange resin layer in this order, and can be manufactured by stacking the layers in this order. One embodiment of this invention is a method for manufacturing a diaphragm for a redox flow battery comprising a first ion exchange resin layer, an anion exchange resin layer, and a second ion exchange resin layer in this order. The method comprises: forming an anion exchange resin layer on the first ion exchange resin layer to obtain a first ion exchange resin layer / anion exchange resin layer structure; and forming a second ion exchange resin layer on the anion exchange resin layer of the aforementioned structure.

[0147] The diaphragm of this embodiment can also be manufactured by stacking two of the above-described ion exchange resin layer / anion exchange resin layer structures. Therefore, one embodiment of this embodiment is a method for manufacturing a redox flow battery diaphragm comprising, in sequence, a first ion exchange resin layer, an anion exchange resin layer, and a second ion exchange resin layer. The method comprises: forming an anion exchange resin layer on the first ion exchange resin layer to obtain a first ion exchange resin layer / anion exchange resin layer structure; forming an anion exchange resin layer on the second ion exchange resin layer to obtain a second ion exchange resin layer / anion exchange resin layer structure; and laminating the first ion exchange resin layer / anion exchange resin layer structure and the second ion exchange resin layer / anion exchange resin layer structure to each other via the surfaces of their respective anion exchange resin layers, and bonding them by hot pressing.

[0148] The separator of this embodiment is used in a redox flow battery.

[0149] In particular, the separator of this embodiment exhibits excellent battery performance by using the dried separator incorporating it into a cell.

[0150] [Redox Flow Battery]

[0151] Figure 1 An example of a schematic diagram of a redox flow battery using a redox flow battery separator according to this embodiment is shown. The redox flow battery 10 according to this embodiment includes an electrolytic cell 6 comprising a positive electrode cell 2 containing a positive electrode 1 formed of a carbon electrode, a negative electrode cell 4 containing a negative electrode 3 formed of a carbon electrode, and a separator 5 serving as a separator separating the positive electrode cell 2 from the negative electrode cell 4. The positive electrode cell 2 contains a positive electrolyte containing an active material. The negative electrode cell 4 contains a negative electrolyte containing an active material. The positive and negative electrolytes containing the active material are stored, for example, in a positive electrolyte tank 7 and a negative electrolyte tank 8 and supplied to each cell by a pump or the like. Furthermore, the current generated by the redox flow battery can be converted from direct current to alternating current by an AC / DC converter 9. The redox flow battery according to this embodiment is preferably a redox flow secondary battery.

[0152] The redox flow battery using the redox flow battery diaphragm of this embodiment has the following structure: liquid-permeable and porous collector electrodes (for negative electrode and positive electrode) are arranged on both sides of the diaphragm, respectively, and they are clamped by pressing, one of which is separated by the diaphragm as the positive electrode unit chamber and the other as the negative electrode unit chamber, and the thickness of the two unit chambers is ensured by a spacer.

[0153] In the case of a vanadium-based redox flow secondary battery, a stream containing tetravalent vanadium (V 4+ ) and vanadium pentavalent (V 5+ ) of the positive electrode electrolyte, and a vanadium trivalent (V 3+ ) and vanadium divalent (V 2+ ) of the negative electrode electrolyte, thereby performing the charging and discharging of the battery. At this time, during charging, in the positive electrode unit chamber, the vanadium ions release electrons, so V 4+ Oxidized to V 5+ In the negative electrode unit, the electrons returned from the external circuit are used to 3+ Restore to V 2+ When using this redox reaction, in the positive electrode unit room, protons (H + ) becomes excessive, while in the negative electrode unit cell, protons (H +) is insufficient. The diaphragm selectively moves excess protons in the positive electrode cell chamber to the negative electrode chamber, maintaining electrical neutrality. During discharge, the reverse reaction occurs. The power efficiency (%) at this time is expressed as the ratio (%) obtained by dividing the discharge electric energy by the charging electric energy. Both electric energies depend on the internal resistance of the battery cell and the ion selectivity of the diaphragm and other current losses. Reducing the internal resistance improves the voltage efficiency, and improving the ion selectivity and reducing other current losses improve the power efficiency, so it becomes an important indicator in redox flow batteries.

[0154] Carbon Electrode

[0155] The carbon electrode used in the redox flow battery is not particularly limited. In order to pass the electrolyte, it is preferably a porous body with continuous voids, more preferably a porous body with continuous voids. As a carbon electrode with continuous voids, there is no particular limitation, and examples thereof include carbon felt, carbon paper, and carbon foam. Among them, carbon foam is more preferred from the viewpoint of high flexibility, large surface area, and ability to reduce resistance. The carbon foam preferably has a structure in which the carbon portion is continuous in three dimensions. The carbon foam preferably has a linear portion and a junction connecting the aforementioned linear portion. By having such a structure, an electrode with flexibility and a high surface area can be formed. Even if a thinner film is used for the diaphragm of the redox flow battery, the power efficiency will not be reduced, and a good battery can be obtained.

[0156] Carbon foam can also be compressed and porosity adjusted using known methods, particularly the method described in International Publication No. 2002 / 062879. Compression and porosity adjustment can increase the carbon surface area per unit volume, thereby reducing the resistance of the redox flow battery.

[0157] [Membrane-electrode assembly for redox flow battery]

[0158] The redox flow battery membrane electrode assembly (hereinafter simply referred to as the "membrane electrode assembly") of this embodiment includes the membrane of this embodiment and a carbon electrode bonded to the membrane. The carbon electrode only needs to be formed on at least one side of the membrane, but it can also be formed on both sides. When the carbon electrode is formed on one side of the membrane, the membrane electrode assembly can be used, for example, as the positive electrode 1 and membrane 5, or the negative electrode 3 and membrane 5 in the redox flow battery 10 described above. When the carbon electrodes are formed on both sides of the membrane, the membrane electrode assembly can be used, for example, as the positive electrode 1, membrane 5, and negative electrode 3 in the redox flow battery 10 described above.

[0159] [Cell for redox flow battery]

[0160] The redox flow battery cell (hereinafter simply referred to as a "cell") of this embodiment includes the diaphragm-electrode assembly of this embodiment. For example, the cell of this embodiment includes the diaphragm-electrode assembly of this embodiment and a non-impregnated current collector plate in contact with the carbon electrode in the diaphragm-electrode assembly. The current collector plate is a well-known current collector plate used in redox flow batteries.

[0161] Example

[0162] The present embodiment will be described in more detail below using examples, but the present embodiment is not limited to the following examples. It should be noted that the evaluation method and measurement method used in the present embodiment are as follows.

[0163] <Film thickness>

[0164] (Coating film and laminated film)

[0165] The film thickness of the ion exchange resin layer produced by coating and the film thickness of the final separator (laminated film) were evaluated using a film thickness meter "543-551-1 / 215-151" (manufactured by Mitutoyo Co., Ltd.).

[0166] (Anion exchange resin layer)

[0167] The thickness of the anion exchange resin layer was evaluated by observing a cross section of the membrane using a scanning electron microscope (SEM). The SEM used was a "SU8010" (manufactured by Hitachi High-Technologies Corporation), and the membrane thickness was evaluated based on images observed at 20,000 times magnification. The membrane cross section was formed using a microtome "EM UC7" (manufactured by Leica).

[0168] Curl Evaluation

[0169] The curling was evaluated by immersing a 5 cm square of the film in distilled water for 5 minutes and measuring the degree of curling with a ruler immediately after removal. Figure 2 The degree of warping refers to the distance (height) from the ground surface to the end surface of the warped film when the film is placed on a flat surface ( Figure 2 Warpage was evaluated by the largest value among the four sides of the film.

[0170] A: 0mm or more and less than 5mm

[0171] B: 5mm or more and less than 10mm

[0172] C: 10mm or more (including curling)

[0173] <Redox Flow Battery Evaluation>

[0174] In the evaluation of the redox flow battery, a unit consisting of a Viton rubber gasket, a Teflon (registered trademark) flow path frame, a graphite separator, and a stainless steel end plate was used. For the diaphragm, the diaphragms produced in the examples and comparative examples were cut into 40×150 mm pieces for use. The gasket thickness was adjusted so that the compression rate of the electrode (the ratio of the thickness before and after compression) was 62%. For the electrode, a carbon fiber nonwoven fabric "AAF304ZF" (product name, manufactured by Toyobo Co., Ltd.) was cut into 10×50 mm pieces for use.

[0175] Combine two electrodes, a diaphragm, and unit components in a prescribed order and fasten them with stainless steel bolts. Connect the assembled unit to an electrolyte circulation device consisting of an electrolyte tank and a liquid delivery pump. Add 30 mL of a vanadium sulfuric acid solution with a vanadium ion concentration of 1.5 M, a vanadium ion valence of 3.5, and a sulfate ion concentration of 4.5 M to the electrolyte tank and circulate it at a flow rate of 7.5 mL / min. The charge and discharge test was performed using a charge and discharge power supply device "PFX2011" (product name, manufactured by Kikusui Electronics Industry Co., Ltd.) and a control unit "PFX2121" (product name, manufactured by Kikusui Electronics Industry Co., Ltd.) using a constant current method. The voltage range was set to 1.00-1.55 V and the current density was set to 80 mA / cm 2 .

[0176] (Power efficiency)

[0177] The power efficiency was determined by dividing the discharge energy by the charge energy after 2 charge and discharge cycles and 100 cycles. The evaluation criteria were as follows.

[0178] Evaluation Benchmarks

[0179] A: Power efficiency is above 88%

[0180] B: Power efficiency is 87% or more and less than 88%

[0181] C: Power efficiency is less than 87%

[0182] [Synthesis Example 1: Synthesis of PBI-O]

[0183] In a glove box, 250 g of polyphosphoric acid (115% H₃PO₄ conversion, manufactured by Sigma-Aldrich Co., LLC) was placed in a separable flask, sealed, and removed from the glove box. The flask was heated to 90°C in an oil bath and stirred at 100 rpm for 4 hours. Then, 6.43 g of 3,3'-diaminobenzidine (Sigma-Aldrich Co., LLC) was added, and the internal temperature was raised to 120°C. Next, 7.75 g of 4,4'-dicarboxy ether (Sigma-Aldrich Co., LLC) was added, and the internal temperature was raised to 200°C. After reaching 200°C, the reaction was allowed to proceed for 24 hours. After 24 hours, 192 g (100 mL) of polyphosphoric acid (105% H₃PO₄ conversion, manufactured by Nacalai Tesque, Inc.) was added, and the internal temperature was cooled to 100°C to obtain a dark brown polymer solution. The reaction was carried out under an argon atmosphere.

[0184] The resulting polymer solution was reprecipitated with 4 L of ion-exchanged water and filtered to obtain a filamentous solid (filamentous solid 1). The resulting filamentous solid 1 was cut, washed with stirring in 4 L of ion-exchanged water for 8 hours, and then washed with stirring in 3 L of methanol (manufactured by FUJIFILM Wako Pure Chemical Corporation) for 1 hour, then filtered and dried under reduced pressure at 100°C for 4 hours to obtain a black solid (dried solid 1).

[0185] The dried solid 1 was added to 1110 g (750 mL) of methanesulfonic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), heated and stirred at 100°C for dissolution, reprecipitated with 7.5 L of ion-exchanged water, and filtered to obtain a filamentous solid (filamentous solid 2). The obtained filamentous solid 2 was washed with stirring in 2 L of 0.1 M ammonia water (manufactured by Kanto Chemical Industry Co., Ltd.) for 8 hours, washed with stirring in 5 L of ion-exchanged water for 8 hours, washed with stirring in 4 L of N,N-dimethylacetamide (manufactured by FUJIFILM Wako Pure Chemical Corporation) for 1 hour, and washed with stirring in 4 L of methanol for 1 hour. After washing, the mixture was filtered and dried under reduced pressure at 100°C for 24 hours to obtain 10.88 g of a dark brown solid (PBI-O).

[0186] [Examples 1 to 17]

[0187] An anion exchange compound solution was prepared so as to have 1% by mass of the anion exchange compound shown in Table 1. A 20% by mass cation exchange resin dispersion shown in Table 1 was cast onto a polyimide (PI) film using a doctor blade coater, and dried and annealed at the temperature and time shown in Table 1 to produce a cation exchange resin membrane (first ion exchange resin layer) having the thickness after drying shown in Table 1.

[0188] The prepared cation exchange resin membrane was attached to a 50°C stage of a spray coating apparatus "PCS2020" (product name, manufactured by ASAHISUNAC CORPORATION). The anion exchange compound solution was sprayed onto the membrane within a vacuum chuck at 50°C. The membrane was then dried under the conditions shown in Table 1 to form an anion exchange resin layer.

[0189] On the formed anion exchange resin layer, a second ion exchange resin layer was formed by the formation method shown in Table 1 under the following "pressing" or "coating" conditions to obtain a redox flow battery separator.

[0190] <Pressure>

[0191] A cation exchange resin membrane (second ion exchange resin layer) was prepared under the same conditions as for the first ion exchange resin layer. The prepared cation exchange resin membrane was superimposed on the anion exchange resin layer and hot pressed under the conditions shown in Table 1.

[0192] <Coating>

[0193] The anion exchange resin layer was cast using a doctor blade coater, and dried and annealed at the temperature and time shown in Table 1 to prepare a cation exchange resin membrane (second ion exchange resin layer) having the thickness after drying shown in Table 1.

[0194] [Comparative Example 1]

[0195] A redox flow battery separator was obtained in the same manner as in Example 1 except that the anion exchange resin layer was not formed.

[0196] [Comparative Example 2]

[0197] A redox flow battery separator was obtained in the same manner as in Example 2 except that the second ion exchange resin layer was not formed.

[0198] [Comparative Example 3]

[0199] A redox flow battery separator was obtained in the same manner as in Example 2 except that the spraying amount was adjusted so that the thickness of the anion exchange resin layer would be 5.0 μm.

[0200] [Comparative Examples 4 and 5]

[0201] A redox flow battery separator was obtained in the same manner as in Example 2 except that the thickness of the cation exchange resin membranes (first and second ion exchange resin layers) was adjusted and the value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer was changed.

[0202] [Table 1]

[0203]

[0204] In Table 1, the meanings of various abbreviations and the like are as follows.

[0205] C-1: Nafion dispersion (EW 1100 g / mol, solid content 20 wt%, manufactured by Sigma-Aldrich Co., LLC)

[0206] C-2: Aquivion dispersion D72-25BS (EW 720 g / mol, solid content 25 wt%, manufactured by Sigma-Aldrich Co., LLC)

[0207] C-3: Aquivion dispersion D98-25BS (EW 980 g / mol, solid content 25 wt%, manufactured by Sigma-Aldrich Co., LLC)

[0208] P4VP: polyvinylpyridine (weight average molecular weight Mw: 60,000, manufactured by Sigma-Aldrich Co., LLC)

[0209] VBTMA / DVB: Vinylbenzyltrimethylammonium chloride (VBDMA) / divinylbenzene (DVB) copolymer

[0210] PBI: polybenzimidazole "MRS0810H" (weight average molecular weight Mw: 55,000, manufactured by SATO LIGHT INDUSTRIAL Co., Ltd., a polymer represented by the following formula (A))

[0211] PBI-O: polybenzimidazole produced in Synthesis Example 1 (weight average molecular weight Mw 60,000, polymer represented by the following formula (A))

[0212]

[0213] EtOH: ethanol

[0214] DMAc: dimethylacetamide

[0215] The above-mentioned evaluations were performed using the separators obtained in the above-mentioned Examples and Comparative Examples. The results are shown in Table 2.

[0216] [Table 2]

[0217]

Claims

1. A redox flow battery separator comprising, in this order, a first ion exchange resin layer, an anion exchange resin layer containing an anion exchange compound, and a second ion exchange resin layer. The value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer is 0.8 or more and 1.2 or less, The thickness of the anion exchange resin layer is 0.1 μm or more and 1.0 μm or less. in, The first ion exchange resin layer is a first ion exchange resin layer containing a cation exchange resin, and the second ion exchange resin layer is a second ion exchange resin layer containing a cation exchange resin.

2. The redox flow battery separator according to claim 1, wherein The value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer is 0.85 or more and 1.15 or less.

3. The redox flow battery separator according to claim 1, wherein The value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer is 0.9 or more and 1.1 or less.

4. The redox flow battery separator according to claim 1, wherein The thickness of the first ion exchange resin layer and the second ion exchange resin layer are respectively 5 μm or more and 50 μm or less.

5. The redox flow battery separator according to claim 1 or 4, wherein The thickness of the first ion exchange resin layer and the second ion exchange resin layer are respectively 8 μm or more and 30 μm or less.

6. The redox flow battery separator according to claim 1 or 4, wherein The thickness of the first ion exchange resin layer and the second ion exchange resin layer are respectively 10 μm or more and 20 μm or less.

7. The redox flow battery separator according to claim 1, wherein The cation exchange resin contained in the first ion exchange resin layer contains a fluorine-based polyelectrolyte polymer.

8. The redox flow battery separator according to claim 1, wherein The cation exchange resin contained in the second ion exchange resin layer contains a fluorine-based polyelectrolyte polymer.

9. The redox flow battery separator according to claim 7 or 8, wherein The fluorine-based polyelectrolyte polymer includes a perfluorocarbon polymer having an ion exchange group.

10. The redox flow battery separator according to claim 7 or 8, wherein The cation exchange resin has an ion exchange group equivalent weight (EW) of 450 g / eq or more and 2000 g / eq or less, where the EW refers to a dry weight in grams of the cation exchange resin per 1 equivalent of the ion exchange group.

11. The redox flow battery separator according to claim 7 or 8, wherein The cation exchange resin has an ion exchange group equivalent weight (EW) of 500 g / eq or more and 1700 g / eq or less, where the equivalent weight (EW) refers to the dry weight in grams of the cation exchange resin per 1 equivalent of ion exchange groups.

12. The redox flow battery separator according to claim 7 or 8, wherein The cation exchange resin has an ion exchange group equivalent weight (EW) of 600 g / eq or more and 1500 g / eq or less, where the equivalent weight (EW) refers to the dry weight in grams of the cation exchange resin per 1 equivalent of ion exchange groups.

13. The redox flow battery separator according to claim 7 or 8, wherein The cation exchange resin has an ion exchange group equivalent weight (EW) of 700 g / eq or more and 1200 g / eq or less, where the equivalent weight (EW) refers to the dry weight in grams of the cation exchange resin per 1 equivalent of the ion exchange group.

14. The redox flow battery separator according to claim 1 or 4, wherein The anion exchange compound has a tertiary amino group or a quaternary ammonium group.

15. The redox flow battery separator according to claim 7 or 8, wherein The anion exchange compound has a tertiary amino group or a quaternary ammonium group.

16. The redox flow battery separator according to claim 15, wherein The fluorine-based polyelectrolyte polymer includes a perfluorocarbon polymer having an ion exchange group.

17. The redox flow battery separator according to claim 15, wherein The cation exchange resin has an ion exchange group equivalent weight (EW) of 450 g / eq or more and 2000 g / eq or less, where the EW refers to a dry weight in grams of the cation exchange resin per 1 equivalent of the ion exchange group.

18. The redox flow battery separator according to claim 15, wherein The cation exchange resin has an ion exchange group equivalent weight (EW) of 500 g / eq or more and 1700 g / eq or less, where the equivalent weight (EW) refers to the dry weight in grams of the cation exchange resin per 1 equivalent of ion exchange groups.

19. The redox flow battery separator according to claim 15, wherein The cation exchange resin has an ion exchange group equivalent weight (EW) of 600 g / eq or more and 1500 g / eq or less, where the equivalent weight (EW) refers to the dry weight in grams of the cation exchange resin per 1 equivalent of ion exchange groups.

20. The redox flow battery separator according to claim 15, wherein The cation exchange resin has an ion exchange group equivalent weight (EW) of 700 g / eq or more and 1200 g / eq or less, where the equivalent weight (EW) refers to the dry weight in grams of the cation exchange resin per 1 equivalent of the ion exchange group.

21. The redox flow battery separator according to any one of claims 16 to 20, wherein The redox flow battery separator has a thickness of 10 μm or more and 100 μm or less.

22. The redox flow battery separator according to any one of claims 16 to 20, wherein The redox flow battery separator has a thickness of 15 μm or more and 60 μm or less.

23. The redox flow battery separator according to any one of claims 16 to 20, wherein The redox flow battery separator has a thickness of 20 μm or more and 40 μm or less.

24. A method for producing a redox flow battery separator according to any one of claims 1 to 23, comprising: a method for producing a redox flow battery separator comprising, in order, a first ion exchange resin layer, an anion exchange resin layer, and a second ion exchange resin layer; The manufacturing method comprises: forming an anion exchange resin layer on the first ion exchange resin layer to obtain a first ion exchange resin layer / anion exchange resin layer structure; a step of forming a second ion exchange resin layer on the anion exchange resin layer of the structure.

25. A method for producing a redox flow battery separator according to any one of claims 1 to 23, comprising: a method for producing a redox flow battery separator comprising, in order, a first ion exchange resin layer, an anion exchange resin layer, and a second ion exchange resin layer; The manufacturing method comprises: forming an anion exchange resin layer on the first ion exchange resin layer to obtain a first ion exchange resin layer / anion exchange resin layer structure; forming an anion exchange resin layer on the second ion exchange resin layer to obtain a second ion exchange resin layer / anion exchange resin layer structure; A step of attaching the first ion exchange resin layer / anion exchange resin layer structure and the second ion exchange resin layer / anion exchange resin layer structure to each other with the surfaces of the respective anion exchange resin layers, and bonding them by heat pressing. 26 . A redox flow battery separator electrode assembly comprising the redox flow battery separator according to claim 1 , and a carbon electrode bonded to the redox flow battery separator. 27 . A redox flow battery cell comprising the membrane electrode assembly according to claim 26 .

28. A redox flow battery comprising an electrolytic cell, the electrolytic cell comprising: a positive electrode cell chamber including a positive electrode formed of a carbon electrode, a negative electrode cell chamber including a negative electrode formed of a carbon electrode, and a separator separating the positive electrode cell chamber from the negative electrode cell chamber. The positive electrode unit chamber contains a positive electrode electrolyte containing an active material, The negative electrode unit chamber contains a negative electrode electrolyte containing an active material, The separator is the separator for a redox flow battery according to any one of claims 1 to 23.

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