Ion exchange membrane, membrane electrode assembly, cell for redox flow batteries, and redox flow battery

Abstract

An ion exchange membrane comprising a resin composition that contains a cation exchange resin and a side chain heteroaromatic resin having a structural unit represented by general formula 1 (in the formula, R1, R2, and R3 may be the same or different from each other, and each represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1-10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6-10 carbon atoms, R4 represents a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1-10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6-10 carbon atoms, and Hc represents a substituted or unsubstituted heteroaromatic group having 4-30 carbon atoms, having at least one nitrogen atom in the heteroaromatic ring structure, and including a 5-membered ring and / or 6-membered ring structure.).

Description

Title of Invention: ION-EXCHANGE MEMBRANE, MEMBRANE ELECTRODE ASSEMBLY, CELL FOR REDOX FLOW BATTERY, AND REDOX FLOW BATTERY Technical Field

[0001] The present invention relates to an ion-exchange membrane, a membrane electrode assembly, a cell for a redox flow battery, and a redox flow battery. Background Art

[0002] Redox flow batteries are secondary batteries storing and discharging electricity, and are suitable as large-scale stationary batteries used for equalization of electricity usage. Such a redox flow battery has a structure in which a positive electrode electrolyte solution (positive electrode cell) including a positive electrode and a positive electrode redox active material, and a negative electrode electrolyte solution (negative electrode cell) including a negative electrode and a negative electrode redox active material are partitioned by a separation membrane, and carries out charge and discharge by use of the oxidation-reduction reaction of both of these redox active materials. The respective electrolyte solutions including both of these redox active materials can be allowed to flow from storage tanks to an electrolyzer, resulting in an increase in capacity.

[0003] As the redox active materials included in the electrolyte solutions, for example, iron / chromium-based, chromium / bromine-based or zinc / bromine-based redox active materials, or vanadium-based redox active materials utilizing the difference in charge are used. In particular, a vanadium-based redox flow battery has the advantages of being high in electromotive force, providing a quick electrode reaction of a vanadium ion, being small in the amount of hydrogen generated in a side reaction, and being high in output, and therefore the development thereof is seriously advanced.

[0004] Such a vanadium-based redox flow battery utilizes oxidation-reduction reactions of bivalence (V2+) / trivalence (V3+) of vanadium in a negative electrode cell, and of tetravalence (V4+) / pentavalence (V5+) of vanadium in a positive electrode cell. Thus, redox active materials included in electrolyte solutions of the positive electrode cell and the negative electrode cell are the same type of vanadium ions, and therefore the electrolyte solutions can be reproduced by an electrical process even if mixed through a separation membrane and are excellent from the viewpoint of being usable for a long period. However, such a separation membrane is demanded to suppress permeation of the redox active materials as much as possible because permeation of the redox active materials leads to neutralization of any charge stored and thus a reduction in current efficiency. On the other hand, such a separation membrane is demanded not to prevent permeation of protons as much as possible because such protons included in the electrolyte solutions sufficiently easily permeate through such a separation membrane, allowing the battery to be reduced in resistance and enhanced in voltage efficiency. In other words, there is a demand for a separation membrane which has both a high current efficiency and a high voltage efficiency, namely, which can achieve a high power efficiency (the power efficiency is a product of the current efficiency and the voltage efficiency).

[0005] In order to suppress permeation of redox active materials and achieve a high power efficiency, application of processing to an ion-exchange membrane is disclosed (Patent Literatures 1 to 3). Patent Literature 1 discloses an excellent initial power efficiency by alternately stacking of a cationexchange group layer and an anion-exchange group layer. Patent Literature 2 discloses a low proton area resistivity and an excellent vanadium ion permeation selectivity by use of a membrane including a sulfonated polymer and a heterocyclic molecule having a plurality of nitrogen atoms. Patent Literature 3 discloses at least one or more of discharge capacity, current efficiency, voltage efficiency, and power efficiency which are excellent by use of a polyelectrolyte membrane provided with a crossover prevention layer as a metal layer formed by reduction of a cationic metal, therein. Patent Literature 4 discloses a suppressed curl and an excellent power efficiency by use of a separation membrane for a redox flow battery, including a first ionexchange resin layer, an anion-exchangeable resin layer containing an anion-exchangeable compound, and a second ion-exchange resin layer in the listed order.

[0006] Patent Literature 5 discloses a 5% by mass solution in which a fluororesin having an acidic group is dissolved in a solvent of ethanol and water at a mass ratio of 50:50. Patent Literature 6 discloses a thin membrane having high strength, favorable adhesiveness with a substrate, and favorable chemical resistance, obtained by use of a polyelectrolyte solution in which a fluororesin having an acidic group is dissolved in a solvent containing a polar solvent which is hydrophilic and which has a high boiling point. Patent Literature 7 and Non Patent Literature 1 each indicate that, in a case where a polymer which has a high rate of sulfonic acid group in a fluororesin having a specified acidic group is tried to be produced, it is difficult to provide a sufficiently large molecular weight of the polymer and to produce a polyelectrolyte membrane having sufficient mechanical strength. Patent Literature 8 discloses co-extrusion of a perfluorosulfonic acid polymer precursor together with an immiscible polymer, which thus allows for formation of a multi-layer film having a perfluorosulfonic acid polymer precursor layer supported by an immiscible polymer layer and reduced in thickness and also provides a protonexchange membrane reduced in thickness. Citation List Patent Literatures

[0007] Patent Literature 1: Japanese Patent Laid-Open No. Hll-260390 Patent Literature 2: International Publication No. WO 2017 / 155648 Patent Literature 3: International Publication No. WO 2016 / 163773 Patent Literature 4: International Publication No. WO 2021 / 215126 Patent Literature 5: Japanese Patent Laid-Open No. H07-296634 Patent Literature 6: Japanese Patent Laid-Open No. 2004164854 Patent Literature 7: International Publication No. WO 2008 / 090990 Patent Literature 8: International Publication No. WO 2013 / 091073 Non Patent Literature

[0008] Non Patent Literature 1: W. Vielstich, H.A. Gasteiger, A. Lamm, "Handbook of Fuel Cells, vol.3", USA, John Wiley & Sons, Ltd., 2003, Chapter 30, p.351-352 Summary of Invention

[0009] Embodiments of the present invention are as follows . <1> An ion-exchange membrane comprising a resin composition comprising a side-chain heteroaromatic resin having a structural unit represented by the following general formula 1: R1 R3 wherein, R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, and He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure, and a cation-exchangeable resin. <2> The ion-exchange membrane according to <1>, wherein a weight ratio between the side-chain heteroaromatic resin and the cation-exchangeable resin is 1:100 to 100 :1. <3> The ion-exchange membrane according to <1> or <2>, wherein the cation-exchangeable resin is a fluororesin. <4> The ion-exchange membrane according to <3>, wherein the fluororesin has a structural unit represented by the following general formula G1: F X6. F F CF2X8 wherein, X5, X6, X7, and X8 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X5 and X6 or X5 and X7 are optionally bound to each other to form a cyclic structure, R5 and R6 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, X9 is a group represented by -COOZ, -SO3Z, -PO3Z2, or -PO3HZ, Z is at least one selected from the group consisting of a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, and an amine, and the fluororesin is optionally crosslinked to each other by ion crosslinking via X9, h and p each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < h < 1, 0 < p < 1, and h + p = 1, i is an integer of 0 to 8, j is 0 or 1, and k, 1, and m are each optionally the same or different, and are each an integer of 0 to 6, provided that, when k, 1, and m are 0 at the same time, X9 is CF(CF2X10)2, X10 is a group represented by -COOZ, -SO3Z, -PO3Z2, or -PO3HZ, and Z is the same as described above. <5> The ion-exchange membrane according to any one of <1> to <4>, alternately comprising at least one layer (L) comprising the resin composition, and at least one layer (M) comprising a fluororesin having a structural unit represented by the following general formula G1: F X6. F F wherein the definition of each substituent has the same meaning as in the general formula G1 described above. <6> The ion-exchange membrane according to <5>, comprising one layer (L) and one layer (M). <7> The ion-exchange membrane according to <5> or <6>, comprising the layer (L), the layer (M), and the layer (L) in the listed order. <8> An ion-exchange membrane comprising a side-chain heteroaromatic resin having a structural unit represented by the following general formula 2: wherein, R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure, Rf is an aliphatic hydrocarbon group substituted with at least one fluorine atom, and X" is a counter anion. <9> The ion-exchange membrane according to <8>, alternately comprising at least one layer (L) comprising the side-chain heteroaromatic resin, and at least one layer (M) comprising a fluororesin having a structural unit represented by the following general formula G1: F X6. F F wherein the definition of each substituent has the same meaning as in the general formula G1 described above. <10> The ion-exchange membrane according to <9>, comprising one layer (L) and one layer (M). <11> The ion-exchange membrane according to <9>, comprising the layer (L), the layer (M), and the layer (L) in the listed order. <12> The ion-exchange membrane according to any one of <9> to <11>, wherein the layer (L) further comprises a cation-exchangeable resin. <13> The ion-exchange membrane according to <12>, wherein a weight ratio between the side-chain heteroaromatic resin and the cation-exchangeable resin is 1:100 to 100 :1. <14> The ion-exchange membrane according to <12> or <13>, wherein the cation-exchangeable resin is a fluororesin. <15> The ion-exchange membrane according to <14>, wherein the fluororesin has a structural unit represented by the following general formula G1: wherein the definition of each substituent has the same meaning as in the general formula G1 described above. <16> The ion-exchange membrane according to <1>, wherein the side-chain heteroaromatic resin further has a structural unit represented by the following general formula 2: [2] wherein, R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure, Rf is an aliphatic hydrocarbon group substituted with at least one fluorine atom, and X- is a counter anion. <17> The ion-exchange membrane according to <16>, wherein a molar ratio between the structural unit represented by the general formula 1 and the structural unit represented by the general formula 2 is 1:100 to 100:1. <18> The ion-exchange membrane according to <16> or <17>, wherein a weight ratio between the side-chain heteroaromatic resin and the cation-exchangeable resin is 1:100 to 100:1. <19> The ion-exchange membrane according to any one of <16> to <18>, wherein the cation-exchangeable resin is a fluororesin . <20> The ion-exchange membrane according to any one of <16> to <19>, wherein the fluororesin has a structural unit represented by the following general formula Gl: cf2x8 [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above. <21> The ion-exchange membrane according to <20>, alternately comprising at least one layer (L) comprising the resin composition, and at least one layer (M) comprising a fluororesin having a structural unit represented by the following general formula Gl: [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above. <22> The ion-exchange membrane according to <21>, comprising one layer (L) and one layer (M). <23> The ion-exchange membrane according to <21>, comprising the layer (L), the layer (M), and the layer (L) in the listed order. <24> An ion-exchange membrane comprising a layer (LI) comprising a heteroaromatic structure containing fluororesin having a structural unit represented by the following general formula Al, a saponified product thereof or a salt thereof: [Al] cf2x4 wherein, X1, X2, X3, and X4 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X1 and X2 or X1 and X3 are optionally bound to each other to form a cyclic structure, R1 and R2 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, R3 is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R4 is a linking group that links NR3 and He, and is a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, X10 is a divalent group represented by formula -CO2-or -SO2-, He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group containing at least one nitrogen atom and containing a five-membered ring and / or six-membered ring structure, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1, b is an integer of 0 to 8, c is 0 or 1, and d, e, and f are each optionally the same or different, and are each an integer of 0 to 6, provided that d, e, and f are not 0 at the same time, and a layer (Ml) comprising a fluororesin (Gl) having a structural unit represented by the following general formula Gl: wherein the definition of each substituent has the same meaning as in the general formula Gl described above. <25> The ion-exchange membrane according to <24>, comprising three or more layers, the three or more layers alternately comprising the layer (LI), and the layer (Ml). <26> The ion-exchange membrane according to <24> or <25>, wherein a thickness of the layer (LI) is 10 p.m or less. <27> The ion-exchange membrane according to any one of <24> to <26>, wherein a thickness of the ion-exchange membrane is 200 gm or less. <28> An ion-exchange membrane comprising a layer (L3) comprising a side-chain nitrogen atomcontaining fluororesin having a structural unit represented by the following general formula A3, a saponified product thereof or a salt thereof: X21, I —c- I I -a X20 X22 • F1             r R24 ■ —c--x24-nr22—-r23-n— I LFJf         L Jh R26 r25-n ^R27 [A3] wherein, X20 , X21 , X22 , and X23 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X20 and X21 or X20 and X22 optionally form a cyclic structure, R20 and R21 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, R22 and R24 are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R26 and R27 are each a hydrogen atom, or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, and at least one of R26 and R27 is a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, R23 and R25 are each optionally the same or different, and are each a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, wherein, when h is 2 or more, R23s repeated are each optionally the same or different, X24 is a divalent group represented by -CO2- or -SO2-, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1, b is an integer of 0 to 8, c is 0 or 1, and d, e, f, and h are each optionally the same or different, and are each an integer of 0 to 6, provided that d, e, and f are not 0 at the same time, and a layer (M3) comprising a fluororesin (Gl) having a structural unit represented by the following general formula Gl: r f i r f I -c— I L R6 J r f i cf2x8 [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above. <29> The ion-exchange membrane according to <28>, comprising three or more layers, the three or more layers alternately comprising the layer (L3), and the layer (M3). <30> The ion-exchange membrane according to <28> or <29>, wherein a thickness of the layer (L3) is 10 gm or less. <31> The ion-exchange membrane according to any one of <28> to <30>, wherein a thickness of the ion-exchange membrane is 200 p.m or less. <32> The ion-exchange membrane according to any one of <1> to <31>, for a redox flow battery. <33> A membrane electrode assembly, wherein the ionexchange membrane according to any one of <1> to <31> and at least one electrode are bonded. <34> The membrane electrode assembly according to <33>, for a redox flow battery. <35> A cell for a redox flow battery, the cell comprising a first electrolyte solution comprising a first redox active material, a second electrolyte solution comprising a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a separation membrane located between the first electrolyte solution and the second electrolyte solution, wherein the separation membrane is the ion-exchange membrane according to any one of <1> to <31>. <36> The cell for a redox flow battery according to <35>, wherein the cell is a membrane electrode assembly in which the separation membrane and at least one electrode are bonded. <37> The cell for a redox flow battery according to <35> or <36>, wherein at least one of the first electrode and the second electrode is a carbon electrode. <38> The cell for a redox flow battery according to any one of <35> to <37>, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metallic redox active material, a non-metallic redox active material, and an organic redox active material. <39> A redox flow battery, wherein the cell for a redox flow battery according to any one of <35> to <38> is stacked. <40> A cell for a redox flow battery, the cell comprising a first electrolyte solution comprising a first redox active material, a second electrolyte solution comprising a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a separation membrane located between the first electrolyte solution and the second electrolyte solution, wherein the separation membrane comprises at least a first cation-exchangeable resin layer, and an anion-exchangeable resin layer, an equivalent weight of the separation membrane is 1150 g / eq or less, a thickness of the anion-exchangeable resin layer is 0.001 p.m or more and less than 5 Jim, and the anion-exchangeable resin layer of the separation membrane is located facing an electrode acting as a negative electrode. <41> The cell for a redox flow battery according to <40>, wherein the first cation-exchangeable resin layer is located closer to an electrode acting as a positive electrode than the anion-exchangeable resin layer. <42> The cell for a redox flow battery according to <40> or <41>, wherein a distance Dneg between the anion-exchangeable resin layer of the separation membrane and the electrode acting as a negative electrode, and a distance Dpos between the anion-exchangeable resin layer of the separation membrane and an electrode acting as a positive electrode exhibit the following relationship: Dneg / Dpos < 1 • <43> The cell for a redox flow battery according to any one of <40> to <42>, wherein a thickness of the first cation-exchangeable resin layer is 1 jim or more and 150 p.m or less. <44> The cell for a redox flow battery according to any one of <40> to <43>, wherein the first cationexchangeable resin layer comprises a fluororesin. <45> The cell for a redox flow battery according to any one of <40> to <44>, wherein the first cationexchangeable resin layer has at least one functional group selected from the group consisting of a sulfo group, a carboxyl group, and a phosphoric acid group. <46> The cell for a redox flow battery according to any one of <40> to <45>, wherein the first cationexchangeable resin layer comprises a fluororesin having a structural unit represented by the following general formula G1: F X6. F F CF2X8 wherein the definition of each substituent has the same meaning as in the general formula G1 described above. <47> The cell for a redox flow battery according to any one of <40> to <46>, wherein the anion-exchangeable resin layer comprises at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, an amino salt structure as a reaction product of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group, and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, a nitrogen atom-containing heterocyclic ring structure, a salt structure of a nitrogen-containing heterocyclic ring as a reaction product of a nitrogencontaining heterocyclic ring structure and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, and a quaternary ammonium group. <48> The cell for a redox flow battery according to any one of <40> to <47>, wherein the separation membrane comprises the first cation-exchangeable resin layer, the anion-exchangeable resin layer, and a second cation-exchangeable resin layer, in the listed order, and a thickness of the first cationexchangeable resin layer is larger than a thickness of the second cation-exchangeable resin layer. <49> The cell for a redox flow battery according to <48>, wherein the first cation-exchangeable resin layer is located closer to an electrode acting as a positive electrode than the anion-exchangeable resin layer. <50> The cell for a redox flow battery according to <48> or <49>, wherein a distance Dneg between the anion-exchangeable resin layer of the separation membrane and the electrode acting as a negative electrode, and a distance Dpos between the anion-exchangeable resin layer of the separation membrane and an electrode acting as a positive electrode exhibit the following relationship: Dneg / Dpos < 1 • <51> The cell for a redox flow battery according to any one of <48> to <50>, wherein the second cationexchangeable resin layer comprises a fluororesin. <52> The cell for a redox flow battery according to any one of <48> to <51>, wherein a thickness of the second cation-exchangeable resin layer is 0.01 p.m or more and less than 150 p.m. <53> The cell for a redox flow battery according to any one of <48> to <52>, wherein a value obtained by dividing the thickness of the second ion-exchangeable resin layer by the thickness of the first cation-exchangeable resin layer is less than 0.7. <54> The cell for a redox flow battery according to any one of <40> to <53>, wherein at least one of the first electrode and the second electrode is a carbon electrode. <55> The cell for a redox flow battery according to any one of <40> to <54>, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metallic redox active material, a non- metallic redox active material, and an organic redox active material. <56> The cell for a redox flow battery according to any one of <40> to <55>, wherein at least one of the first electrode and the second electrode is a separation membrane electrode assembly bonded with the separation membrane . <57> A redox flow battery, wherein the cell for a redox flow battery according to any one of <40> to <56> is stacked. <58> A method for producing a separation membrane, the separation membrane comprising at least a first cation-exchangeable resin layer, and an anion-exchangeable resin layer, in which an equivalent weight of the separation membrane is 1150 g / eq or less, and a thickness of the anion-exchangeable resin layer is 0.001 p.m or more and less than 5 Jim, wherein the method comprises a step of forming the first cation-exchangeable resin layer, and a step of forming the anion-exchangeable resin layer . <59> The method for producing a separation membrane according to <58>, wherein the method comprises a step of reacting a fluororesin precursor layer serving as a precursor of the first cation-exchangeable resin layer, and containing at least one selected from the group consisting of a sulfonyl halide group, an acyl halide group, and a halogenated phosphoric acid group, with a modification compound having at least two nitrogen atom-containing groups, in which the nitrogen atom-containing groups comprise at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, an amino salt structure as a reaction product of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group, and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, a nitrogen atom-containing heterocyclic ring structure, a salt structure of a nitrogen-containing heterocyclic ring as a reaction product of a nitrogencontaining heterocyclic ring structure and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, and a quaternary ammonium group, and a step of converting at least one selected from the group consisting of the sulfonyl halide group, the acyl halide group, and the halogenated phosphoric acid group contained in the fluororesin precursor layer, into at least one selected from the group consisting of a sulfo group, a carboxyl group, and a phosphoric acid group, after the above step. <60> The method for producing a separation membrane according to <58>, the separation membrane comprising the first cation-exchangeable resin layer, the anion-exchangeable resin layer, and a second cation-exchangeable resin layer, in the listed order, in which a thickness of the first cation-exchangeable resin layer is larger than a thickness of the second cation-exchangeable resin layer, wherein the method comprises a step of forming the first cation-exchangeable resin layer, a step of forming the anion-exchangeable resin layer, and a step of forming the second cation-exchangeable resin layer. <61> The method for producing a separation membrane according to <60>, comprising a step of overlapping the anion-exchangeable resin layers of membranes each having the first cation-exchangeable resin layer and the anion-exchangeable resin layer. <62> A polyelectrolyte solution comprising a fluororesin having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and having a structural unit represented by the following general formula Gl, and a solvent containing water, an aliphatic alcohol, and an aliphatic carboxylic acid, wherein a ratio of a total mass of the aliphatic carboxylic acid and a reaction product thereof to a total mass of the solvent is 100:1 to 100:50: F F k I I o_c—c CF2X8 c—X9 [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above. <63> The polyelectrolyte solution according to <62>, wherein a mass ratio between the aliphatic carboxylic acid and the aliphatic alcohol is 100:1 to 1:100. <64> An ion-exchange membrane comprising a fluororesin having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and having a structural unit represented by the following general formula Gl, wherein the number of crack defects per unit area of the ion-exchange membrane is less than 10 / m2: wherein the definition of each substituent has the same meaning as in the general formula Gl described above. <65> The ion-exchange membrane according to <64>, wherein an orientation ratio OR in a membrane surface direction, as determined by X-ray scattering measurement, is 1.0 or more and less than 1.1. < 6 6> The ion-exchange membrane according to <64> or <65>, wherein an average membrane thickness is 75 p.m or less. <67> The ion-exchange membrane according to any one of <64> to <66>, wherein an average membrane thickness is 25 p,m or more. <68> The ion-exchange membrane according to any one of <64> to <67>, wherein a minimum membrane thickness is 90% or more of an average membrane thickness, and a maximum membrane thickness is 110% or less of an average membrane thickness . < 6 9> A wound body configured by winding the ion-exchange membrane according to any one of <64> to <68>. <70> The wound body according to <68>, wherein a width of the ion-exchange membrane is 50 mm or more and 5,000 mm or less. <71> The wound body according to <69> or <70>, wherein a length of the ion-exchange membrane is 100 mm or more. <72> A membrane electrode assembly, wherein the ionexchange membrane according to any one of <64> to <68> and at least one electrode are bonded. <73> The ion-exchange membrane according to any one of <64> to <68>, for a redox flow battery. <74> The membrane electrode assembly according to <72>, for a redox flow battery. <75> A cell for a redox flow battery, the cell comprising a first electrolyte solution comprising a first redox active material, a second electrolyte solution comprising a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a separation membrane located between the first electrolyte solution and the second electrolyte solution, wherein the separation membrane is the ion-exchange membrane according to any one of <64> to <68>. <76> The cell for a redox flow battery according to <75>, wherein the separation membrane and at least one electrode are bonded. <77> The cell for a redox flow battery according to <75> or <76>, wherein at least one of the first electrode and the second electrode is a carbon electrode. <78> The cell for a redox flow battery according to any one of <75> to <77>, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metallic redox active material, a non-metallic redox active material, and an organic redox active material. <79> A redox flow battery, wherein the cell for a redox flow battery according to any one of <75> to <78> is stacked. <80> A method for producing an ion-exchange membrane, the method comprising a step of applying and drying the polyelectrolyte solution according to <62> or <63>, wherein the ion-exchange membrane comprises a fluororesin having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and having a structural unit represented by the following general formula Gl, and the number of crack defects per unit area of the ion-exchange membrane is less than 10 / m2: F X6. F F CF2X8 wherein the definition of each substituent has the same meaning as in the general formula G1 described above. Brief Description of Drawing

[0010] [Figure 1] Figure 1 illustrates one example of a schematic view of a redox flow battery in which a separation membrane for a redox flow battery in the present embodiment is used. Description of Embodiments

[0011] Hereinafter, modes for carrying out the present invention (hereinafter, referred to as "the present embodiment".) are described in detail, and the present invention is not limited to the following description and can be variously modified and carried out within the gist thereof .

[0012] [First embodiment] First, a first embodiment is described.

[0013] Patent Literature 1 discloses use of an aromatic polysulfone-based polymer in an anion-exchange group layer, for enhancements in current efficiency and power efficiency, and indicates that, although an excellent current efficiency is achieved, an increase in cell resistance and a reduction in voltage efficiency are caused. Therefore, there is a demand for an anion-exchange group layer excellent in current efficiency, voltage efficiency, and current efficiency in a well-balanced manner. Patent Literature 2 discloses Nafion (registered trademark) 117 reacted with several heterocyclic molecules, for not only suppression of an increase in proton surface resistance, but also an enhancement in vanadium ion permeation selectivity, in which, if a reduction in proton surface resistance is tried, a reduction in vanadium ion permeation selectivity is caused, and on the other hand, if an enhancement in vanadium ion permeation selectivity is tried, an enhancement in proton surface resistance is caused, and there is still a challenge for satisfaction of both thereof. In addition, no redox flow battery has been evaluated in Examples, and current efficiency, voltage efficiency, and power efficiency are unclear. A high numerical value of the proton surface resistance has been exhibited as compared with Nafion (registered trademark) 117 in Examples, and it can be thus presumed that a lowered voltage efficiency has been exhibited as compared with Nafion (registered trademark) 117. From the foregoing, there is a demand for a material excellent in current efficiency, voltage efficiency, and current efficiency in a well-balanced manner. Patent Literature 3 discloses a polyelectrolyte membrane which is provided with a crossover prevention layer as a metal layer formed by reduction of a cationic metal, therein, for enhancements in at least one or more characteristics of discharge capacity, current efficiency, voltage efficiency, and power efficiency, but such characteristics are demanded to be higher. Patent Literature 4 discloses use of several polymer compounds in an anion-exchangeable resin layer, for a high power efficiency. However, it is indicated that, in a case where the anion-exchangeable resin layer is not located between ion-exchange resin layers, a high power efficiency may be obtained as the initial characteristic, but a high power efficiency is not obtained after 100 cycles. The anion-exchangeable compounds included in the anion-exchangeable resin layer used in Patent Literature 4 are thus demanded to be higher in characteristics.

[0014] An object of the present invention relates to a side-chain heteroaromatic resin, a resin composition, an ion-exchange membrane, a membrane electrode assembly, a cell for a redox flow battery using them, and a redox flow battery, in which a cell for a redox battery, having excellent current efficiency and voltage efficiency in a well-balanced manner and having a high power efficiency, is obtained.

[0015] The present inventors have made intensive studies about the above object, and as a result, have found that excellent current efficiency and voltage efficiency in a well-balanced manner and a high power efficiency are obtained by use of a side-chain heteroaromatic resin having a specified structural unit, in a separation membrane of a cell for a redox flow battery.

[0016] The ion-exchange membrane according to the first embodiment includes the following resin composition. In other words, the resin composition includes a side-chain heteroaromatic resin having a structural unit represented by the following general formula 1: wherein, R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, and He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure, and a cation-exchangeable resin. According to the present embodiment, it is possible to provide a novel side-chain heteroaromatic resin having a specified structural unit. According to the present embodiment, it is also possible to provide a side-chain heteroaromatic resin, a resin composition, an ionexchange membrane, a membrane electrode assembly, a cell for a redox flow battery using them, and a redox flow battery, in which a cell for a redox battery, having excellent current efficiency and voltage efficiency in a well-balanced manner and exhibiting a high power efficiency, is obtained.

[0017] The ion-exchange membrane according to the first embodiment includes a side-chain heteroaromatic resin having a structural unit represented by the following general formula 2: wherein, R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure, Rf is an aliphatic hydrocarbon group substituted with at least one fluorine atom, and X- is a counter anion.

[0018] <Side-chain heteroaromatic resin> The side-chain heteroaromatic resin in the first embodiment has a structural unit represented by the following general formula 1: wherein, R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, and He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure.

[0019] R1, R2, and R3 in the general formula 1 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms.

[0020] In the case of the substituted aliphatic hydrocarbon group or the substituted aromatic hydrocarbon group, the substituent is not particularly limited, and examples thereof include halogen atoms such as a fluorine atom, a chlorine atom, and a bromine atom, a nitrile group (-CN), an alkoxy group (-ORa) , an alkyl carbonate group (-OCO2Ra), an alkyl ester group (-CO2Ra) , an acyl group (-CORa), a sulfide group (-SRa) , a sulfoxide group (-SORa) , a sulfone group (-SO2Ra) , and an urethane group (-NHCO2Ra) • Ra is an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms. In the case of such an aliphatic hydrocarbon group, the substituent may be an aromatic hydrocarbon group having 6 to 10 carbon atoms, and in the case of such an aromatic hydrocarbon group, the substituent may be an aliphatic hydrocarbon group having 1 to 10 carbon atoms. In a case where the substituent is contained, the substituent may be adopted singly or in combinations of a plurality thereof.

[0021] R1, R2, and R3 are each preferably a hydrogen atom, or a substituted or unsubstituted aliphatic hydrocarbon group, more preferably a hydrogen atom, or an unsubstituted aliphatic hydrocarbon group because a starting material compound in production of the sidechain heteroaromatic resin is easily available, and further preferably a hydrogen atom because a starting material compound in production of the side-chain heteroaromatic resin is high in reactivity and the production cost tends to be able to be suppressed.

[0022] The number of carbon atoms in the substituted or unsubstituted aliphatic hydrocarbon group is 1 to 10. The number of carbon atoms is preferably 1 to 6, more preferably 1 to 4, further preferably 1, or 2, further preferably 1 because a starting material compound in production of the side-chain heteroaromatic resin is easily available.

[0023] The number of carbon atoms in the substituted or unsubstituted aromatic hydrocarbon group is 6 to 10. The number of carbon atoms is preferably 6 to 10, more preferably 6 to 8, further preferably 6 because a starting material compound in production of the sidechain heteroaromatic resin is easily available.

[0024] R4 in the general formula 1 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms. The substituent here is the same as the above-mentioned substituent.

[0025] The "direct bond" here refers to direct binding between He in the structural unit represented by the general formula 1 and a carbon atom constituting a main chain bound with R3 . (Hereinafter, the same meaning is indicated in the description for R4. )

[0026] The number of carbon atoms in the substituted or unsubstituted divalent aliphatic hydrocarbon group is 1 to 10. The number of carbon atoms is preferably 1 to 6, more preferably 1 to 4, further preferably 1, or 2, further preferably 1 because a starting material compound in production of the side-chain heteroaromatic resin is easily available.

[0027] The number of carbon atoms in the substituted or unsubstituted divalent aromatic hydrocarbon group is 6 to 10. The number of carbon atoms is preferably 6 to 10, more preferably 6 to 8, further preferably 6 because a starting material compound in production of the sidechain heteroaromatic resin is easily available.

[0028] R4 in the general formula 1 is preferably a direct bond, or a substituted or unsubstituted aliphatic hydrocarbon group, more preferably a direct bond, or an unsubstituted aliphatic hydrocarbon group because a starting material compound in production of the sidechain heteroaromatic resin is easily available, and further preferably a direct bond because a starting material compound in production of the side-chain heteroaromatic resin is high in reactivity and the production cost tends to be able to be suppressed. In a case where R4 is a direct bond, the structural unit represented by the general formula 1 is represented by the following general formula 1-2. The substituent here is the same as the above-mentioned substituent. In the formula, the definition of the substituent is as defined in the above general formula 1.

[0029] He in the general formula 1 is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a fivemembered ring and / or six-membered ring structure.

[0030] The five-membered ring and / or six-membered ring structure in He in the general formula 1 is not particularly limited, and examples thereof include an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a pyridazine structure, a pyrimidine structure, a cinnoline structure, a quinazoline structure, a phthalazine structure, a quinoxaline structure, a pteridine structure, a purine structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, a 1,10-phenanthroline structure, and a 2,2':6',2''-terpyridine structure. The structure of He exemplified above may have such a structure singly, or a plurality of such structures.

[0031] He has at least one nitrogen atom in the heteroaromatic ring structure, and therefore preferably has, among the above-mentioned five-membered ring and / or six-membered ring structure, an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, or a 1,10-phenanthroline structure, more preferably has an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2'-bipyridyl structure, or a 1, 10-phenanthroline structure, and further preferably has an imidazole structure, a benzimidazole structure, an imidazopyridine structure, or a pyridine structure, particularly preferably an imidazole structure or a pyridine structure because, in a case where the sidechain heteroaromatic resin is used in a cell for a redox flow battery, durability tends to be enhanced.

[0032] The substituent in He is the same as the abovementioned substituent.

[0033] Examples of He include an imidazolyl group, a benzimidazolyl group, an imidazopyridinyl group, a pyridinyl group, an oxazonyl group, a thiazolyl group, a pyridazinyl group, a pyrimidinyl group, a cinnolinyl group, a quinazolinyl group, a phthalazinyl group, a quinoxalinyl group, a pteridinyl group, a purinyl group, a 2,2'-bipyridinyl, a 2,3'-bipyridinyl group, a 2,4'-bipyridinyl group, a 1,7-phenanthrolinyl group, a 1,10-phenanthrolinyl group, and a 2,2 ' :6',2' '-terpyridinyl group. In particular, an imidazolyl group or a pyridinyl group is preferred.

[0034] In a case where He is an imidazolyl group, the structural unit represented by the general formula 1 is a structural unit represented by the following general formula 1-3.

[0035] In a case where He is a pyridinyl group, the structural unit represented by the general formula 1 is a structural unit represented by the following general formula 1-4.

[0036] The structural unit represented by the general formula 1 is preferably a structural unit represented by the following general formula 1-5 or the following general formula 1-6.

[0037]

[0038] The side-chain heteroaromatic resin preferably further has a structural unit represented by the following general formula 2: [2] wherein R1, R2, R3, R4, He, and n each have the same meaning as in the general formula 1, Rf is an aliphatic hydrocarbon group substituted with at least one fluorine atom, and X" is a counter anion.

[0039] The side-chain heteroaromatic resin, when further having the structural unit represented by the general formula 2, tends to have enhanced water resistance, chemical resistance, acid resistance, and alkali resistance .

[0040] The number of carbon atoms in the aliphatic hydrocarbon group in Rf is preferably 1 to 20, more preferably 3 to 16, further preferably 3 to 11, further preferably 3 to 9.

[0041] The number of fluorine atoms for substitution in the aliphatic hydrocarbon group in Rf is preferably 1 to 41, more preferably 3 to 25, further preferably 5 to 18.

[0042] Rf is preferably a group represented by formula: -(CH2) o- (CF2) p-CFs (wherein 0 + p is 1 to 19, and 0 is 0 to 19. ) . 0 and p are each optionally an integer. 0 + p is preferably 1 to 19, more preferably 2 to 15, further preferably 2 to 10, further preferably 2 to 8.  0 is preferably 0 to 19, more preferably 1 to 10 from the same viewpoint, and is further preferably 2 to 4, further preferably 2 from the viewpoint of more enhancements in water resistance and chemical resistance of the sidechain heteroaromatic resin, p is preferably 0 to 19, more preferably 2 to 10, further preferably 3 to 7, further preferably 4 to 6 from the viewpoint that a compound serving as a precursor of Rf is easily available and the production cost of the side-chain heteroaromatic resin can be suppressed.

[0043] More specific examples of Rf include -(CH2) 2 (CF2) 3CF3, - (CH2) 2 (CF2) 4CF3, and - (CH2) 2 (CF2) 6CF3.

[0044] Examples of X" include F", Cl", Br~, I", HSO4~, (SO42’)i / 2, N03", and OH".

[0045] The structural unit represented by the general formula 2 is preferably a structural unit represented by the following general formula 2-2. R1 R3 Rf [ 2 - 2 ]

[0046] The structural unit represented by the general formula 2 is preferably a structural unit represented by the following general formula 2-3 or the following general formula 2-4.

[0047]

[0048] Examples of the structural unit represented by the general formula 2 more preferably include a structure represented by the following general formula 2-5 or the following general formula 2-6. Rf [ 2 - 5 ]

[0049] Rf [ 2 - 6 ]

[0050] The side-chain heteroaromatic resin preferably has the structural unit represented by the general formula 2, more preferably has the structural unit represented by the general formula 1 and the structural unit represented by the general formula 2.

[0051] <Cation-exchangeable resin> The resin composition in the present embodiment preferably includes a cation-exchangeable resin. The cation-exchangeable resin is a resin having ionexchange ability of a cation (hereinafter, also referred to as "positive ion").

[0052] The cation-exchangeable resin is not particularly limited, and may be any of a hydrocarbon-based resin and a fluororesin. A hydrocarbon-based resin is preferred in an application in which suppression in production cost is demanded, and a fluororesin is preferred in an application in which durability for a long period is demanded. Such hydrocarbon resin and fluororesin may be each used singly or in combinations of two or more kinds thereof .

[0053] The cation-exchangeable resin preferably contains a functional group having ion-exchange ability. The functional group having ion-exchange ability is not particularly limited, and examples thereof include a sulfo group (SO3H), a carboxyl group (CO2H) , a phenolic hydroxyl group (OH), a phosphoric acid group (PO3H2) , a thiol group (SH), and any alkali metal salt, any alkaline earth metal salt or any transition metal salt of such a functional group. The functional group having ionexchange ability may be such a functional group singly, or a plurality of such functional groups.

[0054] Among such functional groups having ion-exchange ability, at least one selected from a sulfo group, a carboxyl group, and a phosphoric acid group is preferred, at least one selected from a sulfo group and a carboxyl group is more preferred, and a sulfo group is particularly preferred because the ion-exchange ability tends to be excellent.

[0055] The hydrocarbon-based resin is not particularly limited, and examples thereof include a resin which is, for example, polystyrene, polyphenylene ether, polybenzimidazole, polyetheretherketone, polyimide, polyetherimide, polyaryletherketone, polysulfone, polyether sulfone, polyphenylene sulfide, or polyphenylsulfone, and which has the functional group having ion-exchange ability. The hydrocarbon-based cation-exchangeable resin may be crosslinked, may be a copolymer, or may have various substituents (for example, halogen atoms such as a fluorine atom, a chlorine atom, and a bromine atom; a nitrile group, aliphatic hydrocarbon groups such as a methyl group, an ethyl group, a vinyl group, an allyl group, a 1-methylvinyl group, a n-propyl group, an iso-propyl group, a n-butyl group, an iso-butyl group, a sec-butyl group, and a tertbutyl group; aromatic hydrocarbon groups such as a benzyl group, a phenyl group, and a nitrile-substituted phenyl group; an amino group; a nitro group; a hydroxyl group; and a silyl group). The hydrocarbon resin may be used singly or in combinations of a plurality thereof.

[0056] The fluororesin is not particularly limited, and examples thereof include a partially fluorinated resin and a fully fluorinated resin each having the functional group having ion-exchange ability. A resin in which not all hydrogen atoms, but at least one hydrogen atom, among hydrogen atoms on carbon atoms contained in the hydrocarbon-based cation-exchangeable resin is replaced with a fluorine atom, and a resin in which all such hydrogen atoms on carbon atoms are replaced with fluorine atoms are respectively exemplified as the partially fluorinated resin and the fully fluorinated resin.

[0057] The fluororesin is preferably a fluororesin having a structural unit represented by the following general formula G1 (hereinafter, also referred to as "fluororesin Gl") : F X6, F F \ J । o—c—c c—X9 cf2x8 [Gl] wherein, X5, X6, X7, and X8 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X5 and X6 or X5 and X7 are optionally bound to each other to form a cyclic structure, R5 and R6 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, X9 is a group represented by -COOZ, -SO3Z, -PO3Z2, or -PO3HZ, Z is at least one selected from the group consisting of a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, and an amine, and the fluororesin is optionally crosslinked to each other by ion crosslinking via X9, h and p each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < h < 1, 0 < p < 1, and h + p = 1, i is an integer of 0 to 8, j is 0 or 1, and k, 1, and m are each optionally the same or different, and are each an integer of 0 to 6, provided that, when k, 1, and m are 0 at the same time, X9 is CF(CF2X10)2, X10 is a group represented by -COOZ, -SO3Z, -PO3Z2, or -PO3HZ, and Z is the same as described above.

[0058] X5, X6, X7, and X8 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X5 and X6 or X5 and X7 are optionally bound to each other to form a cyclic structure .

[0059] The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, further preferably 1 to 3. The perfluoroalkyl group may be linear or branched. Examples of the perfluoroalkyl group include a trimethylfluoromethyl group and a pentafluoroethyl group.

[0060] The number of carbon atoms in the cyclic perfluoroalkyl group is preferably 6 to 8. Examples of the cyclic perfluoroalkyl group include a perfluorocyclohexyl group.

[0061] X5, X6, X7, and X8 are each preferably a fluorine atom, or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms from the viewpoint that a starting material is easily available and the production cost of the fluororesin tends to be able to be suppressed. Furthermore, a fluorine atom or a trifluoromethyl group is more preferred and a fluorine atom is further preferred from the viewpoint that the fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance.

[0062] In a case where X5 and X6, or X5 and X7 are bound to each other to form a cyclic structure, the cyclic structure may be, for example, a substituted or unsubstituted cyclic perfluoroalkyl structure having 5 to 10 carbon atoms, and a substituted or unsubstituted cyclic perfluoroether structure having 4 to 9 carbon atoms .

[0063] R5 and R6 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. R5 and R6 are each preferably a fluorine atom or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms from the viewpoint that a starting material is easily available and the production cost of the fluororesin tends to be able to be suppressed. Furthermore, a fluorine atom and a trifluoromethyl group are more preferred and a fluorine atom is particularly preferred from the viewpoint that the fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance.

[0064] X9 is a group represented by -COOZ, -SO3Z, -PO3Z2, or -PO3HZ, Z is at least one selected from the group consisting of a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, and an amine, and the fluororesin is optionally crosslinked to each other by ion crosslinking via X9.

[0065] The alkali metal atom is not particularly limited, and examples thereof include a lithium atom, a sodium atom, a potassium atom, a rubidium atom, a cesium atom, and a francium atom. In particular, a lithium atom, a sodium atom, or a potassium atom is preferred from the viewpoint that a starting material is easily available and the production cost of the fluororesin tends to be able to be suppressed, and a sodium atom or a potassium atom is more preferred from the same viewpoint.

[0066] The alkaline earth metal atom is not particularly limited, and examples thereof include a beryllium atom, a magnesium atom, a calcium atom, a strontium atom, a barium atom, and a radium atom. In particular, a magnesium atom or a calcium atom is preferred from the viewpoint that a starting material is easily available and the production cost of the fluororesin G1 tends to be able to be suppressed.

[0067] The amine is not particularly limited, and examples thereof include structures of NH4, NH3R30, NH2R30R31, NHR30R31R32, and NR30R31R32R33 . R30, R31, R32, and R33 are each optionally the same or different, and are each a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. In particular, an unsubstituted aliphatic hydrocarbon group having 1 to 6 carbon atoms, and a phenyl group are preferred, an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms is more preferred, and a methyl group or an ethyl group is further preferred from the viewpoint that a starting material is easily available and the production cost of the fluororesin tends to be able to be suppressed. In a case where the fluororesin is crosslinked to each other by ion crosslinking via X9, Z is an alkaline earth metal atom.

[0068] h and p are numbers satisfying 0 < h < 1, 0 < p < 1, and h + p = 1. i is an integer of 0 to 8. j is 0 or 1. k, 1, and m are each optionally the same or different, and are each an integer of 0 to 6 (provided that, when k, 1, and m are 0 at the same time, X9 is CF(CF2X10)2, X10 is a monovalent group represented by formula of -COOZ, -SO3Z, -PO3Z2, or -PO3HZ, and Z is the same as described above. The substituent in the case of "substituted" is the same as the substituent exemplified with respect to the general formula 1.

[0069] The fluororesin G1 preferably contains a structural unit represented by the following general formula G2, and at least one selected from a structural unit represented by the following general formula G3, a structural unit represented by the following general formula G4 and a structural unit represented by the following general formula G5, from the viewpoint that the fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance, and from the viewpoint that the production cost of the fluororesin tends to be able to be suppressed: - (CF2-CF2) - [G2] - (CF2-CF (-0-(CF2CFXO)n-A) ) - [G3] wherein X is F, or a perfluoroalkyl group having 1 to 3 carbon atoms, N is an integer of 0 to 5, and A represents (CF2)M-SO3H (M represents an integer of 0 to 6, provided that N and M are not 0 at the same time.); - (CF2-CF (-0- (CF2) p-CFX (-0- (CF2)K-SO3H) ))- [G4] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, P represents an integer of 0 to 12, and K represents an integer of 1 to 5, provided that P and K are not 0 at the same time; - (CF2-CF(-O- (CF2)q-CFX(- (CF2)l-O- (CF2)o-S03H) ) ) - [G5] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, Q represents an integer of 0 to 12, L represents an integer of 1 to 5, and o represents an integer of 0 to 6, provided that Q and 0 are not 0 at the same time.

[0070] The fluororesin G1 more preferably contains the structural unit represented by the general formula G2, and at least one selected from the structural unit represented by the general formula G3, the structural unit represented by the general formula G4 and the structural unit represented by the general formula G5, further preferably contains the structural unit represented by the general formula G2 and the structural unit represented by the general formula G3 (provided that X is F, or a trifluoromethyl group, N is an integer of 0 to 2, and M is an integer of 1 to 4.), further preferably contains the structural unit represented by the general formula G2 and the structural unit represented by the general formula G3 (provided that X is F, or a trifluoromethyl group, N is 0 or 1, and M is an integer of 2 to 4.).

[0071] The structural unit represented by the general formula G1 in the fluororesin G1 is preferably a structural unit represented by the following general formula Gl-2, more preferably a structural unit represented by the following general formula Gl-3.

[0072] cf3 [Gl-2] In the formula, h and p each represent the molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < h < 1, 0 < p < 1, and h + p = 1, and i is 0 or 1.

[0073] F F F F —c—c---c—c— In the formula, h and p each represent the molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < h < 1, 0 < p < 1, and h + p = 1.

[0074] Some functional groups having ion-exchange ability contained in the fluororesin G1 may be intermolecularly directly or indirectly partially crosslinked. The partial crosslinking may be preferred because solubility in an electrolyte solution tends to be able to be suppressed and excess swellability tends to be able to be suppressed.

[0075] Evan in a case where the fluororesin G1 has a high melt flow index (hereinafter also referred to as "MFI", measured according to ASTM: D1238 (measurement conditions: temperature 270°C, load 2160 g)) (in a case where the fluororesin has a low molecular weight), the partial crosslinking can increase intermolecular entanglement and reduce solubility and / or excess swellability.

[0076] The partial crosslinking reaction is, for example, a reaction of the functional group having ion-exchange ability and a functional group or a main chain of other molecule, a reaction of such functional groups having ion-exchange ability, or a crosslinking reaction (covalent bond) via, for example, a low-molecular compound, oligomer or polymer substance excellent in oxidation resistance, and may be optionally a reaction with a substance forming a salt (including an ionic bond with the functional group having ion-exchange ability). Examples of the low-molecular compound, oligomer or polymer substance excellent in oxidation resistance include a polyhydric alcohol compound and an organic diamine .

[0077] The equivalent weight of the fluororesin G1 is not particularly limited, and is preferably 2000 g / eq or less, more preferably 1500 g / eq or less, further preferably 1100 or less from the viewpoint that ionexchange ability tends to be excellent, and is still further preferably 1050 g / eq or less, still further preferably 1000 or less in an application in which the fluororesin G1 is adopted in the form of a membrane and the property of a cation to be moved in the membrane is utilized, because movement resistance of a cation tends to be reduced. The equivalent weight of the fluororesin G1 is further preferably 500 g / eq or more, still further preferably 700 g / eq or more because the fluororesin tends to be more enhanced in water resistance and chemical resistance, and is preferably 800 g / eq or more, more preferably 880 g / eq or more in an application in which the fluororesin is utilized in the form of a membrane, because the membrane tends to be enhanced in mechanical strength. The equivalent weight refers to a dry mass in grams of an ion-exchangeable resin as a resin having ion exchange ability, per equivalent of an ion-exchange group having ion-exchange ability in the ion-exchangeable resin, and the equivalent weight of the fluororesin is a dry mass in grams of the fluororesin, per equivalent of an ion-exchange group in the fluororesin. Hereinafter, the expression "equivalent weight" is appropriately used in the present embodiment. A method used in measurement of the equivalent weight can be a method in which the fluororesin is substituted with a salt and its solution is back titrated with an alkaline solution. The equivalent weight can be appropriately adjusted by selecting the ratio of copolymerization of a monomer as a starting material of the fluororesin Gl, the type of the monomer, and the like.

[0078] <Method for producing fluororesin Gl> The method for producing the fluororesin Gl is not particularly limited, and is, for example, a method in which a copolymer containing a fluorinated olefin monomer represented by the following general formula G8, and a fluorinated vinyl ether compound represented by at least one selected from the following general formula G9, the following general formula GIO, and the following general formula Gil is adopted as a fluororesin Gl precursor and subjected to hydrolysis treatment and acid treatment described below: CFZ1=CZ2Z3 [G8] wherein Z1, Z2, and Z3 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a cyclic perfluoroalkyl group, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; CF2=CF-O-(CF2CFXO)n-A [G9] wherein X is F, or a perfluoroalkyl group having 1 to 3 carbon atoms, N is an integer of 0 to 5, A is (CF2)m~W (M is an integer of 0 to 6, and N and M are not 0 at the same time.), and W is a functional group which can be converted into a -SOaH group by hydrolysis treatment and acid treatment; CF2=CF-O- (CF2) p-CFX (-0- (CF2)k-W) [GIO] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, P represents an integer of 0 to 12, K is an integer of 1 to 5 (provided that P and K are not 0 at the same time.), and W is a functional group which can be converted into a -SO3H group by hydrolysis treatment and acid treatment; CF2=CF-O- (CF2)q-CFX(- (CF2)l-O- (CF2)m-W)

[11] wherein X is a perfluoroalkyl group having 1 to 3 carbon atoms, Q is an integer of 0 to 12, L is an integer of 1 to 5 (provided that Q and L are not 0 at the same time.), m is an integer of 0 to 6 (Q, L, and m are not 0 at the same time.), and W is a functional group which can be converted into a -SO3H group by hydrolysis treatment and acid treatment.

[0079] The method for producing the fluororesin G1 is preferably a method in which a copolymer including the fluorinated olefin monomer represented by the general formula G8, and the fluorinated vinyl ether compound represented by at least one selected from the group consisting of the general formula G9, the general formula GIO, and the general formula Gil is adopted as a fluororesin G1 precursor and subjected to hydrolysis treatment and acid treatment. The precursor further preferably includes the fluorinated olefin monomer represented by the general formula G8 (provided that Z1, Z2, and Z3 are each F) , and the fluorinated vinyl ether compound represented by the general formula G9 (provided that X is F, or a trifluoromethyl group, N is an integer of 0 to 2, and M is an integer of 1 to 4.), particularly preferably includes the fluorinated olefin monomer represented by the general formula G8 (provided that Z1, Z2, and Z3 are each F), and the fluorinated vinyl ether compound represented by the general formula G9 (provided that X is F, or a trifluoromethyl group, N is 0 or 1, and M is an integer of 2 to 4.) from the viewpoint that the fluororesin G1 tends to be enhanced in chemical stability such as oxidation degradation resistance and from the viewpoint that the production cost of the fluororesin G1 tends to be able to be suppressed. The fluororesin G1 precursor further particularly preferably includes the fluorinated olefin monomer represented by the general formula G8 (provided that Z1, Z2, and Z3 are each F.), and the fluorinated vinyl ether compound represented by the general formula G9 (provided that X is a trifluoromethyl group, N is 1, and M is 2.) .

[0080] The fluorinated olefin monomer represented by the general formula G8 is preferably a fluorinated olefin monomer represented by the following general formula G12, more preferably a fluorinated olefin monomer represented by the following general formula G13, further preferably a fluorinated olefin monomer represented by the following general formula G14: CF2=CFZ [G12] wherein Z is H, Cl, F, a perfluoroalkyl group having 1 to 10 carbon atoms, or a cyclic perfluoroalkyl group optionally having oxygen as a ring-constituting atom; CF2=CFZ [G13] wherein Z is F, or a perfluoroalkyl group having 1 to 3 carbon atoms; CF2=CF2 [G14] . The fluorinated vinyl ether compound represented by at least one selected from the group consisting of the general formula G9, the general formula GIO, and the general formula Gil is preferably a fluorinated vinyl ether compound represented by the following general formula G15, more preferably a fluorinated vinyl ether compound represented by the following general formula G16: CF2=CF-O-(CF2CFXO) n-A [G15] wherein X is F, or a trifluoromethyl group, n is 0 or 1, A is (CF2)m-W (m is an integer of 2 to 4, and n and m are not 0 at the same time.), and W is a functional group which can be converted into a -SO3H group by hydrolysis treatment and acid treatment; CF2=CF-O-(CF2CFXO) n-A [G16] wherein X is a trifluoromethyl group, n is 1, A is (CF2)m-W (m is 2.), and W is a functional group which can be converted into a -SO3H group by hydrolysis treatment and acid treatment. In the general formulae G9 to Gil, G15, and G16, W which is a functional group which can be converted into a -SO3H group by hydrolysis treatment and acid treatment is not particularly limited, examples include SO2F, SO2CI, and SO2Br, SO2F and SO2CI are preferred, and SO2F is more preferred.

[0081] The fluororesin G1 precursor in the present embodiment can be produced by a known procedure. For example, the precursor can be produced by polymerizing a mixture including the fluorinated olefin monomer represented by the general formula G8, and the fluorinated vinyl ether compound represented by at least one selected from the group consisting of the general formula G9, the general formula GIO, and the general formula Gil, in the presence of a radical generator such as peroxide. The polymerization method is not particularly limited, and there can be used, for example, a polymerization method (solution polymerization) by packing and dissolving a gas of the fluorinated olefin monomer, the fluorinated vinyl ether compound, and the like in a polymerization solvent such as a fluorinecontaining hydrocarbon, and reacting them, a polymerization method (bulk polymerization) with the fluorinated vinyl ether compound as a polymerization solvent without a solvent such as a fluorine-containing hydrocarbon, a polymerization method (emulsification polymerization) of a gas of the fluorinated olefin monomer, the fluorinated vinyl ether compound, and the like with, as a medium, an aqueous solution of a surfactant, a polymerization method (emulsion polymerization) by emulsification of a gas of the fluorinated olefin monomer, the fluorinated vinyl ether compound, and the like with, as a medium, an aqueous solution of an emulsification aid such as a surfactant and an alcohol, and a polymerization method (suspension polymerization) by suspending a gas of the fluorinated olefin monomer, the fluorinated vinyl ether compound, and the like with, as a medium, an aqueous solution of a suspension stabilizer, and reacting them. The fluororesin G1 precursor used in the present embodiment can also be one prepared by any polymerization method described above. A block-shaped or taper-shaped polymer obtained by adjustment of polymerization conditions, for example, the amount of the fluorinated olefin monomer supplied, can also be used as the fluororesin G1 precursor. The fluororesin G1 precursor may be obtained by treating an impure end, and / or a portion (CO group, H-binding portion, or the like) structurally easily oxidized, which are / is generated in a resin molecule structure during a polymerization reaction, under a fluorine gas by a known method, to fluorinate such a portion . In the fluororesin G1 precursor, some of the ionexchange group precursor groups (for example, -SO2F group) may be partially imidated (may be intermolecularly imidated) (for example, alkylimidated).

[0082] The molecular weight of the fluororesin G1 precursor is not particularly limited, and the value of the melt flow index (MFI) measured according to ASTM: D1238 (measurement conditions: temperature 270°C, load 2160 g) is preferably 0.05 g / 10 min or more, more preferably 0.1 g / 10 min or more, further preferably 0.5 g / 10 min or more. The value of MFI is preferably 100 g / 10 min or less, more preferably 80 g / 10 min or less, further preferably 60 g / 10 min or less.

[0083] The shape of the fluororesin G1 precursor is not particularly limited, and is, for example, a shape of a pellet of 0.5 cm3 or less, a dispersion, or a powdery particle from the viewpoint of increases in treatment rates in hydrolysis treatment and acid treatment described below. In particular, a powder after polymerization is more preferably used. The fluororesin G1 precursor, which is in the form of a membrane formed by extrusion, may be used from the viewpoint of the cost.

[0084] The method for producing the fluororesin G1 in the present embodiment from the fluororesin G1 precursor is not particularly limited, and is, for example, a method in which the fluororesin G1 precursor is melt-kneaded, then extruded by a nozzle, a die, or the like with an extruder, and thereafter subjected to hydrolysis treatment described below, or a method in which the fluororesin G1 precursor is directly taken as a product in polymerization, namely, as a dispersion, or a powder obtained by precipitation and filtration, and then subjected to hydrolysis treatment described below. Such hydrolysis treatment provides a fluororesin G1 in which Z in the general formula G1 is an alkali metal atom or an alkaline earth metal atom. The fluororesin G1 (Z = alkali metal atom or alkaline earth metal atom) is subjected to acid treatment, to obtain a fluororesin G1 in which Z in the general formula G1 is a hydrogen atom. Furthermore, the fluororesin G1 (Z = hydrogen atom) is reacted with an amine, to obtain a fluororesin G1 in which Z in the general formula G1 is the amine.

[0085] Specifically, the fluororesin G1 precursor obtained as described above and, if necessary, molded, can be subsequently immersed in a basic reaction liquid, and subjected to hydrolysis treatment. The basic reaction liquid used in such hydrolysis treatment is not particularly limited, and examples thereof include an aqueous solution of any amine compound such as dimethylamine, diethylamine, monomethylamine and monoethylamine, and an aqueous solution of an alkali metal or alkaline earth metal hydroxide. In particular, an aqueous solution of sodium hydroxide or potassium hydroxide is preferred. In a case where an alkali metal or alkaline earth metal hydroxide is used, the content thereof is not particularly limited, and is preferably 10% by mass or more and 30% by mass or less relative to the entire basic reaction liquid. The basic reaction liquid more preferably further contains a swellable organic compound such as methyl alcohol, ethyl alcohol, acetone, and dimethylsulfoxide. The content of the swellable organic compound is preferably 1% by mass or more and 60% by mass or less relative to the entire basic reaction liquid.

[0086] The fluororesin G1 precursor can be subjected to hydrolysis treatment in the basic reaction liquid, then, if necessary, sufficiently washed with warm water or the like, thereafter subjected to acid treatment, and thus obtained as a fluororesin having a structural unit in which Z in the general formula G1 is a hydrogen atom. The acid used in the acid treatment is not particularly limited, examples include mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid and trifluoroacetic acid, and a mixture of the acid with water is preferred. The acid may be used singly or in combinations of a plurality thereof. The basic reaction liquid used in the hydrolysis treatment may be treated with a cation-exchange resin and thus removed in advance before the acid treatment. The fluororesin G1 subjected to the hydrolysis treatment and the acid treatment may be dispersible or soluble in a protonic organic solvent, water, or a mixed solvent thereof, and can be in the form of a suspension or a solution.

[0087] The fluororesin G1 may be able to be enhanced in mechanical strength, and may be preferably of two or more fluororesin compositions different in structure of a starting material constituting the fluororesin G1. When two or more such fluororesins are mixed, excellent properties in which respective functions of these fluororesins are fused may be able to be exhibited. When two or more such fluororesins are mixed, the ratio of a fluororesin having a larger equivalent weight is preferably more than 50% by mass, more preferably more than 55% by mass, further preferably more than 60% by mass from the viewpoint of an increase in crystallinity and an enhancement in mechanical strength.

[0088] <Resin composition> The resin composition according to the present embodiment includes a side-chain heteroaromatic resin and a cation-exchangeable resin. The weight ratio between the side-chain heteroaromatic resin and the cation-exchangeable resin in the resin composition is not particularly limited, and is preferably 1:100 to 100:1. While it differs depending on the application of the resin composition according to the present embodiment, the weight ratio between the sidechain heteroaromatic resin and the cation-exchangeable resin is preferably 10:90 or more, more preferably 20:80 or more, further preferably 30:70 or more in the case of use as a separation membrane for a redox flow battery, from the viewpoint of suppression of elution of the sidechain heteroaromatic resin into the electrolyte solution. While it differs depending on the application in which the mixture is utilized, the weight ratio of the sidechain heteroaromatic resin is preferably 90:10 or less, more preferably 80:20 or less, further preferably 70:30 or less in the case of use as a separation membrane for a redox flow battery, because the side-chain heteroaromatic resin tends to result in an enhancement in power efficiency.

[0089] The resin composition according to the present embodiment is preferably a styrene resin, a vinyl chloride resin, chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a polyetheretherketone resin, a polysulfone resin, a polyether sulfone resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a polyphenylene ether resin, a polyphenylene sulfide resin, a syndiotactic polystyrene resin, polyetherimide, a siloxane-modified polyetherimide resin, a polyamide imide resin, a cycloolefin-based resin, a cycloolefin copolymer, a polyetherketoneetherketoneketone resin, a polyaryletherketone resin, or a perfluororesin, and may further include a styrene resin, a vinyl chloride resin, chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a syndiotactic polystyrene resin, a cycloolefin-based resin, or a cycloolefin copolymer. The resin which may be included in the resin composition according to the present embodiment may be used singly or in combinations of a plurality thereof.

[0090] <Ion-exchange membrane> The ion-exchange membrane according to the present embodiment includes the side-chain heteroaromatic resin having the structural unit represented by the general formula 1, the side-chain heteroaromatic resin having the structural unit represented by the general formula 2, or the resin composition according to the present embodiment.

[0091] In a case where the side-chain heteroaromatic resin having the structural unit represented by the general formula 1, the side-chain heteroaromatic resin having the structural unit represented by the general formula 2, or the resin composition according to the present embodiment is molded into a membrane, the molding method is not particularly limited, and examples include a method in which a substance including the side-chain heteroaromatic resin or the resin composition according to the present embodiment is formed into a molten state, and extruded by a nozzle, a die, or the like with an extruder and thus processed into a film, and a method in which the side-chain heteroaromatic resin or the resin composition according to the present embodiment is formed into a solution state, applied to a substrate by a die, a gravure roll, a knife or spraying and dried, and thus processed into a film. The resulting membrane of the side-chain heteroaromatic resin or the resin composition according to the present embodiment is hereinafter also referred to as "side-chain heteroaromatic resin membrane". The solvent usable in formation of the side-chain heteroaromatic resin or the resin composition into a solution is not particularly limited, and examples include saturated hydrocarbon compounds such as n-pentane, n-hexane, n-octane, n-decane, cyclopentane, cyclohexane and cyclooctane; aromatic hydrocarbon compounds such as benzene, toluene, xylene and ethylbenzene; halogenated hydrocarbon compounds such as methylene chloride, chloroform, carbon tetrachloride, chlorobenzene and dichlorobenzene; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol and benzyl alcohol; ketones such as acetone, ethyl methyl ketone, methyl butyl ketone, methyl isobutyl ketone and cyclohexanone; as well as esters such as ethyl acetate, butyl acetate and methyl benzoate; ethers such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and dioxane; polyols such as ethylene glycol, propylene glycol and glycerin, and multimers and polyols of compounds each having two hydroxyl groups, among these polyols; and esterified compounds of these multimers, and nitriles such as acrylonitrile and benzonitrile; nitromethane; N,N-dimethylformamide; dimethylsulfoxide; hexamethylphosphoric triamide; carbon disulfide; and fluorine-based compounds (for example, Novec (trademark) manufactured by 3M, and Asahiklin manufactured by AGC Inc.) . Such a solvent may be adopted singly or in combinations of a plurality thereof.

[0092] When the side-chain heteroaromatic resin according to the present embodiment or the resin composition according to the present embodiment is molded into a membrane, a substrate can also be used. The substrate can be used to sometimes more stably produce such a membrane of the side-chain heteroaromatic resin according to the present embodiment or the resin composition according to the present embodiment. The material used in the substrate is not particularly limited, and examples include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, a cycloolefin polymer, polycarbonate, polyamide, polyimide, polyamide imide, polyvinyl chloride, polystyrene, polyphenylene ether, polyetheretherketone, polysulfone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, a polyimide resin, polyetherketoneetherketoneketone, and polyaryletherketone. The material may be modified, and may be used singly or in combinations of a plurality thereof .

[0093] The ion-exchange membrane according to the present embodiment alternately includes at least one layer (L) including the resin composition, and at least one layer (M) including a fluororesin having a structural unit represented by the following general formula Gl: \ J । o—c—c c—X9 cf2x8 [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

[0094] A fluororesin-containing membrane (hereinafter, also referred to as "fluororesin membrane") can be used as a substrate in the layer (M), thereby providing an ion-exchange membrane having the fluororesin membrane (layer (M)) and the side-chain heteroaromatic resin membrane (layer (L)). The layer (M) may include no sidechain heteroaromatic resin. The ion-exchange resin in the present embodiment may include one layer (L) and one layer (M) (a membrane including one layer as the layer (M) and one layer as the layer (L) is also referred to as "bipolar membrane"). A membrane by stacking can provide an ion-exchange membrane having both respective characteristics of the fluororesin membrane and the side-chain heteroaromatic resin membrane. Hereinafter, when they are in the state of being stacked, the fluororesin membrane and the sidechain heteroaromatic resin membrane are also respectively referred to as "fluororesin layer" and "side-chain heteroaromatic resin layer".

[0095] The interface between the layer (L) including the side-chain heteroaromatic resin and the layer (M) including the fluororesin having the structural unit represented by the general formula G1 included in the ion-exchange membrane is specified with respect to the presence thereof, from a numerical value at which the maximum signal strength of a peak assigned to the sidechain heteroaromatic resin reaches 1 / 10, as measured with a time-of-flight secondary ion mass spectrometry apparatus with reference to JIS K 0146:2002. The region in which the maximum signal strength of a peak assigned to the side-chain heteroaromatic resin shows 1 / 10 or more is defined as the layer (L), and the region in which the maximum signal strength of a peak assigned to the sidechain heteroaromatic resin shows less than 1 / 10 is defined as the layer (M).

[0096] The method for producing the fluororesin membrane (layer (M)) is not particularly limited, and the fluororesin membrane can be obtained by processing the resin composition including the fluororesin Gl, into a film, or by processing a resin composition including a fluororesin Gl precursor having a functional group having ion-exchange ability, into a film, by hydrolysis, and performing the above hydrolysis treatment and acid treatment. Examples include a method in which the resin composition including the fluororesin is melt-kneaded, then extruded with an extruder by a nozzle, a die, or the like, and thus processed into a film. Examples include a method in which the resin composition including the fluororesin G1 precursor is melt-kneaded and then extruded with an extruder by a nozzle, a die, or the like, to form a film, and then the hydrolysis treatment and acid treatment are performed to form an ion-exchange group. A substance including the fluororesin may be dispersed in a solvent and then cast on the substrate, and thus processed into a film.

[0097] The method for forming the layer (L) can be a molding method including molding the side-chain heteroaromatic resin having the structural unit represented by the general formula 1, the side-chain heteroaromatic resin having the structural unit represented by the general formula 2, or the resin composition according to the present embodiment, into a membrane .

[0098] The method for producing the side-chain heteroaromatic resin membrane and the method for producing the fluororesin membrane can be repeatedly used for the membrane by stacking, thereby producing a membrane in which the side-chain heteroaromatic resin membrane and the fluororesin membrane are stacked in a multi-layer manner.

[0099] The side-chain heteroaromatic resin membrane and the fluororesin membrane of the bipolar membrane can be stacked so as to be alternate, and these membranes can be pressure-bonded by pressing, thereby producing a membrane by multi-layer stacking. Such side-chain heteroaromatic resin membranes or such fluororesin membranes of two such bipolar membranes can be mutually laminated, and these membranes can be pressure-bonded by pressing, thereby producing a membrane of three layers stacked.

[0100] The side-chain heteroaromatic resin membrane of the present embodiment, and an ion-exchange membrane (the ion-exchange membrane is not particularly limited as long as it includes two or more layers, the same also applies to the following description) including the side-chain heteroaromatic resin membrane and the fluororesin membrane can be each used in various applications. Examples of such an application include a redox flow battery, a fuel cell, salt electrolysis, alkaline water electrolysis, and carbon dioxide reduction electrolysis, and, in particular, use in a cell for a redox flow battery, and a redox flow battery is suitably exemplified. Use in a cell for a redox flow battery, and a redox flow battery tends to lead to an excellent power efficiency as compared with conventional use in a separation membrane.

[0101] The total thickness of the ion-exchange membrane of the present embodiment is not particularly limited, and is preferably 0.01 jim or more and 200 jim or less in a cell for a redox flow battery, and a redox flow battery exemplified as a suitable application, more preferably 1 p,m or more because the membrane tends to be enhanced in handleability and mechanical strength, and is further preferably 10 Jim or more, particularly preferably 20 Jim or more particularly in a case where pulsation of the membrane is large and high mechanical strength is demanded. The total thickness of the ion-exchange membrane of the present embodiment is more preferably 150 ji or less, further preferably 130 Jim or less, particularly preferably 100 jim or less because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0102] The thickness of the layer (L) (side-chain heteroaromatic resin membrane) in the ion-exchange membrane of the present embodiment is not particularly limited, is preferably 0.01 Jim or more and 10 Jim or less in a cell for a redox flow battery, and a redox flow battery exemplified as a suitable application, and is more preferably 0.1 Jim or more, further preferably 0.2 jim or more because permeation of a redox active material through the membrane tends to be able to be more suppressed in use for a cell for a redox flow battery, and a redox flow battery. The thickness of the layer (L) (side-chain heteroaromatic resin membrane) is particularly preferably 0.3 p.m or more, further particularly preferably 0.4 p,m or more in a case where pulsation of the side-chain heteroaromatic resin membrane is large and high mechanical strength is demanded, and is more preferably 7 jim or less, further preferably 5 Jim or less, particularly preferably 3 Jim or less, further particularly preferably 2 jim or less because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0103] The equivalent weight of the ion-exchange membrane is not particularly limited, is preferably 500 g / eq or more and 2000 g / eq or less, is more preferably 700 g / eq or more, further preferably 800 g / eq or more, because the membrane tends to be enhanced in handleability and mechanical strength, and is particularly preferably 880 g / eq or more, further particularly preferably 900 g / eq or more particularly in a case where pulsation of the membrane is large and high mechanical strength is demanded. The equivalent weight of the ion-exchange membrane is more preferably 1500 g / eq or less, further preferably 1400 g / eq or less, particularly preferably 1200 g / eq or less, further particularly preferably 1150 g / eq or less, because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0104] [Second embodiment] Subsequently, a second embodiment is described.

[0105] Patent Literature 1 discloses use of an aromatic polysulfone-based polymer in an anion-exchange group layer, for enhancements in current efficiency and power efficiency, and indicates that, although an excellent current efficiency is achieved, an increase in cell resistance and a reduction in voltage efficiency are caused. Therefore, there is a demand for an anion-exchange group layer excellent in current efficiency, voltage efficiency, and current efficiency in a well-balanced manner. Patent Literature 2 discloses Nafion (registered trademark) 117 reacted with several heterocyclic molecules, for not only suppression of an increase in proton surface resistance, but also an enhancement in vanadium ion permeation selectivity, in which, if a reduction in proton surface resistance is tried, a reduction in vanadium ion permeation selectivity is caused, and on the other hand, if an enhancement in vanadium ion permeation selectivity is tried, an enhancement in proton surface resistance is caused, and there is still a challenge for satisfaction of both thereof. In addition, no redox flow battery has been evaluated in Examples, and current efficiency, voltage efficiency, and power efficiency are unclear. Here, a high numerical value of the proton surface resistance has been exhibited as compared with Nation (registered trademark) 117 in Examples, and it can be thus presumed that a lowered voltage efficiency has been exhibited as compared with Nafion (registered trademark) 117. From the foregoing, there is a demand for a material excellent in current efficiency, voltage efficiency, and current efficiency in a well-balanced manner. Patent Literature 3 discloses a polyelectrolyte membrane which is provided with a crossover prevention layer as a metal layer formed by reduction of a cationic metal, therein, for enhancements in at least one or more characteristics of discharge capacity, current efficiency, voltage efficiency, and power efficiency, but such characteristics are demanded to be higher. Patent Literature 4 discloses use of several polymer compounds in an anion-exchangeable resin layer, for a high power efficiency. However, it is indicated that, in a case where the anion-exchangeable resin layer is not located between ion-exchange resin layers, a high power efficiency may be obtained as the initial characteristic, but a high power efficiency is not obtained after 100 cycles. The anion-exchangeable compounds included in the anion-exchangeable resin layer used in Patent Literature 4 are thus demanded to be higher in characteristics.

[0106] An object of the present embodiment relates to an ion-exchange membrane, a membrane electrode assembly, a cell for a redox flow battery, and a redox flow battery, in which a cell for a redox battery, having excellent current efficiency and voltage efficiency in a well-balanced manner and having a high power efficiency, is obtained.

[0107] The present inventors have made intensive studies about the above object, and as a result, have found that a heteroaromatic structure-containing fluororesin having a specified structural unit, a saponified product thereof or a salt thereof can be utilized in an ion-exchange membrane, to provide a cell for a redox battery, having excellent current efficiency and voltage efficiency in a well-balanced manner and imparting a high power efficiency.

[0108] <Ion-exchange membrane according to second embodiment> An ion-exchange membrane according to the second embodiment includes a layer (LI) including a heteroaromatic structurecontaining fluororesin having a structural unit represented by the following general formula Al, a saponified product thereof or a salt thereof: EA1] cf2x4 wherein, X1, X2, X3, and X4 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X1 and X2 or X1 and X3 are optionally bound to each other to form a cyclic structure, R1 and R2 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, R3 is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 1 to 10 carbon atoms, R4 is a linking group that links NR3 and He, and is a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, X10 is a divalent group represented by formula -CO2- or -SO2-, Ho is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group containing at least one nitrogen atom and containing a five-membered ring and / or six-membered ring structure, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1, b is an integer of 0 to 8, c is 0 or 1, and d, e, and f are each optionally the same or different, and are each an integer of 0 to 6, provided that d, e, and f are not 0 at the same time, and a layer (Ml) including a fluororesin (Gl) having the structural unit represented by the general formula Gl.

[0109] According to the present embodiment, it is possible to provide an ion-exchange membrane, a membrane electrode assembly, a cell for a redox flow battery, and a redox flow battery, in which a cell for a redox battery, having excellent current efficiency and voltage efficiency in a well-balanced manner and having a high power efficiency, is obtained.

[0110] <Heteroaromatic structure-containing fluororesin> The heteroaromatic structure-containing fluororesin according to the present embodiment has a structural unit represented by the following general formula Al. cf2x4 LAI]

[0111] X1, X2, X3, and X4 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X1 and X2 or X1 and X3 are optionally bound to each other to form a cyclic structure. X1, X2, X3 and X4 are each preferably a fluorine atom, or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms from the viewpoint that a starting material is easily available and the production cost of the heteroaromatic structure-containing fluororesin tends to be able to be suppressed. Furthermore, a fluorine atom or a trifluoromethyl group is more preferred and a fluorine atom is particularly preferred from the viewpoint that the heteroaromatic structure-containing fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance .

[0112] R1 and R2 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. R1 and R2 are each preferably a fluorine atom, or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms from the viewpoint that a starting material is easily available and the production cost of the heteroaromatic structure-containing fluororesin tends to be able to be suppressed. Furthermore, a fluorine atom or a trifluoromethyl group is more preferred and a fluorine atom is particularly preferred from the viewpoint that the heteroaromatic structure-containing fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance.

[0113] The substituent in the case of "substituted" is the same as the substituent exemplified with respect to the general formula 1.

[0114] R3 is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. R3 is preferably a hydrogen atom, or an aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrogen atom, or an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms, from the viewpoint that a starting material is easily available and the production cost of the heteroaromatic structurecontaining fluororesin tends to be able to be suppressed. A hydrogen atom is further preferred from the viewpoint that the production cost of the heteroaromatic structurecontaining fluororesin can be more suppressed, and an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms is further preferred from the viewpoint of an enhancement in stability of the heteroaromatic structure-containing fluororesin under an alkaline condition. The substituent in the case of "substituted" is the same as the substituent exemplified with respect to the general formula 1.

[0115] R4 is a linking group that links NR3 and He, and is a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms. R4 is preferably an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably an unsubstituted aliphatic hydrocarbon group having 1 to 6 carbon atoms, further preferably an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms, from the viewpoint that a starting material is easily available and the production cost of the heteroaromatic structure-containing fluororesin tends to be able to be suppressed. An unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms is particularly preferred, and an unsubstituted aliphatic hydrocarbon group having 1 carbon atom is further particularly preferred, from the viewpoint that the heteroaromatic structure-containing fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance. The substituent in the case of "substituted" is the same as the substituent exemplified with respect to the general formula 1.

[0116] X10 is a divalent group represented by formula -CO2- or -SO2-. The divalent group represented by formula -SO2- is preferred from the viewpoint that the heteroaromatic structure-containing fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance.

[0117] He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group containing at least one nitrogen atom and containing a five-membered ring and / or six-membered ring structure . The five-membered ring and / or six-membered ring structure in He is not particularly limited, and examples thereof include an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a pyridazine structure, a pyrimidine structure, a cinnoline structure, a quinazoline structure, a phthalazine structure, a quinoxaline structure, a pteridine structure, a purine structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, a 1,10-phenanthroline structure, and a 2,2':6',2''-terpyridine structure. The structure of He exemplified above may have such a structure singly, or a plurality of such structures. The structure of He exemplified above may be used singly or in combinations of a plurality of such structures .

[0118] He has at least one nitrogen atom in the heteroaromatic ring structure, and therefore is preferably, among the above-mentioned five-membered ring and / or six-membered ring structure, an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, or a 1,10-phenanthroline structure, more preferably has an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2'-bipyridyl structure, or a 1,10- phenanthroline structure, and is further preferably an imidazole structure, a benzimidazole structure, an imidazopyridine structure, or a pyridine structure, particularly preferably an imidazole structure or a pyridine structure because, in a case where the heteroaromatic structure-containing fluororesin is utilized in a cell for a redox flow battery, durability tends to be enhanced.

[0119] The substituent in He is the same as the substituent exemplified with respect to the general formula 1.

[0120] Examples of He include an imidazolyl group, a benzimidazolyl group, an imidazopyridinyl group, a pyridinyl group, an oxazonyl group, a thiazolyl group, a pyridazinyl group, a pyrimidinyl group, a cinnolinyl group, a quinazolinyl group, a phthalazinyl group, a quinoxalinyl group, a pteridinyl group, a purinyl group, 2,2'-bipyridinyl, a 2,3'-bipyridinyl group, a 2,4'-bipyridinyl group, a 1,7-phenanthrolinyl group, a 1,10-phenanthrolinyl group, and a 2,2 ' : 6',2' '-terpyridinyl group. In particular, an imidazolyl group or a pyridinyl group is preferred.

[0121] The heteroaromatic structure-containing fluororesin preferably includes the structural unit represented by the general formula A2, and at least one selected from the group consisting of a structural unit represented by the following general formula A4, a structural unit represented by the following general formula A5, and a structural unit represented by the following general formula A6, from the viewpoint that the heteroaromatic structure-containing fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance and from the viewpoint that the production cost of the heteroaromatic structurecontaining fluororesin tends to be able to be suppressed and the production cost of a cell for a redox flow battery tends to be able to be suppressed: - (CF2-CF2) - [A2] - (CF2-CF (-0- (CF2CFXO) N-Ag) )- [A4] wherein X represents F, or a perfluoroalkyl group having 1 to 3 carbon atoms, Ag represents (CF2) f-X10-NR3-R4-Hc in the general formula Al, and N represents an integer of 0 to 5, - (CF2-CF (-0- (CF2) p-CFX (-0- (CF2)k-SO2NX41Ax) ) ) - [A5] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, X41 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group and Ax represents -R4-Hc in the general formula Al, P represents an integer of 0 to 12, and K represents an integer of 1 to 5, provided that P and K are not 0 at the same time, - (CF2-CF (-0- (CF2) q-CFX (- (CF2) L-0- (CF2) o-S02NX41Ax) ))- [A6] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, X41 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group and Ax represents -R4-Hc in the general formula Al, Q represents an integer of 0 to 12, L represents an integer of 1 to 5, and o represents an integer of 0 to 6, provided that Q and 0 are not 0 at the same time.

[0122] The heteroaromatic structure-containing fluororesin more preferably includes the structural unit represented by the general formula A2, and at least one selected from the group consisting of the structural unit represented by the general formula A4, the structural unit represented by the general formula A5, and the structural unit represented by the general formula A6, further preferably includes the structural unit represented by the general formula A2 and the structural unit represented by the general formula A4 (provided that X is F, or a trifluoromethyl group, N is an integer of 0 to 2, and f is an integer of 1 to 4.), particularly preferably contains the structural unit represented by the general formula A2 and the structural unit represented by the general formula A4 (provided that X is F, or a trifluoromethyl group, N is 0 or 1, and f is an integer of 2 to 4.).

[0123] The heteroaromatic structure-containing fluororesin more preferably includes a structural unit represented by the following general formula Al-1, further preferably includes a structural unit represented by the following general formula Al-2: - [CF2CF2]a- [CF2-CF( (-O-CF2- (CF(CF3) ) ) b-O- (CF2) 2-SO2NX41Ax) ] g-[Al-1] wherein X41 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group and Ax represents -R4-Hc in the general formula Al, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1, and b is 0, or 1, - [CF2CF2] a- [CF2-CF ( (-O-CF2- (CF (CF3) ) ) -0- (CF2) 2-SO2NX41Ax) ] g— [Al-2] wherein X41 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group and Ax represents -R4-Hc in the general formula Al, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1.

[0124] X41 in the general formulae A5, A6, Al-1, and Al-2 is preferably a hydrogen atom, or an aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrogen atom, or an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms, from the viewpoint that a starting material is easily available and the production cost of the heteroaromatic structurecontaining fluororesin tends to be able to be suppressed. A hydrogen atom is further preferred from the viewpoint that the production cost of the heteroaromatic structurecontaining fluororesin can be more suppressed, and an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms is further preferred from the viewpoint of an enhancement in stability of the heteroaromatic structure-containing fluororesin under an alkaline condition .

[0125] The method for producing the heteroaromatic structure-containing fluororesin is not particularly limited, and examples include a method in which a fluororesin precursor and a modification compound described below are reacted. The modification compound has at least two nitrogen atom-containing groups. At least one nitrogen atomcontaining group of these nitrogen atom-containing groups is a substituted or unsubstituted heteroaromatic group (corresponding to He) having 4 to 30 carbon atoms, the group containing at least one nitrogen atom and containing a five-membered ring and / or six-membered ring structure. At least one nitrogen atom-containing group of these nitrogen atom-containing groups is a primary amino group or a secondary amino group, and is preferably a primary amino group from the viewpoint of an enhancement in reactivity between the modification compound and the fluororesin precursor and is preferably a secondary amino group from the viewpoint of an enhancement in stability of the heteroaromatic structurecontaining fluororesin. In addition, examples of the nitrogen atom-containing group which may be contained in the modification compound include an amino salt structure of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group, and at least one selected from the group consisting of an acidic substance and a halogen atomcontaining aliphatic hydrocarbon compound, a salt structure of a nitrogen atom-containing heterocyclic ring structure, and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, and a quaternary ammonium group. Herein, the quaternary ammonium group is a quaternary ammonium group different from the amino salt structure and the salt structure.

[0126] More specific examples of the modification compound include 1-(3-aminopropyl) imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4- (ethylaminomethyl)pyridine, 4-(4-piperidyl)pyridine, 2-methyltryptamine, 5-methoxytryptamine, 6-methoxytryptamine, necrostatin-1, alosetron, sulfamethoxypyridazine, 1- (3-chloroanilino)-4-phenylphthalazine, 4-amino-5-aminomethyl-2-methylpyrimidine, 2-(aminomethyl)-5-methylpyrazine, 2-(4-piperidinyl)benzimidazole, 2-(4-aminophenyl)benzimidazole, 5-amino-2-(4-aminophenyl)benzimidazole, 6-(aminomethyl)quinoline, 2-methyl-7-[phenyl(phenylamino)methyl]-8-quinolinol, and 1-(2-amino-l-naphthyl)isoquinoline . Such a modification compound may be used singly or in combinations of a plurality thereof.

[0127] At least one selected from the group consisting of 1-(3-aminopropyl) imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(ethylaminomethyl)pyridine, 4-(2-aminoethyl)pyridine, 4-(4-piperidyl)pyridine, 2-(4-piperidinyl)benzimidazole, 2-(4-aminophenyl)benzimidazole, and 5-amino-2-(4-aminophenyl) benzimidazole is preferred, at least one selected from the group consisting of 1-(3-aminopropyl)imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(4-piperidyl)pyridine, and 2-(4-aminophenyl)benzimidazole is more preferred, and at least one selected from the group consisting of 1-(3-aminopropyl)imidazole, 4-picolylamine, and 4-(2-aminoethyl) pyridine is further preferred, from the viewpoint that the modification compound is easily available and the production cost of the heteroaromatic structure-containing fluororesin tends to be able to be suppressed.

[0128] The heteroaromatic structure-containing fluororesin in the present embodiment has a sulfonamide bond (-SO2NR-) (R in the formula representing sulfonamide is not particularly limited). The heteroaromatic structure-containing fluororesin having the sulfonamide bond can be analyzed by a common analysis method, and the analyzer here used can be, for example, FT-IR or TOF-SIMS .

[0129] The heteroaromatic structure-containing fluororesin in the present embodiment may be a saponified product thereof or a salt thereof.

[0130] The saponified product of the heteroaromatic structure-containing fluororesin is a saponified product obtained by reaction of the heteroaromatic structurecontaining fluororesin and an alkaline substance. Examples of such a basic substance include amine compounds such as dimethylamine, diethylamine, monomethylamine and monoethylamine, and alkali metal hydroxides and alkaline earth metal hydroxides, such as sodium hydroxide and potassium hydroxide. In particular, sodium hydroxide or potassium hydroxide is preferred.

[0131] The salt of the heteroaromatic structurecontaining fluororesin is a salt of the heteroaromatic structure-containing fluororesin and an acidic substance. Examples of the acidic substance include mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid and trifluoroacetic acid.

[0132] <Fluororesin Gl> The heteroaromatic structure-containing fluororesin in the present embodiment may be used as a resin composition in which other resin is mixed. The resin composition can include the heteroaromatic structure-containing fluororesin in the present embodiment, and the fluororesin G1. In the present embodiment, a fluororesin mixture such as a composition including the heteroaromatic structure-containing fluororesin and the fluororesin G1 is referred to as "resin composition". The fluororesin G1 is a fluororesin having ionexchange ability with a cation (hereinafter, also referred to as "positive ion").

[0133] The fluororesin G1 has a structural unit represented by the following general formula G1: cf2x8 [Gl] wherein the definition of each substituent has the same meaning as in the general formula G1 described above. A preferred fluororesin G1 is also as described above .

[0134] The weight ratio between the heteroaromatic structure-containing fluororesin and the fluororesin G1 in the resin composition is not particularly limited, and is preferably 1:100 to 100:1. While it differs depending on the application of the resin composition according to the present embodiment, the weight ratio between the heteroaromatic structure-containing fluororesin and the fluororesin G1 is preferably 5:95 or more, more preferably 10:90 or more, further preferably 15:85 or more, from the viewpoint of suppression of elution of the heteroaromatic structure-containing fluororesin into the electrolyte solution in the case of use as a separation membrane for a redox flow battery. While it differs depending on the application in which the mixture is utilized, the weight ratio of the heteroaromatic structure-containing fluororesin is preferably 90:10 or less, more preferably 80:20 or less, further preferably 70:30 or less because the heteroaromatic structurecontaining fluororesin tends to result in an enhancement in power efficiency in the case of use as a separation membrane for a redox flow battery.

[0135] The content of the heteroaromatic structurecontaining fluororesin in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more. While it differs depending on the application in which the mixture is utilized, the content of the heteroaromatic structure-containing fluororesin in the resin composition is preferably 90% by mass or less, more preferably 80% by mass or less, further preferably 70% by mass or less because the heteroaromatic structurecontaining fluororesin tends to result in an enhancement in power efficiency in the case of use as a separation membrane for a redox flow battery.

[0136] In the case of use of the heteroaromatic structure-containing fluororesin having the structural unit represented by the general formula Al, the ratio of each resin is exemplified as follows. The weight ratio between a side-chain nitrogen atomcontaining fluororesin and the fluororesin G1 in the resin composition is not particularly limited, and is preferably 1:100 to 100:1. While it differs depending on the application of the resin composition according to the present embodiment, the weight ratio between the sidechain nitrogen atom-containing fluororesin and the fluororesin G1 is preferably 10:90 or more, more preferably 20:80 or more, further preferably 30:70 or more, from the viewpoint of suppression of elution of the heteroaromatic structure-containing fluororesin into the electrolyte solution in the case of use as a separation membrane for a redox flow battery. While it differs depending on the application in which the mixture is utilized, the weight ratio of the side-chain nitrogen atom-containing fluororesin is preferably 90:10 or less, more preferably 80:20 or less, further preferably 70:30 or less because the side-chain nitrogen atom-containing fluororesin tends to result in an enhancement in power efficiency in the case of use as a separation membrane for a redox flow battery.

[0137] The content of the side-chain nitrogen atomcontaining fluororesin in the resin composition is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more. While it differs depending on the application in which the mixture is utilized, the content of the side-chain nitrogen atom-containing fluororesin in the resin composition is preferably 90% by mass or less, more preferably 80% by mass or less, further preferably 70% by mass or less in the case of use as a separation membrane for a redox flow battery, because the side-chain nitrogen atom-containing fluororesin tends to result in an enhancement in power efficiency.

[0138] The resin composition according to the present embodiment is preferably a styrene resin, a vinyl chloride resin, chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a polyetheretherketone resin, a polysulfone resin, a polyether sulfone resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a polyphenylene ether resin, a polyphenylene sulfide resin, a syndiotactic polystyrene resin, polyetherimide, a siloxane-modified polyetherimide resin, a polyamide imide resin, a cycloolefin-based resin, a cycloolefin copolymer, a polyetherketoneetherketoneketone resin, a polyaryletherketone resin, or a fluororesin, and may further include a styrene resin, a vinyl chloride resin, chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a syndiotactic polystyrene resin, a cycloolefin-based resin, or a cycloolefin copolymer. The resin which may be included in the resin composition according to the present embodiment may be used singly or in combinations of a plurality thereof.

[0139] <Ion-exchange membrane> The ion-exchange membrane according to the present embodiment includes the heteroaromatic structurecontaining fluororesin, or the resin composition according to the present embodiment.

[0140] In a case where the resin composition including the heteroaromatic structure-containing fluororesin is molded into a membrane, the molding method is not particularly limited, and examples thereof include a method in which the resin composition including the heteroaromatic structure-containing fluororesin is formed into a molten state, and extruded by a nozzle, a die, or the like with an extruder and thus processed into a film, and a method in which the resin composition including the heteroaromatic structure-containing fluororesin is formed into a solution state, applied to a substrate by a die, a gravure roll, a knife or spraying and dried, and thus processed into a film. The resulting membrane of the heteroaromatic structure-containing fluororesin is hereinafter also referred to as "heteroaromatic structure-containing fluororesin membrane".

[0141] The solvent usable in formation of the heteroaromatic structure-containing fluororesin into a solution is not particularly limited, and examples include saturated hydrocarbon compounds such as n-pentane, n-hexane, n-octane, n-decane, cyclopentane, cyclohexane and cyclooctane; aromatic hydrocarbon compounds such as benzene, toluene, xylene and ethylbenzene; halogenated hydrocarbon compounds such as methylene chloride, chloroform, carbon tetrachloride, chlorobenzene and dichlorobenzene; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol and benzyl alcohol; ketones such as acetone, ethyl methyl ketone, methyl butyl ketone, methyl isobutyl ketone and cyclohexanone; as well as esters such as ethyl acetate, butyl acetate and methyl benzoate; ethers such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and dioxane; polyols such as ethylene glycol, propylene glycol and glycerin, and multimers and polyols of compounds each having two hydroxyl groups, among these polyols; and esterified compounds of these multimers, and nitriles such as acrylonitrile and benzonitrile; nitromethane; N,N-dimethylformamide; dimethylsulfoxide; hexamethylphosphoric triamide; carbon disulfide; and fluorine-based compounds (for example, Novec (trademark) manufactured by 3M, and Asahiklin manufactured by AGC Inc.) . Such a solvent may be adopted singly or in combinations of a plurality thereof.

[0142] When the composition including the heteroaromatic structure-containing fluororesin is molded into a membrane, a substrate can also be used. The substrate can be used to sometimes more stably produce such a membrane of the composition including the heteroaromatic structure-contain!ng fluororesin. The material used in the substrate is not particularly limited, and examples include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, a cycloolefin polymer, polycarbonate, polyamide, polyimide, polyamide imide, polyvinyl chloride, polystyrene, polyphenylene ether, polyetheretherketone, polysulfone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, a polyimide resin, polyetherketoneetherketoneketone, and polyaryletherketone. The material used in the substrate may be modified, and may be used singly or in combinations of a plurality thereof.

[0143] The ion-exchange membrane according to the present embodiment alternately includes at least one layer (LI) including the heteroaromatic structure-containing fluororesin, and at least one layer (Ml) including the fluororesin having a structural unit represented by the following general formula Gl: cf2x8 [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

[0144] A membrane (hereinafter, also referred to as "fluororesin membrane") containing the fluororesin Gl can be used as a substrate in the layer (Ml), thereby providing an ion-exchange membrane having the fluororesin membrane (Ml) and the heteroaromatic structure-containing fluororesin membrane (LI). The layer (Ml) may include no heteroaromatic structure-containing fluororesin. The ion-exchange resin in the present embodiment may include one layer (LI) and one layer (Ml) (an ionexchange membrane including one layer as the layer (LI) and one layer as the layer (Ml) is also referred to as "bipolar membrane"). A membrane by stacking can provide an ion-exchange membrane having both respective characteristics of the fluororesin G1 and the heteroaromatic structure-containing fluororesin. Hereinafter, when they are in the state of being stacked, the fluororesin membrane and the heteroaromatic structure-containing fluororesin membrane are also respectively referred to as "fluororesin layer" and "heteroaromatic structure-containing fluororesin layer".

[0145] The interface between the layer (LI) including the heteroaromatic structure-containing fluororesin and the layer (Ml) including the fluororesin having the structural unit represented by the general formula G1 included in the ion-exchange membrane is specified with respect to the presence thereof, from a numerical value at which the maximum signal strength of NSO2 (m / z 78, two peaks are detected, and the peak located at the smaller mass is used) reaches 1 / 10, as measured with a time-of-flight secondary ion mass spectrometry apparatus with reference to JIS K 0146:2002. The region in which the maximum signal strength of the peak assigned to NSO2 shows 1 / 10 or more is defined as the layer (L), and the region in which the maximum signal strength of the peak assigned to NSO2 shows less than 1 / 10 is defined as the layer (M).

[0146] The method for producing the fluororesin membrane is as described above.

[0147] The method for molding the heteroaromatic structure-containing fluororesin into a membrane can also be made by reacting the fluororesin G1 precursor membrane with the modification compound and then performing hydrolysis treatment, to produce the heteroaromatic structure-containing fluororesin membrane. Furthermore, acid treatment can also be performed. In other words, the hydrolysis treatment can provide a saponified product of the heteroaromatic structure-containing fluororesin membrane, and furthermore the acid treatment can provide a salt of the heteroaromatic structure-containing fluororesin membrane. The hydrolysis treatment and the acid treatment are performed in the same manner as in the general formula G1. In the case of use of the present method, the reaction between the fluororesin G1 precursor and the modification compound can be controlled to provide a membrane in which the heteroaromatic structurecontaining fluororesin membrane and the fluororesin membrane are integrated, and such a membrane is a suitable membrane if adhesiveness between the heteroaromatic structure-containing fluororesin membrane and the fluororesin membrane is desired to be increased. Such a membrane obtained by the present method can also be controlled in distribution of the heteroaromatic structure-containing fluororesin in the membrane by control of the reaction between the fluororesin precursor and the modification compound. Specifically, for example, the reaction progresses from a location in which the fluororesin G1 precursor membrane and the modification compound are contacted, and thus a membrane can be provided in which the concentration of the heteroaromatic structure-containing fluororesin has a gradient from such a location of contact.

[0148] The ion-exchange membrane containing the heteroaromatic structure-containing fluororesin membrane of the present embodiment, and an ion-exchange membrane (the ion-exchange membrane is not particularly limited as long as it has two or more layers, and the same also applies to the following description) containing the heteroaromatic structure-containing fluororesin membrane and the fluororesin membrane can be each used in various applications. Examples of such an application include a redox flow battery, a fuel cell, salt electrolysis, alkaline water electrolysis, and carbon dioxide reduction electrolysis, and, in particular, use in a cell for a redox flow battery, and a redox flow battery is suitably exemplified. Use in a cell for a redox flow battery, and a redox flow battery tends to lead to an excellent power efficiency as compared with conventional use in a separation membrane.

[0149] The total thickness of the ion-exchange membrane according to the present embodiment is not particularly limited, is preferably 0.01 jim or more and 200 jim or less in a cell for a redox flow battery, and a redox flow battery exemplified as a suitable application, is more preferably 1 |im or more because the membrane tends to be enhanced in handleability and mechanical strength, and is further preferably 10 jim or more, particularly preferably 20 p.m or more particularly in a case where the pulsation of the membrane is large and high mechanical strength is demanded. The thickness is more preferably 150 ji or less, further preferably 130 Jim or less, particularly preferably 100 jim or less because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0150] The thickness of the layer (LI) (heteroaromatic structure-containing fluororesin membrane) in the ionexchange membrane according to the present embodiment is not particularly limited, and is preferably 0.001 jim or more and 10 jim or less in a cell for a redox flow battery, and a redox flow battery exemplified as a suitable application. The thickness of the layer (LI) is more preferably 0.01 Jim or more, further preferably 0.1 jim or more because permeation of a redox active material through the membrane tends to be able to be more suppressed in use for a cell for a redox flow battery, and a redox flow battery, and is particularly preferably 0.2 p,m or more, further particularly preferably 0.3 Jim or more in a case where the pulsation of the heteroaromatic structure-containing fluororesin membrane is large and high mechanical strength is demanded. The thickness of the layer (LI) is more preferably 7 jim or less, further preferably 5 Jim or less, particularly preferably 3 Jim or less, further particularly preferably 1 Jim or less because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0151] The equivalent weight of the ion-exchange membrane according to the present embodiment is not particularly limited, is preferably 500 g / eq or more and 2000 g / eq or less, is more preferably 700 g / eq or more, further preferably 800 g / eq or more because the membrane tends to be enhanced in handleability and mechanical strength, and is particularly preferably 880 g / eq or more, further particularly preferably 900 g / eq or more particularly in a case where the pulsation of the membrane is large and high mechanical strength is demanded. The equivalent weight of the ion-exchange membrane according to the present embodiment is more preferably 1500 g / eq or less, further preferably 1400 g / eq or less, particularly preferably 1200 g / eq or less, further particularly preferably 1150 g / eq or less because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0152] An ion-exchange membrane of the second embodiment according to another embodiment includes a layer (L3) including a side-chain nitrogen atomcontaining fluororesin having a structural unit represented by the following general formula A3, a saponified product thereof or a salt thereof: X21, I —c- I I -a X20 X22 c—c • F1             r R24 ■ —c--x24-nr22—-r23-n— I L F L -k R26 r25-n ^R27 [A3] wherein, X20, X21, X22 , and X23 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X20 and X21 or X20 and X22 optionally form a cyclic structure, R20 and R21 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, R22 and R24 are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R26 and R27 are each a hydrogen atom, or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, and at least one of R26 and R27 is a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, R23 and R25 are each optionally the same or different, and are each a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, wherein, when h is 2 or more, R23s repeated are each optionally the same or different, X24 is a divalent group represented by -CO2- or -SO2-, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1, b is an integer of 0 to 8, c is 0 or 1, and d, e, f, and h are each optionally the same or different, and are each an integer of 0 to 6, provided that d, e, and f are not 0 at the same time, and a layer (M3) including a fluororesin (Gl) having a structural unit represented by the following general formula Gl: r f i r f I -c— I L R6 J r f i cf2x8 [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

[0153] <Side-chain nitrogen atom-containing fluororesin A3> A side-chain nitrogen atom-containing fluororesin A3 has a structural unit represented by the following general formula A3. Hereinafter, the side-chain nitrogen atom-containing fluororesin having the structural unit represented by the general formula A3 is also referred to as "side-chain nitrogen atom-containing fluororesin A3". X2\ I —c— X20 x22 a R24 I -c--x24-nr22--r23-n I L F Jf L Jh p26 R25-N7 R27 [A3]

[0154] X20 , X21 , X22 , and X23 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X20 and X21 or X20 and X22 optionally form a cyclic structure. X20 , X21 , X22 , and X23 are each preferably a fluorine atom, or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms from the viewpoint that a starting material is easily available and the production cost of the sidechain nitrogen atom-containing fluororesin tends to be able to be suppressed. Furthermore, a fluorine atom or a trifluoromethyl group is more preferred and a fluorine atom is particularly preferred from the viewpoint that the side-chain nitrogen atom-containing fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance.

[0155] R20 and R21 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. R20 and R21 are each preferably a fluorine atom, or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms from the viewpoint that a starting material is easily available and the production cost of the sidechain nitrogen atom-containing fluororesin tends to be able to be suppressed. Furthermore, a fluorine atom or a trifluoromethyl group is more preferred and a fluorine atom is particularly preferred from the viewpoint that the side-chain nitrogen atom-containing fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance.

[0156] R22 and R24 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. R22 and R24 are each preferably a hydrogen atom, or an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrogen atom, or an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms, from the viewpoint that a starting material is easily available and the production cost of the sidechain nitrogen atom-containing fluororesin tends to be able to be suppressed, and, from the same viewpoint, R24 is further preferably a hydrogen atom, or an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms, particularly preferably a hydrogen atom. R22 is further preferably a hydrogen atom from the viewpoint that the production cost of the side-chain nitrogen atom-containing fluororesin can be more suppressed, and further preferably an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms from the viewpoint of an enhancement in stability of the side-chain nitrogen atom-containing fluororesin under an alkaline condition.

[0157] R26 and R27 are each a hydrogen atom, or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms. At least one of R26 and R27 is a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, and thus excellent current efficiency, voltage efficiency and power efficiency tend to be achieved in a well-balanced manner in use for a cell for a redox flow battery, and a redox flow battery. Both R26 and R27 are each more preferably a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms from the same viewpoint. R26 and R27 are each preferably an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably an unsubstituted aliphatic hydrocarbon group having 1 to 6 carbon atoms, further preferably an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms because excellent current efficiency, voltage efficiency and power efficiency tend to be achieved in a well-balanced manner in use for a cell for a redox flow battery, and a redox flow battery.

[0158] R23 and R25 are each optionally the same or different, and are each a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms. When h is 2 or more, R23s repeated are each optionally the same or different. R23 and R25 are each preferably an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably an unsubstituted aliphatic hydrocarbon group having 2 to 6 carbon atoms, further preferably an unsubstituted aliphatic hydrocarbon group having 2 to 4 carbon atoms, particularly preferably an unsubstituted aliphatic hydrocarbon group having 2 to 3 carbon atoms, from the viewpoint that a starting material is easily available and the production cost of the sidechain nitrogen atom-containing fluororesin tends to be able to be suppressed.

[0159] The substituent in the case of "substituted" is the same as the substituent exemplified with respect to the general formula 1.

[0160] X24 is a divalent group represented by formula -CO2- or -SO2-. The divalent group represented by formula -SO2- is preferred from the viewpoint that the side-chain nitrogen atom-containing fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance .

[0161] The side-chain nitrogen atom-containing fluororesin preferably includes a structural unit represented by the following general formula A2, and at least one selected from the group consisting of a structural unit represented by the following general formula A17, a structural unit represented by the following general formula A18, and a structural unit represented by the following general formula A19, from the viewpoint that the side-chain nitrogen atomcontaining fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance and from the viewpoint that the production cost of the sidechain nitrogen atom-containing fluororesin tends to be able to be suppressed and the production cost of a cell for a redox flow battery tends to be able to be suppressed: - (CF2-CF2) - [A2] - (CF2-CF (-0- (CF2CFXO) N-Bg) ) - [A17] wherein X represents F, or a perfluoroalkyl group having 1 to 3 carbon atoms, Ag represents ( (CF2) f-X24-NR22-(R23-NR24) h-R25-NR26R27) in the general formula A3, and N represents an integer of 0 to 5, - (CF2-CF (-0- (CF2) p-CFX (-0- (CF2)k-SO2NX51Bx) ) ) - [A18] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, X51 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group and Bx represents - (R23-NR24) h-R25-NR26R27) in the general formula A3, P represents an integer of 0 to 12, and K represents an integer of 1 to 5, provided that P and K are not 0 at the same time, - (CF2-CF(-O- (CF2)q-CFX(- (CF2)l-O- (CF2)o-S02NX51Bx) ) ) - [A19] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, X41 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group and Ax represents - (R23-NR24) h-R25-NR26R27) in the general formula A3, Q represents an integer of 0 to 12, L represents an integer of 1 to 5, and o represents an integer of 0 to 6, provided that Q and 0 are not 0 at the same time.

[0162] The side-chain nitrogen atom-containing fluororesin more preferably includes the structural unit represented by the general formula A2, and at least one selected from the group consisting of the structural unit represented by the general formula A17, the structural unit represented by the general formula A18, and the structural unit represented by the general formula A19, and, from the same viewpoint, further preferably contains the structural unit represented by the general formula A2 and the structural unit represented by the general formula A17 (provided that X is F, or a trifluoromethyl group, n is an integer of 0 to 2, and m is an integer of 1 to 4.), particularly preferably includes the structural unit represented by the general formula A2 and the structural unit represented by the general formula A17 (provided that X is F, or a trifluoromethyl group, n is 0 or 1, and m is an integer of 2 to 4.).

[0163] The side-chain nitrogen atom-containing fluororesin more preferably has a structural unit represented by the following general formula A20, further preferably has a structural unit represented by the following general formula A21: - [CF2CF2]a- [CF2-CF( (-O-CF2- (CF(CF3) ) ) b-O- (CF2) 2-SO2NX51Bx) ] g-[A20] wherein X51 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group and Ax represents -(R23-NR24) h-R25-NR26R27) in the general formula A3, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1, and b is 0 or 1, - [CF2CF2] a- [CF2-CF ( (-O-CF2- (CF (CF3) ) ) -0- (CF2) 2-SO2NX51Bx) ] g— [A21] wherein X51 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group and Ax represents -(R23-NR24) h-R25-NR26R27) in the general formula A3, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1.

[0164] The method for producing the side-chain nitrogen atom-containing fluororesin is not particularly limited, and examples include a method in which the above fluororesin G1 precursor and a reforming compound described below are reacted. The reforming compound has at least two nitrogen atoms. A functional group containing a first nitrogen atom of such nitrogen atoms is a primary amino group or a secondary amino group, and is preferably a primary amino group from the viewpoint of an enhancement in reactivity between the reforming compound and the side-chain nitrogen atom-containing fluororesin precursor and is preferably a secondary amino group from the viewpoint of an enhancement in stability of the side-chain nitrogen atom-containing fluororesin. A functional group containing a second nitrogen atom of such at least two nitrogen atoms contained in the reforming compound is at least one functional group selected from the group consisting of a secondary amino group, a tertiary amino group, and the above amino group and acidic substance. In a case where suppression of side reaction is demanded in reaction of an acidic fluororesin precursor and the reforming compound, a secondary amino group or a tertiary amino group is preferred, and a tertiary amino group is more preferred.

[0165] Examples of the reforming compound include N-methylethylenediamine, N-ethylethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N,N'-trimethylethylenediamine, N,N-diethylethylenediamine, N-benzylethylenediamine, N,N-dibutylethylenediamine, 1,2-diphenylethylenediamine, N,N-dicyclohexyl-1,2-ethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-diethyl-1,3-propanediamine, N,N-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyl-1,4-cyclohexanediamine, 3-aminopiperidine, isophoronediamine, 4-(aminomethyl)piperidine, 3-aminopyrrolidine, 4-aminopiperidine, 3-aminopyrrolidine, N,N-dimethyltrimethylenediamine, and N,N-dibutyltrimethylenediamine. The reforming compound may be used singly or in combinations of a plurality thereof.

[0166] Among such reforming compounds, N-methylethylenediamine, N-ethylethylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-diethyl-1,3-propanediamine, N,N-dimethyl-1,4-butanediamine, N,N- diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyl-1,4-cyclohexanediamine, N,N-dimethyltrimethylenediamine, or N,N-dibutyltrimethylenediamine is more preferred because the reforming compound is easily available and the production cost of the ion-exchange membrane for a redox flow battery, the membrane including the side-chain nitrogen atom-containing fluororesin, tends to be able to be suppressed.

[0167] Among such reforming compounds, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N, N-dibutyldipropylenetriamine, N,N-dimethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, or N,N-dimethyltrimethylenediamine is particularly preferred, because excellent current efficiency, voltage efficiency and power efficiency tend to be achieved in a well-balanced manner in use of the ion-exchange membrane for a redox flow battery, the membrane including the side-chain nitrogen atom-containing fluororesin, as a separation membrane for a cell for a redox flow battery, and a redox flow battery, and in use thereof for a cell for a redox flow battery, and redox flow battery.

[0168] N,N-dimethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyldipropylenetriamine, or N,N-dimethyltrimethylenediamine is further particularly preferred from the same viewpoint.

[0169] The side-chain nitrogen atom-containing fluororesin in the present embodiment has a sulfonamide bond (-SO2NR-) (R in the formula representing sulfonamide is not particularly limited). The heteroaromatic structure-containing fluororesin having the sulfonamide bond can be analyzed by a common analysis method, and the analyzer here used can be, for example, FT-IR or TOF-SIMS .

[0170] The side-chain nitrogen atom-containing fluororesin in the present embodiment may be a saponified product thereof or a salt thereof.

[0171] The saponified product of the side-chain nitrogen atom-containing fluororesin is a saponified product obtained by reaction of the side-chain nitrogen atomcontaining fluororesin and an alkaline substance. Examples of a basic substance include amine compounds such as dimethylamine, diethylamine, monomethylamine and monoethylamine, and alkali metal hydroxides and alkaline earth metal hydroxides, such as sodium hydroxide and potassium hydroxide. In particular, sodium hydroxide or potassium hydroxide is preferred.

[0172] The salt of the side-chain nitrogen atomcontaining fluororesin is a salt of the side-chain nitrogen atom-containing fluororesin and an acidic substance. Examples of the acidic substance include mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid and trifluoroacetic acid.

[0173] <Fluororesin Gl> The side-chain nitrogen atom-containing fluororesin in the present embodiment may be used as a resin composition in which other resin is mixed. The resin composition can include the side-chain nitrogen atom-containing fluororesin in the present embodiment, and the fluororesin G1. In the present embodiment, a fluororesin mixture such as a composition including the side-chain nitrogen atom-containing fluororesin and the fluororesin G1 is referred to as "fluororesin composition". The fluororesin G1 is a fluororesin having ionexchange ability with a cation (hereinafter, also referred to as "positive ion").

[0174] The fluororesin G1 has a structural unit represented by the following general formula G1: [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above. A preferred fluororesin G1 is also as described above .

[0175] In the case of use of the side-chain nitrogen atom-containing fluororesin having the structural unit represented by the general formula A3, the ratio of each resin is exemplified as follows. The weight ratio between the side-chain nitrogen atom-containing fluororesin and the fluororesin G1 in the resin composition is not particularly limited, and is preferably 1:100 to 100:1. While it differs depending on the application of the resin composition according to the present embodiment, the weight ratio between the sidechain nitrogen atom-containing fluororesin and the fluororesin G1 is preferably 5:95 or more, more preferably 10:90 or more, further preferably 15:85 or more in the case of use as a separation membrane for a redox flow battery, from the viewpoint of suppression of elution of the side-chain nitrogen atom-containing fluororesin into the electrolyte solution. While it differs depending on the application in which the mixture is utilized, the weight ratio of the side-chain nitrogen atom-containing fluororesin is preferably 90:10 or less, more preferably 70:30 or less, further preferably 60:40 or less in the case of use as a separation membrane for a redox flow battery, because the side-chain nitrogen atomcontaining fluororesin tends to result in an enhancement in power efficiency.

[0176] The content of the side-chain nitrogen atomcontaining fluororesin in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more. While it differs depending on the application in which the mixture is utilized, the content of the side-chain nitrogen atom-containing fluororesin in the resin composition is preferably 90% by mass or less, more preferably 70% by mass or less, further preferably 60% by mass or less in the case of use as a separation membrane for a redox flow battery, because the side-chain nitrogen atom-containing fluororesin tends to result in an enhancement in power efficiency.

[0177] The resin composition according to the present embodiment is preferably a styrene resin, a vinyl chloride resin, chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a polyetheretherketone resin, a polysulfone resin, a polyether sulfone resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a polyphenylene ether resin, a polyphenylene sulfide resin, a syndiotactic polystyrene resin, polyetherimide, a siloxane-modified polyetherimide resin, a polyamide imide resin, a cycloolefin-based resin, a cycloolefin copolymer, a polyetherketoneetherketoneketone resin, a polyaryletherketone resin, or a fluororesin, and may further include a styrene resin, a vinyl chloride resin, chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a syndiotactic polystyrene resin, a cycloolefin-based resin, or a cycloolefin copolymer. The resin which may be included in the resin composition according to the present embodiment may be used singly or in combinations of a plurality thereof.

[0178] <Ion-exchange membrane> The ion-exchange membrane according to the present embodiment includes the side-chain nitrogen atomcontaining fluororesin, or the resin composition according to the present embodiment.

[0179] In a case where the resin composition including the side-chain nitrogen atom-containing fluororesin is molded into a membrane, the molding method is not particularly limited, and examples include a method in which the resin composition including the side-chain nitrogen atom-containing fluororesin is formed into a molten state, and extruded by a nozzle, a die, or the like with an extruder and thus processed into a film, and a method in which the resin composition including the side-chain nitrogen atom-containing fluororesin is formed into a solution state, applied to a substrate by a die, a gravure roll, a knife or spraying and dried, and thus processed into a film. The resulting membrane of the side-chain nitrogen atom-containing fluororesin is hereinafter also referred to as "side-chain nitrogen atom-containing fluororesin membrane".

[0180] The solvent usable in formation of the side-chain nitrogen atom-containing fluororesin into a solution is not particularly limited, and examples include saturated hydrocarbon compounds such as n-pentane, n-hexane, n-octane, n-decane, cyclopentane, cyclohexane and cyclooctane; aromatic hydrocarbon compounds such as benzene, toluene, xylene and ethylbenzene; halogenated hydrocarbon compounds such as methylene chloride, chloroform, carbon tetrachloride, chlorobenzene and dichlorobenzene; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol and benzyl alcohol; ketones such as acetone, ethyl methyl ketone, methyl butyl ketone, methyl isobutyl ketone and cyclohexanone; as well as esters such as ethyl acetate, butyl acetate and methyl benzoate; ethers such as diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and dioxane; polyols such as ethylene glycol, propylene glycol and glycerin, and multimers and polyols of compounds each having two hydroxyl groups, among these polyols; and esterified compounds of these multimers, and nitriles such as acrylonitrile and benzonitrile; nitromethane; N,N-dimethylformamide; dimethylsulfoxide; hexamethylphosphoric triamide; carbon disulfide; and fluorine-based compounds (for example, Novec (trademark) manufactured by 3M, and Asahiklin manufactured by AGC Inc.) . Such a solvent may be adopted singly or in combinations of a plurality thereof.

[0181] When the composition including the side-chain nitrogen atom-containing fluororesin is molded into a membrane, a substrate can also be used. The substrate can be used to sometimes more stably produce such a membrane of the composition including the side-chain nitrogen atom-containing fluororesin. The material used in the substrate is not particularly limited, and examples include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, a cycloolefin polymer, polycarbonate, polyamide, polyimide, polyamide imide, polyvinyl chloride, polystyrene, polyphenylene ether, polyetheretherketone, polysulfone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, a polyimide resin, polyetherketoneetherketoneketone, and polyaryletherketone. The material used in the substrate may be modified, and may be used singly or in combinations of a plurality thereof.

[0182] The ion-exchange membrane according to the present embodiment alternately includes at least one layer (L3) including the side-chain nitrogen atom-containing fluororesin, and at least one layer (M3) including a fluororesin having a structural unit represented by the following general formula Gl: cf2x8 [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

[0183] A membrane (hereinafter, also referred to as "fluororesin membrane") containing the fluororesin Gl can be used as a substrate in the layer (M3), thereby providing an ion-exchange membrane having the fluororesin membrane (M3) and the side-chain nitrogen atom-containing fluororesin membrane (L3). The layer (M3) may include no heteroaromatic structure-containing fluororesin. The ion-exchange resin in the present embodiment may include one layer (L3) and one layer (M3) (an ionexchange membrane including one layer as the layer (L3) and one layer as the layer (M3) is also referred to as "bipolar membrane"). A membrane by stacking can provide an ion-exchange membrane having both respective characteristics of the fluororesin Gl and the heteroaromatic structure-containing fluororesin. Hereinafter, when they are in the state of being stacked, the fluororesin membrane and the side-chain nitrogen atom-containing fluororesin membrane are also respectively referred to as "fluororesin layer" and "side-chain nitrogen atom-containing fluororesin layer".

[0184] The interface between the layer (L3) including the side-chain nitrogen atom-containing fluororesin and the layer (M3) including the fluororesin having the structural unit represented by the general formula G1 included in the ion membrane is specified with respect to the presence thereof, from a numerical value at which the maximum signal strength of NSO2 (m / z 78, two peaks are detected, and the peak located at the smaller mass is used) reaches 1 / 10, as measured with a time-of-flight secondary ion mass spectrometry apparatus with reference to JIS K 0146:2002. The region in which the maximum signal strength of the peak assigned to NSO2 shows 1 / 10 or more is defined as the layer (L), and the region in which the maximum signal strength of the peak assigned to NSO2 shows less than 1 / 10 is defined as the layer (M).

[0185] The method for producing the fluororesin membrane is as described above.

[0186] The method for molding the side-chain nitrogen atom-containing fluororesin into a membrane can also be made by reacting the fluororesin G1 precursor membrane with the modification compound and then performing hydrolysis treatment, to produce the side-chain nitrogen atom-containing fluororesin membrane. Furthermore, acid treatment can also be performed. In other words, the hydrolysis treatment can provide a saponified product of the heteroaromatic structure-containing fluororesin membrane, and furthermore the acid treatment can provide a salt of the heteroaromatic structure-containing fluororesin membrane. The hydrolysis treatment and the acid treatment are performed in the same manner as in the general formula G1. In the case of use of the present method, the reaction between the fluororesin G1 precursor and the modification compound can be controlled to provide a membrane in which the side-chain nitrogen atomcontaining fluororesin membrane and the fluororesin membrane are integrated, and such a membrane is a suitable membrane if adhesiveness between the side-chain nitrogen atom-containing fluororesin membrane and the fluororesin membrane is desired to be increased. Such a membrane obtained by the present method can also be controlled in distribution of the side-chain nitrogen atom-containing fluororesin in the membrane by control of the reaction between the fluororesin G1 precursor and the modification compound. Specifically, for example, the reaction progresses from a location in which the fluororesin G1 precursor membrane and the modification compound are contacted, and thus a membrane can be provided in which the concentration of the side-chain nitrogen atom-containing fluororesin has a gradient from such a location of contact.

[0187] The ion-exchange membrane including the chain nitrogen atom-containing fluororesin in the present embodiment, and an ion-exchange membrane (the ionexchange membrane is not particularly limited as long as it includes two or more layers, the same also applies to the following description) containing the side-chain nitrogen atom-containing fluororesin membrane and the fluororesin membrane can be each used in various applications. Examples of such an application include a redox flow battery, a fuel cell, salt electrolysis, alkaline water electrolysis, and carbon dioxide reduction electrolysis, and, in particular, use in a cell for a redox flow battery, and a redox flow battery is suitably exemplified. Use in a cell for a redox flow battery, and a redox flow battery tends to lead to an excellent power efficiency as compared with conventional use in a separation membrane.

[0188] The total thickness of the ion-exchange membrane according to the present embodiment is not particularly limited, is preferably 0.01 jim or more and 200 jim or less in a cell for a redox flow battery, and a redox flow battery exemplified as a suitable application, is more preferably 1 jim or more because the membrane tends to be enhanced in handleability and mechanical strength, and is further preferably 10 Jim or more, particularly preferably 20 p.m or more particularly in a case where the pulsation of the membrane is large and high mechanical strength is demanded. The thickness is more preferably 150 p or less, further preferably 130 pm or less, particularly preferably 100 pm or less because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0189] The thickness of the layer (L3) (side-chain nitrogen atom-containing fluororesin membrane) in the ion-exchange membrane according to the present embodiment is not particularly limited, and is preferably 0.001 pm or more and 10 pm or less in a cell for a redox flow battery, and a redox flow battery exemplified as a suitable application. The thickness of the layer (L3) is more preferably 0.003 pm or more, further preferably 0.005 pm or more, because permeation of a redox active material through the membrane tends to be able to be more suppressed in use for a cell for a redox flow battery, and a redox flow battery, and is particularly preferably 0.01 pm or more, further particularly preferably 0.04 pm or more in a case where pulsation of the heteroaromatic structure-containing fluororesin membrane is large and high mechanical strength is demanded. The thickness of the layer (L3) is more preferably 7 pm or less, further preferably 5 pm or less, particularly preferably 3 pm or less, further particularly preferably 1.5 pm or less, because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0190] The equivalent weight of the ion-exchange membrane according to the present embodiment is not particularly limited, is preferably 500 g / eq or more and 2000 g / eq or less, is more preferably 700 g / eq or more, further preferably 800 g / eq or more because the membrane tends to be enhanced in handleability and mechanical strength, and is particularly preferably 880 g / eq or more, further particularly preferably 900 g / eq or more particularly in a case where the pulsation of the membrane is large and high mechanical strength is demanded. The equivalent weight of the ion-exchange membrane according to the present embodiment is more preferably 1500 g / eq or less, further preferably 1400 g / eq or less, particularly preferably 1200 g / eq or less, further particularly preferably 1150 g / eq or less because electrical resistance during operating of a cell for a redox flow battery, and a redox flow battery tends to be suppressed to result in an enhancement in power efficiency.

[0191] <Cell for redox flow battery> A cell for a redox flow battery, exemplified as a suitable application of the ion-exchange membrane of the present embodiment, is configured to include a first electrolyte solution including a first redox active material, a second electrolyte solution including a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a separation membrane located between the first electrolyte solution and the second electrolyte solution. Any component other than the constituent components, which is commonly utilized by those skilled in the art, and / or any component which can be known from known information, for example, known literatures and patents each relating to a cell for a redox flow battery, may be included. Examples of such components include a bipolar plate, a frame, a compressible seal, a conductive additive, and a balancing cell.

[0192] Figure 1 illustrates one example of a schematic view of the cell for a redox flow battery. A cell 10 for a redox flow battery has an electrolyzer 6 including a cell chamber 2 including an electrode 1 (in Figure 1, positive electrode) composed of a first electrode, a cell chamber 4 including an electrode 3 (in Figure 1, negative electrode) composed of a second electrode, and a separation membrane 5 as a separation membrane which separates the cell chamber 2 and the cell chamber 4. The cell chamber 2 and the cell chamber 4 include electrolyte solutions containing redox active materials. Such electrolyte solutions containing redox active materials are respectively stored in, for example, electrolyte solution tanks 7 and 8, and are supplied to the cell chambers by pumps or the like. The current generated by the cell for a redox flow battery may be converted from DC to AC through an AC / DC converter 9 or may be converted from AC to DC through the AC / DC converter 9, and the cell for a redox flow battery may be packed. The cell for a redox flow battery of the present embodiment is preferably a cell for a redox flow secondary battery.

[0193] <Redox flow battery> The cell for a redox flow battery can be stacked to provide a redox flow battery. When stacked, such cells for redox flow batteries can be electrically conducted through a bipolar plate. The material of the bipolar plate is not particularly limited, and examples include carbon, graphite, and a metal. A carbon particle, a carbon fiber, a metal particle, a metal fiber, graphene, and a carbon nanotube may be dispersed in the material. The material may be used singly or in combinations of a plurality thereof. The bipolar plate can sometimes enhance the contact between an electrode and an electrolyte solution, and thus may have various flow channels. Such a flow channel is not particularly limited, and examples can include Serpentine, Interdigitated, Pararell, Multi-parallel, Discontinuous, and any combination of such flow channels.

[0194] <Electrolyte solution> The electrolyte solution in the present embodiment is a liquid containing a redox active material and a solvent. The redox active material is a substance having redox activity directly involving in an electromotive force in the cell for a redox flow battery. The redox active material used in the present embodiment is not particularly limited, and examples thereof include a metallic redox active material, a non-metallic redox active material, and an organic redox active material, and such each redox active material may be a neutral compound or an ionic compound. The metallic redox active material is a substance containing at least one metal atom, and may contain a plurality of the same type of metal atoms or a plurality of different types of metals. The metal atom used in the metallic redox active material is not particularly limited, examples thereof include aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, lead, and cerium, and in particular, titanium, vanadium, chromium, manganese, iron, and cerium are preferred. Vanadium, iron, copper, and tin are preferred, vanadium and iron are further preferred, and vanadium is particularly preferred from the viewpoint that the first redox active material and the second redox active material can be the same in type. The metallic redox active material may have a ligand for active materials, commonly used, and examples of the ligand include a cyanated product ion, acetylacetone, ethylenediamine, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, carbon monoxide, bipyridine, bipyrazine, ethylene glycol, propylene glycol, ethanedithiol, butanedithiol, terpyridine, diethylenetriamine, triazacyclononane, tris(hydroxymethyl)aminomethane, ascorbic acid, citric acid, glycolic acid, gluconic acid, acetic acid, formic acid, benzoic acid, malic acid, maleic acid, phthalic acid, sarcosine acid, salicylic acid, oxalic acid, urea, aminophenolate, and lactic acid. Such a ligand for active material ligands may be adopted singly or in combinations of a plurality thereof. The material used in the non-metallic redox active material is not particularly limited, and examples thereof include chlorine, bromine, sulfur, and polysulfide . The organic redox active material is not particularly limited, and examples thereof include viologen, a derivative thereof, and a compound having a viologen structure in a polymer side chain, a 2,2,6,6-tetramethyl-l-piperidinyloxy radical, a derivative thereof, and a compound having a 2,2,6,6-tetramethyl-l-piperidinyloxy radical structure in a polymer side chain, ferrocene, a derivative thereof, and a compound having a ferrocene structure in a polymer side chain, quinone, a derivative thereof, and a compound having a quinone structure in a polymer side chain, anthraquinone, a derivative thereof, and a compound having an anthraquinone structure in a polymer side chain, and quinoxaline, a derivative thereof, and a compound having a quinoxaline structure in a polymer side chain. The redox active material may be adopted singly or in combinations of a plurality thereof.

[0195] When the redox active material is used in the cell for a redox flow battery, the redox active material used in the electrolyte solution of the positive electrode and the redox active material used in the electrolyte solution of the negative electrode can be used in combination depending on desired characteristics. The combination of such redox active materials is not particularly limited, and examples thereof include respective combinations of vanadium / vanadium, iron / iron, lead / lead, copper / copper, iron / chromium, chromium / bromine, zinc / bromine, polysulfide / bromine, zinc / cerium, zinc / nickel, zinc / cerium, zinc / iodine, titanium / manganese, vanadium / cerium, and vanadium / manganese . In particular, vanadium / vanadium, iron / iron, iron / chromium, chromium / bromine, zinc / bromine, and titanium / manganese are preferred, vanadium / vanadium, iron / iron, and zinc / bromine are more preferred, and vanadium / vanadium is particularly preferred because a high electromotive force is obtained and stability in charge and discharge is excellent. In a case where the redox active materials of the positive electrode and the negative electrode are each vanadium, the cell for a redox flow battery, and the redox flow battery are also designated respectively as "cell for a vanadium redox flow battery", and "vanadium redox flow battery". In addition, in a case where the redox active materials of the positive electrode and the negative electrode are each vanadium, charge and discharge are performed by utilizing an oxidationreduction reaction, by use of each redox coupling of V02+ / V02+ in the positive electrode and V2+ / V3+ in the negative electrode. When charge is performed, protons (H+) are excess in the cell chamber of the positive electrode and, on the other hand, protons (H+) are deficient in the cell chamber of the negative electrode, along with the oxidation-reduction reaction. The separation membrane allows excess protons in the cell chamber of the positive electrode to be selectively moved to the chamber of the negative electrode, and electrical neutrality is kept. When discharge is performed, its opposite reaction progresses and electrical neutrality is kept.

[0196] The solvent used in the electrolyte solution is not particularly limited, and examples thereof include water, alcohols, nitriles, esters, ketones, ethers, aliphatic hydrocarbons, and aromatic hydrocarbons. In particular, water is preferred from the viewpoint of an enhancement in stability in operating of the cell for a redox flow battery. Specific examples of the solvent include alcohols such as methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, ethylene glycol, diethylene glycol, and glycerol, nitriles such as acetonitrile, propionitrile, and benzonitrile, esters such as ethyl acetate and butyl acetate, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, ethers such as diethyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, ethylene glycoldiethyl ether, and diethylene glycol dimethyl ether, aliphatic hydrocarbons such as pentane, hexane, cyclohexane, heptane, octane, chloroform, dichloromethane, and tetrachloromethane, and aromatic hydrocarbons such as benzene, toluene, xylene, chlorobenzene, dichlorobenzene, phenol, and cresol. The solvent used in the electrolyte solution may be adopted singly or in combinations of a plurality thereof.

[0197] An electrolyte may be further used in the electrolyte solution. The electrolyte is a substance which releases ions in the electrolyte solution to enhance electrical conductivity of the electrolyte solution. The electrolyte is not particularly limited, and examples thereof include sulfuric acid, hydrochloric acid, nitric acid, acetic acid, phosphoric acid, sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium acetate. The electrolyte used in the electrolyte solution may be adopted singly or in combinations of a plurality thereof .

[0198] An additive may be added to the electrolyte solution depending on desired characteristics of the electrolyte solution. The additive is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, polyethylene glycol, glycerol, mannitol, sorbitol, pentaerythritol, tris(hydroxymethyl)aminomethane, cornstarch, corn syrup, gelatin, glycerol, guar gum, pectin, and a surfactant. The additive used in the electrolyte solution may be adopted singly or in combinations of a plurality thereof.

[0199] <Electrode> The electrode of the present embodiment is not particularly limited. Examples of the electrode include a metal electrode and a carbon electrode. The material of the metal electrode is not particularly limited, and examples thereof include aluminum, gold, silver, copper, chromium, molybdenum, nickel, thallium, titanium, iridium, zinc, tin, and any composite of such metals. The shape of the metal electrode is not particularly limited, and examples thereof include a plate shape, a lattice shape, a network shape (rhombic shape, testudinal shape), a linear shape, and a rod shape. The carbon electrode is not particularly limited, and examples thereof include a glassy carbon electrode, a pyrolytic carbon electrode, a carbon felt electrode, a carbon paper electrode, a carbon foam electrode, a carbon cloth electrode, a carbon knit electrode, a carbon nanofiber sheet electrode, and an activated carbon fiber sheet electrode. The electrode preferably has continuous voids and is more preferably a porous body having continuous voids in an application in which a liquid and a gas are allowed to flow in the electrode. Examples of such a carbon electrode having continuous voids include a carbon felt electrode, a carbon paper electrode, a carbon foam electrode, a carbon cloth electrode, a carbon knit electrode, a carbon nanofiber sheet electrode, and an activated carbon fiber sheet electrode. In particular, carbon felt, carbon paper, and carbon foam are preferred, and carbon foam is more preferred, from the viewpoint that high flexibility and a large surface area can result in a reduction in resistance. The carbon foam preferably has a structure in which a carbon portion is three-dimensionally continuous. The carbon foam can have high flexibility and a high surface area, and therefore preferably has a linear portion and a binding portion which binds the linear portion. Specific examples of the carbon felt and the carbon paper include SIGRACELL (registered trademark) KFD series, GFA series, GFD series, SGL series, and SIGRACET (registered trademark) series manufactured by SGL CARBON, carbon felt (for example, XF30A, BW-309) manufactured by Toyobo Co., Ltd., CARBORON (registered trademark) GF series (for example, GF-20, GF-3F) manufactured by Nippon Carbon Co., Ltd., Torayca (trademark) TGP series manufactured by Toray Industries, Inc., PYROFIL (trademark) series and GRAFIL (trademark) series manufactured by Mitsubishi Chemical Corporation, VGCF (registered trademark) sheet manufactured by Showa Denko K.K., and carbon felt and graphite felt manufactured by MERSEN. These may be each, if necessary, subjected to activation treatment such as oxidation. The carbon foam can be produced by any known method (International Publication No. WO 2018 / 096895, International Publication No. WO 2018 / 168741, International Publication No. WO 2020 / 045645). The electrode may be used singly or in combinations of a plurality thereof.

[0200] <Membrane electrode assembly> The membrane electrode assembly in the present embodiment has a structure in which the ion-exchange membrane (hereinafter, ion-exchange membrane is also referred to as "membrane for an assembly") and at least one electrode are bonded. The bonding means that the membrane for an assembly and at least one electrode are joined, and the bonding can allow the membrane for an assembly and at least one electrode to be integrated. For example, the bonding may be preferably used in a separation membrane electrode assembly including the membrane for an assembly and two electrodes because assembling of the cell for a redox flow battery does not require a step of sequentially applying an electrode, the membrane for an assembly and an electrode and can be made as one step and the production cost tends to be able to be suppressed. The method for bonding the membrane for an assembly and at least one electrode is not particularly limited, and examples thereof include a method with heat press and / or heat roll press. The temperature in the bonding is not particularly limited, and is preferably equal to or more than room temperature in a case in which the bonding between the membrane for an assembly and the electrode is insufficient, because the membrane for an assembly tends to be reduced in elastic modulus to enhance the bonding between the membrane for an assembly and the electrode. The temperature in the bonding is preferably 250°C or less, more preferably 200°C or less, further preferably 170°C or less, particularly preferably 150°C or less because the change in quality of the membrane for an assembly tends to be able to be suppressed. The pressure in the bonding is not particularly limited, and is a pressure of more than 0 MPa. The pressure is preferably 0.01 MPa or more, more preferably 0.05 MPa or more, further preferably 0.08 MPa or more, particularly preferably 0.1 MPa or more, because the bonding between the membrane for an assembly and the electrode tends to be enhanced. The pressure is preferably 100 MPa or less, more preferably 50 MPa or less, further preferably 20 MPa or less, particularly preferably 10 MPa or less, because the change in quality of the electrode tends to be able to be suppressed. The time in the bonding is not particularly limited, and is a time of more than 0 seconds. The time is preferably 0.01 seconds or more, more preferably 0.1 seconds or more, further preferably 0.5 seconds or more, particularly preferably 1 second or more, because the bonding between the membrane for an assembly and the electrode tends to be enhanced. The time is preferably 10 hours or less, more preferably 5 hours or less, further preferably 2 hours or less, particularly preferably 1 hour or less, because the cost in production of the membrane electrode assembly tends to be able to be reduced. The atmosphere in the bonding is not particularly limited, and examples include air, nitrogen, and argon. Air or nitrogen is preferred and air is more preferred because the cost in production of the membrane electrode assembly tends to be able to be reduced.

[0201] The membrane electrode assembly of the present embodiment can be used in various applications, and use in a cell for a redox flow battery, and a redox flow battery is suitably exemplified. Use in a cell for a redox flow battery, and a redox flow battery tends to result in an excellent power efficiency as compared with conventional use in a combination of a separation membrane and an electrode.

[0202] In a case where the side-chain heteroaromatic resin membrane, the heteroaromatic structure-containing fluororesin membrane, and the side-chain nitrogen atomcontaining fluororesin membrane are used in the separation membrane for a cell for a redox flow battery, and a redox flow battery of the present embodiment, the side-chain heteroaromatic resin layer, the heteroaromatic structure-containing fluororesin membrane, and the sidechain nitrogen atom-containing fluororesin membrane are preferably located facing the electrode acting as the negative electrode, preferably located closer to the electrode, when demanded are excellent current efficiency and voltage efficiency in a well-balanced manner and a high power efficiency. The "closer to" means that the distance of the side-chain heteroaromatic resin layer, the heteroaromatic structure-containing fluororesin membrane, and the side-chain nitrogen atom-containing fluororesin membrane, from the electrode acting as the negative electrode, is smaller than the distance of that from the electrode acting as the positive electrode. The reason why the above special effects are obtained by locating the side-chain heteroaromatic resin layer, the heteroaromatic structure-containing fluororesin membrane, and the side-chain nitrogen atom-containing fluororesin membrane, closer to the electrode acting as the negative electrode, although not clear, is presumed as follows: the amount of the redox active material moved from the positive electrode to the negative electrode and the amount of the redox active material moved from the negative electrode to the positive electrode are different, and thereby the side-chain heteroaromatic resin layer, the heteroaromatic structure-containing fluororesin layer, and the side-chain nitrogen atomcontaining fluororesin layer more effectively function to any of the redox active materials that moved more. In a case where a higher current efficiency is demanded, the side-chain heteroaromatic resin layer is preferably disposed on each of both surfaces of the separation membrane .

[0203] The cell for a redox flow battery, and the redox flow battery of the present embodiment can be used to provide a mechanism which smooths the amount of supply and demand of power and stabilizes the varying power obtained from a renewable energy source such as solar energy or wind energy. More specifically, it is possible to provide, for example, integration of the power obtained from a renewable energy source, power peak load shifting, stabilization of a transmission and distribution grid, base load power, energy arbitrage, supporting of a weak transmission and distribution grid, frequency adjustment, and any combination thereof. The cell for a redox flow battery, and the redox flow battery can also be used as a power supply of a remote camping, a forward operating base, transmission and distribution communication, a remote sensor, or the like utilizing no transmission and distribution grid. The cell for a redox flow battery, and the redox flow battery of the present embodiment can include a control system and a power regulation unit. The control system can be used to control operating of various valves, pumps, circulation circuits, sensors, relaxation equipment, other electronic / hardware controllers, safeguard apparatuses, and the like. The power adjustment unit can be used to convert the voltage of the input power, and the current into optimal modes for the cell for a redox flow battery, and / or the redox flow battery, and convert the voltage of the output power, and the current into optimal modes for any application. For example, in a case where the cell for a redox flow battery, and / or the redox flow battery are / is connected to a transmission and distribution grid, the power regulation unit can convert the input AC power into the DC power of suited voltage and current in a charge cycle. The cell for a redox flow battery, and / or the redox flow battery can generate the DC power and the power regulation unit can convert the DC power to the AC power of suitable voltage and frequency for sending to the transmission and distribution grid in a discharge cycle .

[0204] [Third embodiment] Subsequently, a third embodiment is described.

[0205] Patent Literature 1 discloses alternate stacking of a cation-exchange group layer and an anion-exchange group layer, for an increase in initial power efficiency, but does not indicate the thicknesses of the cationexchange group layer and the anion-exchange group layer anywhere except for Examples. The Literature, although discloses a preferred range of the ion-exchange capacity of an ion-exchange membrane configured from an ionexchanger layer having an ion-exchange group and a porous support layer having no ion-exchange group, does not describe any reason why such a range is preferred, and any Examples indicating that such a range is preferred, at all. Examples do not indicate any ion exchange capacity of a copolymer having a structural formula (1) in Patent Literature 1. The Literature, although discloses the cation-exchange group layer in an ionexchange group layer, capable of being arranged facing a positive electrode liquid to allow for an increase in lifetime of the ion-exchange group layer, does not indicate any arrangement of the anion-exchange group layer .

[0206] Patent Literature 2 discloses reformation of Nation (registered trademark) 117 with a heterocyclic molecule having a plurality of nitrogen atoms, but Nafion (registered trademark) 117 is large in membrane thickness, and thus is demanded to be lower in proton area resistivity when actually used in a redox flow battery, even if it has a comparable proton area resistivity. Although also disclosed is thinning by use of a support, Nafion (registered trademark) 117 itself is large in proton area resistivity, and is demanded as described above to be lower in proton area resistivity when actually used in a redox flow battery. Not indicated is any operation of a redox flow battery with a membrane disclosed. Although the heterocyclic molecule having a plurality of nitrogen atoms, which is optionally bound with being located closer to the negative half-cell of the battery in order to improve performance of the membrane, is disclosed, there is not any description about which performance is improved and there is also not such any description in Examples. The degree of thickness of the heterocyclic molecule having a plurality of nitrogen atoms, in the membrane, is not indicated at all.

[0207] Patent Literature 3 discloses a polyelectrolyte membrane including a crossover prevention layer as a metal layer formed by reduction of a cationic metal, therein, for an enhancement in at least one or more characteristics of discharge capacity, current efficiency, voltage efficiency, and power efficiency, but such characteristics are demanded to be higher. A preferred range of the thickness of the metal layer formed is indicated to be as relatively large as 10 p.m or more and 50 Jim or less. A preferred range of the equivalent weight (Equivalent Weight, hereinafter, also referred to as "EW") of the polyelectrolyte membrane is not indicated at all. The location of the crossover prevention layer in the polyelectrolyte membrane is indicated to be at a position corresponding to 10% or more and 90% or less of the thickness of the electrolyte membrane, from the surface of the polyelectrolyte membrane. However, whether the crossover prevention layer faces either the positive electrode or the negative electrode in the case of a flow battery is not indicated at all.

[0208] Patent Literature 4 discloses setting of the value obtained by dividing the thickness of a first ionexchange resin layer by the thickness of a second ionexchange resin layer, to 0.7 or more and 1.3 or less, for curl suppression, and indicates that the thickness of the first ion-exchange resin layer and the thickness of the second ion-exchange resin layer are equal to each other, namely, an anion-exchange resin layer is located at the center in the thickness direction of the entire membrane. There is not any indication about whether the anion-exchange resin layer is placed facing either the positive electrode or the negative electrode in a redox flow battery cell even if the thickness of the first ionexchange resin layer and the thickness of the second ionexchange resin layer are not equal to each other.

[0209] An object of the present embodiment relates to methods for producing a cell for a redox battery, a redox flow battery, and a separation membrane each having a high power efficiency.

[0210] The present inventors have made intensive studies about the above object, and as a result, have found that, in a case where a separation membrane constituting a cell for a redox flow battery includes at least a first cation-exchangeable resin layer and an anion-exchangeable resin layer and the anion-exchangeable resin layer is located facing the electrode acting as the negative electrode, surprisingly a high power efficiency is obtained as compared with a case where the anion-exchangeable resin layer is located facing the electrode acting as the positive electrode. Furthermore, it has been found that a particularly high power efficiency is obtained by setting the equivalent weight of the separation membrane and the thickness of the anion-exchangeable resin layer within specified ranges.

[0211] The cell for a redox flow battery according to the present embodiment includes a first electrolyte solution including a first redox active material, a second electrolyte solution including a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a separation membrane located between the first electrolyte solution and the second electrolyte solution, wherein the separation membrane includes at least a first cation-exchangeable resin layer, and an anion-exchangeable resin layer, the equivalent weight of the separation membrane is 1150 g / eq or less, the thickness of the anion-exchangeable resin layer is 0.001 p.m or more and less than 5 Jim, and the anion-exchangeable resin layer of the separation membrane is located facing the electrode acting as the negative electrode. According to the present embodiment, it is possible to provide methods for producing a cell for a redox battery, a redox flow battery, and a separation membrane each having a high power efficiency.

[0212] <Cell for redox flow battery> A cell for a redox flow battery of the present embodiment is configured to include a first electrolyte solution including a first redox active material, a second electrolyte solution including a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a separation membrane located between the first electrolyte solution and the second electrolyte solution. Any component other than the constituent components, which is commonly utilized by those skilled in the art, and / or any component which can be known from known information, for example, known literatures and patents each relating to a cell for a redox flow battery, may be included. Examples of such components include a bipolar plate, a frame, a compressible seal, a conductive additive, and a balancing cell.

[0213] Figure 1 illustrates one example of a schematic view of the cell for a redox flow battery of the present embodiment. A cell 10 for a redox flow battery of the present embodiment has an electrolyzer 6 including a cell chamber 2 including an electrode 1 (in Figure 1, positive electrode) composed of a first electrode, a cell chamber 4 including an electrode 3 (in Figure 1, negative electrode) composed of a second electrode, and a separation membrane 5 as a separation membrane which separates the cell chamber 2 and the cell chamber 4. The cell chamber 2 and the cell chamber 4 include electrolyte solutions containing redox active materials. Such electrolyte solutions containing redox active materials are respectively stored in, for example, electrolyte solution tanks 7 and 8, and are supplied to the cell chambers by pumps or the like. The current generated by the cell for a redox flow battery may be converted from DC to AC through an AC / DC converter 9 or may be converted from AC to DC through the AC / DC converter 9, to pack the cell for a redox flow battery. The cell for a redox flow battery of the present embodiment is preferably a cell for a redox flow secondary battery.

[0214] <Electrolyte solution> The electrolyte solution in the present embodiment is a liquid containing a redox active material and a solvent. The redox active material is a substance having redox activity directly involving in an electromotive force in the cell for a redox flow battery. The redox active material used in the present embodiment is not particularly limited, and examples thereof include a metallic redox active material, a non-metallic redox active material, and an organic redox active material, and such each redox active material may be a neutral compound or an ionic compound.

[0215] The metallic redox active material is a substance containing at least one metal atom, and may contain a plurality of the same type of metal atoms or a plurality of different types of metals. The metal atom used in the metallic redox active material is not particularly limited, examples thereof include aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, lead, and cerium, and in particular, titanium, vanadium, chromium, manganese, iron, and cerium are preferred. Vanadium, iron, copper, and tin are preferred, vanadium and iron are further preferred, and vanadium is particularly preferred, from the viewpoint that the first redox active material and the second redox active material can be the same in type.

[0216] The metallic redox active material may have a ligand for active materials, commonly used, and examples of the ligand include a cyanated product ion, acetylacetone, ethylenediamine, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, carbon monoxide, bipyridine, bipyrazine, ethylene glycol, propylene glycol, ethanedithiol, butanedithiol, terpyridine, diethylenetriamine, triazacyclononane, tris(hydroxymethyl)aminomethane, ascorbic acid, citric acid, glycolic acid, gluconic acid, acetic acid, formic acid, benzoic acid, malic acid, maleic acid, phthalic acid, sarcosine acid, salicylic acid, oxalic acid, urea, aminophenolate, and lactic acid. Such a ligand for active materials may be adopted singly or in combinations of a plurality thereof.

[0217] The material used in the non-metallic redox active material is not particularly limited, and examples thereof include chlorine, bromine, sulfur, and polysulfide .

[0218] The organic redox active material is not particularly limited, and examples thereof include viologen, a derivative thereof, and a compound having a viologen structure in a polymer side chain, a 2,2,6,6-tetramethyl-l-piperidinyloxy radical, a derivative thereof, and a compound having a 2,2,6,6-tetramethyl-l-piperidinyloxy radical structure in a polymer side chain, ferrocene, a derivative thereof, and a compound having a ferrocene structure in a polymer side chain, quinone, a derivative thereof, and a compound having a quinone structure in a polymer side chain, anthraquinone, a derivative thereof, and a compound having an anthraquinone structure in a polymer side chain, and quinoxaline, a derivative thereof, and a compound having a quinoxaline structure in a polymer side chain. The redox active material may be adopted singly or in combinations of a plurality thereof.

[0219] When the redox active material is used in the cell for a redox flow battery, the redox active material used in the electrolyte solution of the positive electrode and the redox active material used in the electrolyte solution of the negative electrode can be used in combination depending on desired characteristics. The combination of such redox active materials is not particularly limited, and examples thereof include respective combinations of vanadium / vanadium, iron / iron, lead / lead, copper / copper, iron / chromium, chromium / bromine, zinc / bromine, polysulfide / bromine, zinc / cerium, zinc / nickel, zinc / cerium, zinc / iodine, titanium / manganese, vanadium / cerium, and vanadium / manganese . In particular, vanadium / vanadium, iron / iron, iron / chromium, chromium / bromine, zinc / bromine, and titanium / manganese are preferred, vanadium / vanadium, iron / iron, and zinc / bromine are more preferred, and vanadium / vanadium is particularly preferred because a high electromotive force is obtained and stability in charge and discharge is excellent.

[0220] In a case where the redox active materials of the positive electrode and the negative electrode are each vanadium, the cell for a redox flow battery, and the redox flow battery are also designated respectively as "cell for a vanadium redox flow battery", and "vanadium redox flow battery". In addition, in a case where the redox active materials of the positive electrode and the negative electrode are each vanadium, charge and discharge are performed by utilizing an oxidationreduction reaction, by use of each redox coupling of V02+ / V02+ in the positive electrode and V2+ / V3+ in the negative electrode. When charge is performed, protons (H+) are excess in the cell chamber of the positive electrode and, on the other hand, protons (H+) are deficient in the cell chamber of the negative electrode, along with the oxidation-reduction reaction. The separation membrane allows excess protons in the cell chamber of the positive electrode to be selectively moved to the chamber of the negative electrode, and electrical neutrality is kept. When discharge is performed, its opposite reaction progresses and electrical neutrality is kept.

[0221] The solvent used in the electrolyte solution is not particularly limited, and examples thereof include water, alcohols, nitriles, esters, ketones, ethers, aliphatic hydrocarbons, and aromatic hydrocarbons. In particular, water is preferred from the viewpoint of an enhancement in stability in operating of the cell for a redox flow battery. Specific examples of the solvent include alcohols such as methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, ethylene glycol, diethylene glycol, and glycerol, nitriles such as acetonitrile, propionitrile, and benzonitrile, esters such as ethyl acetate and butyl acetate, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, ethers such as diethyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, ethylene glycoldiethyl ether, and diethylene glycol dimethyl ether, aliphatic hydrocarbons such as pentane, hexane, cyclohexane, heptane, octane, chloroform, dichloromethane, and tetrachloromethane, and aromatic hydrocarbons such as benzene, toluene, xylene, chlorobenzene, dichlorobenzene, phenol, and cresol. The solvent used in the electrolyte solution may be adopted singly or in combinations of a plurality thereof.

[0222] An electrolyte may be further used in the electrolyte solution. The electrolyte is a substance which releases ions in the electrolyte solution to enhance electrical conductivity of the electrolyte solution. The electrolyte is not particularly limited, and examples thereof include sulfuric acid, hydrochloric acid, nitric acid, acetic acid, phosphoric acid, sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium acetate. The electrolyte used in the electrolyte solution may be adopted singly or in combinations of a plurality thereof .

[0223] An additive may be added to the electrolyte solution depending on desired characteristics of the electrolyte solution. The additive is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, polyethylene glycol, glycerol, mannitol, sorbitol, pentaerythritol, tris(hydroxymethyl)aminomethane, cornstarch, corn syrup, gelatin, glycerol, guar gum, pectin, and a surfactant. The additive used in the electrolyte solution may be adopted singly or in combinations of a plurality thereof.

[0224] <Electrode> The electrode used in the cell for a redox flow battery of the present embodiment is not particularly limited, and is preferably a carbon electrode. The carbon electrode preferably has continuous voids and is more preferably a porous body having continuous voids in order to allow the electrolyte solution to flow through. Examples of such a carbon electrode having continuous voids include carbon felt, carbon paper, carbon foam, a carbon cloth, a carbon knit, a carbon nanofiber sheet, and an activated carbon fiber sheet, preferably include carbon felt, carbon paper, and carbon foam. In particular, carbon foam is preferred from the viewpoint that high flexibility and a large surface area can result in a reduction in resistance. The carbon foam preferably has a structure in which a carbon portion is three-dimensionally continuous. The carbon foam can have high flexibility and a high surface area and thus obtain a high power efficiency, and therefore preferably has a linear portion and a binding portion which binds the linear portion.

[0225] Specific examples of the carbon felt and the carbon paper include SIGRACELL (registered trademark) KFD series, GFA series, GFD series, SGL series, and SIGRACET (registered trademark) series manufactured by SGL CARBON, carbon felt (for example, XF30A, BW-309) manufactured by Toyobo Co., Ltd., CARBORON (registered trademark) GF series (for example, GF-20, GF-3F) manufactured by Nippon Carbon Co., Ltd., Torayca (trademark) TGP series manufactured by Toray Industries, Inc., PYROFIL (trademark) series and GRAFIL (trademark) series manufactured by Mitsubishi Chemical Corporation, VGCF (registered trademark) sheet manufactured by Showa Denko K.K., and carbon felt and graphite felt manufactured by MERSEN. These may be each, if necessary, subjected to activation treatment such as oxidation.

[0226] The carbon foam can be produced by any known method (International Publication No. WO 2018 / 096895, International Publication No. WO 2018 / 168741, International Publication No. WO 2020 / 045645).

[0227] The first electrode and the second electrode may be each a single electrode, or may be different electrodes, and each single electrode or a combination of a plurality of electrodes may be used in the first electrode and / or the second electrode.

[0228] <Separation membrane> In the present embodiment, the separation membrane is a membrane located between the first electrolyte solution and the second electrolyte solution, and includes at least a first cation-exchangeable resin layer and an anion-exchangeable resin layer, in which the equivalent weight of the separation membrane is 1150 g / eq or less, the thickness of the anion-exchangeable resin layer is 0.001 p.m or more and less than 5 p.m, and the anion-exchangeable resin layer of the separation membrane is located facing the electrode acting as the negative electrode in the cell for a redox flow battery.

[0229] The equivalent weight of the separation membrane is not particularly limited, and is preferably 1150 g / eq or less, more preferably 1100 g / eq or less because there is a tendency of a reduction in proton movement resistance and an enhancement in power efficiency. The equivalent weight is more preferably 1050 g / eq or less, particularly preferably 1030 g / eq or less, further particularly preferably 1000 g / eq or less because the separation membrane tends to be enhanced in affinity. The equivalent weight is preferably 500 g / eq or more, more preferably 700 g / eq or more because the separation membrane tends to be enhanced in solubility in the electrolyte solutions. The equivalent weight is further preferably 800 g / eq or more, particularly preferably 880 g / eq or more because the separation membrane tends to be enhanced in mechanical strength against pulsation of the electrolyte solutions, contact thereof with the electrodes, and / or the like.

[0230] The equivalent weight refers to a dry mass in grams of an ion-exchangeable resin as a resin having ionexchange ability, per equivalent of an ion-exchange group having ion-exchange ability in the ion-exchangeable resin, and the equivalent weight of the first cationexchangeable resin layer is a dry mass in grams of the first cation-exchangeable resin layer, per equivalent of an ion-exchange group in the first cation-exchangeable resin layer. Hereinafter, the expression "equivalent weight" is appropriately used in the present embodiment. A method used in measurement of the equivalent weight can be a method in which the ion-exchangeable resin is substituted with a salt and its solution is back titrated with an alkaline solution. The equivalent weight can be appropriately adjusted by selecting the ratio of copolymerization of a monomer as a starting material of the cation-exchangeable resin, the type of the monomer, and the like.

[0231] The anion-exchangeable resin layer included in the separation membrane in the present embodiment is preferably located facing the electrode acting as the negative electrode, preferably located closer to the electrode. The "closer to" means that the distance of the anion-exchangeable resin layer from the electrode acting as the negative electrode is smaller than the distance of that from the electrode acting as the positive electrode. The present inventors have found in the present application that the anion-exchangeable resin layer is located facing the electrode acting as the negative electrode to surprisingly result in an enhancement in power efficiency. The reason for an enhancement in power efficiency, although not clear, is presumed as follows: the amount of the redox active material moved from the positive electrode to the negative electrode and the amount of the redox active material moved from the negative electrode to the positive electrode are different, and thereby the anion-exchangeable resin layer more effectively functions to any of the redox active materials that moved more. It is presumed that the influence by the anion-exchangeable resin layer located facing the electrode acting as the negative electrode is provided and therefore an effective action is made on the amount of the redox active material moved from the negative electrode to the positive electrode .

[0232] The distance Dneg between the anion-exchangeable resin layer of the separation membrane and the electrode acting as the negative electrode, and the distance Dpos between the anion-exchangeable resin layer of the separation membrane and the electrode acting as the positive electrode preferably exhibit the following relationship : Dneg / Dpos < 1 wherein the distance Dneg means the distance from a face of the anion-exchangeable resin layer, the face being closest to the negative electrode, toward the closest surface of the negative electrode. The distance Dpos means the distance from a face of the anion-exchangeable resin layer, the face being closest to the positive electrode, toward the closest surface of the positive electrode . The Dneg / DpOs is preferably 0.8 or less, more preferably 0.7 or less, further preferably 0.6 or less, more preferably 0.5 or less, from the viewpoint of a more enhancement in power efficiency. The lower limit of the Dneg / DpOs is not particularly limited, and may be, for example, 0 or more. In other words, the anion-exchangeable resin layer and the negative electrode may be contacted.

[0233] The first cation-exchangeable resin layer is preferably located closer to the electrode acting as the positive electrode than the anion-exchangeable resin layer from the viewpoint of a more enhancement in power efficiency.

[0234] <First cation-exchangeable resin layer> The first cation-exchangeable resin layer is a layer formed with a substance containing a resin (hereinafter, also referred to as "cation-exchangeable resin") having ion-exchange ability with a cation (hereinafter, also referred to as "positive ion").

[0235] The cation-exchangeable resin is not particularly limited, and examples thereof include a hydrocarbon-based resin and a fluororesin. A hydrocarbon-based resin is preferred from the viewpoint of suppression of the production cost of the cell for a redox flow battery, and a fluororesin is preferred from the viewpoint of an enhancement in durability of the cell for a redox flow battery.

[0236] The hydrocarbon-based resin and the fluororesin may be each used singly or in combinations of two or more kinds thereof.

[0237] The functional group having ion-exchange ability contained in the cation-exchangeable resin is not particularly limited, and examples thereof include a sulfo group (SO3H), a carboxyl group (CO2H) , a phenolic hydroxyl group (OH), a phosphoric acid group (PO3H2) , a thiol group (SH), and such a functional group in which hydrogen is an alkali metal, an alkaline earth metal, or an transition metal. The functional group having ion-exchange ability may be used singly, or in combinations of a plurality of such functional groups.

[0238] Among such functional groups having ion-exchange ability, a sulfo group, a carboxyl group, and / or a phosphoric acid group are / is preferred, a sulfo group and / or a carboxyl group are / is more preferred, and a sulfo group is particularly preferred, because the ionexchange ability tends to be excellent.

[0239] The hydrocarbon-based resin is not particularly limited, and examples thereof include a resin which is, for example, polystyrene, polyphenylene ether, polybenzimidazole, polyetheretherketone, polyimide, polyetherimide, polyaryletherketone, polysulfone, polyether sulfone, polyphenylene sulfide, or polyphenylsulfone, and which has the functional group having ion-exchange ability. The resin, which depends on required physical properties, may be crosslinked, may be a copolymer, or may have various substituents (for example, halogen atoms such as a fluorine atom, a chlorine atom, and a bromine atom; nitrile groups, aliphatic hydrocarbon groups such as a methyl group, an ethyl group, a vinyl group, an allyl group, a 1-methylvinyl group, a n-propyl group, an iso-propyl group, a n-butyl group, an iso-butyl group, a sec-butyl group, and a tert-butyl group; aromatic hydrocarbon groups such as a benzyl group, a phenyl group, and a nitrilesubstituted phenyl group; an amino group; a nitro group; a hydroxyl group; and a silyl group). The hydrocarbon-based resin may be used singly or in combinations of a plurality thereof.

[0240] The fluororesin is not particularly limited, and examples thereof include a partially fluorinated resin and a fully fluorinated resin each having the functional group having ion-exchange ability. A resin in which not all hydrogen atoms, but at least one hydrogen atom, among hydrogen atoms on carbon atoms contained in the hydrocarbon-based cation-exchangeable resin is replaced with a fluorine atom, and a resin in which all such hydrogen atoms on carbon atoms are replaced with fluorine atoms are respectively exemplified as the partially fluorinated resin and the fully fluorinated resin.

[0241] The fluororesin is preferably a fluororesin (hereinafter, also referred to as "fluororesin Gl") having the structural unit represented by the general formula Gl, from the viewpoint that the cell for a redox flow battery tends to be enhanced in durability: F X6 CF2X8 [Gl] wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

[0242] The equivalent weight of the first cationexchangeable resin layer is not particularly limited, and is preferably less than 1100 g / eq, more preferably 1050 g / eq or less, because there is a tendency of a reduction in proton movement resistance and an enhancement in power efficiency. Furthermore, the equivalent weight is more preferably 1030 g / eq or less, particularly preferably 1000 or less because the first cation-exchangeable resin layer tends to be enhanced in affinity. The equivalent weight is preferably 500 g / eq or more, more preferably 700 g / eq or more, because there is a tendency of an enhancement in solubility in the electrolyte solutions. Furthermore, the equivalent weight is further preferably 800 g / eq or more, particularly preferably 880 g / eq or more because enhancement in mechanical strength against pulsation of the electrolyte solutions, contact thereof with the electrodes, and / or the like is likely to be achieved.

[0243] The thickness of the first cation-exchangeable resin layer is not particularly limited, and is preferably 1 Jim or more and 150 Jim or less. The thickness is more preferably 100 jim or less, further preferably 80 Jim or less, particularly preferably 60 Jim or less, because there is a tendency of a reduction in proton movement resistance and an enhancement in power efficiency. The thickness is more preferably 5 Jim or more, further preferably 10 Jim or more, particularly preferably 20 Jim or more, further particularly preferably 25 p.m or more, because enhancement in mechanical strength against pulsation of the electrolyte solutions, contact thereof with the electrodes, and / or the like is likely to be achieved.

[0244] The content of the cation-exchangeable resin in the first ion-exchangeable resin layer is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more. The upper limit of the content of a positive ion-exchange resin is not particularly restricted, and is preferably 100% by mass or less in the first ion-exchangeable resin layer. The content is more preferably 99.5% by mass or less, further preferably 99% by mass or less because the cost for removal of a substance different from the cationexchangeable resin in the first ion-exchangeable resin layer tends to be able to be suppressed and the cost for a cell for a battery for redox flow tends to be able to be suppressed.

[0245] The method for producing the first cationexchangeable resin layer used in the separation membrane of the present embodiment is not particularly limited, and the first cation-exchangeable resin layer can be obtained by processing the cation-exchangeable resin into a film, or by processing a cation-exchangeable resin precursor having the functional group having ion-exchange ability, into a film, by hydrolysis, and performing the above hydrolysis treatment and acid treatment. Examples include a method in which the cation-exchangeable resin is melt-kneaded and then extruded with an extruder by a nozzle, a die, or the like, and thus processed into a film. Examples also include a method in which the cation-exchangeable resin precursor is melt-kneaded and then extruded with an extruder by a nozzle, a die, or the like, to form a film, and then the hydrolysis treatment and acid treatment are performed to form an ion-exchange group. The cation-exchangeable resin may be dispersed in a solvent and then cast on the substrate, and thus processed into a film.

[0246] The method for producing the fluororesin G1 is as described above.

[0247] <Anion-exchangeable resin layer> The anion-exchangeable resin layer is a layer including an anion-exchangeable compound. The anion-exchangeable compound is a compound having a functional group and a molecule structure each containing a nitrogen atom, such as a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, a pyridine ring structure, and a derivative structure thereof, a pyridinium group, an imidazole ring structure, and a derivative structure thereof, an imidazolium group, a pyrrole ring structure, and a derivative structure thereof, and is a compound which is positively charged at least under an acidic condition.

[0248] The separation membrane of the present embodiment has the anion-exchangeable resin layer, and thus not only electrostatic repulsion against a cation in the electrolyte solution can be imparted to the separation membrane and a redox active material high in charge density can be inhibited from permeating through the separation membrane, but also a proton low in charge density can be allowed to permeate through the separation membrane and the power efficiency can be enhanced.

[0249] The anion-exchangeable compound is not particularly limited, and examples thereof include anion-exchangeable polymers such as a polyvinylpyridine polymer, and a salt thereof, a vinylpyridine / divinylbenzene copolymer, and a salt thereof, a vinylpyridine / styrene copolymer, and a salt thereof, polyethyleneimine, and a salt thereof, a vinylbenzyltrimethylammonium chloride polymer, a polyvinylimidazole polymer, and a salt thereof, a vinylimidazole / divinylbenzene copolymer, and a salt thereof, a vinylimidazole / styrene copolymer, and a salt thereof, a polyvinylpyrrolidone polymer, and a salt thereof, polybenzimidazole, and a salt thereof, a polymer having a benzimidazole structure, and a salt thereof, polypyrrole, and a salt thereof, polyaniline, poly(4-aminostyrene), and a salt thereof, and poly(vinylcarbazole), and a salt thereof, quaternary ammonium compounds each having a quaternary ammonium group, such as tetrabutylammonium and octyltrimethylammonium, a pyridinium compound having a pyridinium structure such as butylpyridinium, and a derivative thereof, trimethylamine, and a salt thereof, triethylamine, and a salt thereof, tributylamine, and a salt thereof, triethanolamine, and a salt thereof, pyrrole, and a salt thereof, a pyrrole derivative, and a salt thereof, 1,8-diazabicyclo[5.4.0]undecene-7, and a salt thereof, 1,5-diazabicyclo[4.3.0]nonene-5, and a salt thereof, 1,4-diazabicyclo[2.2.2]octane, and a salt thereof, 1-azabicyclo[2.2.2.]octane, and a salt thereof, N,N,N',N'-tetramethylbutanediamine, and a salt thereof, ethylenediamine, N,N-dimethylethylenediamine, N-methylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyldipropylenetriamine, 1-(3-aminopropyl) imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, 4-aminopyridine, 1,2,3-triaminobenzene, hexamethylenetetramine, imidazole, oxazole, thiazole, pyrazole, aminobenzimidazole, 4-aminopiperidine, tetrafluoro-p-phenylenediamine, hexamethylenediamine, 4,4'-diaminodiphenyl ether, and 4-benzylpyridine.

[0250] The anion-exchangeable compound may be an anion-exchangeable fluororesin represented by the following general formula B17, and a saponified product thereof, or a salt thereof: - [CFXiCXSXSJa- [CF2-CF( (-O-CF2- (CF(CF2X4) ) )b-Oc- (CFR1)d_ (CFR2)e-(CF2) f-Ae) ]g- [B17] wherein X1, X2, X3 and X4 are each optionally the same or different, and are each a halogen atom, or a perfluoroalkyl group having 1 to 10 carbon atoms or a cyclic perfluoroalkyl group, the group being optionally substituted or unsubstituted, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X1 and X2 or X1 and X3 optionally form a cyclic structure; R1 and R2 are each optionally the same or different and are each a hydrogen atom, a halogen atom, or a perfluoroalkyl group having 1 to 10 carbon atoms or a fluorochloroalkyl group, the group being optionally substituted or unsubstituted, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; Ae is a monovalent group represented by formula -CONX6Ax or -SO2NX6Ax, X6 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group, the group being optionally substituted or unsubstituted, Ax is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group, or a heteroaromatic group, the group containing at least one nitrogen atom and being optionally substituted or unsubstituted; a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1; b is an integer of 0 to 8; c is 0 or 1; and d, e, and f are each optionally the same or different and are each an integer of 0 to 6 (provided that, when d, e, and f are 0 at the same time, Ae is -CF(CF2Az)2, Az is a monovalent group represented by formula -CONX6Ax or -SO2NX6Ax, and Ax and X6 have the same meanings as described above). The anion-exchangeable compound may be used singly or in combinations of a plurality thereof.

[0251] The substituent in the case of "substituted" is the same as the substituent exemplified with respect to the general formula 1.

[0252] The anion-exchangeable compound is preferably at least one anion-exchangeable compound selected from the group consisting of a polyvinylpyridine polymer, and a salt thereof, a vinylpyridine / divinylbenzene copolymer, and a salt thereof, a vinylpyridine / styrene copolymer, and a salt thereof, polyethyleneimine, and a salt thereof, a vinylbenzyltrimethylammonium chloride polymer, a polyvinylimidazole polymer, and a salt thereof, a vinylimidazole / divinylbenzene copolymer, and a salt thereof, a vinylimidazole / styrene copolymer, and a salt thereof, a polyvinylpyrrolidone polymer, and a salt thereof, polybenzimidazole, and a salt thereof, a polymer having a benzimidazole structure, and a salt thereof, polypyrrole, and a salt thereof, polyaniline, poly(4-aminostyrene), and a salt thereof, poly(vinylcarbazole), and a salt thereof, and the anion-exchangeable fluororesin represented by the general formula B17, and a saponified product thereof, or a salt thereof, more preferably at least one anion-exchangeable compound selected from the group consisting of a polyvinylpyridine polymer, and a salt thereof, a vinylpyridine / divinylbenzene copolymer, and a salt thereof, a vinylpyridine / styrene copolymer, and a salt thereof, a polyvinylimidazole polymer, and a salt thereof, a vinylimidazole / divinylbenzene copolymer, and a salt thereof, a vinylimidazole / styrene copolymer, and a salt thereof, polybenzimidazole, and a salt thereof, a polymer having a benzimidazole structure, and a salt thereof, and the anion-exchangeable fluororesin represented by the general formula B17, because there is a tendency of suppression of dissolution in the electrolyte solution and an enhancement in durability of the cell for a redox flow battery. The anion-exchangeable compound is further preferably at least one anion-exchangeable compound selected from the group consisting of a polyvinylpyridine polymer, and a salt thereof, a polyvinylimidazole polymer, and a salt thereof, polybenzimidazole, and a salt thereof, a polymer having a benzimidazole structure, and a salt thereof, and the anion-exchangeable fluororesin represented by the general formula B17, particularly preferably at least one anion-exchangeable compound selected from the group consisting of a polyvinylpyridine polymer, and a salt thereof, a polyvinylimidazole polymer, and a salt thereof, and the anion-exchangeable fluororesin represented by the general formula B17, because there is a tendency of an increase in electrostatic repulsion of the anion-exchangeable resin layer against a cation and an enhancement in power efficiency of the cell for a redox flow battery.

[0253] The saponified product of the anion-exchangeable fluororesin represented by the general formula B17 is a saponified product obtained by reaction of the anion-exchangeable fluororesin and an alkaline substance. Examples of a basic substance include amine compounds such as dimethylamine, diethylamine, monomethylamine and monoethylamine, and alkali metal hydroxides and alkaline earth metal hydroxides, such as sodium hydroxide and potassium hydroxide. In particular, sodium hydroxide or potassium hydroxide is preferred.

[0254] The salt of the anion-exchangeable fluororesin is a salt of the anion-exchangeable fluororesin and an acidic substance. Examples of the acidic substance include mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid and trifluoroacetic acid.

[0255] The anion-exchangeable fluororesin represented by the general formula B17, which can be utilized in the anion-exchangeable compound, preferably includes a constituent unit represented by the following general formula B16, and at least one selected from the group consisting of a constituent unit represented by the following general formula B18, a constituent unit represented by the following general formula B19, and a constituent unit represented by the following general formula B20, from the viewpoint that the anion-exchangeable fluororesin tends to be enhanced in chemical stability such as oxidation degradation resistance and from the viewpoint that the production cost of the anion-exchangeable fluororesin tends to be able to be suppressed and the production cost of the cell for a redox flow battery tends to be able to be suppressed: - (CF2-CF2) - [B16] - (CF2-CF (-0- (CF2CFXO) N-Ag) ) - [B18] wherein X represents F, or a perfluoroalkyl group having 1 to 3 carbon atoms, and Ag represents (CF2) m-SO2NX6Ax (X6 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group, the group being optionally substituted or unsubstituted, and Ax is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group, or a heteroaromatic group, the group having at least one nitrogen atom and being optionally substituted or unsubstituted, N represents an integer of 0 to 5, and M represents an integer of 0 to 6, provided that N and M are not 0 at the same time.), - (CF2-CF (-0- (CF2) P-CFX (-0- (CF2)k-SO2NX6Ax) ) ) - [B19] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, X6 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group, the group being optionally substituted or unsubstituted, and Ax is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group, or a heteroaromatic group, the group having at least one nitrogen atom and being optionally substituted or unsubstituted; and P represents an integer of 0 to 12, and K represents an integer of 1 to 5, provided that P and K are not 0 at the same time, - (CF2-CF(-O- (CF2)q-CFX(- (CF2)l-O- (CF2)o-S02NX6Ax) ) ) - [B20] wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, X6 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group, the group being optionally substituted or unsubstituted, and Ax is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group, or a heteroaromatic group, the group having at least one nitrogen atom and being optionally substituted or unsubstituted; and Q represents an integer of 0 to 12, L represents an integer of 1 to 5, and o represents an integer of 0 to 6, provided that Q and 0 are not 0 at the same time. The anion-exchangeable fluororesin more preferably includes the constituent unit represented by the general formula B16, and at least one selected from the group consisting of the constituent unit represented by the general formula B18, the constituent unit represented by the general formula B19, and the constituent unit represented by the general formula B20, further preferably contains the constituent unit represented by the general formula B16 and the constituent unit represented by the general formula B18 (provided that X is F, or a trifluoromethyl group, n is an integer of 0 to 2, and m is an integer of 1 to 4.) from the same viewpoint, particularly preferably includes the constituent unit represented by the general formula B16 and the constituent unit represented by the general formula B18 (provided that X is F, or a trifluoromethyl group, n is 0 or 1, and m is an integer of 2 to 4.).

[0256] The anion-exchangeable fluororesin more preferably has a structural unit represented by the following general formula B21, further preferably has a structural unit represented by the following general formula B22: - [CF2CF2]a- [CF2-CF( (-O-CF2- (CF(CF3) ) ) b-O- (CF2) 2-SO2NX6Ax) ] g-[B21] wherein X6 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, Ax is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group, or a heteroaromatic group, the group having at least one nitrogen atom and being optionally substituted or unsubstituted, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1, and b is 0 or 1, - [CF2CF2] a- [CF2-CF ( (-O-CF2- (CF (CF3) ) ) -0- (CF2) 2-SO2NX6Ax) ] g-[B22 ] wherein X6 is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group, the group being optionally substituted or unsubstituted, Ax is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group, or a heteroaromatic group, the group having at least one nitrogen atom and being optionally substituted or unsubstituted, and a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1.

[0257] In the general formulae B17 to B22, X6 is preferably a hydrogen atom, or an aliphatic hydrocarbon group having 1 to 10 carbon atoms, the group being optionally substituted or unsubstituted, because production of the anion-exchangeable fluororesin tends to be simplified and the production cost of the cell for a redox flow battery tends to be able to be suppressed. A hydrogen atom is further preferred from the viewpoint that the production cost of the anion-exchangeable fluororesin can be more suppressed, and an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms is further preferred from the viewpoint of an enhancement in stability of the anion-exchangeable fluororesin under an alkaline condition.

[0258] In the general formulae B17 to B22, Ax is preferably an unsubstituted aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group or a heteroaromatic group, the group containing at least one nitrogen atom, more preferably an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a heteroaromatic group, the group containing at least one nitrogen atom, because the cost of a starting material tends to be reduced and the production cost of the cell for a redox flow battery tends to be able to be suppressed. More specific examples of the nitrogen atom structure contained in Ax preferably include a primary amino group, a secondary amino group, a tertiary amino group, a pyridine ring structure, and a derivative structure thereof, a pyridinium group, an imidazole ring structure, and a derivative structure thereof, an imidazolium group, a pyrrole ring structure, and a derivative structure thereof, and more preferred is a tertiary amino group, a pyridine ring structure, and a derivative structure thereof, an imidazole ring structure, and a derivative structure thereof.

[0259] The method for producing the anion-exchangeable fluororesin is not particularly limited, and examples include a method in which the fluororesin precursor, and the anion-exchangeable compound (hereinafter, also referred to as "modification compound".) except for the anion-exchangeable fluororesin are reacted.

[0260] Examples of the modification compound include a modification compound having at least two nitrogen atomcontaining groups, in which the nitrogen atom-containing groups include at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, an amino salt structure as a reaction product of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group, and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, a nitrogen atom-containing heterocyclic ring structure, a salt structure of a nitrogen-containing heterocyclic ring as a reaction product of a nitrogencontaining heterocyclic ring structure and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, and a quaternary ammonium group. In particular, at least one nitrogen atom-containing group is preferably a primary amino group or a secondary amino group, more preferably a primary amino group because reactivity with the fluororesin precursor tends to be enhanced. Herein, the quaternary ammonium group is a quaternary ammonium group different from the amino salt structure and the salt structure.

[0261] More specific examples of the modification compound include ethylenediamine, N-methylethylenediamine, N-ethylethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N,N'-trimethylethylenediamine, N-benzylethylenediamine, N,N-dibutylethylenediamine, 1,2-diphenylethylenediamine, N,N'-dicyclohexyl-1,2-ethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-diethyl-1,3-propanediamine, N,N-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyl-1,4-cyclohexanediamine, 3-aminopiperidine, isophoronediamine, 4-(aminomethyl)piperidine, 3-aminopyrrolidine, 4-aminopiperidine, 3-aminopyrrolidine, N,N-dimethyltrimethylenediamine, N,N-dibutyltrimethylenediamine, 1-(3-aminopropyl) imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(ethylaminomethyl)pyridine, 4-(4-piperidyl)pyridine, 2-methyltryptamine, 5- methoxytryptamine, 6-methoxytryptamine, necrostatin-1, alosetron, sulfamethoxypyridazine, 1-(3-chloroanilino)-4-phenylphthalazine, 4-amino-5-aminomethyl-2-methylpyrimidine, 2-(aminomethyl)-5-methylpyrazine, 2-(4-piperidinyl)benzimidazole, 2-(4-aminophenyl)benzimidazole, 5-amino-2-(4-aminophenyl)benzimidazole, 6-(aminomethyl)quinoline, 2-methyl-7-[phenyl(phenylamino)methyl]-8-quinolinol, and 1-(2-amino-1-naphthyl)isoquinoline. The modification compound may be used singly or in combinations of a plurality thereof.

[0262] The modification compound is preferably ethylenediamine, N-methylethylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N, N-dibutyldipropylenetriamine, N,N-dimethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyltrimethylenediamine, N,N-dibutyltrimethylenediamine, 1-(3-aminopropyl) imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(ethylaminomethyl)pyridine, 4-(2-aminoethyl)pyridine, 4-(4-piperidyl)pyridine, 2-(4-piperidinyl)benzimidazole, 2-(4-aminophenyl)benzimidazole, or 5-amino-2-(4-aminophenyl) benzimidazole because a starting material is easily available and the production cost of the anion- exchangeable fluororesin tends to be suppressed, more preferably N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-dimethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyltrimethylenediamine, 1-(3-aminopropyl) imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(4-piperidyl)pyridine, or 2-(4-aminophenyl) benzimidazole because excellent current efficiency, voltage efficiency and power efficiency tend to be achieved in a well-balanced manner in use for the cell for a redox flow battery, and the redox flow battery, and is further preferably N,N-dimethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyldipropylenetriamine, N,N-dimethyltrimethylenediamine, 1-(3-aminopropyl)imidazole, 4-picolylamine, or 4-(2-aminoethyl)pyridine from the same viewpoint.

[0263] The anion-exchangeable resin layer is preferably a styrene resin, a vinyl chloride resin, chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a polyetheretherketone resin, a polysulfone resin, a polyether sulfone resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a polyphenylene ether resin, a polyphenylene sulfide resin, a syndiotactic polystyrene resin, polyetherimide, a siloxane-modified polyetherimide resin, a polyamide imide resin, a cycloolefin-based resin, a cycloolefin copolymer, a polyetherketoneetherketoneketone resin, a polyaryletherketone resin, or a fluororesin, and may further include a styrene resin, a vinyl chloride resin, chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a syndiotactic polystyrene resin, a cycloolefin-based resin, a cycloolefin copolymer, and a fluororesin represented by the general formula G1. The resin which may be included in the anion-exchangeable resin layer may be used singly or in combinations of a plurality thereof.

[0264] A fluororesin is preferred from the viewpoint that the cell for a redox flow battery tends to be enhanced in durability.

[0265] The content of the anion-exchangeable compound included in the anion-exchangeable resin layer is not particularly limited, and is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, from the viewpoint that there is an increased tendency of suppression of permeation of the redox active material through the separation membrane. The upper limit of the content of the anion-exchangeable compound included in the anion-exchangeable resin layer is not particularly set, and is preferably 100% by mass or less. The upper limit is more preferably 99.9% by mass or less, more preferably 99.5% by mass or less, further preferably 99% by mass or less in a case where availability is increased and the cost of formation of the anion-exchangeable resin layer is reduced.

[0266] In a case where the anion-exchangeable resin layer includes the anion-exchangeable compound and a fluororesin, the content of the anion-exchangeable compound included in the anion-exchangeable resin layer is not particularly limited, and is preferably 1% by mass or more, more preferably 5% by mass or more, further preferably 10% by mass or more, particularly preferably 15% by mass or more, from the viewpoint that there is an increased tendency of suppression of permeation of the redox active material through the separation membrane. The content is preferably 99% by mass or less, more preferably 90% by mass or less, further preferably 80% by mass or less, particularly preferably 70% by mass or less from the viewpoint that the anion-exchangeable resin layer tends to be enhanced in durability.

[0267] The thickness of the anion-exchangeable resin layer is 0.001 p.m or more and less than 5 p.m. The thickness is preferably 4 jim or less, more preferably 3 p,m or less, further particularly preferably 1.5 Jim or less because there is a tendency of a reduction in proton movement resistance and an enhancement in power efficiency. The thickness is preferably 0.01 Jim or more, more preferably 0.02 jim or more, particularly preferably 0.04 jim or more because there is a tendency of suppression of permeation of the redox active material through the separation membrane and an enhancement in power efficiency. The thickness is further preferably 0.1 Jim or more, particularly preferably 0.3 Jim or more, further particularly preferably 0.4 jim or more, because enhancement in mechanical strength against pulsation of the electrolyte solutions, contact thereof with the electrodes, and / or the like is likely to be achieved.

[0268] In the method for producing the separation membrane including at least the first cation-exchangeable resin layer and the anion-exchangeable resin layer of the present embodiment, the separation membrane can be produced by a process including a step of forming the first cation-exchangeable resin layer and a step of forming the anion-exchangeable resin layer. The method for producing the separation membrane of the present embodiment preferably includes a step of reacting a fluororesin precursor layer serving as a precursor of the first cation-exchangeable resin layer, and containing at least one selected from the group consisting of a sulfonyl halide group, an acyl halide group, and a halogenated phosphoric acid group, with a modification compound having at least two nitrogen atom-containing groups, in which the nitrogen atom-containing groups include at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, an amino salt structure as a reaction product of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group, and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, a nitrogen atom-containing heterocyclic ring structure, a salt structure of a nitrogen-containing heterocyclic ring as a reaction product of a nitrogencontaining heterocyclic ring structure and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, and a quaternary ammonium group, and a step of converting at least one selected from the group consisting of the sulfonyl halide group, the acyl halide group, and the halogenated phosphoric acid group contained in the fluororesin precursor layer, into at least one selected from the group consisting of a sulfo group, a carboxyl group, and a phosphoric acid group, after the above step. Herein, the quaternary ammonium group is a quaternary ammonium group different from the amino salt structure and the salt structure. The fluororesin precursor layer is a layer serving as a precursor of the first cation-exchangeable resin layer, and is a layer containing at least one selected from the group consisting of a sulfonyl halide group, an acyl halide group, and a halogenated phosphoric acid group .

[0269] The method for producing the anion-exchangeable resin layer is not particularly limited, and examples include a method in which the anion-exchangeable compound or a mixture containing the anion-exchangeable compound is formed into a molten state, and extruded by a nozzle, a die, or the like with an extruder and thus processed into a film, and a method in which the anion-exchangeable compound or a mixture containing the anion-exchangeable compound is formed into a solution state, applied to a substrate by a die, a gravure roll, a knife or spraying and dried, and thus processed into a film.

[0270] The separation membrane can be produced by forming the anion-exchangeable resin layer and then stacking the anion-exchangeable resin layer and the first cation exchangeable resin layer. The stacking method is not particularly limited, and examples include a stacking method with heat press and / or heat roll press.

[0271] The separation membrane can also be produced by melt-kneading the fluororesin precursor and extruding it with an extruder by a nozzle, a die, or the like, to process the resultant into a film, then contacting the film with a mixture containing the modification compound, to form a layer including the anion-exchangeable fluororesin, and thereafter performing hydrolysis to provide a fluororesin, thereby forming a layer including a fluororesin, serving as the first cation-exchangeable resin layer, and a layer including the anion-exchangeable fluororesin, serving as the anion-exchangeable resin layer .

[0272] When the separation membrane is produced, a substrate can also be used. The substrate can be used to sometimes more stably produce the first cationexchangeable resin layer and / or the anion-exchangeable resin layer.

[0273] The material used in the substrate is not particularly limited, and examples include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, a cycloolefin polymer, polycarbonate, polyamide, polyimide, polyamide imide, polyvinyl chloride, polystyrene, polyphenylene ether, polyetheretherketone, polysulfone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, a polyimide resin, polyetherketoneetherketoneketone, and polyaryletherketone . The material may be, if necessary, modified, and may be used singly or in combinations of a plurality thereof.

[0274] The solvent used in formation of the mixture containing the anion-exchangeable compound into a solution is not particularly limited, and examples include saturated hydrocarbon compounds such as n-pentane, n-hexane, n-octane, n-decane, cyclopentane, cyclohexane and cyclooctane; aromatic hydrocarbon compounds such as benzene, toluene, xylene and ethylbenzene; halogenated hydrocarbon compounds such as methylene chloride, chloroform, carbon tetrachloride, chlorobenzene and dichlorobenzene; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol and benzyl alcohol; ketones such as acetone, ethyl methyl ketone, methyl butyl ketone, methyl isobutyl ketone and cyclohexanone; as well as esters such as ethyl acetate, butyl acetate and methyl benzoate; ethers such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and dioxane; polyols such as ethylene glycol, propylene glycol and glycerin, and multimers and polyols of compounds each having two hydroxyl groups, among these polyols; and esterified compounds of these multimers, and nitriles such as acrylonitrile and benzonitrile; nitromethane; N,N-dimethylformamide; dimethylsulfoxide; hexamethylphosphoric triamide; carbon disulfide; and fluorine-based compounds (for example, Novec (trademark) manufactured by 3M, and Asahiklin manufactured by AGC Inc .) . Such a solvent may be adopted singly or in combinations of a plurality thereof.

[0275] <Second cation-exchangeable resin layer> The separation membrane of the present embodiment may further include a second cation-exchangeable resin layer. The separation membrane may include the first cation-exchangeable resin layer, the anion-exchangeable resin layer, and the second cation-exchangeable resin layer in the listed order.

[0276] In the separation membrane with the second cationexchangeable resin layer, the thickness of the first cation-exchangeable resin layer is larger than the thickness of the second cation-exchangeable resin layer. The thickness of the second cation-exchangeable resin layer is not particularly limited as long as it is a value smaller than the thickness of the first cationexchange layer, and is preferably 0.01 jim or more and less than 150 jim. The thickness is more preferably 100 p,m or less, further preferably 50 Jim or less, particularly preferably 20 jim or less, because there is a tendency of a reduction in proton movement resistance and an enhancement in power efficiency. The thickness is more preferably 0.1 Jim or more, further preferably 0.5 Jim or more, particularly preferably 1 Jim or more, because the enhancement in mechanical strength against pulsation of the electrolyte solutions, contact thereof with the electrodes, and / or the like is likely to be achieved.

[0277] The value obtained by dividing the thickness of the second ion-exchangeable resin layer by the thickness of the first cation-exchangeable resin layer is not particularly limited, and is preferably less than 0.7. The value is more preferably 0.6 or less, further preferably 0.5 or less because the anion-exchangeable resin layer can be located closer to the electrode acting as the negative electrode and there is a tendency of suppression of permeation of the redox active material through the separation membrane and an enhancement in power efficiency. The value obtained by dividing the thickness of the second ion-exchangeable resin layer by the thickness of the first cation-exchangeable resin layer is needed to be more than 0, and is preferably 0.0001 or more from the viewpoint of more simplification of production of the second ion-exchangeable resin layer. The value is more preferably 0.001 or more, particularly preferably 0.01 or more, because enhancement in mechanical strength against pulsation of the electrolyte solutions, contact thereof with the electrodes, and / or the like is likely to be achieved.

[0278] The second cation-exchangeable resin layer is a layer formed with a substance containing a cationexchangeable resin, as in the first cation-exchangeable resin layer. The cation-exchangeable resin used in the second cation-exchangeable resin layer is not particularly limited, and a cation-exchangeable resin preferably used is the same as in the first cationexchangeable resin layer. The second cation-exchangeable resin layer more preferably includes a fluorine-based cation-exchangeable resin from the viewpoint that the cell for a redox flow battery tends to be enhanced in durability. The cation-exchangeable resin included in the first cation-exchangeable resin layer and the cationexchangeable resin included in the second cationexchangeable resin layer may be the same as or different from each other.

[0279] The method for producing the separation membrane including the first cation-exchangeable resin layer, the anion-exchangeable resin layer, and the second cationexchangeable resin layer is not particularly limited, and examples include a production method in which a cationexchangeable resin to be formed into the second cationexchangeable resin layer is melt-kneaded, then extruded onto a two-layered membrane including the first cationexchangeable resin layer and the anion-exchangeable resin layer with an extruder by a nozzle, a die, or the like, and thus processed into a film, a production method in which a cation-exchangeable resin precursor to be formed into the second cation-exchangeable resin layer is melt-kneaded, then extruded with an extruder by a nozzle, a die, or the like, and thus processed into a film, and thereafter subjected to the above hydrolysis treatment and acid treatment, to form an ion-exchange group, and a production method in which a cation-exchangeable resin to be formed into the second cation-exchangeable resin layer is dispersed in a solvent and then cast, and thus processed into a film. The separation membrane can also be produced by overlapping the anion-exchangeable resin layers of two kinds of two-layered membranes each including the cation-exchangeable resin layer and the anion-exchangeable resin layer. When the overlapping is made, heat press and / or heat roll press can also be used because peeling of the anion-exchangeable resin layers tends to be able to be reduced.

[0280] A support can also be used in the separation membrane of the present embodiment. The support is not particularly limited, and examples thereof include a support made of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, a cycloolefin polymer, polyamide, polyimide, polyamide imide, polyvinyl chloride, polystyrene, polyphenylene ether, polyetheretherketone, polysulfone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, a polyimide resin, polyetherketoneetherketoneketone, polyaryletherketone, a fluororesin, or the like. No support is preferably used because any gap generated between the cation-exchangeable resin layer and / or the anion-exchangeable resin layer, and the support may cause reductions in characteristics of the cell for a redox flow battery.

[0281] <Separation membrane electrode assembly> The separation membrane electrode assembly of the present embodiment has a structure in which at least one of the first electrode and the second electrode, and the separation membrane are bonded. The bonding means that at least one of the first electrode and the second electrode, and the separation membrane are joined, and the bonding can allow at least one of the first electrode and the second electrode, and the separation membrane to be integrated. For example, the bonding may be preferably used in a separation membrane electrode assembly including the first electrode, the second electrode and the separation membrane because assembling of the cell for a redox flow battery does not require a step of sequentially applying the first electrode, the separation membrane and the second electrode and can be made as one step and the production cost tends to be able to be suppressed.

[0282] The method for bonding at least one of the first electrode and the second electrode, and the separation membrane is not particularly limited, and examples thereof include a method with heat press and / or heat roll press .

[0283] The temperature in the bonding is not particularly limited, and is preferably equal to or more than room temperature in a case in which the bonding between the separation membrane and the electrode is insufficient because the separation membrane tends to be reduced in elastic modulus to enhance the bonding between the separation membrane and the electrode. The temperature in the bonding is preferably 250°C or less, more preferably 200°C or less, further preferably 170°C or less, particularly preferably 150°C or less, because the change in quality of the separation membrane tends to be able to be suppressed.

[0284] The pressure in the bonding is not particularly limited, and is a pressure of more than 0 MPa. The pressure is preferably 0.01 MPa or more, more preferably 0.05 MPa or more, further preferably 0.08 MPa or more, particularly preferably 0.1 MPa or more, because the bonding between the separation membrane and the electrode tends to be enhanced. The pressure is preferably 100 MPa or less, more preferably 50 MPa or less, further preferably 20 MPa or less, particularly preferably 10 MPa or less, because the change in quality of the electrode tends to be able to be suppressed.

[0285] The time in the bonding is not particularly limited, and is a time of more than 0 seconds. The time in the bonding is preferably 0.01 seconds or more, more preferably 0.1 seconds or more, further preferably 0.5 seconds or more, particularly preferably 1 second or more, because the bonding between the separation membrane and the electrode tends to be enhanced. The time is preferably 10 hours or less, more preferably 5 hours or less, further preferably 2 hours or less, particularly preferably 1 hour or less, because the cost in production of the separation membrane electrode assembly tends to be able to be reduced.

[0286] The atmosphere in the bonding is not particularly limited, and examples include air, nitrogen, and argon. Air or nitrogen is preferred and air is more preferred because the cost in production of the separation membrane electrode assembly tends to be able to be reduced.

[0287] <Redox flow battery> The cell for a redox flow battery of the present embodiment can be stacked to provide a redox flow battery. When stacked, such cells for redox flow batteries can be electrically conducted through a bipolar plate .

[0288] The material of the bipolar plate is not particularly limited, and examples include carbon, graphite, and a metal. A carbon particle, a carbon fiber, a metal particle, a metal fiber, graphene, and a carbon nanotube may be dispersed in the material. The material may be used singly or in combinations of a plurality thereof.

[0289] The bipolar plate can sometimes enhance the contact between an electrode and an electrolyte solution, and thus may have various flow channels. Such a flow channel is not particularly limited, and examples can include Serpentine, Interdigitated, Pararell, Multiparallel, Discontinuous, and any combination of such flow channels .

[0290] The cell for a redox flow battery, and the redox flow battery of the present embodiment can be used to provide a mechanism which smooths the amount of supply and demand of power and stabilizes the varying power obtained from a renewable energy source such as solar energy or wind energy. More specifically, it is possible to provide, for example, integration of the power obtained from a renewable energy source, power peak load shifting, stabilization of a transmission and distribution grid, base load power, energy arbitrage, supporting of a weak transmission and distribution grid, frequency adjustment, and any combination thereof. The cell for a redox flow battery, and the redox flow battery can also be used as a power supply of a remote camping, a forward operating base, transmission and distribution communication, a remote sensor, or the like utilizing no transmission and distribution grid.

[0291] The cell for a redox flow battery, and the redox flow battery of the present embodiment can include a control system and a power regulation unit.

[0292] The control system can be used to control operating of various valves, pumps, circulation circuits, sensors, relaxation equipment, other electronic / hardware controllers, safeguard apparatuses, and the like.

[0293] The power adjustment unit can be used to convert the voltage of the input power, and the current into optimal modes for the cell for a redox flow battery, and / or the redox flow battery, and convert the voltage of the output power, and the current into optimal modes for any application. For example, in a case where the cell for a redox flow battery, and / or the redox flow battery are / is connected to a transmission and distribution grid, the power regulation unit can convert the input AC power into the DC power of suited voltage and current in a charge cycle. The cell for a redox flow battery, and / or the redox flow battery can generate the DC power and the power regulation unit can convert the DC power to the AC power of suitable voltage and frequency for sending to the transmission and distribution grid in a discharge cycle .

[0294] [Fourth embodiment] Subsequently, a fourth embodiment is described.

[0295] In Patent Literature 5, a solvent (having a content of ethanol of 50% by mass in Examples in Patent Literature 1) containing a large amount of ethanol being a protonic solvent is used, there is a tendency of an increase in viscosity of a solution in the case of an increased content of a fluororesin in the solution, and a problem is that the solution is difficult to store in an optimal viscosity range in a membrane formation step with applying and drying. There is also a tendency of an increase in rate of change over time in solution viscosity of the solution, and a problem is that the solution is difficult to store in an optimal viscosity range in a membrane formation step with applying and drying.

[0296] In Patent Literature 6, N,N-dimethylformamide is used as a solvent having affinity and also having a high boiling point, and a problem is that, in the case of production of an ion-exchange membrane by applying and drying, and heat-treating a polyelectrolyte solution, N,N-dimethylformamide remaining in the ion-exchange membrane is decomposed to generate dimethylamine serving as an impurity, in the ion-exchange membrane, and thus the impurity causes deteriorated characteristics depending on the application.

[0297] In Patent Literature 7 and Non Patent Literature 1, a perfluorosulfonic acid polymer having a large ratio of a sulfonic acid group has a difficulty in having a sufficiently increased molecular weight, and in a case where an ion-exchange membrane is tried to be obtained by applying and drying with a solution of a perfluorosulfonic acid polymer having no sufficiently large molecular weight and having a large ratio of a sulfonic acid group, no membrane having sufficient mechanical strength can be obtained by a solvent composition according to a conventionally known technique. Therefore, there is a demand for a perfluorosulfonic acid polymer membrane having sufficient mechanical strength and having a large ratio of a sulfonic acid group.

[0298] In Patent Literature 8, an ion-exchange membrane having a membrane thickness of 25 p.m or less, which is difficult to produce by extrusion according to a conventionally known technique, is obtained by coextrusion of a perfluorosulfonic acid polymer precursor with an immiscible polymer. However, the ion-exchange membrane produced by this invention, although is reduced in anisotropy as compared with a conventionally known ion-exchange membrane of a perfluorosulfonic acid polymer extruded, causes swelling of a polyelectrolyte membrane by an electrolyte solution due to in-plane anisotropy derived from a molding method, for example, in an application in which the ion-exchange membrane is used in the state of being immersed in the electrolyte solution or a solvent, such as a redox flow battery or water electrolysis, and thus the ion-exchange membrane can be changed in dimension anisotropically to a membrane surface, to have an adverse effect on characteristics. In other words, there is a demand for an ion-exchange membrane which is more reduced in anisotropy and which includes a perfluorosulfonic acid polymer.

[0299] As described above, a conventionally known technique has a difficulty in providing a polyelectrolyte solution in which the solution viscosity of a solution containing a fluororesin having a large ratio of sulfonic acid is less changed over time and the solution viscosity of the solution can be in an optimal viscosity range in a membrane formation step with applying and drying, and an ion-exchange membrane obtained by applying and drying the solution, in which the ion-exchange membrane not only has sufficient mechanical strength, but also is small in number of crack defects per unit area and has an appropriate membrane thickness capable of achieving low electrical resistance, and exhibits decreased in-plane anisotropy in an electrolyte membrane.

[0300] An object of the present embodiment is to provide a novel polyelectrolyte solution or the like which forms a polymer membrane.

[0301] The polyelectrolyte solution according to the present embodiment is a polyelectrolyte solution including a fluororesin having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and having a structural unit represented by the following general formula Gl, and a solvent containing water, an aliphatic alcohol, and an aliphatic carboxylic acid, wherein the ratio of the total mass of the aliphatic carboxylic acid and a reaction product thereof to the total mass of the solvent is 100:1 to 100:50: wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

[0302] According to the present embodiment, it is possible to provide a novel polyelectrolyte solution or the like which forms a polymer membrane.

[0303] According to the foregoing embodiment, it is possible to provide a polyelectrolyte solution in which the solution viscosity is less changed over time, the solution viscosity of the solution can be in an optimal viscosity range in a membrane formation step with applying and drying, and a fluororesin having a large ratio of sulfonic acid is contained. It is also possible to provide an ion-exchange membrane which not only has sufficient mechanical strength, but also is small in number of crack defects per unit area and has an appropriate membrane thickness capable of achieving low electrical resistance, exhibits decreased in-plane anisotropy in an electrolyte membrane, has excellent membrane thickness uniformity, has a sufficiently large area, and includes a fluororesin having a large ratio of sulfonic acid. Furthermore, it is possible to provide a cell for a redox flow battery, and a redox flow battery, in which the ion-exchange membrane is used.

[0304] (Fluororesin Gl) The fluororesin (hereinafter, also referred to as "fluororesin Gl") in the present embodiment has an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and has a structural unit represented by the following general formula Gl: wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

[0305] In the fourth embodiment, the fluororesin G1 preferably has a structural unit represented by the following general formula C3: - [CF2CX1X2]a- [CF2-CF( (-O-CF2-CF (CF2X3) )b-Oc- (CFRi)d- (CFR2)e-(CF2) f-X4) ]g- [C3] wherein X1, X2, and X3 are each independently a halogen atom, or a perfluoroalkyl group having 1 to 3 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; R1 and R2 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X4 is a monovalent group represented by formula -COOZ, -SO3Z, -PO3Z2 or -PO3HZ, or a divalent group represented by formula -COOMOOC-, -SO3MO3S-, -PO3M2O3P- or -PO3HMHO3P-; when X4 is a divalent group, such fluororesins G1 are optionally crosslinked each other via X4; Z is a hydrogen atom, an alkali metal atom, or an amine; M is an alkaline earth metal atom; and when X4 is -PO3Z2, two Zs are optionally the same or different.

[0306] X1, X2, and X3 are each independently a halogen atom, or a perfluoroalkyl group having 1 to 3 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. X1, X2, and X3 are each preferably a fluorine atom, a chlorine atom, or a perfluoroalkyl group having 1 to 3 carbon atoms, more preferably a fluorine atom, a chlorine atom, or a perfluoroalkyl group having 1 carbon atom, further preferably a fluorine atom or a chlorine atom, particularly preferably a fluorine atom, because a starting material is easily available and the production cost of the fluororesin G1 tends to be reduced. R1 and R2 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. R1 and R2 are each preferably a fluorine atom, or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms from the viewpoint that a starting material is easily available and the production cost of the fluororesin G1 tends to be able to be suppressed. Furthermore, a fluorine atom and a trifluoromethyl group are more preferred and a fluorine atom is particularly preferred from the viewpoint that the fluororesin G1 tends to be enhanced in chemical stability such as oxidation degradation resistance. X4 is a monovalent group represented by formula -COOZ, -SO3Z, -PO3Z2 or -PO3HZ, or a divalent group represented by formula -COOMOOC-, -SO3MO3S-, -PO3M2O3P- or -PO3HMHO3P-. When X4 is a divalent group, such fluororesins G1 are optionally crosslinked each other via X4. Z is a hydrogen atom, an alkali metal atom, or an amine. M is an alkaline earth metal atom. When X4 is -PO3Z2, two Zs are optionally the same or different. The alkali metal is not particularly limited, and is preferably a lithium atom, a sodium atom, or a potassium atom, more preferably a sodium atom or a potassium atom. The amine is not particularly limited, and examples include structures of NH4, NH3R10, NH2R10Rn, NHR10R1:LR12, and NR10R1:l-R12R13 .  R10, R11, R12, and R13 are each optionally the same or different, and are each not particularly limited as long as each thereof is a structure commonly used, and examples include an aliphatic hydrocarbon group and an aromatic hydrocarbon group. The aliphatic hydrocarbon group is preferably a monovalent group represented by CnH2n+i (n represents an integer of 1 or more, preferably an integer of 1 to 20, more preferably an integer of 1 to 10.) . The aromatic hydrocarbon group is preferably a phenyl group or a naphthyl group. M is an alkaline earth metal atom, is not particularly limited, and is preferably a magnesium atom or a calcium atom. a and g are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1. b is an integer of 0 to 8. c is 0 or 1. d, e, and f are each independently an integer of 0 to 6 (provided that d, e and f are not 0 at the same time.).

[0307] The fluororesin G1 having the structural unit represented by the general formula C3 is preferably represented by the following general formula Cl or the following general formula C4, more preferably represented by the following general formula C4, from the viewpoint that both dispersibility and membrane strength are satisfied in a further well-balanced manner: - [CF2CF2]a- [CF2-CF( (-O-CF2-CF (CF3) ) b-0- (CF2)c-SO3X) ] d- [Cl] wherein a and d satisfy 0 < a < 1, 0 < d < 1, and a + d = 1, b is an integer of 1 to 8, c is an integer of 0 to 10, and X is a hydrogen atom or an alkali metal atom; - [CF2CF2]e-[CF2-CF( (-0-(CF2) f-SO3X) ] g- [C4] wherein e and g satisfy 0 < e < 1, 0 < g < 1, and e + g = 1, f is an integer of 0 to 10, and Y is a hydrogen atom or an alkali metal atom. The fluororesin G1 here used can be a prepared product prepared by a known method, or a commercially available product.

[0308] (Polyelectrolyte) The polyelectrolyte in the present embodiment includes the fluororesin G1 as one polyelectrolyte. The ratio of the fluororesin G1 to the polyelectrolyte is preferably 70% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, particularly preferably 98% by mass or more. When the ratio of the fluororesin G1 to the polyelectrolyte is 70% by mass or more, a fuel cell formed tends to be excellent in current efficiency. The fluororesin G1 used in the polyelectrolyte may be used singly or in combinations of a plurality thereof.

[0309] The polyelectrolyte in the present embodiment may contain, as a different polyelectrolyte from the fluororesin Gl, a perfluorocarboxylic acid polymer, a partially fluorinated sulfonic acid polymer or a partially fluorinated carboxylic acid polymer as an acidic polymer, an azole polymer (also including an imidazole polymer) or an amine polymer as a basic polymer, and the like. The acidic polymer and the basic polymer may be each used singly or in combinations of a plurality thereof. In a case where the polyelectrolyte is an electrolyte including the fluororesin Gl and the basic polymer, a fuel cell with the resulting ion-exchange membrane tends to be enhanced in chemical durability during running of the fuel cell. The polyelectrolyte in the present embodiment may contain a polymer such as polyethylene glycol, polyphenylene ether, polyphenylene sulfide, polyetherimide, polysulfone, polyether ketone, polyetheretherketone, polyetheretherimide, polyamide, polyimide, or polyamide imide. The polymer may be used singly or in combinations of a plurality thereof. The polyelectrolyte preferably includes 5% by mass or less, more preferably 3% by mass or less, further preferably 1% by mass or less of the polymer optionally contained, because not only characteristics of the polymer optionally contained are imparted to the ionexchange membrane, but also the ion-exchange membrane tends to be suppressed in deterioration in mechanical strength.

[0310] The equivalent weight (hereinafter, also referred to as "EW") of the fluororesin G1 having the structural unit represented by the general formula Cl is preferably 600 g / eq or more and less than 1,000 g / eq, more preferably 650 g / eq or more and 980 g / eq or less, further preferably 700 g / eq or more and 950 g / eq or less, from the view point that, when an ion-exchange membrane including the fluororesin G1 is used as a separation membrane for a redox flow battery, the separation membrane is reduced in electrical resistance and the separation membrane is enhanced in mechanical strength. The "equivalent weight (EW) of the fluororesin Gl" refers to a dry weight per equivalent of a sulfonic acid group .

[0311] The equivalent weight (EW) of the fluororesin Gl having the structural unit represented by the general formula C4 is preferably 400 g / eq or more and less than 1,000 g / eq, more preferably 450 g / eq or more and 980 g / eq or less, further preferably 500 g / eq or more and 950 g / eq or less, further preferably 600 g / eq or more and 950 g / eq or less, further preferably 700 g / eq or more and 950 g / eq or less, from the view point that, when an ion-exchange membrane including the fluororesin Gl is used as a separation membrane for a redox flow battery, the separation membrane is reduced in electrical resistance and the separation membrane is enhanced in mechanical strength.

[0312] The melt flow rate (hereinafter, also referred to as "MFR".) can be used as an indicator of the degree of polymerization of the fluororesin G1 precursor. The MFR of the fluororesin G1 precursor is not particularly limited, and is preferably 100 g / 10 min or less, more preferably 50 g / 10 min or less, further preferably 30 g / 10 min or less. The MFR is 100 g / 10 min or less, resulting in a tendency to enable an ion-exchange membrane excellent in mechanical strength to be obtained. The MFR is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, further preferably 0.3 g / 10 min or more. The MFR is 0.01 g / 10 min or more, resulting in a tendency to enable the fluororesin G1 in the form of a solution to be more efficiently finely dispersed and dissolved. The MFR can be measured by a method described in Examples.

[0313] (Polyelectrolyte solution) The polyelectrolyte solution in the present embodiment includes a fluororesin G1 having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq, and a solvent containing water, an aliphatic alcohol, an aliphatic carboxylic acid, and an aliphatic ester. A dissolution facility for providing a homogeneous, and clear and transparent polyelectrolyte solution from an emulsion containing the fluororesin G1 and the solvent is not particularly limited, and is preferably a facility which continuously dissolves the fluororesin G1 and the solvent. The facility for continuous dissolution is heated by a heating tool described below, and a perfluorosulfonic acid polymer in the emulsion passing through the dissolution facility can be dissolved in the solvent by conditions in the dissolution facility, to discharge a homogeneous polyelectrolyte solution from the dissolution facility.

[0314] The facility for continuous dissolution preferably has a pump for continuously supplying the emulsion including the fluororesin G1 and the solvent into the dissolution facility, the dissolution facility for continuously dissolving the fluororesin G1 in the solvent, a heating tool heating the dissolution facility, and a cooling tool.

[0315] The pump is used for continuously supplying the emulsion including the fluororesin G1 and the solvent to the dissolution facility. The type of the pump is not particularly limited, and examples include a turbo-type pump, a piston pump, a plunger pump, a diaphragm pump, a gear pump, a vane pump, and a screw pump. In particular, preferred are a plunger pump, a diaphragm pump, a multiple pump, and an accumulator with excellent pressure resistance in consideration of safety and with high quantitative performance and high ejection pressure in consideration of producibility. A multiple pump and an accumulator are more preferred from the viewpoint that pulsation can be suppressed. The pump may be used singly or in combinations of a plurality thereof.

[0316] The dissolution facility is not particularly limited, and examples include an apparatus in which the flow of a fluid in the dissolution facility is of plug flow type.

[0317] The shape of the dissolution facility is not particularly limited, and is preferably, for example, a tube shape. The tube shape tends to more enhance producibility and dissolution efficiency. The tube shape is not particularly restricted, and examples include linear, coil, and rectangular shapes. In particular, a coil shape is preferred from the viewpoint of the installation area and stable running. The outer diameter of the tube is preferably 1 / 16 to 2 inches, more preferably 1 / 4 to 1 / 2 inches from the viewpoint of producibility and dissolution efficiency. A commonly commercially available pipe of 6 A to 500 A may be used. An in-line mixer, a wire mesh, a metal filling, and / or the like may be disposed in the tube from the viewpoint of producibility and dissolution efficiency.

[0318] The dissolution facility is not particularly restricted, and is preferably a metallic tubular dissolution facility. The material of the dissolution facility is not particularly limited, an optimal material may be selected from the viewpoint of corrosion resistance, and examples include a SUS-based material, a Hastelloy-based material, a titanium-based material, a zirconia-based material, and a tantalum-based material. In particular, a material having the same compositional ratio as in a SUS-based material and Hastelloy (registered trademark of Haynes International Inc., USA) is preferred, a material having the same compositional ratio as in SUS316 and Hastelloy C is more preferred, and a material having the same compositional ratio as in Hastelloy C276 is particularly preferred, because of being excellent in balance between corrosion resistance and cost. The same compositional ratio as in Hastelloy, Hastelloy C, and Hastelloy C276 means that the material has a compositional ratio of 56 to 60% by mass of Ni, 16 to 22% by mass of Cr, 13 to 16% by mass of Mo, 2 to 6% by mass of W, 3 to 8% by mass of Fe, and 2.5% by mass or less of Co. Such a metallic dissolution facility is used, and thus a dissolution step can be performed at a high temperature and a high pressure and a perfluorosulfonic acid polymer included in the resulting polyelectrolyte solution tends to be enhanced in stability of a main chain end of the perfluorosulfonic acid polymer. The inner wall of the tube may be lined. Such lining is not particularly limited, and examples thereof include fluorine lining and glass lining. Such a dissolution facility thus lined is used, and thus a dissolution step can be performed at a relatively low temperature and a low pressure and the concentrations of F and Fe ions in the resulting polyelectrolyte solution tend to be kept low.

[0319] The thickness of the tube is not particularly limited, and an optimal thickness may be selected from the viewpoint of pressure resistance. The inner diameter of the tube is not particularly limited, and is preferably 1 to 50 mm, more preferably 4 to 50 mm from the viewpoint of producibility and dissolution efficiency.

[0320] The inner wall of the tube is not particularly limited in terms of the surface roughness thereof, and may have irregularities or may be a mirror surface. The maximum height of the surface roughness of the inner wall of the tube is preferably 50 jim or less, more preferably 25 p.m or less, further preferably 10 Jim or less from the viewpoint of dissolution efficiency. The maximum height of the surface roughness of the inner wall of the tube is, for example, a value determined by using a laser microscope to sample only a reference length in a parallel line direction from a roughness curve and measure the interval between the peak line and the valley line of this portion sampled, in the longitudinal magnification direction of the roughness curve.

[0321] The length of the tube depends on the dissolution time (= retention time) determined. Specifically, the length of the tube can be calculated by a relationship with the inner diameter of the tube so that the product of the dissolution time (min) and the speed of supply (L / min) is equal to or less than the inner volume of the tube heated. Dissolution time (min) x Speed of supply (L / min) < Inner volume of tube Inner volume of tube = (Inner diameter of tube / 2)2 x k x tube length

[0322] In a case where a plurality of tube-shaped such dissolution facilities is used in series, an equiform union, a deformed union, a T-type union, a check valve, a safety valve, a back pressure valve, a pressure gauge, a thermometer, or the like for connection of one dissolution facility and another dissolution facility may be provided between such dissolution facilities. A plurality of such dissolution facilities can also be used in parallel to increase the inner volume, thereby allowing for an increase in producibility.

[0323] The heating tool of the dissolution facility is used for heating the dissolution facility. The heating method is not particularly limited, and examples thereof include a method for heating the dissolution facility with a heat medium such as hot air, hot water, steam, or silicon oil. The heat medium may be used singly or in combinations of a plurality thereof. Among such heat mediums, hot air is preferred because of being simply usable, and the dissolution facility can be placed in a constant-temperature bath in an atmosphere set to a specified temperature by hot air.

[0324] The pressure in the dissolution facility in the facility for continuous dissolution is not particularly restricted, and a pressure adjustment tool which adjusts the pressure so as to exceed the vapor pressure of the solvent at the heating temperature of the dissolution facility is preferably further provided. Such a unit for adjusting the pressure may be installed downstream, upstream, or downstream and upstream in the supply direction in the dissolution facility, or may be provided inside the dissolution facility. The pressure adjustment tool is not particularly limited, and examples thereof include a back pressure valve, an automatic pressure regulation valve (PIC), and the pump. A back pressure valve or an automatic pressure regulation valve (PIC) is used to result in a tendency to keep the pressure in the dissolution facility constant, namely, suppress the variation in pressure as much as possible and thus enhance the dispersibility of the polyelectrolyte solution and prevent clogging in the dissolution facility. The pump is used to enable the interior of the dissolution facility to be pressurized. The zone from the pump to the pressure adjustment tool (back pressure valve) can be regarded as a closed container under a constant pressure. The facility for continuous dissolution tends to impart more enhanced dispersibility of polyelectrolyte in the polyelectrolyte solution and provide such an electrolyte solution enhanced in dispersibility, at a higher concentration in a shorter time.

[0325] The facility for continuous dissolution preferably includes a cooling tool located downstream of the dissolution facility, in which the cooling tool cools the polyelectrolyte solution in a state where a pressure exceeding the vapor pressure of the solvent at a heating temperature in the dissolution facility is kept. This cooling tool can be included to result in a tendency to more suppress clogging in the dissolution facility during discharge of the polyelectrolyte solution. The cooling method is not particularly limited, and examples include a cooling method involving allowing the polyelectrolyte solution to pass through a cooling tube, and an air cooling method involving allowing the polyelectrolyte solution to pass not through a cooling tube, but in a tube at room temperature.

[0326] <Solvent> The polyelectrolyte solution according to the present embodiment includes water, an aliphatic alcohol, and an aliphatic carboxylic acid. The polyelectrolyte solution according to the present embodiment may contain a reaction product of the aliphatic carboxylic acid. Examples of the reaction product of the aliphatic carboxylic acid include an aliphatic carboxylic acid ester obtained by condensation of the aliphatic carboxylic acid and the aliphatic alcohol.

[0327] The ratio of the total mass of the aliphatic carboxylic acid and the reaction product thereof to the total mass of the solvent is 100:1 to 100:50. The range enables crack defect generation in the resulting ionexchange membrane to be suppressed. The mass ratio is preferably 100:3 to 100:40, more preferably 100:4 to 100:35, further preferably 100:5 to 100:30.

[0328] (Aliphatic carboxylic acid) In the present embodiment, the aliphatic carboxylic acid is a compound having a carboxyl group (-COOH group), the number of carbon atoms in the aliphatic carboxylic acid is preferably 1 to 5, and example include formic acid, acetic acid, propionic acid, butyric acid, and isobutyric acid. The number of carbon atoms in the aliphatic carboxylic acid is more preferably 1 to 4, further preferably 1 to 3, and acetic acid is particularly preferred, because, when water co-exists in film formation with the polyelectrolyte solution, the balance between miscibility with water and solvation of a hydrophobic site of the polyelectrolyte tends to be excellent. The boiling point of the carboxylic acid is preferably 165°C or less, more preferably 150°C or less because drying ability during film formation tends to be enhanced. The ratio of the aliphatic carboxylic acid relative to the amount of the solvent in the polyelectrolyte solution is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, further preferably 3% by mass or more and 30% by mass or less, because, when water co-exists in film formation with the polyelectrolyte solution, the balance between miscibility with water and solvation of a hydrophobic site of the polyelectrolyte tends to be excellent. The ratio of the aliphatic carboxylic acid is 1% by mass or more, resulting in a tendency to decrease the rate of change over time in solution viscosity of the polyelectrolyte solution. The ratio of the aliphatic carboxylic acid is 30% by mass or less, resulting in a tendency to enhance drying ability during cast film formation of the polyelectrolyte solution.

[0329] (Aliphatic alcohol) In the present embodiment, the aliphatic alcohol is a compound having a hydroxyl group (-OH group), and the number of carbon atoms is preferably 1 to 10, more preferably 1 to 7, further preferably 1 to 4, from the viewpoint that, when water co-exists in film formation with the polyelectrolyte solution, the balance between miscibility with water and solvation of a hydrophobic site of the polyelectrolyte tends to be excellent. Specific examples of the aliphatic alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and isobutanol, and, in particular, methanol, ethanol, 1-propanol, and 1-butanol are preferred. The boiling point of the alcohol is preferably 165°C or less, more preferably 150°C or less because drying ability during film formation is enhanced. The ratio of the aliphatic alcohol relative to the amount of the solvent in the polyelectrolyte solution is preferably 5% by mass or more and 70% by mass or less, more preferably 5% by mass or more and 60% by mass or less, further preferably 5% by mass or more and 50% by mass...

Claims

1. An ion-exchange membrane comprisinga resin composition comprisinga side-chain heteroaromatic resin having a structural unit represented by the following general formula 1:wherein,R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms,R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, andHe is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having atleast one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure, anda cation-exchangeable resin.

2. The ion-exchange membrane according to claim 1, wherein a weight ratio between the side-chain heteroaromatic resin and the cation-exchangeable resin is 1:100 to 100:1.

3. The ion-exchange membrane according to claim 1, wherein the cation-exchangeable resin is a fluororesin.

4. The ion-exchange membrane according to claim 3, wherein the fluororesin has a structural unit represented by the following general formula G1:F X® F FCF2X8wherein,X5, X6, X7, and X8 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclicperfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X5 and X6 or X5 and X7 are optionally bound to each other to form a cyclic structure,R5 and R6 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom,X9 is a group represented by -COOZ, -SO3Z, -PO3Z2, or -PO3HZ, Z is at least one selected from the group consisting of a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, and an amine, and the fluororesin is optionally crosslinked to each other by ion crosslinking via X9, h and p each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < h < 1, 0 < p < 1, and h + p = 1, i is an integer of 0 to 8, j is 0 or 1, and k, 1, and m are each optionally the same or different, and are each an integer of 0 to 6, provided that, when k, 1, and m are 0 at the same time, X9 isCF(CF2X10)2, X10 is a group represented by -COOZ, -SO3Z, -PO3Z2, or -PO3HZ, and Z is the same as described above.

5. The ion-exchange membrane according to claim 1, alternately comprisingat least one layer (L) comprising the resin composition, andat least one layer (M) comprising a fluororesin having a structural unit represented by the following general formula G1:F Fk I I o-c—C--Oicf2x8c—X9[Gl]wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

6. The ion-exchange membrane according to claim 5, comprising one layer (L) and one layer (M).

7. The ion-exchange membrane according to claim 5, comprising the layer (L), the layer (M), and the layer (L) in the listed order.

8. An ion-exchange membrane comprising a side-chain heteroaromatic resin having a structural unit represented by the following general formula 2:wherein,R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms,R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure,Rf is an aliphatic hydrocarbon group substituted with at least one fluorine atom, andX" is a counter anion.

9. The ion-exchange membrane according to claim 8, alternately comprisingat least one layer (L) comprising the side-chain heteroaromatic resin, andat least one layer (M) comprising a fluororesin having a structural unit represented by the following general formula G1:wherein the definition of each substituent has the same meaning as in the general formula G1 described above.

10. The ion-exchange membrane according to claim 9, comprising one layer (L) and one layer (M).

11. The ion-exchange membrane according to claim 9, comprising the layer (L), the layer (M), and the layer (L) in the listed order.

12. The ion-exchange membrane according to claim 9, wherein the layer (L) further comprises a cationexchangeable resin.

13. The ion-exchange membrane according to claim 12, wherein a weight ratio between the side-chain heteroaromatic resin and the cation-exchangeable resin is 1:100 to 100:

1.

14. The ion-exchange membrane according to claim 12, wherein the cation-exchangeable resin is a fluororesin.

15. The ion-exchange membrane according to claim 14, wherein the fluororesin has a structural unit represented by the following general formula G1:r fI -c—IL R6 Jcf2x8r f iL F Jm[Gl]wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

16. The ion-exchange membrane according to claim 1, wherein the side-chain heteroaromatic resin further has astructural unit represented by the following general formula 2:wherein,R1, R2, and R3 are each optionally the same or different, and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms,R4 is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group having at least one nitrogen atom in a heteroaromatic ring structure and containing a five-membered ring and / or sixmembered ring structure,Rf is an aliphatic hydrocarbon group substituted with at least one fluorine atom, andX' is a counter anion.

17. The ion-exchange membrane according to claim 16, wherein a molar ratio between the structural unit represented by the general formula 1 and the structural unit represented by the general formula 2 is 1:100 to 100 :

1.

18. The ion-exchange membrane according to claim 16, wherein a weight ratio between the side-chain heteroaromatic resin and the cation-exchangeable resin is 1:100 to 100:

1.

19. The ion-exchange membrane according to claim 16, wherein the cation-exchangeable resin is a fluororesin.

20. The ion-exchange membrane according to claim 16, wherein the fluororesin has a structural unit represented by the following general formula G1:cf2x8[Gl]wherein the definition of each substituent has the samemeaning as in the general formula Gl described above.

21. The ion-exchange membrane according to claim 20, alternately comprisingat least one layer (L) comprising the resin composition, andat least one layer (M) comprising a fluororesin having a structural unit represented by the following general formula G1:wherein the definition of each substituent has the same meaning as in the general formula G1 described above.

22. The ion-exchange membrane according to claim 21, comprising one layer (L) and one layer (M).

23. The ion-exchange membrane according to claim 21, comprising the layer (L), the layer (M), and the layer (L) in the listed order.

24. An ion-exchange membrane comprisinga layer (LI) comprising a heteroaromatic structurecontaining fluororesin having a structural unitrepresented by the following general formula Al, a saponified product thereof or a salt thereof:cf2x4[Al] wherein,X1, X2, X3, and X4 are each optionally the same or different, and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X1 and X2 or X1 and X3 are optionally bound to each other to form a cyclic structure,R1 and R2 are each optionally the same or different, and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom,R3 is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms,R4 is a linking group that links NR3 and He, and is a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms,X10 is a divalent group represented by formula -CO2-or -SO2-,He is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, the group containing at least one nitrogen atom and containing a five-membered ring and / or six-membered ring structure, a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1, b is an integer of 0 to 8, c is 0 or 1, and d, e, and f are each optionally the same or different, and are each an integer of 0 to 6, provided that d, e, and f are not 0 at the same time, anda layer (Ml) comprising a fluororesin (Gl) having a structural unit represented by the following general formula Gl:wherein the definition of each substituent has the same meaning as in the general formula G1 described above.

25. The ion-exchange membrane according to claim 24, comprising three or more layers, the three or more layers alternately comprisingthe layer (LI), andthe layer (Ml).

26. The ion-exchange membrane according to claim 24, wherein a thickness of the layer (LI) is 10 pm or less.

27. The ion-exchange membrane according to claim 24, wherein a thickness of the ion-exchange membrane is 200 pm or less.

28. An ion-exchange membrane comprisinga layer (L3) comprising a side-chain nitrogen atomcontaining fluororesin having a structural unit represented by the following general formula A3, a saponified product thereof or a salt thereof:X21, I —c-I I -a X20 X22c—c• F1             r R24 ■-c--x24-nr22--r23-n—IL F L -kR26 r25-n ^R27[A3]wherein.X20 , X21 , X22 , and X23 are each optionally the same ordifferent, and are each a halogen atom, a substituted orunsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and X20 and X21 or X20 and X22 optionally form a cyclic structure,R20 and R21 are each optionally the same or different, and are each a hydrogen atom, a halogen atom,a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom,R22 and R24 are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstitutedaromatic hydrocarbon group having 6 to 10 carbon atoms,R26 and R27 are each a hydrogen atom, or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, and at least one of R26 and R27 is a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms,R23 and R25 are each optionally the same or different, and are each a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, wherein, when h is 2 or more, R23s repeated are each optionally the same or different,X24 is a divalent group represented by -CO2- or -SO2-,a and g each represent a molar ratio in the total constituent unit contained in the resin, and are numbers satisfying 0 < a < 1, 0 < g < 1, and a + g = 1,b is an integer of 0 to 8,c is 0 or 1, andd, e, f, and h are each optionally the same or different, and are each an integer of 0 to 6, provided that d, e, and f are not 0 at the same time, anda layer (M3) comprising a fluororesin (Gl) having a structural unit represented by the following general formula Gl:wherein the definition of each substituent has the same meaning as in the general formula G1 described above.

29. The ion-exchange membrane according to claim 28, comprising three or more layers, the three or more layers alternately comprisingthe layer (L3), andthe layer (M3).

30. The ion-exchange membrane according to claim 28, wherein a thickness of the layer (L3) is 10 pm or less.

31. The ion-exchange membrane according to claim 28, wherein a thickness of the ion-exchange membrane is 200 pm or less.

32. The ion-exchange membrane according to any one of claims 1 to 31, for a redox flow battery.

33. A membrane electrode assembly, wherein the ionexchange membrane according to any one of claims 1 to 31 and at least one electrode are bonded.

34. The membrane electrode assembly according to claim 33, for a redox flow battery.

35. A cell for a redox flow battery, the cell comprising a first electrolyte solution comprising a first redox active material, a second electrolyte solution comprising a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, anda separation membrane located between the first electrolyte solution and the second electrolyte solution, whereinthe separation membrane is the ion-exchange membrane according to any one of claims 1 to 31.

36. The cell for a redox flow battery according to claim 35, wherein the cell is a membrane electrode assembly in which the separation membrane and at least one electrode are bonded.

37. The cell for a redox flow battery according to claim 35, wherein at least one of the first electrode and the second electrode is a carbon electrode.

38. The cell for a redox flow battery according to claim 35, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metallic redox active material, a non-metallic redox active material, and an organic redox active material.

39. A redox flow battery, wherein the cell for a redox flow battery according to claim 35 is stacked.

40. A cell for a redox flow battery, the cell comprising a first electrolyte solution comprising a first redox active material, a second electrolyte solution comprising a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a separation membrane located between the first electrolyte solution and the second electrolyte solution, whereinthe separation membrane comprises at leasta first cation-exchangeable resin layer, and an anion-exchangeable resin layer, an equivalent weight of the separation membrane is 1150 g / eq or less,a thickness of the anion-exchangeable resin layer is 0.001 p.m or more and less than 5 Jim, andthe anion-exchangeable resin layer of the separation membrane is located facing an electrode acting as a negative electrode.

41. The cell for a redox flow battery according to claim 40, wherein the first cation-exchangeable resin layer is located closer to an electrode acting as a positive electrode than the anion-exchangeable resin layer.

42. The cell for a redox flow battery according to claim 40, wherein a distance Dneg between the anion-exchangeable resin layer of the separation membrane and the electrode acting as a negative electrode, and a distance Dpos between the anion-exchangeable resin layer of the separation membrane and an electrode acting as a positive electrode exhibit the following relationship:Dneg / Dpos < 1 •

43. The cell for a redox flow battery according to claim 40, wherein a thickness of the first cation-exchangeable resin layer is 1 Jim or more and 150 Jim or less.

44. The cell for a redox flow battery according to claim 40, wherein the first cation-exchangeable resin layer comprises a fluororesin.

45. The cell for a redox flow battery according to claim 40, wherein the first cation-exchangeable resin layer has at least one functional group selected from the group consisting of a sulfo group, a carboxyl group, and a phosphoric acid group.

46. The cell for a redox flow battery according to claim40, wherein the first cation-exchangeable resin layer comprises a fluororesin having a structural unit represented by the following general formula G1:[Gl]wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

47. The cell for a redox flow battery according to claim 40, wherein the anion-exchangeable resin layer comprises at least one selected from the group consisting ofa primary amino group,a secondary amino group,a tertiary amino group,an amino salt structure as a reaction product of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group, and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound,a nitrogen atom-containing heterocyclic ring structure,a salt structure of a nitrogen-containing heterocyclic ring as a reaction product of a nitrogencontaining heterocyclic ring structure and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, anda quaternary ammonium group.

48. The cell for a redox flow battery according to claim 40, wherein the separation membrane comprisesthe first cation-exchangeable resin layer,the anion-exchangeable resin layer, anda second cation-exchangeable resin layer,in the listed order, and a thickness of the first cationexchangeable resin layer is larger than a thickness of the second cation-exchangeable resin layer.

49. The cell for a redox flow battery according to claim 48, wherein the first cation-exchangeable resin layer is located closer to an electrode acting as a positive electrode than the anion-exchangeable resin layer.

50. The cell for a redox flow battery according to claim 48, wherein a distance Dneg between the anion-exchangeable resin layer of the separation membrane and the electrode acting as a negative electrode, and a distance Dpos between the anion-exchangeable resin layer of the separation membrane and an electrode acting as a positive electrode exhibit the following relationship:Dneg / Dpos < 1 •

51. The cell for a redox flow battery according to claim 48, wherein the second cation-exchangeable resin layer comprises a fluororesin.

52. The cell for a redox flow battery according to claim 48, wherein a thickness of the second cation-exchangeable resin layer is 0.01 p.m or more and less than 150 p.m.

53. The cell for a redox flow battery according to claim 48, wherein a value obtained by dividing the thickness of the second ion-exchangeable resin layer by the thicknessof the first cation-exchangeable resin layer is less than 0.7.

54. The cell for a redox flow battery according to claim 40, wherein at least one of the first electrode and the second electrode is a carbon electrode.

55. The cell for a redox flow battery according to claim 40, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metallic redox active material, a non-metallic redox active material, and an organic redox active material.

56. The cell for a redox flow battery according to claim 40, wherein at least one of the first electrode and the second electrode is a separation membrane electrode assembly bonded with the separation membrane.

57. A redox flow battery, wherein the cell for a redox flow battery according to any one of claims 40 to 56 is stacked.

58. A method for producing a separation membrane, the separation membrane comprising at least a first cation-exchangeable resin layer, and an anion-exchangeable resin layer, in whichan equivalent weight of the separation membrane is 1150 g / eq or less, anda thickness of the anion-exchangeable resin layer is 0.001 p.m or more and less than 5 jim, whereinthe method comprisesa step of forming the first cation-exchangeable resin layer, anda step of forming the anion-exchangeable resin layer .

59. The method for producing a separation membrane according to claim 58, wherein the method comprises a step of reactinga fluororesin precursor layer serving as a precursor of the first cation-exchangeable resin layer, and containing at least one selected from the group consisting of a sulfonyl halide group, an acyl halide group, and a halogenated phosphoric acid group, witha modification compound having at least two nitrogen atom-containing groups, in which the nitrogen atom-containing groups comprise at least one selected from the group consisting ofa primary amino group,a secondary amino group,a tertiary amino group,an amino salt structure as a reaction product of at least one amino group selected from thegroup consisting of a primary amino group, a secondary amino group, and a tertiary amino group, and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound,a nitrogen atom-containing heterocyclic ring structure,a salt structure of a nitrogen-containing heterocyclic ring as a reaction product of a nitrogencontaining heterocyclic ring structure and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, anda quaternary ammonium group, anda step of converting at least one selected from the group consisting of the sulfonyl halide group, the acyl halide group, and the halogenated phosphoric acid group contained in the fluororesin precursor layer, into at least one selected from the group consisting of a sulfo group, a carboxyl group, and a phosphoric acid group, after the above step.

60. The method for producing a separation membrane according to claim 58, the separation membrane comprising the first cation-exchangeable resin layer, the anion-exchangeable resin layer, and a second cation-exchangeable resin layer,in the listed order, in which a thickness of the first cation-exchangeable resin layer is larger than a thickness of the second cation-exchangeable resin layer, whereinthe method comprisesa step of forming the first cation-exchangeable resin layer,a step of forming the anion-exchangeable resin layer, anda step of forming the second cation-exchangeable resin layer.

61. The method for producing a separation membrane according to claim 60, comprising a step of overlapping the anion-exchangeable resin layers of membranes each having the first cation-exchangeable resin layer and the anion-exchangeable resin layer.

62. A polyelectrolyte solution comprisinga fluororesin having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and having a structural unit represented by the following general formula Gl, anda solvent containing water, an aliphatic alcohol, and an aliphatic carboxylic acid, whereina ratio of a total mass of the aliphatic carboxylic acid and a reaction product thereof to a total mass of the solvent is 100:1 to 100:50:cf2x8[Gl]wherein the definition of each substituent has the same meaning as in the general formula Gl described above.

63. The polyelectrolyte solution according to claim 62, wherein a mass ratio between the aliphatic carboxylic acid and the aliphatic alcohol is 100:1 to 1:

100.

64. An ion-exchange membrane comprising a fluororesin having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and having a structural unit represented by the following general formula Gl, whereinthe number of crack defects per unit area of the ion-exchange membrane is less than 10 / m2:wherein the definition of each substituent has the same meaning as in the general formula G1 described above.

65. The ion-exchange membrane according to claim 64, wherein an orientation ratio OR in a membrane surface direction, as determined by X-ray scattering measurement, is 1.0 or more and less than 1.

1.

66. The ion-exchange membrane according to claim 64, wherein an average membrane thickness is 75 p.m or less.

67. The ion-exchange membrane according to claim 66, wherein an average membrane thickness is 25 p.m or more.

68. The ion-exchange membrane according to claim 64, wherein a minimum membrane thickness is 90% or more of an average membrane thickness, and a maximum membrane thickness is 110% or less of an average membrane thickness .

69. A wound body configured by winding the ion-exchange membrane according to claim 64.

70. The wound body according to claim 69, wherein a width of the ion-exchange membrane is 50 mm or more and 5,000 mm or less.

71. The wound body according to claim 69, wherein a length of the ion-exchange membrane is 100 mm or more.

72. A membrane electrode assembly, wherein the ionexchange membrane according to any one of claims 64 to 68 and at least one electrode are bonded.

73. The ion-exchange membrane according to any one of claims 64 to 68, for a redox flow battery.

74. The membrane electrode assembly according to claim 72, for a redox flow battery.

75. A cell for a redox flow battery, the cell comprising a first electrolyte solution comprising a first redox active material, a second electrolyte solution comprising a second redox active material, a first electrode in contact with the first electrolyte solution,a second electrode in contact with the second electrolyte solution, anda separation membrane located between the first electrolyte solution and the second electrolyte solution, whereinthe separation membrane is the ion-exchange membrane according to any one of claims 64 to 68.

76. The cell for a redox flow battery according to claim 75, wherein the separation membrane and at least one electrode are bonded.

77. The cell for a redox flow battery according to claim 75, wherein at least one of the first electrode and the second electrode is a carbon electrode.

78. The cell for a redox flow battery according to claim 75, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metallic redox active material, a non-metallic redox active material, and an organic redox active material.

79. A redox flow battery, wherein the cell for a redox flow battery according to claim 75 is stacked.

80. A method for producing an ion-exchange membrane, the method comprisinga step of applying and drying the polyelectrolyte solution according to claim 62 or 63, whereinthe ion-exchange membrane comprises a fluororesin having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and having a structural unit represented by the following general formula Gl, and the number of crack defects per unit area of the ion-exchange membrane is less than 10 / m2:[Gl]wherein the definition of each substituent has the samemeaning as in the general formula Gl described above.

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