Redox flow secondary battery and electrolyte membrane for redox flow secondary battery

1. A redox flow secondary battery comprising an electrolytic bath comprising:

a positive electrode cell chamber comprising a positive electrode composed of a carbon electrode;

a negative electrode cell chamber comprising a negative electrode composed of a carbon electrode; and

an electrolyte membrane as a separation membrane to separate the positive electrode cell chamber and the negative electrode cell chamber,

wherein the positive electrode cell chamber comprises a positive electrode electrolyte solution comprising a positive electrode active substance; and the negative electrode cell chamber comprises a negative electrode electrolyte solution comprising a negative electrode active substance;

wherein the redox flow secondary battery charges and discharges based on changes in valences of the positive electrode active substance and the negative electrode active substance in the electrolyte solutions;

wherein the electrolyte membrane comprises an ion-exchange resin composition comprising a fluorine-based polyelectrolyte polymer having a structure represented by the following formula (1):

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

wherein X 1 , X 2 , and X 3 each independently represent one or more selected from the group consisting of halogen atoms and perfluoroalkyl groups having 1 to 3 carbon atoms; X 4 represents COOZ, SO 3 Z, PO 3 Z 2 , or PO 3 HZ wherein Z represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an amine (NH 4 , NH 3 R 1 , NH 2 R 1 R 2 , NHR 1 R 2 R 3 , NR 1 R 2 R 3 R 4 ) wherein R 1 , R 2 , R 3 , and R 4 each independently represent one or more selected from the group consisting of alkyl groups and arene groups, when X 4 is PO 3 Z 2 , Z may be identical or different; R 1 and R 2 each independently represent one or more selected from the group consisting of halogen atoms and perfluoroalkyl groups and fluorochloroalkyl groups having 1 to 10 carbon atoms; and a and g represent numbers satisfying 0≦a<1, 0<g≦1, and a+g=1, b represents an integer of 0 to 8, c represents 0 or 1, and d, e, and f each independently represent an integer of 0 to 6 (with the proviso that d, e, and f are not 0 at the same time); and

wherein the electrolyte membrane has an ion cluster diameter of 1.00 to 2.95 nm as measured in water at 25° C. by a small angle X-ray method.

2. The redox flow secondary battery according to claim 1 , wherein the positive electrode electrolyte solution and the negative electrode electrolyte solution comprise sulfuric acid and vanadium.

3. The redox flow secondary battery according to claim 1 , wherein the fluorine-based polyelectrolyte polymer is a perfluorocarbonsulfonic acid resin having a structure represented by the following formula (2):

—[CF 2 —CF 2 ] a —[CF 2 —CF(—O—(CF 2 ) m —SO 3 H)] g —  (2)

wherein a and g represent numbers satisfying 0≦a<1, 0<g≦1, and a+g=1; and m represents an integer of 1 to 6.

4. The redox flow secondary battery according to claim 1 , wherein the fluorine-based polyelectrolyte polymer has an equivalent weight EW (dry mass in grams per equivalent of ion-exchange groups) of 300 to 1,300 g/eq; and the electrolyte membrane has an equilibrium moisture content of 5 to 80% by mass.

5. The redox flow secondary battery according to claim 1 , wherein the ion-exchange resin composition comprises 0.1 to 200 parts by mass of a polyazole-based compound with respect to 100 parts by mass of the fluorine-based polyelectrolyte polymer.

6. The redox flow secondary battery according to claim 5 , wherein the polyazole-based compound is one or more selected from the group consisting of polymers of a heterocyclic compound having one or more nitrogen atoms in a ring thereof, and polymers of a heterocyclic compound having one or more nitrogen atoms and oxygen and/or sulfur in a ring thereof.

7. The redox flow secondary battery according to claim 6 , wherein the polyazole-based compound is one or more selected from the group consisting of polyimidazole-based compounds, polybenzimidazole-based compounds, polybenzobisimidazole-based compounds, polybenzoxazole-based compounds, polyoxazole-based compounds, polythiazole-based compounds, and polybenzothiazole-based compounds.

8. The redox flow secondary battery according to claim 5 , wherein the fluorine-based polyelectrolyte polymer and the polyazole-based compound at least partially form an ionic bond therebetween.

9. The redox flow secondary battery according to claim 1 , further comprising 0.1 to 20 parts by mass of a polyphenylene ether resin and/or a polyphenylene sulfide resin with respect to 100 parts by mass of the fluorine-based polyelectrolyte polymer.

10. The redox flow secondary battery according to claim 1 , comprising 50 to 100 parts by mass of the fluorine-based polyelectrolyte polymer with respect to 100 parts by mass of the ion-exchange resin composition.

11. An electrolyte membrane for a redox flow secondary battery, comprising an ion-exchange resin composition comprising a fluorine-based polyelectrolyte polymer having a structure represented by the following formula (1):

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

wherein X 1 , X 2 , and X 3 each independently represent one or more selected from the group consisting of halogen atoms and perfluoroalkyl groups having 1 to 3 carbon atoms; X 4 represents COOZ, SO 3 Z, PO 3 Z 2 , or PO 3 HZ wherein Z represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an amine (NH 4 , NH 3 R 1 , NH 2 R 1 R 2 , NHR 1 R 2 R 3 , NR 1 R 2 R 3 R 4 ) wherein R 1 , R 2 , R 3 , and R 4 each independently represent one or more selected from the group consisting of alkyl groups and arene groups, when X 4 is PO 3 Z 2 , Z may be identical or different; R 1 and R 2 each independently represent one or more selected from the group consisting of halogen atoms and perfluoroalkyl groups and fluorochloroalkyl groups having 1 to 10 carbon atoms; and a and g represent numbers satisfying 0≦a<1, 0<g≦1, and a+g=1, b represents an integer of 0 to 8, c represents 0 or 1, and d, e, and f each independently represent an integer of 0 to 6 (with the proviso that d, e, and f are not 0 at the same time); and

wherein the electrolyte membrane has an ion cluster diameter of 1.00 to 2.95 nm as measured in water at 25° C. by a small angle X-ray method.

12. The electrolyte membrane for the redox flow secondary battery according to claim 11 , wherein the fluorine-based polyelectrolyte polymer is a perfluorocarbonsulfonic acid resin having a structure represented by the following formula (2):

—[CF 2 —CF 2 ] a —[CF 2 —CF(—O—(CF 2 ) m —SO 3 H)] g —  (2)

wherein a and g represent numbers satisfying 0≦a<1, 0<g≦1, and a+g=1; and m represents an integer of 1 to 6.

13. The electrolyte membrane for the redox flow secondary battery according to claim 11 , wherein the fluorine-based polyelectrolyte polymer has an equivalent weight EW (dry mass in grams per equivalent of ion-exchange groups) of 300 to 1,300; and the electrolyte membrane has an equilibrium moisture content of 5 to 80% by mass.

14. The electrolyte membrane for the redox flow secondary battery according to claim 11 , wherein the ion-exchange resin composition comprises 0.1 to 200 parts by mass of a polyazole-based compound with respect to 100 parts by mass of the fluorine-based polyelectrolyte polymer.

15. The electrolyte membrane for the redox flow secondary battery according to claim 14 , wherein the polyazole-based compound is one or more selected from the group consisting of polymers of a heterocyclic compound having one or more nitrogen atoms in a ring thereof, and polymers of a heterocyclic compound having one or more nitrogen atoms and oxygen and/or sulfur in a ring thereof.

16. The electrolyte membrane for the redox flow secondary battery according to claim 15 , wherein the polyazole-based compound is one or more selected from the group consisting of polyimidazole-based compounds, polybenzimidazole-based compounds, polybenzobisimidazole-based compounds, polybenzoxazole-based compounds, polyoxazole-based compounds, polythiazole-based compounds, and polybenzothiazole-based compounds.

17. The electrolyte membrane for the redox flow secondary battery according to claim 14 , wherein the fluorine-based polyelectrolyte polymer and the polyazole-based compound at least partially form an ionic bond therebetween.

18. The electrolyte membrane for the redox flow secondary battery according to claim 11 , further comprising 0.1 to 20 parts by mass of a polyphenylene ether resin and/or a polyphenylene sulfide resin with respect to 100 parts by mass of the fluorine-based polyelectrolyte polymer.

19. The electrolyte membrane for the redox flow secondary battery according to claim 11 , further comprising a reinforcing material.

20. The electrolyte membrane for the redox flow secondary battery according to claim 11 , comprising 50 to 100 parts by mass of the fluorine-based polyelectrolyte polymer with respect to 100 parts by mass of the ion-exchange resin composition.