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

1. 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 SO 3 Z, wherein Z represents a hydrogen atom;

R 1 and R 2 each independently represents one or more selected from the group consisting of halogen atoms, perfluoroalkyl groups having 1 to 10 carbon atoms, 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 fluorine-based polyelectrolyte polymer has a terminal group of a main molecular chain of CF 3 ;

in a test in which 0.1 g of the fluorine-based polyelectrolyte polymer is immersed in 50 g of a Fenton's reagent solution containing a 3% hydrogen peroxide solution and 200 ppm of divalent iron ions at 40° C. for 16 hours, an amount of fluorine ions eluted detected in a solution is 0.03% or smaller of a whole amount of fluorine in an immersed polymer.

2. The electrolyte membrane for a redox flow secondary battery according to claim 1 , wherein in the test in which 0.1 g of the fluorine-based polyelectrolyte polymer is immersed in 50 g of the Fenton's reagent solution containing the 3% hydrogen peroxide solution and 200 ppm of divalent iron ions at 40° C. for 16 hours, the amount of fluorine ions eluted detected in the solution is 0.002% or smaller of the whole amount of fluorine in the immersed polymer.

3. The electrolyte membrane for a redox flow secondary battery according to claim 1 , wherein the fluorine-based polyelectrolyte polymer is a perfluorocarbonsulfonic acid resin (PFSA) 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 electrolyte membrane for a 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 electrolyte membrane for a redox flow secondary battery according to claim 1 ,

wherein the ion-exchange resin composition comprises 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.

6. The electrolyte membrane for a redox flow secondary battery according to claim 5 , wherein the fluorine-based polyelectrolyte polymer is a perfluorocarbonsulfonic acid resin (PFSA) 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.

7. The electrolyte membrane for a redox flow secondary battery according to claim 5 , 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.

8. The electrolyte membrane for a redox flow secondary battery according to claim 1 ,

wherein the ion-exchange resin composition comprises one or more selected from the group consisting of a Ce-based additive, a Co-based additive, and a Mn-based additive.

9. The electrolyte membrane for a redox flow secondary battery according to claim 8 , wherein the fluorine-based polyelectrolyte polymer is a perfluorocarbonsulfonic acid resin (PFSA) 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.

10. The electrolyte membrane for a redox flow secondary battery according to claim 8 , 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.

11. 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

electrolyte membrane according to claim 1 as a separation membrane to separate the positive electrode cell chamber and the negative electrode cell chamber.

12. The redox flow secondary battery according to claim 11 , wherein sulfuric acid electrolyte solutions comprising vanadium are used as the positive electrode electrolyte solution and the negative electrode electrolyte solution.

13. The redox flow secondary battery according to claim 11 ,

wherein the ion-exchange resin composition comprises 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.

14. The redox flow secondary battery according to claim 13 , wherein sulfuric acid electrolyte solutions comprising vanadium are used as the positive electrode electrolyte solution and the negative electrode electrolyte solution.

15. The redox flow secondary battery according to claim 11 ,

wherein the ion-exchange resin composition comprises one or more selected from the group consisting of a Ce-based additive, a Co-based additive, and a Mn-based additive.

16. The redox flow secondary battery according to claim 15 , wherein sulfuric acid electrolyte solutions comprising vanadium are used as the positive electrode electrolyte solution and the negative electrode electrolyte solution.

17. A method of producing the electrolyte membrane for a redox flow secondary battery according to claim 1 , comprising:

fluorinating a precursor of fluorine-based polyelectrolyte polymer, and

hydrolyzing and acidizing the fluorinated precursor into a fluorine-based polyelectrolyte polymer, and then obtaining the electrolyte membrane using a cast membrane formation method with the fluorine-based polyelectrolyte polymer, or

extrusion-mixing the fluorinated precursor, and then obtaining the electrolyte membrane of a fluorine-based polyelectrolyte polymer with a hydrolysis treatment and an acid treatment on the extrusion-mixed fluorinated precursor,

wherein a terminal group of a side molecular chain of the precursor contains SO 2 F;

wherein the fluorine-based polyelectrolyte polymer has a terminal group of a main molecular chain of CF 3 ;

wherein, the fluorine-based polyelectrolyte polymer has 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 SO 3 Z, wherein Z represents a hydrogen atom;

R 1 and R 2 each independently represents one or more selected from the group consisting of halogen atoms, perfluoroalkyl groups having 1 to 10 carbon atoms, 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);

wherein in a test in which 0.1 g of the fluorine-based polyelectrolyte polymer is immersed in 50 g of a Fenton's reagent solution containing a 3% hydrogen peroxide solution and 200 ppm of divalent iron ions at 40° C. for 16 hours, an amount of fluorine ions eluted detected in a solution is 0.03% or smaller of a whole amount of fluorine in an immersed polymer.