Electrolyte emulsion and process for producing same

1. An electrolyte emulsion, comprising:

an aqueous medium; and

a fluoropolymer electrolyte dispersed in the aqueous medium,

the fluoropolymer electrolyte comprising ionic clusters that are 0.1 to 2.6 nm apart at 25° C. and relative humidity 50% RH as calculated by small angle X-ray measurement based on the following formula (1):

d=λ/ 2/sin(θ m )  (1)

wherein d is a distance between ionic clusters, λ is an incident X-ray wavelength used in the small angle X-ray measurement, and θm is a Bragg angle which indicates a peak, and

a monomer unit that has an SO 3 Z group, wherein Z is an alkali metal, an alkaline-earth metal, hydrogen, or NR 1 R 2 R 3 R 4 , wherein R 1 , R 2 , R 3 , and R 4 each are individually a C1-C3 alkyl group or hydrogen,

the electrolyte having an equivalent weight (EW) of 250 or more and 700 or less, a proton conductivity of 0.1 S/cm or higher when measured at 110° C. and relative humidity 50% RH, and a ratio (the number of SO 2 F groups)/(the number of SO 3 Z groups) of 0 to 0.01, and

the electrolyte being a spherical particulate substance having an average particle size of 10 to 500 nm.

2. The electrolyte emulsion according to claim 1 ,

wherein the equivalent weight (EW) of the fluoropolymer electrolyte is 250 or more and 650 or less.

3. The electrolyte emulsion according to claim 1 ,

wherein the fluoropolymer electrolyte comprises:

a repeating unit (cc) derived from an SO 3 Z group-containing monomer represented by the following formula (I):

CF 2 ═CF(CF 2 ) k —O 1 —(CF 2 CFY 1 —O) n —(CFY 2 ) m -A 1   (I)

wherein Y 1 is F, Cl, or a perfluoroalkyl group; k is an integer of 0 to 2; 1 is 0 or 1; n is an integer of 0 to 8; n Y 1 s may be the same as or different from each other; Y 2 is F or Cl; m is an integer of 0 to 6, provided that if m=0, l=0 and n=0; m Y 2 s may be the same as or different from each other; A 1 is SO 3 Z, wherein Z is an alkali metal, an alkaline-earth metal, hydrogen, or NR 1 R 2 R 3 R 4 , wherein R 1 , R 2 , R 3 , and R 4 each are individually a C1-C3 alkyl group or hydrogen; and

a repeating unit (β) derived from an ethylenic fluoromonomer that is different from the monomer that provides the repeating unit (α), and

the repeating unit (α) is in an amount of 10 to 95 mol %, the repeating unit (β) is in an amount of 5 to 90 mol %, and the sum of the amounts of the repeating unit (cc) and the repeating unit (β) is 95 to 100 mol %.

4. The electrolyte emulsion according to claim 3 ,

wherein in the fluoropolymer electrolyte, k is 0, 1 is 1, Y 1 is F, n is 0 or 1, Y 2 is F, m is 2 or 4, and A 1 is SO 3 H.

5. The electrolyte emulsion according to claim 4 ,

wherein in the fluoropolymer electrolyte, n is 0 and m is 2.

6. The electrolyte emulsion according to claim 1 ,

wherein the fluoropolymer electrolyte is obtained by chemically treating a fluoropolymer electrolyte precursor which has a group to be converted, by the chemical treatment, into SO 3 Z, wherein Z is an alkali metal, an alkaline-earth metal, hydrogen, or NR 1 R 2 R 3 R 4 , wherein R 1 , R 2 , R 3 , and R 4 each are individually a C1-C3 alkyl group or hydrogen, which is melt-flowable, and which has a melt-flow rate of 0.01 to 100 g/10 min.

7. The electrolyte emulsion according to claim 6 ,

wherein the chemical treatment is a treatment of making the fluoropolymer electrolyte precursor in contact with a basic reactive liquid.

8. The electrolyte emulsion according to claim 1 ,

wherein the electrolyte emulsion contains 2 to 80% by mass of the fluoropolymer electrolyte.

9. The electrolyte emulsion according to claim 1 ,

wherein the aqueous medium has a water content of more than 50% by mass.