Flexible polymer electrolyte

Polymer electrolyte based on a fluoropolymer hybrid organic/inorganic composite comprising inorganic domains, said hybrid being obtained by a process comprising:

• (I) providing a mixture of:
• at least one a semi-crystalline vinylidene fluoride (VDF) copolymer [polymer (A)] comprising:
• (a) recurring units derived from vinylidene fluoride (VDF);
• (b) recurring units derived from chlorotrifluoroethylene (CTFE);
• (c) recurring units derived from at least one hydrophilic (meth) acrylic monomer [monomer (MA)] of formula (I):
• wherein each of R1, R2, R3, equal or different from each other, is independently an hydrogen atom or a C1-C3 hydrocarbon group, and Rx is a C1-C5 hydrocarbon moiety optionally comprising at least one hydroxyl group;
• and
• (d) recurring units derived from one or more fluorinated comonomers (F) different from VDF and from CTFE;
• wherein the total amount of recurring units b) is comprised between 6% and 25% by weight with respect to the total weight of recurring units of polymer (A) and the total amount of recurring units d) is comprised between 0.5% and 4% by weight with respect to the total weight of recurring units of polymer (A), and wherein polymer (A) has a heat of fusion of at least 0.4 Jig, as measured according to ASTM D 3418;
• at least one compound (M) of formula (II):
• X4-mAYm (II)
• wherein m is an integer from 1 to 4, A is a metal selected from the group consisting of Si, Ti and Zr, Y is a hydrolysable group, X is a hydrocarbon group, optionally comprising one or more functional groups;
• and
• an electrolyte solution (ES) comprising at least one metal salt [metal salt (MS)] and a liquid medium [medium (L)];
• (II) reacting at least a fraction of hydroxyl groups of the Rx groups of said monomer (MA) of said polymer (A) with at least a fraction of said compound (M), so as to obtain a grafted polymer comprising pendant —Ym-1AX4-m groups, with m, Y, A and X having same meaning as above detailed;
• (III) hydrolyzing and/or polycondensing compound (M) and/or pendant —Ym-1AX4-m groups, as above detailed to yield a polymer electrolyte based on a fluoropolymer hybrid organic/inorganic composite comprising inorganic domains incorporating the electrolyte solution(ES).