A process for the preparation of a composite material comprising the steps of: a) providing a porous substrate P consisting of an electrically non-conductive polymeric material; b) mixing, optionally in the presence of a liquid medium L1, an electrolyte salt ES-1, an ionic liquid IL-1 and a compound M of formula X 4-m AY m wherein X is a hydrocarbon group, optionally comprising one or more functional groups, m is an integer from 1 to 4, A is an element selected from the group consisting of Si, Ti and Zr, and Y is a hydrolysable group selected from the group consisting of an alkoxy group, an acyloxy group and a hydroxyl group, to form an electrolyte composition EC-1; c) mixing electrolyte composition EC-1 with a composition C1, said composition C1 comprising at least one fluoro co-polymer F, that comprises recurring units deriving from vinylidene difluoride and recurring units deriving from at least monomer R1 having at least one functional group -O-Rx and/or -C O-Rx, wherein each Rx, optionally independently from the others, is a hydrogen group or a C 1 -C 5 hydrocarbon group comprising at least one hydroxyl group, to obtain a composition C; d) impregnating the support P with the composition C obtained in step c); e) removing the liquid medium L1, if present, to obtain a composite material, wherein the inorganic residues deriving from compound M are bound with the functional groups deriving from -O-Rx and/or -C O-Rx of copolymer F; wherein the viscosity of composition C used in the impregnation step d) is from 50 to 500 mPa.s when measured at a shear rate of 200 sec -1, and at a temperature of 20°C, according to ISO/DIN 3219. a) providing a porous substrate P consisting of an electrically non-conductive polymeric material; b) mixing, optionally in the presence of a liquid medium L1, an electrolyte salt ES-1, an ionic liquid IL-1 and a compound M of formula X 4-m AY m wherein X is a hydrocarbon group, optionally comprising one or more functional groups, m is an integer from 1 to 4, A is an element selected from the group consisting of Si, Ti and Zr, and Y is a hydrolysable group selected from the group consisting of an alkoxy group, an acyloxy group and a hydroxyl group, to form an electrolyte composition EC-1; c) mixing electrolyte composition EC-1 with a composition C1, said composition C1 comprising at least one fluoro co-polymer F, that comprises recurring units deriving from vinylidene difluoride and recurring units deriving from at least monomer R1 having at least one functional group -O-Rx and/or -C O-Rx, wherein each Rx, optionally independently from the others, is a hydrogen group or a C 1 -C 5 hydrocarbon group comprising at least one hydroxyl group, to obtain a composition C; d) impregnating the support P with the composition C obtained in step c); e) removing the liquid medium L1, if present, to obtain a composite material, wherein the inorganic residues deriving from compound M are bound with the functional groups deriving from -O-Rx and/or -C O-Rx of copolymer F; wherein the viscosity of composition C used in the impregnation step d) is from 50 to 500 mPa.s when measured at a shear rate of 200 sec -1, and at a temperature of 20°C, according to ISO/DIN 3219.