Process for preparing ionomeric membranes

A process to prepare membranes formed by (per)fluorinated ionomeric electrolytes salified with the lithium ion, comprising the following steps:

• a) obtaining of (per)fluorinated polymer membranes, containing —SO2F groups pendent with respect to the main chain;
• b) partial or complete salification of the (per)fluorinated polymer membranes containing —SO2F groups with basic lithium compounds and final water washing;
• c) swelling and contemporaneous drying process of the membranes by dipping in a heterogeneous biphasic system formed by a solvent or a mixture of dipolar aprotic solvents wherein solid drying agents insoluble in the organic solvent and inert towards the solvent and the membranes, are dispersed.