*2.3. Swelling Solutions*

Liquid electrolyte solutions were prepared as gelling media of the polymer membranes, in order to evaluate the potentialities of the resulting gelled membranes as polymer electrolytes for lithium batteries. In particular, in view of their potential application in lithium-sulfur batteries, two similar solutions, with and without a polysulfide (henceforward called "PS-containing sol" and "PS-free sol," respectively), were prepared. PS-containing sol was formed using PyR14TFSI 77 wt.%, EC:DMC (1:1 volume ratio) 18.4 wt.%, LiTFSI 0.5 mol/kg, Li2S8 4.6 wt.%, and PS-free sol used PyR14TFSI 80 wt.%, EC:DMC (1:1 volume ratio) 20 wt.%, and LiTFSI 0.5 mol/kg.

The ionic liquid N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) was bought from Solvionic (99.9%, Toulouse, France) and used as received; the lithium salt (bis(trifluoromethane)sulfonyl imide (LiTFSI) was purchased from Fluka (99.9%, Munich, Germany) and used without further purification; carbonates solvents, i.e., ethylene carbonate (EC) and dimethyl carbonate (DMC), were provided by Sigma-Aldrich. Polysulfide (in form of Li2S8) was produced in situ via direct reactions between metallic lithium (Chemetall, Frankfurt am Main, Germany) and elemental sulfur (Sigma-Aldrich) in stoichiometric ratio, in a corked vial where the other components were already presents; the mixture was heated to 60–70 ◦C, stirred for the first four hours, and let it stand for the next twenty hours. These operations were performed in a controlled argon atmosphere dry box having a humidity content below 1 ppm.
