New electrolyte membranes for Li-based cells: Methacrylic polymers encompassing pyrrolidinium-based ionic liquid by single step photo-polymerisation

We demonstrate herein the application of an in situ single-step free radical photo-polymerisation process to incorporate room temperature ionic liquids (RTILs) into polymer membranes to be used as quasi-solid electrolytes in lithium-based batteries. The membranes are prepared by UV irradiating a mixture of photo-curable dimethacrylic oligomers and a proper radical photo-initiator along with a large quantity (i.e., 60 wt%) of ether-functionalized pyrrolidinium-imide ionic liquid (PYRA1201TFSI) and LiTFSI lithium salt. Stable and flexible polymer films with homogeneous nature are easily produced: they combine the advantages of polymer electrolytes swollen by conventional organic liquid electrolytes with the non-flammability, high thermal and electrochemical stability typical of RTILs. Appreciable ionic conductivity values (0.1–1 mS cm−1) and good overall electrochemical performances are obtained in a wide temperature range. The polymer electrolyte membranes are tested in lab-scale cells using LiFePO4 as the cathode and Li metal as the anode. Good charge/discharge capacities, Coulombic efficiency close to unity, and low capacity loss at medium C-rates during preliminary cycling are obtained. These interesting properties highlight that such green and safe electrolyte systems could become a strong contender in the field of thin and flexible Li-based power sources.