The PiHCIL-SPEs were prepared using solvent casting within an argon-filled glovebox as shown in Figure . First, LiFSI and C3mpyrFSI (LiFSI:IL molar ratio equal to 1:1) were mixed and fully dissolved. The obtained solution was then mixed with various amounts of PEO in acetonitrile to form SPEs with EO:Li:IL molar ratios equal to 8:1:1, 10:1:1, 15:1:1 and 20:1:1. The obtained mixtures were then cast into silicon moulds inside the glovebox (MBraun UNILab, H2O and O2 content <1 ppm) and rested for 48 h to ensure slow solvent evaporation. The obtained solid membranes were then put between two Mylar sheets and hot pressed (70°C, 2 MPa, 10 mins) to obtain a homogenous, free-standing and pin-hole free SPE with a thickness of 120 ± 10 μm. The membranes were transferred to a Buchi oven and vacuum-dried at 50 °C for another 24 h before further characterization and cell assembly. The SPEs are named as PiHCIL-SPEx:1:1 where x is the polymer content.