Improved electrochemical performance of EMIMFSI ionic liquid based gel polymer electrolyte with temperature for rechargeable lithium battery

Free-standing, flexible ionic liquid based gel polymer electrolyte (ILGPE) membranes containing polymer PVdF-HFP, imidazolium-based ionic liquid EMIMFSI with lithium salt LiTFSI are synthesized and characterized by various techniques. Thermal, electrochemical and electrical properties of prepared ILGPE membranes are investigated by thermogravimetric analysis, linear sweep voltammetry, cyclic voltammetry and impedance spectroscopy techniques. Prepared membranes are found to be thermally stable upto 200 °C. The ionic conductivity is found to be ∼3.8 × 10−4 S cm−1 at 25 °C and ∼6.0 × 10−4 S cm−1 at 50 °C for 40 wt% IL containing GPE. Lithium transference number and lithium ion conductivity of 40 wt% IL containing GPE shows the maximum value ∼0.4 and ∼1.5 × 10−4 S cm−1 respectively with electrochemical window ∼4.7 V versus Li/Li+ at 25 °C. The 40 wt% IL containing GPE is used for battery application because of its better compatibility with lithium electrode compared to other prepared ILGPEs. The discharge capacity attains a maximum value ∼141.2 mAh g−1 and ∼160.3 mAh g−1 at 25 °C and 50 °C respectively at 0.1C. About ∼99% Coulombic efficiency is obtained upto 100th cycles at 50 °C. These results indicate that the Li/40 wt% IL containing GPE/LiFePO4 cell shows high Coulombic efficiency, good charge-discharge capacity and cyclic stability upto 100th cycles.