Effect of temperature on electrochemical performance of ionic liquid based polymer electrolyte with Li/LiFePO4 electrodes

Abstract Poly ethylene oxide based polymer electrolytes containing salt lithium bis(trifluoromethylsulfonyl)imide and ionic liquid 1-butyl-3-methyl pyridinium bis(trifluoromethylsulfonyl)imide are synthesized. The prepared polymer electrolytes are found to be thermally stable up to 340–360 °C. Ionic conductivity is observed ~ 2.5 × 10 − 5  S cm − 1 at 25 °C and 2.3 × 10 − 4  S cm − 1 at 40 °C for 30% IL containing polymer electrolyte. Also, ionic transference number > 0.99 and cationic transference number ~ 0.41 with electrochemical window ~ 5.2 V at 25 °C is observed for the electrolyte containing 30% IL. The highest Li + ion conducting polymer electrolyte is further optimised for battery application. The specific discharge capacity of the prepared cell (Li/polymer electrolyte/LiFePO 4 ) is found to be 106 mAh g − 1 at 25 °C and 160 mAh g − 1 at 40 °C up to 25 cycles with 0.1 C current rate. The increment in discharge capacity at higher temperature may be due to the better electrode-electrolyte contact. Decrement in cell resistance is also observed at higher temperature.