Poly ethylene oxide based polymer electrolytes containing salt lithium bis(trifluoromethylsulfonyl)imide and ionic liquid 1-butyl-3-methyl pyridinium bis(trifluoromethylsulfonypimide are synthesized. The prepared polymer electrolytes are found to be thermally stable up to 340-360 degrees C. Ionic conductivity is observed 2.5 x 10(-5) S cm(-1) at 25 degrees C and 2.3 x 10(-4) S cm(-1) at 40 degrees C for 30% IL containing polymer electrolyte. Also, ionic transference number > 0.99 and cationic transference number similar to 0.41 with electrochemical window similar to 5.2 V at 25 degrees 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/LiFePO4) is found to be 106 mAh g(-1) at 25 degrees C and 160 mAh g(-1) at 40 degrees 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.