Gel polymer electrolyte based on polyvinylidenefluoride-co- hexafluoropropylene and ionic liquid for lithium ion battery

Gel-type polymer electrolytes with 1-butyl-4-methylpyridinium bis(trifluoromethanesulfonyl)imide (B4MePyTFSI) ionic liquid are formed by the solution casting method. The conductivity and transference number measurements are carried out to investigate conductivity and charge transport in the gel polymer electrolytes. The conductivity of the samples increases when the amount of B4MePyTFSI ionic liquid is increased. The lithium ion ionic conductivity reaches the maximum value (2.01 × 10^-4 S cm^-1) when GPE contains 33.3 wt% B4MePyTFSI. The electrochemical stability window of ILGPE is about 5.5 V versus Li⁺/Li at 20 C, meeting the basic requirement of rechargeable lithium batteries. Discharge performance of lithium battery using this ILGPE membrane shows a capacity of about 160 mAh g^-1. The excellent performance with higher capacity, good cycle stability and compatibility are observed for the Li/ILGPE/LiFePO₄ cells. The interfacial resistances between ILGPE and electrodes have the less change after 10 cycles.