Lithium bis(fluorosulfonyl)imide/poly(ethylene oxide) polymer electrolyte

New solid polymer electrolytes (SPEs) comprising of lithium bis(fluorosulfonyl)imide (LiFSI) and high molecular weight poly(ethylene oxide) (PEO, Mv = 5 × 106 g mol−1) have been prepared and characterized, and are comparatively studied with the representative SPEs, Li[N(SO2CF3)2] (LiTFSI)/PEO, at a molar ratio of EO/Li+ = 20. Their physicochemical properties have been investigated in terms of phase transition behavior, ionic conductivity, lithium-ion transference number (tLi+), electrochemical stability, and with particular attention to the interfacial behavior between lithium electrode and SPEs. It has been demonstrated that the ionic conductivities of LiFSI/PEO electrolyte are higher than those of LiTFSI/PEO one above 60 °C, and exceeds 10−3 S cm−1 at 80 °C. The interface resistances of Li symmetric cell (Li metal | polymer electrolytes | Li metal) using LiFSI/PEO electrolyte are much lower than those using LiTFSI/PEO. The Li/LiFePO4 cell using LiFSI/PEO electrolyte exhibits good cycling performance at 80 °C. These outstanding properties of the LiFSI/PEO electrolyte make it attractive as SPEs for Li battery.