Non-flammable super-concentrated polymer electrolyte with “solvated ionic liquid” for lithium-ion batteries

The ambient temperature application of PEO-based polymer electrolytes has been restrained by their poor ionic conductivity. Herein, we report a super-concentrated polymer in "solvated ionic liquid" which is composed of polyethylene oxide (PEO), LiN(SO2CF3)2 (LiTFSI), and solvent with low viscosity. It is found that the maximum coordination during Li, polymer, and the solvent can be formed by the molar ratio of PEO/Li = 1:1 with 25 wt% of solvent, left no free solvent exits in the mixture. The electrochemical performance of the designed electrolyte was evaluated by using a LiFePO4/Li cell. Comparing to the conventional carbonate liquid electrolyte, the designed electrolyte achieves comparable rate performance (155.4 and 157.8 mAh g−1 discharge at 1 C for the designed and carbonate electrolyte, respectively) and higher cycle performance (capacity retention of 95.5% and 75.5% after 100 cycles for the designed and carbonate electrolyte, respectively). It has been further proven that incombustibility can be obtained by only adding ~15 wt% fire-retardant. We believe that the developed electrolyte is promising and practical for being applied in the polymer lithium-ion battery.