The electrolyte optimum composition consists of 1mol/L LiTFSI in the [EMIM]+[TFSI]-mixed with EC and DMC in weight ratio of 60:20:20. The LiFePO4/Li cell using 1 mol/L LiTFSI/([EMIM]+[TFSI]-/EC/DMC) as electrolyte show that the first coulomb efficiency was 90% and the first discharge capacity was 168mAh g-1. The 15th reversible capacities were maintain 157mAh g-1at 0.2C. Compared with traditional organic electrolyte and pure IL electrolyte, IL-based mixed electrolyte have good coulomb efficiencies and higher charge and discharge performances. The lithium transference number of IL-based mixed electrolyte at room temperature are 0.59. Thermal stability of IL-based mixed electrolyte higher than traditional organic electrolyte, and show almost non-flammability by the burning tests.