The effect of lithium salts in electrolytes on the high-temperature performance of LiFePO₄ electrode is investigated systematically and the related mechanism is revealed. Differential scanning calorimetry measurements show that lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and LiBF₄ are more favorable for the use at high temperature than LiPF₆ because of their water insensitivities and excellent thermal stabilities. Inductively coupled plasma is used to examine the dissolving degree of ferrous ions from LiFePO₄ in the different electrolytes at 55 ℃. It is found that little ferrous ions can be dissolved from LiFePO₄ in LiTFSI and fluorine-free lithium salt electrolytes. On the contrary, it is quite serious in LiPF₆ electrolyte. In addition, FePO₄ is easier to release iron ions than LiFePO₄ in the LiPF₆ electrolyte. The experimental results of cyclic voltammetry and light microscope indicate that a small amount of LiBF₄ can inhibit the corrosion of aluminum foil current collector from LiTFSI. The electrolyte containing mixed salts of LiTFSI and LiBF₄ significantly improves the high-temperature performance of LiFePO₄/Li cell. The discharge capacity is still 147.7 mAh/g after 40 cycles at 55 ℃ and 1 C rate.

Key words: electrolyte, lithium bis(trifluoromethylsulfonyl)imide, LiFePO₄, iron dissolution, high- temperature performance