A safe electrolyte for high-performance lithium-ion batteries containing lithium difluoro(oxalato)borate, gamma-butyrolactone and non-flammable hydrofluoroether

A safe electrolyte of lithium difluoro(oxalato)borate in the mixture of gamma-butyrolactone and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is initially proposed in this work. This electrolyte owns higher safety level and better wettability than a commercial electrolyte. Its conductivity reaches 7.12 mS cm−1 at 25 °C. The remarkable electrochemical performances of graphite/LiNi0.5Co0.2Mn0.3O2 full cells with this safe electrolyte are confirmed. Its cycling and rate performances present well at room temperature (25 °C). Meanwhile, high-temperature and low-temperature performances of the full cells with this safe electrolyte also surpass those of the cell with a commercial electrolyte. The capacity retention of the full cell with this safe electrolyte reaches 82.2% after the prolonged cycle test (500 cycles at 1 C and 25 °C). And its capacity retention of 100 cycles at 1 C is up to 87.1% at elevated temperature (60 °C). In particular, the cell still has a capacity of about 100 mAh g−1 at -40 °C. The potential of this safe electrolyte for practical application has been proved by the test results.