Mixed Salts of Lithium Difluoro (Oxalate) Borate and Lithium Tetrafluorobotate Electrolyte on Low-Temperature Performance for Lithium-Ion Batteries

The finding of appropriate electrolytes and applying them to low-temperature lithium-ion batteries is of special interest. Lithium difluoro (oxalate) borate (LiODFB) and lithium tetrafluorobotate (LiBF 4 ) are promising salts for lithium-ion batteries owing to their unique characteristics. In this work, the electrochemical behaviors of blend salts of LiODFB and LiBF 4 with different mole ratio were studied by employment of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl sulfite (DMS) as mixed solvents in order to optimize the low-temperature performance for lithium-ion batteries. The results show that the electrolyte system of LiODFB/LiBF 4 (1:1, by molar)-EC/DEC/DMS (1:2:1, by volume) is the optimized electrolyte, and the discharge capacity of the electrodes in the optimized electrolyte is 82.5 mAh g −1 at −40°C, maintaining 55.7% of the room temperature capacity and nearly 100% of capacity retention for 50 cycles. The electrolyte exhibits not only excellent film-forming characteristics, but also low impedance of the interface film at low temperature. Especially, the action mechanism of LiODFB, LiBF 4 as well as functional solvent on optimization of low-temperature performance is discussed.