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 (LiBF4) are promising salts for lithium-ion batteries owing to their unique characteristics. In this work, the electrochemical behaviors of blend salts of LiODFB and LiBF4 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/LiBF4 (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 degrees 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, LiBF4 as well as functional solvent on optimization of low-temperature performance is discussed. (C) 2017 The Electrochemical Society. All rights reserved.