Research Progress and Perspectives on High Voltage, Flame Retardant Electrolytes for Lithium-Ion Batteries

The electrolyte is an indispensable constituent in lithium ion batteries, and its role conducts electricity by means of the transportation of charge carries between the pair of electrodes. Its properties directly affect the energy density, cycle life and safety of the battery. However, there are two major challenges to using carbonate-based electrolytes in recent lithium ion batteries (LIBs) to further increase the energy density of the devices without compromising the safety. One is that carbonate- based electrolytes are not sufficiently stable at the positive electrode, and the other is their relatively high flammability. Therefore, developing high voltage and flame retardant electrolytes for LIBs is highly desired. Herein, we review the recent progress and challenges in new electrolytes, focusing on high-voltage electrolytes, flame retardant electrolytes and highly concentrated electrolytes. Among the reported electrolytes, highly concentrated electrolytes are worth a special attention, showing various unusual functionalities, for example, high oxidative stability, low volatility, high reductive stability, and non-corrosive to Al. These special properties are totally different from that of the conventional 1 mol•L^-1 LiPF₆/EC-based electrolytes, which are result from solution structures. A discussion is also provided in this review on the prospects of further development of new electrolytes for LIBs.