Toward Low-Temperature Lithium Batteries: Advances and Prospects of Unconventional Electrolytes

Lithium batteries have been widely used in various fields such as portable electronic devices, electric vehicles, and grid storages devices. However, the low temperature-tolerant performances (-70 to 0 degrees C) of lithium batteries are still mainly hampered by low ionic conductivity of bulk electrolyte and interfacial issues. In general, there are four threats in developing low-temperature lithium batteries when using traditional carbonate-based electrolytes: 1) low ionic conductivity of bulk electrolyte, 2) increased resistance of solid electrolyte interphase (SEI), 3) sluggish kinetics of charge transfer, 4) slow Li diffusion throughout bulk electrodes. Meanwhile, conventional electrolytes have been close to the upper limit of optimum low-temperature performance owing to their intrinsic molecular structural properties. As a result, it is urgent to design unconventional electrolytes with lower melting point and higher ionic conductivity. Herein, the recent key advances in regard to unconventional electrolytes including fluorinated ester, ethyl acetate, gamma-butyrolactone, liquefied gas, ether, plastic crystal, and aqueous electrolytes are overviewed. Solvation structure modification and SEI optimization of unconventional electrolytes for low-temperature lithium batteries are focused. Finally, aiming at the deficiencies in current understanding, the inherent limitations and envision the future prospects of low-temperature lithium batteries are explored.