Thermally Stable and Nonflammable Electrolytes for Lithium Metal Batteries: Progress and Perspectives

Lithium (Li) metal battery is considered as a promising next-generation high-energy-density battery system. Battery safety is a foundation for the practical applications of Li metal batteries. In addition to uncontrollable Li plating/stripping, however, the employment of solvents and Li salts with poor thermal stability and high flammability also induces potential safety hazards to Li metal batteries based on liquid electrolytes, which emerges as a challenging but uncompromising task for Li metal batteries. Therefore, it is of great significance to focus and improve the thermal stability and nonflammability of liquid electrolytes while maintaining its role in regulating the uniformity of Li deposition. Herein, the possible thermal runaway mechanism of Li metal batteries is first discussed, especially the difference from the thermal runaway mechanism of Li-ion batteries. Second, the measurement methods of thermal stability and nonflammability of liquid electrolytes are summarized, including the basic principles and application examples. Third, recent progress of nonflammable electrolytes for Li metal batteries is reviewed according to the types of electrolyte. Finally, the perspectives of further designing thermally stable and nonflammable electrolytes for Li metal batteries are presented.