Entropy‐Driven Nonflammable Low‐Temperature Alkali Metal Molten Salt Electrolytes for Lithium Metal Batteries

Abstract Lithium metal batteries (LMBs) are endowed with an intriguingly high energy density but suffer from continuous parasitic reaction with the electrolyte due to the high reactivity of the metallic Li. Molten salt electrolytes (MSEs) are emerging solutions for LMBs due to the combination of liquid fluidity and nonflammability, while the high melting temperature limits their further applications. Here a series of low‐melting‐point alkali metal MSEs is reported by simultaneously introducing the cationic and anionic entropy effects, which effectively reduces the melting point and enables the operating temperature of the LMBs down to 50 °C. The optimizing ternary alkali metal MSE with solvent‐free Li + coordination structure enables an inorganic rich electrolyte electrode interphase, and thus ensures the stable operation of LMBs using high‐voltage LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode over 200 cycles. This work deepens the fundamental understanding on the entropy effects during the salt melting process and provides a feasible approach on designing intrinsically nonflammable electrolytes for mitigating the safety issues of LMBs.