Host–Guest Interactions for Electrochemically Stable and Thermally Safe Lithium Metal Batteries

Safety concerns have been a long-standing barrier hindering widespread applications of lithium metal batteries. Herein, we introduce host–guest interactions to regulate the working models of electrolytes with a built-in safety switch. At ambient temperature, the host–guest liquid electrolyte with high-concentration-electrolyte host and polymer monomer 1,1′-(methylenedi-4,1- phenylene)bismaleimide guest renders Li||LiNi0.5Co0.2Mn0.3O2 (3 mAh cm–2) coin battery 87% capacity retention after 210 cycles due to the regulations in the solvation structure and anode interface. When facing thermal safety hazards, polymer monomers undergo molecular conformation change. It rapidly constructs a thermally stable polymer matrix with various binding sites of lithium ions to host the high-concentration electrolyte, enabling batteries to work when they cool to room temperature. Under extreme abuse conditions, thermal runaway triggering temperatures of 2.0 Ah cycled pouch batteries are increased from 150 to 194 °C. The host–guest interactions are highly effective in constructing electrochemically stable and thermally safe lithium metal batteries.