Thermoresponsive Mono-Solvent Electrolyte Inhibiting Parasitic Reactions for Safe Lithium Metal Batteries

Solvents in liquid and gel polymer electrolytes are recognized for contributing to high ionic conductivity in high-energy-density lithium metal batteries. However, parasitic reactions involving solvents and lithium metal induce safety risks under thermal abuse conditions and poor lifespan during room-temperature cycles, which are rarely investigated. This study introduces a thermoresponsive mono-solvent electrolyte as a built-in safety switch. The mono-solvent electrolyte polymerizes at elevated temperatures, creating a passivate polymer network without residue solvents. The polymer exhibits high thermal stability with 91% mass retention at 200 °C and significantly suppresses side reactions between lithium metal and the electrolyte, reducing thermal runaway risks. Ah-level Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 pouch batteries employing this electrolyte can efficiently improve the critical temperature of thermal runaway by 75 °C compared to the thermoresponsive gel polymer electrolyte. At ambient temperatures, the electrolyte promotes the formation of a stable solid electrolyte interphase (SEI) rich in LiF and Li 2 O, effectively reducing side reactions and dendrite growth on the lithium anode. Consequently, Li||LiNi 0.5 Co 0.2 Mn 0.3 O 2 cells retain 91% capacity after 152 cycles, even under high-loading cathodes (19.7 mg cm −2 , 3 mAh cm −2 ). This research offers valuable insights into inhibiting parasitic reactions during the electrochemical cycle and thermal runaway, enhancing the lifespan and safety of high-energy-density batteries.