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_0.8Co_0.1Mn_0.1O₂ 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 Li₂O, effectively reducing side reactions and dendrite growth on the lithium anode. Consequently, Li||LiNi_0.5Co_0.2Mn_0.3O₂ 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.