Flame Suppression in Lithium-Ion Batteries During Thermal Runaway Through Solvent Design Considering the...

An asymmetric sulfonate-based linear solvent, 2,2,2-trifluoromethyl mesylate (FMS), is designed and used as the primary solvent in liquid electrolytes to enhance the thermal safety of lithium-ion batteries (LIBs). The highly polar FMS molecule, composed of trifluoroethyl and methyl groups asymmetrically bound to a sulfonate core, significantly suppresses solvent vaporization and shows a significantly higher flash point than the conventional LIB solvent dimethyl carbonate. Low volatility contributes to the non-flammability of the FMS electrolyte. Upon electrochemical cycling, the FMS-based electrolyte facilitates the formation of thermally stable SO_x-containing passivation films on both graphite and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) electrodes. These robust interfacial films effectively suppress side reactions, reduce self-discharge-induced heat accumulation, and improve the overall thermal stability of the system under abusive conditions. Furthermore, the interfacial reinforcement and non-flammability of FMS effectively suppress the thermal propagation-induced flame hazard potential of LIBs. Without reducing the battery cycle life, the FMS electrolyte improves individual cell safety while effectively suppressing thermal propagation within stacked batteries. Additionally, the electrolyte formulation proposed in this study includes only fluoroethylene carbonate and LiPF₆, which are both compatible with commercial LIB systems, thereby exhibiting high potential practicability in real systems.