Flame-Retardant Local High-Concentration Electrolyte for High-Voltage Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been widely applied in electric vehicles, smart grids, and other fields due to their high energy density and long cycle life. However, the flammability of conventional carbonate-based electrolytes poses significant safety risks and hinders the large-scale deployment of high-energy-density batteries. Herein, we propose a nonflammable carbonate-based local high-concentration electrolyte (LHCE) composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/fluorinated ethylene carbonate (FEC)/1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). This formulation replaces highly flammable conventional solvents with FEC and highly fluorinated TTE, substantially reducing fire hazards. The electrolyte exhibits an electrochemical window up to 5.5 V. Synergistic interactions between TFSI⁻ anions and FEC facilitate the formation of a robust, LiF-rich solid electrolyte interphase (SEI) on the graphite (Gr) anode and an effective cathode electrolyte interphase (CEI) on the high-voltage LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode, suppressing structural degradation and transition metal dissolution. Consequently, the NCM811||Gr full battery using LHCE demonstrates superior cyclability, with a capacity loss below 8% over 200 cycles at a high cutoff voltage of 4.5 V and an average coulombic efficiency (CE) of 99.9%. This work provides a promising electrolyte design for stable and safe high-voltage LIBs, offering potential guidance for advanced battery systems.