Doping in Solvation Structure: Enabling Fluorinated Carbonate Electrolyte for High-Voltage and High-Safety Lithium-Ion Batteries

Operating a Ni-rich cathode beyond 4.3 V safely holds promise for boosting the energy density in lithium-ion batteries (LIBs). Methyl 2,2,2-trifluoroethyl carbonate (FEMC) shows oxidative stability and high safety but suffers from degraded LUMO energy levels once coordinated with Li+ within electrolytes. Here, we utilize propylene carbonate (PC) as a functional dopant, which deliberately tunes the FEMC-dominated solvation chemistry and improves LUMO energy levels by dipole–dipole interaction and microsolvating competition. As a result, the optimized electrolyte demonstrates an expanded electrochemical window (4.7 V for NCM811), fire resistance, and a wide liquid range (−60–120 °C), affording 75.6% capacity retention in 1.2 Ah NCM811/graphite pouch cells over 1200 cycles. This "doping strategy" is generalized to other electrolytes (e.g., carbonates, fluorinated esters, and carboxylic esters) and qualifies as ameliorated interfacial compatibility, providing insights for designing a high-safety electrolyte in high-energy LIBs.