A fluorinated phosphite enabling safe low‐concentration Li‐ion electrolytes via radical capture and weak solvation

Abstract Low‐concentration electrolytes (LCEs) offer economic benefits for lithium‐ion batteries (LIBs) but suffer from poor conductivity, interfacial instability and safety risks. Here we show that tuning additive molecules for electrophilic radical capture and weak Li + solvation effectively overcomes these limitations. A rationally designed fluorinated phosphite, tris(2,2,2‐trifluoroethyl)phosphite (TTFPi), exhibits strong radical‐quenching capability enabled by a negative hyperconjugation effect (LP(P) → σ*(C–O)), which promotes rapid bond cleavage and enhances flame retardancy. Meanwhile, the absence of a P=O group and perfluorination markedly weaken its interaction with Li + , confining TTFPi to outer solvation sheath. TTFPi further weakens Li + ‐solvent interactions via dipole coupling, increases ion aggregates and induces a stable inorganic‐rich interface. The resulting 0.75 M electrolyte enables an NCM811||graphite pouch cell to retain 85.9% capacity after 1200 cycles, with a high thermal runaway temperature of 266.0°C and stable operation from −20 to 55°C, providing a promising approach for high‐safety LCEs for LIBs.