Fluorinated Solvent Molecule Tuning Enables Fast‐Charging and Low‐Temperature Lithium‐Ion Batteries

Abstract

AbstractPopularly‐used fluorination can effectively weaken Li+‐solvent interaction to facilitate the desolvation process at low temperature; however, high fluorination degree sacrifices salt dissociation and ionic conductivity. Herein, functional fluorinations are well tuned with different amounts of F atoms to balance Li+‐solvent binding energy and ion movement, which reveals the fluorination effect on the solvation behavior and low‐temperature performance. Noteworthily, the moderately‐fluorinated ethyl difluoroacetate (EDFA) successfully favors a lower binding energy than less‐fluorinated ethyl fluoroacetateand superior salt dissociation more than highly‐fluorinated ethyl trifluoroacetate, realizing the trade‐off between weak affinity and sufficient ionic conductivity. The well‐formulated EDFA‐based electrolyte exhibits a unique solvation sheath and generates inorganic‐rich solid electrolyte interphase with low resistance for smooth Li+ diffusion, which enables graphite anodes with excellent fast‐charging capability (196 mAh g−1 at 6 C) and impressive low‐temperature performance with a reversible capacity of 279 mAh g−1 under −40 °C. Subsequently, the wide electrochemical potential window of EDFA‐based electrolyte endows the 1.2 Ah LiNi0.8Co0.1Mn0.1O2 (NCM811)||graphite pouch cells with a high reversible capacity retention of 58.3% at −30 °C and discharge capacity of 790 mAh at −40 °C. Such solvent molecules with a moderately‐fluorinated strategy promise advanced electrolyte design for lithium‐ion batteries operating under harsh conditions.