Solvation Stabilization via Non-Coordinating Benzotrifluoride for High-Voltage Sodium-Ion Batteries

Developing high-energy sodium-ion batteries (SIBs) with layered cathodes at elevating voltage is hindered by the trade-off between the oxidative resistance and the sluggish ion kinetics of viscous fluorinated electrolytes. Here, we introduce benzotrifluoride (BTF) as a non-coordinating diluent in a fluorinated carbonate electrolyte to regulate the solvation structure. Through steric and dipolar effects, BTF promotes the participation of fluorinated carbonates in the primary solvation sheath while retaining controlled anion involvement. This reconstructed solvation environment simultaneously accelerates bulk ion transport and facilitates the formation of a robust, fluorine-rich cathode electrolyte interphase (CEI), enabling oxidative resistance beyond 5 V and optimized ionic conductivity. When adapting this electrolyte, the NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) cathode delivers a discharge capacity of 147.6 mAh g −1 at 4.2 V with improved cycling stability compared to baseline fluorinated electrolytes. This work demonstrates the efficacy of aromatic diluent-mediated solvation engineering for SIBs.