Strengthening coordination for electrolyte diluent via dipole polarization enables rapid Na+ solvation/desolvation kinetics

Local high concentration electrolytes (LHCEs) have great potential for sodium-ion batteries (SIBs) owing to their anion-enriched solvation structures that facilitate the formation of inorganic-rich solid electrolyte interphases (SEIs). However, insufficient solvent-cation interactions in solvation structure inherently lead to limited ion migration kinetics and compromised electrolyte thermodynamics. Here, we report a novel LHCE design employing methyl 2,2,2-trifluoroethyl ester (FEMC) as a functional diluent. The dipole-dipole interaction between FEMC and ethylene carbonate (EC) induces the electrons polarization of fluorine atoms toward carbonyl group in FEMC, thereby strengthening the coordination ability of FEMC. The solvation structure, maintaining more anion participation, with enhanced FEMC diluent coordination significantly improves ion migration kinetics and derives a stable inorganic-rich (NaF/Na x PO y ) SEI, effectively mitigating cell interfacial concentration polarization. This reconfigured LHCE enables hard carbon (HC) anode to deliver a remarkable specific capacity of 287.00 mAh g −1 with 80.1 % capacity retention over 1000 cycles under 0.1 A g −1 and achieve extraordinary cycling stability over a wide temperature range. This work provides a new insight into designing electrolyte solvation structure via intermolecular dipole-dipole interactions.