Stable Operation of High-Voltage Sodium-Ion Batteries via Cathode Interphase Reconstruction with Competitive Anion Coordination Chemistry

Abstract

High-voltage sodium-ion batteries (SIBs) have significant application prospects in low-cost energy-storage systems. However, their performance is limited by sluggish Na⁺ desolvation kinetics and the formation of an unstable cathode-electrolyte interphase (CEI) in traditional electrolyte systems. This study introduces an anionic competitive coordination strategy in which SO₂CF₃⁻ from sodium trifluoromethanesulfonate (NaSO₂CF₃), with delocalized electron structures, preferentially occupy the inner layer of the Na⁺ solvation sheath, replacing traditional sodium salt anions and solvent molecules to construct a highly dynamic solvation microstructure. This novel solvation structure facilitates Na⁺ ion desolvation and induces the formation of a thin and robust CEI rich in sulfur/fluorine-containing organic and inorganic species by regulating the interfacial decomposition pathway, thereby ensuring interfacial stability at a high voltage of 4.4 V. As a proof of concept, the optimized electrolyte effectively mitigates the structural degradation of high-voltage cathodes such as NaFe_1/3Ni_1/3Mn_1/3O₂ and Na₃V₂(PO₄)₂O₂F and simultaneously enhances their rate performance and cycling stability. Furthermore, NFN||hard carbon full cells incorporating the optimized electrode exhibit excellent cycling stability under a high mass loading. This study establishes an innovative electrolyte design paradigm that overcomes interface failure issues in high-voltage SIBs by precisely regulating the CEI composition and structure via anionic coordination chemistry.