Extending Ether-Based Electrolyte toward High-Voltage Sodium Batteries via Reduction-Derived Cathode–Electrolyte Interphase Engineering

High-voltage sodium batteries have attracted extensive attention due to their high energy density and low cost while imposing stringent requirements on electrolytes with wide electrochemical windows. The cathode–electrolyte interphase (CEI) can mitigate the potential difference between two phases, with its interfacial chemistry and physicochemical properties hinged largely on the electrolyte decomposition mechanism. Herein, a prereduction strategy was performed to construct the inorganic-dominated CEI, which effectively improves the oxidation stability of the ether-based electrolyte from 3.9 to 4.5 V vs Na+/Na. Systematic investigations suggest that the organic components in reduction-derived CEI are ultimately oxidized via gas evolution without any electrolyte contamination. When evaluated in Na3V2(PO4)2F3 (NVPF)||Na cells, this strategy delivers significantly improved Coulombic efficiency and rate capability, retaining 86.2% capacity after 4000 cycles at 5 C. Overall, this work enhanced the oxidation resistance of the ether-based electrolyte without solvent regulation, offering a strategy for their practical application in high-voltage sodium batteries.