Rational Design of Carbonate‐Ether Hybrid Electrolytes for High‐Voltage Sodium Metal Batteries

The distinct chemical properties of carbonate (high oxidation stability) and ether (high reduction stability) solvents pose a fundamental challenge in designing electrolytes capable of simultaneously stabilizing the sodium metal anode and high‐voltage cathodes. In this work, we report an ester‐ether hybrid electrolyte. By manipulating the solvation structure, intermolecular interactions between solvents weaken the coordination of C=O groups to Na + , which accelerates Na + transport and desolvation kinetics, significantly suppressing parasitic reactions. This strategy concurrently achieves a high ionic conductivity (8.62 mS cm −1 ) comparable to ester‐based electrolytes and superior oxidation stability (up to 4.84 V vs. Na + /Na). Synergistic additives fluoroethylene carbonate (FEC) and sodium difluoro(oxalato)borate (NaDFOB) induce the formation of a stable cathode electrolyte interphase rich in inorganic components. Consequently, the hybrid electrolyte enables stable sodium metal plating/stripping for 600 h in symmetric cells. More importantly, Na 3 V 2 (PO 4 ) 2 F 3 (NVPF),| Na full cells (operating at ~4.30 V) deliver exceptional cycling stability, retaining 90.51% capacity after 1100 cycles at 500 mA g −1 (ultralow average capacity decay rate of 8.48 × 10 −3 % per cycle) and achieve an energy density of 420 Wh kg −1 under low current densities. This work provides an efficient electrolyte solution for high‐voltage sodium‐metal batteries.