Unveiling the cathode compatibility of diglyme-based electrolytes in Na₃V₂(PO₄)₃ sodium-ion batteries

Ether-based electrolytes are attractive for sodium-ion batteries (SIBs) due to their good compatibility with hard‑carbon anodes, but their oxidative stability on cathodes remains a concern. Herein, carbonate-based (ethylene carbonate (EC)/diethyl carbonate (DEC) and ether-based (diglyme) electrolytes are systematically compared in Na₃V₂(PO₄)₃ (NVP)-based SIBs. Although diglyme shows a higher tendency toward initial oxidation, it forms a thin, uniform, and organic-rich cathode electrolyte interphase (CEI) on NVP, which suppresses continuous electrolyte decomposition and lowers interfacial resistance. As a result, NVP/Na half-cells with the diglyme-based electrolyte deliver 105.4 mAh·g^-1 after 430 cycles with 96.3% capacity retention and retain 83.4 mAh·g^-1 at 9C, outperforming the EC/DEC-based counterpart. Sodium-replacement experiments confirm that the improvement arises from both enhanced sodium-metal compatibility and stabilized NVP cathode interface. Moreover, NVP/spherical hard carbon (s-HC) full cells using the diglyme-based electrolyte exhibit higher initial coulombic efficiency (CE), better cycling stability, and lower polarization. This work demonstrates the feasibility of diglyme ether-based electrolytes for moderate-voltage sodium-ion cathodes and highlights the importance of electrolyte-derived CEI chemistry in electrolyte design.