Competitive Anionic Coordination in Polymer Electrolytes Enables Stable 4.5 V Sodium Metal Batteries via Dual‐Interphase Engineering

Abstract All‐solid‐state sodium metal batteries (ASSMBs) represent promising energy storage technologies owing to their high energy density and safety. However, electrode/electrolyte interfacial issues severely hinder high‐voltage ASSMB applications. Herein, the concept of anion receptor competitive coordination (ARCC) and a poly(ethylene oxide) (PEO) electrolyte (PFCE) containing sodium fluorophosphate (Na 2 FPO 3 ) is designed. This approach reveals the intrinsic correlation between the local coordination structure of PEO and high‐voltage interfacial stability, and achieves stable Na metal interfaces through electronic orbital modulation. Theoretical calculations and experiments demonstrate that strong ion‐dipole coordination between the FPO 3 2− electrophilic centers and PEO coupled with in situ decomposition forms a robust inorganic cathode‐electrolyte interface (CEI) framework comprising NaF, Na x PO y F z , and P‐O composites. Furthermore, the Na + ‐mediated anionic delocalized orbital hybridization in PFCE creates a chemically and mechanically stable solid electrolyte interface (SEI). Based on the anion coordination‐regulated electrolyte, Na||Na cells can cycle stably for 2000 h at 0.1 mA cm −2 with low interfacial polarization of 40 mV. Furthermore, PFCE exhibits a wide electrochemical window (>5 V vs. Na + /Na) and demonstrates impressive cycling stability in 4.5 V Na|Na 3 V 2 (PO 4 ) 2 O 2 F cells, retaining 84.43% capacity after 100 cycles. The ARCC strategy provides a promising pathway toward high‐energy‐density sodium metal batteries.