Anion‐Reinforced Solvation for a Gradient Inorganic‐Rich Interphase Enables High‐Rate and Stable Sodium Batteries

Abstract Metallic Na is a promising anode for rechargeable batteries, however, it is plagued by an unstable solid electrolyte interphase (SEI) and Na dendrites. Herein, a robust anion‐derived SEI is constructed on Na anode in a high‐concentration 1,2‐dimethoxyethane (DME) based electrolyte with a cosolvent hydrofluoroether, which effectively restrains Na dendrite growth. The hydrofluoroether can tune the solvation configuration of the electrolyte from three‐dimensional network aggregates to solvent–cation–anion clusters, enabling more anions to enter and reinforce the inner solvation sheath and their stepwise decomposition. The gradient inorganic‐rich SEI leads to a reduced energy barrier of Na + migration and enhanced interfacial kinetics. These render the Na||Na 3 V 2 (PO 4 ) 3 battery with an excellent rate capability of 79.9 mAh g −1 at 24 C and a high capacity retention of 94.2 % after 6000 cycles at 2 C. This highlights the modulation of the electrode–electrolyte interphase chemistry for advanced batteries.