Anion-coordination-driven solvation engineering tailoring electrolyte interphases for high-voltage, fast-charging sodium metal batteries.

Sodium metal batteries have emerged as compelling candidates for next-generation energy storage systems, by virtue of their high energy density and low cost. Their fast-charging capability under high-voltage operation, however, has remained severely constrained by the narrow electrochemical window of conventional electrolytes and the instability of the cathode electrolyte interphase (CEI). Herein, an electrolyte design strategy predicated on the reinforcement of anionic coordination through solvation-structure regulation was formulated. Distinct from the conventional preferential coordination between cations and solvent molecules, a novel anion-enhanced Na+ solvation structure has been judiciously engineered through the judicious deployment of a ternary anionic system. This strategy markedly reduces the Na+ desolvation energy barrier and accelerates interfacial charge-transfer kinetics, thereby endowing the batteries with exceptional fast-charging capability. Furthermore, an inorganic-rich and structurally robust CEI was preferentially constructed by this electrolyte, endowing the interphase with superior mechanical robustness and chemical stability. By virtue of this anion-enhanced solvation architecture, outstanding high-voltage and fast-charging performance was realized in the assembled full cell. Under a high cutoff voltage of 4.7 V, a capacity retention of 98% was sustained over 200 cycles at 0.5C, and a capacity retention of 94% was further delivered over 1000 cycles at a high rate of 5C.