Nonflammable Electrolyte Interfacial and Solvation Chemistry for High‐Voltage Sodium Metal Batteries

Abstract High‐voltage sodium metal batteries exhibit excellent advantages in low cost and high energy density. However, the poor compatibility of the traditional electrolyte with sodium (Na) anode and high‐voltage cathode leads to interfacial instability and potential flammable risks. In this work, a nonflammable electrolyte is developed to address the cycling stability of 4.7 V sodium metal battery by constructing electrode–electrolyte interphases with sodium perchlorate (NaClO 4 ) additive. The NaClO 4 additive not only enables efficient Na plating/stripping with an average Coulombic efficiency of 97.1% in Na||Cu cells, but also enhances the high‐voltage stability of Na||Na 3 V 2 (PO 4 ) 2 O 2 F batteries with capacity retention of 97.9% after 200 cycles. The superior performance is attributed to the high ion‐conductivity solid/cathode electrolyte interphases, which are tuned by the solvation shell with NaClO 4 .