Molecular Engineering on Solvation Structure of Carbonate Electrolyte toward Durable Sodium Metal Battery at −40 °C

Abstract Carbonate electrolytes have excellent chemical stability and high salt solubility, which are ideally practical choice for achieving high‐energy‐density sodium (Na) metal battery at room temperature. However, their application at ultra‐low temperature (−40 °C) is adversely affected by the instability of solid electrolyte interphase (SEI) formed by electrolyte decomposition and the difficulty of desolvation. Here, we designed a novel low‐temperature carbonate electrolyte by molecular engineering on solvation structure. The calculations and experimental results demonstrate that ethylene sulfate (ES) reduces the sodium ion desolvation energy and promotes the forming of more inorganic substances on the Na surface, which promote ion migration and inhibit dendrite growth. At −40 °C, the Na||Na symmetric battery exhibits a stable cycle of 1500 hours, and the Na||Na 3 V 2 (PO 4 ) 3 (NVP) battery achieves 88.2 % capacity retention after 200 cycles.