Homogeneous and Mechanically Stable SEI Enables Sodium‐Metal Batteries for Extreme Working Conditions

Abstract Sodium metal has attracted considerable interest as an anode for next‐generation high‐energy‐density sodium‐metal batteries, owing to its superior specific capacity, low electrochemical potential, and economic viability. Despite the advantages, sodium‐metal anodes encounter critical challenges, such as side reactions and dendrite growth, which diminish Coulombic efficiency and compromise long‐term cycling performance. In this work, a multifunctional artificial NaF‐Zn hybrid interfacial layer is in situ formed on the sodium metal surface. Both NaF and Zn exhibit strong binding affinity for PF ₆ ⁻ , which facilitates Na ⁺ desolvation and accelerates the formation of a homogeneous and NaF‐rich solid‐electrolyte interphase (SEI). The resulting homogeneous and mechanically stable SEI enhances Na ion transport, reduced the side reactions and suppresses the dendrite formation. Consequently, the symmetric cells based on NaF‐Zn modified Na operate stably for 1900 h at a high current density of 3 mAh cm ⁻² , while the full cell with Na ₃ V ₂ (PO ₄ ) ₃ cathode maintains stability for 8000 cycles at a high rate of 20C with a capacity retention of 75%. Moreover, the full cell demonstrated outstanding stability even under extreme working conditions, including low temperatures of −20 °C, high cathode loading, and reduced N/P ratios.