Fabrication of a Mechanically Robust Solid‐Electrolyte Interphase on Sodium‐Metal Anodes by Anion Modulation for Ambient Sodium‐Air Batteries

Abstract The stabilization of metallic‐Na anodes by the fabrication of a mechanically stable solid‐electrolyte interphase (SEI) can enable the construction of stable Na‐air batteries (NABs) that can be used as practicable energy‐storage devices in ambient air. This study reports in situ fabrication of air‐stable Na anodes protected by SEI films for stable NABs. The regulation of anions in the electrolyte generated hierarchically layered SEI on Na anodes; the sequential deposition of inorganic salts and organic components is modulated by controlling the competitive reduction of salt and solvent molecules on the Na surface. Metallic‐Na anodes with hierarchical SEI comprising an outer salt‐rich and inner organic‐component‐rich layer showed highly reversible stripping/plating. The high stability of the SEI layer in ambient air can be attributed to synergism between its hydrophilic inorganic and hydrophobic organic components. NABs with hierarchical‐SEI‐modified Na anodes showed stable cycling for >1900 h in ambient air. This study can guide the design of stable metallic anodes and facilitate the future development of diverse Na‐based rechargeable batteries.