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

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.