An Inorganic Interface Protection Layer Enabling Coupled Charge Transport for Stable Sodium Metal Anodes

Sodium (Na) metal anodes have garnered significant interest for advanced rechargeable batteries owing to their key attributes of their high theoretical specific capacity and low electrochemical potential. Unfortunately, its practical deployment remains limited by poor cycling stability and serious safety risks, stemming from an unstable solid electrolyte interphase (SEI) and uncontrolled dendrite growth. Herein, a bifunctional Na3P/Na3Sb (NPS) interfacial layer was formed on the Na metal surface (denoted as NPS@Na) via an in situ spontaneous chemical reaction between metallic Na and a red P/Sb powder mixture. The high ionic conductivity of Na3P facilitates Na-ion transport, while Na3Sb acts as an electron-blocking barrier, effectively decoupling ion and electron transport across the interface. This separation of charge carriers eliminates the tip effect, promotes uniform Na deposition, and reduces parasitic reactions with the electrolyte. Furthermore, the mechanically robust NPS interfacial layer physically suppresses dendrite penetration and maintains the interfacial integrity during cycling, allowing Na to be plated beneath the interfacial layer. As a result, the Na3V2(PO4)3||NPS@Na full cell maintains stable cycling with a high capacity retention of 80.09% after 500 cycles at 10 C. These findings provide a blueprint for designing high-performance artificial interfacial layers for alkali metal anodes.