Sodiophilic and Electron‐Insulating Interphase for Stable Solid‐State Sodium Metal Batteries

ABSTRACT Sodium superionic conductor (NASICON)‐type solid‐state electrolytes (SSEs) are promising candidates for solid‐state sodium batteries (SSSBs) due to their high room‐temperature ionic conductivity and excellent chemical stability. However, their interphascial incompatibility with sodium metal anodes leads to poor contact, slow ion transport, and dendrite growth. In this work, we demonstrate a dual‐component interphase with both sodiophilicity and electron‐insulating capability to prolong the cyclability of SSSBs. SbF ₃ was spin‐coated onto Na _3.4 Zn _0.2 Zr _1.8 Si _2.2 P _0.8 O ₁₂ (NZZP) electrolyte surface and then converted to the Na ₃ Sb/NaF (NSF) composite interlayer via the reaction with Na. Na ₃ Sb exhibits high sodiophilicity, enhancing interphascial wettability. Meanwhile, NaF possesses a wide bandgap of 6.17 eV and high mechanical strength, blocking electron leakage and suppressing dendrite propagation. As a result, Na|NSF‐NZZP‐NSF|Na symmetric cells demonstrate ultra‐low interphascial resistance of 4.7 Ω cm ² , high critical current density of 2.2 mA cm ⁻² at 25°C and stable cycles over 2400 h at 0.5 mA cm ⁻² . Using Na ₃ V ₂ (PO ₄ ) ₃ (NVP) cathode, the solid‐state full cell displays an impressive capacity retention of 94.5% after 600 cycles at 2 C. This work provides a simple, effective, and scalable approach for constructing stable SSSBs.