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

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. SbF₃ was spin-coated onto Na_3.4Zn_0.2Zr_1.8Si_2.2P_0.8O₁₂ (NZZP) electrolyte surface and then converted to the Na₃Sb/NaF (NSF) composite interlayer via the reaction with Na. Na₃Sb 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 cm², 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 Na₃V₂(PO₄)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.