Artificial Interface Layer for Long-Life Performance NASICON-Based Sodium-Ion Solid-State Batteries

Significant interest has been directed toward sodium metal batteries owing to their high theoretical specific capacity, low cost, and abundant resources. However, the high reactivity of sodium metal leads to dendrite growth and uncontrolled solid electrolyte interphase (SEI) formation, resulting in safety risks and increased impedance. In this work, a zinc–magnesium codoped Na3.65Zr1.675Zn0.2Mg0.125Si2PO12 (NZZMSPO, SE) solid electrolyte with high Na+ conductivity was synthesized. A facile solution-coating method enabled uniform surface modification, allowing in situ formation of a stable artificial SEI at the solid electrolyte|sodium metal interface. This protective layer effectively stabilizes the interface and markedly enhances cycling stability, elucidated by density functional theory (DFT) calculations. Sodium symmetric cells with the artificial SEI exhibited lifetimes exceeding 1200 h at 0.3 mA cm–2, attributed to suppressed dendrite growth and regulated SEI formation. Full cells using Na4Fe3(PO4)2P2O7 cathodes delivered a specific capacity of 78.82 mAh g–1 with 89% capacity retention after 200 cycles, demonstrating the broad potential of this artificial SEI strategy for solid-state sodium-ion batteries.