Robust Na ₂ ZrF ₆ Artificial Interphase for Durable and High‐Rate Sodium Metal Anodes

ABSTRACT With high theoretical specific capacity and abundant raw materials, metallic sodium has become an extremely appealing anode candidate for sodium‐metal batteries (SMBs). Nonetheless, its commercial application is limited by the interfacial instability and severe dendritic growth. Constructing a functional artificial interface can effectively regulate the growth behavior of sodium metal and stabilize the anode in SMBs. In this work, we fabricated a strong and multifunctional Na 2 ZrF 6 artificial interphase on the surface of the sodium anode using a simple drop‐casting method. Combined experimental results and theoretical simulations show that the Na 2 ZrF 6 interphase could mitigate electric field concentration, weaken the sodium nucleation potential barrier, and accelerate ion transport, thus guiding uniform sodium deposition without dendrite formation. Furthermore, the excellent mechanical stability of the Na 2 ZrF 6 interphase can reduce interface side reactions and limit excessively large expansion of the electrode. Based on these merits, the Na 2 ZrF 6 ‐Na symmetric cell exhibits excellent long‐term cycling properties and can maintain a steady state for more than 800 h at a current density up to 8 mA cm −2 . The Na 3 V 2 (PO 4 ) 3 ||Na 2 ZrF 6 ‐Na full cell delivers superior capacity retention of 95.3% after 1200 cycles at 10 C with a high cathode loading of 10 mg cm −2 .