Regulating Interface Chemistry with Topological Insulator for Ultra‐Stable and Dendrite‐Free Sodium Metal Batteries

Metallic sodium (Na) is an attractive anode material for sodium metal batteries (SMBs) due to its high theoretical capacity and natural abundance. However, the unstable electrolyte/electrode interface and uncontrollable Na dendrite growth arising from the inhomogeneous Na⁺ transfer have significantly restricted its practical feasibility. Herein, the topological insulator of bismuth selenide (Bi₂Se₃), which has protected conducting states on its surface, is selected as a regulator to guide uniform Na⁺ transfer. An in situ conversion/alloying reaction between Bi₂Se₃ and Na can construct a multifunctional heterogeneous interlayer composed of sodium bismuth alloy (Na₃Bi) and sodium selenide (Na₂Se). Such a heterogeneous interlayer with excellent sodiophilic capability and superior ionic conductivity can facilitate rapid Na⁺ diffusion and guide uniform Na deposition. Consequently, the Bi₂Se₃-Na symmetric cell achieves an ultralong cycling lifespan over 2100 h at 1 mA cm^-2/1 mA h cm^-2 with extremely low voltage hysteresis of 14 mV. In addition, the Bi₂Se₃-Na||Na₃V₂(PO₄)₃ (NVP) full cell exhibits a high-capacity retention of 93.7% after 1500 cycles at a high current density of 20 C. More impressively, the constructed anode-free Bi₂Se₃-Cu||NVP cell demonstrates excellent cycling stability (75.1 mA h g^-1 at 1 C after 100 cycles).