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).