Modulation of Surface/Interface States in Bi ₂ S ₃ /VS ₄ Heterostructure With CN Layer for High‐Performance Sodium‐Ion Batteries: Enhanced Built‐in Electric Field and Polysulfide Capture

Abstract Metal sulfides are promising materials for sodium‐ion batteries (SIBs) owing to unique structures and high theoretical capacity. However, issues like poor conductivity, large volume changes, and polysulfide dissolution limit practical application. This study introduces a novel Christmas tree‐like heterostructure composed of Bi ₂ S ₃ and VS ₄ encapsulated in nitrogen‐doped carbon shell (Bi ₂ S ₃ /VS ₄ @CN), synthesized by sulfurizing dopamine‐coated BiVO ₄ precursor. The in situ synthesis ensures excellent lattice matching between Bi ₂ S ₃ and VS ₄ , minimizing interface states and enhancing effective built‐in electric field. This design accelerates electrochemical reaction kinetics; moreover, it promotes progressive reaction that mitigates structural fragmentation, suppresses degradation, and prevents polysulfide dissolution and shuttle. Additionally, the CN shell effectively passivates the surface states of Bi ₂ S ₃ and VS ₄ nanostructures, lowering surface barrier and improving overall conductivity. As a result, Bi ₂ S ₃ /VS ₄ @CN‐based half‐SIBs demonstrate remarkable long‐cycle stability, maintaining 387.1 mAh g ⁻¹ after 1600 cycles at 2 A g ⁻¹ , and excellent rate performance with 376.3 mAh g ⁻¹ at 5 A g ⁻¹ . Full‐SIBs using Na ₃ V ₂ (PO ₄ ) ₃ //Bi ₂ S ₃ /VS ₄ @CN exhibit outstanding cycling stability, retaining 117.2 mAh g ⁻¹ after 200 cycles at 1 A g ⁻¹ , along with 218 Wh kg ⁻¹ high energy density at 145.3 W kg ⁻¹ . This work highlights the potential of heterostructures in advancing metal sulfide‐based SIBs for high‐performance energy storage.