Chalcogen-Directed Dual-Heterointerfaced Bi₂Te₃/BiS_x in N-Doped Carbon Nanofibers for Sodium Storage

Developing anode materials with both high volumetric capacity and robust cycling stability remains a critical challenge for sodium-ion batteries (SIBs). Bismuth (Bi) offers promise due to its high theoretical volumetric capacity and suitable sodiation potential, yet its practical application is hindered by severe volume expansion during cycling. Herein, we report a rationally engineered dual heterointerfaced system of crystalline/amorphous Bi₂Te₃/BiS_x encapsulated in N-doped porous carbon nanofibers (Bi₂Te₃/BiS_x@NPCNFs), prepared via electrospinning coupled with in situ tellurization/sulfidation. The dual heterointerfaces-spanning both crystalline-amorphous and chalcogen-domain junctions of Bi₂Te₃/BiS_x synergistically enable fast charge transport, effective strain buffering, and stable structural integrity, while the conductive carbon matrix with Te vacancies further enhances electronic conductivity. As an anode for SIBs, the optimized Bi₂Te₃/BiS_x@NPCNFs deliver exceptional performance, including a high reversible capacity (341.6 mAh g^-1 at 0.1 A g^-1), excellent rate capability (263.4 mAh g^-1 at 2 A g^-1), and long-term cycling stability (288.7 mAh g^-1 after 1000 cycles at 1 A g^-1). Ex situ spectroscopy and microscopy elucidate the reversible phase evolution and sodium storage pathways, highlighting the critical role of dual heterointerfaces and defect engineering. This work establishes a general strategy for advancing high-energy, long-life sodium-ion batteries by exploiting dual crystalline/amorphous and chalcogen heterointerfaces within nanostructured composites.