Sulfur Vacancy‐Regulated NiS ₂ /NiS Heterostructure for High‐Performance Sodium Storage

Abstract Conversion‐type transition metal sulfides for sodium‐ion batteries have attracted enormous attention due to their high theoretical capacities. However, the poor high‐rate performance and limited cycling stability hinder their application. In this study, NiS ₂ /NiS nanocomposite with sulfur vacancies (Vs‐NiS ₂ /NiS) is prepared. The presence of the vacancies significantly regulates the heterostructured interface between these two sulfides, and the corresponding density functional theory (DFT) calculations show improved electronic conductivity and reduced sodium diffusion barrier. As a result, the as‐prepared composite achieves high specific capacity of 590 mAh g ⁻¹ after 100 cycles at 0.5 Ag ⁻¹ , excellent rate performance with 447 mAh g ⁻¹ at 10 A g ⁻¹ , and long‐term cycling performance with 516 mAh g ⁻¹ after 1400 cycles at 8 A g ⁻¹ . Moreover, the assembled Vs‐NiS ₂ /NiS//Na ₃ V ₂ (PO ₄ ) ₂ F ₃ full‐cell shows a reversible capacity of 350 mAh g ⁻¹ after 200 cycles at 0.5 A g ⁻¹ and 180 mAh g ⁻¹ after 1000 cycles at 1 A g ⁻¹ , confirming its practicability.