Deciphering the Role of Crystallinity in Polysulfides Conversion: Defect-Rich Amorphous Co₃S₄ for Accelerated Li–S Chemistry

Li–S batteries (LSBs) are promising next-generation energy storage systems; however, their practical application is severely hindered by the shuttle effect of soluble lithium polysulfides and sluggish redox kinetics. Although separator functionalization with catalytic materials has been widely explored, the fundamental role of crystallinity in governing polysulfide conversion remains insufficiently understood. Herein, the effect of crystallinity on polysulfides regulation is systematically investigated using Co₃S₄ as a model system. Amorphous Co₃S₄ (A-Co₃S₄) and crystalline Co₃S₄ (C-Co₃S₄) are deliberately constructed to establish a direct structure–property correlation. Compared with its crystalline counterpart, A-Co₃S₄ features a disordered atomic configuration with abundant coordination-unsaturated sites and defect-induced electronic states, enabling stronger polysulfides adsorption and accelerated catalytic conversion. When integrated onto a polypropylene separator, the A-Co₃S₄-based interfacial layer effectively suppresses polysulfide migration, enhances interfacial charge transfer, and promotes ion transport kinetics. As a result, the A-Co₃S₄@PP-based cell delivers an initial capacity of 748 mAh g⁻¹ at 1 C and maintains 537 mAh g⁻¹ after 1000 cycles, corresponding to a low capacity decay rate of 0.02% per cycle. This work clarifies the critical role of crystallinity in polysulfide conversion and provides fundamental insights into the rational design of defect-engineered catalytic interfaces for advanced LSBs.