Rational Construction of Sulfur-Deficient NiCo₂S_{4- x}Hollow Microspheres as an Effective Polysulfide Immobilizer toward High-Performance Lithium/Sulfur Batteries

The synergistic strategy combining architectural design with defect engineering in transition-metal sulfides offers a promising opportunity to realize high-efficiency polysulfide adsorption/conversion surface catalysis in lithium/sulfur (Li/S) batteries. Here, defect-rich yolk-shell hollow spheres composed of ultrafine NiCo2S4-x nanoparticles as sulfur hosts prepared by an anion-exchange method are reported. The elaborate design of sulfur defects endows the NiCo2S4-x hollow spheres with significantly enhanced electronic conductivity and superior affinity for polysulfides as well as expedited sulfur conversion. Meanwhile, the unique yolk-shell NiCo2S4-x hollow sphere structure provides large cavities that not only increase sulfur storage but also relieve the electrode volume expansion during cycling. Combining these favorable features, the NiCo2S4-x-hosted sulfur cathode revealed enhanced cycling stability, corresponding to a negligible capacity fading rate of 0.0754% per cycle after 500 cycles at 1 C, and achieved an outstanding rate capability (628.9 mAh g-1 up to 5 C).