Optimization of Yolk–Shell NiCo₂S₄ Spheres as Catalysts for High-Performance Rechargeable Li–O₂ Batteries

Development and practical applications of rechargeable Li–O2 batteries call for efficient cathode electrocatalysts. Recently, spinel sulfides with controlled morphology and structure attracted increasing attention and demonstrated promising electrocatalytic performance. In this work, yolk–shell-structured NiCo2S4 (YS-NCS) spheres were synthesized by a simple solvothermal method with various sulfidation times, and the effects of sulfidation time on the yolk–shell morphology and catalytic performance of YS-NCS materials as cathode catalysts for Li–O2 batteries were comparatively investigated. The results indicated that 18 h is the optimal sulfidation duration to synthesize YS-NCS spheres with the best catalytic performance, and the battery with YS-NCS-18 as the catalyst could deliver the highest specific capacity, the best rate capability, and the most stable cycling performance, owing to its largest gap between the yolk and shell and the highest catalytic activity of the (531) surface as verified by the transmission electron microscopy characterizations and density functional theory calculations. This work provides a simple and effective strategy for improving the catalytic activity of yolk–shell-structured metal sulfides as cathode catalysts for Li–O2 batteries.