Hierarchical Co₉S₈@Carbon Hollow Microspheres as an Anode for Sodium Ion Batteries with Ultralong Cycling Stability

Herein, hierarchical Co₉S₈@carbon hollow microspheres (Co₉S₈@CHSs) were designed and facilely prepared via a simple solvothermal approach, following a thermal treatment process. The surfaces of the hierarchical Co₉S₈ hollow microspheres are homogeneously coated by a fluffy ultrathin carbon layer, which not only acts as a buffer material to suppress pulverization but also serves as a conductive matrix to boost charge transfer. Leveraging the advantage of the fascinating hierarchical structure and the synergistic effect with carbon layers, they show impressive electrochemical properties. They deliver a large sodium storage capacity of 492 mAh g^-1 after 100 cycles at a current density of 0.5 A g^-1 and excellent rate performance. Additionally, a high capacity of 223 mAh g^-1 is maintained, even after 10 000 cycles at 5 A g^-1, demonstrating prolonged cycle stability. The remarkable sodium storage performance expects a future application for sodium ion batteries.