Nickel sulfide nanospheres anchored on reduced graphene oxide in situ doped with sulfur as a high performance anode for sodium-ion batteries.

NiS_x–rGOS is prepared via a facile and cost effective hydrothermal process, with the structure of ultrafine NiS_x nanospheres uniformly wrapped in the in situ S-doped rGO matrix. The uniform nanostructural NiS_x and high conductivity of S-doped rGO (rGOS) can effectively increase the ionic and electronic conductivity of the NiS_x–rGOS composite, thus resulting in high capacity utilization of the active materials. Moreover, the buffering layer provided by the rGOS matrix can accommodate the volume change of the NiS_x and protect the nanoparticles from aggregation during the repeated cycling process. The as-prepared NiS_x–rGOS composite demonstrates a high reversible capacity of 516 mA h g⁻¹ at 0.2 A g⁻¹ with a capacity retention of 96.8% over 100 cycles and a remarkable rate performance of 414 mA h g⁻¹ at 4 A g⁻¹, possibly exhibiting the best electrochemical performances of nickel sulfide for sodium-ion batteries. [ABSTRACT FROM AUTHOR]