Facile synthesis of in situ carbon-coated CoS ₂ micro/nano-spheres as high-performance anode materials for sodium-ion batteries

In situ carbon-coated CoS₂ micro/nano-spheres were successfully prepared by sulfuric calcination using the solvothermal method with glycerol as the carbon source without introducing extraneous carbon. This method prevents carbon agglomeration and avoids the cumbersome steps of the current technology. The composite demonstrates excellent sodium storage capacity as an anode material for sodium-ion batteries. The initial charge and discharge capacities were 1027 and 1224 mA h g^-1 at 50 mA g^-1, respectively, with an initial coulombic efficiency of 83.9%. The capacity of CoS₂@C at 350 °C was maintained at 937 mA h g^-1 after 140 cycles at a current density of 2 A g^-1. The outstanding electrochemical performance is mainly attributed to the nanostructure design and the presence of in situ carbon. As revealed by the kinetic analysis, the pseudo-capacitive behaviour also contributed to the excellent electrochemical performance.