Ultrafine CoS nanoparticles embedded in a nitrogen-doped porous carbon hollow nanosphere composite as an anode for superb sodium-ion batteries and lithium-ion batteries.

Cobalt sulfides are attractive as intriguing candidates for anodes in SIBs and LIBs owing to their unique chemical and physical properties. In this study, a precursor of CoS with a uniform and hollow nanospherical architecture is obtained with a high yield via a mild solvothermal method in the presence of 2-methylimidazole at first. Then, CoS, CoS/C (ultrafine CoS nanoparticles embedded in the shells of the nitrogen-doped porous carbon hollow nanosphere), and CoS@C (CoS nanoparticles entirely covered by an external amorphous carbon layer) were selectively fabricated via direct calcination or PPy coating & calcination of the obtained precursor. CoS/C shows best electrochemical performance than the other two materials as anodes for sodium-ion batteries (SIBs). Besides the excellent rate performance, a high reversible discharge capacity of 320 mA g can be retained after 130 cycles at 1 A g. The impressive performance may be attributed to the unique structure, higher conductivity, and more active sites of CoS/C. In addition, 559 mA h g was maintained after 100 cycles at 500 mA g when the CoS/C composite was applied as an anode in lithium-ion batteries (LIBs). The high reversible capacity, excellent cycle stability combined with the facile synthesis procedure render CoS/C a prospective anode material for rechargeable batteries.