Template-free formation of carbon nanotube-supported cobalt sulfide@carbon hollow nanoparticles for stable and fast sodium ion storage

Abstract Carbon-coated cobalt sulfide (CoS) hollow nanoparticles on carbon nanotube (CNT) networks are synthesized by combining three simple approaches: direct growth of Co 3 O 4 nanocrystals on the CNT backbones, chemical conversion of the Co 3 O 4 nanocrystals to CoS hollow nanoparticles, and the spatial introduction of conformal surface modification by carbon. It is noteworthy that the CoS hollow nanoparticles with inner cavity of −1 at 100 mA g −1 and a capacity retention rate of 90% after 200 cycles at a higher current density of 500 mA g −1 are obtained. Moreover, a superior rate capability is observed with reversible specific capacities of 341 and 276 mAh g −1 at 2000 and at 5000 mA g −1 , respectively.