Ultrafine Cobalt Sulfide Nanoparticles Encapsulated Hierarchical N-doped Carbon Nanotubes for High-performance Lithium Storage

In this work, we report a multistep method to synthesize ultrafine cobalt sulfide nanoparticles encapsulated in hierarchical N-doped carbon nanotubes (CoSx@HNCNTs). Co-based zeolitic imidazolate framework (ZIF-67) nanotubes are obtained from the reaction between electrospun polyacrylonitrile/cobalt acetate and 2-methylimidazole, followed by the dissolution of template. Next, a combined calcination and sulfidation process is employed to convert the ZIF-67 nanotubes to CoSx@HNCNTs. Benefited from the compositional and structural features, the as-prepared nanostructured hybrid materials deliver superior lithium storage properties with high capacity of 1200 mAh g−1at 0.25 A g−1. More importantly, a remarkable capacity of 1086 mAh g−1can be maintained after 100 cycles at the current density of 0.5 A g−1. Even at a high rate of 5 A g−1, a reversible capacity of 592 mAh g−1after 1600 cycles can still be achieved.