Yolk-Shell Structured Assembly of Bamboo-Like Nitrogen-Doped Carbon Nanotubes Embedded with Co Nanocrystals and Their Application as Cathode Material for Li-S Batteries

Despite their high theoretical specific capacity (1675 mA h g(-1)), the practical application of Li-S batteries remains limited because the capacity rapidly degrades through severe dissolution of lithium polysulfide and the rate capability is low because of the low electronic conductivity of sulfur. This paper describes novel hierarchical yolk-shell microspheres comprising 1D bamboo-like N-doped carbon nanotubes (CNTs) encapsulating Co nanoparticles (Co@BNCNTs YS microspheres) as efficient cathode hosts for Li-S batteries. The microspheres are produced via a two-step process that involves generation of the microsphere followed by N-doped CNTs growth. The hierarchical yolk-shell structure enables efficient sulfur loading and mitigates the dissolution of lithium polysulfides, and metallic Co and N doping improves the chemical affinity of the microspheres with sulfur species. Accordingly, a Co@BNCNTs YS microsphere-based cathode containing 64 wt% sulfur exhibits a high discharge capacity of 700.2 mA h g(-1) after 400 cycles at a current density of 1 C (based on the mass of sulfur); this corresponds to a good capacity retention of 76% and capacity fading rate of 0.06% per cycle with an excellent rate performance (752 mA h g(-1) at 2.0 C) when applied as cathode hosts for Li-S batteries.