A strongly coupled CoS₂/ reduced graphene oxide nanostructure as an anode material for efficient sodium-ion batteries

Sodium-ion batteries (SIBs) are highly attractive electrochemical devices for massive energy storage because of their low cost and abundance of sodium, but insufficient anode performance remains a key challenge for the commercialization of this attractive technology. In this study, a hierarchically porous CoS₂/graphene composite with an architecture of CoS₂ nanoparticles embedded in reduced graphene oxide (rGO) is synthesized through a one-step hydrothermal route allowing the growth of the CoS₂ phase and the reduction of the graphene oxide simultaneously. This composite is applied as an anode material for SIBs, delivering favorable performance. The CoS₂ phase consists of nanoparticles of ∼10 nm that are uniformly anchored on the rGO, forming a CoS₂/rGO hybrid with strong phase interaction. As a conversion-type anode for SIBs, the electrochemical testing results show significantly enhanced sodium-storage properties for the CoS₂/rGO composite compared with that of bare CoS₂. Impressively, the CoS₂/rGO nanostructure exhibits a high discharge capacity of approximately 400 mAh g⁻¹ after 100 cycles at specific current of 100 mA g⁻¹, corresponding to approximately 80% of the discharge capacity in the second cycle. Such improvement may be due to the two-dimensional conductive network, homogeneous dispersion and immobilization of the CoS₂ nanoparticles, as well as the enhanced wettability of the active material in the electrolyte by introducing rGO. The results suggest that this well-designed conversion-type CoS₂ is a promising anode material for high-performance SIBs.