Double-layer carbon protected CoS₂ nanoparticles as an advanced anode for sodium-ion batteries

Cobalt disulfides with high theoretical capacity are regarded as appropriate anode materials for sodium ion batteries (SIBs), but their intrinsically low conductivity and large volume expansion lead to a poor electrochemical performance. In this work, graphitic carbon coated CoS₂ nanoparticles are encapsulated in bamboo-like carbon nanotubes by pyrolysis and sulfidation process. Graphitic carbon can improve the electrical conductivity and prevent the agglomeration of CoS₂ nanoparticles. Meanwhile, bamboo-like carbon nanotubes can serve as conductive skeleton frames to provide rapid and constant transport pathways for electrons and offer void space to buffer the volume change of CoS₂ nanoparticles. The advanced anode material exhibits a long-term capacity of 432.6 mA h g^-1 at 5 A g^-1 after 900 cycles and a rate capability of 419.6 mA h g^-1 even at 10 A g^-1 in the carbonate ester-based electrolyte. This avenue can be applicable for preparing other metal sulfide/carbon anode materials for sodium-ion batteries.