A yolk-shell structured CoS2@NC@CNC with double carbon shell coating from confined derivatization of ZIF-67 growth in carbon nanocages for superior Li storage

Abstract Over the years, CoS2 as typical anode material of lithium-ion batteries (LIBs) has aroused great attention on account of its remarkable electrical conductivity and high capacity. Nevertheless, CoS2 is subjected to poor cycling and rate performance originating from severe expansion effect and sluggish ion/electron transport kinetics. Herein, a novel yolk-shell structured CoS2@NC@CNC with double carbon shell coating from the derivation of ZIF-67 confined in carbon nanocages (CNC) is synthesized to enhance the properties of CoS2. Specifically, ZIF-67 was firstly confined in CNC to form yolk-shell structured ZIF-67@CNC through simple co-precipitation method; and then the ZIF-67 inside CNC was in situ converted into CoS2@NC to form CoS2@NC@CNC with CoS2 as active core and N-doped C and CNC as double carbon shell. As LIBs electrode material, CoS2@NC@CNC exhibited high electrochemical performance with 641 mAh g−1 at 1.0 A g−1 after 100 cycles. The improved electrochemical performance is mainly attributed to the yolk-shell structure and the synergistic effect of active material CoS2@NC and conductive CNC. The yolk-shell structure with abundant void spaces between CNC and CoS2@NC can buffer the huge volume expansion effect. Simultaneously, the CNC can enhance the conductivity and retain the structural integrity to improve the cycling stability. As active material, the nano-scale CoS2@NC can shorten the diffusion distance of lithium ions, increase available active sites and improve the rate capacity. In addition, the mesoporous structure and large specific surface area are conductive to capacitive contribution and the rapid diffusion of electrolyte ions, which further improve the electrochemical performance.