Synthesis of microflower-like vacancy defective copper sulfide/reduced graphene oxide composites for highly efficient lithium-ion batteries

Cupper sulfide (CuS) is considered as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and good electrical conductivity. However, inferior cycle performance and low coulombic efficiency of CuS caused by structure detoriation and degradation and the "shuttling effect" of polysulfide intermediates are restricting its practical application. In this work, we report a facile method to generate S vacancies (Vs) in CuS nanoflowers by thermal annealing in Ar. The obtained CuS was composited with reduced graphene oxide (rGO) to prepared an anode for LIBs. The existence of vacancy defects in CuS could lead to the electron delocalization and excitation, which are responsible for the conductivity improvement and fast charge transport kinetics. Meanwhile, the graphene coating layer ensures fast pathways for Li+ ions diffusion and provide a strong physical adsorption of the polysulfides. Furthermore, hierarchical CuS spheres composed of ultrathin nanosheets provide large void space to accommodate the volume expansion of CuS. The synthesized composite exhibited a high initial discharge capacity of 882 mAh g-1 and exhibited stable cyclability along with around 99% coulombic efficiency over 100 cycles. The results of this work reveal that Vs-CuS/rGO composites are promising anodes to enhance the performance of next-generation lithium-ion batteries.