Formation of graphene-encapsulated CoS2 hybrid composites with hierarchical structures for high-performance lithium-ion batteries

Abstract

Transition metal sulfides (TMSs) are considered as the most promising alternative anode materials for advanced lithium-ion batteries (LIBs). Here, we report a hierarchically structured CoS₂ nanosphere/graphene (CoS₂/G) composite, fabricated by a simple hydrothermal method. This composite, assembled with CoS₂ nanoparticles uniformly distributed on the graphene, exhibits excellent electrochemical performance. In particular, the CoS₂/G electrode material delivers a high rate capability of around 398 mA h g⁻¹ at a current density of 3500 mA g⁻¹. Moreover, a discharge capacity of about 400 mA h g⁻¹ can be obtained after 1000 cycles at a current density of 500 mA g⁻¹. X-ray absorption spectroscopy is used to characterize the sample for the first time, and the results demonstrate that CoS₂/G is reduced to metallic Co and Li₂S when discharged to 0.01 V. In subsequent charge–discharge processes, the metallic Co cannot be fully oxidized to CoS₂, which is the main cause of capacity loss for the CoS₂ electrode.