Two dimensional layered Co0.85Se nanosheets as a high-capacity anode for lithium-ion batteries

In recent years, two-dimensional (2D) layered transitional metal chalcogenides (TMCs) have received much attention as promising electrode materials in energy storage. Although recent reports on 2D TMC nanostructures have demonstrated promising electrochemical performances, the major scientific challenge is to develop a viable synthesis process to produce layered structures of chalcogenides (Co, Ni or Fe based TMCs) as anode materials. In this work, we propose the synthesis of layered Co0.85Se nanosheets in a solution based method by using a 2D oriented attachment strategy. The as-prepared Co0.85Se nanosheets exhibit specific capacities as high as 675 mA h g(-1) at 100 mA g(-1). When the current densities were further increased to 200, 500 and 1000 mA g(-1), the reversible capacities can still reach up to 645, 574 and 493 mA h g(-1) with excellent cycling life of 95, 85 and 73%, respectively. Li-ion storage performance of layered Co0.85Se nanosheets is higher than that of Co0.85Se microspheres as well as cobalt sulfide. The superior electrochemical performance of Co0.85Se nanosheets is attributed to their 2D layered structure which enhances electrical conductivity and improves diffusion pathways of the Li-ion within the host material. The synthesis method described in this work serves as a general route for the design and preparation of other 2D layered TMCs.