Design and understanding of core/branch-structured VS2 nanosheets@CNTs as high-performance anode materials for lithium-ion batteries

Revealing the electrochemical property-structure relationship and observing the dynamic structural evolution of electrode materials are critically important for battery performance improvement and the corresponding mechanistic understanding. Here, highly crystalline VS2 nanosheets/carbon nanotubes (CNTs) with a core/branch structure were synthesized, exhibiting reversible discharge capacity of similar to 850 mA h g(-1) at 200 mA g(-1), high coulombic efficiency of similar to 98%, good cycling stability and superior rate capability. The relationship between the electrochemical properties and the corresponding dynamic microstructural evolution was further revealed with the in situ electron microscopy technique. Our results showed that the intercalation process with the formation of amorphous LixVS2 and the subsequent conversion reactions with the formation of crystalline Li2S and V nanocrystals occurred during the discharging process. Crystalline Li2S was oxidized in the charging process. The core/branched structure ensured a large exposed surface area of the VS2 nanosheets and provided extra space to accommodate the volume expansion. Meanwhile, the CNTs surrounded by VS2 nanosheets not only provided a continuous and fast conducting pathway for carriers throughout the electrodes, but also enhanced the mechanical stability of the electrode material. These factors finally contributed to the superior electrochemical performance of the core/branch-structured VS2/CNTs electrode.