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

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 ∼850 mA h g^-1 at 200 mA g^-1, high coulombic efficiency of ∼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 Li_xVS₂ 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.