Design and Understanding of Core/Branch Structured VS2 Nanosheets @ CNT as High-Performance Anode Material 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 corresponding mechanism understanding. Here, high crystalline VS2 nanosheets/carbon nanotube (CNT) with core/branch structure have been synthesized, exhibiting a reversible discharge capacity ~850 mAh/g at 200 mA/g, good cycling property and a high coulombic efficiency of ~98%, good cycling stability and superior rate capability. The relationship between the electrochemical properties and corresponding dynamic microstructural evolution is further revealed with in-situ electron microscopy technique. Our results show that the intercalation process with formation of amorphous LixVS2 and subsequent conversion reactions with formation of crystalline Li2S and V nanocrystals occur during the discharging process. The crystalline Li2S will be oxidized in the charging process. The core/branched structure ensured the large exposed surface area of VS2 nanosheets and provided extra space to accommodate volume expansion. Meanwhile, the CNT surrounded by VS2 nanosheets not only provides continuous and fast conducting pathway for carriers throughout the electrodes, but also enhances the mechanical stability of the electrode material. These factors finally contribute to the superior electrochemical performance of the core/branch structured VS2/CNT electrode.