VN/S Nanoclusters Encapsulated with Graphene via Zeta Potential Control: A Pomegranate-Like Cathode for Lithium-Sulfur Batteries with Enhanced Rate Performance

A pomegranate-like cathode, VN/S@G, is synthesized according to a simple principle of electrostatic attraction through a controllable Zeta potential method, establishing a hierarchical-structured VN/S nanoclusters encapsuled with graphene nanosheets. Internal VN nanoparticles trap lithium polysulphides (LiPSs) and catalyse them transforming from long-chain to short-chain species; whereas the external cladding layers of graphene nanosheets confine the transformations in a nanoscale-catalysis reactors. VN/S@G cathode exhibits excellent long-cycling life at 2 C rate during the 2000 cycles, corresponding to 0.038 percent of capacity fade per cycle. According to in-situ Raman and electrochemical impedance spectroscopies, VN catalyst accelerates chemical transformations of liquid-state LiPSs to solid-state Li2S2/Li2S and graphene intensifies Li+ diffusion behaviour. Improvement of electrochemical performance of the VN/S@G cathode depends on a coefficient of physical and chemical interactions between VN catalyst and LiPSs species.