Template-free formation of various V2O5 hierarchical structures as cathode materials for lithium-ion batteries
Various V2O5 hierarchical structures were successfully synthesized via a template-free method by annealing diverse morphological VO2 sub-microspheres which can be facilely tailored by adjusting the solvothermal reaction duration. The VO2 sub-microspheres undergo a solid → yolk–shell → hollow → yolk–shell structure process with increasing time, which is believed to result from an unusual Ostwald-ripening process. After the annealing process, multi-structural VO2 sub-microspheres changed into hierarchical structures including fist-type structures consisting of nanorods, yolk–shell and hollow sub-microspheres composed of nanorods and a yolk–shell construction made up of nanoplates. As the cathode materials for lithium-ion batteries, among them, yolk–shell sub-microspheres comprised of nanoplates exhibited high reversible capacity, excellent cycling stability at high currents and good rate capacities. Without doping and compositing, the electrode delivered reversible capacities of 119.2 and 87.3 mA h g−1 at high current densities of 2400 and 3600 mA g−1, respectively, as well as a capacity retention of 78.31% after 80 cycles at 1200 mA g−1. The excellent electrochemical performance could be attributed to the purity of the phase and synergistic effect between the yolk–shell structure and hierarchical structure of the sub-microspheres, which make the yolk–shell V2O5 hierarchical structure a promising candidate for the cathode material for lithium-ion batteries.