Facile Preparation and Electrochemical Properties of V₂O₅-Graphene Composite Films as Free-Standing Cathodes for Rechargeable Lithium Batteries

Free-standing, flexible V₂O₅-graphene composite films were prepared by simple filtration of aqueous dispersions of V₂O₅ nanowires and graphene sheets. V₂O₅ nanowires were preferentially oriented along the plane of the film as they were sandwiched between stacked graphene sheets in the composite film. The V₂O₅ content in the composites was adjusted simply by varying the relative amount of the dispersions. Thermal annealing at 300°C increased the conductivity of the composite films. Due to their integrated structure and high flexibility, the composite films were directly usable as flexible electrodes. In binder-free, sandwich-type lithium battery cells, a composite film containing 75.8 wt% V₂O₅ delivered discharge capacities of 283 mAh g^-1 and 252 mAh g^-1 at a current density of 50 mA g^-1 during the first and 50th cycles, respectively. Owing to its higher conductivity, a composite film containing 42.8 wt% V₂O₅ delivered a discharge capacity of 189 mAh g^-1 at 750 mA g^-1. The good performance resulted from the integrated structure of the V₂O₅ network embedded in stratified graphene nanosheets, with V₂O₅ as the Li⁺ host and graphene nanosheets providing the electron pathway. These composite films are promising candidates for electrical energy storage applications that require flexible electrodes.