Graphene Based High Performance Energy Storage Devices

Graphene based materials have provided versatile platforms in developing electrodes in energy storage devices, such as rechargeable batteries and supercapacitors, utilizing their unique physical and chemical properties. We have explored the potential of functionalized graphene to develop positive electrodes for rechargeable batteries (Li ion and Na ion batteries). Graphene electrodes were prepared by two different self-assembly processes. Firstly, graphene hydrogel was assembled by a hydrothermal reduction process. After vacuum drying process, densely packed graphene films were obtained. The graphene films delivered a high gravimetric specific energy of ~140 mAh/g in Li-cells. The electrochemical performance of the electrode showed a positive correlation with the amount of oxygen group, indicating the importance of the surface redox reactions of the oxygen functional groups. Secondly, additional surface redox reactions were introduced into the graphene electrodes by functionalization with a redox-active component, tetrahydroxyl-1,4-benzoquinone (THQ). The functionalized graphene electrodes delivered high gravimetric capacities of ~165 mAh/g in Li-cells and ~120 mAh/g in Na-cells with high redox potentials over ~3 V vs. Li or Na. These results propose that graphene based materials can be promising candidates for positive electrodes in both Li- and Na-ion batteries.