▎ 摘　　要

A three-dimensional graphene hollow sphere is prepared via a green synthetic method by utilizing vacuum residue (VR) and is shown to function as an oxygen electrode material for Li-O-2 batteries. It is noteworthy that VR, which is considered an environmental pollutant and is used primarily in asphalt-paved roads, can be utilized effectively as a novel precursor for carbon electrodes in Li-O-2 batteries. The low-valued VR is converted into graphene hollow sphere carbon by using Fe3O4, which serves as both a catalyst and a template in m-xylene under supercritical conditions. Since the hollow sphere structure is associated with a multi-layer graphene feature, it provides adequate void space for storing the discharge product of Li2O2 and suppresses the formation of Li2CO3. This results in capacities reaching 16805 mA h g(carbon)(-1), which is higher than that of commercial KB600J carbon (5493 mA h g(carbon)(-1)), and in improved cycle performance.