Li-O-2 batteries have attracted significant attention due to their high theoretical energy density. However, the formation of Li2CO3 has resulted in low coulombic efficiency and poor cycling stability of Li-O-2 batteries. To address these issues, Fe3O4@CoO mesospheres with core-shell nanostructure are prepared and added as an efficient component to utilize the advantages of carbon materials, such as high electronic conductivity, low cost, and porous structure, and to reduce the amount of carbon materials in cathodes. Fe3O4@CoO mesospheres delivered low charge potential and significantly enhanced cycling stability of Li-O-2 batteries. The improved electrochemical performances were attributed to the core-shell nanostructure design of Fe3O4 core that promised high electronic conductivity and the porous CoO shell with many active sites reduced the overpotential charge and provided considerable space for the storage of discharge products.