Template-free fabrication of graphene-wrapped mesoporous ZnMnO nanorings as anode materials for lithium-ion batteries.

We rationally designed a facile two-step approach to synthesize ZnMnO@G composite anode material for lithium-ion batteries (LIBs), involving a template-free fabrication of ZnMnO nanorings and subsequent coating of graphene sheets. Notably, it is the first time that ring-like ZnMnO nanostructure is reported. Moreover, our system has been demonstrated to be quite powerful in producing ZnMnO nanorings regardless of the types of Zn and Mn-containing metal salts reactants. The well-known inside-out Ostwald ripening process is tentatively proposed to clarify the formation mechanism of the hollow nanorings. When evaluated as anode material for LIBs, the resulting ZnMnO@G hybrid displays significantly improved lithium-storage performance with high specific capacity, good rate capability, and excellent cyclability. After 500 cycles, the ZnMnO@G hybrid can still deliver a reversible capacity of 958 mAh g at a current density of 200 mA g, much higher than the theoretical capacity of 784 mAh g for pure ZnMnO. The outstanding electrochemical performance should be reasonably ascribed to the synergistic interaction between hollow and porous ZnMnO nanorings and the three-dimensional interconnected graphene sheets.