Template-free fabrication of graphene-wrapped mesoporous ZnMn₂O₄ nanorings as anode materials for lithium-ion batteries

Abstract

We rationally designed a facile two-step approach to synthesize ZnMn₂O₄@G composite anode material for lithium-ion batteries (LIBs), involving a template-free fabrication of ZnMn₂O₄ nanorings and subsequent coating of graphene sheets. Notably, it is the first time that ring-like ZnMn₂O₄ nanostructure is reported. Moreover, our system has been demonstrated to be quite powerful in producing ZnMn₂O₄ 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 ZnMn₂O₄@G hybrid displays significantly improved lithium-storage performance with high specific capacity, good rate capability, and excellent cyclability. After 500 cycles, the ZnMn₂O₄@G hybrid can still deliver a reversible capacity of 958 mAh g^-1 at a current density of 200 mA g^-1, much higher than the theoretical capacity of 784 mAh g^-1 for pure ZnMn₂O₄. The outstanding electrochemical performance should be reasonably ascribed to the synergistic interaction between hollow and porous ZnMn₂O₄ nanorings and the three-dimensional interconnected graphene sheets.