Zn/Fe-MOFs-derived hierarchical ball-in-ball ZnO/ZnFe2O4@carbon nanospheres with exceptional lithium storage performance

Transition metal oxides@carbon(C) nanocomposites with hierarchical three-dimensional (3D) core-shell nanoarchitectures, large surface area and high electrical conductivity as anode materials for lithium ion batteries (LIBs) are very desirable. Herein, we developed a simple and feasible route to fabricate novel hierarchical 3D ball-in-ball ZnO/ZnFe2O4@C nanospheres with well-defined hollow microstructures via one-step carbonization of Zn/Fe-metal organic frameworks for the first time. The as-prepared hierarchical 3D ball-in-ball ZnO/ZnFe2O4@C nanospheres were carefully characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, thermogravimetric analysis, N-2 adsorption/desorption isotherm, transmission electron microscopy and electrochemical techniques. The results showed ultrafine ZnO and ZnFe2O4 nanocrystals were uniformly encapsulated by few carbon layers which was derived from in-situ carbonization of the organic ligands. Benefiting from their special hollow nanoarchitectures, ultrafine ZnO and ZnFe2O4 nanocrystals encapsulated by a few carbon layers, large specific surface area and high electrical conductivity, the hierarchical 3D ball-in-ball ZnO/ZnFe2O4@C nanospheres presented high reversible capacities of 1283 and 1100 mA h g(-1) after first 100 cycles and the following 100 cycles at current density of 100 and 200 mA g(-1), respectively. A high specific capacity of 155 mA h g(-1) was obtained at relatively large current rates of 20 A g(-1). (C) 2016 Elsevier B.V. All rights reserved.