Construction of rGO-Encapsulated Co O -CoFe O Composites with a Double-Buffer Structure for High-Performance Lithium Storage.

Transition metal oxides (TMOs) are promising anode materials for next-generation lithium-ion batteries (LIBs). Nevertheless, their poor electronic and ionic conductivity as well as huge volume change leads to low capacity release and rapid capacity decay. Herein, a reduced graphene oxide (rGO)-encapsulated TMOs strategy is developed to address the above problems. The Co O -CoFe O @rGO composites with rGO sheets-encapsulated Co O -CoFe O microcubes are successfully constructed through a simple metal-organic frameworks precursor route, in which Co[Fe(CN) NO] microcubes are in situ coated by graphene oxide sheets, followed by a two-step calcination process. As anode material of LIBs, Co O -CoFe O @rGO exhibits remarkable reversible capacity (1393 mAh g at 0.2 A g after 300 cycles), outstanding long-term cycling stability (701 mAh g at 2.0 A g after 500 cycles), and excellent rate capability (420 mAh g at 4.0 A g ). The superior lithium storage performance can be attributed to the unique double-buffer structure, in which the outer flexible rGO shells can prevent the structure collapse of the electrode and improve its conductivity, while the hierarchical porous cores of Co O -CoFe O microcubes can buffer the volume expansion. This work provides a general and straightforward strategy for the construction of novel rGO-encapsulated bimetal oxides for energy storage and conversion application.