Facile synthesis of CoFe2O4 quantum dots/N-doped graphene composite with enhanced lithium-storage performance

CoFe2O4 quantum dots/N-doped graphene (CoFe2O4 QDs/N-G) composites have been successfully fabricated through a facile strategy involving a hydrothermal process and subsequent calcination at high temperature. Uniform nanoparticles with high density are homogeneously anchored on the surfaces of graphene sheets. The CoFe2O4 QDs with a distribution within 4-12 nm can be observed clearly, and there is no apparent aggregation of CoFe2O4 QDs on the graphene nanosheets. The CoFe2O4 QDs/N-G obtained as an anode material for LIBs presents an initial discharge capacity of 1616 mAh g(-1) and maintains a reversible capacity of 1223 mAh g(-1) after 90 cycles at a current of 100 mA g(-1). The gradual capacity increase with cycling results primarily from the formation of Co3+ during the electrochemical process. After being cycled at various rates for 90 cycles, the capacity can recover to 1239 mAh g(-1) when the current is switched to 100 mA g(-1). This superior lithium-storage performance can be attributed to the quantum and size effects of CoFe2O4 quantum dots and the excellent electrochemical properties of N-doped graphene. (C) 2016 Elsevier B.V. All rights reserved.