Synthesis and characterization of Fe@Fe2O3 core-shell nanoparticles/graphene anode material for lithium-ion batteries

Abstract Fe@Fe 2 O 3 core-shell nanoparticles anchored on graphene (Fe@Fe 2 O 3 /graphene hybrid material) have been firstly synthesized by using a hydrothermal reaction followed by an in situ thermal reduction. The morphology and structure of the Fe@Fe 2 O 3 /graphene hybrid material are characterized by SEM, XRD, XPS, TEM, EFTEM and EDS, which show that the nanoparticles with diameters around 100 nm are homogeneously anchored on the surface of graphene sheets to form three-dimensional (3D) porous structure, and the shell region with several nanometers is amorphous Fe 2 O 3 . The galvanostatic cycling test shows that the Fe@Fe 2 O 3 /graphene hybrid material displays a reversible charge capacity of 959.3 mAh·g −1 up to 90 cycles at a current density of 100 mA·g −1 , which is 86.4% retention of the first charge capacity. In addition, the Fe@Fe 2 O 3 /graphene hybrid material exhibits an excellent long-life cycling performance at high currents. Furthermore, the first lithiation process of Fe@Fe 2 O 3 /graphene electrode is studied by electrochemical impedance spectroscopy (EIS) at different potentials. According to the results of equivalent circuit analysis, there appear three semicircles respectively representing the Li-ion migration in solid electrolyte interface film (SEI film) and contact problems, electrical conductivity and charge transfer in the first discharge process, and the change of kinetic parameters for lithiation process of Fe@Fe 2 O 3 /graphene electrode as a function of potential is discussed in detail.