Fe<sub>3</sub>O<sub>4</sub>/Graphene Composites with a Porous 3D Network Structure Synthesized through Self-Assembly under Electrostatic Interactions as Anode Materials of High-Performance Li-Ion Batteries

Abstract

Fe3O4/graphene composites with a conductive, porous three-dimensional (3D) graphene network were synthesized through a facile method. In the preparation process, Fe(OH)3 colloid was formed in situ by adding FeCl3 solution to a boiling graphene oxide (GO) suspension, with Fe(OH)3/GO precipitated because of the electrostatic interaction between the two components. The precipitate was separated and added to a second GO suspension to achieve additional GO encapsulation. This self-assembled Fe(OH)3/GO precursor was then hydrothermally and heat treated, resulting in the formation of Fe3O4/graphene composites. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy results revealed that the Fe3O4/graphene composites possess a favorable 3D porous graphene network embedding 50- to 100-nm-sized Fe3O4 nanoparticles. The Fe3O4/graphene composites exhibit good electrochemical performance as an anode material for Li-ion batteries. The electrode composed of the Fe3O4/graphene composite delivered a capacity of 1390 mAh∙g - 1 for the first lithiation and retained a capacity of 819 mAh∙g - 1 after 50 cycles. The electrodes also exhibited good rate capability. The present results demonstrate that the electrochemical performance of the Fe3O4/graphene composite is highly sensitive to its preparation procedure and to the resulting nanostructure. Each of the four preparation procedures was experimentally shown to be important for achieving the final nanostructure and good electrochemical performance. A formation mechanism for the Fe3O4/graphene composite is also proposed.