CO2–expanded ethanol chemical synthesis of a Fe3O4@graphene composite and its good electrochemical properties as anode material for Li-ion batteries

Abstract

In this work, we have developed a new method to synthesize a Fe₃O₄@graphene (Fe₃O₄@GN) composite. First, the precursor was synthesized through the decomposition of ferric nitrate in the presence of graphene oxide in the mixed solvent of CO₂–expanded ethanol. Then, the precursor was converted to the Fe₃O₄@GN composite via thermal treatment in N₂ atmosphere. With the help of the CO₂–expanded ethanol, Fe₃O₄ nanoparticles were coated on the surface of GN completely and uniformly with high loading. However, it is difficult to load Fe₃O₄ particles onto the surface of GN and most of the Fe₃O₄ particles were deviated away from GN and aggregated to form larger units in pure ethanol. When used as anode for Li-ion batteries (LIBs), the Fe₃O₄@GN composite with a graphene content of 25 wt% synthesized in CO₂–expanded ethanol manifested excellent charge–discharge cycling stability and rate performance compared with the sample synthesized in ethanol. Such improved electrochemical performances should be attributed to the intimate contact between the GN and Fe₃O₄ nanoparticles in the composite. Since the present method does not need tedious pre-treatment, surfactant, or precipitate, it is a green or sustainable technology and the solvents could be recycled easily after simple phase separation. This facile method can be extended to the synthesis of other metal oxide composites, which are expected to have good performance as anode materials for LIBs and other applications.