Synthesis and characterization of porous-crystalline C/Fe3O4 microspheres by spray pyrolysis with steam oxidation as anode materials for Li-ion batteries

Abstract

This work introduces a novel synthesis route for the porous-crystalline C/Fe3O4 microspheres by spray pyrolysis with post oxidation under a steam atmosphere. The dense-amorphous C/Fe3O4 microspheres prepared by spray pyrolysis are firstly annealed at 700 °C for 4 h under 3 %H2/N2 atmosphere to crystallize the amorphous carbon and introduce micro- and meso-pores. The reduced Fe3C nanoparticles are then oxidized into highly-crystalline Fe3O4 at 500 °C for 2 h under H2O(g)/N2 atmosphere. The XRD, Raman, XPS, and N2 sorption analysis confirm the successful formation of C/Fe3O4 microspheres with well-developed porous structure and highly conductive graphitic carbon. The porous-crystalline C/Fe3O4 microspheres demonstrate a higher specific capacity of ∼560 mA h g−1 at a current density of 50 mA g−1 than the dense-amorphous microspheres, which corresponds to 92% of its theoretical value. Moreover, the sample has an improved rate capability (240 mA h g−1 even at 5000 mA g−1) and stable long-term cycling performance due to the synergy between porous structure and graphitic carbon.