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In this work, we successfully synthesized porous C/Fe3O4 microspheres by spray pyrolysis at 700ºC with a sodium nitrate (NaNO3) additive in the precursor solution. Furthermore, we studied their electrochemical properties as anode material for Li-ion batteries. The systematic studies by various characterization techniques show that NaNO3 catalyzes the carbonization of sucrose and enhances the crystallization of Fe3O4. Moreover, an aqueous etching can easily remove sodium compounds to produce porous C/Fe3O4 microspheres with large surface areas and pore volumes. The porous C/Fe3O4 microspheres exhibit a reversible capacity of ~780 mAh g–1 in the initial cycles and ~520 mAh g–1 after 30 cycles at a current density of 50 mA g–1. Moreover, a reversible capacity of ~400 mAh g–1 is attainable after 200 cycles, even at a high current density of 500 mA g–1. The wide range of pores produced from the removal of sodium compounds might enable easy electrolyte penetration and facilitate fast Li-ion diffusion, while the N-doping can promote the electronic conductivity of the carbon. These features of porous C/Fe3O4 microspheres led to the improved electrochemical properties of this sample. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spray pyrolysis with steam oxidation produced C/Fe 3 O 4 microspheres. • C/Fe 3 O 4 microspheres had wide-range of pores and high-conductive graphitic carbon. • Synergy between porous and conductive carbon enhanced Li-ion battery performances. This work introduces a novel synthesis route for the porous-crystalline C/Fe 3 O 4 microspheres by spray pyrolysis with post oxidation under a steam atmosphere. The dense-amorphous C/Fe 3 O 4 microspheres prepared by spray pyrolysis are firstly annealed at 700 °C for 4 h under 3 %H 2 /N 2 atmosphere to crystallize the amorphous carbon and introduce micro- and meso-pores. The reduced Fe 3 C nanoparticles are then oxidized into highly-crystalline Fe 3 O 4 at 500 °C for 2 h under H 2 O (g) /N 2 atmosphere. The XRD, Raman, XPS, and N 2 sorption analysis confirm the successful formation of C/Fe 3 O 4 microspheres with well-developed porous structure and highly conductive graphitic carbon. The porous-crystalline C/Fe 3 O 4 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. [ABSTRACT FROM AUTHOR]