Facile synthesis of carbon-coated Fe3O4 core–shell nanoparticles as anode materials for lithium-ion batteries

Core–shell composites, carbon-coated Fe3O4 (Fe3O4@C) with ~30 nm Fe3O4 nanoparticles as cores and 3–7 nm carbon as shells, was successfully prepared through simple hydrothermal reaction followed by heat treatment. High-resolution transmission electron microscopy and energy dispersive spectroscopy mapping showed the formation of a highly developed core–shell structure with uniform carbon coating on the surface of Fe3O4 nanoparticle. In the Fe3O4@C composite, carbon coating layer provides an effective electron conductive paths. It acts as spacers to avoid the aggregation of Fe3O4 and buffers the volume changes of Fe3O4. Accordingly, nano-sized Fe3O4 core in the core–shell structure not only better accommodates large strains but also provides short diffusion paths for Li+ insertion/deinsertion. The Fe3O4@C composite exhibits good cyclability and delivers a high initial discharge capacity of 982 mAh g−1 and a reversible discharge capacity of 718 mAh g−1 after 100 cycles at 0.1 C. Even up to 2 C, a reversible capacity of 302 mAh g−1 is obtained.