Migration behavior, oxidation state of iron and graphitization of carbon nanofibers for enhanced electrochemical performance of composite anodes

Iron oxide/carbon nanofibers (FeOx/CNFs) were prepared by electrospinning FeCl3·6H2O-polyacrylonitrile (PAN) precursors and heat treating at 400, 600, 800, 1000 °C. As carbonization temperature increased, granular FeOx gradually migrated from nanofiber interior with effectual contacts between electrolyte and active materials rising at first and then falling; Oxidation states of iron in FeOx/CNFs changed from Fe2O3 to FeO and Fe with an improvement of capacity retention and an extra reversible capacity catalyzed by Fe; Graphitization process of carbon matrices proceed with less defective structures and heteroatom contents, leading to an increase of conductivity and a diminution of irreversible reactions during cycling. As systematically studied and compared in electrochemical performance, FeOx/CNFs with FeO, Fe state, highly graphitized carbon matrices and migration structure with FeO and Fe both embedded in and dispersed on carbon matrices presented stable cycling performance with a reversible capacity of ∼674 mAhg−1 after 60 cycles and outstanding rate capability. The above trade-off study of all the cooperative factors that affected the electrochemical property might make an effective guidance for preparation of promising FeOx/CNF anodes.