Fe3O4 nanoparticles encapsulated in one-dimensional Li4Ti5O12 nanomatrix: An extremely reversible anode for long life and high capacity Li-ion batteries

Transition metal oxides are very promising electrode materials for lithium -ion batteries that operate through conversion reactions. Energy densities for conversion reactions are higher than for intercalation reactions, but most of transition metal oxides show poor cycling performance and reversibility due to the pulverization of active materials and subsequent volume changes. We here report a facile and scalable synthesis for realizing Li4Ti5O12-coated Fe/Fe3O4 hybrid nanocomposites in the form of one-dimensional nanofibers (C@Fe-Fe3O4/Li4Ti5O12 hybrid NFs). This is a new class of highly -reversible and safe anode material that can significantly reduce the lithium -ion diffusion length and improve strain tolerance during Li ion insertion/extraction. Its oxidation state was also impressively controlled through a carbothermal reaction during annealing. The precise oxidation state control of C@Fe-Fe3O4/Li4Ti5O12 hybrid NFs simultaneously enabled high capacity due to the conversion reaction of Fe3O4 as well as high reversibility and stability resulting from zero-strain characteristics and superb kinetics of Li4Ti5O12.. This new electrode material appears promising for not only future energy systems but also various electronic devices. (C) 2015 Elsevier Ltd. All rights reserved.