Structurally Stabilized Fe Oxides through Conversion Reactions with Li+ By Embedment in a Li4Ti5O12 Matrix

Transition metal oxides are 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 transition metal oxides show poor cycling performance and reversibility due to pulverization of active materials and subsequent volume changes. We report a facile, scalable, electrospinning synthesis for fabrication of Li₄Ti₅O₁₂-coated Fe/Fe₃O₄ nanocomposites into one-dimensional hybrid nanofibers (C@Fe-Fe₃O₄/Li₄Ti₅O₁₂ hybrid NFs). This is a new class of highly-reversible and safe anode material that significantly reduces the lithium-ion diffusion length and improves strain tolerance caused by lithium-ion insertion/extraction. Oxidation state is also impressively controlled through a carbothermal reaction during annealing. The precise oxidation state control of C@Fe-Fe₃O₄/Li₄Ti₅O₁₂ hybrid NFs provided high capacity due to the Fe oxide conversion reaction and substantial reversibility and stability resulting from zero-strain characteristics and superb kinetics of Li₄Ti₅O₁₂. This new electrode material appears promising for future energy systems.