Design of a Nitrogen-Doped, Carbon-Coated Li₄ Ti₅ O₁₂ Nanocomposite with a Core-Shell Structure and Its Application for High-Rate Lithium-Ion Batteries

A facile solution-based synthesis and characterization of a nitrogen-doped, carbon-coated Li₄ Ti₅ O₁₂ (NC-LTO) nanocomposite is reported. The mesoporous TiO₂ nanoparticles (NPTiO₂ ) are first prepared by using nanocrystalline cellulose (NCC) as a template and subsequently transform in situ into an NC-LTO nanocomposite with a core-shell structure by using the ionic liquid 1-ethyl-3-methylimdazolium tricyanomethanide as the carbon source. Various state-of-the-art techniques, including field-emission SEM, TEM, scanning transmission electron microscopy, XRD, X-ray photoelectron spectroscopy, and thermogravimetric analysis, were performed to characterize the morphologies, structures, and compositions. Such NC-LTO nanocomposites have a well-defined LTO core and thin uniform carbon shell with a thickness of 1-2 nm. Electrochemical tests reveal that the NC-LTO nanocomposite delivers a reversible capacity of 171.5 mAh g^-1 at 0.2 C, and shows remarkable rate capability by maintaining 63 % of the capacity at 60 C (vs. 0.2 C), as well as excellent cycling stability with a capacity retention of 95 % after 300 cycles at a rate of 10 C. The excellent electrochemical performance is attributed exclusively to the well-defined core-shell nanostructure and high electric conductivity. The nanosized LTO core can significantly shorten the transport lengths of lithium ions and the admirable electric conductivity of the nitrogen-doped carbon shell can act as an "expressway" for electrons and lithium ions to transport them between the anode material core and the electrolytes.