Design of a nitrogen-doped, carbon-coated Li₄Ti ₅O₁₂ 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 Li₄Ti₅O₁₂ (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 fieldemission 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 mAhg-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.