In situ growth of Li4Ti5O12on multi-walled carbon nanotubes: novel coaxial nanocables for high rate lithium ion batteries

Abstract

We describe here a new approach to the synthesis of morphology-controlled coaxial nanocables consisting of highly conducting multi-walled carbon nanotube (MWNT) cores and well-crystalline Li₄Ti₅O₁₂ sheaths. The nanocables were prepared using a sol–gel method combined with a following hydrothermal process and a short post-annealing, where the TiO₂ was first deposited onto the MWNT core by controlled hydrolysis of tetrabutyl titanate and subsequently transformed in situ into a Li₄Ti₅O₁₂ sheath with the thickness of 25 nm. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption/desorption and thermogravimetric analysis were performed to characterize their morphologies and structures. Such MWNT@Li₄Ti₅O₁₂ coaxial nanocables had rich hierarchical pores and a specific surface area of 80.1 m² g⁻¹. Compared with the bulk Li₄Ti₅O₁₂, these novel MWNT@Li₄Ti₅O₁₂ core/sheath coaxial nanocables exhibited much higher rate capability and even better capacity retention. Firstly, the MWNT core effectively improved the electronic conductivity of the hybrid materials. Secondly, the nanosized and porous Li₄Ti₅O₁₂ sheath provided a larger electrode/electrolyte contact surface, shortened the Li-ion diffusion path and allowed the fast ion diffusion, which resulted in the enhanced Li storage and the kinetics of the Li₄Ti₅O₁₂ sheath.