In situ growth of Li4Ti5O12 on multi-walled carbon nanotubes: novel coaxial nanocables for high rate lithium ion batteries

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 m(2) 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.