Lithium Insertion into Anatase Nanotubes

Anatase nanotubes were synthesized by a hydrothermal route and characterized by FE-SEM, TEM, XRD, and N 2 adsorption. The optimized synthesis route permits careful control of the crystal structure and morphology of the final product, thus giving the highest phase and morphological purities (>90%) of any anatase nanotubes reported to date. The anatase nanotubes were tested in lithium cells at various current rates and their performances compared with bulk and nanoparticulate anatase. The Li uptake of the nanotubes in lithium cells reaches 0.98 per formula unit. Moreover the nanotubes show better reversibility and cyclability compared to both bulk and nanoparticulate anatase. The excellent rate performance is comparable with the best literature values reported for mesostructured anatase nanopowders. By combining experimental data from neutron diffraction and Raman microscopy the lithium insertion mechanism into the anatase nanotubes was investigated. Ex situ neutron diffraction experiments were carried out on pristine, partially lithiated, and fully lithiated anatase nanotubes. In parallel, the structural changes associated with electrochemical lithium insertion were investigated by in situ Raman microscopy. This analysis suggests a Li-poor tetragonal/orthorhombic/Li-rich tetragonal double phase transition mechanism analogous to that previously observed by Wagemaker et al. for anatase nanoparticles smaller than 7 nm.