Self-Organized TiO2/CoO Nanotubes as Potential Anode Materials for Lithium Ion Batteries

Electrode material characteristics need to be improved urgently to fulfill the requirements for high performance lithium ion batteries. Herein, we report the use of the two-phase alloy Ti80Co20 for the growth of Ti–Co–O nanotubes employing an anodic oxidation process in a formamide-based electrolyte containing NH4F. The surface morphology and the current density for the initial nanotube formation are found to be dependent on the crystal structure of the alloy phases. X-ray photoelectron spectroscopy analyses of the grown nanotube arrays along with the oxidation state of the involved elements confirmed the formation of TiO2/CoO nanotubes under the selected process conditions. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at different current densities of 10–400 μA cm–2. The results revealed that TiO2/CoO nanotubes prepared at 60 V exhibited the highest areal capacity of ∼600 μAh cm–2 (i.e., 315 mAh g–1) at a current density of 10 μA cm–2. At higher current densities, TiO2/CoO nanotubes showed nearly doubled lithium ion intercalation and a Coulombic efficiency of 96% after 100 cycles compared to lower effective TiO2 nanotubes prepared under identical conditions. The observed enhancement in the electrochemical performances could be attributed to increasing Li ion diffusion resulting from the presence of CoO nanotubes and the high surface area of the grown oxide tubes. The TiO2/CoO electrodes preserved their tubular structure after electrochemical cycling with only little changes in morphology.