Insertion of lithium ion in anatase TiO<inf>2</inf> nanotube arrays of different morphology

Abstract

Anatase TiO2 nanotube arrays of different morphology were prepared by a two-step process: anodic oxidation at voltages 20–60 V and subsequent annealing at 400 °C. By amplifying anodization voltage the inner diameter of nanotubes increased. At 60 V nanotubes changed the shape from cylindrical tube to truncated cone with elliptical opening. Electrochemical insertion of Li-ion in nanotubes was studied by cyclic voltammetry and galvanostatic charge-discharge experiments. The cyclovoltammetric response was fast for all nanotube arrays. The galvanostatic areal charge/discharge capacity of nanotube arrays increased with increasing anodizaton voltage. Although the mass of nanotubes prepared at 45 V was larger, the gravimetrical capacity was much higher for nanotubes prepared at 60 V because of the larger surface area exposed to the electrolyte. Gravimetrical capacity values exceed theoretical bulk capacity of anatase due to the surface storage of Li-ion. Diffusion coefficient of Li-ion was calculated to be between 5.9·10−16 and 5.9·10−15 cm2 s−1.