TiO2 Nanotubes as an Anode Material for Lithium Ion Batteries

In recent years, TiO2 has been widely investigated as a promising anode material for lithium ion batteries because of its low volume change during the charge/discharge process, environmental benignity, and high safety. However, it suffers from poor electron transport, slow ion diffusion, and low theoretical capacity (335 mAh.g(-1)), which limit its practical application. In this paper, we review the development history and latest progress of TiO2 nanotubes (TNTs) as anode materials. Three typical synthesis methods of TNTs, namely, hydrothermal method, anodic oxidation, and template method, are analyzed in detail. We explain the formation mechanism, compare the advantages and disadvantages of each method, and identify the factors influencing the formation of TNTs. We also carefully analyze the morphology and crystallography of TNTs and describe how they influence the electrochemical performance. It is pointed out that c-axis oriented, arrayed, unsealed TNTs with a wall thickness less than 5 nm show better electrochemical performance. Various approaches for improving the electrochemical performance of TNTs are summarized, including preparation of three-dimensional (3D) structured electrodes, doping, coating, and synthesis of composites. Among these approaches, compositing with materials that have high capacity and high conductivity has proven to be effective, convenient, and controllable. The achievements and the problems associated with each approach are summarized, and the possible research directions and prospects of TNTs as anode materials for Li-ion batteries in the future are discussed.