Electrochemical Lithium Storage of Titanate and Titania Nanotubes and Nanorods

Layered protonated titanate nanotubes, synthesized via a hydrothermal reaction in alkaline solution, were calcined at different temperatures (200−500 °C) in air to achieve the products of various morphologies and crystal-phase compositions. The microstructure of obtained products was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N₂ adsorption. The electrochemical lithium storage of these samples was studied by galvanostatic method and cyclic voltammetry. It is found that the protonated titanate nanotubes maintain layered structure below 300 °C and undergo phase transition to a mixture of anatase and TiO₂(B) with anatase as the main phase between 300 and 500 °C. In addition, the hollow nanotube morphology still remains below 400 °C, but the tubes convert to solid nanorods during the calcination at 500 °C. It is found the nanotubes calcined at 300 and 400 °C have larger surface areas and exhibit relatively large reversible capacity and good reversibility (remain about 200 mA h/g after 80 cycles). Moreover, the electrochemical lithium storage is controlled by the pseudocapacitive effect, the mixed process of both the pseudocapacitive effect, and diffusion-limited reaction, and the diffusion-limited reaction depends on different microstructures of the resulting samples. The relationship among their phase composition, morphology, porous structure, and electrochemical properties is also discussed.