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 degrees 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 N-2 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 degrees C and undergo phase transition to a mixture of anatase and TiO2(B) with anatase as the main phase between 300 and 500 degrees C. In addition, the hollow nanotube morphology still remains below 400 degrees C, but the tubes convert to solid nanorods during the calcination at 500 degrees C. It is found the nanotubes calcined at 300 and 400 degrees 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.