Nanostructured TiO2 and Its Application in Lithium-Ion Storage

Titania nanorods and nanowires are synthesized via a hydrothermal reaction of amorphous TiO2 in alkaline NaOH, followed by ion exchange in HCl aqueous solution, and dehydration at 400 degrees C. Although the hydrothermal treatment produces three different particle morphologies depending on the reaction time (nanosheets, nanorods, and nanowires), the products exhibit the same crystal structure. Ion exchange of Na2Ti3O7 in HCl aqueous solution brings about a phase change to H2Ti3O7, but there is no change in the particle morphology. Dehydration of the nanostructured H2Ti3O7 leads to two types of crystal structure-anatase TiO2 for the nanorods, and TiO2-B for the nanowires-although no significant difference is found in the morphology of the products even after dehydration. The nanorods are 40-50 nm in length and 10 nm in diameter, whereas the nanowires are several micrometers in length and tens to hundreds of nanometers in thickness. In-situ X-ray diffraction revealed the formation of anatase TiO2 from the TiO2-B above 450 degrees C. This finding implies that the phase transformation occurs rather slowly for the TiO2-B nanowires due to the larger particle size and higher crystallinity of H2Ti3O7. Tests with Li-metal half cells indicated that the anatase TiO2 nanorods are more favorable for the storage and release of Li ions because of their greater surface area than the TiO2-B nanowires.