Nanostructured TiO_2 and Its Application in Lithium-Ion Storage

摘要

Titania nanorods and nanowires are synthesized via a hydrothermal reaction of amorphous TiO_2 in alkaline NaOH, followed by ion exchange in HCI aqueous solution, and dehydration at 400 ℃. 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 Na_2Ti_3O_7 in HCI aqueous solution brings about a phase change to H_2Ti_3O_7, but there is no change in the particle morphology. Dehydration of the nanostructured H_2Ti_3O_7 leads to two types of crystal structure-anatase TiO_2 for the nanorods, and TiO_2-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 TiO_2 from the TiO_2-B above 450 ℃. This finding implies that the phase transformation occurs rather slowly for the TiO_2-B nanowires due to the larger particle size and higher crystallinity of H_2Ti_3O_7. Tests with Li-metal half cells indicated that the anatase TiO_2 nanorods are more favorable for the storage and release of Li ions because of their greater surface area than the TiO_2-B nanowires.