Nanostructured TiO₂ and Its Application in Lithium‐Ion Storage

Titania nanorods and nanowires are synthesized via a hydrothermal reaction of amorphous TiO 2 in alkaline NaOH, followed by ion exchange in HCl aqueous solution, and dehydration at 400 °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 Na 2 Ti 3 O 7 in HCl aqueous solution brings about a phase change to H 2 Ti 3 O 7 , but there is no change in the particle morphology. Dehydration of the nanostructured H 2 Ti 3 O 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 °C. 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 2 Ti 3 O 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.