Lithium storage in nanostructured TiO2 made by hydrothermal growth

Nanostructured titania materials were prepared from TiCl4 via autoclaving in 10 M NaOH at 250 degreesC and subsequent treatment in aqueous and/or acidic media. XRD and Raman spectroscopy evidenced the presence of anatase as the main phase, but most materials contained also some XRD-silent component. Cyclic voltammograms of lithium insertion demonstrate two pairs of reversible pseudocapacitive peaks (S-peaks) in addition to the ordinary peaks of diffusion-controlled Li insertion into the anatase lattice. The occurrence of S-peaks is associated with the nanosheet- and/or nanotubular morphology of the materials. This structure developed at hydrothermal conditions via exfoliation of the layered Na+/H+ titanate precursors. The S-peaks were suggested to be the signatures of quantum-size confinement in titania nanosheets. The nanosheet-containing materials are reducible by n-butyllithium to cubic LiTiO2 (at conditions when the ordinary nanocrystalline anatase gives only the orthorhombic Li0.5TiO2). Consequently, the electrochemical Li-storage capacity is larger compared to that of crystalline anatase. The prepared materials also show better insertion kinetics; hence, they are promising for applications in Li-ion batteries. Depending on the applied voltage, they can be charged/discharged either as ordinary Li-insertion hosts or as supercapacitors.