Effect of Chemical Lithium Insertion into Rutile TiO₂ Nanorods

Rutile TiO 2 nanorods were synthesized by hydrolysis of TiCl 4 followed by a hydrothermal method. Lithium insertion into the rutile nanorods was achieved by a chemical lithium insertion process. The structural evolution of nanostructured rutile upon lithium insertion was characterized by several experimental techniques, namely, XRD, TEM, SAED and 6 Li MAS NMR. The XRD and TEM studies indicate the formation of lithium titanate phase (Li x TiO 2 ) during lithium insertion. Additionally, SAED patterns show that the lithium titanate phase has cubic symmetry. Finally, high magnetic field (21.1 T) 6 Li MAS NMR reveals that the lithium titanate phase adopts two different structures depending on lithium content. Taken together, the four techniques consistently show that the insertion of lithium into rutile TiO 2 nanorods causes two consecutive structural phase transformations to lithium titanate phases with spinel ( Fd 3̅ m ) and rocksalt ( Fm 3̅ m ) structures at x = 0.46 and 0.88, respectively. In addition, the broad line widths in the 6 Li MAS NMR spectrum of the rocksalt phase are indicative of a disordered structure. Density functional theory calculations of the rutile, spinel and rocksalt bulk phases as a function of lithium content corroborate the observed phase transformations. These phase transitions could account for the irreversible capacity loss of nanostructured rutile anodes observed in electrochemical cycling experiments.