Morphological Dependence of Lithium Insertion in Nanocrystalline TiO<sub>2</sub>(B) Nanoparticles and Nanosheets

The lithium insertion behavior of nanoparticle (3-D) and nanosheet (2-D) architectures of TiO<sub>2</sub>(B) is quite different, as observed by differential capacity plots derived from galvanostatic charging/discharge experiments. DFT+<i>U</i> calculations show unique lithiation mechanisms for the different nanoarchitectures. For TiO<sub>2</sub>(B) nanoparticles, A2 sites near equatorial TiO<sub>6</sub> octahedra are filled first, followed by A1 sites near axial TiO<sub>6</sub> octahedra. No open-channel C site filling is observed in the voltage range studied. Conversely, TiO<sub>2</sub>(B) nanosheets incrementally fill C sites, followed by A2 and A1. DFT+<i>U</i> calculations suggest that the different lithiation mechanisms are related to the elongated geometry of the nanosheet along the <i>a</i>-axis that reduces Li<sup>+</sup>–Li<sup>+</sup> interactions between C and A2 sites. The calculated lithiation potentials and degree of filling agree qualitatively with the experimentally observed differential capacity plots.