First-principles investigation of phonon dynamics and electrochemical performance of TiO2-x oxides lithium-ion batteries

Compared to titanium oxide(TiO2), non-equilibrium stoichiometry titanium oxides(TiO2-x) are promising electrode materials because oxygen vacancy changes the electronic interaction near E-F. However, the structural configuration of Ti3O5 (alpha-Ti3O5 and beta-Ti3O5) remains considerable controversy. In particular, the electrochemical performance of TiO2-x is entirely unclear. By means of first-principles calculations, we present the results of structure, average open circuit voltage (Vac) and electronic structure of Ti3O5 and Ti2O3, respectively. We find that our predicted Ti3O5(C2/c) monoclinic structure is more stable than (1-Ti3O5 and beta-Ti3O5 because of the cohesive force between layered-layered structure. We demonstrate that alpha-Ti3O5 and beta-Ti3O5 are dynamically instable due to the vibration of the O and Ti at the low frequency region. Importantly, we firstly predict a novel Ti3O5(C2/c) monoclinic structure. Compared to TiO2, Ti3O5 and Ti2O3 exhibit metallic behavior because Ti-3d and O-2p bands across E-F. In particular, the calculated V-oc of Ti3O5 (C2/c) monoclinic structure (3.416 V) is much larger than that of the alpha-Ti3O5 (1.809 V), beta-Ti3O5 (1.454 V) and Ti2O3 (2.255 V) due to the two O sub-boundary layers. We believe that our work opens a new opportunity for developing the titanium oxide as application of lithium ion batteries. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.