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 EF. However, the structural configuration of Ti3O5 (α-Ti3O5 and β-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 (Voc) and electronic structure of Ti3O5 and Ti2O3, respectively. We find that our predicted Ti3O5(C2/c) monoclinic structure is more stable than α-Ti3O5 and β-Ti3O5 because of the cohesive force between layered-layered structure. We demonstrate that α-Ti3O5 and β-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 EF. In particular, the calculated Voc of Ti3O5 (C2/c) monoclinic structure (3.416 V) is much larger than that of the α-Ti3O5 (1.809 V), β-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.