First-principles study on TiO2-B with oxygen vacancies as a negative material of rechargeable lithium-ion batteries

Abstract

Density functional theory calculations were carried out on oxygen-deficient TiO2-B to evaluate the effect of oxygen vacancies on its electrochemical properties. The computational studies focused on the lithium (Li)-ion transport and electronic conductivity of this defect-containing material. Calculations on TiO2-B with low Li-ion concentration (x(Li/Ti) ≤ 0.25) suggest that compared with defect-free TiO2-B, oxygen-deficient TiO2-B has a higher intercalation voltage and lower migration activation energy along the b-axis channel. This facilitates Li-ion intercalation, which is beneficial for the charge process of rechargeable batteries. Meanwhile, for TiO2-B with high Li-ion concentration (x(Li/Ti) = 1), saturated oxygen-deficient TiO2-B with lower insertion voltage favors Li-ion deintercalation, which aids the discharge process. Electronic structure calculations suggest that the band gap of this defect-containing material is within 1.0-2.0 eV, which is narrower than that of defect-free TiO2-B (3.0 eV). The main contributor to the band-gap narrowing is the density of the Ti-Ov-3d state, which becomes much higher as the oxygen vacancy content increases, which increases electronic conductivity.