Thermodynamics of Lithium in TiO2(B) from First Principles

We use first-principles density functional theory (DFT) calculations combined with statistical mechanical techniques based on the cluster expansion method and Monte Carlo simulations to predict the lithium site occupancies, voltage curves, and phase diagram for TiO2(B), a candidate anode material for lithium ion batteries. We find that Li intercalation is thermodynamically favorable up to a Li/Ti ratio of 1.25, higher than the theoretical maximum usually assumed for TiO2. The calculated phase diagram at 300 K contains three first-order phase transformations corresponding to major changes in the favored intercalation sites at increasing Li concentrations. Calculations based on DFT predict the stability of a new Li site at high Li concentrations in TiO2(B) and the occurrence of a dramatic site-inversion as Li is added to the host.