Insertion energetics of lithium, sodium, and magnesium in crystalline and amorphous titanium dioxide: A comparative first-principles study

Titanium dioxide (TiO2) has been proposed as a potential electrode material for lithium, sodium, and magnesium ion batteries. Among the phases of TiO2, anatase, rutile, and (B)-TiO2 are the most commonly used phases for electrochemical storage, while the amorphous phase has also been shown to be a promising candidate. We present a comparative density functional theory study of the insertion energetics of Li, Na, and Mg into anatase, rutile, and (B)-TiO2, as well as into the amorphous phase. Our results show that among the crystalline phases, (B)-TiO2 provides the strongest binding between TiO2 and the inserted Li/Na/Mg atom. We also find that for all Li, Na, and Mg, the amorphous phase provides insertion sites well-dispersed in energies, with a lowest energy site more thermodynamically favorable than insertion sites in the crystalline phases. We also obtain the localized Ti3+ states together with the formation of the defect states in the band gap, which are induced by the insertion, at the GGA level of theory (without the Hubbard correction).