Electronic structure and properties of lithium-rich complex oxides

Lithium-rich complex transition-metal oxides Li${}_2$MoO${}_3$, Li${}_2$RuO${}_3$, Li${}_3$RuO${}_4$, Li${}_3$NbO${}_4$, Li${}_5$FeO${}_4$, Li${}_5$MnO${}_4$ and their derivatives are of interest for high-capacity battery electrodes. Here, we report a first-principles density-functional theory study of the atomic and electronic structure of these materials using the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional which treats all orbitals in the materials on equal footing. Dimerization of the transition-metal ions is found to occur in layered Li${}_2$MoO${}_3$, in both fully lithiated and partially delithiated compounds. The Ru–Ru dimerization does not occur in fully lithiated Li${}_2$RuO${}_3$, in contrast to what is commonly believed; Ru–Ru dimers are, however, found to occur in the presence of lithium vacancies caused by lithium loss during synthesis and/or lithium removal during use. We also analyze the electronic structure of the complex oxides and discuss the delithiation mechanism in these battery electrode materials.