Electronic structure and properties of Li-insertion materials: Li$_2$RuO$_3$ and RuO$_2$
M. D. Johannes, A. M. Stux, and K. E. Swider-Lyons

We synthesize, measure and use first principles density functional theory (DFT) calculations to study two Ru-based metal oxides, layered Li$_2$RuO$_3$ and rutile RuO$_2$, in terms of their electrochemical performance as potential battery cathode materials. Despite being composed of identical constituent elements, and having the same local structure (RuO$_6$ octahedra), the two compounds have very different voltage profiles and conductivities that can be traced back to differences in their long range structures. We find that three basic factors contribute to the superior cathode properties of Li$_2$RuO$_3$ in comparison to RuO$_2$: a lower Ru/O ratio that raises the oxidation state of Ru, more localized electron states and longer Li-Li distances due to quasi-two-dimensionality, and strong Ru-Ru bonding in the metal oxide plane that shifts the electronic energy levels. The principles extracted from the comparison of these two materials are generalizable and can be used to help guide the search for superior cathode compounds.

© 2008 The American Physical Society.