Characterizing the Structure and Phase Transition of Li₂RuO₃ Using Variable-Temperature ¹⁷O and ⁷Li NMR Spectroscopy

Li-excess lithium-ion battery cathode materials and the role that reversible anionic redox may play in their high capacities have generated significant interest, motivating studies of the oxygen local structure. Li 2 RuO 3 is an intriguing Li-excess model compound, which is studied here by local ( 7 Li and 17 O MAS NMR) and long-range (X-ray and neutron diffraction) structural probes. Li 2 RuO 3 is often reported as adopting the C 2/ m or the C /2 c space group, which ignores the important role that Ru–Ru dimerization plays in controlling its properties. 17 O NMR reveals four oxygen sites confirming the room-temperature P 2 1 / m structure proposed by Miura, Y.; Yasui, Y.; Sato, M.; Igawa, N.; Kakurai, K. J. Phys. Soc. Japan 2007, 76, 033705. Through the rationalization of the 17 O NMR shifts, at room temperature and through the phase transition (>260 °C), detailed information concerning the electronic structure and locations of the unpaired electrons in this compound is revealed.