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

Abstract

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. Li2RuO3 is an intriguing Li-excess model compound, which is studied here by local (7Li and 17O MAS NMR) and long-range (X-ray and neutron diffraction) structural probes. Li2RuO3 is often reported as adopting the C2/m or the C/2c space group, which ignores the important role that Ru–Ru dimerization plays in controlling its properties. 17O NMR reveals four oxygen sites confirming the room-temperature P21/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 17O 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.