Wednesday, 4 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
L. Li (Center for Nanoscale Materials, Argonne National Laboratory), F. Castro (Department of Materials Science and Engineering, Northwestern University), J. S. Park, E. Lee (Chemical Sciences and Engineering, Argonne National Laboratory), J. W. Freeland (X-ray Science Division, Argonne National Laboratory), Z. Yao (Department of Materials Science and Engineering, Northwestern University), T. T. Fister (Chemical Sciences and Engineering Division, Argonne National Laboratory), J. Vinson, E. Shirley (National Institute of Standards and Technology), C. Wolverton, V. Dravid (Department of Materials Science and Engineering, Northwestern University), M. M. Thackeray (Chemical Sciences and Engineering Division, Argonne National Laboratory), and M. K. Y. Chan (Center for Nanoscale Materials, Argonne National Laboratory)
In the pursuit of novel cathode materials with high Li capacities, the Li-rich oxides with Li/TM (transition metal) ratio larger than 1 have recently gained increased interest. For instance, the active role of oxygen ions in the charge compensation has been reported in layered rocksalt Li
2IrO
3,
1 which serve as a model system to understand the structural response of Li-rich cathodes to Li extraction, as well the role of oxygen in compensating Li
+ loss.
In this study, we employed various experimental techniques as well as first-principles density functional theory (DFT) to investigate the structural and electronic evolution of Li2IrO3 upon electrochemical cycling. It is found that Li2IrO3 undergoes phase transition and slight capacity fading at each cycle. All the thermodynamically stable phases of Li2-xIrO3 (0≤x<2) are identified through a complete structural screening based on electrostatic energy and DFT calculations. Electron Energy Loss Spectroscopy (EELS) and X-ray Absorption Near Edge Spectroscopy (XANES) are adopted to probe the changes in the oxygen electronic structure at various (de)lithiation stages, and corresponding O K-edge spectra are simulated based on first-principles calculations. The cationic/anionic charge compensation mechanism of Li2IrO3 upon delithiation is discussed based on the spectroscopic observations.
1. E. McCalla et al., Science, 350, 1516–1521 (2015)
