Affiliation: | 1. Chemistry Division, Brookhaven National Laboratory, Upton, NY, 11973 USA Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China;2. Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD, 20740 USA;3. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China;4. Chemistry Division, Brookhaven National Laboratory, Upton, NY, 11973 USA;5. National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, 11973 USA |
Abstract: | Following the fundamental research conducted by J. B. Goodenough, the important role of electron localization induced by elemental substitution is studied. The size and electron negativity of host and substituting ions are two important factors in tuning material properties such as local structure and transition metal (TM) oxygen covalency. However, another factor, electron localization, which is widely studied in catalyst research but largely overlooked for battery materials, deserves systematic studies. A combined investigation using synchrotronbased X-ray spectroscopy and theoretical calculations is carried out on the Li-Co-Mn-O model system in which the substituting cation Mn4+, with its 3d3 electronic structure, is used as a promoter for electron localization. Results indicate that electron localization greatly influences the Co O bond by making it less covalent, which increases the delithiation voltage. It is also found that during charge/discharge, electron localization tends to make TM K-edge X-ray absorption near edge spectroscopy (XANES) spectra show a more “rigid shift” behavior while electron delocalization makes the XANES exhibit a “shape change.” It clearly explains why the K-edge XANES data of some TM oxides show no “rigid shift” while the nominal valence states changed. This work highlights the importance of electron localization with guidance for XANES interpretation. |