Abstract
The desire to increase the energy density of stoichiometric layered TM (TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true -redox, as observed in -excess cathodes. Through a high-resolution K-edge resonant inelastic x-ray spectroscopy (RIXS) study of the -free -rich layered oxide , we demonstrate that the same oxidized oxygen environment exists in both -excess and non--excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.
- Received 21 October 2022
- Revised 7 February 2023
- Accepted 21 February 2023
DOI:https://doi.org/10.1103/PRXEnergy.2.013005
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The stabilization of oxygen redox at high states of de-lithiation is critical for increasing the energy storage of next generation cathodes based on alkali-ion intercalation. However, the underlying mechanism of oxygen redox remains a topic of intense investigation and requires better understanding of the nature of the oxidized oxygen species. Here, a high-resolution O K-edge resonant inelastic x-ray scattering (RIXS) study of a stoichiometric Mn-free layered cathode (W-doped ), where only transition metal redox is expected, shows that the same oxidized species as that observed for alkali-excess systems forms in a reversible manner. Considering the differences in the structure and de-lithiation pathways between stoichiometric layered and alkali-excess cathodes, this observation demonstrates the importance of oxygen participation in the charge compensation even in systems without Mn, nano-pore formation and/or Li-O-Li configurations. As a result, this work supports the importance of metal-oxygen re-hybridization in facilitating charge compensation and highlights the need for beyond density-functional theory (DFT) studies.
