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Deciphering the oxygen absorption pre-edge: a caveat on its application for probing oxygen redox reactions in batteries

preprint
revised on 28.05.2020 and posted on 29.05.2020 by Subhayan Roychoudhury, Ruimin Qiao, Zengqing Zhuo, Qinghao Li, Yingchun Lyu, Jung-Hyun Kim, Jun Liu, Eungje Lee, Bryant J. Polzin, Jinghua Guo, Shishen Yan, Yongsheng Hu, Hong Li, David Prendergast, Wanli Yang
The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal (TM) oxide studies in various fields, especially on the fervent topic of oxygen redox states in battery electrodes. However, critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions, which has been a popular practice in the battery field. This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements, structures and electrochemical states through combined experimental and theoretical analyses. It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states. Furthermore, the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window, leading to a summary map of the relative energy positions of the low-lying TM states, with higher TM oxidation states at lower energies, corresponding to higher electrochemical potentials. The results naturally clarify some unusual redox reactions, such as Cr3+/6+. This work provides a critical clarification on O-K pre-edge interpretation and more importantly, a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.

Funding

US DOE Contract No. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory

US DOE DAMP by DOE VTO at Argonne National Laboratory

LDRD of Lawrence Berkeley National Laboratory

History

Email Address of Submitting Author

wlyang@lbl.gov

Institution

Lawrence Berkeley National Laboratory

Country

United States

ORCID For Submitting Author

0000-0003-0666-8063

Declaration of Conflict of Interest

None

Version Notes

Version 3 with merged main and supplementary information

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