Deciphering the Oxygen Absorption Pre‐edge: A Caveat on its Application for Probing Oxygen Redox Reactions in Batteries. Issue 2 (28th December 2020)

• Record Type: Journal Article
• Authors: Roychoudhury, Subhayan; Qiao, Ruimin; Zhuo, Zengqing; Li, Qinghao; Lyu, Yingchun; Kim, Jung‐Hyun; Liu, Jun; Lee, Eungje; Polzin, Bryant J.; Guo, Jinghua; Yan, Shishen; Hu, Yongsheng; Li, Hong; Prendergast, David; Yang, Wanli
• Other Names: Wu Yuping guestEditor.; Zhu Yusong guestEditor.; Shi Feifei guestEditor.
• Is Part Of: Energy & environmental materials. Volume 4:Issue 2(2021)
• Page Start: 246
• Page End: 254
• Publication Date: 2020-12-28
• Subjects: battery -- oxygen redox -- x‐ray absorption spectroscopy -- cathode material -- redox reaction; Power resources -- Environmental aspects -- Periodicals; Renewable energy sources -- Periodicals; Environmental engineering -- Periodicals; 333.79
• DOI: 10.1002/eem2.12119
• Languages: English
• ISSNs: 2575-0356

Abstract

Abstract : 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 Cr 3+/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. Abstract : The oxygen‐ K pre‐edge has been broadly used to discuss the oxygen redox states in batteries. Here, through combined experimental and in theoretical studies of a number of oxide electrodes, we conclude that the O‐ K pre‐edge evolution predominantly represents the transition metal state variation, which is summarized to benchmark future research.