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What Triggers Oxygen Loss in Oxygen Redox Cathode Materials?

House, Robert A., Maitra, Urmimala, Jin, Liyu, Lozano, Juan G., Somerville, James W., Rees, Nicholas H., Naylor, Andrew J., Duda, Laurent C., Massel, Felix, Chadwick, Alan V., and others. (2019) What Triggers Oxygen Loss in Oxygen Redox Cathode Materials? Chemistry of Materials, 31 (9). pp. 3293-3300. ISSN 0897-4756. (doi:10.1021/acs.chemmater.9b00227) (KAR id:74307)

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https://doi.org/10.1021/acs.chemmater.9b00227

Abstract

It is possible to increase the charge capacity of transition-metal (TM) oxide cathodes in alkali-ion batteries by invoking redox reactions on the oxygen. However, oxygen loss often occurs. To explore what affects oxygen loss in oxygen redox materials, we have compared two analogous Na-ion cathodes, P2-Na0.67Mg0.28Mn0.72O2 and P2-Na0.78Li0.25Mn0.75O2. On charging to 4.5 V, >0.4e– are removed from the oxide ions of these materials, but neither compound exhibits oxygen loss. Li is retained in P2-Na0.78Li0.25Mn0.75O2 but displaced from the TM to the alkali metal layers, showing that vacancies in the TM layers, which also occur in other oxygen redox compounds that exhibit oxygen loss such as Li[Li0.2Ni0.2Mn0.6]O2, are not a trigger for oxygen loss. On charging at 5 V, P2-Na0.78Li0.25Mn0.75O2 exhibits oxygen loss, whereas P2-Na0.67Mg0.28Mn0.72O2 does not. Under these conditions, both Na+ and Li+ are removed from P2-Na0.78Li0.25Mn0.75O2, resulting in underbonded oxygen (fewer than 3 cations coordinating oxygen) and surface-localized O loss. In contrast, for P2-Na0.67Mg0.28Mn0.72O2, oxygen remains coordinated by at least 2 Mn4+ and 1 Mg2+ ions, stabilizing the oxygen and avoiding oxygen loss.

Item Type: Article
DOI/Identification number: 10.1021/acs.chemmater.9b00227
Uncontrolled keywords: Physics of Quantum Materials
Divisions: Faculties > Sciences > School of Physical Sciences
Depositing User: Alan Chadwick
Date Deposited: 07 Jun 2019 13:56 UTC
Last Modified: 17 Jul 2019 10:01 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/74307 (The current URI for this page, for reference purposes)
Ramos, Silvia: https://orcid.org/0000-0003-2725-7706
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