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Oxygen redox chemistry without excess alkali-metal ions in Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\)

Maitra, Urmimala, House, Robert A., Somerville, James W., Tapia-Ruiz, Nuria, Lozano, Juan G., Guerrini, Niccoló, Hao, Rong, Luo, Kun, Jin, Liyu, Pérez-Osorio, Miguel A., and others. (2018) Oxygen redox chemistry without excess alkali-metal ions in Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\). Nature Chemistry, 10 . pp. 288-295. ISSN 1755-4330. E-ISSN 1755-4349. (doi:10.1038/nchem.2923) (KAR id:65829)

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Abstract

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2\(p\) orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li\(^+\)–O(2\(p\))–Li\(^+\) interactions). Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\) exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg\(^{2+}\) resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\) does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg\(^{2+}\) remains in Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\), which stabilizes oxygen.

Item Type: Article
DOI/Identification number: 10.1038/nchem.2923
Uncontrolled keywords: Physics of Quantum Materials
Subjects: Q Science > QC Physics
Divisions: Faculties > Sciences > School of Physical Sciences
Depositing User: Alan Chadwick
Date Deposited: 31 Jan 2018 15:20 UTC
Last Modified: 27 Jan 2020 11:14 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/65829 (The current URI for this page, for reference purposes)
Ramos, Silvia: https://orcid.org/0000-0003-2725-7706
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