Redox chemistry and the role of trapped molecular O2 in li-rich disordered rocksalt oxyfluoride cathodes
In the search for high energy density cathodes for next-generation lithium-ion batteries, the disordered rocksalt oxyfluorides are receiving significant attention due to their high capacity and lower voltage hysteresis compared with ordered Li-rich layered compounds. However, a deep understanding of...
| Main Authors: | , , , , , , , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
American Chemical Society
2020
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| _version_ | 1797087589036982272 |
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| author | Sharpe, R House, RA Clarke, MJ Förstermann, D Marie, J-J Cibin, G Zhou, K-J Playford, HY Bruce, PG Islam, MS |
| author_facet | Sharpe, R House, RA Clarke, MJ Förstermann, D Marie, J-J Cibin, G Zhou, K-J Playford, HY Bruce, PG Islam, MS |
| author_sort | Sharpe, R |
| collection | OXFORD |
| description | In the search for high energy density cathodes for next-generation lithium-ion batteries, the disordered rocksalt oxyfluorides are receiving significant attention due to their high capacity and lower voltage hysteresis compared with ordered Li-rich layered compounds. However, a deep understanding of these phenomena and their redox chemistry remains incomplete. Using the archetypal oxyfluoride, Li<sub>2</sub>MnO<sub>2</sub>F, we show that the oxygen redox process in such materials involves the formation of molecular O<sub>2</sub> trapped in the bulk structure of the charged cathode, which is reduced on discharge. The molecular O<sub>2</sub> is trapped rigidly within vacancy clusters and exhibits minimal mobility unlike free gaseous O<sub>2</sub>, making it more characteristic of a solid-like environment. The Mn redox process occurs between octahedral Mn<sup>3+</sup> and Mn<sup>4+</sup> with no evidence of tetrahedral Mn<sup>5+</sup> or Mn<sup>7+</sup>. We furthermore derive the relationship between local coordination environment and redox potential; this gives rise to the observed overlap in Mn and O redox couples and reveals that the onset potential of oxide ion oxidation is determined by the degree of ionicity around oxygen, which extends models based on linear Li-O-Li configurations. This study advances our fundamental understanding of redox mechanisms in disordered rocksalt oxyfluorides, highlighting their promise as high capacity cathodes. |
| first_indexed | 2024-03-07T02:37:47Z |
| format | Journal article |
| id | oxford-uuid:a95e2129-e58c-43bb-bc97-6a7153b35681 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T02:37:47Z |
| publishDate | 2020 |
| publisher | American Chemical Society |
| record_format | dspace |
| spelling | oxford-uuid:a95e2129-e58c-43bb-bc97-6a7153b356812022-03-27T03:08:07ZRedox chemistry and the role of trapped molecular O2 in li-rich disordered rocksalt oxyfluoride cathodesJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:a95e2129-e58c-43bb-bc97-6a7153b35681EnglishSymplectic ElementsAmerican Chemical Society2020Sharpe, RHouse, RAClarke, MJFörstermann, DMarie, J-JCibin, GZhou, K-JPlayford, HYBruce, PGIslam, MSIn the search for high energy density cathodes for next-generation lithium-ion batteries, the disordered rocksalt oxyfluorides are receiving significant attention due to their high capacity and lower voltage hysteresis compared with ordered Li-rich layered compounds. However, a deep understanding of these phenomena and their redox chemistry remains incomplete. Using the archetypal oxyfluoride, Li<sub>2</sub>MnO<sub>2</sub>F, we show that the oxygen redox process in such materials involves the formation of molecular O<sub>2</sub> trapped in the bulk structure of the charged cathode, which is reduced on discharge. The molecular O<sub>2</sub> is trapped rigidly within vacancy clusters and exhibits minimal mobility unlike free gaseous O<sub>2</sub>, making it more characteristic of a solid-like environment. The Mn redox process occurs between octahedral Mn<sup>3+</sup> and Mn<sup>4+</sup> with no evidence of tetrahedral Mn<sup>5+</sup> or Mn<sup>7+</sup>. We furthermore derive the relationship between local coordination environment and redox potential; this gives rise to the observed overlap in Mn and O redox couples and reveals that the onset potential of oxide ion oxidation is determined by the degree of ionicity around oxygen, which extends models based on linear Li-O-Li configurations. This study advances our fundamental understanding of redox mechanisms in disordered rocksalt oxyfluorides, highlighting their promise as high capacity cathodes. |
| spellingShingle | Sharpe, R House, RA Clarke, MJ Förstermann, D Marie, J-J Cibin, G Zhou, K-J Playford, HY Bruce, PG Islam, MS Redox chemistry and the role of trapped molecular O2 in li-rich disordered rocksalt oxyfluoride cathodes |
| title | Redox chemistry and the role of trapped molecular O2 in li-rich disordered rocksalt oxyfluoride cathodes |
| title_full | Redox chemistry and the role of trapped molecular O2 in li-rich disordered rocksalt oxyfluoride cathodes |
| title_fullStr | Redox chemistry and the role of trapped molecular O2 in li-rich disordered rocksalt oxyfluoride cathodes |
| title_full_unstemmed | Redox chemistry and the role of trapped molecular O2 in li-rich disordered rocksalt oxyfluoride cathodes |
| title_short | Redox chemistry and the role of trapped molecular O2 in li-rich disordered rocksalt oxyfluoride cathodes |
| title_sort | redox chemistry and the role of trapped molecular o2 in li rich disordered rocksalt oxyfluoride cathodes |
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