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Kinyanjui, M. K., Axmann, P., Mancini, M., Gabrielli, G., Balasubramanian, P., Boucher, F., Wohlfahrt-Mehrens, M. & Kaiser, U. (2017) Understanding the spectroscopic signatures of Mn valence changes in the valence energy loss spectra of Li-Mn-Ni-O spinel oxides. Physical Review Materials, 1 074402.
Added by: Richard Baschera (2018-02-08 09:30:13) Last edited by: Richard Baschera (2018-02-08 09:31:23) |
| Type de référence: Article DOI: 10.1103/PhysRevMaterials.1.074402 Clé BibTeX: Kinyanjui2017 Voir tous les détails bibliographiques  |
Catégories: INTERNATIONAL, ST2E Créateurs: Axmann, Balasubramanian, Boucher, Gabrielli, Kaiser, Kinyanjui, Mancini, Wohlfahrt-Mehrens Collection: Physical Review Materials |
Consultations : 1/400
Indice de consultation : 4% Indice de popularité : 1% |
| Résumé |
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The valence energy loss spectrum which is characterized by valence-to-conduction band and plasmon excitations is rarely used in spectroscopy of Li-ion battery materials. One reason being the large number of different excitations observed in this region as well as the difficulty in interpreting their nature and origin. We have determined the nature and origin of spectral features observed in Li-Mn-Ni-O spinel oxides with respect to Mn valency changes during the insertion of lithium ion. The lithiation process is accompanied by a Mn valency change from Mn 4+ in LiNi0.5Mn1.5O4 to Mn 3+ in lithium rich Li2Ni0.5Mn1.5O4. The valence energy loss spectrum of LiNi0.5Mn1.5O4 is characterized by sharp peaks in the 7-10 eV energy loss range whose intensity decrease with lithiation to Li2Ni0.5Mn1.5O4. Using electronic structure calculations and molecular orbital considerations we show that the intense peaks in the valence loss spectra of LiNi0.5Mn1.5O4 have a large contribution from ligand-metal charge transfer transitions. These transitions arise from the mainly O 2p nonbonding t(2u) and bonding t(1u) orbitals to the mainly Mn 3d antibonding t(2g)* and e(g)* orbitals. We discuss the origins of the observed valence spectra differences between the two phases in relation to peaks shift, variations in occupancy, and variations in covalency as a result of Mn valency changes occurring during lithiation.
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