| 1. |
- Luo, Kun, et al.
(författare)
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Anion Redox Chemistry in the Cobalt Free 3d Transition Metal Oxide Intercalation Electrode Li[Li0.2Ni0.2Mn0.6]O-2
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 138:35, s. 11211-11218
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Tidskriftsartikel (refereegranskat)abstract
- Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g., Mn3+/4+ in LiMn2O4, and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li0.2Ni0.2Mn0.6]O-2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V versus Li+/Li. The capacity at 4.5 V is dominated by oxidation of the O-2(-) anions accounting for similar to 0.43 e(-)/formula unit, with an additional 0.06 e(-)/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V is mainly O loss, similar to 0.08 e(-)/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn4+/Li+). The results have been obtained by combining operando electrochemical mass spec on 180 labeled Li[Li0.2Ni0.2Mn0.6]O-2 with XANES, soft X-ray spectroscopy, resonant inelastic X-ray spectroscopy, and Raman spectroscopy. Finally the general features of O redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal oxygen interaction on anion redox in lithium rich cathode materials.
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| 2. |
- Luo, Kun, et al.
(författare)
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Charge-compensation in 3d-transition-metal-oxide intercalation cathodes through the generation of localized electron holes on oxygen
- 2016
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Ingår i: Nature Chemistry. - 1755-4330 .- 1755-4349. ; 8:7, s. 684-691
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Tidskriftsartikel (refereegranskat)abstract
- During the charging and discharging of lithium-ion-battery cathodes through the de-and reintercalation of lithium ions, electroneutrality is maintained by transition-metal redox chemistry, which limits the charge that can be stored. However, for some transition-metal oxides this limit can be broken and oxygen loss and/or oxygen redox reactions have been proposed to explain the phenomenon. We present operando mass spectrometry of O-18-labelled Li-1.2[Ni0.132+Co0.133+Mn0.544+]O-2, which demonstrates that oxygen is extracted from the lattice on charging a Li-1.2[Ni0.132+Co0.133+Mn0.544+]O-2 cathode, although we detected no O-2 evolution. Combined soft X-ray absorption spectroscopy, resonant inelastic X-ray scattering spectroscopy, X-ray absorption near edge structure spectroscopy and Raman spectroscopy demonstrates that, in addition to oxygen loss, Li+ removal is charge compensated by the formation of localized electron holes on O atoms coordinated by Mn4+ and Li+ ions, which serve to promote the localization, and not the formation, of true O-2(2-)( peroxide, O-O similar to 1.45 angstrom) species. The quantity of charge compensated by oxygen removal and by the formation of electron holes on the O atoms is estimated, and for the case described here the latter dominates.
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