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Direct Observation of Reductive Coupling Mechanism between Oxygen and Iron/Nickel in Cobalt-Free Li-Rich Cathode Material: An in Operando X-Ray Absorption Spectroscopy Study

Dixon, Ditty 1; Mangold, Stefan 2; Knapp, Michael 1; Ehrenberg, Helmut 1; Bhaskar, Aiswarya 1
1 Karlsruher Institut für Technologie (KIT)
2 Institut für Photonenforschung und Synchrotronstrahlung (IPS), Karlsruher Institut für Technologie (KIT)

Abstract:
Li-rich cathodes possess high capacity and are promising candidates in next-generation high-energy density Li-ion batteries. This high capacity is partly attributed to its poorly understood oxygen-redox activity. The present Li-rich cathodes contain expensive and environmentally-incompatible cobalt as a main transition metal. In this work, cobalt-free, iron-containing Li-rich cathode material (nominal composition Li$_{1.2}$Mn$_{0.56}$Ni$_{0.16}$Fe$_{0.08}$O$_{2}$) is synthesized, which exhibits excellent discharge capacity (≈250 mAh g$^{-1}$ and cycling stability. In operando, X-ray absorption spectroscopy at Mn, Fe, and Ni K edges reveals its electrochemical mechanism. X-ray absorption near edge structure (XANES) features of Fe and Ni K edges show unusual behavior: when an electrode is charged to 4.5 V, Fe and Ni K edges’ XANES features shift to higher energies, evidence for Fe$^{3+}$→Fe$^{4+}$ and Ni$^{2+}$→Ni$^{4+}$ oxidation. However, when charged above 4.5 V, XANES features of Fe and Ni K edges shift back to lower energies, indicating Fe$^{4+}$→Fe$^{3+}$ and Ni$^{4+}$→Ni$^{3+}$ reduction. This behavior can be linked to a reductive coupling mechanism between oxygen and Fe/Ni. ... mehr


Verlagsausgabe §
DOI: 10.5445/IR/1000133587
Veröffentlicht am 03.06.2021
Originalveröffentlichung
DOI: 10.1002/aenm.202100479
Scopus
Zitationen: 2
Dimensions
Zitationen: 3
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Angewandte Materialien – Energiespeichersysteme (IAM-ESS)
Institut für Photonenforschung und Synchrotronstrahlung (IPS)
Publikationstyp Zeitschriftenaufsatz
Publikationsjahr 2021
Sprache Englisch
Identifikator ISSN: 1614-6832, 1614-6840
KITopen-ID: 1000133587
HGF-Programm 38.02.02 (POF IV, LK 01) Components and Cells
Erschienen in Advanced Energy Materials
Verlag Wiley-VCH Verlag
Band 11
Heft 24
Seiten Art.-Nr. 2100479
Schlagwörter Li-rich; cathodes; cobalt-free; in operando; Ni/Fe; reductive coupling; X-ray absorption spectroscopy
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Web of Science
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