4.6 Article

Quantifying the Capacity Contributions during Activation of Li2Mno3

Journal

ACS ENERGY LETTERS
Volume 5, Issue 2, Pages 634-641

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsenergylett.9b02799

Keywords

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Funding

  1. NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0012583]
  2. Research Corporation for Science Advancement through the Scialog program
  3. Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
  4. DOE Office of Science [DE-SC0012704]
  5. Diamond Light Source [SI22250-1, 5122148-1]

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Though Li2MnO3 was originally considered to be electrochemically inert, its observed activation has spawned a new class of Li-rich layered compounds that deliver capacities beyond the traditional transition-metal redox limit. Despite progress in our understanding of oxygen redox in Li-rich compounds, the underlying origin of the initial charge capacity of Li2MnO3 remains hotly contested. To resolve this issue, we review all possible charge compensation mechanisms including bulk oxygen redox, oxidation of Mn4+, and surface degradation for Li2MnO3 cathodes displaying capacities exceeding 350 mAh g(-1). Using elemental and orbital selective X-ray spectroscopy techniques, we rule out oxidation of Mn4+ and bulk oxygen redox during activation of Li2MnO3. Quantitative gas-evolution and titration studies reveal that O-2 and CO2 release accounted for a large fraction of the observed capacity during activation with minor contributions from reduced Mn species on the surface. These studies reveal that, although Li2MnO3 is considered critical for promoting bulk anionic redox in Li-rich layered oxides, Li2MnO3 by itself does not exhibit bulk oxygen redox or manganese oxidation beyond its initial Mn4+ valence.

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