X-ray Photoemission Spectroscopy Study of Cationic and Anionic Redox Processes in High-Capacity Li-Ion Battery Layered-Oxide Electrodes

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Abstract
Electrode materials based on Li-rich layered oxides are of growing interest for high energy Li-ion battery applications because of their staggering capacities associated to the emergence of a novel reversible anionic process. However, the fundamental science at work behind this new process needs to be well understood for further optimization. Here we report on the redox mechanisms in high capacity Li-rich materials Li2Ru1-xMxO3 and Li2Ir1-xMxO3, by combining XPS core peaks and valence intensity analyses. We fully confirm that these materials electrochemically react with Li via a cumulative reversible cationic/anionic redox processes, but more importantly we reveal that depending on the nature of the metal (Ru or Ir), there is a delicate balance between metal and oxygen contributions. For instance, we show a greater implication of oxide ions for Ir based electrodes consistent with the higher covalent character of Ir-O bonds comparing to Ru-O bonds. We equally provide evidences that the oxygen redox process is responsible for the high capacity displayed by the Li-rich NMC Li1.2Ni0.13Co0.13Mn0.54O2 electrodes that are serious contenders for the next generation of Li-ion batteries. These combined results highlight the benefit of collecting both XPS core and valence spectra for a better understanding of anionic redox mechanisms in Li-rich layered oxides. Keywords: Li-rich oxides, positive electrodes, oxygen redox, XPS core peaks, XPS valence spectra
Funding Information
  • Agence Nationale de la Recherche
  • Ministère de l'Enseignement Supérieur et de la Recherche
  • ALISTORE European Research Institute

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