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

• Published in: Journal of physical chemistry. C Vol. 120; no. 2; pp. 862 - 874
• Main Authors: Foix, Dominique, Sathiya, Mariyappan, McCalla, Eric, Tarascon, Jean-Marie, Gonbeau, Danielle
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.01.2016
• Subjects: Chemical Sciences
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.5b10475

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 with 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–x M x O3 and Li2Ir1–x M x O3, by combining X-ray photoemission spectroscopy (XPS) core peaks and valence intensity analyses. We fully confirm that these materials electrochemically react with Li via 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 compared to Ru–O bonds. We equally provide evidence 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.