Gi-Hyeok Lee1,Wanli Yang1
Lawrence Berkeley National Lab1
Gi-Hyeok Lee1,Wanli Yang1
Lawrence Berkeley National Lab1
As the development of analytical technology has helped to identify ambiguous phenomena, applying the state-of-art resonant inelastic X-ray scattering (RIXS) technique to cathode materials closely identifies various phenomena in batteries. One of the most important discoveries through RIXS is oxygen redox, which can experimentally show the redox activity of oxygen, which was impossible to analyze with classical X-ray absorption or emission spectra. In highly charged electrodes, the discovery of features distinguishable from those of TM hybridized O further elucidates the redox mechanism oversimplified with the concept of the formal charge. The redox mechanism of Li-rich anode materials, which cannot be solely explained by TM oxidation, has been explained with a focus on their characteristic oxygen redox feature.<br/>However, the discovery of oxygen redox features is not limited to cathode materials with Li-rich chemical composition. Oxygen redox features through RIXS were found in commercial anode materials such as LiCoO<sub>2</sub> and LiNi<sub>x</sub>Co<sub>y</sub>Mn<sub>1-x-y</sub>O<sub>2</sub> as well as trendy cathode materials such as LiNi<sub>0.85</sub>Co<sub>0.10</sub>Al<sub>0.05</sub>O<sub>2</sub> and LiNiO<sub>2</sub>. This means that the understanding of oxygen in the existing redox process was inaccurate and suggests a lot about the strategy for coping with material degradation in the high state of charge established based on the incorrect understanding. Here, we look back at the generation of oxygen redox in “non-Li-rich” commercial cathode materials and revisit their redox mechanism. In addition, we intend to interpret based on a new redox mechanism along with the observed results of material degradation at high SOC, such as X-ray diffraction and differential electrochemical mass spectroscopy.