Distinction between Intrinsic and X-ray-Induced Oxidized Oxygen States in Li-Rich 3d Layered Oxides and LiAlO2

Resonant inelastic X-ray scattering (RIXS) at the O K-edge is considered a prime technique to identify bulk oxidized oxygen formation, but its fundamental interpretation is not straightforward. In this study, we intentionally induce RIXS signatures of oxidized oxygen upon beam exposure in LiAlO2 polymorphs that are easily distinguished because of their wide band gaps. After careful consideration of beam exposure effects on Li[Li0.144Ni0.136Mn0.544Co0.136]O2 (LR-NMC), we conclude that oxidized oxygen features are inherent at high states of charge and are lost upon aggressive beam exposure. The extracted oxidized oxygen line shapes from our X-ray irradiation studies for both LiAlO2 (induced) and LR-NMC (inherent) are found to have an additional oxidized oxygen RIXS feature not observed in O2 gas studies. This study highlights the unique insight of O K-edge RIXS into determining the nature and stability of oxidized oxygen states.