The coordination environment of Ni and Mn at the various states of charge were evaluated by extended X-ray absorption fine structure (EXAFS) analysis for O3-NaNMO, O3-NaMNMO, and O3-NaSNMO (Figures fits well with the proposed solid solution-type reaction found from the operando XRD results in the high voltage region. In the case of the Sc-doped material, the coordination number also increases in the same voltage region, but the interatomic distance decreases significantly for the Ni-O bond, where the change is found to become even larger than that of the undoped material. This huge decrease is related to the highest activity of the Ni redox, which is in line with the XANES results discussed above. At the subsequent discharge state at 2.5 V, the curves of all three samples are found to not return to their original OCV state, which indicates that the coordination environment of Ni is only partially reversible for all samples, especially in the case of the undoped material. Overall, Mg doping was found to effectively suppress changes in the Ni environment and enhance the reversibility of the Ni redox activity, while Sc doping causes a large and only partially reversible change in the Ni environment. When comparing both doped materials, the lower degree in Ni redox for the Mg-doped sample is not in line with the higher specific capacity found for this material. This can be only explained by an additional redox activity of the oxygen anions ("oxygen redox") that would need to be enhanced by Mg doping. O K-edge resonant inelastic X-ray scattering (RIXS) was measured to elucidate the impact of the dopants on the degree of oxygen redox. Figures ) show the RIXS data for O3-NaNMO, O3-NaMNMO, and O3-NaSNMO at the OCV, charged to 4.4 V, and discharged to 2.5 V states. A unique peak located at an energy loss of 8 eV is related to the O-O signature, which is widely associated with an oxygen redox feature. In Figures ), this signal is only visible after charging to 4.4 V, and could be observed in all three materials, indicating that oxygen redox does indeed occur for all materials. However, the intensity of this signal is different amongst the three samples, with the highest intensity being observed for O3-NaNMO, followed by O3-NaMNMO, and O3-NaSNMO. Meanwhile, the RIXS maps (Figure ) with excitation energy ranging from 526 to 534 eV were also conducted at the fully charged state (4.4 V). The fingerprint signal of the oxygen redox is highlighted with a light blue circle, which corresponds to the signal at an energy loss of 8 eV as discussed with the 1D RIXS spectra. It can be observed that the intensities of this fingerprint signal are slightly different amongst the materials, but their intensities also follow the observations in the 1D RIXS spectra. Moreover, the progression of peaks close to 0 eV has been magnified and is shown in Figure . A series of peaks with gradually decreasing intensity can be observed for all samples at a state of charge to 4.4 V, which are reported to reflect the vibration between O-O bonds. The intensities of these peaks are associated with the strength of the oxygen redox signal at an energy loss of 8 eV. As expected, the undoped material exhibits peaks with higher intensity, while the two doped materials appear to have relatively lower intensity. This is especially evident in the case of Sc doping, which further shows the lowest degree of oxygen redox among the three materials. The distance between the first peak and 0 eV for all samples is close to that reported for the vibration of molecular O 2 by Bruce et al. Although the presence of molecular oxygen in the lattice of these materials is a matter of debate, the results nevertheless confirm that oxygen redox occurs in all materials when being charged to 4.4 V. However, doping decreases the degree of oxygen redox, and this is observed most strongly in the case of Sc doping.