X-ray absorption near edge structure (XANES) analysis was used to investigate the changes in oxidation states of Ni and Mn for all samples. Figure ) shows the XANES data for the Ni K-edge at different charge/discharge states. When charging to 4.0 V, P2-NaNMO and P2-NaM0.10NMO show a small shift towards higher energies relative to the OCV state, whereas P2-NaS0.10NMO shows a stronger shift, indicating that more Ni redox is involved in the electrochemical reaction for P2-NaS0.10NMO at this stage than in the other compositions. In the high voltage region at 4.4 V, all three samples exhibit distinct energy shifts, indicating that Ni redox also takes place in the high voltage regime. Upon discharge, P2-NaNMO and P2-NaM0.10NMO show a high degree of reversibility, almost perfectly overlapping the XAS spectra of the OCV state. For the P2-NaS0.10NMO sample, however, the Ni redox is clearly only partially reversible with Ni remaining in a higher oxidation state compared to what was found at OCV, as can be observed by the jump remaining at higher energy for the fully discharged state. This indicates that P2-NaNMO and P2-NaM0.10NMO have a better Ni redox reversibility compared to P2-NaS0.10NMO in the first cycle, which is consistent with the XRD results. In addition, the Mn K-edge XANES at the different charge/discharge states was also collected (see Figure ). These results show that Mn is only electrochemically active in the Sc-doped material. In this case, a Mn 3+/4+ redox is most probable because the high valence Sc 3+ replacing the low valence Ni 2+ requires lowering of the Mn valence for charge compensation. This has the additional consequence of increasing distortion in the MnO6 octahedra, as evidenced in the comparison of the Mn K-edge EXAFS of the samples at OCV in Figure . Here is it shown that despite an overall average octahedral coordination in the samples, the intensity of the Mn-O signal is reduced and shifted slightly to lower radial distances in the case of Sc doping. This suggests greater disorder in the structure which would be consistent with Mn and O existing in multiple sites. This is strongly related to the reported pseudo-Jahn Teller Effect which is known to impact the structural reversibility in Ni-free Mn layered oxides, and can help explain the observed structural irreversibility found during cycling for the Sc-doped material. Local structural variations around Ni and Mn were monitored through analysis of the extended X-ray absorption fine structure (EXAFS) at the Ni and Mn K-edges (see Figures ) and S10, respectively) for all samples. All of the corresponding EXAFS spectra are characterized by two main features that correspond to the TM-O in the first coordination shell and the TM-Me in the second coordination shell (where TM is Ni or Mn, and Me is Ni, Mn, or the doping atoms Mg or Sc). In Figure ), the Fourier transformed (FT) EXAFS spectra at the Ni K-edge are shown, where it can be seen that the signal intensities of the Ni-O shell for P2-NaNMO and P2-NaS0.10NMO both decrease between the OCV and charged to 4.0 V states, indicating a decrease in coordination number. No change in signal intensity is observed between these two voltages in the case of P2-NaM0.10NMO, supporting a higher structure stability in the Mgdoped material. When the voltage is increased to 4.4 V, all materials show a significant reduction in both the radial distance and intensity related to the Ni-O shell, implying that the bond length of Ni-O and the coordination number both decrease. However, the Mn-O bond length in the Mn K-edge EXAFS does not appear to change appreciably (see Figure ).