## 3 Results
In fact, both distributions are quite similar at the fully deintercalated sample P05. Nevertheless, looking at P08 the coated sample seems to show slightly poorer reversibility and a more irregular distribution of areas with different colors. The uncoated sample instead shows a more ordered arrangement, from the edge to the bulk, of lower-higher-lower ratio, which seems to correspond to concentric layers with different thickness. As proposed by [PERSON] et al. the surface layer could correspond to a densified, oxygen-poor region [14], while the bulk should have an evenly distributed concentration of trapped oxygen. However, we notice also a layer of high concentration of oxygen that may accumulate at the interior of the densified shell, confirming that the shell may act as a barrier for further oxygen release. It is interesting also to follow the evolution of the \(A\)/\(C\) ratio (Figure 5). This is more complex than the previous because of the asynchronous evolution of \(A\) and \(C\) components. The larger width indicates the heterogeneity of the metal oxidation, already present in the pristine P01, which becomes substantial at P03, particularly in the coated sample, where \(A\) and \(C\) are still both low, in contrast to the uncoated where \(A\) is already high. However, the following distributions are remarkably sharp, indicating that increases in oxygen content are spatially correlated with a higher Ni oxidation. We propose an alternative representation as phase maps, based on the comparison of the pixel-by-pixel absorbance collected at two particular energy values. The distributions expressed as ratios can be resolved by plotting one component vs. the other, obtaining scatter plots, where different ratios or a different thickness can be systematically selected in the field of view. Pixels with different absorbance ratios of the two selected peaks will be easily identified. For instance, in Figure 6, the phase map for P05 is reported for peak \(C\) (\(\sim\)530.3 eV) versus the absorbance value in the pre-edge region (\(\sim\)523.0 eV). Because of the great number of pixels (\(\approx\)10\({}^{6}\)) the density of point is reported using different colors. The scatter plot has a characteristic plume shape, with the spot at the origin corresponds to background pixels outside any object. Larger sample thickness will correspond to points more distant from the origin. Two populations of pixels distributed along two lines with different slope are clearly visible (Figure 6a). Selecting the pixels corresponding to the small slope line (Figure 6b), i.e., small oxygen content, we are able to select regions in the sample where instead the carbon additive is abundant (Figure 6c). Alternatively, pixels selection on the phase map itself will allow the reproducible and automatic selection of pixels corresponding to a different thickness as reported for P01, P05 (uncoated), and P05 VC (coated) measures in Figures 7-9, respectively. Scatter representation of ratio between main spectral components \(C\) and \(A\) (**a**) is cut at zones of different thickness. The spatial localization of each zone is then represented in (**b**), with different colors, while in (**c**) the corresponding normalized spectra are shown, including a zoom on the prepeaks O-K edge region. With the previous method we compared spectral component ratios that indirectly reflect spectral changes but cannot detect possible local deviations from the general variants observed at a first inspection. In this case, we instead directly obtain average spectra that can be compared entirely. For P01 the progression of the concentric zones from border to bulk shows a slight shift towards higher energy but no significant change in the peak ratio. Instead, P05 has an evolution that more clearly demonstrates indications of Figure 4. Peak \(C\) is relatively low at the edge, increases in the intermediate zone, and then decreases again towards the bulk.