**6. Conclusions**

in agreement with the tiny yellow fragments that can be noted embedded in the carbonate matrix, without being accessible even to the mediators, making the corresponding capacity

112 X-ray Characterization of Nanostructured Energy Materials by Synchrotron Radiation

**Figure 11.** (a and b) TXM images of a carbon‐coated Au TEM grid after being fully discharged in a Li‐O2

have been obtained by the same method. The gray noisy area results from regions with low LiO2

(cyan), Li peroxide (green), and carbonate (red). (c) Map of the LiO2

reference Li2

Chemical Society.

O2 and Li2 CO3

images are the result of overlapping three color maps with intensities proportional to the amounts of Li superoxide

Corresponding O K‐edge XANES spectra at the selected points indicated by arrows in figures a and b, together with

/Li2 O2

spectra. Reprinted with permission from Olivares‐Marín et al. [11]. Copyright 2015 American

ratio. The respective LiO2

cell. The

intensities

values. (d)

 and Li2 O2

 and Li2 O2

highly irreversible.

Full‐field transmission soft X‐ray microscopy is a powerful tool for the characterization of nanocomposites and nanostructured materials. Its high energy and space resolution provide accurate and semiquantitative chemical information at the scale of few tens of nm. This technique is particularly useful to inspect heterogeneities in all those materials involving the redox activity of several elements, including O and N. The unique access to the oxygen chemical state is extremely valuable to the investigation of metal air batteries. In this field, the technique contributes to understand the morphology and nature of the discharge products, their formation, and removal mechanism during discharge and charge of metal‐air batteries. In particular, it is likely the most effective technique in detecting the critical superoxide component and its interplay with the other compounds present. The correlation between the respective spatial distributions gives one of the most comprehensive pictures of the reactivity and failure mechanisms, which hopefully will lead to strategies able to turn the Li/O2 and other metal‐air chemistries into a technological reality.
