**5.2. Toroidal particles**

**5.1. Spatial distribution of products**

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

batteries are reported in the literature with different mor-

phology and composition. When the product is well crystalline electron diffraction coupled to TEM may help to assign a given composition to a certain morphology. In our case, we can attribute a composition to most oxygen‐bearing objects, regardless of the crystallinity. To illustrate this, **Figure 10** shows a typical example. The overall spectrum of this sample presents features of superoxide (529 eV), peroxide (531 eV), and a component typical for fully oxidized oxygen, such as carbonate or hydroxide (533 eV). However, spectra at different points differ significantly, which implies that heterogeneity is larger than the spatial resolution, and that the spectral (and hence chemical) difference between the various independent components is remarkable. By inspecting differential images we can localize the spots where each component has maximum concentration. We can distinctly observe oblate particles with an essentially peroxide composition, probably corresponding to platelets reported in the literature [29]. Centering at the 533 eV peak some needle‐like particles, but also a more diffuse background can be imaged. Local spectra strongly suggest a hydroxide‐like composition. The weaker superoxide component cannot be localized at specific points. A very characteristic spectrum, that is not evident in the overall spectrum, is instead found in a few spots, and corresponds to ice, probably deposited during the transfer process. Even if this component is external to the cathode material, it shows that statistically less relevant components that do not appear in the total spectrum can be detected if spatially well localized. Thus, the fluctuating local spectra not only greatly facilitate the attribution of the components that appear mixed in the

**Figure 10.** Left: Combination of differential images for different spectral components. Each component is represented with a respective color: superoxide (yellow), peroxide (magenta), hydroxide (green), and ice (cyan). Right: Absorption

integrated spectrum, but even allow lowering the detection limit.

spectra in the O K region at selected points and for the overall image.

The discharge products of Li/O2

The sample reported in **Figure 11** includes the characteristic toroidal‐shaped particles also reported by several authors working with ether‐based solvents. Beside these main objects, we actually also appreciate platelet‐like particles and irregular aggregates. Also in this case, differently shaped particles present different composition. Small platelets and irregular particle aggregates are mainly composed of carbonate (red). Instead, Li superoxide and peroxide dominate in toroidal objects (green). From intensity maps, it is also possible to generate ratio or fraction maps that are useful to tell if some components are associated.

Such estimations indicate that toroidal peroxide particles included 10–30% superoxide‐like phases. Superoxide does not appear to show any preferential localization with respect to peroxide in the particles, suggesting some coprecipitation mechanism that may favor toroid formation. In fact, smaller particles have smaller superoxide content than large particles. Significant amount of carbonates were found irregularly distributed on the electrode, appearing as aggregates, but also coating lithium peroxide particles. A closer analysis suggests that carbonates form a shell on the surface of all particles, so that smaller particles seem associated to relatively larger quantities of carbonate. This resembles a passivating layer, indicating that carbonate formation is a surface reaction and forms a kind of passivating layer. Thus, a strategy for more reversible batteries appears to be conditions that favor operation with larger particles.
