Reactivity at interfaces between Li-ion battery cathodes and electrolytes imposes limitations to activity and durability. Before solutions can be devised, it is indispensable to precisely define the underlying chemical mechanisms. Interfacial instability is driven by the formation of highly oxidized species on the surface of the cathode particles, but these mechanisms are inherently local and they depend on their morphology and chemistry. A combination of X-ray absorption spectroscopy and X-ray microscopy will be presented to establish the changes undergone by cathode particles at different points of the charge, revealing the consequences of interfacial reactions at very high spatial resolution.

Modifying the surface of the cathode particles with redox-inactive cations is an established strategy to prevent these undesired reactions and increase electrode durability generally. Developments will be discussed in the manipulation of chemical assembly to achieve the highest level of sophistication in this approach, through core-(epitaxial) shell architectures at the level of primary particles. The nanostructures are produced via colloidal methods that generate objects with high chemical and morphological definition. As a consequence, they constitute valuable models to evaluate effect of surface modifications on cathode-electrolyte interfacial interactions. The presentation will establish comparisons of the changes at the surface of cathode particles depending on the presence and identity of a passivating shell. These comparisons inform the definition of mechanisms of stabilization, which will be subsequently used to propose further avenues of design towards cathodes with high capability for energy storage with long life.