Best practices for operando depth-resolving battery experiments

Operando studies that probe how electrochemical reactions propagate through a battery provide valuable feedback for optimizing the electrode architecture and for mitigating reaction heterogeneity. Transmission-geometry depth-profiling measurements carried out with the beam directed parallel to the battery layers - in a radial geometry - can provide quantitative structural insights that resolve depth-dependent reaction heterogeneity which are not accessible from conventional transmission measurements that traverse all battery layers. However, these spatially resolved measurements are susceptible to aberrations that do not affect conventional perpendicular-beam studies. Key practical considerations that can impact the interpretation of synchrotron depth-profiling studies, which are related to the signal-to-noise ratio, cell alignment and lateral heterogeneity, are described. Strategies to enable accurate quantification of state of charge during rapid depth-profiling studies are presented.