Quantification of Chemical Heterogeneity in Battery Cathodes—Where Should We Look?

The evolution of local chemistry determines the performance of electrodes and electrolytes used in batteries because limitations can be tracked to slow kinetics and transport, and irreversibilities in the storage reaction. Tools that provide insight into local chemistry are critical for identifying the underpinnings of electrochemical function. This information must be resolved within architectures, from individual particles to microscale domains, to pinpoint the relationship between local phenomena and their role in macroscopic metrics and degradation. Technical developments in X-ray microscopy and mapping have built a flexible suite of tools that combine the desired spatial resolution and 3D capabilities with a suite of possible contrasts mechanisms, such as diffraction and spectroscopy. In this talk, we will discuss our recent research that demonstrates the diversity of length scales at which important chemical heterogeneity can be induced in battery electrodes, from their synthesis to their operation. For this purpose, the systems of study will be the leading cathodes for Li-ion batteries. We will highlight the new fundamental insight generated by the tools, but also showcase the value of continuously seek to extend analytical capabilities into outcomes of high statistical significance. The insight generated by our approaches will be related to their impact on material and architecture properties. Along the way, we will discuss the prospects of probing time-resolved phenomena using operando measurements to avoid uncertainty due to relaxation under open circuit conditions. We will also provide a glimpse into the future by showing how emerging synchrotron techniques can enhance the impact of X-ray microscopy in fundamental battery science.