Emerging new applications demand expanded function of Li-ion batteries (LIB). However, many issues, including complex phase transitions of electroactive materials, the kinetics of ion transport, and electrode-electrolyte interfacial reactions, still limit the full realization of LIBs. Many interrogation approaches of batteries are static and are unable to track phenomena arising from dynamic battery (dis)charge behavior. Meaningful understanding of mechanisms can be gained where the measurements are in sequence with the active electrochemistry of the battery.

Operando x-ray diffraction has proven to be useful in determining phase changes induced by high levels of (de)lithiation under expanded discharge or charge voltages. X-ray absorption spectroscopy (XAS) provides insight into the changes in oxidation state and local coordination environment of transition metals used as active materials. As XAS is element specific and does nor rely on long range order, the method is particularly applicable to multi-element compositions such as NMC as well as to samples with limited crystallinity including nanomaterials. A less used method of whole cell interrogation is isothermal microcalorimetry. The heat dissipated by a battery is measured under active charge and discharge. The heat released can be analyzed in detail to determine the contributions from polarization, entropy, and parasitic processes. Insights into electrolyte decomposition at electrode surfaces as function of potential have been elucidated using this method. This presentation will include applications of in situ and operando methods that provide insight into dynamic electrochemical processes.