Toward Operando Characterization of Interphases in Batteries

Electrode/electrolyte interfaces are the most importantand leastunderstood components of Li-ion and next-generation batteries. Animproved understanding of interphases in batteries will undoubtedlylead to breakthroughs in the field. Traditionally, evaluating thoseinterphases involves using ex situ surface sensitiveand/or imaging techniques. Due to their very dynamic and reactivenature, ex situ sample manipulation is undesirable.From this point of view, operando surface sensitivetechniques represent a major opportunity to push boundaries in batterydevelopment. While numerous bulk spectroscopic, scattering, and imagingtechniques are well established and widely used, surface sensitive operando techniques remain challenging and, to a largerextent, restricted to the model systems. Here, we give a perspectiveon techniques with the potential to characterize solid/liquid interfacesin both model and realistic battery configurations. The focus is ontechniques that provide chemical and structural information at lengthand time scales relevant for the solid electrolyte interphase (SEI)formation and evolution, while also probing representative electrodeareas. We highlight the following techniques: vibrational spectroscopy,X-ray photoelectron spectroscopy (XPS), neutron and X-ray reflectometry,and grazing incidence scattering techniques. Comprehensive overviews,as well as promises and challenges, of these techniques when used operando on battery interphases are discussed in detail.