Trapping and imaging dynamic battery nanointerfaces via electrified cryo-EM

The electrified interface between a liquid and a solid underpins diverse phenomena, from ion-transfer during battery operation to action potentials enabling biological communication. However, conventional tools are blind to the nanoscale dynamics of this metastable interface, leaving key gaps in our understanding. We introduce electrified cryogenic electron microscopy (eCryo-EM), a tool that rapidly freezes and kinetically traps these dynamic states during battery operation for nanoscale imaging. This allows quantification of early-stage growth kinetics of the solid electrolyte interphase (SEI) that governs battery performance. We discover an ultrathin inorganic layer (<2 nm) within the SEI interior that is found to control ion and electron transport, revising our understanding of battery calendar aging, rate performance, and SEI growth mechanism. Slower growth kinetics of this inner SEI layer correlates with improved battery performance, providing new insight into enhancing the passivation properties of this interior structure. Our work establishes eCryo-EM as a foundational technique to image the electrified liquid-solid interface, which has broad impact spanning electrochemistry and biology.