Ionic Gradients at Active Battery Interfaces Revealed Through Time-Resolved Cryo-EM

Characterizing the structural and chemical evolution of battery interfaces during cycling and aging is critical to realizing longer device lifetimes. Cryogenic electron microscopy (cryo-EM) has greatly advanced our ability to study such interfaces at high spatial resolution without damaging sensitive organic or lithium-containing components. The temporal resolution, however, is limited by time-consuming traditional sample preparation techniques that allow structural changes to occur between electrochemical cycling and the later ex-situ freezing process. Here, we demonstrate a method to freeze active battery interfaces <i>in situ</i> on sub-second timescales, allowing the native structures and chemistry that arise at different points in cycling to be captured for cryo-EM study. We apply this technique to study the role of ionic gradients at charged nanostructured interfaces on formation and evolution of the solid-electrolyte-interphase (SEI) on silicon anodes. This allows us to capture diffuse features that form at the active interface, which otherwise relax too quickly to be studied with ex-situ sample preparation techniques. We discuss the potential to expand this technique to other electrochemical systems and advance characterization of broader energy materials.