Diffraction‐Enabled Operando Nanoscale Tracking of Li‐ion Dynamics of Solid Electrolyte and Inhomogeneous Diffusion in Composite Cathode

Li⁺ diffusion has mostly been studied in cathode active materials (CAMs) in liquid batteries, whereas it remains rarely explored in solid-state electrolytes (SSEs) and all-solid-state batteries. Herein, diffraction was established as an effective method for all-solid-state lithium batteries (ASSLBs) by focusing on SSE in composite cathodes. Operando synchrotron x-ray diffraction presented diffraction angle shifts of certain Li₃InCl₆ Bragg planes during the first ASSLB cycle due to lithiation/delithiation into its lattice, whose preferred Li⁺ migration pathways were suggested by the partiality of these shifts, and the three-phase evolution indicated the fundamental Li⁺ diffusion kinetics factors. X-ray nanodiffraction (XND) mapped nanoscale inhomogeneous Li⁺ distributions and diffusion within individual Li₃InCl₆ particles, revealing facilitated Li⁺ conduction in high-crystallinity regions and their role as pathways across SSE/CAM interfaces, and the most negatively strained regions were shown to be less susceptible to Li⁺ insertion. XND from various electrochemical techniques inferred high transient charging rates to be the culprit of irreversible Li⁺ diffusion instead of the overall charging depth. This study proved diffraction to be a potent tool to probe intricate Li⁺ dynamics in ASSLBs and provide microscopic insights for optimal battery designs.