Unveiling Physical and Chemical Changes in All‐Solid‐State Battery: An Operando Synchrotron Chemical Imaging Study

Understanding the dynamics of complex heterogeneous battery materials under realistic operation conditions with micrometer spatial and relevant temporal resolutions remains challenging. This work presents a synchrotron‐based operando chemical imaging methodology using microfocus X‐ray diffraction (µ‐XRD) scanning imaging. The approach is applied to an all‐solid‐state battery (ASSB) with high‐energy lithium‐rich nickel manganese cobalt layered oxide (Li‐rich NCM) as active cathode material, Li 3 YCl 6 as catholyte, amorphous Li 3 PS 4 separator layer, and metallic lithium as anode. Operando XRD mapping unveils the nature and location of phase transformations along one complete cycle. The ASSB is integrated in the multipurpose custom‐designed electrochemical cell, which allows optimal exit solid angle for XRD analysis, permitting the resolution of the local chemistry in time and space across a relatively large field of view. We observed the following phenomena: (i) heterogeneous lithiation and delithiation processes within tens of individual Li‐rich NCM particles, indicating intraparticle differential lithium diffusion, (ii) the reversible formation of YCl 2 (H 2 O) 6 Cl, attributed to water residues, and (iii) the irreversible dissolution of Li 2 S and formation of LiOH parasitic phases. (iii) This study opens new perspectives for broader applications in energy technologies, such as Na‐ion, Zinc–Air, Li‐air, Li‐ion, and Li‐S.