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, Li₃YCl₆ as catholyte, amorphous Li₃PS₄ 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 YCl₂(H₂O)₆Cl, attributed to water residues, and (iii) the irreversible dissolution of Li₂S 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.