Development of <i>Operando</i> Hard X-ray Ptychography: Application to Thin-Film All-Solid-State Lithium-Ion Batteries

Hard X-ray ptychography is a promising technique for operando analysis of electrochemical reactions in energy materials, owing to its high spatial resolution and lensless imaging capability. However, its application to battery systems has been limited by weak absorption signals and low throughput, which have made operando implementation challenging. In this study, we overcame these limitations through optimization of beamline optics and detector configuration. This advancement enabled the demonstration of operando hard X-ray ptychography to visualize the evolution of chemical states in a thin-film-type all-solid-state lithium-ion battery (ASSLiB) during charge/discharge. Hard X-ray spectroscopic ptychography provided projection images of the LixCoO2 cathode layer from the cross-section with a spatial resolution of better than 40 nm. Spatially resolved X-ray absorption near-edge spectra revealed homogeneous lithiation and delithiation of the cathode layer under voltage-hold conditions. Moreover, time-resolved ptychography showed that the reaction proceeded predominantly via the Hex-II phase. These results demonstrate that operando X-ray ptychography is a powerful tool for visualizing reactions at the tens of nanometer scale. The integration of coherent X-ray diffraction imaging with operando analysis holds promise for the real-time visualization of electrochemical and thermodynamic processes in various functional materials.