Spectroscopic X-ray diffraction for microfocus inspection of Li-ion batteries

We developed spectroscopic X-ray diffraction (XRD) analysis to visualize electrochemical reactions occurring at various locations in Li-ion batteries (LIBs). Continuous irradiation with monochromatic X-rays in an energy region using a confocal setup provided a fixed observation position on the order of several tens of microns. Unlike three-dimensionally position sensitive XRD analyses, e.g., angle-scanning XRD and energy-dispersive XRD, this energy-scanning XRD analysis with angle-scanning of the monochromator instead of the detector-scanning has the advantage of profile resolution, position sensitivity, and time-resolution for mapping concentration gradients and diffusion of Li⁺ associated with the electrochemical properties of LIBs. The microscopic structural inhomogeneity in a sheet-like composite electrode of LiNi_1/3Co_1/3Mn_1/3O₂ with a thickness of 150 μm was successfully determined with a depth resolution of 50 μm during cell operation. This work demonstrates the potential of spectroscopic XRD as a nondestructive and pinpoint analysis method, thus contributing to the development of high-performance LIBs.