Quantitative Imaging Method of Metallic Lithium Surface Density Using Muonic X-rays

Quantitative and nondestructive detection of metallic lithium (Li) deposition on Li-ion battery anodes is crucial for understanding degradation mechanisms and ensuring operational safety. Muonic X-ray spectroscopy (μXRS) is highly sensitive to light elements such as Li and can probe deep into bulk materials but has not been applied to practical devices because conventional detectors cannot map element distributions across the anode surface. Here, we present a novel imaging system that advances μXRS with a newly developed large-area silicon double-sided strip detector and a 3D-printed tungsten parallel-hole collimator. Using Li plate samples, we demonstrate for the first time quantitative two-dimensional imaging of metallic Li surface density with a spatial resolution of 5 mm in the plane. An original image-processing algorithm suppresses crosstalk from muonic carbon X-rays and corrects nonuniform beam profiles, enabling accurate quantification. Our system achieves a 1-σ detection sensitivity of approximately 2.5 μg/mm², which is sufficient to detect practically relevant levels of localized Li accumulation. This approach extends μXRS from bulk-average measurements to spatially resolved quantification, offering a promising nondestructive diagnostic tool for battery safety inspection and other challenges in light-element imaging.