Unveiling reaction distributions in silicon composite anodes of solid-state batteries via in-situ X-ray CT imaging

Silicon is a promising anode material for solid-state batteries due to its exceptionally high theoretical gravimetric capacity (∼3600 mAh g −1 ), far exceeding that of conventional graphite (372 mAh g −1 ). However, higher-rate charging of silicon is likely to result in nonuniform lithiation along with the electrode depth, inducing localized degradation such as mechanical expansion and reductive decomposition, especially in over-lithiated regions. To improve electrode performance and durability, it is essential to quantitatively evaluate the spatial distribution of lithiation reactions. In this study, we conducted in-situ synchrotron X-ray computed tomography on a silicon–solid electrolyte composite anode under operating conditions. Depth-resolved analysis based on void segmentation revealed that over-lithiation near the separator-layer side during higher-rate charging led to undesirable localized void formation, although lower-rate charging exhibited a much more uniform reaction distribution. These insights provide a fundamental basis for optimizing electrode design in all-solid-state lithium-ion batteries. • In-situ synchrotron X-ray CT visualized lithiation in silicon composite anodes. • Void segmentation revealed nonuniform reactions under high-rate charging. • At high rate, separator-side over-lithiation caused local expansion and voids. • Findings inform strategies to enhance ionic conduction in Si anodes for ASSBs.