In-Situ Internal Observation of Silicon Composite Anode in All-Solid-State Battery Using X-ray CT

Silicon is anticipated to be a next-generation anode active material with a high theoretical capacity density of ∼3600 mAh g–1 around room temperature. However, the volume expansion and contraction derived from lithiation (charging) and delithiation (discharging) are understood to be significant challenges. Particularly in all-solid-state batteries, not only does cracking of the silicon particles themselves occur, but also the disruption of contact between silicon and the solid electrolyte, leading to difficulties in maintaining battery performance, which requires a certain level of mechanical restraint for effective battery operation. Therefore, accurately understanding the internal nanometer-order structure of the silicon/solid electrolyte composite electrode under restrained conditions is crucial for improving the performance of all-solid-state batteries by using silicon anodes. In this study, an all-solid-state battery with a composite anode consisting of silicon and the sulfide solid electrolyte Li6PS5Cl was charged and discharged under constrained conditions, and the internal structure during battery operation was observed using in situ computed tomography measurements. As a result of the observation, different cracking modes were identified during charging and discharging. The modes of cracking and subsequent reattachment were observed during the charging process, whereas anisotropic void formation became evident during the discharge process.