Observation of morphological changes in silicon-based negative-electrode active materials during charging/discharging using <i>Operando</i> scanning electron microscopy

The direct observation of the morphological changes in silicon-based negative electrode (Si-based negative electrode) materials during battery charging and discharging is useful for handling such materials and in electrode plate design. We developed an operando scanning electron microscopy (operando SEM) technique to quantitatively evaluate the expansion and contraction of Si-based negative electrode materials. A small all-solid-state lithium-ion battery was charged and discharged, and the expansion/contraction of particles while harnessing capacity was observed using SEM. We found that in a silicon monosilicate (SiO)/graphite negative electrode, SiO expanded first during charging, and graphite contracted first during discharging. Our study provides insights into the relationship between capacity and expansion and contraction coefficient of Si-based negative electrode materials.