Visualization of Local Strain Distributions in All-Solid-State Batteries with Silicon Negative Electrodes Using Digital Image Correlation for Operando/In situ Microscopy Images

Investigating local strain distributions is essential for developing long-life all-solid-state batteries (ASSBs) because capacity fading primarily results from cracks and contact loss caused by volume changes in electrode active materials during battery operation. Digital image correlation (DIC) analysis can be used to create strain distribution maps from continuous images of materials under applied pressure. In this study, DIC analysis of operando confocal microscopy images of an ASSB cross-section was conducted to elucidate the mechanical degradation mechanism in ASSBs with Si electrodes exhibiting ~300 % volume change. The Si electrode layer exhibited irreversible strain changes, whereas the solid electrolyte (SE) layer exhibited no significant strain changes. Furthermore, DIC analysis was performed using in situ SEM images focused on the Si electrode layer to investigate detailed strain distribution maps for individual Si particles. Higher strain changes were observed in the vertical direction within the SE layer, which led to cracks forming in relatively large Si particles at the beginning of the lithiation process. Visualizing local strain distribution in the electrode layer through DIC analysis of operando/in situ images is a powerful approach for understanding how and where cracks form.