Therefore, we conclude that cracks are the most likely defect responsible for the decrease in characteristic failure diameter shown in Figure . However, such cracks responsible for lithiumintrusion initiation are not detectable using standard microscopy techniques, such as SEM or optical imaging. Recent TEM imaging of crack formation in Al2O3 highlights that cracks may be only a few nanometers in width , posing a challenge for non-destructive characterization of LLZO surfaces.