To further reveal the mechanical origin of lithium metal intrusions, we conducted operando SEM microprobe experiments on a strained LLZO cantilever. As schematically shown in Figure , a 15 mm-long LLZO cantilever (attached to a thin layer of lithium and copper) was clamped at one end and pushed upward at the free end. This setup results in a linear variation in strain along the length of the cantilever, in which there is zero strain at the free end and maximum strain at the clamped end. This geometry enables different mechanical strains to be probed along the same cantilever.