Figure reveals that lithium intrusions do not have a preferred direction at 0% strain (free end of cantilever), indicating the random nature of the pre-existing defect distribution. At 0.033% compressive strain (the middle of the cantilever), the lithium intrusions start to show more geometric alignment as shown in Figure . Strikingly, at the base of the cantilever where the compressive strain is only ~0.070%, the intrusions exhibit a strong directionality along the cantilever longitudinal direction, i.e., along the compressively strained direction (see Figure and Figure ). Tests were consistently performed in the low contact force regime (0.1 ± 0.03 mN). To rule out the possibility that the rotational angle between the microprobe and sample influences the intrusion direction, we conducted experiments on a cantilever that was rotated 20 and 45 degrees relative to the probe (Figures ) and found lithium intrusions remained predominantly aligned along the cantilever longitudinal direction rather than perpendicular to the microprobe. We propose that the directional propagation of intrusions occurs because the uniaxial compression facilitates crack closure and increases the effective fracture toughness in the transverse direction. Recently, the stress influence on the in-plane propagation of lithium within the solid electrolyte was also observed via optical microscopy . These results show that mechanical strain controls the propagation of intrusions after their initiation and provides further evidence of the mechanical origin of lithium metal intrusions.