As the applied potential is swept to more anodic potentials, the current increases nonlinearly. At a critical Vapp, metallic lithium is observed via SEM to induce cracks in the LLZO at some distance away from the probe, resulting in lithium intrusion. This typically occurs after the lithium whisker has reached many microns in diameter. These two lithium growth modes, preintrusion and post-intrusion, are shown in a tilted SEM image in Figure , with the lithium metal whisker highlighted in red and intrusions highlighted in orange. Once the onset of intrusions (indicating fracture) is visible in the SEM, we observe rapid propagation of intrusions on the LLZO surfaces with an accompanying increase in current magnitude (See Figure for additional SEM images of intrusion morphology). We rule out electron-beam-induced effects (e.g., charging) since the electrochemistry as well as lithium and intrusion morphology proceed identically with the electron-beam turned off during plating. Importantly, large variation is observed in current and voltage at intrusion onset (see Figures and).