This occurs because the current density decreases as the whisker diameter grows. Therefore, the applied voltage primarily controls the diameter of the lithium whisker, rather than the chargetransfer overpotential. The magnitude of η WE estimated by this method (typically tens of mV) is significantly smaller than the magnitude of Vapp at fracture (typically 1 V), in agreement with previous literature on LLZO interfacial kinetics , verifying that our results here are insensitive to the charge-transfer mechanism assumed in the model.