Other mechanisms have been proposed to explain how lithium intrusions develop and propagate in LLZO. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy experiments have shown that LLZO is chemically stable to lithium metal . As such, a coupled electro-chemo-mechanical intrusion mechanism, which has been observed in Li1+xAlxGa2-x(PO4)3 and Li10GeP2S12 , is unlikely. The two mechanisms that have gained the most attention center on fracture mechanics and electronic conductivity. The fracture mechanics hypothesis posits that lithium metal builds up stress inside of pre-existing cracks and eventually causes fracture, similar to traditional brittle fracture . Fracture events have been directly observed during lithium plating via scanning electron microscopy (SEM) and optical microscopy . Previous work relates the electrochemical driving forces to the size of the defects , with literature dating back to the 1980s for β-alumina , though quantitative experimental data (both electrochemical and mechanical) to verify these models is sparse. Alternatively, the electronic conductivity hypothesis proposes that a small leakage of electrons into the solid electrolyte causes lithium metal to plate internally (i.e. without a direct connection to the surface lithium), which eventually short circuits the cell . We note that internal plating in the bulk of transparent LLZO was not directly observed in operando optical microscopy . In a hybrid mechanism, electronic conductivity could facilitate internal plating at pores near the Li-LLZO interface which then couples to fracture once the pore is completely filled . The difficulty of rigorously testing these hypotheses arises from the ill-defined nature of the lithium metal-LLZO interface. For example, unknown electrode geometries due to void formation on the stripping electrode in macroscopic lithium electrodes results in uncertain contact potentials for symmetric cells . Chemically, carbonate contamination due to reactions with ambient moisture and CO2 and the use of lithium-metal foils with surface organics and oxides further contribute to the complexity of the interface between lithium metal and LLZO. These complexities lead us to conclude that, similar to other material failure, lithium intrusion needs to be interrogated statistically.