Upon disassembly of the cell, we indeed observe severe blackening of the LLZO tube due to possible reduction reactions either from charging, or simply due to contact with the molten lithium. Photographs of the LLZO tube after the experiment are shown in Figure . If the reduced phase of the solid electrolyte is electronically conductive, then the reduction reaction will continue through the entire solid. However, it is also possible that this blackening is due to the chemical reaction alone between the LLZO tube and lithium metal, without applied potential. More detailed examination of the chemical reactions between the LLZO and lithium at high temperatures are required to determine the origin of this color change. In addition to the color change in the LLZO tube, a small amount of color change was observed on the YSZ tube. The origin of this color change is less certain, but it may also be due to the low oxygen partial pressure in the tube, as set by the presence of lithium metal on the anode. It may also be due to the molten salt mixture depositing on the tube, which has a different color. Additional experiments are required to understand the degradation of all cell components in this system.