Fully solid-state lithium batteries offer some key advantages over the current liquid electrolyte based systems. But these solid electrolytes under development can be unreliable and their degradation mechanisms are unclear. This investigation employed transmission electron microscopy (TEM) to study the evolution of these materials while they operate. They found that differences between the expansion of the cathode material and solid electrolyte induced delamination at their interface. They also noted microscopic cracks forming in the cathode material, and reduction of LCO to metallic Co when the potential was allowed to drop below 1.5 V vs Li/Li+.