Considering the potential implications of Co on LLZO, in-depth studies are needed to understand the role of Co in the degradation processes at high temperature to develop contingency strategies for safe processing of SSBs. The questions to be answered are: Does Co incorporate in to the LLZO structure? If so, to which extent, which site does it occupy and in which oxidation state? What are the consequences in respect of structure, ionic and electronic conductivity, as well as electrochemical stability?