ИСТИНА

Operation of Li-O2 batteries which are associated now with future high-energy storage devices includes reactions of molecular oxygen. In this case AP XPS is rather relevant tool to probe reaction mech- anisms and to reveal the reasons of the current capacity and cyclability of the Li-O2 batteries. First, we have developed model electrochemical cell for operando studies with solid electrolyte to exclude influence of electrolyte. As a positive electrode transferred graphene was used. This approach en- ables to observe electrochemical reactions and side chemical reactions separately using different discharge and charge regimes. We observed directly in O 1s spectra short-living superoxide radical species (oxygen reduction intermediate) and their reactions with electrode materials. In addition, different electrode materi- als were tested. Using the same cell, we find the way to evaluate solid electrolyte instability towards metallic lith- ium negative electrode and trace the formation of SEI. Second, we have studies side reactions with electrolyte by admitting solvent vapor. This approach allows us to reveal some reactivity even for relative stable solvents such as acetonitrile. Unfortunately, this kind of studies is technically limited for many solvents since they are not safe for the spectrometer. Third, in our experiments with liquid nonaqueous electrolytes we used approach with graphene window. We were able to observe EDL formation, however the lifetime of the corresponding cell is rather limiter from of radical attack of the species formed by radiolysis and final destruction of graphene. The radiolysis was not detectable in free liquid probably due to fast mixing with the bulk, and becomes rather critical in the case of small electrochemical cell. All in all, AP XPS enables important findings for Li-O2 batteries especially in the case when ade- quate model system is used. At the same time the approaching to the realistic operation conditions requires additional efforts including technical issues.