Oxygen Redox Reaction in Ionic Liquid and Ionic Liquid-like Based Electrolytes: A Scanning Electrochemical Microscopy Study.

Improving the stability of the cathode interface is one of the critical issues for the development of high-performance Li/O2 batteries. The most critical feature to address is the development of electrolytes that mitigate side reactions that bring about cathode passivation. It is well-known that the superoxide anion (O2•-) plays a critical role. Here, we propose scanning electrochemical microscopy (SECM) as an analytical tool to screen the electrolyte of Li/O2 batteries. We demonstrate that by using SECM it is possible to evaluate the stability of O2•- and of the cathode to the passivation process occurring during the oxygen redox reaction. Specifically, we report a study carried out at a glassy carbon electrode in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and in tetraethylene glycol dimethyl ether with LiTFSI, the latter ranging from the salt-in-solvent to solvent-in-salt regions.