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.