In Situ Infrared Micro and Nanospectroscopy for Discharge Chemical Composition Investigation of Non‐Aqueous Lithium–Air Cells

Abstract Metal–air batteries, such as Li–air, may be the key for large‐scale energy storage as they have the highest energy density among all electrochemical devices. However, these devices suffer from irreversible side reactions leading to battery failure, especially when ambient air is used as the O₂ source, so a deep understanding over the surface chemistry evolution is imperative for building better devices. Herein, a multi‐scale (nano‐micro) FTIR analysis is made over the electrode surface during cell discharge employing synchrotron infrared nanospectroscopy (SINS) for the first time, to track the chemical composition changes at the nanoscale which are successfully correlated with in operando micro‐FTIR characterization. The in situ results reveal homogeneous product distribution from the nano to the micro scale, and that the discharge rate does not interfere in chemical composition. In operando micro‐FTIR shows the atmosphere dependency over Li products formation; the presence of HCOO^– species occurring due to CO₂ electroreduction in water, LiOH and Li₂CO₃, are also detected and even the lowest concentration of CO₂ and H₂O affects the O₂ reactions. Finally, evidence of the Li₂O₂ reaction with DMSO forming DMSO₂ after just 140 s of cell discharge shows this new technique's relevance in aiding the search for stable electrolytes.