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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.

The Li–O2 battery is a promising technology due to its high theoretical specific energy. However, its practical capacity and cycling performance need further improvement. In this scenario, the influence of the electrolyte and the supply of air/O2 to the device are essential to enhance the performance and build a commercial prototype. This paper presents a study focusing on the influence of oxygen flow and pressure in the gravimetric capacity of Li–O2 batteries using two different electrolytes: dimethyl sulfoxide (DMSO/LiClO4) and tetraethylene glycol dimethyl ether (TEGDME/LiClO4). This study pointed out the negative influence of flow over the capacity when combined in an open cell. Due to electrolyte loss, the life cycle was also deeply affected using the open cell, especially for DMSO. However, DMSO leads to the best performance due to higher ionic conductivity, oxygen diffusivity, and absence of a direct reaction with the lithium anode. Thus, the closed cell reached a maximum discharge capacity of 22537 mAh g–1 with 26 cycles of 1000 mAh g–1 for DMSO and 8764 mAh g–1 with 13 cycles of 1000 mAh g–1 for TEGDME.

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