Scanning electrochemical microscopy of oxygen permeation through air-electrodes in lithium-air batteries
Non-aqueous Li-air-batteries can provide potentially a very high energy density. The reaction at the positive electrode is the oxygen reduction reaction. Its products are lithium oxides (mainly Li2O2) that deposit as solid compound in the porous gas diffusion electrode (GDE). This can cause passivation of the electrode surface or clogging of gas diffusion pathway though the porous material. Here a new method is reported to measure in-situ the oxygen permeation though a GDE during the discharge process. It is based on the concepts of scanning electrochemical microscopy (SECM) in which a positionable microelectrode (ME) is used to detect the influx of oxygen in an deaerated electrolyte close to the outer surface of the GDE. However, no steady-state current for oxygen reduction at the ME can be obtained in Li-containing electrolytes because solid lithium oxides also deposit on the ME. Therefore, a pulsed potential program was developed that periodically removes deposits from the surface of the ME and eliminates the effect of surface passivation of the probe electrode. We validated this method by monitoring the oxygen reduction current at the ME as a result of oxygen permeating GDEs of different thickness.