Distribution of discharge products inside of the lithium/oxygen battery cathode

During the discharge of an aprotic Li/O-2 battery solid products assemble inside of the gas diffusion electrodes (GDE). The distribution of these in dependence of pore size of the GDE is investigated by X-ray Photoelectron Spectroscopy (XPS). Depth profiling of the electrolyte facing side of the cathode reveal that macroporous electrodes are able to store discharge products homogeneously in the pore structure. Mesoporous GDE, however, develop a concentration gradient with large amounts of discharge product at the electrode/electrolyte interface and low amount in the bulk of the electrode. The investigation of the cross-section of these GDE reveals that most of the discharge products form near the oxygen facing side of the GDE. Here, the chemical compositions differ strongly from those at the electrolyte facing side. The high oxygen concentration and the limited lithium supply lead to the formation of lithium carbonate, lithium oxide and lithium fluoride. Also a thin layer of discharge product blocking further oxygen supply into the GDE through macroporous cracks is formed at the gas/electrolyte interface.