Spatial Variations of Cathode Reaction and Discharge Precipitate in Li-Air Batteries: Analysis and Experimental Measurement

In this study, we investigate the spatial variations of discharge precipitate and cathode reaction rate in lithium (Li)-air battery both theoretically and experimentally: (1) the reaction variation of local oxygen reduction reaction (ORR) rate is theoretically analyzed, with analytical solutions as a function of the Damkohler (Da) number; (2) a novel experimental method is proposed to probe local ORR rate by designing a multi-layer cathode which consists of three identical Toray (R) carbon clothes that have a porosity of 0.8 and a thickness of about 0.4 mm. The morphology of insoluble Li compounds at different thickness locations is uncovered by SEM images. An overall very small volume fraction of precipitates was observed in the air cathode. It is found that the local ORR rate decreases from the air side of cathode to the separator side in the case of study, which is consistent with our model predictions for two orders of the cathode reaction. The theoretical analysis and experimental method can be applied to design and optimize materials for the air cathode of Li-air batteries. (C) 2022 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.