Direct Visualization of Dynamic Mobility of Li₂O₂ in Li-O₂ Batteries: A Differential Interference Microscopy Study

The reversibility and the discharge/charge performance in nonaqueous lithium-oxygen (Li-O₂) batteries are critically dependent on the kinetics of interfacial reactions. However, the interfacial reaction dynamic behaviors, especially the quantitative analysis, are still far from deep understanding. Using the method of laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM), we monitored the Li-O₂ interfacial reaction and in situ traced the Li₂O₂ migration processes promoted by the solution catalyst. Different dynamic behaviors exist when regulating the concentration of the redox mediator. Quantitative analysis of the discharged Li₂O₂ particles shows high mobility at the early discharge stage and decayed motion in the subsequent process, indicating the solution-mediated pathway participating Li₂O₂ formation in the low-concentration redox mediator addition, while particles/aggregates confined into the amorphous film demonstrate simultaneous solution and surface route-mediated pathway participation in the high-concentration case. These distinctive observations of Li₂O₂ formation and decomposition processes present the advantage of LCM-DIM to fundamentally understand the dynamic evolution in Li-O₂ batteries.