Sluggish Li2O2 dissolution - a key to unlock high-capacity lithium-oxygen batteries

While lithium-oxygen batteries have a high theoretical specific energy, the practical discharge capacity is much lower due to the passivation of the solid discharge product, Li2O2, on the electrode surface. Herein, we studied and quantified the deposition and dissolution kinetics of Li2O2 using an electrochemical quartz crystal microbalance (EQCM). It is found that the orientation of the electrode greatly influences the formation path and deposition amount of Li2O2. We identified two distinct dissolution modes: surface dissolution and bulk fragmentation, with the latter 100 times faster than the former. By revealing the underlying factors affecting dissolution, 80% of Li2O2 can dissolve within 3 minutes when a desorption potential of 2.9 V is applied. Consequently, we designed an intermittent-desorption discharge strategy, which increased the discharge capacity by an order of magnitude. This work shows that high practical specific energy of Li-O2 batteries can be achieved once problems of Li2O2 dissolution are addressed.