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.