Mass and charge transport relevant to the formation of toroidal lithium peroxide nanoparticles in an aprotic lithium-oxygen battery： An experimental and theoretical modeling study

The discharge and charge mechanisms of rechargeable Li-O2 batteries have been the subject of extensive investigation recently. However, they are not fully understood yet. Here we report a systematic study of the morphological transition of Li2O2 from a single crystalline structure to a toroid like particle during the discharge-charge cycle, with the help of a theoretical model to explain the evolution of the Li2O2 at different stages of this process. The model suggests that the transition starts in the first monolayer of Li2O2, and is subsequently followed by a transition from particle growth to film growth if the applied current exceeds the exchange current for the oxygen reduction reaction in a Li-O2 cell. Furthermore, a sustainable mass transport of the diffusive active species （e.g., O2 and Li＋） and evolution of the underlying interfaces are critical to dictate desirable oxygen reduction （discharge） and evolution （charge） reactions in the oorous carbon electrode of a Li-O2 cell.