The mystery of Li₂O₂ formation pathways in aprotic Li–O₂ batteries

The solid-state discharge product Li₂O₂ is closely related to the performance of Li–O₂ batteries, which exacerbates the concentration polarization and charge transfer resistance, leading to sudden death and poor cyclability. Although previous theories of the Li₂O₂ formation pathway help to guide battery design, it is still difficult to explain the full observed Li₂O₂ behaviors, especially for those with unconventional morphologies. Thus, the pathways of Li₂O₂ formation remain mysterious. Herein, the evolution of the understanding of Li₂O₂ formation over the past decades is traced, including the variable Li₂O₂ morphologies, the corresponding reaction pathways, and the reaction interfaces. This perspective proposes that some Li₂O₂ particles are strongly dependent on the electrode surface as a result of the dynamic coupling of solution and surface pathways and emphasizes a possible mechanism based on previous experimental results and theories. Further methods are expected to be developed to reveal complex Li₂O₂ formation pathways and spearhead advanced Li–O₂ batteries.