The mystery of Li<sub>2</sub>O<sub>2</sub> formation pathways in aprotic Li–O<sub>2</sub> batteries

Abstract

The solid-state discharge product Li<sub>2</sub>O<sub>2</sub> is closely related to the performance of Li–O<sub>2</sub> batteries, which exacerbates the concentration polarization and charge transfer resistance, leading to sudden death and poor cyclability. Although previous theories of the Li<sub>2</sub>O<sub>2</sub> formation pathway help to guide battery design, it is still difficult to explain the full observed Li<sub>2</sub>O<sub>2</sub> behaviors, especially for those with unconventional morphologies. Thus, the pathways of Li<sub>2</sub>O<sub>2</sub> formation remain mysterious. Herein, the evolution of the understanding of Li<sub>2</sub>O<sub>2</sub> formation over the past decades is traced, including the variable Li<sub>2</sub>O<sub>2</sub> morphologies, the corresponding reaction pathways, and the reaction interfaces. This perspective proposes that some Li<sub>2</sub>O<sub>2</sub> 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 Li<sub>2</sub>O<sub>2</sub> formation pathways and spearhead advanced Li–O<sub>2</sub> batteries.