Recent advances in understanding of the mechanism and control of Li2O2 formation in aprotic Li–O2 batteries

Abstract

Aprotic Li–O₂ batteries represent promising alternative devices for electrical energy storage owing to their extremely high energy densities. Upon discharge, insulating solid Li₂O₂ forms on cathode surfaces, which is usually governed by two growth models, namely the solution model and the surface model. These Li₂O₂ growth models can largely determine the battery performances such as the discharge capacity, round-trip efficiency and cycling stability. Understanding the Li₂O₂ formation mechanism and controlling its growth are essential to fully realize the technological potential of Li–O₂ batteries. In this review, we overview the recent advances in understanding the electrochemical and chemical processes that occur during the Li₂O₂ formation. In the beginning, the oxygen reduction mechanisms, the identification of O₂⁻/LiO₂ intermediates, and their influence on the Li₂O₂ morphology have been discussed. The effects of the discharge current density and potential on the Li₂O₂ growth model have been subsequently reviewed. Special focus is then given to the prominent strategies, including the electrolyte-mediated strategy and the cathode-catalyst-tailoring strategy, for controlling the Li₂O₂ growth pathways. Finally, we conclude by discussing the profound implications of controlling Li₂O₂ formation for further development in Li–O₂ batteries.