Charge Rate‐Dependent Decomposition Mechanism of Toroidal Li2O2 in Li‐O2 Batteries

Abstract

Main observation and conclusionUsing in situ atomic force microscopy, we visualized the oxidation dynamic process of toroidal lithium peroxide (Li2O2) in a working Li‐O2 battery and clarified the correlation between the decomposition behavior and the charging rate. It was found that at a low charge rate, the decomposition could occur at the Li2O2/electrolyte interface, providing strong evidence that a tiny current is allowed to pass through the bulk phase of toroidal Li2O2. Further, the evolution of the periphery thickness, diameter and center thickness of the toroid as a function of charge capacity was quantitatively analyzed. In the early stage of charging, the diameter of the toroid radially shrinks and the shrinking rate slows down in the later stage. Besides, the periphery thickness of the toroid decreases at a faster and uniform rate, while the center thickness decreases obviously in the later stage of charging. Increasing the charging rate promotes the decomposition occurring at the Li2O2/electrode interface, causing direct desorption of the Li2O2 from the electrode and irreversible capacity degradation.