Effects of Bending on Nucleation and Injection of Oxygen Vacancies into the Bulk Lattice of Li-Rich Layered Cathodes

The degradation of Li- and Mn-rich (LMR) cathodes primarily results from the thermodynamic instability of lattice oxygen and the resulting oxygen release. This is promoted by localized lattice strain, which develops dynamically during electrochemical reactions involving repeated Li-ion intercalation and extraction. However, the role of chemomechanical strain in degrading lattice oxygen's stability is not yet well-understood. Here, the research indicates that uneven strain distribution causes bending, resulting in lower activation energy for oxygen vacancy creation and injection into particle interiors at bending points. Combining in situ transmission electron microscopy and theoretical simulations, it is shown that the largest OO interaction occurs at the maximum curvature point, reducing MnO bonding strength, promoting oxygen dimer formation, and eventually initiating oxygen release from LMR. As a result, a process is designed to adjust the Li-content and the distribution of the two-phase structure, achieving better cycling stability in LMR cathodes with a more balanced distribution of strain. These results provide insights into enhancing LMR cycling stability while utilizing their high capacity.