Sequential Structural Evolution Triggered by O─O Dimerization in Oxygen‐Redox Reactions

Abstract The participation of oxygen in electrochemical reactions increases the capacity of lithium‐ion battery positive electrodes beyond conventional cationic‐redox limits. However, structural degradation due to oxidized oxide ions significantly reduces the discharge voltage compared with that in the first charge, mostly with a capacity loss. In this study, it is shown that O─O dimerization triggers transition‐metal migration in an oxygen‐redox positive electrode upon charging. First‐principles calculations are performed to reveal the thermodynamic and kinetic energy landscapes of the full structural evolution of a typical lithium‐rich oxide, i.e., Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 . The oxygen oxidation process can be divided into three sequential steps: i) generation of persistent oxidized oxide ion O − ; ii) peroxide formation; and iii) transition‐metal migration. The elusive use of O 2− /O − while blocking O─O dimerization is the key to avoiding structural degradation due to transition‐metal migration and realizing energy‐efficient oxygen‐redox reactions.