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, we showed that O-O dimerization triggers transition-metal migration in an oxygen-redox positive electrode upon charging. First-principles calculations were performed to reveal the thermodynamic and kinetic energy landscapes of the full structural evolution of a typical lithium-rich oxide, i.e., Li1.2Ni0.13Co0.13Mn0.54O2. 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 O2−/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.