Oxygen Dimerization as a Defect-Driven Process in Bulk LiNiO 2 .

To explore the possibility of oxygen dimerization-particularly, the formation of molecular oxygen-like species-in the bulk of LiNiO 2 lithium ion cathode materials at high states of charge, we conduct a redox-product structure search inspired by recent methodological developments for point-defect structure prediction. We find that (1) delithiated Li 1- x NiO 2 ( x = 1) has good kinetic stability toward decomposition into molecular oxygen and reduced transition-metal oxides but (2) defects can act as nucleation sites for oxygen dimerization. These results help reconcile conflicting reports on the formation of bulk molecular oxygen in LiNiO 2 and other nickel-rich cathode materials, highlighting the role of defect chemistry in driving the bulk degradation of these compounds.