Atomic-Scale Observation of O1 Faulted Phase-Induced Deactivation of LiNiO at High Voltage.

LiNiO and cobalt-free ultrahigh-Ni content cathodes suffer from rapid capacity loss and severe chemomechanical degradation, especially when operated at high voltages. Here, by cycling LiNiO up to 4.7 V, we report the atomic-scale observation of O1 faulted phase-induced deactivation of LiNiO. We find that, although a thin layer of the O3 phase forms on the particle surface by reversible O3 → O1 transformation during discharge, the bulk interior still maintains the O1 faulted phase, leading to rapid capacity loss of LiNiO. Moreover, the atomic configuration of the O1/O3 interface is investigated comprehensively. We reveal that the misfit along the axes of the O1 and O3 phases results in the formation of misfit dislocations, whereby cation mixing is promoted at the dislocation cores. A transition zone with continuous shear along the plane is uncovered between the O1 and O3 phases for the first time. Besides, severe oxygen loss-induced pore formation and concurrent rock salt transformation are also identified.