A comparative study of structural changes in lithium nickel cobalt manganese oxide as a function of Ni content during delithiation process

Abstract

First-principles calculations and in-situ X-ray diffraction (XRD) experiment have been performed to investigate the structural changes and potential oxygen evolution in Li(Ni(y)Co(1−y)/2Mn(1−y)/2)O2 (y = 0.33, 0.56, and 0.78) and LiNiO2 cathode materials during electrochemical activities. They reveal that as the Ni content is increased, the change in lattice parameters becomes more significant during charging, which could induce the mechanical degradation in the cathode. Detailed analysis of delithiation process demonstrates the origin of the characteristic variations in the lattice parameters. Open-circuit voltage (OCV) calculations and charge–discharge experiments suggest that at the same voltage, more Li ions are extracted from Ni-rich structures, leading to further structural instability. Atomic charge analysis indicates that Ni mainly participates in charge compensation process in the practical range of delithiation, and then Co covers after further severe Li extraction. With increasing Ni content, the oxidation of oxygen, which is initially more oxidized, is accelerated during charging; this result explains the poorer oxygen stability observed in Ni-rich structures.