Atomistic Origins of Asymmetric Charge–Discharge Kinetics in Off-Stoichiometric LiNiO₂

LiNiO2 and Ni-rich layered oxide cathodes exhibit slow Li transport at both ends of the charge and discharge processes, significantly reducing their practical capacity. The atomistic origins of these kinetic limits have not been fully understood. Here, we investigate Li transport by first-principles-based kinetic Monte Carlo simulations to achieve a large length scale and long time scale, enabling direct comparison with experiments. Our results explain the asymmetric overpotentials between charge and discharge at the same Li content and reveal different rate-limiting steps at both ends of the first cycle. The asymmetric effects of excess Ni in the Li layer (NiLi) are also captured. At low voltages, the first cycle irreversible capacity loss at the end of discharge is reproduced without empirical input. The concentration-dependent Li hopping barrier is explained by interactions beyond the first nearest neighbor. NiLi increases the overpotential during discharge but not during charge because it only impedes Li diffusion in a particular range of Li concentration and does not change the equilibrium voltage profile. The trends from varying NiLi content and temperature are consistent with the experimental observations. At high voltages, charge becomes the slower process. The transport bottleneck is moving Li from the Li-rich H2 phase into the Li-poor H3 phase, while the Li diffusion barriers in both phases are relatively low. The roles of pre-existing nucleation sites and NiLi are also discussed. These results provide new atomistic insights into the kinetic hindrances, paving the road to unleash the full potential of high-Ni layered oxides.