The energetics are based on density functional theory (DFT) calculations with the PBE+U exchange-correlation functional using VASP. The effect of lattice strain on the H3 phase is examined with the strongly constrained and appropriately normed (SCAN) functional with the van der Waals correction in the rVV10 form. A surrogate lattice Hamiltonian is trained on DFT data using cluster expansion for rapid energy evaluation. Time evolution is driven by the rejection-free kinetic Monte Carlo (KMC) algorithm. The cation hopping barriers are dynamically updated based on the local environments through the Brønsted-Evans-Polanyi (BEP) relation. The simulation box contains 32 × 32 × 8 O3-type layered LiNiO 2 primitive cells (∼ 9.6 nm × 9.6 nm × 4.8 nm, 8192 Li sites). More computational details can be found in the Supplementary Information. to the pristine particle, the fatigued particle begins delithiation at a slightly higher voltage but proceeds at a similar rate. A major deviation appears when the Li content, x, drops to 0.25 and below. Both particles reach 4.4 V in voltage. The fatigued particle takes 10000 longer to extract the last 25% of Li than the pristine one. There is a long incubation period where x stabilizes at 0.25. This suggests that the last 25% of Li will be kinetically trapped in practice when the surface is covered by the β phase. The above result corroborates Xu et al.'s observation of a bulk fatigue phase with 25% of Li trapped inside at the end of charge after hundreds of cycles. For the entire range of x, the discharge time of the fatigued particle is of the same order of magnitude as that of the pristine one. There is no incubation period for x ≤ 0.25, indicating that the β phase does not impede discharge at high SOC.