Using ab initio calculations combined with experiments, we clarified how the kinetics of Li-ion diffusion can be tuned in LiNixMnyCozO2 (NMC, x + y + z = 1) materials. It is found that Li-ions tend to choose oxygen dumbbell hopping (ODH) at the early stage of charging (delithiation), and tetrahedral site hopping (TSH) begins to dominate when more than 1/3 Li-ions are extracted. In both ODH and TSH, the Li-ions surrounded by nickel (especially with low valence state) are more likely to diffuse with low activation energy and form an advantageous path. The Li slab space, which also contributes to the effective diffusion barriers, is found to be closely associated with the delithiation process (Ni oxidation) and the contents of Ni, Co, and Mn.