The effects of synthesis conditions, especially the heating rate, on the reaction kinetics of Ni-rich cathodes were systematically studied. The growth rate of Ni-rich oxide increases continuously as the heating rate increases. Ab initio molecular dynamics simulations demonstrate that a high heating rate induces anabatic oscillations, indicating a decrease in thermodynamic stability and a tendency for the crystal surface to undergo reconstruction. The presence of an intermediate phase at the grain boundary amplifies atomic migration-induced interface fusion and consequently augments crystal growth kinetics. However, the excessively high heating rate aggravates the Li⁺/Ni²⁺ mixing in the Ni-rich cathode. The single-crystal Ni-rich cathode exhibits enhanced structural/thermal stability but a decreased specific capacity and rate performance compared with its polycrystalline counterpart.