Revealing Cycling Rate-Dependent Structure Evolution in Ni-Rich Layered Cathode Materials

High-rate cycling of a battery often leads to a compromised performance, such as reduced capacity, rapid voltage decay, and thermal runaway. Although the cycling rate-dependent performance is generally perceived to be associated with the equilibrium state of systems, the correlation between cycling rate and cathode degradation, in terms of structure evolution, has not been established. Using scanning transmission electron microscopy, we demonstrate that varying cycling rate alters phase transition products in the Ni-rich materials. Under low cycling rates, the sufficient Li vacancies favor the thorough mixing between transition metal and Li layers, resulting in the formation of a disordered rock salt structure; at high cycling rates, the significant kinetic barrier arising from the Li retention impedes Ni migration, leading to the growth of the spinel phase. Our subtle characterizations at atomic scale bridge the gap between the structure evolution and cycling rate and provide mechanistic insight into tailoring the battery rate capability.