Kinetic Limitations in Cycled Nickel-Rich NCM Cathodes and Their Effect on the Phase Transformation Behavior

Layered lithium transition-metal oxides of the general formula Li1+x(Ni1–y–zCoyMnz)1–xO2 (NCM or NMC) represent a promising class of cathode active materials for Li-ion battery applications. However, especially Ni-rich NCMs, enabling high capacity and energy density, tend to undergo more severe degradation during cycling than low and medium Ni materials. In this work, the kinetics of phase transitions in cycle-aged Li1+x(Ni0.85Co0.1Mn0.05)1–xO2 (NCM851005) upon electrochemical (de)lithiation have been studied by operando X-ray diffraction. The focus is set on the onset of kinetic impairment, evident from the coexistence of differently delithiated phases for cell voltages greater than ∼4.1 V after ≥150 cycles, to examine if the behavior observed with NCM851005 is analogous to the H2–H3 transformation in isostructural LiNiO2.