Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Layered Li(Ni1−x−yCoxMny)O2 (NCM, with Ni ≥ 0.8) cathode materials are essential in achieving high energy densities in the next generation of lithium-ion batteries. To extend the materials' lifetime, it is necessary to understand the role played by crystal defects in the degradation during electrochemical cycling. In this study, NCM851005 (85% Ni) is investigated in the pristine state and after 100 and 200 cycles using scanning transmission electron microscopy, with the focus on the defects in the material. The formation of antiphase boundaries (APBs) from a dislocation in a pristine sample is proven. After 100 cycles, the APBs' length and width are enlarged compared with the pristine state. After 200 cycles, APBs further evolve into an intragranular rock-salt-like phase, distorting the nearby layered structure. It is suggested that the behavior of APBs plays a critical role in determining the performance of this cathode material with prolonged electrochemical cycling.