Defect Physics and Chemistry in Layered Mixed Transition Metal Oxide Cathode Materials: (Ni,Co,Mn) vs (Ni,Co,Al)

Although layered lithium transition-metal oxides with different compositions of (Ni,Co,Mn) [NCM] or (Ni,Co,Al) [NCA] have been used in commercial lithium-ion battery cathodes, their defect physics and chemistry is still not well understood, despite having important ramifications for cycling properties, particularly capacity fade. Herein we report a hybrid density functional study of the crystal and electronic structures of and intrinsic point defects in the compositions LiNi1/3Co1/3Mn1/3O2 (NCM1/3) and LiNi1/3Co1/3Al1/3O2 (NCA1/3), which also serve as model compounds for NCM and NCA. We find that the transition metals can exist in different charge and spin states at different lattice sites. In NCM1/3, nickel/lithium antisite pairs, i.e., NiLi–LiNi, are estimated to be about 3% in samples prepared at 1000 °C. In NCA1/3, in addition to nickel antisites NiLi, aluminum antisites AlLi can also occur with a very high concentration. The AlLi defect has a high energy except when it is located between two Al atoms...