Understanding structural defects in lithium-rich layered oxide cathodes

Planar defects in lithium-rich layered oxides were examined by aberration-corrected scanning transmission electron microscopy (STEM) to understand their formation. Planar defects were found to form during the transition of the transition metal layer from a disordered Rm state to a lithium-ordered C2/m state. This disorder-to-order transition resulted in three orientation variants, namely [100], [110], and [10]. The fundamental mechanism behind the observed defects is a shear of ±b/3[010] on the (001) transition metal planes, which is equivalent to the point group operations lost during the disorder-to-order transition. These displacements also produced twins and single unit cells with P3112 symmetry. Lithium-rich layered oxides with and without nickel show the presence of these three orientation variants.