Imaging voids and defects inside Li-ion cathode LiNi0.6Mn0.2Co0.2O2 single crystals

Li-ion battery cathode active materials obtained from different sources or preparation methods often exhibit broadly divergent performance and stability, despite no obvious differences in morphology, purity, and crystallinity. We show how state-of-theart, commercial, nominally single crystalline LiNi0.6Mn0.2Co0.2O2 (NMC-622) particles possess extensive internal nanostructure even in the pristine state. Scanning X-ray diffraction microscopy reveals the presence of interlayer strain gradients and crystal bending attributed to oxygen vacancies. Phase contrast X-ray nano-tomography detects substantial quantities of nano-voids hidden inside the bulk.