Fig. 8

Schematic drawing of Al functioning mechanism in NCA. a Pristine primary particle of NC with layered structure. b The formation of core–shell structure and the development of Al₂O₃ nano-islands upon the high-temperature annealing during the materials synthesis stage. The green masked area indicates the core part with a Al concentration of <2 at% and the areas between the primary particle surface and green mask edge represent the shell part with a concentration of ~6 at%. The black arrow point to the Al₂O₃ nano-islands formed on top of NCA surface. c Formation of CEI layers upon the electrochemical cycling