Fig. 3

Spatial distribution of Al in NCA. a STEM-HAADF image of pristine NCA. b Atomic compositional profile of Ni, Co, and Al along the arrow in a. c The enlarged view of Al compositional profile, indicating enrichment of Al on the surfaces. HAADF-STEM image d and corresponding EDS mapping e of pristine NCA sample. The blue dashed lines represent the surface boundary of NCA primary particle, and the green color depicts the Al elements distribution. f, h The ABF images of pristine and 100 cycled NC surfaces, respectively. The blue dashed lines depict the boundary of NC surfaces. g, i The ABF images of pristine and 100 cycled NCA surfaces, respectively. The green dashed lines outline the Al₂O₃ phase. The white and green lines represent the (01\(\bar 2\)) planes of parent phase and (\(\bar 1\)20) planes of Al₂O₃ phase, respectively. Scale bar, 5 nm (a, d), 1 nm (f)