Fig. 1: Heterogeneous nucleation and Kirkendall effect-induced synthesis of the hk-LiNi_0.96Al_0.04O₂ cathode materials.

a Scheme of the proposed heterogeneous nucleation and Kirkendall effect-induced synthesis route. b Cross-sectional SEM image showing Ni(OH)₂ precursor grown on the Al₂O₃ nucleus and c corresponding EDS mapping photograph during the developed synthesis route. d, e Cross-sectional SEM images of the c-LiNi_0.96Al_0.04O₂ (classical synthesis route) and hk-LiNi_0.96Al_0.04O₂ (developed synthesis route) secondary particles after calcination. f–h Compositional and morphological characteristics of the hk-LiNi_0.96Al_0.04O₂ secondary particle shown in (e), including f Cross-sectional Ni mapping image of the hk-LiNi_0.96Al_0.04O₂ (the dashed square in e), g the relative content of Al and Ni as a function of the distance from the center of the hk-LiNi_0.96Al_0.04O₂ particle to the scan point (white spots) on the two scanning routes and h primary particle morphology of hk-LiNi_0.96Al_0.04O₂ in TEM image. The inset displays the HRTEM image of hk-LiNi_0.96Al_0.04O₂ from [010] axis. i HAADF-STEM image of secondary particle. Scale bar, 5 μm (b, c); 2 μm (d–f, i); 100 nm (h) and the scale bar in the inset of h is 2 nm.