Theoretical analysis and structural characterization. (a) Diagrams of LiNiO₂, Ta-doped LiNiO₂ and Ce-doped LiNiO₂ and their doping energy barriers on (003), (111), (104) and (012) planes. (b) Intensity ratios of (003)/(104) XRD peaks of LiNi_0.9Co_0.1O₂ with various Ta contents after normalizing the (003) peak. (c) STEM–HAADF image of the cross section for NCTa1–CeO₂. (d) High-resolution TEM. (e) Corresponding EDS mapping images of NCTa1–CeO₂. (f) Cs-STEM–HAADF image with the corresponding FT image of NCTa1–CeO₂. (g) Enlarged STEM–HAADF image and the diagram of EDS line scan. (h) EDS line analysis of annular dark-field signals and Ta signals.