Crystal structure of O3-NaNCMMT cathode material. (a) Powder XRD pattern and Rietveld refinement plot. (b) Crystal structures viewed along the (010) and (001) crystallographic directions. (c) Optical photograph. (d) SEM image. (e) TEM image. (f, g) HR-TEM images. (h–k) In situ HRXRD patterns of the formation process and thermal stability as well as corresponding intensity contour maps (bird’s eye view) concerning the evolution of the characteristic diffraction peaks.