Fig. 7. (a) Powder XRD patterns taken from pristine and cycled NCMF cathodes. (b) The schematic description of TM migration in subtle structure. (c) TM migration pathway in subtle structure. Atomic-resolution HAADF image and GPA image, respectively, for the (d) pristine and (e) cycled NCMF cathode. The STEM-HAADF image and its FFT patterns viewed along the [100] zone axis for (f) pristine and (g) charged to 4.0 V. (h) Line profiles taken along the STEM-HAADF image. White-line ratios (L₃/L₂) for (i) pristine and (j) charged to 4.0 V. (k) Enlarged STEM-HAADF image taken from panel g. (l) Atomic-resolution STEM-HAADF image and EDS elemental mappings of the NCMF cathode after 50 cycles along the [100] zone axis. (m) EDS mapping line profiles of Ni, Fe, Co, and Mn acquired from the white rectangles. Yellow peaks indicate cation octahedra on the Na layer (marked with asterisks), and green peaks indicate cation tetrahedra on the Na layer (marked with arrowheads). (a)–(m) are reprinted with permission from ref. 109. Copyright 2020 Chemical Society Japan.