Fig. 6. The atomic structural evolution and oxidation-state change of samples before and after cycling.

a–e Atomic configuration of the S-200 before cycling. The overview of HAADF-STEM image (a) shows the crystal structure from surface to the bulk of S-200; the blue and orange dash square showed two regions with different atomic configurations. The interior region marked by the blue dashed square in (a) has been FFT-filtered and shown in (b), and the corresponding atomic model is shown in (c). The spots with higher contrast in (b) show TM ions with higher Z than Li ions; the Li, M, and O ions have been shown as green, blue, and red spheres in (c), respectively. The surface region with cation-mixed Mn₃O₄ feature marked by orange dash square in (a) has been FFT-filtered and shown in (d), and the corresponding atomic model has been drawn (e). f–j The atomic configuration of S-200 electrode after 100 cycles. The HAADF-STEM image from the surface to the bulk of charged S-200 (f) shows the different atomic configurations on the surface area; the blue and orange dashed square shows two regions with different atomic configurations. The layered feature region marked by the blue dashed square in (f) has been FFT-filtered as shown in (g), and the corresponding atomic model is shown in (h). The region with a spinel feature that is marked by an orange dashed square in (f) has been FFT-filtered and shown in (i), and the corresponding atomic model is shown in (j). The scale bar donates 1 nm. k Normalized Mn K-edge XANES spectra of cycled LP and S-200. The valence states of Mn were determined by comparison with the spectra of pure-phase MnO, Mn₂O₃, and MnO₂. l Normalized Ni K-edge XANES spectra of cycled LP and S-200. The valence states of Ni were determined by comparison against the spectra of pure-phase Ni and NiO. m The k³-weighted Fourier transform magnitudes of Mn K-edge EXAFS spectra obtained from cycled LP and S-200.