Fig. 6: Microscopic TEM observation for cycled SC81-air and structural degradation mechanism under air exposure.

a Low-magnification TEM image of discharged SC81-air sample after 100 cycles at a specific current of 0.5 C (100 mA g−1) and a temperature of 25 ± 1 °C within the voltage ranges of 2.8–4.5 V. b HRTEM image of the crack. c Corresponding FFT pattern. d Line-scan EELS along the arrow direction in (b). e, f HRTEM image (e) and color HRTEM images (f) in the bulk. g The comparison between PC and SC positive electrodes and the corresponding structural degradation mechanism under air exposure. The blue spheres in structural models denote Ni atoms, and the red spheres denote O atoms.