Fig. 6. Interfacial stability, stress evolution, and CEI chemistries at the positive electrode NNM/COF/PNSE interface.

a SEM image of NNM electrodes cycled with COF/PNSE electrolyte (Inset: Schematic of a single NNM particle structure.). b FIB-SEM image revealing the structural evolution. c TEM image and (d) corresponding GPA strain map of the NNM positive electrode. e–h SEM, FIB-SEM, TEM, and GPA strain mapping for NNM electrodes cycled with PNSE electrolyte (Inset: Schematic of a single NNM particle with cracks after cycling.). i Cryo-TEM image of the cycled NNM with COF/PNSE. j HRTEM image of the positive electrode-electrolyte interphase, the elliptical regions indicate different inorganic phases: yellow represents NaF, blue represents Na₂O phase, and red regions represent amorphous areas. k Atomic-resolution TEM analysis of CEI nanostructure. l Elemental mapping via TEM-EDS and EELS line scans across F K-edge and Na K-edge transitions. XPS depth profiles for (m) C 1 s and (n) F 1 s spectra at the cycled NNM interface. XAS curves for (o) Ni K-edge and (p) Mn K-edge transitions at various charging/discharging states.