Fig. 4. Characterization and electrochemical performance of all-solid-state symmetric cells with pristine Na (Na|Na) and 1 M NaClO4/FEC modified Na (M-Na|M-Na). (a) IR spectra of the pristine SN-based SSE and SSE in different symmetric cells after cycling (Na: about 16 h, M-Na: 4000 h). (b) Optical photographs of the SSE and (c) SEM images of Na metal in different symmetric cells after cycling. (d) High-resolution XPS spectra of Na 1s, N 1s, and C 1s of pristine Na after cycling. (e) EIS results of different symmetric cells at the initial state, after resting for 24 h, and after cycling. (f) Rs and Rct of each EIS spectrum in (e). (g) CV curves in the voltage range of –0.5 to 0.5 V at 5 mV s–1 and (h) voltage profiles of different symmetric cells; the insets are the detailed voltage profiles.
