Fig. 7: Ex-situ postmortem XPS and SEM characterizations.

a XPS C 1s, O 1s, F 1s, and Na 1s spectra of the TPDBD-CNa-QSSE/TPBD-QSSE in Na||Na cells over 20 cycles at 0.02 mA cm−2 and 25 ± 1 °C and TPDBD-CNa-NaTFSI/TPBD-NaTFSI. b XPS C 1s, O 1s, F 1s, and Na 1s depth profiles of cycled Na metal over 20 cycles at 0.02 mA cm−2 and 25 ± 1 °C in a Na|TPDBD-CNa-QSSE|Na symmetric cell. SEM images of cycled membranes of the TPBD-QSSE (c) and TPDBD-CNa-QSSE (d) over 20 cycles at 0.02 mA cm−2 and 25 ± 1 °C. SEM images of the cycled Na metal of the TPBD-QSSE (e) and TPDBD-CNa-QSSE (f) over 20 cycles at 0.02 mA cm−2 and 25 ± 1 °C.