Fig. 5: The influence of unsaturation degree in Fe–Nx from geometric structure aspect.
a and b GITT curves (a) and calculated Na+ diffusion coefficient (b) of Na||S batteries with Fe–N1/S, Fe–N2/S, Fe–N4/S, and NC/S positive electrodes. c and d Multi-temperature EIS spectra (c) and calculated activation energy barriers (d) for Na||S batteries with Fe–N1/S, Fe–N2/S, Fe–N4/S, and NC/S positive electrodes. e UV–vis spectra and the optical photo of Na2S6 solutions with host materials (solutions (1)–(5) in the inset are reference Na2S6 solution, and adsorbed solution with Fe–N1, Fe–N2, Fe–N4, and NC). f Relationship between geometric structure descriptor (γ) and absorbance of Na2S6 in UV–vis spectra for Fe–N1, Fe–N2, and Fe–N4. g Visual cells under different states employing Fe–N1/S, Fe–N2/S, Fe–N4/S, and NC/S positive electrodes. h UV–vis spectra and the optical photos visual cells employing different positive electrodes at the end of the charging process. Source data are provided as a Source Data file.
