Extended Data Fig. 9: Characterizations of intermediates during cycling to diagnose the S_9.3I cathode working mechanism.

(a) The corresponding ratios of S₀, S_b, S_t, and S_2- in the S_9.3I cathode in Fig. 3b at different discharge/charge states. (b) Ex situ Raman spectra of S_9.3I during the discharge/charge processes. The ex situ Raman spectra suggest the good reversibility of S_9.3I cathode at RT. X-band EPR spectra obtained on (c) the pristine S_9.3I cathode, and on (d) the SSE and carbon mixture (LPS-VGCF). (e) Ex situ EPR data obtained on cathode samples harvested from cells stopped at various stages of the initial discharge/charge processes. (f) Parameters obtained from fits of the EPR spectra in (e), including the ratios of the signal intensities from the S_9.3I cathode material and from the VGCF additive, and the linewidth of the S_9.3I EPR signal. The ratio of S_9.3I radicals to carbon decreases during initial discharge and grows upon subsequent charge (f). This trend is consistent with the following model, assuming that polysulfide chains that form in the solid-state exist as dianions and cannot be detected in our EPR measurements, unlike EPR-active polysulfide radicals formed in solution through disproportionation of polysulfide dianions (as in conventional Li-S cells). (g) The S_2p high resolution XPS of comparison samples, including LPS/VGCF mixture, S cathode discharge to 1.3 V (D-1.3 V) and chemically lithiated S_9.3I prepared by reacting with Li powder with an equivalent capacity of ~800 mAh g⁻¹. (h) Digital photos of elemental S cathode discharged to 1.3 V, S_9.3I cathode discharged to 1.3 V, chemically lithiated S_9.3I immersed in THF solution and standard Li₂S₄, Li₂S₆ THF solutions. (i) The UV-Vis spectra of corresponding samples in (h). The S_9.3I cathode discharged to 1.3 V and chemically lithiated S_9.3I suspensions exhibit the color of LiS_x solutions immediately, but elemental S cathode discharged to 1.3 V doesn’t show any change.