2.

Spatial and time-resolved XRD analysis. (a) Phase maps of the individual compounds: orthorhombic sulfur (S), cubic Na₂S, and rhombohedral Na₂S₂, along with the corresponding voltage profile. The only observable phases are crystalline polysulfides, with sulfur remaining mostly undetectable throughout the experiment. The vertical axis represents the position within the battery cell, in which 0 μm and 100 μm are the position of the current collector. The cathode, electrolyte, and anode region are denoted as CAT, SE, and AN, respectively. The 2D XRD plot for a typical individual scan is shown in Supporting Information Figure 14 (b) Compositional changes across the cross-section over time, correlated with the thickness variation of the composite cathode and synchronized with the dq/dV plot. Not all peaks in the dq/dV plot align with the phases formed during charge and discharge, suggesting the presence of noncrystalline phases.