NEXAFS spectra of model sulfide chains: implications for sulfur networks obtained from inverse vulcanization

Inverse vulcanization is a promising route to stabilize sulfur in lithium-sulfur batteries, but the resulting sulfur strand lengths in the materials are elusive. We address the strand length by characterization via sulfur near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Theoretical predictions of NEXAFS spectra for model molecules containing strands with up to three sulfur atoms are verified by experiment. The near perfect agreement between simulation and experiment on the absolute energy scale allows for the predictions for larger chain lengths also. Inspection and interpretation of NEXAFS spectra from real battery materials on this basis reveals the appearance of single connecting sulfur atoms for very low sulfur content, and of longer strands when the sulfur fraction increases.