Theoretical study of reactions between polysulfides and ethylene carbonate and raman spectra in lithium-sulfur battery

Two mechanisms of the reaction between polysulfides (S_n^2-, n=2-4) and ethylene carbonate (EC) and Raman spectra of the reactants and main products were investigated by density functional theory(DFT) method. The results showed that the reaction of polysulfides attacking the ethyl carbon of EC is more favorable than that attacking the carbonyl carbon of EC in terms of the activation energies and Gibbs free energies. Sulfur groups in polysulfides display strong Raman signals, so that simulated Raman spectra of the products of the S_n^2-+EC reaction significantly change after the reaction. The coordination effect of Li⁺ cation also influenced the simulated Raman spectra of reaction products. DFT results and Raman spectroscopic analysis provide a new insight on structural stability of polysulfides and EC electrolyte in the lithium sulfur battery.