Diphenyl polysulfides: cathodes with excellent lithiation performance and high specific energy for LSBs

Abstract

Reversible lithium–sulfur batteries (LSBs) are considered one of the most promising next-generation energy storage systems. However, the shuttling effect of lithium polysulfide significantly weakens the electrochemical properties and the cycle life, hindering its practical application. Organo-sulfides are unique materials with low cost, profuse content and high capacity. Here, via quantum chemical calculations, we introduce a class of diphenyl polysulfides, PhS_nPh (2 ≤ n ≤ 15), which are all structurally stable, confirmed by calculation of their Gibbs free energies. The theoretical specific energy of PhS₁₅Ph is high, up to 2632 W h kg⁻¹, exceeding that of S₈. By calculating the bond dissociation energy of S–S in PhS_nPh molecules, we analyze the breaking processes of the S–S bonds in each step of lithiation. The microscopic mechanism of the fast reaction kinetics of PhS_nPh cathodes is explored. It is phenyl that prevents the formation of soluble long-chain polysulfide molecules (Li₂S₄, Li₂S₆, Li₂S₈) in the lithiation process, efficiently weakening the “shuttle effect”.