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

摘要

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, PhSnPh (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 S-8. By calculating the bond dissociation energy of S-S in PhSnPh 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 PhSnPh 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".