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

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(n)Ph (2 ≤ n ≤ 15), which are all structurally stable, confirmed by calculation of their Gibbs free energies. The theoretical specific energy of PhS(15)Ph is high, up to 2632 W h kg(−1), exceeding that of S(8). By calculating the bond dissociation energy of S–S in PhS(n)Ph 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(n)Ph cathodes is explored. It is phenyl that prevents the formation of soluble long-chain polysulfide molecules (Li(2)S(4), Li(2)S(6), Li(2)S(8)) in the lithiation process, efficiently weakening the “shuttle effect”.