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 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 À1 , 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".

First‐Principles Investigations to Evaluate NiCl2/NiF2 as Cycle‐Catalyzed Electrolyte Additives to Improve Li–S Batteries’ Performance

“…The “alloy‐like” diagram [ 27,28 ] was used to analyze the thermodynamic stability of the overall structure of the two catalysts after reacting with Li 2 S n or S 8 . If a compound is above the convex envelope, it will be unstable and decompose into two nearby compounds.…”

“…[ 26 ] In addition, the static permittivity was set to ε = 7.07. In order to verify the stability of Li 2 S n after binding with NiCl 2 and NiF 2 and the possibility of further conversion, “alloy‐like” diagram [ 27,28 ] was used to analyzed the stability and possibility. The Gibbs free energy difference (Δ G ) was used to analyze the relative stability and possibility of further reactions of NiCl 2 ‐Li 2 S n and NiF 2 ‐Li 2 S n , the formation energies were defined as…”

“…The stable configurations of Li 2 S n (n = 1, 2, 4, 6, 8) and S 8 clusters after the reaction with NiCl 2 and NiF 2 , respectively, are shown in Figure 1. The "alloy-like" diagram [27,28] was used to analyze the thermodynamic stability of the overall structure of the two catalysts after reacting with Li 2 S n or S 8 . If a compound is above the convex envelope, it will be unstable and decompose into two nearby compounds.…”

Lithium Bond-Enhanced Capacity of Dipyridyl Polysulfides for LSBs

“…Molclus and Gaussian 16 code were used to scan N–C–S bond angles and optimize molecules with the B3LYP-D3­(BJ)/6-311+G­(d) DFT functional and basis set . The optimized structures are thermally stable without negative frequency.…”