Lithium polysulfide conformer analysis in ether-based solvents for Li?S batteries

JAVIER LUQUE DI SALVO; GUILLERMINA LUQUE; GIORGIO DE LUCA

Molecular Systems Design & Engineering

Royal Society of Chemistry

Año: 2022

2058-9689

A fundamental understanding of polysulfide conformers in common (ether-based) solvents used inprototype lithium?sulfur batteries is mandatory to push the technology towards practical applications. Inthis work, molecular dynamics simulations were used to perform a detailed conformational analysis anddynamics ascertainment of lithium hexasulfide Li2S6 as a representative of soluble long-chain lithiumpolysulfides. This novel conformational dynamics study based on 106 structures per studied systemprovides important insights into open questions such as how many Li+ coordinate polysulfides arecorrelated to lithium transport and polysulfide clustering. The simulations predict that monoanionic LiS6− inits closed conformation is the predominant structure in 1,2-dioxolane and dimethoxyethane equimolarmixtures. If a second Li+ approaches, that leads to the opening of the polysulfide chain and the formationof neutral Li2S6 (open conformer). By changing the electrolyte composition, the relative distribution ofclosed and open conformers varies, although closed LiS6− remains the most abundant conformercompared to the open one. There are three major findings from this work: the first is that there is a greaterabundance of the closed conformer, in which the closed/open aspect ratio depends on electrolytecomposition; the second is that the polysulfide charge distribution resulting from the nearby coordinatinglithium cations was determined; and the third is that the number and type of solvent moleculescoordinating the lithium polysulfide were determined. These findings, which have been missing up to nowto the best of our knowledge, provide crucial information for the design of strategies to suppress theunwanted polysulfide shuttle effect, such as engineered separators and cathode protective layers.