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

Li–S batteries are promising alternatives due to their proven increased gravimetric capacity compared to Li–ion batteries. However, their development is hindered by many technical issues, one of the most challenging being the dissolution and shuttle of polysulfide species, which causes irreversible loss of cathode material leading to rapid capacity fading. Among the possible strategies to mitigate this effect, the choice of suitable solvents is easy to implement and has large room for improvement. To guide this quest, computationally-aided optimization is a powerful tool, provided that suitable descriptors are used to screen possible solvents. In this work, molecular dynamics simulations were performed for a typical lithium polysulfide Li₂S₆ dissolved in different solvents. Diffusion coefficients and their related activation energies were calculated, and thermodynamic properties like solvation energies and entropies were also evaluated. Additionally, a theoretical framework for computing the relative solubilities of lithium polysulfide is provided. For the set of solvents considered, we found that the system's viscosity appears as an important descriptor to correlate with different system properties. The donor number of the solvent also appears as a valid descriptor, for low-viscosity solvents. In general, it was found that higher viscosity solvents lead to lower diffusion rates and higher polysulfide solubility. These results suggest that the optimal choice to reduce the shuttle is a trade-off between high-viscosity solvents to reduce polysulfide diffusion and low-viscosity solvents to reduce its solubility, which could be further improved by properly tuning the donor number.