The performance of modern lithium-sulfur (Li/S) battery systems critically depends on the electrolyte and solvent compositions. For fundamental molecular insights and rational guidance of experimental developments, efficient and sufficiently accurate molecular simulations are thus in urgent need. Here, we construct a molecular dynamics (MD) computer simulation model of representative state-of-the art electrolyte-solvent systems for Li/S batteries constituted by lithium-bis(trifluoromethane)sulfonimide (LiTFSI) and LiNO 3 electrolytes in mixtures of the organic solvents 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL). We benchmark and verify our simulations by comparing structural and dynamic features with various available experimental reference systems and demonstrate their applicability for a wide range of electrolyte-solvent compositions. For the state-of-the-art battery solvent, we finally calculate and discuss the detailed composition of the first lithium solvation shell, the temperature dependence of lithium diffusion, as well as the electrolyte conductivities and lithium transference numbers. Our model will serve as a basis for efficient future predictions of electrolyte structure and transport in complex electrode confinements for the optimization of modern Li/S batteries (and related devices).
Lithium-sulfur (Li/S) batteries are regarded as one of the most promising energy storage devices beyond lithium-ion batteries because of their high energy density of 2600 W h kg −1 and an affordable cost of sulfur. Meanwhile, some challenges inherent to Li/S batteries remain to be tackled, for instance, the polysulfide (PS) shuttle effect, the irreversible solidification of Li2S, and the volume expansion of the cathode material during discharge. On the molecular level, these issues originate from the structural and solubility behavior of the PS species in bulk and in the electrode confinement. In this study, we use classical molecular dynamics (MD) simulations to develop a working model for PS of different chain lengths in applied electrolyte solutions of lithium bistriflimide (LiTFSI) in 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) mixtures. We investigate conductivities, diffusion coefficients, solvation structures, and clustering behavior and verify our simulation model with experimental measurements available in literature and newly performed by us. Our results show that diffusion coefficients and conductivities are significantly influenced by the chain length of PS. The conductivity contribution of the short chains, like S 2-4 , is lower than of longer PS chains, such as S 2-6 or S 2-8 , despite the fact that the diffusion coefficient of S 2-4 is higher than for longer PS chains. The low conductivity of Li2S4 can be attributed to its low degree of dissociation and even to a formation of large clusters in the solution. It is also found that an addition of 1 M LiTFSI into PS solutions considerably reduces the clustering behavior. Our simulation model enables future systematic studies in various solvating and confining systems for the rational design of Li/S electrolytes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.