Solvation Structure of Conjugated Organosulfur Polymers for Lithium–Sulfur Battery Cathodes

Lithium–sulfur (Li/S) batteries constitute a promising, next-generation energy storage technology due to their high theoretical energy density and low cost. To increase sustainability, processability, and battery performance, conducting organic polymers have become a focus of research for the development of better cathode materials. Here, we investigate the solvation structure of a single conjugated poly(4-(thiophen-3-yl)benzenethiol) (PTBT) polymer as a high-potential macromolecular candidate for synthesizing optimized cathodes in Li/S batteries. Using molecular dynamics (MD) simulation with newly optimized force-field parameters, we examine the effects of polymer length and various molar fractions of the popular dimethoxyethane (DME) and dioxolane (DOL) solvents on the structure of the PTBT polymer at a temperature of 300 K. We characterize basic polymeric properties as well as the composition-dependent solvent adsorption structure and thermodynamics and uncover significant tunability by the solvent. Importantly, we find an interesting cosolvency effect, namely that a solvent mixture composed of 25% DME and 75% DOL leads to maximum swelling behavior, which should be important for optimizing cathode fractality and permeability in applications. Our study thus reveals intriguing polymer–solvent correlations and serves as an important prerequisite for future MD studies of realistic polymeric cathode structures and processes, e.g., toward charge transport in vulcanized (S-linked) network topologies.