Solvation structure of conjugated organosulfur polymers for lithium-sulfur battery cathodes

Abstract

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 the conjugated poly(4-thiophen-3-yl) benzenethiol) (PTBT) polymer as a high-potential macromolecular candidate for 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. Importantly, we find an interesting co-solvency effect, namely that a solvent comprised of about 25% DME and 75% DOL leads to maximum swelling (best solvent quality) behavior, which should be important for optimizing cathode fractality and permeability in applications. Our study thus reveals intriguing polymer-solvent correlations and serves as a first step for further MD studies of realistic polymeric cathode structures and processes, e.g., toward charge transport in vulcanized (S-linked) network topologies.

How Regiochemistry Influences Aggregation Behavior and Charge Transport in Conjugated Organosulfur Polymer Cathodes for Lithium–Sulfur Batteries

“…Our systems are simulated on an all-atom level using the large-scale atomic/molecular massively parallel simulator package in combination with the OPLS force field. , Details on the Hamiltonian of the force field and its adjustments regarding our specific system can be found in ref and the Supporting Information (SI). The simulations are performed in an isothermal–isobaric ( NPT ) ensemble with periodic boundary conditions.…”

“…Chains. In a recent study of ours, 48 we investigated the conformational behavior of a single oligomeric PTBT chain in solution by means of MD simulations. Due to the conjugated nature of our system, one of the most important terms to be considered when evaluating the force field is the energetic profile governing the dihedral dynamics between neighboring monomers.…”

How regiochemistry influences aggregation behavior and charge transport in conjugated organosulfur polymer cathodes for lithium-sulfur batteries

“…In a recent study of ours, 47 we investigated the conformational behavior of a single oligomeric PTBT chain in solution by means of classical molecular dynamics (MD) simulations. Due to the conjugated nature of our system, one of the most important terms to be considered when evaluating the force field is the energetic profile governing the dihedral dynamics between neighboring monomers.…”

“…94,95 Details on the Hamiltonian of the force field and its adjustments regarding our specific system can be found in ref. 47 and the Supporting Information (SI). The simulations are performed in an isothermal-isobaric (NPT ) ensemble with periodic boundary conditions.…”