Atomistic discharge studies of sulfurized-polyacrylonitrile through ab initio molecular dynamics

Abstract Sulfurized-polyacrylonitrile (SPAN) in lithium-sulfur batteries (LiSBs) is a conductor polymer that can chemisorb sulfur. The sulfur in the polymer reversible reacts with Li and produces Li2S. Performing ab initio molecular dynamics (AIMD), we investigated the discharge of SPAN. Li-ions were added to the system in the vicinity of the sulfur chain and the total charge of the system was modified during the simulation. We observed that polysulfides (PSs) are formed and dissolved during lithiation, the polymer motif affects the capturing of Li-ions from the solvent, and SPAN acts also as active material. Nitrogen atoms on SPAN indicate to capture the PSs dissolved, and the Li-S structure tends to grow on top of the nitrogen atoms. The stair-like configuration of SPAN contributes to improving the performance of the LiSBs, but also how the sulfur is attached to the backbone, e.g. interconnected in the same backbone, is a factor to change cyclability. Thus beyond the solvent, the SPAN motifs also affect the battery cycles. Additionally, sulfur structures contribute to not form long chains with both edges attached to the polymer as an interconnected structure, but small disulfides or sulfur chains attached with only one edge connected to the polymer.