Sulfurized-polyacrylonitrile in lithium-sulfur batteries: Interactions between undercoordinated carbons and polymer structure under low lithiation

Abstract Lithium-sulfur battery (LSB) represents an important candidate to be used in energy storage applications, due to its high specific capacities. Sulfurized-polyacrylonitrile (SPAN) is a candidate as a host material in LSB to replace graphite, due to its ability to chemisorb polysulfides (PSs). The sulfur chains attached to the polymer can reversibly form Li2S, and SPAN indicates to have a good cyclability and better performance than graphite, thus, SPAN acts partially as an active and also as a host material. In this study, we investigated the capacity of the solvent or the SPAN to lose a hydrogen atom from the backbone, to predict possible anodic reactions between solvent and host material. The simulation suggests that the photophilic salts may preferentially react with the solvent, and possibly building a cathode electrolyte interphase (CEI). We observed that an undercoordinated carbon (Cuc) can be thermodynamically created, due to lithiation. The Cuc can react with the solvent on the polymer backbone through different mechanisms, however, the simulations indicated that the reaction should be affected by the interaction between the solvent and Cuc, according to SPAN’s configuration. Moreover, Cuc reacts with long sulfur chains attached to SPAN, capturing sulfur and forming a C-S bond. A sulfur chain from one SPAN can connect to another polymer backbone, however, this process is affected by lithiation and vice-versa. Therefore, this work also investigates the formation of interconnected SPAN structures and the multiple Cuc effects.