Theoretical Studies on the Charging and Discharging of Poly(acrylonitrile)-Based Lithium-Sulfur Batteries

Based on a previous study where key structural motifs of poly (acrylonitrile) (PAN) and sulfur/PAN (SPAN) were identified and their energies evaluated by using density functional theory, here plausible mechanisms for battery charging and discharging at a SPAN cathode were identified. Based on a simplified model for battery operation, we find that discharging the battery involves the formation of lithium polysulfide intermediates and the reductive adsorption of Li+ ions onto S(n)PAN. In both discharg-ing and charging, Li atoms preferentially coordinate with N atoms on the backbone, leading to strong Li-SnPAN adsorption energies. Furthermore, we found that spatially separating a dissociated SnLi fragment from the backbone is difficult, providing a plausible explanation for the ability of a SPAN cathode to hinder polysulfides from diffusing to the cathode, leading to a reduction of the polysulfide shuttle mechanism.