Effects of Dimethyl Disulfide Cosolvent on Li–S Battery Chemistry and Performance

Lithium–sulfur battery’s (LISB) performance is still held back by undesirable side reactions. One of these side reactions is known as the polysulfide shuttle effect which is a consequence of soluble sulfur reduction products, polysulfides. Polysulfide migration induces other side reactions at the anode surface. In addition, slow kinetics of the main discharge products induces large overpotentials during charge. Researchers have been searching for ways to counteract these effects through many different strategies. One such strategy that could mitigate part of these problems is to use novel electrolytes that contain sulfur that can modify battery chemistry while providing additional energy capacity. Sulfur-containing electrolytes such as dimethyl disulfide (DMDS) have shown increased performance, but the mechanisms are not known. First-principles computational chemistry simulations are used to determine different aspects of battery performance to ascertain why this additive helps. We found that DMDS modifies the reduction pathway that leads to a different final product, LiSCH₃, than a traditional LISB, and this product is more soluble in the electrolyte, which could facilitate the charge reaction. DMDS favorably reacts with S₈ to form dimethyl polysulfides in agreement with experimental results. The new final reduction products are electronically insulating, but they are more soluble and therefore more reversible than the traditional end product, Li₂S, which would increase the battery performance. The results indicate that DMDS will change the sulfur battery chemistry for the better in some ways and similar in others which provide fundamental insight into the experimental evidence. In addition, we provide a schematic for screening novel electrolytes for the LISB.