Sulfur crystallization in the cathode of lithium-sulfur battery during the charging process: A possible alternative to reduce the shuttle effect

Abstract

Most studies on lithium-sulfur batteries have paid attention to eliminating the shuttle effect caused by polysulfides via trapping polysulfides in cathodes. However, the charging process is neglected because the formation of an eight-membered sulfur ring is hindered by the low probability of head-to-tail contact in the long eight-membered chain. However, reducing the polysulfide concentration in an electrolyte can also be a good alternative. In this study, benefiting from electrolyte additives, polysulfide concentration in the electrolyte is reduced by oxidizing soluble polysulfides into insoluble sulfur disposing on surface of graphene during charging. Furthermore, high-resolution transmission electron microscopy images of the cathode charged to 3.0 V show that this sulfur crystal transforms from rectangular to regular hexagonal in a single crystal plane, revealing that the most stable crystal type for sulfur in this system is hexagonal and not rhombic. And reducing the shuttle effect by decreasing the density of polysulfides in the electrolyte via sulfur crystallization during charging is a novel and promising method.