Recent Advances in Electrolytes for Lithium-Sulfur Batteries

The rapidly increasing demand for electrical and hybrid vehicles and stationary energy storage requires the development of "beyond Li-ion batteries" with high energy densities that exceed those of state-of-the-art Li-ion batteries. Li-S batteries, which have very high theoretical capacities and energy densities, are believed to be one of the most promising candidates. The sulfur-based electrochemical reaction requires novel electrolytes to replace the classical carbonate-based electrolyte systems inherited from Li-ion batteries because carbonates are incompatible with the intermediate polysulfides in Li-S batteries. In addition, the theoretical specific capacities and projected energy densities of Li-S batteries are difficult to achieve experimentally, mainly because of the electronically insulating nature of sulfur and lithium sulfide cathodes, and the shuttle effect; this is a serious issue associated with the dissolution and diffusion of soluble polysulfides in most potential electrolytes and causes rapid capacity fading. It is therefore highly desirable to explore, modify, and/or optimize electrolytes for Li-S batteries to address these issues and improve their capacities, cycling stabilities, rate performances, and energy densities. An overview of recent developments in electrolytes for Li-S batteries is provided with a focus on the chemistry of polysulfides in different electrolyte media, including polysulfide solubility and its relevance to battery performance.