Development and Challenges of Functional Electrolytes for High-Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries, as one of the most important candidates of next-generation batteries, are famous for high energy density, low cost, and environmental friendly benignity. However, issues originating from polysulfide shuttle of common liquid electrolytes (e.g., capacity fade, poor cycle life, and safe issue) have hindered the applications of Li–S batteries in various occasions. This review summarizes the main efforts in the electrolytes of Li–S batteries, including liquid, solid state, and hybrid electrolyte systems. The development of functional electrolytes for Li–S batteries is hopeful to alleviate the problems Li–S batteries faced today. The liquid electrolytes circumvent the polysulfide shuttle and the resultant problems by utilizing different functional solvents, lithium salts, and additives. Solid-state electrolytes as promising electrolytes are optimized to enhance the ionic conductivity at room temperature and decrease the interfacial resistance. Hybrid electrolytes that consist of two or more single electrolytes may be considered as unique categories because they have the potential advantages than the single electrolyte systems. Challenges and perspectives of Li–S electrolytes are also proposed based on the requirement for high-performance Li–S batteries.