context: With the new development of electronic products and electric vehicles, state-of-the-art lithium-ion batteries are facing a grand challenge in meeting the rapidly expanding energy demand due to their inherently limited theoretical energy density. Lithium–sulfur (Li–S) batteries, on the other hand, shown to have five times higher theoretical specific capacity and energy density, have demonstrated tremendous potential for next-generation energy storage equipment applications. In addition, the environmental benignity and economic benefits of elemental sulfur further buttress its large-scale commercial manufacture. Despite these merits, the application of Li–S batteries is still hindered by some intractable challenges: firstly, the poor resistivity of elemental sulfur will reduce the utilization of raw materials and the reaction kinetics; secondly, the excessive volume expansion (∼80%) during charging/discharging may result in inevitable evolution of structures and strain; and thirdly, lithium polysulfides (LiPSs) dissolved from the cathode can penetrate the separator and deposit on the anode surface, leading to the “shuttle effect” and anode corrosion. These issues have been the bottlenecks in the development of high-performance Li–S batteries.
answer:  lithium polysulfides (LiPSs) 