Research progress on electrolyte regulation and reaction mechanism of solubility of polysulfides in lithium-sulfur batteries

Lithium sulfur batteries (LSBs) are emerging as the next generation of high-energy-density battery systems in the field of energy storage due to the high theoretical specific capacity and energy density of the sulfur cathode. However, their commercial development is hindered by the serious "shuttle effect" of polysulfides (PS) during charging and discharging, the low conductivity of sulfur and its discharged products (Li ₂S ₂/Li ₂S), the significant volume expansion (~80%) of the sulfur cathode during cycling, and the growth of lithium dendrites on the lithium anode. As a key liquid-phase reaction intermediate, soluble polysulfides are the basis for achieving an efficient "solid-liquid-solid" conversion reaction path. It avoids the slow solid-solid reaction, greatly improves the reaction kinetics and sulfur utilization, and is the key to obtaining high capacity of lithium-sulfur batteries. However, when the solubility is more, a large number of polysulfides will diffuse to the lithium metal anode, which directly leads to the irreversible loss of the active material and the serious self-discharging, resulting in rapid capacity decay. In this context, electrolyte design has emerged as an effective strategy to fundamentally address these problems. This approach typically aims to further balance reaction kinetics and cycle stability by regulating the solubility of polysulfides, thereby achieving efficient conversion and regulation of polysulfides in sulfur cathodes, which is essential for achieving high and stable performance of lithium-sulfur batteries. This paper systematically reviews the main electrolyte design approaches for lithium-sulfur batteries. It focuses on the relationship between polysulfide solubility in the sulfur cathode and the regulation mechanism through electrolyte, highlighting the current development status, application landscape, and future directions. Specifically, insoluble systems completely block polysulfide dissolution via physical/chemical confinement meanwhile reducing sulfur loading and reaction kinetics to enhance the cycle stability of the sulfur electrode; conversely, by reconstructing solvation effects using high-concentration lithium salts or weakly-coordinating solvents, researchers compress the free solvent phase space, enabling quasi-solid-state conversion under lean electrolyte conditions through micro-dissolution equilibrium, which suppresses the shuttle effect at its source and mitigates electrode kinetic hysteresis. Dissoluble systems accelerate reaction kinetics by actively increasing PS solubility and can achieve low electrolyte usage and high-rate performance, but they require solutions to mitigate the shuttle effect resulting from the increased solubility. Finally, we summarize the challenges and provide a prospective outlook on the future development of PS electrolyte solubility regulation in LSBs.