Cosolvent Electrolyte Design for Li–S Batteries: Suppressing the Shuttle Effect via Phase Separation

Abstract Lithium–sulfur batteries are promising candidates for next‐generation energy storage due to their high energy density and low cost. However, their commercialization is hindered by poor cycling performance caused by the polysulfide shuttle effect. While strategies such as physical barriers or chemical adsorption have been proposed, they inevitably introduce inactive components, reducing energy density. These limitations underscore the need for a more fundamental approach that avoids the use of inactive materials. In this study, a cosolvent‐based electrolyte design as a fundamental strategy is presented to suppress the shuttle effect without relying on inactive additives. A high donor number solvent is used as the base, and four cosolvents with distinct physicochemical properties are individually introduced. By varying the cosolvent, the lithium polysulfides solubility is systematically tuned, directly influencing electrochemical kinetics. Notably, the combination of two low‐miscibility solvents induced local phase separation, which hindered the diffusion of lithium polysulfides and effectively mitigated the shuttle effect. As a result, significantly improved cycling stability is achieved. These findings provide a new direction for Li–S battery electrolyte development, emphasizing the importance of solvent miscibility in governing polysulfide transport.