Engineering spin states of metal sites toward advanced lithium–sulfur batteries

Developing efficient catalysts is essential for mitigating the shuttle effect and accelerating the conversion kinetics of polysulfides in lithium–sulfur (Li–S) batteries. To date, numerous strategies have been employed to optimize the performance of catalysts. Among these strategies, regulating the spin state of metal sites can modulate the d orbital occupancy and enable precise control over catalyst–polysulfide interactions, which provides an effective approach for the catalysts to optimize the balance between adsorption and catalysis toward polysulfide conversion. This review offers a comprehensive overview of spin-state engineering of the catalysts for Li–S batteries for the first time, detailing the strategies for spin-state modulation and the relevant characterization techniques for monitoring these changes. Finally, we underscore the critical role of spin-state tuning in optimizing catalytic active centers and propose future research directions in this emerging field.