Breaking the Rate-Limiting Barrier in Solid-Solid Sulfur Redox Reactions via Spin-State Engineering

Elucidating the mechanisms governing sulfur redox reactions is critical for the development of high-energy-density lithium-sulfur (Li-S) batteries. Despite progress, the kinetics of the solid-solid conversion from Li2S2 to Li2S remain poorly understood. Here we show that spin-state transitions within reaction intermediates are the principal source of the sluggish kinetics. Guided by density functional theory and machine-learning-assisted catalyst screening, we have found a negative correlation between the spin moment of the catalyst and the Gibbs free energy barrier for the Li2S2 to Li2S conversion. Among a series of dual-metal doped catalysts, a Co,Ni-MoS2 catalyst, with its exceptional spin moment, effectively regulates the spin states of the reactants, reducing the high reaction energy barrier associated with spin-state transitions. Therefore, Li-S batteries incorporating with the Co,Ni-MoS2 showed accelerated sulfur conversion, particularly during solid-solid transitions, effectively suppressed polysulfide shuttling, and had excellent electrochemical performance. A prototype Li-S pouch cell achieved a capacity exceeding 13.2 Ah and an energy density of 435 Wh kg-1. These findings show critical insights into the role of spin moments in sulfur conversion, providing a way to design efficient and durable catalysts for Li-S batteries.