Breaking the rate limiting barrier in lithium||sulfur batteries via spin state engineering

Elucidating the mechanisms governing sulfur redox reactions is important for the development of high-energy-density Li||S batteries. Despite progress, the kinetics of the solid-solid conversion from Li₂S₂ to Li₂S remain poorly understood. This work demonstrates that spin-state transitions within reaction intermediates are the key factor of the sluggish kinetics. Guided by density functional theory and machine-learning-assisted catalyst screening, we find 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-doped MoS₂ catalyst, with its high spin moment, modulates the spin states of the reactants, reducing the high free-energy barrier associated with spin-state transitions. Therefore, Li||S batteries incorporating this catalyst show accelerated sulfur conversion, particularly during solid-solid transitions, suppressed polysulfide shuttling, and have stable electrochemical performance. A pouch cell achieves a capacity of 13.2 Ah and a specific energy of 435 Wh kg^-1. These findings show mechanistic understanding into the role of spin moments in sulfur conversion, enabling to design efficient and durable catalysts for Li||S batteries.