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. Lithium||sulfur batteries are limited by sluggish solid-state sulfur conversion. Here, authors investigate spin-state transitions as a key kinetic barrier and design a spin-regulated catalyst that accelerates sulfur conversion, suppresses polysulfide shuttling, and enables high-capacity pouch cells.
Jiang et al. (Tue,) studied this question.