Steering Sulfur Reduction Pathways via Cisplatin Enables High Performance in Lithium‐Sulfur Batteries

The sulfur reduction reaction (SRR) is an attractive 16-electron transfer process that endows Li-S batteries with a theoretical capacity of 1,672 mAh g-1. However, the slow kinetics and complex pathways of the SRR cause the shuttling of soluble polysulfides (PSs), thus fast capacity fading. Here, we report using cisplatin (cis-Pt) as a novel mediator to improve the SRR kinetics and a molecular probe to identify the SRR pathways. We show that cis-Pt with a reductive Pt2+ center can directly slice the S-S bonds of PSs, leading to enhanced charge transfer kinetics, guided SRR pathways, and depth conversion of PSs to Li2S. With cis-Pt added, Li-S coin cells deliver a maximum specific capacity of 1,437 mAh g-1 and a capacity decay of 0.017% per cycle after 1000 cycles, while a pouch cell with a practical electrolyte-sulfur ratio (2.5 μl mg-1) exhibits a high energy density of 318.8 Wh kg-1. Our mechanistic studies reveal that cis-Pt steers the cathodic SRR pathways by generating redox active cis-Pt/PSs complexes, enabling the replacement of the sluggish SRR with a faster redox cycling of Pt4+/Pt2+ pairs. These findings provide insights into the rational design of functional mediators for tackling the cathodic challenges inside Li-S batteries.