Designing and mapping cascade catalysis pathway for balanced polysulfide conversion in Li-S batteries

Lithium-sulfur batteries are fundamentally constrained by the sluggish 16-electron sulfur reduction reaction. Electrocatalytic sulfur reduction reaction is inherently complex, involving multiple lithium polysulfide intermediates (Li₂S_n, n = 2-8), each with distinct adsorption and activation requirements, leading to unbalanced polysulfide conversion and severe shuttle effect. Although cascade catalysis has been proposed as a potential solution, the precise pathway and its mechanistic role in regulating polysulfide conversion remain elusive. Here we elucidate and experimentally validate the complete cascade pathway of sulfur reduction on Fe,N,S-codoped holey graphene as a model catalyst. Density functional theory reveals that Fe sites preferentially bind and activate long-chain polysulfides, while N,S-C sites accelerate the conversion of Li₂S₄ to Li₂S₂/Li₂S. Such site-specific synergy balances sulfur reduction kinetics and suppresses polysulfide accumulation. Combined kinetic analysis and operando Raman spectroscopy directly reveal how synergistic cascade catalysis governs the reaction pathway, modulates key intermediates, and enables balanced polysulfide conversion. Together, these results establish cascade catalysis as a mechanism-driven design strategy for lithium-sulfur battery electrodes, where regulation of the reaction pathway suppresses polysulfide shuttling and enables enhanced cycling stability.