Synergetic insights into Nb single atoms and lithiophilic support for high-efficiency sulfur catalysis in Li-S batteries

The sulfur reduction reaction (SRR) is the core of lithium-sulfur (Li-S) batteries, and a comprehensive understanding of the SRR contributes to catalyst design for high-performance Li-S batteries. However, unclear relationships between active lithium ions and lithium polysulfide (LiPS) conversion activity are always overlooked. Here, we elaborately synthesized Nb-single-atom catalysts (Nb-C₃N_4−x), where the strong Nb-S bond reduces the S-S bond energy and accelerates LiPS conversion. Meanwhile, inspired by aqueous electrocatalytic reactions, we propose surface-active Li⁺ (*Li⁺) as a crucial intermediate for SRR kinetics. On Li⁺-rich catalysts, LiPSs can react directly with *Li⁺ which avoids the slow Li⁺ migration across the electrolyte-electrode interface to LiPSs. The Nb-C₃N_4−x-based full cell works steadily at a low negative/positive capacity ratio and a lean electrolyte with a capacity retention rate of 87.01%. This work complements the comprehension of the SRR, and provides theoretical guidance for the screening of Li-S battery catalysts.