Single-atom catalysts anchored on nanostructured frameworks for high-performance lithium-sulfur batteries: a review of catalytic mechanisms.

Li-S batteries offer a theoretical specific capacity of 1675 mAh g-1 and specific energy near 2600 Wh kg-1, but practical cells remain limited by incomplete sulfur utilization, soluble lithium polysulfide (LiPS) shuttling, sluggish liquid-solid conversion, insulating Li2S/Li2S2, and lithium-metal instability. Single-atom catalysts (SACs) anchored on nanostructured frameworks combine high atom utilization and tunable coordination with conductive, porous architectures that regulate transport and confinement. This review examines SAC-based Li-S batteries by connecting site structure, catalytic mechanism, and cell-level performance. Unlike reviews organized mainly by metal identity or support class, it uses a mechanism-centered framework linking coordination and topology to adsorption, bidirectional conversion, Li2S growth, and practical metrics. It also distinguishes isolated-site SAC evidence from cluster and dual-atom comparators, evaluates descriptor and operando-validation limits, and identifies ultrathin bifunctional catalytic separators/interlayers as a near-term deployment route. Reported capacities, rates, sulfur loadings, areal capacities, electrolyte/sulfur ratios, cycle life, activation barriers, adsorption energies, Tafel slopes, and nucleation/decomposition metrics are compared in four comparative tables. The analysis shows that high apparent performance often depends on low sulfur loading, excess electrolyte, or coin-cell conditions, and that descriptors from idealized models must be interpreted with respect to product coverage, electrolyte chemistry, and site stability. SACs are most valuable when strong-but-not-immobilizing LiPS binding, fast electron/ion transport, controlled Li2S deposition, and reversible Li2S oxidation are achieved simultaneously. Future work should pair standardized lean-electrolyte, high-loading, limited-lithium, and pouch-cell testing with state-resolved validation of catalytic pathways and active-site stability.