Synergistic Integration of Fe-N4 Single-Atom Sites and Directionally Aligned Electrode Architecture for High-Performance Lithium-Sulfur Batteries.

Sluggish kinetics of redox reactions and slow ion transport restrict the performance of lithium-sulfur (Li─S) batteries. Here, we fabricate cathodes containing vertically aligned porous structures hosting atomically dispersed Fe─N4 single-atom catalyst (SAC) sites on graphitic carbon nitride (g-C3N4). Density functional theory (DFT) calculations suggest that the Fe─N4 sites strengthen Li2S adsorption, optimize electronic structure, and lower the reaction energy change associated with liquid-solid transition and Li2S oxidation. Experimental results demonstrate that the atomically dispersed Fe─N4 sites in the vertically aligned porous cathodes made by directional ice templating (DIT) accelerate Li+ ion transport and enable high sulfur loading while exposing abundant catalytic centers, resulting in strong polysulfide affinity, promoted nucleation and decomposition of Li2S bidirectional redox catalysis, and suppressed polysulfide shuttle effect. Benefiting from this structural-catalytic synergy, the cathode delivers a high capacity of 1299.2 mAh g-1 at 0.1 C, and the capacity is retained at 505.9 mAh g-1 after 1 000 cycles at 0.5 C, with a low capacity decay rate of ∼0.042% per cycle. This study highlights a scalable strategy to integrate SAC with vertically aligned porous electrode architecture that promotes fast kinetics of sulfur redox in both directions and mass transport for Li─S batteries.