Nitrogen-doped MOF-derived carbon hosts for aluminum-sulfur batteries: Polysulfide confinement and sulfur-loading limitations

Despite being a highly attractive candidate for advanced energy storage systems, aluminum‑sulfur (Al S) batteries suffer from restricted practical viability due to severe polysulfide shuttling and inherently slow redox kinetics. To tackle these issues, a ZIF-67-templated hierarchical nitrogen-doped hollow carbon (HNC) framework is constructed to serve as an advanced sulfur-accommodating matrix. By modulating the nitrogen precursors, specifically using melamine, a densely populated N/O dual-doped matrix is constructed to intrinsically regulate the electrochemical behavior. Kinetic analyses reveal low apparent b-values (0.36–0.40) for the S@HNC-Melamine cathode, indicating substantial deviation from ideal diffusion-controlled behavior and highlighting the important contributions of interfacial charge-transfer constraints and phase-boundary reactions. This robust chemical confinement is unequivocally corroborated by in-situ optical observations, demonstrating a completely transparent electrolyte during standard discharge and maximally delayed polysulfide dissolution under extreme anodic polarization. Crucially, despite the exceptional micro-level electrocatalytic advantages, electrochemical evaluations unveil that the absolute reversible capacity and cycling stability in reduction-type cells are predominantly governed by macroscopic areal sulfur loading. The inherently poor conductivity and sluggish solid-state diffusion of thick S/Al 2 S 3 layers completely override the localized heteroatom-doping benefits. This work not only elucidates the fundamental dual-adsorption mechanisms but also critically highlights that addressing macroscopic mass loading limitations is the primary prerequisite for advancing practical Al S batteries.