Engineering Coral-Inspired Gradient Porosity Composite for High-Performance Batteries

Lithium–sulfur batteries offer high energy density but are limited by polysulfide shuttling, sluggish ion transport, and lithium-dendrite-induced interfacial failure. Conventional nanofibrous separators provide mechanical and thermal stability, yet strong inter-fiber interactions cause dense restacking, low porosity, tortuous ion pathways, and severe concentration polarization. Inspired by the hierarchical porosity and mechanical resilience of coral reefs, we developed a coral-mimetic gradient porous composite separator (APA) integrating aramid nanofibers (ANFs), methacryloxy-functionalized polyhedral oligomeric silsesquioxane (POSS), and 2-amino-5-mercapto-1,3,4-thiadiazole (AMT). The ANF scaffold provides mechanical strength, the POSS-derived hybrid framework suppresses nanofiber restacking and forms continuous mesoporous ion channels, while the AMT-functionalized surface chemically anchors lithium polysulfides. This asymmetric architecture improves electrolyte wettability, ionic conductivity, Li⁺ transference, polysulfide confinement, and dendrite resistance. Benefitting above merits, the assembled Li–S cells with APA exhibit an initial capacity of 945 mAh g⁻¹ at 2.0C and sustain >2000 cycles with only 0.023% capacity decay per cycle. Li||Li symmetric cells remain stable for over 4000 h under harsh conditions (10.0 mA cm⁻²/10.0 mAh cm⁻²). The separator also demonstrates compatibility with LFP/Li and NCM/Li systems, highlighting the versatility of this bioinspired gradient-architecture strategy for advanced lithium metal batteries.