An Integrated Tandem-Structured Separator Enables Dual-Enhanced Stable Interfaces for Long-Cycle-Life and High-Areal-Capacity Aqueous Zinc-Iodine Batteries.

Aqueous zinc-iodine batteries (AZIBs) hold great promise for next-generation energy storage technologies due to their inherent safety, cost-effectiveness, and environmental friendliness. However, unstable interfacial chemistry manifested as polyiodide formation and accumulation at the cathode, alongside dendrite growth and hydrogen evolution reaction (HER) at the anode results in capacity loss. Moreover, polyiodide migration toward the anode further triggers severe Zn corrosion, exacerbating interfacial instability. Herein, we design an integrated tandem-structured separator comprising an InO-SiO (ISO) layer with a buffer-release-repair mechanism and a polyiodide adsorption-catalysis layer featuring Co nanoparticles-encapsulated carbon nanofiber (Co@CNF) to achieve dual-enhanced stable interfaces. Specifically, amphoteric InO within the ISO layer effectively neutralizes OH⁻ generated by localized HER, concurrently releasing soluble indium species. These indium species subsequently electrodeposit to form zincophilic and HER-inhibiting sites on the affected regions, restoring interfacial environment and mitigating Zn anode degradation. Meanwhile, the Co@CNF layer anchors polyiodides and significantly catalyzes conversion kinetics, suppressing the shuttle effect and preventing polyiodide-induced anode corrosion. Benefiting from the synergistic stabilization of both electrode interfaces, the as-fabricated Zn||ISO + Co@CNF||I full cells achieve a high areal capacity of 2.97 mAh cm and remarkable cycling stability over 20 000 cycles. This work provides valuable insights into designing functional separators for practical AZIBs.