Yanbo Zhu, Haodong Zhang, Mengyi Tao, Yuyang Yan, Xiaotang Gan, Chaoji Chen, Jinping Zhou
ABSTRACT Zinc||iodine (Zn||I 2 ) batteries hold great promise for large‐scale energy storage, yet their practical deployment is hindered by Zn dendrite growth, parasitic side reactions, uncontrollable polyiodide shuttling, and sluggish I 2 conversion kinetics. To address these challenges, a “Janus biopolymer separator enabled dual interfacial regulation” strategy was proposed to synchronously stabilize both cathode and anode toward sustainable and long‐life Zn||I 2 batteries. On the anode side, the negatively charged sodium alginate layer modulates Zn 2+ deposition behavior and mitigates surface corrosion through electrostatic repulsion of polyiodides. Simultaneously, the positively charged chitosan layer on the cathode side interacts with polyiodides, suppressing their migration and accelerating I 2 redox kinetics. As a result, Zn||I 2 batteries exhibit a negligible capacity decay of 0.01‰ per cycle over 20,000 cycles at 5000 mA g −1 , maintaining excellent performance even under harsh conditions. The universality of this strategy is further verified by extending it to other types of biopolymers. Furthermore, the biodegradability and biocompatibility of the separator significantly enhance the overall sustainability and biosafety of the proposed Zn||I 2 batteries. This work presents a sustainable, generalizable Janus biopolymer separator design for shuttle‐free and highly durable Zn||I 2 batteries.