Biodegradable and Closed‐Loop Recyclable Hyaluronic Acid/Alginate Gel Electrolyte for Ultra‐Durable Zinc‐Iodine Batteries

ABSTRACT Hydrogel electrolytes are promising candidates for flexible energy storage, yet most rely on petroleum‐derived polymers, raising significant sustainability and environmental concerns. Herein, we report a bio‐based, biodegradable, and closed‐loop recyclable hyaluronic acid (HA)/sodium alginate (SA) hydrogel electrolyte with zinc sulfate (denoted as ZHS) for zinc‐iodine batteries. Leveraging abundant hydrophilic groups (─OH, ─CONH─, and ─COOH) in these natural polysaccharides, ZHS simultaneously addresses the environmental burden of synthetic gels and the electrochemical challenges of Zn‐I 2 batteries. Competitive hydrogen bonding between HA/SA and H 2 O molecules, coupled with dynamic water redistribution along polymer chains, yields a uniform and robust dual‐network architecture. This network provides homogeneous pathways for rapid Zn 2+ transport and suppresses dendrite nucleation, while abundant polar adsorption sites immobilize polyiodides (I 3 − and I 5 − ) through ion‐dipole interactions, alleviating shuttle effects. Consequently, Zn||Zn symmetric cells cycle stably for over 2,600 h, and Zn||I 2 full cells achieve remarkable durability exceeding 35,000 cycles. Notably, the ZHS hydrogel demonstrates excellent biocompatibility and can be readily biodegraded under ambient conditions. Furthermore, cycled ZHS can be regenerated through simple aqueous dissolution and re‐casting, supporting stable operation for an additional 21,000 cycles. This work pioneers a sustainable pathway toward environmentally benign, high‐performance gel electrolytes for zinc‐iodine batteries.