Synergistic Construction of Hierarchical Tree-Ring Structures and Blocked Interfaces for Stable, Flexible Zinc–Iodine Batteries with Ultrahigh Areal/Gravimetric Capacity

The development of aqueous zinc–iodine (Zn–I₂) batteries is plagued by long-term cycling stability, mainly caused by limited iodine loading, polyiodide shuttle, and uneven Zn²⁺ deposition. Herein, a unique tree-ring-like hierarchical structure constructed by polyaniline (PANI) nanofiber arrays and reduced graphene oxide (RGO) was designed to provide the nanopore array for prestoring iodine ions and confine the iodine conversion reaction as well as promote electron and ion transport along PANI nanofibers, thereby enhancing the capacity and cycling durability of Zn–I₂ batteries. Meanwhile, the sulfonic polyacrylamide/glycerol (SPAM/Gly) hydrogel electrolyte containing the ZnI₂ additive is introduced for simultaneously inhibiting the polyiodide shuttle and side reactions on the Zn anode accompanied by excellent antifreezing properties and flexibility. As a result, the assembled flexible battery realized a remarkable areal capacity of 2.3 mAh·cm^–2 at 0.5 mA·cm^–2 (corresponding to 287.5 mAh·g^–1) and a maximum energy density of 2.54 mWh·cm^–2 at a high mass loading of 8 mg·cm^–2. Consequently, the battery still exhibited a capacity of 0.784 mAh·cm^–2 over 6000 cycles and 0.98 mAh·cm^–2 after 200 cycles under −20 °C at 2 mA·cm^–2. Such flexible device also maintains a steady supply of powering electronic gadget during deformations.