Conquering Shuttle Effect and Dendrites Synergistically: A Zwitterionic Bacterial Cellulose Hydrogel Electrolyte for Ultralong‐Lifespan Zn–I2 Batteries

Abstract Rechargeable aqueous zinc–iodine batteries (ZIBs) hold significant promise for energy storage. Their advancement, however, faces critical challenges: soluble polyiodide shuttling and rampant Zn dendrite growth. This work introduces a polyampholyte bacterial cellulose hydrogel electrolyte (SBC) engineered to overcome these limitations. On the cathode side, iodine‐affinitive polycations within SBC suppress shuttling and boost redox kinetics of iodine species. On the anode side, sulfonate anions enable a high Zn 2+ transference number (0.82) and guide epitaxial Zn nucleation. Optimized Zn 2 ⁺ solvation and a restructured H‐bond network further lower desolvation barriers, inhibit corrosion, and minimize parasitic reactions. The interconnected bacterial cellulose network provides robust ion channels while restricting iodine dissolution. Consequently, Zn||Zn symmetric cells with SBC electrolyte achieve exceptional stability (1800 h at 10 mA cm− 2 /10 mAh cm − 2 ; 2500 h at 5 mA cm − 2 /5 mAh cm − 2 ). Zn–I 2 full cells retain capacity over 20 000 cycles at 8 C with a minimal fade rate of 0.006% per cycle. This SBC design offers a blueprint for long‐lasting aqueous conversion batteries.