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

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 Zn²⁺ transference number (0.82) and guide epitaxial Zn nucleation. Optimized Zn²⁺ 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-I₂ 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.