A Versatile Redox‐Active Electrolyte for Solid Fixation of Polyiodide and Dendrite‐Free Operation in Sustainable Aqueous Zinc‐Iodine Batteries

Abstract Practical utilization of zinc‐iodine (Zn‐I 2 ) batteries is hindered by significant challenges, primarily stemming from the polyiodide shuttle effect on the cathode and dendrite growth on the anode. Herein, a feasible redox‐active electrolyte has been introduced with tetraethylammonium iodide as an additive that simultaneously addresses the above mentioned challenges via polyiodide solidification on the cathode and the electrostatic shielding effect on the anode. The tetraethylammonium (TEA + ) captures water‐soluble polyiodide intermediates (I 3 − , I 5 − ), forming a solid complex at the cathode, thereby suppressing capacity loss during charge/discharge. Furthermore, the TEA + mitigates dendrite growth on the Zn anode via the electrostatic shielding effect, promoting uniform and compact Zn deposition at the anode. Consequently, the Zn||Zn symmetric cell demonstrates superior cycling stability during Zn plating/stripping over 4,200 h at 1 mA cm −2 and 1 mAh cm −2 . The Zn||NiNC full‐cell exhibits a stable capacity retention of 98.4% after 20 000 cycles (>5 months) with near‐unity Coulombic efficiency at 1 A g −1 . The study provides novel insights for establishing a new direction for low‐cost, sustainable, and long‐lifespan Zn‐I 2 batteries.