Synergistic I 3 − Scavenging and Spontaneous Interphase Construction for Ultralong‐Life Zinc–Iodine Batteries

Aqueous Zn–I 2 batteries combine safety, sustainability, and high theoretical capacity, making them a promising energy storage solution. However, their practical employment is impeded by challenges such as uncontrolled dendrite growth on the Zn anode, severe polyiodide shuttling effect, and the dissolution of the I 2 cathode. Herein, we propose di‐ tert ‐butyl(3‐sulfonatopropyl) phosphine (DBSP) as a multifunctional electrolyte additive. DBSP mitigates HER and guides highly oriented Zn 2+ deposition and lead to the dendrite‐free (002) plane. Meanwhile, the strongly phosphine reductive center in DBSP effectively scavenges polyiodide intermediates by converting I 3 − into stable I − . Notably, DBSP undergoes a spontaneous oxidative reaction with I 2 , forming a robust protective interphase on the cathode that effectively suppresses I 2 dissolution. This synergistic stabilization results in exceptional electrochemical durability. Specifically, the Zn║Zn symmetric cell with the 10 DBSP electrolyte exhibits 2,300 h cycling stability at 5 mA cm − 2 /5 mAh cm − 2 . Furthermore, the Zn–I 2 full cell retains a capacity of 105.9 mAh g −1 over 220,000 cycles at a current density of 10 A g −1 . This work establishes a new molecular‐level paradigm for designing synergistic electrolyte additives and provides crucial insights for the development of durable and high‐performance aqueous battery systems.