Unlocking Multielectron Halogen Redox via Hydrogel‐Confined Organic Bromine for High‐Performance Zn–I/Br Batteries

ABSTRACT Aqueous Zn‐halogen batteries based on multielectron I/Br conversion hold great promise for achieving high energy density, yet their practical deployment faces critical challenges. The highly electrophilic I + species undergo irreversible hydrolysis in aqueous media, while the Zn anode suffers from severe dendrite growth and parasitic hydrogen evolution reaction (HER). Herein, we propose a bifunctional hydrogel electrolyte confined with organic bromine (2‐bromoacetamide, BA) to address these issues. During operation, BA undergoes partial interfacial conversion at the electrode/hydrogel interface to release Br − and acetamide (AC). The liberated Br − promotes IBr 2 − and IBr 3 − formation, effectively stabilizing the multielectron redox reactions at high potentials. Meanwhile, AC molecules regulate the Zn 2+ solvation structure and form an AC‐enriched adsorption layer, which can suppress HER and direct uniform Zn deposition. Benefiting from this synergistic regulation, symmetric cells achieve stable operation for over 1000 h under a high depth of discharge of 40%. The assembled Zn–I/Br full cell delivers an iodine‐mass‐normalized capacity of 307 mAh g −1 at 5 A g −1 and retains 82.3% of its initial capacity after over 25,000 cycles. Moreover, a 0.1 Ah Zn–I/Br pouch cell operates stably for 300 cycles. This work offers a new interfacial regulation route for unlocking multielectron energy storage systems.