Hofmeister-Regulated Amide-Protonated Hydrogel Enables Organo-Interhalogen Conversion-Type Quasi-Solid-State Zn...

Organo-interhalogen-mediated four-electron iodine conversion (I^-/I⁰/I⁺) promises high-energy Zn batteries (4eZIBs) in noncorrosive aqueous electrolytes. Yet, polyiodide shuttling and I⁺ hydrolysis restrict shorten cycle life at high iodine loadings. Here we report a dual-anionic Hofmeister-regulated amide-protonated polyacrylamide (pPAM) hydrogel electrolyte to solve this issue. Consistent with experimental observations, underlying mechanistic interpretations are proposed. The potential protonated site ─COHNH₂ ⁺ in pPAM can interact with iodine species (I₃ ^-, I₂, and organo-interhalogen adduct), effectively suppressing active material loss during cycling. The dual-anion-regulated Hofmeister effect may contribute to control molecular mediator (2-bromoacetamide, BrAce) flux within the pPAM gel, enabling fast organo-interhalogen conversion. The extensive hydrogen-bonding network of the hydrogel reshapes the hydrogen-bonding environment of water, suppressing organo-interhalogen adduct (I⁺ species) hydrolysis. The resulting quasi-solid-state 4eZIBs substantially outperform aqueous counterparts and state-of-the-art results. At 15.6 mg cm^-2 iodine loading, stable cycling exceeds 2000 cycles at 15 mA cm^-2. At 28.3 mg cm^-2, the battery delivers an areal capacity of 9.95 mAh cm^-2 and an areal energy density of 10.85 mWh cm^-2. An Ah-level pouch cell cycles 50 times at 0.5 mA cm^-2, with an energy density of 305.27 Wh kg_iodine ^-1. This work provides a hydrogel design principle for organo-interhalogen-mediated conversion, advancing practical high-loading 4eZIBs and beyond.