Low-Self-Discharge Nanoconfined Hydrogel Electrolyte for Stable High-Energy-Density Aqueous Zinc–Iodine Batteries

Aqueous zinc-iodine batteries (AZIBs) leveraging four-electron I^-/I⁰/I⁺ redox chemistry show great promise in safe energy storage systems. However, realizing Ah-level AZIBs with industrial-grade parameters (≥10 mg cm^-2 mass loading) remains fundamentally challenging. Here, we prepare the hydrogel electrolyte with mesoporous nanoparticles SBA-15 (MNPHE) by a nanoconfined polymerization strategy. The framework confinement effect, anion confinement effect, and free water confinement effect are achieved through Lewis acid-base interactions and hydrogen bond networks. The multiconfinement effects yield simultaneous ultrahigh mechanical strength (501 kPa tensile strength) and a record-high Zn²⁺ transference number (<i>t</i>_Zn²⁺ = 0.95), which collectively suppressed polyiodide generation and I⁺ species hydrolysis. This results in markedly enhanced reversibility and kinetics for four-electron I^-/I⁰/I⁺ redox chemistry under a high-I₂-mass-loading cathode. Based on MNPHE, the Zn||I₂ full cells display a record-low self-discharge rate with only 20% capacity loss after three months and a prolonged lifetime of 100,000 cycles at 25 C. Furthermore, Ah-level four-electron Zn||I₂ pouch cells achieve excellent cyclability of 800 cycles and an ultrahigh cathode-mass-specific energy density of 466.7 Wh kg^-1, surpassing all aqueous Zn-based systems in the Ah-level regime.