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

Aqueous zinc–iodine batteries (AZIBs) leveraging four-electron I – /I 0 /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 Zn 2+ transference number ( t Zn 2+ = 0.95), which collectively suppressed polyiodide generation and I + species hydrolysis. This results in markedly enhanced reversibility and kinetics for four-electron I – /I 0 /I + redox chemistry under a high-I 2 -mass-loading cathode. Based on MNPHE, the Zn||I 2 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||I 2 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.