Metal-organic molecules for aqueous ZnI2 batteries: synergistic redox acceleration and shuttle effect inhibition

Aqueous zinc‑iodine (Zn I 2 ) batteries are considered promising energy storage systems due to their high energy density, improved safety, and low cost. However, their advanced performances are severely limited by the sluggish redox kinetics of iodine and the polyiodide shuttling effect, which leads to irreversible loss of active material and zinc anode corrosion, thereby degrading cycling stability and overall performance. In this work, copper acetylacetonate (Cu(acac) 2 ) is employed as a metal-organic molecular catalyst to construct high-performance and long-lasting Zn I 2 batteries. Material characterizations and density functional theory calculations reveal that Cu(acac) 2 exhibits dual functionalities: (1) chemically adsorbing iodide/polyiodide species to suppress the shuttling effect, and (2) catalyzing iodine redox reactions to enhance reaction kinetics. The Zn-I₂ batteries assembled with Cu(acac) 2 as the cathode material can achieve an extraordinary cycling lifespan of over 55,000 cycles at 4 A g −1 with a minimal capacity decay rate of 0.00086 % per cycle, along with an average coulombic efficiency of 99.86 %, surpassing the performance of carbon-based cathodes. In-situ Raman spectroscopy further demonstrates that Zn I 2 batteries using Cu(acac) 2 cathodes maintain significantly lower polyiodide concentrations during charge/discharge processes compared to those using active carbon cathodes, confirming its dual role in suppressing shuttling and catalyzing reactions. This work highlights the effectiveness of molecular catalysts in mitigating polyiodide shuttling and offers a novel approach to developing high-performance aqueous Zn I 2 batteries.