Simultaneous Inhibition of I ⁺ Hydrolysis and Polyiodide Shuttle Enabled by Choline-Based Electrolyte Additives toward Long-Life Zinc–Iodine Batteries

Aqueous zinc–iodine (Zn–I 2 ) batteries, leveraging four-electron I – /I 0 /I + redox chemistry, offer advantages such as high voltage, low cost, and high safety. However, their widespread application is hindered by hydrolysis reactions and the shuttle effect of iodine species. Here, a multifunctional electrolyte additive, bethanechol chloride (AChR), is employed to simultaneously stabilize I + and inhibit the polyiodide shuttle, thereby prolonging the cycling life of aqueous Zn–I 2 batteries. The AChR additive, possessing positively charged −N + (CH 3 ) 3 functional groups, electrostatically traps I 3 – anions with an adsorption energy of −0.45 eV, significantly suppressing the polyiodide shuttle. Meanwhile, its nucleophilic −NH 2 and C=O groups effectively disrupt hydrogen-bond networks and reduce water activity, thereby protecting I + from water nucleophilic attack. In situ Raman spectroscopy confirms that the signal intensity of ICl charging product in the AChR-containing aqueous electrolyte is 20 times higher than that in the baseline electrolyte (BE), demonstrating that AChR restrains I + hydrolysis. Benefiting from these advantages, the Zn–I 2 cell achieves a high areal capacity of 5.64 mAh cm –2 and exhibits a high capacity retention ratio of 78.2% after 1000 cycles, even with a high I 2 cathode mass loading of 16.6 mg cm –2, representing a 21.7-fold improvement over the cell in the BE.