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

Aqueous zinc-iodine (Zn-I₂) batteries, leveraging four-electron I⁻/I⁰/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-I₂ batteries. The AChR additive, possessing positively charged -N⁺(CH₃)₃ functional groups, electrostatically traps I₃⁻ anions with an adsorption energy of -0.45 eV, significantly suppressing the polyiodide shuttle. Meanwhile, its nucleophilic -NH₂ 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-I₂ 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 I₂ cathode mass loading of 16.6 mg cm⁻², representing a 21.7-fold improvement over the cell in the BE.