Hydrophobic Quaternary Ammonium Iodides for Highly Stable Four−Electron Zinc−Iodine Batteries

ABSTRACT

Aqueous four−electron zinc−iodine (Zn−I) batteries have attracted extensive attention due to their high capacity, material abundance, and high safety. However, the Zn−I battery suffers from poor reversibility and severe self−discharge due to the polyiodides shuttle effect and high‑valent I ⁺ hydrolysis facing by the conventional I ₂ cathode. Herein, a series of organic iodides is designed by complexing I ₃ ⁻ with quaternary ammonium cations with different alkyl chain lengths. Experimental and theoretical analyses reveal that these organic cations form stable complexes with I ₃ ⁻ , effectively suppressing the shuttle effect of polyiodides and thereby stabilizing Zn metal anode. Meanwhile, their hydrophobic alkyl chains create a physical barrier at the electrode−electrolyte interface, limiting water access and mitigating the I ⁺ hydrolysis. Consequently, the as−designed (CH ₂ ) ₁₈ N(CH ₃ ) ₃ I ₃ (C ₁₈ I ₃ ) cathode for four−electron Zn−I batteries manifest a high reversible capacity of 463.0 mAh g ⁻¹ at 0.5 A g ⁻¹ and excellent cycling stability with 80.0% capacity retention after 42800 cycles at 10 A g ⁻¹ , significantly outperforming the conventional I ₂ @active carbon counterpart. Moreover, the reaction mechanism involving the I ⁻ /I ₃ ⁻ /I ⁰ /I ⁺ redox couples in the C ₁₈ I ₃ cathode has been well elucidated by in situ characterizations. This work provides new guidelines for designing advanced cathode materials for Zn−I batteries.