A dual-function molecule enables stable four-electron conversion and Zn deposition for high-capacity aqueous Zn–I ₂ batteries

l -lysine hydrochloride serves as a multifunctional additive, establishing a reversible four-electron 2I − /I 2 /2I + redox cycle for a capacity up to 502 mAh g −1 . It also prevents corrosion of the zinc anode and enhances cycling stability.