A dual-function molecule enables stable four-electron conversion and Zn deposition for high-capacity aqueous Zn-I₂...

Aqueous zinc-iodine batteries (ZIBs) are a promising energy storage technology due to the abundance of iodine, environmental friendliness, and low cost. This study introduces a multifunctional additive, l-lysine hydrochloride (LLH), designed to activate the four-electron transfer chemistry between I⁺ and I^- species, significantly boosting energy density. LLH stabilizes I⁺ via dual coordination from the amino groups and chloride ion, effectively suppressing hydrolysis and enabling reversible 2I^-/I⁰ ₂/2I⁺ conversion. The preferential adsorption of the carboxyl group of protonated l-lysine at the zinc anode promotes uniform zinc deposition while inhibiting the hydrogen evolution reaction. Additionally, the incorporation of LLH effectively suppresses the shuttle effect by interacting with iodine species through its carboxyl and amino groups. LLH-modified Zn‖Zn symmetric batteries demonstrate extended cycling stability, operating beyond 4000 hours, while Zn‖I₂ full batteries deliver a high specific capacity of 502 mAh g^-1 at 1 A g^-1. This additive strategy renders a facile and efficient approach to realizing high-capacity and durable ZIBs.