Polyiodide Scavenger by Reversible Transformation of Amino Acid Enables Shuttle‐Free and Dendrite‐Free Zn‐Iodine Batteries

Abstract Aqueous rechargeable zinc‐iodide batteries are considered as highly prospective sustainable energy storage devices with features of high abundance and environmental compatibility. However, the current Zn||I ₂ battery cathode has a “shuttle effect” caused by the diffusion of soluble polyiodides, and the Zn anode has serious problems such as dendrite growth and corrosion, which complicates the design of device stability. Herein, a zwitterionic additive, D‐methionine (DMT), is first introduced to address the challenges encountered by both the cathode and anode in Zn||I ₂ batteries. The unique reversible redox reaction between DMT and I ₃ ⁻ suppresses the shuttle effect and accelerates the conversion kinetics of the iodine redox reaction. Meanwhile, DMT adheres securely to the Zn anode and facilitates the directional deposition of Zn (002) surfaces, thus enhancing the corrosion resistance of Zn anode and inhibiting the dendrite growth. The assembled Zn||Zn symmetric cell delivers excellent cycling performance of exceeding 3500 h. In addition, the assembled Zn||I ₂ full cell operates stably for more than 800 h under high mass loading of 10 mg cm ⁻² with an excellent capacity retention of 96%. This innovative strategy provides the potential for zwitterionic additives to greatly enhance Zn‐I ₂ batteries.