A Synchronous Strategy to Zn-Iodine Battery by Polycationic Long-Chain Molecules

Aqueous Zn-iodine batteries (ZIBs) face the formidable challenges towards practical implementation, including metal corrosion and rampant dendrite growth on the Zn anode side, and shuttle effect of polyiodide species from the cathode side. These challenges lead to poor cycle stability and severe self-discharge. From the fabrication and cost point of view, it is technologically more viable to deploy electrolyte engineering than electrode protection strategies. More importantly, a synchronous method for modulation of both cathode and anode is pivotal, which has been often neglected in prior studies. In this work, cationic poly(allylamine hydrochloride) (Pah⁺) is adopted as a low-cost dual-function electrolyte additive for ZIBs. We elaborate the synchronous effect by Pah⁺ in stabilizing Zn anode and immobilizing polyiodide anions. The fabricated Zn-iodine coin cell with Pah⁺ (ZnI₂ loading: 25 mg cm^-2) stably cycles 1000 times at 1 C, and a single-layered 3 × 4 cm² pouch cell (N/P ratio ~ 1.5) with the same mass loading cycles over 300 times with insignificant capacity decay.