Realizing High Performance Four-Electron Zinc-Iodine Batteries with Acidic Eutectic Electrolyte.

Achieving multi-electron redox reaction via halide ions and protons is promising for Zn─I₂ batteries, yet their practical application is hindered by halide ion and proton corrosion, sluggish iodine redox kinetics and poor redox reversibility. Here, a deep eutectic solvent (ZPDES) composed with concentrated ZnCl₂ and H₃PO₄ is engineered as the electrolyte for high performance Zn-I₂ batteries. The chloride atom (Cl) and active hydrogen of H₃PO₄ in DES form hydrogen bonds (Cl⋯H─O) to mitigate the corrosion of Cl^- and protons. Therefore, while achieving four-electron transfer by Cl^-, the protons in DES can accelerate redox reaction kinetics and reduce I₃ ^- formation for improved reversibility. Moreover, the proton can promote the (002) texture formation and reduce by-products on Zn anode. As a result, the Zn─I₂ battery with ZPDES delivers a high specific capacity of 576 mA h g^-1 at 0.5 A g^-1 after 320 cycles, and maintains a capacity retention of 100% over 20,000 cycles at 7 A g^-1.