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

Abstract Achieving multi‐electron redox reaction via halide ions and protons is promising for Zn─I 2 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 ZnCl 2 and H 3 PO 4 is engineered as the electrolyte for high performance Zn‐I 2 batteries. The chloride atom (Cl) and active hydrogen of H 3 PO 4 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 I 3 − 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─I 2 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 .