Iodine/Chlorine Multi‐Electron Conversion Realizes High Energy Density Zinc‐Iodine Batteries
Jiajin Zhao, Yan Chen, Mengyan Zhang, Ziqi An, Binbin Nian, Wenfeng Wang, Hao Bin Wu, Shumin Han, Yuan Li, Lu Zhang
Abstract
Abstract Aqueous zinc‐iodine (Zn‐I 2 ) batteries are promising energy storage devices; however, the conventional single‐electron reaction potential and energy density of iodine cathode are inadequate for practical applications. Activation of high‐valence iodine cathode reactions has evoked a compelling direction to developing high‐voltage zinc‐iodine batteries. Herein, ethylene glycol (EG) is proposed as a co‐solvent in a water‐in‐deep eutectic solvent (WiDES) electrolyte, enabling significant utilization of two‐electron‐transfer I + /I 0 /I − reactions and facilitating an additional reversibility of Cl 0 /Cl − redox reaction. Spectroscopic characterizations and calculations analyses reveal that EG integrates into the Zn 2+ solvation structure as a hydrogen‐bond donor, competitively binding O atoms in H 2 O, which triggers a transition from water‐rich to water‐poor clusters of Zn 2+ , effectively disrupting the H 2 O hydrogen‐bond network. Consequently, the aqueous Zn‐I 2 cell achieves an exceptional capacity of 987 mAh g I2 −1 with an energy density of 1278 Wh kg I2 −1 , marking an enhancement of ≈300 mAh g −1 compared to electrolyte devoid of EG, and enhancing the Coulombic efficiency (CE) from 68.2% to 98.7%. Moreover, the pouch cell exhibits 3.72 mAh cm −2 capacity with an energy density of 4.52 mWh cm −2 , exhibiting robust cycling stability. Overall, this work contributes to the further development of high‐valence and high‐capacity aqueous Zn‐I 2 batteries.