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.