High-Performance Zn-I₂ Batteries Enabled by a Metal-Free Defect-Rich Carbon Cathode Catalyst

Aqueous iodine-zinc (Zn-I₂) batteries based on I₂ conversion reaction are one of the promising energy storage devices due to their high safety, low-cost zinc metal anode, and abundant I₂ sources. However, the performance of Zn-I₂ batteries is limited by the sluggish I₂ conversion reaction kinetics, leading to poor rate capability and cycle performance. Herein, we develop a defect-rich carbon as a high-performance cathode catalyst for I₂ loading and conversion, which exhibits excellent iodine reduction reaction (IRR) activity with a high reduction potential of 1.248 V (vs Zn/Zn²⁺) and a high peak current density of 20.74 mA cm^-2, superior to a nitrogen-doped carbon. The I₂-loaded defect-rich carbon (DG1100/I₂) cathode achieves a large specific capacity of 261.4 mA h g^-1 at 1.0 A g^-1, a high rate capability of 131.9 mA h g^-1 at 10 A g^-1, and long-term stability with a high retention of 88.1% over 3500 cycles. Density functional theory calculations indicated that the carbon seven-membered ring (C7) defect site possesses the lowest adsorption energies for iodine species among several defect sites, which contributes to the high catalytic activity for IRR and the corresponding electrochemical performance of Zn-I₂ batteries. This work offers a defect engineering strategy for boosting the performance of Zn-I₂ batteries.