Recognition of the catalytic activities of graphitic N for zinc-iodine batteries

Rechargeable aqueous Zinc-iodine (Zn-I2) battery is attractive because of its high energy density, intrinsic safety and eco-friendly. However, the formation of highly soluble triiodide (I3- ) intermediates due to the sluggish iodine redox kinetics greatly compromise its durability and practical energy density. Here, we report that the formation and crossover of the triiodide could be suppressed by catalyzing the iodine conversion with nitrogen doped porous carbons, which afford a robust zinc iodine battery with high energy density (320 Wh center dot kg- 1) and ultra-long cycle life of 10,000 cycles. Our fundamental studies reveal the electrocatalytic activities are sensitive to the type of N heteroatoms, as confirmed by the decreased activation energy, Tafel slope and improved faradic current density of the iodine redox took place on the graphitic N enriched host. These merits are stemmed from the significant electron redistribution from graphitic N in carbon to iodine molecules after interaction, which not only thermodynamically strengthen the adsorption/redox conversion efficiency but also dynamically boost the triiodide/iodide conversion by lowering the dissociation energy barrier. In addition, the favorable nucleation/ electrodeposition of solid iodine on graphitic N during cycling also benefits such direct one step conversion. This work provides the reference basis for the correlation of the catalytic activities and performance of Zn-I2 batteries.