Bis-ammonium salts with strong chemisorption to halide ions for fast and durable aqueous redox Zn ion batteries

Elemental halogens have attracted considerable interest as promising electrodes for energy storage, but they are suffering from several inherent drawbacks, including the volatility of iodine, corrosiveness of liquid bromine, and undesired shuttle behavior during cycling. To address these issues, we propose to use bis-ammonium salts with strong chemisorption to halide ions as electrodes to realize safe and reliable aqueous redox Zn ion batteries. Electrodes based on 1,8-octanediamine (ODA) frameworks (ODABr2, ODAI2, and ODABrI) have been comprehensively characterized to reveal their characteristic electrochemical features. Density functional theory simulations combined with the spectroscopy analysis reveal that the enhanced chemisorption interaction between the bis-ammonium host and halide ion guests is responsible for superior redox kinetics and cycle durability. This strong host-guest chemisorption significantly enhances the shuttle efficiency of electrons and suppresses the cross-diffusion of polyhalides. As a result, close-to-theoretical capacities (235 mAh g−1I for ODAI2 and 312 mAh g−1Br for ODABr2), combined with a long service life (10,000 cycles for ODAI2 and 3000 cycles for ODABr2) have been demonstrated for aqueous Zn ion batteries.