Robust\nI···H–O Intramolecular\nHalogen Bond Boosts Reversible I<sub>3</sub><sup>–</sup>/I<sup>–</sup> Redox Behavior for Sustainable Potassium–Iodine\nBatteries

Potassium–iodine batteries\nshow great promise as alternatives\nfor next-generation battery technology, owing to their high power\ndensity and environmental sustainability. Nevertheless, they suffer\nfrom polyiodide dissolution and the multistep electrode fabrication\nprocess, which leads to severe performance degradation and limitations\nin mass-market adoption. Herein, we report a simple “solution–adsorption”\nstrategy for scale-up production of Ti<sub>3</sub>C<sub>2</sub>(OH)<sub><i>x</i></sub>-wrapped carbon nanotube paper (CNP), as\nan economic host for strengthening the iodine encapsulation. The cutting-edge\ncharacterizations and theoretical calculation results reveal that\nCNP exhibits great affinity to the electrochemically active I<sub>3</sub><sup>–</sup>/I<sup>–</sup> redox couple, while\nthe Ti–OH functional groups on MXene restrict the dissolution\nof polyiodides through forming the stable I···H–O\nintramolecular halogen bond. Benefiting from such a synergistic effect,\nthe free-standing electrode ensures the reversible redox chemistry\nfor developing high-performing potassium–iodine batteries.\nThe fabricated pouch cell (100 mAh) shows a high energy density (130\nWh kg<sup>–1</sup>) with a full charge/discharge of 10 min,\noutperforming state-of-the-art new battery systems that require both\nhigh energy/power density. Such a potassium–iodine battery\nreduces the cost to 255 US$ kW h<sup>–1</sup>, which is much\nlower than that of the cathode materials in lithium-ion batteries\nand offers a sustainable option for grid-scale energy storage.