Robust I···H–O Intramolecular Halogen Bond Boosts Reversible I₃^–/I^– Redox Behavior for Sustainable Potassium–Iodine Batteries

Potassium-iodine batteries show great promise as alternatives for next-generation battery technology, owing to their high power density and environmental sustainability. Nevertheless, they suffer from polyiodide dissolution and the multistep electrode fabrication process, which leads to severe performance degradation and limitations in mass-market adoption. Herein, we report a simple "solution-adsorption" strategy for scale-up production of Ti₃C₂(OH)_<i>x</i>-wrapped carbon nanotube paper (CNP), as an economic host for strengthening the iodine encapsulation. The cutting-edge characterizations and theoretical calculation results reveal that CNP exhibits great affinity to the electrochemically active I₃^-/I^- redox couple, while the Ti-OH functional groups on MXene restrict the dissolution of polyiodides through forming the stable I···H-O intramolecular halogen bond. Benefiting from such a synergistic effect, the free-standing electrode ensures the reversible redox chemistry for developing high-performing potassium-iodine batteries. The fabricated pouch cell (100 mAh) shows a high energy density (130 Wh kg^-1) with a full charge/discharge of 10 min, outperforming state-of-the-art new battery systems that require both high energy/power density. Such a potassium-iodine battery reduces the cost to 255 US$ kW h^-1, which is much lower than that of the cathode materials in lithium-ion batteries and offers a sustainable option for grid-scale energy storage.