Highly Electrically Conductive Polyiodide Ionic Liquid Cathode for High-Capacity Dual-Plating Zinc–Iodine Batteries

Zinc-iodine batteries are one of the most intriguing types of batteries that offer high energy density and low toxicity. However, the low intrinsic conductivity of iodine, together with high polyiodide solubility in aqueous electrolytes limits the development of high-areal-capacity zinc-iodine batteries with high stability, especially at low current densities. Herein, we proposed a hydrophobic polyiodide ionic liquid as a zinc-ion battery cathode, which successfully activates the iodine redox process by offering 4 orders of magnitude higher intrinsic electrical conductivity and remarkably lower solubility that suppressed the polyiodide shuttle in a dual-plating zinc-iodine cell. By the molecular engineering of the chemical structure of the polyiodide ionic liquid, the electronic conductivity can reach 3.4 × 10^-3 S cm^-1 with a high Coulombic efficiency of 98.2%. The areal capacity of the zinc-iodine battery can achieve 5.04 mAh cm^-2 and stably operate at 3.12 mAh cm^-2 for over 990 h. Besides, a laser-scribing designed flexible dual-plating-type microbattery based on a polyiodide ionic liquid cathode also exhibits stable cycling in both a single cell and 4 × 4 integrated cell, which can operate with the polarity-switching model with high stability.