Dual-doped polypyrrole for high-capacity aqueous zinc-ion batteries

Cathode materials for aqueous zinc-ion batteries (AZIBs) often encounter challenges related to low electronic conductivity and sluggish ion transport, particularly when using thick electrode materials. Here, we report for the first time the fabrication of an iodide and heptamolybdate dual-doped polypyrrole (PPy-I-Mo) cathode, prepared through an electrodeposition method for AZIBs. The redox-active dopants not only contribute additional capacity to the composite but also modulate the morphology and electronic structure of the polymer, thereby enhancing both ion and electron transport. Moreover, the strong interactions between heptamolybdate and the I-based species not only effectively confine the dopants within the PPy matrix, preventing counterion depletion, but also facilitate the redox kinetics of iodine. As a result, the PPy-I-Mo electrode, with a high mass loading of 125 mg cm^-2, achieves an exceptional areal capacity of approximately 7 mAh cm^-2, significantly surpassing the capacities of mono-doped PPy-Mo (0.83 mAh cm^-2) and PPy-I (2.07 mAh cm^-2). This performance outperforms other reported conducting polymer-based electrodes for AZIBs. Furthermore, this dual-doping strategy can be extended to fabricate other high-performance conducting polymers, such as poly(3,4-ethylenedioxythiophene) and polyaniline. These findings open new avenues for designing high-performance conducting polymers for advanced energy storage devices.