Fundamental Inhibition of Polyiodide Formation by a Site‐Separated Binder for Highly Stable Aqueous Zinc–Iodine Batteries

ABSTRACT Aqueous Zn–I 2 batteries are promising for sustainable energy storage systems, yet their practical performance is severely limited by the formation and shuttling of polyiodide intermediates. Here, we report a site separation strategy to block the generation paths of polyiodides and address the related issues from the source. This is realized with a site‐separated polymer (SSP) binder that strongly and selectively confines I 2 and I − at varied functional groups on different side chains. It disrupts their coupling to generate polyiodides chemically. Meanwhile, these effective interactions regulate the thermodynamic features of iodine species, which disfavors the formation of polyiodide intermediates and promotes direct I 2 /I − conversion during electrochemical reactions. The binder also reinforces cathode integrity at different iodine loadings. Therefore, the I 2 /SSP cathode delivers 212 mAh g −1 capacity at 0.2 A g −1 and retains 102 mAh g −1 at 50 A g −1 , superior to 172 mAh g −1 /11 mAh g −1 with the conventional polyvinylidene fluoride (PVDF) binder. I 2 /SSP also realizes 97.1% capacity retention over 31000 cycles at 20 A g −1 , again far exceeding 46.8% after 20000 cycles for I 2 /PVDF. Under a high iodine loading of 50 mg cm −2 , the I 2 /SSP cathode further achieves 10.1 mAh cm −2 capacity with 97.9% retention over 400 cycles.