Aqueous zinc–iodine (Zn–I) batteries have attracted considerable research interest as an alternative energy storage system due to their high specific capacity, intrinsic safety, and low cost. However, the notorious shuttle effect of soluble polyiodides causes severe capacity loss and poor electrochemical reversibility, restricting their practical usage. Herein, this study reports a bifunctional binder (polyacrylonitrile copolymer, as known as LA133) with strong iodine-chemisorption capability for aqueous Zn–I batteries to suppress polyiodide shuttling. From both calculation and experimental data, this study reveals that the amide and carboxyl groups in LA133 binder can strongly bond to polyiodides, significantly immobilizing them at cathode side. As a result, fewer byproducts, slower hydrogen evolution, and lesser Zn dendrite in the Zn–I battery are observed. Consequently, the battery shows high specific capacity (202.8 mAh g) with high iodine utilization efficiency (96.1%), and long cycling lifespan (2700 cycles). At the high mass loading of 7.82 mg cm, the battery can still retain 83.3% of its initial capacity after 1000 cycles. The specific capacity based on total cathode slurry mass reaches 71.2 mAh g, higher than most of the recent works. The strategy opens a new avenue to address the shuttling challenge of Zn–I batteries through bifunctional binder.