A Robust Biopolymer Network Binder for High-Loading Iodine Cathodes in Zinc-Iodine Batteries.

Abstract

High energy density and long cycle life are critical for practical aqueous zinc-iodine batteries (AZIBs). However, the development of high-mass-loading iodine cathodes faces bottlenecks, such as structural instability, severe polyiodide shuttling, and sluggish charge transfer kinetics. Herein, a robust biopolymer network (XGP) binder is developed, featuring a 3D network structure with dense hydrogen bonding that provides strong adhesion and good mechanical strength for high-mass-loading active carbon (AC)@I₂ cathodes. Using a scalable slurry-drawing method, the obtained thick AC@I₂ electrodes exhibit a porous architecture with high porosity (47.6%), facilitating rapid Zn² ⁺ diffusion (up to 10^-9 cm² s^-1) and fast electrochemical kinetics. Furthermore, diverse oxygen functional groups in the XGP binder provide strong chemical anchoring sites, effectively suppressing polyiodide shuttling. Consequently, XGP-based cathodes with an ultrahigh iodine loading (82 mg cm^-2, ∼960 µm) achieve an areal capacity of 15.3 mAh cm^-2. Zn-I₂ pouch cells deliver a capacity of 1744 mAh over 600 cycles, yielding a remarkable energy density of 55.0 Wh L^-1 at the cell level. This work solves key challenges in thick iodine electrodes through integrated design of the biopolymer binder and electrode engineering, paving the way for practical AZIBs.