Polycationic Polymer Functionalized Separator to Stabilize Aqueous Zinc-Iodine Batteries

Abstract

Aqueous zinc-iodine (Zn-I₂) batteries have received widespread interest due to their intrinsic safety, cost-effectiveness, and high capacity. However, their commercial application is hindered by the polyiodide shuttle effect, H₂ evolution, and dendritic Zn growth. Herein, a polycationic polymer functionalized glass fiber (denoted as PT@GF) separator is designed to conquer these challenges simultaneously. The as-prepared polycationic polymer composed of poly(diallyl dimethyl ammonium) cation (PDDA) and bis(trifluoromethanesulfonyl)imide anion (TFSI) is uniformly integrated into the GF matrix, prepared by a simple dip-coating method. Mechanism studies reveal that the PDDA cations can chemically anchor the polyiodide anion intermediates to effectively prevent the shuttle effect. Given the intimate contact between the separator and Zn electrode, the hydrophobic polymer can create a water-poor interface on Zn and form H-bonds with H₂O to suppress H₂ evolution, and polycations can homogenize the electric field distribution on Zn, thus enabling compact Zn electrodeposition. Consequently, the PT@GF separator endows Zn//Zn cells with a long lifespan of 1600 h (2.5 mAh cm^-2 at 5 mA cm^-2) and excellent deep-cycling stability under 51.3% depth-of-discharge (15 mAh cm^-2). In addition, the PT@GF separator supports the stable operation of pouch-type Zn-I₂ battery under a high-areal capacity of 5.24 mAh cm^-2 over 400 cycles.