Sulfonated covalent organic framework modified separator enables long-span and high-capacity zinc-iodine batteries

Compared with the most advanced lithium-ion batteries, aqueous zinc-iodine batteries (Zn–I 2 batteries) have higher theoretical capacity and energy density, thus attracting much attention in energy storage. However, due to several technical issues, the commercialization of Zn–I 2 batteries is still at a bottleneck, and among them, the “shuttle effect” of polyiodide anions is considered to be a main challenge. In order to minimize the shuttle of polyiodide species within the cathode compartment, we herein synthesize a zinc-ion conductive covalent organic framework (COF), namely DMSBA-Tp-COF, that is used to assemble a composite separator together with commercial glass fiber (GF) substrate and graphene (Gr) by a simple vacuum filtration coating technology. The negatively charged –SO 3 − ions present in COF coatings enable homogeneous Zn 2+ flux and simultaneously suppress polyiodides shuttling in the Zn–I 2 batteries. As a result, the composite Gr@DMSBA-Tp-COF@GF separator endows the corresponding Zn–I 2 symmetrical cell with excellent long-term cyclic stability with a lifespan over 800 h and high-specific capacity of 3.2 mAh cm −2 (at a current density of 20 mA cm −2 , voltage rage of 0.7–1.7 V). This study provides a prospective strategy to rationally design functional COFs separator and accelerate their applications in high energy storage systems. A sulfonated covalent organic framework based composite separator enables homogeneous Zn 2+ flux and simultaneous suppression of polyiodides shuttling, leading to a long-span and high-capacity aqueous zinc-iodine battery. • A zinc-ion conductive covalent organic framework (COF) was used to assemble a composite separator. • The negatively charged –SO 3 − present in COF coatings enable homogeneous Zn 2+ flux and suppression of polyiodides shuttling in the Zn–I 2 batteries. • The COF composite separator endows the corresponding Zn–I 2 cell with excellent long-term cyclic stability and high-capacity.