A single-ion conducting covalent organic framework for aqueous rechargeable Zn-ion batteries

Despite their potential as promising alternatives to current state-of-the-art lithium-ion batteries, aqueous rechargeable Zn-ion batteries are still far away from practical applications. Here, we present a new class of single-ion conducting electrolytes based on a zinc sulfonated covalent organic framework (TpPa-SO₃Zn_0.5) to address this challenging issue. TpPa-SO₃Zn_0.5 is synthesised to exhibit single Zn²⁺ conduction behaviour via its delocalised sulfonates that are covalently tethered to directional pores and achieve structural robustness by its β-ketoenamine linkages. Driven by these structural and physicochemical features, TpPa-SO₃Zn_0.5 improves the redox reliability of the Zn metal anode and acts as an ionomeric buffer layer for stabilising the MnO₂ cathode. Such improvements in the TpPa-SO₃Zn_0.5-electrode interfaces, along with the ion transport phenomena, enable aqueous Zn-MnO₂ batteries to exhibit long-term cyclability, demonstrating the viability of COF-mediated electrolytes for Zn-ion batteries.