Fast Ion Transport Pathway Provided by Polyethylene Glycol Confined in Covalent Organic Frameworks

Covalent organic frameworks (COFs) with well-tailored channels are able to accommodate ions and offer their conduction pathway. However, due to strong Coulombic interaction and the lack of transport medium, directly including lithium salts into the channels of COFs results in limited ion transport capability. Herein, we propose a strategy of incorporating low-molecular-weight polyethylene glycol (PEG) into COFs with anionic, neutral, or cationic skeletons to accelerate Li+ conduction. The PEG confined in the well-aligned channels retains high flexibility and Li+ solvating ability. The ion conductivity of PEG included in a cationic COF can reach 1.78 × 10-3 S cm-1 at 120 °C. The simplicity of this strategy as well as the diversity of crystalline porous materials holds great promise to design high-performance all-solid-state ion conductors.