Poly(ethylene glycol)-functionalized 3D covalent organic frameworks as solid-state polyelectrolytes

Abstract

Existing lithium-ion-conducting covalent organic frameworks (COFs) are mainly two-dimensional, in which the one-dimensional channels are difficult to completely and uniformly stack in the same direction, particularly in the case of powdered COFs, resulting in the hindrance of ion transport at the grain boundary or at the interface of the powder contact. In this contribution, poly(ethylene glycol) (PEG)-functionalized three-dimensional COFs with 3D channels were successfully constructed for ion conduction in different directions, which is conducive to reducing the grain boundary and interface contact resistance. Combined with the coupling behaviour between the PEG chain segments and Li-ions, the 3D COF incorporated with LiTFSI achieves a high ionic conductivity of 3.6 × 10⁻⁴ S cm⁻¹ at 260 °C. The maximum operating temperature is higher than the boiling point of commercial organic electrolytes, indicating the excellent security of PEG-based COFs as Li-ion polyelectrolytes at high temperature.