Highly conjugated three-dimensional covalent organic frameworks with enhanced Li-ion conductivity as solid-state electrolytes for high-performance lithium metal batteries

Abstract

Covalent organic frameworks (COFs) with well-tailored channels have the potential to efficiently transport ions yet remain to be explored. The ion transport capability is generally limited due to the lack of transport media and strong coulombic interactions. A general and simple strategy to improve the ionic conductivity of COF-based solid-state electrolytes is highly expected. Herein, we demonstrate an effective strategy of incorporating a plastic crystal (PC) into highly conjugated three-dimensional (3D) COFs with elaborate ion channels to accelerate lithium-ion transport. The PC confined in the channels strongly reduces the energy barrier of Li⁺ conduction, endowing the 3D-SpCOF and 3D-SpCOF-OH based solid-state electrolytes (SSEs) with high ionic conductivities (0.64 and 1.3 mS cm⁻¹) and Li⁺ transference numbers (0.7 and 0.64) at ambient temperature. Finally, the practical application of 3D-SpCOF-based SSE is confirmed by assembling solid-state Li/LiFePO₄ and Li/LiCoO₂ batteries, achieving stable and reversible cycling performance at ambient temperature. The simple but effective strategy provides an effective way to study the lithium-ion transport mechanism in solid electrolytes and construct high performance SSEs.