Engineering 4-Connecting 3D Covalent Organic Frameworks with Oriented Li+ Channels for High-Performance Solid-State Electrolyte in Lithium Metal Battery

Abstract

The development of rapid and stable ion-conductive channels is pivotal for solid-state electrolytes (SSEs) in achieving high-performance lithium metal batteries (LMBs). Covalent organic frameworks (COFs) have emerged as promising Li-ion conductors due to their well-defined channel architecture, facile chemical tunability, and mechanical robustness. However, the limited active sites and restricted segmental motion for Li⁺ migration significantly impede their ionic conductivity. Herein, a rational design strategy is presented to construct 3D porous COF frameworks (TP-COF and TB-COF) using linear ditopic monomers connected via C─C and C─N linkages. These COFs, integrated with polymer electrolytes, provide enhanced Li⁺ transport pathways and stabilize lithium anodes in LMBs. The TB-COF, featuring larger pore apertures and abundant ─C═N─ active sites, facilitates superior Li⁺ conduction (8.89 × 10⁻⁴ S cm⁻¹) and a high transference number (0.80) by enhancing lithium salt dissolution. LiF/Li₃N-rich SEI enables uniform Li deposition, enabling PEO-TB-COF SSEs to achieve >1000 h stability at 1 mA cm⁻² while retaining 90% capacity through 800 cycles (0.5 C) in LFP||Li cells. Molecular dynamics simulations and COMSOL Multiphysics modeling reveal that extended Li⁺ transport channels and reduced interfacial diffusion barriers are key to enhanced performance.