Cationic Covalent Organic Framework-Based Electrolyte Enabling Fast Li-Ion Conduction for Lithium Metal Battery Application.

Covalent organic frameworks (COFs) have garnered increasing attention as versatile platforms for Li+ conduction in lithium-based batteries; however, achieving high ionic conductivity in COF-based electrolytes remains a formidable challenge. Herein, we demonstrate a robust cationic vinylene-linked COF (COF-Br) as an efficient host for constructing high-performance composite electrolytes and highlight its great potential for practical application in lithium-metal batteries. The composite electrolyte, named as IL@COF-Br, was prepared by incorporating an ionic-liquid electrolyte (Li-IL) within the well-defined nanochannels of COF-Br. The cationic framework enhances dielectric screening, thereby promoting lithium-salt dissociation, while strong electrostatic interactions between the framework and anions effectively suppress anion mobility, leading to preferential Li+ transport. As a result, IL@COF-Br delivers a high ionic conductivity exceeding 10-3 S cm-1, a large Li+ transference number (0.79), and a wide electrochemical stability window (5.42 V). In addition, the composite electrolyte exhibits excellent interfacial compatibility with lithium metal and effectively mitigates dendrite formation during repeated cycling. When integrated into lithium-metal batteries, IL@COF-Br enables the batteries to achieve outstanding electrochemical performance, including good rate capability, a high specific capacity of 137.6 mAh g-1 at 0.5 C, and remarkable cycling stability, with a capacity retention of 90.4% and a Coulombic efficiency of 99.5% after 300 charge-discharge cycles. This study provides an effective strategy for leveraging cationic COF architectures to develop advanced quasi-solid-state electrolytes for next-generation lithium-metal batteries.