Covalent Organic Framework-Based Electrolytes for Fast Li⁺ Conduction and High-Temperature Solid-State Lithium-Ion Batteries

It has been a long-standing challenge to design and fabricate high Li⁺ conductive polymer electrolytes at the atomic level with superior thermal stability for solid-state lithium-ion batteries. Covalent organic frameworks (COFs) with tailor-made 1D nanochannels provide a potential pathway for fast ion transport, but it remains elusive. In this work, three crystalline thiophene-based imine-linked COFs were constructed and explored as Li⁺-conducting composite electrolytes by doping ionic liquids into their 1D nanochannels. The COF–IL composite electrolytes exhibited excellent thermal stability (up to 400 °C) and high Li⁺ conductivity (up to 2.60 × 10^–3 S/cm at 120 °C, one of the highest values of doped porous organic materials). Furthermore, the COF–IL composite electrolytes exhibited stable cycling in a LiFePO₄–Li full cell with a high initial discharge specific capacity of 140.8 mA·h/g at 100 °C, more stable than common poly­(ethylene oxide)-based electrolytes, indicating great potential application under a high-temperature operation. This work opens a new avenue for the development of fast Li⁺-conducting COF-based electrolytes for high-temperature solid-state lithium-ion batteries.