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.

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Covalent organic frameworks (COFs) are attractive candidates for Li + -conducting electrolytes owing to their regular channels and tailored functionalities. However, most COF electrolytes are employed at high temperatures, challenging their practical use. Herein, tailored COFs coupled with PEG composite electrolytes were designed to construct a flowable network for facilitating Li + transport at lower temperatures. Benefiting from the interaction between the rigid COF structure and flowing PEG chain, the ionic conductivity of the quasi-solid electrolytes reached 9.74 × 10 −7 S cm −1 (−40 °C), 7.10 × 10 −5 S cm −1 (0 °C), and 1.36 × 10 −3 S cm −1 (80 °C). The resultant LiFePO 4 |Li cell delivered a discharge specific capacity of 132.5 mAh g −1 after 80 cycles at 10 °C. The Li−Li symmetrical cell displayed a long-time operation stability of over 800 h when cycled at a low temperature (10 °C). This work opens a new avenue to broaden the practical application of COFs electrolytes in quasi-solid lithium-ion batteries.

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