Homologous Imide Bonds to Build Polymer-Covalent Organic Framework Electrolytes for Efficient Ion Transport

A critical challenge for the safe operation of next-generation lithium (Li) metal batteries lies in the development of the key enabler of solid electrolytes. Herein, a polymer-covalent organic framework (COF) electrolyte with homologous imide bonds was designed and developed for safe and stable solid-state Li metal batteries. The imide-bonded COFs with ordered channels function as Li⁺ selective gates and conduction bridges, facilitating efficient ion transport while maintaining structural stability. Meanwhile, the fluorinated polyimide (FPI) polymer enriched with imide bonds contributes to the mechanical robustness, flexibility, and interfacial compatibility with Li metal electrodes, mitigating dendrite growth and improving long-term cycling stability. Owing to the synergistic effect between the COF and polymer, the polymer-COF delivers an ionic conductivity of 3.3 × 10^-4 S cm^-1 with a transference number of 0.82 and a wide electrochemical stability window. Besides, the polymer-COF solid electrolyte displays stable Li plating/stripping behavior over 2000 h, benefiting from superior interfacial compatibility. The applications of polymer-COF solid electrolytes in Li//LiNi_0.8Co_0.1Mn_0.1O₂ batteries further demonstrate that high Coulombic efficiency (>99.0%) and long life (>200 cycles) can be achieved. This design opens new routes to develop room-temperature solid electrolytes for high-performance solid batteries.