Lithium-ion transport in covalent organic framework membrane

The traditional form of covalent organic framework (COF) is solid powder, which greatly limits its practical application. Besides, owing to the restricted chain dynamics in its highly crystalline regions, polyethylene glycol (PEG)-based electrolytes generally suffer from low ionic conductivity that poses a huge obstacle to its practical applications in solid-state batteries. In this contribution, we developed a confinement-driven strategy to confine PEG into the one-dimensional nanochannels of covalent organic framework membrane, dramatically slashing the crystalline phase and improving ion coupled chain dynamic. The composite electrolyte acquires remarkable ionic conductivity of 2.2 × 10−5 S cm−1 at 20 °C and 1.9 × 10−3 S cm−1 at 120 °C, which is much higher than bulk PEG (only 4.5 × 10−6 S cm−1 at 20 °C and becomes liquid state at elevated temperature). Dielectric permittivity and electric modulus measurement indicated that the ion pairs dissociation, Li-ion coupled chain motion and ion cooperation caused by the confinement effect were all reinforced, bringing out apace Li+ moving from short distance to long distance. Thanks to the flexibility of electrolyte membrane together with excellent thermal and electrochemical stability, the assembled Li-ion battery can operate normally even at 100 °C, obtaining high specific discharge capacity of 135.7 mAh g−1 after 80 cycles and stable interface evolution between electrodes and electrolyte. This work paved the way for the further application of COF membranes as high-performance electrolytes to the construction of high-energy–density solid-state energy storage devices.