A Self-Supporting Covalent Organic Framework Separator with Desolvation Effect for High Energy Density Lithium Metal Batteries

Covalent organic frameworks (COF) displayed strong affinity between COF and Li⁺ in terms of previous works. However, the relationship of COF and solvent molecules in the electrolyte was exclusive. Herein, a self-supporting COF separator (TPB-BD­(OH)₂-COF) was synthesized and served as a separator in lithium metal batteries. The formation of hydrogen bond network is due to the interaction of hydroxyl functional group (−OH) in TPB-BD­(OH)₂-COF and −OH···F and −OH···O in PF₆^–, EC and EMC within solvent sheath to achieve the desolvation process and realize more aggregative electrolyte, thus reducing the free solvent and lithium metal side effects. Therefore, the full cell assembled with self-supporting COF displayed superior cycling stability with a reversible capacity of 114.3 mAh g^–1 after 335 cycles at a current density of 1C and a capacity of 5 mAh cm^–2. Moreover, the COF separator can perform well even in extreme environments (temperature 60 °C).