A Dual-Functional Cationic Covalent Organic Frameworks Modified Separator for High Energy Lithium Metal Batteries

Separator modification is an efficient strategy to handle with the challenges of lithium metal batteries but its success is primarily subject to the modification of the materials. Herein, a cationic covalent organic framework (COF) composed of positively charged organic units and weakly bonded fluoride ions (F-) is introduced to modify the commercial polypropylene separator (COF-F@PP). It is found that the organic unit has abundant nanopores to homogenize the lithium ions (Li+) flux and can interact with electrolyte solvent molecules to form a desolvation structure of Li+. Meanwhile, the F- within the nanopores is proved to assist in building a robust LiF-riched solid electrolyte interphase to avoid the side reactions between lithium anode and electrolyte. Hence, the COF-F@PP delivers feasible practicality for the outstanding cycling stability, high Coulombic efficiency, and superior rate capability of Li//LFP coin cell at 5 C, low N/P ratio (2.19) full cell, and pouch cell at 1 C.

Automated summary

Through material modification, the commercial polypropylene separator is successfully modified with a cationic covalent organic framework (COF-F@PP), which has abundant nanopores to homogenize the lithium ions flux and can interact with electrolyte solvent molecules to form a desolvation structure of Li+. The F- within the nanopores helps to build a robust LiF-riched solid electrolyte interphase to avoid side reactions between the lithium anode and electrolyte. Therefore, COF-F@PP exhibits excellent cycling stability, high Coulombic efficiency, and superior rate capability in Li//LFP coin cell at 5 C, low N/P ratio (2.19) full cell, and pouch cell at 1 C.