Soluble Covalent Organic Frameworks as Efficient Lithiophilic Modulator for High-Performance Lithium Metal Batteries.

Lithium metal batteries (LMBs) are regarded as the potential alternative of lithium-ion batteries due to their ultrahigh theoretical specific capacity (3860 mAh g). However, severe instability and safety problems caused by the dendrite growth and inevitable side reactions have hindered the commercialization of LMBs. To solve them, in this contribution, a design strategy of soluble lithiophilic covalent organic frameworks (COFs) is proposed. By introducing polyethylene glycol as the side chains, two COFs (CityU-28 and CityU-29) not only become soluble for the facile coating technique, but also can facilitate the lithium-ion migration in batteries. Furthermore, when coated on the lithium anode of LMB, both COFs can act as artificial solid electrolyte interphase to prevent dendrite growth thus enabling the long-term stability of the cells. Notably, the symmetric CityU-29@Li cell can work for more than 5000 h at a current density of 2 mA cm and an areal capacity of 1 mAh cm. A remarkable capacity retention of 78.9 % after 1500 cycles and a Coulombic efficiency of about 99.9 % at 1.0 C can also be realized in CityU-29@Li||LiFePO full cell. This work could provide a universal design strategy for soluble COFs and enlighten their application in diverse scenarios, especially energy-related fields.