Multifunctional Asymmetric Soluble Covalent Organic Frameworks: A Versatile Medium for Stabilizing Lithium Anode Interfaces

To address the issues of uncontrollable lithium dendrite growth and an unstable solid electrolyte interphase (SEI) in lithium anodes, we designed an asymmetric and multifunctional COF material (CityU-55) composed of strongly solvating polyether and highly electronegative fluoroalkyl side groups. This material was employed as an artificial interphase layer to create a fast lithium-ion-conducting and fluorine-rich interphase on the anode, thereby mitigating interfacial problems. Notably, the introduction of side chains enhanced the solubility of the COF material, significantly improving its processability. This asymmetric COF enables distinct interfacial regulation. The CityU-55@Li anode exhibited improved reversibility of lithium deposition and substantially reduced the number of interfacial side reactions. Leveraging these synergistic properties, the lithium anode with this multifunctional artificial interphase layer showed a low nucleation barrier of 28 mV and excellent cycling stability of 4500 h at 1 mA cm^-2 and 1 mAh cm^-2. Additionally, compared with bare lithium anodes, full cells paired with LiFePO₄ and LiNi_0.8Co_0.1Mn_0.1O₂ cathodes demonstrated remarkably better cycling stability, capacity retention, and capacity utilization at high rates. Our research indicates that asymmetric multifunctional side-chain engineering in COFs significantly expands structural diversity and provides a promising strategy for the development of high-performance lithium metal batteries.