Zhong Juanqi, Tong Yongfen, Guo Lin, Zhang Aiqing, Xu Qiuhua, Qin Yuancheng
School of Environmental and Chemical Engineering, Nanchang Hangkong University, Nanchang, 330063, China.
ACS Appl Mater Interfaces. 2024 Oct 16;16(41):56106-56115. doi: 10.1021/acsami.4c11328. Epub 2024 Oct 7.
As an important component of lithium batteries, the wettability and thermal stability of the separator play a significant role in cell performance. Despite the availability of numerous commercial separators, issues such as low ion selectivity and poor thermal stability continue to limit the efficiency and reliability of the batteries. Herein, two cationic covalent organic frameworks (Br-COF and TFSI-COF) with abundant imidazole cationic groups were designed to modify commercial polypropylene (PP) separators. The strong lithium-ion affinity of the cationic COF enables the effective dissociation of lithium salt ion clusters, simplifying the solvent structure of lithium ions to promote lithium ions transport. Additionally, solvent anions can be anchored to the cationic COF by electrostatic interactions, reducing side reactions on the lithium metal anode surface to form a favorable SEI layer, which can effectively inhibit the growth of lithium dendrites. The rapid dissociation of anions in lithium salts with some organic solvents and cationic COFs was revealed by a molecular dynamics simulation. A LiF-rich SEI layer on the lithium metal anode surface was formed, which can speed up Li transport at interfaces, leading to consistent lithium deposition and outstanding battery performance. The ordered porous structure of the cationic COF provides interconnected and continuous channels, improving the wettability between the liquid electrolyte and separators, which is conducive to ion transport. When paired with a LiFePO cathode and electrolyte (1.0 M LiTFSI in DEC: EC: DMC = 1:1:1), the LiFePO/TFSI-COF@PP/Li cell demonstrates a prominent cycling capacity of 148.0 mAh g at 0.5 C with a Coulombic efficiency of 98.0% in the first cycle, and the capacity retention is 82.0% after 100 cycles, showing good cycling stability. Thus, this investigation provides inspiration for the expansion of cationic COF-modified separators for next-generation lithium metal batteries.
作为锂电池的重要组成部分，隔膜的润湿性和热稳定性对电池性能起着重要作用。尽管有众多商用隔膜可供使用，但诸如离子选择性低和热稳定性差等问题仍然限制着电池的效率和可靠性。在此，设计了两种具有丰富咪唑阳离子基团的阳离子共价有机框架（Br-COF和TFSI-COF）来改性商用聚丙烯（PP）隔膜。阳离子COF对锂离子的强亲和力能够使锂盐离子簇有效解离，简化锂离子的溶剂结构以促进锂离子传输。此外，溶剂阴离子可通过静电相互作用锚定在阳离子COF上，减少锂金属阳极表面的副反应，形成良好的固体电解质界面（SEI）层，这可以有效抑制锂枝晶的生长。分子动力学模拟揭示了锂盐中的阴离子与一些有机溶剂和阳离子COF的快速解离。在锂金属阳极表面形成了富含LiF的SEI层，这可以加速界面处的Li传输，导致锂的均匀沉积和出色的电池性能。阳离子COF的有序多孔结构提供了相互连接且连续的通道，改善了液体电解质与隔膜之间的润湿性，有利于离子传输。当与LiFePO正极和电解质（1.0 M LiTFSI溶于碳酸二乙酯：碳酸乙烯酯：碳酸二甲酯 = 1:1:1）配对时，LiFePO/TFSI-COF@PP/Li电池在0.5 C下展现出148.0 mAh g的突出循环容量，首次循环的库仑效率为98.0%，100次循环后容量保持率为82.0%，显示出良好的循环稳定性。因此，本研究为下一代锂金属电池扩展阳离子COF改性隔膜提供了思路。
