本文要点：
带电通道被认为是实现有效单价阳离子转运的有效设计；然而，在孔隙内建立电荷微环境和离子电导率之间的直接关系仍然具有挑战性。
在此，作者报道了一系列具有相同骨架但不同电荷微环境的晶体共价有机框架，并探讨了它们的孔内电荷驱动离子传输性能和机制差异。
作者发现，带电性质决定了离子对的作用位点、模式、主客体相互作用，从而影响离子对的解离效率、阳离子的跳跃能力和有效载流子浓度。Li+、Na+和H+的转运效率顺序为阴离子>两性离子>阳离子>中性。
离子COFs的离子电导率比中性COFs高11倍。值得注意的是，阴离子COF的离子电导率在30°C时对Li+达到2.0×10-4 S·cm-1，在160°C时对H+达到3.8×10-2 S·cm-1，超过了大多数基于COF的离子导体。
该COF平台可在锂金属准固态电池中实现高效的离子迁移和稳定的电池循环，并已通过概念验证。这项工作为下一代固态离子导体的开发和构效关系研究提供了新的见解。
Figure 1. Structural and molecular design of COFs with different charge microenvironments. (a–d) Schematic diagram of the framework structure, (e–h) Chemical structures, and (i–l) PXRD patterns and Pawley refinement of nCOF, ciCOF, aiCOF, and ziCOF. Experimental PXRD patterns of four COFs with corresponding Pawley refinement (red), simulated results (orange), and Bragg positions (blue) show a good fit to the experimental data (gray) with minimal differences (brown). The inset shows the structural models of each COF, assuming the eclipsed (AA) stacking mode.
Figure 2. Structural characterization of COFs. (a) 13C NMR spectra, (b) XPS O 1s, (c) XPS N 1s, (d) N2 adsorption–desorption isotherms at 77 K, (e) Pore size distributions, and (f) Zeta potential values of four COFs. Low-dose HR-TEM images of (g) nCOF, (h) ciCOF, (i) aiCOF, and (j) ziCOF.
Figure 3. Studies of Li-ion dissociation and migration in COFs. (a) Nyquist plots at 30°C, (b) Arrhenius plots of the ionic conductivities, and (c) Ionic conductivities of COFs@Li at various temperatures. (d) 7Li NMR spectra and (e) Dissociation energy of LiTFSI, nCOF, ciCOF, aiCOF, and ziCOF. (f) Schematic of Li+ dissociation from LiTFSI and migration in aiCOF. (g) Migration energy and (h) hopping mechanism of Li+ in four COFs.
Figure 4. Analysis of host−guest interaction by MD simulation. (a–d) Model structure profiles after MD simulation and (e–h) the corresponding Li+ RDFs of nCOF, ciCOF, aiCOF, and ziCOF. RDFs and the corresponding coordination number of (i) Li-F (Li+/TFSI−) and (j) Li-O (Li+/TFSI−) in four COFs. (k) Schematic illustration of the dissociation of Li-ion pairs by nanopore-charged COFs. (l) Comparison of Li-O bond lengths of LiTFSI in four COFs.
Figure 5. Transport behavior of Na-ion and proton in nanopore-charged COFs. (a) Chemical structure of aiCOF-COONa and its Na+ transport diagram. (b) Arrhenius plots of the ionic conductivities, and (c) Ionic conductivities at various temperatures of COFs@Na. (d) Chemical structure of aiCOF-COOH and its H+ transport diagram. (e) Arrhenius plots of the ionic conductivities, and (f) Ionic conductivities at various temperatures of COFs@H. (g) Schematic illustration of dissociation and migration of monovalent cations by ionic units in COFs. (h) Comparison of ionic conductivity between aiCOF-COOH and other COF-based proton conductors; see details in Table S2.
Figure 6. Electrochemical performance of COF SSEs. (a) Digital photo of the aiCOF SSE membrane. (b) DC polarization curve (the inset shows the Nyquist plots) of Li symmetric cell with aiCOF SSE. (c) Li+ transfer number and (d) LSV curves of four COF SSEs. (e) Long-term cycling of Li symmetric cells with four COF SSEs. Inserts are the enlarged voltage profile. (f) DRT analysis of the EIS data of Li/COF SSEs/Li cells at 30°C. (g) Cycling performance of Li/COF SSE/LiFePO4 cells with four COF SSEs at 0.5C. DRT analysis of the EIS data of Li/COF SSEs/Li cells at different temperatures using (h) nCOF, (i) ciCOF, (j) aiCOF, and (k) ziCOF.
https://doi.org/10.1002/anie.202420333
