固态锂离子电池具有能量密度高、循环寿命长、安全性较高、充电快速和形状设计灵活等特点，有潜力彻底改变交通、工业和电网存储等多个领域的能源利用方式。目前被广泛使用的固态电解质，包括无机电解质和聚合物电解质，均存在固有的局限性。共价有机框架（covalent organic frameworks, COFs）材料以其独特的可设计孔结构、超高的比表面积和优异的化学稳定性被认为是解决当前锂离子电池关键瓶颈的有力候选。近年来，研究人员设计合成了多种基于COFs的固态电解质，但二维COFs材料活性位点间的较大间距限制了锂离子的传输速率，大多数COFs材料的导电性较差，且其中锂离子的传输机制尚未完全明了。本文旨在探究锂离子在COFs中的传导特性和机制，从而为设计和合成具有更优异性能的COFs材料提供指导。

本文选取了四种阴离子COFs膜进行对比探究，包括三种具有较大羰基（C=O）密度（2.1 nm^-2）但阴离子基团不同的COFs膜（TpMbh-PO₃Li₂、TpMbh-SO₃Li、TpMbh-COOLi）以及较小羰基密度（1.0 nm^-2）的磷酸膜TFBMbh-PO₃Li₂。首先对它们进行结构和形貌的表征以揭示影响锂离子传输的微观结构特征，结果发现COFs膜呈现AB堆叠模式，相邻层间略有错位使得锂离子靠近C=O中的O原子。接下来进行傅里叶变换红外光谱测量，以识别出C=O和苯环骨架的振动特征峰位。并选取这两种类型的伸缩振动为探针，在加电压前后对四种材料进行飞秒时间分辨红外光谱测量以探究锂离子传输动力学。结果表明，对四种COFs膜施加电压时，C=O的振动弛豫速率均加快，而苯环骨架的振动弛豫速率基本不变。结合锂离子所处的空间位置靠近C=O中氧原子的微观结构特点，提出了锂离子在酸性基团位点间传输过程中需要羰基中氧原子辅助的模型，其中阴离子基团的类型以及羰基的种类和密度会对锂离子传输过程造成影响。最后进行了膜电导率测试，发现羰基含量较高的磷酸膜TpMbh-PO₃Li₂具有较高的宏观电导率，其电导率存在温度依赖关系，利用光谱结果以及构建的锂离子传输模型可以从微观角度对其进行合理的解释。

本文主要结合傅里叶变换红外光谱和时间分辨红外光谱来研究阴离子COFs膜中锂离子在结构规整的孔道中的传导，为从分子水平上理解COFs膜的宏观电导率提供了重要线索，同时对优化基于COFs的电解质材料的设计具有一定启发。

Solid-state lithium-ion batteries, with their exceptional energy density, extended cycle longevity, robust safety features, swift charging capabilities, and versatile design adaptability, hold the promise of radically transforming energy consumption practices across a multitude of domains, including but not limited to transportation, industrial applications, and electrical grid storage systems. Currently widely used solid electrolytes, including inorganic electrolytes and polymer electrolytes, have inherent limitations. Covalent organic frameworks (COFs) with their unique designable pore structure, extensive specific surface area and excellent chemical stability are considered to be strong candidates to solve the key bottlenecks of current lithium-ion batteries. In recent years, researchers have designed and synthesized a variety of solid electrolytes based on COFs, but the considerable spacing between the active sites in two-dimensional COF materials limits the transport rate of lithium ions. Additionally, the majority of COF materials exhibit limited electrical conductivity, and the transport mechanism of lithium ions within these materials has not been completely deciphered. This study aims to investigate the conduction properties and mechanisms of lithium ions within COFs, in order to guide the design and synthesis of COF materials with enhanced performance.
 This study examined four types of anionic COF membranes for comparative analysis, including three COF membranes with a high carbonyl (C=O) density (2.1 nm^-2) but different anionic groups (TpMbh-PO₃Li₂, TpMbh-SO₃Li, TpMbh-COOLi), as well as a phosphoric acid membrane with a lower carbonyl density (1.0 nm^-2), TFBMbh-PO₃Li₂. The structures and morphologies of these membranes were characterized to reveal the microstructural features affecting lithium-ion transport. The COF membranes exhibited an AB stacking arrangement, with slight displacement between adjacent layers bringing lithium-ion close to the O atoms of C=O bonds. Next, Fourier transform infrared spectroscopy (FTIR) measurements were performed to identify the vibration characteristic peaks of C=O and the benzene ring skeleton. These two types of stretching vibrations were selected as probes, and the four materials were measured by femtosecond time-resolved infrared spectroscopy (TRIR) before and after the application of voltage to investigate lithium-ion transport kinetics. The results showed that the vibrational relaxation rate of C=O increased when voltage was applied to the four COF membranes, while the vibrational relaxation rate of the benzene ring framework remained relatively unchanged. Considering the microstructural characteristic where lithium-ion are situated near the O atoms in C=O bonds, a model was proposed where the transfer process of lithium-ion between acidic group sites requires the assistance of oxygen atoms in carbonyl groups. Within this model, the type of anionic groups, as well as the variety and density of carbonyl groups, were proposed to have significant effects on the lithium ion transport process.  Finally, the membrane conductivity test was carried out, and it was found that the phosphate membrane TpMbh-PO₃Li₂ with higher carbonyl content had higher macroscopic conductivity, and its conductivity was temperature dependent. The spectral results and the constructed lithium ion transport model could be used to rationally explain it from a microscopic perspective.
This study primarily integrates FTIR and TRIR techniques to investigate the conduction behavior of lithium ions within the ordered pores of anionic COF membranes. It provides crucial insights into the macroscopic conductivity of COF membranes at the molecular level, offering valuable clues for optimizing the design of COF-based electrolyte materials.