Perfluoroalkyl chain and sulfonic acid group modified ternary covalent organic frameworks, methods of making and applications thereof

Abstract

The application discloses a ternary covalent organic framework modified by a perfluoroalkyl chain and a sulfonic acid group and a preparation method and application thereof. The ternary covalent organic framework is prepared by using 2,4,6-triformylphloroglucinol, a fluorocarbon-based hydrazide monomer and a monosulfonic acid monomer as raw materials, 1,4-dioxane and trimethylbenzene as solvents, and acetic acid as a catalyst through a solvothermal reaction. The covalent organic framework material has good crystallinity and thermal stability, has relatively good proton conduction performance, and can be used in fuel cells. Meanwhile, the covalent organic framework material is applied to interface modification of lithium ion batteries, can significantly improve the stability of solid-state lithium batteries, block the side reaction between lithium metal and electrolyte, and improve the safety performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of covalent organic framework compounds, and relates to a ternary covalent organic framework modified by a perfluoroalkyl chain and a sulfonic acid group, and a preparation method and application thereof. BACKGROUND

[0002] Liquid lithium ion batteries have safety risks due to the use of volatile liquid electrolytes. Solid-state lithium ion batteries are considered to be able to replace liquid lithium ion batteries because of their intrinsic safety, high thermal stability, no liquid leakage, higher theoretical capacity and other advantages. Reasonable design and preparation of effective solid-state electrolytes are the basis for improving the performance of solid-state lithium ion batteries. However, solid-state batteries also have problems that cannot be ignored. Compared with liquid batteries, the contact surface of the electrode and the electrolyte of the solid-state battery changes from solid-liquid contact to solid-solid contact, resulting in greater interfacial impedance. Low ionic conductivity of solid-state batteries, interface effects, growth of lithium dendrites and other problems need to be solved.

[0003] Proton exchange membrane fuel cells have excellent energy density and are environmentally friendly, but the currently commercialized proton-conducting membrane polymer materials such as Nafion have the disadvantages of instability, easy failure at high temperature, and disordered polymer chain distribution. Therefore, how to improve the performance of proton exchange membrane fuel cells is an important research direction.

[0004] For the above problems, for lithium ion batteries, the main methods currently used include introducing an interface coating to the electrode or electrolyte, and optimizing the composition of the electrode or electrolyte to improve the performance. For proton exchange membrane fuel cells, embedding non-volatile liquid acid in a porous structure solid is an expected solution to prepare anhydrous proton conductors.

[0005] Covalent organic frameworks (COFs) are a class of organic porous crystalline materials connected by covalent bonds, which have the characteristics of regular structure, large specific surface area, light mass, controllable structure, etc. These characteristics can be used to construct stable lithium ion transport channels, improve lithium ion migration number, give the material more redox sites, improve the mechanical properties of the material, and be used for lithium ion interface modification. At the same time, due to its stable structure and good proton conductivity, it can be used to make proton exchange membrane materials for fuel cells. SUMMARY

[0006] One of the purposes of the present application is to provide a ternary covalent organic framework modified by a perfluoroalkyl chain and a sulfonic acid group, which is formed by connecting 2,4,6-triformylphloroglucinol, fluorocarbon-based hydrazine monomer and monosulfonic acid monomer to form a topological structure, and the structural formula is as follows:

[0007] The structural formula of the 2,4,6-triformylphloroglucinol described in the present application is as follows:

[0008]

[0009] The fluorocarbon-based hydrazide monomer has the following structural formula:

[0010] The monosulfonic acid monomer has the following structural formula:

[0011]

[0012] The second object of the present application is a method for synthesizing the ternary covalent organic framework modified by the perfluoroalkyl chain and the sulfonic acid group, and the specific steps are as follows:

[0013] The 2,4,6-triformylphloroglucinol, the fluorocarbon-based hydrazide monomer and the monosulfonic acid monomer are added to the solvent composed of 1,4-dioxane and trimethylbenzene in a volume ratio of 1:3, and an acetic acid solution is added as a catalyst, and then liquid nitrogen freezing, vacuumizing and degassing are sequentially performed, and then the mixture is sealed under vacuum, and then heated at 120±10℃, and then cooled to room temperature after the reaction is completed, and then the crude product is collected by suction filtration, and then Soxhlet extraction is performed using a mixed solution of acetone, methanol and tetrahydrofuran, and then vacuum drying is performed, so as to obtain the ternary covalent organic framework modified by the perfluoroalkyl chain and the sulfonic acid group.

[0014] Preferably, the synthesis method of the fluorocarbon-based hydrazide monomer is as follows: the diisopropyl azodicarboxylate (DIAD) is added to the mixture of 2,5-dihydroxyterephthalic acid diethyl ester and triphenylphosphine (PPh3) in a molar ratio of 2:1:2, and then the mixture is stirred uniformly under an argon atmosphere, and then 3,3,4,4,5,5,6,6,6-nonafluorohexan-1-ol or 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctan-1-ol is added, and then the mixture is continuously stirred and heated to reflux for more than 3 days under an argon atmosphere, and then the reaction mixture is evaporated to dryness under reduced pressure, and then purified by silica gel column chromatography, and then the column chromatography liquid is a mixed solvent of dichloromethane and methanol in a volume ratio of 40:1 to 20:1, so as to obtain the fluorocarbon-based hydrazide monomer.

[0015] Preferably, the number of repetitions of the liquid nitrogen freezing, vacuumizing and degassing is at least three.

[0016] Preferably, the concentration of the acetic acid solution is 6 mol / L.

[0017] Preferably, the heating reaction time is more than 3 days.

[0018] Preferably, in the mixed solution of acetone, methanol and tetrahydrofuran, the volume ratio of acetone, methanol and tetrahydrofuran is 1:1:1, and the Soxhlet extraction time is 12 h.

[0019] Preferably, the vacuum drying temperature is 80°C and the time is 12 hours.

[0020] A third objective of this invention is to provide a modified solid electrolyte based on the aforementioned ternary covalent organic framework modified with perfluoroalkyl chains and sulfonic acid groups, which is prepared through the following steps:

[0021] (1) Ion exchange of COF powder:

[0022] The ternary covalent organic framework powder modified with perfluoroalkyl chains and sulfonic acid groups was added to an ethanol solution of lithium bis(trifluoromethanesulfonylimide) (LiTFSI), stirred until homogeneous, filtered, and the obtained powder was washed with ethanol. The above steps were repeated three times, and the powder was dried under vacuum to obtain ion-exchanged COF powder.

[0023] (2) Preparation of solid electrolytes:

[0024] After cooling the ion-exchanged COF powder, it was compressed into tablets. Under an argon protective atmosphere, a polycarbonate (PC) solution of LiTFSI was added dropwise to both sides of the tablets. After standing, the modified solid electrolyte was obtained.

[0025] Preferably, in step (1), the vacuum drying time is 80°C and the drying time is 12h.

[0026] The fourth objective of this invention is to provide the application of the modified solid electrolyte based on the ternary covalent organic framework modified with perfluoroalkyl chains and sulfonic acid groups in lithium-ion batteries.

[0027] The fifth objective of this invention is to provide a proton exchange membrane material based on the above-mentioned ternary covalent organic framework modified with perfluoroalkyl chains and sulfonic acid groups, which is prepared through the following steps:

[0028] A ternary covalent organic framework modified with perfluoroalkyl chains and sulfonic acid groups was mixed with phosphoric acid, ground until homogeneous, vacuum dried, cooled, and then pressed into tablets to produce a proton exchange membrane material (COF-Fn-SO3-HX, where X is the percentage of phosphoric acid in the total mass of the membrane).

[0029] Preferably, the vacuum drying time is 80°C and the drying time is 12 hours.

[0030] Preferably, phosphoric acid accounts for 40% of the total mass of the proton exchange membrane material.

[0031] The sixth objective of this invention is to provide the application of the above-mentioned proton exchange membrane material based on a ternary covalent organic framework modified with perfluoroalkyl chains and sulfonic acid groups in fuel cells.

[0032] The COFs of this invention are synthesized using imine-based COFs, which are highly stable and easy to prepare. Their aromatic rings can form large delocalized π bonds to disperse negative charges and increase electron-withdrawing fluorine groups. These polarization effects enhance the compatibility of the polymer with lithium ions. Furthermore, the fluorination design, including the fluorinated electrolyte and fluorinated interface, significantly improves the stability of solid-state lithium batteries. The fluorinated layer in the interface layer can effectively regulate the Li-ion exchange rate. + The diffusion of lithium homogenizes lithium deposition and blocks side reactions between lithium metal and the electrolyte, improving the safety performance of the material. Specifically, lithium salts dissociate into lithium ions and corresponding anions in the electrolyte, which presents an energy barrier. Research has shown that by covalently attaching anionic functional groups to the polymer backbone, the material can easily bind and dissociate lithium ions, and with the assistance of dense and continuous anionic functional group binding sites, lithium deposition can be achieved. + The inherent combination of these elements; furthermore, the COFs of this invention have a functional unit distribution similar to Nafion materials with extremely strong proton conductivity. The superhydrophobic perfluoroalkyl chains restrict water flow around the hydrophilic sulfonic acid groups, while the negatively charged sulfonic acid groups promote the movement of positively charged protons, thereby achieving stronger proton conductivity. Currently, proton conduction membranes need to operate continuously under high temperature and strong acid environments. Fluorine has the strongest electronegativity, and the chemical bonds it forms have extremely high binding energy and strong stability, which helps the material maintain a longer operating time in practical applications. This invention adopts a strategy of assembling perfluoroalkyl chains and sulfonic acid functional groups on COFs to form a ternary covalent organic framework structure, enabling lithium-ion batteries to have higher lithium-ion conductivity, better cycle performance, and superior proton conductivity.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) This invention introduces fluorine and sulfonic acid groups to construct ternary COFs, resulting in superior ionic conductivity, accelerated ion shuttle speed, and improved battery capacity and cycle performance. The lithium-ion battery constructed using COF-F6-SO3 solid electrolyte still exhibits a high capacity of nearly 0.25 mAh and a cycle efficiency of 99.9% after 30 cycles. Regarding lithium-ion batteries, this invention also improves the mechanical strength of the interface film, preventing lithium dendrite puncture and short circuits. The fluorinated COF has a lower polarization voltage and better cycle stability. The LiF generated during battery operation can block the reaction between lithium metal and the electrolyte, acting as a flame retardant and effectively protecting lithium metal, thus improving the safety of the lithium battery.

[0035] (2) The fuel cell constructed using the COF material of the present invention as a proton exchange membrane material exhibits high proton conductivity; for example, the proton conductivity of COF-F6-SO3-H-40% can reach 1.93 × 10⁻⁶. -2 S cm -1 It has excellent proton conduction properties. Attached Figure Description

[0036] Figure 1 XRD comparison diagrams of COF-F0-SO3 with 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer F0, and monosulfonic acid monomer.

[0037] Figure 2 XRD comparison diagram of COF-F6-SO3 with 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer F6 and monosulfonic acid monomer.

[0038] Figure 3 XRD comparison diagrams of COF-F8-SO3 with 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer F8, and monosulfonic acid monomer.

[0039] Figure 4 XRD comparison images of COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3.

[0040] Figure 5 The XRD patterns are of COF-F6-SO3 prepared by different ratios of 1,4-dioxane and trimethyltoluene.

[0041] Figure 6 Fourier transform infrared spectra of COF-F0-SO3 with 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer F0, and monosulfonic acid monomer.

[0042] Figure 7 Fourier transform infrared spectra of COF-F6-SO3 with 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer F6, and monosulfonic acid monomer.

[0043] Figure 8 Fourier transform infrared spectra of COF-F8-SO3 with 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer F8, and monosulfonic acid monomer.

[0044] Figure 9 Thermogravimetric analysis curves for COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 are shown.

[0045] Figure 10 The nitrogen adsorption-desorption curves for COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 are shown.

[0046] Figure 11 The graph shows the ion conduction performance of the membrane COF-F0-SO3-H-40% at different temperatures.

[0047] Figure 12 The graph shows the ion conduction performance of the COF-F6-SO3-H-40% membrane at different temperatures.

[0048] Figure 13 The graph shows the ion conduction performance of the membrane COF-F8-SO3-H-40% at different temperatures.

[0049] Figure 14 The conductivity of the membranes COF-F0-SO3-H-40%, COF-F6-SO3-H-40% and COF-F8-SO3-H-40% at different temperatures.

[0050] Figure 15 Scanning electron microscope images of the surfaces of solid electrolytes modified with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3.

[0051] Figure 16 Comparison of voltage stability of Li-Li symmetric cells assembled with solid electrolytes modified with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3.

[0052] Figure 17 , Figure 18 A schematic diagram showing the first charge-discharge specific capacity of LFP-Li batteries assembled with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 modified solid electrolytes.

[0053] Figure 18 A schematic diagram of the 30th charge-discharge specific capacity of LFP-Li batteries assembled with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 modified solid electrolytes.

[0054] Figure 19 A schematic diagram showing the cycle performance of LFP-Li batteries assembled with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 modified solid electrolytes. Detailed Implementation

[0055] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0056] The 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer (n=0), and monosulfonic acid monomer used in the following examples were all commercially available.

[0057] Fluoroalkyl-functionalized Covalent Organic Frameworks with Superhydrophobicity for Anhydrous Proton Conduction. J. Am. Chem. Soc. 2020, 142, 14357-143641. The monomers (n = 6, 8) were prepared in-house, referencing the literature [Xiaowei Wu, Y.-l. Hong, Bingqing Xu, Y. Nishiyama, W. Jiang, J. Zhu, Gen Zhang, *S. Kitagawa, S. Horike*, Perfluoroalkyl-functionalized Covalent Organic Frameworks with Superhydrophobicity for Anhydrous Proton Conduction. J. Am. Chem. Soc. 2020, 142, 14357-143641].

[0058] Specifically, the synthetic route for the fluorocarbon-based hydrazide monomer (n=6) is as follows:

[0059]

[0060] The synthetic route for fluorocarbon-based hydrazide monomers (n=8) is as follows:

[0061]

[0062] Taking the fluorocarbon-based hydrazide monomer (n=6) as an example, the specific synthesis steps are as follows:

[0063] Diisopropyl diazonium carboxylate (1.56 mL, 8.0 mmol) was added to a mixture of diethyl 2,5-dihydroxyterephthalate (1.02 g, 4.0 mmol) and triphenylphosphine (2.08 g, 8.0 mmol) in tetrahydrofuran (20 mL), and the mixture was stirred under an argon atmosphere for 30 min. Then, 3,3,4,4,5,5,6,6,6-nonafluorohexane-1-ol (1.29 mL, 8.0 mmol) was added to the solution, and the mixture was stirred and refluxed under an argon atmosphere for 3 days. The reaction mixture was evaporated to dryness under reduced pressure and purified by silica gel (dichloromethane / methanol 40 / 1 to 20 / 1) column chromatography to give fluorocarbonylhydrazide monomers (n = 6).

[0064] Example 1

[0065] Preparation of COF-F6-SO3:

[0066] 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer F6 (n=6), and monosulfonic acid monomer were added to 4 ml of a solvent consisting of 1,4-dioxane and trimethyltoluene in a volume ratio of 1:3 at a molar ratio of 4:3:3. 0.4 ml of 6 mol / L acetic acid solution was added as a catalyst. The mixture was subjected to liquid nitrogen freezing, vacuuming, and degassing three times in sequence. Afterward, the mixture was sealed under vacuum and heated at 120 °C for 3 days to obtain the crude product. After cooling to room temperature, the crude product was collected by filtration and extracted using a Soxhlet extraction with a mixed solution of acetone, methanol, and tetrahydrofuran in a volume ratio of 1:1:1. The product was then vacuum dried at 80 °C for 12 h to obtain a brown solid powder, a ternary covalent organic framework COF-F6-SO3 modified with perfluoroalkyl chains and sulfonic acid groups, with a yield of 90%.

[0067] The reaction path is shown below:

[0068]

[0069] Comparative Example 1

[0070] This comparative example is basically the same as Example 1, except that the solvent composed of 1,4-dioxane and trimethyltoluene in a volume ratio of 1:3 was replaced with trimethyltoluene. As can be seen from the XRD pattern, no COF characteristic peak appeared in the product, and the preparation of the target product failed.

[0071] Comparative Example 2

[0072] This comparative example is basically the same as Example 1, except that the solvent composed of 1,4-dioxane and trimethyltoluene in a volume ratio of 1:3 was replaced with 1,4-dioxane. As can be seen from the XRD pattern, no COF characteristic peak appeared in the product, and the preparation of the target product failed.

[0073] Comparative Example 3

[0074] This comparative example is basically the same as Example 1, except that the solvent composed of 1,4-dioxane and trimethyltoluene in a volume ratio of 1:3 was replaced with a solvent composed of 1,4-dioxane and trimethyltoluene in a volume ratio of 1:1, and the yield was 78%.

[0075] Example 2

[0076] This embodiment is basically the same as Example 1, except that the fluorocarbonyl hydrazide monomer F6 (n=6) is replaced with the fluorocarbonyl hydrazide monomer F8 (n=8) to prepare a ternary covalent organic framework COF-F8-SO3 modified with perfluoroalkyl chains and sulfonic acid groups.

[0077] Comparative Example 4

[0078] This comparative example is basically the same as Example 1, except that the fluorocarbonyl hydrazide monomer F6 (n=6) is replaced with the fluorocarbonyl hydrazide monomer F0 (n=0) to prepare a ternary covalent organic framework COF-F0-SO3 modified with perfluoroalkyl chains and sulfonic acid groups.

[0079] Figures 1 to 3 The XRD patterns of COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 are compared with those of 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomers (n = 0, 6, 8), and monosulfonic acid monomers. The figures show a clear diffraction peak at 2° to 5°, while the monomer peaks disappear, indicating the formation of the desired polymer.

[0080] Figure 4 The XRD comparison diagrams of COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 show that the ternary covalent organic frameworks modified with perfluoroalkyl chains of different lengths all have peaks, confirming the successful synthesis of the intended product.

[0081] Figure 5 The XRD patterns of COF-F6-SO3 prepared by different ratios of 1,4-dioxane and trimethyltoluene show that the best crystal form of COF-F6-SO3 is obtained when the ratio of 1,4-dioxane to trimethyltoluene is 1:3. However, when 1,4-dioxane or trimethyltoluene is used as the solvent, no COF characteristic peak is observed, and the final product cannot be obtained.

[0082] Figures 6 to 8 The Fourier transform infrared spectra of COF-F0-SO3, COF-F6-SO3, COF-F8-SO3 with 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomers (n = 0, 6, 8), and monosulfonic acid monomers are shown below. It can be seen that at 1673 cm⁻¹... -1 The appearance of the C=N characteristic peak at the point of synthesis, while the characteristic peak of the monomer disappears, confirms the successful synthesis of the intended product.

[0083] Figure 9 Thermogravimetric analysis (TGA) curves for COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 are shown. COF-F6-SO3 and COF-F8-SO3 are very stable before 300℃, but their mass decreases sharply after 300℃, indicating thermal decomposition. COF-F0-SO3 begins to decompose slowly after 200℃, and its mass decreases sharply after 300℃. This demonstrates that the prepared products exhibit good thermal stability, and the addition of fluorine enhances this stability.

[0084] Figure 10The nitrogen adsorption-desorption curves for COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 are shown. Nitrogen adsorption is highest for COF-F0-SO3, decreasing sequentially for COF-F6-SO3 and COF-F8-SO3. This is consistent with the high crystallinity of COF-F0-SO3 and the absence of longer side chains hindering nitrogen adsorption.

[0085] Example 3

[0086] Preparation of proton exchange membranes COF-F0-SO3-H-40% , COF-F6-SO3-H-40% , and COF-F8-SO3-H-40% :

[0087] With phosphoric acid accounting for 40% of the total mass of the separator, 20 mg of COF-Fn-SO3 and 13.33 mg of phosphoric acid were weighed and mixed. They were then thoroughly ground in a mortar until uniformly mixed, placed in a vacuum drying oven and dried at 80°C for 12 hours. After cooling, the mixture was pressed into sheets to prepare separators COF-F0-SO3-H-40%, COF-F6-SO3-H-40%, and COF-F8-SO3-H-40%. These were then assembled into button cells, and their proton conduction curves were measured at 40-120°C.

[0088] Figures 11 to 13 The figures show the ion conductivity performance of membranes COF-F0-SO3-H-40%, COF-F6-SO3-H-40% and COF-F8-SO3-H-40% at different temperatures. The performance of all three membranes reached its peak at 120℃, with COF-F6-SO3-H-40% exhibiting the highest proton conductivity of 1.77 × 10⁻⁶. -2 S cm -1 The highest proton conductivity of COF-F8-SO3-H-40% is 1.01 × 10⁻⁶. -3 Scm -1 The highest proton conductivity of COF-F0-SO3-H-40% is 1.43 × 10⁻⁶. -4 S cm -1 .

[0089] Figure 14 The proton conductivity of membranes COF-F0-SO3-H-40%, COF-F6-SO3-H-40% and COF-F8-SO3-H-40% at different temperatures was determined. The relationship between conductivity and temperature conforms to the Arrhenius equation, and the proton conductivity of COF-F6-SO3-H-40% reaches its maximum at 120℃, which is 1.77 × 10⁻⁶. -2 S cm-1 .

[0090] Example 4

[0091] Preparation of COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 solid electrolytes:

[0092] (1) Ion exchange of COF powder

[0093] 20 mg of COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 powders were weighed and poured into 20 mL of 1 mol / L LiTFSI ethanol solution. After stirring for 12 h, the mixture was filtered and the powder was washed with ethanol. The above steps were repeated three times. The sample powder was then placed in a vacuum oven and dried at 80 °C for 12 h to obtain ion-exchanged COF powder.

[0094] (2) Preparation of solid electrolytes

[0095] After cooling the ion-exchanged powder, it was compressed into tablets. Under an argon protective atmosphere, 5 μL of 1 mol / L LiTFSI PC solution was added dropwise to both sides of the tablets. After standing for 2 hours, COF-modified solid electrolytes PPL-F0, PPL-F6, and PPL-F8 were obtained, respectively.

[0096] Figure 15 SEM images of the solid electrolyte surfaces modified with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3. The three COFs have similar overall morphology, all of which are coral-like structures. The needle-like protrusions are a characteristic of structures containing sulfonic acid groups. As the fluorine chain grows, the distribution changes from plate-like to spherical.

[0097] Example 5

[0098] Assemble Li-Li symmetric cells using modified solid electrolytes (PPL-F0 / PPL-F6 / PPL-F8):

[0099] In a glove box, the Li-Li symmetric battery was assembled in the following order: negative electrode shell, spring, gasket, lithium plate, solid electrolyte, lithium plate, and positive electrode shell. Then, it was pressed into sheets using a button cell sealing and pressing machine. In the Blue Battery testing system, at a current density of 0.4 mA / cm²... -2 The surface area capacity is 0.4 mAh cm⁻¹ -2 Under the conditions of 25℃, the stability of SSE and Li metal was tested in a Li / SSE / Li symmetric cell. After activation by standing for 6 hours with the electrochemical workstation connected, the stability was tested at 0.4 mA cm⁻¹. -2 The tests were conducted under constant current charge and discharge conditions, and the operating cycle curves of the three batteries were compared.

[0100] Figure 16 This chart compares the voltage stability of Li-Li symmetric batteries assembled using solid-state electrolytes modified with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3. The Li-Li symmetric batteries assembled with COF-F6-SO3 and COF-F8-SO3 modified solid-state electrolytes still exhibit good voltage stability after 100 hours of cycling. The COF-F0-SO3 modified solid-state electrolyte still shows good voltage stability after 90 hours of cycling, but subsequent fluctuations occur. It is speculated that the continuous growth of lithium dendrites during cycling causes the electrolyte membrane to be punctured by lithium dendrites, disrupting the battery cycling system. In contrast, the addition of fluorine groups contributes to the battery's better voltage stability.

[0101] Example 6

[0102] Assemble LFP-Li cells and conduct battery performance tests:

[0103] The LFP-Li full cell was assembled in the glove box in the following order: negative electrode shell, spring, gasket, negative electrode, solid electrolyte, positive electrode, and positive electrode shell. Then, it was pressed into sheets using a button cell sealing and pressing machine. Testing was conducted in the Blue Battery testing system at a current density of 0.5C and a temperature of 25°C.

[0104] Figure 17 , Figure 18 Schematic diagrams showing the specific capacity of LFP-Li batteries measured during the first and thirtieth cycles, respectively, using solid electrolytes modified with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3. Figure 19 The diagram shows the cycle performance of LFP-Li batteries assembled with COF-F0-SO3, COF-F6-SO3, and COF-F8-SO3 modified solid electrolytes, respectively. As can be seen from the figure, the lithium-ion battery using the COF-F6-SO3 modified solid electrolyte still maintains a high capacity of nearly 0.25 mAh and a cycle efficiency of 99.9% after 30 cycles. The lithium-ion battery using the COF-F8-SO3 modified solid electrolyte has a capacity of 0.186 mAh and a cycle efficiency of 99.6% after 30 cycles, while the lithium-ion battery using the COF-F0-SO3 modified solid electrolyte has a capacity of 0.12 mAh and a cycle efficiency of 99.3% after 30 cycles.

Claims

1. A ternary covalent organic framework modified with a perfluoroalkyl chain and a sulfonic acid group, characterized in that, The structural formula is: 。 2. The method for synthesizing a ternary covalent organic framework according to claim 1, characterized in that, The specific steps are as follows: In a molar ratio of 4:3:3, 2,4,6-tricarboxymethyl phloroglucinol, fluorocarbonyl hydrazide monomer, and monosulfonic acid monomer were added to a solvent composed of 1,4-dioxane and trimethyltoluene in a volume ratio of 1:3, with acetic acid solution added as a catalyst. The mixture was subjected to liquid nitrogen freezing, vacuuming, and degassing, followed by sealing under vacuum and heating at 120±10℃. After the reaction was completed, the mixture was cooled to room temperature, and the crude product was collected by filtration and extracted with a Soxhlet extract of acetone, methanol, and tetrahydrofuran. The product was then vacuum dried to obtain a ternary covalent organic framework modified with perfluoroalkyl chains and sulfonic acid groups. The structural formula of the fluorocarbonyl hydrazide monomer is as follows: ， The structural formula of the monosulfonic acid monomer is: 。 3. The synthesis method according to claim 2, characterized in that, The method for synthesizing the fluorocarbonyl hydrazine monomer is as follows: Diisopropyl diazoxide, diethyl 2,5-dihydroxyterephthalate, and triphenylphosphine are added to a mixture of diisopropyl diazoxide, diethyl 2,5-dihydroxyterephthalate, and triphenylphosphine in a molar ratio of 2:1:

2. The mixture is stirred and mixed thoroughly under an argon atmosphere. Then, 3,3,4,4,5,5,6,6,6-nonafluorohexane-1-ol or 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecylfluorooctane-1-ol is added. The mixture is stirred and heated under reflux for at least 3 days under an argon atmosphere. After the reaction is complete, the reaction mixture is evaporated to dryness under reduced pressure and purified by silica gel column chromatography. The column chromatography solvent is a mixture of dichloromethane and methanol in a volume ratio of 40:1 to 20:1 to obtain the fluorocarbonyl hydrazine monomer.

4. The synthesis method according to claim 2, characterized in that, The liquid nitrogen freezing, vacuuming, and degassing processes were repeated at least three times; the concentration of the acetic acid solution was 6 mol / L; the heating reaction time was more than 3 days; in the mixed solution of acetone, methanol, and tetrahydrofuran, the volume ratio of acetone, methanol, and tetrahydrofuran was 1:1:1, and the Soxhlet extraction time was 12 h; the vacuum drying temperature was 80 °C, and the time was 12 h.

5. A modified solid electrolyte prepared based on the ternary covalent organic framework modified with perfluoroalkyl chains and sulfonic acid groups as described in claim 1, characterized in that, Prepared by the following steps: (1) Ion exchange of COF powder: The ternary covalent organic framework powder modified with perfluoroalkyl chains and sulfonic acid groups was added to an ethanol solution of LiTFSI, stirred until homogeneous, filtered, and the obtained powder was washed with ethanol. After repeating the above steps three times, the powder was vacuum dried to obtain ion-exchanged COF powder. (2) Preparation of solid electrolytes: After cooling the ion-exchanged COF powder, it was compressed into tablets. Under an argon protective atmosphere, a polycarbonate solution of LiTFSI was added dropwise to both sides of the tablets. After standing, the modified solid electrolyte was obtained.

6. The modified solid electrolyte according to claim 5, characterized in that, In step (1), the vacuum drying temperature is 80℃ and the drying time is 12h.

7. The application of the modified solid electrolyte according to claim 5 in lithium-ion batteries.

8. A proton exchange membrane material prepared based on the ternary covalent organic framework modified with perfluoroalkyl chains and sulfonic acid groups as described in claim 1, characterized in that, Prepared by the following steps: A proton exchange membrane material is prepared by mixing a perfluoroalkyl chain with a ternary covalent organic framework modified with sulfonic acid groups and phosphoric acid, grinding until homogeneous, vacuum drying, cooling and pressing.

9. The proton exchange membrane material according to claim 8, characterized in that, The vacuum drying temperature was 80℃, and the drying time was 12 hours; phosphoric acid accounted for 40% of the total mass of the proton exchange membrane material.

10. The application of the proton exchange membrane material according to claim 8 in fuel cells.

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