Polymer solid electrolyte based on covalent organic framework, preparation method and application thereof

Abstract

The invention discloses a polymer solid electrolyte based on a covalent organic framework, and a preparation method and application thereof. According to the method, firstly, PVDF-HFP and PEG1-NH2 are synthesized into a PH-PEG1-NH2 thin film, then a trialdehyde phloroglucinol solution is poured on the thin film to generate a PH-PEGCOF composite film, the composite film is impregnated with PEO and lithium salt to form a polymer electrolyte film, the polymer electrolyte film is applied to a solid-state lithium battery, and the assembled battery has good stable cycle performance.

Description

Technical Field

[0001] The present invention belongs to the field of covalent organic framework compounds, and relates to a polymer solid electrolyte based on covalent organic framework, a preparation method thereof and an application thereof. Background Art

[0002] With the rapid development of technology, industries such as electronic devices, new energy vehicles, and low-altitude aircraft have flourished, and the battery industry has entered a new peak. Solid-state batteries have become the focus of a new generation of battery technologies due to their ultra-high safety and potential energy density. However, the defects of solid-state batteries are still obvious, and it is currently difficult to enter the desired application fields.

[0003] Currently, the mainstream solid-state electrolytes (SSEs) can be roughly divided into two categories: inorganic ceramic electrolytes and organic polymer electrolytes. The former is usually based on oxides and sulfides, and the latter is usually composed of a polymer matrix and some lithium salts. Organic polymer electrolytes are inherently lightweight, flexible and scalable, and they are compatible with electrodes and more compatible with state-of-the-art manufacturing processes. However, they still have limitations in thermal stability, poor mechanical strength, dendrite growth problems at the electrolyte-electrode interface, and an ionic conductivity of only 10 -6 to 10 -5 S cm -1 at room temperature and other defects, far from meeting the commercial requirements. Therefore, developing new solid-state electrolytes that can solve the above problems is still a huge challenge.

[0004] Covalent organic framework (COF) is a new type of crystalline porous material. Its uniform pore structure, highly customizable functionality, and adjustable surface charge can effectively inhibit side reactions between the electrolyte and the electrode, promote the dissociation of lithium salts, and guide the uniform deposition of lithium metal in the anode. In addition, the high-performance characteristics of COF enable it to customize the composition of the artificial interface layer and provide a suitable thickness range for constructing the artificial interface layer. This makes COF materials have shown broad application potential in the field of lithium batteries.

[0005] PEG1-COF is a polymer electrolyte material formed by the condensation reaction of 1,3,5-triformylbenzene and PEG1-NH2. The finished product is an electrolyte film with a highly ordered pore structure (pore size of 2.38 nm), which can provide channels for the transport of lithium ions and help improve the ionic conductivity of the assembled battery. However, its performance still has deficiencies. For example, although the ionic conductivity reaches 0.153 mS / cm, it still cannot meet the requirements of current high-power density applications; the long-term stability is poor, and it is difficult to cope with repeated mechanical stress; the energy density of the assembled battery is also difficult to meet the actual application requirements, etc. (Tongtong Liu, Yuan Zhong, Zhiwei Yan, et al. Fabrication of Scalable Covalent Organic Framework Membrane-based Electrolytes for Solid-state Lithium Metal Batteries. Angew. Chem. Int. Ed., 2024, 63, e202411535). Therefore, it is necessary to design a new composite polymer solid electrolyte to improve the battery energy density and optimize the performance by reducing the thickness of the electrolyte membrane and other methods. Summary of the Invention

[0006] To solve the problems of topological disorder of ion transport channels, poor interfacial compatibility leading to lithium dendrite growth, and discontinuous ion transport paths caused by the too high proportion of crystalline phases of polymer segments in the existing solid electrolyte system, the present invention provides a polymer solid electrolyte based on covalent organic framework, its preparation method and application to improve the safety, ionic conductivity and interfacial stability of lithium-ion batteries.

[0007] The technical solution to achieve the present invention is as follows:

[0008] An in-situ preparation method of a PH-PEGCOF composite membrane based on PVDF-HFP and PEG1-COF includes the following steps:

[0009] (1) Preparation of the PH-PEG1-NH2 membrane: Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and PEG-NH are mixed and dissolved in acetone, and then the solution is poured into a mold and dried to obtain a PH-PEG1-NH2 composite membrane. The structural formula of the PEG-NH is

[0010] (2) Ultrasonically dissolve phloroglucinol trialdehyde (TP) in a mesitylene / 1,4-dioxane mixed solvent with a volume ratio of 1:7 to 7:1 to form a phloroglucinol trialdehyde solution. Then add an acetic acid solution, ultrasonically disperse it, and fully infiltrate the PH-PEG1 composite membrane. Conduct a hydrothermal reaction at 120 ± 5 °C. After the reaction, wash and dry to obtain the PH-PEGCOF membrane. The structural formula of the phloroglucinol trialdehyde is

[0011] Preferably, in step (1), the mass ratio of PVDF-HFP to PEG-NH is 1:1.

[0012] Preferably, in step (1), in the mesitylene / 1,4-dioxane mixed solvent, the volume ratio of mesitylene to 1,4-dioxane is 3:1.

[0013] Preferably, in step (2), the concentration of the phloroglucinol trialdehyde solution is 0.02 - 0.6 mol / L.

[0014] Preferably, in step (2), the concentration of the acetic acid solution is 3 - 12 mol / L, more preferably 6 mol / L.

[0015] Preferably, in step (2), the molar ratio of phloroglucinol trialdehyde to acetic acid is 0.04:1.

[0016] Preferably, in step (2), the hydrothermal reaction time is 36 h.

[0017] The present invention provides the PH-PEGCOF composite membrane prepared by the above preparation method.

[0018] Furthermore, the present invention provides a polymer solid electrolyte based on the above PH-PEGCOF composite membrane, which is a PH-PEGCOF composite membrane fully impregnated with polyethylene oxide (PEO) and a lithium salt.

[0019] The preparation method of the above polymer solid electrolyte includes the following steps:

[0020] Fully impregnate the PH-PEGCOF composite membrane in an acetonitrile solution of PEO and a lithium salt, and dry after impregnation to obtain the polymer solid electrolyte.

[0021] The lithium salt described in the present invention is a lithium salt commonly used in the field of lithium batteries, including but not limited to lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), etc. In the specific embodiments of the present invention, LiTFSI is taken as an example.

[0022] Preferably, the ratio of PEO to the lithium salt is 1:1 in terms of the molar ratio of O to Li.

[0023] Preferably, the drying temperature is 60±5° C. and the drying time is 12 to 24 hours.

[0024] The present invention also provides application of the polymer solid electrolyte in a solid-state lithium battery.

[0025] The lithium battery described in the present invention is a lithium metal battery or a lithium ion battery.

[0026] In a specific embodiment of the present invention, the lithium battery used is a lithium ion battery, with a lithium metal sheet as the negative electrode, a lithium iron phosphate (LFP) as the positive electrode, and the above-mentioned polymer solid electrolyte as a solid electrolyte.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) The PH-PEGCOF composite membrane is rich in functionalized ether oxygen chains. At the same time, COF itself has good physical and chemical stability, which helps to improve the problems of low conductivity and poor mechanical properties of PEO-based electrolytes. The battery assembled by the composite polymer electrolyte membrane constructed by immersing the polymer electrolyte has good cycle stability.

[0029] (2) Grafting PEG chains onto the covalent organic framework enables the covalent organic framework to better transport lithium ions, while also improving the structural stability and mechanical strength of the covalent organic framework, which can effectively buffer the drastic volume changes produced by lithium-ion batteries during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the preparation process of PH-PEGCOF composite membrane;

[0031] Figure 2 This is a physical picture of the PH-PEGCOF composite membrane;

[0032] Figure 3 This is the thickness measurement diagram of PH-PEGCOF composite film;

[0033] Figure 4 Infrared spectra (FTIR) of PH-PEGCOF composite membrane, PVDF-HFP membrane, PEG1-COF powder, PEG-NH2, and TP;

[0034] Figure 5 XRD comparison diagrams of PH-PEGCOF composite membrane, PVDF-HFP, PEG1-COF and synthetic monomers, where (a) is compared with PVDF-HFP, and (b) is compared with COF monomer;

[0035] Figure 6SEM images of the PH-PEGCOF composite membrane, where (b) is a partial enlarged view of (a);

[0036] Figure 7 TGA curves of the PH-PEGCOF composite membrane, PVDF-HFP membrane, and PEG1-COF powder;

[0037] Figure 8 Cyclic specific capacity diagram of the lithium-ion battery LFP|PH-PEGCOF|Li. Detailed implementation manners

[0038] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below through examples and in combination with the accompanying drawings. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention. Unless otherwise specified in the context of this application, the professional terms and abbreviations used in this application are widely known to those skilled in the art; unless otherwise indicated as the manufacturer in the following text, all are conventional products that can be prepared by referring to the existing literature or obtained through commercial purchase.

[0039] The preparation of PVDF-HFP described in the present invention refers to the reference (Marcel Roy B. Domalanta, Mark Rigel R. Ali, Reymark D. Maalihan, Eugene B. Caldona. Mechanistic effects of HFP content on the surface structure and protective action of PVDF-HFP coatings. Progress in Organic Coatings, 2025, 198, 108879).

[0040] The preparation of PEG1-NH2 described in the present invention refers to the reference (Tongtong Liu, Yuan Zhong, Zhiwei Yan, et al. Fabrication of Scalable Covalent Organic Framework Membrane-based Electrolytes for Solid-state Lithium Metal Batteries. Angew. Chem. Int. Ed., 2024, 63, e202411535).

[0041] The structural formula of the covalent organic framework material PEG1-COF described in the present invention is:

[0042]

[0043] Example 1

[0044] Synthesis of PH-PEGCOF and battery assembly are as follows:

[0045] 1. Preparation of PH-PEGCOF composite membrane:

[0046] (1) Add 15 mg of PVDF-HFP and 15 mg of PEG1-NH2 into a reagent bottle containing 200 mL of acetone, stir magnetically until completely mixed evenly, pour the mixed solution into a Teflon mold, dry it under an inert atmosphere, cut it, and obtain a PH-PEG1-NH2 composite membrane. Put the membrane into a hydrothermal reaction kettle for standby.

[0047] (2) Add 6.3 mg of phloroglucinol trialdehyde to a solution of 0.75 mL of mesitylene and 0.25 mL of 1,4-dioxane, dissolve it by ultrasound, then add 0.12 mL of 6 M aqueous acetic acid solution, and dissolve and disperse it again by ultrasound into a suspension. Pour the suspension into a hydrothermal reaction kettle, fully infiltrate the PH-PEG1-NH2 composite membrane, tighten the reaction kettle, put it into an oven and react at 120 °C for 36 h, then take out the reaction product, wash it successively with tetrahydrofuran, dichloromethane, and methanol, and finally dry it to obtain a PH-PEGCOF composite membrane.

[0048] 2. Preparation of polymer solid electrolyte:

[0049] Immerse the PH-PEGCOF composite membrane in an acetonitrile solution of PEO and LiTFSI. Among them, the ratio of PEO to LiTFSI is based on the molar ratio of O to Li, and the molar ratio is 10:1. After sufficient immersion, dry the membrane in a vacuum drying oven at 60 °C for 12 hours to obtain a polymer solid electrolyte.

[0050] Figure 1 is a schematic diagram of the preparation process of the PH-PEGCOF composite membrane. Figure 2 is a physical picture of the PH-PEGCOF composite membrane, indicating excellent film-forming performance. Figure 3 is a thickness measurement diagram of the PH-PEGCOF composite membrane. It can be observed that the composite membrane is extremely thin, with a thickness of only 0.100 mm, indicating high energy density.

[0051] The FTIR, XRD, and SEM diagrams of the PH-PEGCOF composite membrane are respectively as Figure 4 , 5 , 6. It can be seen from the figure that the PH-PEGCOF composite membrane has a peak at 1184 cm -1There is a significant shift at this point, which can confirm the synthesis of the desired product. Measuring the diffraction intensity at different diffraction angles shows that the PH-PEGCOF composite membrane has the crystallinity of covalent organic framework materials, and microscopically, PH-PEGCOF has a porous structure, determining the successful synthesis of a new type of COF-based polymer electrolyte membrane.

[0052] TGA tests were respectively carried out on the PVDF-HFP membrane, PEG1-COF powder (Powder-PEGCOF), and PH-PEGCOF membrane. The results are as Figure 7 shown. At different temperatures, the stability of the samples was evaluated by the percentage of the remaining weight of the samples. PH-PEGCOF began to lose weight significantly at about 450 °C, indicating good thermal stability.

[0053] Example 2

[0054] The polymer solid electrolyte prepared in Example 1 was assembled into a lithium-ion battery. The assembly of the battery was completed in a glove box, and the charge-discharge curve of the battery was measured as follows:

[0055] Using a lithium metal sheet as the negative electrode and a lithium iron phosphate (LFP) positive electrode sheet as the positive electrode, with the polymer solid electrolyte sandwiched in the middle, it was encapsulated with an aluminum-plastic film in a dry environment. The battery was placed in a clean constant-temperature oven, and the charge-discharge curve of the battery was measured with a BlueTEC system.

[0056] Figure 8 It is the cyclic specific capacity diagram of LFP|PH-PEGCOF|Li. It can be seen that when a constant current charge-discharge test was carried out at 0.5C, after 90 cycles, the charge-discharge specific capacity of the battery (the battery assembled with the PH-PEGCOF membrane as the electrolyte) still remained above 98%, indicating good cycle stability.

Claims

1. In-situ preparation method of PH-PEGCOF composite membrane based on PVDF-HFP and PEG1-COF, characterized in that, It includes the following steps: (1) Preparation of PH-PEG1-NH2 membrane: PVDF-HFP and PEG1-NH2 were mixed and dissolved in acetone, and then the solution was poured into a mold and dried to obtain a PH-PEG1-NH2 composite membrane. The structural formula of PEG1-NH2 is ; (2)Dissolve phloroglucinol trialdehyde ultrasonically in a mesitylene / 1,4-dioxane mixed solvent with a volume ratio of 1:7 to 7:1 to form a phloroglucinol trialdehyde solution. Then add an acetic acid solution, disperse it ultrasonically, and fully infiltrate the PH-PEG1 composite membrane with it. Carry out a hydrothermal reaction at 120 ± 5 °C. After the reaction is completed, wash and dry it to obtain a PH-PEGCOF membrane. The structural formula of the phloroglucinol trialdehyde is .

2. The in-situ preparation method according to claim 1, wherein, In step (1), the mass ratio of PVDF-HFP to PEG1-NH2 is 1:1; in the mesitylene / 1,4-dioxane mixed solvent, the volume ratio of mesitylene to 1,4-dioxane is 3:

1.

3. The in-situ preparation method according to claim 1, wherein, In step (2), the concentration of the phloroglucinol trialdehyde solution is 0.02 - 0.6 mol / L; the concentration of the acetic acid solution is 3 - 12 mol / L; the molar ratio of phloroglucinol trialdehyde to acetic acid is 0.04:1; the hydrothermal reaction time is 36 h.

4. The PH-PEGCOF composite membrane prepared by the in-situ preparation method according to any one of claims 1 to 3.

5. A polymer solid electrolyte, characterized in that, The PH-PEGCOF composite membrane of claim 4 that is fully impregnated with PEO and lithium salt.

6. The preparation method of the polymer solid electrolyte according to claim 5, wherein, It includes the following steps: Fully immerse the PH-PEGCOF composite membrane in the acetonitrile solution of PEO and lithium salt, and after impregnation, dry it to obtain a polymer solid electrolyte.

7. The preparation method according to claim 5, characterized in that, The lithium salt is LiPF6, LiClO4, LiTFSI or LiFSI; the ratio of PEO to the lithium salt is 1:1 in terms of the molar ratio of O to Li; the drying temperature is 60 ± 5°C, and the drying time is 12 - 24 h.

8. The application of the polymer solid electrolyte according to claim 5 in a solid-state lithium battery.

9. The application according to claim 8, wherein The lithium battery is a lithium metal battery or a lithium-ion battery.

10. The application according to claim 9, characterized in that, The lithium battery is a lithium-ion battery, with a lithium metal sheet as the negative electrode, iron phosphate as the positive electrode sheet, and the polymer solid electrolyte as the solid electrolyte.

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