Method for preparing solid composite electrolyte membrane by using fluorine-containing MOFs as filler

Abstract

The invention provides a method for preparing a solid-state composite electrolyte membrane by using fluorine-containing MOFs as a filler, and belongs to the field of lithium ion battery solid-state electrolyte. The method comprises the following steps: dissolving a polymer, a lithium salt and functionally modified fluorine-containing MOF in an organic solvent, and mixing and stirring to obtain mixed slurry; the functional modified fluorine-containing MOF is selected from one or more of UIO-66-F4, UIO-66-F2, UIO-66-CF3, MOF-OTf or UIO-66-Hf, and the functional modified fluorine-containing MOF is selected from one or more of UIO-66-F4, UIO-66-F2, UIO-66-CF3, MOF-OTf and UIO-66-Hf. And coating the obtained mixed slurry on a substrate at a constant speed, and drying to obtain the solid-state composite electrolyte membrane. The functional modified fluorine-containing MOF is introduced into the polymer solid electrolyte as a filler, so that the crystallinity of the polymer can be effectively reduced, and the dynamic performance of a polymer chain is improved.

Description

Technical Field

[0001] The present invention belongs to the field of solid electrolytes for lithium-ion batteries, and in particular relates to a method for preparing a solid composite electrolyte membrane by using fluorine-containing MOFs as a filler. Background Art

[0002] All-solid-state lithium-ion batteries are considered a promising candidate for the next generation of high-performance energy storage devices due to their potential high energy density, safety, and cycle life. Compared to traditional liquid electrolyte lithium-ion batteries, all-solid-state lithium-ion batteries can effectively address safety hazards such as leakage and flammability caused by liquid electrolytes, while also supporting high voltage and a metallic lithium anode, significantly improving the battery's energy density. The key to achieving all-solid-state lithium-ion batteries lies in the application of solid-state electrolytes.

[0003] As a core component of all-solid-state lithium-ion batteries, solid electrolytes not only play a crucial role in lithium ion conduction but also provide the battery with enhanced thermal and electrochemical stability. Solid electrolyte materials are primarily categorized as inorganic, polymer, and inorganic-polymer composites. Inorganic solid electrolytes typically offer high ionic conductivity and mechanical strength, but their interfacial contact issues require further optimization. Polymer solid electrolytes offer advantages in flexibility and processability, but suffer from insufficient thermal stability and strength. To address these challenges, researchers have begun exploring the incorporation of functional fillers into polymer electrolytes to further enhance their overall performance. Among various functional fillers, metal-organic frameworks (MOFs), a novel crystalline material, have attracted increasing interest due to their unique structural properties and tunability. First, MOFs possess a highly ordered porous structure, which results in an extremely high specific surface area, providing more active sites and ion conduction pathways, thereby significantly improving the electrolyte's ionic conductivity. Furthermore, the structural diversity and tunability of MOFs allow the selection of diverse metal and organic ligands to design materials with specific functionalities. This tunability not only enables MOFs to meet diverse application requirements but also gives them unique advantages in optimizing electrolyte performance. In particular, the introduction of fluorine-containing (F) functional groups into MOFs can not only promote electrode-electrolyte interface stability but also form LiF, thereby obtaining a more stable solid electrolyte interface (SEI) film, which can further optimize its performance. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of low ionic conductivity, poor interface stability and insufficient mechanical strength commonly found in traditional solid electrolytes, thereby providing a method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as fillers.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as a filler, comprising:

[0007] Step 1: dissolving a polymer, a lithium salt and a functionally modified fluorinated MOF in an organic solvent, mixing and stirring to obtain a mixed slurry; the functionally modified fluorinated MOF is one or more of UIO-66-F4, UIO-66-F2, UIO-66-CF3, MOF-OTf or UIO-66-Hf;

[0008] Step 2: coating the mixed slurry obtained in step 1 on a substrate at a uniform speed and drying the mixture to obtain a solid composite electrolyte membrane.

[0009] Preferably, the polymer is selected from one or more of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF) or polyvinyl alcohol (PVA).

[0010] Preferably, the lithium salt is one or more of LiTFSI, LiFSI, LiBF4 or LiPF6.

[0011] Preferably, the mass ratio of the polymer, lithium salt and functionally modified fluorine-containing MOF in step 1 is (60-65):30:(5-10).

[0012] Preferably, the organic solvent in step 1 is acetone or a mixture of acetone and dimethylformamide, dimethylacetamide or anhydrous ethanol.

[0013] Preferably, the mixing and stirring in step 1 is first stirred at 70° C. for 3 hours, and then continuously stirred at 40° C. overnight.

[0014] Preferably, the mixing and stirring described in step 1 is divided into two stirring processes. The two stirring processes are: first, the polymer and lithium salt are dispersed in an organic solvent, and magnetic stirring is performed to obtain a first mixed slurry; then, the functionalized modified fluorine-containing MOF is added to the above-mentioned first mixed slurry, and magnetic stirring is performed to obtain a second mixed slurry.

[0015] Preferably, the temperature of each magnetic stirring is 60-80° C., the time is 8-12 h, and the speed is set to 1000-3000 r / min.

[0016] Preferably, the drying in step 2 is carried out at 30°C, 40°C and 50°C for 5 hours respectively, and finally at 60°C for 8-24 hours.

[0017] Preferably, the substrate in step 2 is a polytetrafluoroethylene plate, copper foil, glass or aluminum foil.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The present invention provides a method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as fillers. The solid composite electrolyte membrane is composed of a polymer, a lithium salt, and a functionally modified fluorine-containing MOF. The present invention introduces the functionally modified fluorine-containing MOF as a filler into the polymer solid electrolyte, which can effectively reduce the crystallinity of the polymer, thereby improving the kinetic properties of the polymer chain. Specifically, the functional filler reduces the crystalline region and increases the amorphous region by interfering with the ordered arrangement of the polymer chain, thereby enhancing the mobility of the polymer chain segments. This structural change improves the flexibility and ionic conductivity of the polymer matrix, which is beneficial for the migration of lithium ions. In addition, the surface functional groups of the functionalized MOFs can also interact with the polymer chains, further promoting the transport of lithium ions. By forming more ion channels and heterogeneous structures, the F-containing MOFs can construct highly ordered ion migration paths in the polymer, while forming a more stable SEI film, significantly improving the overall performance of the electrolyte. These improvements provide all-solid-state lithium-ion batteries with higher cycle stability and electrochemical performance.

[0020] The present invention adopts a simple solvent thermal method and solution coating method to prepare functionalized MOF and solid composite electrolyte membrane, the process steps are simple, and it has high feasibility of industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a surface SEM image of the solid composite electrolyte membrane prepared in Example 2.

[0022] Figure 2 This is a cross-sectional SEM image of the solid composite electrolyte membrane prepared in Example 2.

[0023] Figure 3 This is a linear voltammetric curve of the solid composite electrolyte membrane prepared in Example 2.

[0024] Figure 4 This is a battery test diagram of Example 2, using metallic lithium as the negative electrode, the thin film of the present invention as the solid electrolyte, and lithium iron phosphate as the positive electrode.

[0025] Figure 5 This is a battery test diagram of Example 2, using metallic lithium as the negative electrode, the thin film of the present invention as the solid electrolyte, and lithium iron phosphate as the positive electrode.

[0026] Figure 6 This is a battery test diagram of Example 2, using metallic lithium as the negative electrode, the thin film of the present invention as the solid electrolyte, and lithium iron phosphate as the positive electrode.

[0027] Figure 7This is a battery test diagram of Example 2, using metallic lithium as the negative electrode, the thin film of the present invention as the solid electrolyte, and lithium iron phosphate as the positive electrode. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as a filler, comprising:

[0029] Step 1: dissolving the polymer, lithium salt and functionalized fluorinated MOF in an organic solvent, mixing and stirring to obtain a mixed slurry; the mixing and stirring is preferably a one-time stirring or a two-time stirring. When using a one-time stirring, the polymer, lithium salt and functionalized fluorinated MOF are dissolved in the organic solvent, preferably stirred at 70° C. for 3 hours, and then continuously stirred at 40° C. overnight to obtain a uniform slurry;

[0030] When using the secondary stirring method, the polymer and lithium salt are first dispersed in an organic solvent, and then magnetically stirred after mixing. The temperature of the magnetic stirring is preferably 60-80°C, the time is preferably 8-12 hours, and the speed setting is preferably 1000-3000 r / min, more preferably 1500 r / min, to obtain a first mixed slurry; then, the functionalized modified fluorine-containing MOF is added to the first mixed slurry and magnetically stirred. The temperature of the magnetic stirring is preferably 60-80°C, the time is preferably 8-12 hours, and the speed setting is preferably 1000-3000 r / min, more preferably 1500 r / min, to obtain a second mixed slurry;

[0031] The polymer is preferably selected from one or more of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), or polyvinyl alcohol (PVA); the lithium salt is preferably one or more of LiTFSI, LiFSI, LiBF4, or LiPF6; the mass ratio of the polymer, lithium salt, and functionalized fluorine-containing MOF is preferably (60-65):30:(5-10). The organic solvent is preferably acetone or a mixture of acetone and dimethylformamide, dimethylacetamide, or anhydrous ethanol, more preferably a mixture of acetone and dimethylacetamide, wherein the volume ratio of acetone to dimethylacetamide is preferably 4:1;

[0032] The functionalized fluorinated MOF is preferably one or more of UIO-66-F4, UIO-66-F2, UIO-66-CF3, MOF-OTf, or UIO-66-Hf, with UIO-66-F4 being more preferred. UIO-66-F4 (Zr-MOF) has a highly ordered nanoporous structure, a high specific surface area, and strong framework stability. Furthermore, the -F functionalization of UIO-66-F4 improves the interfacial stability, ion transport capacity, and lithium salt solubility of the electrolyte membrane, and exhibits superior compatibility with polymers such as PVDF-HFP. The amount of the functionalized fluorinated MOF added is preferably 5%-10% of the mass of the first mixed slurry.

[0033] Step 2: Coat the second mixed slurry obtained in step 1 on a substrate, preferably with a uniform speed coating using a scraper gap of 20-200um, and dry in steps of 30°C, 40°C, and 50°C for 5 hours each, and finally dry at 60°C for 8-24 hours, or directly dry at 60°C for 8-24 hours to obtain a uniform dry film, punch the dry film into discs with a diameter of 12mm, 14mm, or 18mm, and store them in a glove box (the oxygen and moisture contents are both less than 0.1ppm) to obtain a solid composite electrolyte membrane; the substrate is preferably a polytetrafluoroethylene plate, copper foil, glass or aluminum foil, more preferably a polytetrafluoroethylene plate.

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments to make the objectives, technical solutions and advantages of the present invention clearer.

[0035] Example 1: Preparation of UIO-66-F4 (Zr-MOF)

[0036] UIO-66-F4 (Zr-MOF) was obtained by a simple solvothermal method. First, 1.16 g ZrCl4 and 1.19 g H2TFBDC were dissolved in 50 ml glacial acetic acid aqueous solution (V 水 :V 醋酸 =3:2) and then sonicated for 30 minutes until the solution was clear. The solution was then transferred to a 100 ml Teflon autoclave and reacted at 110°C for 24 hours. The powder was washed three times with DMF and methanol and finally dried at 80°C overnight to obtain UIO-66-F4 (Zr-MOF) powder, which required vacuum activation at 120°C for 10 hours.

[0037] Example 2: Preparation of composite solid electrolyte membrane

[0038] According to Table 1, LiTFSI, UIO-66-F4 (Zr-MOF), and PVDF-HFP in different mass ratios were dissolved in DMAC / acetone (V:V = 1:2) at one time, stirred at 70 °C for 3 h, and then continuously stirred at 40 °C overnight to obtain a uniform slurry.

[0039] The slurry was then coated onto a polytetrafluoroethylene (PTFE) plate and vacuum-dried at 60°C for 12 hours to obtain a uniform, dry film with a dense structure and uniform thickness, meeting testing requirements. Finally, the resulting film was punched into 18 mm diameter discs using a button cell punch and stored in an argon-filled glove box.

[0040] Table 1

[0041]

[0042] Figure 1 This is a surface SEM image of the solid composite electrolyte membrane prepared with a MOF / wt.% addition of 10% in Example 2. The SEM image of the composite electrolyte membrane shows that its surface structure is dense and uniform, with no obvious holes or cracks, indicating that the membrane has good structural integrity. It can be observed from the image that fine particles are evenly distributed on the membrane surface, without agglomeration or local accumulation, indicating that the filler is well dispersed in the polymer matrix and has a high distribution uniformity. This uniform micromorphology helps to build a continuous lithium ion transmission channel, while reducing interfacial impedance and improving the overall electrochemical performance of the electrolyte.

[0043] Figure 2 This is a cross-sectional SEM image of the solid-state composite electrolyte membrane produced in Example 2 with a MOF / wt.% addition of 10%. This cross-sectional SEM image demonstrates the excellent structural density and uniformity of the composite electrolyte membrane, with no apparent holes, cracks, or delamination within the membrane, indicating excellent membrane quality. The membrane exhibits uniform thickness and well-defined boundaries, demonstrating good mechanical stability and processing consistency, facilitating stable ion transport pathways and good interfacial contact, providing reliable structural support and a foundation for electrochemical performance in battery systems.

[0044] Figure 3 The linear voltammograms of solid composite electrolyte membranes prepared with different MOF / wt.% additions in Example 2 are shown. The LSV curves show that different doping ratios have a significant impact on the electrochemical stability window of the electrolyte, with the solid electrolyte with a 10% addition having the widest electrochemical stability window and the best electrochemical stability.

[0045] Figure 4This is a battery test diagram using the solid composite electrolyte membrane prepared with a MOF / wt.% addition amount of 10% in Example 2 as the solid electrolyte, metallic lithium as the negative electrode, and lithium iron phosphate as the positive electrode. Figure 4 The battery performance test results using metallic lithium as the negative electrode, lithium iron phosphate as the positive electrode, and the solid composite electrolyte membrane as the electrolyte are presented to evaluate the electrochemical stability and cycle life of the electrolyte membrane in an actual battery system. Under conditions of 0.2C and 60°C, the battery maintained a high current density of approximately 150 mA·h·g over nearly 300 cycles. -1 The discharge capacity and coulombic efficiency close to 100% show excellent cycling stability and electrochemical reversibility.

[0046] Figure 5 This figure shows a battery test using the solid composite electrolyte membrane prepared with zero MOF / wt.% added in Example 2 as the solid electrolyte, metallic lithium as the negative electrode, and lithium iron phosphate as the positive electrode. This figure shows good initial cycling stability at 0.2C and 60°C, but a significant drop in coulombic efficiency after 60 cycles indicates gradual deterioration of the interfacial stability or electrolyte structure.

[0047] Figure 6 This figure shows a battery test using the solid composite electrolyte membrane prepared with a 5% MOF / wt.% addition in Example 2 as the solid electrolyte, lithium metal as the negative electrode, the thin film of the present invention as the solid electrolyte, and lithium iron phosphate as the positive electrode. The figure shows that the electrolyte doped with 5% filler performs well initially at 0.2C and 60°C, but its coulombic efficiency drops significantly after 70 cycles, improving its performance compared to pure PVDF-HFP.

[0048] Figure 7 Figure 1 shows a battery test using the solid composite electrolyte membrane prepared with a 15% MOF / wt.% addition in Example 2 as the solid electrolyte, metallic lithium as the negative electrode, the thin film of the present invention as the solid electrolyte, and lithium iron phosphate as the positive electrode. The figure shows that the electrolyte doped with 15% filler exhibits good initial cycling performance at 0.2C and 60°C, but exhibits a slight decrease in coulombic efficiency over long-term cycling, suggesting that excessive filler may affect interfacial stability or structural integrity.

Claims

1. A method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as fillers, characterized in that: include: Step 1: dissolving a polymer, a lithium salt and a functionally modified fluorinated MOF in an organic solvent, mixing and stirring to obtain a mixed slurry; the functionally modified fluorinated MOF is one or more of UIO-66-F4, UIO-66-F2, UIO-66-CF3, MOF-OTf or UIO-66-Hf; Step 2: coating the mixed slurry obtained in step 1 on a substrate at a uniform speed and drying the mixture to obtain a solid composite electrolyte membrane.

2. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 1, characterized in that: The polymer is selected from one or more of polyvinylidene fluoride-co-hexafluoropropylene, polyethylene oxide, polymethyl methacrylate, polyvinylidene fluoride or polyvinyl alcohol.

3. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 1, characterized in that: The lithium salt is one or more of LiTFSI, LiFSI, LiBF4 or LiPF6.

4. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 1, characterized in that: The mass ratio of the polymer, lithium salt and functionalized modified fluorine-containing MOF in step 1 is (60-65):30:(5-10).

5. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 1, characterized in that: The organic solvent in step 1 is acetone or a mixture of acetone and dimethylformamide, dimethylacetamide or anhydrous ethanol.

6. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 1, characterized in that: The mixing and stirring in step 1 is first stirred at 70° C. for 3 hours, and then continuously stirred at 40° C. overnight.

7. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 1, characterized in that: The mixing and stirring described in step 1 is divided into two stirring processes. The two stirring processes are: first, the polymer and lithium salt are dispersed in an organic solvent, and magnetic stirring is performed to obtain a first mixed slurry; then, the functionalized modified fluorine-containing MOF is added to the above-mentioned first mixed slurry, and magnetic stirring is performed to obtain a second mixed slurry.

8. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 7, characterized in that: The temperature of each magnetic stirring is 60-80° C., the time is 8-12 hours, and the speed is set to 1000-3000 r / min.

9. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 1, characterized in that: The drying in step 2 is carried out at 30°C, 40°C and 50°C for 5 hours respectively, and finally at 60°C for 8-24 hours.

10. The method for preparing a solid composite electrolyte membrane using fluorine-containing MOFs as filler according to claim 1, characterized in that: The substrate in step 2 is a polytetrafluoroethylene plate, copper foil, glass or aluminum foil.

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