Functional diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention belongs to the technical field of battery diaphragms, and particularly relates to a functional diaphragm and a preparation method thereof and a lithium ion battery, the preparation method comprises the following steps: dipping a diaphragm base membrane in an aqueous solution of alcohol for pretreatment, then dipping in a mixed aqueous solution of 2, 5-diamino-1, 4-dihydroxybenzene dihydrochloride Pa-OH and a surfactant, and drying to obtain the functional diaphragm. The obtained 2, 5-diamino-1, 4-dihydroxybenzene dihydrochloride modified base membrane is soaked in an organic solution of 1, 3, 5-triformyl phloroglucinol TP, TP and Pa-OH are subjected to a Schiff base reaction on a two-phase interface, and a base membrane with TP-COF generated in situ is obtained; the preparation method comprises the following steps: taking a TP-COF-COOH modified base membrane as a raw material, dipping the TP-COF-COOH modified base membrane in a succinic anhydride or succinic anhydride derivative solution for reaction, introducing carboxyl, and dipping the obtained TP-COF-COOLi modified base membrane in an alcoholic solution of lithium salt to obtain the TP-COF-COOLi functional diaphragm. The-COOLi group generated through modification can provide a lithium ion specific transmission path, the lithium ion transference number and the ion conductivity are remarkably improved, the wettability of the electrolyte and the Li < + > affinity are enhanced through carboxyl, the internal resistance of the battery can be reduced, and the rate performance is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a functionalized separator, its preparation method, and a lithium-ion battery. Background Technology

[0002] The primary function of a battery separator is to physically isolate the positive and negative electrodes to prevent short circuits, while allowing lithium ions to pass freely. Compared to inorganic nanomaterials and conventional organic materials, organic framework materials possess a more ordered and uniform pore structure, with precisely controllable pore size. The nanoscale pores and high specific surface area increase the contact area with the electrolyte, enhancing liquid absorption and improving rate performance and cycle life. Furthermore, the COF covalent backbone exhibits excellent thermal stability, enabling it to withstand higher temperatures.

[0003] However, existing COF materials are all coated onto the membrane surface by surface coating. This method has weak adhesion between the coating and the base membrane, and relies on adhesives to achieve physical adhesion. Coating peeling may cause local short circuits. Adhesives may block some pores, resulting in reduced porosity and increased ion transport resistance. When the slurry is coated onto the base membrane, problems such as agglomeration, cracking or uneven thickness are prone to occur, affecting the cycle stability and service life of the battery. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a functionalized separator, its preparation method, and a lithium-ion battery.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing a functionalized membrane, comprising the following steps: The membrane base was pretreated by immersion in an aqueous alcohol solution; The pretreated base film was immersed in a mixed aqueous solution of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) and a surfactant to obtain a base film modified with 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride. The 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride modified base film was impregnated in an organic solution of 1,3,5-tricarboxymethyl phloroglucinol (TP). TP and Pa-OH underwent a Schiff base reaction at the interface between the two phases to obtain a base film with in-situ generated TP-COF. The in-situ generated TP-COF base film is immersed in a solution of succinic anhydride or its derivative to introduce carboxyl groups, thereby obtaining a TP-COF-COOH modified base film. The TP-COF-COOH modified base membrane was impregnated in an alcohol solution of lithium salt to obtain a TP-COF-COOLi functionalized membrane.

[0006] In a second aspect, the present invention provides a functionalized diaphragm, which is prepared by the method for preparing the functionalized diaphragm described in the first aspect.

[0007] Thirdly, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, and a separator, wherein the separator is the functionalized separator described in the second aspect.

[0008] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention introduces 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) and 1,3,5-tricarboxymethyl phloroglucinol (TP) onto an activated base film to generate a TP-COF coating membrane in situ linked by β-keto-enamine bonds. Then, a carboxyl group is introduced through a ring-opening reaction of succinic anhydride or its derivatives to obtain TP-COF-COOH. Finally, the TP-COF-COOH membrane is immersed in an alcoholic solution of lithium salt to undergo ion exchange, forming a TP-COF-COOLi functionalized membrane. This in-situ modification not only preserves the porous structure of the COF material, achieving surface wettability comparable to surface coating, but also enhances the adhesion between the coating and the base film, reducing peeling defects. Surface coating typically only covers the outer surface of the base film. However, coatings formed through in-situ modification can penetrate both the inner and outer surfaces of the membrane. In-situ synthesis allows COF to grow on the surface and within the pores of the base film, forming an integrated structure. The coating bonds to the base film without the need for adhesives. COF forms a continuous, uniform film on the base film from bottom to top. Strong adhesion and uniformity significantly reduce interfacial resistance and promote Li... + The uniform distribution of COF effectively improves the wettability of the separator, which facilitates rapid lithium-ion transport and uniform deposition, thereby enhancing battery cycle life. Furthermore, COF exhibits significantly improved thermal stability and mechanical strength compared to conventionally coated separators.

[0009] The reaction of Pa-OH with TP results in isomerization to form a β-ketoenamine bond, which exhibits higher chemical stability compared to the imine bond formed by the reaction of TP with p-phenylenediamine (BD), ensuring stability over long cycles. Furthermore, Pa-OH possesses a highly reactive polar functional group, the hydroxyl group (-OH), allowing for effective chemical modification to introduce ion transport functionality. It also exhibits a natural affinity for carbonate electrolytes, significantly improving the wettability and liquid retention of the membrane. The moderate flexibility of Pa-OH provides the membrane with appropriate tensile strength, preventing deformation and brittleness.

[0010] The modified -COOLi groups can provide lithium-ion specific transport pathways. In addition to the porous structure of the COF itself, the -COOLi groups are densely arranged on the inner walls of the COF pores, forming low-energy-barrier lithium-ion transport pathways. +It can move rapidly by jumping between these sites, significantly improving lithium-ion transference number and ionic conductivity. The carboxyl group enhances electrolyte wettability and... + Affinity can reduce the internal resistance of the battery and improve rate performance. The strong dipole moment induced by the introduction of the -COOLi group can promote the breaking of the PF bond in lithium hexafluorophosphate (LiPF6), thereby promoting the formation of the solid electrolyte interphase (SEI) film of lithium fluoride (LiF), effectively suppressing undesirable side reactions between the negative electrode and the electrolyte, while significantly reducing the growth of lithium dendrites, optimizing ion transport, improving interface stability, and also helping to improve the thermal stability of the battery. Attached Figure Description

[0011] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0012] Figure 1 This is a SEM image of the TP-COF-COOLi functionalized membrane prepared in Example 1 of this invention. Detailed Implementation

[0013] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0014] The primary function of a battery separator is to physically isolate the positive and negative electrodes to prevent short circuits, while allowing lithium ions to pass freely. The performance requirements for separators generally include: high porosity to ensure ion transport, good mechanical strength to resist puncture, excellent thermal stability to prevent high-temperature shrinkage, appropriate tensile strength to ensure the separator is not easily stretched or deformed during production and use, and sufficient electrolyte wettability to ensure ionic conductivity. These performance indicators directly affect the battery's energy density, cycle life, and safety performance.

[0015] Based on the coating process principle and material composition, diaphragm coating technology can be mainly divided into three categories: inorganic coating, organic coating, and organic-inorganic composite coating. Inorganic coating is a method to improve diaphragm performance by coating inorganic particles onto a base membrane, among which alumina and boehmite are the most commonly used ceramic materials. Alumina has good thermal stability and wettability, but the coating distribution is prone to unevenness, and the coating itself has poor flexibility and cohesion. Boehmite is easier to disperse in slurry to form a stable suspension, and has low raw material and production costs. However, diaphragms coated with inorganic ceramic materials generally face problems such as uneven coating thickness, easy pore blockage, interfacial incompatibility, and brittleness. In addition, the binder used in the coating process may melt or decompose at high temperatures, leading to the peeling off of the coating material.

[0016] Organic coating technology is an important method for modifying base films using polymer materials. PVDF (polyvinylidene fluoride) is one of the earliest and most widely used organic coatings, possessing excellent electrochemical stability, electrolyte affinity, and adhesion. However, it may undergo excessive swelling in carbonate electrolytes, leading to a decrease in coating mechanical strength and changes in pore structure, resulting in poor thermal stability. PMMA (polymethyl methacrylate) molecular chains have strong interactions with carbonate electrolytes, absorbing large amounts of electrolyte and undergoing gelation to form excellent ion transport channels, significantly improving the membrane's liquid retention rate and ionic conductivity. However, it has the worst mechanical strength and thermal stability, and relatively low electrochemical stability.

[0017] Functional organic framework materials, such as covalent organic frameworks (COFs), have been applied to membrane coatings. Compared to inorganic nanomaterials and conventional organic materials, COFs possess a more ordered and uniform pore structure with precisely controllable pore size. The nanoscale pores and high specific surface area increase the contact area with the electrolyte, enhancing liquid absorption and improving rate performance and cycle life. Furthermore, the covalently bonded framework of COFs exhibits excellent thermal stability, enabling it to withstand high temperatures.

[0018] In existing technologies, COF materials are coated onto the membrane surface via surface coating. This method relies on an adhesive for physical adhesion between the coating and the base membrane, resulting in weak bonding. Coating detachment can lead to localized short circuits. Furthermore, ion transport is limited to the COF pores, offering only a limited increase in migration number. The adhesive may also clog some pores, reducing porosity, increasing ion transport resistance, and raising interfacial impedance. Additionally, slurry coating on the base membrane is prone to problems such as agglomeration, cracking, or uneven thickness.

[0019] In the synthesis of functional COFs for battery separators, TP typically undergoes a reversible imine condensation reaction with p-phenylenediamine (BD) to form imine bonds (-C=N-). The COF skeleton consists of benzene rings and imine bonds, exhibiting relatively inert chemical properties and lacking active functional groups. Another method involves the reaction of TP with 1,5-diamino-4,8-dihydroxyanthraquinone (DADHAQ). However, large-planar anthraquinones have significant steric hindrance and structural rigidity, and the quinone groups may interfere with ion pathways, leading to a high risk of reversible redox reactions, side reactions, poor mechanical compatibility with the separator base membrane, brittleness, and high monomer synthesis costs.

[0020] To address the above technical problems, this invention provides a method for preparing a functionalized membrane, comprising the following steps: The membrane base was pretreated by immersion in an aqueous alcohol solution; The pretreated base film was immersed in a mixed aqueous solution of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) and a surfactant to obtain a base film modified with 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride. The base film modified with 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride was immersed in an organic solution of 1,3,5-tricarboxymethyl phloroglucinol (TP). TP and Pa-OH will undergo a Schiff base reaction at the interface between the two phases to obtain a base film with in-situ generated TP-COF. The in-situ generated TP-COF base film is immersed in a solution of succinic anhydride or its derivative to introduce carboxyl groups, thereby obtaining a TP-COF-COOH modified base film. The TP-COF-COOH modified base membrane was impregnated in an alcohol solution of lithium salt to obtain a TP-COF-COOLi functionalized membrane.

[0021] The base membrane of the separator is usually made of polyolefin materials such as polypropylene (PP) or polyethylene (PE). Its surface is highly hydrophobic and lacks active functional groups. When directly growing COF in situ, monomers are difficult to effectively adsorb and react, potentially leading to uneven COF layer growth and weak adhesion. Immersing the base membrane in an aqueous alcohol solution allows the hydroxyl groups (-OH) in the alcohol molecules to interact with molecules on the base membrane surface (e.g., hydrogen bonding or polar adsorption), reducing surface tension and improving the wettability of the base membrane for monomers (such as Pa-OH) in the subsequent aqueous solution. The alcohol-water solution may also create micro-defects or activation sites on the base membrane surface through slight swelling or surface etching, enhancing the adsorption capacity of subsequent monomers and providing an anchoring basis for the in-situ growth of the COF layer.

[0022] When a base film containing Pa-OH (2,5-diamino-1,4-dihydroxyphenyl dihydrochloride) monomer comes into contact with an organic solution of TP (1,3,5-tricarboxymethyl phloroglucinol), the aldehyde group (-CHO) of TP and the amino group (-NH2) of Pa-OH undergo a Schiff base reaction (aldehyde-amine condensation reaction) at the interface, resulting in dehydration and the formation of an imine bond (-C=N-). Subsequently, the imine bond isomerizes to form a more chemically stable β-ketoenamine bond (-C=CN-), ultimately constructing a TP-COF coating with a covalent framework, which grows in situ on the surface and within the pores of the base film. This in-situ reaction achieves integrated bonding between the COF and the base film, eliminating the need for adhesives and improving coating uniformity and adhesion.

[0023] In the TP-COF backbone, the hydroxyl groups (-OH) of the Pa-OH monomer undergo a ring-opening esterification reaction with succinic anhydride (a cyclic anhydride). The ring structure of the succinic anhydride opens, with one carboxyl group forming an ester bond (-O-CO-) with the phenolic hydroxyl group, while the other carboxyl group (-COOH) remains on the COF backbone. This introduces a large number of carboxyl groups (-COOH) onto the TP-COF surface, resulting in a TP-COF-COOH modified base membrane. The introduction of carboxyl groups enhances the wettability and electrolyte retention of the membrane and provides active sites for subsequent ion exchange.

[0024] In TP-COF-COOH, the carboxyl group (-COOH) undergoes an ion exchange reaction in an alcoholic solution of lithium salts (such as LiTFSI). The proton in the carboxyl group is replaced by lithium ions from the solution, forming a lithium carboxylate group (-COOLi). The -COOLi group provides a specific lithium-ion transport pathway, lowers the ion transport barrier, increases the lithium-ion transport number and conductivity, and simultaneously promotes the formation of a stable SEI film while inhibiting lithium dendrite growth. The -COOLi group can be used as a lithium transport pathway in lithium salts. + The jumping sites form a low-energy-barrier lithium-ion conduction network. If sodium salt is used instead of lithium salt for ion exchange, sodium carboxylate (-COONa) modified COF material is obtained. + Will with Li + Competing for transport sites interferes with normal lithium-ion transport, leading to decreased ionic conductivity and increased polarization, thus disrupting lithium-ion conduction channels and weakening the modification effect.

[0025] In some embodiments, the base film is a polypropylene base film or a polyethylene base film.

[0026] In some embodiments, the volume fraction of the alcohol in the aqueous solution is 50%-90%. Preferably, in the aqueous solution of the alcohol, the alcohol is ethanol, isopropanol, n-propanol, n-butanol, or trifluoroethanol.

[0027] Preferably, the base film is pretreated by immersion in an aqueous alcohol solution for 10-60 minutes. By increasing hydrophilicity and active sites, a suitable reaction interface is provided, inducing uniform and dense growth of COF, thus obtaining a pretreated base film.

[0028] In some embodiments, in the mixed aqueous solution of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) and surfactant, the concentration of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride is 0.01wt%-0.2wt%, and the concentration of surfactant is 0.01wt%-1wt%.

[0029] The concentration of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride can be 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.16 wt%, 0.17 wt%, 0.18 wt%, 0.19 wt%, or 0.2 wt%.

[0030] The concentration of the surfactant can be 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, or 0.1wt%.

[0031] Surfactants can reduce the interfacial tension between the aqueous phase (containing Pa-OH monomers) and the substrate surface, making it easier for Pa-OH monomers to diffuse into the substrate surface and pores, ensuring uniform adsorption and enrichment of monomers on the substrate surface. By promoting the uniform distribution of Pa-OH monomers, problems such as local agglomeration or uneven coating thickness during subsequent reactions with Tp monomers are avoided, providing uniform reaction sites for the in-situ formation of a continuous and dense TP-COF coating.

[0032] Preferably, the surfactant is hexadecylpyridinium bromide (CPB), hexadecylpyridinium bromide (CPB), hexadecylpyridinium chloride (CPC), dodecylpyridinium bromide (DPB), sodium dodecyl sulfate (SDS), or sodium α-alkenyl sulfonate (AOS).

[0033] As a cationic surfactant, CPB's long-chain alkyl and pyridinium groups (hydrophilic ends) in its molecular structure can significantly reduce the interfacial tension between the aqueous phase (containing Pa-OH monomers) and the base film surface, making it easier for Pa-OH monomers to diffuse into the base film surface and pores, ensuring uniform adsorption and enrichment of monomers on the base film surface.

[0034] The polar head of CPB can form weak interactions (such as hydrogen bonding or electrostatic attraction) with the amino (-NH2) or hydroxyl (-OH) groups of the Pa-OH monomer, promoting the directional arrangement and uniform distribution of Pa-OH on the substrate film surface. This ordered adsorption avoids defects such as uneven coating thickness and cracking that may occur during subsequent reactions with Tp monomers, ensuring that the TP-COF coating is continuous and dense.

[0035] Preferably, the pretreated base film is immersed in a mixed aqueous solution of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) and a surfactant for 30 min to 120 min. For example, the immersion time can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min.

[0036] In some embodiments, the solvent for the organic solution of 1,3,5-tricarboxymethyl phloroglucinol (TP) is a mixed solvent of 1,4-dioxane and m-xylene, wherein the volume ratio of 1,4-dioxane to m-xylene is 1:0.5-1.5, preferably 1:0.8-1.2. For example, the ratio can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, or 1:1.5.

[0037] 1,4-Dioxane acts as a polar solvent to dissolve TP monomers; however, the solubility of TP in the mixed solvent decreases after it reacts with Pa-OH to form oligomers. The presence of m-xylene causes the COF to precipitate from the solution, thereby driving the reaction equilibrium towards the formation of a higher degree of polymerization product.

[0038] Preferably, in the organic solution of 1,3,5-tricarboxymethyl phloroglucinol (TP), the concentration of TP is 0.01 wt%-0.2 wt%. For example, it can be 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.16 wt%, 0.17 wt%, 0.18 wt%, 0.19 wt%, or 0.2 wt%.

[0039] Preferably, the 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride modified base film is immersed in an organic solution of 1,3,5-tricarboxymethyl phloroglucinol (TP) for 30 min to 120 min. For example, the immersion time can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min.

[0040] In a further preferred embodiment, after the impregnation reaction is completed, the membrane surface is rinsed with methanol to remove unreacted monomers, and then dried to obtain a base membrane in situ generated with TP-COF.

[0041] In some embodiments, the base film for in-situ generation of TP-COF is immersed in a solution of succinic anhydride or its derivative at a temperature of 60°C-100°C for a reaction time of 24-48 hours. The reaction temperature can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C.

[0042] Preferably, the solvent for the succinic anhydride or its derivative solution is anhydrous N,N-dimethylformamide (DMF).

[0043] Succinic anhydride reacts with the hydroxyl groups on the TP-COF backbone to form an ester bond, thereby introducing a carboxyl group.

[0044] Preferably, after the reaction is complete, the membrane is washed with methanol to remove excess reagents, and then dried to obtain the TP-COF-COOH modified base membrane.

[0045] In some embodiments, the alcohol in the lithium salt alcohol solution is anhydrous methanol or anhydrous ethanol; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium difluorooxalate borate (LiDFOB), or lithium tetrafluoroborate (LiBF4).

[0046] Preferably, the concentration of lithium salt in the alcoholic solution is 0.5 mol / L to 1.5 mol / L, more preferably 0.8 mol / L to 1.2 mol / L. For example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, or 1.5 mol / L.

[0047] In some embodiments, the TP-COF-COOH modified base film is immersed in an alcohol solution of lithium salt for 6-24 hours.

[0048] H in the carboxyl group (-COOH) + With Li in solution + Ion exchange occurs, forming lithium carboxylate (-COOLi).

[0049] Preferably, after impregnation, the membrane is rinsed with anhydrous ethanol to remove the physically adsorbed lithium salt on the surface, and finally vacuum dried to obtain the TP-COF-COOLi functionalized membrane.

[0050] Based on the above preparation method, the present invention provides a functionalized diaphragm, which is prepared by the preparation method of the functionalized diaphragm.

[0051] In addition, the present invention also provides a lithium-ion battery, which includes a positive electrode, a negative electrode and a separator, wherein the separator is the functionalized separator.

[0052] The present invention will be further described below with reference to the embodiments.

[0053] Example 1 A method for preparing a functionalized membrane includes the following steps: 1) Immerse the PE base membrane in a mixture of 75% anhydrous ethanol and deionized water for 30 minutes to obtain pretreated membrane A; 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.1 wt%, and add surfactant CPB at a concentration of 0.05 wt%. Immerse membrane A obtained in step 1) completely in the Pa-OH mixed aqueous solution at room temperature for 60 minutes to obtain membrane B containing Pa-OH monomer; 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio) at a concentration of 0.1 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 60 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 80 °C for 8 hours to obtain the membrane C with in-situ TP-COF formation. 4) Dissolve succinic anhydride in anhydrous N,N-dimethylformamide (DMF) at a concentration of 1 mol / L. Immerse the membrane C obtained in step 3) in the above mixture and heat at 80°C for 48 hours. After the reaction is complete, wash the membrane thoroughly with methanol and finally vacuum dry to obtain the TP-COF-COOH modified membrane D; 5) Immerse the membrane D obtained in step 4) in a 1 mol / L LiTFSI alcohol solution for 12 hours at room temperature. Rinse the membrane with anhydrous ethanol and finally vacuum dry to obtain the TP-COF-COOLi functionalized membrane. Its SEM image is shown below. Figure 1 As shown.

[0054] Example 2 A method for preparing a functionalized membrane includes the following steps: 1) Immerse the PE base membrane in a mixture of 75% anhydrous ethanol and deionized water for 30 minutes to obtain pretreated membrane A; 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.01 wt%, and add surfactant CPB at a concentration of 0.05 wt%. Immerse membrane A obtained in step 1) completely in the Pa-OH solution at room temperature for 60 minutes to obtain membrane B containing Pa-OH monomer; 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio) at a concentration of 0.01 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 60 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 80 °C for 8 hours to obtain the membrane C with in-situ TP-COF formation. 4) Dissolve succinic anhydride in anhydrous N,N-dimethylformamide (DMF) at a concentration of 1 mol / L. Immerse the membrane C obtained in step 3) in the above mixture and heat at 80°C for 48 hours. After the reaction is complete, wash the membrane thoroughly with methanol and finally vacuum dry to obtain the TP-COF-COOH modified membrane D; 5) Immerse the membrane D obtained in step 4) in a 1 mol / L LiTFSI alcohol solution and soak for 12 hours at room temperature. Rinse the membrane with anhydrous ethanol and finally vacuum dry to obtain the TP-COF-COOLi functionalized membrane.

[0055] Example 3 A method for preparing a functionalized membrane includes the following steps: 1) Immerse the PE base membrane in a mixture of 75% anhydrous ethanol and deionized water for 30 minutes to obtain pretreated membrane A; 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.2 wt%, and add surfactant CPB at a concentration of 0.05 wt%. Immerse membrane A obtained in step 1) completely in the Pa-OH solution at room temperature for 60 minutes to obtain membrane B containing Pa-OH monomer; 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio) at a concentration of 0.2 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 60 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 80 °C for 8 hours to obtain the membrane C with in-situ TP-COF formation. 4) Dissolve succinic anhydride in anhydrous N,N-dimethylformamide (DMF) at a concentration of 1 mol / L. Immerse the membrane C obtained in step 3) in the above mixture and heat at 80°C for 48 hours. After the reaction is complete, wash the membrane thoroughly with methanol and finally vacuum dry to obtain the TP-COF-COOH modified membrane D; 5) Immerse the membrane D obtained in step 4) in a 1 mol / L LiTFSI alcohol solution and soak for 12 hours at room temperature. Rinse the membrane with anhydrous ethanol and finally vacuum dry to obtain the TP-COF-COOLi functionalized membrane.

[0056] Example 4 A method for preparing a functionalized membrane includes the following steps: 1) Immerse the PE base membrane in a mixture of 75% anhydrous ethanol and deionized water for 30 minutes to obtain pretreated membrane A; 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.1 wt%, and add surfactant CPB at a concentration of 0.05 wt%. Immerse membrane A obtained in step 1) completely in the Pa-OH solution at room temperature for 30 minutes to obtain membrane B containing Pa-OH monomer; 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio) at a concentration of 0.1 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 30 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 60 °C for 6 hours to obtain the membrane C with in-situ TP-COF formation. 4) Dissolve succinic anhydride in anhydrous N,N-dimethylformamide (DMF) at a concentration of 1 mol / L. Immerse the membrane C obtained in step 3) in the above mixture and heat at 60°C for 24 hours. After the reaction is complete, wash the membrane thoroughly with methanol and finally vacuum dry to obtain the TP-COF-COOH modified membrane D; 5) Immerse the membrane D obtained in step 4) in a 1 mol / L LiTFSI alcohol solution and soak for 6 hours at room temperature. Rinse the membrane with anhydrous ethanol and finally vacuum dry to obtain the TP-COF-COOLi functionalized membrane.

[0057] Example 5 A method for preparing a functionalized membrane includes the following steps: 1) Immerse the PE base membrane in a mixture of 75% anhydrous ethanol and deionized water for 30 minutes to obtain pretreated membrane A; 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.1 wt%, and add surfactant CPB at a concentration of 0.05 wt%. Immerse membrane A obtained in step 1) completely in the Pa-OH solution at room temperature for 120 minutes to obtain membrane B containing Pa-OH monomer; 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio) at a concentration of 0.1 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 120 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 100°C for 12 hours to obtain the membrane C with in-situ TP-COF formation. 4) Dissolve succinic anhydride in anhydrous N,N-dimethylformamide (DMF) at a concentration of 1 mol / L. Immerse the membrane C obtained in step 3) in the above mixture and heat at 100°C for 48 hours. After the reaction is complete, wash the membrane thoroughly with methanol and finally vacuum dry to obtain the TP-COF-COOH modified membrane D; 5) Immerse the membrane D obtained in step 4) in a 1 mol / L LiTFSI alcohol solution and soak for 24 hours at room temperature. Rinse the membrane with anhydrous ethanol and finally vacuum dry to obtain the TP-COF-COOLi functionalized membrane.

[0058] Comparative Example 1 1) Dissolve 0.1 wt% of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) and 0.1 wt% of 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio), and sonicate for 10 min. Degas using a three-stage freeze-thaw cycle and seal under vacuum. Heat at 120 °C for 72 h, collect the product by centrifugation, wash with methanol, and then vacuum dry at 80 °C for 8 h to obtain TP-COF powder; 2) Dissolve succinic anhydride in anhydrous N,N-dimethylformamide (DMF) at a concentration of 1 mol / L. Immerse the TP-COF powder obtained in step 1) into the above mixture and heat at 80°C for 48 hours. After the reaction is complete, wash thoroughly with methanol and finally vacuum dry to obtain TP-COF-COOH powder; 3) Dissolve the TP-COF-COOH powder and PVDF (8:1 weight ratio) obtained in step 2) in N-methylpyrrolidone (NMP) and stir for 12 h to obtain a uniform TP-COF-COOH slurry. Then, uniformly coat the obtained slurry on both sides of the PE base film and heat at 60°C for 8 hours to obtain a TP-COF-COOH coated membrane.

[0059] 4) Immerse the membrane D obtained in step 3) in a 1 mol / L LiTFSI alcohol solution and soak for 12 hours at room temperature. Rinse the membrane with anhydrous ethanol and finally vacuum dry to obtain the TP-COF-COOLi functionalized membrane.

[0060] Comparative Example 2 1) Dissolve 0.1 wt% p-diaminobiphenyl (BD) and 0.1 wt% 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio), and sonicate for 10 min. Degas using a three-stage freeze-thaw cycle and seal under vacuum. Heat at 120 °C for 72 h, collect the product by centrifugation, wash with methanol, and then vacuum dry at 80 °C for 8 h to obtain TP-BD-COF powder; 2) Dissolve the TP-BD-COF powder and PVDF (8:1 weight ratio) obtained in step 1) in N-methylpyrrolidone (NMP) and stir for 12 h to obtain a uniform TP-BD-COF slurry. Then, uniformly coat the obtained slurry on both sides of the PE base film and heat at 60°C for 8 hours to obtain a TP-BD-COF coated membrane.

[0061] Comparative Example 3 The difference from Example 1 is that in step 5), the sample is immersed in a LiTFSI alcohol solution; otherwise, the sample is the same as in Example 1.

[0062] 1) Immerse the PE base membrane in a mixture of 75% anhydrous ethanol and deionized water for 30 minutes to obtain pretreated membrane A; 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.1 wt%, and add surfactant CPB at a concentration of 0.05 wt%. Immerse membrane A obtained in step 1) completely in the Pa-OH solution at room temperature for 60 minutes to obtain membrane B containing Pa-OH monomer; 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio) at a concentration of 0.1 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 60 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 80 °C for 8 hours to obtain the membrane C with in-situ TP-COF formation. 4) Dissolve succinic anhydride in anhydrous N,N-dimethylformamide (DMF) at a concentration of 1 mol / L. Immerse the membrane C obtained in step 3) in the above mixture and heat at 80°C for 48 hours. After the reaction is complete, wash the membrane thoroughly with methanol and finally vacuum dry to obtain the TP-COF-COOH modified membrane D; 5) Immerse the membrane D obtained in step 4) in a 1 mol / L NaPF6 alcohol solution and soak for 12 hours at room temperature. Rinse the membrane with anhydrous ethanol and finally vacuum dry to obtain the TP-COF-COONa functionalized membrane.

[0063] Comparative Example 4 The difference from Example 1 is that step 5 is omitted, while everything else is the same as in Example 1.

[0064] The specific preparation method includes the following steps: 1) Immerse the PE base membrane in a mixture of 75% anhydrous ethanol and deionized water for 30 minutes to obtain pretreated membrane A; 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.1 wt%, and add surfactant CPB at a concentration of 0.05 wt%. Immerse membrane A obtained in step 1) completely in the Pa-OH solution at room temperature for 60 minutes to obtain membrane B containing Pa-OH monomer; 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio) at a concentration of 0.1 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 60 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 80 °C for 8 hours to obtain the membrane C with in-situ TP-COF formation. 4) Dissolve succinic anhydride in anhydrous N,N-dimethylformamide (DMF) at a concentration of 1 mol / L. Immerse the membrane C obtained in step 3) in the above mixture and heat at 80°C for 48 hours. After the reaction is complete, wash the membrane thoroughly with methanol and finally dry under vacuum to obtain the TP-COF-COOH modified membrane D.

[0065] Comparative Example 5 The difference from Example 1 is that steps 4) and 5) are omitted; all other steps are the same as in Example 1. The specific preparation method includes the following steps: 1) Immerse the PE base membrane in a mixture of 75% anhydrous ethanol and deionized water for 30 minutes to obtain pretreated membrane A; 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.1 wt%, and add surfactant CPB at a concentration of 0.05 wt%. Immerse membrane A obtained in step 1) completely in the Pa-OH solution at room temperature for 60 minutes to obtain membrane B containing Pa-OH monomer; 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in a mixed organic solvent of 1,4-dioxane and m-xylene (1:1 volume ratio) at a concentration of 0.1 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 60 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 80 °C for 8 hours to obtain the membrane C with in-situ TP-COF formation.

[0066] Comparative Example 6 The difference from Example 1 is that in step 3), the m-xylene in the mixed organic solvent is replaced with 1,4-dioxane, while everything else is the same as in Example 1.

[0067] Specifically: 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in 1,4-dioxane at a concentration of 0.1 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 60 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 80 °C for 8 hours to obtain the membrane C with in-situ TP-COF formation.

[0068] Comparative Example 7 The difference from Example 1 is that in step 3), 1,4-dioxane in the mixed organic solvent is replaced with m-xylene, while everything else is the same as in Example 1.

[0069] Specifically: 3) Dissolve 1,3,5-tricarboxymethyl phloroglucinol (TP) in m-xylene at a concentration of 0.1 wt%. Immerse the membrane B obtained in step 2) in the organic phase solution of TP for 60 minutes at room temperature. After the reaction is complete, rinse the membrane surface with methanol and then vacuum dry at 80 °C for 8 hours to obtain the membrane C with in-situ TP-COF formation.

[0070] Comparative Example 8 The difference from Example 1 is that step 1 is omitted, while everything else is the same as in Example 1.

[0071] Comparative Example 9 The difference from Example 1 is that in step 2), the surfactant is omitted, while everything else is the same as in Example 1.

[0072] Specifically: 2) Dissolve 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride (Pa-OH) in deionized water to a concentration of 0.1 wt%. Immerse the membrane A obtained in step 1) completely in the Pa-OH solution at room temperature for 60 minutes to obtain membrane B containing Pa-OH monomer.

[0073] The relevant performance data of the diaphragms prepared in the examples and comparative examples are shown in Table 1.

[0074] Table 1. Ionic conductivity, contact angle, air permeability, tensile strength, and heat shrinkage of the examples and comparative examples.

[0075] As shown in Table 1, the functionalized membrane material obtained through the embodiments of the present invention has higher ionic conductivity, lower electrolyte contact angle, higher tensile strength, and lower thermal shrinkage.

[0076] A negative electrode slurry was prepared by mixing graphite composite negative electrode material, conductive agent SP, binder SBR, and binder CMC in deionized water at a mass ratio of 96.2:1:1.5:1.3. This slurry was coated onto copper foil, dried, and then rolled to obtain a negative electrode sheet. A positive electrode slurry was prepared by mixing lithium iron phosphate, conductive agent SP, and binder PVDF in N-methylpyrrolidone at a mass ratio of 97:1:2. This slurry was coated onto aluminum foil, dried, and then rolled to obtain a positive electrode sheet. The sheets were stacked in the order of "negative electrode-separator-positive electrode," with separators selected from Examples 1-5 and Comparative Examples 1-5. After welding the tabs, an aluminum-plastic film was inserted, and the top and sides were pre-sealed. The battery cell was vacuum-dried at 80°C for 24 hours, and then injected with an electrolyte solution of 1M LiPF6 dissolved in a mixed solution of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate at a volume ratio of 3:5:2. After vacuuming, the injection port was sealed to obtain a 3Ah soft-pack battery.

[0077] The prepared pouch cells were subjected to DCR, rate discharge, cycle performance and thermal runaway tests. The test results are shown in Table 2.

[0078] Table 2 Performance data of pouch batteries

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a functionalized membrane, characterized in that: Includes the following steps: The membrane base was pretreated by immersion in an aqueous alcohol solution; The pretreated base film was immersed in a mixed aqueous solution of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride Pa-OH and a surfactant to obtain a base film modified with 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride. The 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride modified base film was immersed in an organic solution of 1,3,5-tricarboxymethyl phloroglucinol (TP). TP and Pa-OH underwent a Schiff base reaction at the two-phase interface to obtain a base film with in-situ generated TP-COF. The in-situ generated TP-COF base film is immersed in a solution of succinic anhydride or its derivative to introduce carboxyl groups, thereby obtaining a TP-COF-COOH modified base film. The TP-COF-COOH modified base membrane was impregnated in an alcohol solution of lithium salt to obtain a TP-COF-COOLi functionalized membrane.

2. The method for preparing the functionalized membrane according to claim 1, characterized in that: The base film is a polypropylene base film or a polyethylene base film.

3. The method for preparing the functionalized membrane according to claim 1, characterized in that: In the aqueous solution of the alcohol, the volume fraction of the alcohol is 50%-90%; Alternatively, in the aqueous solution of the alcohol, the alcohol is ethanol, isopropanol, n-propanol, n-butanol, or trifluoroethanol; Alternatively, the base film can be pretreated by immersion in an aqueous alcohol solution for 10-60 minutes.

4. The method for preparing the functionalized membrane according to claim 1, characterized in that: In the mixed aqueous solution of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride and surfactant, the concentration of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride is 0.01wt%-0.2wt%, and the concentration of surfactant is 0.01wt%-1wt%. Alternatively, the surfactant may be hexadecylpyridinium bromide, hexadecylpyridinium bromide, hexadecylpyridinium chloride, dodecylpyridinium bromide, sodium dodecyl sulfate, or sodium α-alkenyl sulfonate. Alternatively, the pretreated base film is immersed in a mixed aqueous solution of 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride and surfactant for 30-120 minutes.

5. The method for preparing the functionalized membrane according to claim 1, characterized in that: The organic solution of 1,3,5-tricarboxymethyl phloroglucinol is a mixed solvent of 1,4-dioxane and m-xylene, with a volume ratio of 1:0.5-1.

5. Alternatively, in an organic solution of 1,3,5-tricarboxymethyl phloroglucinol, the concentration of TP is 0.01 wt%–0.2 wt%. Alternatively, the base film modified with 2,5-diamino-1,4-dihydroxyphenyl dihydrochloride is immersed in an organic solution of 1,3,5-tricarboxymethyl phloroglucinol for 30 min to 120 min. Alternatively, after the impregnation reaction is complete, the membrane surface is rinsed with methanol to remove unreacted monomers, and then dried to obtain the base membrane with in-situ TP-COF generation.

6. The method for preparing the functionalized membrane according to claim 1, characterized in that: The base film of in-situ generated TP-COF is immersed in a solution of succinic anhydride or its derivative at a temperature of 60℃-100℃ for a reaction time of 24h-48h. Alternatively, the solvent for the succinic anhydride or its derivative solution is anhydrous N,N-dimethylformamide; Alternatively, after the reaction is complete, the membrane is washed with methanol to remove excess reagents, and then dried to obtain the TP-COF-COOH modified base membrane.

7. The method for preparing the functionalized membrane according to claim 1, characterized in that: In the alcohol solution of the lithium salt, the alcohol is anhydrous methanol or anhydrous ethanol; the lithium salt is lithium bis(trifluoromethanesulfonylimide), lithium hexafluorophosphate, lithium difluorooxalate borate, or lithium tetrafluoroborate. Alternatively, in the alcoholic solution of the lithium salt, the concentration of the lithium salt is 0.5 mol / L to 1.5 mol / L.

8. The method for preparing the functionalized membrane according to claim 7, characterized in that: The TP-COF-COOH modified base film was immersed in an alcohol solution of lithium salt for 6-24 hours.

9. A functionalized diaphragm, characterized in that: It is prepared by the method of preparing the functionalized diaphragm according to any one of claims 1-8.

10. A lithium-ion battery, characterized in that: It includes a positive electrode, a negative electrode, and a separator, wherein the separator is the functionalized separator as described in claim 9.

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