A magnesium hydroxide-based high-safety lithium ion battery diaphragm and a preparation process thereof

Abstract

The application discloses a magnesium hydroxide-based high-safety lithium ion battery diaphragm and a preparation process thereof, and belongs to the technical field of lithium ion battery materials. The magnesium hydroxide-based high-safety lithium ion battery diaphragm comprises a polyolefin-based film and a composite functional coating attached to the surface of the polyolefin-based film. In the application, the surface of magnesium hydroxide is chemically grafted and modified by using a specific silane coupling agent, so that the interface compatibility between the inorganic filler and the organic matrix and the binder is obviously improved. The chemical bond formed by the hydrolysis product of silane and the hydroxyl group on the surface of magnesium hydroxide is used to introduce an organic molecular layer on the surface of the inorganic particles, effectively reduces the surface energy and inhibits the particle agglomeration, and thus the dispersion uniformity of the filler in the coating slurry is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a magnesium hydroxide-based high-safety lithium-ion battery separator and its preparation process. Background Technology

[0002] With the rapid development of new energy vehicles and portable electronic devices, the energy density of lithium-ion batteries is constantly improving, and their safety performance, especially thermal runaway, is receiving increasing attention. As a key component separating the positive and negative electrodes inside the battery, the thermal stability of the separator directly determines the battery's safety. Traditional polyolefin microporous membranes (such as polyethylene PE and polypropylene PP), while possessing good mechanical strength and chemical stability, have low melting points and are prone to severe thermal shrinkage or even melting and rupture at high temperatures. This can lead to direct contact between the positive and negative electrodes, causing a short circuit and potentially resulting in battery fire or explosion.

[0003] To address this issue, existing technologies typically coat the surface of polyolefin membranes with a layer of inorganic ceramic particles to enhance heat resistance. Magnesium hydroxide, with its endothermic thermal decomposition, flame retardant properties, and smoke suppression characteristics, is considered an ideal high-safety functional coating material. However, commercially available magnesium hydroxide powder is an inorganic polar material with a large number of hydrophilic hydroxyl groups on its surface, while the polyolefin membrane matrix and commonly used coating binders are mostly non-polar or weakly polar organic materials. This significant difference in surface energy results in poor dispersion stability of magnesium hydroxide in organic solvents or binder systems, making it highly susceptible to severe agglomeration. During use, this lack of interfacial compatibility leads to insufficient adhesion strength between the ceramic coating and the base membrane, easily causing coating peeling, powdering, or cracking. This not only damages the integrity of the membrane but may also cause micro-short circuits due to particle detachment puncturing the membrane.

[0004] Furthermore, while traditional ceramic coatings improve the heat resistance of the separator, the dense particle accumulation often blocks the original microporous structure of the separator, increasing the resistance to lithium-ion transport and leading to increased internal resistance, reduced rate performance, and decreased cycle life. Although some studies have attempted to introduce metal-organic frameworks (MOFs) with abundant pore structures to improve ion conduction and electrolyte wettability, existing technologies mostly employ simple physical blending methods. Due to the lack of effective chemical bonding, MOF particles are difficult to achieve stable loading on the surface of the separator or ceramic filler, and are prone to migration and detachment during long-term battery cycling with electrolyte flow, failing to simultaneously achieve high safety and excellent electrochemical performance. Therefore, developing a modified magnesium hydroxide composite material that can significantly enhance interfacial adhesion, prevent coating detachment, and synergistically improve heat resistance, safety, and ion transport efficiency is a pressing technical challenge in the field of high-performance lithium-ion battery separators. Summary of the Invention

[0005] This invention aims to solve the technical problems of poor interfacial compatibility between magnesium hydroxide filler and organic matrix in existing lithium-ion battery ceramic separator coatings, easy agglomeration and detachment, and dense accumulation blocking pores, leading to a decline in battery performance. It provides a magnesium hydroxide-based high-safety lithium-ion battery separator with strong interfacial bonding and excellent heat resistance, safety and ion transport performance, as well as its preparation process.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] 1. A magnesium hydroxide-based high-safety lithium-ion battery separator, characterized in that it comprises a polyolefin-based membrane and a composite functional coating attached to the surface of the polyolefin-based membrane; The coating slurry used to prepare the composite functional coating comprises the following components in parts by weight: 30 to 60 parts of silane coupling agent-modified magnesium hydroxide composite filler for amino-functionalized metal-organic framework material MOF-5-NH2. 2 to 10 parts adhesive; Thickener 0.5 to 3 parts; 0.5 to 2 parts of dispersant; 0.1 to 1 part wetting agent; Solvent: 100 to 300 parts; The silane coupling agent modified magnesium hydroxide composite filler of the amino-functionalized metal-organic framework material MOF-5-NH2 is prepared by magnesium hydroxide, silane coupling agent and amino-functionalized metal-organic framework material MOF-5-NH2.

[0008] Furthermore, the polyolefin-based membrane is selected from one of polyethylene microporous membrane, polypropylene microporous membrane, and multilayer composite microporous membrane of polyethylene and polypropylene; The adhesive is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, polyacrylic acid, polymethyl methacrylate, and polyacrylonitrile.

[0009] Furthermore, the thickener is selected from one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, and guar gum; The dispersant is selected from one or more of sodium polyacrylate, polyvinylpyrrolidone, polyvinyl alcohol, and sodium dodecylbenzenesulfonate; The wetting agent is selected from one or more of octylphenol polyoxyethylene ether, polyether-modified siloxane, and fluorocarbon surfactant.

[0010] Furthermore, the solvent is selected from one or more of deionized water, N-methylpyrrolidone, acetone, and dimethylacetamide; When the solvent system contains deionized water, it is preferable to control the water content to ≤20 vol%, and to avoid framework hydrolysis and deactivation by shortening the contact time between MOF and the aqueous phase, using ethanol pre-dispersion, or performing surface hydrophobic coating / stabilization treatment on MOF. The silane coupling agent is selected from one or more of (3-aminopropyl)triethoxysilane, (3-glycidoxypropyl)trimethoxysilane, and (3-isocyanatepropyl)triethoxysilane.

[0011] Furthermore, in the silane coupling agent modified magnesium hydroxide composite filler of the amino-functionalized metal-organic framework material MOF-5-NH2, the mass ratio of silane coupling agent modified magnesium hydroxide to amino-functionalized metal-organic framework material MOF-5-NH2 is 99.9:0.1-70:30.

[0012] A method for preparing a magnesium hydroxide-based high-safety lithium-ion battery separator includes the following steps: Step 1, Magnesium hydroxide pretreatment and activation: Take magnesium hydroxide powder and add it to a mixed solvent prepared by deionized water and anhydrous ethanol for dispersion. Adjust the pH value of the system to 8.0 to 10.5 and stir at 40 to 80 degrees Celsius for 0.5 to 2 hours. Filter, wash and dry to obtain activated magnesium hydroxide. Step 2, silane coupling agent hydrolysis: The silane coupling agent is added to a mixed solvent of ethanol and water to prepare a hydrolysis solution, the pH value is adjusted to 3.5 to 5.5, and the solution is stirred and hydrolyzed at 20 to 40 degrees Celsius for 10 to 60 minutes to obtain a hydrolyzed silane solution containing silanol. Step 3, Silane grafting modified magnesium hydroxide: The activated magnesium hydroxide obtained in Step 1 is added to the hydrolyzed silane solution obtained in Step 2 to react, so that the silane hydrolysis product condenses with the hydroxyl groups on the surface of the activated magnesium hydroxide. After the reaction is completed, the magnesium hydroxide is washed and heat-treated to solidify, thus obtaining silane-modified magnesium hydroxide with silane organic end groups on the surface. Step 4, Dispersion pretreatment of amino-functionalized metal-organic framework material MOF-5-NH2: The amino-functionalized metal-organic framework material MOF-5-NH2 powder is placed in an anhydrous organic solvent to prepare MOF dispersion. Step 5, Coupling and anchoring of amino-functionalized metal-organic framework material MOF-5-NH2 with silane-modified magnesium hydroxide: The silane-modified magnesium hydroxide obtained in Step 3 is added to the MOF dispersion obtained in Step 4 and stirred to react. The functional groups of the silane coupling agent covalently bond or strongly interact with the amino groups on the surface of the amino-functionalized metal-organic framework material MOF-5-NH2 to form adsorption (hydrogen bonding / electrostatic interaction and van der Waals forces). After the reaction, the mixture is separated, washed and dried to obtain the silane coupling agent modified magnesium hydroxide composite filler of amino-functionalized metal-organic framework material MOF-5-NH2. Step 6, preparation and application of coating slurry: The composite filler, binder, thickener, dispersant and wetting agent obtained in step 5 are added to a solvent and stirred and dispersed to obtain a coating slurry. The slurry is then coated on the surface of a polyolefin-based membrane, and the membrane is obtained after drying and removing the solvent.

[0013] In step five, the organic end groups of the silane coupling agent are used to achieve coupling and anchoring with the functional groups on the surface of MOF-5-NH2. When the silane coupling agent is epoxy or isocyanate group, it can undergo ring-opening addition or urea / carbamate reaction with the -NH2 on the surface of MOF-5-NH2 to form covalent bonds. When the silane coupling agent is amino type, it mainly achieves strong adsorption through hydrogen bonding / electrostatic interaction and van der Waals forces, and is not limited to -NH2-NH2 condensation bonding.

[0014] Furthermore, in step one, the volume ratio of deionized water to anhydrous ethanol is 1:7-3:9, and the solid-liquid ratio is 1 to 10 parts by mass of magnesium hydroxide powder corresponding to 100 to 500 parts by volume of mixed solvent. The concentration of the hydrolysate in step two is 0.5% to 10%, and the volume ratio of ethanol to water is 80:20-98:2.

[0015] Furthermore, in step three, the amount of silane coupling agent used is 0.5% to 15% of the mass fraction of activated magnesium hydroxide, the reaction temperature is 40 to 85 degrees Celsius, and the reaction time is 1 to 6 hours; the heat treatment curing temperature is 80 to 140 degrees Celsius, and the time is 2 to 8 hours.

[0016] Furthermore, the anhydrous organic solvent in step four is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, anhydrous ethanol, and acetone, and the concentration of the MOF dispersion is 0.1 to 10 mg per milliliter; the temperature of the stirring reaction in step five is 20 to 70 degrees Celsius, and the time is 1 to 12 hours.

[0017] Furthermore, the coating method described in step six is ​​selected from gravure coating, dip coating, and spray coating; the drying temperature is 60 to 120 degrees Celsius.

[0018] The magnesium hydroxide-based high-safety lithium-ion battery separator described in this invention is suitable for use in electric vehicles and other motor vehicles, excluding applications in fuel cell vehicles, and / or the manufacture of electric vehicle energy storage devices.

[0019] This invention achieves significant synergistic effects through multiple interfacial chemical modifications and core-shell structure construction: First, by utilizing the silanol groups generated from the hydrolysis of silane coupling agents to undergo an in-situ condensation reaction with the hydroxyl groups on the surface of activated magnesium hydroxide, a strong Si-O-Mg chemical bond is constructed. This not only effectively reduces the surface energy of the inorganic filler to inhibit agglomeration, but also significantly enhances the interfacial compatibility and adhesion strength between the coating and the polyolefin-based film and adhesive through the introduction of organic functional groups, solving the mechanical stability problem of easy peeling and powdering of traditional ceramic coatings; Second, based on a coupling anchoring strategy, the organic end groups at the end of the silane coupling agent achieve covalent bonding with the surface functional groups of MOF-5-NH2. Or strong interaction adsorption allows MOF fine particles (preferably nanoscale) to be stably loaded on the surface of magnesium hydroxide carrier, avoiding migration / detachment caused by simple physical blending; ultimately, this composite material combines the high-temperature endothermic decomposition and flame-retardant properties of the magnesium hydroxide core with the high specific surface area and ordered pore structure of the MOF shell. While using the magnesium hydroxide skeleton to resist high-temperature thermal shrinkage and ensure battery safety, the MOF pores are used as electrolyte reservoirs and rapid lithium-ion transport channels, overcoming the defect of increased internal resistance caused by the accumulation of dense ceramic particles clogging the micropores of the separator. Thus, a synergistic improvement in high safety, long cycle life and excellent rate performance is achieved in a single material system.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention significantly improves the interfacial compatibility between inorganic fillers, organic matrices, and binders by using a specific silane coupling agent to chemically graft magnesium hydroxide onto the surface. Utilizing the chemical bonds formed by the condensation of silane hydrolysis products and hydroxyl groups on the magnesium hydroxide surface, an organic molecular layer is introduced onto the surface of inorganic particles, effectively reducing surface energy and inhibiting particle agglomeration, thereby significantly improving the uniformity of filler dispersion in the coating slurry. This not only enhances the interfacial bonding strength between the functional coating and the polyolefin-based film but also effectively solves the technical problems of peeling, powdering, and brittleness that easily occur in traditional ceramic coatings during use, significantly improving the mechanical stability and processing performance of the diaphragm.

[0021] 2. This invention utilizes a coupling and anchoring strategy to achieve stable loading of functional metal-organic framework (MOF) materials on an inorganic carrier surface, solving the problem of easy detachment and loss of MOF particles. Covalent bonds are formed through chemical reactions between the active functional groups such as epoxy / isocyanate groups at the ends of the silane coupling agent and the -NH2 on the MOF-5-NH2 surface; for amino-type silanes, strong adsorption and anchoring are mainly achieved through hydrogen bonding / electrostatic interactions, thus ensuring that the MOF material is firmly loaded onto the magnesium hydroxide surface. This structural design not only prevents the aggregation of nanoscale MOF particles but also ensures that they do not migrate or detach with electrolyte flow during long-term charge-discharge cycles, guaranteeing the integrity of the separator microstructure and the long-term effectiveness of its function. 3. The separator prepared by this invention successfully balances high safety and excellent electrochemical performance, overcoming the shortcomings of traditional ceramic coatings that sacrifice ion transport efficiency for thermal stability. The magnesium hydroxide core in the composite filler acts as a heat-resistant framework, significantly improving the separator's high-temperature thermal shrinkage resistance and flame-retardant short-circuit protection capabilities through endothermic decomposition and physical barrier effects. Meanwhile, the outer layer loaded with MOF material, with its high porosity and ordered pore structure, serves as a high-speed channel for electrolyte storage and ion transport, effectively improving the separator's wettability and reducing lithium-ion migration resistance. This, in turn, significantly improves battery rate performance and cycle life while enhancing battery safety. Detailed Implementation

[0022] The following will provide a clear and complete description of the technical solutions of this invention. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0023] Example 1 This embodiment provides the raw material composition and preparation method of a magnesium hydroxide-based high-safety lithium-ion battery separator: 1. Raw material composition (by weight): Amino-functionalized metal-organic framework material MOF-5-NH2 with silane coupling agent-modified magnesium hydroxide composite filler: 45 parts; Polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) - binder: 5 parts; Sodium carboxymethyl cellulose - thickener: 1.5 parts; Polyvinylpyrrolidone (PVP) - Dispersant: 1 part; Polyether-modified siloxane - wetting agent: 0.5 parts; N-Methylpyrrolidone - Solvent: 150 parts; In the silane coupling agent modified magnesium hydroxide composite filler of the amino-functionalized metal-organic framework material MOF-5-NH2, the mass ratio of silane-modified magnesium hydroxide to MOF-5-NH2 is 85:15.

[0024] 2. Preparation of amino-functionalized metal-organic framework material MOF-5-NH2: 2.97 g of zinc nitrate hexahydrate and 1.81 g of 2-aminoterephthalic acid were dissolved in 100 mL of N,N-dimethylformamide and magnetically stirred for 30 minutes at room temperature to form a homogeneous solution. 1.0 mL of glacial acetic acid and 0.20 g of polyvinylpyrrolidone (PVP) (molecular weight approximately 40,000) were added, and stirring was continued for 10 minutes. The solution was transferred to a 250 mL stainless steel autoclave lined with polytetrafluoroethylene, sealed, and placed in an oven at 120 °C for 24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The product was washed three times with DMF (50 mL each time) by centrifugation, then three times with anhydrous methanol (50 mL each time), and finally dried under vacuum at 60 °C for 12 hours to obtain a white crystalline powder, MOF-5-NH2, with a yield of 65%.

[0025] 3. Preparation method of composite functional coating: Step 1, Magnesium hydroxide pretreatment and activation: Magnesium hydroxide powder with an average particle size of 1.5 μm (the median volume diameter D measured by a laser particle size analyzer) is pretreated and activated. 50 =1.5μm; the dispersion medium was ethanol, and the sample was tested after ultrasonic pre-dispersion for 5 min. 50g of the sample was added to a mixed solvent prepared by 200mL of deionized water and 600mL of anhydrous ethanol (the volume ratio of deionized water to anhydrous ethanol was 1:3). The pH of the system was adjusted to 9.0 using 10% ammonia water. The mixture was stirred at 500rpm for 1.5 hours in a 60℃ water bath. After filtration, the sample was washed three times with 50mL of anhydrous ethanol each time. The sample was then dried in a vacuum drying oven at 80℃ for 6 hours to obtain 48.5g of activated magnesium hydroxide.

[0026] Step 2, Silane Coupling Agent Hydrolysis: Add 3.0g of (3-aminopropyl)triethoxysilane (KH-550) to a mixed solvent prepared by 190mL of anhydrous ethanol and 10mL of deionized water (ethanol to water volume ratio of 95:5) to prepare a 1.5% hydrolysis solution. Adjust the pH value to 4.0 with glacial acetic acid and hydrolyze at 300rpm for 30 minutes under 30℃ water bath conditions to obtain a silane hydrolysate solution containing silanol.

[0027] Step 3, Silane-grafted modified magnesium hydroxide: 48.5g of activated magnesium hydroxide obtained in Step 1 was added to the hydrolyzed silane solution obtained in Step 2. The mixture was stirred at 400rpm for 3 hours in a 70℃ water bath to allow the silane hydrolysis product to undergo a condensation reaction with the hydroxyl groups on the surface of the activated magnesium hydroxide. After the reaction, the product was washed four times (100mL each time) with anhydrous ethanol by centrifugation. The solid product was collected and heat-treated in a 100℃ vacuum drying oven for 4 hours to obtain 49.2g of silane-modified magnesium hydroxide with aminopropylsilane organic end groups on its surface.

[0028] Step 4, dispersion pretreatment of amino-functionalized metal-organic framework material MOF-5-NH2: 1.5g of MOF-5-NH2 powder prepared in step 2 was placed in 150mL of anhydrous ethanol to prepare a MOF dispersion with a concentration of 10mg / mL. The dispersion was ultrasonically dispersed for 30 minutes (ultrasonic power 200W, working frequency 40kHz) to obtain a uniformly dispersed MOF suspension.

[0029] Step 5: Coupling and anchoring of the amino-functionalized metal-organic framework material MOF-5-NH2 with silane-modified magnesium hydroxide: 8.5 g of the silane-modified magnesium hydroxide obtained in Step 3 was added to the MOF dispersion obtained in Step 4, and the mixture was stirred at 350 rpm for 6 hours in a 50℃ water bath. After the reaction, the mixture was centrifuged (8000 rpm for 10 minutes), washed three times with anhydrous ethanol (50 mL each time), and the solid product was collected and dried in a vacuum drying oven at 70℃ for 8 hours to obtain 9.8 g of the amino-functionalized metal-organic framework material MOF-5-NH2 with silane coupling agent-modified magnesium hydroxide composite filler.

[0030] Step 6, preparation and application of coating slurry: 45g of the composite filler obtained in Step 5, 5g of polyvinylidene fluoride-hexafluoropropylene copolymer binder, 1.5g of sodium carboxymethyl cellulose thickener, 1g of polyvinylpyrrolidone dispersant, and 0.5g of polyether-modified siloxane wetting agent are added sequentially to 150g of N-methylpyrrolidone solvent. The mixture is stirred and dispersed at 800 rpm for 2 hours at room temperature, then ultrasonically dispersed for 30 minutes (ultrasonic power 300W, working frequency 40kHz), and finally stirred at 1200 rpm for 1 hour to obtain a uniform coating slurry with a solid content of approximately 25wt%. The viscosity of the slurry is controlled at 3000mPa·s.

[0031] The above-mentioned coating slurry was applied to one side of a 12 μm thick polyethylene microporous membrane (PE, porosity 40%, average pore size 0.1 μm) using a gravure coating method. The coating speed was 5 m / min, the coating gap was 80 μm, and the wet film thickness after coating was approximately 25 μm. The coated membrane was then dried in an 80℃ oven for 10 minutes, followed by a second drying in a 100℃ oven for 5 minutes to fully remove the solvent, resulting in a magnesium hydroxide-based high-safety lithium-ion battery separator.

[0032] Example 2 This embodiment provides the raw material composition and preparation method of a magnesium hydroxide-based high-safety lithium-ion battery separator. Referring to the steps of Example 1, the silane coupling agent is replaced with (3-glycidoxypropyl)trimethoxysilane (KH-560), and the rest remains the same as in Example 1.

[0033] Example 3 This embodiment provides the raw material composition and preparation method of a magnesium hydroxide-based high-safety lithium-ion battery separator. Referring to the steps of Example 1, the polyolefin-based membrane is replaced with a polypropylene microporous membrane (PP), and the solvent is replaced with a mixed solvent of deionized water and anhydrous ethanol (volume ratio of deionized water: anhydrous ethanol = 1:9) to reduce the influence of water on the zinc-based MOF skeleton. Furthermore, MOF-5-NH2 is always pre-dispersed in anhydrous ethanol before being added to the slurry system, and the contact time with the aqueous phase is controlled to be ≤30 min. Subsequently, it is immediately coated and dried. The binder is replaced with a mixture of styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) (mass ratio of SBR:CMC = 2:1). The rest is the same as in Example 1.

[0034] Example 4 This embodiment provides the raw material composition and preparation method of a magnesium hydroxide-based high-safety lithium-ion battery separator. Referring to the steps of Example 1, the mass ratio of silane-modified magnesium hydroxide to MOF-5-NH2 in the silane coupling agent-modified magnesium hydroxide composite filler of the amino-functionalized metal-organic framework material MOF-5-NH2 is replaced with 90:10, the dispersant is replaced with sodium dodecylbenzenesulfonate, and the thickener is replaced with hydroxyethyl cellulose. The rest remains the same as in Example 1.

[0035] Comparative Example 1 This comparative example provides the raw material composition and preparation method of a magnesium hydroxide-based high-safety lithium-ion battery separator. Referring to the steps of Example 1, the silane coupling agent modified magnesium hydroxide composite filler of the amino-functionalized metal-organic framework material MOF-5-NH2 is replaced with ordinary commercially available magnesium hydroxide powder, and the rest remains the same as in Example 1.

[0036] Comparative Example 2 This comparative example provides the raw material composition and preparation method of a magnesium hydroxide-based high-safety lithium-ion battery separator. Referring to the steps of Example 1, the amino-functionalized metal-organic framework material MOF-5-NH2 silane coupling agent modified magnesium hydroxide composite filler is replaced with (3-isocyanate propyl)triethoxysilane modified magnesium hydroxide (the product of step three in Example 1), and the rest remains the same as in Example 1.

[0037] Comparative Example 3 This comparative example provides the raw material composition and preparation method of a magnesium hydroxide-based high-safety lithium-ion battery separator. Referring to the steps of Example 1, the silane coupling agent modified magnesium hydroxide composite filler of the amino-functionalized metal-organic framework material MOF-5-NH2 is replaced with a simple physical mixture of magnesium hydroxide and amino-functionalized metal-organic framework material MOF-5-NH2 (mass ratio of the two is 85:15), and the rest remains the same as in Example 1.

[0038] Comparative Example 4 This comparative example serves as a blank control for a pure PE membrane: the same polyethylene microporous membrane (PE, porosity 40%, average pore size 0.1μm) as in Example 1 was used, without any composite functional coating, and the rest of the test procedures were the same as in Example 1.

[0039] Performance testing: 1. Ionic conductivity test: Cut the separator into 1cm×1cm sheets and immerse them in electrolyte (1mol / L LiPF6-EC / DEC=1:1, volume ratio) for 12h; assemble symmetrical coin cells (Li / separator / Li) and complete the sealing in a glove box. Set the amplitude of the AC impedance test to 10mV; test the AC impedance spectrum of the cells and record the impedance values. Calculate the ionic conductivity according to the formula σ=L / (R×S) (σ is the ionic conductivity, L is the separator thickness, R is the impedance value, and S is the effective area of ​​the separator), and the data are shown in Table 1.

[0040] 2. Rate performance and cycle life test: CR2032 coin cell was assembled with LiFePO4 as positive electrode, metallic Li as negative electrode and target membrane as electrolyte carrier; the electrolyte was 1 mol / L LiPF6-EC / DEC=1:1 (volume ratio), and the cells were sealed in a glove box and left to stand for 12 hours.

[0041] Rate performance: The charge and discharge voltage range was set to 4.2V, and the charge and discharge cycles were performed at a 2C rate for 15 cycles. The discharge specific capacity was recorded, and the data are shown in Table 1. Cycle life: 100 charge-discharge cycles were performed at a 1C rate. The discharge specific capacity and capacity retention rate were recorded on the 100th cycle. The data are shown in Table 1.

[0042] Table 1

[0043] The ionic conductivity of Example 1 was significantly higher than that of the comparative examples, mainly due to the synergistic effect of MOF material and dispersion technology in the composite coating. Unmodified magnesium hydroxide (Comparative Example 1) is prone to agglomeration due to its high surface energy. The dense particle accumulation will seriously block the micropores of the membrane, resulting in conductivity even lower than that of pure PE membrane (Comparative Example 4, blank control). In contrast, Example 1 achieved uniform dispersion of filler through silane coupling agent, avoiding physical pore blockage. At the same time, the unique porous structure of MOF-5-NH2 anchored on the surface serves as an "electrolyte reservoir" and a high-speed channel for lithium ion transport, greatly reducing ion migration resistance, thereby achieving a qualitative leap in conductivity.

[0044] In the 2C high-rate discharge test, Example 1 exhibited the highest discharge specific capacity, verifying its excellent kinetic performance at high current densities. This is because the battery's capacity at high rates is mainly limited by internal resistance and concentration polarization. The MOF structure in Example 1 effectively improves the electrolyte's wettability to the separator, ensuring efficient and smooth lithium-ion transport between the positive and negative electrodes. In contrast, Comparative Example 1 suffered from pore blockage due to inorganic particle agglomeration, which significantly increased the battery's internal resistance, resulting in excessive voltage drop during high-current discharge and prematurely reaching the cutoff voltage, thus causing severe capacity decay.

[0045] Example 1 exhibited the highest capacity retention after 100 cycles, fully demonstrating the crucial role of interfacial coupling anchoring (covalent bonding or strong physical adsorption) strategies in maintaining coating structural stability. Compared to Comparative Example 3, Example 1 constructed an organic end-base layer on the magnesium hydroxide surface using a silane coupling agent, enabling stable loading of MOF particles through multiple interactions such as hydrogen bonding / electrostatic interactions and pore embedding. For systems using epoxy / isocyanate-based silanes (as shown in Example 2), although covalent bonds can be formed, the ring-opening of epoxy groups may partially consume -NH2 on the MOF surface and introduce a denser organic layer, thereby reducing the polar sites / effective pore flux available for electrolyte adsorption and ion migration, resulting in slightly lower ionic conductivity and cycle retention compared to Example 1. Simultaneously, the improved interfacial compatibility enhanced the adhesion between the coating and the base film, avoiding coating peeling and powder shedding common in Comparative Example 1, thus ensuring the structural integrity and continuous safety protection function of the diaphragm during long-term charge-discharge processes.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A magnesium hydroxide-based high-safety lithium-ion battery separator, characterized in that, It includes a polyolefin-based film and a composite functional coating attached to the surface of the polyolefin-based film; The coating slurry used to prepare the composite functional coating comprises the following components in parts by weight: 30 to 60 parts of silane coupling agent-modified magnesium hydroxide composite filler for amino-functionalized metal-organic framework material MOF-5-NH2. 2 to 10 parts adhesive; Thickener 0.5 to 3 parts; 0.5 to 2 parts of dispersant; 0.1 to 1 part wetting agent; Solvent: 100 to 300 parts; The silane coupling agent modified magnesium hydroxide composite filler of the amino-functionalized metal-organic framework material MOF-5-NH2 is prepared by magnesium hydroxide, silane coupling agent and amino-functionalized metal-organic framework material MOF-5-NH2.

2. The magnesium hydroxide-based high-safety lithium-ion battery separator according to claim 1, characterized in that, The polyolefin-based membrane is selected from one of polyethylene microporous membrane, polypropylene microporous membrane, and multilayer composite microporous membrane of polyethylene and polypropylene. The adhesive is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, polyacrylic acid, polymethyl methacrylate, and polyacrylonitrile.

3. The magnesium hydroxide-based high-safety lithium-ion battery separator according to claim 1, characterized in that, The thickener is selected from one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, and guar gum; The dispersant is selected from one or more of sodium polyacrylate, polyvinylpyrrolidone, polyvinyl alcohol, and sodium dodecylbenzenesulfonate; The wetting agent is selected from one or more of octylphenol polyoxyethylene ether, polyether-modified siloxane, and fluorocarbon surfactant.

4. The magnesium hydroxide-based high-safety lithium-ion battery separator according to claim 1, characterized in that, The solvent is selected from one or more of deionized water, N-methylpyrrolidone, acetone, and dimethylacetamide; The silane coupling agent is selected from one or more of (3-aminopropyl)triethoxysilane, (3-glycidoxypropyl)trimethoxysilane, and (3-isocyanatepropyl)triethoxysilane.

5. The magnesium hydroxide-based high-safety lithium-ion battery separator according to claim 1, characterized in that, In the silane coupling agent modified magnesium hydroxide composite filler of the amino-functionalized metal-organic framework material MOF-5-NH2, the mass ratio of silane coupling agent modified magnesium hydroxide to amino-functionalized metal-organic framework material MOF-5-NH2 is 99.9:0.1-70:

30.

6. A method for preparing a magnesium hydroxide-based high-safety lithium-ion battery separator as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1, Magnesium hydroxide pretreatment and activation: Take magnesium hydroxide powder and add it to a mixed solvent prepared by deionized water and anhydrous ethanol for dispersion. Adjust the pH value of the system to 8.0 to 10.5 and stir at 40 to 80 degrees Celsius for 0.5 to 2 hours. Filter, wash and dry to obtain activated magnesium hydroxide. Step 2, silane coupling agent hydrolysis: The silane coupling agent is added to a mixed solvent of ethanol and water to prepare a hydrolysis solution, the pH value is adjusted to 3.5 to 5.5, and the solution is stirred and hydrolyzed at 20 to 40 degrees Celsius for 10 to 60 minutes to obtain a hydrolyzed silane solution containing silanol. Step 3, Silane grafting modified magnesium hydroxide: The activated magnesium hydroxide obtained in Step 1 is added to the hydrolyzed silane solution obtained in Step 2 to react, so that the silane hydrolysis product condenses with the hydroxyl groups on the surface of the activated magnesium hydroxide. After the reaction is completed, the magnesium hydroxide is washed and heat-treated to solidify, thus obtaining silane-modified magnesium hydroxide with silane organic end groups on the surface. Step 4, Dispersion pretreatment of amino-functionalized metal-organic framework material MOF-5-NH2: The amino-functionalized metal-organic framework material MOF-5-NH2 powder is placed in an anhydrous organic solvent to prepare MOF dispersion. Step 5, Coupling and anchoring of amino-functionalized metal-organic framework material MOF-5-NH2 with silane-modified magnesium hydroxide: The silane-modified magnesium hydroxide obtained in Step 3 is added to the MOF dispersion obtained in Step 4 and stirred to react. The functional groups of the silane coupling agent are chemically bonded or physically adsorbed with the amino groups on the surface of the amino-functionalized metal-organic framework material MOF-5-NH2. After the reaction, the mixture is separated, washed and dried to obtain the silane coupling agent modified magnesium hydroxide composite filler of amino-functionalized metal-organic framework material MOF-5-NH2. Step 6, preparation and application of coating slurry: The composite filler, binder, thickener, dispersant and wetting agent obtained in step 5 are added to a solvent and stirred and dispersed to obtain a coating slurry. The slurry is then coated on the surface of a polyolefin-based membrane, and the membrane is obtained after drying and removing the solvent.

7. The method for preparing the magnesium hydroxide-based high-safety lithium-ion battery separator according to claim 6, characterized in that, The volume ratio of deionized water to anhydrous ethanol in step one is 1:7-3:9, and the solid-liquid ratio is 1 to 10 parts by mass of magnesium hydroxide powder corresponding to 100 to 500 parts by volume of mixed solvent. The concentration of the hydrolysate in step two is 0.5% to 10%, and the volume ratio of ethanol to water is 80:20-98:

2.

8. The method for preparing a magnesium hydroxide-based high-safety lithium-ion battery separator according to claim 6, characterized in that, In step three, the amount of silane coupling agent used is 0.5% to 15% of the mass fraction of activated magnesium hydroxide, the reaction temperature is 40 to 85 degrees Celsius, and the reaction time is 1 to 6 hours; the heat treatment curing temperature is 80 to 140 degrees Celsius, and the time is 2 to 8 hours.

9. The method for preparing a magnesium hydroxide-based high-safety lithium-ion battery separator according to claim 6, characterized in that, The anhydrous organic solvent in step four is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, anhydrous ethanol, and acetone, and the concentration of the MOF dispersion is 0.1 to 10 mg per milliliter; the stirring reaction in step five is carried out at a temperature of 20 to 70 degrees Celsius for 1 to 12 hours.

10. The method for preparing a magnesium hydroxide-based high-safety lithium-ion battery separator according to claim 6, characterized in that, The coating method described in step six is ​​selected from gravure coating, dip coating, and spray coating; the drying temperature is 60 to 120 degrees Celsius.

Images