High-adhesion pmma-coated separator and method for manufacturing the same

Abstract

The application discloses a high-adhesion PMMA-coated diaphragm and a preparation method thereof, and relates to the technical field of battery diaphragm materials. The coated diaphragm is composed of a polyolefin microporous base film and a polymer coating, and the coating raw material comprises the following components in mass parts: 100 parts of polymethyl methacrylate, 20-50 parts of modified nanometer boehmite, 0.5-2 parts of a dispersing agent, and 0.2-1.5 parts of a wetting agent. The modified nanometer boehmite is a core-shell structure nanoparticle which is pretreated with a silane coupling agent on the surface and grafted with an in-situ crosslinking agent. The diaphragm is constructed by the synergistic effect of the steric hindrance of the core-shell structure, the chemical coupling of the crosslinking agent and the physical entanglement, a crosslinking network system with anti-falling and high interfacial compatibility is constructed, the agglomeration of inorganic powder and the peeling and pulverization of the coating can be effectively inhibited, and the product has excellent interfacial bonding strength and good high-temperature heat shrinkage resistance.

Description

Technical Field

[0001] This invention relates to the field of battery separator material technology, specifically to a high-adhesion PMMA coated separator and its preparation method. Background Technology

[0002] With the development of related technologies, energy storage devices are placing higher demands on the overall performance of their internal diaphragms. Polyolefin microporous membranes are widely used as diaphragm substrates due to their excellent chemical stability and mechanical properties. However, traditional polyolefin-based membranes are prone to severe thermal shrinkage at high temperatures, leading to direct contact between the positive and negative electrodes and causing internal short circuits, posing significant safety hazards. To improve the heat resistance and wettability of the diaphragm, a composite coating of polymer and inorganic nanoparticles is typically applied to the surface of the polyolefin-based membrane.

[0003] In composite coating systems, mixing polymer materials such as polymethyl methacrylate (PMMA) with inorganic particles is a common modification method. While the introduction of inorganic particles can effectively improve the high-temperature resistance and mechanical strength of the membrane, the high surface energy of inorganic powders makes them prone to agglomeration in polymer slurries, making uniform dispersion difficult and resulting in uneven coating thickness and pore blockage of the base film. Significant polarity and interfacial differences exist between inorganic particles and organic polymers, leading to poor natural compatibility. Under prolonged immersion in electrolytes or under the stress of charge-discharge cycles, inorganic particles are prone to detaching from the polymer matrix, compromising the structural integrity of the coating.

[0004] Traditional physical mixing methods fail to establish robust chemical bonds between inorganic particles and organic binders. This insufficient interfacial bonding not only weakens the cohesive force within the coating but also results in low interfacial adhesion strength between the entire composite coating and the polyolefin-based film. When the diaphragm is subjected to friction or bending during subsequent processing or assembly, the coating is highly susceptible to pulverization or peeling. These peeled coating fragments remain within the internal environment, severely impacting electrochemical performance and cycle life. Therefore, improving the dispersion of inorganic nanoparticles in the polymer matrix, enhancing the interfacial compatibility between inorganic particles and the polymer, and ultimately improving the overall adhesion and structural stability of the coated diaphragm, is a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art, such as the high surface energy of inorganic nanoparticles making them prone to agglomeration in polymer slurries, poor interfacial compatibility between inorganic particles and organic polymer matrices, insufficient internal bonding force of the coating due to physical mixing, low interfacial adhesion strength with the base film, and easy pulverization and peeling. The invention provides a high-adhesion PMMA coated separator and its preparation method, which features uniformly dispersed nanoparticles, strong interfacial chemical bonding, excellent coating structural stability, and high overall adhesion strength.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a highly adhesive PMMA coated diaphragm, wherein the coated diaphragm is composed of a polyolefin microporous base membrane and a polymer coating coated on one or both sides thereof; the raw materials of the polymer coating include the following components in parts by weight: 100 parts of polymethyl methacrylate, 20-50 parts of modified nano-boehmite, 0.5-2 parts of dispersant, and 0.2-1.5 parts of wetting agent;

[0007] The modified nanoboehmite is a core-shell structured nanoparticle that has been pretreated with a silane coupling agent and then grafted with an in-situ crosslinking agent. The chemical structure of the in-situ crosslinking agent is as follows: .

[0008] Furthermore, the polyolefin microporous base membrane is one of polyethylene microporous membrane, polypropylene microporous membrane, or polyethylene / polypropylene / polyethylene three-layer composite microporous membrane; The polyolefin microporous membrane has a thickness of 5-12 μm and a porosity of 35%-45%.

[0009] Furthermore, the preparation method of the modified nano-boehmite is as follows: (1) Surface double bond treatment: Disperse nano boehmite powder in an ethanol aqueous solution, add silane coupling agent, and react mechanically at a constant temperature of 60-70℃ for 4-6 hours. Then centrifuge, wash, and vacuum dry to obtain pretreated boehmite with unsaturated double bonds on the surface. (2) In-situ crosslinking grafting: The pretreated boehmite obtained in step (1) is ultrasonically dispersed in an organic solvent, the in-situ crosslinking agent and free radical initiator are added, nitrogen gas is introduced to remove oxygen for 30-40 minutes, the temperature is raised to 65-75℃, refluxed and stirred for 8-12 hours, and after the reaction is completed, the product is washed several times and vacuum dried at 40-50℃ to obtain the modified nano boehmite.

[0010] Unmodified nanoboehmite possesses high surface energy and disperses in organic polymer matrices solely through weak physical forces, making it prone to aggregation and exhibiting poor interfacial compatibility. Through the modification process of this invention, its mechanism of action in the system transforms from simple physical blending to robust chemical bonding. First, a silane coupling agent introduces unsaturated double bonds on the nanoparticle surface, reducing the surface energy and improving the initial dispersion. Subsequently, an in-situ crosslinking agent plays a crucial role in interfacial bridging and network construction. Under the action of an initiator, the in-situ crosslinking agent undergoes graft polymerization with the double bonds on the particle surface, constructing an organic shell with specific functional groups around the inorganic core, forming stable core-shell structured nanoparticles. The addition of the crosslinking agent not only blocks direct contact between inorganic particles through the steric hindrance effect of the organic layer, but its outer structure also allows for deep molecular chain entanglement and crosslinking with the polymethyl methacrylate (PMMA) matrix during subsequent coating and film formation. This shift in microscopic mechanism addresses the technical challenges of easy aggregation of inorganic porous carriers and poor interfacial compatibility between inorganic particles and organic matrix in the prior art. It enables a strong bond between the two phases, thereby significantly improving the cohesiveness and structural stability of the coating.

[0011] Furthermore, the silane coupling agent in step (1) is γ-methacryloyloxypropyltrimethoxysilane, and its addition amount is 3%-8% of the mass of nano-boehmite; The amount of in-situ crosslinking agent added in step (2) is 10% of the mass of the unmodified nano-boehmite powder; The free radical initiator in step (2) is azobisisobutyronitrile, and its addition amount is 1.0% of the mass of the in-situ crosslinking agent, and is equivalent to 0.10% of the mass of the unmodified nano-boehmite powder; The organic solvent in step (2) is one of N,N-dimethylformamide or tetrahydrofuran.

[0012] Furthermore, the polymethyl methacrylate has a weight-average molecular weight of 400,000-800,000 and a glass transition temperature of 100℃-115℃. The dispersant is one of sodium polyacrylate and sodium polymethacrylate; The wetting agent is one of polyether-modified trisiloxane, isomeric tridecanol polyoxyethylene ether, or polyoxyethylene dehydrated sorbitan monooleate.

[0013] Furthermore, the unmodified nanoboehmite has a median diameter (D50) of 0.8-1.5 μm and a specific surface area of ​​10-25 m². 2 / g, purity ≥99.9%.

[0014] A method for preparing a highly adhesive PMMA-coated separator includes the following steps: S1. Slurry preparation: Polymethyl methacrylate is dissolved in coating solvent to form a homogeneous adhesive solution with a solid content of 8%-12%; under constant temperature circulating water cooling conditions, dispersant, wetting agent and the modified nano boehmite are added to the adhesive solution in sequence, dispersed using a high shear disperser, and then transferred to a planetary mixer for vacuum stirring to obtain coating slurry; S2. Coating and molding: The coating slurry obtained in step S1 is uniformly coated on one or both sides of the polyolefin microporous base membrane using a microgravure coating machine or an extrusion coating machine. S3. Drying and winding: The coated diaphragm is sent into a multi-stage hot air oven for solvent evaporation and drying. After drying, it is cooled by cooling rollers, and finally slit and wound up to obtain the high-adhesion PMMA coated diaphragm.

[0015] Furthermore, in step S1, the coating solvent is one of acetone, butanone, or N-methylpyrrolidone; The high-shear disperser has a rotation speed of 2000-3500 r / min and a dispersion time of 30-50 minutes; The planetary mixer is evacuated to a vacuum level of -0.08MPa to -0.095MPa, and the mixing time is 2-3 hours.

[0016] Furthermore, in step S2, the gravure coating roller has a line count of 100-150 lines / inch, the coating speed is controlled at 30-50m / min, the unwinding tension of the base film is controlled at 0.5-1.5kgf, and the single-sided thickness of the dried coating is 1-3μm.

[0017] Furthermore, in step S3, the temperature of the multi-segment hot air oven is controlled in three segments: the first segment temperature is 40-45℃, the second segment temperature is 50-55℃, and the third segment temperature is 55-60℃. The exhaust air velocity inside the oven is 15-25m / s.

[0018] This invention provides a highly adhesive PMMA-coated diaphragm. By laminating a polymer coating containing specific modified materials onto the surface of a polyolefin microporous base membrane, a protective network combining mechanical strength and thermal stability is constructed, effectively suppressing the risk of internal short circuits caused by thermal shrinkage and deformation of the substrate. In this system, the introduced novel modified nanoboehmite plays a crucial role in structural reinforcement and interfacial anchoring. Based on its core-shell structure formed by grafting an in-situ crosslinking agent onto its surface, this material completely overcomes the defect of easy agglomeration of traditional inorganic powders. When distributed in a polymethyl methacrylate matrix, the organic groups on the outer layer of the modified particles undergo deep entanglement and bonding with the polymer molecular chains, weaving a dense and tough hybrid crosslinked network within the coating. This network not only enhances the coating's cohesion but also significantly improves the interfacial adhesion between the coating and the base membrane. This mechanism effectively buffers the mechanical stress experienced by the diaphragm during processing, assembly, and cycling, and can prevent particle shedding, coating powdering, and peeling caused by poor compatibility. By combining interfacial bonding and physical entanglement, this invention ensures the structural integrity of the coating, gives the diaphragm better adhesion performance, and solves the technical pain point of easy failure of traditional physical hybrid coatings.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. Higher coating adhesion strength: This invention utilizes the in-situ cross-linked network on the surface of modified boehmite to achieve deep entanglement and bonding with the polymer matrix. Compared with traditional physical mixing, the overall interfacial bonding strength shows a significant improvement trend, effectively improving the problems of easy powdering and peeling of the coating, and enhancing structural stability.

[0020] 2. Superior particle dispersibility and air permeability: The core-shell structure material of this invention reduces the tendency of inorganic powders to agglomerate in the slurry by utilizing the steric hindrance effect. After the coating film is formed, it maintains good air permeability, alleviating the phenomenon that traditional powders easily clog the micropores of the base film, which is beneficial to ensuring the electrochemical performance of the battery.

[0021] 3. Enhanced resistance to high-temperature heat shrinkage: The cross-linked network of this invention, in conjunction with the polymer and inorganic particles, constructs a robust protective framework. At high temperatures, this coating effectively suppresses the thermal deformation of the polyolefin microporous membrane, resulting in a decreasing overall heat shrinkage rate, reducing the risk of internal short circuits and improving safety limits. Attached Figure Description

[0022] Figure 1 This is a comparison of the infrared spectra of modified boehmite and unmodified boehmite. Detailed Implementation

[0023] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 Preparation of a high-adhesion PMMA-coated separator: 1) Preparation of in-situ crosslinking agent: ; The CAS number for raw material 1 is 552-30-7, and its Chinese name is: trimellitic anhydride; The CAS number for raw material 2 is 868-77-9, and its Chinese name is hydroxyethyl methacrylate. The CAS number for raw material 3 is 3047-32-3, and its Chinese name is 3-ethyl-3-oxazolidinylmethanol.

[0025] First, add 5.00 g of raw material 1, 0.159 g of 4-dimethylaminopyridine, and 5 mg of 2,6-di-tert-butyl-p-cresol sequentially to a 250 mL three-necked round-bottom flask. Then, inject 30 mL of anhydrous tetrahydrofuran using a syringe and start magnetic stirring. Cool the reaction flask to 0°C in an ice-water bath. Dissolve 3.32 mL of raw material 2 in the remaining 10 mL of anhydrous tetrahydrofuran, add 7.25 mL of triethylamine, mix thoroughly, and transfer to a constant-pressure dropping funnel. Under stirring conditions at 0°C, slowly add the raw material 2 / triethylamine solution dropwise to the reaction mixture at a rate of approximately 1 drop / second. After the addition is complete, rinse the dropping funnel with 10 mL of anhydrous tetrahydrofuran and add the rinse water to the reaction flask. Then remove the ice-water bath and allow the reaction system to naturally warm to room temperature. Next, place the reaction mixture in a 40°C heated magnetically stirred oil bath and continue stirring for 12 hours. After the reaction is complete, cool the reaction mixture to room temperature. Slowly pour the system into a 500mL beaker pre-filled with 100mL of ice water, place it in an ice-water bath and stir vigorously, while simultaneously adding 60mL of HCl aqueous solution to adjust the pH of the system to 2.5. Transfer the mixture to a 500mL separatory funnel and extract with ethyl acetate (3 × 100mL). Combine the organic phases, wash successively with saturated brine (2 × 50mL), allow to stand for separation, and collect the organic phase. Transfer the organic phase to an Erlenmeyer flask, add 20g of anhydrous sodium sulfate and dry for 30 minutes. Filter to remove the drying agent, and rotary evaporate the filtrate in a water bath below 35°C to concentrate and remove most of the solvent, obtaining the crude product. Dissolve the crude product in 15mL of hot ethyl acetate, and slowly add n-hexane dropwise at 45mL with stirring until slight turbidity appears. Recrystallize overnight at 4°C. The next day, the precipitated white crystals were collected by vacuum filtration. The filter cake was washed with a cold hexane / ethyl acetate mixture (V:V=5:1, 10mL) and dried in a vacuum drying oven (room temperature, protected from light) to constant weight to obtain 5.4g of intermediate 1.

[0026] In the second step, under nitrogen protection, 5.40 g of intermediate 1, 0.41 g of 4-dimethylaminopyridine, and 100 mL of freshly prepared anhydrous dichloromethane solvent were added sequentially to a 250 mL two-necked round-bottom flask. Stirring was started, and then 4.20 mL of starting material 3 was injected in one go using a syringe. After the system was thoroughly stirred, the reaction flask was placed in an ice-water bath at 0°C for 15 minutes to cool. Under stirring, 7.71 g of solid EDC·HCl was slowly added to the reaction system in four batches over 30 minutes. To control exothermic reactions and prevent excessively high local concentrations, the internal temperature of the system was observed after each addition to ensure it did not exceed 5°C. After all additions were completed, the flask walls were washed with an additional 10 mL of anhydrous dichloromethane to remove any residue. The reaction system was stirred at 0°C for 1 hour, then the ice bath was removed, and the system was allowed to rise naturally to room temperature and stirred overnight under constant temperature and light-protected conditions. After the reaction was complete, 30 mL of deionized water was slowly added dropwise to the system. Transfer the mixture to a 500 mL separatory funnel and add 100 mL of DCM for dilution. Shake thoroughly and allow to stand for separation, then separate and collect the lower organic phase. Extract the aqueous phase twice with DCM (50 mL × 2). Combine all organic layers. Wash the organic layers with saturated sodium bicarbonate solution (100 mL × 2) to remove residual acidic impurities, then wash once with 100 mL of saturated saline. Finally, transfer the organic phase to an Erlenmeyer flask, add an appropriate amount of anhydrous sodium sulfate, and dry for 30 minutes. Filter through a sand core funnel lined with a small amount of diatomaceous earth to remove the desiccant. Concentrate the filtrate under reduced pressure using a rotary evaporator at a water bath temperature below 30°C to obtain the crude product. Purify the crude product by silica gel column chromatography (200-300 mesh silica gel, eluent gradient: pure petroleum ether → petroleum ether / ethyl acetate = 3:1 → 1:1), and collect the corresponding R... f =0.45 fraction. A trace amount (10 ppm) of hydroquinone was added to the combined fraction as a polymerization inhibitor, the mixture was evaporated under reduced pressure and filtered under high vacuum for 4 hours to remove residual solvent, yielding 6.08 g of in-situ crosslinking agent.

[0027] Structural assessment: NMR of intermediates 1 HNMR: δ13.35(m,2H),8.35(s,1H),8.21(d,1H),7.85(d,1H),6.05(s,1H),5.70(m,1H),4.60(t,2H),4.45(t,2H),1.88(s,3H); NMR of in-situ crosslinking agent 1HNMR: δ8.85(t,1H),8.82(d,2H),6.16(s,1H),5.61(s,1H),4.67-4.63(m,2H),4.56-4.5 2(m,2H),4.50(s,4H),4.46(d,4H),4.40(d,4H),1.96(s,3H),1.84(q,4H),0.94(t,6H).

[0028] 2). Preparation of modified nano-boehmite: (1) Surface double bond treatment: Take 50g of unmodified nano-boehmite powder (with a diameter D50 of 1.0μm and a specific surface area of ​​15m²). 2 (g, purity ≥99.9%), was uniformly dispersed in an appropriate amount of aqueous ethanol solution. Then, 2.5g of γ-methacryloxypropyltrimethoxysilane was added as a silane coupling agent. The mixture was placed at a constant temperature of 65℃ and mechanically stirred for 5 hours. After the reaction was complete, the mixture was centrifuged, washed, and dried in a vacuum drying oven to obtain pretreated boehmite with unsaturated double bonds on its surface.

[0029] (2) In-situ cross-linking grafting: All the pretreated boehmite obtained in step (1) was added to a reaction flask, and 500 mL of N,N-dimethylformamide was added as an organic solvent. The mixture was then ultrasonically dispersed to ensure uniform suspension. Next, 5.0 g of the aforementioned in-situ crosslinking agent and 0.05 g of azobisisobutyronitrile (AIBN) were added to the system as a free radical initiator. The amount of the in-situ crosslinking agent added was 10% of the mass of the unmodified nano-boehmite powder, and the amount of AIBN added was 1.0% of the mass of the in-situ crosslinking agent, which is equivalent to 0.10% of the mass of the unmodified nano-boehmite powder. Nitrogen gas was continuously introduced into the reaction system for 30 minutes to remove oxygen. After deoxygenation, the system was heated to 70°C and mechanically stirred under reflux for 10 hours. After the reaction, the product was centrifuged and washed multiple times, and finally dried in a vacuum drying oven at 45°C to obtain the modified nano-boehmite.

[0030] The figure shows a comparison of the Fourier transform infrared (FT-IR) spectra of unmodified and modified nanoboehmite. Compared to the relatively simple absorption curve of unmodified boehmite, the modified spectrum shows several obvious new characteristic absorption peaks. At 2900 cm⁻¹... -1 A distinct CH stretching vibration peak appeared nearby, originating from the aliphatic carbon chains introduced into the molecular structures of the silane coupling agent and the in-situ crosslinking agent. At 1720 cm⁻¹... -1A very sharp and strong characteristic peak of C=O stretching vibration appeared nearby, which is the most direct evidence of the successful grafting of a large number of ester carbonyl groups in the crosslinking agent structure. At 1600 cm⁻¹ -1 and 1500cm -1 An absorption peak for the C=C vibration of the benzene ring skeleton in the crosslinking agent was observed nearby; while at 1200 cm⁻¹... -1 Up to 1000cm -1 In the region, a set of distinct overlapping absorption bands appeared, mainly attributed to the characteristic vibrations of the COC ether bonds in the crosslinking agent and the Si-O-Al bonds formed by the reaction of the coupling agent with the boehmite surface. A similar pattern was also observed at 3300 cm⁻¹. -1 The nearby free -OH peaks were relatively weakened due to consumption by surface chemical reactions. The appearance of these typical newly formed characteristic peaks fully confirms that the silane coupling agent and the in-situ crosslinking agent have been successfully grafted onto the surface of nano-boehmite through chemical covalent bonds, thus verifying the success of this surface modification at the microscopic molecular level.

[0031] 3) Raw material components by weight: Polymethyl methacrylate (PMMA): 100 parts (weight average molecular weight of 600,000, glass transition temperature of 105°C); Modified nanoboehmite: 35 parts (prepared from step 2 above); Dispersant: Sodium polyacrylate, 1.0 part; Wetting agent: Polyether-modified trisiloxane, 0.8 parts.

[0032] The polyolefin microporous membrane used is a polyethylene (PE) microporous membrane with a thickness of 9 μm and a porosity of 40%.

[0033] 4) Preparation Method The specific preparation process of the high-adhesion PMMA coated separator in this embodiment includes the following steps: S1. Slurry Preparation: Dissolve 100 parts of the above-mentioned polymethyl methacrylate completely in an appropriate amount of acetone (coating solvent) to form a homogeneous adhesive solution with a solid content of 10%. Under constant temperature circulating water cooling conditions, add 1.0 part of sodium polyacrylate, 0.8 parts of polyether-modified trisiloxane, and 35 parts of modified nano-boehmite sequentially to the adhesive solution. Subsequently, mechanically disperse the mixture using a high-shear disperser at a speed of 2800 r / min for 40 minutes. After dispersion, transfer the mixture to a planetary mixer and vacuum stir at a vacuum degree of -0.09 MPa for 2.5 hours to obtain a uniformly dispersed coating slurry without bubbles. S2. Coating and Forming: The coating slurry obtained in step S1 is uniformly coated onto one side of the above-mentioned polyethylene microporous base film using a microgravure coating machine. During the coating process, the anilox roller of the microgravure coating is set to 120 lines / inch, the coating speed is precisely controlled at 40m / min, and the unwinding tension of the base film is maintained at 1.0kgf; S3. Drying and Rewinding: The single-sided coated separator is continuously fed into a multi-stage hot air oven for solvent evaporation and drying. The oven temperature is precisely controlled in three stages: the first stage is set at 42℃, the second stage at 52℃, and the third stage at 58℃, with the exhaust air velocity maintained at 20m / s. After thorough drying, the single-sided coating thickness is measured to be 2μm. Finally, it is cooled and shaped by cooling rollers, then slit and rewound to obtain the high-adhesion PMMA coated separator described in this invention.

[0034] Example 2 Preparation of a high-adhesion PMMA-coated separator: 1. Raw material components by weight: Polymethyl methacrylate (PMMA): 100 parts (weight average molecular weight of 450,000, glass transition temperature of 102°C); Dispersant: Sodium polyacrylate, 0.5 parts; Wetting agent: Polyether-modified trisiloxane, 0.2 parts; The polyolefin microporous membrane used is a polypropylene (PP) microporous membrane with a thickness of 5 μm and a porosity of 35%.

[0035] 2. The rest remains the same as in Example 1.

[0036] Example 3 Preparation of a high-adhesion PMMA-coated separator: 1. Raw material components by weight: Polymethyl methacrylate (PMMA): 100 parts (weight average molecular weight of 800,000, glass transition temperature of 115°C); Dispersant: Sodium polymethacrylate, 2 parts; Wetting agent: Polyoxyethylene dehydrated sorbitan monooleate, 1.5 parts; The polyolefin microporous membrane used is a polyethylene / polypropylene / polyethylene three-layer composite microporous membrane with a thickness of 12μm and a porosity of 45%.

[0037] 2. The rest remains the same as in Example 1.

[0038] Comparative Example 1 The preparation of a highly adhesive PMMA-coated separator is carried out by referring to the preparation method of Example 1, except that the polymethyl methacrylate (PMMA) is replaced with an equal amount of conventional battery separator coating adhesive polyvinylidene fluoride (PVDF), and the rest is the same as in Example 1.

[0039] Comparative Example 2 The preparation of a highly adhesive PMMA-coated diaphragm is carried out by referring to the preparation method of Example 1, except that the modified nanoboehmite is replaced with an equal amount of ordinary nanoboehmite powder that has not undergone any surface double bond treatment and in-situ cross-linking grafting, and the rest is the same as in Example 1.

[0040] Comparative Example 3 The preparation of a high-adhesion PMMA coated diaphragm is carried out by referring to the preparation method of Example 1, except that the modified nanoboehmite is replaced with an equal amount of nanoboehmite that has only undergone silane coupling agent pretreatment in step (1) but has not undergone in-situ grafting of crosslinking agent in step (2), and the rest is the same as in Example 1.

[0041] Comparative Example 4 The preparation of a high-adhesion PMMA coated diaphragm is carried out according to the preparation method of Example 1. In the S1 slurry preparation step, the dispersant (sodium polyacrylate) and wetting agent (polyether modified trisiloxane) are not used. The PMMA and modified nano-boehmite are directly mechanically dispersed in the coating solvent. The rest is the same as in Example 1.

[0042] Performance testing (1) Test method A1. Coating Peel Strength (Adhesive Strength): Performed according to national standard GB / T2790-1995 "Test Method for 180° Peel Strength of Adhesives - Flexible Materials vs. Rigid Materials". The coated diaphragm was cut into strips 20 mm wide. The coated side was fixed to a standard steel plate using double-sided tape. A 180° peel test was conducted on a universal testing machine at a tensile speed of 50 mm / min. The average force value at which the coating peeled off the base film or cohesive failure occurred was recorded. The data are shown in Table 1.

[0043] A2. Heat shrinkage rate: The standard GB / T36363-2018 "Polyolefin Separators for Lithium-ion Batteries" was followed. The separator was cut into 100mm × 100mm square samples and baked in a constant-temperature drying oven at 150°C for 1 hour. After cooling, the longitudinal (MD) and transverse (TD) dimensional changes were measured, and the maximum value was used to calculate the heat shrinkage rate. The data are shown in Table 1.

[0044] A3. Air permeability (Gurley value): Following the GB / T36363-2018 standard, an automated air permeability tester was used to measure the time required for 100 mL of air to pass through a 1 square inch membrane under a certain pressure, to characterize the effect of the coating on the porosity of the base membrane. Data are shown in Table 1.

[0045] Table 1.

[0046] The comparative trends of the test data above show that the coated diaphragm prepared in the embodiments of the present invention exhibits significant advantages in peel strength, high-temperature thermal shrinkage resistance, and air permeability retention. The comprehensive performance of Comparative Example 2 and Comparative Example 3 shows a precipitous decline, which directly demonstrates that unmodified or incompletely modified inorganic particles, due to their high surface energy, are prone to severe agglomeration in the slurry. This not only directly blocks the micropores of the base membrane, leading to deterioration of air permeability, but also, due to the lack of chemical bonding between the inorganic phase and the organic polymer, macroscopically manifests as the coating being easily powdered and peeled off, and failing to effectively inhibit the high-temperature thermal shrinkage of the base membrane. The data from the embodiments perfectly confirm the mechanism of action of the present invention: the organic core-shell structure constructed by in-situ crosslinking grafting onto the surface of nano-boehmite successfully blocks the physical agglomeration between particles and forms a strong crosslinked network and molecular entanglement with the specific PMMA matrix at the interface. This microscopic transformation from physical mixing to chemical bonding systematically solves the technical pain points of poor interfacial compatibility, easy peeling, and pore blockage of inorganic coatings in the background technology, and endows the diaphragm with excellent structural integrity and thermal stability.

[0047] 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 high-adhesion PMMA-coated separator, characterized in that, The coated diaphragm is composed of a polyolefin microporous base membrane and a polymer coating coated on one or both sides of it; the raw materials of the polymer coating include the following components in parts by weight: 100 parts polymethyl methacrylate, 20-50 parts modified nano boehmite, 0.5-2 parts dispersant, and 0.2-1.5 parts wetting agent; The modified nanoboehmite is a core-shell structured nanoparticle that has been pretreated with a silane coupling agent and then grafted with an in-situ crosslinking agent. The chemical structure of the in-situ crosslinking agent is as follows: .

2. The high-adhesion PMMA-coated separator according to claim 1, characterized in that, The polyolefin microporous base membrane is one of polyethylene microporous membrane, polypropylene microporous membrane, or polyethylene / polypropylene / polyethylene three-layer composite microporous membrane. The polyolefin microporous membrane has a thickness of 5-12 μm and a porosity of 35%-45%.

3. The high-adhesion PMMA-coated separator according to claim 1, characterized in that, The method for preparing the modified nano-boehmite is as follows: (1) Surface double bond treatment: Disperse nano boehmite powder in an ethanol aqueous solution, add silane coupling agent, and react mechanically at a constant temperature of 60-70℃ for 4-6 hours. Then centrifuge, wash, and vacuum dry to obtain pretreated boehmite with unsaturated double bonds on the surface. (2) In-situ crosslinking grafting: The pretreated boehmite obtained in step (1) is ultrasonically dispersed in an organic solvent, the in-situ crosslinking agent and free radical initiator are added, nitrogen gas is introduced to remove oxygen for 30-40 minutes, the temperature is raised to 65-75℃, refluxed and stirred for 8-12 hours, and after the reaction is completed, the product is washed several times and vacuum dried at 40-50℃ to obtain the modified nano boehmite.

4. The high-adhesion PMMA-coated separator according to claim 3, characterized in that, The silane coupling agent in step (1) is γ-methacryloyloxypropyltrimethoxysilane, and its addition amount is 3%-8% of the mass of nano-boehmite; The amount of in-situ crosslinking agent added in step (2) is 10% of the mass of the unmodified nano-boehmite powder; The free radical initiator in step (2) is azobisisobutyronitrile, and its addition amount is 1.0% of the mass of the in-situ crosslinking agent, and is equivalent to 0.10% of the mass of the unmodified nano-boehmite powder; The organic solvent in step (2) is one of N,N-dimethylformamide or tetrahydrofuran.

5. The high-adhesion PMMA-coated separator according to claim 1, characterized in that, The polymethyl methacrylate has a weight-average molecular weight of 400,000-800,000 and a glass transition temperature of 100℃-115℃. The dispersant is one of sodium polyacrylate and sodium polymethacrylate; The wetting agent is one of polyether-modified trisiloxane, isomeric tridecanol polyoxyethylene ether, or polyoxyethylene dehydrated sorbitan monooleate.

6. A high-adhesion PMMA-coated separator according to claim 1 or 3, characterized in that, The unmodified nanoboehmite has a median diameter (D50) of 0.8-1.5 μm and a specific surface area of ​​10-25 m². 2 / g, purity ≥99.9%.

7. A method for preparing a high-adhesion PMMA-coated separator according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Slurry preparation: Polymethyl methacrylate is dissolved in coating solvent to form a homogeneous adhesive solution with a solid content of 8%-12%; under constant temperature circulating water cooling conditions, dispersant, wetting agent and the modified nano boehmite are added to the adhesive solution in sequence, dispersed using a high shear disperser, and then transferred to a planetary mixer for vacuum stirring to obtain coating slurry; S2. Coating and molding: The coating slurry obtained in step S1 is uniformly coated on one or both sides of the polyolefin microporous base membrane using a microgravure coating machine or an extrusion coating machine. S3. Drying and winding: The coated diaphragm is sent into a multi-stage hot air oven for solvent evaporation and drying. After drying, it is cooled by cooling rollers, and finally slit and wound up to obtain the high-adhesion PMMA coated diaphragm.

8. The method for preparing a high-adhesion PMMA-coated separator according to claim 7, characterized in that, In step S1, the coating solvent is one of acetone, butanone, or N-methylpyrrolidone; The high-shear disperser has a rotation speed of 2000-3500 r / min and a dispersion time of 30-50 minutes; The planetary mixer is evacuated to a vacuum level of -0.08MPa to -0.095MPa, and the mixing time is 2-3 hours.

9. The method for preparing a high-adhesion PMMA-coated separator according to claim 7, characterized in that, In step S2, the gravure coating roller has a line count of 100-150 lines / inch, the coating speed is controlled at 30-50m / min, the unwinding tension of the base film is controlled at 0.5-1.5kgf, and the single-sided thickness of the dried coating is 1-3μm.

10. The method for preparing a high-adhesion PMMA-coated separator according to claim 7, characterized in that, In step S3, the temperature of the multi-segment hot air oven is controlled in three segments: the first segment temperature is 40-45℃, the second segment temperature is 50-55℃, and the third segment temperature is 55-60℃. The exhaust air velocity inside the oven is 15-25m / s.

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