A functionalized separator containing microcapsules and a method for preparing the same

Abstract

This application discloses a functionalized separator containing microcapsules and its preparation method, relating to the technical field of lithium battery separators. Addressing the problems of poor thermal stability of existing polyolefin separators, easy damage to microcapsules during coating and drying, and weak coating adhesion, this separator uses a polyethylene membrane as a substrate and is coated with a slurry prepared from microcapsules, acrylate, sodium polycarboxylate, and specially formulated modifying additives. The modifying additives are prepared by mixing a water-soluble metal salt precursor, urea, an amphiphilic block copolymer, and a coupling agent in a specific ratio to form a hollow inorganic structure, which is then surface-modified to improve coating porosity and electrolyte wettability. During preparation, the base membrane is first treated to enhance interfacial adhesion, followed by multi-stage dispersion slurry preparation, and then slit coating and gradient temperature-controlled drying are used to avoid microcapsule damage and coating defects. The resulting separator possesses good mechanical strength, high coating peel strength and adhesion, and excellent liquid absorption and retention performance, effectively improving the cycle stability of lithium batteries.

Description

Technical Field

[0001] This application relates to the technical field of lithium battery separators, and in particular to a functionalized separator containing microcapsules and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, the need for a balance between high energy density and high safety in power lithium batteries is becoming increasingly urgent. As one of the core components of lithium batteries, the performance of the separator directly determines the battery's cycle life, rate performance, and thermal safety level. While traditional polyolefin separators, such as polyethylene and polypropylene single-layer membranes, possess good chemical stability and mechanical strength, their passive isolation function is insufficient to effectively prevent chain reactions under extreme conditions such as thermal runaway, internal short circuits, or abnormal temperature rises. Therefore, functional separators containing microcapsules have emerged. By introducing microcapsules encapsulating closed-cell liquids, flame retardants, or electrolyte additives into the separator coating, the separator maintains its normal ion conduction and mechanical support functions at room temperature, while releasing functional core materials in response to triggering conditions such as abnormal high temperatures or mechanical puncture, achieving active safety protection.

[0003] However, the industrial-scale preparation of microcapsule functionalized membranes faces severe challenges: On the one hand, the polymer shell material of microcapsules uses polymer materials with wall thicknesses of only micrometers or even submicrometers. In traditional blade coating or roller coating processes, high shear forces and mechanical crushing can easily cause capsule rupture, leading to premature release of closed-cell liquid or flame retardants. This not only results in the loss of temperature control and protection effects but may also contaminate the electrolyte and trigger side reactions, leading to consistently low microcapsule survival rates and extremely poor functional consistency. On the other hand, polypropylene and polyethylene-based membranes have extremely low surface energy and poor interfacial wettability with water-based or solvent-based coatings. The coating is prone to defects such as peeling, bubbles, and edge warping, severely weakening the mechanical properties and long-term cycling stability of the membrane. In addition, if the drying process temperature is too high or the heating rate is too fast, the internal pressure generated by the thermal expansion of the core material will far exceed the shell's tolerance limit, causing capsule rupture and coating pore collapse. Especially for systems with low-boiling-point core materials, existing drying processes are almost incompatible. Summary of the Invention

[0004] The purpose of this application is to provide a functionalized diaphragm containing microcapsules and a method for preparing the same, which can improve the adhesion between the diaphragm and the coating, the peel strength of the diaphragm, and the liquid absorption and retention rates.

[0005] Firstly, the functionalized diaphragm containing microcapsules provided in this application adopts the following technical solution: A functionalized membrane containing microcapsules includes: a polyethylene membrane and a slurry coated on the polyethylene membrane; the slurry comprises the following raw materials in parts by weight: 28-55 parts microcapsules, 8-12 parts acrylate, 0.5-1.5 parts sodium polycarboxylate, 100-150 parts water, and 20-35 parts modifying additives; the microcapsules comprise a polymer shell and an encapsulated core material; The modified additive is obtained by surface modification of hollow inorganic powder, including the following raw materials: water-soluble metal salt precursor, urea, amphiphilic block copolymer, and coupling agent; the mass ratio of the water-soluble metal salt precursor, urea, amphiphilic block copolymer, and coupling agent is 100:(2-30):(4-50):(3-30).

[0006] By adopting the above technical solutions, this approach uses polyethylene membranes that balance oxidation resistance and flexibility, making them suitable for high-rate charge / discharge conditions of lithium batteries. Precisely defining the proportions of each slurry ingredient and controlling the ratio of polymer shell to core material allows for the formation of a structurally complete and uniformly thick microcapsule structure. This encapsulates the functional core material, enabling responsive energy release under abnormal conditions such as battery overheating and internal short circuits, thus improving the thermal safety performance of the separator. Acrylic ester, as the binder, combined with trace amounts of sodium polycarboxylate dispersant, ensures uniform dispersion of all slurry components in the aqueous system, preventing coating agglomeration, uneven thickness, and peeling, significantly improving film-forming properties and coating adhesion. Specially formulated modified additives construct a microporous framework within the separator coating, optimizing separator porosity and electrolyte wettability, and reducing battery interfacial impedance. The overall formulation system avoids the shortcomings of traditional functional separator coatings, such as high brittleness, poor wettability, and weak thermal stability, significantly improving the cycle life and safety factor of lithium batteries.

[0007] Optionally, the modified additive is prepared by the following method: S1. Dissolve the amphiphilic block copolymer in a solvent, add water, stir, evaporate by rotary evaporation, and adjust the pH to 5-6 to obtain the base material; S2. Add water-soluble metal salt precursor and water to the base material prepared in step S1, stir, add urea, heat, stir, wash, and vacuum dry to obtain hollow inorganic powder. Add anhydrous ethanol to obtain hollow inorganic solution. S3. Mix the coupling agent with anhydrous ethanol, heat, add to the hollow inorganic solution prepared in step S2, heat in an oil bath, centrifuge, wash, and dry to obtain the modified additive.

[0008] By employing the above technical solution, this stepwise preparation process precisely controls the microstructure and surface properties of the modified additives. Step S1, through modification with amphiphilic block copolymers and control of a weakly acidic environment, precisely regulates the stretching state of polymer molecular chains, preventing molecular aggregation, and the prepared base material possesses excellent emulsifying and dispersing capabilities. Step S2 uses urea as a slow-release precipitant, providing an alkaline environment through slow hydrolysis, allowing the metal salt precursor to precipitate and crystallize uniformly, stabilizing the formation of a hollow inorganic powder structure. This hollow structure can store electrolyte, buffer volume expansion during battery charging and discharging, and significantly reduce the additive's weight. Step S3, through surface modification with coupling agents, grafts organic functional groups onto the surface of the hollow inorganic powder, breaking down the interfacial barrier between the inorganic filler and the organic slurry, and improving the overall density and flexibility of the coating. Optionally, the water-soluble metal salt precursor is any one or more of water-soluble aluminum salt, water-soluble titanium salt, and water-soluble magnesium salt.

[0009] By adopting the above technical solutions, the three types of water-soluble metal salt precursors specified in this solution can all be crystallized under mild aqueous reaction conditions. The hollow alumina particles formed after aluminum salt crystallization possess ultra-high thermal stability and insulation, maintaining the integrity of the separator skeleton under high-temperature conditions and inhibiting thermal shrinkage and perforation of the separator. The titanium dioxide particles derived from titanium salt possess excellent resistance to electrolyte corrosion and ion conductivity, optimizing ion transport efficiency at the separator interface and reducing battery polarization. The magnesium oxide particles prepared from magnesium salt have excellent toughness, improving the separator's puncture and tensile strength, and preventing short-circuit faults caused by burrs inside the cell piercing the separator. Simultaneously, the three types of metal salts have excellent water solubility and can be uniformly dispersed in the slurry without localized agglomeration or sedimentation. They can be selected individually or used in combination according to battery performance requirements, flexibly adapting to different application scenarios such as power lithium batteries and energy storage lithium batteries.

[0010] Optionally, the water-soluble aluminum salt is any one or more of aluminum chloride hexahydrate, aluminum sulfate octadecahydrate, and aluminum nitrate nonahydrate; the water-soluble titanium salt is any one or more of titanium tetrachloride and titanium oxysulfate; and the water-soluble magnesium salt is any one or more of magnesium chloride hexahydrate, magnesium nitrate hexahydrate, and magnesium acetate tetrahydrate.

[0011] By adopting the above technical solutions, the aluminum salt hydrolysis rate is gradual, and the crystallized hollow alumina particles have uniform pore size and dense structure, which can stably improve the high-temperature resistance of the separator. The limited titanium salt has extremely high solubility, the reaction product has high purity, and there are no poorly soluble by-products, which can maximize the retention of the ion conductivity and corrosion resistance advantages of titanium dioxide. The selected magnesium salt has high purity and low cost, and the mechanical and interfacial properties of the additives can be precisely controlled when used in combination. At the same time, the reaction by-products of this type of metal salt are easily removed by washing and centrifugation, and will not remain inside the separator coating to cause problems such as cell self-discharge and electrolyte decomposition. This precisely ensures the purity and performance stability of the modified additives, and greatly improves the batch consistency of functionalized separators.

[0012] Optionally, the amphiphilic block copolymer is either polystyrene-block-polyacrylic acid or polystyrene-block-hydroxyethyl acrylate.

[0013] By adopting the above technical solutions, the two amphiphilic block copolymers specified in this solution possess both hydrophobic carbon chains and hydrophilic functional groups, making them suitable for water-based slurry systems and inorganic filler modification scenarios. The hydrophobic segments of polystyrene can adsorb metal salt crystal particles, inhibiting particle aggregation and stacking, while the hydrophilic segments of polyacrylic acid and hydroxyethyl polyacrylate can form hydrogen bonds with water molecules and coupling agent functional groups, significantly improving the dispersibility and compatibility of the additive in aqueous slurries. Compared to ordinary surfactants, these block copolymers have stable molecular structures and will not decompose or fail under the high and low temperature cycling conditions of battery charging and discharging, maintaining the microscopic hollow structure of the modified additive for a long time. Simultaneously, they can precisely control the particle size and pore size of inorganic powders, avoiding the problems of excessively large pores leading to decreased membrane insulation and excessively small pores leading to obstructed ion transport, effectively balancing the membrane's permeability, porosity, and insulation performance.

[0014] Optionally, the polymer shell material can be either polyurea or gelatin.

[0015] By adopting the above technical solution, the polyurea and gelatin selected in this solution are high-quality polymer shell materials suitable for the microcapsule structure of lithium battery separators, and perfectly compatible with water-based coating systems. Polyurea possesses excellent high and low temperature stability, electrolyte corrosion resistance, and mechanical strength. The molded microcapsule shell is dense and tough, and can stably encapsulate the core material under normal battery operating conditions. It only slowly ruptures under abnormal high-temperature environments such as battery overheating and overcharging, releasing the functional substances of the core material to achieve temperature control and protection. Gelatin has good biocompatibility and excellent film-forming properties. The prepared microcapsules have uniform wall thickness and high flexibility, and can follow the slight deformation of the base film, avoiding microcapsule breakage and failure during separator bending and stretching. Both polymer shell materials can form intermolecular forces with acrylates and sodium polycarboxylate in the slurry, improving the adhesion between the microcapsules and the coating and base film.

[0016] Optionally, the core material is either decahydronaphthalene or ethyl acetate.

[0017] By adopting the above technical solution, both decahydronaphthalene and ethyl acetate are low-boiling-point, high-permeability, and chemically inert organic solvents, suitable for the functional requirements of microcapsule core materials, and exhibit excellent compatibility with lithium battery electrolytes, without triggering side reactions in the electrolyte. Ethyl acetate has a moderate boiling point, allowing for rapid vaporization under localized high temperatures or micro-short-circuit heating in the battery, causing the microcapsule shell to rupture, blocking ion conduction, and promptly shutting down the cell reaction to prevent thermal runaway risks. Decahydronaphthalene exhibits stronger chemical stability and excellent resistance to electrolyte dissolution, preventing leakage at room temperature and allowing for long-term storage inside the microcapsules, resulting in a longer service life. It also possesses excellent wetting assistance, further enhancing the membrane's adsorption and permeation capacity for the electrolyte. These two types of core materials are then paired with corresponding polymer shell materials.

[0018] Optionally, the heating temperature in step S2 is 150-180℃.

[0019] By adopting the above technical solution, when the temperature is below 150℃, the urea hydrolysis rate is too slow, the metal salt precursor crystallizes incompletely, and cannot form a complete hollow spherical structure. It is easy to generate solid fragments, resulting in insufficient porosity of the additives and a significant decrease in the liquid retention and air permeability of the membrane. When the temperature is above 180℃, the urea hydrolyzes rapidly, which will affect the integrity of the complete hollow spherical structure.

[0020] Optionally, in step S2, the stirring speed is 200-500 rpm and the stirring time is 20-24 h.

[0021] By adopting the above technical solution, when the stirring speed is below 200 rpm, the system materials are mixed unevenly, the local concentration of metal salt precursors is too high, and agglomeration and crystallization are prone to occur, generating a large number of solid particles and irregular fragments, making it impossible to form a regular hollow structure. When the stirring speed is above 500 rpm, the fluid shear force is too large, which will destroy the initial shape of the inorganic shell that is forming, leading to shell damage and structural collapse. Long-term uniform stirring for 20-24 hours can ensure continuous and uniform hydrolysis of urea, allowing metal ions to slowly and orderly crystallize and deposit, resulting in uniform wall thickness and particle size of the hollow powder.

[0022] Secondly, the functionalized membrane containing microcapsules and its preparation method provided in this application adopt the following technical solution: A method for preparing a functionalized membrane containing microcapsules includes the following steps: Step 1: Polymerize the polymer shell and core materials to prepare microcapsules; Step 2: Perform plasma treatment on the polyethylene film. Step 3: Mix the microcapsules, sodium polycarboxylate, and water, add acrylate, disperse ultrasonically, add the modifying additive, and stir to obtain a slurry; Step 4: Coat the slurry onto the treated base film, apply it via slit coating, dry it under gradient temperature control, and then roll it up to obtain the functionalized diaphragm containing microcapsules.

[0023] By employing the above technical solutions, plasma treatment of the base film can etch the microscopic texture of the base film surface, introduce polar functional groups, and significantly improve the interfacial adhesion between the hydrophobic base film and the water-based slurry, eliminating defects such as coating peeling, edge lifting, and exposed film. In the slurry preparation process, water-soluble raw materials are first dissolved, followed by the addition of oil-based core materials and ultrasonically dispersed compounding modifiers. This achieves multi-level uniform dispersion of each component, solving problems such as microcapsule aggregation, filler sedimentation, and uneven coating composition, ensuring the stability of the slurry system. Slit coating allows for precise control of coating thickness and uniformity, offering higher precision and better consistency compared to spraying and brushing processes. Gradient temperature-controlled drying avoids problems such as coating cracking, microcapsule breakage, and pore collapse caused by rapid high-temperature drying, gradually evaporating moisture and completely preserving the hollow structure of the microcapsules and the porous skeleton of the coating.

[0024] Modified additives and microcapsules exhibit a multi-layered synergistic effect in functionalized membrane coatings. From the perspective of coating microstructure, the hollow inorganic powder formed by the urea-release hydrolysis and surface grafting of the modified additives with coupling agents constructs a rigid porous framework within the coating. This framework provides stable physical support sites and stress buffering space for the microcapsules, preventing them from rupturing under the shear force of slot coating and the thermal stress of gradient drying due to direct pressure or localized stress concentration, effectively improving the survival rate of the microcapsules throughout the preparation process. Furthermore, the hollow powder and microcapsules create a graded packing effect of particles of varying sizes within the coating, optimizing the pore structure and pore size distribution, resulting in a coating that combines high porosity with good structural density. From an interfacial perspective, the organic functional groups grafted onto the surface of the hollow microspheres by the coupling agent can form hydrogen bonds or covalent bonds with the active groups in the microcapsule shell, firmly anchoring the microcapsules to the inorganic framework network. This prevents the microcapsules from detaching or shifting during the volume expansion and contraction of the battery during long-term charge-discharge cycles. Simultaneously, this interfacial bridging effect significantly improves the overall peel strength and adhesion of the coating. The interconnected pore network constructed by the hollow microspheres greatly enhances the electrolyte absorption and retention rate of the separator, ensuring ion conduction efficiency under normal battery conditions. When the battery experiences abnormal conditions such as overheating or internal short circuits, the microcapsule shell ruptures upon heating, releasing the functional core material. This released core material can rapidly diffuse along the pore network formed by the hollow microsphere framework to the surrounding area of ​​the separator, promptly blocking the spread of abnormal reactions and achieving active thermal protection. The synergistic effect of both in structural support, interfacial enhancement, and functional response enables the functionalized separator to simultaneously achieve excellent mechanical, electrochemical, and thermal safety performance.

[0025] In summary, this application includes at least one of the following beneficial technical effects: 1. Compared with existing technologies, the modified additives prepared using specific ratios and processes in this application can construct a stable porous framework in the separator coating, significantly optimizing the electrolyte wettability and pore structure of the separator. After surface modification, this hollow inorganic structure can effectively improve the interfacial compatibility between the inorganic filler and the organic coating, reduce coating brittleness, and simultaneously enhance the adhesion between the coating and the base film, reducing defects such as peeling and warping. The hollow structure can also improve the separator's liquid absorption and retention capacity, reduce battery interfacial impedance, and allow the separator to maintain stable performance during high and low temperature cycling. 2. Compared with existing technologies, this application uses suitable polymer shell materials and functional core materials to prepare microcapsules. Combined with plasma treatment, slit coating, and gradient temperature-controlled drying processes, the survival rate of microcapsules during preparation can be significantly improved, preventing premature rupture and failure. The synergistic effect of microcapsules and modified additives allows for the release of the core material in response to abnormal battery conditions, achieving active thermal protection and improving battery safety performance. The mild preparation process also maintains the integrity of the coating pores, improving the mechanical properties and interfacial adhesion of the separator, giving the separator good ion conductivity, mechanical strength, and thermal stability, meeting the high-efficiency and stable operation requirements of power lithium batteries. Detailed Implementation

[0026] Unless otherwise specified, all raw materials used in the embodiments and comparative examples of this application are commercially available products: Polyethylene film, model ND12, Shanghai Enjie; Polystyrene-block-polyacrylic acid, Xi'an Ruixi Biotechnology Co., Ltd. Example 1

[0027] A method for preparing a functionalized membrane containing microcapsules includes the following steps: The first step is to prepare the modified additives. 2.5 g of polystyrene-block-polyacrylic acid was dissolved in 50 mL of tetrahydrofuran, and 500 mL of water was added. The mixture was stirred at 25 °C for 2 h to obtain the first mixture. The first mixture was rotary evaporated at 40 °C for 10 min, and the pH was adjusted to 5.5 with 0.1 mol / L sodium hydroxide solution to obtain the base material.

[0028] In a sealed container, 200 mL of the base material was taken, 1 L of 0.2 mol / L aluminum chloride hexahydrate aqueous solution was added, along with 4.8 L of water and 2.4 g of urea. The mixture was stirred at 300 rpm for 22 h at 160 °C to obtain a second mixture. The second mixture was cooled to 25 °C and centrifuged at 8000 rpm for 10 min to obtain a first precipitate. The first precipitate was washed three times with water, and the product from the last water wash was washed three times with anhydrous ethanol. The product from the last anhydrous ethanol wash was dried under vacuum at 80 °C and 0.08 MPa for 18 h to obtain hollow boehmite powder. The hollow boehmite powder was dispersed in 500 mL of anhydrous ethanol and ultrasonically dispersed at 45 kHz for 15 min to obtain a hollow boehmite solution.

[0029] 2.4 g of 3-aminopropyltriethoxysilane was mixed with 100 mL of anhydrous ethanol and stirred at 300 rpm for 30 min at 60 °C. The mixture was then added to a hollow boehmite solution and refluxed in an oil bath at 80 °C for 12 h to obtain a third mixture. The third mixture was cooled to 25 °C and centrifuged at 8000 rpm for 10 min to obtain a second precipitate. The second precipitate was washed three times with anhydrous ethanol. The product after the final wash with anhydrous ethanol was dried under vacuum at 80 °C and 0.08 MPa for 18 h to obtain the modified additive.

[0030] The second step is to prepare the slurry. 75g of toluene diisocyanate and 375g of decahydronaphthalene were mixed, and 5g of Span 80 was added. The mixture was stirred at 500 rpm for 30 min to obtain the oil phase. 1L of water, 10g of Span, and 15g of polyvinyl alcohol were mixed and stirred at 500 rpm for 30 min to obtain the aqueous phase. The oil phase was added to the aqueous phase under stirring at 8000 rpm, and sheared and dispersed for 10 min to obtain a granular emulsion. 50g of diethylenetriamine was mixed with 100g of water to obtain a diethylenetriamine solution. The diethylenetriamine solution was added to the granular emulsion, and the mixture was heated to 60℃ and stirred at 300 rpm for 2 h to obtain a fourth mixture. The fourth mixture was cooled to 25℃, filtered to obtain a precipitate, washed three times with water, and the precipitate from the last wash was dried under vacuum at 50℃ and 0.08 MPa for 24 h to obtain microcapsules. The particle size of the microcapsules was measured to be 3 μm.

[0031] Mix 45g of microcapsules, 5g of sodium polycarboxylate, and 120g of water, and stir at 200rpm for 5min to obtain the fifth mixture. Add 10g of acrylate emulsion to the fifth mixture, continue stirring at 200rpm for 10min, add 22g of modifying additive, and ultrasonically disperse at 400W for 15min to obtain a slurry.

[0032] The third step is to prepare functionalized membranes.

[0033] A 12μm thick, 1200mm wide polyethylene film was surface-treated for 30s in a 300W oxygen atmosphere plasma treatment device to obtain a pretreated base film. Slurry was applied to one side of the pretreated base film through an 80μm wide, 0.3mm gap slit coating head at a coating speed of 100m / min, and the wet film thickness was measured to be 20μm. The wet film was then subjected to a gradient temperature-controlled drying process: the first stage was 50℃, air velocity 4m / s, and time 10s; the second stage was 70℃, air velocity 6m / s, and time 15s; the third stage was 35℃, air velocity 3m / s, and time 5s. After the third stage of drying, the winding tension was controlled at 20N / m, thus obtaining the functionalized diaphragm containing microcapsules. Example 2

[0034] The difference between Example 2 and Example 1 is that the 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution, 2.4g urea, 2.5g polystyrene-block-polyacrylic acid, and 2.4g 3-aminopropyltriethoxysilane in Example 1 are replaced with 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution, 5.3g urea, 7.2g polystyrene-block-polyacrylic acid, and 5.8g 3-aminopropyltriethoxysilane. Example 3

[0035] The difference between Example 3 and Example 1 is that the 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution, 2.4g urea, 2.5g polystyrene-block-polyacrylic acid, and 2.4g 3-aminopropyltriethoxysilane in Example 1 are replaced with 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution, 7.7g urea, 12g polystyrene-block-polyacrylic acid, and 5.8g 3-aminopropyltriethoxysilane. Example 4

[0036] The difference between Example 4 and Example 1 is that the 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution, 2.4g urea, 2.5g polystyrene-block-polyacrylic acid, and 2.4g 3-aminopropyltriethoxysilane in Example 1 are replaced with 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution, 11.6g urea, 18g polystyrene-block-polyacrylic acid, and 12g 3-aminopropyltriethoxysilane. Example 5

[0037] The difference between Example 5 and Example 3 is that the 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution in Example 3 is replaced with 1L 0.2mol / L titanium tetrachloride. Example 6

[0038] The difference between Example 6 and Example 3 is that the 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution in Example 3 is replaced with 1L 0.2mol / L magnesium acetate tetrahydrate. Example 7

[0039] The difference between Example 7 and Example 3 is that 375g of decahydronaphthalene in Example 3 is replaced with 375g of ethyl acetate. Comparative Example 1

[0040] The difference between Comparative Example 1 and Example 1 is that the 1 L 0.2 mol / L aluminum chloride hexahydrate aqueous solution, 2.4 g urea, 2.5 g polystyrene-block-polyacrylic acid, and 2.4 g 3-aminopropyltriethoxysilane in Example 1 are replaced with 1 L 0.2 mol / L aluminum chloride hexahydrate aqueous solution, 19.3 g urea, 1 g polystyrene-block-polyacrylic acid, and 0.5 g 3-aminopropyltriethoxysilane. Comparative Example 2

[0041] The difference between Comparative Example 2 and Example 3 is that the 1L 0.2mol / L aluminum chloride hexahydrate aqueous solution in Example 3 is replaced with 1L 0.2mol / L zinc nitrate. Comparative Example 3

[0042] The difference between Comparative Example 3 and Example 3 is that no modifying additives were added in Comparative Example 3. Comparative Example 4

[0043] The difference between Comparative Example 4 and Example 3 is that no microcapsules were added in Comparative Example 4.

[0044] Test case Coating peel strength: The coating peel strength of the composite diaphragm was tested using a universal tensile testing machine. The standard used was GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". The test results are shown in Table 1. Diaphragm adhesion: Take a complete diaphragm with no abnormalities in appearance, cut it into samples with a width of 25mm and a length of 100mm, take two punched samples and stack them together, and hot press them for 30min at a pressure of 3MPa and a temperature of 80℃. Then test the tensile strength of the two diaphragms bonded together with a tensile tester at a tensile speed of 1m / min. The test results are shown in Table 1. Contact angle: Using a contact angle measuring instrument (Shanghai Zhongchen JC2000D), 2μL of electrolyte was dropped onto the diaphragm surface at 25℃, and the contact angle between the droplet and the diaphragm was measured.

[0045] Liquid absorption rate and liquid retention rate: The separator was used in the assembly of lithium symmetric batteries. The electrolyte was DMC / Pyr13TFSI-LiTFSI (1M). The battery test temperature was 100℃. The liquid absorption rate and liquid retention rate were tested. The test results are shown in Table 1.

[0046]

[0047] By observing the data in Table 1, it was found that the functionalized membrane containing microcapsules prepared in Example 3 had the best overall performance.

[0048] A comparative analysis of Examples 1-4 and Comparative Example 1 revealed that the membrane prepared in Example 3 exhibited the best overall performance. The difference in performance may be attributed to variations in the mass ratios of aluminum chloride hexahydrate aqueous solution, urea, polystyrene-block-polyacrylic acid, and 3-aminopropyltriethoxysilane. These mass ratios directly determine the microstructure and surface properties of the modified boehmite hollow powder, thus affecting the overall performance of the functionalized membrane. In Example 1, when the amount of urea was too low, the urea hydrolysis rate was too slow, and the provided alkaline environment was insufficient for the complete hydrolysis and precipitation of aluminum chloride hexahydrate. This resulted in incomplete crystallization and uneven wall thickness in the generated boehmite hollow microspheres, with some particles exhibiting a solid or semi-hollow structure. This significantly reduced the porosity and specific surface area of ​​the modified additives, ultimately leading to a decrease in the membrane's liquid absorption and retention rates, and an increase in the contact angle. When the amount of polystyrene-block-polyacrylic acid in Comparative Example 1 is insufficient, the amphiphilic block copolymer cannot provide sufficient steric hindrance and electrostatic stabilization during the crystallization process of the metal salt, resulting in the agglomeration and stacking of boehmite particles, uneven particle size distribution, and a high breakage rate of the hollow structure. At the same time, the hydrogen bonding between the hydrophilic segment of the copolymer and the functional group of the coupling agent is weakened, reducing the efficiency of subsequent surface modification. When the amount of 3-aminopropyltriethoxysilane deviates from the optimal value, the grafting density of the coupling agent on the surface of the hollow microspheres becomes unbalanced. When the amount is too low, the surface modification is insufficient, resulting in poor compatibility and a decrease in coating peel strength and membrane adhesion. When the amount is too high, the coupling agent molecules are prone to self-condensation reaction, forming multilayer stacking on the surface of the hollow microspheres, which hinders the effective bonding with the acrylate binder in the slurry. The mass ratio of Example 3 achieved the best synergistic matching of urea slow-release hydrolysis rate, copolymer spatial stabilization effect, and coupling agent surface grafting density. The prepared modified boehmite hollow microspheres have the best shell integrity, porosity, particle size uniformity, and surface grafting rate, so that the functionalized diaphragm achieves the best level in key performance indicators such as coating peel strength, diaphragm adhesion, contact angle, liquid absorption rate, and liquid retention rate.

[0049] A comparative analysis of Examples 3, 5-6, and Comparative Example 2 revealed that the membrane prepared in Example 3 exhibited the best overall performance. The difference in performance may be attributed to the use of different water-soluble metal salt precursors, resulting in different modifiers. Under the alkaline environment provided by the slow-release hydrolysis of urea, different metal salt precursors exhibited significant differences in hydrolysis precipitation behavior, crystallization kinetics, and the surface chemical properties of the resulting hollow metal oxide microspheres, thus affecting the microstructure and functional properties of the modified additives. Example 3 uses boehmite hollow microspheres prepared with aluminum chloride hexahydrate. These microspheres are rich in hydroxyl groups on their surface, exhibiting the strongest reactivity with the 3-aminopropyltriethoxysilane coupling agent and a high surface grafting rate. The layered crystal structure of boehmite also endows them with excellent thermal stability and moderate mechanical strength, enabling the formation of a complete hollow structure. This allows the modified additives to provide both rigid skeletal support and sufficient liquid storage space in the coating. Example 5 uses titanium tetrachloride to prepare titanium dioxide hollow microspheres. Although these microspheres have good resistance to electrolyte corrosion, their surface hydroxyl density is low, and the high hardness of titanium dioxide leads to coating degradation. Microcracks are easily generated during hot pressing, reducing the peel strength of the coating and the adhesion of the diaphragm. In Example 6, magnesium oxide hollow microspheres prepared using magnesium acetate tetrahydrate, while exhibiting good toughness, suffered from excessive surface alkalinity leading to low hydroxyl density. Simultaneously, the rapid hydrothermal crystallization rate of magnesium oxide resulted in a thicker shell layer for the hollow microspheres, reducing the proportion of the internal cavity volume and lowering the porosity. Consequently, the liquid absorption and retention rates were significantly lower than in Example 3. In Comparative Example 2, zinc oxide hollow microspheres prepared using zinc nitrate were prone to a dissolution-reprecipitation process under alkaline urea hydrolysis conditions, leading to severe particle agglomeration and ultimately causing the overall performance of the diaphragm to be significantly inferior to that of Example 3.

[0050] Comparative analysis of Examples 3 and 7 revealed that the membrane prepared in Example 3 exhibited the best overall performance. The difference in performance may be attributed to the use of different core materials. The boiling point and chemical stability of the core material directly affect the survival rate of the microcapsules during preparation and their functional stability during use. The decahydronaphthalene used in Example 3 maintained a low vapor pressure inside the microcapsules during gradient temperature-controlled drying, resulting in low internal pressure stress on the polyurea shell, high microcapsule integrity, and a large number of effective microcapsules in the coating. This provided a larger liquid storage space and stronger interfacial adhesion between the coating and the base membrane, leading to significantly better liquid absorption rate, liquid retention rate, coating peel strength, and membrane adhesion compared to Example 7. In contrast, the ethyl acetate used in Example 7 approached its boiling point during the second stage of drying, causing a sharp increase in the vapor pressure inside the microcapsules. This led to premature rupture and failure of the microcapsules. The fragments of the ruptured microcapsule shells blocked the coating pores, reducing the porosity and hydrophilicity of the coating. At the same time, the released ethyl acetate evaporated rapidly during the drying process, leaving behind polyurea shell residues with stronger hydrophobicity. This resulted in an increased contact angle and a decrease in liquid absorption and retention rates, ultimately making the overall performance of the diaphragm inferior to that of Example 3.

[0051] Comparative analysis of Example 3, Comparative Example 3, and Comparative Example 4 revealed that the membrane prepared in Example 3 had the best overall performance. The reason for this performance difference may be that the slurry prepared with a specific formula in Example 3 had a good synergistic effect between the modified additives and the microcapsules.

[0052] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made to the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A functionalized diaphragm containing microcapsules, characterized in that, include: Polyethylene film, and slurry coated on the polyethylene film; the slurry comprises the following raw materials in parts by weight: 28-55 parts microcapsules, 8-12 parts acrylate, 0.5-1.5 parts sodium polycarboxylate, 100-150 parts water, and 20-35 parts modifying additives; the microcapsules comprise a polymer shell and an encapsulated core material; The modified additive is obtained by surface modification of hollow inorganic powder, including the following raw materials: water-soluble metal salt precursor, urea, amphiphilic block copolymer, and coupling agent; the mass ratio of the water-soluble metal salt precursor, urea, amphiphilic block copolymer, and coupling agent is 100:(2-30):(4-50):(3-30).

2. The functionalized diaphragm containing microcapsules according to claim 1, characterized in that, The modified additive is prepared by the following method: S1. Dissolve the amphiphilic block copolymer in a solvent, add water, stir, evaporate by rotary evaporation, and adjust the pH to 5-6 to obtain the base material; S2. Add water-soluble metal salt precursor and water to the base material prepared in step S1, stir, add urea, heat, stir, wash, and vacuum dry to obtain hollow inorganic powder. Add anhydrous ethanol to obtain hollow inorganic solution. S3. Mix the coupling agent with anhydrous ethanol, heat, add to the hollow inorganic solution prepared in step S2, heat in an oil bath, centrifuge, wash, and dry to obtain the modified additive.

3. The microcapsule-containing functionalized separator according to claim 1, wherein The water-soluble metal salt precursor is any one or more of water-soluble aluminum salt, water-soluble titanium salt, and water-soluble magnesium salt.

4. The microcapsule-containing functionalized separator according to claim 3, characterized in that, The water-soluble aluminum salt is any one or more of aluminum chloride hexahydrate, aluminum sulfate octadechydrate, and aluminum nitrate nonahydrate; the water-soluble titanium salt is any one or more of titanium tetrachloride and titanium oxysulfate; the water-soluble magnesium salt is any one or more of magnesium chloride hexahydrate, magnesium nitrate hexahydrate, and magnesium acetate tetrahydrate.

5. The microcapsule-containing functionalized separator according to claim 1, wherein The amphiphilic block copolymer is either polystyrene-block-polyacrylic acid or polystyrene-block-hydroxyethyl acrylate.

6. The microcapsule-containing functionalized separator according to claim 1, wherein The polymer shell material is either polyurea or gelatin.

7. The microcapsule-containing functionalized separator according to claim 1, wherein The core material is either decahydronaphthalene or ethyl acetate.

8. The microcapsule-containing functionalized separator according to claim 2, wherein The heating temperature in step S2 is 150-180℃.

9. The microcapsule-containing functionalized separator according to claim 2, wherein In step S2, the stirring speed is 200-500 rpm and the stirring time is 20-24 h.

10. A process for the preparation of the microcapsule-containing functionalized separator according to any one of claims 1 to 9, characterized in that, Includes the following steps: Step 1: Polymerize the polymer shell and core materials to prepare microcapsules; Step 2: Perform plasma treatment on the polyethylene film. Step 3: Mix the microcapsules, sodium polycarboxylate, and water, add acrylate, disperse ultrasonically, add the modifying additive, and stir to obtain a slurry; Step 4: Coat the slurry onto the treated base film, apply it via slit coating, dry it under gradient temperature control, and then roll it up to obtain the functionalized diaphragm containing microcapsules.

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