Modified composite separator and preparation method and use thereof

Abstract

This invention belongs to the field of battery materials technology. It provides a modified composite separator, its preparation method, and its applications. The modified composite separator includes a base film and a modified layer. The modified layer is disposed on the surface of the base film. The modified layer comprises a polymer, wherein the monomer of the polymer contains a purine ring structure, and the purine ring structure is connected to one of benzenesulfonic acid groups, benzenesulfonate groups, or benzenesulfonamide groups. The benzenesulfonic acid structure has strong hydrophilicity, which can significantly improve the wettability of the separator to the electrolyte and reduce interfacial impedance. Simultaneously, the negative charge of the sulfonic acid groups can form selective ion channels through electrostatic repulsion, promoting efficient lithium-ion transport and improving rate performance. The purine ring in the polymer structure has excellent rigidity and stability, which can improve the thermal stability of the modified layer.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a modified composite separator, its preparation method and application. Background Technology

[0002] Since their commercialization in the 1990s, lithium-ion batteries have rapidly become the core energy storage component in portable electronic devices, electric vehicles, and large-scale energy storage systems. In recent years, with the continuous advancement of power battery technology, the driving range of electric vehicles has significantly improved, gradually alleviating users' anxiety about range. However, correspondingly, charging speed has become a new bottleneck affecting user experience and widespread adoption. Therefore, developing lithium-ion battery systems with fast charging capabilities has become one of the key directions of current technological development.

[0003] To achieve fast-charging performance targets, it is necessary to further improve the energy density and power density of lithium-ion batteries. Therefore, improvement measures mainly focus on the positive and negative electrode materials.

[0004] In terms of cathode materials, high-nickel ternary materials (such as NCM811 and NCA) have become one of the mainstream choices for high-energy-density power batteries due to their high specific capacity and energy density. The theoretical specific capacity of high-nickel ternary materials can reach over 200 mAh / g, far exceeding that of traditional cathode materials such as lithium iron phosphate (approximately 160 mAh / g) and lithium manganese oxide (approximately 120 mAh / g). However, high-nickel materials suffer from poor structural stability, low thermal stability, and numerous interfacial side reactions under high voltage. Especially under fast charging conditions, they are prone to local lithium deposition and interfacial instability, which in turn affect the cycle life and safety of the battery.

[0005] In terms of anode materials, silicon-based anodes possess a high theoretical specific capacity, making them a strong competitor to graphite anodes. Graphite anodes are approaching their theoretical upper limit of 372 mAh / g, while silicon-based anodes boast a theoretical specific capacity as high as 4200 mAh / g, approximately 10 times that of graphite anodes. Furthermore, silicon-based anode materials exhibit a lower lithium insertion / extraction potential (~0.4V vs. Li / Li). + Slightly higher than graphite (~0.05V vs. Li / Li) + During fast charging, lithium plating on the surface can be avoided. However, the huge volume expansion (over 300%) that occurs in silicon-based materials during repeated lithium insertion / extraction processes leads to the destruction of the electrode material structure, particle pulverization, and breakage of the conductive network, resulting in rapid capacity decay and reduced cycle life.

[0006] Besides improvements in material systems, the separator, as an indispensable key component of lithium-ion batteries, directly affects the battery's ion transport capacity, thermal stability, and safety performance. Currently, commercially available lithium-ion batteries generally use polyolefin separators (such as polyethylene (PE), polypropylene (PP), and their composite multilayer structures). However, commercially available polyolefin separators and coatings suffer from problems such as low porosity, poor heat resistance, easy shrinkage upon heating, and susceptibility to separator puncture leading to lithium dendrite formation and thermal runaway. These issues can easily lead to direct contact between the positive and negative electrodes, puncturing the separator and causing short circuits, severely impacting the safety, lifespan, and performance of lithium-ion batteries.

[0007] Therefore, when constructing a high-nickel ternary / silicon-carbon composite system, it is still necessary to develop a membrane solution with excellent comprehensive performance, including high temperature resistance, high performance, and high safety. Summary of the Invention

[0008] In view of the problems existing in the prior art, the purpose of this invention is to provide a modified composite separator, its preparation method and uses. The modified composite separator includes a base membrane and a modified layer; the modified layer is disposed on the surface of the base membrane; the modified layer includes a polymer, wherein the monomer of the polymer contains a purine ring structure, and the purine ring structure is connected with one of benzenesulfonic acid group, benzenesulfonate group or benzenesulfonamide group. The benzenesulfonic acid structure has strong hydrophilicity, which can significantly improve the wettability of the separator to the electrolyte and reduce interfacial impedance. At the same time, the negative charge characteristics of the sulfonic acid group can form selective ion channels through electrostatic repulsion, promoting efficient lithium ion transport and improving rate performance. The purine ring in the polymer structure has excellent rigidity and stability, which can improve the thermal stability of the modified layer.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a modified composite membrane, the modified composite membrane comprising a base membrane and a modified layer; the modified layer being disposed on the surface of the base membrane; the modified coating comprising a polymer, wherein the monomer of the polymer comprises a compound having the structure shown in Formula A:

[0011]

[0012] In this embodiment, either R1 or R2 is selected from C2 to C4 alkenyl, and the other is selected from hydrogen, C1 to C3 alkyl or C1 to C3 alkoxy; either R3 or R4 is selected from benzenesulfonic acid or benzenesulfonamide, and the other is selected from hydrogen, C1 to C3 alkyl or C1 to C3 alkoxy.

[0013] In the modified layer of this invention, the benzenesulfonic acid groups or benzenesulfonamide groups have strong hydrophilicity, which can significantly improve the wettability of the separator to the electrolyte and reduce interfacial impedance. Simultaneously, the negative charge characteristics of the sulfonic acid groups can form selective ion channels through electrostatic repulsion, promoting efficient lithium-ion transport and improving rate performance. The purine rings in the polymer structure have a certain degree of rigidity and stability, which can improve the thermal stability of the coating layer. During battery use, especially in high-temperature environments, ordinary separators may experience thermal shrinkage and melting, affecting battery safety and performance. The modified layer formed by the polymer can maintain structural stability at higher temperatures, preventing excessive deformation of the separator and maintaining the integrity of the battery's internal structure, thereby improving the battery's thermal safety. Furthermore, the benzenesulfonic acid groups or benzenesulfonamide groups can form hydrogen bonds with the hydroxyl groups on the silicon surface, further enhancing the interaction force between the separator and the negative electrode (especially the silicon negative electrode).

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0015] As a preferred technical solution of the present invention, in the compound with the structure shown in Formula A, R1 is selected from C2 to C4 alkenyl, R2 is selected from C1 to C3 alkyl, R3 is selected from benzenesulfonic acid group or benzenesulfonamide group, and R4 is hydrogen.

[0016] As a preferred embodiment of the present invention, the monomer of the polymer includes at least one compound having the following structural formula:

[0017]

[0018] The compound shown in Formula B is named 4-(1-allyl-3,7-dimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-yl)benzenesulfonic acid, with the chemical formula C. 16 H 16 N4O5S, CAS number 149981-25-9.

[0019] As a preferred embodiment of the present invention, the weight-average molecular weight Mw of the polymer is 50,000 to 200,000 Da, for example, it can be 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, 160,000, 180,000, 190,000, or 200,000, etc.

[0020] In this invention, if the weight-average molecular weight of the polymer is too low, the film-forming properties and interfacial adhesion will be insufficient, and the mechanical strength will be insufficient. If the molecular weight is too high, the viscosity will increase and the coating uniformity will decrease. If the molecular weight of the polymer is too low, the chain segment entanglement will be insufficient and the crystallinity will be low. If the molecular weight is too high (e.g., exceeding 200,000 Da), the molecular chain entanglement will intensify, hindering the orderly arrangement, and the crystallinity will decrease instead. The crystallinity is moderate between 50,000 and 200,000 Da, which can balance rigidity and flexibility. The melting temperature increases, but the brittleness increases.

[0021] Preferably, the modified coating is disposed on one or both sides of the base film, and the thickness of the modified coating is 1 to 4 μm, such as 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm, 3.3 μm, 3.5 μm, 3.8 μm or 4 μm.

[0022] In this invention, the functional coating is too thin and unevenly distributed, resulting in insufficient buffering / protection against the expansion of the silicon anode and limited improvement in thermal stability. + The improvement in transport efficiency is not significant; excessive thickness will increase the total thickness and internal resistance of the modified composite membrane, reduce the energy density and power density of the battery, may lead to excessively high permeability (Gurley value) affecting electrolyte wetting and ion transport, and increase costs.

[0023] Preferably, the base film is made of PP (polypropylene) and / or PE (polyethylene).

[0024] Preferably, the thickness of the base film is 7–16 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or 16 μm, and the porosity is 30%–60%, such as 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, or 60%. When the base film is a single layer, the thickness is preferably 6–12 μm.

[0025] In this invention, the base membrane can be a three-layer composite PP / PE / PP separator, preferably a PE separator. If the base membrane is too small, it results in low mechanical strength and the separator is easily punctured; if the thickness is too large, the ion transport distance increases, leading to a decrease in energy density and a decline in rate performance. If the separator has too high porosity, it results in high high-temperature shrinkage; if the porosity is too low, the liquid absorption rate is low, and rate performance is affected.

[0026] As a preferred embodiment of the present invention, the modified coating further includes inorganic particles, and the polymer is mixed with and / or encapsulates the inorganic particles.

[0027] In this invention, inorganic oxide particles are preferably introduced to co-form the modified coating. The inorganic particles and polymers are mixed or "encapsulated" to form a strong organic-inorganic network, which significantly improves the mechanical strength and toughness of the coating. The synergistic effect is far greater than that of using a single component. At the same time, the polymer provides adhesion and stress buffering, while the inorganic particles (especially high-melting-point Al2O3) provide rigid support and thermal barrier, synergistically improving thermal stability and jointly resisting high-temperature thermal shrinkage and silicon expansion stress.

[0028] Preferably, the inorganic particles include silicon oxide (SiO2) and / or aluminum oxide (Al2O3).

[0029] Preferably, the silicon oxide comprises mesoporous silicon oxide with a pore volume of 1.2–1.5 cm³. 3 / g, for example, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc.; specific surface area of ​​200-300m² 2 / g, for example 200m 2 / g、210m 2 / g、220m 2 / g、230m 2 / g、240m 2 / g、250m 2 / g、260m 2 / g、270m 2 / g、280m 2 / g、290m 2 / g or 300m 2 / g etc.

[0030] Preferably, the inorganic particles have a D 50 The particle size is 5–50 nm, such as 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm.

[0031] Preferably, the D of alumina 50 A particle size of 5–25 nm can improve the puncture resistance of the coating, while Al 3+ It can adsorb HF, which helps to inhibit electrolyte decomposition.

[0032] Preferably, the D of mesoporous silica 50 With a particle size of 25–50 nm, the large pore volume can adsorb electrolyte, increasing the electrolyte absorption rate. At the same time, the high pore volume and specific surface area of ​​mesoporous silica can adsorb more electrolyte, improve interfacial wettability and prolong electrolyte retention time, thereby reducing interfacial polarization and improving fast charging performance.

[0033] In this invention, if the particle size of the inorganic particles is too large, it is difficult for them to form a coating with the polymer or be coated, and the coating thickness will be increased. If the particle size is too small, they are prone to agglomeration, which will reduce the coating strength and may block the pores of the base film.

[0034] Preferably, the inorganic particles comprise alumina and silicon oxide in a mass ratio of (0.2 to 3):1, such as 0.2:1, 0.5:1, 0.8:1, 1:1, 1.3:1, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.8:1, or 3:1.

[0035] In this invention, the combination of inorganic particles should form a reasonable packing pore structure; for example, large particles form a skeleton, and small particles fill the gaps.

[0036] Preferably, the mass ratio of the polymer to the inorganic particles is (1-7):1, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1 or 7:1, etc.

[0037] In this invention, the combination of inorganic particles and polymers should form a reasonable organic-inorganic network.

[0038] In a second aspect, the present invention provides a method for preparing the modified composite diaphragm described in the first aspect, wherein a polymer is formulated into a coating slurry, coated on the surface of a base membrane and then dried to form a modified coating, thereby obtaining a modified composite diaphragm.

[0039] As a preferred technical solution of the present invention, the method for preparing the polymer includes: mixing monomers, organic solvents and initiators, and carrying out a polymerization reaction to obtain the polymer.

[0040] Preferably, the organic solvent includes at least one of benzene, tetrahydrofuran (THF), N-methylpyrrolidone (NMP), or dimethylformamide (DMF).

[0041] Preferably, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide (BPO).

[0042] Preferably, the initiator accounts for 0.5% to 1% of the total mass of the monomer, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%.

[0043] Preferably, the polymerization reaction is carried out under the protection of an inert atmosphere, and the temperature of the polymerization reaction is 60-120°C, such as 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C; the time is 10-36h, such as 10h, 13h, 15h, 18h, 20h, 23h, 25h, 28h, 30h, 33h or 36h.

[0044] Preferably, after the polymerization reaction is completed, a polymer solution is obtained. The polymer solution is mixed with the precipitation solvent to precipitate the polymer. The precipitate is then washed and dried to obtain the polymer.

[0045] Preferably, the precipitation solvent includes at least one of propanol, isopropanol, or acetone.

[0046] As a preferred embodiment of the present invention, the preparation method further includes preparing the coating slurry by combining the polymer with inorganic particles.

[0047] Preferably, the process of preparing the coating slurry includes: first stirring and mixing the dispersant with water, then adding inorganic particles for a second stirring and mixing, and then adding polymer, organic solvent, thickener and wetting agent for a third stirring and mixing to obtain the coating slurry.

[0048] Preferably, the mass ratio of the inorganic particles, dispersant, and water is 1:(2.2~13.2):(0.005~0.06). For example, when the mass ratio of the inorganic particles is 1, the mass ratio of the dispersant can be 2.2, 2.6, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, or 13.2, etc., and the mass ratio of water can be 0.005, 0.008, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, or 0.06, etc.

[0049] Preferably, the mass ratio of the polymer, organic solvent, thickener, and wetting agent is 1:(0.06-0.25):(0.06-0.3):(0.0006-0.004). For example, when the mass ratio of the polymer is 1, the mass ratio of the organic solvent can be 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, or 0.25, etc.; the mass ratio of the thickener can be 0.06, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, or 0.3, etc.; and the mass ratio of the wetting agent can be 0.0006, 0.0008, 0.001, 0.0013, 0.0015, 0.0018, 0.002, 0.0023, 0.0026, 0.003, 0.0033, 0.0035, 0.0038, or 0.004, etc.

[0050] Preferably, the organic solvent includes at least one of ethanol, isopropanol, n-propanol, or propylene glycol methyl ether (PGME).

[0051] In this invention, organic solvents can also act as dispersants. Specifically, they can improve the dispersibility of polymers in aqueous systems (polymers contain hydrophobic groups, and using water alone can easily lead to agglomeration); they can adjust the viscosity of the slurry (reducing surface tension and making the slurry easier to spread); and they can promote subsequent drying efficiency (they have a moderate boiling point, form an azeotrope with water, and accelerate water evaporation). Therefore, low-boiling-point polar organic solvents with good water compatibility can be selected.

[0052] Preferably, the dispersant includes at least one of silicates, sodium polyacrylate, or sodium citrate.

[0053] In this invention, the dispersant can uniformly disperse inorganic particles that are difficult to dissolve in liquid, while also preventing the sedimentation and aggregation of inorganic particles to form a stable suspension.

[0054] Preferably, the thickener includes at least one of carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), or polyvinyl alcohol (PVA).

[0055] In this invention, the thickener increases the viscosity of the slurry through molecular chain entanglement, preventing component sedimentation and ensuring coating uniformity.

[0056] Preferably, the wetting agent includes at least one of sodium hexametaphosphate, sodium tripolyphosphate, or sodium pyrophosphate.

[0057] In this invention, the wetting agent mainly functions to reduce surface tension, enhance the fluidity of the slurry, and prevent "pinholes" from occurring during coating.

[0058] It should also be noted that when preparing a coating slurry that does not contain the aforementioned inorganic particles, it should contain the above-mentioned polymer, water (as the main dispersion medium), organic solvent, thickener, and wetting agent.

[0059] Preferably, the rotation speed of the first stirring and mixing is 2000-3100 rpm, such as 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm or 3100 rpm; the revolution speed is 20-40 rpm, such as 20 rpm, 25 rpm, 28 rpm, 30 rpm, 33 rpm, 36 rpm or 40 rpm; and the stirring time is 5-45 min, such as 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min or 45 min.

[0060] Preferably, the rotation speed of the second stirring and mixing is 2000-3100 rpm, such as 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm or 3100 rpm; the revolution speed is 20-50 rpm, such as 20 rpm, 25 rpm, 28 rpm, 30 rpm, 33 rpm, 36 rpm, 40 rpm, 43 rpm, 48 rpm or 50 rpm; and the stirring time is 10-30 min, such as 10 min, 15 min, 20 min, 25 min or 30 min.

[0061] Preferably, the first stirring and blending and the second stirring and blending are performed under ultrasound, and the ultrasound frequency is 20 to 50 kHz, such as 20 kHz, 23 kHz, 25 kHz, 28 kHz, 30 kHz, 33 kHz, 35 kHz, 38 kHz, 40 kHz, 43 kHz, 45 kHz, 48 kHz or 50 kHz.

[0062] Preferably, the rotation speed of the third stirring and mixing process is 1000-3000 rpm, such as 1000 rpm, 1300 rpm, 1500 rpm, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, or 3000 rpm; the revolution speed is 20-40 rpm, such as 20 rpm, 25 rpm, 28 rpm, 30 rpm, 33 rpm, 36 rpm, or 40 rpm; and the stirring time is 15-30 min, such as 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, or 30 min.

[0063] Preferably, the third stirring and mixing is performed simultaneously with ultrasonic vacuum oscillation, the frequency of which is 5 to 60 kHz, such as 5 kHz, 10 kHz, 15 kHz, 20 kHz, 25 kHz, 30 kHz, 35 kHz, 40 kHz, 45 kHz, 50 kHz, 55 kHz or 60 kHz.

[0064] Preferably, the first stirring and blending, the second stirring and blending, and the third stirring and blending all employ planetary mixing equipment.

[0065] As a preferred embodiment of the present invention, the coating method includes microgravure printing coating, wherein the anilox roller of the microgravure printing coating has a line count of 150-200 lines / cm, such as 150 lines / cm, 160 lines / cm, 170 lines / cm, 180 lines / cm, 190 lines / cm, or 200 lines / cm, etc.; and the coating speed is 10-29 m / min, such as 10 m / min, 13 m / min, 15 m / min, 18 m / min, 20 m / min, etc. The printing speed is m / min, 23m / min, 25m / min or 29m / min, etc.; the printing gap is 0.1 to 0.3 mm, such as 0.1 mm, 0.130 mm, 0.15 mm, 0.18 mm, 0.2 mm, 0.23 mm, 0.25 mm, 0.28 mm or 0.3 mm, etc.; the squeegee angle is 45° to 65°, such as 45°, 48°, 50°, 53°, 55°, 58°, 60°, 62° or 65°, etc.

[0066] Preferably, the drying process involves the material being pulled into a drying device by a traction roller.

[0067] Preferably, the drying temperature is 40-80°C, such as 40°C, 50°C, 60°C, 70°C or 80°C; and the drying time is 1-5 min, such as 1 min, 2 min, 3 min, 4 min or 5 min.

[0068] Preferably, the air velocity during drying is controlled at 15-25 m / s, such as 15 m / s, 16 m / s, 18 m / s, 20 m / s, 22 m / s, or 25 m / s.

[0069] Preferably, the product is wound up after drying, and the winding tension is 10-15 N / m, such as 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m or 15 N / m.

[0070] Thirdly, the present invention provides a battery comprising the modified composite separator described in the first aspect.

[0071] It should be noted that this invention does not specifically limit the selection of the positive electrode and positive electrode material, negative electrode and negative electrode material, and electrolyte in the battery. All materials widely used in the art are applicable to this invention. The modified composite separator described in this invention is particularly suitable for batteries with fast-charging systems. For example, the positive electrode material can be a high-nickel ternary material, and the negative electrode material can be silicon or silicon-carbon composite material, etc. Conductive agents and binders are also used in the positive and negative electrodes. In addition to solvents and lithium salts, the electrolyte can also contain additives that can improve performance such as fast-charging rate, which will not be elaborated further here.

[0072] It should also be noted that, due to space limitations and to avoid redundancy, this invention does not exhaustively list all point values ​​within the above numerical range, but it is not limited to the listed values ​​either; other unlisted values ​​within the above numerical range are also applicable.

[0073] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0074] The modified composite separator of this invention comprises a base membrane and a modified layer; the modified layer is disposed on the surface of the base membrane; the modified coating comprises a polymer, wherein the monomer of the polymer contains a purine ring structure, and the purine ring structure is connected with one of benzenesulfonic acid groups, benzenesulfonate groups, or benzenesulfonamide groups. The benzenesulfonic acid structure has strong hydrophilicity, which can significantly improve the wettability of the separator to the electrolyte and reduce interfacial impedance. Simultaneously, the negative charge characteristic of the sulfonic acid group can form selective ion channels through electrostatic repulsion, promoting efficient lithium-ion transport and improving rate performance. The purine ring in the polymer structure has excellent rigidity and stability, which can improve the thermal stability of the modified layer. Detailed Implementation

[0075] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0076] Those skilled in the art will understand that the embodiments described are merely illustrative of the invention and should not be construed as limiting the invention.

[0077] Example 1

[0078] This embodiment provides a modified composite separator, including a base membrane and modified coatings disposed on both upper surfaces of the base membrane; the base membrane is made of PP / PE / PP composite separator with a total thickness of 14μm and a porosity of 45%; the thickness of the modified coating on each side is 2μm; the modified coating comprises a polymer and inorganic particles in a mass ratio of 3:1, wherein the polymer and the inorganic particles are mixed and / or encapsulated together;

[0079] The inorganic particles comprise alumina and mesoporous silica in a mass ratio of 2.8:1; the mesoporous silica has a pore volume of 1.46 cm³. 3 / g, specific surface area is 282m² 2 / g,D 50 The particle size is 21 nm; the D of alumina 50 The particle size is 9 nm;

[0080] The polymer has a weight-average molecular weight (Mw) of 100,000 Da, and its monomer is compound 4-(1-allyl-3,7-dimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-yl)benzenesulfonic acid, represented by formula B, with the chemical formula C. 16 H 16 N4O5S, CAS number 149981-25-9:

[0081]

[0082] This embodiment also provides a method for preparing the modified composite membrane, including:

[0083] S1. Preparation of polymer: The monomer 4-(1-allyl-3,7-dimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-yl)benzenesulfonic acid was added to the organic solvent dimethylformamide, and 0.8% of the total monomer mass of the initiator benzoyl peroxide was added. Under the protection of argon, the polymerization reaction was carried out at 110°C for 18 h to generate the polymer poly(1-allyl-3,7-dimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-yl)benzenesulfonic acid, and a polymer solution was obtained. The polymer solution was added to the precipitation solvent acetone and mixed to precipitate. The precipitate was washed and dried to obtain the polymer.

[0084] S2. Preparation of coating slurry: In a planetary mixing device, the dispersant silicate dispersant and water are first stirred and mixed, and the mass ratio of dispersant to water is controlled at 60:0.1. The rotation speed of the first stirring and mixing is controlled at 3000 rpm, the revolution speed is controlled at 36 rpm, and the stirring time is 26 min. Ultrasonication is performed simultaneously with the first stirring and mixing, and the ultrasonic frequency is 25 kHz.

[0085] Inorganic particles are then added for a second stirring and mixing process. The mass ratio of the inorganic particles, dispersant and water is controlled to be 7:60:0.1. The rotation speed of the second stirring and mixing process is controlled to be 2400 rpm, the revolution speed is controlled to be 28 rpm, and the stirring time is controlled to be 30 min. Ultrasonication is performed simultaneously with the first stirring and mixing process at a frequency of 28 kHz.

[0086] Then, polymer, isopropanol, thickener CMC, and wetting agent sodium hexametaphosphate are added for a third stirring and mixing. The mass ratio of polymer to inorganic particles is controlled at 3:1, and the mass ratio of polymer, isopropanol, thickener, and wetting agent is controlled at 34:2.3:4.6:0.03. The rotation speed of the third stirring and mixing is controlled at 1200 rpm, the revolution speed is controlled at 26 rpm, and the stirring time is controlled at 28 min. During the third stirring and mixing, ultrasonic vacuum oscillation is performed at a frequency of 44 kHz to obtain the coating slurry.

[0087] S3. Coating: Microgravure printing is used for coating. The anilox roller line count is controlled at 160 lines / cm, the coating speed is 13m / min, the printing gap is 0.16mm, and the squeegee angle is 48°. The coating slurry is applied to the base film, and then the film is pulled into the drying equipment by the traction roller for drying. The drying temperature is controlled at 72℃, the time is 2min, and the air speed is controlled at 21m / s. After drying, the film is wound up with a winding tension of 10.2N / m to obtain the modified composite diaphragm.

[0088] Example 2

[0089] This embodiment provides a modified composite membrane in which the weight-average molecular weight (Mw) of the polymer in the modified coating is adjusted from 100,000 Da to 20,000 Da. Except for the above, the other conditions are exactly the same as in Example 1.

[0090] Example 3

[0091] This embodiment provides a modified composite membrane. The weight-average molecular weight (Mw) of the polymer in the modified coating of the modified composite membrane is adjusted from 100,000 Da to 50,000 Da. Except for the above, the other conditions are exactly the same as in Example 1.

[0092] Example 4

[0093] This embodiment provides a modified composite membrane in which the weight-average molecular weight (Mw) of the polymer in the modified coating is adjusted from 100,000 Da to 200,000 Da. Except for the above, the other conditions are exactly the same as in Example 1.

[0094] Example 5

[0095] This embodiment provides a modified composite membrane. The weight-average molecular weight (Mw) of the polymer in the modified coating of the modified composite membrane is adjusted from 100,000 Da to 250,000 Da. Except for the above, the other conditions are exactly the same as in Example 1.

[0096] Example 6

[0097] This embodiment provides a modified composite membrane, wherein the thickness of the modified coating of the modified composite membrane is adjusted from 2 μm to 0.5 μm, and all other conditions are exactly the same as in Embodiment 1.

[0098] Example 7

[0099] This embodiment provides a modified composite membrane, wherein the thickness of the modified coating of the modified composite membrane is adjusted from 2μm to 1μm, and all other conditions are exactly the same as in Embodiment 1.

[0100] Example 8

[0101] This embodiment provides a modified composite membrane, wherein the thickness of the modified coating of the modified composite membrane is adjusted from 2μm to 4μm, and all other conditions are exactly the same as in Embodiment 1.

[0102] Example 9

[0103] This embodiment provides a modified composite membrane, wherein the thickness of the modified coating of the modified composite membrane is adjusted from 2μm to 5μm, and all other conditions are exactly the same as in Embodiment 1.

[0104] Example 10

[0105] This embodiment provides a modified composite membrane. The modified coating of the modified composite membrane does not contain inorganic particles, but only polymers. Except for the above, the other conditions are exactly the same as those in Example 1.

[0106] Example 11

[0107] This embodiment provides a modified composite membrane. In the modified coating of the modified composite membrane, the mass ratio of polymer to inorganic particles is adjusted from 3:1 to 0.5:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0108] Example 12

[0109] This embodiment provides a modified composite membrane. In the modified coating of the modified composite membrane, the mass ratio of polymer to inorganic particles is adjusted from 3:1 to 1:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0110] Example 13

[0111] This embodiment provides a modified composite membrane. The mass ratio of polymer to inorganic particles in the modified coating of the modified composite membrane is adjusted from 3:1 to 7:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0112] Example 14

[0113] This embodiment provides a modified composite membrane. The mass ratio of polymer to inorganic particles in the modified coating of the modified composite membrane is adjusted from 3:1 to 8:1. Except for the above, the other conditions are exactly the same as those in Example 1.

[0114] Comparative Example 1

[0115] This comparative example uses the base film from Example 1 for subsequent battery assembly and related testing.

[0116] Comparative Example 2

[0117] In this comparative example, the monomer in Example 1 was replaced by 1-(3-CARBOXYPROPYL)3,7-DIMETHYL XANTHINE, with the chemical formula C1. 11 H 14 N4O4, CAS number 6493-07-8, has the following structural formula:

[0118]

[0119] Apart from the above, all other conditions are exactly the same as in Example 1.

[0120] Characterization and testing:

[0121] I. Heat shrinkage rate test of modified composite diaphragm at 150℃ / 30min:

[0122] Referring to the standard test method (GB / T 36363), the dimensional changes of the diaphragm sample in the free state were measured at the specified temperature (150℃) and time (30min), and the transverse (TD) and longitudinal (MD) thermal shrinkage rates were calculated.

[0123] Equipment and materials include: a high-temperature furnace with a temperature control accuracy of ±1℃ and an internal atmosphere of air or an inert gas (such as N2); sample clamps: a stainless steel frame or quartz glass plate to ensure unrestrained free shrinkage of the sample; measuring tools: a vernier caliper with an accuracy of 0.02mm or an optical projector (suitable for micron-level diaphragms); and graph paper or a laser rangefinder (for marking initial dimensions).

[0124] Test Procedure: Sample Preparation: Cut samples to 100mm × 100mm, avoiding the diaphragm edge by 10mm; Marking: Draw cross lines on the sample surface and record the initial transverse (TD) and longitudinal (MD) lengths L0 (accurate to 0.1mm); Pretreatment: Place the sample in an environment of 23±2℃ and 50±5%RH for 24h; High-Temperature Treatment: Place the sample flat on a fixture and put it in the center of a high-temperature furnace preheated to 150℃, ensuring the sample does not contact the furnace wall. After holding at this temperature for 30min, quickly remove the fixture and cool at room temperature for 10min; Dimensional Measurement: Measure the length L1 of the cross lines on the cooled sample (measured separately in the TD and MD directions); Final Calculation: Test 3 parallel samples for each sample and take the average value. Calculate the heat shrinkage rate (in %) as follows: (L0-L1) / L0×100%, and obtain the transverse (TD) and longitudinal (MD) shrinkage rates.

[0125] II. The preparation of lithium-ion batteries includes the following steps:

[0126] 1) Preparation of positive electrode sheet

[0127] The ternary material NCM811(LiNi) 0.8 Co 0.1 Mn 0.1 O2 is used as the positive electrode active material. It is mixed with binder PVDF (polyvinylidene fluoride), conductive agent SP (super-P conductive carbon black), and SWCNT (single-walled carbon nanotubes) in a mass ratio of 96:2:1.9:0.1 to obtain a positive electrode slurry. The positive electrode slurry is then coated onto aluminum foil through a coating process. After drying and cold pressing, a positive electrode sheet is obtained.

[0128] 2) Preparation of negative electrode sheet

[0129] Silicon-carbon anode material, conductive agent SP, SWCNT, binder PAA (polyacrylic acid) and SBR are mixed and stirred evenly in a mass ratio of 90:2:0.5:5:2.5 to obtain anode slurry. The solid content is controlled at 30%. Then, the anode slurry is coated onto copper foil current collector through a coating process. After vacuum drying and cold pressing, anode sheet is obtained.

[0130] 3) Selection of electrolyte

[0131] Solvents and additives include EC:PC:DMC:DEC:FEC in a volume ratio of 15:20:25:30:10, and LiPF6 with a lithium salt concentration of 1 mol / L.

[0132] 4) Manufacturing lithium-ion batteries

[0133] The modified composite separators from Examples 1-14 and Comparative Examples 1-2 are stacked sequentially with the positive and negative electrode sheets, respectively. The separators are positioned between the positive and negative electrode sheets to act as a separator. The cells are then wound to obtain bare cells. The bare cells are placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0134] III. Electrochemical Performance Testing

[0135] The LAND battery test system of Wuhan Jinno Electronics Co., Ltd. was tested at room temperature (25℃), and the charge and discharge voltage was limited to 2.5V to 4.2V.

[0136] 1) First Coulomb efficiency

[0137] At 25°C, the lithium-ion battery was charged at a constant current and constant voltage of 0.33C to 4.2V, allowed to stand for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V, allowed to stand for 1 minute. The initial coulombic efficiency of the lithium-ion battery was calculated.

[0138] Initial coulombic efficiency (in %) = Total capacity of lithium-ion battery during initial discharge at 0.33C / Total capacity of lithium-ion battery during initial charge at 0.33C × 100%.

[0139] 2) Capacity retention rate after 1000 cycles at room temperature (1°C / 2°C)

[0140] At 25℃, the lithium-ion battery was charged at a 1C rate using constant current and constant voltage to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the battery was discharged at a 2C rate using constant current to 2.5V, followed by a 10-minute rest. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 1000 charge-discharge cycles using the above method. The capacity retention rate after 1000 charge-discharge cycles using 1C / 2C was calculated. The capacity retention rate (%) after N cycles is calculated as follows: (Discharge capacity of the Nth cycle / Initial discharge capacity) × 100%, where N is the number of cycles.

[0141] 3) Room temperature 6C rate performance - constant current charge ratio

[0142] At 25℃, the lithium-ion battery was discharged at a constant current rate of 1C to 2.5V, left to stand for 10 minutes, and then charged at a constant current and constant voltage rate of 6C to 4.2V with a cutoff current of 0.05C. After standing for 10 minutes, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 of the lithium-ion battery were recorded. The constant current charge ratio of the 6C rate charging was calculated according to the following formula: 6C rate charging constant current charge ratio = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 × 100%.

[0143] 4) Cell thermal runaway ARC test

[0144] The ARC adiabatic thermal runaway test begins (the test sample is heated from room temperature to 45±2℃ inside the chamber, left to stand for 90 minutes, and the change in battery temperature rise rate is monitored). If the temperature rise exceeds 0.2℃ within 10 minutes (i.e., SHR>0.02℃ / min), it is considered that a self-heating reaction has occurred inside the battery, and the adiabatic environment is maintained until the battery experiences thermal runaway; if the temperature rise does not exceed 0.2℃ within 10 minutes (i.e., SHR≤0.02℃ / min), the next temperature rise step test continues; each temperature step is 5℃, and the steps are repeated at each step. The ARC test temperature range is 45℃~300℃, the self-heating initiation temperature is T1 (temperature rise rate SHR>0.02℃ / min), and the thermal runaway initiation temperature is T2 (temperature rise rate SHR>1℃ / min). SHR refers to the self-heating rate (SHR).

[0145] The above data is recorded in Table 1.

[0146] Table 1

[0147]

[0148] As can be seen from Table 1:

[0149] Example 1 vs. Comparative Example 1: The performance of Example 1 is significantly better than that of Comparative Example 1, with a higher thermal runaway initiation temperature and a lower thermal shrinkage rate at 150°C. This is because: Comparative Example 1 is only a polyolefin-based film, which has at least three major defects: ① strong hydrophobicity, poor electrolyte wettability (liquid absorption rate <200%), and high interfacial impedance; ② lack of sulfonic acid groups to guide lithium-ion transport, resulting in low ion transference number (<0.5) and poor rate performance; ③ lack of purine rings and inorganic particles to enhance thermal stability, making it prone to shrinkage at high temperatures (shrinkage rate >10% at 150°C), leading to a high risk of short circuits at the positive and negative electrode contacts. In contrast, the modified coating of Example 1 solves the above problems synergistically through "benzenesulfonic acid group hydrophilicity + purine ring thermal stability + inorganic particle mechanical support," thus comprehensively improving performance.

[0150] Example 1 vs Examples 2 to 5 (molecular weight difference): The performance of Examples 1 (100,000 Da), 3 (50,000 Da), and 4 (200,000 Da) is superior to that of Examples 2 (20,000 Da) and 5 (250,000 Da). For example, the retention rate after 1000 cycles is: 85.2% (Example 1) > 84.8% (Example 3) > 84.5% (Example 4) > 79.5% (Example 2) > 80.2% (Example 5). This is because: Too low a molecular weight (e.g., 20,000 Da, Example 2): short polymer chain segments, insufficient entanglement, poor film formation, easy cracking of the modified layer, leading to a decrease in electrolyte retention (<250%), and a continuous increase in interfacial impedance during cycling. Too high a molecular weight (e.g., 250,000 Da, Example 5): excessively dense molecular chain entanglement, decreased solvation ability, high viscosity of the coating slurry (>5000 mPa·s), resulting in poor coating uniformity, obstructed lithium-ion transport paths, and decreased rate performance. Within the preferred range (50,000 to 200,000 Da): the chain segment length is moderate, which ensures the integrity of film formation (mechanical strength > 30 MPa) and avoids excessive viscosity, while also ensuring unobstructed ion transport channels, thus resulting in optimal performance.

[0151] Example 1 vs Examples 6 to 9: The performance of Examples 1 (thickness 2 μm), 7 (thickness 1 μm), and 8 (thickness 4 μm) is superior to that of Examples 6 (thickness 0.5 μm) and 9 (thickness 5 μm). For example, the 6C constant current charge ratio is: 80.5% (Example 1) > 78.6% (Example 7) > 77.5% (Example 8) > 74.5% (Example 6) > 75.8% (Example 9). This is because: If the thickness is too thin (e.g., 0.5 μm, Example 6): the modified layer cannot completely cover the pores of the base film, and the hydrophobic polyolefin is still exposed locally, resulting in uneven electrolyte wettability and severe local lithium deposition during cycling. If the thickness is too thick (e.g., 5 μm, Example 9): the ion transport distance increases, the total resistance of the membrane increases (>100 mΩ), and the excessively thick coating is prone to clogging the pores of the base film (air permeability decreases by 30%), leading to a deterioration in rate performance. Preferred range (thickness 1-4 μm): can completely cover the base film (coverage >99%) without significantly increasing resistance (<50 mΩ), balancing wettability and ion transport efficiency.

[0152] Example 1 vs Examples 10 to 14: The performance of Example 1 (polymer to inorganic particles mass ratio 3:1), Example 12 (mass ratio 1:1), and Example 13 (mass ratio 7:1) is superior to that of Example 10 (no inorganic particles), Example 11 (mass ratio 0.5:1), and Example 14 (mass ratio 8:1). For example, the heat shrinkage rate at 150°C is: 0.4% / 0.5% (Example 1) < 1.0% / 1.2% (Example 12) < 0.8% / 0.9% (Example 13) < 2.1% / 2.3% (Example 10) < 2.3% / 2.5% (Example 11). This is because: the modified coating without inorganic particles (Example 10) is only polymer, and the chain segments are prone to relaxation at high temperatures (150°C), resulting in an increased heat shrinkage rate; moreover, the mechanical strength is low (puncture strength < 500g), and it cannot resist the expansion stress of the silicon anode. Too low a mass ratio (e.g., 0.5:1, Example 11): Insufficient polymer, inorganic particles cannot be effectively encapsulated, and the coating is prone to embrittlement and cracking (coating peeling rate >20% after 500 cycles). Too high a mass ratio (e.g., 8:1, Example 14): Insufficient proportion of inorganic particles, unable to form an effective thermal barrier and mechanical support, resulting in limited improvement in thermal stability (thermal runaway temperature only 155.3℃). Preferred range (mass ratio (1-7):1): The polymer and inorganic particles form an "organic-inorganic interpenetrating network," with the polymer providing adhesion and stress buffering, and the inorganic particles (Al2O3 / SiO3) providing rigidity and thermal stability, synergistically improving overall performance.

[0153] Example 1 vs. Comparative Example 2: The performance of Example 1 is significantly better than that of Comparative Example 1, with a higher thermal runaway initiation temperature and a lower thermal shrinkage rate at 150°C. This is because, compared to Comparative Example 2, the monomer of the polymer in Example 1 contains a purine ring structure, and the purine ring structure is connected to one of the following: benzenesulfonic acid group, benzenesulfonate group, or benzenesulfonamide group. The benzenesulfonic acid structure has strong hydrophilicity, which can significantly improve the wettability of the membrane to the electrolyte and reduce interfacial impedance. At the same time, the negative charge of the sulfonic acid group can form selective ion channels through electrostatic repulsion, promoting efficient lithium ion transport and improving rate performance. The purine ring in the polymer structure has excellent rigidity and stability, which can improve the thermal stability of the modified layer.

[0154] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0155] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0156] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A modified composite diaphragm, characterized in that, The modified composite membrane includes a base membrane and a modified coating; The modified coating is disposed on the surface of the base film; the modified coating comprises a polymer, wherein the monomer of the polymer comprises a compound having the structure shown in Formula A: ； In this embodiment, either R1 or R2 is selected from C2-C4 alkenyl, and the other is selected from hydrogen, C1-C3 alkyl or C1-C3 alkoxy; either R3 or R4 is selected from benzenesulfonic acid or benzenesulfonamide, and the other is selected from hydrogen, C1-C3 alkyl or C1-C3 alkoxy.

2. The modified composite diaphragm according to claim 1, characterized in that, In the compound with the structure shown in Formula A, R1 is selected from C2~C4 alkenyl, R2 is selected from C1~C3 alkyl, R3 is selected from benzenesulfonic acid group or benzenesulfonamide group, and R4 is hydrogen.

3. The modified composite diaphragm according to claim 1, characterized in that, The monomer of the polymer includes at least one compound having the following structural formula: 。 4. The modified composite diaphragm according to claim 1, characterized in that, The weight-average molecular weight (Mw) of the polymer is 50,000 to 200,000 Da.

5. The modified composite diaphragm according to claim 1, characterized in that, The modified coating is disposed on one or both sides of the base film, and the thickness of the modified coating is 1~4μm.

6. The modified composite diaphragm according to claim 1, characterized in that, The base film is made of PP and / or PE.

7. The modified composite diaphragm according to claim 1, characterized in that, The thickness of the base film is 7~16μm and the porosity is 30%~60%.

8. The modified composite diaphragm according to claim 1, characterized in that, The modified coating also includes inorganic particles, and the polymer is mixed with and / or encapsulates the inorganic particles.

9. The modified composite diaphragm according to claim 8, characterized in that, The inorganic particles include silicon oxide and / or aluminum oxide.

10. The modified composite diaphragm according to claim 9, characterized in that, The silicon oxide includes mesoporous silicon oxide having a pore volume of 1.2 to 1.5 cm 3 / g and a specific surface area of 200 to 300 m 2 / g.

11. The modified composite diaphragm according to claim 8, characterized in that, The inorganic particles' D 50 The particle size is 5~50nm.

12. The modified composite diaphragm according to claim 8 or 9, characterized in that, The inorganic particles comprise aluminum oxide and silicon oxide in a mass ratio of (0.2~3):

1.

13. The modified composite diaphragm according to claim 8, characterized in that, The mass ratio of the polymer to the inorganic particles is (1~7):

1.

14. A method for preparing the modified composite membrane according to any one of claims 1-13, characterized in that, The polymer is formulated into a coating slurry, coated on the surface of the base membrane, and then dried to form a modified coating, thus obtaining a modified composite membrane.

15. The method for preparing the modified composite membrane according to claim 14, characterized in that, The method for preparing the polymer includes: mixing monomers, organic solvents, and initiators, and carrying out a polymerization reaction to obtain the polymer.

16. The method for preparing the modified composite membrane according to claim 15, characterized in that, The organic solvent includes at least one of benzene, tetrahydrofuran, N-methylpyrrolidone, or dimethylformamide.

17. The method for preparing the modified composite membrane according to claim 15, characterized in that, The initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide.

18. The method for preparing the modified composite membrane according to claim 15, characterized in that, The initiator accounts for 0.5% to 1% of the total mass of the monomer.

19. The method for preparing the modified composite membrane according to claim 15, characterized in that, The polymerization reaction is carried out under an inert atmosphere, at a temperature of 60-120°C, for a time of 10-36 hours.

20. The method for preparing the modified composite membrane according to claim 15, characterized in that, After the polymerization reaction is completed, a polymer solution is obtained. The polymer solution is mixed with the precipitation solvent to precipitate the polymer. The precipitate is then washed and dried to obtain the polymer.

21. The method for preparing the modified composite membrane according to claim 20, characterized in that, The precipitation solvent includes at least one of propanol, isopropanol, or acetone.

22. The method for preparing the modified composite membrane according to claim 14, characterized in that, The preparation method further includes preparing the coating slurry by combining the polymer with inorganic particles.

23. The method for preparing the modified composite membrane according to claim 22, characterized in that, The process of preparing the coating slurry includes: first stirring and mixing the dispersant with water, then adding inorganic particles for a second stirring and mixing, and then adding polymer, organic solvent, thickener and wetting agent for a third stirring and mixing to obtain the coating slurry.

24. The method for preparing the modified composite diaphragm according to claim 23, characterized in that, The mass ratio of the inorganic particles, dispersant and water is 1:(2.2~13.2):(0.005~0.06).

25. The method for preparing the modified composite diaphragm according to claim 23, characterized in that, The mass ratio of the polymer, organic solvent, thickener, and wetting agent is 1:(0.06~0.25):(0.06~0.3):(0.0006~0.004).

26. The method for preparing the modified composite membrane according to claim 23, characterized in that, The organic solvent includes at least one of ethanol, isopropanol, n-propanol, or propylene glycol methyl ether.

27. The method for preparing the modified composite membrane according to claim 23, characterized in that, The dispersant includes at least one of silicates, sodium polyacrylate, or sodium citrate.

28. The method for preparing the modified composite membrane according to claim 23, characterized in that, The thickener includes at least one of carboxymethyl cellulose, hydroxypropyl methyl cellulose, or polyvinyl alcohol.

29. The method for preparing the modified composite diaphragm according to claim 23, characterized in that, The wetting agent includes at least one of sodium hexametaphosphate, sodium tripolyphosphate, or sodium pyrophosphate.

30. The method for preparing the modified composite membrane according to claim 23, characterized in that, The first stirring and mixing process has a rotation speed of 2000~3100 rpm, a revolution speed of 20~40 rpm, and a stirring time of 5~45 min.

31. The method for preparing the modified composite membrane according to claim 23, characterized in that, The second stirring and mixing process has a rotation speed of 2000~3100 rpm, a revolution speed of 20~50 rpm, and a stirring time of 10~30 min.

32. The method for preparing the modified composite diaphragm according to claim 23, characterized in that, The first stirring and blending and the second stirring and blending are carried out under ultrasound, and the ultrasound frequency is 20~50kHz.

33. The method for preparing the modified composite membrane according to claim 23, characterized in that, The rotation speed of the third stirring and mixing process is 1000~3000 rpm, the revolution speed is 20~40 rpm, and the stirring time is 15~30 min.

34. The method for preparing the modified composite membrane according to claim 23, characterized in that, The third stirring and mixing process is performed simultaneously with ultrasonic vacuum oscillation, the frequency of which is 5~60kHz.

35. The method for preparing the modified composite membrane according to claim 14, characterized in that, The coating method includes microgravure printing coating.

36. The method for preparing the modified composite membrane according to claim 14, characterized in that, The drying temperature is 40~80℃ and the time is 1~5min.

37. A battery, characterized in that, Contains the modified composite membrane according to any one of claims 1-13.

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