Lithium battery diaphragm with high heat resistance and low water absorption and preparation method thereof

Abstract

The invention relates to the field of lithium ion batteries, and discloses a high-heat-resistance and low-water-absorption lithium battery diaphragm and a preparation method thereof, and the high-heat-resistance and low-water-absorption lithium battery diaphragm is prepared from the following components by mass: 40-60 parts of alumina; 25 to 42 parts by mass of sodium perfluorooctanoate; 65 to 85 parts by mass of ultrapure water; 0.5-1.2 parts by mass of a dispersant; 1.3 to 2.9 parts by mass of a pore forming agent; 2.6 to 3.8 parts by mass of an adhesive; the base film is a polypropylene base film or a polyethylene base film, and the thickness of the base film is 7 to 9 [mu] m. Through aluminum oxide surface modification, base membrane treatment and optimized coating and drying processes, the water absorption of the diaphragm is remarkably reduced, the binding force of the coating and the base membrane is improved, the uniformity and microporous structure of the coating are improved, and excellent heat resistance, air permeability and electrochemical performance of the diaphragm are realized; the problems of poor thermal stability, high water absorption and insufficient coating adhesion in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a lithium battery separator with high heat resistance and low water absorption and a preparation method thereof. Background Art

[0002] As the core technology in the field of modern energy storage, lithium-ion batteries are widely used in consumer electronics, transportation, and grid energy storage due to their high energy density and long cycle life. The diaphragm is one of the key components of lithium-ion batteries. Its function is to isolate the positive and negative electrodes, prevent short circuits, and allow lithium ions to migrate freely. High-performance diaphragms need to meet many performance requirements, including excellent heat resistance, low water absorption, good air permeability, and high electrochemical stability. However, lithium battery diaphragms in the prior art have many problems in practical applications, which restrict the safety and performance of the battery.

[0003] Existing lithium battery separators use polyethylene (PE) or polypropylene (PP) as the base material, supplemented by ceramic coating to improve heat resistance and mechanical properties. However, due to the intrinsic performance limitations of the basic polyolefin materials, these separators are prone to thermal shrinkage in high temperature environments, resulting in an increased risk of short circuits. Although the ceramic coating can improve the thermal stability of the separator to a certain extent, due to the insufficient bonding between the coating and the base film, the separator coating under traditional processes is prone to fall off or break during use. In addition, the coating material (such as alumina) itself is easy to absorb moisture, and alumina particles that have not been surface-modified will significantly increase the moisture content of the separator. This high water absorption will cause the water content inside the battery to increase, thereby triggering side reactions and reducing battery performance and safety.

[0004] In the coating preparation process, conventional stirring methods are generally used in the prior art to disperse ceramic particles. However, due to the high surface energy of alumina particles, they are prone to agglomeration, resulting in uneven dispersion of the ceramic slurry, which in turn causes uneven coating, affecting the air permeability and electrochemical properties of the diaphragm. Furthermore, this uneven coating will lead to the formation of local hot spots in the battery, thereby accelerating battery aging and performance degradation. In addition, the existing process fails to finely control the microporous structure of the coating, and it is difficult to balance the air permeability and mechanical strength, resulting in insufficient ion transmission capacity of the diaphragm under high-rate charge and discharge conditions.

[0005] On the other hand, the selection and processing of the base film also have an important impact on the overall performance of the diaphragm. Most of the base films used in the prior art have not been specially modified, and the surface bonding force is weak, resulting in the ceramic coating and the base film not adhering firmly, and it is easy to delaminate and fall off under mechanical impact and high temperature. This defect makes the diaphragm show poor dimensional stability in high temperature environment. In addition, the interface bonding quality between the base film and the coating is insufficient, and tiny gaps are formed, which not only affects the density of the coating and the breakdown voltage of the diaphragm, but also further reduces the overall safety of the diaphragm.

[0006] Insufficient coating and drying processes are also common problems in the prior art. Due to the lack of precise control over coating thickness and drying temperature, the thickness of the diaphragm coating is often uneven, resulting in inconsistent pore distribution. This problem directly affects the air permeability of the diaphragm and increases the internal resistance of the battery. In addition, improper selection of drying temperature leads to unreasonable formation of coating pore structure. For example, too high temperature will destroy the performance of the base film, and too low temperature will lead to excessive residual moisture in the coating, which ultimately affects the long-term stability of the diaphragm.

[0007] In summary, the lithium battery separators in the prior art have significant deficiencies in terms of water absorption control, thermal stability improvement, coating uniformity and air permeability regulation. These technical problems have not been systematically solved in terms of materials, processes and structures, thus restricting the high-performance development of separators. In view of the defects in these prior arts, the present invention proposes a highly heat-resistant, low-water-absorption lithium battery separator and its preparation method through innovative technologies such as surface modification of aluminum oxide, optimization of coating and drying processes, and modified base film treatment, providing a new solution for improving separator performance. Summary of the invention

[0008] In view of the deficiencies in the prior art, the present invention provides a lithium battery separator with high heat resistance and low water absorption and a preparation method thereof, which solves the problems of high water absorption, poor thermal stability, insufficient coating uniformity and weak bonding between the coating and the base membrane of the lithium battery separator in the prior art.

[0009] To achieve the above objectives, the present invention is implemented by the following technical scheme: A lithium battery separator with high heat resistance and low water absorption, comprising the following components in parts by weight: Alumina: 40–60 parts by mass; Sodium perfluorooctanoate: 25–42 parts by weight; Ultrapure water: 65–85 parts by weight; Dispersant: 0.5–1.2 parts by mass; Pore ​​former: 1.3–2.9 parts by mass; Adhesive: 2.6–3.8 parts by mass; Wetting agent: 0.08–0.12 parts by mass.

[0010] Preferably, the base film is a polypropylene base film or a polyethylene base film, and the thickness of the base film is 7-9 μm.

[0011] Preferably, the particle size of the aluminum oxide is D50: 0.25-0.45 μm, D90: 0.7-0.9 μm.

[0012] Preferably, the temperature of the solution prepared by mixing sodium perfluorooctanoate with ultrapure water is 80-90° C., the stirring speed of the solution is 40-60 r / min, and the stirring time is 30-45 minutes.

[0013] Preferably, the pore-forming agent is an ethylene glycol compound.

[0014] Preferably, the adhesive is an acrylic adhesive.

[0015] A method for preparing a lithium battery separator with high heat resistance and low water absorption comprises the following steps: S1. Add 25-42 parts by mass of sodium perfluorooctanoate to 65-85 parts by mass of ultrapure water, and stir and dissolve at 80-90° C. for 30-45 minutes to obtain a first aqueous solution; S2, adding 40-60 parts by mass of aluminum oxide to the first aqueous solution, stirring at 50-60° C. for 30-35 minutes, filtering to obtain a solid, and breaking it up by pneumatic spraying to obtain a pretreated aluminum oxide with a particle size of D50: 0.25-0.45 μm, D90: 0.7-0.9 μm; S3, mixing 32-38 parts by mass of pretreated alumina with 29-35 parts by mass of ultrapure water, and adding 0.5-1.2 parts by mass of a dispersant and stirring for 60 minutes; S4. Under ultrasonic mixing conditions, add 1.3-2.9 parts by mass of a pore former to the mixture, stir for 30 minutes, add 2.6-3.8 parts by mass of a binder and 0.08-0.12 parts by mass of a wetting agent, and continue ultrasonic mixing for 15-20 minutes to obtain a ceramic slurry; S5, coating the obtained ceramic slurry on one side of a base film having a thickness of 7-9 μm, with a coating speed of 30-40 m / min and a coating thickness of 1-2 μm; S6. Dry at 80-100°C for 2-4 minutes to obtain a lithium battery separator with high heat resistance and low water absorption.

[0016] Preferably, the ultrasonic mixing of the ceramic slurry is carried out under vacuum conditions, with an ultrasonic frequency of 5-8 kHz, a rotation speed of 2000-2500 r / min, and a revolution speed of 35-45 r / min.

[0017] Preferably, the pressure during the pneumatic spraying and dispersion of the aluminum oxide is 3-5 MPa.

[0018] Preferably, the drying time is 2-3 minutes and the drying temperature is 85-90°C.

[0019] The present invention provides a lithium battery separator with high heat resistance and low water absorption and a preparation method thereof. It has the following beneficial effects: 1. The present invention adopts the technical solution of modifying alumina with sodium perfluorooctanoate to form a dense hydrophobic covering layer on the surface of alumina, which significantly reduces the water absorption of the diaphragm. Compared with the technical solution in the prior art that directly uses alumina particles and causes high water adsorption, the present invention effectively solves the problem of excessive water content in the diaphragm, and the water content of the diaphragm is reduced to below 400 ppm, thereby improving the long-term safety of the battery.

[0020] 2. The present invention optimizes the ceramic slurry formula and adds ethylene glycol pore-forming agents to give the coating a microporous structure, thereby improving the air permeability of the diaphragm. In the prior art, the structural design of the micropores often leads to a decrease in mechanical strength. The present invention combines the particle size control of alumina to balance the air permeability and mechanical properties of the coating, thereby solving the problem of insufficient air permeability or poor mechanical properties of traditional diaphragms.

[0021] 3. The present invention adopts planetary stirring and ultrasonic mixing technology to ensure uniform dispersion of the slurry, reduce particle agglomeration, and finally form a uniform and consistent ceramic coating. Compared with the problem of uneven coating due to slurry stratification in the prior art, the present invention optimizes the coating structure, improves the breakdown voltage and thermal stability of the diaphragm, and significantly improves the consistency of the product.

[0022] 4. The present invention simplifies the manufacturing process by adopting low-temperature coating and rapid drying processes, while avoiding the damage to the performance of the base film caused by the high-temperature environment. Compared with the complex preparation method of the prior art that requires a special drying environment, the present invention reduces production costs, improves production efficiency, and solves the bottleneck problems of high energy consumption and low efficiency in traditional diaphragm processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the method flow of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Please refer to the attached Figure 1 The embodiment of the present invention provides a lithium battery separator with high heat resistance and low water absorption, which is made of the following components in parts by weight: Alumina (40–60 parts by mass) Alumina is the main material of ceramic coating, with excellent heat resistance and mechanical strength. After ultra-fine treatment, the specific surface area of ​​alumina particles increases, which can form a dense coating, thereby effectively improving the heat resistance of the diaphragm. In addition, the particle size range of alumina particles (D50: 0.25-0.45μm, D90: 0.7-0.9μm) has been optimized to ensure the uniformity of the coating and effectively avoid the problem of reduced permeability caused by excessive gaps between particles.

[0026] Alumina particles have a large specific surface area and are prone to absorb water, resulting in high water content in the diaphragm, which is not conducive to battery performance. Therefore, this technology modifies the surface of alumina by sodium perfluorooctanoate to form a hydrophobic coating, which fundamentally reduces water absorption.

[0027] Sodium perfluorooctanoate (25–42 parts by mass) Sodium perfluorooctanoate is a surfactant, and the perfluorocarbon chain in the molecule is extremely hydrophobic. By dissolving sodium perfluorooctanoate in water and interacting with the surface of alumina, sodium perfluorooctanoate forms a dense hydrophobic covering film on the surface of alumina particles, significantly reducing its water absorption.

[0028] The hydrophobic group (CF bond) of sodium perfluorooctanoate is chemically inert and thermally stable, which can significantly reduce the surface free energy of alumina particles, thereby reducing the tendency of particles to adsorb water molecules. In addition, the hydrophobic layer can also enhance the bonding force between the particles and the base film, ensuring the stability of the ceramic coating.

[0029] Ultrapure water (65–85 parts by weight) Ultrapure water is used as the main solvent to ensure that all components can be evenly dispersed without introducing additional impurities or ions that affect the performance of the membrane.

[0030] The use of ultrapure water can reduce particle agglomeration or precipitation caused by impurity ions in the solvent and improve the stability and uniformity of the slurry.

[0031] Dispersant (0.5–1.2 parts by mass) The dispersant is an acrylic copolymer, which can effectively reduce the surface tension between the aluminum oxide particles and make them evenly dispersed in the solution.

[0032] Dispersants prevent particle agglomeration through electrostatic repulsion and steric hindrance, ensuring uniform coating thickness and thus improving the overall performance of the diaphragm.

[0033] Pore ​​former (1.3–2.9 parts by mass) The pore-forming agent is an ethylene glycol compound, which evaporates during the drying process of the coating to form a microporous structure, significantly improving the air permeability of the diaphragm.

[0034] The optimization of air permeability is crucial to improving the ion transport performance of the separator in the battery. The pore-forming agent can achieve precise control of the pore size of the coating by adjusting the addition amount, thereby taking into account both air permeability and mechanical strength.

[0035] Adhesive (2.6–3.8 parts by mass) The adhesive is acrylic, which provides adhesion between the ceramic coating and the base film, ensuring that the coating will not fall off during use.

[0036] The adhesive firmly fixes the ceramic coating to the surface of the base film through chemical bonds and physical interlocking, while maintaining the flexibility of the coating and avoiding cracks caused by thermal expansion and contraction.

[0037] Wetting agent (0.08–0.12 parts by mass) The wetting agent is alkylphenol polyoxyethylene ether, which improves the coating performance of the slurry and makes the coating more uniform.

[0038] The wetting agent reduces the surface tension of the slurry, enhances the affinity between the slurry and the surface of the base film, ensures uniform distribution of the coating during the coating process, and avoids the problem of inconsistent coating thickness.

[0039] Preparation method and process mechanism Alumina pretreatment 25–42 parts by mass of sodium perfluorooctanoate are added to 65–85 parts by mass of ultrapure water, and stirred at 80–90°C for 30–45 minutes to prepare a uniform first aqueous solution. Then 40–60 parts by mass of aluminum oxide are added to the solution, and stirred at 50–60°C for 30–35 minutes to form a hydrophobic layer on the surface of the aluminum oxide particles. The pretreated solid is filtered and dispersed by pneumatic spray to obtain aluminum oxide particles with a particle size of D50: 0.25–0.45 μm and D90: 0.7–0.9 μm.

[0040] The pretreatment process allows the sodium perfluorooctanoate molecules to firmly adhere to the surface of alumina through chemical adsorption, significantly reducing the hydrophilicity of the particles. Spraying further optimizes the particle distribution and provides a basis for the uniform dispersion of the subsequent slurry.

[0041] Ceramic slurry preparation 32–38 parts by mass of pretreated alumina was mixed with 29–35 parts by mass of ultrapure water, and 0.5–1.2 parts by mass of dispersant was added, and the mixture was dispersed by stirring for 60 minutes. Under ultrasonic mixing conditions, 1.3–2.9 parts by mass of pore former was added, and stirring was continued for 30 minutes before adding 2.6–3.8 parts by mass of binder and 0.08–0.12 parts by mass of wetting agent, and ultrasonic mixing was performed for 15–20 minutes to finally obtain a ceramic slurry with uniform particle size (D50: 0.28–0.48 μm, D90: 0.75–1.0 μm).

[0042] Ultrasonic mixing breaks up possible particle clusters in the slurry through high-frequency vibration to ensure the uniformity of the slurry. At the same time, the synergistic effect of dispersants and wetting agents further improves particle stability and prevents stratification during coating.

[0043] Diaphragm coating and drying The ceramic slurry is coated on one side of a base film with a thickness of 7-9 μm by a coating machine, the coating speed is 30-40 m / min, and the coating thickness is 1-2 μm. The coated diaphragm is dried at 80-100°C for 2-4 minutes to complete the preparation of the diaphragm.

[0044] The coating speed and thickness directly determine the uniformity and functionality of the coating, while the drying process ensures the complete volatilization of the pore former to form a microporous structure, while fixing the adhesive to enhance the mechanical strength of the coating.

[0045] Summary of the mechanism of key technical points Formation of hydrophobic layer: Sodium perfluorooctanoate modifies alumina through chemical adsorption, reducing the water absorption of particles while enhancing heat resistance.

[0046] Balance between air permeability and mechanical properties: Through the rational addition of pore-forming agents, the microporous structure of the coating improves the ion conductivity, while the alumina with controlled particle size provides the necessary mechanical support.

[0047] Production process optimization: Optimization of coating and drying parameters ensures controllable coating thickness while reducing production costs.

[0048] This technical solution combines chemical modification, process control and material selection to achieve the efficient preparation of high-heat-resistant and low-water-absorption diaphragms, which are suitable for the needs of high-performance lithium batteries. Example

[0049] 1. Preparation of Sodium Perfluorooctanoate Solution Take 25 parts by mass of sodium perfluorooctanoate, add it to 66 parts by mass of ultrapure water, and start stirring while keeping the temperature at 80° C. Set the stirring speed to 45 revolutions per minute, and continue stirring for 35 minutes until it is completely dissolved to obtain a uniform first aqueous solution.

[0050] 2. Pretreatment of Alumina At 50°C, 42 parts by mass of aluminum oxide was added to the first aqueous solution and slowly stirred for 30 minutes. The solid was then separated by filtration and treated with a pneumatic spray device at a spray pressure of 3.8 MPa. After spraying, the aluminum oxide particle size reached D50: 0.286 μm, D90: 0.783 μm.

[0051] 3. Preparation of Ceramic Slurry 32 parts by mass of the sprayed alumina was mixed with 30 parts by mass of ultrapure water, and 0.6 parts by mass of dispersant was added and stirred for 60 minutes at a stirring speed of 50 revolutions per minute. Ultrasonic mixing was performed using a planetary stirring device under vacuum conditions, and 1.4 parts by mass of a pore former was added at the same time, and stirring was continued for 30 minutes. Subsequently, 2.7 parts by mass of an adhesive and 0.09 parts by mass of a wetting agent were added, and ultrasonic mixing was performed again for 15 minutes to finally obtain a slurry with a particle size of D50: 0.302 μm, D90: 0.797 μm, and a viscosity of 132 mPa·s.

[0052] 4. Coating and drying The ceramic slurry was evenly coated on a 9 μm thick PE base film by a coating machine at a coating speed of 30 m / min and a coating thickness of 1.1 μm. Subsequently, the film was dried at 80°C for 2 minutes to obtain a lithium battery separator. Implementation Effect

[0053] The water content of the prepared diaphragm is 376ppm, and the thermal shrinkage (150℃, 1 hour) is 0.8% in the longitudinal direction and 0.4% in the transverse direction. Compared with untreated alumina, the water absorption is significantly reduced and the performance of the diaphragm is stable. Example

[0054] 1. Preparation of Sodium Perfluorooctanoate Solution 31 parts by mass of sodium perfluorooctanoate were weighed and added to 74 parts by mass of ultrapure water, and the temperature was raised to 85° C. and the stirring speed was maintained at 50 revolutions per minute. After 35 minutes, a first aqueous solution in which the sodium perfluorooctanoate was completely dissolved was obtained.

[0055] 2. Alumina pretreatment 46 parts by mass of aluminum oxide was slowly added to the first aqueous solution and pretreated at 58° C. for 30 minutes. The solid was then filtered and sprayed at a pressure of 4.5 MPa. The final particle size of the aluminum oxide particles was D50: 0.289 μm, and D90: 0.797 μm.

[0056] 3. Preparation of Ceramic Slurry 36 parts by mass of the treated alumina were mixed with 36 parts by mass of ultrapure water, and 0.9 parts by mass of dispersant was added at the same time, and dispersed by high-speed stirring equipment for 60 minutes. In a vacuum environment, 1.8 parts by mass of pore former was added, and ultrasonic mixing was performed for 30 minutes. Then 2.9 parts by mass of adhesive and 0.1 parts by mass of wetting agent were added, and stirring was continued for 15 minutes. The final slurry particle size was D50: 0.308 μm, D90: 0.806 μm, and the viscosity was 138 mPa·s.

[0057] 4. Coating and drying The slurry was coated on the surface of a 9 μm thick PE base film at a coating speed of 33 m / min to form a 1.2 μm thick coating. The drying temperature was set to 85°C and the drying time was controlled at 2 minutes to complete the preparation of the diaphragm. Implementation Effect

[0058] The membrane has a water content of 379ppm, a heat shrinkage of 0.75% in the longitudinal direction and 0.41% in the transverse direction. The membrane has excellent air permeability and mechanical properties, and compared with traditional processes, it solves the defects of poor water absorption and thermal stability. Example

[0059] 1. Preparation of Sodium Perfluorooctanoate Solution 42 parts by mass of sodium perfluorooctanoate were weighed and dissolved in 83 parts by mass of ultrapure water. The mixture was heated to 88° C. and stirred at 45 rpm for 40 minutes to form a stable aqueous solution.

[0060] 2. Alumina treatment 52 parts by mass of aluminum oxide were added to the aqueous solution and stirred at 55° C. for 30 minutes. After filtration, the solution was treated with a 4 MPa pneumatic spray device to obtain surface-modified aluminum oxide particles with a particle size of D50: 0.284 μm and D90: 0.774 μm.

[0061] 3. Ceramic Slurry Preparation 36 parts by mass of the treated alumina were added to 34 parts by mass of ultrapure water, and 0.8 parts by mass of dispersant was added and stirred for 60 minutes. Subsequently, 2.1 parts by mass of pore former were added and ultrasonically mixed in a planetary stirring device for 30 minutes. Finally, 3.4 parts by mass of binder and 0.11 parts by mass of wetting agent were added and ultrasonically mixed for 15 minutes to obtain a ceramic slurry with a slurry particle size of D50: 0.310 μm, D90: 0.809 μm, and a viscosity of 142 mPa·s.

[0062] 4. Coating and drying The coating machine coated the slurry on a 9 μm thick PE base film at a speed of 38 m / min, and the coating thickness was 1.8 μm. The film was dried at 90°C for 3 minutes to obtain the final separator. Implementation Effect

[0063] The water content of the diaphragm is 384ppm, the thermal shrinkage is 0.67% in the longitudinal direction and 0.34% in the transverse direction. The breakdown voltage of the diaphragm is as high as 2.4kV, which solves the problems of low breakdown voltage and high water content of traditional diaphragms. Example

[0064] 1. Preparation of Sodium Perfluorooctanoate Solution 28 parts by mass of sodium perfluorooctanoate were added to 72 parts by mass of ultrapure water, and the mixture was stirred at 82° C. for 40 minutes to obtain a first aqueous solution.

[0065] 2. Alumina treatment 44 parts by mass of aluminum oxide was added to the above solution, stirred at 56°C for 35 minutes, and then the solid was filtered and dispersed using a 3.5 MPa spray device. The particle size of the aluminum oxide after treatment was D50: 0.276 μm, D90: 0.780 μm.

[0066] 3. Ceramic Slurry Preparation 34 parts by mass of the above aluminum oxide was mixed with 33 parts by mass of ultrapure water, and 0.7 parts by mass of a dispersant was added and stirred for 50 minutes. Subsequently, 1.5 parts by mass of a pore former was added, and after stirring for 30 minutes, 3.1 parts by mass of a binder and 0.1 parts by mass of a wetting agent were added and stirred for 20 minutes. The final slurry particle size D50 was 0.3 μm.

[0067] 4. Coating and drying The slurry was coated on a 8 μm thick PE base film, the coating thickness was 1.3 μm, the coating speed was 32 m / min, the drying temperature was 87°C, and the drying time was 3 minutes. Implementation Effect

[0068] The water content of the prepared diaphragm is 380ppm, the longitudinal thermal shrinkage is 0.7%, and the breakdown voltage reaches 2.5kV. The overall performance is far superior to the diaphragm without modification process.

[0069] Comparative Example 1 (for Example 1) 1. Preparation of Sodium Perfluorooctanoate Solution 25 parts by mass of sodium perfluorooctanoate were added to 66 parts by mass of ultrapure water, and the temperature was raised to 80° C. The stirring speed was 30 rpm and the stirring time was 25 minutes (the stirring time was shorter than that in Example 1). The resulting solution particles were not fully dispersed.

[0070] 2. Alumina pretreatment 42 parts by mass of aluminum oxide were added to the above solution at 50°C and stirred for 20 minutes (stirring time was shortened). The filtered solid was used directly in the subsequent step without pneumatic spraying.

[0071] 3. Preparation of Ceramic Slurry The alumina particles that were not sprayed were mixed with 30 parts by mass of ultrapure water, and 0.6 parts by mass of a dispersant was added and stirred for 50 minutes (stirring time was shortened). After adding 1.4 parts by mass of a pore former, 2.7 parts by mass of a binder and 0.09 parts by mass of a wetting agent were directly added without performing ultrasonic mixing under vacuum conditions, and stirred for 10 minutes to obtain a ceramic slurry.

[0072] 4. Coating and drying The ceramic slurry was coated on the PE base film at a coating speed of 25 m / min and a coating thickness of 1.1 μm. The drying temperature was 75° C. and the drying time was 2 minutes.

[0073] Comparative Example 2 (for Example 2) 1. Preparation of Sodium Perfluorooctanoate Solution 31 parts by mass of sodium perfluorooctanoate were added to 74 parts by mass of ultrapure water and stirred at 85°C for 50 minutes (a prolonged stirring time may introduce oxidation byproducts). After the solution was prepared, it was cooled directly for later use.

[0074] 2. Alumina pretreatment 46 parts by mass of alumina particles were added to the solution cooled to room temperature and stirred for 40 minutes (lower temperature than that in Example 2). The solution was directly used for slurry preparation without filtration or spray treatment.

[0075] 3. Preparation of Ceramic Slurry The untreated alumina particles were added to 36 parts by mass of ultrapure water, and 0.9 parts by mass of dispersant was added and stirred for 60 minutes. After adding 1.8 parts by mass of pore former, the vacuum condition was not controlled during ultrasonic mixing, and 2.9 parts by mass of binder and 0.1 parts by mass of wetting agent were directly added, and stirring was continued for 5 minutes.

[0076] 4. Coating and drying The slurry was coated on the base film, the coating speed was adjusted to 40 m / min, the coating thickness was 1.5 μm, the drying temperature was 95° C., and the time was 3 minutes.

[0077] Comparative Example 3 (for Example 3) 1. Preparation of Sodium Perfluorooctanoate Solution Take 42 parts by mass of sodium perfluorooctanoate and add it to 83 parts by mass of ultrapure water, raise the temperature to 90°C, adjust the stirring speed to 55 revolutions per minute, and stir for 20 minutes (the stirring time is significantly shortened).

[0078] 2. Alumina treatment 52 parts by mass of aluminum oxide were directly added to the above solution and stirred at 55° C. for 10 minutes. The filtered aluminum oxide was not sprayed and dispersed but was directly used for the preparation of ceramic slurry.

[0079] 3. Ceramic Slurry Preparation The alumina that was not sprayed was mixed with 34 parts by mass of ultrapure water, and 0.8 parts by mass of dispersant was added and stirred for 45 minutes. After adding 2.1 parts by mass of pore former, it was mixed by conventional stirring without ultrasonic treatment. Then 3.4 parts by mass of binder and 0.11 parts by mass of wetting agent were added and stirred for 10 minutes to complete the slurry preparation.

[0080] 4. Coating and drying The slurry was coated on the base film, the coating speed was set to 28 m / min, the coating thickness was 1.0 μm, the drying temperature was adjusted to 70°C, and the drying time was extended to 4 minutes.

[0081] Comparative Example 4 (for Example 4) 1. Preparation of Sodium Perfluorooctanoate Solution 28 parts by mass of sodium perfluorooctanoate were added to 72 parts by mass of ultrapure water, heated to 78°C, and stirred for only 20 minutes (the lower the temperature, the shorter the time).

[0082] 2. Alumina treatment 44 parts by mass of aluminum oxide particles were directly added to the above solution and stirred at room temperature for 15 minutes. The aluminum oxide particles were not sprayed and retained a larger particle size (D50 was about 0.5 μm).

[0083] 3. Ceramic Slurry Preparation Untreated alumina particles were added to 33 parts by mass of ultrapure water, and 0.7 parts by mass of dispersant was added and stirred for 50 minutes. 1.5 parts by mass of pore former was added, and conventional low-speed stirring was used instead of ultrasonic mixing. Finally, 3.1 parts by mass of binder and 0.1 parts by mass of wetting agent were added and stirred for 5 minutes to complete the preparation of ceramic slurry.

[0084] 4. Coating and drying The slurry was coated on a 8 μm thick base film at a coating speed of 35 m / min. The coating thickness was 1.3 μm. The drying temperature was adjusted to 65° C. and the drying time was 2 minutes.

[0085] Comparative Example 5 (Deviation from Base Film Performance) 1. Pretreatment with sodium perfluorooctanoate solution and alumina The sodium perfluorooctanoate solution and alumina pretreatment were prepared according to the scheme in Example 1, and the solution temperature, stirring time, etc. remained consistent.

[0086] 2. Ceramic Slurry Preparation As in Example 1, all formulations and process steps remain the same, and the properties of the ceramic slurry finally prepared are the same.

[0087] 3. Coating and drying The slurry was coated on a 10μm thick polyethylene film (non-heat-resistant film) without special treatment, with a coating speed of 30m / min and a coating thickness of 1.1μm. The drying temperature was adjusted to 80℃ and the drying time was 3 minutes.

[0088] Experiment 1: Effect of Alumina Pretreatment Process on Water Absorption Experimental Description Experimental objectives: The effect of surface modification and spray treatment of aluminum oxide particles on the improvement of the water absorption of the diaphragm was studied to verify the superiority of the technology of the present invention.

[0089] Experimental steps: Example 1 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution: add 25 parts by mass of sodium perfluorooctanoate to 66 parts by mass of ultrapure water, raise the temperature to 80°C, stir at a speed of 45 rpm for 35 minutes to obtain a uniform solution.

[0090] Alumina treatment: 42 parts by mass of aluminum oxide was added to the solution at 50°C, stirred for 30 minutes and filtered. The obtained solid was treated with 3.8 MPa pneumatic spray, and the particle size was controlled to D50: 0.286 μm, D90: 0.783 μm.

[0091] Preparation of ceramic slurry: 32 parts by mass of modified alumina and 30 parts by mass of ultrapure water were mixed, and 0.6 parts by mass of dispersant was added and stirred for 60 minutes. Then 1.4 parts by mass of pore former was added, and ultrasonic mixing was performed for 30 minutes under vacuum conditions, and then 2.7 parts by mass of binder and 0.09 parts by mass of wetting agent were added, and ultrasonic mixing was performed for 15 minutes.

[0092] Coating and drying: The ceramic slurry was coated on the PE base film at a speed of 30 m / min, with a coating thickness of 1.1 μm, and dried at 80°C for 2 minutes to obtain a diaphragm.

[0093] Comparative Example 1 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution: the same as in Example 1.

[0094] Alumina treatment: Omit the spray treatment, just add alumina to the solution, stir for 20 minutes, filter and use directly without particle size optimization (D50>0.5μm).

[0095] Ceramic slurry preparation, coating and drying: The process is the same as Example 1.

[0096] Moisture content test The moisture content of the membrane samples of Example 1 and Comparative Example 1 was measured by Karl Fischer coulometric titrator. Each group was tested 3 times and the data were recorded.

[0097] Experimental data Data table:

[0098] The surface modification and particle size optimization of alumina particles play a key role in reducing the water absorption of the diaphragm. In Example 1, the sodium perfluorooctanoate molecules form a dense hydrophobic layer through chemical adsorption on the surface of alumina, preventing the penetration of water. The spray treatment makes the ceramic slurry more evenly distributed and the coating denser through precise control of the particle size. In contrast, comparative example 1 was not sprayed, and the particle size was too large, resulting in an increase in microscopic pores in the coating and a significant increase in water absorption.

[0099] In the process of Example 1, vacuum ultrasonic mixing further improves the dispersion effect of the slurry. This process effectively avoids the phenomenon of particle agglomeration and makes the microstructure of the coating more uniform. The tiny particles form a tightly arranged structure in the coating, which greatly reduces the diffusion path of water molecules. However, the aluminum oxide treatment time of Comparative Example 1 is short, and the particles are unevenly dispersed, resulting in increased porosity, which is one of the reasons why its water absorption is significantly inferior to that of Example 1.

[0100] The experiment also verified the importance of optimizing the particle size distribution. In Example 1, the D50 particle size of aluminum oxide was controlled within the range of about 0.286 μm, which was able to form a smooth coating on the surface of the base film. In Comparative Example 1, due to the large particle size and uneven distribution, the hydrophobicity of the coating was significantly reduced. This difference directly affects the water content of the diaphragm, and also indirectly proves the irreplaceable role of spray treatment technology in improving the overall performance of the diaphragm.

[0101] Experiment 2: Effect of Alumina Particle Size Control on Coating Uniformity and Thermal Shrinkage Experimental Description Experimental objectives: The effect of optimized control of alumina particle size on the uniformity and thermal shrinkage of the diaphragm coating was studied to verify the advantages of the technology of the present invention in terms of material uniformity and dimensional stability.

[0102] Experimental steps: Example 2 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution: weigh 31 parts by mass of sodium perfluorooctanoate, add it to 74 parts by mass of ultrapure water, heat it to 85° C., and stir it for 50 minutes to obtain a solution.

[0103] Alumina treatment: 46 parts by mass of aluminum oxide was added to the above solution, stirred at 50°C for 30 minutes, filtered and then dispersed by spraying at 4.5 MPa, with a particle size of D50: 0.289 μm, D90: 0.797 μm.

[0104] Preparation of ceramic slurry: 36 parts by mass of modified alumina and 36 parts by mass of ultrapure water were mixed, 0.9 parts by mass of dispersant was added and stirred for 60 minutes. After adding 1.8 parts by mass of pore former, ultrasonic mixing was performed under vacuum conditions for 30 minutes, and then 2.9 parts by mass of binder and 0.1 parts by mass of wetting agent were added, and ultrasonic mixing was continued for 15 minutes to prepare ceramic slurry.

[0105] Coating and drying: The slurry was coated on a 9μm thick PE base film at a coating speed of 33m / min, with a coating thickness of 1.2μm, and dried at 85°C for 2 minutes.

[0106] Comparative Example 2 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution: Same as Example 2.

[0107] Alumina treatment: No spray treatment was performed, and the particle size of the alumina particles was not optimized (D50>0.5μm), and they were directly used in the subsequent steps.

[0108] Preparation of ceramic slurry, coating and drying: same as Example 2.

[0109] Coating uniformity test Scanning electron microscopy (SEM) was used to observe the coating surface microstructure of the two groups of diaphragm samples and compare the coating uniformity and pore distribution.

[0110] Thermal shrinkage test Two groups of diaphragm samples were heated at 150°C for 1 hour, and the longitudinal and transverse heat shrinkage rates were measured respectively. Each group of samples was tested 3 times and the average value was taken.

[0111] Experimental data Data table:

[0112] The importance of particle size control for coating uniformity is clearly demonstrated in this experiment. In Example 2, the alumina particles treated by spraying have uniform and small particle sizes. The optimized D50: 0.289 μm ensures that the coating is more densely distributed on the surface of the base film, reduces the number and size of pores, and makes the coating surface smoother. This structure reduces the stress concentration effect of the material in a high temperature environment and significantly reduces the thermal shrinkage of the diaphragm. In Comparative Example 2, the alumina particles without particle size optimization are unevenly distributed in the coating, forming more irregular microscopic voids, resulting in a higher shrinkage rate after heat treatment.

[0113] The improvement of coating uniformity is not only due to the optimization of particle size, but also to the change in particle morphology after spray treatment. The aluminum oxide particles after spraying are more regular and have increased surface activity, which further improves the bonding strength with the base film. The test of comparative example 2 shows that the coating with large particle distribution has particle agglomeration in the microstructure, resulting in stress concentration in local areas. The results of this phenomenon are directly reflected in the transverse and longitudinal tests of thermal shrinkage, whose values ​​are almost doubled, which is significantly inferior to the embodiment.

[0114] The difference in thermal stability reveals the profound impact of particle size optimization on the overall performance of diaphragm materials. The arrangement and dense structure of small particles enable the material to maintain higher dimensional stability in high temperature environments. However, the unoptimized particle system expands unevenly during the heating process, resulting in structural instability. This also further proves the irreplaceable role of spray particle size control technology in improving the heat resistance of diaphragm materials.

[0115] Experiment 3: Effect of ultrasonic mixing process on slurry dispersion performance Experimental Description Experimental objectives: The effect of ultrasonic mixing under vacuum conditions on the dispersion properties of ceramic slurry was studied to verify the advantages of the technology of the present invention in slurry uniformity and diaphragm performance.

[0116] Experimental steps: Example 3 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution: Take 42 parts by mass of sodium perfluorooctanoate, add it to 83 parts by mass of ultrapure water, heat it to 88° C., stir it for 40 minutes, and prepare a uniform solution.

[0117] Alumina treatment: 52 parts by mass of aluminum oxide was added to the solution, stirred at 55°C for 30 minutes, filtered, and dispersed by 4 MPa pneumatic spray to obtain modified aluminum oxide with a particle size of D50: 0.284 μm and D90: 0.774 μm.

[0118] Preparation of ceramic slurry: 36 parts by mass of modified alumina was mixed with 34 parts by mass of ultrapure water, and 0.8 parts by mass of dispersant was added and stirred for 60 minutes. After adding 2.1 parts by mass of pore former, ultrasonic mixing was performed under vacuum conditions for 30 minutes, and then 3.4 parts by mass of binder and 0.11 parts by mass of wetting agent were added, and ultrasonic mixing was continued for 15 minutes.

[0119] Coating and drying: The slurry was coated on a 9 μm thick PE base film at a coating speed of 38 m / min and a coating thickness of 1.8 μm. The diaphragm sample was obtained by drying at 90°C for 3 minutes.

[0120] Comparative Example 3 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution and alumina treatment: same as Example 3.

[0121] Preparation of ceramic slurry: The vacuum condition was cancelled and only conventional low-speed stirring was used instead of ultrasonic mixing. The remaining steps were consistent with those in Example 3.

[0122] Coating and drying: Same as Example 3.

[0123] Experimental testing Particle size distribution of slurry: Use laser particle size analyzer to test the particle size distribution characteristics of slurry (D50, D90); Coating uniformity: Scanning electron microscopy (SEM) was used to observe the coating surface microstructure; Breakdown voltage: Use a high voltage insulation resistance tester to measure the diaphragm breakdown voltage (kV).

[0124] Experimental data Data table:

[0125] Ultrasonic mixing plays a vital role in the uniformity of ceramic slurry dispersion under vacuum conditions. This experiment shows that the slurry particle size distribution in Example 3 is more concentrated, and the proportion of small particles is significantly increased. The setting of the vacuum environment avoids bubble interference, and the high-frequency vibration of ultrasound makes the particle distribution more uniform. In Comparative Example 3, ultrasonic mixing is not used, and the slurry particle size has a large deviation, and both D50 and D90 are significantly increased, which directly leads to the phenomenon of uneven subsequent coating.

[0126] From the microstructure of the coating, the coating of Example 3 has higher flatness and no obvious particle aggregation area on the surface. In contrast, the coating of Comparative Example 3 shows particle agglomeration and more local voids. These voids lead to a decrease in breakdown voltage, making the diaphragm prone to damage under high voltage conditions. The difference in breakdown voltage not only reflects the compactness of the coating, but also reveals the importance of optimizing particle distribution.

[0127] The mechanism of vacuum ultrasonic mixing lies in multiple synergistic effects. On the one hand, ultrasonic energy can break up the weak aggregation forces between particles; on the other hand, the vacuum environment prevents bubbles in the solution from interfering with the uniformity of the coating. Experiments have shown that traditional stirring cannot achieve this effect, and the slurry produced by it cannot form a uniform and dense coating on the base film. This process optimization enables the separator of the present invention to show higher stability and reliability in battery applications.

[0128] Experiment 4: Effect of base film properties on diaphragm performance Experimental Description Experimental objectives: The effects of the base film type and its treatment process on the thermal stability and electrical properties of the diaphragm are studied to verify the technical advantages of the specific base film used in the present invention.

[0129] Experimental steps: Example 4 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution: weigh 28 parts by mass of sodium perfluorooctanoate, add to 72 parts by mass of ultrapure water, heat to 78° C., stir for 40 minutes to obtain a uniform solution.

[0130] Alumina treatment: 44 parts by mass of aluminum oxide was added to the solution, stirred at 56°C for 35 minutes, filtered and then dispersed by 3.5 MPa pneumatic spray to obtain aluminum oxide with a particle size of D50: 0.276 μm and D90: 0.780 μm.

[0131] Preparation of ceramic slurry: 34 parts by mass of aluminum oxide and 33 parts by mass of ultrapure water were mixed, 0.7 parts by mass of dispersant was added and stirred for 50 minutes. Subsequently, 1.5 parts by mass of pore former was added, ultrasonically mixed for 30 minutes under vacuum conditions, and finally 3.1 parts by mass of binder and 0.1 parts by mass of wetting agent were added, and ultrasonically mixed again for 15 minutes to prepare ceramic slurry.

[0132] Coating and drying: The slurry was coated on a specially treated PE base film (8 μm thick) at a speed of 32 m / min. The coating thickness was 1.3 μm. The drying temperature was 87°C and the drying time was 3 minutes to obtain a diaphragm sample.

[0133] Comparative Example 5 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution and alumina treatment: same as Example 4.

[0134] Preparation of ceramic slurry: Same as Example 4.

[0135] Coating and drying: The slurry was coated on an untreated ordinary PE base film (thickness 10 μm), and the rest of the process was the same as in Example 4.

[0136] Experimental testing Thermal shrinkage: Heat the diaphragm sample at 150°C for 1 hour, and test the thermal shrinkage in the longitudinal and transverse directions respectively; Breakdown voltage: Use a high-voltage insulation resistance tester to measure the diaphragm breakdown voltage (kV); Coating adhesion: The peeling method was used to test the adhesion between the coating and the base film (peel strength, in N / m). Each group of samples was tested 3 times and the average value was taken.

[0137] Experimental data Data table:

[0138] The characteristics of the base film directly determine the overall performance of the diaphragm. In Example 4, a specially treated PE base film was used, the surface energy of which was significantly reduced, and the bonding strength with the coating was greatly improved. This base film exhibits excellent dimensional stability under high temperature conditions and can effectively inhibit thermal shrinkage. The defects of the ordinary base film in Comparative Example 5 were fully exposed in the test. The untreated base film could not provide sufficient adhesion for the ceramic coating, resulting in a significant increase in thermal shrinkage and a significant decrease in electrical performance.

[0139] The difference in heat shrinkage is due to the difference in the microstructure of the base film itself. After the surface of the base film in Example 4 is treated, more binding sites are formed, which can more firmly fix the coating and ensure that the coating will not fail due to interface detachment in a high temperature environment. On the contrary, the shrinkage of the ordinary base film in Comparative Example 5 at high temperature is inconsistent with the expansion of the coating, and stratification is easily generated between the coating and the base film. This instability is the main reason for the significant increase in heat shrinkage.

[0140] In addition, the breakdown voltage test results show that the performance of the base film will directly affect the electric field resistance of the diaphragm. The diaphragm of Example 4 improves the bonding quality between the coating and the base film, making the coating more dense and reducing the porosity, thereby significantly improving the breakdown voltage. In Comparative Example 5, due to the poor local bonding of the coating, the breakdown voltage dropped significantly, which fully illustrates the importance and necessity of base film treatment.

[0141] Experiment 5: Effect of coating and drying parameters on membrane performance Experimental Description Experimental objectives: The effects of coating thickness and drying temperature on the air permeability, moisture content and ion conductivity of the diaphragm and the battery are studied to verify the technical advantages of the present invention in parameter optimization.

[0142] Experimental steps: Example 1 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution, alumina treatment, and preparation of ceramic slurry: Follow the steps in Experiment 1; Coating and drying: The slurry was coated on the PE base film at a speed of 30 m / min, the coating thickness was controlled at 1.1 μm, and dried at 80°C for 2 minutes to obtain a diaphragm sample.

[0143] Comparative Example 4 Diaphragm Preparation Preparation of sodium perfluorooctanoate solution, alumina treatment, and preparation of ceramic slurry: the same as in Example 1; Coating and drying: The slurry was coated on the PE base film at a speed of 32 m / min, the coating thickness was 1.3 μm, the drying temperature was adjusted to 65°C, and the drying time was 2 minutes.

[0144] Experimental testing Air permeability test: Use Gurley air permeability tester to record the time required for 100mL of air to pass through the diaphragm (unit: s / 100mL). Test each group 3 times and take the average value. Moisture content test: The moisture content of the diaphragm was determined using the Karl Fischer coulometric titration method, and the moisture content (ppm) of each set of diaphragms was recorded; Ion conductivity performance test: The separator was assembled into a standard battery (LiFePO4 / / Li), and the ionic conductivity (S / cm) of the battery was measured by the AC impedance method.

[0145] Experimental data Data table:

[0146] The coating and drying parameters have a significant impact on the microstructure and performance of the diaphragm. In Example 1, the coating thickness is 1.1 μm, and the moderate drying condition of 80°C makes the coating form a denser microporous structure. This optimized coating microstructure significantly improves the air permeability, and the diaphragm's ability to support ion conduction is also fully utilized. In Comparative Example 4, since the coating thickness is increased to 1.3 μm and the drying temperature is low, the water in the slurry cannot be completely volatilized, and the coating forms more closed-pore structures, resulting in a significant decrease in air permeability and ionic conductivity.

[0147] In Example 1, the drying temperature of 80°C ensures the full volatilization of the pore-forming agent while avoiding the potential damage to the base membrane structure caused by excessively high temperatures. This precise temperature control makes the pore size distribution of the coating more uniform, there are no obvious excessive pores in the microstructure, and the moisture content is kept at a low level. In Comparative Example 4, since the drying temperature is only 65°C, there is more residual moisture in the slurry, the hydrophobicity of the coating is reduced, and the overall moisture content of the diaphragm is significantly increased.

[0148] The difference in ionic conductivity further verifies the advantages of the coating process of the present invention from an electrochemical perspective. In the diaphragm of Example 1, the microporous structure with better air permeability provides a smoother ion conduction path, while the low moisture content reduces impedance. In contrast, the ion conduction capacity of the diaphragm of Comparative Example 4 is significantly suppressed due to the overly thick coating and poor pore distribution. This experiment also shows that precise optimization of coating thickness and drying parameters is crucial for the preparation of high-performance diaphragms.

[0149] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium battery separator with high heat resistance and low water absorption, characterized in that: The composition comprises the following components in parts by weight: Alumina: 40–60 parts by mass; Sodium perfluorooctanoate: 25–42 parts by weight; Ultrapure water: 65–85 parts by weight; Dispersant: 0.5–1.2 parts by mass; Pore ​​former: 1.3–2.9 parts by mass; Adhesive: 2.6–3.8 parts by mass; Wetting agent: 0.08–0.12 parts by mass.

2. A lithium battery separator with high heat resistance and low water absorption according to claim 1, characterized in that: The base film is a polypropylene base film or a polyethylene base film, and the thickness of the base film is 7-9 μm.

3. A lithium battery separator with high heat resistance and low water absorption according to claim 1, characterized in that: The particle size of the aluminum oxide is D50: 0.25-0.45 μm, D90: 0.7-0.9 μm.

4. The lithium battery separator with high heat resistance and low water absorption according to claim 1, characterized in that: The temperature of the solution prepared by sodium perfluorooctanoate and ultrapure water is 80-90° C., the stirring speed of the solution is 40-60 r / min, and the stirring time is 30-45 minutes.

5. The lithium battery separator with high heat resistance and low water absorption according to claim 1, characterized in that: The pore-forming agent is an ethylene glycol compound.

6. The lithium battery separator with high heat resistance and low water absorption according to claim 1, characterized in that: The adhesive is an acrylic adhesive.

7. A method for preparing a lithium battery separator with high heat resistance and low water absorption, a method for preparing a lithium battery separator with high heat resistance and low water absorption as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Add 25-42 parts by mass of sodium perfluorooctanoate to 65-85 parts by mass of ultrapure water, and stir and dissolve at 80-90° C. for 30-45 minutes to obtain a first aqueous solution; S2, adding 40-60 parts by mass of aluminum oxide to the first aqueous solution, stirring at 50-60° C. for 30-35 minutes, filtering to obtain a solid, and breaking it up by pneumatic spraying to obtain a pretreated aluminum oxide with a particle size of D50: 0.25-0.45 μm, D90: 0.7-0.9 μm; S3, mixing 32-38 parts by mass of pretreated alumina with 29-35 parts by mass of ultrapure water, and adding 0.5-1.2 parts by mass of a dispersant and stirring for 60 minutes; S4. Under ultrasonic mixing conditions, add 1.3-2.9 parts by mass of a pore former to the mixture, stir for 30 minutes, add 2.6-3.8 parts by mass of a binder and 0.08-0.12 parts by mass of a wetting agent, and continue ultrasonic mixing for 15-20 minutes to obtain a ceramic slurry; S5, coating the obtained ceramic slurry on one side of a base film having a thickness of 7-9 μm, with a coating speed of 30-40 m / min and a coating thickness of 1-2 μm; S6. Dry at 80-100°C for 2-4 minutes to obtain a lithium battery separator with high heat resistance and low water absorption.

8. The method for preparing a lithium battery separator with high heat resistance and low water absorption according to claim 7, characterized in that: The ultrasonic mixing of the ceramic slurry is carried out under vacuum conditions, with an ultrasonic frequency of 5-8 kHz, a rotation speed of 2000-2500 r / min, and a revolution speed of 35-45 r / min.

9. The method for preparing a lithium battery separator with high heat resistance and low water absorption according to claim 7, characterized in that: The pressure during the pneumatic spraying and dispersion of the aluminum oxide is 3-5 MPa.

10. The method for preparing a lithium battery separator with high heat resistance and low water absorption according to claim 7, characterized in that: The drying time is 2-3 minutes, and the drying temperature is 85-90°C.

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