High-heat-resistance and low-water-absorption lithium battery separator and preparation method thereof

Abstract

The application 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, which is prepared from the following components in mass fractions: 40-60 parts of aluminum oxide, 25-42 parts of sodium perfluorooctanoate, 65-85 parts of ultrapure water, 0.5-1.2 parts of a dispersing agent, 1.3-2.9 parts of a pore-forming agent, 2.6-3.8 parts of a bonding agent and 0.08-0.12 parts of a wetting agent; the base film is a polypropylene base film or a polyethylene base film, and the thickness of the base film is 7-9 microns. The surface of the aluminum oxide is modified, the base film is treated, and the coating and drying processes are optimized, so that the water absorption of the diaphragm is significantly reduced, the bonding force between the coating and the base film is improved, the coating uniformity and the microporous structure are improved, the diaphragm has excellent heat resistance, air permeability and electrochemical performance, and the problems of poor heat stability, high water absorption and insufficient coating adhesion in the prior art are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a high-heat-resistant and low-water-absorption lithium battery separator and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries, as the core technology in modern energy storage field, are widely used in consumer electronics, transportation and grid energy storage due to their high energy density and long cycle life. The separator is one of the key components of lithium ion batteries, which separates the positive and negative electrodes to prevent short circuit while allowing lithium ions to migrate freely. High-performance separators need to meet multiple performance requirements, including excellent heat resistance, low water absorption, good air permeability and high electrochemical stability. However, the existing lithium battery separators have many problems in practical application, which restricts the safety and performance of the battery.

[0003] The existing lithium battery separator uses polyethylene (PE) or polypropylene (PP) as the base material, supplemented by a ceramic coating to improve heat resistance and mechanical properties. However, due to the intrinsic performance limitations of the basic polyolefin material, these separators are prone to thermal shrinkage in high-temperature environments, increasing the risk of short circuits. Although the ceramic coating can improve the thermal stability of the separator to some extent, the coating layer of the separator prepared by traditional processes is prone to peeling or damage during use due to insufficient adhesion between the coating and the base film. In addition, the coating material (such as aluminum oxide) itself is prone to water absorption, and unmodified aluminum oxide particles can significantly increase the water content of the separator. This high water absorption can lead to an increase in water content in the battery, triggering side reactions and reducing battery performance and safety.

[0004] In the coating preparation process, the existing technology generally uses conventional stirring to disperse ceramic particles. However, due to the high surface energy of aluminum oxide particles, agglomeration easily occurs, leading to uneven dispersion of the ceramic slurry, and thus causing uneven coating, affecting the air permeability and electrochemical performance of the separator. Further, this uneven coating can cause the formation of local hotspots in the battery, thereby accelerating battery aging and performance degradation. In addition, the existing process fails to finely control the pore structure of the coating, making it difficult to balance the air permeability and mechanical strength, resulting in insufficient ion transport capacity of the separator under high-rate charging and discharging 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 separator. The base film used in the existing technology is mostly not specially modified, with weak surface adhesion, leading to poor adhesion of the ceramic coating to the base film, which is prone to delamination and peeling under mechanical impact and high temperature. This defect makes the separator exhibit poor dimensional stability in high-temperature environments. In addition, the insufficient interface bonding quality between the base film and the coating also forms small voids, which not only affects the denseness of the coating and the breakdown voltage of the separator, but also further reduces the overall safety of the separator.

[0006] The deficiencies of the coating and drying process are also common problems in the prior art. Due to the lack of precise control of the coating thickness and the drying temperature, the thickness of the coating of the separator is often uneven, resulting in inconsistent pore distribution. This problem directly affects the air permeability of the separator and increases the internal resistance of the battery. In addition, improper selection of the drying temperature leads to unreasonable formation of the pore structure of the coating, for example, too high a temperature will damage the performance of the base film, and too low a temperature will result in too high residual moisture in the coating, ultimately affecting the long-term stability of the separator.

[0007] In summary, the lithium battery separator in the prior art has significant deficiencies in water absorption control, thermal stability improvement, coating uniformity, and air permeability regulation. These technical problems have not been systematically solved from the aspects of material, process, and structure, thus restricting the development of high-performance separators. In view of the defects in the prior art, the present application proposes a high-heat-resistant and low-water-absorption lithium battery separator and a preparation method thereof through surface modification of alumina, optimization of coating and drying process, and modification of base film treatment, providing a new solution for improving the performance of the separator. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application provides a high-heat-resistant and low-water-absorption lithium battery separator and a preparation method thereof, solving the problems of high water absorption, poor thermal stability, insufficient coating uniformity, and weak bonding force between the coating and the base film of the lithium battery separator in the prior art.

[0009] To achieve the above purpose, the present application is implemented by the following technical solutions: a high-heat-resistant and low-water-absorption lithium battery separator, which is made of the following components in mass fraction:

[0010] Alumina: 40-60 mass parts;

[0011] Sodium perfluorooctanoate: 25-42 mass parts;

[0012] Ultra-pure water: 65-85 mass parts;

[0013] Dispersant: 0.5-1.2 mass parts;

[0014] Pore-forming agent: 1.3-2.9 mass parts;

[0015] Binder: 2.6-3.8 mass parts;

[0016] Wetting agent: 0.08-0.12 mass parts.

[0017] 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.

[0018] Preferably, the particle size of the alumina is D50: 0.25-0.45 μm, D90: 0.7-0.9 μm.

[0019] Preferably, the temperature of the solution prepared by dissolving sodium perfluorooctanoate in ultrapure water is 80-90℃, the stirring speed of the solution is 40-60 r / min, and the stirring time is 30-45 minutes.

[0020] Preferably, the pore-forming agent is an ethylene glycol compound.

[0021] Preferably, the adhesive is an acrylate adhesive.

[0022] A preparation method of a high-heat-resistant and low-water-absorption lithium battery separator includes the following steps:

[0023] S1. 25-42 parts by mass of sodium perfluorooctanoate is added to 65-85 parts by mass of ultrapure water, and stirred and dissolved at 80-90℃ for 30-45 minutes to obtain a first aqueous solution;

[0024] S2. 40-60 parts by mass of alumina is added to the first aqueous solution, and stirred at 50-60℃ for 30-35 minutes and then filtered to obtain a solid, which is dispersed by pneumatic spraying to obtain pretreated alumina with a particle size of D50: 0.25-0.45 μm, D90: 0.7-0.9 μm;

[0025] S3. 32-38 parts by mass of the pretreated alumina is mixed with 29-35 parts by mass of ultrapure water, and 0.5-1.2 parts by mass of a dispersant is added and stirred for 60 minutes;

[0026] S4. Under ultrasonic mixing conditions, 1.3-2.9 parts by mass of a pore-forming agent is added to the mixture, and after stirring for 30 minutes, 2.6-3.8 parts by mass of an adhesive and 0.08-0.12 parts by mass of a wetting agent are added, and ultrasonic mixing is continued for 15-20 minutes to obtain a ceramic slurry;

[0027] S5. The obtained ceramic slurry is coated on one side of a base film with a thickness of 7-9 μm at a coating speed of 30-40 m / min, and the coating thickness is 1-2 μm;

[0028] S6. Drying is performed at 80-100℃ for 2-4 minutes to obtain a high-heat-resistant and low-water-absorption lithium battery separator.

[0029] Preferably, the ultrasonic mixing of the ceramic slurry is performed under vacuum conditions, the ultrasonic frequency is 5-8 kHz, the rotation speed is 2000-2500 r / min, and the revolution speed is 35-45 r / min.

[0030] Preferably, the pressure during the pneumatic spraying dispersion of the alumina is 3-5 MPa.

[0031] Preferably, the drying time is 2-3 minutes, and the drying temperature is 85-90℃.

[0032] The application provides a high-heat-resistance and low-water-absorption lithium battery diaphragm and a preparation method thereof.

[0033] 1. The application forms a dense hydrophobic covering layer on the surface of the alumina by adopting the technical scheme of sodium perfluorooctanoate modified alumina, significantly reduces the water absorption of the diaphragm, effectively solves the problem of excessive water content of the diaphragm compared with the technical scheme in the prior art that directly uses alumina particles to cause high water adsorption, reduces the water content of the diaphragm to below 400 ppm, and improves the long-term safety of the battery.

[0034] 2. The application adds a glycol pore-forming agent to the ceramic slurry formula to make the coating have a microporous structure, improve the air permeability of the diaphragm, and solve the problem of insufficient air permeability or poor mechanical performance of the traditional diaphragm.

[0035] 3. The application adopts a planetary stirring and ultrasonic mixing process to ensure uniform dispersion of the slurry and reduce particle agglomeration, finally forming a uniform ceramic coating, compared with the problem of uneven coating caused by stratification of the slurry in the prior art, the application optimizes the coating structure, improves the breakdown voltage and thermal stability of the diaphragm, and significantly improves the consistency of the product.

[0036] 4. The application simplifies the manufacturing process by adopting a low-temperature coating and rapid drying process, avoids damage to the performance of the base film in a high-temperature environment, reduces production costs, improves production efficiency compared with the complex preparation method of the prior art which requires a special drying environment, and solves the bottleneck problem of high energy consumption and low efficiency in the traditional diaphragm process. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The application provides a method flowchart. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the application will be described clearly and completely in combination with the drawings of the application specification. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0039] Please refer to the drawings of the application Figure 1The embodiment of the present application provides a kind of high heat resistance low water absorption lithium battery separator, including the following mass fraction of component made:

[0040] Alumina (40-60 parts by mass)

[0041] Alumina is the main material of ceramic coating, with excellent heat resistance and mechanical strength. After superfine treatment of alumina particles, its specific surface area increases, and a dense coating can be formed, thereby effectively improving the heat resistance of the separator. In addition, the particle size range (D50: 0.25-0.45 μm, D90: 0.7-0.9 μm) of alumina particles is optimized, which can not only ensure the uniformity of the coating, but also effectively avoid the problem of reduced air permeability caused by excessive inter-particle voids.

[0042] Due to the large specific surface area of alumina particles, they are prone to adsorb water, resulting in high water content in the separator, which is not conducive to the performance of the battery. Therefore, the present technology modifies the surface of alumina with sodium perfluorooctanoate to form a hydrophobic coating, thereby fundamentally reducing water absorption.

[0043] Sodium perfluorooctanoate (25-42 parts by mass)

[0044] Sodium perfluorooctanoate is a surfactant, and the perfluorocarbon chain in its molecule has extremely high hydrophobicity. By dissolving sodium perfluorooctanoate in water and interacting with the surface of alumina, a dense hydrophobic covering film is formed on the surface of alumina particles, significantly reducing their water absorption.

[0045] The hydrophobic group (C-F bond) of sodium perfluorooctanoate has chemical inertness and thermal stability, which can significantly reduce the surface free energy of alumina particles, thereby reducing their tendency to adsorb water molecules. In addition, this hydrophobic layer can also enhance the bonding force between the particles and the base film, ensuring the stability of the ceramic coating.

[0046] Ultra-pure water (65-85 parts by mass)

[0047] Ultra-pure water as the main solvent ensures that each component can be uniformly dispersed without introducing additional impurities or ions affecting the performance of the separator.

[0048] The use of ultra-pure water can reduce particle agglomeration or precipitation caused by impurity ions in the solvent, improving the stability and uniformity of the slurry.

[0049] Dispersant (0.5-1.2 parts by mass)

[0050] The dispersant is an acrylic ester copolymer that can effectively reduce the surface tension between alumina particles, allowing them to disperse uniformly in the solution.

[0051] The dispersant prevents particle agglomeration through electrostatic repulsion and steric hindrance, ensuring uniform coating thickness and thereby improving the overall performance of the separator.

[0052] Pore-forming agent (1.3-2.9 parts by mass)

[0053] The pore-forming agent is an ethylene glycol compound that volatilizes during the drying of the coating to form a microporous structure, significantly improving the gas permeability of the separator.

[0054] The optimization of gas permeability is crucial for the improvement of ion transport performance of the separator in the battery. The pore-forming agent achieves precise control of the coating pore size by adjusting the amount added, thereby balancing gas permeability and mechanical strength.

[0055] Binder (2.6-3.8 parts by mass)

[0056] The binder is an acrylate that provides adhesion between the ceramic coating and the base film, ensuring that the coating does not fall off during use.

[0057] The binder firmly fixes the ceramic coating on the surface of the base film through chemical bonding and physical embedding, while maintaining the flexibility of the coating, avoiding cracks caused by thermal expansion and contraction.

[0058] Wetting agent (0.08-0.12 parts by mass)

[0059] The wetting agent is an alkyl phenol polyoxyethylene ether that improves the coating performance of the slurry, making the coating more uniform.

[0060] The wetting agent reduces the surface tension of the slurry, enhances the affinity of the slurry to the surface of the base film, and ensures uniform distribution of the coating during the coating process, avoiding problems of inconsistent coating thickness.

[0061] Preparation method and process mechanism

[0062] Alumina pretreatment

[0063] Add 25-42 parts by mass of sodium perfluorooctanoate to 65-85 parts by mass of ultrapure water, stir at 80-90°C for 30-45 minutes to prepare a uniform first aqueous solution. Then add 40-60 parts by mass of alumina to the solution, stir at 50-60°C for 30-35 minutes to form a hydrophobic layer on the surface of the alumina particles. The pretreated solid is filtered and dispersed by pneumatic spraying to obtain alumina particles with a particle size D50: 0.25-0.45 μm, D90: 0.7-0.9 μm.

[0064] Pretreatment firmly attaches sodium perfluorooctanoate molecules to the surface of the alumina through chemical adsorption, significantly reducing the hydrophilicity of the particles. Spray dispersion further optimizes particle distribution, providing a basis for uniform dispersion of the subsequent slurry.

[0065] Ceramic slurry preparation

[0066] Pre-treatment alumina 32-38 parts by mass was mixed with ultrapure water 29-35 parts by mass, and a dispersant 0.5-1.2 parts by mass was added and dispersed by stirring for 60 minutes. Under ultrasonic mixing conditions, a pore-forming agent 1.3-2.9 parts by mass was added, and after stirring for 30 minutes, a binder 2.6-3.8 parts by mass and a wetting agent 0.08-0.12 parts by mass were added, and ultrasonic mixing was carried out for 15-20 minutes, finally obtaining a ceramic slurry with uniform particle size (D50: 0.28-0.48 μm, D90: 0.75-1.0 μm).

[0067] Ultrasonic mixing disperses the particle clusters that may form in the slurry by high-frequency vibration, ensuring the uniformity of the slurry. At the same time, the synergistic effect of the dispersant and the wetting agent further improves the stability of the particles, preventing delamination during coating.

[0068] Separation membrane coating and drying

[0069] The ceramic slurry was coated on one side of the base film with a thickness of 7-9 μm by a coating machine, the coating speed was 30-40 m / min, and the coating thickness was 1-2 μm. The coated separation membrane was dried at 80-100 °C for 2-4 minutes to complete the preparation of the separation membrane.

[0070] 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-forming agent to form a microporous structure, and fixes the binder to enhance the mechanical strength of the coating.

[0071] Mechanism summary of key technical points

[0072] Formation of hydrophobic layer: Sodium perfluorooctanoate modifies alumina through chemical adsorption, reducing the water absorption of particles and enhancing the heat resistance.

[0073] Balance of air permeability and mechanical properties: The microporous structure of the coating improves the ion conduction performance through the reasonable addition of the pore-forming agent, while the particle size controlled alumina provides the necessary mechanical support.

[0074] Production process optimization: Optimization of coating and drying parameters ensures the controllability of the coating thickness, while reducing production costs.

[0075] This technical solution combines chemical modification, process control and material selection to achieve efficient preparation of high-heat-resistant and low-water-absorption separation membranes, suitable for the needs of high-performance lithium batteries. Examples

[0076] 1. Preparation of sodium perfluorooctanoate solution

[0077] Take 25 parts by mass of sodium perfluorooctanoate, add 66 parts by mass of ultrapure water, and start stirring while keeping the temperature at 80°C. The stirring speed is set to 45 rpm, and stirring is continued for 35 minutes until complete dissolution, obtaining a homogeneous first aqueous solution.

[0078] 2. Pretreatment of alumina

[0079] At 50°C, 42 parts by mass of alumina is added to the first aqueous solution, and stirring is continued slowly for 30 minutes. After that, the solid is separated by filtration, and the obtained solid is treated with a pneumatic spraying device at a spraying pressure of 3.8 MPa. After spraying, the alumina particle size reaches D50: 0.286 μm, D90: 0.783 μm.

[0080] 3. Preparation of ceramic slurry

[0081] After the alumina treated by spraying is mixed with 30 parts by mass of ultrapure water, 0.6 parts by mass of dispersant is added and stirred for 60 minutes at a stirring speed of 50 rpm. Under vacuum conditions, ultrasonic mixing is performed using a planetary stirring device, and 1.4 parts by mass of pore-forming agent is added, and stirring is continued for 30 minutes. Subsequently, 2.7 parts by mass of binder and 0.09 parts by mass of wetting agent are added, and ultrasonic mixing is performed again for 15 minutes, and finally a slurry is obtained, with a particle size of D50: 0.302 μm, D90: 0.797 μm, and a viscosity of 132 mPa·s.

[0082] 4. Coating and drying

[0083] The ceramic slurry is uniformly coated on a PE-based film with a thickness of 9 μm by a coating machine at a coating speed of 30 m / min, and the coating thickness is controlled at 1.1 μm. Subsequently, drying is performed at 80°C for 2 minutes, and a lithium battery separator is prepared.

[0084] Implementation effect

[0085] The prepared separator has a water content of 376 ppm, and a heat shrinkage rate (150°C, 1 hour) of 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 separator is stable. Example

[0086] 1. Preparation of sodium perfluorooctanoate solution

[0087] 31 parts by mass of sodium perfluorooctanoate is weighed and added to 74 parts by mass of ultrapure water, and the temperature is raised to 85°C, and the stirring speed is kept at 50 rpm. After 35 minutes, a completely dissolved first aqueous solution is obtained.

[0088] 2. Pretreatment of alumina

[0089] The 46 parts by mass of alumina was slowly added to the first aqueous solution and pretreated at 58°C for 30 minutes. Subsequently, the resulting solid was filtered and treated by spray at a spray pressure of 4.5 MPa, and the particle size of the alumina particles was ultimately D50: 0.289 μm, D90: 0.797 μm.

[0090] 3. Preparation of ceramic slurry

[0091] The above treated alumina 36 parts by mass was mixed with 36 parts by mass of ultrapure water, while adding 0.9 parts by mass of dispersant, and dispersed by a high-speed stirring device for 60 minutes. In a vacuum environment, 1.8 parts by mass of pore-forming agent was added and ultrasonically mixed for 30 minutes. Then 2.9 parts by mass of binder and 0.1 parts by mass of wetting agent were added, and stirring was continued for 15 minutes. The final particle size of the slurry was D50: 0.308 μm, D90: 0.806 μm, and the viscosity was 138 mPa·s.

[0092] 4. Coating and drying

[0093] The slurry was coated on the surface of a 9 μm thick PE-based film at a coating speed of 33 m / min to form a 1.2 μm thick coating layer. The drying temperature was set to 85°C, and the time was controlled to 2 minutes, and the preparation of the separator was completed.

[0094] Implementation effect

[0095] The water content of the separator was 379 ppm, the thermal shrinkage rate was 0.75% in the longitudinal direction and 0.41% in the transverse direction. The separator had excellent air permeability and mechanical properties, and solved the defects of poor water absorption and thermal stability compared with the traditional process. Example

[0096] 1. Preparation of sodium perfluorooctanoate solution

[0097] 42 parts by mass of sodium perfluorooctanoate was weighed and dissolved in 83 parts by mass of ultrapure water. It was heated to 88°C, the stirring speed was 45 revolutions per minute, and the stirring time was 40 minutes to form a stable aqueous solution.

[0098] 2. Alumina treatment

[0099] 52 parts by mass of alumina was added to the above aqueous solution and stirred at 55°C for 30 minutes. After filtration, it was treated by a 4 MPa pneumatic spray device to obtain surface-modified alumina particles with a particle size of D50: 0.284 μm, D90: 0.774 μm.

[0100] 3. Preparation of ceramic slurry

[0101] 36 parts by weight of the treated alumina were added to 34 parts by weight of ultrapure water, followed by 0.8 parts by weight of dispersant and stirring for 60 minutes. Then, 2.1 parts by weight of pore-forming agent were added, and the mixture was ultrasonically mixed in a planetary mixer for 30 minutes. Finally, 3.4 parts by weight of binder and 0.11 parts by weight of wetting agent were added, and the mixture was ultrasonically mixed for 15 minutes to obtain a ceramic slurry with a particle size of D50: 0.310 μm, D90: 0.809 μm, and a viscosity of 142 mPa·s.

[0102] 4. Coating and drying

[0103] The slurry was coated onto a 9μm thick PE base film using a coating machine at a speed of 38m / min, resulting in a coating thickness of 1.8μm. The film was then dried at 90℃ for 3 minutes to obtain the final diaphragm.

[0104] Implementation effect

[0105] The membrane has a water content of 384 ppm and a thermal shrinkage rate of 0.67% longitudinally and 0.34% transversely. The membrane has a breakdown voltage as high as 2.4 kV, which solves the problems of low breakdown voltage and high water content in traditional membranes. Example

[0106] 1. Preparation of sodium perfluorooctanoate solution

[0107] Add 28 parts by mass of sodium perfluorooctanoate to 72 parts by mass of ultrapure water and stir at 82°C for 40 minutes to obtain the first aqueous solution.

[0108] 2. Alumina treatment

[0109] 44 parts by mass of alumina were added to the above solution, and the mixture was stirred at 56°C for 35 minutes. The solid was then filtered and dispersed using a 3.5 MPa spray gun. The alumina particle size after treatment was D50: 0.276 μm and D90: 0.780 μm.

[0110] 3. Preparation of ceramic slurry

[0111] 34 parts by weight of the above-mentioned alumina were mixed with 33 parts by weight of ultrapure water, and 0.7 parts by weight of dispersant were added and stirred for 50 minutes. Then 1.5 parts by weight of pore-forming agent were added and stirred for 30 minutes. After that, 3.1 parts by weight of binder and 0.1 parts by weight of wetting agent were added and stirred for 20 minutes. The final slurry particle size D50 was 0.3 μm.

[0112] 4. Coating and drying

[0113] The slurry was coated onto an 8μm thick PE base film, resulting in a coating thickness of 1.3μm, at a coating speed of 32m / min. The drying temperature was 87℃, and the drying time was 3 minutes.

[0114] Implementation effect

[0115] The prepared separator has a water content of 380 ppm, a longitudinal heat shrinkage of 0.7%, and a breakdown voltage of 2.5 kV, and the overall performance is far superior to that of the separator without modification.

[0116] Comparative Example 1 (for Example 1)

[0117] 1. Preparation of sodium perfluorooctanoate solution

[0118] 25 parts by mass of sodium perfluorooctanoate was added to 66 parts by mass of ultrapure water, and the temperature was raised to 80°C. The stirring speed was 30 revolutions per minute, and the stirring time was 25 minutes (compared with Example 1, the stirring time was shortened). The obtained solution had insufficient particle dispersion.

[0119] 2. Pretreatment of alumina

[0120] At 50°C, 42 parts by mass of alumina was added to the above solution, and stirred for 20 minutes (stirring time was shortened). The filtered solid was not subjected to pneumatic spraying treatment, and was directly used in the subsequent step.

[0121] 3. Preparation of ceramic slurry

[0122] The alumina particles without spraying treatment were mixed with 30 parts by mass of ultrapure water, and 0.6 parts by mass of dispersant was added and stirred for 50 minutes (stirring time was shortened). After adding 1.4 parts by mass of pore-forming agent, no ultrasonic mixing under vacuum conditions was performed, and 2.7 parts by mass of binder and 0.09 parts by mass of wetting agent were directly added, and stirred for 10 minutes to obtain the ceramic slurry.

[0123] 4. Coating and drying

[0124] The ceramic slurry was coated on the PE-based film at a coating speed of 25 m / min, and the coating thickness was 1.1 μm. The drying temperature was 75°C, and the time was 2 minutes.

[0125] Comparative Example 2 (for Example 2)

[0126] 1. Preparation of sodium perfluorooctanoate solution

[0127] 31 parts by mass of sodium perfluorooctanoate was added to 74 parts by mass of ultrapure water, and stirred at 85°C for 50 minutes (stirring time was prolonged, which may introduce oxidation by-products). After the solution was prepared, it was directly cooled for standby.

[0128] 2. Pretreatment of alumina

[0129] 46 parts by mass of alumina particles were added to the solution cooled to room temperature, and stirred for 40 minutes (lower temperature than Example 2). Without filtration and spraying treatment, it was directly used for slurry preparation.

[0130] 3. Preparation of ceramic slurry

[0131] The untreated alumina particles were added to 36 parts by mass of ultrapure water, 0.9 parts by mass of dispersant was added and stirred for 60 minutes. After adding 1.8 parts by mass of pore-forming agent, the vacuum condition was not controlled during the ultrasonic mixing process, 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.

[0132] 4. Coating and drying

[0133] The slurry was coated on the base film, the coating speed was adjusted to 40 m / min, the coating thickness was 1.5 μm, and the drying temperature was 95 °C for 3 minutes.

[0134] Comparative Example 3 (for Example 3)

[0135] 1. Preparation of sodium perfluorooctanoate solution

[0136] 42 parts by mass of sodium perfluorooctanoate was added to 83 parts by mass of ultrapure water, heated to 90 °C, and the stirring speed was adjusted to 55 revolutions per minute, and stirred for 20 minutes (the stirring time was significantly shortened).

[0137] 2. Alumina treatment

[0138] 52 parts by mass of alumina was directly added to the above solution and stirred at 55 °C for 10 minutes. The filtered alumina was not spray-dispersed, but was directly used for ceramic slurry preparation.

[0139] 3. Ceramic slurry preparation

[0140] The alumina without spray-dispersion was mixed with 34 parts by mass of ultrapure water, 0.8 parts by mass of dispersant was added, and stirred for 45 minutes. After adding 2.1 parts by mass of pore-forming agent, the mixing was carried out 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 the slurry preparation was completed after simple stirring for 10 minutes.

[0141] 4. Coating and drying

[0142] The slurry was coated on the base film, the coating speed was set to 28 m / min, and the coating thickness was 1.0 μm. The drying temperature was adjusted to 70 °C, and the drying time was extended to 4 minutes.

[0143] Comparative Example 4 (for Example 4)

[0144] 1. Preparation of sodium perfluorooctanoate solution

[0145] 28 parts by mass of sodium perfluorooctanoate was added to 72 parts by mass of ultrapure water, heated to 78 °C, and the stirring time was only 20 minutes (the temperature was reduced and the time was shortened).

[0146] 2. Alumina treatment

[0147] 44 parts by mass of alumina particles were directly added to the above solution and stirred for 15 minutes at room temperature. The alumina particles were not subjected to spray treatment and directly retained a large particle size (D50 of about 0.5 μm).

[0148] 3. Ceramic slurry preparation

[0149] The untreated alumina particles were added to 33 parts by mass of ultrapure water, and after adding 0.7 parts by mass of dispersant, stirred for 50 minutes. 1.5 parts by mass of pore-forming agent was added, and instead of ultrasonic mixing, conventional low-speed stirring was used. Finally, 3.1 parts by mass of binder and 0.1 parts by mass of wetting agent were added, stirred for 5 minutes, and the preparation of the ceramic slurry was completed.

[0150] 4. Coating and drying

[0151] The slurry was coated on an 8 μm thick base film at a coating speed of 35 m / min, a coating thickness of 1.3 μm, and the drying temperature was adjusted to 65 °C, and the drying time was 2 minutes.

[0152] Comparative Example 5 (deviation from the performance of the base film)

[0153] 1. Sodium perfluorooctanoate solution and alumina pretreatment

[0154] The sodium perfluorooctanoate solution and alumina pretreatment were prepared according to the scheme in Example 1, and the solution temperature, stirring time, etc. were kept the same.

[0155] 2. Ceramic slurry preparation

[0156] As in Example 1, all formulations and process steps were kept the same, and the performance of the ceramic slurry finally prepared was not different.

[0157] 3. Coating and drying

[0158] The slurry was coated on a 10 μm thick polyethylene base film (non-heat-resistant base film) without special treatment at a coating speed of 30 m / min, and a coating thickness of 1.1 μm. The drying temperature was adjusted to 80 °C, and the time was 3 minutes.

[0159] Experiment 1: Effect of alumina pretreatment process on water absorption

[0160] Experiment description

[0161] Experiment goal:

[0162] To study the improvement effect of surface modification and spray treatment of alumina particles on the water absorption of the separator, and to verify the superiority of the present technology.

[0163] Experiment steps:

[0164] Example 1 separator preparation

[0165] Preparation of sodium perfluorooctanoate solution: 25 parts by mass of sodium perfluorooctanoate was added to 66 parts by mass of ultrapure water, heated to 80°C, and stirred at 45 rpm for 35 minutes to obtain a uniform solution.

[0166] Alumina treatment: 42 parts by mass of alumina was added to the solution at 50°C, and after stirring for 30 minutes, the solution was filtered. The obtained solid was treated by 3.8 MPa pneumatic spraying, and the particle size was controlled to D50: 0.286 μm, D90: 0.783 μm.

[0167] 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-forming agent was added, and the mixture was ultrasonically mixed under vacuum for 30 minutes. Then 2.7 parts by mass of binder and 0.09 parts by mass of wetting agent were added, and the mixture was ultrasonically mixed for 15 minutes.

[0168] Coating and drying: The ceramic slurry was coated on the PE-based film at a speed of 30 m / min, and the coating thickness was 1.1 μm. The coated film was dried at 80°C for 2 minutes to obtain the separator.

[0169] Preparation of the separator of Comparative Example 1

[0170] Preparation of sodium perfluorooctanoate solution: The same as Example 1.

[0171] Alumina treatment: The spraying treatment was omitted, and only alumina was added to the solution and stirred for 20 minutes before filtering. The particle size was not optimized (D50> 0.5 μm), and the obtained solid was directly used.

[0172] Preparation of ceramic slurry, coating and drying: The same as Example 1.

[0173] Moisture content test

[0174] The moisture content of the separator samples of Example 1 and Comparative Example 1 was determined by Karl Fischer coulometric titrator. Each group was tested 3 times, and the data was recorded.

[0175] Experimental data

[0176] Data table:

[0177]

[0178] The surface modification and particle size optimization of alumina particles played a key role in reducing the water absorption of the separator. In Example 1, sodium perfluorooctanoate molecules formed a dense hydrophobic layer on the surface of alumina through chemical adsorption, preventing water from penetrating. The spraying treatment precisely controlled the particle size, making the ceramic slurry more uniform and the coating more dense. In contrast, Comparative Example 1 did not undergo spraying treatment, and the particle size was larger, resulting in an increase in micro-pores in the coating and a significant increase in water absorption.

[0179] In the process of Example 1, the vacuum ultrasonic mixing further improves the dispersion effect of the slurry. This process effectively avoids particle agglomeration, making the microstructure of the coating more uniform. The small particles form a closely arranged structure in the coating, greatly reducing the diffusion path of water molecules. The alumina treatment time in Comparative Example 1 is shorter, and the particles are not uniformly dispersed, leading to an increase in porosity, which is one of the reasons why its water absorption is significantly worse than that of Example 1.

[0180] The experiment also verifies the importance of optimizing the particle size distribution. In Example 1, the D50 particle size of alumina is controlled within the range of about 0.286 μm, which can 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 hydrophobic performance of the coating is significantly reduced. This difference directly affects the water content of the separator and also proves the irreplaceability of the spray treatment technology for improving the overall performance of the separator.

[0181] Experiment 2: Effect of Alumina Particle Size Control on Coating Uniformity and Thermal Shrinkage

[0182] Experiment Description

[0183] Experiment Goal:

[0184] The experiment aims to study the effect of optimized control of alumina particle size on the uniformity of the separator coating and thermal shrinkage, and to verify the advantages of the invention in material uniformity and dimensional stability.

[0185] Experiment Steps:

[0186] Preparation of Example 2 Separator

[0187] Prepare a solution of sodium perfluorooctanoate: weigh 31 parts by mass of sodium perfluorooctanoate and add it to 74 parts by mass of ultrapure water. Heat to 85°C and stir for 50 minutes to obtain the solution.

[0188] Alumina treatment: Add 46 parts by mass of alumina to the above solution and stir at 50°C for 30 minutes. Filter and disperse by spraying at 4.5 MPa. The particle size D50 is 0.289 μm and the D90 is 0.797 μm.

[0189] Prepare the ceramic slurry: Mix 36 parts by mass of modified alumina with 36 parts by mass of ultrapure water, add 0.9 parts by mass of dispersant and stir for 60 minutes. Add 1.8 parts by mass of pore former and ultrasonically mix under vacuum for 30 minutes. Then add 2.9 parts by mass of binder and 0.1 parts by mass of wetting agent and continue to ultrasonically mix for 15 minutes to prepare the ceramic slurry.

[0190] Coating and drying: Apply the slurry to a 9 μm thick PE base film at a coating speed of 33 m / min, with a coating thickness of 1.2 μm. Dry at 85°C for 2 minutes.

[0191] Comparative Example 2 Separator Preparation

[0192] Formulation of Sodium Perfluorooctanoate Solution: Same as Example 2.

[0193] Alumina Treatment: No spray treatment was performed, and the alumina particle size was not optimized (D50 > 0.5 pm), which was directly used in the subsequent steps.

[0194] Ceramic Slurry Preparation, Coating and Drying: Same as Example 2.

[0195] Coating Uniformity Test

[0196] The coating surface microstructure of two groups of separator samples was observed using a scanning electron microscope (SEM) to compare the coating uniformity and pore distribution.

[0197] Thermal Shrinkage Test

[0198] Two groups of separator samples were heated at 150°C for 1 hour, and the thermal shrinkage in the longitudinal and transverse directions was measured, respectively. Each group of samples was tested 3 times, and the average value was taken.

[0199] Experimental Data

[0200] Data Table:

[0201]

[0202] The importance of particle size control for coating uniformity was clearly demonstrated in this experiment. In Example 2, the alumina particles after spray treatment had uniform and small particle sizes. The optimized D50: 0.289 pm ensured that the coating was more tightly distributed on the surface of the base film, reducing the number and size of pores, and the coating surface was smoother. This structure reduced the stress concentration effect of the material in a high-temperature environment, significantly reducing the thermal shrinkage of the separator. In Comparative Example 2, the alumina particles without particle size optimization were unevenly distributed in the coating, forming more irregular microvoids, resulting in higher shrinkage after heat treatment.

[0203] The improvement of coating uniformity is not only due to particle size optimization, but also due to the change in particle morphology after spray treatment. The alumina particles after spray dispersion are more regular, with increased surface activity, which further improves the bonding force with the base film. The test of Comparative Example 2 shows that the coating with large particles has the phenomenon of particle agglomeration in the microstructure, leading to stress concentration in local areas. The result of this phenomenon is directly reflected in the transverse and longitudinal tests of thermal shrinkage, which almost doubles the value, significantly inferior to the example.

[0204] The difference in thermal stability reveals the profound impact of particle size optimization on the overall performance of the separator material. The arrangement and dense structure of small particles enable the material to maintain higher dimensional stability in high-temperature environments. The unoptimized particle system expands unevenly during the heating process, leading to structural instability. This further demonstrates the irreplaceability of spray particle size control technology in improving the heat resistance of the separator material.

[0205] Experiment 3: Effect of ultrasonic mixing process on the dispersion performance of the slurry

[0206] Experiment description

[0207] Experiment goal:

[0208] To study the effect of ultrasonic mixing under vacuum conditions on the dispersion performance of ceramic slurry and verify the advantages of the present technology in slurry uniformity and separator performance.

[0209] Experiment steps:

[0210] Example 3: Separator preparation

[0211] Prepare a sodium perfluorooctanoate solution: Take 42 parts by mass of sodium perfluorooctanoate and add it to 83 parts by mass of ultrapure water. Heat to 88°C and stir for 40 minutes to obtain a uniform solution.

[0212] Alumina treatment: Add 52 parts by mass of alumina to the solution and stir for 30 minutes at 55°C, then filter and disperse by 4MPa pneumatic spraying to obtain modified alumina with a particle size D50: 0.284μm, D90: 0.774μm.

[0213] Prepare ceramic slurry: Mix 36 parts by mass of modified alumina with 34 parts by mass of ultrapure water, add 0.8 parts by mass of dispersant and stir for 60 minutes. Add 2.1 parts by mass of pore former and ultrasonically mix under vacuum conditions for 30 minutes, then add 3.4 parts by mass of binder and 0.11 parts by mass of wetting agent and continue ultrasonic mixing for 15 minutes.

[0214] Coating and drying: The slurry is coated on a 9μm thick PE-based film at a coating speed of 38m / min, with a coating thickness of 1.8μm. Dry at 90°C for 3 minutes to obtain a separator sample.

[0215] Preparation of Comparative Example 3 Separator

[0216] Prepare a sodium perfluorooctanoate solution and alumina treatment: The same as Example 3.

[0217] Prepare ceramic slurry: Cancel the vacuum condition and use only conventional low-speed stirring instead of ultrasonic mixing, and the rest of the steps are the same as Example 3.

[0218] Coating and drying: The same as Example 3.

[0219] Experimental test

[0220] Particle size distribution of slurry: The particle size distribution characteristics (D50, D90) of the slurry were tested using a laser particle size analyzer;

[0221] Coating uniformity: The microstructure of the coating surface was observed using a scanning electron microscope (SEM);

[0222] Breakdown voltage: The breakdown voltage of the separator (kV) was measured using a high-voltage insulation resistance tester.

[0223] Experimental data

[0224] Data table:

[0225]

[0226] Ultrasonic mixing plays a crucial role in the uniformity of ceramic slurry dispersion under vacuum conditions. The experiment shows that the particle size distribution of the slurry in Example 3 is more concentrated, with a significant increase in the proportion of small particles. The setting of the vacuum environment avoids bubble interference, combined with the high-frequency vibration of ultrasonic waves, making the particle distribution more uniform, while Comparative Example 3 does not use ultrasonic mixing, resulting in a large deviation in the particle size of the slurry, with significant increases in D50 and D90, which directly leads to the phenomenon of uneven coating in the subsequent process.

[0227] 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 has many local voids. These voids lead to a decrease in breakdown voltage, making the separator prone to damage under high voltage conditions. The difference in breakdown voltage not only reflects the density of the coating, but also reveals the importance of optimizing particle distribution.

[0228] The mechanism of vacuum ultrasonic mixing lies in multiple synergistic effects. On the one hand, ultrasonic energy can break the weak aggregation force between particles; on the other hand, the vacuum environment avoids bubble interference with coating uniformity in the solution. Experiments show that traditional stirring cannot achieve this effect, and the slurry produced cannot form a uniform and dense coating on the base film. This process optimization enables the separator of the present invention to exhibit higher stability and reliability in battery applications.

[0229] Experiment 4: Effect of base film properties on separator performance

[0230] Experimental explanation

[0231] Experimental objective:

[0232] To study the effect of base film type and its processing technology on the thermal stability and electrical performance of the separator, and to verify the technical advantages of using a specific base film in the present invention.

[0233] Experimental steps:

[0234] Example 4 Preparation of the separator

[0235] Preparation of sodium perfluorooctanoate solution: 28 parts by mass of sodium perfluorooctanoate was weighed into 72 parts by mass of ultrapure water, heated to 78°C, and stirred for 40 minutes to obtain a uniform solution.

[0236] Alumina treatment: 44 parts by mass of alumina was added to the solution, stirred at 56°C for 35 minutes, and then filtered and dispersed by 3.5 MPa pneumatic spraying to obtain alumina with a particle size D50 of 0.276 μm and a D90 of 0.780 μm.

[0237] Preparation of ceramic slurry: 34 parts by mass of alumina was mixed with 33 parts by mass of ultrapure water, 0.7 parts by mass of dispersant was added, and stirred for 50 minutes. Then 1.5 parts by mass of pore-forming agent was added, and ultrasonic mixing was performed under vacuum for 30 minutes. Finally, 3.1 parts by mass of binder and 0.1 parts by mass of wetting agent were added, and ultrasonic mixing was performed again for 15 minutes to prepare the ceramic slurry.

[0238] Coating and drying: the slurry was coated on a specially treated PE-based film (thickness 8 μm) at a speed of 32 m / min, the coating thickness was 1.3 μm, the drying temperature was 87°C, and the time was 3 minutes to obtain the separator sample.

[0239] Comparative Example 5 Preparation of the separator

[0240] Preparation of sodium perfluorooctanoate solution and alumina treatment: the same as Example 4.

[0241] Preparation of ceramic slurry: the same as Example 4.

[0242] Coating and drying: the slurry was coated on an untreated ordinary PE-based film (thickness 10 μm), and the rest of the process was the same as Example 4.

[0243] Experimental test

[0244] Thermal shrinkage: the separator sample was heated in a 150°C environment for 1 hour, and the thermal shrinkage in the longitudinal and transverse directions was tested respectively;

[0245] Breakdown voltage: a high-voltage insulation resistance tester was used to measure the breakdown voltage (kV) of the separator;

[0246] Coating adhesion: the adhesion between the coating and the base film (peeling strength, unit: N / m) was tested by peeling method, each group of samples was tested 3 times, and the average value was taken.

[0247] Experimental data

[0248] Data table:

[0249]

[0250] The properties of the base film directly determine the overall performance of the separator. In Example 4, a specially treated PE base film was used, which significantly reduced the surface energy and greatly improved the adhesion to the coating. This base film showed excellent dimensional stability at high temperatures, effectively suppressing thermal shrinkage. The defects of the ordinary base film in Comparative Example 5 were fully exposed in the test, and 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.

[0251] The difference in thermal 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 does not fail due to interface separation in a high-temperature environment. On the contrary, the shrinkage of the ordinary base film in Comparative Example 5 at high temperatures is inconsistent with the expansion of the coating, and delamination between the coating and the base film is easy to occur. This instability is the main reason for the significant increase in thermal shrinkage.

[0252] In addition, the test results of the breakdown voltage show that the performance of the base film will also directly affect the electric field resistance of the separator. The separator of Example 4 significantly improves the breakdown voltage by improving the bonding quality between the coating and the base film, making the coating more dense and reducing porosity. In Comparative Example 5, the breakdown voltage decreases significantly due to poor local bonding of the coating, which fully illustrates the importance and necessity of base film treatment.

[0253] Experiment 5: Effect of coating and drying parameters on the performance of the separator

[0254] Experiment description

[0255] Experiment goal:

[0256] To study the effect of coating thickness and drying temperature on the air permeability, moisture content, and ion conduction performance of the separator, and to verify the technical advantages of the invention in parameter optimization.

[0257] Experiment steps:

[0258] Preparation of Example 1 separator

[0259] Prepare a sodium perfluorooctanoate solution, treat with aluminum oxide, and prepare a ceramic slurry: follow the steps in Experiment 1;

[0260] Coating and drying: coat the slurry on the PE base film at a speed of 30 m / min, control the coating thickness to be 1.1 μm, and dry at 80°C for 2 minutes to obtain a separator sample.

[0261] Preparation of Comparative Example 4 separator

[0262] Preparation of sodium perfluorooctanoate solution, alumina treatment, preparation of ceramic slurry: same as Example 1;

[0263] Coating and drying: the slurry was coated on PE base film at a speed of 32 m / min, the coating thickness was 1.3 pm, the drying temperature was adjusted to 65 °C, and the drying time was 2 minutes.

[0264] Experimental test

[0265] Air permeability test: using Gurley air permeability tester, record the time required for 100 mL of air to pass through the membrane (unit: s / 100 mL), test 3 times for each group, take the average value;

[0266] Moisture content test: using Karl Fischer coulometric titration method to determine the moisture content of the membrane, record the moisture content (ppm) of each group of membranes;

[0267] Ion conduction performance test: assemble the membrane into a standard battery (LiFeP04 / / Li), measure the ion conductivity (S / cm) of the battery by AC impedance method.

[0268] Experimental data

[0269] Data table:

[0270]

[0271] The coating and drying parameters have a significant impact on the microstructure of the membrane and its performance. In Example 1, the coating thickness is 1.1 pm, and with moderate drying conditions at 80 °C, the coating forms a more dense microporous structure. This optimized coating microstructure significantly improves the air permeability, and the support ability of the membrane for ion conduction is fully exerted. In Comparative Example 4, the coating thickness is increased to 1.3 pm, and the drying temperature is lower, the water in the slurry cannot be completely volatilized, and the coating forms more closed pore structure, resulting in a significant decrease in air permeability and ion conductivity.

[0272] In Example 1, the drying temperature of 80 °C ensures the complete volatilization of the pore-forming agent, while avoiding potential damage to the base film structure at high temperatures. This precise temperature control makes the coating pore size distribution more uniform, and there are no obvious large pores in the microstructure, and the moisture content remains at a low level. In Comparative Example 4, due to the drying temperature of only 65 °C, there is more residual water in the slurry, the hydrophobicity of the coating is reduced, resulting in a significant increase in the overall moisture content of the membrane.

[0273] The difference in ionic conductivity further validates the advantages of the coating process of the present application from an electrochemical perspective. In the separator of Example 1, the more optimal microporous structure provides a smoother path for ion conduction, while the low moisture content reduces impedance. In contrast, the separator of Comparative Example 4 is significantly inhibited in its ability to conduct ions due to the over-thick coating and poor pore distribution. This experiment also shows that precise optimization of coating thickness and drying parameters is critical for the preparation of high performance separators.

[0274] While embodiments of the present application have been shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the application. The scope of the application is thus defined by the appended claims and equivalents thereof.

Claims

1. A lithium battery separator with high heat resistance and low water absorption, characterized in that, It is made from the following components in parts by weight: Alumina: 40–60 parts by weight; Sodium perfluorooctanoate: 25–42 parts by weight; Ultrapure water: 65–85 parts by weight; Dispersant: 0.5–1.2 parts by weight; Pore-forming agent: 1.3–2.9 parts by weight; Adhesive: 2.6–3.8 parts by weight; Wetting agent: 0.08–0.12 parts by weight; The temperature of the solution prepared by sodium perfluorooctanoate and ultrapure water is 80–90°C, the stirring speed is 40–60 r / min, and the stirring time is 30–45 minutes. The method for preparing the lithium battery separator includes the following steps: S1. Add 25–42 parts by weight of sodium perfluorooctanoate to 65–85 parts by weight of ultrapure water, and stir and dissolve at 80–90°C for 30–45 minutes to obtain the first aqueous solution; S2. Add 40–60 parts by mass of alumina to the first aqueous solution, stir at 50–60°C for 30–35 minutes, filter to obtain a solid, and disperse it by pneumatic spraying to obtain pretreated alumina with particle sizes of D50: 0.25–0.45 μm and D90: 0.7–0.9 μm. S3. Mix 32–38 parts by weight of pretreated alumina with 29–35 parts by weight of ultrapure water, and add 0.5–1.2 parts by weight of dispersant and stir for 60 minutes. S4. Under ultrasonic mixing conditions, add 1.3–2.9 parts by weight of pore-forming agent to the mixture, stir for 30 minutes, then add 2.6–3.8 parts by weight of binder and 0.08–0.12 parts by weight of wetting agent, and continue ultrasonic mixing for 15–20 minutes to obtain ceramic slurry. S5. Coat the obtained ceramic slurry onto one side of a base film with a thickness of 7–9 μm at a coating speed of 30–40 m / min and a coating thickness of 1–2 μm. S6. Dry at 80–100℃ for 2–4 minutes to obtain a lithium battery separator with high heat resistance and low water absorption.

2. The 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. 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.

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

5. The lithium battery separator with high heat resistance and low water absorption according to claim 1, 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.

6. The lithium battery separator with high heat resistance and low water absorption according to claim 1, characterized in that, The pressure during the pneumatic spraying and dispersing process of the alumina is 3–5 MPa.

7. The lithium battery separator with high heat resistance and low water absorption according to claim 1, characterized in that, The drying time is 2–3 minutes, and the drying temperature is 85–90℃.

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