Hydrophobic ceramic diaphragm and preparation method thereof

Abstract

The invention discloses a hydrophobic ceramic diaphragm and a preparation method thereof, the hydrophobic ceramic diaphragm comprises a base membrane and a coating on the base membrane, the coating comprises modified alumina, lithium carboxymethyl cellulose, polyacrylate and polyacrylic acid, the modified aluminum oxide is obtained by synergistically modifying 3-(trimethoxysilyl) propyl dimethyl octadecyl ammonium chloride and a silane coupling agent; the silane coupling agent is one or a mixture of more of vinyl triethyl silane, vinyl trimethoxy silane, trimethyl methoxy silane, aminopropyl trimethoxy silane, methacryloyloxy silane and ureido propyl triethoxy silane. The silane coupling agent is one or a mixture of more of vinyl triethyl silane, vinyl trimethoxy silane, trimethyl methoxy silane, aminopropyl trimethoxy silane, methacryloyloxy silane and ureido propyl triethoxy silane. The hydrophobic ceramic diaphragm disclosed by the invention has excellent ionic conductivity and peel strength and relatively low water content.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a hydrophobic ceramic separator and its preparation method. Background Technology

[0002] With the development of the times, new energy electric vehicles have gradually become an integral part of people's lives. As the power source of electric vehicles, the safety and range of lithium-ion batteries are the focus of scientific research. Lithium battery separators play an important role in lithium-ion batteries.

[0003] Conventional alumina-coated separators suffer from drawbacks such as strong hydrophilicity, high water absorption, and easy adsorption of moisture from the environment, leading to separator curling. Furthermore, their lithium-ion transport efficiency is relatively low, failing to meet current requirements for lithium-ion battery separators. Therefore, the development of novel lithium-ion battery separators is imperative. In recent years, there has been considerable research on modifying lithium-ion battery separators using inorganic materials. This is because combining inorganic and organic materials can significantly improve the separator's hydrophobicity and interfacial compatibility. However, its effect on improving the separator's peel strength and lithium-ion transport efficiency is relatively limited, failing to meet application requirements. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a hydrophobic ceramic membrane.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned hydrophobic ceramic membrane.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] A hydrophobic ceramic membrane includes: a base membrane and a coating on the base membrane, the coating comprising: modified alumina, lithium carboxymethyl cellulose (CMC-Li), polyacrylate, and polyacrylic acid, wherein the ratio of modified alumina, lithium carboxymethyl cellulose (CMC-Li), polyacrylate, and polyacrylic acid by mass parts is (4-7):(0.02-0.045):(0.5-0.75):(0.015-0.03), wherein the modified alumina is obtained by synergistic modification with 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (TMSPDAC) and a silane coupling agent, wherein the silane coupling agent is one or a mixture of several selected from vinyltriethylsilane, vinyltrimethoxysilane, trimethylmethoxysilane, aminopropyltrimethoxysilane, methacryloxysilane, and ureopropyltriethoxysilane.

[0008] In the above technical solution, the method for obtaining modified alumina includes: mixing and curing a dispersion containing 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (TMSPDAC) and a silane coupling agent with alumina to obtain the modified alumina. The ratio of 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (TMSPDAC), silane coupling agent and alumina by mass is (1-1.5):(1.5-2):100.

[0009] In the above technical solution, the silane coupling agent is preferably vinyltriethylsilane.

[0010] In the above technical solution, the method for obtaining modified alumina specifically includes:

[0011] S1, mix the silane coupling agent and anhydrous ethanol until homogeneous, add the first part of water, mix until homogeneous to obtain the first dispersion, add 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (TMSPDAC) and the second part of water to the first dispersion, mix until homogeneous to obtain the second dispersion. By mass parts, the ratio of 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (TMSPDAC), silane coupling agent, anhydrous ethanol, the first part of water used to form the first dispersion and the second part of water used to form the second dispersion is (1~1.5):(1.5~2):(9~13):(1~1.5):(1~1.5);

[0012] S2, the second dispersion and alumina are mixed until uniform, solidified, and sieved to obtain modified alumina. By mass fraction, the ratio of 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (TMSPDAC) to alumina in the second dispersion is (1-1.5):100.

[0013] In S2, the alumina is nano-alumina with a particle size of 300-400 nm.

[0014] In S2, the curing temperature is 100-120℃ and the curing time is 1-2 hours.

[0015] In S2, the sieving process uses a 10,000-mesh sieve.

[0016] The above-mentioned method for preparing hydrophobic ceramic separators includes: coating a lithium battery separator coating slurry onto at least one side of a base membrane, drying it, forming a coating on the base membrane, and obtaining a hydrophobic ceramic separator. The lithium battery separator coating slurry includes: a slurry solvent, modified alumina, lithium carboxymethyl cellulose, a pore-forming agent, a binder, and a wetting agent.

[0017] In the above technical solution, the drying temperature is 105℃~110℃. The drying is achieved by infrared radiation, using infrared electromagnetic wave radiation with a wavelength of 2.5~25 micrometers for at least 15 seconds.

[0018] A lithium battery separator coating slurry includes: a slurry solvent, modified alumina, lithium carboxymethyl cellulose (CMC-Li), a pore-forming agent, a binder, and a wetting agent. By mass parts, the ratio of the slurry solvent, modified alumina, lithium carboxymethyl cellulose (CMC-Li), pore-forming agent, binder, and wetting agent is (7.97-13.47): (4-7): (0.02-0.045): (0.5-1): (0.5-0.75): (0.015-0.03).

[0019] In the above technical solution, the pore-forming agent is isopropanol, the binder is polyacrylate, the wetting agent is polyacrylic acid, and the slurry solvent is water.

[0020] The method for preparing the above-mentioned lithium battery separator coating slurry includes: mixing the slurry solvent, modified alumina, lithium carboxymethyl cellulose, pore-forming agent, binder and wetting agent until uniform to obtain the lithium battery separator coating slurry. The ratio of slurry solvent, modified alumina, lithium carboxymethyl cellulose (CMC-Li), pore-forming agent, binder and wetting agent by mass parts is (7.97~13.47):(4~7):(0.02~0.045):(0.5~1):(0.5~0.75):(0.015~0.03).

[0021] In the above technical solution, the slurry solvent is added in two stages.

[0022] In the above technical solution, the method for preparing the lithium battery separator coating slurry specifically includes the following steps:

[0023] Step 1: Add water and lithium carboxymethyl cellulose (CMC-Li) to the slurry solvent for the first time and mix until homogeneous to obtain an aqueous solution of lithium carboxymethyl cellulose (CMC-Li) (as a dispersant). The ratio of water to lithium carboxymethyl cellulose (CMC-Li) added to the slurry solvent for the first time by mass is (0.97~1.47):(0.02~0.045).

[0024] Step 2: Mix the modified alumina, the slurry solvent, and the second addition of water and carboxymethyl cellulose lithium (CMC-Li) aqueous solution until homogeneous to obtain solution A. By mass fraction, the ratio of carboxymethyl cellulose lithium (CMC-Li) in the modified alumina, the second addition of water, and the carboxymethyl cellulose lithium (CMC-Li) aqueous solution is (4-7):(7-12):(0.02-0.045).

[0025] Step 3: Mix the A solution and the pore-forming agent until homogeneous to obtain the B solution. The ratio of modified alumina to pore-forming agent in the A solution by mass is (4-7):(0.5-1).

[0026] Step 4: Mix the B solution and binder until uniform, then add the wetting agent and mix until uniform. Grind to obtain the lithium battery separator coating slurry. The ratio of pore-forming agent, binder and wetting agent in the B solution is (0.5~1):(0.5~0.75):(0.015~0.03).

[0027] Application of synergistic modification of alumina with 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (TMSPDAC) and silane coupling agents in improving membrane ionic conductivity and / or peel strength.

[0028] Application of synergistic modification of alumina with 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (TMSPDAC) and silane coupling agents in reducing membrane water content.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention utilizes the chemical reaction between the siloxane group (-Si(OCH3)3) of 3-(trimethoxysilyl)propyl dimethyl octadecyl ammonium chloride (TMSPDAC) and the hydroxyl group (-OH) on the surface of alumina to form a stable Si-O-Al bond. Furthermore, the long-chain alkyl group (C...) of 3-(trimethoxysilyl)propyl dimethyl octadecyl ammonium chloride (TMSPDAC)... 18 H 37 By electrostatically adsorbing and oriented onto the surface of alumina, the surface energy is reduced, which can effectively optimize the hydrophobicity of the diaphragm, giving it hydrophobicity and antifouling properties. At the same time, the silane coupling agent can form a chemical bridge between the inorganic filler (nano alumina) and the organic material (polyacrylate), thereby enhancing interfacial compatibility. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope image of the separator prepared from the lithium battery separator coating slurry of Example 1;

[0032] Figure 2 The image shows a scanning electron microscope (SEM) image of the separator prepared by coating the lithium battery separator with the slurry of Comparative Example 1.

[0033] Figure 3 The image shows a scanning electron microscope (SEM) image of the separator prepared by coating the lithium battery separator with the slurry of Comparative Example 2. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0035] 3-(trimethoxysilyl)propyl dimethyl octadecyl ammonium chloride (TMSPDAC): Molecular formula is C 26 H 58 ClNO3Si appears as a pale yellow to colorless viscous liquid with a density of 0.95-1.05 g / cm³. 3 (25℃).

[0036] Nano-aluminium oxide has a melting point of 2054℃, a boiling point of 2980℃, and a particle size of 300-400nm.

[0037] Polyacrylic acid: weight average molecular weight is 8000 g / mol.

[0038] Polyacrylate: with a weight-average molecular weight of 80,000 g / mol, it is polymerized from methyl methacrylate.

[0039] In the following examples, the water used is deionized water.

[0040] In the following examples, the base film is a PE film with a thickness of 7 μm.

[0041] Ionic conductivity: measured in a glove box at 25°C with H2O < 10 ppm.

[0042] Peel strength: Prepare a standard-sized sample (10-25mm wide, 150mm long), attach 3M transparent tape to the coated surface of the sample, leaving a sufficient peel end (at least 20mm), use a standard roller to evenly press the sample 3 times, fix both ends of the sample in the upper and lower clamps respectively, peel in the direction of 180°, and use a tensile tester to tear off one end of the 3M transparent tape to obtain the peel strength.

[0043] Example 1

[0044] A method for preparing a lithium battery separator coating slurry includes: mixing a slurry solvent, modified alumina, lithium carboxymethyl cellulose (CMC-Li), a pore-forming agent, a binder, and a wetting agent until homogeneous to obtain a lithium battery separator coating slurry. The ratio of the slurry solvent, modified alumina, lithium carboxymethyl cellulose (CMC-Li), pore-forming agent, binder, and wetting agent, by mass parts, is 7.974:5:0.026:0.5:0.5:0.015. The slurry solvent is water, and the solvent is added in two stages. The method specifically includes the following steps:

[0045] Step 1: Add water and lithium carboxymethyl cellulose (CMC-Li) to the slurry solvent for the first time and mix. Stir at a rotation speed of 3300 r / min and a revolution speed of 20 r / min for 10 min until uniform to obtain an aqueous solution of lithium carboxymethyl cellulose (CMC-Li) (as a dispersant). The ratio of water to lithium carboxymethyl cellulose (CMC-Li) added for the first time is 0.974:0.026 by mass.

[0046] Step 2: Mix the modified alumina, the second addition of water and carboxymethyl cellulose lithium (CMC-Li) aqueous solution to the slurry solvent, and stir at a rotation speed of 3300 r / min and a revolution speed of 20 r / min for 10 min until homogeneous to obtain solution A. By mass parts, the ratio of modified alumina, the second addition of water and the carboxymethyl cellulose lithium (CMC-Li) aqueous solution is 5:7:0.026.

[0047] Step 3: Mix solution A and the pore-forming agent, and stir at a rotation speed of 3300 r / min and a revolution speed of 20 r / min for 10 min until homogeneous to obtain solution B. By mass fraction, the ratio of modified alumina to pore-forming agent in solution A is 5:0.5, and the pore-forming agent is isopropanol.

[0048] Step 4: Mix solution B and binder, and sonicate for 2 hours under stirring conditions until homogeneous (ultrasound frequency 5kHz, stirring speed 1000r / min, stirring speed 20r / min). Then add wetting agent, stir at 3300r / min rotation speed and 20r / min revolution speed for 10 minutes, and grind in a grinder at 400r / min speed for 10 minutes to obtain lithium battery separator coating slurry. The ratio of pore-forming agent, binder and wetting agent in solution B is 0.5:0.5:0.015. The binder is polyacrylate and the wetting agent is polyacrylic acid.

[0049] The method for preparing the above-mentioned modified alumina includes the following steps:

[0050] S1, mix the silane coupling agent and anhydrous ethanol, stir at 2000 rpm for 60 minutes until homogeneous, add the first part of water, stir at 2000 rpm for 60 minutes until homogeneous to obtain the first dispersion, add 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (TMSPDAC) and the second part of water to the first dispersion, stir at 2000 rpm for 60 minutes until homogeneous to obtain the second dispersion. By mass, the ratio of 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (TMSPDAC), silane coupling agent, anhydrous ethanol, the first part of water used to form the first dispersion and the second part of water used to form the second dispersion is 1.5:1.5:9:1:1, and the silane coupling agent is vinyltriethylsilane;

[0051] S2, the second dispersion and nano-alumina are mixed and stirred at 2000 rpm for 1 hour until uniform. The mixture is then cured in a vacuum drying oven at 100°C for 2 hours, ground into powder, and sieved through a 10000-mesh sieve to obtain modified alumina. By mass, the ratio of 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (TMSPDAC) to nano-alumina in the second dispersion is 1:100.

[0052] Example 2

[0053] A method for preparing a lithium battery separator coating slurry is basically the same as in Example 1, except that the ratio of "by mass parts, the slurry solvent, modified alumina, lithium carboxymethyl cellulose (CMC-Li), pore-forming agent, binder and wetting agent is 7.974:5:0.026:0.5:0.5:0.015" is replaced with "by mass parts, the slurry solvent, modified alumina, lithium carboxymethyl cellulose (CMC-Li), pore-forming agent, binder and wetting agent is 7.974:7:0.026:0.5:0.5:0.015".

[0054] Example 3

[0055] A method for preparing a lithium battery separator coating slurry is basically the same as that in Example 1, except that “vinyltriethylsilane” is replaced with “trimethylmethoxysilane”.

[0056] Comparative Example 1

[0057] A method for preparing a lithium battery separator coating slurry includes: mixing water and a dispersant, stirring at a rotation speed of 3300 r / min and a revolution speed of 20 r / min for 10 min until homogeneous, adding nano-alumina, stirring at a rotation speed of 3300 r / min and a revolution speed of 20 r / min for 10 min until homogeneous, then sonicating at a frequency of 5 kHz for 10 min, adding a binder, and sonicating under stirring conditions for 2 h until homogeneous (ultrasound frequency of 5 kHz, rotation speed of stirring of 1000 r / min, revolution speed of stirring of 20 r / min), and grinding in a grinder at a speed of 400 r / min for 10 min to obtain the lithium battery separator coating slurry. The ratio of dispersant, water, nano-alumina, and binder by mass is 0.2:24.8:17.5:2. The dispersant is ammonium polyacrylate (Mw of 5000 g / mol), and the binder is polyacrylate.

[0058] Comparative Example 2

[0059] A method for preparing a lithium battery separator coating slurry is basically the same as that in Example 1, except that 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (TMSPDAC) is not added in the method for preparing modified alumina.

[0060] Comparative Example 3

[0061] A method for preparing a lithium battery separator coating slurry is basically the same as that in Example 1, except that no silane coupling agent is added in the method for preparing modified alumina.

[0062] Examples 4-6 and Comparative Examples 4-6

[0063] A method for preparing a diaphragm includes: applying a slurry to one side of a base film using an anilox roller (with a mesh depth of 2 μm), drying it at 106°C (achieved by irradiating the slurry-coated side of the base film with an infrared electromagnetic wave of 5 μm wavelength for 15 seconds), forming a coating on the base film to obtain a diaphragm. The slurry is one of Examples 1-3 and Comparative Examples 1-3.

[0064] Table 1

[0065]

[0066]

[0067] Figure 1 This is a scanning electron microscope (SEM) image of the separator prepared from the lithium battery separator coating slurry of Example 1. Figure 2 This is a scanning electron microscope (SEM) image of the separator prepared from the lithium battery separator coating slurry of Comparative Example 1. Figure 3The image shows a scanning electron microscope (SEM) image of the separator prepared by coating the lithium battery separator with the slurry of Comparative Example 2.

[0068] The particle sizes of the lithium battery separator coating slurries of Examples 1-3 and Comparative Examples 1-3 are shown in Table 2 (test conditions: temperature: 20℃~28℃; relative humidity: 55%~65%; atmospheric pressure: 90kPa~98kPa).

[0069] Table 2

[0070]

[0071] The specific surface areas of the membranes prepared in Examples 4-6 and Comparative Examples 4-6 are shown in Table 3.

[0072] Table 3

[0073] diaphragm <![CDATA[Specific surface area (m 2 / g)]]> Example 4 2.895 Example 5 2.941 Example 6 3.054 Comparative Example 4 3.387 Comparative Example 5 3.317 Comparative Example 6 3.418

[0074] As shown in Table 3, the separator prepared by the lithium battery separator coating slurry of Example 1 has the lowest specific surface area and is not easy to absorb water, which helps to reduce the water content of the separator.

[0075] The ionic conductivity of the membranes prepared in Examples 4-6 and Comparative Examples 4-6 is shown in Table 4.

[0076] Table 4

[0077] diaphragm Ionic conductivity σ (S / cm) Example 4 0.0845 Example 5 0.0838 Example 6 0.0841 Comparative Example 4 0.0704 Comparative Example 5 0.0708 Comparative Example 6 0.0645

[0078] As shown in Table 4, the ionic conductivity of the membranes prepared in Examples 4-6 is higher than that of the comparative examples 4-6. Among them, the ionic conductivity of the membrane prepared in Example 4 is the highest. This indicates that the amount of modified alumina added and the type of silane coupling agent and 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (TMSPDAC) used to synergistically modify alumina will affect the performance of the membrane.

[0079] The peel strength of the diaphragms prepared in Examples 4-6 and Comparative Examples 4-6 is shown in Table 5.

[0080] Table 5

[0081] diaphragm Peel strength (N / m) Example 4 139 Example 5 125 Example 6 122 Comparative Example 4 91 Comparative Example 5 94 Comparative Example 6 88

[0082] As shown in Table 5, the membranes prepared in Examples 4-6 have good peel strength. In the embodiments of the present invention, the siloxane group (-Si(OCH3)3) of 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (TMSPDAC) reacts with the hydroxyl group (-OH) on the surface of alumina to form a stable Si-O-Al bond, thereby enhancing the interfacial adhesion between the coating and the base film. At the same time, the silane coupling agent can form a chemical bridge between the inorganic filler (nano-alumina) and the organic material (polyacrylate), thereby enhancing the interfacial compatibility and improving the peel strength.

[0083] The thickness and water content of the membranes prepared in Examples 4-6 and Comparative Examples 4-6 are shown in Table 6.

[0084] Table 6

[0085] diaphragm Thickness (μm) Water content (ppm) Example 4 9.26 364 Example 5 9.23 387 Example 6 9.19 543 Comparative Example 4 9.31 782 Comparative Example 5 9.21 735 Comparative Example 6 9.22 748

[0086] As shown in Table 6, the hydrolyzable group (alkoxy group) of the silane coupling agent undergoes a hydrolysis reaction to generate silanol, which then forms siloxane through a condensation reaction. This results in a strong bonding layer between the coating and the base film, reducing the penetration path of water molecules at the interface and thus lowering the water content in the coating.

[0087] The test results of the separator prepared from the lithium battery separator coating slurry of Example 1 are as follows:

[0088]

[0089] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A hydrophobic ceramic diaphragm, characterized in that, include: The base film and the coating on the base film, the coating comprising: modified alumina, lithium carboxymethyl cellulose, polyacrylate and polyacrylic acid, wherein the ratio of modified alumina, lithium carboxymethyl cellulose, polyacrylate and polyacrylic acid by mass parts is (4-7):(0.02-0.045):(0.5-0.75):(0.015-0.03), wherein the modified alumina is obtained by synergistic modification with 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride and a silane coupling agent, wherein the silane coupling agent is one or a mixture of several of vinyltriethylsilane, vinyltrimethoxysilane, trimethylmethoxysilane, aminopropyltrimethoxysilane, methacryloxysilane and ureopropyltriethoxysilane.

2. The hydrophobic ceramic diaphragm according to claim 1, characterized in that, A method for obtaining modified alumina includes: mixing and curing a dispersion containing 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride and a silane coupling agent with alumina to obtain the modified alumina, wherein the ratio of 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride, silane coupling agent and alumina by mass is (1-1.5):(1.5-2):

100.

3. The hydrophobic ceramic membrane according to claim 2, characterized in that, The specific methods for obtaining modified alumina include: S1, mix the silane coupling agent and anhydrous ethanol until homogeneous, add the first part of water, mix until homogeneous to obtain the first dispersion, add 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride and the second part of water to the first dispersion, mix until homogeneous to obtain the second dispersion. By mass parts, the ratio of 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride, silane coupling agent, anhydrous ethanol, the first part of water used to form the first dispersion and the second part of water used to form the second dispersion is (1~1.5):(1.5~2):(9~13):(1~1.5):(1~1.5); S2, the second dispersion and alumina are mixed until uniform, solidified, and sieved to obtain modified alumina. By mass fraction, the ratio of 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride to alumina in the second dispersion is (1-1.5):

100.

4. A lithium battery separator coating slurry, characterized in that, include: The ratio of slurry solvent, modified alumina, lithium carboxymethyl cellulose, pore-forming agent, binder and wetting agent by mass parts is (7.97~13.47):(4~7):(0.02~0.045):(0.5~1):(0.5~0.75):(0.015~0.03).

5. The lithium battery separator coating slurry according to claim 4, characterized in that, The pore-forming agent is isopropanol, the binder is polyacrylate, the wetting agent is polyacrylic acid, and the slurry solvent is water.

6. A method for preparing the lithium battery separator coating slurry according to claim 5, characterized in that, include: The slurry solvent, modified alumina, lithium carboxymethyl cellulose, pore-forming agent, binder and wetting agent are mixed until uniform to obtain a lithium battery separator coating slurry. The ratio of slurry solvent, modified alumina, lithium carboxymethyl cellulose, pore-forming agent, binder and wetting agent by mass parts is (7.97~13.47):(4~7):(0.02~0.045):(0.5~1):(0.5~0.75):(0.015~0.03).

7. The method according to claim 6, characterized in that, The method for preparing lithium battery separator coating slurry specifically includes the following steps: Step 1: Add water and lithium carboxymethyl cellulose to the slurry solvent for the first time and mix until homogeneous to obtain an aqueous solution of lithium carboxymethyl cellulose. The ratio of water to lithium carboxymethyl cellulose added to the slurry solvent for the first time by mass is (0.97~1.47):(0.02~0.045). Step 2: Mix the modified alumina, the slurry solvent, water and lithium carboxymethyl cellulose aqueous solution for the second time until homogeneous to obtain solution A. By mass fraction, the ratio of modified alumina, water added for the second time in the slurry solvent and lithium carboxymethyl cellulose aqueous solution is (4-7):(7-12):(0.02-0.045). Step 3: Mix the A solution and the pore-forming agent until homogeneous to obtain the B solution. The ratio of modified alumina to pore-forming agent in the A solution by mass is (4-7):(0.5-1). Step 4: Mix the B solution and binder until uniform, then add the wetting agent and mix until uniform. Grind to obtain the lithium battery separator coating slurry. The ratio of pore-forming agent, binder and wetting agent in the B solution is (0.5~1):(0.5~0.75):(0.015~0.03). Application of 8,3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride and silane coupling agent in synergistic modification of alumina to improve the ionic conductivity of membranes. Application of 9,3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride and silane coupling agent in synergistic modification of alumina to improve diaphragm peel strength. Application of synergistic modification of alumina with 10,3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride and silane coupling agent in reducing membrane water content.

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