A high heat-resistant lithium-ion battery separator and its preparation method

Abstract

The present invention discloses a high heat-resistant lithium-ion battery separator and its preparation method, which includes a polyolefin-based film and a composite coating applied on one or both sides thereof. By formulating a thickening adhesive solution and uniformly coating the thickening adhesive solution on the surface of the polyolefin-based film, the thickening effect of the adhesive enhances the binding force between the ceramic particles and the base film, enabling the ceramic particles to firmly adhere to the separator surface and not easily fall off. At the same time, the addition of the thickening adhesive solution can also optimize the fluidity of the coating, making the coating more uniform during the coating process and effectively avoiding the problem of uneven coating. This separator has a low thermal shrinkage rate, enhanced adhesion and mechanical properties, significantly improving the thickness uniformity and stability of the coated separator, and further enhancing the safety performance of the lithium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and particularly to a lithium-ion battery separator with high heat resistance and a preparation method thereof. Background Art

[0002] As one of the key technologies in the new energy field, the improvement of the performance and safety of lithium-ion batteries has always been a research hotspot. As a key component in the battery, the separator undertakes the important functions of isolating the positive and negative electrodes, preventing short circuits, and allowing lithium ions to pass through. With the rapid development of electric vehicles and portable electronic devices, the requirements for battery performance are constantly increasing, and traditional polyolefin separators are difficult to meet the needs of high energy density and high safety. The coated separator technology has emerged. By coating specific materials such as inorganic ceramics, glass fiber, or solid electrolytes on the base film, the thickness uniformity, thermal stability, mechanical strength, and puncture resistance of the separator are effectively improved. In particular, the coated separator can significantly reduce the safety risk of the battery under extreme conditions, such as thermal runaway caused by high temperature. In addition, the introduction of the coating material also helps to improve the wettability of the separator, thereby improving the charge and discharge performance and cycle life of the battery.

[0003] Patent CN 110048057 A discloses a surface-modified PMMA / PVDF hybrid-coated lithium battery composite separator and a preparation method thereof. The present invention aims to provide a surface-modified PMMA / PVDF hybrid-coated lithium battery composite separator and a preparation method thereof that can effectively solve the problems of insufficient adhesion performance of PVDF, the influence of crystallinity on ionic conductivity, and improve the electrolyte wetting consistency of PMMA. In addition, the present invention also solves the problems of uneven mixing and easy sedimentation of PMMA and PVDF. However, the surface energy of polyethylene (PE) and polypropylene (PP) separators is relatively high, which makes it difficult to firmly coat these materials on the surface of the separator, resulting in insufficient bonding strength after coating and easy occurrence of coating peeling. This phenomenon will ultimately cause uneven thickness of the separator and a decrease in heat resistance, which may lead to battery safety problems. Summary of the Invention

[0004] In order to overcome the above problems existing in the prior art, the present invention provides a lithium-ion battery separator with high heat resistance and a preparation method thereof. The separator has a low thermal shrinkage rate, enhanced adhesion and mechanical properties, can significantly improve the thickness uniformity and stability of the coated separator, and further enhance the safety performance of the lithium battery.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A high heat-resistant lithium-ion battery separator is composed of a polyolefin base film and a composite coating applied on one or both sides thereof; the composite coating includes, by weight, 20-40 parts of ceramic particles, 1-4 parts of ethylene-vinyl acetate copolymer type aqueous binder, 0.01-0.3 parts of crosslinking agent, 1-8 parts of polyacrylate type aqueous binder, 0.1-3 parts of thickener, 1-3% of the weight of the ceramic particles as dispersant, 0.1-0.5 parts of wetting agent, and 70-100 parts of deionized water;

[0007] The ethylene-vinyl acetate copolymer type aqueous binder is a copolymer emulsion of 40-80% vinyl acetate, prepared by a polymerization reaction, and includes, by weight: 100-150 parts of deionized water, 2-10 parts of non-ionic emulsifier, 0.1-0.5 parts of initiator, 0.1-0.5 parts of stabilizer, and 100 parts of a mixture of ethylene and vinyl acetate, and the molar ratio of ethylene to vinyl acetate is 1:0.67 to 1:4.

[0008] Due to the relatively high surface energy of PE and PP separators, it is difficult for ceramic particles to adhere to the surface of the separator, and the bonding strength with the base film after coating is poor, and the coating is prone to powder falling, which increases the difficulty of surface coating of the slurry. Therefore, before coating the slurry, by preparing a thickened binder solution and uniformly coating the thickened binder solution on the surface of the polyolefin base film, through the thickening effect of the binder, the bonding force between the ceramic particles and the base film is improved, so that the ceramic particles can firmly adhere to the surface of the separator and are not easy to fall off. At the same time, the addition of the thickened binder solution can also improve the fluidity of the coating, making the coating more uniform during the coating process and avoiding the problem of uneven coating.

[0009] Preferably, the ceramic particles are selected from one or more of alumina, silica, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, and barium oxide, with an average particle size of 0.5-0.8 μm and a coating thickness of 1.5-3 μm.

[0010] Preferably, the non-ionic emulsifier is selected from one or a mixture in any proportion of polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkyl alcohol ether, and polyoxyethylene alkyl phenol.

[0011] Preferably, the crosslinking agent is selected from one or a mixture in any proportion of tert-butyl peroxycarbonate-2-ethylhexyl ester (TBEC) and dicumyl peroxide (DCP).

[0012] Preferably, the thickener is a carboxymethyl cellulose (CMC) thickener.

[0013] Preferably, the dispersant is selected from one or more of triethylhexyl phosphoric acid, polyethylene glycol, polyvinyl alcohol, polyacrylate or cellulose derivatives, and its common grades are BYK2010 and BYK9151 of BYK Chemie GmbH, Germany.

[0014] Preferably, the wetting agent belongs to the wetting agent for aqueous systems and is selected from one or more of polyether-modified silicone, sodium butylnaphthalene sulfonate and polyols, and its common grade is BYK-996.

[0015] The present invention also provides a method for preparing the above-mentioned lithium-ion battery separator, which includes the following steps: according to the raw material formula of the composite coating, mixing the ceramic particles, ethylene-vinyl acetate copolymer (EVA) type aqueous binder, crosslinking agent, polyacrylate type aqueous binder, thickener, dispersant, wetting agent and water to prepare a composite coating, and coating the composite coating on a polyolefin-based film and drying.

[0016] Preferably, the preparation process of the composite coating includes: Step 1: preparing an aqueous solution of the thickener; Step 2: preparing an EVA type aqueous binder; Step 3: preparing a thickened binder solution; Step 4: adding the ceramic particles, thickened binder solution, crosslinking agent, dispersant, wetting agent and deionized water into a feed tank and dispersing at high speed for 20-30 minutes to obtain a composite coating.

[0017] Preferably, Step 1: the preparation process of preparing an aqueous solution of the thickener includes:

[0018] Weighing deionized water and the thickener and adding them into a feed tank, and dispersing with an electric high-speed disperser so that the thickener can be uniformly dissolved in deionized water to obtain an aqueous solution of the thickener.

[0019] Step 2: the preparation process of preparing an ethylene-vinyl acetate copolymer type aqueous binder includes:

[0020] S1: adding 100-150 parts by mass of deionized water and 2-10 parts by mass of non-ionic emulsifier into a reaction kettle and stirring until uniform;

[0021] S2: adding 0.1-0.5 parts by mass of initiator and 0.1-0.5 parts by mass of stabilizer, and stirring for 0.5-2 hours until the solution is uniform to form an initiator solution;

[0022] S3: mixing ethylene and vinyl acetate in a molar ratio of 1:0.67 to 1:4 (the total mass of the mixture is 100 parts) and adding them into the reaction kettle, heating the reaction kettle to a set temperature of 60-80 °C, and continuously stirring for 3-18 hours under nitrogen protection to complete the polymerization reaction;

[0023] S4: After the polymerization reaction is completed, stop heating and wait for the reaction system to cool to room temperature;

[0024] S5: Filter the reaction product to remove unreacted monomers and impurities, and adjust the pH value of the emulsion to neutral, thereby obtaining a copolymer emulsion with a vinyl acetate content of 40 - 80%.

[0025] Step three: The process of preparing the thickening adhesive solution includes:

[0026] S1: Weigh the thickener aqueous solution, EVA - type water - based adhesive, and polyacrylate - type water - based adhesive and add them to the feed tank;

[0027] S2: Use a high - speed disperser to disperse evenly, so that the two adhesives are evenly dispersed in the thickener aqueous solution, where the molecular chains of the adhesives and the thickener are entangled with each other to form a thickening adhesive solution.

[0028] Step four: The process of preparing the composite coating includes:

[0029] S1: Weigh the dispersant, wetting agent, and deionized water and add them to the feed tank, and use an electric high - speed disperser to disperse evenly for 15 - 20 min, so that the dispersant and wetting agent are evenly dispersed in the deionized water medium to obtain a premixed liquid;

[0030] S2: Add ceramic particles to the premixed liquid and disperse at high speed for 20 - 30 min, so that the ceramic particles are fully adsorbed on the surface by the dispersant to form a ceramic dispersion liquid with better uniformity;

[0031] S3: Add the thickening adhesive and cross - linker, and continue to disperse at high speed for 20 - 30 min to obtain a composite coating.

[0032] Preferably, the prepared composite coating is coated on one or both sides of the polyolefin - based film and dried with hot air; control the hot - air temperature to be 100°C - 120°C and the drying time to be 3 min - 4 min.

[0033] Therefore, the present invention has the following beneficial effects.

[0034] (1) By precisely controlling the raw material ratio, an ethylene - vinyl acetate copolymer - type water - based adhesive with a vinyl acetate content between 40% and 80% is prepared. This type of adhesive is rich in ester - based functional groups and exhibits excellent molecular chain flexibility. When it is mixed with a thickener rich in hydroxyl - functional groups and a polyacrylate adhesive, hydrogen - bond interactions and intermolecular forces are preferentially formed. This interaction promotes the entanglement of molecular chains and then forms a stable compatible state.

[0035] (2)When the ethylene-vinyl acetate copolymer-based aqueous adhesive, polyacrylate adhesive, and thickener are entangled with each other in the coating and, under the action of the crosslinking agent and high temperature, they can penetrate into the molecular chains of the PE or PP separator to form a three-dimensional network structure. This process significantly improves the adhesion between the coating and the surface of the PE or PP separator.

[0036] (3)Through the synergistic effect of ceramic particles and high heat-resistant polyacrylate adhesive, the heat resistance of the separator is significantly improved. This not only enhances the heat shrinkage resistance of the separator but also ensures its safety in use under high-temperature environments.

[0037] Therefore, during the use of the battery, the separator is not easily deformed, which helps prevent potential safety hazards in the battery. Description of the Drawings

[0038] Figure 1 It is a SEM image of the lithium-ion battery separator according to the embodiment of the present invention.

[0039] 1. Coating, 2. PP separator. Detailed Embodiments

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0041] Example 1

[0042] This example provides a method for preparing a lithium-ion battery separator, including the following steps:

[0043] According to the raw material formula of the composite coating, the ceramic particles, ethylene-vinyl acetate (EVA) copolymer-based aqueous adhesive, crosslinking agent, polyacrylate-based aqueous adhesive, thickener, dispersant, wetting agent, and water are mixed to prepare a composite coating, and the composite coating is coated on a polyolefin-based film and dried.

[0044] Step 1: Prepare an aqueous thickener solution

[0045] Weigh 98.00 g of deionized water and 2.00 g of thickener and add them to the feed tank. Use a high-speed disperser to disperse at a rotation speed of 600 rpm / min for 24 h. Ensure that the thickener is evenly dissolved in deionized water to obtain an aqueous thickener solution with a solid content of 2%.

[0046] Step 2: Prepare an EVA-based aqueous adhesive

[0047] S1: Add 100.00 g of deionized water and 4.00 g of polyoxyethylene alkyl ether into the reaction kettle. Stir for 0.5 h until the solution is homogeneous;

[0048] S2: Add 0.20 g of potassium persulfate and 0.20 g of sodium hydroxide into the reaction kettle. Stir for 1 h until the solution is homogeneous to form an initiator solution;

[0049] S3: Mix ethylene and vinyl acetate in a molar ratio of 1:1.5 (the mixed mass is 100 g) and add them into the reaction kettle. Heat the reaction kettle to the set temperature of 65 °C, and under nitrogen protection, continuously stir for 12 h for the polymerization reaction;

[0050] S4: When the polymerization reaction reaches the predetermined time, stop the reaction and cool the reaction system to room temperature;

[0051] S5: Filter the reaction product to remove unreacted monomers and impurities, and adjust the pH value of the emulsion to neutral to obtain an EVA copolymer emulsion with a VA content of 40%.

[0052] Step 3: Prepare a thickening adhesive solution

[0053] Weigh 50.00 g of an aqueous solution of a thickener with a solid content of 2%, 4.00 g of an EVA copolymer emulsion with a VA content of 40%, and 5.00 g of a polyacrylate-based waterborne adhesive, add them into the feed tank, and disperse evenly using a high-speed disperser at a rotation speed of 1500 rpm for 1.5 h. Make the two adhesives evenly dispersed in the aqueous solution of the thickener, where the molecular chains of the adhesive and the thickener are entangled with each other to form a thickening adhesive solution.

[0054] Step 4: Prepare a coating

[0055] S1: Weigh dispersant BYK 9151 (0.20 g), wetting agent (0.12 g), and deionized water (50.00 g) and add them into the feed tank, and perform high-speed dispersion using a high-speed disperser at a rotation speed of 1500 rpm for 15 min. Make the dispersant and the wetting agent evenly dispersed in the deionized water medium to obtain a premixed solution;

[0056] S2: Add boehmite particles (20.00 g) (particle size 0.5 μm) to the premixed solution and perform high-speed dispersion at a rotation speed of 1500 rpm for 30 min. Make the ceramic particles fully adsorbed on the surface by the dispersant to form a ceramic dispersion with a good degree of uniformity;

[0057] S3: Finally, add the thickening adhesive configured in Step 3 and 0.10 g of the crosslinking agent, and continue high-speed dispersion at a rotation speed of 1500 rpm / min for 30 min to obtain the coating.

[0058] Step 5: Coating film

[0059] Use a wire bar coater to coat the coating on the upper layer of the PP separator (18 μm), and use an oven to dry it with hot air (conditions: 120 °C, 5 min) to promote water evaporation and crosslinking reaction. After drying, the coating thickness is 4 μm, and finally a single-layer coated separator with a thickness of 18 + 4 μm is obtained.

[0060] Example 2

[0061] The difference from Example 1 is only that the dosage of ceramic particles in the composite coating is different, which is 30.00 g.

[0062] Example 3

[0063] The difference from Example 1 is only that the dosage of ceramic particles in the composite coating is different, which is 40.00 g.

[0064] Example 4

[0065] The difference from Example 1 is only that the dosage of ethylene-vinyl acetate copolymer type water-based adhesive in the composite coating is different, which is 1.00 g.

[0066] Example 5

[0067] The difference from Example 1 is only that the dosage of ethylene-vinyl acetate copolymer type water-based adhesive in the composite coating is different, which is 2.00 g.

[0068] Example 6

[0069] The difference from Example 1 is only that the dosage of ethylene-vinyl acetate copolymer type water-based adhesive in the composite coating is different, which is 3.00 g.

[0070] Example 7

[0071] The difference from Example 1 is only that the dosage of polyacrylate type water-based adhesive in the composite coating is different, which is 1.00 g.

[0072] Example 8

[0073] The difference from Example 1 is only that the dosage of polyacrylate type water-based adhesive in the composite coating is different, which is 8.00 g.

[0074] Example 9

[0075] The difference from Example 1 is only that: the vinyl acetate content of the ethylene-vinyl acetate copolymer type water-based adhesive is different, and it is an EVA copolymer emulsion with a VA content of 50%.

[0076] Example 10

[0077] The difference from Example 1 is only that: the vinyl acetate content of the ethylene-vinyl acetate copolymer type water-based adhesive is different, and it is an EVA copolymer emulsion with a VA content of 60%.

[0078] Example 11

[0079] The difference from Example 1 is only that: the vinyl acetate content of the ethylene-vinyl acetate copolymer type water-based adhesive is different, and it is an EVA copolymer emulsion with a VA content of 70%.

[0080] Example 12

[0081] The difference from Example 1 is only that: the vinyl acetate content of the ethylene-vinyl acetate copolymer type water-based adhesive is different, and it is an EVA copolymer emulsion with a VA content of 80%.

[0082] Comparative Example 1

[0083] An ordinary PP separator without coating.

[0084] Comparative Example 2

[0085] The difference from Example 1 is only that: the composite coating does not contain an ethylene-vinyl acetate copolymer type water-based adhesive.

[0086] Comparative Example 3

[0087] The difference from Example 1 is only that: the composite coating does not contain a polyacrylate adhesive.

[0088] The lithium battery separators prepared in the above examples and comparative examples were cut into A4 size, and their performances were tested. The results are shown in Table 1. The test methods are as follows:

[0089] (1) Average thickness: The thicknesses of different positions of the coated separator were measured using a micrometer, and their average value was calculated;

[0090] (2) Heat resistance test: The heat resistance of the separator was characterized by the thermal shrinkage rate, and the test was carried out according to the test method of thermal shrinkage rate in the national standard 《GB / T - 36363 - 2018》. The instrument used was a forced-air oven;

[0091] (3) Tensile strength test: The test was carried out according to the test method of tensile strength in the national standard 《GB / T - 36363 - 2018》;

[0092] (4)Ionic conductivity test: The assembly method of steel sheet / diaphragm / steel sheet is adopted, and the bulk resistance is tested by the electrochemical impedance spectroscopy (EIS) mode of the VMP 3 B-10 electrochemical workstation (Bio-Logic Science Instruments), where the amplitude of the perturbation voltage is 5 mV and the frequency is 10 mHz - 1 MHz; the calculation relationship between the bulk resistance and the ionic conductivity is: ionic conductivity = diaphragm thickness / (diaphragm resistance * contact area between the diaphragm and the electrode) * 10-2, where the unit of the diaphragm thickness is mm, the unit of the diaphragm resistance is Ω, and the unit of the contact area between the diaphragm and the electrode is ㎡;

[0093] (5)Peeling force test: The test is carried out according to the method in the national standard "GB / T 2792-2014 Adhesive Tape Peeling Strength", and the universal material testing machine is used as the instrument.

[0094] Table 1 Summary table of the performance test results of the battery diaphragms prepared in Examples 1-12 and Comparative Examples 1-3.

[0095] From the data in Table 1, it can be observed that compared with Comparative Example 1, that is, the uncoated PP diaphragm, the diaphragms prepared in Examples 1-3 and Example 8 of the present invention, due to the synergistic effect of ceramic particles and the highly heat-resistant polyacrylate binder, have significantly improved heat resistance. This indicates that the introduction of the coating enhances the heat shrinkage resistance of the diaphragm and ensures its use safety in high-temperature environments.

[0096] By comparing Example 1 with Examples 4-6, Examples 9-12 and Comparative Example 2, it can be clearly seen that the adhesion force of Examples 1, 9-12 is far beyond that of Comparative Example 2, which indicates that the stable compatible state significantly improves the bonding strength between the coating and the substrate. Further observing Examples 4-6, their mechanical properties (including heat shrinkage rate and tensile strength) are also better than those of Comparative Example 2, which is attributed to the abundance of ester group functional groups in the binder, endowing it with excellent molecular chain flexibility. These ester group functional groups form hydrogen bonds and intermolecular forces with the thickener containing hydroxyl group functional groups and the polyacrylate binder, promoting the mutual entanglement of molecular chains, thus forming a stable compatible state. This compatible state not only significantly enhances the adhesion force and mechanical properties of the coating, but also improves the overall stability. Relatively, Comparative Example 2 lacks sufficient ester group and hydroxyl group functional groups, and cannot effectively form hydrogen bonds and intermolecular forces, resulting in poor compatibility and correspondingly reduced performance.

[0097] By comparing Example 1 with Examples 7 and 8 and Comparative Example 3, it can be clearly seen that due to the polyacrylate binder, the ethylene-vinyl acetate copolymer-based waterborne binder and the thickener are entangled with each other in the coating, and under the action of the crosslinking agent and high temperature, they can penetrate into the molecular chains of the PE or PP separator to form a three-dimensional network structure. This significantly improves the adhesion between the coating and the surface of the PE or PP separator.

[0098] Comparative analysis with Examples 7 and 8: In Examples 7 and 8, due to the use of different contents of polyacrylate binder, the adhesion of the coating is inferior to that of Example 1. This shows that in Example 1, the content of polyacrylate binder can more effectively bind to the PE or PP separator.

[0099] The comparison with Comparative Example 3 shows that Comparative Example 3 did not use polyacrylate binder, resulting in significantly lower adhesion of its coating than that of Example 1. This further confirms the significant advantage of polyacrylate binder in enhancing the adhesion between the coating and the PE or PP separator.

Claims

1. A highly heat-resistant lithium-ion battery separator, characterized in that: The invention is composed of a polyolefin base film and a composite coating applied on one or both sides thereof; the composite coating comprises, by weight, 20-40 parts of ceramic particles, 1-4 parts of ethylene-vinyl acetate copolymer type water-based adhesive, 0.01-0.3 parts of a cross-linking agent, 1-8 parts of a polyacrylate type water-based adhesive, 0.1-3 parts of a thickener, 1-3% of the weight of the ceramic particles by a dispersant, 0.1-0.5 parts of a wetting agent and 70-100 parts of deionized water; The ethylene-vinyl acetate copolymer water-based adhesive is a copolymer emulsion of 40-80% vinyl acetate, prepared by polymerization reaction, and includes, by weight: 100-150 parts of deionized water, 2-10 parts of non-ionic emulsifier, 0.1-0.5 parts of initiator, 0.1-0.5 parts of stabilizer and 100 parts of ethylene and vinyl acetate mixture, wherein the molar ratio of ethylene to vinyl acetate is 1:0.67 to 1:4; The preparation method of the high heat-resistant lithium-ion battery separator comprises the following steps: according to the raw material formula of the composite coating, the ceramic particles, ethylene-vinyl acetate copolymer type water-based adhesive, crosslinking agent, polyacrylate type water-based adhesive, thickener, dispersant, wetting agent and water are mixed to prepare a composite coating, and the composite coating is coated on a polyolefin base film and dried.

2. A high heat-resistant lithium-ion battery separator according to claim 1, characterized in that: The ceramic particles are selected from one or more of aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide and barium oxide, with an average particle size of 0.5-0.8 μm and a coating thickness of 1.5-3 μm.

3. The high heat-resistant lithium-ion battery separator according to claim 1, characterized in that: The nonionic emulsifier is selected from one of polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene alkyl alcohol ethers, polyoxyethylene alkyl phenols, or a mixture in any proportion; And / or, the cross-linking agent is selected from tert-butyl peroxycarbonate-2-ethylhexyl ester, diisopropylbenzene peroxide, or a mixture in any proportion; And / or, the thickener is a carboxymethyl cellulose thickener; And / or, the dispersant is selected from one or more of triethylhexyl phosphoric acid, polyethylene glycol, polyvinyl alcohol, polyacrylate or cellulose derivatives; And / or, the wetting agent is a water-based wetting agent selected from one or more of polyether-modified silicones, sodium butylnaphthalene sulfonate and polyols.

4. The high heat-resistant lithium-ion battery separator according to claim 1, characterized in that: The polyolefin-based film is selected from at least one of a PP diaphragm and a PE diaphragm; And / or, the thickness of the polyolefin-based film is 6 μm-20 μm, and the thickness of the composite coating is 2 μm-6 μm.

5. The high heat-resistant lithium-ion battery separator according to claim 1, characterized in that: The preparation process of the composite coating comprises: Step S1: preparing a thickener aqueous solution; Step S2: preparing an ethylene-vinyl acetate copolymer type water-based adhesive; Step S3: preparing a thickening adhesive solution; Step S4: adding ceramic particles, thickening adhesive solution, crosslinking agent, dispersant, wetting agent and deionized water into a material tank, and dispersing at high speed for 20-30 minutes to obtain a composite coating.

6. A high heat-resistant lithium-ion battery separator according to claim 5, characterized in that: The step S2: the preparation process of the ethylene-vinyl acetate copolymer type water-based adhesive comprises: S1: Add 100-150 parts by mass of deionized water and 2-10 parts by mass of nonionic emulsifier into a reactor and stir until uniform; S2: adding 0.1-0.5 parts by mass of an initiator and 0.1-0.5 parts by mass of a stabilizer, stirring for 0.5-2 hours until the solution is uniform, to form an initiator solution; S3: Ethylene and vinyl acetate are mixed in a molar ratio of 1:0.67 to 1:4, and the total weight of the mixture is 100 parts, and the mixture is added into a reactor, and the reactor is heated to a set temperature of 60-80° C., and under nitrogen protection, stirring is continued for 3-18 hours to complete the polymerization reaction; S4: After the polymerization reaction is completed, heating is stopped and the reaction system is cooled to room temperature; S5: filtering the reaction product to remove unreacted monomers and impurities, and adjusting the pH value of the emulsion to neutral, thereby obtaining a copolymer emulsion with a vinyl acetate content of 40-80%.

7. A highly heat-resistant lithium-ion battery separator according to claim 5, Its characteristics are: The process of step S3: preparing the thickening adhesive solution comprises: S1: Weigh thickener aqueous solution, EVA type water-based adhesive, polyacrylate type water-based adhesive and add them into a material tank; S2: Use a high-speed disperser to disperse evenly, so that the two adhesives are evenly dispersed in the thickener aqueous solution, wherein the molecular chains of the adhesive and the thickener are entangled with each other to form a thickened adhesive solution.

8. The high heat-resistant lithium-ion battery separator according to claim 5, characterized in that: The process of step S4: configuring the composite coating comprises: S1: Weigh the dispersant, wetting agent and deionized water and add them to the material tank, use an electric high-speed disperser to disperse them evenly at high speed for 15-20 minutes, so that the dispersant and wetting agent are evenly dispersed in the deionized water medium to obtain a premixed solution; S2: adding ceramic particles to the premixed liquid and dispersing at high speed for 20-30 min, so that the ceramic particles are fully adsorbed on the surface by the dispersant to form a uniform ceramic dispersion; S3: Add thickening adhesive and cross-linking agent, and continue to disperse at high speed for 20-30 minutes to obtain a composite coating.

9. The high heat-resistant lithium-ion battery separator according to claim 1, characterized in that: The composite coating is coated on one side or both sides of the polyolefin base film and dried by hot air; the hot air temperature is controlled to be 100° C.-120° C. and the drying time is 3 min-4 min.

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