An aqueous adhesive and a lithium battery separator using the aqueous adhesive

Abstract

The present invention discloses a water-based adhesive and a lithium battery separator using the water-based adhesive, and relates to the technical field of adhesives. The present invention uses epoxy acrylate as a bonding material, and by adding polyimide, aluminum oxide powder, boron nitride-silicon polymer composite material, dispersant, thickener, wetting agent, and then using deionized water as solvent to prepare a coating slurry with good heat resistance. Boron nitride has excellent high temperature resistance, can work stably for a long time under high temperature environment, and boron nitride is pretreated with thioglycolic acid, and then cobalt acetate is added to further react to prepare the boron nitride with cobalt on the surface, and the load of cobalt improves the heat resistance of boron nitride, thereby improving the heat resistance of the coating slurry. Modified boron nitride is compounded with it using silicon polymer, and the hydroxyl group on the surface of silicon polymer reacts with the epoxy group on epoxy acrylate, improves the dispersibility of modified boron nitride in the adhesive, and further improves the heat resistance of the coating slurry.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and specifically to an aqueous adhesive and a lithium battery separator using the aqueous adhesive. Background Art

[0002] As a key technology for modern energy storage and power drive, lithium batteries are widely used in consumer electronics, electric vehicles, and energy storage systems. The performance and safety of lithium batteries largely depend on their internal structure and materials. As a key component inside the battery, the main function of the separator is to isolate the positive and negative electrode materials to prevent short circuits, thereby ensuring the normal operation of the battery. Therefore, in the production of lithium battery separators, the selection of adhesives is crucial for the performance of the separators.

[0003] The adhesive needs to have excellent thermal stability and bonding strength to ensure the stability and safety of the separator in a high-temperature environment. The aqueous adhesive needs to maintain good adhesion performance under high-temperature conditions so as not to melt or fall off, which may cause the separator material to melt, shrink, or lose the ability to penetrate the electrolyte, thereby affecting the safety of the battery.

[0004] To solve the above problems and improve the heat resistance of lithium battery separators, the present invention provides an aqueous adhesive and a lithium battery separator using the aqueous adhesive. Summary of the Invention

[0005] The purpose of the present invention is to provide an aqueous adhesive and a lithium battery separator using the aqueous adhesive to solve the problems raised in the prior art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] An aqueous adhesive, the aqueous adhesive is epoxy acrylate, and the preparation method of the epoxy acrylate is as follows: Take acrylic acid, tetrabutylammonium bromide, and p-methoxyphenol, stir evenly to obtain mixture A; Take bisphenol A type epoxy resin and tetrabutylammonium bromide, heat up to 100 °C, stir evenly, add pentaerythritol, carry out condensation reflux for 2 - 3 h, cool down to 80 - 85 °C, add mixture A, react for 3 - 5 h, and then cool to obtain epoxy acrylate.

[0008] A coating slurry, the coating slurry includes the following components by weight: 30 - 35 parts of polyimide, 450 - 460 parts of alumina powder, 20 - 25 parts of boron nitride-silicon polymer composite, 1000 - 1050 parts of deionized water, 20 - 22 parts of dispersant, 2 - 3 parts of thickener, 2.2 - 2.5 parts of wetting agent, and 55 - 60 parts of epoxy acrylate.

[0009] A preparation method of a coating slurry includes the following steps:

[0010] Step 1: Take modified boron nitride and deionized water, and disperse them by ultrasonic treatment to obtain a modified boron nitride solution; take a silicone polymer and deionized water, and disperse them by ultrasonic treatment to obtain a silicone polymer solution; add the silicone polymer solution to the modified boron nitride solution, react at 60 - 65 °C for 5 - 7 h, filter and dry to obtain a boron nitride - silicone polymer composite material;

[0011] Step 2: Take polyimide, alumina powder, and the boron nitride - silicone polymer composite material, add deionized water, a dispersant, a thickener, a wetting agent, and epoxy acrylate, and stir evenly to obtain an aqueous adhesive.

[0012] Preferably, the preparation method of the modified boron nitride is as follows: Take cobalt acetate and deionized water, stir evenly, add pretreated boron nitride, disperse by ultrasonic treatment for 40 - 60 min, then stir for 22 - 24 h, filter, wash, and dry to obtain modified boron nitride.

[0013] Preferably, the preparation method of the pretreated boron nitride is as follows: Take boron nitride and ethanol, disperse by ultrasonic treatment, add benzoin dimethyl ether, stir for 10 - 15 min, add mercaptoacetic acid, and stir for 10 - 20 min under the action of ultraviolet light, centrifuge, wash, and dry to obtain pretreated boron nitride.

[0014] Preferably, the preparation method of the silicone polymer is as follows: Take sodium hydroxide and deionized water, stir evenly, then add silicon dioxide, stir for 3 - 4 h, add sodium chloride, tetrahydrofuran, and hydrochloric acid, react for 20 - 40 min, filter and dry to obtain a silicone polymer.

[0015] Preferably, the dispersant is ammonium polyacrylate; the wetting agent is a silicone alcohol - type non - ionic surfactant; the thickener is sodium carboxymethyl cellulose.

[0016] A preparation method of a lithium - battery separator includes the following steps: Coating the coating slurry according to any one of claims 2 - 7 on both sides of a polyvinyl film, drying and winding to obtain a lithium - battery separator.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. The present invention uses epoxy acrylate as a bonding material, and by adding polyimide, alumina powder, boron nitride - silicone polymer composite material, a dispersant, a thickener, and a wetting agent, and then using deionized water as a solvent, a coating slurry with good heat resistance is prepared.

[0019] Boron nitride has excellent high-temperature resistance and can work stably in high-temperature environments for a long time. Boron nitride pretreated with mercaptoacetic acid is then added with cobalt acetate for further reaction to prepare boron nitride with cobalt on its surface. The loading of cobalt improves the heat resistance of boron nitride, thereby enhancing the heat resistance of the coating slurry.

[0020] 2. Use a silicone polymer to compound it with the modified boron nitride. The silicone polymer has abundant hydroxyl groups on its surface that can react with the epoxy groups on the epoxy acrylate, thereby improving the dispersibility of the modified boron nitride in the adhesive, solving the agglomeration problem of unmodified boron nitride, and further enhancing the heat resistance of the coating slurry. Detailed implementation manners

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] There are no special restrictions on the purchase manufacturers of all raw materials involved in the present invention. Exemplarily, they include:

[0023] Bisphenol A epoxy resin: Model: E-51; Alumina powder: Particle size is 1-2 μm; Polyimide powder: Can be purchased from Evonik Industries AG in Germany, Model: P84; The dispersant is ammonium polyacrylate: Can be purchased from Solpro Solewend in the Netherlands, Model: AN33; The wetting agent is a silicone alcohol non-ionic surfactant: Can be purchased from Dongguan Gaosijin Fine Chemical Co., Ltd., Model: GSK-588; Silicon dioxide: Particle size is 60-80 μm; COPNA resin, can be purchased from Wuhan Baohua Petrochemical New Materials Development Co., Ltd., Model: FJSZ.

[0024] Example 1: An aqueous adhesive and a lithium battery separator using the aqueous adhesive, including the following steps:

[0025] Step 1: Preparation of modified boron nitride:

[0026] Take 2 g of boron nitride and 100 mL of ethanol, ultrasonically disperse, add 0.1 g of benzoin dimethyl ether, stir for 12 min, add 5 g of mercaptoacetic acid, stir for 15 min under the action of ultraviolet light, centrifuge, wash, and dry to obtain pretreated boron nitride;

[0027] Take 8 g of cobalt acetate and 100 mL of deionized water, stir evenly, add 2 g of pretreated boron nitride, ultrasonically disperse for 50 min, then stir for 23 h, filter, wash, and dry to obtain modified boron nitride;

[0028] Step 2: Preparation of silicone polymer:

[0029] Take 0.1 g of sodium hydroxide and 70 mL of deionized water, stir evenly, then add 3.2 g of silicon dioxide, stir for 3.5 h, add 35 g of sodium chloride, 180 mL of tetrahydrofuran, and 60 mL of hydrochloric acid, react for 30 min, filter and dry to obtain the silicone polymer;

[0030] Step 3: Preparation of boron nitride-silicone polymer composite:

[0031] Take modified boron nitride and deionized water, ultrasonically disperse to obtain a modified boron nitride solution with a concentration of 0.2 mg / mL; take the silicone polymer and deionized water, ultrasonically disperse to obtain a silicone polymer solution with a concentration of 2 mg / mL; add 100 mL of the silicone polymer solution to 100 mL of the modified boron nitride solution, react at 62 °C for 6 h, filter and dry to obtain the boron nitride-silicone polymer composite;

[0032] Step 4: Preparation of epoxy acrylate:

[0033] Take 5 g of acrylic acid, 0.4 g of tetrabutylammonium bromide, and 0.03 g of p-hydroxyanisole, stir evenly to obtain mixture A; take 150 g of bisphenol A type epoxy resin E-51 and 0.45 g of tetrabutylammonium bromide, heat up to 100 °C, stir evenly, add 5.2 g of pentaerythritol, carry out condensation reflux for 2.5 h, cool down to 82 °C, add mixture A, react for 4 h, and cool to obtain epoxy acrylate;

[0034] Step 5: Preparation of coating slurry:

[0035] Take polyimide, alumina powder, and boron nitride-silicone polymer composite, add deionized water, dispersant, thickener, wetting agent, and epoxy acrylate, stir evenly to obtain the coating slurry;

[0036] The coating slurry comprises the following components by weight: 32 parts of polyimide, 455 parts of alumina powder, 22 parts of boron nitride-silicone polymer composite, 1030 parts of deionized water, 21 parts of dispersant, 2.5 parts of thickener, 2.4 parts of wetting agent, and 57 parts of epoxy acrylate;

[0037] Step 6: Preparation of lithium battery separator:

[0038] Coat the coating slurry on both sides of a lithium battery polyethylene film with a thickness of 9 μm, the thickness of the single-sided coating is the same, and the thickness of the single-sided coating is 3 μm, dry at 66 °C to obtain the lithium battery separator.

[0039] Example 2: An aqueous adhesive and a lithium battery separator using the aqueous adhesive, comprising the following steps:

[0040] Step 1: Preparation of modified boron nitride:

[0041] Take 2 g of boron nitride and 100 mL of ethanol, ultrasonically disperse, add 0.1 g of benzoin dimethyl ether, stir for 10 min, add 5 g of mercaptoacetic acid, stir for 10 min under the action of ultraviolet light, centrifuge, wash, and dry to obtain pretreated boron nitride;

[0042] Take 8 g of cobalt acetate and 100 mL of deionized water, stir evenly, add 2 g of pretreated boron nitride, ultrasonically disperse for 40 min, then stir for 22 h, filter, wash, and dry to obtain modified boron nitride;

[0043] Step 2: Preparation of silicone polymer:

[0044] Take 0.1 g of sodium hydroxide and 70 mL of deionized water, stir evenly, then add 3.2 g of silicon dioxide, stir for 3 h, add 35 g of sodium chloride, 180 mL of tetrahydrofuran, and 60 mL of hydrochloric acid, react for 20 min, filter, and dry to obtain silicone polymer;

[0045] Step 3: Preparation of boron nitride - silicone polymer composite:

[0046] Take modified boron nitride and deionized water, ultrasonically disperse to obtain a modified boron nitride solution with a concentration of 0.2 mg / mL; take silicone polymer and deionized water, ultrasonically disperse to obtain a silicone polymer solution with a concentration of 2 mg / mL; add 100 mL of silicone polymer solution to 100 mL of modified boron nitride solution, react at 60 °C for 5 h, filter, and dry to obtain boron nitride - silicone polymer composite;

[0047] Step 4: Preparation of epoxy acrylate:

[0048] Take 5 g of acrylic acid, 0.4 g of tetrabutylammonium bromide, and 0.03 g of p - hydroxyanisole, stir evenly to obtain mixture A; take 150 g of bisphenol A epoxy resin E - 51 and 0.45 g of tetrabutylammonium bromide, heat to 100 °C, stir evenly, add 5.2 g of pentaerythritol, reflux for 2 h, cool to 80 °C, add mixture A, react for 3 h, and cool to obtain epoxy acrylate;

[0049] Step 5: Preparation of coating slurry:

[0050] Take polyimide, alumina powder, and boron nitride - silicone polymer composite, add deionized water, dispersant, thickener, wetting agent, and epoxy acrylate, stir evenly to obtain coating slurry;

[0051] The coating slurry comprises the following components by weight: 30 parts of polyimide, 450 parts of alumina powder, 20 parts of boron nitride-silicon polymer composite, 1000 parts of deionized water, 20 parts of dispersant, 2 parts of thickener, 2.2 parts of wetting agent, and 55 parts of epoxy acrylate;

[0052] Step Six: Preparation of lithium battery separator:

[0053] The coating slurry is coated on both sides of a 9-μm-thick polyethylene film for lithium battery, with the same thickness of the single-sided coating, which is 3 μm. It is dried at 65 °C to obtain the lithium battery separator.

[0054] Example 3: An aqueous adhesive and a lithium battery separator using the aqueous adhesive, comprising the following steps:

[0055] Step One: Preparation of modified boron nitride:

[0056] Take 2 g of boron nitride and 100 mL of ethanol, ultrasonically disperse, add 0.1 g of benzoin dimethyl ether, stir for 15 min, add 5 g of mercaptoacetic acid, stir for 20 min under the action of ultraviolet light, centrifuge, wash, and dry to obtain pretreated boron nitride;

[0057] Take 8 g of cobalt acetate and 100 mL of deionized water, stir evenly, add 2 g of pretreated boron nitride, ultrasonically disperse for 60 min, then stir for 24 h, filter, wash, and dry to obtain modified boron nitride;

[0058] Step Two: Preparation of silicon polymer:

[0059] Take 0.1 g of sodium hydroxide and 70 mL of deionized water, stir evenly, then add 3.2 g of silicon dioxide, stir for 4 h, add 35 g of sodium chloride, 180 mL of tetrahydrofuran, and 60 mL of hydrochloric acid, react for 40 min, filter, and dry to obtain silicon polymer;

[0060] Step Three: Preparation of boron nitride-silicon polymer composite:

[0061] Take modified boron nitride and deionized water, ultrasonically disperse to obtain a modified boron nitride solution with a concentration of 0.2 mg / mL; take silicon polymer and deionized water, ultrasonically disperse to obtain a silicon polymer solution with a concentration of 2 mg / mL; add 100 mL of silicon polymer solution to 100 mL of modified boron nitride solution, react at 65 °C for 7 h, filter, and dry to obtain boron nitride-silicon polymer composite;

[0062] Step Four: Preparation of epoxy acrylate:

[0063] Take 5 g of acrylic acid, 0.4 g of tetrabutylammonium bromide, and 0.03 g of p-hydroxyanisole, stir evenly to obtain mixture A; take 150 g of bisphenol A epoxy resin E-51 and 0.45 g of tetrabutylammonium bromide, heat up to 100 °C, stir evenly, add 5.2 g of pentaerythritol, carry out condensation reflux for 3 h, cool down to 85 °C, add mixture A, react for 5 h, and cool to obtain epoxy acrylate;

[0064] Step Five: Preparation of Coating Slurry:

[0065] Take polyimide, alumina powder, boron nitride-silicon polymer composite, add deionized water, dispersant, thickener, wetting agent, and epoxy acrylate, stir evenly to obtain coating slurry;

[0066] The coating slurry comprises the following components by weight: 35 parts of polyimide, 460 parts of alumina powder, 25 parts of boron nitride-silicon polymer composite, 1050 parts of deionized water, 22 parts of dispersant, 3 parts of thickener, 2.5 parts of wetting agent, and 60 parts of epoxy acrylate;

[0067] Step Six: Preparation of Lithium Battery Separator:

[0068] Coat the coating slurry on both sides of a lithium battery polyethylene film with a thickness of 9 μm, the single-sided coating thickness is the same, the single-sided coating thickness is 3 μm, and dry at 70 °C to obtain a lithium battery separator.

[0069] Comparative Example 1: Do not compound the silicon polymer with the modified boron nitride, and the rest is the same as in Example 1:

[0070] An aqueous adhesive and a lithium battery separator using the aqueous adhesive, comprising the following steps:

[0071] Step One: Preparation of Modified Boron Nitride:

[0072] Take 2 g of boron nitride and 100 mL of ethanol, carry out ultrasonic dispersion, add 0.1 g of benzoin dimethyl ether, stir for 12 min, add 5 g of mercaptoacetic acid, stir for 15 min under the action of ultraviolet light, centrifuge, wash, and dry to obtain pretreated boron nitride;

[0073] Take 8 g of cobalt acetate and 100 mL of deionized water, stir evenly, add 2 g of pretreated boron nitride, carry out ultrasonic dispersion for 50 min, then stir for 23 h, filter, wash, and dry to obtain modified boron nitride;

[0074] Step Two: Preparation of Silicon Polymer:

[0075] Take 0.1 g of sodium hydroxide and 70 mL of deionized water, stir evenly, then add 3.2 g of silicon dioxide, stir for 3.5 h, add 35 g of sodium chloride, 180 mL of tetrahydrofuran, and 60 mL of hydrochloric acid, react for 30 min, filter and dry to obtain a silicone polymer;

[0076] Step 3: Preparation of epoxy acrylate:

[0077] Take 5 g of acrylic acid, 0.4 g of tetrabutylammonium bromide, and 0.03 g of p - hydroxyanisole, stir evenly to obtain mixture A; take 150 g of bisphenol A epoxy resin E - 51 and 0.45 g of tetrabutylammonium bromide, heat to 100 °C, stir evenly, add 5.2 g of pentaerythritol, carry out reflux condensation for 2.5 h, cool to 82 °C, add mixture A, react for 4 h, and cool to obtain epoxy acrylate;

[0078] Step 4: Preparation of coating slurry:

[0079] Take polyimide, alumina powder, modified boron nitride, and silicone polymer, add deionized water, dispersant, thickener, wetting agent, and epoxy acrylate, and stir evenly to obtain a coating slurry;

[0080] The coating slurry comprises the following components by weight: 32 parts of polyimide, 455 parts of alumina powder, 12 parts of modified boron nitride, 10 parts of silicone polymer, 1030 parts of deionized water, 21 parts of dispersant, 2.5 parts of thickener, 2.4 parts of wetting agent, and 57 parts of epoxy acrylate;

[0081] Step 5: Preparation of lithium - battery separator:

[0082] Coat the coating slurry on both sides of a 9 - μm - thick polyethylene film for lithium - battery, with the same thickness of the single - side coating, and the thickness of the single - side coating is 3 μm, and dry at 66 °C to obtain a lithium - battery separator.

[0083] Comparative Example 2: Do not load cobalt on the surface of boron nitride, and the rest is the same as in Example 1:

[0084] An aqueous adhesive and a lithium - battery separator using the aqueous adhesive, comprising the following steps:

[0085] Step 1: Preparation of silicone polymer:

[0086] Take 0.1 g of sodium hydroxide and 70 mL of deionized water, stir evenly, then add 3.2 g of silicon dioxide, stir for 3.5 h, add 35 g of sodium chloride, 180 mL of tetrahydrofuran, and 60 mL of hydrochloric acid, react for 30 min, filter and dry to obtain a silicone polymer;

[0087] Step 2: Preparation of boron nitride - silicone polymer composite:

[0088] Take boron nitride and deionized water, and ultrasonically disperse them to obtain a boron nitride solution with a concentration of 0.2 mg / mL; take a silicone polymer and deionized water, and ultrasonically disperse them to obtain a silicone polymer solution with a concentration of 2 mg / mL; add 100 mL of the silicone polymer solution to 100 mL of the boron nitride solution, react at 62 °C for 6 h, filter and dry to obtain a boron nitride-silicone polymer composite material;

[0089] Step 3: Preparation of epoxy acrylate:

[0090] Take 5 g of acrylic acid, 0.4 g of tetrabutylammonium bromide, and 0.03 g of p-methoxyphenol, stir evenly to obtain mixture A; take 150 g of bisphenol A type epoxy resin E-51 and 0.45 g of tetrabutylammonium bromide, heat up to 100 °C, stir evenly, add 5.2 g of pentaerythritol, carry out condensation reflux for 2.5 h, cool down to 82 °C, add mixture A, and react for 4 h, then cool to obtain epoxy acrylate;

[0091] Step 4: Preparation of coating slurry:

[0092] Take polyimide, alumina powder, and boron nitride-silicone polymer composite material, add deionized water, dispersant, thickener, wetting agent, and epoxy acrylate, and stir evenly to obtain a coating slurry;

[0093] The coating slurry comprises the following components by weight: 32 parts of polyimide, 455 parts of alumina powder, 22 parts of boron nitride-silicone polymer composite material, 1030 parts of deionized water, 21 parts of dispersant, 2.5 parts of thickener, 2.4 parts of wetting agent, and 57 parts of epoxy acrylate;

[0094] Step 5: Preparation of lithium battery separator:

[0095] Coat the coating slurry on both sides of a lithium battery polyethylene film with a thickness of 9 μm, the thickness of the single-sided coating is the same, and the thickness of the single-sided coating is 3 μm, and dry at 66 °C to obtain a lithium battery separator.

[0096] Comparative Example 3: Use COPNA resin instead of epoxy acrylate, and the rest is the same as in Example 1:

[0097] An aqueous adhesive and a lithium battery separator using the aqueous adhesive, comprising the following steps:

[0098] Step 1: Preparation of modified boron nitride:

[0099] Take 2 g of boron nitride and 100 mL of ethanol, ultrasonically disperse, add 0.1 g of benzoin dimethyl ether, stir for 12 min, add 5 g of mercaptoacetic acid, stir for 15 min under the action of ultraviolet light, centrifuge, wash, and dry to obtain pretreated boron nitride;

[0100] Take 8 g of cobalt acetate and 100 mL of deionized water, stir evenly, add 2 g of pretreated boron nitride, ultrasonically disperse for 50 min, then stir for 23 h, filter, wash, and dry to obtain modified boron nitride;

[0101] Step 2: Preparation of silicone polymer:

[0102] Take 0.1 g of sodium hydroxide and 70 mL of deionized water, stir evenly, then add 3.2 g of silicon dioxide, stir for 3.5 h, add 35 g of sodium chloride, 180 mL of tetrahydrofuran, and 60 mL of hydrochloric acid, react for 30 min, filter and dry to obtain silicone polymer;

[0103] Step 3: Preparation of boron nitride-silicone polymer composite:

[0104] Take modified boron nitride and deionized water, ultrasonically disperse to obtain a modified boron nitride solution with a concentration of 0.2 mg / mL; take silicone polymer and deionized water, ultrasonically disperse to obtain a silicone polymer solution with a concentration of 2 mg / mL; add 100 mL of silicone polymer solution to 100 mL of modified boron nitride solution, react at 62 °C for 6 h, filter and dry to obtain boron nitride-silicone polymer composite;

[0105] Step 4: Preparation of coating slurry:

[0106] Take polyimide, alumina powder, and boron nitride-silicone polymer composite, add deionized water, dispersant, thickener, wetting agent, and COPNA resin, stir evenly to obtain coating slurry;

[0107] The coating slurry comprises the following components by weight: 32 parts of polyimide, 455 parts of alumina powder, 22 parts of boron nitride-silicone polymer composite, 1030 parts of deionized water, 21 parts of dispersant, 2.5 parts of thickener, 2.4 parts of wetting agent, and 57 parts of COPNA resin;

[0108] Step 5: Preparation of lithium battery separator:

[0109] Coat the coating slurry on both sides of a lithium battery polyethylene film with a thickness of 9 μm, the thickness of the single-sided coating is the same, the thickness of the single-sided coating is 3 μm, and dry at 66 °C to obtain a lithium battery separator.

[0110] Experiment:

[0111] Take the lithium battery separators prepared in Examples 1 to 3 and Comparative Examples 1 to 3 for performance testing, and test the needle punching strength and thermal shrinkage of the lithium battery separators with reference to GB / T36363-2018. The obtained data are as follows:

[0112]

[0113] Conclusion: It can be seen from the comparison of the data in the table that in Comparative Example 1, the silicone polymer is not compounded with the modified boron nitride, and the dispersion of boron nitride in the adhesive is poor, and it is easy to agglomerate. The puncture strength of the lithium battery separator decreases, the mechanical properties decrease, the heat resistance becomes poor, and the thermal shrinkage becomes large. At this time, the puncture strength is only 552 N, the heat resistance is poor, the longitudinal thermal shrinkage of the lithium battery separator is 1.8%, and the transverse thermal shrinkage is 1.5%. In Comparative Example 2, cobalt is not loaded on the surface of boron nitride, the heat resistance of boron nitride becomes poor, the heat resistance of the coating slurry decreases, and the lithium battery separator is also affected. In Comparative Example 3, COPNA resin is used instead of epoxy acrylate. At this time, the dispersion of the boron nitride-silicone polymer composite material in the adhesive is not good, and it is easy to agglomerate. The puncture strength of the lithium battery separator decreases, the mechanical properties decrease, the heat resistance becomes poor, and the thermal shrinkage becomes large. At this time, the puncture strength of the lithium battery separator is only 555 N, the heat resistance is poor, the longitudinal thermal shrinkage of the lithium battery separator is 1.6%, and the transverse thermal shrinkage is 1.3%. In Examples 1-3 of the present invention, epoxy acrylate is used as the bonding material, and a coating slurry with good heat resistance is prepared by adding polyimide, alumina powder, boron nitride-silicone polymer composite material, dispersant, thickener, and wetting agent, and then using deionized water as the solvent. Boron nitride has excellent high-temperature resistance and can work stably in a high-temperature environment for a long time. Boron nitride is pretreated with mercaptoacetic acid, and then cobalt acetate is added for further reaction to obtain boron nitride with cobalt on its surface. The loading of cobalt improves the heat resistance of boron nitride, thereby improving the heat resistance of the coating slurry. The modified boron nitride is compounded with the silicone polymer. The surface of the silicone polymer has rich hydroxyl groups that can react with the epoxy groups on the epoxy acrylate, thereby improving the dispersion of the modified boron nitride in the adhesive, solving the agglomeration problem of unmodified boron nitride, and further improving the heat resistance of the coating slurry. The coating slurry prepared according to the scheme provided by the present invention has good heat resistance, and the lithium battery separator prepared therefrom has good mechanical properties and excellent heat resistance. The puncture strength of the lithium battery separator can reach 570 N, the heat resistance is good, the longitudinal thermal shrinkage can reach 0.9%, and the transverse thermal shrinkage can reach 0.7%.

[0114] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A method for preparing a lithium battery separator, characterized in that: The following steps are involved: Applying the coating slurry to both sides of the polyethylene base film, drying and rolling up to obtain a lithium battery separator; The coating slurry comprises the following components, by weight: 30-35 parts of polyimide, 450-460 parts of aluminum oxide powder, 20-25 parts of boron nitride-silicon polymer composite material, 1000-1050 parts of deionized water, 20-22 parts of dispersant, 2-3 parts of thickener, 2.2-2.5 parts of wetting agent, and 55-60 parts of epoxy acrylate; The preparation method of the epoxy acrylate is as follows: take acrylic acid, tetrabutylammonium bromide and p-hydroxyanisole, stir evenly to obtain a mixture A; take bisphenol A epoxy resin and tetrabutylammonium bromide, heat to 100°C, stir evenly, add pentaerythritol, condense and reflux for 2-3h, cool to 80-85°C, add the mixture A, react for 3-5h, cool, and obtain epoxy acrylate; the epoxy acrylate is a water-based adhesive; The method for preparing the coating slurry comprises the following steps: Step 1: taking modified boron nitride and deionized water, and ultrasonically dispersing them to obtain a modified boron nitride solution; taking silicon polymer and deionized water, and ultrasonically dispersing them to obtain a silicon polymer solution; adding the silicon polymer solution to the modified boron nitride solution, reacting at 60-65° C. for 5-7 hours, filtering, and drying to obtain a boron nitride-silicon polymer composite material; Step 2: Take polyimide, aluminum oxide powder, boron nitride-silicon polymer composite material, add deionized water, dispersant, thickener, wetting agent, epoxy acrylate, stir evenly to obtain a water-based adhesive; The preparation method of the modified boron nitride is as follows: cobalt acetate and deionized water are taken, stirred evenly, the pretreated boron nitride is added, ultrasonically dispersed for 40-60 minutes, then stirred for 22-24 hours, filtered, washed, and dried to obtain the modified boron nitride; The preparation method of the pretreated boron nitride is as follows: taking boron nitride and ethanol, ultrasonically dispersing, adding benzoin dimethyl ether, stirring for 10-15 minutes, adding thioglycolic acid, stirring for 10-20 minutes under the action of ultraviolet light, centrifuging, washing, and drying to obtain the pretreated boron nitride.

2. The method for preparing a lithium battery separator according to claim 1, characterized in that: The preparation method of the silicon polymer is: take sodium hydroxide and deionized water, stir evenly, then add silicon dioxide, stir for 3-4 hours, add sodium chloride, tetrahydrofuran and hydrochloric acid, react for 20-40 minutes, filter and dry to obtain the silicon polymer.

3. The method for preparing a lithium battery separator according to claim 1, characterized in that: The dispersant is ammonium polyacrylate; the wetting agent is a silanol nonionic surfactant; and the thickener is sodium hydroxymethyl cellulose.

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