Composite diaphragm with double-layer functional coating and preparation method of composite diaphragm

Abstract

The invention relates to the technical field of battery diaphragms, and provides a composite diaphragm with double functional coatings and a preparation method thereof.The composite diaphragm with the double functional coatings sequentially comprises a base diaphragm, a bottom layer and a surface layer from bottom to top, the bottom layer is a ceramic coating, and the surface layer is a rubber coating. According to the technical scheme, the problems of insufficient high-temperature dimensional stability, thermal safety and electrode interface adhesion of the composite diaphragm in related technologies are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery separator, in particular, relates to a composite separator with double-layer functional coating and a preparation method thereof. BACKGROUND

[0002] Lithium ion battery separator is the core component inside the battery. It avoids the risk of short circuit caused by direct contact of the two poles by physical isolation of the positive and negative poles; at the same time, the specific size of the aperture can ensure the efficient shuttle of lithium ions, providing key protection for the stable process of battery charging and discharging.

[0003] The existing single-layer coating separator technology has obvious shortcomings. Although the single-layer ceramic coating separator improves the high temperature resistance and electrolyte wettability of the separator, the ceramic layer is hard and brittle, and has poor adhesion with the electrode, and dust is easily produced during coating process; the single-layer polymer coating such as PVDF separator provides certain adhesion, but the melting point of PVDF is also not high, which will melt and fail at high temperature, and cannot provide long-term thermal shutdown protection.

[0004] The common double-sided coating separator also fails to break through the bottleneck. One kind of common double-sided coating separator is double-sided ceramic separator, and the other kind is one side ceramic and one side PVDF. The adhesion problem of double-sided ceramic still exists; the combination of ceramic and PVDF has short board in maintaining performance at high temperature.

[0005] The existing technology cannot perfectly solve the three key problems of high temperature dimensional stability, thermal safety and electrode interface adhesion of the separator, therefore, it is urgent to develop a new type of composite separator structure. SUMMARY

[0006] The present application provides a composite separator with double-layer functional coating and a preparation method thereof, which solves the problems of insufficient high temperature dimensional stability, thermal safety and electrode interface adhesion of the composite separator in the related art.

[0007] The technical scheme of the present application is as follows: the present application provides a composite separator with double-layer functional coating, which comprises a base film, a bottom layer and a surface layer from bottom to top, the bottom layer is a ceramic coating, and the surface layer is a rubber coating.

[0008] As a further technical scheme, the thickness of the ceramic coating is 1.2-1.8 microns, and the thickness of the rubber coating is 1-2.3 microns.

[0009] As a further technical scheme, the base film is a porous polyolefin base film, the base film comprises one or both of polyethylene film and polypropylene film, preferably polypropylene film, and the thickness of the base film is 5-16 microns.

[0010] As a further technical solution, the solid component of the ceramic coating includes the following components by weight: 20-30 parts of inorganic ceramic particles, 0.05-0.1 parts of a cosolvent, 8-15 parts of meta-aramid, and 1-3 parts of a binder.

[0011] As a further technical solution, the inorganic ceramic particles include one or more of alumina, silica, boehmite, zirconia, boron nitride, and hollow ceramic microbeads, and preferably are alumina, and the average particle size of the inorganic ceramic particles is 0.3-1 μm.

[0012] As a further technical solution, the inorganic ceramic particles are composite inorganic ceramic particles, and the preparation method of the composite inorganic ceramic particles includes the following steps: dispersing 4-hydroxybenzoic acid allyl ester in anhydrous ethanol, adding the inorganic ceramic particles, mixing, and then drying to obtain the composite inorganic ceramic particles.

[0013] As a further technical solution, the mass ratio of the 4-hydroxybenzoic acid allyl ester to the inorganic ceramic particles is 3-4:50.

[0014] As a further technical solution, the mass ratio of the anhydrous ethanol to the inorganic ceramic particles is 5:1.

[0015] As a further technical solution, the mixing time is 4 h.

[0016] As a further technical solution, the cosolvent includes one or more of lithium chloride, calcium chloride, BYK-110, and BYK-180, and preferably is BYK-110.

[0017] As a further technical solution, the binder includes one or more of polyvinylidene fluoride, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, styrene-butadiene rubber, and polyacrylonitrile, and preferably is polyvinylidene fluoride.

[0018] As a further technical solution, the solid component of the rubber coating includes the following components by weight: 1.5-4.3 parts of elastomer rubber, 2-7 parts of thermoplastic polyurethane, 1.2-2.2 parts of a compatibilizer, and 7-12 parts of a pore-forming material.

[0019] In the present application, the rubber coating contains elastomer rubber, polyurethane, and a compatibilizer, and the ternary synergist can improve the long-term interface stability of the separator. The elastomer rubber improves the adhesion between the separator and the pole piece, the thermoplastic polyurethane can increase the viscosity of the slurry and enhance the toughness of the separator, and the addition of the compatibilizer can improve the interfacial bonding force between the rubber and the polyurethane, making the surface layer slurry more uniform at the microscopic level. At the same time, the thermoplastic polyurethane and the compatibilizer can synergistically reduce the air permeability of the separator, so that the composite separator has a lower air permeability and a higher adhesion.

[0020] As a further technical solution, the elastomer rubber comprises one or more of hydrogenated nitrile rubber, acrylate rubber, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, fluororubber, preferably hydrogenated nitrile rubber.

[0021] As a further technical solution, the compatibilizer is a maleic anhydride grafted polymer, preferably a maleic anhydride grafted hydrogenated styrene-ethylene-butylene-styrene polymer.

[0022] As a further technical solution, the pore-forming material comprises one or more of sodium chloride, dimethyl carbonate, polyacrylonitrile, polyimide, polyacrylic acid, sodium lignosulfonate, preferably dimethyl carbonate.

[0023] The application also provides a preparation method of a composite separator with a double-layer functional coating. S1, mix the inorganic ceramic particles, the cosolvent and the organic solvent to obtain a ceramic dispersion liquid, dilute the meta-aramid in an organic solvent to obtain a dilution liquid, add the dilution liquid to the ceramic dispersion liquid, stir to obtain a mixed liquid, mix the binder in an organic solvent to obtain a bonding solution, and add the bonding solution to the mixed liquid, and after secondary stirring and sanding, obtain a ceramic coating slurry; S2, add the elastomer rubber to an organic solution, stir to obtain a rubber solution, add the thermoplastic polyurethane to an organic solution, stir to obtain a polyurethane solution, add the compatibilizer to an organic solution, stir to obtain a compatibilization solution, mix the rubber solution, the polyurethane solution and the compatibilization solution, add organic solvent, and then add the pore-forming material, and after secondary mixing, obtain a rubber coating slurry; S3, coat the ceramic coating slurry on the base film to obtain a ceramic coating separator precursor, extract, and dry to obtain a separator with a ceramic coating as the bottom layer; S4, coat the rubber coating slurry on the surface of the ceramic coating, extract, and dry to obtain the composite separator with a double-layer functional coating.

[0024] As a further technical solution, the organic solvent comprises one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, methanol, ethanol, preferably N-methylpyrrolidone.

[0025] As a further technical solution, in step S1, the mass ratio of the inorganic ceramic particles, the organic solvent and the cosolvent in the ceramic dispersion liquid is (40-50):(50-60):(0.05-1), the rotation speed of the mixing is 300-500 r / min, and the mixing time is 90-120 min.

[0026] As a further technical solution, in step S1, the mass ratio of the meta-aramid and the organic solvent in the diluent is (8-9):(26-37).

[0027] As a further technical solution, in step S1, the mass ratio of the binder and the organic solvent in the bonding solution is 1:4.

[0028] As a further technical solution, in step S1, during the preparation of the mixed solution, the stirring speed is 300-700 r / min, and the stirring time is 30-60 min.

[0029] As a further technical solution, in step S1, the secondary stirring speed is 300-700 r / min, and the stirring time is 20-30 min.

[0030] As a further technical solution, in step S1, the sanding speed is 400-600 r / min, and the sanding time is 10-30 min.

[0031] As a further technical solution, in step S1, in the ceramic coating slurry, the mass ratio of the ceramic dispersion liquid, the diluent, and the bonding liquid is (40-60):(30-66):(10-11).

[0032] As a further technical solution, in step S2, in the rubber solution, the mass ratio of the elastomeric rubber and the organic solvent is (5-18):(82-95).

[0033] As a further technical solution, in step S2, during the preparation of the rubber solution, the stirring speed is 400-600 r / min, and the time is 240-480 min.

[0034] As a further technical solution, in step S2, in the polyurethane solution, the mass ratio of the thermoplastic polyurethane and the organic solvent is (5-20):(80-95).

[0035] As a further technical solution, in step S2, during the preparation of the polyurethane solution, the stirring speed is 400-600 r / min, and the time is 120-180 min.

[0036] As a further technical solution, in step S2, the mass ratio of the compatibilizer to the organic solvent in the compatibilizing solution is (5-12):(88-95).

[0037] As a further technical solution, in step S2, during the preparation of the compatibilizing solution, the stirring speed is 400-600 r / min, and the stirring time is 240-480 min.

[0038] As a further technical solution, in step S2, the mixing speed of the rubber solution, the polyurethane solution, the compatibilizing solution, and the organic solution is 200-500 r / min, and the mixing time is 20-30 min.

[0039] As a further technical solution, in step S2, the secondary mixing speed is 300-500 r / min, and the secondary mixing time is 20-30 min.

[0040] As a further technical solution, in step S2, the mass ratio of the rubber solution, the polyurethane solution, the compatibilizing solution, the additional organic solution, and the pore-forming material is (10-28):(13-43):(12-21):(1-58):(7-12).

[0041] As a further technical solution, in steps S3 and S4, the extraction liquid for extraction includes N-methyl pyrrolidone and / or water.

[0042] As a further technical solution, in steps S3 and S4, the extraction includes the following steps: sequentially using a first extraction liquid, a second extraction liquid, a third extraction liquid, and a fourth extraction liquid for extraction.

[0043] As a further technical solution, in steps S3 and S4, the first extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 65%-80%, the second extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 40%-60%, the third extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 20%-40%, and the fourth extraction liquid is water.

[0044] As a further technical solution, in steps S3 and S4, the total extraction time is 2-5 min, and the time for each of the four extractions is independently 0.5-1.5 min.

[0045] As a further technical solution, in steps S3 and S4, the drying temperature is 35-60℃.

[0046] The working principle and beneficial effects of the present application are as follows: 1. In this invention, the composite coating membrane rich in ceramics and rubber has a clever "sandwich" structure that integrates the characteristics of temperature resistance and high adhesion that are difficult to achieve in a single material, thus achieving a synergistic effect of 1+1>2.

[0047] 2. In this invention, the bottom ceramic coating of the composite separator has good temperature resistance and can effectively inhibit the melting and shrinkage of the base film at high temperatures. Even if the base film shrinks or even melts, the ceramic coating can still maintain the integrity of the separator and prevent the positive and negative large area contact. At the same time, the excellent adhesion of the surface rubber coating makes the separator and the electrode almost a whole, which can effectively prevent the coating from falling off, improve the cycle life of the lithium-ion battery, extend the service life of the lithium-ion battery, and give the separator a wider electrochemical stability window. Attached Figure Description

[0048] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0049] Figure 1 This is a scanning electron microscope image of the composite membrane prepared in Example 3 of the present invention; Figure 2 This is a scanning electron microscope image of the composite membrane prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0050] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0051] In the following examples and comparative examples: Polypropylene film: 9μm thick; Alumina: average particle size is 0.5 μm; Polyvinylidene fluoride: Model number LBG; Hydrogenated nitrile butadiene rubber: purchased from Zannan Technology Co., Ltd., 99% saturation; Maleic anhydride-grafted hydrogenated styrene-ethylene-butene-styrene polymer: model number FG1901G; Thermoplastic polyurethane: purchased from Dongguan Ruiqian New Materials Co., Ltd., molecular weight 300,000; Ceramic layer thickness: 1.5μm; Rubber coating thickness: 2μm.

[0052] Example 1 A method for preparing a composite diaphragm with a dual-layer functional coating includes the following steps: S1, mix alumina, BYK-110 and N-methyl pyrrolidone (the mass ratio of alumina, N-methyl pyrrolidone and BYK-110 is 45:55:0.05), the stirring speed is 400r / min, the stirring time is 90min, the ceramic dispersion liquid is obtained, the meta-aramid is added into N-methyl pyrrolidone for dilution (the mass ratio of meta-aramid and N-methyl pyrrolidone is 9:26), the dilution liquid is obtained, the dilution liquid is added into the ceramic dispersion liquid, and after fully mixing at a speed of 450r / min for 30min, a mixed liquid is obtained, polyvinylidene fluoride is added into N-methyl pyrrolidone (the mass ratio of polyvinylidene fluoride and N-methyl pyrrolidone is 1:4), and after stirring at a speed of 400r / min for 120min, a bonding solution is obtained, the bonding solution is added into the mixed liquid, stirring is carried out at a speed of 350r / min for 30min, sand grinding is carried out at a speed of 600r / min for 20min, and a ceramic coating slurry is obtained; wherein the mass ratio of the ceramic dispersion liquid, the dilution liquid and the bonding liquid is 55:35:10; S2, hydrogenated butyl rubber is added into N-methyl pyrrolidone (the mass ratio of hydrogenated butyl rubber and N-methyl pyrrolidone is 15:85), stirring is carried out at a speed of 500r / min for 480min, and after stirring, a rubber solution is obtained, thermoplastic polyurethane is added into N-methyl pyrrolidone (the mass ratio of thermoplastic polyurethane and N-methyl pyrrolidone is 16:84), stirring is carried out at a speed of 400r / min for 120min, and after stirring, a polyurethane solution is obtained, maleic anhydride grafted hydrogenated styrene-ethylene-butylene-styrene polymer is added into N-methyl pyrrolidone (the mass ratio of maleic anhydride grafted hydrogenated styrene-ethylene-butylene-styrene polymer and N-methyl pyrrolidone is 1:9), stirring is carried out at a speed of 400r / min for 480min, and after stirring, a compatibilization solution is obtained, the rubber solution, the polyurethane solution and the compatibilization solution are mixed, N-methyl pyrrolidone is added, stirring is carried out at a speed of 400r / min for 30min, dimethyl carbonate is added, and after secondary mixing, a rubber coating slurry is obtained; wherein the mass ratio of the rubber solution, the polyurethane solution, the compatibilization solution, the added N-methyl pyrrolidone and the dimethyl carbonate is 25:43:21:4:7; S3, the ceramic coating slurry is coated on a base film to obtain a ceramic coating separator precursor, and extraction is carried out in sequence using a first extraction liquid, a second extraction liquid, a third extraction liquid and a fourth extraction liquid, wherein the first extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 80%, the extraction time is 0.5min, the second extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 50%, the extraction time is 0.5min, the third extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 30%, the extraction time is 0.5min, the fourth extraction liquid is water, the extraction time is 0.5min, and 45°C drying is carried out to obtain a separator with a ceramic coating as a bottom layer. S4, the rubber coating slurry is applied on the surface of the ceramic coating, and extraction is sequentially performed using a first extraction liquid, a second extraction liquid, a third extraction liquid and a fourth extraction liquid, wherein the first extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 80%, the extraction time is 0.5 min, the second extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 50%, the extraction time is 0.5 min, the third extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 30%, the extraction time is 0.5 min, the fourth extraction liquid is water, the extraction time is 0.5 min, and the temperature is 45°C, and the obtained composite diaphragm has a double-layer functional coating.

[0053] Example 2 A method for preparing a composite diaphragm with a double-layer functional coating, comprising the following steps: S1, mixing alumina, BYK-110 and N-methyl pyrrolidone (the mass ratio of alumina, N-methyl pyrrolidone and BYK-110 is 45:55:0.05), the stirring speed is 400 r / min, and the stirring time is 90 min, to obtain a ceramic dispersion liquid, adding meta-aramid into N-methyl pyrrolidone for dilution (the mass ratio of meta-aramid and N-methyl pyrrolidone is 9:26) to obtain a dilution liquid, adding the dilution liquid into the ceramic dispersion liquid, mixing at a speed of 450 r / min for 30 min, adding polyvinylidene fluoride into N-methyl pyrrolidone (the mass ratio of polyvinylidene fluoride and N-methyl pyrrolidone is 1:4), stirring at a speed of 400 r / min for 120 min to obtain a bonding solution, adding the bonding solution into the mixed liquid, stirring at a speed of 350 r / min for 30 min, and then sanding at a speed of 600 r / min for 20 min to obtain a ceramic coating slurry; wherein the mass ratio of the ceramic dispersion liquid, the dilution liquid and the bonding solution is 45:45:10; S2, hydrogenated butyl rubber is added into N-methyl pyrrolidone (the mass ratio of hydrogenated butyl rubber and N-methyl pyrrolidone is 15:85), stirring at a speed of 500 r / min for 480 min, after stirring, a rubber solution is obtained, thermoplastic polyurethane is added into N-methyl pyrrolidone (the mass ratio of thermoplastic polyurethane and N-methyl pyrrolidone is 16:84), stirring at a speed of 400 r / min for 120 min, after stirring, a polyurethane solution is obtained, maleic anhydride grafted hydrogenated styrene-ethylene-butylene-styrene polymer is added into N-methyl pyrrolidone (the mass ratio of maleic anhydride grafted hydrogenated styrene-ethylene-butylene-styrene polymer and N-methyl pyrrolidone is 1:9), stirring at a speed of 400 r / min for 480 min, after stirring, a compatibilizing solution is obtained, the rubber solution, the polyurethane solution and the compatibilizing solution are mixed, N-methyl pyrrolidone is added, stirring at a speed of 400 r / min for 30 min, dimethyl carbonate is added, after mixing for the second time, a rubber coating slurry is obtained; wherein the mass ratio of the rubber solution, the polyurethane solution, the compatibilizing solution, the added N-methyl pyrrolidone and the dimethyl carbonate is 18:13:18:4:7; S3, the ceramic coating slurry is coated on the base film to obtain a ceramic coating separator precursor, and the first extraction liquid, the second extraction liquid, the third extraction liquid and the fourth extraction liquid are used for extraction in sequence, wherein the first extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 80%, the extraction time is 1 min, the second extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 50%, the extraction time is 1 min, the third extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 30%, the extraction time is 1 min, the fourth extraction liquid is water, the extraction time is 1 min, and the obtained product is dried at 45°C to obtain a separator with a ceramic coating as the bottom layer; S4, the rubber coating slurry is coated on the surface of the ceramic coating, and the first extraction liquid, the second extraction liquid, the third extraction liquid and the fourth extraction liquid are used for extraction in sequence, wherein the first extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 80%, the extraction time is 1 min, the second extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 50%, the extraction time is 1 min, the third extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 30%, the extraction time is 1 min, the fourth extraction liquid is water, the extraction time is 1 min, and the obtained product is dried at 45°C to obtain a composite separator with a double-layer functional coating.

[0054] Example 3 A preparation method of a composite separator with a double-layer functional coating, comprising the following steps: S1, mix the alumina, BYK-110 and N-methyl pyrrolidone (the mass ratio of alumina, N-methyl pyrrolidone and BYK-110 is 45:55:0.05), the stirring speed is 400r / min, the stirring time is 90min, the ceramic dispersion liquid is obtained, the meta-aramid is added into N-methyl pyrrolidone for dilution (the mass ratio of meta-aramid and N-methyl pyrrolidone is 9:26), the dilution liquid is obtained, the dilution liquid is added into the ceramic dispersion liquid, and after fully mixing at a speed of 450r / min for 30min, a mixed liquid is obtained, polyvinylidene fluoride is added into N-methyl pyrrolidone (the mass ratio of polyvinylidene fluoride and N-methyl pyrrolidone is 1:4), and after stirring at a speed of 400r / min for 120min, a bonding solution is obtained, the bonding solution is added into the mixed liquid, stirring is carried out at a speed of 350r / min for 30min, sand grinding is carried out at a speed of 600r / min for 20min, and a ceramic coating slurry is obtained; wherein the mass ratio of the ceramic dispersion liquid, the dilution liquid and the bonding liquid is 45:45:10; S2, hydrogenated butyl rubber is added into N-methyl pyrrolidone (the mass ratio of hydrogenated butyl rubber and N-methyl pyrrolidone is 15:85), stirring is carried out at a speed of 500r / min for 480min, and after stirring, a rubber solution is obtained, thermoplastic polyurethane is added into N-methyl pyrrolidone (the mass ratio of thermoplastic polyurethane and N-methyl pyrrolidone is 16:84), stirring is carried out at a speed of 400r / min for 120min, and after stirring, a polyurethane solution is obtained, maleic anhydride grafted hydrogenated styrene-ethylene-butylene-styrene polymer is added into N-methyl pyrrolidone (the mass ratio of maleic anhydride grafted hydrogenated styrene-ethylene-butylene-styrene polymer and N-methyl pyrrolidone is 1:9), stirring is carried out at a speed of 400r / min for 480min, and after stirring, a compatibilization solution is obtained, the rubber solution, the polyurethane solution and the compatibilization solution are mixed, N-methyl pyrrolidone is added, stirring is carried out at a speed of 400r / min for 30min, dimethyl carbonate is added, and after secondary mixing, a rubber coating slurry is obtained; wherein the mass ratio of the rubber solution, the polyurethane solution, the compatibilization solution, the added N-methyl pyrrolidone and the dimethyl carbonate is 10:13:18:52:7; S3, the ceramic coating slurry is coated on the base film to obtain a ceramic coating separator precursor, and extraction is carried out in sequence using a first extraction liquid, a second extraction liquid, a third extraction liquid and a fourth extraction liquid, wherein the first extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 80%, the extraction time is 1min, the second extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 50%, the extraction time is 1min, the third extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 30%, the extraction time is 1min, the fourth extraction liquid is water, the extraction time is 1min, and 45°C drying is carried out to obtain a separator with a ceramic coating as a bottom layer; S4, the rubber coating slurry is applied on the surface of the ceramic coating, and extraction is sequentially performed using a first extraction liquid, a second extraction liquid, a third extraction liquid and a fourth extraction liquid, wherein the first extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 80%, the extraction time is 1 min, the second extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 50%, the extraction time is 1 min, the third extraction liquid is an N-methyl pyrrolidone aqueous solution with a mass concentration of 30%, the extraction time is 1 min, the fourth extraction liquid is water, the extraction time is 1 min, and the obtained composite diaphragm has a double-layer functional coating after drying at 45 DEG C; Figure 1 The scanning electron microscope image of the composite diaphragm prepared in the present embodiment is shown in the following figure.

[0055] Example 4 The preparation method of the composite alumina comprises the following steps: dispersing 3 parts of allyl 4-hydroxybenzoate in 250 parts of anhydrous ethanol, adding 50 parts of alumina, mixing for 4 h, and drying to obtain the composite alumina. Compared with Example 1, the difference of Example 4 is that the alumina is replaced by an equal amount of the composite alumina prepared by the above preparation method.

[0056] Example 5 Compared with Example 4, the difference of Example 5 is that the amount of allyl 4-hydroxybenzoate added is 4 parts.

[0057] Comparative Example 1 Compared with Example 1, the difference of Comparative Example 1 is that no polyurethane solution is added in step S2, i.e. the rubber coating slurry in Comparative Example 1 is composed of rubber solution, compatibilizing solution, additional N-methyl pyrrolidone and dimethyl carbonate with a mass ratio of 25:21:4:7. Figure 2 The scanning electron microscope image of the composite diaphragm prepared in the present embodiment is shown in the following figure. Figure 1 and Figure 2 From the electron microscope images of the surface layer adhesive layer rubber coating, the pore size is relatively uniform, the hydrogenated nitrile rubber is well combined with the thermoplastic polyurethane, and the ceramic membrane is also well combined.

[0058] Comparative Example 2 Compared with Example 1, the difference of Comparative Example 2 is that the hydrogenated nitrile rubber in step S2 is replaced by an equal amount of polyvinylidene fluoride.

[0059] Comparative Example 3 Compared with Example 1, the difference of Comparative Example 3 is that the composite diaphragm in the present comparative example only comprises a base film and a ceramic coating.

[0060] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the composite separator in the present comparative example only includes the base film and the rubber coating layer.

[0061] Experimental Example 1 The composite separators prepared in Examples 1-5 and Comparative Examples 1-4 were tested according to the following test methods.

[0062] 1. Air permeability value: Take a 1000 mm * 120 mm separator sample and place it on the air permeability tester to test 10 points uniformly, with a distance of 100 mm between adjacent two points. Take the average value of the 10 points to obtain the air permeability value.

[0063] 2. Temperature resistance: Cut the separator into 4 cm * 6 cm, measure the area change in a 150°C oven for 1 h to obtain the thermal shrinkage rate.

[0064] 3. Adhesion between the separator and the electrode: Cut the separator into a shape with a width of 25 mm and a length of 150 mm, and cut the electrode into a shape with a width of 25 mm and a length of 60 mm. Then, stack the separator and the electrode together and hot-press using a battery electrode press under the conditions of a pressure of 1000 KG, a temperature of 80°C, and a time of 1 s to prepare a test sample. Then, use a tensile testing machine to tear the electrode and the separator, and the force used is the adhesion of the battery electrode. The electrode is a positive electrode or a negative electrode. The positive electrode material in the positive electrode is ternary material (LiNi 0.8 Co 0.1 Mn 0.1 O2), and the negative electrode material in the negative electrode is graphite.

[0065] The test results are shown in Table 1. Table 1. Performance test results of Examples 1-5 and Comparative Examples 1-4

[0066] As can be seen from Table 1, the air permeability value of Comparative Example 1 is significantly higher than that of Example 1. In combination with the electron microscope Figure 2 analysis, Comparative Example 1 coats the ceramic surface with rubber slurry without adding thermoplastic polyurethane material, and the prepared separator does not form many pores, resulting in a large air permeability value. The surface pore size of the separator prepared in Example 1 is relatively uniform, and the performance is good. The adhesion data of Comparative Examples 2 and 3 decrease significantly compared with Example 1, that is, the rubber coating layer can effectively improve the adhesion performance of the separator. The temperature resistance of Comparative Example 4 is significantly worse than that of Example 1, that is, the ceramic coating layer can effectively improve the temperature resistance of the separator. Compared with Example 1, the shrinkage rate of Examples 4-5 is smaller, and the adhesion is greater, indicating that the addition of composite alumina can improve the high-temperature dimensional stability of the composite separator and the adhesion of the electrode interface.

[0067] Experimental Example 2 The composite separators prepared in Examples 1-3 and Comparative Examples 1-4 were assembled into 18650 batteries, and the batteries were subjected to 500 cycles of charge and discharge tests.

[0068] The test results are shown in Table 2: Table 2 Performance test results of Examples 1-3 and Comparative Examples 1-4

[0069] As shown in Table 2, the efficiency of Comparative Example 3 and Comparative Example 4 is lower than that of Examples 1-3, indicating that the battery prepared using the composite separator with ceramic coating and rubber coating can effectively improve the charge and discharge cycle performance of the battery, and improve the safety performance and cycle life of the battery.

[0070] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A composite diaphragm with a dual-layer functional coating, characterized in that, From bottom to top, it includes a base film, a bottom layer, and a top layer. The bottom layer is a ceramic coating, and the top layer is a rubber coating.

2. The composite diaphragm with a dual-layer functional coating according to claim 1, characterized in that, The base membrane is a porous polyolefin base membrane, which includes one or both of polyethylene membrane and polypropylene membrane, and the thickness of the base membrane is 5~16μm.

3. The composite diaphragm with a dual-layer functional coating according to claim 1, characterized in that, The solid components of the ceramic coating include the following raw materials in parts by weight: 20-30 parts inorganic ceramic particles, 0.05-0.1 parts co-solvent, 8-15 parts meta-aramid, and 1-3 parts binder.

4. A composite diaphragm with a dual-layer functional coating according to claim 3, characterized in that, The inorganic ceramic particles include one or more of alumina, silicon dioxide, boehmite, zirconium oxide, boron nitride, and hollow ceramic microspheres, and the average particle size of the inorganic ceramic particles is 0.3~1μm.

5. A composite diaphragm with a dual-layer functional coating according to claim 1, characterized in that, The inorganic ceramic particles are composite inorganic ceramic particles. The preparation method of the composite inorganic ceramic particles includes the following steps: dispersing allyl 4-hydroxybenzoate in anhydrous ethanol, adding the inorganic ceramic particles, mixing and drying to obtain the composite inorganic ceramic particles.

6. A composite diaphragm with a dual-layer functional coating according to claim 5, characterized in that, The mass ratio of the allyl 4-hydroxybenzoate to the inorganic ceramic particles is 3~4:

50.

7. A composite diaphragm with a dual-layer functional coating according to claim 1, characterized in that, The co-solvent includes one or more of lithium chloride, calcium chloride, BYK-110, and BYK-180; The adhesive includes one or more of polyvinylidene fluoride, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, styrene-butadiene rubber, and polyacrylonitrile.

8. A composite diaphragm with a dual-layer functional coating according to claim 1, characterized in that, The solid components of the rubber coating include the following raw materials in parts by weight: 1.5 to 4.3 parts of elastomer rubber, 2 to 7 parts of thermoplastic polyurethane, 1.2 to 2.2 parts of compatibilizer, and 7 to 12 parts of pore-forming material.

9. A composite diaphragm with a dual-layer functional coating according to claim 8, characterized in that, The elastomer rubber includes one or more of hydrogenated nitrile rubber, acrylate rubber, styrene-butadiene-styrene block copolymer, styrene-ethylene-butene-styrene block copolymer, and fluororubber; The compatibilizer is a maleic anhydride-grafted polymer; The pore-forming material includes one or more of sodium chloride, dimethyl carbonate, polyacrylonitrile, polyimide, polyacrylic acid, and sodium lignosulfonate.

10. A method for preparing a composite separator with a dual-layer functional coating, used to prepare the composite separator with a dual-layer functional coating as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. The inorganic ceramic particles, the co-solvent, and the organic solvent are mixed to obtain a ceramic dispersion. The meta-aramid is added to the organic solvent for dilution to obtain a diluted solution. The diluted solution is added to the ceramic dispersion and stirred to obtain a mixed solution. The binder is added to the organic solvent for mixing to obtain a binder solution. The binder solution is added to the mixed solution, and after secondary stirring and sand milling, a ceramic coating slurry is obtained. S2. The elastomer rubber is added to an organic solution and stirred to obtain a rubber solution. The thermoplastic polyurethane is added to the organic solution and stirred to obtain a polyurethane solution. The compatibilizer is added to the organic solution and stirred to obtain a compatibilizing solution. The rubber solution, the polyurethane solution, and the compatibilizing solution are mixed. After adding organic solvent, the pore-forming material is added. After a second mixing, a rubber coating slurry is obtained. S3. The ceramic coating slurry is coated onto the base membrane to obtain a ceramic coating membrane precursor. After extraction and drying, a membrane with a ceramic coating as the bottom layer is obtained. S4. The rubber coating slurry is applied to the surface of the ceramic coating, extracted, and dried to obtain the composite diaphragm with a dual-layer functional coating. The organic solvent includes one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, methanol, and ethanol.

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