Modified ceramic powder, ceramic composite diaphragm and lithium ion battery

Abstract

The invention provides modified ceramic powder, a ceramic composite diaphragm and a lithium ion battery. The modified ceramic powder is obtained by adding ceramic particles into an organic solvent containing a polymeric monomer for emulsion polymerization and forming a polymer coating layer on the surfaces of the ceramic particles. According to the modified ceramic powder, the ceramic composite diaphragm and the lithium ion battery provided by the invention, the polymer coating layers are formed on the surfaces of the ceramic particles to obtain the modified ceramic powder, and when the modified ceramic powder is compounded with the high-temperature-resistant polymer microspheres to form the ceramic composite diaphragm, ceramic slurry has relatively good dispersion stability and uniformity; meanwhile, excellent thermal protection effect and high-temperature thermal size stability are shown on the diaphragm, the liquid holdup of the diaphragm can be greatly improved, and the cycle performance of the battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery separator, in particular to a modified ceramic powder, a ceramic composite separator and a lithium ion battery. BACKGROUND

[0002] Among many energy storage devices, lithium ion batteries are widely used in digital products, automobiles and daily necessities due to their light weight, long service life and high energy density. Generally, each lithium ion battery is composed of a cathode, an anode, a separator and an electrolyte. Among them, the separator does not directly participate in the electrochemical reaction of the battery, but it is an indispensable part of the current lithium ion battery. Its main role is to realize the physical isolation of the positive and negative electrodes to prevent the direct contact of the positive and negative electrodes from causing short circuit. Therefore, the separator should not curl or shrink at high temperature, which requires the separator to have certain mechanical strength to withstand the stress during manufacturing and assembly, and certain thermal stability to maintain the structural integrity at high temperature to prevent the direct contact of the positive and negative electrodes.

[0003] At present, the material commonly used as a separator is polyolefin material, which is due to the high chemical stability and high porosity of polyolefin material. However, polyolefin material also has certain disadvantages. First, it has poor thermal stability and low melting point, and has high thermal shrinkage rate at high temperature, which causes the shrinkage of the separator to lead to the direct contact of the positive and negative electrodes, resulting in short circuit. Second, it has poor wettability to electrolyte, which affects ion transmission and has negative impact on the rate performance and cycle life of the battery.

[0004] To solve the above problems, the mainstream method used in the industry now is to use inorganic ceramic nanoparticles such as silicon dioxide, aluminum trioxide, boehmite and magnesium hydroxide, and one or more of additives such as wetting agent, surfactant, dispersant, emulsifier and adhesive to prepare a slurry, which is coated on the surface of the polyolefin separator. Compared with the traditional polyolefin separator, the above ceramic coated separator shows better high temperature resistance and more excellent electrolyte wettability. However, since the ceramic particles are generally inorganic particles with high density, the areal density of the ceramic coated separator is significantly higher than that of the polyolefin separator, resulting in the decrease of the energy density of the battery.

[0005] In view of the above shortcomings, by including high temperature resistant polymer microspheres in the ceramic coating slurry, since it is an organic matter, it is more closely combined with the adhesive, which can show excellent thermal protection effect and high temperature dimensional stability to the separator, and the high temperature resistant polymer microspheres have relatively light density, which can greatly improve the liquid retention rate of the separator and also improve the cycle performance and temperature resistance of the battery. However, since the ceramic coating slurry is a typical non-equilibrium particle suspension system, the micron or micron sub-micron inorganic ceramic particles and the sub-micron or nanometer organic high temperature resistant microspheres are different in size, density and shape, so they are prone to stratification and aggregation, resulting in poor stability of the ceramic coating slurry.

[0006] The poor stability of the ceramic coating slurry can cause the components of the slurry to settle and the overall performance and production efficiency of the diaphragm coating to be weakened, which is not conducive to the quality of the diaphragm. SUMMARY

[0007] Based on the technical problems in the background art, the present application provides a modified ceramic powder, a ceramic composite diaphragm and a lithium ion battery. By forming a polymer coating layer on the surface of the ceramic particles to obtain the modified ceramic powder, when it is combined with high-temperature-resistant polymer microspheres to form a ceramic composite diaphragm, not only does the ceramic slurry have good dispersion stability and uniformity, but also the diaphragm exhibits excellent thermal protection effect and high-temperature thermal dimensional stability, and can greatly improve the liquid retention rate of the diaphragm and improve the cycle performance of the battery.

[0008] The modified ceramic powder provided by the present application is obtained by adding ceramic particles to an organic solvent containing polymer monomers for emulsion polymerization, and forming a polymer coating layer on the surface of the ceramic particles.

[0009] Preferably, the polymer monomer is at least one of styrene, methylstyrene, vinyltoluene, methyl acrylate, isobutyl acrylate, n-octyl acrylate, vinyl acetate, methyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, n-butyl methacrylate, isobutyl methacrylate and isooctyl methacrylate.

[0010] Preferably, the mass ratio of the ceramic particles to the polymer monomer is 100:1-10.

[0011] Preferably, the organic solvent further contains a crosslinking agent, a dispersant, an emulsifier and an initiator.

[0012] Preferably, the crosslinking agent is at least one of ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, divinylbenzene or N,N'-methylenebisacrylamide; the dispersant is at least one of polyvinylpyrrolidone, hydroxypropyl cellulose, sodium polyacrylate, polyvinyl alcohol, polyethylene glycol or polyvinyl methyl ether; the emulsifier is at least one of a sulfate, a carboxylate or a sulfonate; and the initiator is at least one of azobisethylbutyronitrile, benzoyl peroxide or dilauroyl peroxide.

[0013] Preferably, the ceramic particles are at least one of alumina, silicon dioxide, silicon carbide, silicon nitride, magnesium silicate, magnesium hydroxide, barium titanate or boehmite.

[0014] Preferably, before the ceramic particles are added to the organic solvent containing polymer monomers for emulsion polymerization, the ceramic particles are further coupled with a halogenated alkyl silane coupling agent for a coupling reaction, and then subjected to a quaternary ammonium reaction with an alkenyl tertiary amine compound.

[0015] Preferably, the halogenated alkyl silane coupling agent is at least one of 3-chloropropyl trimethoxysilane, 3-chloropropyl triethoxysilane, 3-chloropropyl methyl dimethoxysilane or 3-chloropropyl methyl diethoxysilane, and the alkenyl tertiary amine compound is at least one of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate or diethylaminoethyl acrylate.

[0016] The present application also provides a ceramic composite separator, comprising a base film and a ceramic coating layer coated on at least one surface of the base film, wherein the ceramic coating layer comprises high-temperature-resistant polymer microspheres and the modified ceramic powder as described above.

[0017] The weight ratio of the high-temperature-resistant polymer microspheres and the modified ceramic powder is 10-30:70-90.

[0018] Preferably, the base film is a polyethylene microporous film, a polypropylene microporous film or a multi-layer composite microporous film composed of polyethylene and polypropylene; and the high-temperature-resistant polymer microspheres are at least one of polyimide microspheres, PMMA microspheres, aramid microspheres, polyphosphazene microspheres or polyacrylonitrile microspheres.

[0019] Preferably, the ceramic coating layer further comprises a polymer binder.

[0020] Preferably, the polymer binder is at least one of polyacrylic acid, pure acrylic emulsion, styrene-acrylic emulsion, polyamide acid salt or butyl-styrene emulsion.

[0021] The present application also provides a lithium ion battery comprising the ceramic composite separator as described above.

[0022] In the present application, the ceramic particles have high surface energy and surface effect, which easily causes agglomeration. In addition, the density of the ceramic particles is quite different from that of the high-temperature-resistant polymer microspheres, i.e. the density of the ceramic particles is large, which easily causes the ceramic particles to be stratified from the polymer microspheres in the coating slurry, resulting in uneven coating. Therefore, by forming a non-polar cross-linked polymer coating layer on the surface of the ceramic powder through emulsion polymerization, on one hand, the ceramic powder will not agglomerate when forming the ceramic coating layer, and on the other hand, the ceramic powder and the high-temperature-resistant polymer microspheres will not be stratified, which ensures the stability of the coating slurry system and the uniformity of the coating, thereby effectively forming a lap joint three-dimensional network, improving the high-temperature resistance and high-temperature dimensional stability of the separator, and also improving the rate performance and cycle life of the battery. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be described in detail below through specific examples, but it should be clear that these examples are used for illustration, but not to be construed as limiting the scope of the present application.

[0024] Example 1

[0025] A ceramic composite diaphragm is prepared by the following method:

[0026] (1) Modified ceramic powder: ceramic particles Al2O3 (average particle size 0.5 μm) are added to water and stirred to disperse uniformly, then styrene, methyl acrylate, ethyl methacrylate, crosslinking agent ethylene glycol dimethacrylate, dispersant polyvinyl alcohol, emulsifier sodium cetyl sulfonate and initiator benzoyl peroxide are added in a mass ratio of 40:30:30:5:15:1:1, the mass ratio of ceramic particles Al2O3 and styrene is 100:3, after stirring and dispersing uniformly, the temperature is raised to 60°C, and the reaction is kept constant for 10 h, then filtered, washed and dried to obtain the modified ceramic powder;

[0027] (2) Polyimide microspheres: 4,4'-diamino diphenyl ether and pyromellitic dianhydride in a molar ratio of 1:1 are added to N,N-dimethylformamide and stirred to dissolve completely, then stirred for 6 h under nitrogen protection to obtain a polyamide acid solution, the polyamide acid solution is subjected to electrostatic spraying in an electric field with an electric field intensity of 1 kV / cm to obtain polyamide acid microspheres, and the polyamide acid microspheres are heated to 350°C at a heating rate of 5°C / min and subjected to thermal imidization treatment for 1 h to obtain the polyimide microspheres;

[0028] (3) Ceramic composite diaphragm: the modified ceramic powder, polyimide microspheres and water-based polyacrylate binder (BYK-381) are added to water in a mass ratio of 80:20:5 and stirred to disperse uniformly to obtain a ceramic slurry (solid content 40 wt.%), the ceramic slurry is coated on one side surface of a polyethylene single-layer film (thickness 12 μm, porosity 45%) by gravure roll method, dried at 60°C to form a coating layer (thickness 4 μm), and the ceramic composite diaphragm is obtained.

[0029] Example 2

[0030] A ceramic composite diaphragm is prepared by the following method:

[0031] (1) Modified ceramic powder: ceramic particles Al2O3 (average particle size 0.5 μm) are added to water and stirred to disperse uniformly, then styrene, methyl acrylate, ethyl methacrylate, crosslinking agent ethylene glycol dimethacrylate, dispersant polyvinyl alcohol, emulsifier sodium cetyl sulfonate and initiator benzoyl peroxide are added in a mass ratio of 40:30:30:5:15:1:1, the mass ratio of ceramic particles Al2O3 and styrene is 100:3, after stirring and dispersing uniformly, the temperature is raised to 60°C, and the reaction is kept constant for 10 h, then filtered, washed and dried to obtain the modified ceramic powder;

[0032] (2) PMMA microspheres: polyvinyl alcohol was added to water to prepare a 2wt% aqueous solution, then methyl methacrylate, benzoyl peroxide and n-octanol with a mass ratio of 97.5:0.5:52.5 were added, stirred and uniformly dispersed, then heated to 70°C, and kept at this temperature for 24h, washed with water, filtered and dried to obtain the PMMA microspheres;

[0033] (3) Ceramic composite separator: the modified ceramic powder, PMMA microspheres and water-based polyacrylate binder (BYK-381) described above were added to water with a mass ratio of 80:20:5, stirred and uniformly dispersed to obtain a ceramic slurry (solid content of 40wt%), the ceramic slurry was coated on one side of a polyethylene single-layer film (thickness of 12μm, porosity of 45%) by gravure roll method, dried at 60°C to form a coating layer (thickness of 4μm), and the ceramic composite separator was obtained.

[0034] Example 3

[0035] A ceramic composite separator was prepared by the following method:

[0036] (1) Modified ceramic powder: ceramic particles Al2O3 (average particle size of 0.5μm) were added to water, stirred and uniformly dispersed, then styrene, methyl acrylate, ethyl methacrylate, crosslinking agent ethylene glycol dimethacrylate, dispersant polyvinyl alcohol, emulsifier sodium cetyl sulfonate and initiator benzoyl peroxide with a mass ratio of 40:30:30:5:15:1:1 were added, the mass ratio of ceramic particles Al2O3 and styrene was 100:3, stirred and uniformly dispersed, then heated to 60°C, kept at this temperature for 10h, filtered, washed and dried to obtain the modified ceramic powder;

[0037] (2) Aramid microspheres: m-phenylenediamine and isophthaloyl chloride with a molar ratio of 1:1 were added to N,N-dimethylformamide, stirred and completely dissolved, then stirred at -10°C for 1h under nitrogen protection to obtain a poly-m-phenylene isophthaloyl diamine solution, the poly-m-phenylene isophthaloyl diamine solution was electrostatically sprayed in an electric field with an electric field intensity of 1kV / cm to obtain aramid microspheres;

[0038] (3) Ceramic composite separator: the modified ceramic powder, aramid microspheres and water-based polyacrylate binder (BYK-381) described above were added to water with a mass ratio of 80:20:5, stirred and uniformly dispersed to obtain a ceramic slurry (solid content of 40wt%), the ceramic slurry was coated on one side of a polyethylene single-layer film (thickness of 12μm, porosity of 45%) by gravure roll method, dried at 60°C to form a coating layer (thickness of 4μm), and the ceramic composite separator was obtained.

[0039] Example 4

[0040] A ceramic composite diaphragm is prepared by the following method:

[0041] (1) Modified ceramic powder: ceramic particles Al203 (average particle size 0.5 μm) are added to water and stirred to disperse uniformly, then styrene, isobutyl acrylate, crosslinking agent ethylene glycol dimethacrylate, dispersant polyvinyl alcohol, emulsifier sodium cetyl sulfonate and initiator benzoyl peroxide are added in a mass ratio of 40:60:5:15:1:1, the mass ratio of ceramic particles Al203 and styrene is 100:3, after stirring and dispersing uniformly, the temperature is raised to 60°C, and after constant temperature reaction for 10 h, filtration, washing and drying, the modified ceramic powder is obtained;

[0042] (2) Polyimide microspheres: 4,4'-diamino diphenyl ether and pyromellitic dianhydride in a molar ratio of 1:1 are added to N,N-dimethylformamide and stirred to dissolve completely, after stirring and reaction for 6 h under nitrogen protection, a polyamide acid solution is obtained, the polyamide acid microspheres are obtained by electrostatic spraying in an electric field with an electric field intensity of 1 kV / cm, and the polyamide acid microspheres are heated to 350°C at a heating rate of 5°C / min, and heat imidization treatment is carried out for 1 h to obtain the polyimide microspheres;

[0043] (3) Ceramic composite diaphragm: the modified ceramic powder, polyimide microspheres and water-based polyacrylate binder (BYK-381) are added to water in a mass ratio of 80:20:5, stirred and dispersed uniformly to obtain a ceramic slurry (solid content 40 wt%), and the ceramic slurry is coated on one side surface of a polyethylene single-layer film (thickness 12 μm, porosity 45%) by gravure roll method, dried at 60°C to form a coating layer (thickness 4 μm) to obtain the ceramic composite diaphragm.

[0044] Example 5

[0045] A ceramic composite diaphragm is prepared by the following method:

[0046] (1) Modified ceramic powder: ceramic particles Al203 (average particle size 0.5 μm) are added to water and stirred to disperse uniformly, then styrene, isobutyl acrylate, crosslinking agent ethylene glycol dimethacrylate, dispersant polyvinyl alcohol, emulsifier sodium cetyl sulfonate and initiator benzoyl peroxide are added in a mass ratio of 40:60:5:15:1:1, the mass ratio of ceramic particles Al203 and styrene is 100:3, after stirring and dispersing uniformly, the temperature is raised to 60°C, and after constant temperature reaction for 10 h, filtration, washing and drying, the modified ceramic powder is obtained;

[0047] (2) Polyimide microspheres: p-phenylenediamine and 3,3',4,4'-biphenyl tetracarboxylic dianhydride with a molar ratio of 1:1 were added into N,N-dimethylformamide and stirred to completely dissolve, and then stirred under nitrogen protection for 6 h after reaction to obtain a polyamic acid solution. The polyamic acid solution was subjected to electrostatic spraying in an electric field with an electric field intensity of 1 kV / cm to obtain polyamic acid microspheres. The polyamic acid microspheres were heated to 350°C at a heating rate of 5°C / min and then heat imidized for 1 h to obtain the polyimide microspheres;

[0048] (3) Ceramic composite separator: the modified ceramic powder, polyimide microspheres and water-based polyacrylate binder (BYK-381) described above were added into water with a mass ratio of 80:20:5 and stirred to uniformly disperse to obtain a ceramic slurry (solid content of 40 wt%). The ceramic slurry was coated on one side surface of a polyethylene single-layer film (thickness of 12 μm, porosity of 45%) by a gravure roll method, and then dried at 60°C to form a coating layer (thickness of 4 μm) to obtain the ceramic composite separator.

[0049] Example 6

[0050] A ceramic composite separator is prepared by the following method:

[0051] (1) Modified ceramic powder: ceramic particles Al2O3 (average particle size of 0.5 μm) were added into water and stirred to uniformly disperse, and then styrene, methyl acrylate, ethyl methacrylate, crosslinking agent ethylene glycol dimethacrylate, dispersant polyvinyl alcohol, emulsifier sodium cetyl sulfonate and initiator benzoyl peroxide with a mass ratio of 40:30:30:5:15:1:1 were added. The mass ratio of ceramic particles Al2O3 and styrene was 100:3. After stirring and uniformly dispersing, the temperature was increased to 60°C, and then constant temperature reaction was performed for 10 h. After filtration, washing and drying, the modified ceramic powder was obtained.

[0052] (2) Polyimide microspheres: 2,2'-bis(trifluoromethyl)diaminobiphenyl and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride with a molar ratio of 1:1 were added into N,N-dimethylformamide and stirred to completely dissolve, and then stirred under nitrogen protection for 6 h after reaction to obtain a polyamic acid solution. The polyamic acid solution was subjected to electrostatic spraying in an electric field with an electric field intensity of 1 kV / cm to obtain polyamic acid microspheres. The polyamic acid microspheres were heated to 350°C at a heating rate of 5°C / min and then heat imidized for 1 h to obtain the polyimide microspheres;

[0053] (3) Ceramic composite separator: the modified ceramic powder, polyimide microspheres and water-based polyacrylate binder (BYK-381) described above are added to water in a mass ratio of 80:20:5, stirred and dispersed uniformly to obtain a ceramic slurry (solid content of 40wt%), the ceramic slurry is coated on one side surface of a polyethylene single-layer film (thickness of 12μm, porosity of 45%) by gravure roll method, dried at 60℃ to form a coating layer (thickness of 4μm), and the ceramic composite separator is obtained.

[0054] Example 7

[0055] A ceramic composite separator is prepared by the following method:

[0056] (1) Modified ceramic powder: ceramic particles Al2O3 (average particle size of 0.5μm) are added to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, stirred and dispersed for 3h, filtered, washed with water, then added to water, stirred and dispersed uniformly, 3-chloropropyltrimethoxysilane is added, the mass ratio of ceramic particles Al2O3 to 3-chloropropyltrimethoxysilane is 100:5, after heating to 90℃, stirring for 2h, dimethylaminoethyl acrylate is added and stirred for 2h, the mass ratio of ceramic particles Al2O3 to dimethylaminoethyl acrylate is 100:5, then styrene, methyl acrylate, ethyl methacrylate, crosslinking agent ethylene glycol dimethacrylate, dispersant polyvinyl alcohol, emulsifier sodium hexadecyl sulfonate and initiator benzoyl peroxide are added in a mass ratio of 40:30:30:5:15:1:1, the mass ratio of ceramic particles Al2O3 to styrene is 100:3, after stirring and dispersing uniformly, heating to 60℃, constant temperature reaction for 10h, suction filtration, washing and drying, the modified ceramic powder is obtained;

[0057] (2) Polyimide microspheres: 4,4'-diamino diphenyl ether and pyromellitic dianhydride in a molar ratio of 1:1 are added to N,N-dimethylformamide and stirred to dissolve completely, after stirring for 6h under nitrogen protection, a polyamide acid solution is obtained, the polyamide acid solution is subjected to electrostatic spraying in an electric field with an electric field intensity of 1kV / cm to obtain polyamide acid microspheres, the polyamide acid microspheres are heated to 350℃ at a heating rate of 5℃ / min, and heat imidization treatment is carried out for 1h to obtain the polyimide microspheres;

[0058] (3) Ceramic composite separator: the modified ceramic powder, polyimide microspheres and water-based polyacrylate binder (BYK-381) described above are added to water in a mass ratio of 80:20:5, stirred and dispersed uniformly to obtain a ceramic slurry (solid content of 40wt%), the ceramic slurry is coated on one side surface of a polyethylene single-layer film (thickness of 12μm, porosity of 45%) by gravure roll method, dried at 60℃ to form a coating layer (thickness of 4μm), and the ceramic composite separator is obtained.

[0059] Comparative Example 1

[0060] A ceramic composite separator is prepared by the following method:

[0061] (1) Polyimide microspheres: 4,4'-diaminodiphenyl ether and pyromellitic dianhydride in a molar ratio of 1:1 were added to N,N-dimethylformamide and stirred to completely dissolve, and then stirred for 6 h under nitrogen protection to obtain a polyamic acid solution. The polyamic acid solution was subjected to electrostatic spraying in an electric field with an electric field intensity of 1 kV / cm to obtain polyamic acid microspheres. The polyamic acid microspheres were heated to 350°C at a heating rate of 5°C / min, and then heat imidized for 1 h to obtain the polyimide microspheres;

[0062] (2) Ceramic composite separator: ceramic particles Al2O3 (average particle size 0.5 μm), polyimide microspheres and water-based polyacrylate binder (BYK-381) in a mass ratio of 80:20:5 were added to water and stirred to uniformly disperse to obtain a ceramic slurry (solid content 40 wt%). The ceramic slurry was coated on one side surface of a polyethylene single-layer film (thickness 12 μm, porosity 45%) by a gravure roll method, and then dried at 60°C to form a coating layer (thickness 4 μm) to obtain the ceramic composite separator.

[0063] Comparative Example 2

[0064] A ceramic composite separator is prepared by the following method:

[0065] (1) Modified ceramic powder: ceramic particles Al2O3 (average particle size 0.5 μm) were added to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, stirred and dispersed for 3 h, filtered, washed with water, then added to water and stirred to uniformly disperse. Vinyltrimethoxysilane was added, and the mass ratio of ceramic particles Al2O3 to vinyltrimethoxysilane was 100:5. Then styrene, methyl acrylate, ethyl methacrylate, crosslinking agent ethylene glycol dimethacrylate, dispersant polyvinyl alcohol, emulsifier sodium hexadecyl sulfonate and initiator benzoyl peroxide were added in a mass ratio of 40:30:30:5:15:1:1. The mass ratio of ceramic particles Al2O3 to styrene was 100:3. After stirring and uniformly dispersing, the temperature was raised to 60°C, and then constant temperature reaction was carried out for 10 h. After suction filtration, washing and drying, the modified ceramic powder was obtained.

[0066] (2) Polyimide microspheres: 4,4'-oxydianiline and pyromellitic dianhydride with a molar ratio of 1:1 were added into N,N-dimethylformamide and stirred to completely dissolve, and then stirred under nitrogen protection for 6 h to obtain a polyamic acid solution. The polyamic acid solution was subjected to electrostatic spraying in an electric field with an electric field intensity of 1 kV / cm to obtain polyamic acid microspheres. The polyamic acid microspheres were heated to 350°C at a heating rate of 5°C / min and subjected to thermal imidization treatment for 1 h to obtain the polyimide microspheres;

[0067] (3) Ceramic composite separator: the modified ceramic powder, polyimide microspheres and water-based polyacrylate binder (BYK-381) described above were added into water in a mass ratio of 80:20:5 and stirred to uniformly disperse to obtain a ceramic slurry (solid content of 40 wt%). The ceramic slurry was coated on one side surface of a polyethylene single-layer film (thickness of 12 μm, porosity of 45%) by a gravure roll method, and then dried at 60°C to form a coating layer (thickness of 4 μm) to obtain the ceramic composite separator.

[0068] Performance test:

[0069] The ceramic composite separators obtained in the above examples and comparative examples were subjected to heat shrinkage rate, puncture strength, tensile strength and battery performance tests, and the test results are shown in Table 1.

[0070] Heat shrinkage rate: a ceramic composite separator sample with a size of 5 cm x 5 cm was cut, and the size in the machine direction (MD) and the transverse direction (TD) was measured before baking, and was recorded as L1 and H1, respectively. Then the ceramic composite separator was baked at 150°C for 1 h, and the size in the MD and TD was measured again, and was recorded as L2 and H2, respectively. The MD heat shrinkage rate was (L1-L2) / L1 x 100%, and the TD heat shrinkage rate was (H1-H2) / H1 x 100%. The higher value of the heat shrinkage rates in the MD and TD was defined as the heat shrinkage rate of the separator.

[0071] Puncture strength and tensile strength: an electronic universal testing machine was used to stretch a ceramic composite separator with a certain size and shape, and the tensile strength was recorded. An electronic universal testing machine was used to puncture a ceramic composite separator with a certain size and shape, and the puncture strength was recorded.

[0072] Battery performance: the ceramic composite separator and the positive electrode sheet (the positive electrode slurry was prepared by mixing lithium cobaltate, conductive agent acetylene black and polyvinylidene fluoride in a mass ratio of 97:1:2 in N-methylpyrrolidone solvent, coating on aluminum foil and drying, then cold pressing and slitting to prepare the positive electrode sheet), the negative electrode sheet (the negative electrode slurry was prepared by mixing graphite, conductive carbon black Super P and butadiene rubber in a mass ratio of 97:1:2 in deionized water, coating on copper foil and drying, then cold pressing and slitting to prepare the negative electrode sheet) and 1 mol / L lithium hexafluorophosphate electrolyte (lithium hexafluorophosphate LiPF6 was dissolved in a mixed solvent of ethylene carbonate EC, dimethyl carbonate DMC and methyl ethyl carbonate EMC in a volume ratio of 1:1:1 to prepare lithium hexafluorophosphate electrolyte) were assembled into lithium ion batteries in a conventional manner, and then the battery performance test was carried out. Specifically, 1C constant current constant voltage charging was carried out to 4.35V, the cutoff battery was 0.1C, and the capacity retention rate of 300 cycles was recorded.

[0073] Table 1 Performance test results of the ceramic composite separator of the examples and the comparative examples

[0074]

[0075]

[0076] As shown in the above Table 1, in the examples, the introduction of the modified ceramic powder can significantly improve the high temperature resistance and high heat dimensional stability of the separator, and also improve the cycle life of the battery; as can be seen from the comparison data of Example 7 and Example 1, the coupling reaction of the modified ceramic powder with the halogenated alkyl silane coupling agent first, and then the quaternary ammonium reaction with the alkenyl tertiary amine compound, can introduce double bonds and quaternary ammonium salt groups on the surface of the ceramic particles, which helps the subsequent emulsion polymerization with the polymeric material, thereby further improving the high temperature resistance and high heat dimensional stability of the ceramic composite separator; as can be seen from the results of Example 7 and Comparative Example 2, simply using a silane coupling agent containing double bonds for coupling reaction cannot further improve the high temperature resistance and high heat dimensional stability of the ceramic composite separator.

[0077] The above description is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent substitutions or changes within the technical scope disclosed by the present application according to the technical solution and inventive concept of the present application, which should be covered within the protection scope of the present application.

Claims

1. A modified ceramic powder, characterized in that: The modified ceramic powder is obtained by adding ceramic particles into an organic solvent containing polymerization monomers to carry out emulsion polymerization, and forming a polymer coating layer on the surface of the ceramic particles.

2. The modified ceramic powder according to claim 1, characterized in that: The polymerizable monomer is at least one of styrene, methylstyrene, vinyltoluene, methyl acrylate, isobutyl acrylate, n-octyl acrylate, vinyl acetate, methyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, n-butyl methacrylate, isobutyl methacrylate and isooctyl methacrylate; Preferably, the mass ratio of the ceramic particles to the polymerizable monomers is 100:1-10.

3. The modified ceramic powder according to claim 1 or 2, characterized in that: The organic solvent also contains a cross-linking agent, a dispersant, an emulsifier and an initiator; Preferably, the cross-linking agent is at least one of ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, divinylbenzene or N,N'-methylenebisacrylamide; the dispersant is at least one of polyvinyl pyrrolidone, hydroxypropyl cellulose, sodium polyacrylate, polyvinyl alcohol, polyethylene glycol or polyvinyl methyl ether; the emulsifier is at least one of sulfate, carboxylate or sulfonate; and the initiator is at least one of azobis(ethylbutyronitrile), benzoyl peroxide or dilauroyl peroxide.

4. The modified ceramic powder according to any one of claims 1 to 3, characterized in that: The ceramic particles are at least one of aluminum oxide, silicon dioxide, silicon carbide, silicon nitride, magnesium silicate, magnesium hydroxide, barium titanate or boehmite.

5. The modified ceramic powder according to any one of claims 1 to 4, characterized in that: Before adding the ceramic particles into an organic solvent containing polymerization monomers for emulsion polymerization, the method further includes carrying out a coupling reaction between the ceramic particles and a halogenated alkylsilane coupling agent, and then carrying out a quaternization reaction with an alkenyl tertiary amine compound.

6. The modified ceramic powder according to claim 5, characterized in that: The haloalkylsilane coupling agent is at least one of 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 3-chloropropylmethyldimethoxysilane or 3-chloropropylmethyldiethoxysilane, and the alkenyl tertiary amine compound is at least one of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate or diethylaminoethyl acrylate.

7. A ceramic composite diaphragm, characterized in that: It comprises a base film and a ceramic coating coated on at least one surface of the base film, wherein the ceramic coating comprises high temperature resistant polymer microspheres and the modified ceramic powder according to any one of claims 1 to 6; The weight ratio of the high temperature resistant polymer microspheres to the modified ceramic powder is 10-30:70-90.

8. The ceramic composite diaphragm according to claim 7, characterized in that: The base film is a polyethylene microporous film, a polypropylene microporous film or a multilayer composite microporous film composed of polyethylene and polypropylene; the high temperature resistant polymer microspheres are at least one of polyimide microspheres, PMMA microspheres, aramid microspheres, polyphosphazene microspheres or polyacrylonitrile microspheres.

9. The ceramic composite diaphragm according to claim 7 or 8, characterized in that: The ceramic coating further comprises a polymer binder; Preferably, the polymer binder is at least one of polyacrylic acid, pure acrylic emulsion, styrene acrylic emulsion, polyamic acid salt or styrene butadiene emulsion.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the ceramic composite diaphragm according to any one of claims 7 to 9.

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