Lithium ion battery separator with high adhesion strength to pole piece

Abstract

The present application belongs to the technical field of lithium ion battery separators, and in particular to a lithium ion battery separator with high adhesion strength to electrode sheets, characterized in that it comprises: a base film; and a composite coating layer arranged on at least one side of the base film, wherein: the composite coating layer comprises raspberry structure polymer microspheres.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium ion battery separator, in particular, a separator with high adhesion strength to electrode tab. BACKGROUND

[0002] Due to the advantages of lithium ion battery, such as light weight, high energy density, long cycle life, etc., it is widely used in: batteries used in thin electronic devices, such as smart phones, tablets, wearable devices, and notebook computers; batteries for electric vehicles and hybrid electric vehicles; or solar power storage systems. Among them, the performance of the "separator" in the internal structure of the lithium ion battery has a significant impact on the electrochemical performance and safety performance of the lithium ion battery.

[0003] The current mainstream lithium ion battery separator is a stretched polyolefin film, but its heat resistance is poor. The melting point of the polyethylene separator is about 130℃, and the melting point of the polypropylene separator is about 170℃. Therefore, it is understandable that when using a lithium ion battery made of a polyolefin film under harsh conditions, the separator may be softened and damaged by heat, causing the positive and negative electrodes in the lithium ion battery to come into contact with each other, resulting in a short circuit in the battery, which poses a safety hazard. In order to avoid the above situation, the current solution is to coat the polyolefin separator with a coating containing inorganic particles and a binder to improve the thermal stability of the polyolefin separator. In addition, in order to improve the adhesion strength between the separator and the electrode tab, a binder is coated on one side of the separator. The binder used is mostly microspheres obtained by emulsion polymerization or dispersion polymerization, such as polyvinylidene fluoride (PVDF) or polymethyl methacrylate (PMMA). PVDF has good chemical stability and liquid absorption and retention capacity, but its adhesion strength to the electrode tab is not high. Although PMMA has excellent adhesion strength to the electrode tab at room temperature, its softening temperature is low, so it is easy to melt during the heat drying process, causing the electrode tab to easily separate from the separator. In summary, it is necessary to provide a separator with high thermal stability and high adhesion strength to the electrode tab. SUMMARY

[0004] The purpose of the present application is to provide a lithium ion battery separator with excellent thermal stability and high adhesion strength to the electrode tab.

[0005] In order to achieve the above purpose, the present application provides a lithium ion battery separator with high adhesion strength to the electrode tab, characterized in that it comprises: a base film; and a composite coating layer provided on at least one side of the base film, wherein the composite coating layer comprises raspberry structure polymer microspheres.

[0006] More preferably, the composite coating further comprises: a ceramic particle, a dispersing agent, a thickening agent, a wetting agent, a binder, or water.

[0007] More preferably, the raspberry structure polymer microspheres comprise: an amino-activated microsphere, and at least one epoxy-activated high polymer microsphere connected to the outer circumferential side of the amino-activated microsphere.

[0008] More preferably, the Tg of the amino-activated microsphere is greater than the Tg of the epoxy-activated high polymer microsphere.

[0009] More preferably, the ceramic particle comprises: titanium dioxide, aluminum oxide, aluminum trioxide, boehmite, copper oxide, zinc oxide, silicon dioxide, or barium sulfate; the dispersing agent comprises: polyether silane, polyacrylamide, sodium polyacrylate, ammonium polyacrylate, sodium hexametaphosphate, or polyacrylic acid; the thickening agent comprises: hydroxymethyl cellulose (CMC), carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium carboxymethyl cellulose, sodium alginate, casein, sodium polyacrylate, polyoxyethylene, or polyvinylpyrrolidone; the wetting agent comprises: sodium butylnaphthalene sulfonate, sodium isopropyl naphthalene sulfonate, sodium aryl naphthalene sulfonate, sodium dodecyl benzene sulfonate, or sodium alkyl sulfate; or the binder comprises: polyacrylic acid, polyacrylonitrile, styrene and butadiene copolymer, or polyurethane.

[0010] More preferably, the diameter of the amino-activated microsphere is 2 to 8 μm, and the ratio of the diameter of the amino-activated microsphere to the diameter of the epoxy-activated high polymer microsphere is greater than 5.

[0011] More preferably, the amino-activated microsphere comprises: a first high Tg polymer monomer, and a first low Tg polymer monomer; and the epoxy-activated high polymer microsphere comprises: a second high Tg polymer monomer, and a second low Tg polymer monomer, and the ratio of the number of moles of the second low Tg polymer monomer to the number of moles of the second high Tg polymer monomer is greater than the ratio of the number of moles of the first low Tg polymer monomer to the number of moles of the first high Tg polymer monomer.

[0012] More preferably, the first high Tg polymer monomer or the second high Tg polymer monomer comprises: styrene, glycidyl methacrylate, or methacrylamide; and the first low Tg polymer monomer or the second low Tg polymer monomer comprises: methyl methacrylate, butyl acrylate, or butyl methacrylate.

[0013] More preferably, the method for preparing the composite coating layer comprises: a mixing step (S1) of mixing and stirring water, a dispersant, a thickening agent, and ceramic particles to obtain a mixture; a grinding step (S2) of grinding the mixture to obtain a refined mixture; an adding step (S3) of adding raspberry-structured polymer microspheres, a binder, and a wetting agent to the refined mixture and stirring uniformly to obtain a slurry; and a coating step (S4) of coating the slurry on the base film to form the composite coating layer.

[0014] More preferably, in the mixing step (S1), the stirring time is 1.5 hours; in the grinding step (S2), the mixture is ground at least twice; in the adding step (S3), the stirring time is 2 hours; or in the coating step (S4), the slurry is coated on the base film by gravure roll coating, wire bar coating, or extrusion coating.

[0015] More preferably, the material of the base film comprises polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), or polyimide.

[0016] More preferably, the method for preparing the raspberry-structured polymer microspheres comprises: (S5) mixing amino-activated microspheres and water at a weight ratio of 10:90 to 30:70 to obtain a micron-sized microsphere seed emulsion; and (S6) mixing epoxy-activated polymer microspheres and the micron-sized microsphere seed emulsion at a weight ratio of 2:100 to 10:100, and stirring and mixing at a temperature of 60 to 80°C for 6 to 48 hours to obtain the raspberry-structured polymer microspheres.

[0017] More preferably, the method for preparing the raspberry-structured polymer microspheres further comprises: (S7) drying the raspberry-structured polymer microspheres.

[0018] More preferably, the method for preparing the amino-activated microspheres comprises: (S8) mixing a hydrophilic polymer and ethanol at a weight ratio of 1:100 to 3:100 to obtain an ethanol mixed solution; (S9) mixing a first high-Tg polymer monomer and a first low-Tg polymer monomer at a weight ratio of 1:1 to 1:3 to obtain a first mixed solution; (S10) mixing a second high-Tg polymer monomer and a second low-Tg polymer monomer at a weight ratio of 1:1 to 1:3 to obtain a second mixed solution; (S11) mixing the first mixed solution and the second mixed solution at a weight ratio of 1:1 to 1:3 to obtain a third mixed solution; (S12) mixing the third mixed solution and the ethanol mixed solution at a weight ratio of 1:1 to 1:3 to obtain a fourth mixed solution; (S13) mixing the fourth mixed solution and a crosslinking agent at a weight ratio of 1:1 to 1:3 to obtain a fifth mixed solution; and (S14) mixing the fifth mixed solution and a catalyst at a weight ratio of 1:1 to 1:3 to obtain the amino-activated microspheres. 3 to 3.9 : 95 to 96.1(S10) mixing the first monomer mixture with an initiator at a weight ratio of 100:2 to 100:5 to obtain a first monomer mixed solution; (S11) mixing the ethanol mixed solution with the first monomer mixed solution at a weight ratio of 25:100 to 50:100, and stirring and reacting at a temperature of 60 to 85°C for 8 to 24 hours to obtain a microsphere seed emulsion; and (S12) mixing the microsphere seed emulsion with a polyamine reagent at a weight ratio of 100:2 to 100:5, and reacting at a temperature of 50 to 75°C for 8 to 36 hours to obtain the amino-activated microspheres.

[0019] More preferably, the method for preparing the epoxy-activated polymer microspheres comprises: (S13) mixing a surfactant, a polymerization initiator, and deionized water at a weight ratio of (0 to 0.5):(0.1 to 0.3):(100) to obtain a mixed aqueous solution; (S14) mixing a second high-Tg polymer monomer and a second low-Tg polymer monomer at a molar ratio of 4.1 to 30:70 to 95.9 to obtain a second monomer mixture, wherein the percentage of the number of moles of the second low-Tg polymer monomer relative to the number of moles of the second high-Tg polymer monomer is greater than the percentage of the number of moles of the first low-Tg polymer monomer relative to the number of moles of the first high-Tg polymer monomer; and (S15) weighing the mixed aqueous solution and the second monomer mixture at a weight ratio of 12.75:1, and adding the second monomer mixture to the mixed aqueous solution at a temperature of 60 to 80°C over a period of 8 to 24 hours to obtain the epoxy-activated polymer microspheres.

[0020] More preferably, the hydrophilic polymer comprises polyvinyl alcohol, polyvinylpyrrolidone, or sodium carboxymethyl cellulose; the initiator comprises azobisisobutyronitrile or benzoyl peroxide; or the polyamine reagent comprises ethylenediamine, 2-ethylenediamine, propylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, butylenediamine, 1,4-butylenediamine, pentylenediamine, 1,5-pentylenediamine, hexylenediamine, 1,6-hexylenediamine, trimethylhexamethylenediamine, or (ethylenedioxy)bisethylamine.

[0021] More preferably, the surfactant comprises sodium dodecylsulfate, sodium dodecylbenzenesulfonate, or alkyl alcohol polyoxyethylene sulfate ammonium; or the polymerization initiator comprises sodium persulfate, potassium persulfate, or ammonium persulfate.

[0022] The efficacy of the present application over the prior art is that: (1) the raspberry structure polymer microspheres have a core-shell structure, the inner layer is an amino-activated microsphere, and the outer layer is an epoxy-activated high molecular microsphere, wherein the proportion of low Tg polymer monomers contained in the amino-activated microsphere < the proportion of low Tg polymer monomers contained in the epoxy-activated high molecular microsphere, because the glass transition temperature (Tg) of the amino-activated microsphere > the glass transition temperature (Tg) of the epoxy-activated high molecular microsphere, so when the epoxy-activated high molecular microsphere is melted by heat and contacts the separator and the electrode tab, the amino-activated microsphere can still maintain its mechanical properties without being deformed by heat. (2) The particle size of the raspberry structure polymer microspheres is large, so after the hot pressing of the separator and the electrode tab is completed, the raspberry structure polymer microspheres can be bonded to the separator and the electrode tab respectively to provide good bonding performance between them. (3) In the raspberry structure polymer microspheres, the amino group of the amino-activated microsphere and the epoxy group of the epoxy-activated high molecular microsphere can undergo ring-opening reaction and independently complete polymerization, and the polymerization process is simple and efficient. (4) In the raspberry structure polymer microspheres, the amino-activated microsphere and the epoxy-activated high molecular microsphere are connected by covalent bond, so the connection strength between them is high and not easy to be destroyed. (5) In the raspberry structure polymer microspheres, the epoxy-activated high molecular microsphere does not completely cover the amino-activated microsphere, so it can be understood that compared with the traditional full-coated core-shell structure, the raspberry structure polymer microspheres of the present application can greatly save raw materials. (6) The epoxy-activated high molecular microsphere of the outer layer of the raspberry structure polymer microspheres forms multiple-point contact with the tab, so the bonding performance between the separator and the tab can be strengthened. (7) The raspberry structure polymer microspheres can be mixed with ceramic particles, dispersants, thickeners, wetting agents, adhesives, or water for coating to control the coating performance, consistency, or leveling property of the slurry, so that the coating efficiency of the slurry is greatly improved. In summary, the raspberry structure polymer microspheres provided by the present application have the advantages of simple synthesis, excellent adhesion, and wide processing window, and have good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a structural diagram for explaining the structural characteristics of the "lithium ion battery separator with high adhesion strength to the tab";

[0024] Figure 2 It is a structural diagram for explaining the structural characteristics of the "raspberry structure polymer microspheres";

[0025] Figure 3 It is a block flow chart for explaining the formation method of the "composite coating";

[0026] Figures 4A to 6 It is a series of block flow charts for explaining the preparation method of the "raspberry structure polymer microspheres". DETAILED DESCRIPTION

[0027] To make the above and / or other purposes, effects, features of the present application more obvious and easy to understand, the preferred embodiments are specifically described below:

[0028] The present application aims to provide a lithium ion battery separator with high adhesion strength to the pole piece, wherein as shown in Figure 1 , it comprises a base film 1 and a composite coating 2 arranged on at least one side of the base film 1, wherein the composite coating 2 comprises raspberry structure polymer microspheres 3. In a preferred embodiment, in order to improve the liquid absorption or retention rate of the base film 1 for electrolyte, improve the thermal stability of the base film 1, improve the lithium ion conduction efficiency of the base film 1, enhance the protection performance of the base film 1 to prevent it from being punctured by lithium dendrites, or improve the electrochemical performance of the base film 1, the composite coating 2 further comprises ceramic particles, a dispersing agent, a thickening agent, a wetting agent, an adhesive, or water, but not limited thereto. In another preferred embodiment, as shown in Figure 2 , the raspberry structure polymer microspheres 3 comprise amino-activated microspheres 4 and at least one epoxy-activated polymer microsphere 5 connected to the outer edge of the amino-activated microspheres 4. Specifically, the raspberry structure polymer microspheres 3 are microspheres with a structure like raspberries formed by the ring-opening reaction polymerization of the amino groups of the amino-activated microspheres 4 and the epoxy groups of the epoxy-activated polymer microspheres 5. Wherein: the particle size of the amino-activated microspheres 4 is larger than that of the epoxy-activated polymer microspheres 5, so it can be understood that the amino-activated microspheres 4 act as carriers for the epoxy-activated polymer microspheres 5, and the outer edge of each amino-activated microsphere 4 can be connected to multiple epoxy-activated polymer microspheres 5 to form multiple protruding anchor points, which can increase the contact area between the separator and the pole piece and strengthen the adhesion effect between the separator and the pole piece. In yet another preferred embodiment, the surface of the amino-activated microspheres 4 has abundant amino groups and hydroxyl groups, and the surface of the epoxy-activated polymer microspheres 5 has abundant carboxyl groups and epoxy groups, so the amino-activated microspheres 4 and the epoxy-activated polymer microspheres 5 can be covalently bonded to each other to form the raspberry structure polymer microspheres 3, and the amino-activated microspheres 4 and the epoxy-activated polymer microspheres 5 are spherical particles obtained by self-assembly through emulsion polymerization, suspension polymerization, or dispersion polymerization, but not limited thereto.

[0029] Preferably, in order to increase the adhesion strength between the base film 1 coated with the composite coating 2 and the pole piece after the hot-pressing composite process, the Tg of the amino-activated microspheres 4 is higher than the Tg of the epoxy-activated high-molecular microspheres 5, while maintaining the mechanical properties of the raspberry-structured polymer microspheres 3. Specifically, since the epoxy-activated high-molecular microspheres 5 have a lower glass transition temperature (Tg), they are preferentially melted during the heating process, thereby increasing the contact area and the adhesion strength with the pole piece. In addition, since the amino-activated microspheres 4 have a higher Tg, they remain solid after the epoxy-activated high-molecular microspheres 5 are melted, thereby maintaining the overall mechanical strength of the raspberry-structured polymer microspheres 3 without deformation. In another preferred embodiment, the ceramic particles include titanium dioxide, aluminum oxide, aluminum trioxide, boehmite, copper oxide, zinc oxide, silicon dioxide, or barium sulfate; the dispersant includes polyether silane, polyacrylamide, sodium polyacrylate, ammonium polyacrylate, sodium hexametaphosphate, or polyacrylic acid; the thickening agent includes hydroxymethyl cellulose (CMC), carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, starch sodium phosphate, sodium carboxymethyl cellulose, sodium alginate, casein, sodium polyacrylate, polyoxyethylene, or polyvinylpyrrolidone; the wetting agent includes sodium butylnaphthalene sulfonate, sodium isopropyl naphthalene sulfonate, sodium aryl naphthalene sulfonate, sodium dodecyl benzene sulfonate, or sodium alkyl sulfate; or the binder includes polyacrylic acid, polyacrylonitrile, styrene and butadiene copolymer, or polyurethane, but not limited thereto.

[0030] Preferably, to prevent excessive deformation of the raspberry-structured polymer microspheres 3 during heating, which could reduce the adhesion strength between them and the electrode, the diameter of the amino-activated microspheres 4 is 2 to 8 μm, and the ratio of the diameter of the amino-activated microspheres 4 to the length of the epoxy-activated polymer microspheres 5 is >5. In a preferred embodiment, to adjust the glass transition temperature (Tg) of the amino-activated microspheres 4 and the epoxy-activated polymer microspheres 5, the amino-activated microspheres 4 comprise: a first high-Tg polymer monomer and a first low-Tg polymer monomer; and the epoxy-activated polymer microspheres 5 comprise: a second high-Tg polymer monomer and a second low-Tg polymer monomer, wherein the ratio of the molar number of the second low-Tg polymer monomer to the molar number of the second high-Tg polymer monomer is greater than the ratio of the molar number of the first low-Tg polymer monomer to the molar number of the first high-Tg polymer monomer. In another preferred embodiment, the first high-Tg polymer monomer or the second high-Tg polymer monomer comprises: styrene, glycidyl methacrylate, or methacrylamide; and the first low-Tg polymer monomer or the second low-Tg polymer monomer comprises: methyl methacrylate, butyl acrylate, or butyl methacrylate, but is not limited thereto. In yet another preferred embodiment, the material used for the base film 1 includes: polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), or polyimide, but is not limited thereto. It is understood that, in order to enhance the electrolyte absorption and retention rate of the lithium-ion battery separator, the base film 1 includes a microporous structure, for example, a polyethylene separator including a microporous structure, but is not limited thereto.

[0031] Preferably, such as Figure 3 As shown, the preparation method of the composite coating 2 includes: a mixing step (S1), in which water, a dispersant, a thickener, and ceramic particles are mixed and stirred to obtain a mixture; a grinding step (S2), in which the mixture is ground to obtain a refined mixture; an adding step (S3), in which the raspberry structured polymer microspheres 3, an adhesive, and a wetting agent are added to the refined mixture and stirred evenly to obtain a slurry; and a coating step (S4), in which the slurry is coated onto the base film 1 to form the composite coating 2. In a preferred embodiment, in order to obtain a slurry with uniform texture and good fluidity, so that the slurry has good contact and adhesion with the base film 1, or to facilitate control of the thickness of the slurry coating, the stirring time in the mixing step (S1) is 1.5 hours; in the grinding step (S2), the mixture is ground at least twice; in the adding step (S3), the stirring time is 2 hours; or in the coating step (S4), the slurry is coated onto the base film 1 by gravure roller coating, wire rod coating, or extrusion coating, but not limited thereto.

[0032] Preferably, the following provides a method for preparing "raspberry structured polymer microspheres 3", specifically as follows: Figure 4A As shown, the process includes: (S5) mixing an amino-activated microsphere 4 with water at a weight ratio of 10:90 to 30:70 to obtain a micron-sized microsphere seed emulsion; and (S6) mixing an epoxy-activated polymer microsphere 5 with the micron-sized microsphere seed emulsion at a weight ratio of 2:100 to 10:100, and stirring at a temperature of 60 to 80°C for 6 to 48 hours to obtain the raspberry structural polymer microsphere 3. In a preferred embodiment, to obtain powdered raspberry structural polymer microsphere 3 for subsequent slurry preparation, such as... Figure 4B As shown, the preparation method of the raspberry structured polymer microspheres 3 further includes: (S7) drying the raspberry structured polymer microspheres 3. In another preferred embodiment, as... Figure 5 As shown, the preparation method of the amino-activated microspheres 4 includes: (S8) mixing a hydrophilic polymer with ethanol in a weight ratio of 1:100 to 3:100 to obtain an ethanol mixed solution; (S9) mixing a first high-Tg polymer monomer with a first low-Tg polymer monomer in a molar ratio of 3 to 3.9:95 to 96.1 to obtain a first monomer mixture; (S10) mixing the first monomer mixture with an initiator in a weight ratio of 100:2 to 100:5 to obtain an ethanol mixed solution. (11) Obtain a first monomer mixed solution; mix the ethanol mixed solution with the first monomer mixed solution at a weight ratio of 25:100 to 50:100, and stir the mixture at a temperature of 60 to 85°C for 8 to 24 hours to obtain a microsphere seed emulsion; and (S12) react the microsphere seed emulsion with a polyamine reagent at a weight ratio of 100:2 to 100:5 at a temperature of 50 to 75°C for 8 to 36 hours to obtain the amino-activated microspheres 4. In another preferred embodiment, as Figure 6As shown, the preparation method of the epoxy-activated high polymer microspheres 5 comprises: (S13) stirring and mixing a surfactant, a polymerization initiator, and deionized water in a weight ratio of (0-0.5):(0.1-0.3):(100) to obtain a mixed aqueous solution; (S14) mixing a second high-Tg polymer monomer and a second low-Tg polymer monomer in a molar ratio of 4.1-30:70-95.9 to obtain a second monomer mixture, wherein the percentage of the moles of the second low-Tg polymer monomer relative to the moles of the second high-Tg polymer monomer is greater than the percentage of the moles of the first low-Tg polymer monomer relative to the moles of the first high-Tg polymer monomer; and (S15) weighing the mixed aqueous solution and the second monomer mixture in a weight ratio of 12.75:1, and adding the second monomer mixture into the mixed aqueous solution at a temperature of 60-80°C within 8-24 hours to obtain the epoxy-activated high polymer microspheres 5.

[0033] Preferably, the hydrophilic polymer comprises polyvinyl alcohol, polyvinylpyrrolidone, or sodium carboxymethyl cellulose; the initiator comprises azobisisobutyronitrile or benzoyl peroxide; or the polyamine agent comprises ethylenediamine, 2-ethylenediamine, propylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, butylenediamine, 1,4-butylenediamine, pentylenediamine, 1,5-pentylenediamine, hexylenediamine, 1,6-hexylenediamine, trimethylhexamethylene diamine, or (ethylenedioxy)bisethylamine, but not limited thereto. In a preferred embodiment, the surfactant comprises sodium dodecyl sulfonate, sodium dodecylbenzenesulfonate, or alkyl alcohol polyoxyethylene sulfate ammonium; or the polymerization initiator comprises sodium persulfate, potassium persulfate, or ammonium persulfate, but not limited thereto.

[0034] Examples 1-3 and Comparative Examples 1-4 are provided below to illustrate different preparation methods of the lithium ion battery separator with high electrode sheet adhesion strength, wherein for the sake of brevity of description, the “lithium ion battery separator with high electrode sheet adhesion strength” is referred to as “composite separator” hereinafter.

[0035] “Example 1” is provided below to illustrate a first embodiment of the preparation method of the composite separator, specifically, the preparation method is: first obtaining raspberry structure polymer microspheres 3, then preparing a slurry by dispersing the raspberry structure polymer microspheres 3, and then coating the slurry on a base film 1.

[0036] The preparation method of the raspberry structure polymer microspheres 3 comprises an amino-activated microspheres 4 preparation step, an epoxy-activated polymer microspheres 5 preparation step, and a polymerization step. First, the amino-activated microspheres 4 preparation step comprises mixing polyvinylpyrrolidone and ethanol at a weight ratio of 1:100 to 3:100 to obtain an ethanol mixed solution; mixing styrene, glycidyl methacrylate, and butyl acrylate at a weight ratio of 23:1:1 (wherein the molar ratio of butyl acrylate is 3.31%) to obtain a first monomer mixture; mixing the first monomer mixture and azobisisobutyronitrile at a weight ratio of 100:2 to 100:5 to obtain a first monomer mixed solution; mixing the ethanol mixed solution and the first monomer mixed solution at a weight ratio of 25:100 to 50:100, and stirring and reacting at a temperature of 70°C for 12 hours to obtain a microsphere seed emulsion; and reacting the microsphere seed emulsion and (ethylenedioxy)bisethylamine at a weight ratio of 100:2 to 100:5 at a temperature of 50 to 75°C for 8 to 36 hours to obtain the amino-activated microspheres 4.

[0037] Then, the epoxy-activated polymer microspheres 5 preparation step comprises stirring and mixing a surfactant, potassium persulfate, and deionized water at a weight ratio of (0 to 0.5):(0.1 to 0.3):(100) to obtain a mixed aqueous solution; mixing styrene, glycidyl methacrylate, and butyl acrylate at a weight ratio of 8:1:1 (wherein the molar ratio of butyl acrylate is 8.51%) to obtain a second monomer mixture; and weighing the mixed aqueous solution and the second monomer mixture at a weight ratio of 12.75:1, and adding the second monomer mixture to the mixed aqueous solution at a temperature of 60 to 80°C over a period of 6 hours to obtain the epoxy-activated polymer microspheres 5.

[0038] Next, the polymerization step comprises mixing the amino-activated microspheres 4 and water at a weight ratio of 10:90 to 30:70 to obtain a micron-sized microsphere seed emulsion; and mixing the epoxy-activated polymer microspheres 5 and the micron-sized microsphere seed emulsion at a weight ratio of 2:100 to 10:100, and stirring and mixing at a temperature of 60°C for 12 hours to obtain the raspberry structure polymer microspheres 3. In the raspberry structure polymer microspheres 3, the particle size of the inner layer of amino-activated microspheres 4 is 4.3 μm, and the particle size of the epoxy-activated polymer microspheres 5 is 0.2 μm.

[0039] The following describes the method of preparing the slurry: the raspberry structure polymer microspheres 3 are spray-dried to form a powder, and the slurry is prepared by mixing the following ingredients: 5.54 parts by weight of water, 0.02 parts by weight of a 40% solid content sodium acrylate dispersant, 0.8 parts by weight of 4% sodium carboxymethyl cellulose, 2.2 parts by weight of alumina particles, 0.03 parts by weight of a 4% solid content acrylic adhesive, 0.03 parts by weight of a 0.3% solid content wetting agent, and 0.05 parts by weight of the powder raspberry structure polymer microspheres 3.

[0040] The following describes the method of preparing the composite separator: the slurry is coated on a PE base film 1 using a gravure roll coating method to form a composite coating layer 2 on the PE base film 1, wherein the thickness of the PE base film 1 is 9 μm, the composite separator does not melt at a drying temperature of 90°C, or at a hot pressing temperature, and the adhesion of the composite coating layer 2 to the electrode sheet is 15 N / m.

[0041] The following provides "Example 2" to describe a second embodiment of the method of preparing the composite separator, wherein the difference between Example 2 and Example 1 is that the first monomer mixture contains styrene, methyl methacrylamide, glycidyl methacrylate, and butyl acrylate in a weight ratio of 25.5:3:1.5:1.5 (wherein the molar ratio of butyl acrylate is 3.87%), and the second monomer mixture contains styrene, glycidyl methacrylate, and butyl acrylate in a weight ratio of 19.1:2.2:1.1 (wherein the molar ratio of butyl acrylate is 4.14%). In the raspberry structure polymer microspheres 3 obtained in Example 2, the particle size of the amino-activated microspheres 4 in the inner layer is 2.6 μm, and the particle size of the epoxy-activated polymer microspheres 5 is 0.2 μm.

[0042] Since the method of preparing the slurry in Example 2 is the same as in Example 1, no further description is provided herein. The composite separator obtained does not melt at a temperature of 85°C, and the adhesion of the composite coating layer 2 to the electrode sheet is 11.5 N / m.

[0043] The following provides "Example 3" to illustrate a third implementation example of the composite separator preparation method, wherein the difference between Example 3 and Example 1 is that the first monomer mixture comprises styrene, glycidyl methacrylate, and butyl acrylate in a weight ratio of 23:1:1 (wherein the molar ratio of butyl acrylate is 3.31%), and the second monomer mixture comprises styrene, glycidyl methacrylate, and butyl acrylate in a weight ratio of 11:7:7 (wherein the molar ratio of butyl acrylate is 26.1%). In the raspberry-structured polymer microspheres 3 obtained in Example 3, the particle size of the amino-activated microspheres 4 in the inner layer is 6.9 μm, and the particle size of the epoxy-activated polymer microspheres 5 is 0.5 μm.

[0044] Since the slurry preparation method in Example 3 is the same as that in Example 1, no further description is provided herein. The composite separator obtained has a wide processing window and does not melt at a temperature of 60-80°C. The adhesion of the composite coating 2 to the pole piece is 13 N / m.

[0045] The following provides "Comparative Example 1" to illustrate a fourth implementation example of the composite separator preparation method, wherein in Comparative Example 1, the microsphere seed emulsion is not mixed with the polyamine reagent, so that in the polymerization step, the microsphere seed emulsion cannot be polymerized with the epoxy-activated polymer microspheres 5, but a mixed emulsion comprising two types of microspheres with different structures is obtained. Subsequently, the mixed emulsion is dried into a powder, which is used to replace the powdered raspberry-structured polymer microspheres 3 added in Example 1 to prepare the slurry.

[0046] Since the slurry preparation method in Comparative Example 1 is the same as that in Example 1, no further description is provided herein. The composite separator obtained has a narrow processing window and partially melts at a temperature of 70°C. The adhesion of the composite coating 2 to the pole piece is 7.1 N / m.

[0047] The following provides "Comparative Example 2" to illustrate a fifth implementation example of the composite separator preparation method, which is different from Example 1 in that the first monomer mixture comprises styrene, glycidyl methacrylate, and butyl acrylate in a weight ratio of 23:1:1, and the second monomer mixture comprises styrene, glycidyl methacrylate, and butyl acrylate in a weight ratio of 23:1:1. Since the slurry preparation method in Comparative Example 2 is the same as that in Example 1, no further description is provided herein. The composite separator obtained melts at a temperature of 80°C, and the adhesion of the composite coating 2 to the pole piece is 7.4 N / m.

[0048] The following provides "Comparative Example 3" to illustrate a sixth embodiment of the method of preparing the composite separator, which differs from Example 1 in that the first monomer mixture comprises styrene, glycidyl methacrylate, and butyl acrylate in a weight ratio of 8:1:1, and the second monomer mixture comprises styrene, glycidyl methacrylate, and butyl acrylate in a weight ratio of 23:1:1. Since the slurry is prepared and the composite separator is prepared in the same manner as in Example 1, no further description is provided here. The composite separator obtained melts at a temperature of 65°C or higher, and the adhesion of the composite coating layer 2 to the electrode sheet is 7.0 N / m.

[0049] The following provides "Comparative Example 4" to illustrate a seventh embodiment of the method of preparing the composite separator, which differs from Example 1 in that the ratio of the particle size of the amino-activated microspheres 4 to the particle size of the epoxy-activated polymer microspheres 5 is <5. Since the slurry is prepared and the composite separator is prepared in the same manner as in Example 1, no further description is provided here. The composite separator obtained melts at a temperature of 80°C or higher, and the adhesion of the composite coating layer 2 to the electrode sheet is 8.1 N / m.

[0050] Based on the results of Examples 1 to 3 and Comparative Examples 1 to 4, the physical parameters of the composite separator obtained in each example and comparative example are listed in Table 1 below. In Comparative Example 1, no polyamine reagent was used to graft the surface of the microsphere seed emulsion, so that no covalent bond was formed between the microsphere seed emulsion and the epoxy-activated polymer microsphere 5. Because the interaction between the two is weak, the microsphere seed emulsion and the epoxy-activated polymer microsphere 5 cannot self-assemble into a raspberry-like structure. As shown in Table 1 below, it can be seen that, compared with Examples 1 to 3, the composite coating 2 of Comparative Example 1 cannot provide effective adhesion, and the processing window is narrow, and melting occurs at a temperature of 70°C, so that the separator and the electrode tab cannot be firmly bonded. In addition, based on the results of Comparative Examples 2 and 3, it can be seen that when the percentage of the number of moles of the second low-Tg polymer monomer to the number of moles of the second high-Tg polymer monomer in the epoxy-activated polymer microsphere 5 is less than or equal to the percentage of the number of moles of the first low-Tg polymer monomer to the number of moles of the first high-Tg polymer monomer in the amino-activated microsphere 4, the epoxy-activated polymer microsphere 5 cannot be melted first during the heating of the composite separator, so that the separator and the tab cannot be firmly bonded. In addition, because the Tg of the amino-activated microsphere 4 of Comparative Example 3 is less than the Tg of the epoxy-activated polymer microsphere 5, it melts at 65°C, and the processing window is narrow. In addition, based on the results of Comparative Example 4, it can be seen that if the particle size of the epoxy-activated polymer microsphere 5 is greater than 1 / 5 of the particle size of the amino-activated microsphere 4, although the composite coating 2 still has a certain adhesion, reaching 8.1 N / m, the adhesion is still significantly less than that of Examples 1 to 3, and the processing window is narrow. This result is due to the fact that the diameter of the epoxy-activated polymer microsphere 5 is too large, causing the overall raspberry structure to soften and deform.

[0051] As shown in Table 1, based on the results of the examples and comparative examples, when the particle size ratio of the amino-activated microsphere 4 to the epoxy-activated polymer microsphere 5 is greater than 5, the Tg of the amino-activated microsphere 4 is greater than the Tg of the epoxy-activated polymer microsphere 5, and the amino-activated microsphere 4 and the epoxy-activated polymer microsphere 5 can be covalently bonded and self-assembled into a raspberry-like structure, the composite separator obtained can have sufficient adhesion to the tab, and will not melt at a temperature of 80°C, has a wide processing window, and thus has high commercial value.

[0052] Table 1. Physical parameters of the composite separator prepared in each example and comparative example

[0053]

[0054] The efficacy of the present application relative to the prior art is that: (1) the raspberry structure polymer microspheres 3 have a core-shell structure, the inner layer is an amino-activated microsphere 4, and the outer layer is an epoxy-activated high molecular microsphere 5, wherein the proportion of low-Tg polymer monomers contained in the amino-activated microsphere 4 < the proportion of low-Tg polymer monomers contained in the epoxy-activated high molecular microsphere 5, and because the glass transition temperature (Tg) of the amino-activated microsphere 4 > the glass transition temperature (Tg) of the epoxy-activated high molecular microsphere 5, therefore when the epoxy-activated high molecular microsphere 5 is melted by heat and contacts the separator and the electrode tab, the amino-activated microsphere 4 can still maintain its mechanical properties without being deformed by heat. (2) The particle size of the raspberry structure polymer microspheres 3 is large, so when the hot pressing and compounding of the separator and the electrode tab is completed, the raspberry structure polymer microspheres 3 can be bonded to the separator and the electrode tab respectively to provide good bonding performance between them. (3) In the raspberry structure polymer microspheres 3, the amino group of the amino-activated microsphere 4 and the epoxy group of the epoxy-activated high molecular microsphere 5 can undergo ring-opening reaction and independently complete polymerization, and the polymerization process is simple and efficient. (4) In the raspberry structure polymer microspheres 3, the amino-activated microsphere 4 and the epoxy-activated high molecular microsphere 5 are connected by covalent bond, so the connection strength between them is high and not easy to be damaged. (5) In the raspberry structure polymer microspheres 3, the epoxy-activated high molecular microsphere 5 does not completely cover the amino-activated microsphere 4, so it can be understood that compared with the traditional full-coated core-shell structure, the raspberry structure polymer microspheres 3 of the present application can greatly save raw materials. (6) The epoxy-activated high molecular microsphere 5 of the outer layer of the raspberry structure polymer microspheres 3 forms multiple-point contact with the tab, so the bonding performance between the separator and the tab can be strengthened. (7) The raspberry structure polymer microspheres 3 can be mixed with ceramic particles, dispersants, thickening agents, wetting agents, adhesives, or water for coating to control the coating performance, consistency, or leveling property of the slurry, so that the coating efficiency of the slurry is greatly improved. In summary, the raspberry structure polymer microspheres 3 provided by the present application have the advantages of simple synthesis, excellent adhesion, and wide processing window, and have good application prospect.

[0055] The above is only the preferred embodiment of the present application, but cannot limit the patent protection scope of the present application; therefore, any simple equivalent change and modification made according to the patent protection scope and content of the specification of the present application still falls within the patent protection scope of the present application.

Claims

1. A lithium ion battery separator having high adhesion strength with electrode tabs, characterized by, Comprising: a base film; and a composite coating layer disposed on at least one side of the base film, wherein: the composite coating layer comprises raspberry structure polymer microspheres and ceramic particles, the raspberry structure polymer microspheres comprise amino-activated microspheres and at least one epoxy-activated polymer microspheres connected to the outer circumferential side of the amino-activated microspheres, the ratio of the diameter of the amino-activated microspheres to the diameter of the epoxy-activated polymer microspheres is > 5, the Tg of the amino-activated microspheres is > the Tg of the epoxy-activated polymer microspheres, the amino-activated microspheres comprise a first high-Tg polymer monomer and a first low-Tg polymer monomer, the epoxy-activated polymer microspheres comprise a second high-Tg polymer monomer and a second low-Tg polymer monomer, and the ratio of the number of moles of the second low-Tg polymer monomer to the number of moles of the second high-Tg polymer monomer is > the ratio of the number of moles of the first low-Tg polymer monomer to the number of moles of the first high-Tg polymer monomer. The composite coating layer further comprises a dispersant, a thickening agent, a wetting agent, a binder, and water.

2. The lithium-ion battery separator with high tab adhesion according to claim 1, characterized in that, 3. The lithium ion battery separator with high adhesion strength to electrode sheets according to claim 2, characterized in that: the ceramic particles comprise titanium dioxide, aluminum oxide, boehmite, copper oxide, zinc oxide, silicon dioxide, or barium sulfate; the dispersant comprises polyether silane, polyacrylamide, sodium polyacrylate, ammonium polyacrylate, sodium hexametaphosphate, or polyacrylic acid; the thickening agent comprises hydroxymethyl cellulose, carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, starch sodium phosphate, sodium carboxymethyl cellulose, sodium alginate, casein, sodium polyacrylate, polyethylene oxide, or polyvinylpyrrolidone; the wetting agent comprises sodium butylnaphthalene sulfonate, sodium isopropyl naphthalene sulfonate, sodium aryl naphthalene sulfonate, sodium dodecyl benzene sulfonate, or sodium alkyl sulfate; or the binder comprises polyacrylic acid, polyacrylonitrile, styrene and butadiene copolymer, or polyurethane. The diameter of the amino-activated microspheres is 2 to 8 μm.

4. The lithium-ion battery separator with high tab adhesion according to claim 1, characterized in that, 5. The lithium ion battery separator with high adhesion strength to electrode sheets according to claim 1, characterized in that: the first high-Tg polymer monomer or the second high-Tg polymer monomer comprises styrene, glycidyl methacrylate, or methacrylamide; and the first low-Tg polymer monomer or the second low-Tg polymer monomer comprises methyl methacrylate, butyl acrylate, or butyl methacrylate. The method for preparing the composite coating layer comprises:

6. The lithium ion battery separator with high tab adhesion according to claim 1, wherein a mixing step (S1) of mixing and stirring water, a dispersant, a thickening agent, and ceramic particles to obtain a mixture; a grinding step (S2) of grinding the mixture to obtain a refined mixture; an adding step (S3) of adding the raspberry structure polymer microspheres, a binder, and a wetting agent to the refined mixture and stirring uniformly to obtain a slurry; and a coating step (S4) of coating the slurry on the base film to form the composite coating layer. ​ 7.The lithium-ion battery separator with high adhesion strength to electrode tab according to claim 6, wherein: the stirring time in the mixing step (S1) is 1.5 hours; the grinding step (S2) is grinding the mixture at least 2 times; the stirring time in the adding step (S3) is 2 hours; or the coating step (S4) is coating the slurry on the base film by gravure roll coating, wire bar coating or extrusion coating. The material of the base film comprises polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) or polyimide. The preparation method of the raspberry structure polymer microspheres comprises: (S5) mixing the amino-activated microspheres with water in a weight ratio of 10:90 to 30:70 to obtain a micron-sized microsphere seed emulsion; and (S6) mixing the epoxy-activated polymer microspheres with the micron-sized microsphere seed emulsion in a weight ratio of 2:100 to 10:100, and stirring and mixing at a temperature of 60 to 80℃ for 6 to 48 hours to obtain the raspberry structure polymer microspheres.

8. The lithium ion battery separator with high tab adhesion according to claim 1, wherein, The preparation method of the raspberry structure polymer microspheres further comprises (S7) drying the raspberry structure polymer microspheres.

9. The lithium-ion battery separator with high tab adhesion according to claim 1, wherein, The preparation method of the amino-activated microspheres comprises: (S8) mixing a hydrophilic polymer with ethanol in a weight ratio of 1:100 to 3:100 to obtain an ethanol mixed solution; (S9) mixing a first low-Tg polymer monomer with a first high-Tg polymer monomer in a molar ratio of 3 to 3.9:95 to 96.1 to obtain a first monomer mixture; 10. The lithium-ion battery separator with high tab adhesion according to claim 9, characterized in that, (S10) mixing the first monomer mixture with an initiator in a weight ratio of 100:2 to 100:5 to obtain a first monomer mixed solution; 11. The lithium-ion battery separator with high tab adhesion according to claim 9, characterized in that, (S11) mixing the ethanol mixed solution with the first monomer mixed solution in a weight ratio of 25:100 to 50:100, and stirring and reacting at a temperature of 60 to 85℃ for 8 to 24 hours to obtain a microsphere seed emulsion; and (S12) reacting the microsphere seed emulsion with a polyamine reagent in a weight ratio of 100:2 to 100:5 at a temperature of 50 to 75℃ for 8 to 36 hours to obtain the amino-activated microspheres. The preparation method of the epoxy-activated polymer microspheres comprises: (S13) stirring and mixing a surfactant, a polymerization initiator and deionized water in a weight ratio of (0 to 0.5):(0.1 to 0.3):(100) to obtain a mixed aqueous solution; (S14) mixing a second low-Tg polymer monomer with a second high-Tg polymer monomer in a molar ratio of 4.1 to 30:70 to 95.9 to obtain a second monomer mixture, wherein: the percentage of the moles of the second low-Tg polymer monomer relative to the moles of the second high-Tg polymer monomer > the percentage of the moles of the first low-Tg polymer monomer relative to the moles of the first high-Tg polymer monomer; and (S15) mixing the second monomer mixture with the mixed aqueous solution in a weight ratio of 2:100 to 10:100, and stirring and mixing at a temperature of 60 to 80℃ for 6 to 48 hours to obtain the epoxy-activated polymer microspheres.

12. The lithium-ion battery separator with high tab adhesion according to claim 11, characterized in that, ​ ​ ​ (S15) weighing the mixed aqueous solution and the second monomer mixture in a weight ratio of 12.75:1, and adding the second monomer mixture into the mixed aqueous solution dropwise at a temperature of 60-80°C within 8-24 hours to obtain the epoxy-activated polymer microspheres.

13. The lithium ion battery separator with high adhesion strength to electrode sheet according to claim 11, characterized in that: the hydrophilic polymer comprises polyvinyl alcohol, polyvinylpyrrolidone or sodium carboxymethyl cellulose; the initiator comprises azobisisobutyronitrile or benzoyl peroxide; or the polyamine agent comprises ethylenediamine, 2-ethylenediamine, propylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, butylenediamine, 1,4-butylenediamine, pentanediamine, 1,5-pentanediamine, hexanediamine, 1,6-hexanediamine, trimethylhexamethylenediamine or (ethylenedioxy)bisethylamine.

14. The lithium ion battery separator with high adhesion strength to electrode sheet according to claim 12, characterized in that: the surfactant comprises sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate or alkyl alcohol polyoxyethylene sulfate ammonium; or the polymerization initiator comprises sodium persulfate, potassium persulfate or ammonium persulfate.

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