A lithium-ion battery composite coated diaphragm and preparation method thereof

Abstract

This invention relates to the field of separator technology, specifically to a composite coated separator for lithium-ion batteries and its preparation method. The lithium-ion battery composite coated separator includes a polymer porous base membrane, a first coating surface, and a second coating surface. The first coating surface is disposed on the upper surface of the polymer porous base membrane, and the second coating surface is disposed on the lower surface of the polymer porous base membrane. The first coating surface includes multiple first adhesive polymer microspheres and multiple first supporting polymer microspheres; the second coating surface includes multiple second adhesive polymer microspheres. The adhesive polymer microspheres in the composite coated separator mainly provide adhesion between the separator and the electrode, ensuring that the battery cell does not deform during cycling. The supporting polymer microspheres in the composite coated separator provide good support, ensuring that a certain gap is maintained between the separator and the electrode after hot pressing, improving the electrolyte retention performance of the battery cell. The preparation method is easy to control, has high production efficiency, and produces products with stable quality.

Description

Technical Field

[0001] This invention relates to the field of separator technology, specifically to a composite coated separator for lithium-ion batteries and its preparation method. Background Technology

[0002] With the development of lithium-ion battery technology, the market has placed higher demands on the energy density, cycle performance, and rate performance of lithium-ion batteries. Currently, the commonly used gravure-coated water-based PVDF separators and oil-based separators have strong adhesion to the electrodes but poor liquid retention, which can easily lead to the deterioration of the cell's cycle performance. Rotary spray-coated separators have good liquid retention, but the adhesion between the separator and the electrodes is relatively poor, which can easily cause the cell to deform during cycling. Therefore, it is urgent to develop a separator that combines high liquid retention and high adhesion. Summary of the Invention

[0003] In order to overcome the shortcomings and deficiencies of the existing technology, the present invention aims to provide a lithium-ion battery composite coated separator. When the lithium-ion battery composite coated separator is used, it can make the separator and the electrode have good adhesion, the cell is not easily deformed during cycling, and it helps to improve the liquid retention performance of the cell.

[0004] Another objective of this invention is to provide a method for preparing a composite coated separator for lithium-ion batteries. This method is easy to control, has high production efficiency, and produces products with stable quality. It can improve the stability and safety performance of lithium-ion batteries during use and is conducive to large-scale industrial production.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a lithium-ion battery composite coated separator, comprising a polymer porous base membrane, a first coating surface, and a second coating surface; the first coating surface is disposed on the upper surface of the polymer porous base membrane, and the second coating surface is disposed on the lower surface of the polymer porous base membrane; the first coating surface comprises a plurality of first adhesive polymer microspheres and a plurality of first supporting polymer microspheres, the first adhesive polymer microspheres and the first supporting polymer microspheres being arranged on the upper surface of the polymer porous base membrane; the second coating surface comprises a plurality of second adhesive polymer microspheres, the second adhesive polymer microspheres being arranged on the lower surface of the polymer porous base membrane.

[0006] The lithium-ion battery composite coated separator of the present invention comprises a first coating surface and a second coating surface formed on a polymer porous base film. The first coating surface includes a plurality of first adhesive polymer microspheres and a plurality of first supporting polymer microspheres, and the second coating surface includes a plurality of second adhesive polymer microspheres. The adhesive polymer microspheres in the composite coated separator mainly provide adhesion between the separator and the electrode, ensuring that the cell does not deform during cycling. The supporting polymer microspheres in the composite coated separator provide good support, ensuring that a certain gap is maintained between the separator and the electrode after hot pressing, thereby improving the electrolyte retention performance of the cell.

[0007] Furthermore, the second coating surface also includes a plurality of second supporting polymer microspheres, which are bonded to the lower surface of the polymer porous base film.

[0008] Furthermore, the lithium-ion battery composite coated separator also includes an inorganic ceramic layer, which is disposed between the first coating surface and the polymer porous base film, and the first adhesive polymer microspheres and the first supporting polymer microspheres are arranged on the upper surface of the inorganic ceramic layer.

[0009] Furthermore, both the first and second coating surfaces are made of an aqueous adhesive coating liquid, which comprises the following raw materials in parts by weight: 2.0-8 parts of supporting polymer microspheres, 2-10 parts of adhesive polymer microspheres, 0.1-2 parts of adhesive, 0.1-1.0 parts of dispersant, 0.1-1.0 parts of wetting agent, and 100 parts of water. The adhesive polymer microspheres are either a first type of adhesive polymer microsphere or a second type of adhesive polymer microsphere. The supporting polymer microspheres are either a first type of supporting polymer microsphere or a second type of supporting polymer microsphere.

[0010] Furthermore, the adhesive is at least one of polymethacrylic acid, polymethyl methacrylate, styrene-butadiene rubber, polyurethane, epoxy resin, acrylate polymer, acrylic polymer or acrylonitrile polymer.

[0011] Furthermore, the wetting agent is at least one of fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, fluoroalkyl methoxy ether alcohol, fluoroalkyl ethoxy ether alcohol or alkylphenol polyoxyethylene ether.

[0012] Furthermore, the dispersant is at least one of polyacrylate, polyethylene glycol ether, and phosphate compound.

[0013] Furthermore, the mass ratio of the supporting polymer microspheres to the adhesive polymer microspheres is 0.3-4:1.

[0014] Furthermore, the particle size D50 of both the first and second adhesive polymer microspheres is 0.5-8 μm.

[0015] Furthermore, the particle size D50 of the first and second supporting polymer microspheres is 2-10 μm.

[0016] Furthermore, the adhesive polymer microspheres are one or more of polyacrylates, PVDF, SBR, butyl rubber, nitrile rubber, and natural rubber, preferably polyacrylate polymer microspheres.

[0017] Furthermore, the supporting polymer microspheres are one or more of PMMA, silicone, SBR, and PVDF, preferably PMMA.

[0018] Furthermore, the polyacrylate polymer adhesive microspheres adopt a core-shell structure design, with the microsphere core having a partial glass transition temperature >50℃ and a crosslinking degree >10%; and the microsphere shell having a partial glass transition temperature <70℃ and a crosslinking degree of 4% <20%.

[0019] Furthermore, the PMMA-supported microspheres have a glass transition temperature > 80°C and a melting temperature > 200°C.

[0020] Another objective of this invention is achieved through the following technical solution: the preparation method of the above-mentioned lithium-ion battery composite coated separator includes the following steps:

[0021] (1) Preparation of aqueous coating liquid for adhesive layer;

[0022] (2) Apply an aqueous coating liquid to both sides of the polymer porous base membrane to form a first coating surface and a second coating surface; or apply an inorganic ceramic coating to the upper surface of the polymer porous base membrane and dry it to form an inorganic ceramic layer; apply an aqueous coating liquid to the upper surface of the inorganic ceramic layer 2 and the lower surface of the polymer porous base membrane to form a first coating surface and a second coating surface.

[0023] (3) Curing and drying to obtain a lithium-ion battery composite coated separator.

[0024] Furthermore, in step (2), the solid content of the aqueous coating liquid is 1-20 wt%.

[0025] The beneficial effects of this invention are as follows: The lithium-ion battery composite coated separator of this invention, by setting a first coating surface and a second coating surface on a polymer porous base film, wherein the first coating surface includes a plurality of first adhesive polymer microspheres and a plurality of first supporting polymer microspheres, and the second coating surface includes a plurality of second adhesive polymer microspheres, the adhesive polymer microspheres in the composite coated separator mainly provide adhesion between the separator and the electrode, ensuring that the cell does not deform during cycling; the supporting polymer microspheres in the composite coated separator provide good support, ensuring that a certain gap is maintained between the separator and the electrode after hot pressing, thus improving the electrolyte retention performance of the cell. The lithium-ion battery composite coated separator has good adhesion and cycle performance. The preparation method of the lithium-ion battery composite coated separator is easy to control, has high production efficiency, and produces products with stable quality, which can improve the stability and safety performance of lithium-ion batteries during use and is conducive to large-scale industrial production. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view of the composite coated separator for lithium-ion batteries in Examples 1-6.

[0027] Figure 2 This is a cross-sectional view of the composite coated separator for a lithium-ion battery in Example 7.

[0028] Figure 3 This is a SEM schematic diagram of the composite coated separator for the lithium-ion battery in Example 1.

[0029] The reference numerals in the figures include:

[0030] 1-Porous polymer base membrane, 2-Inorganic ceramic layer, 3-First coating surface, 31-First adhesive polymer microsphere, 32-First supporting polymer microsphere, 4-Second coating surface, 41-Second adhesive polymer microsphere, 42-Second supporting polymer microsphere. Detailed Implementation

[0031] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0032] In an embodiment of the present invention, a lithium-ion battery composite coated separator includes a polymer porous base membrane 1, a first coating surface 3, and a second coating surface 4; the first coating surface 3 is disposed on the upper surface of the polymer porous base membrane 1, and the second coating surface 4 is disposed on the lower surface of the polymer porous base membrane 1; the first coating surface 3 includes a plurality of first adhesive polymer microspheres 31 and a plurality of first supporting polymer microspheres 32, the first adhesive polymer microspheres 31 and the first supporting polymer microspheres 32 being arranged on the upper surface of the polymer porous base membrane 1; the second coating surface 4 includes a plurality of second adhesive polymer microspheres 41, the second adhesive polymer microspheres 41 being arranged on the lower surface of the polymer porous base membrane 1.

[0033] The lithium-ion battery composite coated separator of the present invention comprises a first coating surface 3 and a second coating surface 4 formed on a polymer porous base membrane 1. The first coating surface 3 includes a plurality of first adhesive polymer microspheres 31 and a plurality of first supporting polymer microspheres 32, and the second coating surface 4 includes a plurality of second adhesive polymer microspheres 41. The adhesive polymer microspheres in the composite coated separator mainly provide adhesion between the separator and the electrode, ensuring that the cell does not deform during cycling. The supporting polymer microspheres in the composite coated separator provide good support, ensuring that a certain gap is maintained between the separator and the electrode after hot pressing, thereby improving the liquid retention performance of the cell.

[0034] In one embodiment of the present invention, the second coating surface 4 further includes a plurality of second supporting polymer microspheres 42, which are bonded to the lower surface of the polymer porous base film 1.

[0035] In one embodiment of the present invention, the lithium-ion battery composite coated separator further includes an inorganic ceramic layer, which is disposed between the first coating surface 3 and the polymer porous base film 1.

[0036] Furthermore, both the first adhesive polymer microspheres 31 and the first supporting polymer microspheres 32 are bonded to the upper surface of the inorganic ceramic layer 2, and multiple first adhesive polymer microspheres 31 and first supporting polymer microspheres 32 are arranged sequentially. Each first adhesive polymer microsphere 31 is adjacent to another first adhesive polymer microsphere 31 and / or first supporting polymer microsphere 32. Due to the above structure, the first coating surface 3, by employing the first adhesive polymer microspheres 31, can improve the adhesion between the lithium-ion battery separator and the electrode, and by employing the first supporting polymer microspheres 32, it can provide support, helping to ensure that a certain gap is maintained between the separator and the electrode after hot pressing, improving the liquid retention performance of the battery cell, and achieving both high liquid retention and high adhesion. Preferably, the first adhesive polymer microspheres 31 and the first supporting polymer microspheres 32 are arranged alternately in sequence, and the first adhesive polymer microspheres 31 and the first supporting polymer microspheres 32 are bonded to the upper surface of the inorganic ceramic layer 2.

[0037] Furthermore, the second adhesive polymer microspheres 41 and the second supporting polymer microspheres 42 are bonded to the lower surface of the polymer porous base film 1, and multiple second adhesive polymer microspheres 41 and second supporting polymer microspheres 42 are arranged sequentially. Each second adhesive polymer microsphere 41 is adjacent to another second adhesive polymer microsphere 41 and / or second supporting polymer microsphere 42. Due to the above structure, the second coating surface 4, by employing the second adhesive polymer microspheres 41, can improve the adhesion between the lithium-ion battery separator and the electrode, and by employing the second supporting polymer microspheres 42, it plays a supporting role, which helps to maintain a certain gap between the separator and the electrode after hot pressing, improves the liquid retention performance of the battery cell, and balances high liquid retention and high adhesion. Preferably, the second adhesive polymer microspheres 41 and the second supporting polymer microspheres 42 are arranged alternately in sequence, and the second adhesive polymer microspheres and the second supporting polymer microspheres 42 are bonded to the lower surface of the polymer porous base film 1.

[0038] Furthermore, the polymer porous base membrane 1 is a polyolefin porous membrane. This invention uses a polyolefin porous membrane as the base membrane and coats an inorganic ceramic layer 2 on the surface of the polyolefin porous membrane, resulting in a lithium-ion battery composite coated separator with advantages such as good heat resistance and low internal resistance.

[0039] In one embodiment of the present invention, both the first coating surface 3 and the second coating surface 4 are made of an aqueous adhesive coating liquid, which comprises the following raw materials in parts by weight: 2.0-8 parts of supporting polymer microspheres, 2-10 parts of adhesive polymer microspheres, 0.1-2 parts of adhesive, 0.1-1.0 parts of dispersant, 0.1-1.0 parts of wetting agent, and 100 parts of water.

[0040] In one embodiment of the present invention, the adhesive is at least one selected from polymethacrylic acid, polymethyl methacrylate, styrene-butadiene rubber, polyurethane, epoxy resin, acrylic polymer, acrylate polymer or acrylonitrile polymer.

[0041] In one embodiment of the present invention, the wetting agent is at least one of fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, fluoroalkyl methoxy ether alcohol, fluoroalkyl ethoxy ether alcohol or alkylphenol polyoxyethylene ether.

[0042] In one embodiment of the present invention, the dispersant is at least one of polyacrylate, polyethylene glycol ether, and phosphate compound.

[0043] In one embodiment of the present invention, the mass ratio of the supporting polymer microspheres to the adhesive polymer microspheres is 0.3-4:1.

[0044] In one embodiment of the present invention, the particle size D50 of both the first adhesive polymer microsphere 31 and the second adhesive polymer microsphere 41 is 0.5-8 μm. The lithium-ion battery composite coated separator of the present invention, by using one or more of the following materials with a particle size D50 of 0.5-8 μm: polyacrylates, PVDF, SBR, butyl rubber, nitrile rubber, and natural rubber, helps to improve the adhesion between the separator and the electrode, thereby improving product performance.

[0045] In one embodiment of the present invention, the particle size D50 of the first supporting polymer microsphere 32 and the second supporting polymer microsphere 42 is 2-10 μm.

[0046] In one embodiment of the present invention, the adhesive polymer microspheres are one or more selected from polyacrylates, PVDF, SBR, butyl rubber, nitrile rubber, and natural rubber, preferably polyacrylate polymer microspheres. The supporting polymer microspheres are one or more selected from PMMA, silicone, SBR, and PVDF, preferably PMMA polymer microspheres. The lithium-ion battery composite coated separator of this embodiment uses the aforementioned supporting microspheres as fulcrums on the first coating surface 3, which helps to improve the supporting performance, thereby ensuring that a certain gap is maintained between the separator and the electrode after hot pressing, improving the electrolyte retention performance of the battery cell.

[0047] Furthermore, the polyacrylate polymer adhesive microspheres adopt a core-shell structure design, with the microsphere core having a partial glass transition temperature >50℃ and a crosslinking degree >10%; and the microsphere shell having a partial glass transition temperature <60℃ and a crosslinking degree of 4% <20%.

[0048] Furthermore, the glass transition temperature of the supporting PMMA polymer microspheres is >80°C, and the melting temperature is >200°C.

[0049] In one embodiment of the present invention, a method for preparing a composite coated separator for a lithium-ion battery includes the following steps:

[0050] (1) Preparation of aqueous coating liquid for adhesive layer;

[0051] (2) Apply the water-based adhesive coating liquid to both sides of the polymer porous base membrane 1 to form the first coating surface 3 and the second coating surface 4.

[0052] (3) Curing and drying to obtain a lithium-ion battery composite coated separator.

[0053] Furthermore, in step (2), the solid content of the aqueous coating liquid is 1-20 wt%.

[0054] In one embodiment of the present invention, a method for preparing a composite coated separator for a lithium-ion battery includes the following steps:

[0055] (1) Preparation of aqueous coating liquid for adhesive layer;

[0056] (2) The inorganic ceramic coating is applied to the upper surface of the polymer porous base membrane 1 and dried to form an inorganic ceramic layer 2; the water-based coating liquid is applied to the upper surface of the inorganic ceramic layer 2 and the lower surface of the polymer porous base membrane 1 to form a first coating surface 3 and a second coating surface 4.

[0057] (3) Curing and drying to obtain a lithium-ion battery composite coated separator.

[0058] Specific embodiments 1-6 and comparative examples 1-2 of the present invention are as follows: The coated membranes in the following embodiments and comparative examples are all composed of a polyolefin porous membrane, a first coating surface 3, and a second coating surface 4, with the first coating surface 3 and the second coating surface 4 located on opposite sides of the polyolefin porous membrane. The first coating surface 3 and the second coating surface 4 are made from an aqueous adhesive coating liquid, with the aqueous adhesive coating liquid content in Examples 1-6 being 1-20 wt%. The aqueous adhesive coating liquid comprises the following raw materials in parts by weight: 2.0-8 parts of supporting polymer microspheres PMMA, 2-10 parts of polyacrylate adhesive polymer microspheres, 0.1-2 parts of adhesive, 0.1-1.0 parts of dispersant, 0.1-1.0 parts of wetting agent, and 100 parts of water. The polyacrylate adhesive polymer microspheres adopt a core-shell structure design, with the microsphere core having a partial glass transition temperature >50℃ and a crosslinking degree >10%; and the microsphere shell having a partial glass transition temperature <60℃ and a crosslinking degree of 4% <20%. The PMMA microspheres have a glass transition temperature > 80°C and a melting temperature > 200°C.

[0059] In Examples 1-3, the supporting polymer microspheres were PMMA microspheres with a D50 particle size of 2.0 μm, and the binding polymer microspheres were polyacrylate microspheres with a D50 particle size of 0.6 μm. In Examples 4-6, the supporting polymer microspheres had a D50 particle size of 5.5 μm, and the binding polymer had a D50 particle size of 6.3 μm. The PVDF microspheres used were polyvinylidene fluoride with a weight-average molecular weight of 300,000-800,000. The PMMA microspheres had a glass transition temperature > 80°C and a melting temperature > 200°C. The coating method in Examples 1-6 was gravure coating.

[0060] The aqueous coating layers of Comparative Examples 1 and 2 had a liquid-to-solid content of 1-20 wt%. The solid components included adhesive polymer microspheres, adhesives, dispersants, and wetting agents. The adhesive polymer microspheres were acrylate polymers. The D50 particle size of Comparative Example 1 was 300-400 nm, and the D50 particle size of Comparative Example 2 was 5-7 μm. The coating method for Comparative Example 1 was gravure coating, and the coating method for Comparative Example 2 was spin coating.

[0061] The raw material composition and weight ratio of the aqueous coating liquid for Examples 1-6 and Comparative Examples 1-2 are shown in Table 1 below:

[0062]

[0063] Furthermore, the adhesive is polyacrylic acid, the dispersant is sodium polyacrylate, and the wetting agent is fatty alcohol polyoxyethylene ether.

[0064] The performance of Examples 1-6 and Comparative Examples 1-2 was characterized, and the performance characteristics included thickness, air permeability, heat shrinkage, adhesive strength, and cycle performance.

[0065] (I) Thickness Comparison

[0066] The thickness of the adhesive layer before and after hot pressing was tested using the following method: Composite films from Examples 1-6 and Comparative Examples 1-2, as well as the base film used to prepare the examples, were tested for thickness before hot pressing. The sample size was 100mm × 100mm (MD × TD). A micrometer was used for testing, and the test results were a1, a2, and a3, respectively. Then, the films were hot-pressed at 80℃ / 1MPa for 30 minutes, and the thicknesses of the diaphragms after hot pressing were b1, b2, and b3, respectively. The thickness of the adhesive layer before and after hot pressing was then calculated using the following formulas: Thickness of the adhesive layer before hot pressing = Thickness of the coated film before hot pressing - Thickness of the base film; Thickness of the adhesive layer after hot pressing = Thickness of the coated film after hot pressing - Thickness of the base film. The test results are shown in Table 2 below.

[0067] Example Thickness of adhesive layer before hot pressing / μm Thickness of adhesive layer after hot pressing / μm Example 1 1.0 0.7 Example 2 1.5 1.3 Example 3 1.2 0.8 Example 4 0.9 0.6 Example 5 2.5 1.9 Example 6 2.4 2.2 Comparative Example 1 1.0 0.5 Comparative Example 2 3.9 2.0

[0068] Comparing the thicknesses of Examples 1-3 and Comparative Example 1, the thickness of the coating before and after hot pressing gradually increases with the increase of the weight ratio of supporting polymer to binding polymer in the water-based adhesive layer. Comparing the thicknesses of Examples 4-6 and Comparative Example 2, the thickness of the coating before and after hot pressing also gradually increases with the increase of the weight ratio of supporting polymer to binding polymer in the water-based adhesive layer. Comparing Examples 1-3 and Examples 4-6 reveals that when the weight ratio of supporting polymer to binding polymer in the water-based adhesive layer is the same, the particle size of the supporting polymer microspheres and binding polymer microspheres is larger, resulting in a greater coating thickness before and after hot pressing. Comparing Examples 1-6 and Comparative Examples 1-2 shows that the thickness after hot pressing in Examples 1-3 is greater than that of the PVDF roll-coated separator but less than that of the PVDF spray-coated separator; while the thickness of the water-based adhesive layer after hot pressing in Examples 5-6 is basically equivalent to that of the PVDF spray-coated separator after hot pressing.

[0069] (ii) Breathability

[0070] The air permeability of Examples 1-6 and Comparative Example 1 was compared by testing the diaphragms. Specifically, the air permeability test method is as follows: Measurement method: The composite diaphragms of Examples 1 to 6 and Comparative Example 1 were tested for air permeability. The sample size was 100mm × 100mm (MD × TD). An Asahi Kasei air permeability meter was used. The test results are shown in Table 3 below:

[0071]

[0072]

[0073] As can be seen from Examples 1-6, the increase in air permeability of the water-based coating layer does not significantly increase with the increase in the proportion of supporting polymer and binding polymer in the water-based coating layer. A comparison of Examples 1-6 with Comparative Example 1 shows that the air permeability increase of the composite-coated diaphragm is smaller than that of the PVDF roll-coated diaphragm, while a comparison of Examples 1-6 with Comparative Example 2 shows that the air permeability increase of the composite-coated diaphragm is not significantly different from that of the PVDF spray-coated diaphragm.

[0074] (III) Adhesion

[0075] Positive electrode preparation: Lithium manganese oxide, polyvinylidene fluoride, acetylene black, and NMP were mixed and stirred to form a slurry, which was then coated on both sides of aluminum foil and dried to obtain the positive electrode. Hot pressing: The positive electrode, separator, positive electrode, separator, etc., were stacked sequentially to 4 layers. After cooling at 80℃ and 1MPa for 30 min, the peel force between the separator and the electrode was tested. The peel force (N / m) test results are shown in Table 4 below.

[0076]

[0077] As can be seen from Table 4, the dry-press adhesion of the diaphragm coated with acrylate adhesive polymer is significantly greater than that of the water-based PVDF gravure-coated diaphragm and the spray-coated diaphragm. Furthermore, the dry-press adhesion of the coating decreases slightly as the particle size of the supporting polymer microspheres in the diaphragm coating increases.

[0078] (iv) Cyclic performance

[0079] Using the polymer separators of Examples 1-6 and Comparative Examples 1 and 2 described above, along with lithium cobalt oxide positive electrode sheets and graphite negative electrode sheets, soft-pack lithium-ion batteries were fabricated using a winding process and subjected to cycle testing.

[0080] Cyclic testing: At room temperature, the lithium-ion battery was charged to 4.4V at constant currents of 1.0C, 3.0C, and 5.0C, respectively, then charged at constant voltage until the current dropped to 0.05C (cutoff point), and then discharged to 3.0V at 1.0C. This cycle was repeated 1000 times. The test results are shown in Table 5 below.

[0081]

[0082] The results of the above cyclic tests show that, regardless of whether it is a 1C, 2C or 3C system, the thickness expansion of Examples 1-6 is less than that of Comparative Example 2; and under the 2C and 3C fast charging systems, the capacity retention rate of Examples 1-6 is greater than that of Comparative Example 1.

[0083] The present invention also provides Embodiment 7, which differs from Embodiment 1 in that: the lithium-ion battery composite coated separator further includes an inorganic ceramic layer, which is disposed between the first coating surface 3 and the polymer porous base membrane 1, and the first adhesive polymer microspheres 31 and the first supporting polymer microspheres 32 are arranged on the upper surface of the inorganic ceramic layer of the polymer porous base membrane 1. The preparation method of the lithium-ion battery composite coated separator in Embodiment 7 includes the following steps:

[0084] (1) Preparation of aqueous coating liquid for adhesive layer;

[0085] (2) The inorganic ceramic coating is applied to the upper surface of the polymer porous base membrane 1 and dried to form an inorganic ceramic layer 2; the water-based coating liquid is applied to the upper surface of the inorganic ceramic layer 2 and the lower surface of the polymer porous base membrane 1 to form a first coating surface 3 and a second coating surface 4.

[0086] (3) Curing and drying to obtain a lithium-ion battery composite coated separator.

[0087] The lithium-ion battery composite coated separator of the present invention comprises a first coating surface 3 and a second coating surface 4 formed on a polymer porous base membrane 1. The first coating surface 3 includes a plurality of first adhesive polymer microspheres 31 and a plurality of first supporting polymer microspheres 32, and the second coating surface 4 includes a plurality of second adhesive polymer microspheres 41. The adhesive polymer microspheres in the composite coated separator mainly provide adhesion between the separator and the electrode, ensuring that the cell does not deform during cycling. The supporting polymer microspheres in the composite coated separator provide good support, ensuring that a certain gap is maintained between the separator and the electrode after hot pressing, thus improving the electrolyte retention performance of the cell. The lithium-ion battery composite coated separator has good adhesion and cycle performance. The preparation method of the lithium-ion battery composite coated separator is easy to control, has high production efficiency, and produces a stable product quality, which can improve the stability and safety performance of lithium-ion batteries during use and is conducive to large-scale industrial production.

[0088] The above description is only a preferred embodiment of the present invention. For those skilled in the art, there will be changes in the specific implementation and application scope based on the ideas of the present invention. The content of this specification should not be construed as a limitation of the present invention.

Claims

1. A composite coated separator for lithium-ion batteries, characterized in that: It includes a polymer porous base membrane, a first coating surface, and a second coating surface; the first coating surface is disposed on the upper surface of the polymer porous base membrane, and the second coating surface is disposed on the lower surface of the polymer porous base membrane; the first coating surface includes a plurality of first adhesive polymer microspheres and a plurality of first supporting polymer microspheres, and the first adhesive polymer microspheres and the first supporting polymer microspheres are arranged on the upper surface of the polymer porous base membrane; The second coating surface includes a plurality of second adhesive polymer microspheres arranged on the lower surface of the polymer porous base membrane; the second coating surface also includes a plurality of second supporting polymer microspheres bonded to the lower surface of the polymer porous base membrane. The particle size D50 of both the first and second adhesive polymer microspheres is 0.5-8 μm; The particle size D50 of the first and second supported polymer microspheres is 2-10 μm; Both the first and second coating surfaces are made of an aqueous adhesive coating liquid, which comprises the following raw materials in parts by weight: 2.0-8 parts of supporting polymer microspheres, 2-10 parts of adhesive polymer microspheres, 0.1-2 parts of adhesive, 0.1-1.0 parts of dispersant, 0.1-1.0 parts of wetting agent, and 100 parts of water; The supporting polymer microspheres are PMMA-supported microspheres; the glass transition temperature of the PMMA-supported microspheres is >80℃, and the melting temperature is >200℃. The adhesive polymer microspheres are polyacrylate polymer adhesive microspheres; the polyacrylate polymer adhesive microspheres adopt a core-shell structure design, with the glass transition temperature of the core portion of the microsphere being >50℃ and the glass transition temperature of the shell portion being <70℃. The adhesive is at least one of polymethacrylic acid, polymethyl methacrylate, styrene-butadiene rubber, polyurethane, epoxy resin, acrylate polymer, acrylic polymer or acrylonitrile polymer; The wetting agent is at least one of fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, fluoroalkyl methoxy ether alcohol, fluoroalkyl ethoxy ether alcohol or alkylphenol polyoxyethylene ether. The dispersant is at least one of polyacrylate, polyethylene glycol ether, and phosphate compound.

2. The lithium-ion battery composite coated separator according to claim 1, characterized in that: The mass ratio of the supporting polymer microspheres to the binding polymer microspheres is 0.3-4:

1.

3. The lithium-ion battery composite coated separator according to claim 1, characterized in that: The lithium-ion battery composite coated separator also includes an inorganic ceramic layer, which is disposed between the first coating surface and the polymer porous base film. The first adhesive polymer microspheres and the first supporting polymer microspheres are arranged on the upper surface of the inorganic ceramic layer.

4. A method for preparing a lithium-ion battery composite coated separator as described in any one of claims 1-3, characterized in that: Includes the following steps: (1) Preparation of aqueous coating liquid for adhesive layer; (2) Apply an aqueous coating liquid to both sides of the polymer porous base membrane to form a first coating surface and a second coating surface; or apply an inorganic ceramic coating to the upper surface of the polymer porous base membrane and dry it to form an inorganic ceramic layer. An aqueous coating liquid is applied to the upper surface of an inorganic ceramic layer and the lower surface of a polymer porous base film to form a first coating surface and a second coating surface. (3) Curing and drying to obtain a lithium-ion battery composite coated separator.

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