Coated separator and preparation method therefor

Abstract

The present invention relates to the technical field of battery separators. Disclosed are a coated separator and a preparation method therefor. A mixed coating of polyethylene wax and ceramic is applied on the separator, and the separator quickly achieves pore closure at a low temperature, thereby forming a novel multifunctional lithium-ion battery separator having high fast-charging safety.

Description

A coated diaphragm and its preparation method Technical Field

[0001] This invention relates to the field of battery separator technology, and in particular to a coated separator and its preparation method. Background Technology

[0002] With the widespread application of lithium-ion batteries in new energy vehicles, higher requirements have been placed on the performance of lithium batteries. As a safety component inside the lithium battery that controls the passage of particulate ions, the separator directly affects the cycle life and safety performance of the battery. Currently, ceramics or high-temperature resistant polymers are commonly used as thermal management coatings for polyolefin separators.

[0003] The thermal safety of the separator is primarily affected by its melting point. Currently used polyolefin membrane materials exhibit deterioration in mechanical properties at high temperatures, leading to pores and potentially causing thermal runaway and explosions due to direct contact between the positive and negative electrodes. This fails to meet the safety requirements of high-power batteries. Modifying the separator can allow micropores to close before thermal runaway occurs, forming a barrier layer to restrict ion transport and shut down the battery reaction, thus protecting the battery. The temperature at which the micropores close is the pore-closing temperature, so a lower pore-closing temperature is desirable. Furthermore, simultaneously improving the separator's heat resistance will significantly enhance the battery's safety and stability in high-temperature environments.

[0004] Therefore, it is of great significance to prepare diaphragms with low pore closure temperature and high membrane rupture temperature. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a coated diaphragm and its preparation method. The coating uses a combination of a thermosensitive material and ceramic particles, further uses a combination of a thermosensitive material and two types of ceramic particles, and then further uses a combination of a thermosensitive material, fluorine-free polymer particles, and ceramic particles of two different particle sizes. This not only allows for pore closure at lower temperatures and rapid response to thermal runaway, but also results in a higher pore breaking temperature and better thermal stability.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] The first aspect of the present invention provides a coated diaphragm, comprising: a base film and a coating layer covering one or both sides of the base film;

[0008] The coating layer comprises inorganic particles and a thermosensitive material with a melting point of 80-140℃;

[0009] The mass ratio of inorganic particles to thermosensitive materials is 40-80:10-40.

[0010] The particle size D(50) of the inorganic particles and the particle size D3(50) of the thermosensitive material satisfy the following relationship: D3(50)≤2D(50); D(50)=400-1000nm.

[0011] Preferably, the closed-cell temperature of the coated diaphragm of the present invention is ≤130℃;

[0012] The difference between the air permeability of the coated diaphragm at the closed-cell temperature and at room temperature is 700-1000s / 100cc.

[0013] The thermal shrinkage rate of the coated diaphragm of this invention is ≤5%.

[0014] This invention combines inorganic particles and thermosensitive materials in a specific ratio, with both having a particle size D50 that meets certain requirements. The resulting coated separator has a low pore-closing temperature. Before thermal runaway occurs, it relies on a phase change mechanism to create micropores between the electrodes, forming a barrier layer to restrict ion transport and thus shutting off the battery reaction. This enables a rapid response to thermal runaway.

[0015] The first aspect of the present invention also provides a coated diaphragm, comprising: a base film and a coating layer covering one or both sides of the base film;

[0016] The coating layer comprises first inorganic particles, second inorganic particles, and a thermosensitive material with a melting point of 80-140℃;

[0017] The mass ratio of the first inorganic particles, the second inorganic particles, and the thermosensitive material is 12-48:12-48:10-40.

[0018] The particle size D1 (50) of the first inorganic particle, the particle size D2 (50) of the second inorganic particle, and the particle size D3 (50) of the thermosensitive material satisfy the following relationship:

[0019] D1(50)≤D3(50)≤≤2D1(50)≤D2(50);

[0020] Preferably, D1(50) = 400-500nm, D2(50) = 800-1000nm.

[0021] Preferably, the closed-cell temperature of the coated diaphragm of the present invention is ≤120℃;

[0022] The difference between the air permeability of the coated diaphragm at the closed-cell temperature and at room temperature is 1000-2000s / 100cc.

[0023] The thermal shrinkage rate of the coated diaphragm of this invention is ≤3%.

[0024] This invention further combines two inorganic particles of different particle sizes and a thermosensitive material in a specific ratio. The particle size of the thermosensitive material is no more than twice the particle size of the smaller ceramic particle and is smaller than the particle size of the larger ceramic particle. That is, when there is a relationship of D1(50)≤D3(50)≤2D1(50)≤D2(50), the two ceramic particles of different particle sizes can form a denser coating. The coating is easier to cure after the thermosensitive material is melted. After treatment under the same temperature conditions, the air permeability is 2-3 times higher than that of a coating with a single particle size, and the closed-cell effect is better.

[0025] The first aspect of the present invention further provides a coated diaphragm, comprising: a base film and a coating layer covering one or both sides of the base film;

[0026] The coating layer comprises first inorganic particles, second inorganic particles, a thermosensitive material with a melting point of 80-140℃, and fluorine-free polymer particles;

[0027] The mass ratio of the first inorganic particles, the second inorganic particles, the thermosensitive material, and the fluoropolymer particles is 12-48:12-48:10-40:1-20.

[0028] The particle sizes D1(50) of the first inorganic particle, D2(50) of the second inorganic particle, D3(50) of the thermosensitive material, and D4(50) of the fluoropolymer particle satisfy the following: D1(50)≤D3(50)≤≤2D1(50)≤D2(50)<D4(50); D1(50)=400-500nm, D2(50)=800-1000nm, D4(50)=2000-6000nm.

[0029] Preferably, the membrane rupture temperature of the coated diaphragm of the present invention is ≥190℃, the pore-closure temperature is ≤120℃, and the difference between the membrane rupture temperature and the pore-closure temperature is ≥70℃.

[0030] The difference between the air permeability of the coated diaphragm at the closed-cell temperature and at room temperature is 2000-3000s / 100cc.

[0031] The thermal shrinkage rate of the coated diaphragm of this invention is ≤3%.

[0032] Fluoropolymer particles can provide some support in the coating. After the polyethylene wax melts, it only solidifies in the coating and does not directly affect the pore structure of the base film. The melting of fluoropolymer particles can also help the polyethylene wax to quickly open up the pores after melting.

[0033] The present invention further combines two inorganic particles, a thermosensitive material and a fluorine-free polymer particle in a specific ratio, and the particle size satisfies D1(50)≤D3(50)≤2D1(50)≤D2(50)<D4(50). The resulting coated diaphragm not only has a better pore-closing temperature, but also a higher pore-breaking temperature and good thermal stability.

[0034] Descriptions of the base film in the above three cases (unless otherwise specified, the base film in all three cases is described below):

[0035] The base film is a thermoplastic material, including but not limited to any one of polyethylene porous membrane, polypropylene porous membrane, polyethylene / polypropylene mixed porous membrane, and polyimide porous membrane.

[0036] There is no particular limitation on the thickness of the base film; for example, it can be 4-20 μm.

[0037] There is no particular limitation on the average pore size of the base film; for example, it can be 10-40 nm.

[0038] There are no particular limitations on the porosity of the base membrane; for example, it can be 30-50%. The porosity of the base membrane can be tested according to the method specified in GB / T36363-2018.

[0039] There are no particular limitations on the air permeability of the base membrane; for example, it can be 50-300s / 100cc.

[0040] Explanation of the coating layers in the above three cases:

[0041] First scenario:

[0042] The coating layer comprises inorganic particles in a mass ratio of 40-80:10-40 and a thermosensitive material with a melting point of 80-140℃.

[0043] The inorganic particles are selected from any one or more of α-alumina, γ-alumina, boehmite, calcium carbonate, barium sulfate, hydrotalcite, montmorillonite, spinel, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide, magnesium hydroxide, calcium hydroxide, and silicon carbide.

[0044] Preferably, the particle size D(50) of the inorganic particles is in the range of 400-1000 nm.

[0045] The mass fractions of inorganic particles are, for example, 40, 42, 45, 46, 48, 50, 52, 54, 55, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 75, 76, 78, and 80 parts.

[0046] The heat-sensitive material with a melting point of 80-140℃ is selected from any one or more of polyethylene wax, polypropylene wax, and polyethylene oxide wax.

[0047] The particle size D(50) of the inorganic particles and the particle size D3(50) of the thermosensitive material satisfy the following relationship: D3(50)≤2D(50); D(50)=400-1000nm.

[0048] The mass fractions of the heat-sensitive material are, for example, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, and 40 parts.

[0049] The second scenario:

[0050] The coating layer comprises a first inorganic particle, a second inorganic particle, and a thermosensitive material with a melting point of 80-140℃, in a mass ratio of 12-48:12-48:10-40.

[0051] The first inorganic particle and the second inorganic particle are each independently selected from any one or more of α-alumina, γ-alumina, boehmite, calcium carbonate, barium sulfate, hydrotalcite, montmorillonite, spinel, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide, magnesium hydroxide, calcium hydroxide, and silicon carbide.

[0052] Preferably, the particle size D1(50) of the first inorganic particle is 400-500 nm, for example 450 nm, and the particle size D2(50) of the second inorganic particle is 800-1000 nm, for example 950 nm.

[0053] The mass fractions of the first inorganic particles are, for example, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, 46, and 48 parts; the mass fractions of the second inorganic particles are, for example, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, 42, 45, 46, and 48 parts, and preferably the mass ratio of the first inorganic particles to the second inorganic particles is 4:6.

[0054] The heat-sensitive material with a melting point of 80-140℃ is selected from any one or more of polyethylene wax, polypropylene wax, and polyethylene oxide wax.

[0055] The particle size D1 (50) of the first inorganic particle, the particle size D2 (50) of the second inorganic particle, and the particle size D3 (50) of the thermosensitive material satisfy the following relationship:

[0056] D1(50)≤D3(50)≤2D1(50)≤D2(50); Preferably, the particle size D3(50) of the thermosensitive material is 500-800nm, for example 700nm.

[0057] The mass fractions of the heat-sensitive material are, for example, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, and 40 parts.

[0058] The third scenario:

[0059] The coating layer comprises a first inorganic particle, a second inorganic particle, a thermosensitive material with a melting point of 80-140℃, and fluorine-free polymer particles in a mass ratio of 12-48:12-48:10-40:1-20.

[0060] The first inorganic particle and the second inorganic particle are each independently selected from any one or more of α-alumina, γ-alumina, boehmite, calcium carbonate, barium sulfate, hydrotalcite, montmorillonite, spinel, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide, magnesium hydroxide, calcium hydroxide, and silicon carbide.

[0061] Preferably, the particle size D1(50) of the first inorganic particle is 400-500 nm, for example 450 nm, and the particle size D2(50) of the second inorganic particle is 800-1000 nm, for example 950 nm.

[0062] The mass fractions of the first inorganic particles are, for example, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, 46, and 48 parts; the mass fractions of the second inorganic particles are, for example, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, 42, 45, 46, and 48 parts, and preferably the mass ratio of the first inorganic particles to the second inorganic particles is 4:6.

[0063] The heat-sensitive material with a melting point of 80-140℃ is selected from any one or more of polyethylene wax, polypropylene wax, and polyethylene oxide wax.

[0064] The mass fractions of the heat-sensitive material are, for example, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, and 40 parts.

[0065] The fluorine-free polymer particles are selected from any one or more of polymethyl methacrylate (PMMA), thermoplastic polyurethane elastomer rubber (TPU), and polyethylene terephthalate (PET).

[0066] The mass fractions of the fluoropolymer particles are, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 parts.

[0067] The particle sizes D1 (50) of the first inorganic particles, D2 (50) of the second inorganic particles, D3 (50) of the thermosensitive material, and D4 (50) of the fluoropolymer particles satisfy the following relationship:

[0068] D1(50)≤D3(50)≤2D1(50)≤D2(50)<D4(50);

[0069] Preferably, the particle size D3(50) of the thermosensitive material is in the range of 500-800 nm, for example 700 nm.

[0070] Preferably, the particle size D4(50) of the fluoropolymer particles is in the range of 2000-8000 nm, for example 5000 nm.

[0071] It should be noted that D1(50) represents the D50 particle size of the first inorganic particle; D2(50) represents the D50 particle size of the second inorganic particle, and so on.

[0072] Other descriptions of the coating layers in the above three cases (unless otherwise specified, the coating layers in all three cases are described below):

[0073] The coating may also include an adhesive.

[0074] The adhesive is selected from any one or more of polyacrylic acid, polyacrylate, and polyurethane.

[0075] There is no particular limitation on the thickness of the coating layer; for example, it can be 1-3 μm.

[0076] A second aspect of the present invention provides a method for preparing the above-mentioned coated diaphragm, comprising the following steps:

[0077] Mix 40-80 parts by weight of inorganic particles (12-48 parts by weight of the first inorganic particles and 12-48 parts by weight of the second inorganic particles) and 90-220 parts by weight of deionized water thoroughly, stir at room temperature (15-30°C), then add 1-20 parts by weight of optional fluoropolymer particles, stir evenly, then add 2-8 parts by weight of binder, 0.02-0.5 parts by weight of optional dispersant, and 0.1-2 parts by weight of optional thickener, stir evenly, and finally add 10-40 parts by weight of heat-sensitive material, stir evenly to obtain the coating slurry;

[0078] The coating slurry is coated onto the base membrane and dried to obtain the coated diaphragm.

[0079] The dispersant is selected from any one or more of polyvinyl alcohol (PVA), acrylate copolymer (ACA), polyethylene glycol octylphenyl ether (Triton X-100, T-100), polyvinylpyrrolidone (PVP), and carboxymethyl cellulose (CMC).

[0080] The thickener is selected from any one or more of sodium alginate, cellulose (carboxymethyl cellulose, nanocellulose, carboxypropyl cellulose), natural gum, and starch.

[0081] Coating methods include, but are not limited to, micro-gravure roller coating and wire bar coating.

[0082] The drying process uses hot air drying, with a preferred drying temperature of 40-80℃. Beneficial effects:

[0083] This invention combines inorganic particles and thermosensitive materials in a specific ratio, with both having a particle size D50 that meets certain requirements. The resulting coated separator has a low pore-closing temperature. Before thermal runaway occurs, it relies on a phase change mechanism to create micropores between the electrodes, forming a barrier layer to restrict ion transport and thus shutting off the battery reaction. This enables a rapid response to thermal runaway.

[0084] The present invention further combines two inorganic particles and a thermosensitive material in a specific ratio, and when there is a relationship of D1(50)≤D3(50)≤2D1(50)≤D2(50), the two ceramics with different particle sizes can form a denser coating. The coating is easier to cure after the thermosensitive material is melted. After treatment under the same temperature conditions, the air permeability is 2-3 times higher than that of a coating with a single particle size, and the closed-cell effect is better.

[0085] The present invention further combines two inorganic particles, a thermosensitive material and a fluorine-free polymer particle in a specific ratio, and when there is a relationship of D1(50)≤D3(50)≤2D1(50)≤D2(50)<D4(50), the obtained coated diaphragm not only has a better closed-cell temperature, but also a higher pore breaking temperature and good thermal stability.

[0086] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Detailed Implementation

[0087] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0088] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0089] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0090] Test method:

[0091] Closing temperature and film breaking temperature:

[0092] The test was conducted using a diaphragm closed-cell membrane rupture tester (Dongguan Bairui Automation Co., Ltd., ART-GMT-35). The test method was as follows: the sample was cut into 40mm×40mm pieces. Using a syringe, 3-5 drops of electrolyte were dripped into the center of the base plate of the test fixture. The diaphragm was then laid flat in the center of the base plate, allowing the electrolyte to fully wet the diaphragm. A ceramic plate was placed on top of the diaphragm, with the end of the ceramic plate with small holes facing outwards. Electrolyte was then added into the small holes of the ceramic plate using a syringe. An electrode plate was then placed on the ceramic plate. Electrolyte was added into the center hole of the electrode plate from bottom to top using a syringe, with the liquid level slightly higher than the electrode plate. The air in the center hole was expelled. The pressure cap was then placed on top, the pressure head was tightened, and the sample was placed in an oven. The oven door was then closed. A staged heating method was used. Stage 1 involved raising the internal temperature to 110℃, with a heating rate of 7℃ / min for the internal temperature chamber and 1℃ / min for the fixture. Stage 2 involved raising the internal temperature to 200℃, with a heating rate of 3℃ / min for the internal temperature chamber and 0℃ / min for the fixture. Under these conditions, the battery resistance was tested. The temperature recorded when the resistance instantaneously rose to 1000Ω was the pore-closing temperature of the separator. The temperature recorded when the resistance continued to rise and then fell back to 1000Ω was the pore-breaking temperature.

[0093] Heat shrinkage rate: Tested according to the method specified in GB / T12027-2004.

[0094] Breathability: Tested according to the method specified in GB / T 1038.

[0095] The air permeability value at closed-cell temperature refers to the air permeability value of the diaphragm after it has been placed at the closed-cell temperature for 30-60 seconds and then removed.

[0096] The air permeability value at room temperature refers to the air permeability value of the diaphragm after it has been placed at room temperature for 30-60 seconds and then removed.

[0097] Examples 1-3 and Comparative Examples 1-3: Ceramic + Thermosensitive Material

[0098] (1) Mix boehmite and deionized water thoroughly, and stir for 1 hour at room temperature (25°C).

[0099] (2) Add polyacrylic acid emulsion binder (Hunan Gaorui Power Materials Co., Ltd., brand name LIB-S105B, solid content 45%), polyacrylate emulsion binder (Japan Zeon Co., Ltd., brand name BM5000, solid content 20.5%), polyvinyl alcohol emulsion dispersant (solid content 45%), and carboxymethyl cellulose (CMC) emulsion thickener (Suzhou Fosai New Materials Co., Ltd., brand name 1220, prepared as an aqueous solution with a concentration of 4% by weight before use) to the solution obtained in step (1) and stir evenly to obtain a mixed solution;

[0100] (3) Add polyethylene wax emulsion (Weng Kai'er Company, model E-842N, solid content 39%) to the solution obtained in step (2) and stir evenly to obtain coating slurry;

[0101] (4) The coating slurry obtained in step (3) is coated on both sides of a polyethylene diaphragm (wet-process synchronous biaxially oriented polyethylene with a porosity of 34%, a pore size of 20nm, and an air permeability of 145s / 100cc), and the diaphragm is obtained after thorough drying.

[0102] Examples 4-6 and Comparative Examples 4-6: Two types of ceramic + thermosensitive materials with different particle sizes

[0103] (1) Mix the first boehmite, the second boehmite and deionized water thoroughly, and stir for 1 hour at room temperature (25°C).

[0104] (2) Add polyacrylic acid emulsion binder, polyacrylate emulsion binder, polyvinyl alcohol emulsion dispersant, and carboxymethyl cellulose (CMC) emulsion thickener to the solution obtained in step (1) and stir until uniform to obtain a mixed solution;

[0105] (3) Add the solution obtained in step (2) to polyethylene wax emulsion and stir evenly to obtain coating slurry;

[0106] (4) The coating slurry obtained in step (3) is coated on both sides of a polyethylene diaphragm (wet-process synchronous biaxially oriented polyethylene with a porosity of 34%, a pore size of 20nm, and an air permeability of 145s / 100cc), and the diaphragm is obtained after thorough drying.

[0107] Examples 7-9 and Comparative Examples 7-9: two particle sizes of ceramic + thermosensitive material + fluorine-free polymer particles

[0108] (1) Mix the first boehmite, the second boehmite and deionized water thoroughly, and stir for 1 hour at room temperature (25°C).

[0109] (2) Add the solution obtained in step (1) to polymethyl methacrylate large particle glue and stir evenly to obtain a polymethyl methacrylate and ceramic mixed solution;

[0110] (3) Add polyacrylic acid emulsion binder, polyacrylate emulsion binder, polyvinyl alcohol emulsion dispersant, and carboxymethyl cellulose (CMC) emulsion thickener to the solution obtained in step (2) and stir until uniform to obtain a mixed solution;

[0111] (4) Add the solution obtained in step (3) to polyethylene wax emulsion and stir evenly to obtain coating slurry;

[0112] (5) The coating slurry obtained in step (4) is coated on both sides of a polyethylene diaphragm (wet-process synchronous biaxially oriented polyethylene with a porosity of 34%, a pore size of 20m, and an air permeability of 145s / 100cc), and the diaphragm is obtained after thorough drying.

[0113] The specific formulations and parameters of the examples and comparative examples are shown in Tables 1-3.

[0114] The test results of the examples and comparative examples are shown in Table 4.

[0115] Table 1

[0116] Table 2

[0117] Table 3

[0118] Table 4

[0119] Compared to PE-based films and diaphragms without added heat-sensitive materials, the diaphragm of this invention exhibits a lower pore-closing temperature and a significantly higher pore-breaking temperature. By adjusting the amount of heat-sensitive material added and its relationship with the particle size of inorganic particles, a coated diaphragm with better pore-closing effect is obtained. Furthermore, the combination of two specific inorganic particles further enhances the pore-closing effect and thermal stability of the diaphragm; the addition of fluorine-free polymer particles further enhances the pore-closing effect of the diaphragm.

[0120] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A coated diaphragm, characterized in that, include: The base film and the coating layer covering one or both sides of the base film; The coating layer comprises inorganic particles and a thermosensitive material with a melting point of 80-140℃; The mass ratio of inorganic particles to thermosensitive materials is 40-80:10-40. The particle size D(50) of the inorganic particles and the particle size D3(50) of the thermosensitive material satisfy the following relationship: D3(50)≤2D(50); D(50)=400-1000nm.

2. The coated diaphragm according to claim 1, characterized in that, The closed-cell temperature of the coated diaphragm is ≤130℃; and / or The difference between the air permeability of the coated diaphragm at closed-cell temperature and at room temperature is 700-1000 s / 100cc; and / or The heat shrinkage rate of the coated diaphragm is ≤5%.

3. A coated diaphragm, characterized in that, include: The base film and the coating layer covering one or both sides of the base film; The coating layer comprises first inorganic particles, second inorganic particles, and a thermosensitive material with a melting point of 80-140℃; The mass ratio of the first inorganic particles, the second inorganic particles, and the thermosensitive material is 12-48:12-48:10-40. The particle size D1 (50) of the first inorganic particle, the particle size D2 (50) of the second inorganic particle, and the particle size D3 (50) of the thermosensitive material satisfy the following relationship: D1(50)≤D3(50)≤≤2D1(50)≤D2(50); D1(50)=400-500nm, D2(50)=800-1000nm.

4. The coated diaphragm according to claim 3, characterized in that, The closed-cell temperature of the coated diaphragm is ≤120℃; and / or The difference between the air permeability of the coated diaphragm at closed-cell temperature and at room temperature is 1000-2000 s / 100cc; and / or The heat shrinkage rate of the coated diaphragm is ≤3%.

5. A coated diaphragm, characterized in that, include: The base film and the coating layer covering one or both sides of the base film; The coating layer comprises first inorganic particles, second inorganic particles, a thermosensitive material with a melting point of 80-140℃, and fluorine-free polymer particles; The mass ratio of the first inorganic particles, the second inorganic particles, the thermosensitive material, and the fluoropolymer particles is 12-48:12-48:10-40:1-20. The particle sizes D1 (50) of the first inorganic particles, D2 (50) of the second inorganic particles, D3 (50) of the thermosensitive material, and D4 (50) of the fluoropolymer particles satisfy the following relationship: D1(50)≤D3(50)≤2D1(50)≤D2(50)<D4(50); D1(50)=400-500nm, D2(50)=800-1000nm, D4(50)=2000-6000nm.

6. The coated diaphragm according to claim 5, characterized in that, The membrane rupture temperature is ≥190℃, the pore-closure temperature is ≤120℃, and the difference between the rupture temperature and the pore-closure temperature is ≥70℃; and / or The difference between the air permeability of the coated diaphragm at closed-cell temperature and at room temperature is 2000-3000 s / 100cc; and / or The heat shrinkage rate of the coated diaphragm is ≤3%.

7. The coated diaphragm according to claim 5, characterized in that, The fluorine-free polymer particles are selected from any one or more of polymethyl methacrylate (PMMA), thermoplastic polyurethane elastomer rubber (TPU), and polyethylene terephthalate (PET).

8. The coated diaphragm according to any one of claims 1-4, characterized in that, The heat-sensitive material with a melting point of 110-120℃ is selected from any one or more of polyethylene wax, polypropylene wax, and polyethylene oxide wax.

9. A method for preparing a coated diaphragm according to any one of claims 1-8, characterized in that, Includes the following steps: Mix 40-80 parts by weight of inorganic particles and 90-220 parts by weight of deionized water thoroughly, stir at room temperature (15-30°C), then add 1-20 parts by weight of optional non-fluorinated polymer particles, stir evenly, then add 2-8 parts by weight of binder, 0.02-0.5 parts by weight of optional dispersant, and 0.1-2 parts by weight of optional thickener, stir evenly, and finally add 10-40 parts by weight of heat-sensitive material, stir evenly to obtain coating slurry; The coating slurry is coated onto the base membrane and dried to obtain the coated diaphragm.

10. The preparation method according to claim 9, characterized in that, The adhesive is selected from any one or more of polyacrylic acid, polyacrylate, and polyurethane. The dispersant is selected from any one or more of polyvinyl alcohol (PVA), acrylate copolymer (ACA), polyethylene glycol octylphenyl ether (Triton X-100), polyvinylpyrrolidone (PVP), and carboxymethyl cellulose (CMC); The thickener is selected from any one or more of sodium alginate, cellulose, natural gum, and starch.

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