Separator, preparation method therefor, and use thereof

Abstract

A separator, a preparation method therefor, and a use thereof. The separator comprises a substrate and a coating layer disposed on at least one surface of the substrate. The coating layer comprises inorganic particles and polymer microspheres. The mass ratio of the inorganic particles to the polymer microspheres is 1:(0.25–4). An inner layer and an outer layer of the coating layer each independently have inorganic particles and polymer microspheres distributed therein. In the inner layer of the coating layer, the number of the inorganic particles is greater than that of the polymer microspheres. In the outer layer of the coating layer, the number of the inorganic particles is less than that of the polymer microspheres. The separator has both high adhesion and excellent thermal stability, and exhibits good wettability, and a battery comprising said separator has good safety performance.

Description

A diaphragm, its preparation method and application Technical Field

[0001] This application relates to the field of lithium-ion battery technology, such as a separator, its preparation method, and its application. Background Technology

[0002] The separator is a crucial component of lithium-ion batteries. Its primary function is to separate the positive and negative electrodes, preventing short circuits caused by contact between them. It also allows electrolyte ions to pass through. Using a high-performance separator is one of the effective ways to achieve high-performance lithium-ion batteries.

[0003] The most common separators used in lithium-ion batteries are polyolefin separators, such as polyethylene separators, polypropylene separators, or composite separators formed by polyethylene and polypropylene. However, polyolefin separators have poor thermal stability and are prone to large-area shrinkage or melting at high temperatures, which can lead to thermal runaway or short circuits inside the battery, thus affecting battery safety. Furthermore, polyolefin separators have poor wettability to the electrolyte, affecting the battery's cycle performance. In addition, polyolefin separators have poor adhesion properties. Therefore, to obtain high-performance separators, it is usually necessary to modify the separator, such as by applying polymer coatings and / or ceramic coatings to the surface of the base membrane, thereby improving the relevant performance of the separator.

[0004] However, the modified diaphragms in the relevant technologies still cannot simultaneously achieve the desired adhesion, thermal stability, wettability, and safety performance of the diaphragm.

[0005] Therefore, developing a separator that combines high adhesion, excellent thermal stability, and good wettability, while also improving battery safety performance, is an urgent problem to be solved in this field. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] This application provides a separator, its preparation method, and its application. The separator exhibits both high adhesion and excellent thermal stability, as well as good wetting properties, resulting in high battery safety performance.

[0008] In a first aspect, this application provides a diaphragm, comprising a substrate and a coating layer disposed on at least one surface of the substrate, the coating layer comprising inorganic particles and polymer microspheres; the mass ratio of the inorganic particles to the polymer microspheres is 1:(0.25-4); the inner and outer layers of the coating layer are each independently distributed with inorganic particles and polymer microspheres, the number of inorganic particles in the inner layer of the coating layer being greater than the number of polymer microspheres; and the number of inorganic particles in the outer layer of the coating layer being less than the number of polymer microspheres.

[0009] In this application, the coating layer includes inorganic particles and polymer microspheres. By controlling the mass ratio of inorganic particles to polymer microspheres within a specific range and controlling the number of inorganic particles in the inner layer of the coating layer to be greater than the number of polymer microspheres, and the number of inorganic particles in the outer layer to be less than the number of polymer microspheres, the separator can achieve both excellent adhesion and thermal stability, as well as good wetting properties. In addition, since the number of inorganic particles in the inner layer of the coating layer is greater than the number of polymer microspheres, the number of polymer microspheres in the outer layer of the coating layer is greater than the number of inorganic particles. When the battery experiences a short circuit and releases a large amount of heat, the polymer microspheres melt, causing the separator to close its pores, thereby improving the safety performance of the battery.

[0010] In this application, the mass ratio of the inorganic particles to the polymer microspheres is 1:(0.25-4), where the specific values ​​of (0.25-4) can be, for example, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, etc.

[0011] In this application, if the content of inorganic particles in the outer layer of the coating is too high, it will further reduce the adhesion performance; if the content is too low, the thermal stability performance will be poor.

[0012] In this application, the inner layer of the coating refers to the side closer to the substrate; the outer layer of the coating refers to the side farther from the substrate; the method for testing the number of inorganic particles and polymer microspheres in the outer or inner layer of the coating includes: freezing the diaphragm with liquid nitrogen, cutting it to obtain a cross-section, then analyzing the morphology of the cross-section using a scanning electron microscope, and using Origin software to determine the percentage of particles with different sizes (i.e., inorganic particles and polymer microspheres) in the inner or outer layer.

[0013] In one embodiment, with the total number of inorganic particles and polymer microspheres in the inner layer of the coating layer being 100%, the percentage of inorganic particles in the inner layer of the coating layer is 60% to 90%, for example, it can be 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, etc.

[0014] In one embodiment, with the total number of inorganic particles and polymer microspheres in the outer layer of the coating layer being 100%, the percentage of polymer microspheres in the outer layer of the coating layer is 70% to 99%, for example, it can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, etc.

[0015] In this application, the number of polymer microspheres in the outer layer of the coating is within the above-mentioned range, which is beneficial to improving the adhesion of the diaphragm.

[0016] In one embodiment, the ratio of the D50 particle size of the inorganic particles to the D50 particle size of the polymer microspheres is 0.15 to 0.8, for example, it can be 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.33, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, etc.

[0017] In this application, the ratio of the D50 particle size of the inorganic particles to the D50 particle size of the polymer microspheres is within the above-mentioned range, which can further improve the adhesion of the membrane; if the particle size of the inorganic particles is too large, the adhesion will be low; and if the particle size of the inorganic particles is too large, the content of inorganic particles in the outer layer of the coating will increase, which will further reduce the adhesion.

[0018] In one embodiment, the polymer microspheres include a first polymer microsphere and a second polymer microsphere, wherein the D50 particle size of the first polymer microsphere is greater than the D50 particle size of the second polymer microsphere.

[0019] In this application, when two types of polymer microspheres are selected, the ratio of the D50 particle size of the inorganic particles to the D50 particle size of any one type of polymer microsphere is in the range of 0.15 to 0.8.

[0020] In one embodiment, the mass ratio of the first polymer microsphere and the second polymer microsphere is ≤0.6, and can be, for example, 0.05, 0.06, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5, 0.52, 0.55, 0.58, 0.6, etc.; it can be selected as 0.2 to 0.5.

[0021] In this application, two polymer microspheres with different D50 particle sizes are used and their mass ratio is controlled within a specific range. This increases the proportion of polymer microspheres in the outer layer of the coating, resulting in small polymer microspheres being evenly distributed between the large polymer microspheres in the outer layer. This maximizes the contact area between the polymer microspheres in the separator and the electrode, further improving adhesion and wettability of the separator. Furthermore, because the outer layer is covered with polymer microspheres, when a short circuit occurs and a large amount of heat is released, the polymer microspheres melt, causing the separator to close its pores and improving battery safety.

[0022] In one embodiment, the D50 particle size of the inorganic particles is 0.05 to 1 μm, for example, it can be 0.05 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, etc.

[0023] In one embodiment, the inorganic particles have a D50 particle size of 0.1 to 0.8 μm, and the inorganic particles include at least one of boehmite, alumina, calcium oxide, barium sulfate, silicon dioxide, or silicon carbide.

[0024] In one embodiment, the D50 particle size of the polymer microspheres is 0.5 to 3 μm, for example, it can be 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, etc.

[0025] In this application, the D50 particle size can be tested using a TopSizer particle size analyzer.

[0026] In one embodiment, the melting point (T) of the polymer microspheres is 105-120°C, for example, it can be 105°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, etc.

[0027] In one embodiment, the polymer microspheres include at least one of polyethylene wax microspheres, modified polyethylene wax microspheres, polyvinylidene fluoride microspheres, or polymethacrylate microspheres.

[0028] In this application, the modified polyethylene wax microspheres refer to polyethylene wax microspheres with molecular chain side chains grafted onto their surface to increase the length of the molecular chain side chains, such as grafting long chain groups such as butyl and octyl.

[0029] In one embodiment, the coating layer further includes an adhesive.

[0030] In one embodiment, the mass ratio of the binder to the inorganic particles is (0.1 to 0.5):1, wherein the specific values ​​of (0.1 to 0.5) can be, for example, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.25, 0.30, 0.4, 0.45, 0.5, etc.

[0031] In one embodiment, the glass transition temperature (Tg) of the adhesive is -70 to -4°C, for example, it can be -70°C, -65°C, -60°C, -55°C, -50°C, -45°C, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -4°C, etc.

[0032] In one embodiment, the adhesive comprises alkyl acrylate adhesives and their modifications, and / or alkyl methacrylate adhesives and their modifications. In one embodiment, the alkyl acrylate comprises at least one selected from ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, or 2-ethylhexyl acrylate; the alkyl methacrylate comprises hexyl methacrylate.

[0033] In this application, the alkyl acrylate binder and alkyl methacrylate binder refer to alkyl acrylate polymers and alkyl methacrylate polymers, which can be homopolymers or copolymers; the phrase "and its modified products" refers to (meth)acrylate alkyl acrylate binders and / or their modified products; the modified product refers to grafting modification of (meth)acrylate alkyl acrylate binders, grafting side chains into their molecular structure to increase the length of the molecular chain side chains, such as grafting long-chain groups such as butyl and octyl.

[0034] In this application, the alkyl acrylate includes at least one of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, or 2-ethylhexyl acrylate; the alkyl methacrylate includes hexyl methacrylate.

[0035] In this application, polymer microspheres with specific melting points and binders with specific glass transition temperatures are used to further improve the adhesion of the diaphragm.

[0036] In this application, the melting point and glass transition temperature can be tested by differential scanning calorimetry.

[0037] In one embodiment, the thickness of the coating layer is ≥0.7μm, for example, it can be 0.7μm, 0.8μm, 0.9μm, 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm, 3μm, etc.; the thickness of the inner layer of the coating layer is ≥0.2μm, for example, it can be 0.2μm, 0.4μm, 0.6μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm, 2.2μm, 2.4μm, etc.

[0038] In this application, the thickness of the outer layer of the coating is the D50 particle size range of the polymer microspheres (in μm), and the thickness of the inner layer is the coating thickness minus the outer layer thickness.

[0039] In this application, the thickness of the substrate is 3 to 16 μm, for example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, etc.

[0040] In one embodiment, the substrate includes at least one of a polypropylene substrate, a polyethylene substrate, and a multilayer composite substrate of polypropylene and polyethylene.

[0041] In a second aspect, this application provides a method for preparing a diaphragm according to the first aspect, the method comprising: S1: providing a substrate; S2: preparing a slurry for coating, coating the obtained slurry onto at least one surface of the substrate, and drying to obtain the diaphragm; the coating process further comprises an oscillation process.

[0042] In this application, the method for preparing the diaphragm involves adding an oscillation process during coating, which enables inorganic particles to be deposited on the inner side of the coating, while polymer microspheres are distributed on the outer layer of the coating.

[0043] In one embodiment, the method for preparing the slurry includes: mixing inorganic particles, polymer microspheres and solvent evenly to obtain the slurry.

[0044] In one embodiment, the solvent includes at least one of water, acetone, ethanol, and N-methylpyrrolidone (NMP).

[0045] In one embodiment, the solid content of the slurry is 25% to 90%, for example, it can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

[0046] In one embodiment, the mixed material further includes a binder and / or additives.

[0047] In one embodiment, the mass percentage of the additives in the slurry is 0.02% to 15%, for example, it can be 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, etc.

[0048] In one embodiment, the adjuvant includes a wetting agent and / or a dispersant.

[0049] In one embodiment, the oscillation is performed using a coating machine.

[0050] In one embodiment, the oscillation frequency of the coating machine is 0.1 to 2 Hz, for example, it can be 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz, 0.5 Hz, 0.6 Hz, 0.7 Hz, 0.8 Hz, 0.9 Hz, 1 Hz, 1.1 Hz, 1.2 Hz, 1.3 Hz, 1.4 Hz, 1.5 Hz, 1.6 Hz, 1.7 Hz, 1.8 Hz, 1.9 Hz, 2 Hz, etc.

[0051] In this application, the proportion of inorganic particles and polymer microspheres in the inner and outer layers of the coating is adjusted by controlling the oscillation frequency of the coating machine.

[0052] In this application, the oscillation frequency of the coating machine can be obtained by adjusting the speed and speed ratio of the coating machine.

[0053] In this application, the speed of the coating machine is 80-120 m / min, for example, it can be 80 m / min, 82 m / min, 84 m / min, 86 m / min, 88 m / min, 90 m / min, 92 m / min, 94 m / min, 96 m / min, 98 m / min, 100 m / min, 102 m / min, 104 m / min, 106 m / min, 108 m / min, 110 m / min, 112 m / min, 114 m / min, 116 m / min, 118 m / min, 120 m / min, etc.

[0054] In this application, the speed ratio of the coating machine is 0.8 to 1.2, for example, it can be 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 1, 1.02, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, 1.16, 1.18, 1.2, etc.

[0055] In one embodiment, the drying temperature is 50-80°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc.

[0056] Thirdly, this application provides a battery, the battery comprising the separator described in the first aspect or the separator prepared by the preparation method described in the second aspect.

[0057] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0058] Compared with related technologies, the beneficial effects of this application are as follows:

[0059] The separator provided in this application has a coating layer comprising inorganic particles and polymer microspheres. By controlling the mass ratio of inorganic particles to polymer microspheres within a specific range and controlling the number of inorganic particles in the inner layer of the coating layer to be greater than the number of polymer microspheres, the separator can achieve both excellent adhesion and thermal stability, as well as good wetting properties and high battery safety performance.

[0060] After reading, understanding, and describing it in detail, other aspects can be understood. Detailed Implementation

[0061] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0062] All materials used in this application are commercially available or prepared using conventional methods. Unless otherwise specified, the materials used in this application are as follows:

[0063] polymer microspheres

[0064] Polyethylene wax microspheres 1: melting point 105℃, D50≤0.53μm, purchased from Guangzhou Zhuhai Carbon Language New Materials Co., Ltd.

[0065] Polyethylene wax microspheres 2: melting point 118℃, D50≤2μm, purchased from Guangzhou Zhuhai Carbon Language New Materials Co., Ltd.

[0066] Polyethylene wax microspheres 3: melting point 100℃, D50 particle size 1μm, custom-made.

[0067] Polyethylene wax microspheres 4: melting point 124℃, D50 particle size 1μm, custom-made.

[0068] adhesive

[0069] Isobutyl acrylate adhesive, with a glass transition temperature of -4°C, was purchased from Maclean Chemicals.

[0070] n-Butyl methacrylate adhesive, with a glass transition temperature of 20°C, was purchased from Merck Life Sciences.

[0071] 2-Ethylhexyl acrylate adhesive, with a glass transition temperature of -70°C, was purchased from Merck Life Sciences.

[0072] Boehmite of different particle sizes was purchased from Xinke New Materials Co., Ltd.

[0073] Wetting agent: SY-190 from Guangdong Fangding New Materials Co., Ltd.

[0074] Dispersant: 8823 from Shenzhen Yanyi New Materials Co., Ltd.

[0075] Example 1

[0076] This embodiment provides a diaphragm, comprising a substrate (a 7μm thick polyethylene substrate, Shenzhen Xingyuan Material Technology Co., Ltd.) and a coating layer (1.8μm thick) disposed on one surface of the substrate; the coating layer comprises polyethylene wax microspheres 2 (T = 118℃, D50 particle size = 1μm), boehmite particles (D50 particle size = 0.5μm), and 2-ethylhexyl acrylate binder 4 (Tg = -70℃); the mass ratio of boehmite particles to polyethylene wax microspheres is 1:1, and the D50 particle size ratio is 0.5; the mass ratio of 2-ethylhexyl acrylate binder to boehmite particles is 0.1:1.

[0077] This embodiment provides a method for preparing a diaphragm, specifically including the following steps:

[0078] According to the formula, polyethylene wax microspheres, boehmite particles, 2-ethylhexyl acrylate binder, wetting agent, and dispersant are mixed evenly with solvent to obtain a slurry with a solid content of 14.5%. The slurry contains 0.15% by mass of wetting agent and 1.5% by mass of dispersant. The slurry is coated onto one surface of a substrate. During the coating process, the speed and speed ratio of the coating machine are controlled to ensure that the oscillation frequency of the coating machine is 1Hz. Then, it is dried at 60°C to obtain the diaphragm.

[0079] Examples 2-14, Comparative Examples 1-4

[0080] Examples 2-14 and Comparative Examples 1-4 each provide a diaphragm, differing from Example 1 only in the coating layer. The thickness of the coating layer, the mass ratio of polymer microspheres to inorganic particles in the coating layer, the mass ratio of inorganic particles to binder, the D50 particle size ratio of inorganic particles to polymer microspheres, the composition of polymer microspheres, and the mass percentage content of inorganic particles and polymer microspheres in the outer and inner layers of the coating layer are shown in Tables 1-4. " / " indicates that the component is not in the formulation. When two different polymer microspheres with different D50 particle sizes are included, the total amount of polymer microspheres remains unchanged. The only difference in the preparation method of the diaphragm is the oscillation frequency of the coating machine, with specific parameters shown in Tables 1-4. " / " in the preparation method indicates that this step is not performed. All other unspecified parameters are the same as in Example 1.

[0081] Table 1

[0082] Table 2

[0083] Table 3

[0084] Table 4

[0085] Performance testing

[0086] (1) Adhesion: The separators and positive and negative electrode sheets provided in Examples 1 to 14 and Comparative Examples 1 to 4 were cut to the same size. Then, the positive electrode sheet, separator and negative electrode sheet were bonded together and cold-pressed at 60°C and 6.5MPa for 60s. The separator was stretched at a speed of 200mm / min using a stretching machine to test the adhesion between the separator and the negative electrode sheet.

[0087] (2) Thermal stability: The diaphragms provided in Examples 1-14 and Comparative Examples 1-4 were cut into 160×130mm sizes. A 100×100mm square was drawn in the middle of each diaphragm. Five sheets of paper were placed on the top and bottom of the diaphragm. After placing them in an oven at 130℃ for 1 hour, the shrinkage rate of the diaphragm in the MD direction was tested.

[0088] (3) Air permeability increment: The air permeability of the diaphragm and substrate provided in Examples 1-14 and Comparative Examples 1-4 was tested with an air permeability instrument. The air permeability increment was obtained by subtracting the air permeability of the substrate from the air permeability of the diaphragm.

[0089] (4) Wettability: Cut the diaphragm into a 10×10mm square, place it on a glass slide and stretch it with tape to keep the membrane surface flat. Use a syringe to take 2 microliters of propylene carbonate and drop it onto the diaphragm sample. Measure the MD droplet diameter at 0 min and 5 min and calculate the diffusion layer width. Diffusion layer width = MD droplet diameter at 5 min - MD droplet diameter at 0 min.

[0090] The specific test results are shown in Table 5:

[0091] Table 5

[0092] As shown in Table 5, the diaphragm provided in this application has a coating layer comprising inorganic particles and polymer microspheres. By controlling the mass ratio of inorganic particles to polymer microspheres within a specific range, and by controlling the number of inorganic particles in the inner layer of the coating layer to be greater than the number of polymer microspheres, and the number of inorganic particles in the outer layer of the coating layer to be less than the number of polymer microspheres, the diaphragm can achieve both excellent adhesion and thermal stability, as well as good wetting properties. The adhesion force between the diaphragm and the negative electrode sheet is ≥6 N / m, and can even reach 15 N / m or more; the thermal shrinkage rate is ≤1.5%, and can even be as low as 0.4% or less; the diffusion layer width is ≥2.8 mm.

[0093] As can be seen from Comparative Examples 1 to 4, when the mass ratio of inorganic particles to polymer microspheres is not within a specific range, or when the number of inorganic particles and polymer microspheres in the inner and outer layers of the coating does not meet a specific quantitative content relationship, the adhesion performance, thermal stability, air permeability, or wettability of the diaphragm deteriorates.

[0094] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A diaphragm, comprising a substrate and a coating layer disposed on at least one surface of the substrate, wherein, The coating layer comprises inorganic particles and polymer microspheres; The mass ratio of the inorganic particles to the polymer microspheres is 1:(0.25-4); The inner and outer layers of the coating layer each contain independently distributed inorganic particles and polymer microspheres. The number of inorganic particles in the inner layer of the coating layer is greater than the number of polymer microspheres, while the number of inorganic particles in the outer layer of the coating layer is less than the number of polymer microspheres.

2. The diaphragm according to claim 1, wherein, With the total number of inorganic particles and polymer microspheres in the inner layer of the coating layer being 100%, the percentage of inorganic particles in the inner layer of the coating layer is 60-90%.

3. The diaphragm according to claim 1 or 2, wherein, With the total number of inorganic particles and polymer microspheres in the outer layer of the coating layer being 100%, the percentage content of polymer microspheres in the outer layer of the coating layer is 70-99%.

4. The diaphragm according to any one of claims 1-3, wherein, The ratio of the D50 particle size of the inorganic particles to the D50 particle size of the polymer microspheres is 0.15 to 0.

8.

5. The diaphragm according to any one of claims 1-4, wherein, The polymer microspheres include a first polymer microsphere and a second polymer microsphere, wherein the D50 particle size of the first polymer microsphere is greater than the D50 particle size of the second polymer microsphere. Optionally, the mass ratio of the first polymer microsphere and the second polymer microsphere is ≤0.6, and can be 0.2 to 0.

5.

6. The diaphragm according to any one of claims 1-5, wherein, The inorganic particles have a D50 particle size of 0.05–1 μm.

7. The diaphragm according to claim 6, wherein, The inorganic particles have a D50 particle size of 0.1 to 0.8 μm, and the inorganic particles include at least one of boehmite, alumina, calcium oxide, barium sulfate, silicon dioxide, or silicon carbide.

8. The diaphragm according to any one of claims 1-7, wherein, The D50 particle size of the polymer microspheres is 0.5–3 μm; Optionally, the melting point of the polymer microspheres is 105–120°C; Optionally, the polymer microspheres include at least one of polyethylene wax microspheres, modified polyethylene wax microspheres, polyvinylidene fluoride microspheres, or polymethacrylate microspheres.

9. The diaphragm according to any one of claims 1-8, wherein, The coating layer also includes an adhesive; Optionally, the mass ratio of the binder to the inorganic particles is (0.1 to 0.5):1; Optionally, the glass transition temperature of the adhesive is -70 to -4°C; Optionally, the adhesive includes alkyl acrylate adhesives and their modifications, and / or alkyl methacrylate adhesives and their modifications; Optionally, the alkyl acrylate includes at least one of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, or 2-ethylhexyl acrylate; the alkyl methacrylate includes hexyl methacrylate.

10. The diaphragm according to any one of claims 1-9, wherein, The thickness of the coating layer is ≥0.7μm, and the thickness of the inner layer of the coating layer is ≥0.2μm.

11. A method for preparing a diaphragm according to any one of claims 1-10, comprising: S1: Provides substrate; S2: Prepare a slurry for the coating layer, and coat the obtained slurry onto at least one surface of the substrate, and dry it to obtain the diaphragm; The coating process also includes a vibration process.

12. The preparation method according to claim 11, wherein, The method for preparing the slurry includes: mixing inorganic particles, polymer microspheres and solvent evenly to obtain the slurry; Optionally, the solvent includes at least one of water, acetone, ethanol, and N-methylpyrrolidone; Optionally, the solid content of the slurry is 25% to 90%.

13. The preparation method according to claim 12, wherein, The mixed materials also include binders and / or additives; Optionally, the mass percentage of the additives in the slurry is 0.02-15%; Optionally, the additives include wetting agents and / or dispersants.

14. The preparation method according to any one of claims 11-13, wherein, The oscillation is performed using a coating machine; Optionally, the oscillation frequency of the coating machine is 0.1 to 2 Hz; Optionally, the drying temperature is 50–80°C.

15. A battery, wherein, The battery includes the separator according to any one of claims 1-10 or the separator prepared by the preparation method according to any one of claims 11-14.

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