Isolation film and preparation method and application thereof

Abstract

The application provides an isolation film and a preparation method and application thereof, comprising a base film and a bonding layer; the bonding layer is coated on at least one surface of the base film, and the bonding layer comprises a first bonding agent and polymer particles; wherein D50 of the polymer particles is greater than the thickness of the bonding layer, and the compression ratio of the polymer particles is 20-90%. Compared with the prior art, the isolation film provided by the application adds polymer particles in the bonding layer, the D50 of the polymer particles is greater than the thickness of the bonding layer, and the compression ratio of the polymer particles is 20-90%, which effectively solves the problem that the current isolation film bonding layer is prone to film formation after swelling in electrolyte and heat pressing in the formation process, improves the rate performance and cycle life of the lithium ion battery while ensuring the bonding force of the bonding agent.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, specifically to a separator membrane, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in 3C digital products and electric vehicles due to their high energy density, good rate performance, and environmental friendliness. A lithium-ion battery mainly consists of a positive electrode, a negative electrode, a separator, an electrolyte, and an aluminum-plastic film. The separator plays a crucial role in conducting ions, isolating the positive and negative electrodes, and preventing short circuits.

[0003] As end-users demand increasingly higher charging rates for lithium-ion batteries, higher kinetic performance of the separator is also required. Currently, the adhesive coating on the separator surface is prone to forming a film and blocking pores after swelling in the electrolyte and hot pressing during the formation process, affecting the rate performance and cycle performance of lithium-ion batteries. Furthermore, during cycling, the untimely transfer of free electrolyte between the separator and the electrode can easily cause lithium plating on the anode surface, severely impacting the cycle life of lithium-ion batteries.

[0004] To overcome these problems, there are currently two main approaches: one is to increase the cross-linking degree of the binder, thereby reducing its swelling degree in the electrolyte; the other is to adjust the conditions of the formation process, such as lowering the formation temperature, reducing the formation pressure, or shortening the formation time. However, both of these approaches can easily lead to a decrease in the adhesion between the separator and the electrode, thereby reducing the hardness of the lithium-ion battery and increasing the risk of battery deformation.

[0005] In view of this, it is indeed necessary to provide a technical solution to the above problems. Summary of the Invention

[0006] One of the objectives of this invention is to provide a separator that solves the problem that the adhesive layer of current separators easily forms a film after swelling in the electrolyte and hot pressing during the formation process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A separating membrane, comprising:

[0009] Base film;

[0010] An adhesive layer, coated on at least one surface of the base film, comprises a first adhesive and polymer particles;

[0011] Wherein, the D50 of the polymer particles is greater than the thickness of the adhesive layer, and the compression ratio of the polymer particles is 20-90%.

[0012] Preferably, the adhesive layer has a network structure on the base film; the polymer particles are distributed in the adhesive layer in an island-like manner.

[0013] Preferably, the polymer particles have a spherical structure and / or a spherical structure; the polymer particles are at least one of polypropylene microspheres, polyethylene microspheres, polystyrene microspheres, and their corresponding modified polymer microspheres.

[0014] Preferably, the value of D50 of the polymer particles is: 1.2 * the thickness of the adhesive layer ≤ the D50 of the polymer particles ≤ 1.9 * the thickness of the adhesive layer.

[0015] Preferably, the thickness of the adhesive layer is 1 to 3 μm.

[0016] Preferably, the mass ratio of the first binder to the polymer particles is 0.1 to 0.9.

[0017] Preferably, the first adhesive is one or more of the following: polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene ether, epoxy resin, and epoxy resin derivatives.

[0018] Preferably, the thickness of the base membrane is 3–200 μm; the porosity of the base membrane is 20–80%; and the air permeability of the base membrane is 50–200 s / 100cc.

[0019] Preferably, the separator further includes a heat-resistant layer coated between the base film and the adhesive layer; the heat-resistant layer includes a second adhesive and an inorganic filler.

[0020] Preferably, the second adhesive is polymerized from at least one monomer selected from ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, and maleic acid; and the inorganic filler is at least one of alumina, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

[0021] A second objective of this invention is to provide a method for preparing the separator membrane described in any of the above claims, comprising the following steps:

[0022] S1. Dissolve the first adhesive to form a particle-free first adhesive solution;

[0023] S2. Add polymer particles to the first adhesive solution and stir to obtain the first slurry;

[0024] S3. The first slurry is coated onto at least one surface of the base film and dried to obtain a separating film.

[0025] Preferably, in step S3, the coating method of the first slurry is as follows: firstly, the first slurry is coated onto at least one surface of the base film using a micro-recessed coating method, and then placed in a coagulation bath for washing with water and drying to obtain a separation film.

[0026] A third objective of this invention is to provide an electrochemical device comprising a positive electrode, a negative electrode, and a separator, wherein the separator is any of the separators described above.

[0027] Compared to existing technologies, the advantages of this invention are as follows: The separator provided by this invention incorporates polymer particles in the adhesive layer. The D50 of these polymer particles is greater than the thickness of the adhesive layer, and the compression ratio of the polymer particles is 20-90%. Thus, during electrolyte swelling or hot pressing in the formation process, the polymer particles preferentially bear the force, effectively preventing the adhesive from being hot-pressed into a film, ensuring the adhesive strength, and consequently guaranteeing the hardness of the lithium-ion battery and reducing the risk of battery deformation. Furthermore, the presence of polymer particles increases the gap between the separator and the electrode, promoting electrolyte transport on the separator surface, especially enhancing the ability of free electrolyte to replenish the battery during cycling, thereby improving the rate performance and cycle life of the lithium-ion battery. Attached Figure Description

[0028] Figure 1 This is one of the structural schematic diagrams of the isolation membrane of the present invention.

[0029] Figure 2 This is the second schematic diagram of the structure of the separator membrane of the present invention.

[0030] In the figure: 1-base film; 2-adhesive layer; 21-first adhesive; 22-polymer particles; 3-heat resistant layer. Detailed Implementation

[0031] The first aspect of the present invention provides a separating membrane, comprising a base membrane 1 and an adhesive layer 2; the adhesive layer 2 is coated on at least one surface of the base membrane 1, and the adhesive layer 2 comprises a first adhesive 21 and polymer particles 22; wherein the D50 of the polymer particles 22 is greater than the thickness of the adhesive layer 2, and the compression ratio of the polymer particles 22 is 20 to 90%.

[0032] Preferably, the D50 of the polymer particles 22 is less than twice the thickness of the adhesive layer 2. The compression ratio of the polymer particles 22 can be 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, or 80-90%, and more preferably, the compression ratio of the polymer particles 22 is 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%.

[0033] By setting the particle size and compression ratio of the polymer particles 22 within the aforementioned range, on the one hand, at least half of the polymer particles 22 have a particle size greater than the thickness of the adhesive layer 2. In this case, during hot pressing, the polymer particles 22 will be subjected to force preferentially over the adhesive, thereby effectively reducing the risk of adhesive film formation. On the other hand, the polymer particles 22 have a high compression ratio. When subjected to force preferentially, the higher the compression ratio, the better they can withstand the pressure of hot pressing and the swelling of the electrolyte, thereby further reducing the risk of adhesive film formation.

[0034] Furthermore, the adhesive layer has a network structure on the base film 1; the polymer particles 22 are distributed in an island-like pattern within the adhesive layer 2. This network structure primarily refers to the network distribution of the adhesive within the adhesive layer. Compared to conventional dot-distributed adhesives, the network structure increases the contact area between the adhesive and the electrode, while also improving the electrolyte retention capacity of the adhesive layer 2. The network structure adhesive can be prepared through microgravure coating and coagulation bath phase separation. The island-like polymer particles 22 can be accommodated within the network structure adhesive, not only receiving preferential stress compared to the adhesive but also providing support and stabilizing the overall structure of the adhesive layer 2.

[0035] Furthermore, the polymer particles 22 have a spherical and / or near-spherical structure; the polymer particles 22 are at least one of polypropylene microspheres, polyethylene microspheres, polystyrene microspheres, and their corresponding modified polymer microspheres. Spherical or near-spherical polymer particles 22 exhibit better load-bearing and buffering effects. In addition, the polymer particles 22 also possess electrolyte resistance, improving electrolyte retention through the structure of the polymer particles 22 and the first binder 21 without damaging the separator membrane.

[0036] Further, the value of the polymer particle 22D50 can be: 1.2 * thickness of the adhesive layer 2 ≤ polymer particle 22D50 ≤ 1.3 * thickness of the adhesive layer 2, 1.3 * thickness of the adhesive layer 2 ≤ polymer particle 22D50 ≤ 1.4 * thickness of the adhesive layer 2, 1.4 * thickness of the adhesive layer 2 ≤ polymer particle 22D50 ≤ 1.5 * thickness of the adhesive layer 2, 1.5 * thickness of the adhesive layer 2 ≤ polymer particle 22D50 ≤ 1.6 * thickness of the adhesive layer 2, 1.6 * thickness of the adhesive layer 2 ≤ polymer particle 22D50 ≤ 1.7 * thickness of the adhesive layer 2, 1.7 * thickness of the adhesive layer 2 ≤ polymer particle 22D50 ≤ 1.8 * thickness of the adhesive layer 2, 1.8 * thickness of the adhesive layer 2 ≤ polymer particle 22D50 ≤ 1.9 * thickness of the adhesive layer 2.

[0037] Furthermore, the thickness of the adhesive layer 2 is 1–3 μm. When the thickness of the adhesive layer 2 is large, the value of the polymer particle 22D50 can be appropriately increased, and the pressure that can be withstood is greater; conversely, when the thickness of the adhesive layer 2 is small, the value of the polymer particle 22D50 can be reduced.

[0038] Further, the mass ratio of the first adhesive 21 to the polymer particles 22 can be 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.8, or 0.8-0.9.

[0039] Furthermore, the first adhesive 21 is one or more of the following: polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene ether, epoxy resin, and epoxy resin derivatives.

[0040] Further, the thickness of the base membrane 1 is 3–200 μm; the porosity of the base membrane 1 is 20–80%; and the air permeability of the base membrane 1 is 50–200 s / 100cc. The base membrane 1 can be selected from any one of the following: ethylene microporous membrane, polypropylene microporous membrane, polypropylene / polyethylene / polypropylene three-layer composite microporous membrane, polyvinylidene fluoride microporous membrane, polyvinylidene fluoride-hexafluoropropylene microporous membrane, polyimide microporous membrane, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyester nonwoven fabric, polyimide nonwoven fabric, aramid nonwoven fabric, and spandex nonwoven fabric.

[0041] Furthermore, the separator also includes a heat-resistant layer 3 coated between the base film 1 and the adhesive layer 2; the heat-resistant layer 3 includes a second adhesive and an inorganic filler. Adding a heat-resistant layer can further enhance the safety performance of the battery cell and allow for wider application of polymer particles.

[0042] The inorganic filler is at least one of alumina, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite; the second binder is polymerized from at least one monomer selected from ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, and maleic acid; specifically, the second binder may be at least one of polyethyl acrylate, polybutyl acrylate, polyethyl methacrylate, polystyrene, polychlorostyrene, polyfluorostyrene, polymethylstyrene, polyacrylic acid, and polymethacrylic acid.

[0043] A second aspect of the present invention provides a method for preparing the separator membrane, comprising the following steps:

[0044] S1. Dissolve the first adhesive 21 to form a particle-free first adhesive solution;

[0045] S2. Add polymer particles 22 to the first adhesive solution and stir to obtain the first slurry;

[0046] S3. The first slurry is coated onto at least one surface of the base film 1 and dried to obtain a separating film.

[0047] The solvent for dissolving the first binder 21 can be one or more of ethanol, isopropanol, DMAC, tripropylene glycol, and NMP. After drying in step S3, the solvent will evaporate.

[0048] Further, in step S3, the coating method for the first slurry is as follows: firstly, the first slurry is coated onto at least one surface of the base film 1 using a microgravure coating method, then placed in a coagulation bath for washing with water and drying to obtain a release film. This coating method can yield a network-structured first binder 21, and polymer particles 22 can also be distributed in an island-like pattern within it.

[0049] A third aspect of the present invention applies the separator to an electrochemical device, the electrochemical device comprising a positive electrode, a negative electrode, and a separator, wherein the separator is any of the separators described above.

[0050] The active material layer coated on the positive electrode can be, but is not limited to, a chemical formula such as Li. a Ni x Co y M z O 2-b N b (where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active material can be one or more combinations of O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The positive electrode active material can also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the positive electrode active material. The materials used for modification can be one or more combinations of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W, including but not limited to. The positive electrode current collector used in the positive electrode sheet is typically a structure or component that collects current. The positive electrode current collector can be any material suitable for use as a positive electrode current collector in lithium-ion batteries. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil, among others.

[0051] The active material layer coated on the negative electrode sheet can be one or more of the following, including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector used in the negative electrode sheet is typically a structure or component that collects current. This current collector can be any material suitable for use as a negative electrode current collector in lithium-ion batteries, for example, it can be, but is not limited to, metal foil, and more specifically, copper foil.

[0052] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below with reference to specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0053] Example 1

[0054] like Figure 1 As shown, a separating membrane includes a base membrane 1, an adhesive layer 2, and a heat-resistant layer 3; the adhesive layer 2 is coated on at least one surface of the base membrane 1, and the heat-resistant layer 3 is coated between the base membrane 1 and the adhesive layer 2.

[0055] The thickness of the base membrane 1 is 3–200 μm; the porosity of the base membrane 1 is 20–80%; the air permeability of the base membrane 1 is 50–200 s / 100cc; the base membrane 1 can be selected from any one of the following: ethylene microporous membrane, polypropylene microporous membrane, polypropylene / polyethylene / polypropylene three-layer composite microporous membrane, polyvinylidene fluoride microporous membrane, polyvinylidene fluoride-hexafluoropropylene microporous membrane, polyimide microporous membrane, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyester nonwoven fabric, polyimide nonwoven fabric, aramid nonwoven fabric, and spandex nonwoven fabric.

[0056] The adhesive layer 2 has a thickness of 1.5 μm. The polymer particles 22 have a D50 of 3 μm and a compression ratio of 50%. The mass ratio of the first adhesive 21 to the polymer particles 22 is 0.3. The polymer particles 22 are at least one of polypropylene microspheres, polyethylene microspheres, polystyrene microspheres, and their corresponding modified polymer microspheres. The first adhesive 21 is one or more of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene ether, epoxy resin, and epoxy resin derivatives.

[0057] The heat-resistant layer 3 comprises a second binder and an inorganic filler. The inorganic filler is at least one of alumina, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite. The second binder is polymerized from at least one monomer selected from ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, and maleic acid. The mass ratio of the inorganic filler to the heat-resistant layer 3 is 55:45.

[0058] The preparation method of this separator is as follows:

[0059] S1. Dissolve the first adhesive 21 in a solvent and stir thoroughly to form a transparent and particle-free first adhesive solution; wherein the solvent used may be one or more of ethanol, isopropanol, DMAC, tripropylene glycol, and NMP.

[0060] S2. Pour the polymer particles 22 into the first adhesive solution and stir thoroughly to distribute them evenly in the first adhesive solution to obtain the first slurry;

[0061] S3. A heat-resistant layer 3 is coated on at least one surface of the base film 1. Then, the first slurry is coated on the surface of the heat-resistant layer 3 away from the base film 1 by micro-recessed coating. Then, it is placed in a coagulation bath for washing with water and then placed in an oven for drying to obtain a separation film.

[0062] The prepared separator is applied in a lithium-ion battery, which includes a positive electrode, a negative electrode, and a separator spaced between the positive and negative electrodes. In this embodiment, the positive electrode active material is lithium cobalt oxide, and the negative electrode active material is graphite.

[0063] Example 2

[0064] The design of the isolation membrane differs from that in Example 1.

[0065] like Figure 1 As shown, a separating membrane includes a base membrane 1 and an adhesive layer 2; the adhesive layer 2 is coated on at least one surface of the base membrane 1, and the adhesive layer 2 includes a first adhesive 21 and polymer particles 22. The mass ratio of the first adhesive 21 to the polymer particles 22 is 0.6.

[0066] The rest is the same as in Example 1, and will not be repeated here.

[0067] Examples 3-11 and Comparative Example 1

[0068] The design of the separator membrane differs from that of Example 1, but the rest is the same as that of Example 1.

[0069] The specific settings are shown in Table 1 below.

[0070] Table 1

[0071]

[0072] The separators and lithium-ion batteries obtained in Examples 1-11 and Comparative Example 1 were tested, and the test results are shown in Table 2.

[0073] Table 2

[0074]

[0075] As can be seen from the above test results, the present invention adds polymer particles with a certain compression ratio to the adhesive layer and limits the D50 of the polymer particles, which can effectively improve the rate performance of the battery cell. It is evident that the polymer particles effectively prevent the binder from swelling in the electrolyte and forming a film after hot pressing in the formation process.

[0076] However, due to the influence of polymer particles, when too many polymer particles are added, i.e., the mass ratio of the first binder to the polymer particles is too small, the polymer particles will conversely affect the adhesion between the separator and the electrode, resulting in a decrease in their adhesion, as in Examples 1 and 3. When the content of added polymer particles is moderate, i.e., the mass ratio of the first binder to the polymer particles is moderate, as in Examples 2 and 7-9, the negative impact of the polymer particles is small, and the separator and the electrode can still maintain good adhesion, while the cell rate is also significantly improved. In addition, the test results of Examples 10 and 11 show that the D50 of the polymer particles and the thickness of the adhesive layer also affect the adhesion between the separator and the electrode and the rate performance of the battery.

[0077] In summary, the results show that the separator provided by the present invention effectively solves the problem that the current separator adhesive layer is prone to film formation after electrolyte swelling and hot pressing in the formation process. While ensuring the adhesive strength of the adhesive, it improves the rate performance and cycle life of lithium-ion batteries.

[0078] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A separating membrane, characterized in that, include: Base film; An adhesive layer, coated on at least one surface of the base film, comprises a first adhesive and polymer particles; It also includes a heat-resistant layer coated between the base film and the adhesive layer; the heat-resistant layer includes a second adhesive and an inorganic filler; Wherein, the value of D50 of the polymer particles is: 1.2 * the thickness of the adhesive layer ≤ the D50 of the polymer particles ≤ 1.9 * the thickness of the adhesive layer, and the compression ratio of the polymer particles is 20-90%; the polymer particles have a spherical structure and / or a spherical structure; the polymer particles are at least one of polypropylene microspheres, polyethylene microspheres, polystyrene microspheres and their corresponding modified polymer microspheres; The mass ratio of the first binder to the polymer particles is 0.1 to 0.9, the adhesive layer has a network structure on the base film, and the polymer particles are distributed in an island-like manner in the adhesive layer.

2. The separator membrane according to claim 1, characterized in that, The thickness of the adhesive layer is 1–3 μm.

3. The separator membrane according to claim 1, characterized in that, The first adhesive is one or more of the following: polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene ether, epoxy resin, and epoxy resin derivatives.

4. The separator according to claim 1, characterized in that, The thickness of the base membrane is 3–200 μm; the porosity of the base membrane is 20–80%; and the air permeability of the base membrane is 50–200 s / 100cc.

5. The separator membrane according to claim 1, characterized in that, The second adhesive is polymerized from at least one monomer selected from ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, and maleic acid; the inorganic filler is at least one of alumina, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

6. A method for preparing a separator membrane according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Dissolve the first adhesive to form a particle-free first adhesive solution; S2. Add polymer particles to the first adhesive solution and stir to obtain the first slurry; S3. The first slurry is coated onto at least one surface of the base film and dried to obtain a separating film.

7. The method for preparing the separator according to claim 6, characterized in that, In step S3, the coating method of the first slurry is as follows: firstly, the first slurry is coated onto at least one surface of the base film using a micro-recessed coating method, and then placed in a coagulation bath for washing with water and drying to obtain a separation film.

8. An electrochemical device comprising a positive electrode, a negative electrode, and a separator, characterized in that, The separator is the separator as described in any one of claims 1 to 7.

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