Composite diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention relates to a composite diaphragm, a preparation method thereof and a lithium ion battery. The composite separator includes: a base film; the ceramic coating is positioned on at least one side of the base membrane, and the ceramic coating comprises a plurality of ceramic particles and a binder; and the PTFE porous membrane is positioned on one side, far away from the base membrane, of the ceramic coating. According to the composite diaphragm in the technical scheme, through the innovative three-layer structural design of'base membrane-ceramic coating-PTFE porous membrane ', on one hand, the ceramic coating and the PTFE porous membrane have a synergistic effect, the high-temperature resistance and the thermal size stability of the composite diaphragm are greatly improved, high-temperature shrinkage is effectively prevented, and the safety of a battery is enhanced; and on the other hand, the adhesive in the ceramic coating ensures that the ceramic coating is firmly combined with the base membrane and the PTFE porous membrane, meanwhile, the damage of high temperature to the membrane structure is avoided, and the process is simple and suitable for continuous production.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems. As a key internal component of the battery, the separator not only needs to isolate the positive and negative electrodes to prevent short circuits, but also needs to maintain structural stability and prevent thermal runaway when the battery overheats abnormally.

[0003] Currently, commercial lithium-ion battery separators are mostly microporous membranes made of polyolefin materials (such as PP and PE). While these materials possess good mechanical properties and electrochemical stability, their melting points are relatively low (PE approximately 135℃, PP approximately 165℃), resulting in poor heat resistance. When the battery generates abnormal heat due to overcharging, short circuits, or fast charging, the polyolefin separator is prone to large-area melting and shrinkage, leading to direct contact between the positive and negative electrodes, potentially causing short circuits, fires, or even explosions—serious safety issues. This is especially true in power battery applications that demand high energy density and high-power fast charging, where internal heat generation is more significant, placing even higher demands on the thermal stability of the separator. Therefore, developing a high-safety separator that is simple in structure, resistant to high temperatures, and easy to industrialize is of great importance. Summary of the Invention

[0004] Therefore, it is necessary to provide a composite separator that is simple in structure, resistant to high temperatures, and easy to prepare for industrialization, as well as its preparation method and lithium-ion battery.

[0005] A composite membrane, the composite membrane comprising: Base film; A ceramic coating, located on at least one side of the base film, comprising a plurality of ceramic particles and a binder; and A PTFE porous membrane is located on the side of the ceramic coating away from the base membrane.

[0006] The composite separator of this invention features an innovative three-layer structure design: a base membrane, a ceramic coating, and a PTFE porous membrane. On one hand, the ceramic coating and the PTFE porous membrane work synergistically to greatly improve the high-temperature resistance and thermal dimensional stability of the composite separator, effectively preventing high-temperature shrinkage and enhancing battery safety. On the other hand, the binder in the ceramic coating ensures a strong bond between the ceramic coating and the base membrane and the PTFE porous membrane, while avoiding damage to the membrane structure from high temperatures. Furthermore, the process is simple and suitable for continuous production.

[0007] In one embodiment, the ceramic particles are selected from one or a mixture of more than one of oxide ceramics, nitride ceramics and carbide ceramics.

[0008] In one embodiment, the thickness of the ceramic coating is 0.5 micrometers to 5 micrometers; In one embodiment, the adhesive accounts for 1% to 15% of the mass fraction of the ceramic coating, and the adhesive includes one or a mixture of water-based adhesives and oil-based adhesives.

[0009] In one embodiment, the thickness of the PTFE porous membrane is 10 micrometers to 35 micrometers.

[0010] In one embodiment, the composite membrane further includes an adhesive layer located on the side of the PTFE porous membrane away from the base membrane.

[0011] In one embodiment, a ceramic coating and a PTFE porous membrane are provided on both sides of the base membrane.

[0012] A method for preparing any of the above-mentioned composite membranes includes the following steps: A ceramic slurry is prepared by uniformly mixing several ceramic particles, a binder, and a solvent; and The ceramic slurry is coated onto at least one surface of the base film, followed by drying to allow the solvent to completely evaporate, forming a ceramic coating; and A composite membrane is obtained by combining a base membrane with a ceramic coating with a PTFE porous membrane.

[0013] The composite separator of this invention has a simple preparation process. The prepared composite separator adopts an innovative three-layer structure design of "base membrane-ceramic coating-PTFE porous membrane". On the one hand, the ceramic coating and PTFE porous membrane work synergistically to greatly improve the high temperature resistance and thermal dimensional stability of the composite separator, effectively prevent high temperature shrinkage, and enhance battery safety. On the other hand, the binder in the ceramic coating ensures a firm bond between the ceramic coating and the base membrane and the PTFE porous membrane, while avoiding damage to the membrane structure at high temperature. Moreover, the process is simple and suitable for continuous production.

[0014] In one embodiment, the plurality of ceramic particles account for 20% to 70% of the mass fraction of the ceramic slurry; The drying temperature is 50℃~120℃; The compounding method is roller pressing, with a pressing temperature of 60℃~100℃ and a pressing pressure of 0.5MPa~5MPa.

[0015] A lithium-ion battery comprising any of the composite separators described above.

[0016] The lithium-ion battery of this invention includes the aforementioned composite separator. This composite separator features an innovative three-layer structure design of "base membrane-ceramic coating-PTFE porous membrane". On the one hand, the ceramic coating and the PTFE porous membrane work synergistically to greatly improve the high-temperature resistance and thermal dimensional stability of the composite separator, effectively preventing high-temperature shrinkage and enhancing battery safety. On the other hand, the binder in the ceramic coating ensures a strong bond between the ceramic coating and the base membrane and the PTFE porous membrane, while avoiding damage to the membrane structure from high temperatures. Moreover, the process is simple and suitable for continuous production.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the composite diaphragm according to the first embodiment of the present invention; Figure 2 This is a schematic diagram of the composite diaphragm according to the second embodiment of the present invention; Figure 3 This is a schematic diagram of the composite diaphragm according to the third embodiment of the present invention; Figure 4 This is a flowchart of a method for preparing a composite membrane according to an embodiment of the present invention. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] Please see Figure 1The composite membrane 100 of the first embodiment of the present invention includes a base membrane 110, a ceramic coating 120, and a PTFE porous membrane 130. The ceramic coating 120 is located on at least one side of the base membrane 110, and includes a plurality of ceramic particles and a binder, wherein the binder binds the ceramic particles together. The PTFE porous membrane 130 is located on the side of the ceramic coating 120 away from the base membrane 110.

[0022] This basic three-layer structure achieves synergistic effects through functional layering: the base membrane 110 provides excellent mechanical support and closed-cell characteristics; the ceramic coating 120 containing binder imparts excellent thermal stability and rigidity to the separator, preventing high-temperature shrinkage. The binder in the ceramic coating 120 ensures a strong bond between the ceramic coating 120 and the base membrane 110 and the PTFE porous membrane 130, while avoiding high-temperature damage to the membrane structure. Furthermore, the process is simple and suitable for continuous production; the surface PTFE porous membrane 130 provides extremely high porosity and excellent electrolyte wettability, ensuring low ion transport resistance. The synergy between the ceramic coating and the PTFE porous membrane significantly improves the high-temperature resistance and thermal dimensional stability of the composite separator, effectively preventing high-temperature shrinkage and enhancing battery safety. The combination of the base membrane 110, ceramic coating 120, and PTFE porous membrane 130 significantly improves the overall performance of the composite separator 100, giving it high safety, excellent electrochemical performance, and mechanical integrity.

[0023] The base membrane 110 can be selected from polyolefin (such as PE, PP, PE / PP, PE / PP / PE, PP / PE / PP) membranes, polyester (PET) membranes, polyimide (PI) membranes, aramid membranes, non-woven fabric base membranes, or composite membranes of the above materials. Using these commercially viable and technologically mature membranes as the base membrane not only ensures that the separator possesses good mechanical strength, electrochemical stability, and inherent thermal shutdown function, but also makes the composite separator easy to integrate into the existing battery manufacturing industry chain, possessing excellent mass production feasibility and cost-effectiveness.

[0024] It is understood that the present invention does not impose any restrictions on the material of the base film layer. Any film that can be used as a lithium battery separator substrate, including known base films modified by various physical or chemical methods, falls within the protection scope of the present invention.

[0025] Based on the aforementioned embodiments, the ceramic particles are selected from one or a mixture of oxide ceramics, nitride ceramics, and carbide ceramics. These ceramic particles can maintain their physical and chemical stability within the operating temperature range of lithium-ion batteries and the temperature range where the separator undergoes thermal shrinkage, thereby improving the heat resistance, mechanical strength, and safety of the composite separator.

[0026] It is understood that a wide variety of ceramic particles can be used in this invention. For example, oxide ceramics include silicon dioxide, boehmite, alumina, zirconium oxide, titanium oxide, magnesium oxide, zinc oxide, aluminum hydroxide, etc.; nitride ceramics include boron nitride, silicon nitride, etc.; carbides include silicon carbide, titanium carbide, zirconium carbide, tungsten carbide, boron carbide, etc. These materials have excellent electrochemical stability and heat resistance, and are preferred solutions in this invention. In addition, ceramic-based solid electrolytes (such as lithium lanthanum zirconium oxide LLZO, lithium lanthanum titanium oxide LLTO, etc.) can also be used as a special type of ceramic particle because they possess lithium-ion conductivity. In summary, all ceramic particle materials that can meet the basic requirements of electrochemical stability and heat resistance and can be applied to lithium-ion battery systems fall within the protection scope of this invention.

[0027] Introducing these highly heat-resistant ceramic particles can greatly enhance the thermal insulation and thermal dimensional stability of the coating, making the composite separator less prone to melting and shrinkage at high temperatures, thereby effectively preventing battery thermal runaway. If ceramic-based solid electrolyte particles are added, the ionic conductivity can be enhanced to a certain extent and the penetration of lithium dendrites can be suppressed, further improving the safety and rate performance of the battery.

[0028] Based on the aforementioned embodiments, the thickness of the ceramic coating 120 is 0.5 micrometers to 5 micrometers. Controlling the thickness of the ceramic coating 120 within this optimized range ensures sufficient thermal stability and mechanical reinforcement of the composite diaphragm 100 while avoiding problems such as decreased overall porosity, reduced ionic conductivity, or reduced flexibility due to excessive coating thickness, thus achieving an optimal balance between the diaphragm's thermal safety and electrochemical performance. Furthermore, the thickness of the ceramic coating 120 can be, but is not limited to, 0.5 micrometers, 1 micrometer, 2 micrometers, 3 micrometers, 4 micrometers, or 5 micrometers, as well as specific values ​​between these values.

[0029] Based on the aforementioned embodiments, the binder accounts for 1% to 15% of the mass fraction of the ceramic coating 120. Controlling the binder content within this range ensures a strong bond between ceramic particles and between the ceramic coating 120 and the base film 110, preventing coating detachment. It also avoids excessive binder clogging the pores between ceramic particles, thus maintaining the stability of the coating structure while maximizing the preservation of its porous structure, ensuring good electrolyte permeability and ionic conductivity. Furthermore, the mass fraction of the binder in the ceramic coating 120 can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, as well as specific values ​​between these values.

[0030] Based on the aforementioned embodiments, the adhesive includes one or a mixture of more than one of water-based adhesives and oil-based adhesives.

[0031] This application does not impose any special restrictions on the specific type of binder. Any binder component suitable for battery systems can be used in this invention without departing from the inventive concept of this application.

[0032] For example, the water-based adhesive includes any one or a mixture of several of the following: cellulose acetate (CA), methylcellulose (MC), sodium carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), styrene-butadiene rubber (SBR), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), polyvinyl alcohol (PVA), polyacrylamide (PAM), polyacrylic acid (PAA), sodium polyacrylate (NaPAA), lithium polyacrylate (LiPAA), polyacrylic acid copolymers (such as polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer), polyurethane (PU), polyethylene oxide (PEO), polyimide, ethylene-vinyl acetate copolymer, epoxy resin, sodium alginate, and lithium alginate.

[0033] For example, the oily adhesive includes any one or a mixture of several of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride copolymers (such as PVDF-HFP copolymer, PVDF-TFE copolymer).

[0034] The above examples are merely illustrative and are not intended to limit the scope of protection of this invention.

[0035] Preferably, the binder is an oil-based binder, which has excellent bonding properties. It not only ensures a strong bond between ceramic particles and between the ceramic coating 120 and the base film 110, but also forms a good bond between the ceramic coating 120 and the PTFE porous membrane 130, giving the battery higher overall hardness and interface smoothness. Specifically, when PVDF-HFP is used as the binder, during hot-pressing assembly, the PVDF-HFP layer is activated by heat, releasing a small amount of PVDF components, which promotes a tighter bond between the ceramic coating 120 and the base film 110, and between the ceramic coating 120 and the PTFE porous membrane 130 at the interface. After subsequent cold pressing, the binder is re-cured, further eliminating interlayer voids and enhancing the structural integrity and interface stability of the composite separator.

[0036] Based on the aforementioned embodiments, the thickness of the PTFE porous membrane 130 is 10 micrometers to 35 micrometers. Controlling the thickness of the PTFE porous membrane 130 within this range ensures it possesses sufficiently high porosity and excellent electrolyte retention, thereby providing unobstructed migration channels for lithium ions and reducing battery internal resistance. Simultaneously, this thickness of the PTFE porous membrane 130 also maintains good flexibility and mechanical strength, and does not affect the overall processability of the separator after being composited with the ceramic coating 120. Furthermore, the thickness of the PTFE porous membrane 130 can be, but is not limited to, 10 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, or 35 micrometers, as well as specific values ​​between these values.

[0037] It should be noted that this PTFE porous membrane is an independent pre-fabricated membrane, rather than a functional layer formed in situ on the surface of a base membrane through coating or other methods. It is a microporous film formed from PTFE material through processes such as extrusion and stretching, and its microscopic structure exhibits a three-dimensional network of porous pores composed of interconnected fibrous structures. The PTFE porous membrane described in this application refers only to PTFE membranes with a porous structure, and not to a specific type of product or structure named "PTFE porous membrane." This application does not have specific requirements regarding the pore structure of PTFE.

[0038] Based on the aforementioned embodiments, the composite diaphragm 100 further includes an adhesive layer 140, such as... Figure 2 As shown, the adhesive layer 140 is located on the side of the PTFE porous membrane 130 away from the base membrane 110. Further, the adhesive layer 140 comprises one or a mixture of water-based and oil-based adhesives. Preferably, the adhesive in the adhesive layer is an oil-based adhesive, which includes any one or a mixture of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride copolymers (such as PVDF-HFP copolymer, PVDF-TFE copolymer). Adding an adhesive layer to the outermost layer can greatly enhance the adhesion between the separator and the electrode (especially the positive electrode), reduce interfacial slippage and gaps between the electrode and the separator during charging and discharging, thereby reducing interfacial impedance, improving current distribution uniformity, and effectively suppressing polarization during cycling, which helps to improve the rate performance and cycle life of the battery.

[0039] It should be noted that the composite membrane of the present invention is not limited to the above embodiments, and may also have a ceramic coating and a PTFE porous membrane on both sides of the base membrane.

[0040] Please see Figure 3The composite membrane 200 of the third embodiment of the present invention includes a base membrane 210, a ceramic coating 220, and a PTFE porous membrane 230. The base membrane 210 has a ceramic coating 220 and a PTFE porous membrane 230 on both sides. Specifically, the two ceramic coatings 220 are located on opposite sides of the base membrane 210, and each ceramic coating 220 includes an adhesive. The PTFE porous membrane 230 is located on the side of the ceramic coating 220 away from the base membrane 210.

[0041] This embodiment employs a double-sided symmetrical structure design, ensuring that both sides of the separator have identical thermal stability and interfacial properties, completely eliminating the stress asymmetry or uneven thermal shrinkage problems that may occur with single-sided coatings. This structure is particularly suitable for applications with extremely high safety requirements, and eliminates the need to distinguish between the front and back sides during battery assembly, improving production efficiency and reliability.

[0042] The composite separator of this invention features an innovative three-layer structure design: a base membrane, a ceramic coating, and a PTFE porous membrane. On one hand, the ceramic coating and the PTFE porous membrane work synergistically to greatly improve the high-temperature resistance and thermal dimensional stability of the composite separator, effectively preventing high-temperature shrinkage and enhancing battery safety. On the other hand, the binder in the ceramic coating ensures a strong bond between the ceramic coating and the base membrane and the PTFE porous membrane, while avoiding damage to the membrane structure from high temperatures. Furthermore, the process is simple and suitable for continuous production.

[0043] Please see Figure 4 The method for preparing the composite separator according to one embodiment of the present invention includes the following steps: S10. Mix a number of ceramic particles, binder and solvent evenly to obtain ceramic slurry.

[0044] In one embodiment, the ceramic particles constitute 20% to 70% of the ceramic slurry by mass. Further, the percentage of ceramic particles in the ceramic slurry by mass may be, but is not limited to, 20%, 30%, 40%, 50%, 60%, or 70%, or specific values ​​between these values.

[0045] S20. The ceramic slurry obtained in step S10 is coated on at least one surface of the base film, and then dried to form a ceramic coating after the solvent has completely evaporated.

[0046] In one embodiment, the drying temperature is 50°C to 120°C. Further, the drying temperature may be, but is not limited to, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or 120°C, or specific values ​​between these values.

[0047] S30. The ceramic-coated base membrane obtained in step S20 is combined with a PTFE porous membrane to obtain a composite membrane.

[0048] In one embodiment, the compounding method is roller pressing, with a pressing temperature of 60°C to 100°C and a pressing pressure of 0.5 MPa to 5 MPa. Further, the pressing temperature can be, but is not limited to, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C, and specific values ​​between these values. Further, the pressing pressure can be, but is not limited to, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, or 5 MPa, and specific values ​​between these values.

[0049] In this preparation method, the composite step preferably adopts a roller pressing method. Under the above temperature and pressure, the binder (such as PVDF) in the ceramic coating can be effectively activated, thereby forming a strong and stable bonding interface between the base film and the PTFE porous film.

[0050] The composite separator of this invention has a simple preparation process. The prepared composite separator adopts an innovative three-layer structure design of "base membrane-ceramic coating-PTFE porous membrane". On the one hand, the ceramic coating and PTFE porous membrane work synergistically to greatly improve the high temperature resistance and thermal dimensional stability of the composite separator, effectively prevent high temperature shrinkage, and enhance battery safety. On the other hand, the binder in the ceramic coating ensures a firm bond between the ceramic coating and the base membrane and the PTFE porous membrane, while avoiding damage to the membrane structure at high temperature. Moreover, the process is simple and suitable for continuous production.

[0051] One embodiment of the lithium-ion battery includes the composite separator of any of the above-described embodiments. The lithium-ion battery also includes a positive electrode and a negative electrode, with the composite separator located between the positive and negative electrodes.

[0052] For example, the positive electrode includes a positive current collector and a positive active material layer coated thereon, the active material layer including a positive active substance, and may also add conductive agents and / or binders as needed; any known positive active substances may be used in this application without departing from the inventive concept of this application.

[0053] The negative electrode includes a negative electrode current collector and a negative electrode active material layer coated thereon. The active material layer includes a negative electrode active substance and may also include conductive agents and / or binders as needed.

[0054] Meanwhile, the negative electrode can also be metallic lithium or a lithium-based composite.

[0055] It is understood that the description of the electrode structure in this application is a typical example, but the scope of protection is not limited thereto and also covers other structural forms known in the art. The active material includes known single materials, coating materials, doped materials, nanocomposites, and derivatives obtained through other optimization methods. Meanwhile, the conductive agent, binder, current collector, and other components include conventional and functionalized forms. Any known combination of materials and structural design that does not depart from the core concept of this invention is applicable to this application and will not be elaborated upon here.

[0056] The lithium-ion battery of this invention includes the aforementioned composite separator. This composite separator features an innovative three-layer structure design of "base membrane-ceramic coating-PTFE porous membrane". On the one hand, the ceramic coating and the PTFE porous membrane work synergistically to greatly improve the high-temperature resistance and thermal dimensional stability of the composite separator, effectively preventing high-temperature shrinkage and enhancing battery safety. On the other hand, the binder in the ceramic coating ensures a strong bond between the ceramic coating and the base membrane and the PTFE porous membrane, while avoiding damage to the membrane structure from high temperatures. Moreover, the process is simple and suitable for continuous production.

[0057] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0058] Example 1 (1) Mix 60% Al2O3, 10% PVDF and 30% NMP evenly to obtain a ceramic slurry. Coat the ceramic slurry onto one surface of a PE base film and then dry it at 85°C to allow the solvent to evaporate completely and form a ceramic coating. The final thickness of the ceramic coating is 4 micrometers.

[0059] (2) The base membrane with ceramic coating is rolled and compounded with a 15-micron PTFE porous membrane. The rolling temperature is 75°C and the rolling pressure is 3MPa. After the composite rolling, the composite membrane of Example 1 is obtained.

[0060] Example 2 The ceramic slurry was prepared by mixing 60% LLZO, 10% PVDF and 30% NMP, with the remaining conditions being the same as in Example 1.

[0061] Example 3 The ceramic slurry was prepared by mixing 60% Al2O3, 10% (CMC+SBR) and 30% deionized water, with the remaining conditions being the same as in Example 1.

[0062] Example 4 The ceramic slurry was prepared by mixing 25% Al2O3, 5% PVDF and 70% NMP, and the ceramic coating thickness was 1 micrometer. The other conditions were the same as in Example 1.

[0063] Example 5 The thickness of the PTFE porous membrane was 10 micrometers, and the other conditions were the same as in Example 1.

[0064] Example 6 Based on the conditions of Example 1, a ceramic layer and a PTFE porous membrane are provided on both sides of the base membrane.

[0065] Comparative Example 1 The PE base film was directly rolled and laminated with a 15-micron PTFE porous membrane at a temperature of 75°C and a pressure of 3 MPa. After the composite rolling process, the composite membrane of Comparative Example 1 was obtained.

[0066] Comparative Example 2 The PE membrane with ceramic coating obtained in step (1) of Example 1 was used as the final separator.

[0067] Battery assembly: The composite separators, positive electrode sheets, and negative electrode sheets provided in Examples 1-6 and Comparative Examples 1-2 were respectively wound and stacked to assemble batteries.

[0068] Heating test: (1) The composite diaphragm was subjected to a high temperature resistance test at 150°C.

[0069] (2) The test method is as follows: After the assembled battery is fully charged, it is placed in a temperature chamber. The temperature chamber is heated to 120°C at a heating rate of 5°C / min and held for 30 minutes. The temperature is then raised to 130°C and held for 30 minutes. This method is used to raise the temperature to 140°C, 150°C, 160°C and up to 210°C respectively, and held for 30 minutes each time. The temperature is then observed for 1 hour to see if fire or explosion occurs. The test results are shown in Table 1 below.

[0070] Table 1 Performance test results of the examples and comparative examples Based on the heating test results in Table 1 above, it can be concluded that the composite separator of the present invention exhibits excellent thermal stability and safety. All embodiments (1-6) showed no deformation in the isothermal test at 150°C, demonstrating their thermal dimensional stability. In the continuous heating test, their critical safety temperatures were significantly higher than the comparative examples, reaching above 180°C. The preferred double-sided structure (Example 6) could withstand extreme high temperatures above 210°C. In contrast, Comparative Example 1 (without ceramic layer) and Comparative Example 2 (without PTFE membrane) curled and deformed at 150°C, and experienced thermal failure at lower temperatures of 180°C and 170°C, respectively. This demonstrates the necessity and synergistic effect of the three-layer structure design of the present invention: "base film-ceramic coating-PTFE porous membrane." The ceramic coating effectively inhibits the thermal shrinkage of the base film, while the PTFE porous membrane further enhances safety at high temperatures, providing an effective technical solution to the problem of thermal runaway in lithium-ion batteries.

[0071] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite diaphragm, characterized in that, The composite diaphragm comprises: Base film; A ceramic coating, located on at least one side of the base film, comprising a plurality of ceramic particles and a binder; and A PTFE porous membrane is located on the side of the ceramic coating away from the base membrane.

2. The composite diaphragm according to claim 1, characterized in that, The ceramic particles are selected from one or a mixture of more than one of oxide ceramics, nitride ceramics and carbide ceramics.

3. The composite diaphragm according to claim 1, characterized in that, The thickness of the ceramic coating is 0.5 micrometers to 5 micrometers.

4. The composite diaphragm according to claim 1, characterized in that, The binder accounts for 1% to 15% of the mass fraction of the ceramic coating, and the binder includes one or a mixture of water-based binders and oil-based binders.

5. The composite diaphragm according to claim 1, characterized in that, The thickness of the PTFE porous membrane is 10 micrometers to 35 micrometers.

6. The composite diaphragm according to claim 1, characterized in that, The composite membrane also includes an adhesive layer located on the side of the PTFE porous membrane away from the base membrane.

7. The composite diaphragm according to claim 1, characterized in that, Both sides of the base membrane are provided with a ceramic coating and a PTFE porous membrane.

8. A method for preparing a composite diaphragm according to any one of claims 1 to 7, characterized in that, Includes the following steps: A ceramic slurry is prepared by uniformly mixing several ceramic particles, a binder, and a solvent; and The ceramic slurry is coated onto at least one surface of the base film, followed by drying to allow the solvent to completely evaporate, forming a ceramic coating; and A composite membrane is obtained by combining a base membrane with a ceramic coating with a PTFE porous membrane.

9. The method for preparing the composite diaphragm according to claim 8, characterized in that, The ceramic particles account for 20% to 70% of the mass fraction of the ceramic slurry; The drying temperature is 50℃~120℃; The compounding method is roller pressing, with a pressing temperature of 60℃~100℃ and a pressing pressure of 0.5MPa~5MPa.

10. A lithium-ion battery, characterized in that, The composite diaphragm includes any one of claims 1 to 7.

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