Puncture-resistant composite diaphragm and preparation method thereof

Abstract

The invention belongs to the technical field of battery diaphragms, and discloses an anti-puncture composite diaphragm and a preparation method thereof.The preparation method comprises the following steps that two-dimensional boron-nitrogen alkene and nanofibers are subjected to dry mixing according to the mass ratio of (20-100): (1-10), then the mixture is mixed with water and a dispersing agent, then the mixture is mixed with a sodium carboxymethylcellulose solution, a binder and a surfactant, and slurry is obtained; coating one side of a base membrane with the slurry, and drying to obtain a coating; and the other base membrane and the base membrane attached with the coating are subjected to hot-pressing compounding, so that the coating is positioned between the two base membranes, and the puncture resistance of the prepared battery diaphragm is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a puncture-resistant composite separator and its preparation method. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] The separator in a lithium-ion battery is a crucial component located between the positive and negative electrodes. Made of polymer materials such as polyethylene (PE) and polypropylene (PP), it features a microporous structure. Its main functions include physically isolating the positive and negative electrodes to prevent short circuits, allowing lithium ions to freely transport and form a current loop through its porous structure, and maintaining a uniform electrolyte distribution to sustain battery performance. In particular, the separator's puncture resistance effectively resists sharp lithium dendrites formed on the negative electrode surface during overcharging and edge burrs generated during electrode cutting, preventing puncture short circuits and avoiding the risk of thermal runaway.

[0004] The industry typically employs base film coating technology to enhance the puncture resistance of diaphragms. For example, coating hydrated aluminum silicate onto the base film strengthens the diaphragm's puncture resistance; similarly, coating magnesium hydroxide onto the base film improves the diaphragm's puncture resistance to some extent. However, the main coating materials of existing diaphragms have relatively low hardness, making them prone to damage, peeling, and failure during processing and service. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a puncture-resistant composite diaphragm and its preparation method.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing a puncture-resistant composite diaphragm, comprising the following steps: Two-dimensional boron nitride and nanofibers are dry-mixed at a mass ratio of 20-100:1-10, then mixed with water and dispersant, and then mixed with sodium carboxymethyl cellulose solution, binder and surfactant to obtain slurry; The slurry is coated onto one side of the base film, and after drying, a coating is obtained; Another base film is hot-pressed onto the base film with the coating, so that the coating is located between the two base films.

[0007] Secondly, the present invention provides a puncture-resistant composite diaphragm, which is prepared by the aforementioned preparation method.

[0008] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention uses PE particles and paraffin oil for co-extrusion casting, followed by extraction and pore-forming with dichloromethane, and finally stretching and shaping to obtain a single-layer porous PE wet-process separator. Two-dimensional boron nitride is co-coated with electrospun polyacrylonitrile nanofibers. The two-dimensional boron nitride, with its two-dimensional sheet-like structure, forms a fish-scale-like puncture-resistant structure through stacking, effectively improving the separator's puncture resistance. The polyacrylonitrile nanofibers act as a coating framework, enhancing the coating's mechanical properties. Subsequently, it is thermally composited with another base membrane after pore-forming to form a high-safety composite separator material based on two-dimensional boron nitride. Under the protection of the base membranes on both sides, the two-dimensional boron nitride coating is effectively prevented from peeling off. Attached Figure Description

[0009] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0010] Figure 1 This is a schematic diagram of the structure of the composite diaphragm according to an embodiment of the present invention. Detailed Implementation

[0011] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0012] To address the technical problems mentioned in the background art, the present invention provides a method for preparing a puncture-resistant composite diaphragm, comprising the following steps: Two-dimensional boron nitride and nanofibers are dry-mixed at a mass ratio of 20-100:1-10, then mixed with water and dispersant, and then mixed with sodium carboxymethyl cellulose solution, binder and surfactant to obtain slurry; The slurry is coated onto one side of the base film, and after drying, a coating is obtained; Another base film is hot-pressed onto the base film with the coating, so that the coating is located between the two base films.

[0013] The two-dimensional sheet-like structure of two-dimensional borazine forms a fish-scale-like puncture-resistant structure through stacking, which directly improves the puncture resistance of the membrane and is the core functional component for puncture resistance. Nanofibers serve as the framework support for the coating, interspersed between the two-dimensional boron nitride sheets to form a three-dimensional network support. This helps to improve the overall mechanical strength of the coating, avoids the increased brittleness caused by the stacking of two-dimensional boron nitride sheets, ensures that the puncture-resistant structure is not easily broken under stress, and maintains the stability of the coating structure. The dispersant promotes the uniform dispersion of two-dimensional boron nitride and nanofibers in water, prevents particle agglomeration, ensures uniform distribution of each component in the slurry, and ensures uniformity of coating and consistent puncture resistance. Sodium carboxymethyl cellulose solution acts as a thickener and stabilizer for the slurry, adjusting the slurry viscosity, maintaining the stability of the slurry system, ensuring that each component adheres uniformly to the base film during the coating process, and avoiding excessively high local concentrations or coating defects. The binder binds solid components such as two-dimensional boron nitride and nanofibers into a whole, and enhances the interfacial adhesion between the coating and the base film, improves the cohesive strength of the coating and the bonding force with the base film, and reduces the risk of coating peeling off. Surfactants reduce the interfacial tension of the components in the slurry, promote the compatibility of dispersants, binders and other agents with solid particles, improve the coating leveling properties of the slurry, make the coating adhere more evenly to the base film surface, and enhance the integrity of the coating. The base films on both sides serve as the carrier and protective layer of the coating. The coating is sandwiched in the middle by hot-pressing the base films on both sides to form a physical barrier, which effectively prevents the coating from falling off due to external friction or impact during processing or service.

[0014] In some embodiments, the nanofibers are electrospun polyacrylonitrile nanofibers with a diameter of 50-3000 nm and a length of 1000-20000 nm.

[0015] In some embodiments, the two-dimensional borazine has a sheet diameter of 0.1-10 μm and a thickness of 1-100 nm.

[0016] In some embodiments, the slurry further includes a stabilizer, and the mass ratio of two-dimensional boron nitride, nanofibers, water, surfactant, binder, dispersant and stabilizer is 20-100:1-10:30-200:0.01-0.1:1-10:0.1-1:0.1-2.

[0017] Preferably, the mass ratio of two-dimensional boron nitride, nanofibers, water, surfactant, binder, dispersant, and stabilizer is 20-50:1-6:30-100:0.04-0.08:3-8:0.1-0.8:0.3-1.5.

[0018] More preferably, the mass ratio of two-dimensional boron nitride to nanofibers is 30-50:1-4.

[0019] In some embodiments, the surfactant is at least one selected from silane coupling agents, alkylphenol polyoxyethylene ethers, fatty alcohol polyoxyethylene ethers, fatty acid polyoxyethylene ethers, and polyether-modified polysiloxanes.

[0020] In some embodiments, the dispersant is selected from ammonium polyacrylate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium hexametaphosphate, or octylphenol polyoxyethylene ether.

[0021] In some embodiments, the coating is 0.5-5 μm, preferably 1-4 μm, and more preferably 2-4 μm.

[0022] In some embodiments, the base film is prepared by: melt-blending ultra-high molecular weight polyethylene and paraffin oil in a mass ratio of 2-4:6-10, extruding and casting, cooling and shaping, extracting pores with dichloromethane, and then stretching and shaping to obtain the base film.

[0023] Preferably, the thickness of the base film is 2-10 μm.

[0024] In some embodiments, the two-dimensional borazine and nanofibers are dry-mixed for 30-60 minutes.

[0025] Dry mixing of two-dimensional boron nitride and nanofibers allows for preliminary uniform mixing of the two solid particles through mechanical action. This avoids localized agglomeration caused by density differences or surface tension when directly added to a liquid, laying the foundation for uniform dispersion when mixed with subsequent liquid components such as water and dispersants. It ensures the consistent distribution of the two in the slurry, thereby guaranteeing the uniformity of the synergistic effect between the puncture-resistant structure (two-dimensional boron nitride fish-scale stacking) and the mechanical support framework (nanofiber three-dimensional network) in the coating, and improving the stability of the puncture resistance of the diaphragm.

[0026] Preferably, after the two-dimensional boron nitride and nanofibers are dry-mixed, they are stirred with water and dispersant for 60-240 minutes to obtain slurry A.

[0027] Dry mixing has already achieved a preliminary uniform mixing of the two solid particles through mechanical action, while the dispersant can promote the uniform dispersion of the two in water and prevent particle agglomeration. Combined with stirring for 60-240 minutes, it can further ensure that the solid particles are evenly distributed in the liquid and guarantee the uniformity of each component in the slurry.

[0028] If two-dimensional borazine and nanofibers are directly mixed with water and a dispersant, the lack of mechanical pre-dispersion through a dry mixing step will cause localized agglomeration of the two solid particles due to density differences or surface tension. This agglomeration is difficult to completely eliminate through dispersants and stirring. This results in uneven distribution of the two-dimensional borazine sheets and nanofibers in the slurry, leading to localized defects in the coating, weakening the continuity of the fish-scale puncture-resistant structure and the supporting role of the three-dimensional nanofiber network, ultimately reducing the stability of the membrane's puncture resistance. Simultaneously, agglomerated particles may reduce the interfacial adhesion between the coating and the base film, increasing the risk of coating detachment during processing or service.

[0029] Further preferred, a sodium carboxymethyl cellulose solution is added to slurry A and stirred for 30-180 minutes to obtain slurry B.

[0030] The sodium carboxymethyl cellulose solution is added in this step mainly because it acts as a thickener and stabilizer for the slurry. After the two-dimensional boron nitride and nanofibers are dry-mixed and initially stirred with water and dispersant to form slurry A, the solid particles have already achieved initial uniform dispersion through mechanical action and the action of the dispersant. Adding the sodium carboxymethyl cellulose solution allows the polymer chains to fully extend and be uniformly dispersed in the slurry through stirring for 30-180 minutes. This effectively regulates the viscosity of the system, prevents the solid particles from settling and agglomerating, and provides a stable dispersion medium for the subsequently added binders, surfactants, and other components. It also avoids problems such as sudden increases in local viscosity and uneven dispersion caused by premature addition.

[0031] In a further preferred embodiment, after adding binder, surfactant and stabilizer to slurry B, stir for 60-120 minutes.

[0032] Adding the sodium carboxymethyl cellulose solution after adjusting the slurry viscosity and forming a stable system can prevent the binder from combining with the insufficiently dispersed solid particles too early to form agglomerates, avoid the surfactant from changing the interfacial tension in advance and affecting the dispersant's effect, and ensure that the two-dimensional boron nitride sheets and nanofibers are uniformly distributed in the slurry. The binder must be added after the solid particles are evenly dispersed in order to uniformly coat the particles and enhance the cohesive strength of the coating and the adhesion of the base film; the surfactant added to the stable system can precisely reduce the interfacial tension of the coating and improve the leveling; the stabilizer added last can maintain the stability of the final state of the slurry and avoid functional failure due to changes in the system during the initial stirring process. First, the solid particles are initially dispersed by dry mixing and dispersant. Then, a stable rheological system is constructed using sodium carboxymethyl cellulose. Finally, functional additives are added to ensure the uniformity of the synergistic effect between the fish-scale puncture-resistant structure (two-dimensional boron nitride) and the three-dimensional support network (nanofiber) in the coating, thereby improving the puncture resistance and mechanical stability of the diaphragm.

[0033] In some embodiments, the temperature of hot pressing is 70-120°C, and the hot pressing pressure is 0.1-5 MPa.

[0034] Secondly, the present invention provides a puncture-resistant composite diaphragm, which is prepared by the aforementioned preparation method.

[0035] The present invention will be further described below with reference to the embodiments.

[0036] Example 1 A method for preparing a puncture-resistant composite diaphragm includes the following steps: 1) Preparation of membrane substrate: Ultra-high molecular weight polyethylene 2 million and paraffin oil are melt-blended at a mass ratio of 3:7, extruded and cast, cooled and shaped, extracted with dichloromethane to create pores, and then stretched and shaped to obtain the base membrane substrate. The thickness of the base membrane substrate is controlled at 4μm. 2) Preparation of coating slurry: Sodium carboxymethyl cellulose powder was added to deionized water and mixed with a high-speed mixer to obtain sodium carboxymethyl cellulose solution. The mixing time was 60 min. Two-dimensional boron nitride and electrospun polyacrylonitrile nanofibers (average diameter 500 nm, average length 10000 nm) were dry-blended for 50 min, and then deionized water and dispersant were added to prepare a slurry. The slurry was stirred with a planetary mixer for 120 min. Add sodium carboxymethyl cellulose solution and stir for 120 minutes. Finally, add polyacrylate binder and surfactant and stir for 90 minutes to obtain slurry. The mass ratio of two-dimensional boron nitride, nanofibers, deionized water, surfactant, binder, dispersant, and stabilizer is 35:2:54:0.06:5:0.4:0.5. The two-dimensional boron nitride sheet has a diameter of 2μm and a thickness of 20nm; the surfactant is polyether-modified polysiloxane, the dispersant is ammonium polyacrylate, and the stabilizer is sodium carboxymethyl cellulose.

[0037] 3) Preparation of coated diaphragm: The slurry prepared in step 2) is coated on one side of the base film prepared in step 1) using a micro-gravure roller. The coating thickness is controlled at about 3μm. After coating, it is dried in an oven at a temperature of 80℃. 4. Preparation of composite membrane: The base membrane prepared in step 1) and the composite membrane layer coated in step 3) are hot-pressed together at a temperature of 90°C and a pressure of 3MPa to obtain a high-ratio composite membrane.

[0038] Example 2 The difference from Example 1 is that the coating thickness is 4 μm.

[0039] A method for preparing a puncture-resistant composite diaphragm includes the following steps: 1) Preparation of membrane substrate: Ultra-high molecular weight polyethylene and paraffin oil are melt-blended at a mass ratio of 3:7, extruded and cast, cooled and shaped, extracted with dichloromethane to create pores, and then stretched and shaped to obtain the base membrane substrate, wherein the thickness of the base membrane substrate is controlled at 4μm. 2) Preparation of coating slurry: Sodium carboxymethyl cellulose powder was added to deionized water and mixed with a high-speed mixer to obtain sodium carboxymethyl cellulose solution. The mixing time was 60 min. Two-dimensional boron nitride and nanofibers were dry-blended for 50 min, then deionized water and dispersant were added to prepare a slurry and stirred with a planetary mixer for 120 min. Add sodium carboxymethyl cellulose solution and stir for 120 minutes; Finally, add polyacrylate binder and surfactant and stir for 90 minutes to obtain slurry; The mass ratio of two-dimensional boron nitride, nanofibers, deionized water, surfactant, binder, dispersant, and stabilizer is 35:2:54:0.06:5:0.4:0.5. The two-dimensional boron nitride sheet has a diameter of 2μm and a thickness of 20nm; the surfactant is polyether-modified polysiloxane, the dispersant is ammonium polyacrylate, and the stabilizer is sodium carboxymethyl cellulose.

[0040] 3) Preparation of coated diaphragm: The slurry prepared in step 2) is coated on one side of the base film in step 1 using a micro-gravure roller. The coating thickness is controlled at about 4μm. After coating, it is dried in an oven at a temperature of 80℃. 4) Preparation of composite membrane: The base membrane prepared in step 1) is hot-pressed with the composite membrane layer coated in step 3) at a temperature of 90°C and a pressure of 3MPa to obtain a high-ratio composite membrane.

[0041] Example 3 The difference from Example 1 is that the mass ratio of two-dimensional boron nitride, nanofibers, deionized water, surfactant, binder, dispersant and stabilizer is 50:4:100:0.05:7:0.6:1, while all other aspects are the same as in Example 1.

[0042] Example 4 The difference from Example 1 is that the mass ratio of two-dimensional boron nitride, nanofibers, deionized water, surfactant, binder, dispersant and stabilizer is 70:6:150:0.07:10:0.5:1.5, while all other aspects are the same as in Example 1.

[0043] Comparative Example 1 The difference from Example 1 is that the electrospun polyacrylonitrile nanofibers are omitted; otherwise, they are the same as in Example 1. Specifically: A method for preparing a puncture-resistant composite diaphragm includes the following steps: 1) Preparation of membrane substrate: Ultra-high molecular weight polyethylene and paraffin oil are melt-blended at a mass ratio of 3:7, extruded and cast, cooled and shaped, extracted with dichloromethane to create pores, and then stretched and shaped to obtain the base membrane substrate, wherein the thickness of the base membrane substrate is controlled at 4μm. 2) Preparation of coating slurry: Sodium carboxymethyl cellulose powder was added to deionized water and mixed with a high-speed mixer to obtain sodium carboxymethyl cellulose solution. The mixing time was 60 min. Two-dimensional boron nitride was added to deionized water and dispersant to prepare a slurry, which was then stirred using a planetary mixer for 120 minutes. Add sodium carboxymethyl cellulose solution and stir for 120 minutes. Finally, add polyacrylate binder and surfactant and stir for 90 minutes to obtain slurry. The mass ratio of two-dimensional boron nitride, deionized water, surfactant, binder, dispersant, and stabilizer is 35:54:0.06:5:0.4:0.5. The two-dimensional boron nitride has a sheet diameter of 2 μm and a thickness of 20 nm; the surfactant is polyether-modified polysiloxane, the dispersant is ammonium polyacrylate, and the stabilizer is sodium carboxymethyl cellulose.

[0044] 3) Preparation of coated diaphragm: The slurry prepared in step 2) is coated on one side of the base film in step 1 using a micro-gravure roller. The coating thickness is controlled at about 3μm. After coating, it is dried in an oven at a temperature of 80℃. 4) Preparation of composite membrane: The base membrane prepared in step 1) is hot-pressed with the composite membrane layer coated in step 3) at a temperature of 90°C and a pressure of 3MPa to obtain a high-ratio composite membrane.

[0045] Comparative Example 2 A comparative experiment was conducted using a commercially available 9μm high-strength base film (KS099, Lankotu) with 2μm alumina ceramic. The alumina ceramic slurry was coated onto one side of the base film using a gravure roller to obtain a composite diaphragm.

[0046] Comparative Example 3 A comparative experiment was conducted using a commercially available 9μm ordinary porosity base membrane (KS093, Lankotu) with 2μm alumina ceramic. The alumina ceramic slurry was coated onto one side of the base membrane using a gravure roller to obtain a composite membrane.

[0047] Comparative Example 4 The difference from Example 1 is that the two-dimensional boron nitride is omitted, while everything else is the same as in Example 1.

[0048] Comparative Example 5 The difference from Example 1 is that the step of dry mixing the two-dimensional boronazine and electrospun polyacrylonitrile nanofibers is omitted; instead, the nanofibers are directly mixed with deionized water and a dispersant. Everything else is the same as in Example 1. The slurry agglomerates, resulting in poor consistency and making it difficult to apply.

[0049] Comparative Example 6 The difference from Example 1 is that the two-dimensional boron nitride is replaced with aluminum oxide.

[0050] A method for preparing a puncture-resistant composite diaphragm includes the following steps: 1) Preparation of membrane substrate: The base membrane substrate is prepared by melt blending ultra-high molecular weight polyethylene and paraffin oil at a mass ratio of 3:7, extruding and casting, cooling and shaping, extracting and creating pores with dichloromethane, and then stretching and shaping. The thickness of the base membrane substrate is controlled at 4μm. 2) Preparation of coating slurry: Sodium carboxymethyl cellulose powder was added to deionized water and mixed with a high-speed mixer to obtain sodium carboxymethyl cellulose solution. The mixing time was 60 min. Alumina and nanofibers were dry-blended for 50 minutes, then deionized water and dispersant were added to prepare a slurry, which was then stirred with a planetary mixer for 120 minutes. Add sodium carboxymethyl cellulose solution and stir for 120 minutes. Finally, add polyacrylate binder and surfactant and stir for 90 minutes to obtain slurry. The mass ratio of alumina, nanofibers, deionized water, surfactant, binder, dispersant, and stabilizer is 35:2:54:0.06:5:0.4:0.5. The two-dimensional boron nitride sheet has a diameter of 2μm and a thickness of 20nm; the surfactant is polyether-modified polysiloxane, the dispersant is ammonium polyacrylate, and the stabilizer is sodium carboxymethyl cellulose.

[0051] 3) Preparation of coated diaphragm: The slurry prepared in step 2) is coated on one side of the base film in step 1) using a micro-gravure roller. The coating thickness is controlled at about 4μm. After coating, it is dried in an oven at a temperature of 80℃. 4) Preparation of composite membrane: The base membrane prepared in step 1) is hot-pressed with the composite membrane layer coated in step 3) at a temperature of 90°C and a pressure of 3MPa to obtain a high-ratio composite membrane.

[0052] Test methods: The air permeability of the coated diaphragm was tested using a Wang Yanshi EG01-55-1MR air permeability tester; heat shrinkage was tested using an oven.

[0053] A comparison of Examples 1 and 3 shows that two-dimensional boron nitride helps improve the puncture resistance of the separator. A comparison of Examples 1 and 2 shows that increasing the thickness of the composite coating increases the separator's resistance to heat shrinkage and puncture strength, but increases its brittleness, which is detrimental to the cell manufacturing process. A comparison of Example 1 and Comparative Example 1 shows that the needle penetration strength of the composite separator decreases to some extent due to the loss of nanofiber support, which is detrimental to the cell's safety characteristics. A comparison of Examples 1 and Comparative Examples 2-3 shows that the two-dimensional boron nitride composite separator effectively improves the separator's puncture resistance, ensuring the safety of the cell, as shown in Table 1.

[0054] Table 1 Comparison of diaphragms in Examples and Comparative Examples

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a puncture-resistant composite diaphragm, characterized in that: Includes the following steps: Two-dimensional boron nitride and nanofibers are dry-mixed at a mass ratio of 20-100:1-10, then mixed with water and dispersant, and then mixed with sodium carboxymethyl cellulose solution, binder and surfactant to obtain slurry; The slurry is coated onto one side of the base film, and after drying, a coating is obtained; Another base film is hot-pressed onto the base film with the coating, so that the coating is located between the two base films.

2. The method for preparing the puncture-resistant composite diaphragm according to claim 1, characterized in that: The nanofibers are electrospun polyacrylonitrile nanofibers with a diameter of 50-3000 nm and a length of 1000-20000 nm.

3. The method for preparing the puncture-resistant composite diaphragm according to claim 1, characterized in that: Two-dimensional borazine sheets have a diameter of 0.1-10 μm and a thickness of 1-100 nm.

4. The method for preparing the puncture-resistant composite diaphragm according to claim 1, characterized in that: The slurry also includes a stabilizer, and the mass ratio of two-dimensional boron nitride, nanofibers, water, surfactant, binder, dispersant, and stabilizer is 20-100:1-10:30-200:0.01-0.1:1-10:0.1-1:0.1-2; Preferably, the mass ratio of two-dimensional borazine, nanofibers, water, surfactant, binder, dispersant, and stabilizer is 20-50:1-6:30-100:0.04-0.08:3-8:0.1-0.8:0.3-1.5; Preferably, the mass ratio of two-dimensional boron nitride to nanofibers is 30-50:1-4.

5. The method for preparing the puncture-resistant composite diaphragm according to claim 1, characterized in that: The surfactant is at least one of silane coupling agents, alkylphenol polyoxyethylene ethers, fatty alcohol polyoxyethylene ethers, fatty acid polyoxyethylene ethers, and polyether-modified polysiloxanes. Alternatively, the dispersant may be selected from ammonium polyacrylate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium hexametaphosphate, or octylphenol polyoxyethylene ether.

6. The method for preparing the puncture-resistant composite diaphragm according to claim 1, characterized in that: The coating is 0.5-5 μm thick.

7. The method for preparing the puncture-resistant composite diaphragm according to claim 1, characterized in that: The base film is prepared by: melt blending ultra-high molecular weight polyethylene and paraffin oil in a mass ratio of 2-4:6-10, extruding and casting, cooling and shaping, extracting and creating pores with dichloromethane, and then stretching and shaping to obtain the base film. Preferably, the thickness of the base film is 2-10 μm.

8. The method for preparing the puncture-resistant composite diaphragm according to claim 1, characterized in that: The time for dry mixing of two-dimensional boron nitride and nanofibers is 30-60 minutes. Preferably, after the two-dimensional boron nitride and nanofibers are dry-mixed, the mixture is stirred with water and dispersant for 60-240 minutes to obtain slurry A; Preferably, sodium carboxymethyl cellulose solution is added to slurry A and stirred for 30-180 min to obtain slurry B; Preferably, after adding the binder, surfactant and stabilizer to slurry B, the mixture is stirred for 60-120 minutes.

9. The method for preparing the puncture-resistant composite diaphragm according to claim 1, characterized in that: The hot-pressing temperature is 70-120℃, and the hot-pressing pressure is 0.1-5MPa.

10. A puncture-resistant composite diaphragm, characterized in that: It is prepared by any one of the preparation methods described in claims 1-9.

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