High-strength battery diaphragm, preparation method thereof and secondary battery

Abstract

The invention discloses a high-strength battery diaphragm, a preparation method thereof and a secondary battery. The raw materials of the diaphragm comprise polyolefin resin and a pore-forming agent, based on the total mass of the raw materials, the weight content of the polyolefin resin is 10%-25%, and the weight content of the pore-forming agent is 75%-90%; the polyolefin resin is ultra-high molecular weight polyethylene, and the average molecular weight of the ultra-high molecular weight polyethylene is 1 million to 5 million. The high-strength battery diaphragm provided by the invention has excellent mechanical strength, and the reliability of the battery can be improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a high-strength battery separator and its preparation method, and a secondary battery. Background Technology

[0002] The separator has electronic insulation properties, acting as a barrier to prevent electrons from directly contacting the positive and negative electrodes and causing a short circuit. At the same time, the separator has a certain pore size and porosity, giving it high ionic conductivity and allowing for good ion permeability.

[0003] The mechanical strength of the separator is crucial to the safety of rechargeable batteries. After being subjected to stress during battery assembly, damage from impacts and drops, and damage from lithium dendrites during cycling, the separator needs to maintain good mechanical integrity to prevent short circuits or even battery failure. Therefore, improving the mechanical strength of the separator is one of the most pressing issues to be addressed. Summary of the Invention

[0004] Based on the above-mentioned technical problems, this application provides a high-strength battery separator and its preparation method, as well as a secondary battery, in order to improve the mechanical strength of the separator.

[0005] In a first aspect, embodiments of this application provide a high-strength battery separator, wherein the raw materials of the separator include polyolefin resin and a pore-forming agent, and based on the total mass of the raw materials, the weight content of the polyolefin resin is 10%-25%, and the weight content of the pore-forming agent is 75%-90%; the polyolefin resin is ultra-high molecular weight polyethylene, and the average molecular weight of the ultra-high molecular weight polyethylene is 1 million to 5 million.

[0006] In some embodiments, the average molecular weight of the ultra-high molecular weight polyethylene is 1.2 million to 4 million.

[0007] In some embodiments, the polyolefin resin has a weight content of 15%-22% and the pore-forming agent has a weight content of 78%-85% based on the total mass of the raw materials.

[0008] In some embodiments, the pore-forming agent includes one or more of paraffin oil, p-xylene, and nonane.

[0009] In some embodiments, the thickness of the diaphragm is 2 μm-9 μm.

[0010] In some embodiments, the porosity of the membrane is 25%-45%.

[0011] In some embodiments, the air permeability of the diaphragm is 90s / 100mL-160s / 100mL.

[0012] In some embodiments, the pore size of the diaphragm is 20nm-100nm.

[0013] In some embodiments, the MD tensile strength of the diaphragm is greater than or equal to 3500 kgf / cm. 2 .

[0014] In some embodiments, the TD tensile strength of the diaphragm is greater than or equal to 3500 kgf / cm. 2 .

[0015] In some embodiments, the puncture strength of the diaphragm is greater than or equal to 400 gf.

[0016] In some embodiments, the MD thermal shrinkage rate of the diaphragm is less than or equal to 3%.

[0017] In some embodiments, the TD heat shrinkage rate of the diaphragm is less than or equal to 32%.

[0018] Secondly, embodiments of this application provide a method for preparing a high-strength battery separator, comprising the following steps:

[0019] A homogeneous mixture comprising a polyolefin resin and a pore-forming agent is provided;

[0020] The homogeneous mixture is extruded to obtain a diaphragm sheet;

[0021] The membrane sheet is subjected to longitudinal stretching, one transverse stretching, extraction pore forming, and a second transverse stretching in sequence to obtain the high-strength battery separator.

[0022] In some embodiments, the longitudinal stretching ratio is 8-20 times.

[0023] In some embodiments, the stretching ratio of the single lateral stretch is 8-20 times.

[0024] In some embodiments, the stretching ratio of the secondary transverse stretching is 2-15 times.

[0025] In some embodiments, the temperature of the longitudinal stretching is 30°C-100°C.

[0026] In some embodiments, the temperature of the first transverse stretching is 30°C-200°C.

[0027] In some embodiments, the temperature of the secondary transverse stretching is 100℃-230℃.

[0028] In some embodiments, after extruding the homogeneous mixture and cooling it to form a diaphragm sheet, the method further includes: trimming at least one side of the diaphragm sheet, wherein the trimming width H1 and the width H2 of the diaphragm sheet satisfy: 10mm≤H1≤0.5H2.

[0029] In some embodiments, after the secondary transverse stretching, the process further includes: heat setting treatment, in which the membrane material obtained by the secondary transverse stretching is heat-treated at 20℃-80℃ for 20s-180s to obtain the diaphragm.

[0030] Thirdly, embodiments of this application provide a secondary battery, including a separator according to the first aspect of this application or a separator prepared according to the preparation method of the second aspect of this application. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0032] Figure 1 Scanning electron microscope (SEM) image (2k) of a high-strength battery separator provided in an embodiment of this application;

[0033] Figure 2 Scanning electron microscope (SEM) image (20k) of a high-strength battery separator provided for another embodiment of this application. Detailed Implementation

[0034] The features and exemplary embodiments of various aspects of this application will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a comprehensive understanding of this application. However, it will be apparent to those skilled in the art that this application can be implemented without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of this application by illustrating examples. In the accompanying drawings and the following description, at least some well-known structures and techniques are not shown to avoid unnecessarily obscuring the application; and, for clarity, the dimensions of some structures may be exaggerated. Furthermore, the features, structures, or characteristics described below can be combined in any suitable manner in one or more embodiments.

[0035] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0036] This application provides a high-strength battery separator with high tensile strength and high puncture strength to improve the problem of the separator being easily damaged during battery assembly and punctured by lithium dendrites during cycling, thereby improving the reliability of the battery; the high-strength battery separator provided in this application also has high thermal stability.

[0037] High-strength battery separator

[0038] The first aspect of this application provides a high-strength battery separator. The raw materials of the separator include polyolefin resin and a pore-forming agent. Based on the total mass of the raw materials, the weight content of the polyolefin resin is 10%-25%, and the weight content of the pore-forming agent is 75%-90%. The polyolefin resin is ultra-high molecular weight polyethylene, and the average molecular weight of ultra-high molecular weight polyethylene is 1 million to 5 million.

[0039] In this embodiment, ultra-high molecular weight polyethylene is used as the main raw material for high-strength battery separators. By adjusting the proportion of polyolefin resin in the raw materials, the resulting high-strength battery separator can have high tensile strength and puncture strength, while also having a low thermal shrinkage rate. This gives the high-strength battery separator high mechanical strength and high-temperature resistance, thereby reducing damage to the separator caused by stress, collisions, and drops during battery assembly. It also reduces the risk of lithium dendrites puncturing the separator during cycling, thereby lowering the risk of short circuits or even secondary battery failure and improving the reliability of secondary batteries. Figure 1 and Figure 2 SEM images of high-strength battery separators prepared in some embodiments of this application are shown. It can be seen that the separators have a good pore structure.

[0040] In some embodiments, the average molecular weight of ultra-high molecular weight polyethylene can be 1.2 million to 4 million, more preferably 1.3 million to 3 million, and even more preferably 1.4 million to 2 million.

[0041] By controlling the average molecular weight of ultra-high molecular weight polyethylene within the aforementioned range, high-strength battery separators can have higher tensile and puncture strength, further enhancing their mechanical strength and thus improving the reliability of secondary batteries.

[0042] In some embodiments, based on the total mass of the raw materials, the weight content of the polyolefin resin can be 15%-22%, optionally 18%-22%; the weight content of the pore-forming agent can be 78%-85%, optionally 78%-82%.

[0043] By controlling the proportions of polyolefin resin and pore-forming agent in the raw materials of high-strength battery separators within the above-mentioned range, high-strength battery separators can achieve both higher mechanical strength and higher porosity, as well as uniform pore size distribution.

[0044] In some embodiments, the pore-forming agent includes one or more of paraffin oil, p-xylene, and nonane.

[0045] The aforementioned pore-forming agent can be uniformly dispersed in polyolefin resin, and can form pores of uniform size and distribution on high-strength battery separators through extraction pore formation, so that the high-strength battery separators have high porosity and ion permeability.

[0046] In some embodiments, the thickness of the high-strength battery separator is 2μm-9μm, and optionally 3μm-8μm.

[0047] In some embodiments, the porosity of the high-strength battery separator is 25%-45%, optionally 28%-40%.

[0048] The porosity of a battery separator refers to the ratio of the pore volume to the total volume of the separator. It can be measured using methods commonly used in the field, such as the liquid absorption method, calculation method, and instrumental testing method. Controlling the porosity of a high-strength battery separator within the above-mentioned range can give the separator higher ion permeability, thereby improving the electrochemical performance of the secondary battery.

[0049] In some embodiments, the air permeability of the high-strength battery separator is 90s / 100mL-160s / 100mL.

[0050] The gas permeability of a high-strength battery separator refers to the time it takes for a certain volume of air to pass through a specified area of ​​the separator under a certain pressure, and it can be tested using methods commonly used in the field. For example, it can be tested according to the methods specified in GB / T 1038-2022 "Test Method for Gas Permeability of Plastic Films and Sheets".

[0051] In some embodiments, the pore size of the high-strength battery separator is 20nm-100nm, and optionally 25nm-90nm.

[0052] By limiting the pore size of the high-strength battery separator to the above-mentioned range, the separator can have better ion permeability, resulting in lower internal resistance of the secondary battery and thus improving the electrochemical performance of the secondary battery. At the same time, when the pore size of the separator is limited to the above-mentioned range, the separator has higher puncture strength, which can reduce the risk of lithium dendrite growth puncturing the separator and improve the reliability of the secondary battery.

[0053] In some embodiments, the MD tensile strength of the diaphragm is greater than or equal to 3500 kgf / cm². 2 .

[0054] In some embodiments, the tensile strength (TD) of the diaphragm is greater than or equal to 3500 kgf / cm². 2 .

[0055] In some embodiments, the puncture strength of the diaphragm is greater than or equal to 400 gf.

[0056] In some embodiments, the MD thermal shrinkage rate of the diaphragm is less than or equal to 3%.

[0057] In some embodiments, the TD heat shrinkage rate of the diaphragm is less than or equal to 2%.

[0058] Preparation method of high-strength battery separator

[0059] An embodiment of the second aspect of this application provides a method for preparing a high-strength battery separator, comprising the following steps S100 to S300:

[0060] S100 provides a homogeneous mixture comprising a polyolefin resin and a pore-forming agent;

[0061] S200, a homogeneous mixture is extruded to obtain a diaphragm sheet;

[0062] S300 involves sequentially stretching the separator sheet longitudinally (MD), performing a first transverse stretch (TD1), extracting pores, and performing a second transverse stretch (TD2) to obtain a high-strength battery separator.

[0063] In this embodiment, the high-strength battery separator is obtained by extrusion molding followed by biaxial stretching. The stretched film is then extracted to remove the pore-forming agent, forming uniformly distributed pores on the membrane material. This results in a high-strength battery separator with high porosity and ion permeability. Simultaneously, longitudinal stretching and two transverse stretching operations enhance the tensile and puncture strength of the high-strength battery separator, thereby improving its mechanical strength and increasing the reliability of the rechargeable battery.

[0064] In some embodiments, extruding the homogeneous mixture to obtain a diaphragm sheet includes: heating and melting the homogeneous mixture in a twin-screw extruder to form a homogeneous melt, extruding the melt through a die, and cooling and shaping it on a chilling roller to obtain a diaphragm sheet.

[0065] In some embodiments, the longitudinal stretch (MD) stretch ratio can be 8-20 times, optionally 9-18 times, and more preferably 9-14 times.

[0066] In some embodiments, the longitudinal stretching temperature can be 30℃-100℃, and optionally 50℃-80℃.

[0067] By controlling the longitudinal stretching ratio and processing temperature within the above range, high-strength battery separators can have higher tensile strength and puncture strength, thereby improving their mechanical strength properties.

[0068] In some embodiments, the stretching ratio of a single transverse stretch (TD1) can be 8-20 times, optionally 9-18 times, and more preferably 10-15 times.

[0069] In some embodiments, the temperature for a single transverse stretching can be 30℃-200℃, optionally 40℃-180℃, and more preferably 50℃-170℃.

[0070] By controlling the stretching ratio and processing temperature of a single transverse stretch within the above range, the high-strength battery separator can have higher tensile strength and puncture strength, thereby improving the mechanical strength performance of the high-strength battery separator.

[0071] In some embodiments, the stretching ratio of the secondary transverse stretching (TD2) can be 2-15 times, optionally 4-12 times, and more preferably 5-10 times.

[0072] In some embodiments, the temperature for the secondary transverse stretching can be 100℃-230℃, optionally 120℃-210℃, and more preferably 140℃-200℃.

[0073] By controlling the stretching ratio and temperature of the secondary transverse stretching within the above range, the high-strength battery separator can have higher tensile strength and puncture strength, thereby improving the mechanical strength performance of the high-strength battery separator.

[0074] In some embodiments, the diaphragm sheet further includes a shrinkage process after secondary transverse stretching, with a shrinkage ratio of 10%-30%, optionally 15%-28%, and more preferably 20%.

[0075] Immediately shrinking the membrane material after secondary lateral stretching can further stabilize the membrane's shape, giving it higher thermal stability. This reduces the thermal shrinkage rate of high-strength battery separators, thereby improving their high-temperature resistance.

[0076] In some embodiments, after secondary transverse stretching and retraction, the membrane material is further subjected to heat treatment; the heat treatment temperature can be 20℃-80℃, optionally 30℃-70℃, and more preferably 40℃-60℃; the heat treatment time can be 20s-180s, optionally 30s-160s, and more preferably 40s-150s.

[0077] Heat treatment can eliminate thermal stress inside high-strength battery separators and improve their thermal stability.

[0078] In some embodiments, before longitudinal stretching of the diaphragm sheet, the method further includes: edge trimming of the diaphragm sheet. The diaphragm sheet obtained by extrusion molding is trimmed, with the trimmed side being the width side of the diaphragm sheet. The trimming can be done on one side or both sides. Pre-treating the width of the diaphragm sheet by trimming allows the transverse stretching ratio of the diaphragm sheet to be less constrained by the theoretically designed width of the production equipment, thereby increasing the transverse stretching ratio of the diaphragm and thus improving its tensile strength and puncture strength. Furthermore, the trimming process makes the sheet edges smoother and flatter, reducing the risk of the diaphragm sheet breaking under high stretching conditions.

[0079] In some embodiments, the slit width H1 of the diaphragm sheet and the width H2 of the diaphragm sheet satisfy the following condition: 10mm ≤ H1 ≤ 0.5H2.

[0080] Optionally, the slice width can be 50mm-400mm, optionally 80mm-300mm, or even more preferably 100mm-200mm.

[0081] By limiting the cutting edge width to the above range, the limitation of the theoretical design width of the equipment on the lateral stretching ratio can be further reduced, thereby increasing the lateral stretching ratio of the separator and thus improving the tensile strength and puncture strength of the high-strength battery separator.

[0082] In some embodiments, extraction pore formation includes: extracting pores in an extractant on a membrane material that has undergone one lateral stretching, followed by drying.

[0083] After the membrane material is immersed in the extractant following a transverse stretching process, the pore-forming agent in the membrane material is dissolved by the extractant and separated from the membrane. Micropores are formed at the locations of the pore-forming agent on the membrane, resulting in a membrane with a porous structure. The extractant may include volatile substances, such as one or more of dichloromethane and cyclohexane.

[0084] In some embodiments, the drying temperature can be 25°C-100°C, optionally 30°C-90°C, and more preferably 40°C-80°C.

[0085] In some embodiments, the drying time can be 5s-120s, optionally 10s-110s, or more preferably 20s-100s.

[0086] In some embodiments, the diaphragm further includes an electrostatic elimination treatment after drying.

[0087] By installing an electrostatic eliminator near the diaphragm to eliminate static electricity, the static electricity generated by friction between the diaphragm and guide rollers can be reduced or eliminated, thereby reducing the risk of the diaphragm being damaged due to excessive static electricity.

[0088] Secondary batteries

[0089] An embodiment of the third aspect of this application provides a secondary battery, including a high-strength battery separator according to the first aspect of this application or a high-strength battery separator obtained according to the preparation method of the second aspect of this application.

[0090] Example

[0091] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0092] Example 1

[0093] A high-strength battery separator is prepared by the following method:

[0094] S100 is prepared by mixing ultra-high molecular weight polyethylene with a molecular weight of 1 million to 5 million with pore-forming agent paraffin oil at a mass ratio of 18:82 to obtain a homogeneous mixture.

[0095] S200: The homogeneous mixture is added to a twin-screw extruder, heated and melted at 60℃-30℃ and then cooled and shaped on a chiller roll to obtain a diaphragm sheet with uniform thickness and a total width of 780mm.

[0096] S300, the diaphragm sheet is treated with double-sided edge trimming, the total width of the trimmed edges is 80mm, and the width of the diaphragm sheet after trimming is 700mm;

[0097] S400 involves longitudinally stretching (MD) the trimmed diaphragm sheet at 80°C with a stretching ratio of 8.5 times.

[0098] S500 involves subjecting the longitudinally stretched sheet to a transverse stretching (TD1) treatment at 120°C, with a stretching ratio of 10 times.

[0099] S600 extracts the membrane material after one transverse stretching with dichloromethane. The extracted membrane is dried at 80°C for 60 seconds and then destatically removed by an electrostatic eliminator.

[0100] S700 involves subjecting the membrane material to a secondary transverse stretching (TD2) treatment at 150℃, followed by immediate shrinkage after the secondary transverse stretching, with a shrinkage ratio of 20% and a stretching ratio of 8 times.

[0101] S800 heat-treated the separator at 60°C for 130s to obtain a high-strength battery separator with a thickness of 5μm.

[0102] Examples 2 to 11

[0103] The preparation method of the high-strength battery separator is the same as that in Example 1. The differences are detailed in Table 1. All other parameters and conditions are the same as those in Example 1.

[0104] Comparative Examples 1 to 2

[0105] The preparation method of the high-strength battery separator is the same as that in Example 1. The differences are detailed in Table 1. All other parameters and conditions are the same as those in Example 1.

[0106] Table 1

[0107]

[0108] Example 13

[0109] The difference from Example 1 is that no retraction process is performed after the second transverse stretching, while the other parameters and conditions remain the same as in Example 1.

[0110] Example 14

[0111] The difference from Example 1 is that the polyolefin resin selected is polyethylene with a molecular weight of 1.2 million to 4 million, while the other conditions and parameters are the same as in Example 1.

[0112] Comparative Example 3

[0113] The difference from Example 1 is that the polyolefin resin selected is polyethylene with a molecular weight of 550,000-650,000, while the other conditions and parameters are the same as in Example 1.

[0114] Test section

[0115] The performance of the battery separators prepared in the examples and comparative examples was tested.

[0116] Porosity test: Cut a 100mm × 100mm square sample, weigh the square diaphragm sample, and calculate the basis weight ρ1 of the diaphragm sample (unit: g / m³). 2 The average thickness d (unit: μm) of the square diaphragm sample was calculated by measuring the thickness at five points on the sample using a Marl thickness gauge. The density of the polyethylene raw material was taken as ρ0 = 0.95 g / cm³. 3 The formula for calculating porosity is as follows: Porosity = (1 - ρ1 / (d*ρ0)) * 100%.

[0117] Pore ​​size testing: The surface morphology of the diaphragm was characterized using a scanning electron microscope (SEM) to obtain the pore size of the diaphragm.

[0118] Air permeability test: The air permeability of the diaphragm was tested using an EG01-55-1MR digital Wang Yan type air permeability tester under a pressure of 0.25MPa.

[0119] Tensile strength test: Using an intelligent electronic tensile testing machine, the diaphragms of each embodiment and comparative example were cut into samples with a length of 100 mm and a width of 15 mm, and tensile strength data were obtained by stretching at 250 mm / min.

[0120] Puncture strength test: The puncture strength of the diaphragm is determined using a puncture instrument. Specifically, a 1mm diameter needle with no sharp edge at the tip is used to puncture the diaphragm vertically at a speed of 0.1cm / s, and the puncture strength data is obtained.

[0121] Heat shrinkage rate test: Cut a 100mm×100mm square sample from the diaphragm of each example and comparative example, measure the length in the MD / TD direction and record it as L0. Place the sample in an electric heating oven and bake at 105℃ for 1 hour. Take it out and measure the length in the MD / TD direction and record it as L. The formula for calculating the heat shrinkage rate is as follows: Heat shrinkage rate = (L0-L) / L0×100%.

[0122] The test results are detailed in Table 2.

[0123] Table 2

[0124]

[0125] As can be seen from the data in Table 2, by adjusting the raw material composition of the separator and optimizing the process parameters for preparing the separator in this embodiment of the application, the battery separator can have good mechanical strength, which can effectively reduce the loss of the separator during battery assembly and the risk of lithium dendrite growth puncturing the separator during battery cycling.

[0126] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A high-strength battery separator, characterized in that, The raw materials for the diaphragm include polyolefin resin and pore-forming agent. Based on the total mass of the raw materials, the weight content of the polyolefin resin is 10%-25%, and the weight content of the pore-forming agent is 75%-90%. The polyolefin resin is ultra-high molecular weight polyethylene, and the average molecular weight of the ultra-high molecular weight polyethylene is 1 million to 5 million.

2. The battery separator according to claim 1, characterized in that, The average molecular weight of the ultra-high molecular weight polyethylene is 1.2 million to 4 million.

3. The battery separator according to claim 1, characterized in that, Based on the total mass of the raw materials, the polyolefin resin has a weight content of 15%-22%, and the pore-forming agent has a weight content of 78%-85%.

4. The battery separator according to any one of claims 1 to 3, characterized in that, The diaphragm has a tensile strength of MD greater than or equal to 3500 kgf / cm². 2 ; and / or The TD tensile strength of the diaphragm is greater than or equal to 3500 kgf / cm. 2 ; and / or The puncture strength of the diaphragm is greater than or equal to 400 gf; and / or The MD heat shrinkage rate of the diaphragm is less than or equal to 3%; and / or The TD thermal shrinkage rate of the diaphragm is less than or equal to 2%.

5. A method for preparing a high-strength battery separator as described in any one of claims 1 to 4, characterized in that, Includes the following steps: A homogeneous mixture comprising a polyolefin resin and a pore-forming agent is provided; The homogeneous mixture is extruded to obtain a diaphragm sheet; The separator sheet is subjected to longitudinal stretching, first transverse stretching, extraction pore forming, and second transverse stretching in sequence to obtain the battery separator.

6. The method for preparing the high-strength battery separator according to claim 5, characterized in that, The longitudinal stretching ratio is 8-20 times; and / or The stretching ratio of the single transverse stretch is 8-20 times; and / or The stretching ratio of the secondary transverse stretching is 2-15 times.

7. The method for preparing the high-strength battery separator according to claim 5, characterized in that, The longitudinal stretching temperature is 30℃-100℃; and / or The temperature of the first transverse stretching is 30℃-200℃; and / or The temperature for the secondary transverse stretching is 100℃-230℃.

8. The method for preparing the high-strength battery separator according to claim 5, characterized in that, After extruding and cooling the homogeneous mixture to obtain a diaphragm sheet, the process further includes: At least one side of the diaphragm sheet is trimmed, and the trimmed width H1 and the width H2 of the diaphragm sheet satisfy: 10mm≤H1≤0.5H2.

9. The method for preparing a high-strength battery separator according to claim 5, characterized in that, Following the secondary lateral stretching, the method further includes: Heat setting treatment involves heat-treating the membrane material obtained by secondary transverse stretching at 20℃-80℃ for 20s-180s to obtain the diaphragm.

10. A secondary battery, characterized in that, This includes the high-strength battery separator according to any one of claims 1 to 4 or the high-strength battery separator obtained by the preparation method according to any one of claims 5 to 9.

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