Diaphragm, secondary battery and electric device

Abstract

The invention discloses a diaphragm, a secondary battery and an electric device, and belongs to the technical field of batteries. According to the diaphragm provided by the invention, the corresponding hole area SD50 is selected to be within the range given by the invention when the area distribution of the accumulation holes in the base membrane reaches 50%, so that the air permeability of the base membrane can be improved, heat accumulation and gas retention in the cycle process of the secondary battery can be reduced, and the safety performance of the secondary battery can be improved; and uniform passing of ions can be facilitated, and an ion polarization phenomenon when the ions pass through the diaphragm is reduced, so that the internal resistance of the secondary battery is reduced, and the cycle performance of the secondary battery is improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to a diaphragm, a secondary battery and an electrical device. Background Art

[0002] The separator sits between the positive and negative electrodes of a secondary battery, separating them and preventing contact and short circuits. The separator's structure can affect the battery's dynamic performance, such as its internal resistance. Currently, battery manufacturers lack a clear understanding of how to reduce material costs while ensuring long-term reliability and improving battery dynamics. Summary of the Invention

[0003] The purpose of this application is to overcome the problem in the prior art that the dynamic performance and cycle performance of secondary batteries cannot be effectively improved from the diaphragm end, and to propose a diaphragm, secondary battery and electrical device that can effectively improve the dynamic performance of secondary batteries, reduce the internal resistance of secondary batteries, and improve the cycle performance of secondary batteries.

[0004] To achieve the above object, the first aspect of the present application provides a diaphragm, comprising a base membrane, wherein the pore area corresponding to the cumulative pore area distribution reaching 50% on the base membrane is S D50 nm 2 , satisfying 1865≤S D50 ≤5420.

[0005] As an embodiment of the present application, when the cumulative pore area distribution on the base film reaches 10%, the corresponding pore area is S D10 nm 2 When the cumulative pore area distribution on the basement membrane reaches 90%, the corresponding pore area is S D90 nm 2 , satisfying 1.982≤(S D90 -S D10 ) / S D50 ≤3.775.

[0006] As an embodiment of the present application, the S D10 102≤S D10 ≤620.

[0007] As an embodiment of the present application, the S D90 5879≤S D90 ≤21082.

[0008] As an embodiment of the present application, the average volume V nm of the pores of the base film is 3 , meeting 4.07×10 4 ≤V≤6.01×10 5.

[0009] As an embodiment of the present application, the thickness h of the base film is 3 μm≤h≤25 μm.

[0010] As an embodiment of the present application, the base film has two opposite surfaces, and the total number N of holes on one surface of the base film is 52≤N≤998.

[0011] As an embodiment of the present application, the base film has two opposite surfaces, the ratio of the total area of ​​the holes in the preset area of ​​one surface of the base film to the area of ​​the preset area is P1, the porosity of the base film is P2, and 0<P1<P2<1 is satisfied. The area of ​​the preset area is 36110μm 2 .

[0012] As an implementation scheme of the present application, the P1 satisfies: 0.073≤P1≤0.321.

[0013] As an implementation scheme of the present application, the P2 satisfies: 0.254≤P2≤0.788.

[0014] As an embodiment of the present application, the surface density m of the base film satisfies: 1.6 g / m 2 ≤m≤13.2g / m 2 .

[0015] As an embodiment of the present application, the true density m0 of the base film material satisfies: 0.9 g / cm 3 ≤m0≤2.3g / cm 3 .

[0016] As an embodiment of the present application, the area of ​​the pores in the basement membrane is less than 2500nm 2 The percentage S1 of the total pore area to the overall pore area of ​​the basement membrane is 15.3%≤S1≤62.8%.

[0017] As an embodiment of the present application, the area of ​​the pores in the basement membrane is greater than 1000 nm 2 The percentage S2 of the total pore area to the overall pore area of ​​the basement membrane is 1.6%≤S2≤39.8%.

[0018] As an embodiment of the present application, the short axis of the pores of the basement membrane is D1 nm, the long axis of the pores of the basement membrane is D2 nm, and the short axis D1 of the pores of the basement membrane is 38≤D1≤85;

[0019] And / or, the major axis D2 of the pores of the basement membrane is 105≤D2≤345.

[0020] As an embodiment of the present application, the diaphragm further comprises a functional coating provided on at least one side of the base film, and the functional coating comprises at least one of a heat-resistant coating and an adhesive coating.

[0021] As an implementation scheme of the present application, the short axis of the pores of the base film is D1 nm, the long axis of the pores of the base film is D2 nm, the functional coating includes organic particles and / or inorganic particles, and the particle size value corresponding to the cumulative distribution of the particle size of the organic particles and / or the inorganic particles reaches 50% is d50 nm, satisfying 0.5×(D1+D2)<d50≤10000.

[0022] As an embodiment of the present application, the short axis D1 of the pores of the basement membrane is 38≤D1≤85.

[0023] As an embodiment of the present application, the major axis D2 of the pores of the basement membrane is 105≤D2≤345.

[0024] As an embodiment of the present application, when the cumulative distribution of particle sizes of the particles in the functional coating reaches 50%, the corresponding particle size value d50 is 200≤d50≤10000.

[0025] As an embodiment of the present application, the material of the base film includes polypropylene.

[0026] As an embodiment of the present application, the base film is prepared by uniaxial stretching through a dry process.

[0027] In a second aspect of the present application, a secondary battery is provided, comprising the above-mentioned separator.

[0028] In a third aspect of the present application, an electrical device is provided, comprising the above-mentioned secondary battery.

[0029] In the diaphragm provided in the present application, the pore area S corresponding to the cumulative pore area distribution on the base membrane reaches 50% is selected. D50 Within the range given in this application, it can not only increase the permeability of the base membrane, reduce heat accumulation and gas retention during the cycle of the secondary battery, and improve the safety performance of the secondary battery; it can also facilitate the uniform passage of ions, reduce the ion polarization phenomenon when ions pass through the diaphragm, thereby reducing the internal resistance of the secondary battery and improving the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a SEM image of the basement membrane surface prepared in Example 1;

[0031] Figure 2 This is a diagram of the surface porosity of the base film prepared in Example 1;

[0032] Figure 3This is a SEM image of the basement membrane surface prepared in Example 4;

[0033] Figure 4 This is a diagram of the surface porosity of the base film prepared in Example 4;

[0034] Figure 5 This is a schematic diagram of the diaphragm structure prepared in Example 1;

[0035] Figure 6 This is a schematic diagram of the diaphragm structure prepared in Example 11;

[0036] Figure 7 This is a schematic diagram of the diaphragm structure prepared in Example 12;

[0037] Figure 8 This is the SEM image of the base film prepared by the polyethylene (PE) wet double-drawing process. DETAILED DESCRIPTION

[0038] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0040] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0041] In one embodiment of the present application, the present application provides a diaphragm, comprising a base membrane, wherein the pore area corresponding to the cumulative pore area distribution on the base membrane reaching 50% is S D50 nm 2 , satisfying 1865≤S D50 ≤5420.

[0042] In the diaphragm provided in the present application, the pore area S corresponding to the cumulative pore area distribution on the base membrane reaches 50% is selected. D50Within the scope given in this application, it can not only increase the permeability of the base membrane, reduce heat accumulation during the cycle of the secondary battery, and improve the safety performance of the secondary battery; it can also facilitate the uniform passage of ions, reduce the ion polarization phenomenon when ions pass through the diaphragm, thereby reducing the internal resistance of the secondary battery; in addition, it can also provide more ion channels, improve ion transmission efficiency, improve the charge and discharge performance of the secondary battery, and improve the cycle performance of the secondary battery.

[0043] It should be noted that when the cumulative pore area distribution on the basement membrane reaches 50%, the corresponding pore area is S D50 The test method includes the following steps:

[0044] After the secondary battery separator is taken out, dimethyl carbonate (DMC) is used to soak for 20 to 40 minutes to clean the residual by-products on the surface and pore structure of the separator, and then an appropriate amount of alcohol is added to the coating surface of the separator, and then the coating surface is wiped to make the coating fall off to obtain a base membrane sample; the base membrane sample is placed on the scanning electron microscope SEM sample stage, 10 positions on the surface of the base membrane are randomly selected, and a magnification of 30,000 times is taken at each position; then the picture is placed in the software Image J and the test is completed according to the steps of setting the scale (200nm), field of view selection, measurement, data processing and analysis, etc., and the raw data can be exported by the software to obtain the S D50 .

[0045] For example, S D50 Can be 1865≤S D50 Any point value or any two point range value within the range of ≤5420, such as S D50 It can be a range value of one or any two of 1865, 2000, 2200, 2500, 2800, 3000, 3200, 3500, 3800, 4000, 4200, 4500, 4800, 5000, 5200, 5420.

[0046] In one embodiment, S D50 Satisfy 3775≤S D50 ≤5420. For example, S D50 It can be a range of one or any two of 3775, 3800, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, 5000, 5100, 5200, 5300, 5420. D50 When the content is within the above range, the comprehensive performance of the obtained secondary battery is better.

[0047] In one embodiment, the pore area corresponding to the cumulative pore area distribution on the base film reaching 10% is S D10 nm2 When the cumulative pore area distribution on the basement membrane reaches 90%, the corresponding pore area is S D90 nm 2 , satisfying 1.982≤(S D90 -S D10 ) / S D50 ≤3.775.

[0048] It should be noted that when the cumulative pore area distribution on the basement membrane reaches 10%, the corresponding pore area is S D10 When the cumulative pore area distribution on the basement membrane reaches 90%, the corresponding pore area is S D90 The test method is similar to S D50 The testing method remains consistent.

[0049] Exemplarily, the base film satisfies 1.982≤(S D90 -S D10 ) / S D50 Any point value or any two point range value within the range of ≤3.775, such as (S D90 -S D10 ) / S D50 The range value can be one or any two of 1.1982, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.775.

[0050] This study found that when the basement membrane satisfies 1.982≤(S D90 -S D10 ) / S D50 When ≤3.775, the pore size distribution uniformity of the base membrane is better, that is, the pore size distribution of the base membrane is more concentrated, so that the migration uniformity of ions is better while maintaining a certain transmission efficiency, that is, it can effectively avoid excessively high or low ion concentration in local areas, reduce the polarization of ions in the diaphragm, effectively reduce the internal resistance of the secondary battery, improve the kinetic performance of the secondary battery, and improve the cycle performance of the secondary battery.

[0051] In one embodiment, the S D10 102≤S D10 ≤620.

[0052] For example, S D10 Can be 102≤S D10 Any point value or any two-point range value within the range of ≤620, such as S D10 The range value may be one or any two of 102, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 620.

[0053] In one embodiment, the SD10 200≤S D10 ≤620. For example, S D10 It can be a range value of one or any two of 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500, 520, 540, 560, 580, 600, 620.

[0054] In one embodiment, the S D90 5879≤S D90 ≤21082.

[0055] For example, S D90 Can be 5879≤S D90 Any point value or any two-point range value within the range of ≤21082, such as S D90 It can be a range value of one or any two of 5879, 6000, 6500, 7000, 8000, 9000, 10000, 12000, 14000, 16000, 18000, 20000, 21082.

[0056] In one embodiment, the S D90 8730≤S D90 ≤21082. For example, S D90 It can be a range value of one or any two of 8730, 9000, 9500, 15000, 12500, 14500, 16500, 18500, 21000, 21082.

[0057] This study found that when further selecting S D10 and S D90 When within the above range, the pore size of the base membrane is appropriate. In addition to effectively reducing the heat accumulation during the secondary battery cycle, it can also effectively improve the ion transmission efficiency of the secondary battery, reduce the internal resistance of the secondary battery, and improve the capacity retention rate of the secondary battery, thereby making the overall performance of the secondary battery better.

[0058] In one embodiment, the average volume of the pores of the basement membrane is V nm 3 , meeting 4.07×10 4 ≤V≤6.01×10 5 .

[0059] The present study found that the average volume V of the pores of the basement membrane further meets the requirement of 4.07×10 4 ≤V≤6.01×10 5, which can better improve the uniformity of ion migration within an appropriate range, effectively reduce internal resistance, and improve the dynamic performance of the secondary battery; at the same time, since the average volume V of the pores of the base membrane is within the above range, it has better air permeability, thereby reducing the heat accumulation during the cycle of the secondary battery, thereby effectively improving the safety performance and cycle performance of the secondary battery.

[0060] It should be noted that the average volume V of the pores of the basement membrane is obtained by calculation; specifically, V=S D50 ×h / N;

[0061] h is the thickness of the basement membrane;

[0062] N is the total number of pores on one surface of the basement membrane.

[0063] It should be noted that the method for testing the thickness h of the base film includes the following steps:

[0064] After taking out the secondary battery diaphragm, soak it in dimethyl carbonate (DMC) for 20 to 40 minutes to clean the by-products remaining on the surface and pore structure of the diaphragm, then add an appropriate amount of alcohol to the coating surface of the diaphragm, and then wipe the coating surface to make the coating fall off to obtain the base film sample; lay 5 layers of 2-3 meter long base film flat and place the sample on the Marr thickness gauge C1202 equipment to test 32 points and obtain the average value to obtain the base film thickness h.

[0065] It should be noted that the basement membrane has two opposite surfaces, and the method for testing the total number N of holes on one surface of the basement membrane includes the following steps:

[0066] After taking out the secondary battery diaphragm, use dimethyl carbonate (DMC) to soak it for 20 minutes to 40 minutes to clean the by-products remaining on the surface of the diaphragm and in the pore structure, then add an appropriate amount of alcohol to the coating surface of the diaphragm, and then wipe the coating surface to make the coating fall off to obtain a base film sample; place the base film sample on the scanning electron microscope SEM sample stage, randomly select 10 positions on the surface of the base film, and take a picture at a magnification of 30,000 times at each position; then put the picture into the software Image J and complete the test according to the steps of setting the scale (200nm), field of view selection, measurement, data processing and analysis, and calculate the average value of the 10 samples to obtain the total number N of holes on the surface of one side of the base film. Specifically, the following steps are included: 1. Sample preparation: remove the three layers on the surface of the sample film roll, and then take a sample every 10 meters, for a total of 5 samples; Note: The diaphragm should be kept flat, wrinkle-free, clean, and free of foreign matter;

[0067] 2. Sample Testing: The following steps are required: Perform SEM testing on the sample's base film surface. Magnification: 30,000X. Focus on photographing the base film surface (glossy surface). Note: Magnification: 30,000X, scale: 200nm.

[0068] 3. Set the ruler: The steps are as follows: Use image J to process the image.

[0069] Click File--Open in the ImageJ menu bar, find the TIF or JPG file you want to open, and open it. Then, select the line drawing tool in the toolbar and use it to draw a straight line that coincides with the ruler length. Set the ruler according to the diagram (click Analyze → Set Scale, enter the ruler length 200 in the Known Distance box and the ruler unit nm in the Unit of Length box. For batches of images with the same ruler length, check Global.

[0070] 4. Field of View Selection: The steps are as follows: 1. Select the Rectangle tool (□); 2. Select a clearly focused area in the image; 3. Select the Crop tool in the Image section to capture the selected area and create a new image. Notes: 1. Select a clearly focused area; 2. Remove the scale and test instructions from the SEM image to prevent them from being included in the area calculation.

[0071] 5. Measure the number and area of ​​holes: The steps are as follows: 1. Select image-type-8-bit; 2. Select process-find edges; 3. Select image-adjust-threshold to set the threshold; 4. Select analyze-analyzeparticles, click ok, and count the number and area of ​​holes; Notes: 1. Set the second column of threshold setting to 255. 2. Set the first column of threshold setting to between 30-200 according to the situation to make the image well distinguishable. 3. Set the minimum test area in the analyze particles interface to 100nm 2 4. In the Show box of the analyze particles interface, select Outlines to export the contour map for comparison; check Display results and Summarize to export statistical data.

[0072] 6. Data Processing and Interpretation: The steps are as follows: Extract the data from the Summary, select the target row, right-click and select Copy, and copy it to the corresponding location in Excel. Extract the data from the Results, Edit → Select All, right-click and select Copy, and copy it to the corresponding location in Excel, retaining the Area column and deleting any extra columns. Use Excel to calculate the number of holes and the area distribution ratio, and make an assessment based on the specifications. Notes: 1. The total area value can be extracted from the Summary; 2. Perform a statistical assessment for each sample roll; 3. Extract and copy the data for each image processed to avoid data loss due to manipulation.

[0073] After the thickness h of the base film and the total number N of holes on one side of the base film are obtained through testing, the thickness h of the base film and the total number N of holes on the surface of the base film can be calculated based on V=S D50 × h / N to calculate the average volume of the pores in the basement membrane.

[0074] In one embodiment, h is 3 μm≤h≤25 μm.

[0075] Exemplarily, h may be any point value or any two point range values ​​within the range of 3μm≤h≤25μm, for example, h may be one or any two range values ​​of 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, and 25μm.

[0076] The research in this application found that controlling the thickness of the base film within a certain range can effectively ensure the balance between the mechanical properties and internal resistance of the diaphragm, and can also ensure the safety performance of the secondary battery; when the thickness of the base film is further selected to be within the above range, the secondary battery obtained not only has a lower internal resistance, but also has higher safety performance.

[0077] In one embodiment, N is 52≤N≤998.

[0078] Exemplarily, the N may be any point value or any two point range values ​​in the range of 52≤N≤998, for example, N may be one of 52, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 998 or any two range values.

[0079] The research in this application found that further selecting the total number N of holes on the surface of one side of the base membrane within the above range can not only facilitate the rapid and uniform migration of ions, but also reduce the temperature rise caused by heat release of the system during the charging and discharging process of the secondary battery, thereby improving the cycle performance and safety performance of the secondary battery.

[0080] In one embodiment, N is 200 ≤ N ≤ 340. For example, N may be in a range of one or any two of 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, and 340. The present application has found that when N is further selected within the above range, the overall performance of the secondary battery obtained is better.

[0081] In one embodiment, the base film has two opposite surfaces, the ratio of the total area of ​​the holes in the preset area of ​​one surface of the base film to the area of ​​the preset area is P1, the porosity of the base film is P2, and 0<P1<P2<1 is satisfied. The area of ​​the preset area is 36110 μm 2 .

[0082] The research in this application found that by controlling the ratio P1 of the total area of ​​the holes in the preset area on the surface of one side of the base membrane to the area of ​​the preset area and the porosity P2 of the base membrane to satisfy 0<P1<P2<1, the base membrane has good air permeability, which can effectively alleviate the temperature rise and pressure rise during the cycle of the secondary battery; at the same time, the migration of ions on the base membrane is more uniform, which can effectively reduce the internal resistance of the secondary battery and improve the cycle performance and safety performance of the secondary battery.

[0083] It should be noted that the P2 is obtained by calculation, specifically, P2 = 1-m / (h×m0);

[0084] mg / m 2 is the surface density of the basement membrane;

[0085] m0 g / cm 3 It is the true density of the base film material.

[0086] It should be noted that the method for testing the surface density m of the base film includes the following steps:

[0087] After taking out the secondary battery diaphragm, soak it in dimethyl carbonate (DMC) for 20 to 40 minutes to clean the by-products remaining on the surface and in the pore structure of the diaphragm, then add an appropriate amount of alcohol to the coating surface of the diaphragm, and then gently wipe the coating surface to make the coating fall off to obtain the base film sample; use a mold to cut a 100mm*100mm base film sample and place it on an electronic balance device to weigh it, test 20 points to calculate the average value, and then divide the average value by the area (100mm*100mm) to obtain the surface density m of the base film.

[0088] After the surface density m of the base film is obtained by testing, P2 can be calculated according to the formula P2 = 1-m / (h×m0). Among them, m0 is the true density of the base film raw material, which is an intrinsic parameter of the base film material. For example, the true density m0 of polypropylene PP is 0.91g / cm 3 In addition, you can refer to GB / T533-A, GB / T1033.1 and other methods for true density testing.

[0089] In one embodiment, 0.073≤P1≤0.321.

[0090] It should be noted that the method for testing the total area of ​​the holes on one side of the basement membrane includes the following steps:

[0091] After the secondary battery separator was taken out, dimethyl carbonate (DMC) was used to soak for 20 to 40 minutes to clean the by-products remaining on the separator surface and in the pore structure. Then, an appropriate amount of alcohol was added to the separator coating surface, and then the coating surface was wiped to remove the coating to obtain a base film sample. The base film sample was placed on the scanning electron microscope (SEM) sample stage, and 10 positions on the base film surface were randomly selected (the area of ​​the preset area at each position was 36110 μm 2 ), and photographed at each position at a magnification of 30,000x; then the image was placed in the Image J software and the test was completed according to the steps of setting the scale (200 nm), field of view selection, measurement, data processing and analysis to obtain the total area of ​​the holes in the preset area.

[0092] It should be noted that the area of ​​the preset region on the surface of the base film is obtained by direct measurement and calculation with a ruler.

[0093] Exemplarily, the P1 may be any point value or any two point range values ​​within the range of 0.073≤P1≤0.321, for example, P1 may be one or any two range values ​​of 0.073, 0.080, 0.100, 0.120, 0.150, 0.180, 0.200, 0.220, 0.250, 0.280, 0.300, 0.321.

[0094] In one embodiment, 0.254≤P2≤0.788.

[0095] Exemplarily, the P2 may be any point value or any two point range values ​​within the range of 0.254≤P2≤0.788, for example, P1 may be one of 0.254, 0.280, 0.300, 0.320, 0.350, 0.380, 0.400, 0.420, 0.450, 0.480, 0.500, 0.520, 0.550, 0.580, 0.600, 0.620, 0.650, 0.680, 0.700, 0.720, 0.750, 0.780, 0.788 or any two range values.

[0096] In one embodiment, the surface density m of the base film satisfies: 1.6 g / m 2 ≤m≤13.2g / m 2 .

[0097] For example, the m may be 1.6 g / m 2 ≤m≤13.2g / m 2 Any point value within the range or any two point range values, for example, m can be 1.6g / m 2 , 2g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 , 9g / m 2 , 10g / m 2 , 11g / m 2 , 12g / m 2 , 13g / m 2 , 13.2g / m 2 The range of values ​​for one or both of .

[0098] In one embodiment, the true density m0 of the base film material satisfies: 0.9 g / cm 3 ≤m0≤2.3g / cm 3 .

[0099] For example, the m0 may be 0.9 g / cm 3 ≤m0≤2.3g / cm 3 Any point value within the range or any two point range value, for example, m0 can be 0.9g / cm 3 , 1.0g / cm 3 , 1.2g / cm 3 , 1.4g / cm 3 , 1.6g / cm 3 , 1.8g / cm 3 , 2.0g / cm3 , 2.2g / cm 3 , 2.3g / cm 3 The range of values ​​for one or both of .

[0100] The present application has found that when P1, P2, m and m0 are further selected within the above ranges, the overall performance of the secondary battery obtained is better.

[0101] In one embodiment, the area of ​​the pores in the basement membrane is less than 2500 nm. 2 The percentage S1 of the total pore area to the overall pore area of ​​the basement membrane is 15.3%≤S1≤62.8%.

[0102] Exemplarily, the S1 may be any point value or any two point range values ​​within the range of 15.3%≤S1≤62.8%, for example, S1 may be one or any two range values ​​of 15.3%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 62.8%.

[0103] In one embodiment, the area of ​​the pores in the basement membrane is greater than 1000 nm. 2 The percentage S2 of the total pore area to the overall pore area of ​​the basement membrane is 1.6%≤S2≤39.8%.

[0104] Exemplarily, the S2 may be any point value or any two point range values ​​within the range of 1.6%≤S2≤39.8%, for example, S2 may be one or any two range values ​​of 1.6%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 39.8%.

[0105] It should be noted that the area of ​​the pores in the basement membrane is less than 2500nm 2 The total pore area of ​​the basement membrane accounts for the percentage of the total pore area of ​​the basement membrane S1 and the area of ​​the pores in the basement membrane is greater than 1000nm 2 The total pore area of ​​the base film accounts for the percentage of the total pore area of ​​the base film. The test method of S2 is the same as that of S D50 Stay consistent.

[0106] The research in this application found that further selecting the range of S1 and S2 in the base membrane within the above range can improve the uniformity of ion migration while ensuring sufficient mechanical properties of the base membrane, and reduce heat accumulation during the cycle of the secondary battery, thereby effectively improving the kinetic performance, cycle performance and safety performance of the secondary battery.

[0107] Exemplarily, the preparation method of the base film includes the following steps: (1) extruding a polymer melt and cooling it at a certain pulling rate to obtain a semi-finished product; (2) subjecting the semi-finished product to a heat treatment, cold drawing, hot drawing and heat setting treatment at a certain heat treatment speed ratio to obtain a base film. In one embodiment, the polymer includes polypropylene; the melt index of the polypropylene is 0.1g / 10min to 4.0g / 10min; the melt index of the polypropylene is based on GB / T 3682.1-2018 test results; in the melt extrusion, the die temperature of the extruder used is 200℃~220℃, the die opening is 0.6mm~2.0mm, and the extrusion volume is 70kg / h~140kg / h; the traction rate is 50m / min~130m / min; in the cooling, the temperature of the main cooling roller is 60~80℃; the temperature of the heat treatment is 138~158℃; the heat treatment speed ratio is 1.1-1.2; the cold drawing speed ratio of the cold drawing is 1.02~1.10, and the cold drawing temperature is 80~100℃; the hot drawing speed ratio of the hot drawing is 1.60~2.65, and the hot drawing temperature is 138~150℃; the heat setting temperature is 150~160℃, and the shrinkage rate is 0.80~0.94; the total speed ratio is 1.6~3.0. Among them, the total speed ratio = heat treatment speed ratio × cold drawing speed ratio × hot drawing speed ratio × shrinkage rate.

[0108] In one embodiment, the short axis of the hole of the basement membrane is D1 nm, the long axis of the hole of the basement membrane is D2 nm, and the short axis D1 of the hole of the basement membrane is 38≤D1≤85; in another embodiment, the long axis D2 of the hole of the basement membrane is 105≤D2≤345; in yet another embodiment, the short axis D1 of the hole of the basement membrane is 38≤D1≤85, and the long axis D2 of the hole of the basement membrane is 105≤D2≤345.

[0109] like Figure 1 As shown, the base film is prepared by uniaxial stretching using a dry process, and the major axis or minor axis of the base film pores meets the above conditions so that the base film has Figure 1 The structure shown, compared Figure 8 The pore structure of the base film prepared by the wet double-drawing process, the pore structure design of the narrow through-holes in the embodiment of the present application has a low tortuosity, which is conducive to the transmission of lithium ions at high rates.

[0110] In one embodiment, the diaphragm further comprises a functional coating disposed on at least one side of the base film, and the functional coating comprises at least one of a heat-resistant coating and an adhesive coating.

[0111] In one embodiment, the short axis of the pores of the base film is D1 nm, the long axis of the pores of the base film is D2 nm, and the particle size value corresponding to the cumulative distribution of the particle size of the particles in the functional coating reaching 50% is d50 nm, satisfying 0.5×(D1+D2)<d50≤10000.

[0112] It should be noted that the method for testing the minor axis and major axis of the basement membrane pores includes the following steps:

[0113] After taking out the secondary battery diaphragm, use dimethyl carbonate (DMC) to soak it for 20 minutes to 40 minutes to clean the by-products remaining on the surface of the diaphragm and in the pore structure, then add an appropriate amount of alcohol to the coating surface of the diaphragm, and then wipe the coating surface to make the coating fall off to obtain a base film sample; then use SEM equipment to measure 20 holes online, and take the average value to obtain the corresponding short axis and long axis of the base film hole. It can be understood that the MD direction of the base film is defined as the long axis and the TD direction as the short axis. Generally, the direction perpendicular to the roll width is the longitudinal direction (MD direction), and the direction parallel to the roll width is the transverse direction (TD direction). Specifically, the longitudinal direction (Machine Direction, MD) refers to the direction consistent with the mechanical processing direction during material production, usually the direction in which the material is pulled out of the extruder and wound. The transverse direction (Transverse Direction, TD) refers to the direction perpendicular to the mechanical processing direction, that is, the width direction of the material. That is, in the TD direction of the basement membrane, the minimum width of the basement membrane hole is the short axis of the basement membrane hole, and in the MD direction of the basement membrane, the maximum width of the basement membrane hole is the long axis of the basement membrane hole.

[0114] It should be noted that the functional coating includes organic and / or inorganic particles, and the particle size corresponding to the 50% cumulative distribution of the organic and / or inorganic particles is measured using a Malvern particle size analyzer. It is understood that the inorganic particles include ceramic particles, and the organic particles include polymer particles.

[0115] The research in this application found that when the d50 of the particles in the functional coating introduced on at least one side of the base membrane satisfies 0.5×(D1+D2)<d50≤10000, the obtained functional coating can achieve good mutual matching ability with the base membrane, that is, it helps to reduce the risk of particles in the functional coating blocking the pores of the base membrane, so that while the functional coating is used to improve the strength of the diaphragm, it also helps to maintain the ion path of the base membrane pores, reduce the risk of ions being blocked through the diaphragm, reduce the internal resistance of the secondary battery, and improve the cycle performance of the secondary battery.

[0116] In one embodiment, the short axis D1 of the pores of the basement membrane is 38≤D1≤85.

[0117] In one embodiment, the major axis D2 of the hole of the basement membrane is 105≤D2≤345.

[0118] In one embodiment, when the cumulative distribution of particle sizes of the particles in the functional coating reaches 50%, the corresponding particle size value d50 is 200≤d50≤10000.

[0119] In one embodiment, the thickness of the functional coating is 1 μm to 20 μm.

[0120] It should be noted that the thickness of the functional coating is obtained by testing with a Mahr thickness gauge.

[0121] The research in this application found that by limiting the short axis and long axis of the pores of the base membrane and the particle size value d50 corresponding to the cumulative distribution of the particle size of the particles in the functional coating reaching 50%, the above relationship is satisfied, which can effectively reduce the degree of pore blockage of the functional coating, facilitate lithium ion transmission, and provide more effective channels for lithium ion transmission, thereby improving the overall performance of the secondary battery.

[0122] In one embodiment, the total surface density of the separator is 2.2 g / m 2 ~13.8g / m 2 .

[0123] It should be noted that the test method for the total surface density of the diaphragm is as follows: after taking out the diaphragm from the secondary battery, cut a sample, measure the length and width of the sample, calculate the area, use an electronic balance to weigh the sample, test three samples in parallel, and then calculate the total surface density of the diaphragm according to total surface density = mass / area and take the average value.

[0124] The present application has no particular restrictions on the materials in the heat-resistant coating, and materials commonly used in the art may be used. For example, the heat-resistant coating includes at least one of aluminum oxide, boehmite, silicon dioxide, magnesium hydroxide, barium sulfate, and barium titanate.

[0125] The present application does not particularly limit the materials in the adhesive coating, and any materials commonly used in the art may be used. For example, the adhesive coating includes a copolymer or homopolymer of one or more monomers, such as fluoroolefin monomer units, acrylate monomer units, unsaturated nitrile monomer units, acrylic acid monomer units, and vinyl acetate monomer units, as well as one or more modified polymers of the aforementioned homopolymers and copolymers.

[0126] The present application has no particular limitation on the introduction of the functional coating, and the functional coating can be provided on the surface of the base film using conventional methods in the art.

[0127] In one embodiment, the base film is made of polypropylene.

[0128] At present, the market will consider using dry-process polypropylene (PP) separators under the premise of pursuing the ultimate cost of secondary batteries. The structural state of the dry-process PP base membrane will affect the dynamic performance of the secondary battery, for example, affecting the internal resistance of the secondary battery.

[0129] It is understood that the dry process uniaxial stretching can produce Figure 1The base film with the pore structure shown in the figure is generally a narrow pore structure (such as Figure 1 If the pore area is not properly controlled, the permeability of the diaphragm will be affected, the uniform distribution of ions passing through the diaphragm will be reduced, and the internal resistance of the secondary battery will be affected. The base film is made of polypropylene and is prepared by uniaxial stretching through a dry process. D50 The condition of ≤5420 is helpful to improve the cycle performance of secondary batteries.

[0130] Exemplarily, the method for preparing the separator includes the following steps: applying a functional coating slurry on at least one side of a base film by any of rotary spray coating and gravure roller coating.

[0131] In one embodiment of the present application, a secondary battery is provided, comprising the separator described in the present application.

[0132] In one embodiment, the secondary battery further includes a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0133] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; the positive electrode active material layer includes a positive electrode active material. This application does not particularly limit the positive electrode active material; any known positive electrode active material may be used.

[0134] Illustratively, the positive electrode active material includes at least one of a nickel-cobalt-manganese ternary material, a lithium iron phosphate material, and a lithium iron manganese phosphate material.

[0135] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material. This application does not particularly limit the negative electrode active material, and any known negative electrode active material may be used.

[0136] Illustratively, the negative electrode active material includes at least one of a carbon-based material, a silicon-based material, and a tin-based material.

[0137] In one embodiment, the electrolyte includes an organic solvent, a lithium salt, and an additive. The present application has no limitation on the organic solvent, lithium salt, and additive in the electrolyte, and any known organic solvent, lithium salt, and additive can be used.

[0138] Illustratively, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; and the additive includes at least one of a film-forming additive, a conductive additive, and a flame retardant additive.

[0139] In one embodiment of the present application, an electrical device is provided, comprising the secondary battery described in the present application.

[0140] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0141] Example 1

[0142] The present invention provides a separator and a secondary battery. The preparation method of the separator and the secondary battery includes the following steps:

[0143] (1) Preparation of diaphragm

[0144] S1. Preparation of base film: Two granular raw materials with polypropylene PP melt index of 1.3g / 10min and 2.0g / 10min (Daehan Petrochemical Co., Ltd.) were selected and respectively put into two separate extruders for melting and die extrusion, wherein the die temperature of the extruder was 210°C, the die opening was 1.3mm, and the extrusion rate was 120kg / h; then, the semi-finished base film with partial crystal orientation was formed by passing through a series of cooling rollers at a certain pulling speed, wherein the temperature of the main cooling roller was 70°C; then, the semi-finished base film was put into the base film. The base film was subjected to heat treatment, cold drawing, hot drawing and heat setting processes to prepare a base film having a certain pore size and porosity structure, wherein the drawing rate was 110 m / min, the heat treatment speed ratio was 1.115, the total speed ratio was 2.10, the heat treatment temperature was 149°C, the cold drawing speed ratio was 1.06, the cold drawing temperature was 93°C, the hot drawing speed ratio was 2.04, the hot drawing temperature was 145°C, the heat setting temperature was 159°C, and the shrinkage rate was 0.87; finally, the prepared base film was rolled up and left to stand at room temperature for 3 days to eliminate internal stress, thereby obtaining the base film;

[0145] Among them, the SEM images and porosity images of the base film surface are as follows: Figures 1-2 As shown;

[0146] S2. Preparation of diaphragm: The first adhesive polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and the second adhesive polyacrylonitrile multipolymer were mixed uniformly in a mass ratio of 9:1 to prepare a slurry, and the slurry was applied to one side of the base film by rotary spray coating to form a 5 μm thick adhesive coating. The surface density of the single-sided sprayed PVDF-HFP was 0.6 g / m 2 , get diaphragm;

[0147] The schematic diagram of the structure of the obtained diaphragm is shown in FIG. Figure 5 As shown;

[0148] (2) Preparation of positive electrode sheet

[0149] Lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon black, and polyvinyl pyrrolidone powders were mixed in a weight ratio of 97.55:1.8:0.5:0.15, added to N-methylpyrrolidone (NMP), and stirred thoroughly to form a positive electrode slurry with a solid content of 65% and a viscosity of 6000-9000 mPa·s. The positive electrode slurry was then coated on carbon-coated aluminum foil, dried, rolled, and cut to obtain positive electrode sheets.

[0150] (3) Preparation of negative electrode sheet

[0151] Graphite, carbon black, sodium carboxymethyl cellulose, polyacrylonitrile, and styrene acrylate powders were mixed in a weight ratio of 97:0.3:0.6:1.0:1.1, added to deionized water, and stirred thoroughly to form a negative electrode slurry with a solid content of 48.5% and a viscosity of 2000 mPa·s to 8000 mPa·s. The negative electrode slurry was then coated on copper foil, dried, rolled, and slit to obtain negative electrode sheets.

[0152] (4) Preparation of electrolyte

[0153] In a glove box, dimethyl carbonate (DMC): ethyl methyl carbonate (EMC): ethylene carbonate (EC) were mixed in a volume ratio of 5:2:3, and 5 wt% of fluoroethylene carbonate (FEC) and lithium hexafluorophosphate were added, wherein the molar concentration of lithium hexafluorophosphate was 1 mol / L, to obtain an electrolyte;

[0154] (5) Preparation of secondary batteries

[0155] The diaphragm and the positive electrode sheet and the negative electrode sheet are stacked in order so that the diaphragm is located between the positive and negative electrode sheets, and the inner core is formed by winding, and hot pressing is performed (temperature is 95°C, pressure is 3MPa, and time is 30s). The tabs are welded to obtain a bare battery cell, which is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10°C for 24h. The electrolyte is injected into the dried battery, allowed to stand, formed, and capacity divided to obtain a secondary battery.

[0156] Example 2

[0157] Based on Example 1, the process conditions in the diaphragm preparation process (including die opening, pulling rate, extrusion amount, heat treatment temperature, total speed ratio, cold drawing speed ratio, cold drawing temperature, hot drawing speed ratio, hot drawing temperature, and retraction ratio) were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0158] Example 3

[0159] On the basis of Example 1, the process conditions in the diaphragm preparation process (including die opening, pulling rate, extrusion amount, heat treatment temperature, total speed ratio, cold drawing temperature, hot drawing speed ratio, retraction ratio, and heat setting temperature) were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0160] Example 4

[0161] On the basis of Example 1, the process conditions in the diaphragm preparation process (including die opening, pulling rate, extrusion amount, heat treatment temperature, total speed ratio, cold drawing temperature, hot drawing speed ratio, retraction ratio, and heat setting temperature) were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0162] Example 5

[0163] Based on Example 1, the process conditions in the diaphragm preparation process (including die opening, pulling rate, extrusion amount, heat treatment temperature, total speed ratio, cold drawing temperature, hot drawing speed ratio, hot drawing temperature, and retraction ratio) were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0164] Example 6

[0165] On the basis of Example 1, the process conditions (including extrusion amount, heat treatment temperature, total speed ratio, hot drawing speed ratio, and retraction ratio) during the preparation of the diaphragm were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0166] Example 7

[0167] On the basis of Example 1, the process conditions (including extrusion amount, heat treatment temperature, total speed ratio, cold drawing speed ratio, and hot drawing speed ratio) in the diaphragm preparation process were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0168] Example 8

[0169] On the basis of Example 1, the process conditions (including extrusion amount, heat treatment temperature, total speed ratio, cold drawing speed ratio, and hot drawing speed ratio) in the diaphragm preparation process were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0170] Example 9

[0171] On the basis of Example 1, the process conditions (including heat treatment temperature, total speed ratio, cold drawing temperature, hot drawing speed ratio, hot drawing temperature, and heat setting temperature) in the diaphragm preparation process were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0172] Example 10

[0173] On the basis of Example 1, the process conditions (including heat treatment temperature, total speed ratio, cold drawing temperature, hot drawing speed ratio, hot drawing temperature, and heat setting temperature) in the diaphragm preparation process were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0174] The SEM images and porosity images of the base film surface obtained in Example 4 are shown in FIG. Figures 3-4 shown.

[0175] The differences between Examples 6, 7, and 8 and Examples 6-1, 7-1, and 8-1 are: Example 6-1 does not apply an adhesive coating on the surface of the base film based on Example 6; Example 7-1 does not apply an adhesive coating on the surface of the base film based on Example 7; Example 8-1 does not apply an adhesive coating on the surface of the base film based on Example 8.

[0176] Example 11

[0177] The present embodiment provides a diaphragm and a secondary battery. The only difference between the preparation method of the diaphragm and the secondary battery and that of Example 1 is that the slurry is double-sided coated in step S2 to achieve the parameters in Tables 1 and 2; wherein the thickness of the single-sided adhesive coating is 3 μm;

[0178] The schematic diagram of the structure of the obtained diaphragm is shown in FIG. Figure 6 shown.

[0179] Example 12

[0180] The present embodiment provides a diaphragm and a secondary battery. The only difference between the preparation method of the diaphragm and the secondary battery and that of Example 1 is step S2. Step S2 of this embodiment includes the following steps:

[0181] S2. Preparation of diaphragm: Inorganic particles (boehmite, Dv50 = 0.3 μm), binder (modified polyacrylic acid amide polymer solution, glass transition temperature Tg of 180°C), dispersant (sodium carboxymethyl cellulose) and additives (ammonium salts) are added to a stirring tank at a dry weight ratio of 95:1:3:1 and stirred thoroughly to obtain a heat-resistant coating slurry with a solid content of 30%. The slurry is then coated on one side of the base film by gravure roller coating, dried and rolled up to obtain a heat-resistant coating; the thickness of the heat-resistant coating is 2 μm.

[0182] Subsequently, a first adhesive, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and a second adhesive, polyacrylonitrile multi-polymer, were uniformly mixed in a mass ratio of 9:1 to prepare a slurry, and the slurry was applied to the side of the heat-resistant coating away from the base film by a rotary spray coating method to obtain an adhesive coating, wherein the thickness of the adhesive coating was 5 μm, thereby obtaining a diaphragm;

[0183] The schematic diagram of the structure of the obtained diaphragm is shown in FIG. Figure 7 shown.

[0184] Example 13

[0185] The present embodiment provides a diaphragm and a secondary battery. The only difference between the preparation method of the diaphragm and the secondary battery and that of Example 1 is step S2. Step S2 of this embodiment includes the following steps:

[0186] S2. Preparation of a diaphragm: Inorganic particles (boehmite, Dv50 = 0.3 μm), a binder (modified polyacrylic acid amide polymer solution, glass transition temperature Tg of 180°C), a dispersant (sodium carboxymethyl cellulose), and an additive (ammonium salt) are added to a stirring tank in a dry weight ratio of 95:1:3:1 and stirred thoroughly to obtain a heat-resistant coating slurry with a solid content of 30%. The slurry is then coated on both sides of the base film using a gravure roller coating method, dried, and rolled up to obtain a heat-resistant coating; wherein the thickness of the heat-resistant coating on one side is 1 μm;

[0187] Subsequently, the first adhesive polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and the second adhesive polyacrylonitrile multipolymer are evenly mixed in a mass ratio of 9:1 to prepare a slurry, and the slurry is coated on the side of the heat-resistant coating away from the base film by rotary spray coating to obtain an adhesive coating, wherein the thickness of the adhesive coating is 2.5 μm, and a diaphragm is obtained.

[0188] Example 14

[0189] On the basis of Example 1, the process conditions (including pulling rate, heat treatment temperature, total speed ratio, cold drawing speed ratio, cold drawing temperature) in the diaphragm preparation process were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0190] Example 15

[0191] On the basis of Example 1, the process conditions (including pulling rate, heat treatment temperature, total speed ratio, and hot pulling speed ratio) during the preparation of the diaphragm were changed to obtain diaphragms with the parameters in Tables 1 and 2.

[0192] Example 16, Example 17

[0193] On the basis of Example 1, as shown in Table 3, the d50 of the PVDF-HFP particles was changed to obtain the separators with the parameters in Table 1 and Table 2.

[0194] Comparative Examples 1-2

[0195] The comparative example of the present application provides a diaphragm and a secondary battery. The only difference between the preparation method of the diaphragm and the secondary battery and that of Example 1 is that the preparation parameters of the base film in step S1 (including heat treatment temperature, total speed ratio, cold drawing speed ratio, cold drawing temperature, hot drawing speed ratio, hot drawing temperature, shrinkage ratio, and heat setting temperature) are changed to achieve the parameters in Tables 1 to 2.

[0196] The difference between Comparative Examples 1 and 2 and Comparative Examples 1-1 and 2-1 is that Comparative Example 1-1 does not apply an adhesive coating on the surface of the base film based on Comparative Example 1; Comparative Example 2-1 does not apply an adhesive coating on the surface of the base film based on Comparative Example 2.

[0197] The parameters of the base film and the diaphragm provided in the examples and comparative examples and the air permeability of the diaphragm are shown in Tables 1 and 2. The air permeability test method is as follows: take an area of ​​10 mm 2 The battery separator sample is placed in the Gurley air permeability tester and the time required for 100cc of gas to pass through is calculated;

[0198] Among them, the total thickness is the sum of the base film thickness and the coating thickness;

[0199] Table 1 Experimental data list

[0200]

[0201]

[0202] Table 2 Experimental data list

[0203]

[0204]

[0205] The performance test of the secondary batteries prepared in the examples and comparative examples includes the following parts:

[0206] 1. DCR test: Adjust the secondary battery to 50% SOC state in a 25℃ constant temperature box, and then test the DC resistance value of the secondary battery corresponding to 4C DC discharge for 10s;

[0207] 2. Secondary battery cycle performance: Place the secondary battery in a 25°C constant temperature box, charge at an equivalent 2.2C condition in the range of 0-100% SOC, and discharge at an equivalent 1C condition. Repeat this charge and discharge pattern until the capacity retention rate reaches 2500 cycles. Record the capacity retention rate of the secondary battery at this time. The voltage range is 2.5V-3.65V. Capacity retention rate (%) = discharge specific capacity at the 2500th cycle / discharge specific capacity at the first cycle * 100%;

[0208] The test results are shown in Table 3;

[0209] Table 3 Performance list

[0210] DCR / mΩ Capacity retention rate / % DCR / mΩ Capacity retention rate / % Example 1 15.72 86.5 Example 10 15.53 86.8 Example 2 16.71 86.2 Example 11 15.91 86.5 Example 3 16.19 86.3 Example 12 16.04 86.4 Example 4 15.50 86.4 Example 13 16.52 86.3 Example 5 14.25 84.5 Example 14 15.86 86.2 Example 6 17.30 83.4 Example 15 17.08 85.7 Example 6-1 17.25 83.0 Example 16 15.73 86.4 Example 7 15.17 87.6 Example 17 16.22 86.2 Example 7-1 15.08 87.2 Comparative Example 1 21.15 75.3 Example 8 12.33 88.3 Comparative Example 2 15.09 79.5 Example 8-1 12.20 87.9 Comparative Example 1-1 21.06 75.0 Example 9 15.69 86.7 Comparative Example 2-1 14.92 80.8

[0211] As can be seen from Table 3, when the technical solution provided by the present application is adopted, the comprehensive performance of the obtained secondary battery is excellent; specifically, the DCR of the obtained secondary battery is below 17.30 mΩ, and the capacity retention rate is above 83.4%.

[0212] It can be seen from Examples 1 to 17 and Comparative Examples 1 to 2 that when the S D50 If the content is outside the range given in this application, the secondary battery obtained will be difficult to achieve the effects of this application.

[0213] Finally, it should be noted that the above embodiments are intended to illustrate the technical solutions of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A diaphragm comprising a base film, characterized in that: When the cumulative pore area distribution on the basement membrane reaches 50%, the corresponding pore area is S D50 nm 2 , satisfying 1865≤S D50 ≤5420.

2. The diaphragm according to claim 1, characterized in that When the cumulative pore area distribution on the basement membrane reaches 10%, the corresponding pore area is S D10 nm 2 When the cumulative pore area distribution on the basement membrane reaches 90%, the corresponding pore area is S D90 nm 2 , satisfying 1.982≤(S D90 -S D10 ) / S D50 ≤3.

775.

3. The diaphragm according to claim 2, characterized in that The S D10 Satisfy: 102≤S D10 ≤620; and / or, the S D90 Satisfaction: 5879≤S D90 ≤21082.

4. The diaphragm according to claim 1, characterized in that The average volume Vnm of the pores of the basement membrane 3 , meeting 4.07×10 4 ≤V≤6.01×10 5 .

5. The diaphragm according to claim 1, characterized in that The thickness h of the base film is 3 μm≤h≤25 μm; And / or, the base film has two opposite surfaces, and the total number N of holes on one surface of the base film is 52≤N≤998.

6. The diaphragm according to claim 1, characterized in that The base film has two opposite surfaces. The ratio of the total area of ​​the holes in the preset area on one surface of the base film to the area of ​​the preset area is P1. The porosity of the base film is P2, which satisfies 0<P1<P2<1. The area of ​​the preset area is 36110μm 2 .

7. The diaphragm according to claim 6, characterized in that The P1 satisfies: 0.073≤P1≤0.321; And / or, P2 satisfies: 0.254≤P2≤0.788; And / or, the surface density m of the base film satisfies: 1.6 g / m 2 ≤m≤13.2g / m 2 ; And / or, the true density m0 of the base film material satisfies: 0.9 g / cm 3 ≤m0≤2.3g / cm 3 .

8. The diaphragm according to claim 1, wherein The area of ​​the pores in the basement membrane is less than 2500 nm 2 The percentage of the total pore area of ​​the basement membrane to the total pore area S1 is 15.3%≤S1≤62.8%; And / or, the area of ​​the pores in the basement membrane is greater than 1000nm 2 The percentage S2 of the total pore area to the overall pore area of ​​the basement membrane is 1.6%≤S2≤39.8%.

9. The diaphragm according to claim 1, wherein The short axis of the pores of the basement membrane is D1 nm, the long axis of the pores of the basement membrane is D2 nm, and the short axis D1 of the pores of the basement membrane is 38≤D1≤85; And / or, the major axis D2 of the pores of the basement membrane is 105≤D2≤345.

10. The diaphragm according to claim 1, wherein The diaphragm also includes a functional coating provided on at least one side of the base film, the functional coating including at least one of a heat-resistant coating and an adhesive coating; the minor axis of the pores of the base film is D1 nm, the major axis of the pores of the base film is D2 nm, the functional coating includes organic particles and / or inorganic particles, and the particle size value corresponding to the cumulative distribution of the particle size of the organic particles and / or the inorganic particles reaches 50% is d50, in nm, satisfying 0.5×(D1+D2)<d50≤10000.

11. The diaphragm according to claim 10, characterized in that When the cumulative distribution of particle sizes of particles in the functional coating reaches 50%, the corresponding particle size value d50 is 200≤d50≤10000.

12. The diaphragm according to any one of claims 1 to 11, characterized in that The material of the base film includes polypropylene; And / or, the base film is prepared by uniaxial stretching through a dry process.

13. A secondary battery, characterized in that: The diaphragm according to any one of claims 1 to 12 is included.

14. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 13.

Images