High tension slurry and diaphragm suitable for matrix dotting and process of preparation

Abstract

The application relates to the technical field of battery diaphragm, and discloses a high-tension slurry suitable for matrix point coating, a diaphragm and a preparation process. The high-tension slurry suitable for matrix point coating comprises the following components in parts by weight: 0.5-1 parts of a dispersing agent, 15-20 parts of PVDF powder, 45-55 parts of water, 15-18 parts of a thickening agent, 13-23 parts of a binder and 2.5-4 parts of a surfactant. The thickening agent comprises hydroxymethyl cellulose, polyvinyl alcohol and cashew phenol ether compound in a mass ratio of 5:10:1-5. Through the technical scheme, the problems of coating connection, excessively high air permeability and low coating coverage caused by the small slurry tension and large fluidity of the slurry in the matrix point coating in the related art are solved.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a high-tension slurry suitable for matrix dot coating, a separator, and a preparation process. Background Technology

[0002] With the rapid updates in electronic products and the rapid expansion of the market share of new energy electric vehicles, lithium batteries, as an important energy storage device with high energy density and long lifespan, are receiving increasing attention from manufacturers and users. One of the core components of a lithium battery is the separator, which effectively isolates the positive and negative electrodes, preventing short circuits and electrolyte immersion, thus ensuring the safety and performance stability of the lithium battery. Compared to PP or PE base films, coated films offer better high-temperature stability, chemical stability, and higher mechanical strength and toughness. Therefore, the lithium battery separator coating process is crucial to the performance and lifespan of lithium batteries.

[0003] Regarding diaphragm coating processes, the commonly used methods currently include roller coating, spray coating, blade coating, and spin coating. Among these, roller coating and spray coating are widely used due to their relatively simple processes, stable coating effects, and ease of operation. Roller coating uses an anilox roller to transfer the slurry onto the diaphragm, resulting in full-screen coating where the slurry covers 100% of the coated area. Spray coating uses a spray head to apply the slurry to the diaphragm surface, resulting in irregular dotted coating where the slurry covers less than 100% of the coated area.

[0004] Currently, a new coating method—matrix dot coating—adds a contact coating roller to the coating process compared to roll coating. It utilizes tension difference to transfer the coating liquid from the anilox roller to the separator. Its coating characteristics include relatively regular circular coating dots, and the size and spacing of the dots can be varied through equipment and process adjustments. However, due to the characteristics of matrix dot coating, the requirements for the slurry are relatively high. For example, high slurry fluidity can easily cause the slurry to flow from the top of the roller protrusions to the bottom before being transferred to the separator. Over time, the slurry accumulates at the bottom to a certain height, causing the coating dots to connect, affecting the appearance and properties. When coating the base film surface, if the slurry tension is too low, it can easily cause the slurry to flow into the pores of the base film, resulting in abnormal air permeability and irregular diffusion of the coating dots, leading to irregular dot shapes. Excessive air permeability affects the electrochemical performance and safety performance of the battery. Therefore, it is necessary to obtain a high-tension slurry suitable for matrix dotting, so that it can better match the dotting process and solve the problems of coating blockage, excessive air permeability and low coating coverage caused by the low tension and high fluidity of the slurry. Summary of the Invention

[0005] This invention proposes a high-tension slurry, diaphragm, and preparation process suitable for matrix dot coating, which solves the problems of coating blockage, excessively high air permeability, and low coating coverage caused by the low slurry tension and high fluidity of matrix dot coating slurries in related technologies.

[0006] The technical solution of the present invention is as follows:

[0007] This invention proposes a high-tension slurry suitable for matrix dot coating, comprising the following components in parts by weight: 0.5-1 parts dispersant, 15-20 parts PVDF powder, 45-55 parts water, 15-18 parts thickener, 13-23 parts binder, and 2.5-4 parts surfactant.

[0008] The thickener comprises hydroxymethyl cellulose, polyvinyl alcohol, and cashew phenol ether compounds in a mass ratio of 5:10:1~5.

[0009] As a further technical solution, the cashew ether compound includes one or more of the following: cashew ether sulfosuccinate disodium salt, cashew ether polyoxyethylene ether sodium sulfate, and cashew ether polyoxyethylene ether ammonium sulfate.

[0010] Preferably, the cashew ether compound comprises disodium cashew ether sulfosuccinate half ester and ammonium cashew ether polyoxyethylene ether sulfate in a mass ratio of 1:3 to 3:1.

[0011] In this invention, when the cashew ether compound is a mixture of cashew ether sulfosuccinate half ester disodium salt and cashew ether polyoxyethylene ether ammonium sulfate in a mass ratio of 1:3 to 3:1, the air permeability of the battery separator is further reduced.

[0012] As a further technical solution, the degree of polymerization of the polyvinyl alcohol is ≥1200.

[0013] In this invention, when the degree of polymerization of polyvinyl alcohol in the high-tension slurry is ≥1200, the high-tension slurry prepared and coated on the surface of the battery separator further reduces the air permeability of the battery separator, which is more conducive to the passage of electrons.

[0014] As a further technical solution, the degree of polymerization of the polyvinyl alcohol is 1650~2500.

[0015] In this invention, when the degree of polymerization of polyvinyl alcohol in the high-tension slurry is 1650~2500, the high-tension slurry is coated on the surface of the battery separator, which further reduces the air permeability of the battery separator.

[0016] As a further technical solution, the surfactant includes one or more of sodium dodecyl sulfate, fatty acid sucrose lipids, sodium dodecylbenzene sulfonate, hexadecyl triethanolamine, diols, and inorganic salts.

[0017] As a further technical solution, the adhesive includes one or more of methyl methacrylate copolymer, acrylate copolymer, and styrene-butyl methacrylate copolymer;

[0018] The dispersant includes ammonium polyacrylate.

[0019] This invention also proposes a preparation process for a high-tension slurry suitable for matrix dot coating, comprising the following steps:

[0020] The water, dispersant, and surfactant are mixed for the first time, PVDF powder is added for the second mixing, and thickener and binder are added for the third mixing to obtain a slurry.

[0021] As a further technical solution, the temperature of the first mixing is 50~65℃, the time is 10~150min, the rotation speed is 1800~2200r / min, and the revolution speed is 30~50r / min;

[0022] The second mixing time is 60-70 minutes, the rotation speed is 1500-2000 r / min, and the revolution speed is 30-50 r / min;

[0023] The third mixing time is 25-30 minutes, the rotation speed is 1200-1500 r / min, and the revolution speed is 30-40 r / min.

[0024] The present invention also proposes a diaphragm comprising a base membrane and a coating applied to one or both sides of the base membrane, the coating being made from the high-tension slurry or a slurry prepared by the preparation process described above.

[0025] As a further technical solution, the coating speed is 50~150m / min; the coating method includes matrix dot coating.

[0026] In this invention, when the high-tension slurry is coated onto the surface of the base membrane, it can be completely retained on the surface of the base membrane, reducing slurry waste caused by flowing into the pores of the diaphragm, saving slurry and reducing costs.

[0027] The working principle and beneficial effects of this invention are as follows:

[0028] In this invention, the thickener in the high-tension slurry comprises hydroxymethyl cellulose, polyvinyl alcohol, and cashew phenol ether compounds in a mass ratio of 5:10:1~5, which synergistically regulate the surface tension of the slurry. Combined with the remaining components of the high-tension slurry, the resulting high-tension slurry is less prone to patchy coating after application, especially achieving high coverage. This increases the upper limit of the patch coverage and the upper limit of the coating coverage of a single roller. It also reduces the problems of abnormal air permeability caused by slurry flowing into the pores of the separator and the decrease in coating qualification rate caused by abnormal air permeability, significantly reducing the air permeability value of the battery separator. The high-tension slurry of this invention has controllable coating properties, which can better control the shape of the coating dots and meet the requirements of battery winding processes with high dot shape requirements. Attached Figure Description

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0030] Figure 1 This is a morphology diagram of the coating spots on the surface of the battery separator obtained in Example 1 of the present invention;

[0031] Figure 2 This is a morphology diagram of the coating spots on the surface of the battery separator prepared in Comparative Example 1 of the present invention;

[0032] Figure 3 This is a microscopic morphology image of the coating points on the surface of the battery separator obtained in Example 1 of the present invention;

[0033] Figure 4 This is a microscopic morphology diagram of the coating points on the surface of the battery separator prepared in Comparative Example 1 of the present invention.

[0034] Figure 5 This is a diagram showing the coverage of the slurry prepared in Comparative Example 1 of this invention after coating.

[0035] Figure 6 This is a diagram showing the coverage of the slurry after coating in Example 1 of the present invention. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] In the following examples and comparative examples, the PVDF powder is of type FR902;

[0038] The polyvinyl alcohol (degree of polymerization 500) is designated as model BF05;

[0039] The grade of polyvinyl alcohol (degree of polymerization 1200~1400) is 1399;

[0040] The polyvinyl alcohol (degree of polymerization 2750~2850) is designated as BP28;

[0041] Polyvinyl alcohol (degree of polymerization 1650~1750) is designated as 100-27S;

[0042] The polyvinyl alcohol (degree of polymerization 2300~2500) is designated as PVA2488;

[0043] The ammonium cashew phenol polyoxyethylene ether sulfate, model number CPE-458Y, the sodium cashew phenol polyoxyethylene ether sulfate, model number CPE-430Y, and the disodium salt of cashew phenol ether sulfosuccinate, model number CPE-330Y, were all purchased from Guangzhou Shuangjian Trading Co., Ltd.

[0044] The model number of the styrene-methyl methacrylate copolymer is TX-100S;

[0045] The base membrane is a polyethylene membrane with a porosity of 36%.

[0046] Example 1

[0047] A high-tension slurry suitable for matrix dotting comprises the following components in parts by weight: 1 part of ammonium polyacrylate dispersant SN5027, 18 parts of PVDF powder, 50 parts of water, 16 parts of thickener, 18 parts of styrene-methyl methacrylate copolymer, and 3.5 parts of sodium dodecyl sulfate.

[0048] The thickener consists of hydroxymethyl cellulose, polyvinyl alcohol (degree of polymerization 500), and cashew phenol polyoxyethylene ether ammonium sulfate in a mass ratio of 5:10:3.

[0049] The preparation process of a high-tension slurry suitable for matrix dot coating includes the following steps:

[0050] Water, ammonium polyacrylate dispersant SN5027, and sodium dodecyl sulfate were mixed at 60°C, a rotation speed of 2000 r / min, and a revolution speed of 40 r / min for 75 min. PVDF powder was added, and the mixture was mixed and milled at a rotation speed of 1700 r / min and a revolution speed of 40 r / min for 65 min. Thickener and styrene-methyl methacrylate copolymer were added, and the mixture was mixed at a rotation speed of 1300 r / min and a revolution speed of 35 r / min for 28 min to obtain a slurry.

[0051] The method for preparing a battery separator includes the following steps:

[0052] A slurry was applied in a matrix pattern to the surface of a 9 μm thick base film at a coating speed of 100 m / min, and then dried at 55 °C for 2 min to obtain a battery separator.

[0053] Example 2

[0054] A high-tension slurry suitable for matrix dot coating comprises the following components in parts by weight: 1 part of ammonium polyacrylate dispersant SN5027, 20 parts of PVDF powder, 55 parts of water, 18 parts of thickener, 23 parts of styrene-methyl methacrylate copolymer, 2 parts of sodium dodecyl sulfate, and 2 parts of sodium dodecylbenzene sulfonate.

[0055] The thickener consists of hydroxymethyl cellulose, polyvinyl alcohol (degree of polymerization 500), and cashew phenol polyoxyethylene ether ammonium sulfate in a mass ratio of 5:10:5.

[0056] The preparation process of a high-tension slurry suitable for matrix dot coating includes the following steps:

[0057] Water, ammonium polyacrylate dispersant SN5027, sodium dodecylbenzenesulfonate, and sodium dodecyl sulfate were mixed at 65°C, a rotation speed of 1800 r / min, and a revolution speed of 50 r / min for 10 min. PVDF powder was added, and the mixture was mixed at a rotation speed of 2000 r / min and a revolution speed of 30 r / min and then milled for 60 min. Thickener and styrene-methyl methacrylate copolymer were added, and the mixture was mixed at a rotation speed of 1500 r / min and a revolution speed of 30 r / min for 25 min to obtain a slurry.

[0058] The method for preparing a battery separator includes the following steps:

[0059] A slurry was applied in a matrix pattern to the surface of a 9 μm thick base film at a coating speed of 150 m / min, and then dried at 45 °C for 3 min to obtain a battery separator.

[0060] Example 3

[0061] A high-tension slurry suitable for matrix dotting comprises the following components in parts by weight: 0.5 parts of ammonium polyacrylate dispersant SN5027, 15 parts of PVDF powder, 45 parts of water, 15 parts of thickener, 13 parts of styrene-methyl methacrylate copolymer, and 2.5 parts of sodium dodecyl sulfate.

[0062] The thickener consists of hydroxymethyl cellulose, polyvinyl alcohol (degree of polymerization 500), and sodium cashew phenolate polyoxyethylene ether sulfate in a mass ratio of 5:10:1.

[0063] The preparation process of a high-tension slurry suitable for matrix dot coating includes the following steps:

[0064] Water, ammonium polyacrylate dispersant SN5027, and sodium dodecyl sulfate were mixed at 50°C, a rotation speed of 2200 r / min, and a revolution speed of 30 r / min for 150 min. PVDF powder was added, and the mixture was mixed at a rotation speed of 1500 r / min and a revolution speed of 50 r / min and then milled for 70 min. Thickener and styrene-methyl methacrylate copolymer were added, and the mixture was mixed at a rotation speed of 1200 r / min and a revolution speed of 40 r / min for 30 min to obtain a slurry.

[0065] The method for preparing a battery separator includes the following steps:

[0066] A slurry was applied in a matrix pattern to the surface of a 9 μm thick base film at a coating speed of 50 m / min, and then dried at 60 °C for 1 min to obtain a battery separator.

[0067] Example 4

[0068] The only difference between this embodiment and Embodiment 1 is that polyvinyl alcohol (degree of polymerization 500) is replaced with polyvinyl alcohol (degree of polymerization 1200~1400).

[0069] Example 5

[0070] The only difference between this embodiment and Embodiment 1 is that polyvinyl alcohol (degree of polymerization 500) is replaced with polyvinyl alcohol (degree of polymerization 2750~2850).

[0071] Example 6

[0072] The only difference between this embodiment and Embodiment 1 is that polyvinyl alcohol (degree of polymerization 500) is replaced with polyvinyl alcohol (degree of polymerization 1650~1750).

[0073] Example 7

[0074] The only difference between this embodiment and Embodiment 1 is that polyvinyl alcohol (degree of polymerization 500) is replaced with polyvinyl alcohol (degree of polymerization 2300~2500).

[0075] Example 8

[0076] The only difference between this embodiment and Embodiment 7 is that cashew phenol polyoxyethylene ether ammonium sulfate is replaced with an equal amount of cashew phenol ether sulfosuccinate disodium salt.

[0077] Example 9

[0078] The only difference between this embodiment and Embodiment 7 is that cashew phenol polyoxyethylene ether ammonium sulfate is replaced with an equal amount of a mixture of cashew phenol ether sulfosuccinate half ester disodium salt and cashew phenol polyoxyethylene ether ammonium sulfate.

[0079] The mass ratio of disodium cashew ether sulfosuccinate half ester to cashew ether ammonium sulfate is 1:3.

[0080] Example 10

[0081] The only difference between this embodiment and Embodiment 7 is that cashew phenol polyoxyethylene ether ammonium sulfate is replaced with an equal amount of a mixture of cashew phenol ether sulfosuccinate half ester disodium salt and cashew phenol polyoxyethylene ether ammonium sulfate.

[0082] The mass ratio of disodium cashew ether sulfosuccinate half ester to ammonium cashew ether polyoxyethylene ether sulfate is 3:1.

[0083] Example 11

[0084] The only difference between this embodiment and Embodiment 7 is that cashew polyoxyethylene ether ammonium sulfate is replaced with an equal amount of a mixture of cashew ether sulfosuccinate half ester disodium salt and cashew polyoxyethylene ether sodium sulfate.

[0085] The mass ratio of disodium cashew ether sulfosuccinate half ester to sodium cashew ether polyoxyethylene ether sulfate is 3:1.

[0086] Comparative Example 1

[0087] The only difference between this comparative example and Example 1 is that cashew phenol polyoxyethylene ether ammonium sulfate is replaced with an equal amount of sodium dodecyl sulfate.

[0088] Comparative Example 2

[0089] The only difference between this comparative example and Example 1 is that the thickener components include hydroxymethyl cellulose and polyvinyl alcohol (degree of polymerization 500) in a mass ratio of 5:10.

[0090] Comparative Example 3

[0091] The only difference between this comparative example and Example 1 is that the thickener components include hydroxymethyl cellulose and cashew phenol polyoxyethylene ether ammonium sulfate in a mass ratio of 5:3.

[0092] Comparative Example 4

[0093] The only difference between this comparative example and Example 1 is that the thickener components include polyvinyl alcohol (degree of polymerization 500) and cashew phenol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:3.

[0094] The morphology of the coating points on the battery separators prepared in Example 1 and Comparative Example 1 were observed under a microscope, and the results are as follows: Figures 1-2 As shown;

[0095] Figure 1 This is a morphology image of the coating spots on the surface of the battery separator prepared in Example 1. Figure 2This is a morphology image of the coating spots on the surface of the battery separator prepared in Comparative Example 1. As can be seen, Figure 1 The morphology of the coating points on the battery separator is closer to that of a circle, while Figure 2 The deformation of the coating points on the battery separator is severe, indicating that the high-tension slurry prepared by the formula of this invention has better control over the shape of the coating points on the separator surface, which can meet the requirements of the battery winding process with high point shape.

[0096] The battery separators prepared in Example 1 and Comparative Example 1 were placed under an electron microscope, and the finer microstructure of the coating points on the battery separators was captured at 5kx magnification. The results are as follows. Figures 3-4 As shown;

[0097] Figure 3 This is a microscopic morphology image of the coating spots on the surface of the battery separator prepared in Example 1. Figure 4 This is a microscopic morphology image of the coating spots on the surface of the battery separator prepared in Comparative Example 1. It can be seen that... Figure 3 The coating points on the base film showed good particle aggregation, and the slurry basically did not clog the pores. Figure 4 The coating points on the base film are relatively scattered, and the slurry seeps into the pores of the base film, clogging the pores.

[0098] The viscosity of the slurries prepared in Example 1 and Comparative Example 1 was tested using a viscometer. The viscosity of the slurry in Example 1 was 430 mPa·s, and the viscosity of the slurry in Comparative Example 1 was 440 mPa·s.

[0099] The surface tension of the slurries prepared in Examples 1-11 and Comparative Examples 1-4 was tested using a surface tension meter. The air permeability of the battery separators prepared in Examples 1-11 and Comparative Examples 1-4 was tested according to the method in GB / T 36363-2018: transverse samples were taken from the battery separator, one sample was taken every 100m, and then the air permeability was tested. Ten points were measured for each sample, and the average value of the results was taken, as shown in Table 1.

[0100] Table 1 Test Results

[0101]

[0102] Compared with Comparative Examples 1-4, the slurries prepared in Examples 1-11 had higher surface tension. After being coated on the surface of the battery separator, the air permeability of the battery separator was lower. This indicates that the thickener components in the high-tension slurry consist of hydroxymethyl cellulose, polyvinyl alcohol, and cashew phenol ether compounds in a mass ratio of 5:10:1-5. Combined with the remaining components of the high-tension slurry, the high-tension slurry prepared and coated on the surface of the battery separator significantly reduced the air permeability of the battery separator.

[0103] Compared with Example 1, the slurries prepared in Examples 4 and 5 have higher surface tension. After being coated on the surface of the battery separator, the air permeability of the battery separator is lower. This indicates that when the degree of polymerization of polyvinyl alcohol in the high-tension slurry is ≥1200, the high-tension slurry prepared and coated on the surface of the battery separator further reduces the air permeability of the battery separator.

[0104] Compared with Examples 4-5, the slurries prepared in Examples 6-7 have higher surface tension. After being coated on the surface of the battery separator, the air permeability of the battery separator is lower. This indicates that when the degree of polymerization of polyvinyl alcohol in the high-tension slurry is 1650-2500, the high-tension slurry prepared and coated on the surface of the battery separator further reduces the air permeability of the battery separator.

[0105] Compared with Examples 7-8 and Example 11, the slurry prepared in Examples 9-10 has a higher surface tension. After being coated on the surface of the battery separator, the air permeability of the battery separator is lower. This indicates that when the cashew ether compound is cashew ether sulfosuccinate half ester disodium salt and cashew ether polyoxyethylene ether ammonium sulfate in a mass ratio of 1:3 to 3:1, the air permeability of the battery separator is further reduced.

[0106] The upper limit of coating coverage for the two slurries in Comparative Example 1 and Comparative Example 1 was determined by continuously increasing the coverage during slurry coating until individual points appeared to be connected. The coverage results are as follows: Figures 5-6 As shown.

[0107] Figure 5 The diagram shows the coverage rate of the slurry after coating in Comparative Example 1. Figure 6 The diagram shows the coverage rate of the slurry after coating in Example 1. The coverage rate of the slurry after coating in Example 1 is 66.30%, while the coverage rate of the slurry after coating in Comparative Example 1 is 57.00%. Compared with Comparative Example 1, the coverage rate of the slurry after coating in Example 1 is higher, indicating that the slurry prepared by the formulation of the present invention can effectively improve the upper limit of the coating coverage of the printing roller and broaden the coating capability of the printing roller.

[0108] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-tension slurry suitable for matrix dot coating, characterized in that, It includes the following components in parts by weight: 0.5-1 part dispersant, 15-20 parts PVDF powder, 45-55 parts water, 15-18 parts thickener, 13-23 parts binder, and 2.5-4 parts surfactant; The thickener comprises hydroxymethyl cellulose, polyvinyl alcohol, and cashew phenol ether compounds in a mass ratio of 5:10:1~5. The cashew ether compounds include one or more of the following: cashew ether sulfosuccinate disodium salt, cashew ether polyoxyethylene ether sodium sulfate, and cashew ether polyoxyethylene ether ammonium sulfate. The surfactant includes one or more of sodium dodecyl sulfate, fatty acid sucrose lipids, sodium dodecylbenzene sulfonate, hexadecyl triethanolamine, diols, and inorganic salts; The adhesive includes one or more of methyl methacrylate copolymer, acrylate copolymer, and styrene-butyl methacrylate copolymer; The dispersant includes ammonium polyacrylate.

2. The high-tension slurry suitable for matrix dot coating according to claim 1, characterized in that, The cashew ether compound comprises disodium salt of cashew ether sulfosuccinate half ester and cashew polyoxyethylene ether ammonium sulfate in a mass ratio of 1:3 to 3:

1.

3. The high-tension slurry suitable for matrix dot coating according to claim 1, characterized in that, The degree of polymerization of the polyvinyl alcohol is ≥1200.

4. The high-tension slurry suitable for matrix dot coating according to claim 3, characterized in that, The degree of polymerization of the polyvinyl alcohol is 1650~2500.

5. A preparation process for a high-tension slurry suitable for matrix dot coating according to any one of claims 1 to 4, characterized in that, Includes the following steps: The water, dispersant, and surfactant are mixed for the first time, PVDF powder is added for the second mixing, and thickener and binder are added for the third mixing to obtain a slurry.

6. The preparation process of a high-tension slurry suitable for matrix dot coating according to claim 5, characterized in that, The temperature of the first mixing is 50~65℃, the time is 10~150min, the rotation speed is 1800~2200r / min, and the revolution speed is 30~50r / min; The second mixing time is 60-70 minutes, the rotation speed is 1500-2000 r / min, and the revolution speed is 30-50 r / min; The third mixing time is 25-30 minutes, the rotation speed is 1200-1500 r / min, and the revolution speed is 30-40 r / min.

7. A diaphragm, characterized in that, It includes a base film and a coating applied to one or both sides of the base film, the coating being made from the high-tensile slurry according to any one of claims 1 to 4 or the slurry prepared by the preparation process according to any one of claims 5 to 6.

8. A diaphragm according to claim 7, characterized in that, The coating speed is 50~150m / min; the coating method includes matrix dot coating.

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