High-temperature resistant and puncture-resistant coated diaphragms and their preparation method

Abstract

This invention discloses a coated diaphragm with high temperature resistance and puncture resistance, and its preparation method, comprising the following steps: mixing and grinding a ceramic powder dispersion and a modified boron phenolic resin to obtain a mixed liquid, wherein the mass ratio of ceramic powder to modified boron phenolic resin is 15-40:5-31; the D50 of the ceramic powder is 0.3-0.6 μm; the modification method of the modified boron phenolic resin is as follows: uniformly mixing the boron phenolic resin with a surface treatment agent, wherein the surface treatment agent is polyether siloxane; mixing the mixed liquid with a hydroxymethyl cellulose solution, then adding a binder and a wetting agent, grinding and dispersing uniformly to obtain a coating slurry; coating the coating slurry onto a base film, and drying to obtain the final product.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a coated separator with high temperature resistance and puncture resistance, and its preparation method. Background Technology

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

[0003] As an important component of lithium-ion batteries, the battery separator plays a role in preventing short circuits between the positive and negative electrodes and providing ion transport channels during charging and discharging. Its performance affects the battery's interface structure and internal resistance, which in turn affects the battery's cycle performance, capacity, and charge / discharge current density.

[0004] Currently, the raw materials for commercially used lithium-ion battery separators are mainly PE and PP, which have relatively low melting points. With the rapid development of battery positive and negative electrodes, high energy density and high-current fast charging pose greater challenges to separators. During charging and discharging, batteries generate high temperatures, which can cause localized membrane rupture, leading to internal short circuits and safety accidents. Therefore, higher requirements are placed on the high-temperature resistance of the separators.

[0005] Existing technologies include coating the membrane surface with a phenolic resin layer to improve the membrane's heat resistance and flame retardant properties. However, the decomposition temperature of phenolic resin is around 200℃, which is relatively low. Once the decomposition temperature is reached, small molecule gases such as CO, CO2, and H2O will be produced, which can easily cause the battery to swell and create safety hazards.

[0006] Furthermore, during battery manufacturing, uneven electrode surfaces or burrs often occur, and dendritic crystals may gradually form inside the battery during use. Uneven electrode surfaces, burrs, and dendritic crystals can all puncture the separator, causing internal micro-short circuits. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a coated diaphragm with high temperature resistance and puncture resistance and its preparation method.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a coated diaphragm that is resistant to high temperatures and punctures, comprising the following steps:

[0010] The ceramic powder dispersion and the modified boron phenolic resin were mixed, ground and dispersed to obtain a mixture. The mass ratio of ceramic powder to modified boron phenolic resin was 15-40:5-31.

[0011] Preferably, the ceramic powder has a D50 of 0.3-0.6 μm;

[0012] The modification method of the modified boron phenolic resin is as follows: the boron phenolic resin is uniformly mixed with a surface treatment agent to obtain the modified boron phenolic resin, wherein the surface treatment agent is a polyether siloxane.

[0013] The mixture is mixed with a hydroxymethyl cellulose solution, then a binder and a wetting agent are added, and the mixture is ground and dispersed evenly to obtain a coating slurry;

[0014] The coating slurry is applied to the base film and then dried to obtain the final product.

[0015] The present invention uses nano-sized ceramic powder, which has the problem of easy agglomeration. When it is directly mixed with boron phenolic resin, it is difficult to mix the two evenly. In addition, after the ceramic powder and boron phenolic resin are mixed and diluted to prepare a coating, the ceramic particles and boron phenolic resin microspheres are prone to agglomerate and settle in the slurry system, affecting the quality stability of the coating and thus affecting the quality of the coated diaphragm.

[0016] Therefore, the present invention mainly addresses the above problems from the following aspects:

[0017] 1) Pre-disperse the nano-sized ceramic powder. Since the ceramic powder has a high surface energy, it is easy to agglomerate internally. By coating the surface of the ceramic powder with small molecules of dispersant, the surface energy is reduced, and the energy and time required for dispersion are reduced, so as to prepare a ceramic powder dispersion with relatively uniform dispersion.

[0018] 2) There is a strong interfacial tension between boron phenolic resin and ceramics and dispersion. The surface of boron phenolic resin needs to be modified to reduce the interfacial energy between it and ceramic powder and aqueous phase, so that boron phenolic resin can have better affinity with ceramic powder dispersion without internal agglomeration, which is conducive to further improving the mixing uniformity of the two.

[0019] 3) After mixing the ceramic powder dispersion with the modified boron phenolic resin, grind it with a high-speed grinder. Use mechanical force to break up and redisperse some of the undispersed agglomerates, thereby improving the uniformity of the mixture.

[0020] 4) Prepare a hydroxymethyl cellulose (CMC) solution by mixing a ceramic powder dispersion (which has been fully dispersed by a high-speed mill) and a mixture of modified boron phenolic resin with the CMC solution. The hydrophobic backbone of the CMC molecules associates with the surrounding water molecules through hydrogen bonds, which increases the fluid volume of the polymer itself and reduces the space for free movement of particles, thereby increasing the viscosity of the system and thus helping to obtain a stable slurry system.

[0021] Boron-phenolic resin is a high-temperature resistant material obtained by modifying the C / C bonds of a resin with the introduction of boron (BO) element. Its heat resistance far surpasses that of traditional resins. The introduced BO bonds have a bond energy of 561-690 kJ / mol, significantly higher than the original C / C bond energy of 348 kJ / mol. Therefore, while the initial decomposition temperature of traditional phenolic resin is approximately 200℃, that of boron-phenolic resin is approximately 330℃, and the residual carbon content can reach 75% under a nitrogen atmosphere. The introduced BO bonds form a cross-linked network within the phenolic resin, making its carbonized layer denser and improving the material's high-temperature resistance and resistance to airflow erosion.

[0022] After coating, boron phenolic resin and ceramic particles are uniformly mixed to form a high-temperature resistant coating. Its dense coating layer helps improve needle penetration strength. When boron phenolic resin is used alone for coating, the battery temperature rises, causing the separator to rupture and melt. During the curing and cross-linking process of the boron phenolic resin, some small molecules volatilize, preventing the formation of a dense insulating layer. This results in problems such as cracking and collapse of the coating material, failing to achieve the desired isolation between the positive and negative electrode materials.

[0023] The uniform mixing of boron phenolic resin and ceramic particles forms a high-temperature resistant coating. When the internal temperature of the battery rises to 90-130℃, the separator substrate experiences pore closure, blocking ion exchange channels. Locally, the separator tends to shrink. However, the boron phenolic resin undergoes cross-linking and curing, forming a boron phenolic resin skeleton that inhibits thermal shrinkage and prevents direct contact between the positive and negative electrodes, thus avoiding internal short circuits. When the temperature continues to rise to 130-300℃, local membrane rupture and melting occur in the separator substrate. The dense and sufficient coupling of the boron phenolic resin / inorganic ceramics allows the high-temperature resistant coating to play a major barrier role. With continued temperature increases, the separator substrate completely decomposes under heat, while the boron phenolic resin carbonizes, coating the ceramic particles to form a carbonized layer, which also acts as a barrier, preventing direct burn-through and improving safety performance.

[0024] In some embodiments, the mass ratio of ceramic powder, dispersant and water in the ceramic dispersion is 15-40:0.3-1:30-60.

[0025] Preferably, the dispersant is polyacrylamide.

[0026] In some embodiments, the mass ratio of boron phenolic resin to surface treatment agent in the modified boron phenolic resin is 5-30:0.2-1.

[0027] Preferably, a planetary mixer is used to mix boron phenolic resin and surface treatment agent, with a revolution speed of 10-50 rpm and a rotation speed of 600-1400 rpm.

[0028] In some embodiments, the ceramic powder dispersion and the modified boron phenolic resin are mixed, ground and dispersed using a high-speed grinder at a speed of 800-1200 rpm, with a feed pump air pressure of 0.1-0.25 MPa, and the mixture is repeated 2-5 times.

[0029] In some embodiments, the adhesive is polyacrylate, and the mass ratio of the adhesive to boron phenolic resin is 2-10:5-30.

[0030] In some embodiments, the wetting agent is alkylphenol polyoxyethylene ether, and the mass ratio of the wetting agent to the boron phenolic resin is 0.02-0.12:5-30.

[0031] In some embodiments, the slurry is coated on one or both sides of the base film, the coating thickness is 0.5-5 μm, and the coating speed ratio is 0.5-1.8.

[0032] In some embodiments, the thickness of the base film is 4-16 μm.

[0033] Secondly, the present invention provides a coated diaphragm that is resistant to high temperature and puncture, prepared by the aforementioned preparation method.

[0034] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0035] The boron phenolic resin and ceramic particles are uniformly mixed to form a high-temperature resistant coating. Within a certain temperature range, the boron phenolic resin undergoes cross-linking and curing to form a boron phenolic resin skeleton, which inhibits the thermal shrinkage of the diaphragm and avoids direct contact between the positive and negative electrodes, thus preventing internal short circuits.

[0036] When the battery temperature continues to rise and localized membrane rupture and melting occur in the separator substrate, the high-temperature resistant coating plays a major barrier role due to the dense and sufficient coupling of boron phenolic resin / inorganic ceramic. Even when the battery temperature reaches a certain level, causing the separator substrate to completely decompose due to heat, the boron phenolic resin carbonizes, coating the ceramic particles to form a carbonized layer, which acts as a barrier, preventing direct burn-through and improving safety performance.

[0037] The dense coating layer obtained by mixing boron phenolic resin with ceramic particles has high needle penetration strength, which can effectively improve the puncture resistance of the diaphragm.

[0038] This invention uses water as the solvent, which is more environmentally friendly and less expensive than traditional organic solvents. A stable coating slurry is prepared by adding CMC thickener and surface treatment agent for dispersion, followed by repeated grinding to ensure thorough dispersion. Attached Figure Description

[0039] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0040] Figure 1 This is a schematic diagram illustrating the principle of membrane preparation according to an embodiment of the present invention;

[0041] Figure 2 This is a comparison diagram of the thermal decomposition of boron phenolic resin and phenolic resin coated diaphragms;

[0042] Figure 3 These are tensile comparison curves of the diaphragms prepared in the embodiments and comparative examples of the present invention;

[0043] Figure 4 This is a comparison diagram of the needle penetration strength of the diaphragms prepared in the embodiments and comparative examples of the present invention. Detailed Implementation

[0044] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045]

[0046] Boron phenolic resin is a high-temperature resistant material obtained by modifying the resin by introducing boron elements into the C and C bonds. The main raw materials for synthesis are formaldehyde, phenol and boric acid. The synthesis method is shown above. The boron phenolic resin used is obtained by purchasing externally, and its grade is FB88#.

[0047] The present invention will be further described below with reference to the embodiments.

[0048] Example 1

[0049] The preparation method of the diaphragm is as follows:

[0050] 1) Take 0.5 kg of CMC powder and add it to 9.5 kg of water. Mix and stir using a high-speed mixer at 800 rpm for 40 min to prepare a CMC solution.

[0051] 2) Take a certain amount of alumina with D50 of 0.4μm, 30kg, add dispersant polyacrylamide 0.5kg, add water 50kg, stir for 60min, and use a planetary mixer to pre-dispersegate at 30rpm and 800rpm.

[0052] 3) Take a certain amount of boron phenolic resin (5 kg) and add 0.45 kg of surface treatment agent polyether siloxane to mix and treat to obtain boron phenolic resin dispersion solution;

[0053] 4) The stirred boron phenolic resin / alumina solution was stirred at 800 rpm for 30 minutes, and then ground using a high-speed grinder at 1000 rpm with a feed pump pressure of 0.2 MPa for 3 grinding and dispersion cycles.

[0054] 5) Add the ground solution to the CMC solution in step 1, stir for 30 minutes, then add 4 kg of adhesive polyacrylate and stir. Add 0.05 kg of wetting agent alkylphenol polyoxyethylene ether and stir.

[0055] 6) Use a 9μm PE base film and unwind it under unwinding tension; when passing the coating end, use a gravure roller to coat the prepared slurry on both sides, with the coating thickness on one side controlled at 2μm and the coating speed ratio at 1.1; after coating, use an oven to dry it, with the drying temperature controlled at 85℃, and after drying, rewind the coated diaphragm under a certain tension.

[0056] Example 2

[0057] The preparation method of the diaphragm is as follows:

[0058] 1) Take 0.5 kg of CMC powder and add it to 9.5 kg of water. Mix and stir using a high-speed mixer at 800 rpm for 40 min to prepare a CMC solution.

[0059] 2) Take a certain amount of 25 kg of alumina with D50 at 0.5 μm, add 0.5 kg of dispersant polyacrylamide, add 50 kg of water, stir for 60 min, and use a planetary mixer to pre-dispersegate at 30 rpm and 800 rpm.

[0060] 3) Take a certain amount of boron phenolic resin (10 kg) and add 0.45 kg of surface treatment agent polyether siloxane to mix and treat to obtain boron phenolic resin dispersion solution;

[0061] 4) The stirred boron phenolic resin / alumina solution was stirred at 800 rpm for 30 minutes, and then ground using a high-speed grinder at 1000 rpm with a feed pump pressure of 0.2 MPa for 3 grinding and dispersion cycles.

[0062] 5) Add the ground solution to 10 kg of the CMC solution in step 1, stir for 30 min, then add 4 kg of the binder polyacrylate and stir. Add 0.05 kg of the wetting agent alkylphenol polyoxyethylene ether and stir.

[0063] 6) Use a 9μm PE base film and unwind it under unwinding tension; when passing the coating end, use a gravure roller to coat the prepared slurry on both sides, with the coating thickness on one side controlled at 2μm and the coating speed ratio at 1.1; after coating, use an oven to dry it, with the drying temperature controlled at 85℃, and after drying, rewind the coated diaphragm under a certain tension.

[0064] Comparative Example 1

[0065] A 9μm PE base film was used without any coating treatment.

[0066] Comparative Example 2

[0067] The preparation method of the diaphragm is as follows:

[0068] 1) Take 0.5 kg of CMC powder and add it to 9.5 kg of water. Mix and stir using a high-speed mixer at 800 rpm for 40 min to prepare a CMC solution.

[0069] 2) Take a certain amount of 25 kg of alumina with D50 at 0.5 μm, add 0.5 kg of dispersant polyacrylamide, add 50 kg of water, stir for 60 min, and use a planetary mixer to pre-dispersegate at 30 rpm and 800 rpm.

[0070] 3) Take a certain amount of phenolic resin 10kg, add 0.45kg of surface treatment agent polyether siloxane and mix to obtain phenolic resin solution;

[0071] 4) Mix the stirred phenolic resin and alumina solution at a stirring speed of 35 rpm for 30 minutes, then grind them using a high-speed grinder at a speed of 1000 rpm, with the cylinder pressure controlled at around 0.1 MPa and the feed pump air pressure at 0.2 MPa, and perform three grinding and dispersion processes.

[0072] 5) Add the ground solution to 10 kg of CMC solution, stir for 30 min, then add 4 kg of binder polyacrylate and stir. Add 0.05 kg of wetting agent alkylphenol polyoxyethylene ether and stir.

[0073] 6) Use a 9μm PE base film and unwind it under unwinding tension; when passing the coating end, use a gravure roller to coat the prepared slurry on both sides, with the coating thickness on one side controlled at 2μm and the coating speed ratio at 1.1; after coating, use an oven to dry it, with the drying temperature controlled at 85℃, and after drying, rewind the coated diaphragm under a certain tension.

[0074] Performance testing

[0075] Depend on Figure 2It can be seen that after the boron-phenolic resin coating, the organic coating begins to decompose at a relatively high temperature. The introduced boron element helps to increase the degree of cross-linking within the phenolic structure, achieving high-temperature resistance. The phenolic resin exhibits a significant decreasing trend around 220℃; after 380℃, the membrane substrate begins to decompose, and the residual carbon rate decreases sharply. The boron-phenolic resin tends to stabilize at 620℃. The boron oxide produced during decomposition is a ceramic material, increasing the residual carbon rate of the material and helping to prevent the coated membrane from being directly burned through.

[0076] The diaphragms prepared in the examples and comparative examples were tested separately, and the heat shrinkage was tested at 200°C:

[0077] Depend on Figure 3 The data shows that after the high-temperature resistant coating was applied, the mechanical strength of the diaphragm was not damaged, and its tensile strength did not decrease.

[0078] By comparing Examples 1-2 and Comparative Examples 1-2, the dense coating provides a certain degree of buffering protection against the puncture of sharp objects, and the high-temperature resistant coating improves the needle penetration strength of the diaphragm (detailed data are shown in the table below). Figure 4 .

[0079] Table 1 Comparison of slurry particle size and diaphragm properties in the examples and comparative examples

[0080] Experimental sample D10 D50 D90 Breathability (s / 100cc) Needle puncture intensity (gf) Example 1 0.26 0.459 0.736 205 577 Example 2 0.33 0.561 0.838 226 567 Comparative Example 1 / / / 156 547 Comparative Example 2 0.28 0.484 0.758 215 554

[0081] As shown in Table 1, after adding CMC thickener and surface treatment agent for dispersion treatment, and after repeated grinding for thorough dispersion, the particle size values ​​are similar, and the slurry is uniformly mixed. After coating, due to the blockage of the base film pores by some small-diameter boron phenolic resin particles, the air permeability increases to a certain extent, resulting in an increase in the battery's internal resistance.

[0082] Table 2 compares the heat resistance (200℃ / 1h) and residual carbon rate (850℃) of the diaphragms in the examples and comparative examples.

[0083]

[0084]

[0085] As shown in Table 2, the BO bonds introduced by boron phenolic resin form a cross-linked network in the phenolic resin, resulting in better high-temperature resistance. After modification and coating the diaphragm with boron phenolic resin / ceramic slurry, it exhibits superior heat shrinkage performance and a higher carbon residue rate, resulting in better heat resistance and safety performance of the composite diaphragm.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a coated diaphragm with high temperature resistance and puncture resistance, characterized in that: Includes the following steps: The ceramic powder dispersion and the modified boron phenolic resin were mixed, ground, and dispersed to obtain a mixture. The modification method of the modified boron phenolic resin is as follows: the boron phenolic resin is uniformly mixed with a surface treatment agent to obtain the modified boron phenolic resin, wherein the surface treatment agent is a polyether siloxane. The mixture is mixed with a hydroxymethyl cellulose solution, then a binder and a wetting agent are added, and the mixture is ground and dispersed evenly to obtain a coating slurry; The coating slurry is applied to the base film and then dried to obtain the final product.

2. The method for preparing a coated diaphragm with high temperature resistance and puncture resistance according to claim 1, characterized in that: In the ceramic dispersion, the mass ratio of ceramic powder, dispersant, and water is 15-40:0.3-1:30-60; Preferably, the dispersant is polyacrylamide; Preferably, the mass ratio of ceramic powder to modified boron phenolic resin is 15-40:5-31; Preferably, the D50 of the ceramic powder is 0.3-0.6 μm.

3. The method for preparing a coated diaphragm with high temperature resistance and puncture resistance according to claim 1, characterized in that: In modified boron phenolic resin, the mass ratio of boron phenolic resin to surface treatment agent is 5-30:0.2-1.

4. The method for preparing a coated diaphragm with high temperature resistance and puncture resistance according to claim 1, characterized in that: The boron phenolic resin and surface treatment agent were mixed using a planetary mixer with a revolution speed of 10-50 rpm and a rotation speed of 600-1400 rpm.

5. The method for preparing a coated diaphragm with high temperature resistance and puncture resistance according to claim 1, characterized in that: The ceramic powder dispersion and modified boron phenolic resin were mixed, ground and dispersed using a high-speed grinder at a speed of 800-1200 rpm and a feed pump pressure of 0.1-0.25 MPa, with the mixture being repeated 2-5 times.

6. The method for preparing a coated diaphragm with high temperature resistance and puncture resistance according to claim 1, characterized in that: The adhesive is polyacrylate, and the mass ratio of the adhesive to boron phenolic resin is 2-10:5-30.

7. The method for preparing a coated diaphragm with high temperature resistance and puncture resistance according to claim 1, characterized in that: The wetting agent is alkylphenol polyoxyethylene ether, and the mass ratio of the wetting agent to boron phenolic resin is 0.02-0.12:5-30.

8. The method for preparing a coated diaphragm with high temperature resistance and puncture resistance according to claim 1, characterized in that: The slurry is coated on one or both sides of the base film, with a coating thickness of 0.5-5μm and a coating speed ratio of 0.5-1.

8.

9. The method for preparing a coated diaphragm with high temperature resistance and puncture resistance according to claim 1, characterized in that: The thickness of the base film is 4-16 μm.

10. A coated diaphragm with high temperature resistance and puncture resistance, characterized in that: It is prepared by any one of the preparation methods described in claims 1-9.

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