A diaphragm, its preparation method and use

Abstract

The application discloses a diaphragm and a preparation method and application thereof, and belongs to the technical field of battery diaphragms. The diaphragm comprises a base film layer and a ceramic coating layer. The base film layer comprises a first base film layer and a second base film layer. The ceramic coating layer is arranged between the first base film layer and the second base film layer. The composition of the ceramic coating layer comprises an adhesive and ceramic. The mass ratio of the adhesive to the ceramic is less than 0.08. By arranging the ceramic coating layer between the first base film layer and the second base film layer, the base film layer can provide support force to the ceramic coating layer to offset a part of the gravity of the ceramic, the dependence of the ceramic on the adhesive provided bonding force can be reduced, the problem that a large amount of adhesive is needed due to the fact that the gravity of the ceramic is completely offset by the adhesive force is avoided, the amount of the adhesive is effectively reduced, and then the adhesive is prevented from blocking the first base film layer and the second base film layer, and the problem that the electrochemical performance is reduced due to the fact that the adhesive blocks the micropores of the diaphragm is solved.

Description

Technical Field

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

[0002] Lithium-ion batteries have been widely used since their invention, offering advantages such as long cycle life, high energy density, and no memory effect. A lithium-ion battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte, with the separator being one of its core components, directly affecting the battery's electrochemical and safety performance.

[0003] Currently, the base membrane of most mainstream lithium-ion battery separators is made of polyolefins through uniaxial or biaxial stretching. However, polyolefin porous membranes have poor heat resistance; for example, polyethylene has a melting point of only about 130°C, while polypropylene has a melting point of about 150°C. Under abnormal operating conditions, the separator may break, easily causing a short circuit between the positive and negative electrodes, resulting in irreparable safety problems. Modern separators often require coating one or more layers of functional materials onto the polyolefin base membrane.

[0004] The most common approach is to coat one or more layers of high-strength ceramic particles onto one or both sides of the membrane. The ceramic particles enhance the membrane's heat resistance. Since ceramics lack adhesive properties, an adhesive must be added to the slurry during preparation to ensure a uniform and stable coating of the ceramic particles onto the membrane. These adhesives provide good adhesion between ceramic particles and between the ceramic particles and the membrane. However, because these adhesives are polymers, while providing bonding, they can also clog the membrane's micropores, leading to a decrease in the membrane's electrochemical performance. Summary of the Invention

[0005] The purpose of this application is to provide a diaphragm, its preparation method, and its application, so as to improve the problem of reduced electrochemical performance caused by adhesive clogging of diaphragm micropores.

[0006] This application provides a diaphragm, which includes a base film layer and a ceramic coating; the base film layer includes a first base film layer and a second base film layer; the ceramic coating is disposed between the first base film layer and the second base film layer, and the ceramic coating comprises an adhesive and ceramic, wherein the mass ratio of the adhesive to the ceramic is less than 0.08.

[0007] By adopting the above design, the ceramic coating is placed between the first base film layer and the second base film layer. The base film layer can provide support to the ceramic coating to offset part of the weight of the ceramic. This reduces the ceramic's dependence on the adhesive force provided by the adhesive, avoiding the problem of needing a large amount of adhesive due to relying entirely on adhesive force to offset the weight of the ceramic. This effectively reduces the amount of adhesive used, thereby preventing the adhesive from clogging the micropores of the first and second base film layers. This can improve the problem of reduced electrochemical performance caused by adhesive clogging the membrane micropores.

[0008] As an optional implementation, the mass ratio of the adhesive to the ceramic is less than 0.06;

[0009] Preferably, the mass ratio of the adhesive to the ceramic is less than 0.04;

[0010] More preferably, the mass ratio of the adhesive to the ceramic is 0.006-0.027.

[0011] Reducing the amount of adhesive will lead to a decrease in the peel strength of the base film layer. After comprehensively considering the peel strength and air permeability of the base film layer, the applicant believes that controlling the mass ratio of adhesive to ceramic to be 0.006-0.027 is a better range.

[0012] As an optional implementation, the ceramic comprises ceramic particles of at least two particle sizes;

[0013] Preferably, the ceramic comprises first ceramic particles and second ceramic particles, and the particle size ratio of the first ceramic particles and the second ceramic particles is not less than 3.

[0014] As an alternative implementation, at least a portion of the components of the ceramic coating can react with lithium dendrites to prevent lithium dendrite penetration.

[0015] As an optional embodiment, the adhesive is prepared by crosslinking a first adhesive and a second adhesive; and / or

[0016] The first adhesive comprises at least one of polyacrylic acid, polyurethane, polyvinyl alcohol, styrene, and butadiene copolymer; and / or

[0017] The second adhesive comprises 4-maleimide butyric acid.

[0018] As an optional implementation, the air permeability of the first base film layer is 60s / 100ml-120s / 100ml; and / or

[0019] The air permeability of the second base film layer is 60s / 100ml-120s / 100ml.

[0020] As an optional implementation, the ceramic coating further comprises functional additives, including functional materials that improve heat resistance, functional materials that improve mechanical properties, and functional materials that improve adhesion; and / or

[0021] The functional materials for improving heat resistance include at least one of aramid fibers and carbon fibers; and / or

[0022] The functional materials for improving mechanical properties include at least one of glass fibers and inorganic nanowires; and / or

[0023] The functional material that enhances adhesive properties includes at least one of polyvinylidene fluoride and polymethyl methacrylate.

[0024] As an optional implementation, the diaphragm further includes a functional membrane layer, which is applied to the outside of the first base membrane layer and / or the second base membrane layer;

[0025] The functional film layer includes at least one of a base film layer, a ceramic coating layer, and an adhesive layer;

[0026] The coating layer comprises at least one of PVDF and its copolymers, PMMA and its copolymers, PAN and its copolymers, styrene-butadiene copolymers, aramid, nanowires, graphene, and graphene oxide.

[0027] This application also provides a method for preparing a diaphragm, the method comprising:

[0028] A slurry for obtaining a ceramic coating is provided, the slurry comprising a binder and ceramic, wherein the mass ratio of the binder to the ceramic is less than 0.08.

[0029] The ceramic coating slurry is applied between the first base film layer and the second base film layer, and then dried to obtain a diaphragm.

[0030] This application also provides a battery, which includes the separator described above. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A schematic diagram of the diaphragm structure provided for the prior art;

[0033] Figure 2Force analysis diagram of ceramic particles in a diaphragm provided for the prior art;

[0034] Figure 3 Force analysis diagram of ceramic particles of the diaphragm provided in the embodiments of this application;

[0035] Figure 4 A schematic diagram of the structure of a diaphragm using single ceramic particles and a common adhesive, provided in an embodiment of this application;

[0036] Figure 5 A schematic diagram of the structure of a diaphragm using two types of ceramic particles and a special adhesive, provided for an embodiment of this application;

[0037] Figure 6 A flowchart illustrating the method provided in an embodiment of this application.

[0038] Reference numerals: 1-base film layer, 11-first base film layer, 12-second base film layer, 2-ceramic particles, 3-adhesive. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0040] It should be noted that, unless otherwise specified, the particle size referred to in this application refers to the median particle size D50.

[0041] See Figure 1 In a conventional coating process, ceramics and adhesive 3 are prepared into a slurry, which is then coated onto a diaphragm and dried to obtain a ceramic-coated diaphragm. To fix the ceramics onto the diaphragm, a large amount of adhesive 3 needs to be added. While providing adhesion, adhesive 3, being a polymer, can clog the micropores of the diaphragm, reducing its permeability and consequently its electrochemical performance.

[0042] See Figure 2 The stress analysis of the ceramic particles 2 on the diaphragm shows that the ceramic particles 2 will not fall off when the gravitational force is less than the adhesive force of the adhesive 3.

[0043] This application provides a diaphragm, which includes a first base film layer 11, a second base film layer 12, and a ceramic coating; the ceramic coating is disposed between the first base film layer 11 and the second base film layer 12, and the ceramic coating comprises an adhesive 3 and ceramic, wherein the mass ratio of the adhesive 3 to the ceramic is less than 0.08.

[0044] Using the above design, by placing the ceramic coating between the first base film layer 11 and the second base film layer 12, the ceramic particles 2, in addition to being subjected to adhesive force, are also subjected to the supporting force provided by the base film layer 1 to the ceramic coating, which together counteracts the weight of the ceramic. See [link to design]. Figure 3 Therefore, even with a smaller adhesive force, force balance can be achieved, preventing the ceramic particles 2 from shedding powder. This effectively reduces the amount of adhesive 3 used, thereby preventing adhesive 3 from clogging the first base film layer 11 and the second base film layer 12, reducing the impact of adhesive 3 on air permeability, and solving the problem of reduced electrochemical performance caused by adhesive 3 clogging the micropores of the diaphragm; at the same time, the reduced amount of adhesive 3 also leads to some cost savings.

[0045] Based on the above implementation principle, those skilled in the art will understand that the smaller the mass ratio of adhesive 3 to ceramic, the lower the probability that adhesive 3 will clog the base film layer 1, and the smaller the impact of adhesive 3 on air permeability; that is, the smaller the amount of adhesive 3 added, the better. Optionally, the mass ratio of adhesive 3 to ceramic is less than 0.06; preferably, the mass ratio of adhesive 3 to ceramic is less than 0.05; more preferably, the mass ratio of adhesive 3 to ceramic is less than 0.04; considering the peel force between the base film layers 1, more preferably, the mass ratio of adhesive 3 to ceramic is 0.006-0.027; the mass ratio of adhesive 3 to ceramic includes, but is not limited to, 0.08, 0.07, 0.06, 0.055, 0.05, 0.045, 0.04, 0.035, 0.03, 0.025, 0.02, 0.015, 0.01, and 0.006, etc.

[0046] Through experiments, the applicant verified that the amount of adhesive 3 added is smaller than that in the prior art (the ratio of adhesive 3 to ceramic in the prior art is generally around 0.1). Within this range, the peel force between the first base film layer 11 and the second base film layer 12 is still 7-10 N / m. This force has reached the adhesive force between the PVDF coated separator and the electrode in the prior art. Therefore, we believe that under this condition, there will be no problem of detachment between the first base film layer 11 and the second base film layer 12.

[0047] In some embodiments, the ceramic includes ceramic particles 2 with at least two particle sizes, such as ceramic particles 2 with two particle sizes, ceramic particles 2 with three particle sizes, ceramic particles 2 with four particle sizes, and ceramic particles 2 with five particle sizes.

[0048] The above design uses a combination of ceramics with different particle sizes. This combination of large and small particle sizes allows the smaller ceramic particles 2 to enter the voids between the larger ceramic particles 2. (See [reference needed]). Figure 5 Compared to loose structures with a single particle size, see [link to relevant documentation]. Figure 4 The ceramic particles 2 of this type of ceramic coating have a tighter contact, smaller gaps between them, and more significant van der Waals forces, thus requiring less binder 3. Simultaneously, the reduced gaps between the ceramic particles 2 mean less liquid can be contained, and since binder 3 is typically found in aqueous solutions, this combination of ceramic particle sizes further reduces the amount of binder 3 required.

[0049] Preferably, the ceramic comprises first ceramic particles and second ceramic particles, wherein the particle size ratio of the first ceramic particles and the second ceramic particles is not less than 1.2; more preferably, the particle size ratio of the first ceramic particles and the second ceramic particles is not less than 3; further, the particle size ratio of the first ceramic particles and the second ceramic particles is 3-10; even further, the particle size ratio of the first ceramic particles and the second ceramic particles is 3-8; the particle size ratio of the first ceramic particles and the second ceramic particles includes, but is not limited to, 1.2, 1.5, 2, 3, 4, 5, 6, 7, and 8. The applicant has found that by adopting the above design, a better bonding effect can be achieved, and the amount of adhesive used can be further reduced.

[0050] In some embodiments, the adhesive 3 comprises a first adhesive and a second adhesive, which are capable of crosslinking. Specifically, the first adhesive may be selected from at least one of polyacrylic acid, polyurethane, and polyvinyl alcohol. The second adhesive is a small or large molecule that crosslinks with the first adhesive, such as 4-maleimide butyric acid.

[0051] In ordinary ceramic slurries, the adhesive 3 serves to provide contact points between ceramic particles, restricting their movement and thus preventing the ceramic slurry from detaching from the diaphragm. Using the above design, two adhesives 3 capable of cross-linking are employed. After the two adhesives 3 undergo a cross-linking reaction, the polymer structure changes from the original linear structure to a network structure. (See [link to relevant documentation]). Figure 5 The network structure of the adhesive 3 restricts the flowability of the polymer chains and also restricts the movement of the ceramic. Therefore, compared with existing adhesives 3, see [link to adhesive 3]. Figure 4 This adhesive 3 can achieve the purpose of fixing ceramics with a smaller amount added, effectively reducing the amount of adhesive 3 used. At the same time, the network structure greatly improves the heat resistance and solvent resistance of the adhesive, avoiding the problem of deterioration of bonding performance caused by melting of adhesive 3 under high temperature conditions.

[0052] By using ceramic particles 2 of different particle sizes in combination with a first adhesive and a second adhesive that can undergo a cross-linking reaction, and by placing the ceramic coating between the two base film layers 1, the amount of adhesive 3 can be further reduced. To achieve the electrode adhesion strength of ordinary adhesive-coated diaphragms (i.e., about 5-7 N / m), the applicant believes that the minimum content of adhesive 3 should be such that the mass ratio of adhesive 3 to ceramic is greater than 0.005.

[0053] During the invention process, the applicant discovered that when the ratio of the amount of adhesive 3 added to the amount of ceramic added is controlled to be 0.02-0.05, and the ratio of the particle size of the two ceramics is controlled to be 3-5, the peel strength of the diaphragm can be greatly increased while the increase in air permeability per unit thickness is relatively small.

[0054] In this embodiment, the components of the slurry for preparing the ceramic coating, by mass parts, include: water: 5.5 parts, dispersant (40% solid content): 0.02-0.1 parts, thickener (4% solid content): 0.8-1 parts, first ceramic particles: 0.9-1 parts, second ceramic particles: 1.7-2 parts, first binder (43% solid content): 0.02-0.15 parts, second binder: 0.0003-0.0023 parts, and wetting agent (0.3% solid content): 0.03-0.04 parts. The total mass of the first and second binders accounts for no more than 0.5% of the total mass of the slurry.

[0055] The dispersant can be selected from one or a mixture of several of polyethylene glycol (PEG), sodium polyacrylate (PAA-Na), potassium polyacrylate (PAA-K), sodium polyphosphate, sodium silicate, and sodium dodecyl sulfate; the thickener can be selected from sodium carboxymethyl cellulose (CMC), etc., with a solid content of 2-4%; the first ceramic particles and the second ceramic particles can be selected independently from one or a mixture of several of alumina, silica, boehmite, zirconium oxide, titanium dioxide, magnesium oxide, and barium sulfate; the first binder can be selected from one or a mixture of several of polyacrylic acid, polyurethane, polyvinyl alcohol, styrene-butadiene copolymer, etc.; the second binder can be selected from small molecules or macromolecules that can crosslink with the first binder, such as 4-maleimide butyric acid; the wetting agent can be selected from one or a mixture of several surfactants such as sodium dodecyl sulfate and sodium dodecylbenzene sulfonate.

[0056] During the use of lithium batteries, lithium dendrites can form, which can lead to electrical performance degradation and safety hazards. Therefore, in some embodiments, at least a portion of the components of the ceramic coating can react with lithium dendrites to prevent their penetration. Common materials for suppressing lithium dendrites include silicon dioxide, tin dioxide, manganese oxide, ferric oxide, and magnetite.

[0057] By adding a special functional material that can react with lithium dendrites to the ceramic coating, since the ceramic coating in this scheme is between two base film layers 1 and does not directly contact the electrode, the functional material will not react with lithium and lose its activity. With the above design, the lithium dendrites will only come into contact with the functional material and react after penetrating one base film. Therefore, placing the active material between the two base films can protect the functional material.

[0058] Alternatively, at least one ceramic particle 2 in the ceramic coating can react with lithium dendrites. For example, the ceramic particle 2 can be selected from silicon dioxide, which can effectively block the penetration of lithium dendrites.

[0059] Similarly, to achieve other effects, such as improving heat resistance, improving the mechanical properties of the diaphragm, and improving the interlayer adhesion of the diaphragm, other special functional materials can be added to the components of the ceramic coating. These functional materials include, but are not limited to, functional polymer materials for improving heat resistance, specifically selected from aramid fibers, carbon fibers, etc.; functional materials include, but are not limited to, glass fibers, inorganic nanowires, etc. for improving the mechanical properties of the diaphragm; and functional materials include, but are not limited to, polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), etc. for improving the interlayer adhesion of the diaphragm.

[0060] To ensure good air permeability of the entire diaphragm, the selection of the base membrane layer 1 is also a crucial aspect. In some embodiments, the air permeability value of the first base membrane layer 11 is 60s / 100ml-120s / 100ml. The air permeability values ​​of the first base membrane layer 11 include, but are not limited to, 60s / 100ml, 65s / 100ml, 70s / 100ml, 75s / 100ml, 80s / 100ml, 85s / 100ml, 90s / 100ml, 95s / 100ml, 100s / 100ml, 105s / 100ml, 110s / 100ml, 115s / 100ml, and 120s / 100ml; the second... The air permeability of the base film layer 12 is 60s / 100ml-120s / 100ml. The air permeability of the second base film layer 12 includes, but is not limited to, 60s / 100ml, 65s / 100ml, 70s / 100ml, 75s / 100ml, 80s / 100ml, 85s / 100ml, 90s / 100ml, 95s / 100ml, 100s / 100ml, 105s / 100ml, 110s / 100ml, 115s / 100ml and 120s / 100ml. The air permeability of the first base film layer 11 and the second base film layer 12 can be the same or different. Those skilled in the art can choose according to the actual situation.

[0061] In some embodiments, the materials of the first base film layer 11 and the second base film layer 12 can be selected from polymer porous films such as PE (polyethylene), PP (polypropylene), PI (polyimide), PET (polyethylene terephthalate), PBO (poly(p-phenylenebenzodioxazole)), para-aramid, and meta-aramid. The first base film layer 11 and the second base film layer 12 can be prepared by high-ratio biaxial stretching. The materials of the first base film layer 11 and the second base film layer 12 can be the same or different. The thickness of the first base film layer 11 and the second base film layer 12 is 4-9 μm, and the thickness of the first base film layer 11 and the second base film layer 12 includes, but is not limited to, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, and 9 μm. The thickness of the first base film layer 11 and the second base film layer 12 can be the same or different.

[0062] Specifically, the SV7-R02 base membrane produced by Shanghai Enjie can be selected. This membrane has an air permeability of approximately 90 s / 100ml and a thickness of approximately 6.5-7 μm. By selecting this base membrane and using a ceramic coating with low binder content, the total thickness of the membrane can be less than 17 μm, and the air permeability can be less than 250 s / 100ml.

[0063] In some embodiments, the diaphragm further includes a functional film layer, which is applied to the outside of the first base film layer 11 and / or the second base film layer 12. The functional film layer includes at least one of the base film layer 1, a ceramic coating, and an adhesive layer. The main material of the adhesive layer can be a slurry of functional materials coated to improve electrode adhesion, wettability, heat resistance, and resistance to lithium dendrite penetration. Specifically, the components of the adhesive layer can be selected from at least one of PVDF and its copolymers, PMMA and its copolymers, PAN and its copolymers, styrene-butadiene copolymers, aramid fibers, nanowires, graphene, and graphene oxide.

[0064] Please refer to Figure 6 This application also provides a method for preparing a diaphragm, the method comprising:

[0065] S1. Obtain a ceramic coating slurry, the slurry comprising binder 3 and ceramic, wherein the mass ratio of binder 3 to ceramic is less than 0.08;

[0066] Specifically, in this embodiment, the weighed water and dispersant are stirred at low speed for half an hour until they are evenly mixed. Then, the prepared thickener (approximately 4% by mass), ceramics, etc., are added to the container in sequence, accompanied by a stirring speed of 800 rpm for a total stirring time of approximately 2 hours; then, the mixture is ground 2-10 times using a ball mill. The weighed binder 3, wetting agent, etc., are added to the ground slurry in sequence, accompanied by a stirring speed of 800 rpm for a total stirring time of approximately 1.5 hours, to obtain the ceramic coating slurry.

[0067] S2. The ceramic coating slurry is applied between the first base film layer 11 and the second base film layer 12, and then dried to obtain a diaphragm.

[0068] Specifically, in this embodiment, the prepared slurry is coated onto one layer of the base film. Without drying, another layer of base film is quickly applied over the coated layer. The coating can be performed using methods such as roller coating, spray coating, dip coating, or wire rod coating to prepare a preliminary multilayer composite separator. The lamination process of the preliminary multilayer composite separator can be manual or prepared using a specialized multilayer laminating machine. The preliminary multilayer composite separator is then dried in a forced-air oven at 50-60°C for 1-5 minutes. After drying, the separator is obtained.

[0069] This application also provides a battery, which includes the separator provided above.

[0070] Those skilled in the art should know that the battery may also include necessary components such as positive electrode plates and negative electrode plates, which will not be elaborated here.

[0071] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0072] Example 1

[0073] A method for preparing a diaphragm, the method comprising:

[0074] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.03 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.0005 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 16μm, the increase in air permeability per unit thickness was 33s / 100ml / μm, and the peel strength reached 8.5N / m.

[0075] Example 2

[0076] A method for preparing a diaphragm, the method comprising:

[0077] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.06 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.001 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 15.4μm, the increase in air permeability per unit thickness was 34s / 100ml / μm, and the peel strength reached 8.5N / m.

[0078] Example 3

[0079] A method for preparing a diaphragm, the method comprising:

[0080] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.15 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.0025 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 15.4μm, the increase in air permeability per unit thickness was 36s / 100ml / μm, and the peel strength reached 8.5N / m.

[0081] Example 4

[0082] A method for preparing a diaphragm, the method comprising:

[0083] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 150nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.13 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.0022 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 15.8μm, the increase in air permeability per unit thickness was 38s / 100ml / μm, and the peel strength reached 8.4N / m.

[0084] Example 5

[0085] A method for preparing a diaphragm, the method comprising:

[0086] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 100nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.11 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.0018 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 16.4μm, the increase in air permeability per unit thickness was 40s / 100ml / μm, and the peel strength reached 8N / m.

[0087] Example 6

[0088] A method for preparing a diaphragm, the method comprising:

[0089] Weigh out the following by weight: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 2.7 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.03 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.0005 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. Use a small coating machine to evenly coat the slurry onto a 7μm thick SV7-R02 base film. Immediately after coating, cover the coated layer with another layer of SV7-R02 base film. The sample was dried in a 60℃ forced-air oven. The tested thickness was 16.1μm, the increase in air permeability per unit thickness was 30s / 100ml / μm, and the peel strength reached 7.5N / m.

[0090] Example 7

[0091] A method for preparing a diaphragm, the method comprising:

[0092] Weigh out the following by weight: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 1.8 parts; silica ceramic powder B (particle size 350nm): 0.9 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.03 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.0005 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 16μm, the increase in air permeability per unit thickness was 31s / 100ml / μm, and the peel strength reached 7.8N / m.

[0093] Example 8

[0094] A method for preparing a diaphragm, the method comprising:

[0095] Weigh out the following by weight: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add polyacrylic acid binder: 0.2 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. Use a small coating machine to evenly coat the slurry onto a 7μm thick SV7-R02 base film. Immediately after coating, cover the coated layer with another layer of SV7-R02 base film. Dry in a 60℃ forced-air oven. The tested thickness was 16.2 μm, the increase in air permeability per unit thickness was 42 s / 100 ml / μm, and the peel strength reached 8.3 N / m.

[0096] Comparative Example 1

[0097] A method for preparing a diaphragm, the method comprising:

[0098] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.27 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.0045 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 16.4μm, the increase in air permeability per unit thickness was 65s / 100ml / μm, and the peel strength reached 8.5N / m.

[0099] Comparative Example 2

[0100] A method for preparing a diaphragm, the method comprising:

[0101] Weigh out the following by weight: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.3 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.005 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 16.5μm, the increase in air permeability per unit thickness was 85s / 100ml / μm, and the peel strength reached 8.5N / m.

[0102] Comparative Example 3

[0103] A method for preparing a diaphragm, the method comprising:

[0104] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.6 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.003 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 15.8μm, the increase in air permeability per unit thickness was 156s / 100ml / μm, and the peel strength reached 8.5N / m.

[0105] Comparative Example 4

[0106] A method for preparing a diaphragm, the method comprising:

[0107] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 1.2 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.006 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. The slurry was uniformly coated onto a 7μm thick SV7-R02 base film using a small coating machine. Immediately after coating, another layer of SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. The tested thickness was 16.4μm, the increase in air permeability per unit thickness was 218s / 100ml / μm, and the peel strength reached 8.5N / m.

[0108] Comparative Example 5

[0109] A method for preparing a diaphragm, the method comprising:

[0110] By weight, weigh out: water: 5.5 parts; T-61 type dispersant (provided by Dong-A Synthetic Co., Ltd., solid content 40%): 0.03 parts; sodium carboxymethyl cellulose (solid content 4%): 0.91 parts; alumina ceramic powder A (particle size 700nm): 0.9 parts; silica ceramic powder B (particle size 200nm): 1.8 parts. Stir at 800 rpm for two hours. Grind twice using a ball mill. Add binder B16A (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.015 parts; binder B16B (provided by Zhuhai Chenyu New Material Technology Co., Ltd.): 0.00025 parts; German Tigo KL245 wetting agent (0.3% solid content): 0.04 parts. Stir at 800 rpm for 1.5 hours. A small coating machine was used to evenly coat the slurry onto a 7μm thick SV7-R02 base film. Immediately after coating, another SV7-R02 base film was applied over the coated layer. The film was then dried in a 60℃ forced-air oven. Due to the low peel strength of the membrane, the two membrane layers separated, and the experiment failed.

[0111] The main parameter control and diaphragm performance test results of Examples 1-8 and Comparative Examples 1-5 are shown in the table below:

[0112]

[0113]

[0114] It should be noted that the formula for calculating the increase in air permeability per unit thickness is: increase in air permeability per unit thickness = (air permeability value - total air permeability value of base film layer) / coating thickness, wherein the air permeability value of the single-layer base film used in each embodiment and comparative example is 93s / 100ml.

[0115] A comparison of the comparative examples and Example 1 shows that when the ratio of adhesive addition to ceramic addition is approximately 0.011, the increase in air permeability per unit thickness is 33s / 100ml / μm, indicating excellent air permeability and thus superior electrochemical performance. Simultaneously, its peel strength is 8.1 N / m, higher than the electrode adhesion strength of ordinary adhesive-coated diaphragms (approximately 5-7 N / m), indicating that the two diaphragm layers can be well bonded together.

[0116] The comparison of Examples 1-3 shows that when the amount of adhesive added is increased to 2 and 5 times that of Example 1, the increase in air permeability per unit thickness increases to 34s / 100ml / μm and 36s / 100ml / μm, respectively. While the air permeability value increases to some extent, it remains well controlled, indicating good electrochemical stability. Due to the increased amount of adhesive, the peel strength also increases to 8.8 N / m and 9.8 N / m. When the amount of adhesive added in the examples is significantly reduced, the air permeability is improved. Example 4 shows that when the particle size ratio of the two ceramics is further increased, the increase in air permeability increases, but a good peel strength (i.e., a proportional strength greater than 8 N / m) can still be achieved with a smaller amount of adhesive (the adhesive-to-ceramic ratio is smaller, approximately 0.048). This indicates that the combination of the two ceramic particle sizes results in a denser coating, requiring a smaller proportion of adhesive to achieve similar peel strength. Example 5 further reduced the particle size of the small ceramic particles (i.e., ceramic powder B). It was found that when the particle size of the small ceramic particles was reduced to 100 nm, the amount of binder required to achieve a good peel strength (i.e., a specific strength greater than 8 N / m) was further reduced (the binder-to-ceramic ratio was even smaller, approximately 0.041). Examples 6 and 7 show that when all the added ceramic particles were 700 nm in diameter, or when the particle size of both types of ceramics was less than 3 nm, the peel strength was lower than that in Example 1, indicating that the amount of binder needed to be increased to achieve a similar peel strength. Example 8 shows that when the added binder was a polyacrylic acid binder with the same solid content (without a cross-linked structure), the amount of binder needed to be increased, i.e., the binder-to-ceramic ratio needed to be adjusted to 0.074, to achieve a similar peel value, i.e., 8.3 N / m.

[0117] A comparison of Comparative Examples 1-4 and Example 1 shows that when the amount of adhesive added is increased to 9-40 times that used in Example 1, although the peel strength between the two membrane layers is significantly improved to 9.8-21.5 N / m, the increase in air permeability per unit thickness increases from 65 s / 100 ml / μm to 218 s / 100 ml / μm, with a particularly significant increase of over 300 s / 100 ml. This indicates that when a large amount of adhesive 3 is added, the electrochemical performance decreases sharply.

[0118] 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 diaphragm, characterized in that, The diaphragm includes a base membrane layer and a ceramic coating; the base membrane layer includes a first base membrane layer and a second base membrane layer; the ceramic coating is disposed between the first base membrane layer and the second base membrane layer, and the ceramic coating comprises an adhesive and ceramic, the mass ratio of the adhesive to the ceramic is 0.02-0.05, the ceramic comprises first ceramic particles and second ceramic particles, and the particle size ratio of the first ceramic particles to the second ceramic particles is 3-5.

2. The diaphragm according to claim 1, characterized in that, At least a portion of the components of the ceramic coating are capable of reacting with lithium dendrites to prevent lithium dendrite penetration.

3. The diaphragm according to claim 1, characterized in that, The adhesive is prepared by crosslinking a first adhesive and a second adhesive; and / or The first adhesive comprises at least one of polyacrylic acid, polyurethane, polyvinyl alcohol, styrene, and butadiene copolymer; and / or The second adhesive comprises 4-maleimide butyric acid.

4. The diaphragm according to claim 1, characterized in that, The air permeability of the first base film layer is 60s / 100ml-120s / 100ml; and / or The air permeability of the second base film layer is 60s / 100ml-120s / 100ml.

5. The diaphragm according to claim 1, characterized in that, The ceramic coating also includes functional additives, which include functional materials that improve heat resistance, functional materials that improve mechanical properties, and functional materials that improve adhesion. and / or The functional materials for improving heat resistance include at least one of aramid fibers and carbon fibers; and / or The functional materials for improving mechanical properties include at least one of glass fibers and inorganic nanowires; and / or The functional material that enhances adhesive properties includes at least one of polyvinylidene fluoride and polymethyl methacrylate.

6. The diaphragm according to claim 1, characterized in that, The diaphragm also includes a functional membrane layer, which is applied to the outside of the first base membrane layer and / or the second base membrane layer. The functional film layer includes at least one of a base film layer, a ceramic coating layer, and an adhesive layer; The coating layer comprises at least one of PVDF and its copolymers, PMMA and its copolymers, PAN and its copolymers, styrene-butadiene copolymers, aramid, nanowires, graphene, and graphene oxide.

7. A method for preparing a diaphragm, characterized in that, The method includes: A slurry for obtaining a ceramic coating is provided, the slurry comprising a binder and ceramics, wherein the mass ratio of the binder to the ceramics is 0.02-0.05, and the ceramics comprise first ceramic particles and second ceramic particles, wherein the particle size ratio of the first ceramic particles to the second ceramic particles is 3-5. The ceramic coating slurry is applied between the first base film layer and the second base film layer, and then dried to obtain a diaphragm.

8. A battery, characterized in that, The battery includes a separator as described in any one of claims 1 to 6 or a separator prepared by the method described in claim 7.

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