Coating diaphragm, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, and provides a coating diaphragm and a preparation method thereof and a battery, the coating diaphragm comprises a base membrane and a coating arranged on at least one surface of the base membrane, and the coating comprises the following raw materials in parts by weight: 1-1.5 parts of hydroxylated epoxy resin, 2.8-3.3 parts of an emulsion type binder and 15-20 parts of a filler. According to the technical scheme, the problem that a coating diaphragm in the related technology is difficult to meet the comprehensive performance requirements of a high-safety battery on heat resistance, high peel strength and low moisture content of the diaphragm at the same time is solved.

Description

Technical Field

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

[0002] With the development of the new energy industry, batteries have been widely used in electric vehicles, energy storage systems, and other fields. The market has placed higher demands on the energy density, cycle life, and safety of batteries. As a key internal component of the battery, the performance of the separator directly affects the overall performance and safety of the battery.

[0003] To improve the heat resistance of separators, the industry commonly employs a technique of coating the surface of polyolefin-based membranes with heat-resistant coatings. These coatings primarily consist of heat-resistant inorganic particles (such as alumina and boehmite), which can maintain the structural integrity of the separator at high temperatures and delay thermal shrinkage. However, while conventional heat-resistant coatings improve heat resistance, they often fail to address other performance aspects: on the one hand, the peel strength between the coating and the base membrane is relatively low, making it prone to detachment during battery assembly or long-term cycling, potentially leading to internal short circuits; on the other hand, moisture is easily introduced during coating preparation, resulting in high water content in the separator, which disrupts the stability of the electrolyte-electrode interface and accelerates battery performance degradation.

[0004] Therefore, although existing heat-resistant coating technologies have improved the thermal stability of the separator to some extent, they often come at the cost of sacrificing peel strength and increasing the moisture content of the separator, making it difficult to simultaneously meet the comprehensive performance requirements of high-safety batteries for separator heat resistance, high peel strength and low moisture content. Summary of the Invention

[0005] This invention proposes a coated separator, a method for preparing the same, and a battery, thereby solving or at least alleviating one or more of the aforementioned and other problems existing in the prior art.

[0006] The technical solution of the present invention is as follows: The present invention proposes a coated membrane, comprising a base membrane and a coating disposed on at least one surface of the base membrane, wherein the coating comprises the following raw materials in parts by weight: 1-1.5 parts of hydroxylated epoxy resin, 2.8-3.3 parts of emulsion binder, and 15-20 parts of filler.

[0007] As a further technical solution, the hydroxyl content of the hydroxylated epoxy resin is 1.2~1.5 mmol / g.

[0008] As a further technical solution, the coating also includes the following raw materials in parts by weight: 0.3 to 0.6 parts of dispersant and 0.015 to 0.03 parts of wetting agent.

[0009] As a further technical solution, the emulsion-type adhesive includes one or more of acrylate emulsions, polyurethane emulsions, and fluoropolymer emulsions; and / or The filler includes one or more of alumina, boehmite, aluminum nitride, aluminum hydroxide, and solid electrolyte.

[0010] As a further technical solution, the hydroxylated epoxy resin is a hydroxylated epoxy resin grafted with siloxane groups.

[0011] As a further technical solution, the raw materials of the hydroxylated epoxy resin grafted with siloxane groups include the following components in parts by weight: 100-105 parts of hydroxylated epoxy resin and 20-30 parts of silane coupling agent.

[0012] The present invention also proposes a method for preparing a coated diaphragm, comprising the following steps: S1. Provide the raw materials required for the coating; S2. Mix and grind the raw materials to obtain a coating slurry; S3. The coating slurry is coated on at least one surface of the base film and dried to obtain the crosslinked coated diaphragm. S4. The coated membrane to be crosslinked is immersed in a solution containing an initiator and crosslinked to obtain the coated membrane.

[0013] As a further technical solution, step S1 includes the preparation of hydroxylated epoxy resin, specifically by dissolving epoxy resin in ethanol, adding boron trifluoride diethyl ether complex, performing a ring-opening reaction, and distilling under reduced pressure to obtain the hydroxylated epoxy resin.

[0014] As a further technical solution, step S1 also includes grafting the hydroxylated epoxy resin with siloxane groups. The specific method is as follows: the hydroxylated epoxy resin is mixed with toluene, hydroquinone, silane coupling agent and dibutyltin dilaurate, and refluxed to obtain the hydroxylated epoxy resin grafted with siloxane groups.

[0015] The present invention also proposes a battery comprising the coated separator described herein or a coated separator prepared by the preparation method described herein.

[0016] The beneficial effects of this invention are as follows: Compared to other epoxy resins, the hydroxylated epoxy resin in this invention can synergistically enhance the emulsion binder and filler in the coating raw materials, improving the peel strength of the coating membrane while ensuring its heat resistance and reducing its moisture content. Specifically: (1) Hydroxylated epoxy resin has good rheological properties. In the coating slurry, it can promote the uniform dispersion of fillers and emulsion binders, avoid phase separation caused by raw material agglomeration, ensure that the coating forms a uniform coverage on the base film surface, improve the consistency of the coating, avoid stress concentration, and thus improve the peel strength of the coating membrane.

[0017] (2) The hydroxyl groups of hydroxylated epoxy resin can interact with the active groups of emulsion adhesives to enhance the density of the coating, reduce porosity, and reduce water molecule adsorption and permeation channels. On the other hand, they can interact with the hydrophilic sites on the filler surface to effectively passivate the hydrophilicity of the filler surface, reduce the filler's ability to adsorb water, and thus reduce the moisture content of the coating membrane. Attached Figure Description

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0019] Figure 1 The image shows a SEM image of the coating membrane prepared in Example 1. Detailed Implementation

[0020] 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.

[0021] It should be understood that, unless the context clearly indicates otherwise, the terms "comprising," "including," or "having" as used herein refer to the presence of a particular element, but do not exclude the presence or addition of one or more other elements. Furthermore, as used herein, "comprising" and / or "including" specify the presence of shapes, numbers, steps, operations, members, elements, and / or combinations thereof, and do not exclude the presence or addition of one or more other shapes, numbers, operations, elements, and / or combinations thereof.

[0022] In this invention, the numerical range indicated by "~" refers to the range of values ​​specified as the lower and upper limits, respectively, before or after the term. When multiple values ​​for the upper or lower limit of any numerical range are mentioned, the range disclosed herein can be understood as a range with any one of the mentioned upper limits as its upper limit and any one of the mentioned lower limits as its lower limit.

[0023] The following will describe in detail a coated separator, its preparation method, and a battery according to embodiments of the present invention.

[0024] According to one aspect of the present invention, a coated diaphragm is provided, comprising a base film and a coating disposed on at least one surface of the base film, the coating comprising the following raw materials in parts by weight: 1-1.5 parts of hydroxylated epoxy resin, 2.8-3.3 parts of emulsion binder, and 15-20 parts of filler.

[0025] In this invention, the base film serves to provide good support for the coating. Preferably, it is a polyolefin film with good chemical stability and mechanical properties, such as, but not limited to, polyethylene film and polypropylene film. Regarding the coating, through the synergistic effect of the hydroxylated epoxy resin, emulsion-type binder, and filler, the heat resistance of the coated membrane is ensured, while also improving the peel strength and reducing the moisture content of the coated membrane. According to GB / T 36363-2018 "Polyolefin Separators for Lithium-ion Batteries", GB / T 6283-2008 "Determination of Moisture Content in Chemical Products - Karl Fischer Method (General Method)", and GB / T2792-2014 "Test Method for Peel Strength of Adhesive Tapes", Method 1, the coated separator of this invention exhibits a longitudinal shrinkage rate of 0.7% and a transverse shrinkage rate of 0.5% at 130℃ for 1 hour; a longitudinal shrinkage rate of 1.9% and a transverse shrinkage rate of 1.8% at 150℃ for 1 hour; a peel strength of 180~240 N / m; and a water content of 510~655 ppm.

[0026] In this invention, the hydroxylated epoxy resin can be obtained by opening the epoxy groups of an epoxy resin. The hydroxylated epoxy resin can be one or more of hydroxylated alicyclic epoxy resin, hydroxylated aliphatic epoxy resin, and hydroxylated aromatic epoxy resin, preferably hydroxylated alicyclic epoxy resin. The hydroxylated epoxy resin can promote the uniform dispersion of the emulsion binder and filler, forming a dense and uniform coating. It can also passivate the filler surface, reducing the coating's water absorption capacity. If the amount of hydroxylated epoxy resin is too small, the performance improvement will be insignificant; if the amount is too large, excessive cross-linking may occur, which will reduce the mechanical properties of the coating membrane. Therefore, the amount of hydroxylated epoxy resin can be 1 to 1.5 parts, for example, including but not limited to any point value and any range between any two points from 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, and 1.5 parts. The hydroxyl content of the hydroxylated epoxy resin can be measured according to ISO 7142:2007, expressed in mmol / g. Preferably, the hydroxyl content of the hydroxylated epoxy resin can be 1.2~1.5 mmol / g, for example, including but not limited to any point value among 1.2 mmol / g, 1.3 mmol / g, 1.4 mmol / g, and 1.5 mmol / g, and any range between any two point values. The inventors have discovered that when the hydroxyl content of the hydroxylated epoxy resin is within the above range, sufficient synergy can be ensured between the hydroxylated epoxy resin and the emulsion-type binder and filler. This avoids uneven raw material dispersion due to insufficient hydroxyl content, and also prevents excessive hydroxyl content from causing the coating to become brittle and excessively absorb water, thereby further improving the peel strength of the coating membrane and further reducing the moisture content of the coating membrane.

[0027] In this invention, the emulsion-type binder can be one or more of acrylate emulsions, polyurethane emulsions, fluoropolymer emulsions, and styrene-butadiene emulsions, preferably acrylate emulsions. The emulsion-type binder provides good film-forming properties, forming a continuous film layer on the base film surface and enhancing the adhesion between the coating and the base film. If the amount of emulsion-type binder is too small, a complete and effective film layer cannot be formed, resulting in insufficient protective ability of the coating; if the amount of emulsion-type binder is too large, the coating may become too soft, reducing the mechanical properties and heat resistance of the coating. Therefore, the amount of emulsion-type binder can be 2.8 to 3.3 parts, for example, including but not limited to any point value and any range between any two points from 2.8 parts, 2.9 parts, 3.0 parts, 3.1 parts, 3.2 parts, and 3.3 parts.

[0028] In this invention, the filler can be selected according to the required performance. For example, it can be a basic filler for structural reinforcement and heat resistance, including but not limited to alumina, boehmite, aluminum nitride, aluminum hydroxide, etc.; or it can be a special filler for enhancing ion conduction, including but not limited to solid electrolytes, more specifically NASICON-type solid electrolytes, garnet-type solid electrolytes, or combinations of the above two solid electrolytes, preferably lithium aluminum titanium phosphate. If the filler content is too low, the performance improvement of the coating will not be significant; if the filler content is too high, it will affect the uniformity of the coating and reduce the overall performance of the coated membrane. Therefore, the filler content can be 15 to 20 parts, for example, including but not limited to any point value and any range between any two points of 15 parts, 16 parts, 17 parts, 18 parts, and 20 parts.

[0029] In one embodiment of the present invention, the coating further includes the following raw materials in parts by weight: 0.3 to 0.6 parts of dispersant and 0.015 to 0.03 parts of wetting agent.

[0030] In this invention, the dispersant can be selected from fatty acid-based, polyvinyl alcohol-based, cellulose-based, etc., preferably cellulose-based, and more preferably one or more of sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, and calcium carboxymethyl cellulose. The dispersant can reduce the surface tension between raw materials, prevent agglomeration, and make the synergistic effect of the raw materials more efficient. If the amount of dispersant is too small, it cannot effectively reduce the surface tension between the raw materials, and the performance improvement of the coating membrane is not significant; if the amount of dispersant is too large, it will not only fail to improve the dispersion effect, but will also act as a harmful impurity, disrupting the charge balance of the slurry, causing flocculation, and leading to problems such as sedimentation and uneven coating. Therefore, the amount of dispersant can be 0.3~0.6 parts, for example, including but not limited to any point value and any range between any two points of 0.3 parts, 0.4 parts, 0.5 parts, and 0.6 parts.

[0031] In this invention, the wetting agent can be selected from silicone, polyether, or polyacrylate, preferably polyacrylate. The wetting agent effectively wets the surface of the base film, enhancing the adhesion between the coating and the base film and improving battery safety. If the amount of wetting agent is too small, the wetting effect of the coating on the base film will be poor, affecting the overall performance of the coated separator; if the amount of wetting agent is too large, it may lead to excessive local surface tension gradients, resulting in surface defects such as pinholes. Therefore, the amount of wetting agent is 0.015~0.03 parts, for example, including but not limited to any value among 0.015 parts, 0.02 parts, 0.025 parts, and 0.03 parts, and the range between any two values.

[0032] In one embodiment of the present invention, the hydroxylated epoxy resin is a hydroxylated epoxy resin grafted with siloxane groups.

[0033] In this invention, by grafting siloxane groups onto hydroxylated epoxy resin, on the one hand, the non-polar properties of the siloxane groups can be used to improve the wettability between the coating and the base film, enhance the adhesion of the coating, and further improve the peel strength of the coating membrane; on the other hand, the density of the internal grid structure of the coating can be improved, and the hydrophobic properties of the siloxane segments themselves can be used to inhibit the adsorption of water molecules in the coating, further reducing the moisture content of the coating membrane.

[0034] Siloxane groups are commonly used to modify fillers to improve the interfacial bonding between the filler and the organic matrix. Even with this invention's modification of fillers using siloxane groups, it is difficult to significantly improve the peel strength of the coated membrane or reduce its moisture content. This is because the purpose of siloxane group-modified fillers is essentially to promote the interfacial bonding between organic and inorganic components. However, the fillers added to the membrane coating are micron- or nano-sized, and even after surface modification, they are still prone to agglomeration due to van der Waals forces. This leads to increased viscosity and poorer rheological properties of the coating slurry, making it difficult for the coating to form a uniform coverage on the base membrane surface. Furthermore, filler agglomeration may cause stress concentration, making the coating unable to withstand significant external forces. Therefore, the effect of siloxane group-modified fillers on improving the peel strength of the coated membrane is limited. In addition, siloxane group-modified fillers do not significantly improve the density of the internal network structure of the coating and cannot significantly inhibit the adsorption of water molecules in the coating, thus failing to significantly reduce the moisture content of the coated membrane.

[0035] The present invention grafts siloxane groups onto hydroxylated epoxy resin, thereby forming stable Si-OC chemical bonds between the siloxane groups and the hydroxylated epoxy resin. This avoids any agglomeration problems and can also increase the density of the internal network structure of the coating by increasing the chain length. Therefore, it can further improve the peel strength of the coating membrane and reduce the moisture content of the coating membrane.

[0036] In one embodiment of the present invention, the raw material of the hydroxylated epoxy resin grafted with siloxane groups includes the following components in parts by weight: 100-105 parts of hydroxylated epoxy resin and 20-30 parts of silane coupling agent.

[0037] In this invention, by optimizing the dosage of hydroxylated epoxy resin and silane coupling agent, the peel strength of the coated membrane can be further improved and the moisture content of the coated membrane can be reduced. Within this range, on the one hand, insufficient dosage of silane coupling agent prevents the full utilization of the grafting modification advantages; on the other hand, excessive dosage of silane coupling agent avoids excessive viscosity of the coating slurry and increased brittleness of the coating structure, thus affecting the overall performance of the coated membrane. The silane coupling agent can be any silane coupling agent, for example, including but not limited to KH-550, KH-560, and KH-570, preferably KH-570.

[0038] According to another aspect of the present invention, the present invention also provides a method for preparing the above-mentioned coated diaphragm, comprising the following steps: S1. Provide the raw materials required for coating.

[0039] Hydroxylated epoxy resins can be obtained by ring-opening epoxy resins, and hydroxylated epoxy resins with different hydroxyl contents can be prepared by controlling the ring-opening rate of the epoxy resin. A specific preparation method for hydroxylated epoxy resins is as follows: 100-105 parts by weight of epoxy resin and 50-55 parts by weight of ethanol are added to a three-necked flask. The mixture is heated to 60-65°C under a nitrogen atmosphere and stirred at 150-200 rpm for 30-60 minutes to dissolve. Then, a mixture of 0.5-0.8 parts by weight of boron trifluoride diethyl ether complex and 3.5-6.5 parts by weight of water is added dropwise over 30-35 minutes. The mixture is then kept at 60-65°C for 3.5-7.5 hours, following the steps outlined in GB / T [likely a reference standard]. According to GB / T 1677-2023 "Determination of Epoxy Value of Plasticizers", the epoxy value is tested, and the ring-opening rate is calculated based on the formula: (Initial epoxy value of epoxy resin - Residual epoxy value of product) / Initial epoxy value of epoxy resin × 100%, until the ring-opening rate is ≥72%. The resin is then subjected to vacuum distillation at 80~85℃ and -0.05~-0.09MPa to remove the solvent and byproducts, yielding hydroxylated epoxy resin. The remaining raw materials are commercially available.

[0040] S2. Mix and grind the raw materials to obtain the coating slurry.

[0041] By weight, in a planetary mixer, add 20-25 parts water and 0.15-0.03 parts dispersant, and stir at 1500-3600 rpm for 30-60 minutes until evenly dispersed. Then add 15-20 parts filler, and stir at 1500-3600 rpm for 60-120 minutes. Finally, add 1-1.5 parts hydroxylated epoxy resin, and stir at 1000-2000 rpm and an ultrasonic frequency of 5-8 kHz. Mix the mixture with sonication for 15-30 minutes, then stir at a stirring speed of 3300-3500 rpm for 10-15 minutes. Finally, add 2.8-3.3 parts of emulsion-type binder and 0.015-0.03 parts of wetting agent, and ultrasonically mix at a stirring speed of 1000-2000 rpm and an ultrasonic frequency of 5-8 kHz for 15-30 minutes. Then, grind the mixture in a grinder at a grinding speed of 1500-2000 rpm for 10-30 minutes to obtain the coating slurry.

[0042] S3. Apply the coating slurry to at least one surface of the base film and dry it to obtain the coated diaphragm to be crosslinked.

[0043] The coating slurry is applied to at least one surface of the base film by roller coating, with the thickness of the coating on each side being 1~5μm. After drying, the coated diaphragm to be crosslinked is obtained.

[0044] S4. Immerse the coated membrane to be crosslinked in a solution containing an initiator to obtain the crosslinked membrane. Crosslinking can be performed using thermal crosslinking or ultraviolet (UV) crosslinking, with UV crosslinking being preferred. The specific method for UV crosslinking is as follows: Add 5-10 parts by weight of butyl acetate to a reaction vessel. Under a light-protected, room-temperature environment, add 0.1-2 parts of photoinitiator and stir until homogeneous. Then add 0.05-1 parts of co-initiator and stir until the solution is free of precipitate, homogeneous, and transparent, obtaining a solution containing the initiator. Under a light-protected, room-temperature environment, add the above solution containing the initiator to an extraction tank. Dip the above-mentioned crosslinked membrane into the solution. After dipping, place it in a vacuum drying oven and dry at 50-80°C for 3-5 minutes with a power of 80-120 mW / cm². 2 A UV-LED lamp with a wavelength of 365~395nm is used to irradiate the membrane for 10~30s at a transmission speed of 1~5m / min, and then it is dried at 50~70℃ for 10~20min to obtain the coated membrane.

[0045] The photoinitiator may be at least one of thioxanthones, benzophenones, acetophenone derivatives, thioxanthones, and anthraquinones. Preferably, it is at least one of thioxanthones, benzophenones, and acetophenone derivatives. For example, thioxanthones include ITX (2-isopropylthioxanthone), ITX derivatives, and DETX (diethylthioxanthone); benzophenones include benzophenone, 4-methylbenzophenone, and 4-chlorobenzophenone; acetophenone derivatives include michalcone and 4,4'-bis(dimethylamino)benzophenone; more preferably, it is ITX.

[0046] The co-initiator can be selected from at least one of amine co-initiators, thiol co-initiators, phosphine co-initiators, cyclic acetals, alcohols, and thioethers. Among them, amine co-initiators include triethylamine, triethanolamine, methyldiethanolamine, EDAB (ethyl 4-dimethylaminobenzoate), DMEA (dimethylethanolamine), and amine-containing acrylate oligomers; thiol co-initiators include benzyl mercaptan, trimethylolpropane trimercaptopropionate (TMPMP), and pentaerythritol tetramercaptoacetate; phosphine co-initiators include triphenylphosphine and diphenylphosphine oxide derivatives; cyclic acetals include 1,3-dioxolane derivatives; alcohols include isopropanol and ethylene glycol; and thioethers include dibutyl sulfide; preferably, EDAB.

[0047] In one embodiment of the present invention, step S1 further includes grafting hydroxylated epoxy resin with siloxane groups.

[0048] The specific method for grafting hydroxylated epoxy resin with siloxane groups is as follows: Add 100 parts by weight of hydroxylated epoxy resin and 40-45 parts by weight of toluene to a reaction vessel and stir at 150-200 rpm for 5-10 min. Then add 0.1-0.2 parts by weight of hydroquinone and stir at 150-200 rpm for 5-10 min. Add 20-30 parts by weight of silane coupling agent and stir at 150-200 rpm for 5-10 min. Then add 0.3-0.5 parts by weight of dibutyltin dilaurate and stir at 150-200 rpm for 5-10 min. Heat to 70-75℃ and reflux for 4-6 h. Stir at 200-300 rpm until the reflux reaction is complete to obtain the hydroxylated epoxy resin grafted with siloxane groups. The hydroxylated epoxy resin grafted with siloxane groups can be detected by Fourier transform infrared spectroscopy. When the wavelength is 1080 cm⁻¹... -1 When a characteristic peak appears, it can be confirmed that a Si-OC bond has been formed, thus obtaining a hydroxylated epoxy resin grafted with siloxane groups.

[0049] According to another aspect of the present invention, the present invention also provides a battery comprising the above-described coated separator or the coated separator prepared by the above-described preparation method.

[0050] The coated separator in this invention can be used as a separator between the positive and negative electrodes of a battery to prevent short circuits caused by contact between the positive and negative electrodes. During the charging and discharging process of the battery, the coated separator allows active lithium ions to pass through. The active lithium ions migrate back and forth between the positive and negative electrodes through the separator to perform insertion and extraction within the electrodes, thus realizing the charging and discharging process of the battery. A battery is any device in which an electrochemical reaction can occur, including, for example, all types of primary batteries, secondary batteries, solar cells, etc. Specifically, lithium secondary batteries are preferred among secondary batteries, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries, etc.

[0051] The present invention will now be described in detail with reference to examples. The embodiments of the invention described below can be modified in various ways, and therefore the scope of the invention should not be construed as limited to the embodiments described in detail below. Examples are provided to help those skilled in the art to more readily understand the invention.

[0052] In the following examples and comparative examples, the epoxy resin was specifically bis(7-oxabicyclo[4.1.0]heptane-3-methyl) adipate; the acrylate emulsion was grade 8501, purchased from Guangdong Rongdong New Materials Co., Ltd.; the lithium titanium aluminum phosphate was grade LP8002AP, purchased from Zhejiang Aike New Materials Co., Ltd.; the sodium carboxymethyl cellulose was grade BH20, purchased from Shenzhen Dasai Technology Co., Ltd.; and the anionic polyacrylate was grade BYK-ET 3030.

[0053] Example 1 A method for preparing a coated diaphragm includes the following steps: S1. Prepare the following raw materials in parts by weight: 1 part hydroxylated epoxy resin, 2.8 parts acrylate emulsion, 15 parts lithium titanium aluminum phosphate, 0.3 parts sodium carboxymethyl cellulose, and 0.015 parts anionic polyacrylate. The preparation method of hydroxylated epoxy resin is as follows: 100 parts by weight of epoxy resin and 50 parts by weight of ethanol are added to a three-necked flask, heated to 60°C under a nitrogen atmosphere, and stirred at 150 rpm for 60 min to dissolve; then, a mixture of 0.5 parts by weight of boron trifluoride diethyl ether complex and 3.5 parts by weight of water is added dropwise over 30 min, and the reaction is maintained at 60°C for 4 h to ensure a ring-opening rate ≥72%; the hydroxylated epoxy resin is obtained by vacuum distillation at 80°C and -0.05 MPa, and the hydroxyl content is found to be 1 mmol / g. S2. In a planetary mixing apparatus, add 20 parts of water and sodium carboxymethyl cellulose and stir at 1500 rpm for 60 minutes to disperse evenly. Then add lithium titanium aluminum phosphate and stir at 1500 rpm for 120 minutes. Then add hydroxylated epoxy resin and mix ultrasonically at 1000 rpm and 5 kHz for 30 minutes. Then stir at 3300 rpm for 15 minutes. Finally, add acrylate emulsion and anionic polyacrylate and mix ultrasonically at 1000 rpm and 5 kHz for 30 minutes. Finally, grind in a grinder at 1500 rpm for 30 minutes to obtain the coating slurry. S3. The coating slurry is coated onto one surface of a 7μm thick polyethylene film by roller coating. The coating thickness is 1μm. After drying, the coated membrane to be crosslinked is obtained. S4. By weight, add 5 parts of butyl acetate to the reaction vessel, add 0.1 parts of 2-isopropylthioxanthone under a dark and room temperature environment and stir until homogeneous, then add 0.05 parts of ethyl 4-dimethylaminobenzoate and stir until the solution reaches a state of no precipitation, uniformity, and clarity, thus obtaining a solution containing the initiator. Under a dark and room temperature environment, add the above solution containing the initiator to the extraction tank, dip-coat the above-mentioned crosslinked diaphragm, and after dip-coating, place it in a vacuum drying oven and dry at 50°C for 5 minutes with a power of 80mW / cm 2 A UV-LED lamp with a wavelength of 365nm was used to irradiate the membrane for 30 seconds at a transmission speed of 1m / min, followed by drying at 50℃ for 20 minutes to obtain a coated diaphragm. The SEM image of the coated diaphragm is shown below. Figure 1 As shown in the figure, the prepared coating is dense and has no obvious surface defects.

[0054] Example 2 A method for preparing a coated diaphragm includes the following steps: S1. Prepare the following raw materials in parts by weight: 1.5 parts hydroxylated epoxy resin, 3.3 parts acrylate emulsion, 20 parts lithium titanium aluminum phosphate, 0.6 parts sodium carboxymethyl cellulose, and 0.03 parts anionic polyacrylate. The preparation method of hydroxylated epoxy resin is as follows: 100 parts by weight of epoxy resin and 50 parts by weight of ethanol are added to a three-necked flask, heated to 60°C under a nitrogen atmosphere, and stirred at 150 rpm for 60 min to dissolve; then, a mixture of 0.5 parts by weight of boron trifluoride diethyl ether complex and 3.5 parts by weight of water is added dropwise over 30 min, and the reaction is maintained at 60°C for 4 h to ensure a ring-opening rate ≥72%; the hydroxylated epoxy resin is obtained by vacuum distillation at 80°C and -0.05 MPa, and the hydroxyl content is found to be 1 mmol / g. S2. In a planetary mixing apparatus, add 25 parts of water and sodium carboxymethyl cellulose and stir at 3600 rpm for 30 minutes to disperse evenly. Then add lithium titanium aluminum phosphate and stir at 3600 rpm for 60 minutes. Then add hydroxylated epoxy resin and mix ultrasonically at 2000 rpm and 8 kHz for 15 minutes. Then stir at 3500 rpm for 10 minutes. Finally, add acrylate emulsion and anionic polyacrylate and mix ultrasonically at 2000 rpm and 8 kHz for 15 minutes. Finally, grind in a grinder at 200 rpm for 10 minutes to obtain the coating slurry. S3. The coating slurry is coated onto one surface of a 7μm thick polyethylene film by roller coating. The coating thickness is 5μm. After drying, the coated diaphragm to be crosslinked is obtained. S4. By weight, add 10 parts of butyl acetate to the reaction vessel, add 2 parts of 2-isopropylthioxanthone under a dark, room-temperature environment and stir until homogeneous, then add 1 part of ethyl 4-dimethylaminobenzoate and stir until the solution is free of precipitate, homogeneous and transparent, to obtain a solution containing the initiator. Under a dark, room-temperature environment, add the above solution containing the initiator to the extraction tank, dip-coat the above-mentioned crosslinked membrane, and then place it in a vacuum drying oven at 80°C for 3 minutes, with a power of 120mW / cm 2 A UV-LED lamp with a wavelength of 395nm was used to irradiate the membrane for 10 seconds at a transmission speed of 5m / min, and then the membrane was dried at 70℃ for 10 minutes to obtain the coated membrane.

[0055] Example 3 The only difference between this embodiment and Embodiment 2 is that, in this embodiment, the hydroxyl content of the hydroxylated epoxy resin is 2 mmol / g; The preparation method of hydroxylated epoxy resin in this embodiment is as follows: 105 parts by weight of epoxy resin and 55 parts by weight of ethanol are added to a three-necked flask, heated to 65°C under a nitrogen atmosphere, and stirred at 200 rpm for 30 min to dissolve; then, a mixture of 0.8 parts by weight of boron trifluoride diethyl ether complex and 6.5 parts by weight of water is added dropwise, and the addition is completed in 35 min. The reaction is maintained at 65°C for 7.5 h to ensure that the ring-opening rate is ≥99%; the hydroxylated epoxy resin is obtained by vacuum distillation at 85°C and -0.09 MPa.

[0056] Example 4 The only difference between this embodiment and Embodiment 2 is that, in this embodiment, the hydroxyl content of the hydroxylated epoxy resin is 1.2 mmol / g; The preparation method of hydroxylated epoxy resin in this embodiment is as follows: 100 parts by weight of epoxy resin and 50 parts by weight of ethanol are added to a three-necked flask, heated to 65°C under a nitrogen atmosphere, and stirred at 200 rpm for 30 min to dissolve; then, a mixture of 0.8 parts by weight of boron trifluoride diethyl ether complex and 3.8 parts by weight of water is added dropwise, and the addition is completed in 30 min. The mixture is kept at 65°C for 4.5 h to ensure that the ring-opening rate is ≥83%; the hydroxylated epoxy resin is obtained by vacuum distillation at 80°C and -0.09 MPa.

[0057] Example 5 The only difference between this embodiment and Embodiment 2 is that, in this embodiment, the hydroxyl content of the hydroxylated epoxy resin is 1.5 mmol / g; The preparation method of hydroxylated epoxy resin in this embodiment is as follows: 100 parts by weight of epoxy resin and 50 parts by weight of ethanol are added to a three-necked flask, heated to 65°C under a nitrogen atmosphere, and stirred at 200 rpm for 30 min to dissolve; then, a mixture of 0.8 parts by weight of boron trifluoride diethyl ether complex and 4.8 parts by weight of water is added dropwise, and the addition is completed in 30 min. The mixture is kept at 65°C for 5 h to ensure that the ring-opening rate is ≥95%; the hydroxylated epoxy resin is obtained by vacuum distillation at 80°C and -0.09 MPa.

[0058] Example 6 The only difference between this embodiment and Embodiment 4 is that, in this embodiment, the hydroxylated epoxy resin is a hydroxylated epoxy resin grafted with siloxane groups. The specific method for grafting hydroxylated epoxy resin with siloxane groups is as follows: 100 parts by weight of hydroxylated epoxy resin and 40 parts by weight of toluene are added to a reaction vessel and stirred at 150 rpm for 10 min. Then, 0.1 parts by weight of hydroquinone are added and stirred at 150 rpm for 10 min. Next, 20 parts by weight of KH-570 silane coupling agent are added and stirred at 150 rpm for 10 min. Finally, 0.3 parts by weight of dibutyltin dilaurate are added and stirred at 150 rpm for 10 min. The mixture is then heated to 70℃ and refluxed for 6 h. The mixture is stirred at 200 rpm until the reflux reaction is complete. Fourier transform infrared spectroscopy is used to detect the reaction at 1080 cm⁻¹. -1 Characteristic peaks appeared at the point, confirming the formation of Si-OC bonds, thus obtaining a hydroxylated epoxy resin grafted with siloxane groups.

[0059] Example 7 The only difference between this embodiment and Embodiment 4 is that, in this embodiment, the hydroxylated epoxy resin is a hydroxylated epoxy resin grafted with siloxane groups. The specific method for grafting hydroxylated epoxy resin with siloxane groups is as follows: 105 parts by weight of hydroxylated epoxy resin and 45 parts by weight of toluene are added to a reaction vessel and stirred at 200 rpm for 5 minutes. Then, 0.2 parts by weight of hydroquinone are added and stirred at 200 rpm for 5 minutes. Next, 30 parts by weight of KH-570 silane coupling agent are added and stirred at 200 rpm for 5 minutes. Finally, 0.5 parts by weight of dibutyltin dilaurate are added and stirred at 200 rpm for 5 minutes. The mixture is then heated to 75°C and refluxed for 4 hours, stirred at 300 rpm until the reflux reaction is complete. Fourier transform infrared spectroscopy is used to detect the reaction at 1080 cm⁻¹. -1 Characteristic peaks appeared at the point, confirming the formation of Si-OC bonds, thus obtaining a hydroxylated epoxy resin grafted with siloxane groups.

[0060] Example 8 The only difference between this embodiment and Embodiment 4 is that in this embodiment, lithium titanium aluminum phosphate is siloxane-modified lithium titanium aluminum phosphate. The specific method for modifying lithium titanium aluminum phosphate with siloxane groups is as follows: 4 parts of KH-570 silane coupling agent and 96 parts of ethanol aqueous solution (the weight ratio of ethanol to water is 9:1) are mixed, and the pH is adjusted to 4.5 with acetic acid to obtain a mixed solution. 20 parts of lithium titanium aluminum phosphate are added to the above mixed solution, stirred in a water bath at 60°C for 1 hour, filtered, and vacuum dried at 80°C for 2 hours to obtain lithium titanium aluminum phosphate modified with siloxane groups.

[0061] Comparative Example 1 The only difference between this comparative example and Example 1 is that, in this comparative example, the hydroxylated epoxy resin is replaced with an equal amount of epoxy resin.

[0062] Experimental Example 1 The thermal shrinkage rate of the coated separators prepared in Examples 1-8 was tested according to GB / T 36363-2018 "Polyolefin Separators for Lithium-ion Batteries". The results showed that the longitudinal shrinkage rate of the coated separators prepared in this invention was 0.7%~0.9% and the transverse shrinkage rate was 0.5%~0.8% at 130℃ for 1 hour; the longitudinal shrinkage rate was 1.9%~2.3% and the transverse shrinkage rate was 1.8%~2.1% at 150℃ for 1 hour. This indicates that the coated separators prepared in this invention can suppress shrinkage deformation at high temperatures and exhibit good dimensional stability.

[0063] Experiment Example 2 The peel strength and moisture content of the coated diaphragms prepared in Examples 1-8 and Comparative Example 1 were tested according to GB / T 6283-2008 "Determination of Moisture Content in Chemical Products - Karl Fischer Method (General Method)" and GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes" Method 1. The test results are shown in Table 1 below.

[0064] Table 1. Test results of peel strength and moisture content

[0065] A comparison between Example 1 and Comparative Example 1 shows that the hydroxylated epoxy resin in this invention can significantly improve the peel strength of the coated membrane and significantly reduce the moisture content of the coated membrane. A comparison between Examples 4-5 and Examples 2-3 shows that when the hydroxyl content of the hydroxylated epoxy resin is 1.2-1.5 mmol / g, the peel strength of the coated membrane can be further improved and the moisture content of the coated membrane can be further reduced. A comparison between Examples 4 and Examples 6-7 shows that by grafting siloxane groups onto the hydroxylated epoxy resin, this invention can further improve the peel strength of the coated membrane and further reduce the moisture content of the coated membrane. A comparison between Examples 6 and 8 shows that, compared to siloxane group-modified fillers, siloxane group-grafted hydroxylated epoxy resin can further improve the peel strength of the coated membrane and further reduce the moisture content of the coated membrane.

[0066] 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 coated diaphragm, characterized in that, The coating comprises a base film and a coating disposed on at least one surface of the base film, the coating comprising the following raw materials in parts by weight: 1-1.5 parts of hydroxylated epoxy resin, 2.8-3.3 parts of emulsion binder, and 15-20 parts of filler.

2. The coated diaphragm according to claim 1, characterized in that, The hydroxyl content of the hydroxylated epoxy resin is 1.2~1.5 mmol / g.

3. A coated diaphragm according to claim 1, characterized in that, The coating also includes the following raw materials in parts by weight: 0.3 to 0.6 parts of dispersant and 0.015 to 0.03 parts of wetting agent.

4. The coated diaphragm according to claim 1, characterized in that, The emulsion-type adhesive includes one or more of acrylate emulsions, polyurethane emulsions, and fluoropolymer emulsions; and / or The filler includes one or more of alumina, boehmite, aluminum nitride, aluminum hydroxide, and solid electrolyte.

5. A coated diaphragm according to any one of claims 1 to 4, characterized in that, The hydroxylated epoxy resin is a hydroxylated epoxy resin grafted with siloxane groups.

6. The coated diaphragm according to claim 5, characterized in that, The raw materials for the hydroxylated epoxy resin grafted with siloxane groups include the following components in parts by weight: 100-105 parts of hydroxylated epoxy resin and 20-30 parts of silane coupling agent.

7. A method for preparing a coated diaphragm, used to prepare the coated diaphragm as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Provide the raw materials required for the coating; S2. Mix and grind the raw materials to obtain a coating slurry; S3. The coating slurry is coated on at least one surface of the base film and dried to obtain the crosslinked coated diaphragm. S4. The coated membrane to be crosslinked is immersed in a solution containing an initiator and crosslinked to obtain the coated membrane.

8. The method for preparing a coated diaphragm according to claim 7, characterized in that, Step S1 includes the preparation of hydroxylated epoxy resin, specifically by dissolving epoxy resin in ethanol, adding boron trifluoride diethyl ether complex, performing a ring-opening reaction, and distilling under reduced pressure to obtain the hydroxylated epoxy resin.

9. The method for preparing a coated diaphragm according to claim 8, characterized in that, Step S1 also includes grafting the hydroxylated epoxy resin with siloxane groups. The specific method is as follows: the hydroxylated epoxy resin is mixed with toluene, hydroquinone, silane coupling agent and dibutyltin dilaurate, and refluxed to obtain the hydroxylated epoxy resin grafted with siloxane groups.

10. A battery, characterized in that, The coating membrane includes the coating membrane according to any one of claims 1 to 6 or the coating membrane prepared by the preparation method according to any one of claims 7 to 9.

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