A ceramic coating for lithium-ion battery separators and a method of making the same

Abstract

The application provides a ceramic coating for a lithium ion battery diaphragm and a preparation method thereof, and belongs to the technical field of lithium battery diaphragms.The raw material composition of the ceramic coating comprises 100 parts of boehmite, 8-12 parts of modified talcum powder, 20-30 parts of a dispersing agent, 10-15 parts of a thickening agent, 3-5 parts of a water-based polyacrylate adhesive and 6-10 parts of a solvent, wherein the modified talcum powder is prepared by coating talcum powder with chitosan.The ceramic coating for the lithium ion battery diaphragm prepared by the application can ensure that the coating has high bonding strength with the diaphragm substrate, can greatly improve the wettability and high-temperature resistance of the diaphragm, and finally realizes high safety and long cycle life of the battery, which is of great significance for improving the safety and service life of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery separator technology, specifically relating to a ceramic coating for lithium-ion battery separators and its preparation method. Background Technology

[0002] As a basic component of lithium-ion batteries, the separator plays a role in separating the positive and negative electrodes and preventing short circuits. It enables the free transport of lithium ions during charging and discharging, while ensuring the structural integrity and safety of the battery. With the widespread adoption of new energy vehicles, higher requirements have been placed on high-performance battery separators in recent years.

[0003] Traditional polyolefin separators have poor polarity, low wettability to electrolytes, and poor temperature resistance, affecting battery safety and performance. By coating a protective layer on the surface of the polyolefin separator, the surface properties of the material and the overall condition of the separator can be changed. The coating layer is usually composed of inorganic nanoparticles such as Al2O3, SiO2, and TiO2 mixed with a binder. These substances can improve the temperature resistance of the separator to a certain extent, making it applicable to different temperature environments. Another improvement method is to graft hydrophilic segments onto the surface of the polyolefin separator to give it certain wettability, thereby increasing the charge and discharge capacity of the battery and extending its cycle life.

[0004] In the improvement of existing technologies, while coating materials enhance a specific performance of the separator (such as high temperature resistance or wettability), they often fail to address other key indicators. In traditional coating preparation processes, the selection and proportion of each component material are not optimized, which further exacerbates the non-uniformity of the coating's internal structure. This makes the coating prone to microcracks due to stress concentration during long-term charge-discharge cycles, affecting not only the lithium-ion transport efficiency but also potentially causing safety hazards such as internal short circuits in the battery. These problems collectively restrict further improvement in the performance of lithium-ion battery separator ceramic coatings, making it difficult to meet the urgent needs of high-end fields such as new energy vehicles for high battery safety and long cycle life. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a ceramic coating for lithium-ion battery separators and its preparation method, which can significantly improve the wettability and high-temperature resistance of the separator while ensuring high mechanical strength between the coating and the substrate, thereby achieving high battery safety and long cycle life.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A ceramic coating for lithium-ion battery separators, by weight, comprises the following raw materials: 100 parts boehmite, 8-12 parts modified talc, 20-30 parts dispersant, 10-15 parts thickener, 3-5 parts water-based polyacrylate binder, and 6-10 parts solvent.

[0008] Among them, modified talc is prepared by coating talc with chitosan.

[0009] Preferably, the preparation of the modified talc powder includes the following:

[0010] A1. Disperse talc powder with a particle size D50 of 3-10 μm in an ethanol aqueous solution and stir until homogeneous to obtain a talc powder dispersion;

[0011] A2. Dissolve chitosan in an aqueous solution of acetic acid with a mass fraction of 1.5-2.5%, and stir at a water bath temperature of 50-60℃ for 3-6 hours to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution is 2-3%. Then add the chitosan solution to the talc powder dispersion in step A1, stir at a water bath temperature of 40-50℃, filter, and obtain a mixed sol.

[0012] A3. Pour the mixed sol obtained in step A2 into a reaction vessel and gel age it at a temperature of 60-65℃ for 24-36 hours to obtain aged condensate. Immerse the aged condensate completely in deionized water for 8-16 hours, filter it, and then freeze dry it in a freeze dryer. Sieve it through a 400-600 mesh sieve to obtain modified talc powder.

[0013] Preferably, the amount of chitosan added to the mixed sol in step A2 is 20-30% of the mass of talc.

[0014] Preferably, the boehmite grain size D50 is 0.5-1.5 μm.

[0015] Preferably, the thickness of the ceramic coating of the lithium-ion battery separator is 3-10 μm.

[0016] Preferably, the dispersant is one or a mixture of two of fatty acid ethylene oxide and polyethylene glycol.

[0017] Preferably, the thickener is one or a mixture of sodium carboxymethyl cellulose and polyethylene oxide.

[0018] This invention also provides a method for preparing a ceramic coating for lithium-ion battery separators, comprising the following steps:

[0019] S1. Weigh and prepare the materials according to the formula, add boehmite and modified talc to the solvent, mix evenly, and then add dispersant to obtain premix;

[0020] S2. The premix obtained in step S1 is mixed evenly with the thickener, and the pH is adjusted to 4-5 to obtain the premixed slurry;

[0021] S3. The premixed slurry after pH adjustment is mixed with the binder to obtain the ceramic coating slurry;

[0022] S4. Apply the ceramic coating slurry to one or both sides of the base film, dry it, and obtain the ceramic coating for lithium-ion battery separator on the surface of the base film.

[0023] This application has the following beneficial effects:

[0024] 1. This invention provides a ceramic coating for lithium-ion battery separators and its preparation method. By optimizing the selection and proportion of each component material, the uniformity of the ceramic coating structure is ensured, and defects that may occur during the coating process are reduced, thereby improving the overall quality of the separator. The final coating has suitable thickness, high wettability and high-temperature dimensional stability, and sufficient mechanical strength. It can ensure high bonding strength between the coating and the substrate, thereby achieving high battery safety and long cycle life. In addition, the preparation steps of the ceramic coating slurry are simple and efficient, and easy to realize industrial production. It meets the urgent needs of high battery safety and long cycle life in high-end fields such as new energy vehicles, and has high application value and market prospects.

[0025] 2. By modifying talc, the chitosan molecular chain contains a large number of hydroxyl (-OH) and amino (-NH2) groups. These hydrophilic groups give the modified talc a certain number of active groups, significantly enhancing its hydrophilicity and solubility under acidic conditions. This effectively improves the dispersion and bonding strength between boehmite and water-based binders, improves the compatibility between the coating and the substrate, enhances the bonding strength between the coating and the substrate, improves the overall integrity of the coating, prevents coating material from falling off and breaking, and extends the battery's lifespan. It also improves the non-uniformity of the coating's internal structure, preventing the formation of microcracks in the separator during long-term charge-discharge cycles, improving lithium-ion transport efficiency, and further enhancing the performance of the lithium-ion battery separator ceramic coating.

[0026] 3. In the preparation of modified talc powder, chitosan solution gel aging and freeze drying can effectively improve the high temperature resistance of the coating, reduce boehmite sedimentation, effectively reduce water absorption after film formation, reduce the contact area between boehmite and electrolyte during film formation, reduce residual moisture in the coating, further enhance its bonding force with water-based polyacrylate binders, avoid microcrack problems caused by stress concentration, and significantly improve lithium ion transport efficiency. Detailed Implementation

[0027] The present application will be further described in detail below with reference to the embodiments.

[0028] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0029] Example 1

[0030] A ceramic coating for lithium-ion battery separators, by weight, comprises the following raw materials: 100 parts boehmite with a particle size D50 of 0.8 μm, 10 parts modified talc, 25 parts dispersant, 12 parts thickener, 4 parts water-based polyacrylate binder, and 8 parts water. The dispersant is fatty acid ethylene oxide, and the thickener is sodium carboxymethyl cellulose. The coating is prepared using the following steps:

[0031] S1. Weigh and prepare the materials according to the formula. Add boehmite and modified talc to water, mix evenly, and then add dispersant to obtain premix.

[0032] S2. The premix obtained in step S1 is mixed evenly with the thickener, and the pH is adjusted to 5 to obtain the premixed slurry;

[0033] S3. The premixed slurry after pH adjustment is mixed with the binder to obtain the ceramic coating slurry;

[0034] S4. The ceramic coating slurry is coated on both sides of the polypropylene base film with a coating thickness of 5μm and dried to obtain the ceramic coating for lithium-ion battery separator on the surface of the base film.

[0035] The preparation of the modified talc includes the following:

[0036] A1. Disperse talc powder with a particle size D50 of 5 μm in a 25% (w / w) aqueous ethanol solution and stir until homogeneous to obtain a talc powder dispersion, wherein the mass concentration of talc powder in the talc powder dispersion is 20%.

[0037] A2. Dissolve chitosan in an aqueous solution of acetic acid with a mass fraction of 2.0%, and stir at a water bath temperature of 55°C for 4.5 hours to obtain a chitosan solution with a chitosan mass fraction of 2.5%. Then add the chitosan solution to the talc dispersion in step A1, stir at a water bath temperature of 45°C for 1 hour, filter, and obtain a mixed sol, wherein the amount of chitosan added in the chitosan solution is 25% of the mass of talc.

[0038] A3. Pour the mixed sol obtained in step A2 into a reaction vessel and gel age it at 65°C for 24 hours to obtain aged condensate. Immerse the aged condensate completely in deionized water for 12 hours, filter it, and then freeze dry it in a freeze dryer. Sieve it through a 500-mesh sieve to obtain modified talc powder.

[0039] Example 2

[0040] A ceramic coating for lithium-ion battery separators, by weight, comprises the following raw materials: 100 parts boehmite with a particle size D50 of 0.5 μm, 8 parts modified talc, 20 parts dispersant, 10 parts thickener, 3 parts water-based polyacrylate binder, and 6 parts water. The dispersant is polyethylene glycol, and the thickener is polyethylene oxide. The coating is prepared by the following steps:

[0041] S1. Weigh and prepare the materials according to the formula. Add boehmite and modified talc to water, mix evenly, and then add dispersant to obtain premix.

[0042] S2. The premix obtained in step S1 is mixed evenly with the thickener, and the pH is adjusted to 5 to obtain the premixed slurry;

[0043] S3. The premixed slurry after pH adjustment is mixed with the binder to obtain the ceramic coating slurry;

[0044] S4. The ceramic coating slurry is coated on both sides of the polypropylene base film with a coating thickness of 5μm and dried to obtain the ceramic coating for lithium-ion battery separator on the surface of the base film.

[0045] The preparation of the modified talc includes the following:

[0046] A1. Disperse talc powder with a particle size D50 of 3 μm in a 20% (w / w) aqueous ethanol solution and stir until homogeneous to obtain a talc powder dispersion, wherein the mass concentration of talc powder in the talc powder dispersion is 15%.

[0047] A2. Dissolve chitosan in a 1.5% (w / w) aqueous solution of acetic acid and stir at a water bath temperature of 50°C for 6 hours to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution is 2%. Then add the chitosan solution to the talc dispersion in step A1, stir at a water bath temperature of 40°C for 1 hour, filter, and obtain a mixed sol, wherein the amount of chitosan added in the chitosan solution is 20% of the mass of talc.

[0048] A3. Pour the mixed sol obtained in step A2 into a reaction vessel and gel age it at 60℃ for 36 hours to obtain aged condensate. Immerse the aged condensate completely in deionized water for 8 hours, filter it, and then freeze dry it in a freeze dryer. Sieve it through a 500-mesh sieve to obtain modified talc powder.

[0049] Example 3

[0050] A ceramic coating for lithium-ion battery separators, by weight, comprises the following raw materials: 100 parts boehmite with a particle size D50 of 1.5 μm, 12 parts modified talc, 30 parts dispersant, 15 parts thickener, 5 parts water-based polyacrylate binder, and 10 parts water. The dispersant is fatty acid ethylene oxide, and the thickener is polyethylene oxide. The coating is prepared by the following steps:

[0051] S1. Weigh and prepare the materials according to the formula. Add boehmite and modified talc to water, mix evenly, and then add dispersant to obtain premix.

[0052] S2. The premix obtained in step S1 is mixed evenly with the thickener, and the pH is adjusted to 5 to obtain the premixed slurry;

[0053] S3. The premixed slurry after pH adjustment is mixed with the binder to obtain the ceramic coating slurry;

[0054] S4. The ceramic coating slurry is coated on both sides of the polypropylene base film with a coating thickness of 5μm and dried to obtain the ceramic coating for lithium-ion battery separator on the surface of the base film.

[0055] The preparation of the modified talc includes the following:

[0056] A1. Disperse talc powder with a particle size D50 of 10 μm in a 30% (w / w) aqueous ethanol solution and stir until homogeneous to obtain a talc powder dispersion, wherein the mass concentration of talc powder in the talc powder dispersion is 25%.

[0057] A2. Dissolve chitosan in a 2.5% (w / w) aqueous solution of acetic acid and stir at a water bath temperature of 60°C for 3 hours to obtain a chitosan solution, wherein the chitosan solution contains 3% (w / w) of chitosan. Then add the chitosan solution to the talc dispersion from step A1 and stir at a water bath temperature of 50°C for 1 hour. Filter to obtain a mixed sol, wherein the amount of chitosan added to the chitosan solution is 20-30% of the mass of talc.

[0058] A3. Pour the mixed sol obtained in step A2 into a reaction vessel and gel age it at 65°C for 24 hours to obtain aged condensate. Immerse the aged condensate completely in deionized water for 16 hours, filter it, and then freeze dry it in a freeze dryer. Sieve it through a 500-mesh sieve to obtain modified talc powder.

[0059] Comparative Example 1

[0060] The only difference between this comparative example and Example 1 is that the talc powder was not modified; that is, the modified talc powder was replaced with ordinary talc powder, as detailed below:

[0061] A ceramic coating for lithium-ion battery separators, by weight, comprises the following raw materials: 100 parts boehmite with a particle size D50 of 0.8 μm, 10 parts talc, 25 parts dispersant, 12 parts thickener, 4 parts water-based polyacrylate binder, and 8 parts water. The dispersant is fatty acid ethylene oxide, and the thickener is sodium carboxymethyl cellulose.

[0062] Comparative Example 2

[0063] The only difference between this comparative example and Example 1 is that the water-based acrylic adhesive is replaced with a solvent-based acrylic adhesive, as detailed below:

[0064] A ceramic coating for lithium-ion battery separators, by weight, comprises the following raw materials: 100 parts boehmite with a particle size D50 of 0.8 μm, 10 parts modified talc, 25 parts dispersant, 12 parts thickener, 4 parts solvent-based acrylic binder, and 8 parts water. The dispersant is fatty acid ethylene oxide, and the thickener is sodium carboxymethyl cellulose.

[0065] Comparative Example 3

[0066] The only difference between this comparative example and Example 1 is that the talc powder was not modified, and the water-based acrylic adhesive was replaced with a solvent-based acrylic adhesive, as detailed below:

[0067] A ceramic coating for lithium-ion battery separators, by weight, comprises the following raw materials: 100 parts boehmite with a particle size D50 of 0.8 μm, 10 parts talc, 25 parts dispersant, 12 parts thickener, 4 parts solvent-based acrylic binder, and 8 parts water. The dispersant is fatty acid ethylene oxide, and the thickener is sodium carboxymethyl cellulose.

[0068] Proof of effectiveness

[0069] The lithium-ion battery separators obtained in Examples 1-3 and Comparative Examples 1-3 are identical except for the ceramic coating on the surface of the separator. Test samples were made from the battery separators with different ceramic coatings obtained in Examples 1-3 and Comparative Examples 1-3, and their thermal shrinkage rate, wettability, adhesion, and capacity retention were tested. The specific test results are shown in Table 1.

[0070] Heat shrinkage rate: The lithium-ion battery separator was made into a test sample with a size of 3cm×3cm, and treated at 180℃ for 1h. The dimensional change was measured and the heat shrinkage rate was calculated, where heat shrinkage rate = (area reduced after heat treatment / area before heat treatment) × 100%;

[0071] Wetting ability: The lithium-ion battery separator was made into a test sample with a size of 3cm×3cm. The contact angle of the separator was measured using a DSA100 contact angle meter from KRUSS GmbH, Germany. Electrolyte was added drop by drop. The state of the droplet and the contact angle at this time were recorded 1.5s after the electrolyte was dropped onto the separator.

[0072] Adhesion strength: Prepare a sample of lithium-ion battery separator with a size of 6cm×2cm. Adhere the back of the sample to the stainless steel plate A for testing with tape. Apply wide tape to the reverse side, leaving part of the tape exposed. Adhere the tape to the stainless steel plate B. Clamp stainless steel plates A and B on the testing machine and test the adhesion strength at a speed of 20mm / min.

[0073] Capacity retention: After arranging the lithium-ion battery separator in the order of positive electrode / separator / negative electrode / separator, it is wound in one direction, so that the separator is in the middle of the positive and negative electrodes to play a role in isolation. The winding results in the electrode assembly. The electrode assembly is placed in an aluminum-plastic film, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, degassing, and edge trimming, the lithium-ion battery is obtained. The capacity retention of the lithium-ion battery after 1000 cycles is tested.

[0074] Table 1

[0075] Heat shrinkage rate / % Contact angle / ° Adhesion force / N Capacity retention rate / % Example 1 1.9 10.3 7.6 93.2 Example 2 2.2 10.5 7.4 92.9 Example 3 2.0 10.6 7.5 93.1 Comparative Example 1 3.6 15.2 6.1 90.2 Comparative Example 2 2.6 14.1 6.5 89.4 Comparative Example 3 4.1 18.2 5.8 88.2

[0076] Results Analysis

[0077] Analysis of Examples 1-3 and Comparative Examples 1-3, combined with the data in Table 1, shows that the lithium-ion battery separators prepared by the present invention (Examples 1-3) with ceramic coating have lower thermal shrinkage and contact angles, significantly lower than those of Comparative Examples 1-3. At the same time, there is a high adhesion between the lithium-ion battery separator substrate and the ceramic coating, indicating that the lithium-ion separator has high wettability, high-temperature dimensional stability, and mechanical strength. This results in the final lithium-ion battery retaining a capacity of over 92.9% after 1000 cycles, demonstrating a long service life.

[0078] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0079] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A ceramic coating for lithium-ion battery separators, characterized in that, The ceramic coating comprises, by weight, 100 parts boehmite, 8-12 parts modified talc, 20-30 parts dispersant, 10-15 parts thickener, 3-5 parts water-based polyacrylate binder, and 6-10 parts solvent; wherein the modified talc is prepared by coating talc with chitosan. The preparation of the modified talc includes the following: A1. Disperse talc powder with a particle size D50 of 3-10 μm in an ethanol aqueous solution and stir until homogeneous to obtain a talc powder dispersion; A2. Dissolve chitosan in an aqueous solution of acetic acid with a mass fraction of 1.5-2.5%, heat and stir to obtain a chitosan solution with a chitosan mass fraction of 2-3%. Then add the chitosan solution to the talc powder dispersion in step A1, stir in a water bath, filter, and obtain a mixed sol. A3. Pour the mixed sol obtained in step A2 into a reaction vessel and perform gel aging at a temperature of 60-65℃ to obtain an aged condensate. Immerse the aged condensate completely in deionized water for 8-16 hours, filter, freeze-dry, and sieve through a 400-600 mesh sieve to obtain modified talc powder. In step A2, the amount of chitosan added to the mixed sol is 20-30% of the mass of talc.

2. The ceramic coating according to claim 1, characterized in that, The boehmite grain size D50 is 0.5-1.5 μm.

3. The ceramic coating according to claim 1, characterized in that, The thickness of the ceramic coating is 3-10 μm.

4. The ceramic coating according to claim 1, characterized in that, The dispersant is one or a mixture of two of fatty acid ethylene oxide and polyethylene glycol.

5. The ceramic coating according to claim 1, characterized in that, The thickener is one or a mixture of two of sodium carboxymethyl cellulose and polyethylene oxide.

6. A method for preparing a ceramic coating for a lithium-ion battery separator, comprising preparing the ceramic coating according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Weigh and prepare the materials according to the formula, add boehmite and modified talc to the solvent, mix evenly, and then add dispersant to obtain premix; S2. The premix obtained in step S1 is mixed evenly with the thickener, and the pH is adjusted to 4-5 to obtain the premixed slurry; S3. The premixed slurry after pH adjustment is mixed with the binder to obtain the ceramic coating slurry; S4. Apply the ceramic coating slurry to one or both sides of the base film, and dry it to obtain the ceramic coating for lithium-ion battery separator.