Ceramic coating for lithium ion battery diaphragm and preparation method of ceramic coating

Abstract

The invention provides a ceramic coating for a lithium ion battery diaphragm and a preparation method thereof, and belongs to the technical field of lithium ion battery diaphragms.The ceramic coating is prepared from 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 binder and 6-10 parts of a solvent; wherein the modified talcum powder is prepared by coating talcum powder with chitosan. According to the ceramic coating for the lithium ion battery diaphragm prepared by the preparation method disclosed by the invention, relatively high bonding strength between the coating and a diaphragm substrate can be ensured, the wettability and high temperature resistance of the diaphragm can be greatly improved, and finally, high safety and long cycle life of a battery are realized; the method has important significance for improving the safety and prolonging the service life of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery separators, and particularly relates to a ceramic coating for a lithium ion battery separator and a preparation method thereof. BACKGROUND

[0002] As one of the basic components of lithium ion batteries, the separator has the functions of separating the positive and negative electrodes and preventing short circuit of the battery, can realize free transmission of lithium ions in the charging and discharging process, and can guarantee the structural integrity and use safety of the battery. With the large-scale popularization of new energy vehicles, higher requirements for high-performance battery separators have been put forward in recent years.

[0003] Traditional polyolefin separators have poor polarity, low wettability to electrolyte and poor temperature resistance, which affects the safety and use effect of the battery. By coating a protective layer on the surface of the polyolefin separator, the surface properties of the material and the overall situation of the separator can be changed. The coating layer is usually formed by mixing inorganic nanoparticles such as Al2O3, SiO2 and TiO2 with a binder. These substances can improve the temperature resistance of the separator to some extent, so that it can be applied in different temperature environments. Some improvement methods are to graft hydrophilic segments on the surface of the polyolefin separator, so that it has certain wettability, thereby improving the charging and discharging capacity of the battery and prolonging its cycle life.

[0004] In the improvement of the prior art, while the coating material improves a certain performance of the separator (such as high temperature resistance or wettability), it is often difficult to consider other key indicators. In the traditional coating preparation process, the selection and amount of each component material are not optimized, which further aggravates the unevenness of the internal structure of the coating. During the long-term charging and discharging cycle of the separator, the coating is prone to micro-cracks due to stress concentration, which not only affects the transmission efficiency of lithium ions, but also may cause internal short circuit and other safety hazards of the battery. These problems jointly restrict the further improvement of the performance of the lithium ion battery separator ceramic coating, and it is difficult to meet the urgent needs of high-end fields such as new energy vehicles for high safety and long cycle life of the battery. SUMMARY

[0005] To solve the problems in the background art, the application provides a ceramic coating for a lithium ion battery separator and a preparation method thereof, which can greatly improve the wettability and high temperature resistance of the separator on the basis of ensuring high mechanical strength of the coating and the substrate, and realize high safety and long cycle life of the battery.

[0006] To achieve the above-mentioned purposes, the application provides the following technical solutions: 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. Among them, modified talc is prepared by coating talc with chitosan.

[0007] Preferably, the preparation of the modified talc powder 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%, 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. 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.

[0008] Preferably, the amount of chitosan added to the mixed sol in step A2 is 20-30% of the mass of talc.

[0009] Preferably, the boehmite grain size D50 is 0.5-1.5 μm.

[0010] Preferably, the thickness of the ceramic coating of the lithium-ion battery separator is 3-10 μm.

[0011] Preferably, the dispersant is one or a mixture of two of fatty acid ethylene oxide and polyethylene glycol.

[0012] Preferably, the thickener is one or a mixture of sodium carboxymethyl cellulose and polyethylene oxide.

[0013] This invention also provides a method for preparing a ceramic coating for lithium-ion battery separators, comprising 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, dry it, and obtain the ceramic coating for lithium-ion battery separator on the surface of the base film.

[0014] This application has the following beneficial effects: 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.

[0015] 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.

[0016] 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

[0017] The present application will be further described in detail below with reference to the embodiments.

[0018] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0019] Example 1 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: 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. 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; S3. The premixed slurry after pH adjustment is mixed with the binder to obtain the ceramic coating slurry; 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. The preparation of the modified talc includes the following: 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%. 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. 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.

[0020] Example 2 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: 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. 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; S3. The premixed slurry after pH adjustment is mixed with the binder to obtain the ceramic coating slurry; 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. The preparation of the modified talc includes the following: 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%. 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. 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.

[0021] Example 3 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: 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. 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; S3. The premixed slurry after pH adjustment is mixed with the binder to obtain the ceramic coating slurry; 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. The preparation of the modified talc includes the following: 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%. 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. 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.

[0022] Comparative Example 1 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: 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.

[0023] Comparative Example 2 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: 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.

[0024] Comparative Example 3 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: 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.

[0025] Proof of effectiveness 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. 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%; 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. 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. 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.

[0026] Table 1 Heat shrinkage rate / % Contact angle / ° Adhesion / 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 Results Analysis 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.

[0027] 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.

[0028] 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 a lithium-ion battery separator, characterized in that, The raw material composition of the ceramic coating includes, by weight parts: boehmite 100 parts, modified talc powder 8-12 parts, dispersant 20-30 parts, thickening agent 10-15 parts, water-based polyacrylate binder 3-5 parts, and solvent 6-10 parts; wherein the modified talc powder is prepared by coating talc powder with chitosan.

2. The ceramic coating of claim 1, wherein, The preparation of the modified talc powder includes the following steps: A1. Disperse talc powder with a particle size D50 of 3-10 μm in an ethanol aqueous solution, stir uniformly to obtain a talc powder dispersion; A2. Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 1.5-2.5%, heat and stir to obtain a chitosan solution, the mass fraction of chitosan in the chitosan solution is 2-3%, then add the chitosan solution to the talc powder dispersion of step A1, stir under water bath, filter to obtain a mixed sol; A3. Pour the mixed sol obtained in step A2 into a reaction kettle, perform gel aging at a temperature of 60-65°C to obtain an aged gel, immerse the aged gel completely in deionized water for 8-16h, filter, freeze-dry, and sieve 400-600 mesh to obtain modified talc powder.

3. The ceramic coating of claim 2, wherein, The amount of chitosan added in the mixed sol of step A2 is 20-30% of the mass of talc powder.

4. The ceramic coating of claim 1, wherein, The boehmite has a particle size D50 of 0.5-1.5 μm.

5. The ceramic coating of claim 1, wherein, The thickness of the ceramic coating is 3-10 μm.

6. The ceramic coating of claim 1, wherein, The dispersant is one or a mixture of both of fatty acid ethylene oxide and polyethylene glycol.

7. The ceramic coating of claim 1, wherein, The thickening agent is one or a mixture of both of carboxymethyl cellulose sodium and polyethylene oxide.

8. A method for the preparation of a ceramic coating for lithium-ion battery separators for the preparation of a ceramic coating according to any one of claims 1 to 7, characterized in that The method includes the following steps: S1. Weigh and prepare materials according to the formula, add boehmite and modified talc powder to the solvent, mix uniformly, then add the dispersant to obtain a premix; S2. Mix the premix obtained in step S1 with the thickening agent uniformly, adjust the pH to 4-5 to obtain a premix slurry; S3. Mix the premix slurry after adjusting the pH with the binder to obtain a ceramic coating slurry; S4. Perform single-sided or double-sided coating of the ceramic coating slurry on the base film, dry to obtain the ceramic coating for lithium ion battery separators.