A high-safety ceramic separator with double-layer coating and a preparation method and application thereof

Abstract

The application relates to the field of ceramic diaphragms, in particular to a high-safety ceramic diaphragm with double-layer coating as well as a preparation method and application thereof. The ceramic diaphragm comprises a base film and coating A and coating B located on both sides of the base film; the coating A is obtained by coating coating A slurry on the surface of the base film, and the coating B is obtained by coating coating B slurry on the surface of the coating A; the coating A slurry is prepared from the following raw materials: nano ceramic particles, polyvinyl alcohol, inorganic boron aqueous solution, polyacrylate binder, dispersant, wetting agent and deionized water; and the coating B slurry is prepared from the following raw materials: nano ceramic particles, organic boron binder, dispersant, wetting agent and deionized water. The ceramic diaphragm prepared by the application has excellent temperature resistance and safety, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ceramic separators, in particular to a high-safety ceramic separator with a double-layer coating and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have become a hot spot in power supply technology research in recent years due to their high specific energy, long cycle life and no memory effect. In the field of widely used electronic devices such as mobile phones, notebook computers, and currently emerging electric vehicles and hybrid electric vehicles, lithium ion batteries play an irreplaceable role. The main structure of lithium ion batteries includes positive / negative electrode materials, electrolyte, battery separator and battery shell packaging material, etc. The battery separator is an important part of the lithium ion battery, which directly separates the positive and negative electrodes and prevents short circuiting. The performance of the battery separator directly determines the interface performance, cycle performance and safety performance of the battery. Therefore, a separator with excellent performance plays a crucial role in improving the overall performance of the battery.

[0003] Ceramics can be dispersed in water and have good environmental protection. At present, they have been widely used in the coating of separators to prepare high-temperature-resistant ceramic coating separators with good thermal stability. The wettability of electrolyte is an important indicator for evaluating the separator. Excellent electrolyte wettability is beneficial to improve the ionic conductivity of the battery. In order to further improve the ability of lithium battery separator to absorb electrolyte, a high molecular binder containing a polar hydrophilic group is usually introduced into the separator coating. For example, patent technical document CN108305972B discloses a ceramic coating separator and a preparation method and application thereof. The ceramic coating separator includes a base film and a ceramic coating, wherein the ceramic coating is coated by inorganic particles grafted with polyethylene glycol. Although the use of polyethylene glycol with hydroxyl groups for grafting inorganic particles realizes fast liquid absorption rate and high liquid absorption rate of the ceramic coating separator, the ceramic coating separator exhibits a large thermal shrinkage under high temperature conditions, resulting in poor mechanical strength and temperature resistance of the ceramic coating separator under high temperature conditions.

[0004] In order to solve the above problems, a cross-linkable polymer binder can be introduced into the separator coating to form a three-dimensional network structure on the surface of the separator, so as to increase the mechanical strength and temperature resistance of the ceramic coating separator. For example, patent technical document CN113964450A discloses a battery separator coating liquid and a preparation method thereof, a battery separator and a battery. Due to the interaction force or hydrogen bond between the ceramic, adhesive, nanowire and coupling agent in the battery separator coating liquid, the finally prepared battery separator has good heat resistance. However, the ceramic separator prepared by this method has a high cross-linking degree, which makes the system inside more tightly packed, resulting in a decrease in liquid absorption. In addition, the adhesion between the ceramic separator and the pole piece is poor, and the looseness between the separator and the pole piece may cause internal short circuit, thereby causing safety problems such as overheating, fire and even explosion of the battery. SUMMARY

[0005] Therefore, the present application aims to provide a high-temperature-resistant and high-liquid-absorbing ceramic diaphragm, a preparation method and application thereof, which can effectively solve the problems of poor temperature resistance, poor liquid absorption and low safety of the diaphragm, thereby significantly improving the comprehensive performance of the battery.

[0006] To achieve the above purpose, the present application provides a high-safety ceramic diaphragm with double-layer coating, characterized in that the ceramic diaphragm comprises a base film and coating layers A and B on both sides of the base film; the coating layer A is obtained by coating coating layer A slurry on the surface of the base film, and the coating layer B is obtained by coating coating layer B slurry on the surface of the coating layer A.

[0007] Further, the coating layer A slurry is prepared from the following raw materials in parts by weight: nano ceramic particles 70-90 parts, polyvinyl alcohol 4-8 parts, inorganic boron aqueous solution 5-10 parts, polyacrylate binder 2-3 parts, dispersant 0.5-1 part, wetting agent 0.5-1 part and deionized water 10-12 parts.

[0008] Further, the coating layer B slurry is prepared from the following raw materials in parts by weight: nano ceramic particles 70-90 parts, organic boron binder 4-6 parts, dispersant 0.5-1 part, wetting agent 0.5-1 part and deionized water 8-10 parts.

[0009] Further, the preparation method of the organic boron binder is as follows:

[0010] S1: under a nitrogen atmosphere, methyl methacrylate, acrylonitrile, 3-(methacryloyloxy) propyl trimethoxysilane are added to 1,4-dioxane, heated to 75-80℃, then benzoyl peroxide, n-dodecanethiol are added, then heated to 90-100℃, stirred for 2-3h, washed and purified with petroleum ether to obtain an oligomeric random copolymer;

[0011] S2: under a nitrogen atmosphere, the oligomeric random copolymer and boric acid are mixed, heated to 80-90℃, stirred for 3-4h to obtain an organic boron binder;

[0012] Further, the mass ratio of methyl methacrylate, acrylonitrile, 3-(methacryloyloxy) propyl trimethoxysilane, 1,4-dioxane, benzoyl peroxide and n-dodecanethiol in S1 is 10:3:5:50:0.08:1.4.

[0013] Further, the mass ratio of the oligomeric random copolymer and boric acid in S2 is 10:3.

[0014] Further, the base film is one of polyethylene, polypropylene, polymethylpentene and non-woven fabric, and the porosity is 40-55%.

[0015] Further, the thickness ratio of the base film, coating A and coating B is 10-15:1-4:1-4.

[0016] Further, the nano ceramic particles are one or more of nano alumina, aluminum hydroxide, magnesium hydroxide, boehmite and silicon dioxide, and the particle size is 0.4-1.2 μm.

[0017] Further, the concentration of the inorganic boron aqueous solution is 5wt%-10wt%.

[0018] Further, the inorganic boron in the inorganic boron aqueous solution is one or more of borax, potassium tetraborate, lithium tetraborate and ammonium borate.

[0019] Further, the polyacrylate binder is one of poly(methyl acrylate) and poly(butyl acrylate).

[0020] Further, the dispersant is sodium polyacrylate.

[0021] Further, the wetting agent is one or more of acetylenic diol vinyl ether, fatty acid polyoxyethylene ether and polyether-modified siloxane.

[0022] Still further, the application also provides a preparation method of the high-safety ceramic separator with double-layer coating.

[0023] (1) mixing the dispersant and deionized water, stirring for 5-10 min, adding the nano ceramic particles, stirring for 20-90 min, further grinding and dispersing for 10-50 min, then adding the polyacrylate binder, stirring for 30-60 min, further adding polyvinyl alcohol and the inorganic boron aqueous solution, stirring for 30-60 min, further adding the wetting agent, stirring for 30-60 min, and finally passing through a 250-mesh filter to obtain the coating A slurry,

[0024] (2) coating the coating A slurry on the surface of the polyolefin microporous film, and drying to obtain the coating A;

[0025] (3) mixing the dispersant and deionized water, stirring for 5-10 min, adding the nano ceramic particles, stirring for 20-90 min, further grinding and dispersing for 10-50 min, then adding the organic boron binder, stirring for 30-60 min, further adding the wetting agent, stirring for 30-60 min, and finally passing through a 250-mesh filter to obtain the coating B slurry;

[0026] (4) coating the coating B slurry on the surface of the coating A, and drying to obtain the high-safety ceramic separator with double-layer coating.

[0027] Further, the application also provides application of the high-safety ceramic separator with the double-layer coating in a lithium ion power battery.

[0028] Advantages of the application:

[0029] The high-safety ceramic separator with the double-layer coating provided by the application has the following advantages: the cross-linking and curing reaction of the hydroxyl polymer and the boric acid compound in the coating A forms a three-dimensional network structure, which improves the coating skeleton strength and effectively improves the mechanical strength and temperature resistance of the separator; the organic boron binder in the coating B can better bond the separator and the pole piece together, and at the same time, can improve the liquid absorption performance of the separator, and improve the safety and cycle life of the battery.

[0030] The high-safety ceramic separator with the double-layer coating provided by the application has the following advantages: the cross-linking and curing reaction of the hydroxyl polymer and the boric acid compound in the coating A forms a three-dimensional network structure, which improves the coating skeleton strength and effectively improves the mechanical strength and temperature resistance of the separator; the organic boron binder in the coating B can better bond the separator and the pole piece together, and at the same time, can improve the liquid absorption performance of the separator, and improve the safety and cycle life of the battery. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the application more clear, the application is further described in detail below with reference to specific examples.

[0032] Preparation example: preparation of the organic boron binder

[0033] S1: under a nitrogen atmosphere, 10g of methyl methacrylate, 3g of acrylonitrile and 5g of 3-(methacryloyloxy)propyl trimethoxysilane are added to 50g of 1,4-dioxane, the temperature is raised to 75 DEG C, then 0.08g of benzoyl peroxide and 1.4g of n-dodecanethiol are added, then the temperature is raised to 95 DEG C, and stirring is carried out for 2.5h, and petroleum ether is used for purification, to obtain an oligomeric random copolymer;

[0034] S2: under a nitrogen atmosphere, 10g of the oligomeric random copolymer and 3g of boric acid are mixed, the temperature is raised to 85 DEG C, and stirring is carried out for 3.5h, to obtain the organic boron binder.

[0035] Example 1: preparation of a high-safety ceramic separator with a double-layer coating

[0036] (1) 0.5 g of sodium polyacrylate and 10 g of deionized water were mixed and stirred for 5 minutes, 70 g of nano-alumina with a particle size of 1 μm was added, stirred for 20 minutes, and then ground and dispersed for 10 minutes, 2 g of poly(methyl acrylate) was added, stirred for 30 minutes, 4 g of polyvinyl alcohol and 5 g of a 5 wt% potassium tetraborate aqueous solution were added, stirred for 30 minutes, 0.5 g of a wetting agent was added, stirred for 30 minutes, and finally passed through a 250 mesh screen to obtain a coating A slurry,

[0037] (2) The coating A slurry was coated on the surface of a polypropylene microporous membrane with a porosity of 48%, and after drying, coating A was obtained;

[0038] (3) 0.5 g of sodium polyacrylate and 8 g of deionized water were mixed and stirred for 5 minutes, 70 g of nano-alumina with a particle size of 1 μm was added, stirred for 20 minutes, and then ground and dispersed for 10 minutes, 4 g of the organic boron binder prepared in the preparation example was added, stirred for 30 minutes, 0.5 g of a polyether-modified siloxane was added, stirred for 30 minutes, and finally passed through a 250 mesh screen to obtain a coating B slurry;

[0039] (4) The coating B slurry was coated on the surface of coating A, and after drying, a high-safety ceramic separator with a double-layer coating was obtained.

[0040] Example 2: Preparation of a high-safety ceramic separator with a double-layer coating:

[0041] (1) 0.7 g of sodium polyacrylate and 11 g of deionized water were mixed and stirred for 8 minutes, 80 g of nano-alumina with a particle size of 1 μm was added, stirred for 50 minutes, and then ground and dispersed for 30 minutes, 2.5 g of poly(methyl acrylate) was added, stirred for 45 minutes, 6 g of polyvinyl alcohol and 8 g of a 7.5 wt% borax aqueous solution were added, stirred for 45 minutes, 0.8 g of a polyether-modified siloxane was added, stirred for 45 minutes, and finally passed through a 250 mesh screen to obtain a coating A slurry,

[0042] (2) The coating A slurry was coated on the surface of a polypropylene microporous membrane with a porosity of 48%, and after drying, coating A was obtained;

[0043] (3) 0.7 g of sodium polyacrylate and 9 g of deionized water were mixed and stirred for 8 minutes, 80 g of nano-alumina with a particle size of 1 μm was added, stirred for 60 minutes, and then ground and dispersed for 35 minutes, 5 g of the organic boron binder prepared in the preparation example was added, stirred for 45 minutes, 0.8 g of a wetting agent was added, stirred for 40 minutes, and finally passed through a 250 mesh screen to obtain a coating B slurry;

[0044] (4) The coating B slurry was coated on the surface of coating A, and after drying, a high-safety ceramic separator with a double-layer coating was obtained.

[0045] Example 3: Preparation of a high-safety ceramic separator with double-layer coating

[0046] (1) 1 g of sodium polyacrylate and 12 g of deionized water were mixed and stirred for 10 minutes, 90 g of nano-alumina with a particle size of 1 μm was added and stirred for 90 minutes, and then ground and dispersed for 50 minutes, followed by the addition of 3 g of methyl polyacrylate, stirring for 60 minutes, the addition of 8 g of polyvinyl alcohol and 10 g of an aqueous solution of ammonium borate with a concentration of 10 wt%, stirring for 60 minutes, the addition of 1 g of polyether-modified siloxane, stirring for 60 minutes, and finally passing through a 250-mesh filter to obtain a coating A slurry,

[0047] (2) The coating A slurry was coated on the surface of a polypropylene microporous membrane with a porosity of 48%, and coating A was obtained after drying;

[0048] (3) 1 g of sodium polyacrylate and 10 g of deionized water were mixed and stirred for 10 minutes, 90 g of nano-alumina with a particle size of 1 μm was added and stirred for 60 minutes, 1 g of a wetting agent was added and stirred for 60 minutes, and finally passed through a 250-mesh filter to obtain a coating B slurry;

[0049] (4) The coating B slurry was coated on the surface of coating A, and a high-safety ceramic separator with a double-layer coating was obtained after drying.

[0050] Comparative Example 1:

[0051] Comparative Example 1 is a polypropylene microporous membrane with a porosity of 48% without any coating.

[0052] Comparative Example 2:

[0053] Comparative Example 2 differs from Example 2 in that no coating B is provided on Comparative Example 2.

[0054] Comparative Example 3:

[0055] Comparative Example 3 differs from Example 2 in that no inorganic boron aqueous solution is added in step (1).

[0056] Comparative Example 4:

[0057] Comparative Example 4 differs from Example 2 in that the organic boron binder in step (3) is replaced by methyl polyacrylate.

[0058] Performance Test

[0059] The thickness of each sample in Examples 1-3 and Comparative Examples 1-4 was tested in μm using a THI-1801 thickness gauge according to the GB / T 6672-2001 standard "Determination of the thickness of plastic films and sheets - Mechanical method".

[0060] The thermal shrinkage rate (%) of each group of samples in Examples 1-3 and Comparative Examples 1-4 was measured at 150°C for 1 hour by using a FST-3102 film thermal shrinkage tester according to GB / T13519-2016 standard;

[0061] The contact angle of each group of samples in Examples 1-3 and Comparative Examples 1-4 to electrolyte was measured by using a JC2000D1 contact angle tester according to GB / T30447-2013 standard;

[0062] The hot-pressing adhesion of the ceramic separators prepared in Examples 1-3 and Comparative Examples 1-4 was tested by using a plastic sealing roller press and a universal tensile testing machine, wherein the roller temperature was set to 113°C, two ceramic separators were folded in half with the edges aligned, and were sandwiched between two PET films. The temperature of the hot roller was tested by using a temperature gun. After the set temperature was reached, the roller press switch was turned on, and the films were placed parallel in the plastic sealing machine. After the films completely left the plastic sealing machine, the PET films were peeled off, and the adhesion between the ceramic separators was tested by using the universal tensile testing machine peeling method. The results are shown in Table 1 below:

[0063] The adhesion between coating A and coating B was tested by using the universal tensile testing machine peeling method. The results are shown in Table 1.

[0064] Table 1: Performance test results

[0065]

[0066] Data analysis:

[0067] As can be seen from Table 1, compared with the base film in Comparative Example 1, the high-safety ceramic separator with double-layer coating prepared in Examples 1-3 has lower thermal shrinkage rate, higher air permeability value and smaller contact angle at 150°C and 180°C, and has certain hot-pressing adhesion, which ensures safety.

[0068] As can be seen from the data of Example 2 and Comparative Example 2, coating B effectively reduces the thermal shrinkage rate of the separator at 150°C and 180°C, improves the heat resistance, and further improves the contact angle. Most importantly, it gives the separator certain hot-pressing adhesion.

[0069] As can be seen from the data of Example 2 and Comparative Example 3, the addition of inorganic boron significantly improves the heat resistance of the separator, and most importantly, improves the adhesion between coating A and coating B.

[0070] As can be seen from the data of Example 2 and Comparative Example 4, compared with the traditional polyacrylate adhesive, the organic boron adhesive prepared in the present application significantly improves the heat resistance of the separator, and has a significant contribution to the hot-pressing adhesion.

[0071] Those skilled in the art should understand that the above discussion of any embodiment is only intended to be exemplary in nature and is not intended to suggest that the present application is limited to these examples; under the concept of the present application, the above embodiments or technical features among different embodiments can be combined, steps can be implemented in any order, and there are many other variations of different aspects of the present application as described above, which are not provided in details for the sake of brevity.

Claims

1. A high-safety ceramic separator having a double-layer coating, characterized by, The ceramic diaphragm comprises a base film and coating A and coating B on both sides of the base film; the coating A is obtained by coating the base film surface with coating A slurry, and the coating B is obtained by coating the coating A surface with coating B slurry; The coating A slurry is prepared from the following raw materials in parts by weight: nano ceramic particles 70-90 parts, polyvinyl alcohol 4-8 parts, inorganic boron aqueous solution 5-10 parts, polyacrylate binder 2-3 parts, dispersant 0.5-1 part, wetting agent 0.5-1 part, and deionized water 10-12 parts; The coating B slurry is prepared from the following raw materials in parts by weight: nano ceramic particles 70-90 parts, organic boron binder 4-6 parts, dispersant 0.5-1 part, wetting agent 0.5-1 part, and deionized water 8-10 parts; The preparation method of the organic boron binder is as follows: S1: under a nitrogen atmosphere, methyl methacrylate, acrylonitrile, 3-(methacryloyloxy) propyl trimethoxysilane are added to 1,4-dioxane, heated to 75-80℃, then benzoyl peroxide, n-dodecanethiol is added, then heated to 90-100℃, stirred for 2-3h, washed with petroleum ether to purify, to obtain an oligomeric random copolymer; S2: under a nitrogen atmosphere, the oligomeric random copolymer and boric acid are mixed, heated to 80-90℃, stirred for 3-4h, to obtain an organic boron binder; The mass ratio of methyl methacrylate, acrylonitrile, 3-(methacryloyloxy) propyl trimethoxysilane, 1,4-dioxane, benzoyl peroxide and n-dodecanethiol in S1 is 10:3:5:50:0.08:1.4; the mass ratio of oligomeric random copolymer and boric acid in S2 is 10:

3.

2. The high-safety ceramic separator with a dual-layer coating according to claim 1, characterized by, The base film is one of polyethylene, polypropylene, polymethylpentene and non-woven fabric, and the porosity is 40-55%.

3. The high-safety ceramic separator with a dual-layer coating according to claim 1, characterized by, The thickness ratio of the base film, coating A and coating B is 10-15:1-4:1-4.

4. The high-safety ceramic separator with a dual-layer coating according to claim 1, characterized by, The nano ceramic particles are one or more of nano alumina, aluminum hydroxide, magnesium hydroxide, boehmite and silicon dioxide, and the particle size is 0.4-1.2μm.

5. The high-safety ceramic separator with a dual-layer coating according to claim 1, characterized in that, The concentration of the inorganic boron aqueous solution is 5wt%-10wt%.

6. The high-safety ceramic separator with a dual-layer coating according to claim 1, characterized in that, The inorganic boron in the inorganic boron aqueous solution is one or more of borax, potassium tetraborate, lithium tetraborate and ammonium borate.

7. The high-safety ceramic separator with a dual-layer coating according to claim 1, characterized by, The polyacrylate binder is one of poly(methyl acrylate) and poly(butyl acrylate).

8. The high-safety ceramic separator with a dual-layer coating according to claim 1, characterized by, The dispersant is sodium polyacrylate; the wetting agent is one or more of acetylenic glycol vinyl ether, fatty acid polyoxyethylene ether and polyether modified siloxane.

9. A method of manufacturing a high-safety ceramic separator having a double coating according to any one of claims 1 to 8, characterized in that, The specific preparation method is as follows: (1) mix the dispersant and deionized water, stir for 5-10min, add the nano ceramic particles, stir for 20-90min, then grind and disperse for 10-50min, then add the polyacrylate binder, stir for 30-60min, then add the polyvinyl alcohol and inorganic boron aqueous solution, stir for 30-60min, then add the wetting agent, stir for 30-60min, and finally pass through a 250 mesh sieve to obtain the coating A slurry, (2) coat the coating A slurry on the surface of the polyolefin microporous film, and obtain the coating A after drying, (3) mixing dispersant and deionized water, stirring for 5-10 min, adding nano ceramic particles, stirring for 20-90 min, grinding and dispersing for 10-50 min, then adding organic boron binder, stirring for 30-60 min, adding wetting agent, stirring for 30-60 min, and finally passing through a 250-mesh filter to obtain coating B slurry; (4) coating coating B slurry on the surface of coating A, and drying to obtain a high-safety ceramic separator with double-layer coating.

10. Use of a high-safety ceramic separator having a double coating according to any one of claims 1 to 8, characterized in that, It can be applied to lithium ion power batteries.

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