Boehmite for coating of lithium battery separator and method for preparing the same

Abstract

The present application relates to the technical field of materials, and particularly relates to a boehmite for coating lithium battery diaphragm and a preparation method thereof. The boehmite powder is a hollow microspherical structure boehmite. The particle size of the boehmite powder is 0.3-0.5 microns. The present application prepares the hollow microspherical structure boehmite powder, and coats the boehmite powder on both sides of the PP film as ceramic coating, so that the porosity of the coated PP film is greatly improved, thereby minimizing the ion resistance, providing higher battery power, and meeting the ion conductivity requirement. At the same time, the contact angle of the PP film coated with the ceramic coating is greatly reduced, so that the wettability of the film layer to the electrolyte is improved, thereby synergistically improving the liquid absorption rate of the film layer. In addition, the boehmite powder is reasonably modified by using a silane coupling agent, so that the distance between the film breaking temperature and the closing temperature is increased, and the risk of short circuit in the battery caused by the increased porosity is reduced.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a boehmite for coating lithium battery separators and its preparation method. Background Technology

[0002] The separator is a crucial component of lithium-ion batteries, its primary function being to prevent direct contact between the positive and negative electrodes and to facilitate the shuttle of lithium ions between them. Although the separator does not directly participate in the electrochemical reaction, its properties determine the electrochemical and safety performance of the lithium-ion battery. The separator should possess high porosity and electrolyte absorption rate to enable rapid lithium ion transfer. Furthermore, the separator should maintain its structural integrity during lithium dendrite penetration to prevent internal short circuits. Lithium-ion battery separators can be classified into three main categories based on their structure and composition: polyolefin microporous separators, non-woven fabric separators, and inorganic-organic composite separators. The preparation method of the separator directly affects its overall performance, including porosity, pore size, mechanical strength, and thickness. Polyolefin microporous separators are widely used in commercial lithium-ion batteries due to their advantages such as low production cost, high mechanical strength, and good chemical stability. Currently, most common polyolefin microporous separators are made from one or a mixture of two of polyethylene (PE), high-density polyethylene (HDPE), and polypropylene (PP), and the common manufacturing processes are dry and wet methods. Meanwhile, polyolefin separators dominate the lithium-ion battery separator market, widely used in electric vehicles and small portable devices due to their good chemical stability and low production cost. However, because polyolefin separators lack polar groups on their surface, they are difficult to fully wet with electrolyte, resulting in problems such as poor electrolyte wettability, low ionic conductivity, and poor cycle stability. Furthermore, polyolefin separators have poor thermal stability; at high temperatures, they shrink significantly, failing to provide insulation and even causing internal short circuits within the battery. These problems limit the further development of polyolefin separators.

[0003] Because the surface of polyolefin separators is non-polar, their wettability with electrolytes is poor. To improve the electrolyte wettability of the separator, coating or impregnating it with functional materials is an effective way to improve its performance. Inorganic coating modification, also known as ceramic modification, involves coating the surface of the polyolefin separator with a layer of inorganic ceramic material. Since inorganic ceramic particles have a large specific surface area and good hydrophilicity, they can improve the electrolyte wettability of the separator and enhance the electrolyte absorption rate. Furthermore, inorganic ceramic particles have good thermal stability, preventing the separator from thermally shrinking or melting at high temperatures, thus improving the battery's safety factor. Currently, ultrafine alumina is the most widely used inorganic powder in lithium battery separator modification, but it has disadvantages such as high hardness, high energy consumption, and high production costs. Compared to high-purity alumina, boehmite has the following advantages: (1) lower hardness, resulting in less wear on mechanical equipment and reducing the risk of foreign matter introduction; (2) higher heat resistance and better compatibility with organic solvents; (3) lower specific gravity, allowing boehmite to cover 25% more area than alumina of the same mass; (4) higher coating smoothness and lower internal resistance; and (5) lower production energy consumption and environmental friendliness. Therefore, boehmite has gradually replaced alumina as a new type of commercially available powder for modifying lithium battery separators.

[0004] Based on the above, this invention proposes a boehmite for lithium battery separator coating and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide boehmite for coating lithium battery separators and its preparation method.

[0006] To achieve the above objectives, the present invention provides boehmite for coating lithium battery separators. The boehmite for coating lithium battery separators is prepared by the following method: (1) Boehmite powder is mixed with anhydrous ethanol at a mass ratio of 1g:40ml and ultrasonically dispersed for 10min to obtain anhydrous ethanol dispersion of boehmite; (2) Silane coupling agent is weighed at 1 / 8 to 1 / 10 of the mass of boehmite powder, and then 1 / 20 of the volume of anhydrous ethanol of boehmite dispersion is added to form anhydrous ethanol solution of silane coupling agent. The solution is hydrolyzed at 40 to 45℃ for 30 to 35min; (3) The hydrolyzed anhydrous ethanol solution of silane coupling agent is added to the anhydrous ethanol dispersion of boehmite at a rate of 2 to 3 drops per second, heated and refluxed in an oil bath at 80℃ for 12h, then centrifuged at high speed, washed 3 to 4 times with anhydrous ethanol, and dried at 80℃ for 48h to obtain the final product.

[0007] Preferably, the boehmite powder has a particle size of 0.3~0.5μm.

[0008] Preferably, the boehmite powder is a hollow microspherical structure boehmite.

[0009] Preferably, the hollow microspherical boehmite is prepared by the following method: [The method involves] mixing boehmite containing 2.5 × 10⁻⁶ ppm... - 3 A tetrahydrofuran solution of mol / L amphiphilic block copolymer was mixed with a 0.1 mol / L Al2(SO4)3 aqueous solution at a volume ratio of 1:5. Distilled water was added at a volume of 4 times the volume of the mixed solution, followed by 0.004 mol of urea. The mixture was reacted at 150˚C for 24 h. After the reaction was completed, the solution was rapidly cooled to room temperature, then centrifuged at high speed, and repeatedly washed with distilled water until no SO4 was found. 2- If present, wash three more times with anhydrous ethanol to obtain the product.

[0010] Preferably, the amphiphilic block copolymer is polystyrene-block-hydroxyethyl polyacrylate.

[0011] Preferably, the silane coupling agent is an amino-containing silane coupling agent.

[0012] Preferably, the amino-containing silane coupling agent is one of a monoamino silane coupling agent, a diamino silane coupling agent, or a triamino silane coupling agent.

[0013] Preferably, the monoaminosilane coupling agent is one of a monoaminosilane coupling agent containing a secondary amino structure or a tertiary amino structure.

[0014] Preferably, all monoamino silane coupling agents containing secondary amino groups have a symmetrical structure with N as the center of symmetry.

[0015] Preferably, the monoamino silane coupling agent containing a secondary amino group with a symmetrical structure centered on N is one of bis(3-triethoxysilylpropyl)amine or bis(3-trimethoxysilylpropyl)amine.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. This invention prepares hollow microspherical boehmite powder and applies it as a ceramic coating to both sides of a PP membrane. The porosity of the coated PP membrane is significantly increased, thereby minimizing ionic resistance and providing higher battery power to meet the requirements of ionic conductivity. Simultaneously, the contact angle of the PP membrane coated with the ceramic coating is significantly reduced, improving the wettability of the membrane to the electrolyte, thus synergistically increasing the liquid absorption rate of the membrane with the increased porosity. Furthermore, by using a silane coupling agent to rationally modify the boehmite powder, the distance between the membrane rupture temperature and the shut-off temperature is increased, reducing the risk of internal short circuits in the battery due to increased porosity.

[0018] 2. The preparation method of the present invention is convenient to operate, easy to mass-produce, and has stable quality.

[0019] 3. The raw materials for this invention are abundant and reasonably priced in China, which means that there are no high cost restrictions on its large-scale production. Detailed Implementation

[0020] Example 1

[0021] The dosage of each raw material is shown in Table 1.

[0022] (1) Containing 2.5×10 -3 A tetrahydrofuran solution of polystyrene-block-polyhydroxyethyl acrylate was mixed with a 0.1 mol / L Al2(SO4)3 aqueous solution at a volume ratio of 1:5. Distilled water was added at a volume of 4 times the volume of the mixed solution. Then, 0.004 mol of urea was added, and the mixture was reacted at 150˚C for 24 h. After the reaction was complete, the solution was rapidly cooled to room temperature, then centrifuged at high speed, and repeatedly washed with distilled water until no SO4 was detected. 2- If present, wash three times with anhydrous ethanol to obtain hollow microspherical boehmite.

[0023] (2) Take hollow microsphere boehmite powder and mix it with anhydrous ethanol at a mass ratio of 1g:40ml. Disperse it by ultrasonication for 10min to obtain anhydrous ethanol dispersion of boehmite.

[0024] (3) Weigh 1 / 8 of the mass of the hollow microsphere boehmite powder as silane coupling agent bis(3-triethoxysilylpropyl)amine, then add 1 / 20 of the volume of the anhydrous ethanol dispersion of boehmite to form an anhydrous ethanol solution of silane coupling agent, and hydrolyze at 40°C for 35 min.

[0025] (4) Add the hydrolyzed silane coupling agent in anhydrous ethanol solution to the boehmite in anhydrous ethanol dispersion at a rate of 2-3 drops per second, heat and reflux in an oil bath at 80°C for 12 hours, then centrifuge at high speed, wash with anhydrous ethanol 3-4 times, and dry at 80°C for 48 hours to obtain the product.

[0026] Example 2

[0027] The dosage of each raw material is shown in Table 1.

[0028] (1) Containing 2.5×10 -3 A tetrahydrofuran solution of polystyrene-block-polyhydroxyethyl acrylate was mixed with a 0.1 mol / L Al2(SO4)3 aqueous solution at a volume ratio of 1:5. Distilled water was added at a volume of 4 times the volume of the mixed solution. Then, 0.004 mol of urea was added, and the mixture was reacted at 150˚C for 24 h. After the reaction was complete, the solution was rapidly cooled to room temperature, then centrifuged at high speed, and repeatedly washed with distilled water until no SO4 was detected. 2- If present, wash three times with anhydrous ethanol to obtain hollow microspherical boehmite.

[0029] (2) Take hollow microsphere boehmite powder and mix it with anhydrous ethanol at a mass ratio of 1g:40ml. Disperse it by ultrasonication for 10min to obtain anhydrous ethanol dispersion of boehmite.

[0030] (3) Weigh 1 / 10 of the mass of the hollow microsphere boehmite powder as silane coupling agent bis(3-trimethoxysilylpropyl)amine, then add 1 / 20 of the volume of the boehmite anhydrous ethanol dispersion to form an anhydrous ethanol solution of the silane coupling agent, and hydrolyze at 45°C for 30 min.

[0031] (4) Add the hydrolyzed silane coupling agent in anhydrous ethanol solution to the boehmite in anhydrous ethanol dispersion at a rate of 2-3 drops per second, heat and reflux in an oil bath at 80°C for 12 hours, then centrifuge at high speed, wash with anhydrous ethanol 3-4 times, and dry at 80°C for 48 hours to obtain the product.

[0032] Example 3

[0033] The dosage of each raw material is shown in Table 1.

[0034] (1) Containing 2.5×10 -3 A tetrahydrofuran solution of polystyrene-block-polyhydroxyethyl acrylate was mixed with a 0.1 mol / L Al2(SO4)3 aqueous solution at a volume ratio of 1:5. Distilled water was added at a volume of 4 times the volume of the mixed solution. Then, 0.004 mol of urea was added, and the mixture was reacted at 150˚C for 24 h. After the reaction was complete, the solution was rapidly cooled to room temperature, then centrifuged at high speed, and repeatedly washed with distilled water until no SO4 was detected. 2- If present, wash three times with anhydrous ethanol to obtain hollow microspherical boehmite.

[0035] (2) Take hollow microsphere boehmite powder and mix it with anhydrous ethanol at a mass ratio of 1g:40ml. Disperse it by ultrasonication for 10min to obtain anhydrous ethanol dispersion of boehmite.

[0036] (3) Weigh 1 / 10 of the mass of the hollow microsphere boehmite powder as silane coupling agent bis(3-trimethoxysilylpropyl)amine, then add 1 / 20 of the volume of the boehmite anhydrous ethanol dispersion to form an anhydrous ethanol solution of the silane coupling agent, and hydrolyze it at 45°C for 35 min.

[0037] (4) Add the hydrolyzed silane coupling agent in anhydrous ethanol solution to the boehmite in anhydrous ethanol dispersion at a rate of 2-3 drops per second, heat and reflux in an oil bath at 80°C for 12 hours, then centrifuge at high speed, wash with anhydrous ethanol 3-4 times, and dry at 80°C for 48 hours to obtain the product.

[0038] Comparative Example 1

[0039] Unlike Example 3, the silane coupling agent used was N-(n-butyl)-3-aminopropyltrimethoxysilane, a monoamino silane coupling agent containing a secondary amino structure, with CAS number 31024-56-3. The amounts of each raw material are shown in Table 1.

[0040] Comparative Example 2

[0041] Unlike Example 3, the silane coupling agent used was N-cyclohexyl-3-aminopropylmethyldimethoxysilane, a monoamino silane coupling agent containing a secondary amino structure, with CAS number 120218-28-2. The rest was the same as in Example 3. The amounts of each raw material are shown in Table 1.

[0042] Comparative Example 3

[0043] Unlike Example 3, the silane coupling agent used was N,N-diethyl-3-aminopropyltrimethoxysilane, a monoamino silane coupling agent containing a tertiary amino structure, CAS number 41051-80-3. The rest was the same as in Example 3. The amounts of each raw material are shown in Table 1.

[0044] Comparative Example 4

[0045] Unlike Example 3, the silane coupling agent used is γ-aminopropyltriethoxysilane, a monoamino silane coupling agent containing a primary amino structure, i.e., KH550. The rest is the same as in Example 3. The amounts of each raw material are shown in Table 1.

[0046] Table 1

[0047]

[0048] Performance testing and evaluation

[0049] First, dissolve 0.024 g of sodium carboxymethyl cellulose in 10 ml of deionized water to prepare a CMC solution. Then, weigh 3 g of boehmite powder from Examples 1-3 and Comparative Examples 1-4, and 0.006 g of bentonite anti-settling agent, and add them to a ball mill jar equipped with a ball mill. Add 10 ml of deionized water, and then add appropriate amounts of organosilicon surfactant wetting agent BYK-LPC20990, ammonium acrylate dispersant BYK-LPC20992, and non-silicone defoamer BYK-LPD2165 in sequence. Ball mill at 580 rpm / min for 1 h, then add the prepared CMC solution, and ball mill at 580 rpm / min for another 1 h. Finally, add an appropriate amount of polyacrylate adhesive BYK-LPC22346, and ball mill at 580 rpm / min for 4 h to obtain the boehmite coating slurry. A simple impregnation coating method was used to coat both sides of a PP membrane with boehmite slurry. The membrane was then dried in a 50 ℃ forced-air drying oven to remove excess moisture from the membrane surface, followed by 12 h in a 50 ℃ vacuum drying oven to remove moisture from the membrane pores, thus obtaining the boehmite ceramic-coated PP membrane. Its performance parameters, including thickness, porosity, liquid absorption rate, contact angle, membrane breakage temperature, and shut-off temperature, were measured. The test results are shown in Table 2.

[0050] Table 2 Performance Tests

[0051]

[0052] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A boehmite for coating of a lithium battery separator, characterized in that The boehmite for coating the lithium battery diaphragm is prepared by the following method: (1) boehmite powder is mixed with anhydrous ethanol at a mass ratio of 1g:40ml, and ultrasonic dispersion is carried out for 10min to obtain a boehmite anhydrous ethanol dispersion liquid; (2) a silane coupling agent is weighed at 1 / 8~1 / 10 of the mass of the boehmite powder, then 1 / 20 anhydrous ethanol of the volume of the boehmite anhydrous ethanol dispersion liquid is added to form a silane coupling agent anhydrous ethanol solution, and hydrolysis is carried out at 40~45℃ for 30~35min; (3) the hydrolyzed silane coupling agent anhydrous ethanol solution is added to the boehmite anhydrous ethanol dispersion liquid at a speed of 2~3 drops per second, heated to reflux at 80℃ in an oil bath for 12h, then high-speed centrifugation is carried out, washed with anhydrous ethanol for 3~4 times, and dried at 80℃ for 48h, thereby obtaining the boehmite for coating the lithium battery diaphragm. The boehmite powder is a hollow microspherical structure boehmite prepared by the following method: a tetrahydrofuran solution containing 2.5*10 - 3 mol / L of an amphiphilic block copolymer is mixed with a 0.1 mol / L Al2(SO4)3 aqueous solution at a volume ratio of 1:5, 4 times the volume of the mixed solution is added with distilled water, 0.004 mol of urea is added, and then the reaction is carried out at a temperature of 150°C for 24h; after the reaction is completed, the temperature is quickly reduced to room temperature, and then high-speed centrifugation is carried out, and repeated washing with distilled water until there is no SO4 2- , and then washed with anhydrous ethanol for three times, to obtain the product; the amphiphilic block copolymer is polystyrene-block-poly(hydroxyethyl acrylate); The silane coupling agent is one of the secondary amino-containing monoamino silane coupling agents bis(3-triethoxysilylpropyl)amine or bis(3-trimethoxysilylpropyl)amine with a symmetric structure with N as a symmetric center.

2. The boehmite for coating of a lithium battery separator according to claim 1, characterized in that, The particle size of the boehmite powder is 0.3~0.5μm.

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