Hydrophobic nano-alumina powder for battery separator and preparation method thereof, battery separator

Abstract

The application belongs to the technical field of battery separators, and particularly relates to a hydrophobic nano-aluminum oxide powder for a battery separator, a preparation method thereof and a battery separator. The hydrophobic nano-aluminum oxide powder for a battery separator, the preparation method thereof and the battery separator first perform a primary coating on the aluminum oxide through the adsorption capacity of carbon powder, and then perform a secondary coating on the coated powder by using a hydrophobic material. After the coating is completed, the carbon powder is burned off based on the ignition point difference between the carbon powder and the hydrophobic material, pores are left on the secondary coating layer by releasing gas, and semi-coated aluminum oxide powder is formed, so that the small particle size advantage of the aluminum oxide powder can be better exerted, and the disadvantage brought by the large specific surface area can be avoided. The moisture absorption of the powder can be effectively reduced, the water content of the coated separator can be reduced, the powder can be fully dispersed during the slurry preparation process, the adsorption capacity of the powder to the electrolyte is also taken into account, the liquid absorption rate of the separator is maintained, and finally the effects of lightening the separator and improving the energy density of the battery are achieved.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a hydrophobic nano-alumina powder for battery separators, its preparation method, and a battery separator. Background Technology

[0002] In recent years, battery separator ceramic coating technology has made significant progress, with marked improvements in separator performance such as safety, thermal stability, and wettability, further promoting battery performance optimization. One of the main development directions for separators is to make the coated separator lighter and improve its energy density. Current solutions primarily focus on the introduction and use of nano-alumina powder. By reducing the size of the coating powder and further controlling the coating thickness, lightweighting is achieved. Furthermore, reducing the coating thickness allows for a larger electrolyte layer, thereby increasing energy density.

[0003] The advantages of nano-alumina are obvious, but its disadvantages are also significant, mainly in two aspects. First, the material itself: due to the presence of dangling bonds, alumina molecules readily absorb moisture, leading to increased water content in the separator during coating. Increased water content hinders the retention of lithium salts in the electrolyte, ultimately degrading battery performance. Second, the particle size of alumina matters. As the particle size decreases, the specific surface area increases rapidly, significantly amplifying the water adsorption effect of dangling bonds. While this effect can be controlled when using micron- or submicron-sized alumina powders for coating, it is unavoidable at the nanoscale. Furthermore, the increased specific surface area also hinders powder dispersion in solvents, affecting subsequent coating results.

[0004] To address the aforementioned issues, patent CN111630686A discloses a composite separator, its preparation method, and a lithium battery including the composite separator. This method uses a silane coupling agent to coat nano-alumina powder, achieving oleophilic and hydrophobic modification, which effectively reduces the water absorption content on the powder surface. However, in this method, because the powder surface is completely coated, the separator's ability to absorb electrolyte is significantly reduced, thus affecting the subsequent battery performance. Summary of the Invention

[0005] The purpose of this invention is to provide a hydrophobic nano-alumina powder for battery separators, its preparation method, and a battery separator.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing semi-hydrophobic nano-alumina powder, comprising: coating nano-alumina powder with carbon black to obtain a first mixed powder; coating the first mixed powder with active silane to obtain a second mixed powder; sintering the second mixed powder to remove the carbon black, thereby obtaining semi-hydrophobic nano-alumina powder.

[0007] In one embodiment of this application, the method of coating nano-alumina powder with carbon black to obtain a first mixed powder includes:

[0008] 100 parts by weight of α-alumina powder with a particle size of 50-150 nm were mixed with water to form a first mixture with a solid content of 15-25%. Then, 5-15 parts by weight of carbon black were added, and the mixture was stirred, dispersed, and dried to obtain the first mixed powder.

[0009] In one embodiment of this application, the method of coating the first mixed powder with active silane to obtain the second mixed powder includes:

[0010] Weigh out the first mixed powder, citric acid accounting for 1.4%-3.6% of the weight of α-alumina powder, and disodium hydrogen phosphate accounting for 5.1%-7.9% of the weight of α-alumina powder, and fully disperse them in water to prepare a second mixed solution with a solid content of 15-25%.

[0011] Place the second mixture in a constant temperature water bath at 25-50℃, slowly add active silane, the amount of which is 30%-70% of the amount of α-alumina powder, and continue stirring for 10-30 minutes. After the reaction is complete, dry the mixture.

[0012] The dried powder is placed in a crucible and sintered at 270–320°C for 0.5–2 hours. After sintering, semi-hydrophobic nano-alumina powder is obtained.

[0013] In one embodiment of this application, the carbon black is channel black with a particle size of 26-30 nm.

[0014] In one embodiment of this application, the pH value of the second mixture is 5.2 to 7.0.

[0015] In one embodiment of this application, the general formula of the active silane is RnSiX4-n.

[0016] In one embodiment of this application, the active silane includes one of trimethyldisilazane, trimethylethoxysilane, and trimethylsilanol.

[0017] Accordingly, the present invention provides a semi-hydrophobic nano-alumina powder, which is prepared by the preparation method of semi-hydrophobic nano-alumina powder as described above, comprising: α-alumina powder, and a semi-hydrophobic layer coating the outer layer of the α-alumina powder; wherein the particle size of the α-alumina powder is 50-150 nm; and the particle size of the semi-hydrophobic nano-alumina powder is 200-300 nm.

[0018] Accordingly, the present invention provides a battery separator, comprising: a substrate, and semi-hydrophobic nano-alumina powder coated on the substrate; the water content of the battery separator is less than 1200 ppm; and the liquid absorption rate of the separator is greater than 2.5 g / m³. 2 .

[0019] In one embodiment of this application, the substrate is made of PP, PE, or PP / PE composite material, etc.; the coating thickness of the semi-hydrophobic nano-alumina powder on the substrate is 0.5-1.5 μm.

[0020] The beneficial effects of this invention are as follows: the hydrophobic nano-alumina powder for battery separators and its preparation method are as follows: the battery separator first coats the alumina with the adsorption capacity of carbon powder, and then coats the coated powder with a hydrophobic material. After coating, based on the difference in ignition point between carbon powder and hydrophobic material, the carbon powder is burned off, and by releasing gas, pores are left on the double coating layer, forming a semi-coated alumina powder. This allows it to better utilize its small particle size advantage and avoid the disadvantages of large specific surface area. It can effectively reduce the hygroscopicity of the powder, reduce the water content of the coated separator, and facilitate the full dispersion of the powder during the slurry preparation process. At the same time, it also takes into account the adsorption capacity of the powder for electrolyte, maintains the liquid absorption rate of the separator, and ultimately achieves the effect of lightweight separator and improved battery energy density.

[0021] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained in accordance with the structures particularly pointed out in the description, claims and drawings.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a flowchart of the preparation method of hydrophobic nano-alumina powder for battery separators according to the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a method for preparing semi-hydrophobic nano-alumina powder, comprising: coating nano-alumina powder with carbon black to obtain a first mixed powder; coating the first mixed powder with active silane to obtain a second mixed powder; sintering the second mixed powder to remove carbon black and obtain semi-hydrophobic nano-alumina powder.

[0027] Specifically, the method of coating nano-alumina powder with carbon black to obtain the first mixed powder includes: preparing 100 parts by weight of α-alumina powder with a particle size of 50-150 nm with water to form a first mixed solution with a solid content of 15-25%; adding 5-15 parts by weight of carbon black; stirring and dispersing; and drying at a temperature of 70-85°C to obtain the first mixed powder.

[0028] Optionally, the carbon black can be channel black with a particle size of 26–30 nm.

[0029] Specifically, the method for coating the first mixed powder with active silane to obtain the second mixed powder includes:

[0030] Weigh out the first mixed powder, citric acid accounting for 1.4%-3.6% of the weight of α-alumina powder, and disodium hydrogen phosphate accounting for 5.1%-7.9% of the weight of α-alumina powder, and fully disperse them in water to prepare a second mixed solution with a solid content of 15-25%.

[0031] The second mixture is placed in a constant temperature water bath at 25-50℃, and active silane is slowly added dropwise for coating. The amount added is 30%-70% of the amount of α-alumina powder. The coating process requires continuous stirring for 10-30 minutes. After the reaction is completed, the mixture is dried at a temperature of 100-105℃.

[0032] The dried powder is placed in a crucible and sintered at 270–320°C for 0.5–2 hours. After sintering, semi-hydrophobic nano-alumina powder is obtained.

[0033] It should be noted that the pH value of the second mixture is 5.2 to 7.0, which can improve the coating effect.

[0034] Optionally, the active silane can be selected from one or more of the general formula RnSiX4-n, such as trimethyldisilazane, trimethylethoxysilane, and trimethylsilanol; the active silane can also be an organic material hydrolyzed into the RnSiX4-n type, but materials with halogen groups (such as chlorosilanes) should be avoided.

[0035] Optionally, when preparing the first and second mixtures, the stirring equipment can be a magnetic stirrer, a disperser, or other dispersing device, with a rotation speed of 1500 r / min to 2000 r / min.

[0036] It should be noted that in the method of coating the first mixed powder with active silane to obtain the second mixed powder, the active silane is added drop by drop every 8-15 seconds for reaction. The stirring equipment can be a magnetic stirrer, a disperser or other dispersing device. The rotation speed can be adjusted to 300r / min-600r / min during coating.

[0037] The following are specific preparation examples and comparative examples:

[0038] Example 1

[0039] Weigh 20g of α-alumina powder with a particle size of 50nm, add 1g of channel black and 80g of water, stir thoroughly using a disperser and dry at 70℃ to obtain the first mixed powder;

[0040] Weigh 0.71g of citric acid powder and 1.03g of disodium hydrogen phosphate powder and prepare a buffer solution in 80ml of water. The pH value is 5.2. Add 21g of the prepared mixed powder and stir thoroughly with a disperser at a speed of 2500r / min. After thorough dispersion, reduce the disperser speed to 600r / min and add a water bath to control the temperature at 50℃. Add 22.1g of hexamethyldisilazane (70% of the alumina content) dropwise at a rate of 8 drops per second. After dispersing for 30 minutes, transfer the coated mixture to an oven for drying and then to a muffle furnace for calcination at 270℃ for 0.5 hours to obtain semi-hydrophobic nano-alumina powder with a particle size of 259nm.

[0041] Example 2

[0042] Weigh 20g of α-alumina powder with a particle size of 100nm, add 2g of channel black and 80g of water, stir thoroughly using a disperser and then dry at 80℃ to obtain the first mixed powder.

[0043] Weigh 0.57g of citric acid powder and 1.21g of disodium hydrogen phosphate powder and prepare a buffer solution in 80ml of water. The pH value is 6.0. Add 22g of the prepared mixed powder and stir thoroughly with a magnetic stirrer at a speed of 2000r / min. After thorough dispersion, reduce the speed of the stirrer to 500r / min and add a water bath to control the temperature at 40℃. Add 11.7g of trimethylethoxysilane (50% of the alumina content) dropwise at a rate of 10 drops per 10 seconds. After dispersing for 20 minutes, transfer the coated mixture to an oven for drying and then to a muffle furnace to calcine at 300℃ for 1 hour to obtain semi-hydrophobic nano-alumina powder with a particle size of 249nm.

[0044] Example 3

[0045] Weigh 20g of α-alumina powder with a particle size of 150nm, add 3g of channel black and 80g of water, stir thoroughly using a disperser and then dry at 85℃ to obtain the first mixed powder.

[0046] Weigh 0.27g of citric acid powder and 1.58g of disodium hydrogen phosphate powder and prepare a buffer solution in 80ml of water. The pH value is 7.0. Add 23g of the prepared mixed powder and stir thoroughly with a magnetic stirrer at a speed of 1500r / min. After thorough dispersion, reduce the speed of the stirrer to 400r / min and add a water bath to control the temperature at 25℃. Add 5.3g of trimethylsilanol (30% of the alumina content) dropwise at a rate of 15 seconds per drop. After dispersing for 10 minutes, transfer the coated mixture to an oven for drying and then to a muffle furnace to calcine at 320℃ for 1 hour to obtain semi-hydrophobic nano-alumina powder with a particle size of 276nm.

[0047] Comparative Example 1

[0048] α-alumina powder with a particle size of 270±30nm is not coated and is referred to as powder A.

[0049] Comparative Example 2

[0050] Preparation of fully coated alumina powder B:

[0051] Weigh 0.27g of citric acid powder and 1.58g of disodium hydrogen phosphate powder into 80ml of water to prepare a buffer solution with a pH of 7.0. Add 20g of α-alumina powder with a particle size of 250nm and stir thoroughly with a magnetic stirrer at a speed of 1500r / min. After thorough dispersion, reduce the speed of the stirrer to 400r / min and add a water bath to control the temperature at 25℃. Add 5.3g of trimethylsilanol (30% of the alumina mass) dropwise at a rate of 15 seconds per drop. After dispersing for 10min, transfer the coated mixture to an oven for drying to obtain hydrophobic nano-alumina powder with a particle size of 287nm.

[0052] test

[0053] Three powders prepared in Examples 1-3 were selected for comparative experiments, along with uncoated raw powder A and fully coated alumina powder B. The particle size of all powders was controlled within 270±30nm.

[0054] First, the test powder, dispersant (polyacrylic acid, 0.1% by weight of powder), adhesive (LIB-S105 glue, 5% by weight of slurry), wetting agent (BYK-ET3030 wetting agent, 2% by weight of slurry), and suspending agent (CMC, 0.6% by weight of powder) were mixed with water using a disperser to prepare a slurry with a solid content of 20%. The prepared slurry was then coated onto a 7μm thick PP membrane using a micro-grooved roller coater, resulting in a coating thickness of 1.5μm. After the membrane was fabricated, water absorption rate and electrolyte absorption rate were tested, and the results are shown in the table below.

[0055] Powder Solution Membrane moisture content (ppm) <![CDATA[Liquid absorption rate of diaphragm (g / m 2 )]]> A 1636 3.82 B 931 1.51 Example 1 1137 2.87 Example 2 1197 3.01 Example 3 1233 3.17

[0056] As shown in the table, the hydrophobic nano-alumina powder for battery separators of the present invention and its preparation method involve firstly coating the alumina with the adsorption capacity of carbon powder, and then coating the coated powder with a hydrophobic material. After coating, based on the difference in ignition point between carbon powder and hydrophobic material, the carbon powder is burned off, and by releasing gas, pores are left on the double coating layer, forming a semi-coated alumina powder. This allows the powder to better utilize its small particle size advantage and avoid the disadvantages of large specific surface area. It can effectively reduce the hygroscopicity of the powder, reduce the water content of the coated separator, and facilitate the full dispersion of the powder during the slurry preparation process. At the same time, it also takes into account the adsorption capacity of the powder for electrolyte, maintains the liquid absorption rate of the separator, and ultimately achieves the effect of lightweight separator and improved battery energy density.

[0057] It should be noted that the water absorption rate test was conducted according to the Karl Fischer moisture determination method based on the national standard GB / T6283-2008. The method for testing the electrolyte absorption rate of the diaphragm is as follows: three 100*100mm samples were cut from the diaphragm to be tested, with the side length accurate to 1mm, and the area was recorded as S. The samples were weighed and recorded as M1, with the value accurate to 0.01g. The samples were then immersed in the electrolyte for 10±0.5min, and then removed by holding one corner with tweezers. After suspending the samples for 3min to drip off excess electrolyte, the samples were weighed and recorded as M2, with the value accurate to 0.01g. After the test, the absorption rate (g / m2) was calculated according to the formula: (M2-M1) / S. The average absorption rate of the three samples was then taken as the absorption rate of the diaphragm to be tested.

[0058] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing semi-hydrophobic nano-alumina powder, characterized in that, The preparation method comprises the following steps: coating the nano-alumina powder with carbon black to obtain a first mixed powder; coating the first mixed powder with active silane to obtain a second mixed powder; sintering the second mixed powder to remove the carbon black, and obtaining the semi-hydrophobic nano-alumina powder; The method for coating the nano-alumina powder with carbon black to obtain the first mixed powder comprises the following steps: configuring 100 parts of the alpha-alumina powder with a particle size of 50-150 nm and water into a first mixed solution with a solid content of 15-25%, and then adding 5-15 parts of carbon black, stirring and dispersing, and drying to obtain the first mixed powder; The method for coating the first mixed powder with active silane to obtain the second mixed powder comprises the following steps: weighing the first mixed powder, 1.4-3.6% of citric acid based on the weight of the alpha-alumina powder, and 5.1-7.9% of disodium hydrogen phosphate based on the weight of the alpha-alumina powder, and dispersing them in water to configure a second mixed solution with a solid content of 15-25%; placing the second mixed solution in a constant-temperature water bath at 25-50°C, slowly adding active silane in an amount of 30-70% of the amount of substance of the alpha-alumina powder, and continuously stirring for 10-30 min until the reaction is completed, and then drying; placing the dried powder in a crucible, sintering at 270-320°C for 0.5-2 h, and obtaining the semi-hydrophobic nano-alumina powder after sintering; The carbon black is channel black with a particle size of 26-30 nm. The PH value of the second mixed solution is 5.2-7.

0.

2. The preparation method according to claim 1, wherein The active silane has a general formula of RnSiX4-n.

3. The preparation method according to claim 2, wherein The active silane comprises one of trimethyl disilazane, trimethylethoxysilane and trimethylsilanol.

4. A semi-hydrophobic nano-alumina powder, prepared by the method of any one of claims 1 to 3, characterized in that, The preparation method comprises the following steps: alpha-alumina powder, and a semi-hydrophobic layer coated on the outer layer of the alpha-alumina powder; The particle size of the alpha-alumina powder is 50-150 nm. The particle size of the semi-hydrophobic nano-alumina powder is 200-300 nm. The preparation method comprises the following steps:

5. A battery separator characterized by, a substrate, and the semi-hydrophobic nano-alumina powder coated on the substrate according to claim 4; 6. The battery separator according to claim 5, wherein The battery separator has a moisture content of less than 1200 ppm; and a liquid uptake of greater than 2.5 g / m 2 . The substrate is made of PP material, PE material or PP / PE composite material. The coating thickness of the semi-hydrophobic nano-alumina powder on the substrate is 0.5-1.5 μm. ​

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