High-cohesiveness coating diaphragm and preparation method thereof

Abstract

The invention discloses a high-cohesiveness coating diaphragm and a preparation method thereof.The high-cohesiveness coating diaphragm comprises a base diaphragm and a coating on the base diaphragm, the coating comprises titanium lithium aluminum phosphate and a hydrogenated styrene-butadiene block copolymer, and the preparation method of the high-cohesiveness coating diaphragm comprises the steps that the base diaphragm is coated with slurry, extraction and drying are conducted, and the high-cohesiveness coating diaphragm is obtained. The coating is obtained on the base membrane, the high-cohesiveness coating diaphragm is obtained, and the slurry comprises ceramic, a binding agent, a pore forming agent and a slurry solvent. The heat resistance of the diaphragm, the binding power between the diaphragm and a pole piece, the breakdown voltage, the liquid absorption rate and the liquid retention rate are improved through the cooperation of the titanium lithium aluminum phosphate, the hydrogenated styrene-butadiene block copolymer and the polyacrylic acid, and the air permeability value of the diaphragm is also reduced.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a high-adhesion coated separator and its preparation method. Background Technology

[0002] Lithium-ion batteries, as traditional electrochemical energy storage and conversion devices, are widely used in the electronics industry, national power grid systems, and even electric vehicles due to their advantages such as high energy density, stable cycle performance, and rapid charge and discharge capabilities. However, with the rapid development of the new energy industry, new requirements have been placed on the cycle life, discharge rate, and rate performance of lithium-ion batteries. The separator, as a crucial component of lithium-ion batteries, directly affects battery performance. To meet these demands, developing separators with high heat resistance, low permeability, high ionic conductivity, and high adhesion is particularly important. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a highly adhesive coated diaphragm.

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned highly adhesive coated diaphragm.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] A highly adhesive coated diaphragm includes: a base membrane and a coating on the base membrane, wherein the coating includes: lithium aluminum titanium phosphate (LATP) and hydrogenated styrene-butadiene block copolymer (SEBS rubber), wherein the ratio of lithium aluminum titanium phosphate (LATP) to hydrogenated styrene-butadiene block copolymer (SEBS rubber) by mass parts is (4-8):(2-6).

[0007] In the above technical solution, the preferred ratio of lithium aluminum titanium phosphate (LATP) to hydrogenated styrene-butadiene block copolymer (SEBS rubber) by mass is (5-7):(3-5).

[0008] The above-mentioned method for preparing a high-adhesion coated diaphragm includes: coating a slurry onto a base membrane, extracting, drying, obtaining a coating on the base membrane, and obtaining a high-adhesion coated diaphragm.

[0009] In the above technical solution, the drying temperature is 30-60℃ and the drying time is 2-8 minutes.

[0010] In the above technical solution, the extraction includes: sequentially passing through extractants with extractant concentrations ranging from high to low, the extractants being a first extractant, a second extractant, a third extractant, and a fourth extractant in that order. The first, second, and third extractants are each mixtures of extractant and water, while the fourth extractant is water. The extractant concentration in the first extractant is 65–95 wt%, the extractant concentration in the second extractant is 50–65 wt%, and the extractant concentration in the third extractant is 10–50 wt%. The extractant is N-methylpyrrolidone (NMP).

[0011] In the above technical solution, the coating method is scraping.

[0012] A slurry comprising: ceramic, binder, pore-forming agent and slurry solvent, wherein the ratio of ceramic, binder and pore-forming agent by mass parts is (4-8):(2-6):(2-10).

[0013] In the above technical solution, the ceramic is one or a mixture of two of boehmite and lithium aluminum titanium phosphate (LATP), preferably lithium aluminum titanium phosphate (LATP).

[0014] In the above technical solution, the slurry solvent is one or a mixture of several of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, methanol and ethanol.

[0015] In the above technical solution, the binder is one or a mixture of several of hydrogenated nitrile rubber, polyurethane, hydrogenated styrene-butadiene block copolymer (SEBS rubber) and epoxy resin, preferably hydrogenated styrene-butadiene block copolymer (SEBS rubber).

[0016] In the above technical solution, the pore-forming agent is one or a mixture of several of dimethyl carbonate, polyacrylic acid and polyacrylonitrile, preferably polyacrylic acid.

[0017] In the above technical solution, the solid content of the slurry is 6-14 wt%.

[0018] In the above technical solution, the preferred ratio of ceramic, binder and pore-forming agent by mass parts is (5-7):(3-5):5.

[0019] The method for preparing the above-mentioned slurry includes: mixing a ceramic solution, a binder solution, a pore-forming agent, and a third solvent until homogeneous to obtain a slurry, wherein the ceramic solution comprises ceramic and a first solvent, and the solid content of the ceramic solution is 2-30 wt%; the binder solution comprises binder and a second solvent, and the solid content of the binder solution is 5-15 wt%, and the ratio of ceramic in the ceramic solution to binder and pore-forming agent in the binder solution by mass parts is (4-8):(2-6):(2-10).

[0020] In the above technical solution, the preferred ratio of ceramic in ceramic solution to binder and pore-forming agent in binder solution by mass is (5-7):(3-5):5.

[0021] The method for preparing the above-mentioned slurry specifically includes: mixing the ceramic solution and the binder solution, stirring until uniform, adding the pore-forming agent, stirring until uniform, and finally adding the third solvent to obtain the slurry.

[0022] In the above technical solution, the ceramic solution and the binder solution are mixed and stirred at a speed of 200-500 r / min for 0.5-1.5 h, then a pore-forming agent is added and stirred at a speed of 200-500 r / min for 20-40 min, and finally a third solvent is added and stirred at a speed of 200-500 r / min for 20-40 min to obtain a slurry.

[0023] In the above technical solution, the first solvent is one or a mixture of several of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, methanol and ethanol.

[0024] In the above technical solution, the second solvent is one or a mixture of several of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, methanol and ethanol.

[0025] In the above technical solution, the third solvent is one or a mixture of several of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, methanol and ethanol.

[0026] In the above technical solutions, the first solvent, the second solvent, and the third solvent may be the same or different.

[0027] In the above technical solution, the method for obtaining the ceramic solution includes: mixing ceramic (powder) and a first solvent until homogeneous to obtain the ceramic solution.

[0028] In the method for obtaining ceramic solution, ceramic (powder) and a first solvent are mixed and stirred at a speed of 200-500 r / min for 20-40 min, and then milled at a speed of 400-600 r / min for 10-30 min to obtain ceramic solution.

[0029] In the above technical solution, the method for obtaining the adhesive solution includes: mixing the adhesive and the second solvent until homogeneous to obtain the adhesive solution.

[0030] In the method for obtaining the adhesive solution, the adhesive and the second solvent are mixed and stirred until homogeneous to obtain the adhesive solution. The stirring speed is 200–500 r / min, and the stirring time is 2–6 h.

[0031] Application of lithium aluminum titanium phosphate (LATP), hydrogenated styrene-butadiene block copolymer (SEBS rubber) and polyacrylic acid to synergistically improve the heat resistance of diaphragms.

[0032] Application of lithium aluminum titanium phosphate (LATP), hydrogenated styrene-butadiene block copolymer (SEBS rubber) and polyacrylic acid to synergistically improve the adhesion between the separator and the electrode.

[0033] Application of lithium aluminum titanium phosphate, hydrogenated styrene-butadiene block copolymer and polyacrylic acid to synergistically reduce the gas permeability of the membrane.

[0034] Applications of lithium aluminum titanium phosphate, hydrogenated styrene-butadiene block copolymer and polyacrylic acid synergistically to improve membrane breakdown voltage, liquid absorption rate and / or liquid retention rate.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. Lithium aluminum titanium phosphate (LATP) is a NASICON-type lithium-ion conductor with a three-dimensional lithium-ion migration channel. It works synergistically with polyacrylic acid to improve the ionic conductivity of the membrane and increase the thermal stability of the membrane.

[0037] 2. Existing technologies commonly use PVDF as a binder. The binder used in this invention is fluorine-free, which holds promise for further achieving fluorine-free separators. In particular, hydrogenated styrene-butadiene block copolymer (SEBS rubber) has good stability and aging resistance due to the absence of unsaturated double bonds. It can increase the adhesion between the separator and the electrode, and also increase the intermolecular forces in lithium aluminum titanium phosphate (LATP), which is beneficial for improving battery cycle performance. Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0039] Adhesion force between separator and electrode: The separator is cut into pieces with a width of 25mm and a length of 150mm, and the electrode is cut into pieces with a width of 25mm and a length of 60mm. The separator and electrode are then stacked together and hot-pressed using a battery electrode press at a pressure of 1000KG, a temperature of 80℃, and a time of 1s to form a test sample. Then, a tensile testing machine is used to tear the electrode and separator of the test sample (tearing angle of 180°). The force used to tear the electrode and separator is divided by the tensile length (25mm) to obtain the adhesion force between the separator and electrode. The electrode can be either a positive or negative electrode. The adhesion force between the separator and the positive electrode is obtained from the positive electrode, and the adhesion force between the separator and the negative electrode is obtained from the negative electrode. The positive electrode material in the positive electrode is a ternary material (LiNi). 0.8 Co 0.1 Mn 0.1O2), the negative electrode material in the negative electrode sheet is graphite.

[0040] Ionic conductivity: Ionic conductivity was measured at room temperature and RH=100%.

[0041] Breathability value: Take a 1000mm*120mm diaphragm as a sample, place it on the breathability meter and test 10 points evenly (the distance between two adjacent "points" is 100mm), and take the average value of the 10 points to obtain the breathability value.

[0042] Liquid absorption rate: Weigh the 5cm×5cm diaphragm and record it as m0. After soaking it in the electrolyte for 1 hour, take it out, wipe the surface of the electrolyte with a non-woven cloth, weigh it and record it as m1. Calculate the liquid absorption rate of the diaphragm by (m1-m0) / m0*100%.

[0043] Liquid retention rate: After soaking a 5cm×5cm diaphragm in electrolyte for 1 hour, remove it, wipe the surface of electrolyte with non-woven cloth, weigh it and record it as m2. After wiping the surface of electrolyte, place it in the air for 1 hour and weigh it again and record it as m3. The liquid retention rate of the diaphragm is calculated by (m2-m3) / m3*100%.

[0044] In the following examples, the water used is deionized water.

[0045] In the following examples, the base film is a 9μm PE film.

[0046] Lithium aluminum titanium phosphate (LATP): Langgu (Changzhou) New Energy Co., Ltd., LG1115.

[0047] SEBS rubber: TSRC Corporation Limited, 6151.

[0048] Polyacrylic acid: Tianjin Oubokai Chemical Co., Ltd., analytical grade, molecular weight 800-1000.

[0049] Examples 1-3

[0050] A method for preparing a slurry includes: adding a binder solution to a ceramic solution and stirring at 300 r / min for 1 h; adding a pore-forming agent and stirring at 300 r / min for 30 min; finally adding a third solvent and stirring at 300 r / min for 30 min to obtain a slurry. The ceramic solution comprises ceramic and a first solvent, with a solid content of 20 wt%. The binder solution comprises a binder and a second solvent, with a solid content of 10 wt%. The ratio of ceramic in the ceramic solution to binder and pore-forming agent in the binder solution is X by mass. The ceramic is lithium aluminum titanium phosphate (LATP), the binder is hydrogenated styrene-butadiene block copolymer (SEBS rubber, purchased from TSRC Corporation Limited), the pore-forming agent is polyacrylic acid, the first solvent is N-methylpyrrolidone, the second solvent is N-methylpyrrolidone, the third solvent is N-methylpyrrolidone, and the solid content of the slurry is Y (wt%).

[0051] The method for obtaining the ceramic solution includes: mixing ceramic (LATP powder) and a first solvent, stirring at 300 r / min for 30 min, and then grinding in a pin mill at 500 r / min for 20 min to obtain the ceramic solution.

[0052] The method for obtaining the adhesive solution includes: mixing the adhesive and the second solvent, stirring at 300 r / min for 4 hours until homogeneous, to obtain the adhesive solution.

[0053] X and Y are shown in Table 1.

[0054] Table 1

[0055] slurry X Y(wt%) Example 1 6：4：5 10 Example 2 4：4：5 8 Example 3 6：2：5 8

[0056] Comparative Example 1

[0057] A method for preparing a slurry includes: adding a PVDF solution to a ceramic solution and stirring at 300 r / min for 1 h; adding a pore-forming agent and stirring at 300 r / min for 30 min; finally adding N-methylpyrrolidone and stirring at 300 r / min for 30 min to obtain a slurry. The ceramic solution is the same as that in Example 1. The method for obtaining the PVDF solution includes: mixing PVDF and N-methylpyrrolidone and stirring at 300 r / min for 1.5 h to obtain a PVDF solution. The solid content of the PVDF solution is 10 wt%. By mass, the ratio of ceramic in the ceramic solution to PVDF and the pore-forming agent in the PVDF solution is 6:4:5. The pore-forming agent is polyacrylic acid, and the solid content of the slurry is 10 wt%.

[0058] Comparative Example 2

[0059] A method for preparing a slurry is basically the same as that in Example 1, except that “lithium aluminum titanium phosphate (LATP)” is replaced with “alumina”.

[0060] Comparative Example 3

[0061] A method for preparing a slurry is basically the same as that in Example 1, except that polyacrylic acid is not added.

[0062] Comparative Example 4

[0063] A method for preparing a slurry is basically the same as that in Example 1, except that “SEBS rubber” is replaced with “styrene-butadiene rubber”.

[0064] Examples 4-6 and Comparative Examples 5-8

[0065] A method for preparing a diaphragm includes: coating a slurry onto a base membrane using a blade coating method, extracting the slurry, drying at 50°C for 5 minutes, and obtaining coatings (with the same thickness on both sides of the base membrane) to obtain a diaphragm. The extraction process includes: sequentially passing the diaphragm through extractants of decreasing concentrations, namely a first extractant, a second extractant, a third extractant, and a fourth extractant. The first, second, and third extractants are each mixtures of extractant and water, while the fourth extractant is water. The extractant concentration in the first extractant is 80 wt%, in the second extractant is 60 wt%, and in the third extractant is 25 wt%. The extractant is N-methylpyrrolidone (NMP). The slurry is one of Examples 1-3 and Comparative Examples 1-4. The diaphragm prepared from the slurries of Examples 1-3 is a highly adhesive coated diaphragm.

[0066] Table 2

[0067] diaphragm The slurry used to prepare the diaphragm Example 4 Example 1 Example 5 Example 2 Example 6 Example 3 Comparative Example 5 Comparative Example 1 Comparative Example 6 Comparative Example 2 Comparative Example 7 Comparative Example 3 Comparative Example 8 Comparative Example 4

[0068] The test data of the membranes prepared in Examples 4-6 and Comparative Examples 5-8 are as follows:

[0069] Table 3

[0070]

[0071]

[0072] Table 3 shows that the separator prepared in Example 4 has the highest ionic conductivity, the highest adhesion between the separator and the positive electrode, and the highest adhesion between the separator and the negative electrode, while having the lowest air permeability and thermal shrinkage, resulting in the best overall performance. In Comparative Example 3, polyacrylic acid was not added to the slurry, leading to a very high air permeability in the separator prepared in Comparative Example 7, which is detrimental to improving battery performance.

[0073] The present invention achieves superior overall performance of the diaphragm through the synergistic effect of lithium aluminum titanium phosphate (LATP), SEBS rubber and polyacrylic acid. Removing or replacing any one of them cannot achieve the effect of the high-adhesion coating diaphragm of the present invention.

[0074] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A high-adhesion coated diaphragm, characterized in that, include: The base film and the coating on the base film, wherein the coating comprises: lithium aluminum titanium phosphate and hydrogenated styrene-butadiene block copolymer, wherein the ratio of lithium aluminum titanium phosphate and hydrogenated styrene-butadiene block copolymer by mass is (4-8):(2-6).

2. A slurry, characterized in that, include: The ceramic, binder, pore-forming agent and slurry solvent are in the following proportions by mass: (4-8):(2-6):(2-10), and the ceramic is one or a mixture of two of boehmite and lithium aluminum titanium phosphate.

3. The slurry according to claim 2, characterized in that, The adhesive is one or a mixture of several of hydrogenated nitrile rubber, polyurethane, hydrogenated styrene-butadiene block copolymer and epoxy resin; the pore-forming agent is one or a mixture of several of dimethyl carbonate, polyacrylic acid and polyacrylonitrile.

4. The slurry according to claim 2, characterized in that, The solid content of the slurry is 6-14 wt%.

5. A method for preparing the slurry according to claim 2, characterized in that, include: A ceramic solution, a binder solution, a pore-forming agent, and a third solvent are mixed until homogeneous to obtain a slurry. The ceramic solution comprises ceramic and a first solvent, and the solid content of the ceramic solution is 2-30 wt%. The binder solution comprises binder and a second solvent, and the solid content of the binder solution is 5-15 wt%. The ratio of ceramic in the ceramic solution to binder and pore-forming agent in the binder solution is (4-8):(2-6):(2-10) by mass.

6. A method for preparing a highly adhesive coated diaphragm, characterized in that, include: The slurry described in claim 2 is coated onto a base membrane, extracted, and dried to obtain a coating on the base membrane, resulting in a highly adhesive coated diaphragm.

7. Application of lithium aluminum titanium phosphate, hydrogenated styrene-butadiene block copolymer and polyacrylic acid to synergistically improve the heat resistance of diaphragms.

8. Application of lithium aluminum titanium phosphate, hydrogenated styrene-butadiene block copolymer and polyacrylic acid to synergistically improve the adhesion between the separator and the electrode.

9. Application of lithium aluminum titanium phosphate, hydrogenated styrene-butadiene block copolymer and polyacrylic acid synergistically to reduce the gas permeability of the diaphragm.

10. Applications of lithium aluminum titanium phosphate, hydrogenated styrene-butadiene block copolymer and polyacrylic acid in synergistic improvement of membrane breakdown voltage, liquid absorption rate and / or liquid retention rate.

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