Polyamic acid binder and low-moisture lithium ion battery diaphragm

Abstract

The invention provides a polyamic acid binder and a low-moisture lithium ion battery diaphragm. The binder is obtained by carrying out condensation polymerization on a diamine monomer containing sulfonic diamine and fluorine-containing diamine and a dianhydride monomer, and then carrying out condensation polymerization on the obtained product and a ternary amine. According to the polyamic acid binder and the low-moisture lithium ion battery diaphragm provided by the invention, the hydrophobic polyamic acid binder is selected to form the lithium ion battery diaphragm, so that the heat resistance of the obtained diaphragm can be improved, the short circuit risk caused by shrinkage of the diaphragm at high temperature is reduced, the moisture content of the obtained diaphragm can be reduced, and the service life of the lithium ion battery diaphragm is prolonged. And the use safety of the diaphragm is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a polyamic acid binder and a low-moisture lithium-ion battery separator. Background Art

[0002] With the development of the separator market, inorganic ceramic coated separators are gaining increasing attention from the scientific and industrial communities due to their excellent properties, including thermal stability, chemical stability, and high strength. Coated separators are widely used because they can significantly improve the overall performance of lithium-ion batteries. Traditional uncoated separators are mostly made of polypropylene and polyethylene, both of which are hydrophobic materials with low moisture content, so lithium battery manufacturers have not paid much attention to their moisture content.

[0003] However, with increasing demands for battery safety, the market is placing higher demands on new technologies such as coated separators. Existing coated separators primarily consist of a coating layer made by dissolving an inorganic ceramic material and an organic binder in deionized water or other organic solvents. Because both inorganic ceramic materials and organic binders readily absorb moisture, the coating process increases the moisture content of the coated separator. Consequently, blindly using these separators without considering their moisture content can be extremely risky. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a polyamic acid binder and a low-moisture lithium-ion battery separator. By selecting a hydrophobic polyamic acid binder to form a lithium-ion battery separator, not only can the heat resistance of the obtained separator be improved, thereby reducing the risk of short circuit caused by shrinkage of the separator at high temperature, but also the moisture content of the obtained separator can be reduced, greatly improving the safety of the separator.

[0005] The present invention provides a polyamic acid binder, which is obtained by polycondensing a diamine monomer comprising a sulfonic acid group-containing diamine and a fluorine-containing diamine with a dianhydride monomer, and then polycondensing the monomer with a ternary amine.

[0006] In the present invention, since the polyamic acid adhesive is formed by condensing a diamine monomer including a sulfonic acid diamine and a fluorine-containing diamine with a dianhydride monomer, the molecular chain of the obtained polyamic acid adhesive contains a large number of rigid and stable benzene ring structures, thereby exhibiting more excellent heat resistance; it also contains a highly polar sulfonic acid group, which can be combined with ceramic powder through a strong hydrogen bond effect and bonding action, greatly enhancing the adhesion performance between ceramic powders; more importantly, it contains a hydrophobic fluorine-containing group, thereby enhancing the hydrophobicity of the ceramic coating layer and reducing the overall water absorption rate of the obtained diaphragm, thereby greatly improving the safety of the battery diaphragm.

[0007] Preferably, the sulfonic acid group-containing diamine is at least one of 2,4-diaminobenzenesulfonic acid, 2,5-diaminobenzenesulfonic acid, 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid or 4,4′-diaminostilbene-2,2′-disulfonic acid;

[0008] Preferably, the sulfonic acid group-containing diamine accounts for 25-50% of the molar amount of the diamine monomer.

[0009] Preferably, the fluorine-containing diamine is at least one of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl or 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether;

[0010] Preferably, the fluorine-containing diamine accounts for 20-45% of the molar amount of the diamine monomer.

[0011] Preferably, the dianhydride monomer is at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenylethertetracarboxylic dianhydride or hexafluorodianhydride;

[0012] Preferably, the diamine monomer further comprises other diamine monomers, and the other diamine monomers are at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone or 4,4'-diaminobenzophenone.

[0013] Preferably, the triamine is at least one of tris(4-aminophenyl)amine, tris(2-aminoethyl)amine, 1,3,5-triaminobenzene or 1,3,5-tris(4-aminophenyl)benzene.

[0014] In the present invention, a diamine monomer including a sulfonic acid diamine and a fluorine-containing diamine is subjected to a condensation reaction with a dianhydride monomer to obtain a linear polyamic acid, which is then subjected to a condensation reaction with a ternary amine to obtain a branched fluorine-containing polyamic acid. Thus, a polyamic acid adhesive with strong polarity and a branched cross-linked structure is obtained, which not only has excellent adhesive properties but also good hydrophobic properties.

[0015] The present invention also provides a low-moisture lithium-ion battery separator, comprising a base film and a coating layer located on one or both sides of the base film;

[0016] The coating layer includes ceramic powder and the polyamic acid binder.

[0017] Preferably, the ceramic powder is at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, silicon carbide or magnesium nitride;

[0018] Preferably, the mass ratio of the ceramic powder to the polyamic acid binder is 10-30:1.

[0019] Preferably, the coating layer further comprises fluorinated polyimide fibers and / or fluorinated polyimide microspheres;

[0020] Preferably, the fluorinated polyimide fibers or fluorinated polyimide microspheres are obtained by subjecting a diamine monomer including a fluorinated diamine to a dianhydride monomer through a condensation reaction, followed by electrostatic spinning or electrostatic spraying to form polyamic acid fibers or microspheres, and then performing a high-temperature heating treatment.

[0021] Preferably, the base film is a polyolefin film, preferably at least one of a polyethylene single-layer film, a polypropylene single-layer film, a polyethylene-polypropylene-polyethylene three-layer film or a polypropylene-polyethylene-polypropylene three-layer film.

[0022] Preferably, the coating layer is obtained by coating a slurry comprising ceramic powder, polyamic acid binder and solvent on one or both sides of the base film and then drying the slurry.

[0023] Preferably, the solvent is at least one of water, ethanol, ethylene glycol, glycerol, N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone.

[0024] The present invention proposes a polyamic acid binder and a low-moisture lithium-ion battery separator. The polyamic acid binder is selected to prepare the lithium-ion battery separator, which not only enables the lithium-ion battery separator to obtain good heat resistance, but also greatly improves the adhesion between the ceramic coating layer and the base film, and can also effectively improve the hydrophobicity of the separator, thereby preventing battery safety risks, increasing the service life of the lithium-ion battery, and optimizing the performance of the lithium-ion battery. DETAILED DESCRIPTION

[0025] Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration only and are not to be construed as limiting the scope of the present invention.

[0026] Example 1

[0027] A low-moisture lithium-ion battery separator is prepared by the following method:

[0028] (1) Polyamic acid binder: Under nitrogen protection, 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) were added to N-methylpyrrolidone (NMP, 20 mL) and stirred to dissolve completely. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (10 mmol) was added and stirred at room temperature for 4 h to obtain a linear polyamic acid solution. A solution of tris(4-aminophenyl)amine (0.2 mmol) in NMP (10 mL) was added and stirred for 2 h. The resulting reaction solution was added to acetone for precipitation, filtered, washed and dried to obtain a polyamic acid binder.

[0029] (2) Low-moisture lithium-ion battery separator: Aluminum oxide powder (average particle size of 0.5 μm) and the above-mentioned polyamic acid binder are added to water at a mass ratio of 25:1 and stirred and dispersed evenly to obtain a ceramic slurry (solid content of 35 wt%). The ceramic slurry is coated on one side of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) by gravure roller coating, and dried at 60°C to form a coating layer (thickness of 4 μm) to obtain the low-moisture lithium-ion battery separator.

[0030] Example 2

[0031] A low-moisture lithium-ion battery separator is prepared by the method described in Example 1, except that in step (1), 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) are replaced by 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid (3.5 mmol), 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (3.0 mmol) and p-phenylenediamine (3.3 mmol), and 3,3',4,4'-biphenyltetracarboxylic dianhydride is replaced by pyromellitic dianhydride.

[0032] Example 3

[0033] A low-moisture lithium-ion battery separator is prepared by the method described in Example 1, except that in step (1), 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) are replaced by 4,4'-diaminostilbene-2,2'-disulfonic acid (3.5 mmol), 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (3.0 mmol) and 4,4'-diaminodiphenylmethane (3.3 mmol), and 3,3',4,4'-biphenyltetracarboxylic dianhydride is replaced by 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

[0034] Example 4

[0035] A low-moisture lithium-ion battery separator is prepared by the method described in Example 1, except that in step (1), 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) are replaced by 2,4-diaminobenzenesulfonic acid (2.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (4.5 mmol) and 4,4'-diaminodiphenyl ether (2.8 mmol).

[0036] Example 5

[0037] A low-moisture lithium-ion battery separator is prepared by the method described in Example 1, except that in step (1), 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) are replaced by 2,4-diaminobenzenesulfonic acid (5.0 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2.0 mmol) and 4,4'-diaminodiphenyl ether (2.8 mmol).

[0038] Example 6

[0039] A low-moisture lithium-ion battery separator is prepared by the method described in Example 1, except that in step (1), tris(4-aminophenyl)amine (0.2 mmol) is replaced by 1,3,5-triaminobenzene (0.2 mmol).

[0040] Example 7

[0041] A low-moisture lithium-ion battery separator is prepared by the following method:

[0042] (1) Polyamic acid binder: Under nitrogen protection, 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) were added to N-methylpyrrolidone (NMP, 20 mL) and stirred to dissolve completely. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (10 mmol) was added and stirred at room temperature for 4 h to obtain a linear polyamic acid solution. A solution of tris(4-aminophenyl)amine (0.2 mmol) in NMP (10 mL) was added and stirred for 2 h. The resulting reaction solution was added to acetone for precipitation, filtered, washed and dried to obtain a polyamic acid binder.

[0043] (2) Fluoropolyimide microspheres: Under nitrogen protection, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (10 mmol) and pyromellitic dianhydride (10 mmol) were added to N,N-dimethylformamide (DMF, 30 mL) and stirred to dissolve completely. After stirring and reacting for 5 h under nitrogen protection, a polyamic acid solution was obtained. The polyamic acid solution was electrostatically sprayed in an electric field with an electric field strength of 1 kV / cm to obtain polyamic acid microspheres. The polyamic acid microspheres were heated to 350°C at a heating rate of 5°C / min and kept warm for thermal imidization treatment for 1 h to obtain fluorinated polyimide microspheres (average diameter of 0.6 μm);

[0044] (3) Low-moisture lithium-ion battery separator: Aluminum oxide powder (average particle size of 0.5 μm), the above-mentioned fluorinated polyimide microspheres and the above-mentioned polyamic acid binder are added to water in a mass ratio of 20:5:1 and stirred and dispersed evenly to obtain a ceramic slurry (solid content of 35 wt%). The ceramic slurry is coated on one side of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) by gravure roller coating, and dried at 60°C to form a coating layer (thickness of 4 μm) to obtain the low-moisture lithium-ion battery separator.

[0045] Example 8

[0046] A low-moisture lithium-ion battery separator is prepared by the following method:

[0047] (1) Polyamic acid binder: Under nitrogen protection, 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) were added to N-methylpyrrolidone (NMP, 20 mL) and stirred to dissolve completely. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (10 mmol) was added and stirred at room temperature for 4 h to obtain a linear polyamic acid solution. A solution of tris(4-aminophenyl)amine (0.2 mmol) in NMP (10 mL) was added and stirred for 2 h. The resulting reaction solution was added to acetone for precipitation, filtered, washed and dried to obtain a polyamic acid binder.

[0048] (2) Fluorinated polyimide fiber: Under nitrogen protection, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (10 mmol) was added to N,N-dimethylformamide (DMF, 30 mL). After complete dissolution by stirring at room temperature, 3,3',4,4'-biphenyltetracarboxylic dianhydride (10 mmol) was added. After stirring and reacting at room temperature for 4 h, the obtained polyamic acid solution was electrospun under the conditions of a spinning voltage of 25 kV, a propulsion rate of 0.8 mL / h, and a receiving distance of 20 cm. The obtained polyamic acid nanofibers were heated to 100°C, 200°C, and 300°C in stages and then subjected to thermal imidization treatment for 1 h, respectively, to obtain fluorinated polyimide fibers (average diameter of 0.3 μm);

[0049] (3) Low-moisture lithium-ion battery separator: Aluminum oxide powder (average particle size of 0.5 μm), the above-mentioned fluorinated polyimide fiber and the above-mentioned polyamic acid binder are added to water in a mass ratio of 20:5:1 and stirred and dispersed evenly to obtain a ceramic slurry (solid content of 35 wt%). The ceramic slurry is coated on one side of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) by gravure roller coating, and dried at 60°C to form a coating layer (thickness of 4 μm) to obtain the low-moisture lithium-ion battery separator.

[0050] Comparative Example 1

[0051] A low-moisture lithium-ion battery separator is prepared by the method described in Example 1, except that in step (1), 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) are replaced by 4,4'-diaminodiphenyl ether (9.8 mmol).

[0052] Comparative Example 2

[0053] A low-moisture lithium-ion battery separator is prepared by the method described in Example 1, except that in step (1), 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) are replaced by 2,4-diaminobenzenesulfonic acid (3.5 mmol) and 4,4'-diaminodiphenyl ether (6.3 mmol).

[0054] Comparative Example 3

[0055] A low-moisture lithium-ion battery separator is prepared by the method described in Example 1, except that in step (1), 2,4-diaminobenzenesulfonic acid (3.5 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (3.3 mmol) are replaced by 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3.0 mmol) and 4,4'-diaminodiphenyl ether (6.8 mmol).

[0056] Performance testing:

[0057] The lithium-ion battery separators obtained in the above examples and comparative examples were tested for thermal shrinkage, moisture content and battery performance, and the test results are shown in Table 1.

[0058] Thermal shrinkage is tested according to GB / T36363-2018; moisture content is tested according to GB / T 6324.8-2014.

[0059] The battery performance is as follows: lithium iron phosphate is used as the positive electrode active material, mixed with conductive carbon black (conductive agent) and polyvinylidene fluoride (binder) in a mass ratio of 96:2:2, added to N-methylpyrrolidone to form a slurry, and then coated on one side of aluminum foil, dried, and rolled to obtain a positive electrode sheet; graphite is used as the negative electrode active material, mixed with conductive carbon black (conductive agent) and sodium carboxymethyl cellulose (binder) in a mass ratio of 96:2:2, added to deionized water to form a slurry, and then coated on one side of copper foil, dried, and rolled to obtain a negative electrode sheet; A positive electrode sheet, a negative electrode sheet and a lithium-ion battery separator were assembled into a lithium-ion battery, and an electrolyte (1 mol / L lithium hexafluorophosphate electrolyte, a solvent consisting of ethylene carbonate EC, dimethyl carbonate DMC and ethyl methyl carbonate EMC in a volume ratio of 1:1:1) was injected. After standing, a lithium-ion battery was obtained. The battery was charged to 80% SOC at a rate of 1 C at 25° C., charged to 3.5 V at a rate of 0.5 C, charged to 3.65 V at a rate of 0.1 C, and discharged to 2.5 V at a rate of 1 C. The capacity retention rate after 500 cycles was measured.

[0060] Table 1 Performance test results of the lithium-ion battery separators described in Examples and Comparative Examples

[0061]

[0062]

[0063] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A polyamic acid binder, characterized in that The binder is obtained by polycondensing a diamine monomer comprising a sulfonic acid group-containing diamine and a fluorine-containing diamine with a dianhydride monomer, and then polycondensing the monomer with a ternary amine.

2. The polyamic acid binder according to claim 1, characterized in that: The sulfonic acid group-containing diamine is at least one of 2,4-diaminobenzenesulfonic acid, 2,5-diaminobenzenesulfonic acid, 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid or 4,4'-diaminostilbene-2,2'-disulfonic acid; Preferably, the sulfonic acid group-containing diamine accounts for 25-50% of the molar amount of the diamine monomer.

3. The polyamic acid binder according to claim 1 or 2, characterized in that: The fluorine-containing diamine is at least one of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl or 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether; Preferably, the fluorine-containing diamine accounts for 20-45% of the molar amount of the diamine monomer.

4. The polyamic acid binder according to any one of claims 1 to 3, characterized in that: The dianhydride monomer is at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenylethertetracarboxylic dianhydride or hexafluorodianhydride; Preferably, the diamine monomer further comprises other diamine monomers, and the other diamine monomers are at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone or 4,4'-diaminobenzophenone.

5. The polyamic acid binder according to any one of claims 1 to 4, characterized in that: The teramine is at least one of tris(4-aminophenyl)amine, tris(2-aminoethyl)amine, 1,3,5-triaminobenzene or 1,3,5-tris(4-aminophenyl)benzene.

6. A low-moisture lithium-ion battery separator, characterized in that: It includes a base film and a coating layer located on one or both sides of the base film; The coating layer comprises ceramic powder and the polyamic acid binder according to any one of claims 1 to 5.

7. The low-moisture lithium-ion battery separator according to claim 6, characterized in that: The ceramic powder is at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, silicon carbide or magnesium nitride; Preferably, the mass ratio of the ceramic powder to the polyamic acid binder is 15-35:

1.

8. The low-moisture lithium-ion battery separator according to claim 6 or 7, characterized in that: The coating layer further comprises fluorinated polyimide fibers and / or fluorinated polyimide microspheres; Preferably, the fluorinated polyimide fibers or fluorinated polyimide microspheres are obtained by subjecting a diamine monomer including a fluorinated diamine to a dianhydride monomer through a condensation reaction, followed by electrostatic spinning or electrostatic spraying to form polyamic acid fibers or microspheres, and then performing a high-temperature heating treatment.

9. The low-moisture lithium-ion battery separator according to any one of claims 6 to 8, characterized in that: The base film is a polyolefin film, preferably at least one of a polyethylene single-layer film, a polypropylene single-layer film, a polyethylene-polypropylene-polyethylene three-layer film or a polypropylene-polyethylene-polypropylene three-layer film.

10. The low-moisture lithium-ion battery separator according to any one of claims 6 to 9, characterized in that: The coating layer is obtained by coating a slurry comprising ceramic powder, polyamic acid binder and solvent on one or both sides of the base film and then drying the slurry. Preferably, the solvent is at least one of water, ethanol, ethylene glycol, glycerol, N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone.

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