A urea-based polyamide acid salt binder, a method of making and ceramic coated separator

Abstract

The application provides a urea-based polyamide acid salt binder, a preparation method and a ceramic coating separator. The preparation method of the urea-based polyamide acid salt binder comprises the following steps: performing a polycondensation reaction on a diamine monomer containing a urea-based diamine and a dianhydride monomer to obtain polyamide acid; and performing a neutralization reaction on the polyamide acid and an alkali to obtain the urea-based polyamide acid salt binder. The urea-based polyamide acid salt binder, the preparation method and the ceramic coating separator are used to solve the problem that the existing ceramic material for coating the separator cannot simultaneously have sufficient dispersibility, cohesiveness and hydrophobicity.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, and more particularly to a urea-containing polyamic acid salt binder and its preparation method, and a ceramic-coated separator. Background Technology

[0002] Lithium-ion batteries are widely used in energy storage, 3C (computers, communications, and consumer electronics), and power batteries due to their high energy density, low self-discharge, long cycle life, and high voltage platform. The separator, one of the four main components of a lithium-ion battery, lies between the positive and negative electrodes. It acts as a barrier to electron transport while allowing lithium ions to pass through, hence its nickname, the "third electrode" of the battery. The chemical stability, mechanical strength, porosity, liquid retention capacity, thermal stability, and moisture content of the battery separator directly affect the performance of the lithium-ion battery.

[0003] With increasing demands for energy density and safety performance in traditional lithium-ion batteries, higher requirements are being placed on the performance of the separator. Coating the separator with inorganic materials, especially ceramics, can significantly improve its thermal stability, lithium-ion conductivity, and electrolyte wettability. However, inorganic ceramic particles themselves lack adhesiveness and cannot directly adhere to polyolefin separators. Furthermore, ceramic powders are prone to agglomeration during storage and coating, leading to a decline in the quality of the separator coating. The ceramic powder coating also increases the moisture content of the separator, causing side reactions with the lithium-ion battery electrolyte and with the positive and negative electrodes and the solid electrolyte interphase (SEI) membrane. Therefore, the adhesion, dispersibility, and hydrophobicity of the separator coating material are crucial for the overall performance of the lithium-ion battery.

[0004] In the existing patent (CN113517466A), a dispersant is mixed with ceramic coarse powder, surface modifier, etc. to form a mixed slurry. The slurry is then subjected to ball milling, centrifugation, drying and other treatments to obtain ceramic powder that is not easy to agglomerate, has high dispersibility and low particle size. However, since it uses both dispersant and surface modifier, it not only increases the preparation cost, but also does not improve the hydrophobic properties of the material. Summary of the Invention

[0005] Based on the technical problems existing in the background art, the present invention proposes a urea-containing polyamic acid salt binder and its preparation method, as well as a ceramic coated diaphragm, aiming to solve the problem that the existing ceramic materials for coated diaphragms cannot simultaneously have sufficient dispersibility, adhesion and hydrophobicity.

[0006] The present invention proposes a method for preparing a urea-containing polyamic acid acid binder, comprising: performing a polycondensation reaction of a diamine monomer including a urea-containing diamine and a dianhydride monomer to obtain polyamic acid; and then performing a neutralization reaction of the polyamic acid with an alkali to obtain the urea-containing polyamic acid acid binder.

[0007] In this invention, by introducing urea groups into the polyamic acid acid binder, the urea group has extremely strong hydrogen bonding effect and also has strong hydrophobicity with the polymer itself, as well as ceramic particles or polyimide nanospheres. Therefore, by introducing urea groups into the aqueous polyamic acid acid binder, the hydrophobicity of the binder is increased from the perspective of molecular chain structure design, while the adhesion is improved.

[0008] Preferably, the ureidodiamine is at least one of 1,3-bis(4-aminophenyl)urea, 1,3-bis(2-aminophenyl)urea, or 1,3-bis(3-aminophenyl)urea.

[0009] Preferably, the diamine monomer further includes at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 1,3-bis(4-aminophenoxy)benzene, 4,4'-diaminodiphenylmethane, or 4,4'-diamino-2,2'-dimethylbiphenyl.

[0010] Preferably, the ureidodiamine contains 10-40% of the molar percentage of the diamine monomer.

[0011] In this invention, the amount of urea-containing diamine added needs to be controlled within the range of 10-40 mol%. Generally, a small amount will not have any effect, while a large amount will lead to poor water solubility of the polymer, making it difficult to obtain a water-soluble polyamic acid salt binder.

[0012] Preferably, the dianhydride monomer is at least one selected from pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-oxyphthalic dianhydride, diphenyl sulfone-3,3',4,4'-tetracarboxylic dianhydride, benzophenone-3,3',4,4'-tetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, or 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride.

[0013] Preferably, the alkali comprises an inorganic alkali, an organic alkali, or an alkaline ionic liquid; the inorganic alkali is lithium hydroxide; the organic alkali is at least one selected from ammonia, triethylamine, trimethylamine, dimethylimidazole, or tetramethylguanidine; and the alkaline ionic liquid is [EMIM]OH, [BMIM][OH], or [BTMG][OH].

[0014] At least one of [NBMD][OH] or [NBMM]OH.

[0015] Preferably, the molar ratio of the diamine monomer, dianhydride monomer and base is 1:1.0-1.05:2.0-2.2.

[0016] Preferably, the temperature of the polycondensation reaction is 15-30℃ and the time is 6-12h; the temperature of the neutralization reaction is 15-30℃ and the time is 4-8h.

[0017] The present invention also proposes a urea-containing polyamic acid salt adhesive, which is prepared by the above preparation method.

[0018] The present invention also proposes a low-moisture ceramic-coated diaphragm, which is prepared by the following method: ceramic particles and the above-mentioned urea-containing polyamic acid binder are added to an aqueous solvent and dispersed evenly to obtain a ceramic coating slurry; the ceramic coating slurry is coated onto the surface of a base film using a gravure roller coating method, and after drying, the ceramic-coated diaphragm is obtained.

[0019] Preferably, the ceramic particles are at least one of aluminum oxide, magnesium hydroxide, magnesium oxide, barium sulfate, silicon dioxide, or titanium dioxide; the aqueous solvent is at least one of ethanol, water, acetonitrile, and N-methylpyrrolidone.

[0020] Preferably, the mass ratio of the ceramic particles to the binder is 100:1-10.

[0021] This invention proposes a urea-containing polyamic acid salt binder, its preparation method, and a ceramic-coated separator. By introducing urea groups into the molecular chain of the polyamic acid salt binder, the hydrogen bonding and hydrophobicity of the urea groups can be utilized to increase the adhesion to ceramic particles and reduce the adsorption of free water in the air and the binding capacity of bound water by the ceramic particles. Ultimately, this improves the hydrophobicity of the obtained ceramic-coated separator and its yield and electrical performance in lithium-ion batteries. Detailed Implementation

[0022] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0023] Example 1

[0024] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0025] Under nitrogen protection, 1,3-bis(4-aminophenyl)urea (2.5 mmol) and 4,4'-diaminodiphenyl ether (7.5 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, pyromellitic dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. An aqueous solution containing lithium hydroxide (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid binder was obtained.

[0026] A low-moisture ceramic-coated membrane is prepared by the following method:

[0027] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to water at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0028] Example 2

[0029] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0030] Under nitrogen protection, 1,3-bis(4-aminophenyl)urea (2.5 mmol) and p-phenylenediamine (7.5 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. Triethylamine (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid acid binder was obtained.

[0031] A low-moisture ceramic-coated membrane is prepared by the following method:

[0032] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to a mixture of water and ethanol (volume ratio of 9:1) at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0033] Example 3

[0034] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0035] Under nitrogen protection, 1,3-bis(4-aminophenyl)urea (2.5 mmol) and 2,2'-bis(trifluoromethyl)diaminobiphenyl (7.5 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, 3,3',4,4'-oxyphthalic dianhydride (10 mmol) was added and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. [EMIM]OH (20 mmol) was then added and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid acid binder was obtained.

[0036] A low-moisture ceramic-coated membrane is prepared by the following method:

[0037] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to a mixture of water and ethanol (volume ratio of 9:1) at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0038] Example 4

[0039] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0040] Under nitrogen protection, 1,3-bis(2-aminophenyl)urea (2.5 mmol) and 1,3-bis(4-aminophenoxy)benzene (7.5 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, diphenyl sulfone-3,3',4,4'-tetracarboxylic acid dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. An aqueous solution containing lithium hydroxide (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid acid binder was obtained.

[0041] A low-moisture ceramic-coated membrane is prepared by the following method:

[0042] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to water at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0043] Example 5

[0044] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0045] Under nitrogen protection, 1,3-bis(3-aminophenyl)urea (2.5 mmol) and 4,4'-diaminodiphenylmethane (7.5 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, benzophenone-3,3',4,4'-tetracarboxylic acid dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. An aqueous solution containing lithium hydroxide (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid acid binder was obtained.

[0046] A low-moisture ceramic-coated membrane is prepared by the following method:

[0047] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to water at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0048] Example 6

[0049] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0050] Under nitrogen protection, 1,3-bis(4-aminophenyl)urea (1.0 mmol) and 4,4'-diaminodiphenyl ether (9.0 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, pyromellitic dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. An aqueous solution containing lithium hydroxide (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid binder was obtained.

[0051] A low-moisture ceramic-coated membrane is prepared by the following method:

[0052] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to water at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0053] Example 7

[0054] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0055] Under nitrogen protection, 1,3-bis(4-aminophenyl)urea (4.0 mmol) and 4,4'-diaminodiphenyl ether (6.0 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, pyromellitic dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. An aqueous solution containing lithium hydroxide (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid acid binder was obtained.

[0056] A low-moisture ceramic-coated membrane is prepared by the following method:

[0057] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to water at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0058] Comparative Example 1

[0059] A polyamic acid salt adhesive, which is prepared by the following method:

[0060] Under nitrogen protection, 4,4'-diaminodiphenyl ether (10 mmol) was added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, pyromellitic dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. An aqueous solution containing lithium hydroxide (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid acid binder was obtained.

[0061] A low-moisture ceramic-coated membrane is prepared by the following method:

[0062] Alumina powder (average particle size of 0.5 μm) and the above-mentioned polyamic acid binder were added to water at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0063] Comparative Example 2

[0064] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0065] Under nitrogen protection, 1,3-bis(4-aminophenyl)urea (0.5 mmol) and 4,4'-diaminodiphenyl ether (9.5 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, pyromellitic dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. An aqueous solution containing lithium hydroxide (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid binder was obtained.

[0066] A low-moisture ceramic-coated membrane is prepared by the following method:

[0067] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to water at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0068] Comparative Example 3

[0069] A urea-containing polyamic acid salt adhesive is prepared by the following method:

[0070] Under nitrogen protection, 1,3-bis(4-aminophenyl)urea (5.0 mmol) and 4,4'-diaminodiphenyl ether (5.0 mmol) were added to N-methylpyrrolidone (NMP, 30 mL) and stirred until completely dissolved. Then, pyromellitic dianhydride (10 mmol) was added, and the mixture was stirred at room temperature for 10 h to obtain a polyamic acid solution. An aqueous solution containing lithium hydroxide (20 mmol) was then added, and the mixture was stirred at room temperature for 6 h. The resulting reaction solution was then added to acetone to precipitate the precipitate. After filtration, washing, and drying, the urea-containing polyamic acid acid binder was obtained.

[0071] A low-moisture ceramic-coated membrane is prepared by the following method:

[0072] Alumina powder (average particle size of 0.5 μm) and the above-mentioned urea-containing polyamic acid acid binder were added to water at a mass ratio of 100:4 and stirred to disperse evenly, thus obtaining a ceramic coating slurry (solid content of 35 wt%). The ceramic coating slurry was coated onto one side surface of a polyethylene monolayer film (thickness of 12 μm, porosity of 45%) using a gravure roller coating method. After drying at 60°C, a coating layer with a thickness of 4 μm was formed, thus obtaining the low-moisture ceramic-coated diaphragm.

[0073] Performance testing:

[0074] The ceramic-coated separators obtained in the above embodiments and comparative examples were tested for peel strength, moisture content and battery performance, respectively. The test results are shown in Table 1.

[0075] Peel strength: The ceramic coating side of the ceramic-coated diaphragm was adhered to with 3M tape, and the composite diaphragm was fixed between two steel plate clamps. The ceramic coating and the base film were peeled off by stretching the diaphragm in the opposite direction by 180 degrees using an electronic universal tensile testing machine, and the peel strength was recorded.

[0076] Moisture content was tested according to GB / T 6324.8-2014 standard; a Karl Fischer moisture analyzer was used to determine the moisture content.

[0077] The battery performance is achieved by mixing lithium iron phosphate as the positive electrode active material with conductive carbon black (conductive agent) and polyvinylidene fluoride (binder) in a mass ratio of 96:2:2, adding N-methylpyrrolidone to prepare a slurry, coating it onto one side of aluminum foil, drying, and rolling to obtain the positive electrode sheet; and by mixing graphite as the negative electrode active material with conductive carbon black (conductive agent), sodium carboxymethyl cellulose (binder), and styrene-butadiene rubber (binder) in a mass ratio of 95:2:2:1, adding deionized water to prepare a slurry, coating it onto one side of copper foil, drying, and rolling to obtain the positive electrode sheet. The positive electrode, negative electrode, and lithium-ion battery separator are assembled into a lithium-ion battery. An electrolyte (1 mol / L lithium hexafluorophosphate electrolyte, with ethylene carbonate EC, dimethyl carbonate DMC, and ethyl methyl carbonate EMC in a volume ratio of 1:1:1) is injected. After standing, the lithium-ion battery is obtained. It is charged at 25°C at a rate of 1C to 80% SOC, charged at a rate of 0.5C to 3.5V, charged at a rate of 0.1C to 3.65V, and discharged at a rate of 1C to 2.5V. The capacity retention rate after 500 cycles is measured.

[0078] Table 1. Performance test results of the ceramic-coated diaphragms described in the examples and comparative examples.

[0079] Example 1 168 445 92.3 Example 2 172 421 91.5 Example 3 176 408 90.7 Example 4 163 473 91.9 Example 5 156 488 91.2 Example 6 147 507 91.8 Example 7 173 481 92.6 Comparative Example 1 114 1432 83.3 Comparative Example 2 125 905 87.1 Comparative Example 3 103 687 85.6

[0080] As shown in Table 1 above, the ceramic-coated separator described in the embodiments has excellent bonding strength and hydrophobicity, as well as high yield and electrical performance of lithium-ion batteries.

[0081] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a urea-containing polyamic acid salt adhesive, characterized in that, include: The diamine monomer and the dianhydride monomer are subjected to a polycondensation reaction to obtain polyamic acid; then the polyamic acid is subjected to a neutralization reaction with an alkali to obtain the urea-containing polyamic acid acid binder. The diamine monomer includes ureidodiamines and other diamines; The ureidodiamine is at least one of 1,3-bis(4-aminophenyl)urea, 1,3-bis(2-aminophenyl)urea, or 1,3-bis(3-aminophenyl)urea; The other diamine is at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 1,3-bis(4-aminophenoxy)benzene, 4,4'-diaminodiphenylmethane or 4,4'-diamino-2,2'-dimethylbiphenyl. The urea-containing diamine has a molar percentage of 10-40% in the diamine monomer; The alkali includes an inorganic alkali or an organic alkali, wherein the inorganic alkali is at least one of lithium hydroxide or ammonia water, and the organic alkali is at least one of triethylamine, trimethylamine, dimethylimidazole or tetramethylguanidine; The molar ratio of the diamine monomer, dianhydride monomer, and base is 1:1.0-1.05:2.0-2.

2.

2. The method for preparing the urea-containing polyamic acid salt adhesive according to claim 1, characterized in that, The dianhydride monomer is at least one selected from pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, or 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride.

3. The method for preparing the urea-containing polyamic acid salt adhesive according to claim 1 or 2, characterized in that, The polycondensation reaction is carried out at a temperature of 15-30°C for 6-12 hours; the neutralization reaction is carried out at a temperature of 15-30°C for 4-8 hours.

4. A urea-containing polyamic acid salt adhesive, characterized in that, It is prepared by the preparation method described in any one of claims 1-3.

5. A low-moisture ceramic-coated diaphragm, characterized in that, It is prepared by the following method: ceramic particles and the urea-containing polyamic acid acid binder of claim 4 are added to an aqueous solvent and dispersed evenly to obtain a ceramic coating slurry; the ceramic coating slurry is coated on the surface of the base film by gravure roller coating method, and after drying, the low moisture ceramic coating membrane is obtained.

6. The low-moisture ceramic-coated diaphragm according to claim 5, characterized in that, The ceramic particles are at least one of aluminum oxide, magnesium oxide, silicon dioxide, or titanium dioxide; the aqueous solvent is water or an ethanol-water mixture.

7. The low-moisture ceramic-coated diaphragm according to claim 5 or 6, characterized in that, The mass ratio of the ceramic particles to the binder is 100:1-10.