Method for preparing double-sided porous polyimide separator by means of roll-to-roll coating, double-sided porous polyimide separator, and use thereof

Abstract

A method for preparing a double-sided porous polyimide separator by means of roll-to-roll coating, a double-sided porous polyimide separator, and the use thereof. The preparation method comprises the steps of: (1) adding a diamine monomer and a dianhydride monomer to a solvent for reaction, then adding a curing accelerator for further reaction, and cooling same to obtain a polyimide slurry; (2) adding a low-boiling-point solvent to the polyimide slurry, and stirring same until uniform to obtain a coating material; and (3) coating the coating material onto a PET substrate, allowing same entering a pre-heating zone for pre-heating and pre-curing, removing the pre-cured polyimide film from the surface of the substrate, and drying same, so as to obtain a double-sided porous polyimide separator. By means of the combination of the two step operations of adding a low-boiling-point solvent to the polyimide slurry and performing pre-heating before the separator is pre-cured, a double-sided porous polyimide separator having high deformation resistance, high porosity, and small porosity difference between the two sides can be obtained, thereby improving an electrolyte absorption rate.

Description

Method for preparing double-sided porous polyimide membranes by roll-to-roll coating, double-sided porous polyimide membranes and their applications Technical Field

[0001] This invention relates to a method for preparing double-sided porous polyimide separators by roll-to-roll coating, the double-sided porous polyimide separators and their applications, and belongs to the technical field of polyimide separators for batteries. Background Technology

[0002] Lithium-ion batteries play a crucial role in modern electronic devices, electric vehicles, and energy storage systems, and their performance and safety largely depend on their internal components. The separator is one of the most important components inside a lithium-ion battery, responsible for isolating the positive and negative electrodes while allowing lithium ions to pass through. With the increasing demand for lithium-ion batteries, improving the production efficiency and quality of separators has become a key issue, and roll-to-roll coating technology is gradually becoming mainstream.

[0003] Roll-to-roll coating technology is a highly efficient continuous production technology suitable for manufacturing thin film materials, such as lithium battery separators. The basic process includes material unfolding, coating, drying, and winding. The main characteristics of this technology are as follows:

[0004] 1. High-efficiency production: During continuous production, the materials are always in motion, which significantly improves production efficiency and capacity.

[0005] 2. Uniform coating: Precise control of coating thickness and uniformity ensures stable quality of the release liner.

[0006] 3. High degree of automation: The entire production line is highly automated, reducing human intervention and improving product consistency.

[0007] With the rapid growth in demand for lithium batteries, separator manufacturers need to continuously improve their capacity utilization. The introduction of roll-to-roll coating continuous production technology has significantly improved production efficiency, resulting in higher capacity utilization levels. Many companies are further increasing their capacity to meet market demand by adding production lines and upgrading automated equipment.

[0008] However, when roll-to-roll coating is continuous, the diaphragm will undergo a certain deformation due to the stretching force of the roll during continuous production. This deformation will, to some extent, reduce the uniformity of the diaphragm's properties and may even cause the diaphragm to break. Therefore, the current roll-to-roll coating method is only suitable for polyimide diaphragms with low porosity or single-sided pores, and is not suitable for double-sided porous polyimide diaphragms. Summary of the Invention

[0009] To address the aforementioned issues, a method for preparing double-sided porous polyimide membranes using roll-to-roll coating is provided. This method involves adding a low-boiling-point solvent to the polyimide slurry and preheating it before pre-curing the membrane to obtain a double-sided porous polyimide membrane. This polyimide membrane exhibits high resistance to deformation, high porosity, and minimal difference in porosity between the two sides, thereby improving electrolyte absorption rate.

[0010] According to one aspect of the present invention, a method for preparing a double-sided porous polyimide separator by roll-to-roll coating is provided, comprising the following steps:

[0011] (1) Add diamine monomers and dianhydride monomers to a solvent, react in one step, add a curing accelerator to carry out a two-step reaction, and obtain polyimide slurry after cooling.

[0012] (2) Add 5-30 wt% of a low-boiling-point solvent to the polyimide slurry and stir until uniform to obtain the coating material;

[0013] (3) The coating material is applied to the PET substrate using a coating machine and then preheated in a preheating area. The substrate is then immersed in a coagulation bath solution for pre-curing. The pre-cured polyimide film is removed from the substrate surface and dried to obtain a double-sided porous polyimide diaphragm.

[0014] In this method, 5-30 wt% of a low-boiling-point solvent is first added to a polyimide slurry to obtain a coating material. After the coating material is applied, it is placed in a preheating zone for preheating. During the preheating process, the low-boiling-point solvent evaporates and forms micropores, thereby obtaining a double-sided porous polyimide membrane, which increases the porosity of the polyimide membrane and improves the uniformity of the porosity distribution.

[0015] The improvement of the coating slurry and the combination of the preheating step in the above method can improve the deformation resistance of the membrane while realizing the preparation of double-sided porous polyimide membrane, thereby improving the uniformity of the membrane properties. The overall production process will not cause the membrane to break or be damaged, and the double-sided porous polyimide membrane with high porosity can be mass-produced.

[0016] Preferably, the amount of low-boiling-point solvent added is 20 wt%.

[0017] Optionally, the preheating temperature is 60-100℃ and the time is 5-10 minutes;

[0018] Preferably, the preheating temperature is 60-80℃.

[0019] The preheating temperature is used to achieve the evaporation of low-boiling-point solvents. Therefore, if the temperature is too low, the amount of low-boiling-point solvent evaporating will be too small under the same preheating time, reducing the porosity of the membrane. If the temperature is too high, the low-boiling-point solvent will evaporate faster, resulting in larger pores on the upper surface of the polyimide membrane and smaller pores on the lower surface. This leads to an excessive difference in porosity between the two sides of the polyimide membrane, which in turn reduces the mechanical strength and fails to meet the actual application requirements.

[0020] Optionally, the boiling point of the low-boiling solvent is 66-80°C;

[0021] Preferably, the low-boiling-point solvent is selected from at least one of ethyl acetate, hexane, and tetrahydrofuran, with ethyl acetate being the most preferred.

[0022] Optionally, the speed of the coating machine is 0.75-1.5 m / min.

[0023] Optionally, the thickness of the double-sided porous polyimide membrane is 10-20 μm.

[0024] At the same coating output, the coating machine speed determines the separator thickness. A faster coating machine results in a thinner separator, which reduces the evaporation resistance of low-boiling-point solvents during the preheating stage. This prevents the formation of large pores during solvent evaporation and reduces the porosity difference between the two sides of the separator, thus improving internal consistency and overall strength. However, a thinner separator reduces its liquid retention capacity and electronic insulation, consequently decreasing battery life and safety.

[0025] For example, the thickness of the polyimide separator can be 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or any value between these values.

[0026] Optionally, the drying process is carried out in stages: first, drying at 60-100℃ for 5-10 minutes, then drying at 101-200℃ for 5-10 minutes, and finally drying at 201-300℃ for 5-10 minutes.

[0027] The segmented drying process described above can prevent rapid evaporation of liquid inside the membrane, thereby improving pore size uniformity, reducing the porosity difference between the two sides, increasing overall porosity, improving electrolyte absorption rate, and enhancing the mechanical strength and chemical resistance of the separator in the electrolyte. This reduces swelling and disintegration in the electrolyte, thereby improving battery life and safety.

[0028] Optionally, in step (1), the molar ratio of the diamine monomer to the dianhydride monomer is (0.8-1.2):1, and the molar ratio of the curing accelerator to the diamine monomer is (2-3):1.

[0029] Optionally, in step (1), the temperature of the first-step reaction is 22-25℃ and the time is 10-12h; the temperature of the second-step reaction is 90℃ and the time is at least 6h.

[0030] If the temperature of the first-step reaction is too high, the molecular weight will decrease, which is detrimental to improving the mechanical strength of the membrane. If the temperature or time of the first-step reaction is too low, the reaction will be incomplete, the molecular weight of the membrane will decrease, and thus the performance of the membrane will be affected.

[0031] Optionally, an inert gas is introduced for protection during the reaction in step (1), including nitrogen, argon, helium, neon, krypton, and xenon.

[0032] Optionally, the diamine monomer is selected from at least one of 3,4'-diaminodiphenyl ether, 4,4'-diaminobenzoyl aniline, N,N'-bis(4-aminophenyl)terephthalamide, 3,5-diaminobenzoic acid, 4,4-diaminodiphenylmethane, 2,2'-bis(trifluoromethyl)-4,4'-bis(4-aminophenylcarbonylamino)biphenyl, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3,3'-dihydroxybenzidine, and 9,9-bis(4-aminophenyl)fluorene;

[0033] The dianhydride monomer is selected from at least one of pyromellitic dianhydride, 4,4'-oxobisphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, 3,3,4,4-diphenylsulfone tetracarboxylic anhydride, and hexafluorodianhydride.

[0034] The curing accelerator is selected from at least one of triethylamine, benzimidazole, 1-methylimidazole, quinoline, 1,8-diazabicycloundec-7-ene, imidazole, pyridine, and 3-methylpyridine.

[0035] Preferably, the diamine monomer is selected from at least one of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3,4'-diaminodiphenyl ether, and N,N'-bis(4-aminophenyl)terephthalamide;

[0036] The dianhydride monomers are selected from at least one of 4,4'-oxobisphthalic anhydride, pyromellitic dianhydride, and hexafluorodianhydride.

[0037] More preferably, the amount of 2,2'-bis(trifluoromethyl)diaminobiphenyl is 692g, the amount of 3,4'-diaminodiphenyl ether is 432g, and the amount of N,N'-bis(4-aminophenyl)terephthalamide is 498.67g.

[0038] The amount of 4,4'-oxobisphthalic anhydride used is 670g, the amount of pyromellitic dianhydride used is 470.58g, and the amount of hexafluorodianhydride used is 640g.

[0039] The above preparation method involves polymerization via thermal imidization and chemical imidization. The curing accelerator acts as an affinity agent, attacking the carbon atoms on the carboxyl groups of the polyamic acid and transferring hydrogen atoms to these groups. This promotes the catalytic mechanism of cyclization and dehydration, thereby improving the performance of the resulting membrane, reducing reaction time, and saving production costs. However, if the amount of curing accelerator is too small, the improvement in reaction promotion will be insignificant; if the amount is too large, it will increase costs and may reduce the molecular weight. Excessively high reaction temperatures or long reaction times after adding the curing accelerator will increase production time and cause product degradation; conversely, excessively low reaction temperatures or short reaction times will hinder the promotion of the cyclization and dehydration catalytic mechanism.

[0040] In some preferred embodiments, the reaction is carried out using any of the following combinations:

[0041] I: 692g of 2,2'-bis(trifluoromethyl)diaminobiphenyl and 670g of 4,4'-oxobisphthalic anhydride were reacted in 6713g of DMAc solvent, and then 342g of pyridine, 661g of acetic anhydride and 1000g of DMAc were added and stirred to obtain polyimide slurry.

[0042] II: 432g of 3,4'-diaminodiphenyl ether and 470.58g of pyromellitic dianhydride were reacted in 7123g of DMAc solvent, and then 655g of triethylamine and 1000g of DMAc were added and stirred to obtain polyimide slurry.

[0043] III: 498.67 g of N,N'-bis(4-aminophenyl)terephthalamide and 640 g of hexafluorodianhydride were reacted in 7346 g of DMAc solvent. Then, 558 g of quinoline, 661 g of acetic anhydride and 1000 g of DMAc were added and stirred to obtain polyimide slurry.

[0044] In the above preparation method, the initial solid content of the monomer is controlled within the range of 10%-15% by changing the amount of solvent added.

[0045] Optionally, the solvent is selected from at least one of dimethylacetamide (DMAC), m-cresol, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), chloroform, 3-methoxy-N,N-dimethylpropionamide, and γ-butyrolactone (GBL).

[0046] Optionally, the thickness of the PET substrate is 25 μm.

[0047] Optionally, the pre-curing operation of immersing in a coagulation bath solution can be performed by directly immersing in an aqueous solution containing ethanol for one-step pre-curing, or by first immersing in an ethanol solution and then immersing in an aqueous solution for step-by-step pre-curing.

[0048] Optionally, the pre-curing is performed by immersing the sample in ethanol and water for 10 minutes each.

[0049] According to another aspect of the present invention, a double-sided porous polyimide membrane prepared by the roll-to-roll coating method described in any of the preceding claims is provided;

[0050] Preferably, the porosity of the double-sided porous polyimide membrane is above 55%, and the difference in porosity between the two sides is below 13%.

[0051] More preferably, the average pore size of the double-sided porous polyimide membrane is 1.44-1.83 μm, and the difference between the average pore sizes of the two sides is less than 13%.

[0052] According to another aspect of the present invention, the application of the above-described double-sided porous polyimide separator in a battery is provided;

[0053] Preferably, the battery is a lithium battery.

[0054] The beneficial effects of the present invention include, but are not limited to:

[0055] 1. The method for preparing double-sided porous polyimide membranes by roll-to-roll coating of the present invention can overcome the shortcomings of the current roll-to-roll coating method, which cannot produce double-sided porous membranes with high porosity, high mechanical strength and good performance uniformity, and obtain double-sided porous polyimide membranes with the above-mentioned properties.

[0056] 2. The roll-to-roll coating method for preparing double-sided porous polyimide membranes of the present invention has high production efficiency, simple and easy-to-operate process, improves the production efficiency of double-sided porous polyimide membranes, and is convenient for industrial promotion and use.

[0057] 3. The double-sided porous polyimide diaphragm of the present invention has an overall porosity of more than 55%, and the difference between the porosity of the two sides and the average pore size of the two sides is less than 13%, which proves that the porosity and pore size distribution of the diaphragm are uniform, thus the overall uniformity of the diaphragm is good, and the diaphragm will not break during roll-to-roll production.

[0058] 4. The double-sided porous polyimide separator of the present invention has high overall strength and strength uniformity, good wettability of electrolyte, and therefore high electrolyte absorption rate. It can meet the various requirements of battery separators and can be industrially used in lithium-ion batteries to improve the stability of lithium-ion batteries and extend their service life. Attached Figure Description

[0059] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0060] Figure 1 is a process flow diagram of the roll-to-roll coating process for preparing double-sided porous polyimide membranes according to the present invention. Detailed Implementation

[0061] The present invention will now be described in detail with reference to the embodiments, but the present invention is not limited to these embodiments.

[0062] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this invention were all purchased commercially.

[0063] Unless otherwise specified, the methods used in the embodiments and comparative examples of the present invention are conventional methods in the prior art.

[0064] The process flow diagram for preparing double-sided porous polyimide separators by roll-to-roll coating in the following embodiments is shown in Figure 1. The prepared coating material is fed into the coating area and coated. During this process, the coating machine operates at a predetermined speed. After the coating material is coated on the PET substrate, it is first preheated in the preheating area. Then, the wet film is sequentially pre-cured in tank A (ethanol solution) and tank B (aqueous solution). After that, the PET substrate is wound up, and the pre-cured wet film is removed from the surface of the substrate and enters the drying area for segmented drying to obtain a double-sided porous polyimide separator. The polyimide separator is then wound up to obtain a roll of polyimide separator.

[0065] Example 1

[0066] This embodiment relates to a method for preparing a double-sided porous polyimide membrane by roll-to-roll coating, comprising the following steps:

[0067] (1) Under nitrogen atmosphere, 692g of 2,2'-bis(trifluoromethyl)diaminobiphenyl and 6713g of DMAc were added to the reactor and stirred at 22°C. After complete dissolution, 670g of 4,4'-oxophthalic anhydride was gradually added and stirred at 22°C for 12 hours. Then, 342g of pyridine, 661g of acetic anhydride and 1000g of DMAc were added and stirred. The temperature was raised to 90°C and stirred for 12 hours to carry out chemical imidization. Finally, the temperature was lowered to room temperature to obtain polyimide slurry.

[0068] (2) Add ethyl acetate in different proportions to the polyimide slurry and stir for 1 hour to obtain the coating material;

[0069] (3) The coating material is applied to a PET substrate with a thickness of 25μm using a coating machine at a speed of 1m / min. The wet film is then preheated in a preheating area at a temperature of 60-100℃. After that, it is pre-cured in tank A (ethanol) and tank B (water) for 10min each. The pre-cured polyimide film is then removed from the substrate surface and dried at 100℃ for 10min, then at 180℃ for 10min, and finally at 250℃ for 10min to obtain a double-sided porous polyimide membrane.

[0070] Specific parameters and the performance of the prepared double-sided porous polyimide diaphragm are detailed in Table 1. The porosity in Table 1 refers to the overall porosity of the diaphragm. The test method is as follows: immerse the diaphragm in n-butanol for 2 hours, and then calculate the porosity according to the formula: P(%)=(Mw-Md) / ρVd x100, where ρ is the density of n-butanol and Vd is the geometric volume of the diaphragm, and Mw and Md are the mass of n-butanol absorbed by the membrane and the mass of the diaphragm itself.

[0071] The difference in porosity between the two sides is obtained by measuring the porosity of each side of the diaphragm using gas flow rate testing, and then calculated using the formula for the difference in porosity between the two sides: (P1-P2) / P1×100%, where P1 is the larger porosity value of the two sides of the diaphragm, and P2 is the smaller porosity value of the two sides of the diaphragm.

[0072] At least 100 points on both sides of the diaphragm were measured using an electron microscope to obtain the average pore size of the two sides. The average pore size of the diaphragm was then calculated by averaging the two pore sizes to obtain the overall average pore size of the diaphragm. The formula for calculating the difference between the average pore sizes of the two sides is: (A1-A2) / A1×100%, where A1 is the larger average pore size of the two sides of the diaphragm and A2 is the smaller average pore size of the two sides of the diaphragm.

[0073] Table 1

[0074] As shown in Table 1, for the same thickness, the preheating zone is heated to 60-100℃ for the wet film. The main purpose is to allow the low-boiling-point ethyl acetate to evaporate and form micropores, thereby increasing the porosity of the film. The porosity of sample OT15-T6-E30% is 71%, which is about 36% higher than that of sample OT15-T6-E0% without added ethyl acetate. The average pore size increases by 35%, but the film weight decreases by 17.2%. Therefore, although the added low-boiling-point solvent increases the porosity, it will affect the strength of the film to some extent.

[0075] A comparison of OT15-T6-E20% and OT15-T8-E20% shows that when the preheating temperature increases from 60℃ to 80℃, the electrolyte absorption rate, porosity, and pore size all increase without sacrificing mechanical strength. However, when the temperature of OT15-T10-E20% is increased to 100℃, its modulus decreases by 17.5% compared to the OT15-T8-E20% sample, and the porosity difference increases from 7% to 15%. This is likely because the high preheating temperature causes rapid evaporation of ethyl acetate, resulting in larger pores on the surface and smaller pores at the bottom, leading to a significant difference in pore size between the two surfaces and thus affecting mechanical strength.

[0076] Example 2

[0077] This embodiment is based on the OT15-T8-E20% sample, with different low-boiling-point solvents replaced. The specific parameters and the performance of the prepared double-sided porous polyimide membrane are detailed in Table 2.

[0078] Table 2

[0079] As shown in Table 2, at the same thickness, when adding 20 wt% of different low-boiling-point solvents, the sample made with ethyl acetate exhibits a higher modulus than the samples with the same proportions of hexane and tetrahydrofuran. Furthermore, the average pore size difference between the two sides is also lower, at only 7%. This is likely related to the boiling points of the solvents: ethyl acetate has a boiling point of 77°C, hexane 68°C, and tetrahydrofuran 66°C. Ethyl acetate's boiling point is closer to the preheating temperature of this embodiment, thus minimizing the generation of large amounts of sudden boiling pores and resulting in more consistent pore sizes within the membrane. Consequently, its membrane quality and pore size difference are superior. Therefore, it can be concluded that within the preheating temperature range, selecting a suitable low-boiling-point solvent can yield a high-quality polyimide membrane.

[0080] Example 3

[0081] Based on the OT15-T8-E20% sample, this embodiment produced polyimide membranes of different thicknesses using different coating speeds. Specific parameters and the performance of the prepared double-sided porous polyimide membranes are detailed in Table 3.

[0082] Table 3

[0083] Table 3 shows that different thicknesses of membrane materials were produced at different machine speeds. The OT10-T8-E20% sample, produced at a machine speed of 1.5 m / min, had a membrane thickness of 10 μm. Its overall mechanical strength was better than that of the 15 μm and 20 μm samples. It can be observed that the OT10-T8-E20% sample had the smallest average pore size and the smallest difference in average pore size between the two sides. This indicates that when the thickness is smaller, the evaporation resistance of the low-boiling-point solvent is smaller, and a larger pore size will not be formed when the solvent evaporates. This also reduces the pore size difference within the membrane, thereby improving the consistency within the membrane and increasing the overall strength.

[0084] Example 4

[0085] This embodiment relates to a method for preparing a double-sided porous polyimide membrane by roll-to-roll coating, comprising the following steps:

[0086] (1) Under nitrogen atmosphere, 345.6 g of 3,4'-diaminodiphenyl ether and 7123 g of DMAc were added to the reactor and stirred at 25°C. After complete dissolution, 470.58 g of pyromellitic dianhydride was gradually added and stirred at 25°C for 10 hours. Then, 655 g of triethylamine and 1000 g of DMAc were added and stirred. The temperature was raised to 90°C and stirred for 6 hours. Finally, the temperature was lowered to room temperature to obtain polyimide slurry.

[0087] (2) Add ethyl acetate (20 wt% of polyimide slurry) to the polyimide slurry and stir for 1 hour to obtain the coating material;

[0088] (3) The coating material is applied to a PET substrate with a thickness of 25μm using a coating machine at a speed of 1m / min. The wet film is then preheated in a preheating area at a temperature of 80℃. After that, it is pre-cured in tank A (ethanol) and tank B (water) for 10min each. The pre-cured polyimide film is then removed from the substrate surface and dried at 60℃ for 10min, then at 101℃ for 10min, and finally at 201℃ for 10min to obtain a double-sided porous polyimide membrane.

[0089] Example 5

[0090] This embodiment relates to a method for preparing a double-sided porous polyimide membrane by roll-to-roll coating, comprising the following steps:

[0091] (1) Under nitrogen atmosphere, 598.4 g of N,N'-bis(4-aminophenyl)terephthalamide and 7346 g of DMAc were added to the reactor and stirred at 22°C. After complete dissolution, 640 g of hexafluorodianhydride was gradually added and stirred at 22°C for 12 hours. Then, 558 g of quinoline, 661 g of acetic anhydride and 1000 g of DMAc were added and stirred. The temperature was raised to 90°C and stirred for 12 hours. Finally, the temperature was lowered to room temperature to obtain polyimide slurry.

[0092] (2) Add ethyl acetate (20 wt% of polyimide slurry) to the polyimide slurry and stir for 1 hour to obtain the coating material;

[0093] (3) The coating material is applied to a PET substrate with a thickness of 25 μm using a coating machine at a speed of 2 m / min. The wet film is then preheated in a preheating area at a temperature of 80°C. After that, it is pre-cured in tank A (ethanol) and tank B (water) for 10 min each. The pre-cured polyimide film is then removed from the substrate surface and dried at 100°C for 5 min, then at 200°C for 5 min, and finally at 300°C for 5 min to obtain a double-sided porous polyimide membrane.

[0094] Example 6

[0095] The difference between this embodiment and the OT15-T8-E20% sample in Example 1 is that the segmented drying method is not used; instead, it is dried directly at 180°C for 30 minutes. The rest is the same as the OT15-T8-E20% sample.

[0096] Example 7

[0097] The difference between this embodiment and the OT15-T8-E20% sample in Embodiment 1 is that ethanol and water are mixed in tanks A and B at a volume ratio of 50%:50%, while the rest is the same as the OT15-T8-E20% sample.

[0098] The properties of the double-sided porous polyimide membranes prepared in Examples 4-7 are detailed in Table 4.

[0099] Table 4

[0100] The above description is merely an embodiment of the present invention, and the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principle of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a double-sided porous polyimide separator by roll-to-roll coating, characterized by, Includes the following steps: (1) Add diamine monomers and dianhydride monomers to a solvent, react in one step, add a curing accelerator to carry out a two-step reaction, and obtain polyimide slurry after cooling. (2) Add 5-30 wt% of a low-boiling-point solvent to the polyimide slurry and stir until uniform to obtain the coating material; (3) The coating material is applied to the PET substrate using a coating machine and then preheated in a preheating area. The substrate is then immersed in a coagulation bath solution for pre-curing. The pre-cured polyimide film is removed from the substrate surface and dried to obtain a double-sided porous polyimide diaphragm.

2. The method of claim 1, wherein the method is a roll-to-roll coating method for preparing a double-sided porous polyimide separator. The preheating temperature is 60-100℃, and the time is 5-10 minutes.

3. The method of claim 1, wherein the method is a roll-to-roll coating method for preparing a double-sided porous polyimide separator. The boiling point of the low-boiling solvent is 66-80℃; Preferably, the low-boiling solvent is selected from at least one of ethyl acetate, hexane, and tetrahydrofuran.

4. The method of claim 1, wherein the method is a roll-to-roll coating method for preparing a double-sided porous polyimide separator. The coating machine has a speed of 0.75-1.5 m / min; and / or The thickness of the double-sided porous polyimide membrane is 10-20 μm.

5. The method of claim 1, wherein the method is a roll-to-roll coating method for preparing a double-sided porous polyimide separator. The drying process is carried out in stages: first, drying at 60-100℃ for 5-10 minutes, then drying at 101-200℃ for 5-10 minutes, and finally drying at 201-300℃ for 5-10 minutes.

6. The method of claim 1, wherein the method is a roll-to-roll coating method for preparing a double-sided porous polyimide separator. In step (1), the molar ratio of the diamine monomer to the dianhydride monomer is (0.8-1.2):1, and the molar ratio of the curing accelerator to the diamine monomer is (2-3):

1.

7. The method of claim 1, wherein the method is a roll-to-roll coating method for preparing a double-sided porous polyimide separator. In step (1), the temperature of the one-step reaction is 22-25℃ and the time is 10-12h; The two-step reaction is carried out at a temperature of 90°C for at least 6 hours.

8. The method of claim 1, wherein the method is a roll-to-roll coating method for preparing a double-sided porous polyimide separator. The diamine monomer is selected from at least one of 3,4'-diaminodiphenyl ether, 4,4'-diaminobenzoyl aniline, N,N'-bis(4-aminophenyl)terephthalamide, 3,5-diaminobenzoic acid, 4,4-diaminodiphenylmethane, 2,2'-bis(trifluoromethyl)-4,4'-bis(4-aminophenylcarbonylamino)biphenyl, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3,3'-dihydroxybenzidine, and 9,9-bis(4-aminophenyl)fluorene; The dianhydride monomer is selected from at least one of pyromellitic dianhydride, 4,4'-oxobisphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, 3,3,4,4-diphenylsulfone tetracarboxylic anhydride, and hexafluorodianhydride. The curing accelerator is selected from at least one of triethylamine, benzimidazole, 1-methylimidazole, quinoline, 1,8-diazabicycloundec-7-ene, imidazole, pyridine, and 3-methylpyridine.

9. The double-sided porous polyimide membrane prepared by the roll-to-roll coating method according to any one of claims 1-8; Preferably, the porosity of the double-sided porous polyimide membrane is above 55%, and the difference in porosity between the two sides is below 13%. More preferably, the average pore size of the double-sided porous polyimide membrane is 1.44-1.83 μm, and the difference between the average pore sizes of the two sides is less than 13%.

10. Use of the double-sided porous polyimide separator of claim 9 in a battery. Preferably, the battery is a lithium battery.

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