CN108341987B

CN108341987B - Aromatic polyamide porous membrane, preparation method thereof and lithium ion secondary battery

Info

Publication number: CN108341987B
Application number: CN201710043659.9A
Authority: CN
Inventors: 孙庆津; 李翔; 黄和极
Original assignee: Micro Macro Power System (huzhou) Co Ltd
Current assignee: Weihong Advanced Membrane Co.
Priority date: 2017-01-21
Filing date: 2017-01-21
Publication date: 2020-01-14
Anticipated expiration: 2037-01-21
Also published as: CN108341987A

Abstract

The invention provides an aromatic polyamide porous membrane, a preparation method thereof and a lithium ion secondary battery, wherein the whole body of the aromatic polyamide porous membrane is a three-dimensional network porous structure; the size of the holes is in the micron order. The network-shaped porous structure of the aromatic polyamide porous membrane is communicated from the inside to the surface, is a whole, is very suitable for a lithium battery diaphragm, and the preparation method of the porous membrane is simple and is suitable for the requirement of large-scale industrial production.

Description

Aromatic polyamide porous membrane, preparation method thereof and lithium ion secondary battery

Technical Field

The present invention relates to an aromatic polyamide porous film, a method for producing the same, and a lithium ion secondary battery.

Background

The lithium battery diaphragm belongs to one of porous membranes, and with the help of the vigorous development of the lithium battery industry, the production demand of the diaphragm is increased dramatically. The diaphragm is one of the key components of the battery, is positioned between the positive electrode and the negative electrode of the battery and is used for isolating the positive electrode and the negative electrode so as to avoid the internal short circuit of the battery and ensure that lithium ions can smoothly pass through the diaphragm during charging and discharging. At present, the diaphragm widely applied to the lithium ion secondary battery is mainly a polyolefin melt-draw diaphragm, but the use temperature is not high due to the limitation of the polyolefin material. However, in a working environment of large-current charging and discharging, the internal temperature of the battery may rapidly rise, closed pores of the polyolefin diaphragm are easily closed, and even thermal shrinkage occurs, so that the internal resistance of the battery is significantly increased, and finally the battery fails.

The aromatic polyamide polymers (PPTA, PMIA, PBA and PSA) have high heat resistance, the glass transition temperature of the aromatic polyamide polymers is more than 300 ℃, the thermal decomposition temperature of the aromatic polyamide polymers is as high as 560 ℃, and the aromatic polyamide polymers also have high insulativity and chemical corrosion resistance and are very suitable for being used as lithium ion battery separators. At present, there are research institutions in China which apply aramid fibers to lithium ion battery separators, for example, in Chinese patent with publication number CN103242556A and Chinese patent with publication number CN202384420U, aromatic polyamide polymer fibers are coated on the surfaces of polyolefin separators. However, these methods are limited to polyolefin substrates, and the use temperature of the separator is not too high, which limits the range of applications of the separator.

In order to embody the superiority of the aromatic polyamide polymer material in the field of lithium batteries, a porous film which takes the aromatic polyamide polymer as a base material and meets the application requirement of the batteries needs to be prepared. Currently, porous membranes are typically prepared using either a non-solvent induced phase inversion process (DIPS) or a thermally induced phase separation process (TIPS). TIPS is a polymer microporous membrane obtained by forming a homogeneous casting solution from a crystalline and thermoplastic polymer and a diluent with a high boiling point and a low molecular weight at a high temperature, performing solid-liquid or liquid-liquid phase separation when the temperature is reduced, and then removing the diluent. However, TIPS is not suitable for the production of an aromatic polyamide polymer porous film due to the high heat resistance of the aromatic polyamide polymer itself. In a solvent phase inversion method (NIPS), the diaphragm is prepared in the process of converting a polymer solution with a solvent system as a continuous phase into a three-dimensional macromolecular network gel of the continuous phase, but the aromatic polyamide polymer has high molecular orientation degree and very high crystallinity, is easy to form a compact skin layer structure, causes poor air permeability of a porous membrane, and increases the internal resistance of the battery in the application of the battery. Dongli corporation (patent publication No. US20080113177A1) can form an aromatic polyamide porous membrane by adding a phase separation controlling agent for preventing the coagulation of the aramid resin, but this solution has very high requirements for temperature and humidity, and has a long production time, and it is difficult to realize industrialization.

Disclosure of Invention

In order to solve the above problems, the present invention provides an aromatic polyamide porous film having a three-dimensional network-like porous structure as a whole; the size of the holes is in the micron order. The network-shaped porous structure of the aromatic polyamide porous membrane is communicated from the inside to the surface and is an integral structure, and the network-shaped porous structure is a micron-sized porous structure.

In one embodiment, the aromatic polyamide porous film of the present invention has an air permeability of 50 to 500 seconds/100 CC. In another embodiment, the aromatic polyamide porous film of the present invention has an air permeability of 80 to 200 seconds/100 CC.

The invention is not limited to the kind of the aromatic polyamide as the porous film raw material. In one embodiment, the aromatic polyamide is selected from at least one of poly (p-phenylene terephthalamide) (aramid 1414, PPTA), poly (m-phenylene isophthalamide) (aramid 1313, PMIA), poly (p-benzamide) (aramid i, PBA), and poly (phenylene sulfone-terephthalamide).

Another object of the present invention is to provide a method for preparing the above aromatic polyamide porous film, comprising: providing an aromatic polyamide solution; the solution forms a film in a gel bath; the membrane forms a membrane to be treated after the solvent is extracted by the extractant; and removing the surface of the film to be treated to form a porous film. Wherein the membrane to be treated has a structure with a compact surface and porous inside. The membrane to be treated is prepared by an NIPS method, a membrane structure with a compact surface skin and a porous framework inside is formed, and an integrally communicated membrane with a three-dimensional reticular pore structure is obtained by removing an upper skin layer and a lower skin layer on the outer surface of the membrane to be treated. The invention adopts a non-solvent phase conversion method to prepare the porous membrane, has low membrane preparation temperature, is easy to control the parameters of the production process, and is suitable for the requirement of industrial production. The peeling device for peeling can adopt at least one of a scraper blade, a brush and a rubber roller. The rubber roller is preferably a rough-surface rubber roller. The membrane to be treated is formed after the solvent is extracted by the extractant, wherein the solvent extracted by the extractant is the solvent in the aromatic polyamide solution, namely the solvent used for preparing the aromatic polyamide solution, and mainly refers to the solvent capable of dissolving the aromatic polyamide.

In one embodiment, the aromatic polyamide porous membrane is obtained by drying the porous membrane. In another embodiment, the aromatic polyamide porous membrane is obtained by drying and heat-setting the porous membrane in sequence.

The thickness of the film to be treated prepared by the method is 10-40 micrometers; the thickness of the skin is less than 0.1 microns. In one embodiment, the thickness of the film to be treated is 12 to 30 micrometers; the thickness of the skin is less than 0.1 microns. In another embodiment, the thickness of the film to be treated is 15-20 microns; the thickness of the skin is less than 0.1 microns.

The present invention is not limited as to how the aromatic polyamide solution is prepared. As an embodiment, the aromatic polyamide solution preparation method includes: the aromatic polyamide fiber and the solvent are mixed to form an aromatic polyamide solution.

As an embodiment, the aromatic polyamide solution preparation method includes: mixing aromatic polyamide fiber, solvent, cosolvent and pore-foaming agent to form aromatic polyamide solution.

As an embodiment, the aromatic polyamide fibers are selected from aromatic polyamide staple fibers and/or aromatic polyamide fibrids. The aromatic polyamide fibers of the present invention may also be selected from other commonly used aromatic polyamide fibers made from films.

As an embodiment, the solvent is selected from the group consisting of N-methylpyrrolidone (NMP), N-Dimethylacetamide (DMAC), N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), triethyl phosphate (TEP), and concentrated sulfuric acid (H)₂SO₄) At least one of them. The concentrated sulfuric acid (H)₂SO₄) The concentration of (B) is preferably 70 to 80 wt%. The solvent herein means a solvent capable of dissolving the aromatic polyamide.

The aromatic polyamide fiber is dissolved in a solvent, and a cosolvent added in the dissolving process is selected from sodium chloride (NaCl), lithium chloride (LiCl) and calcium chloride (CaCl)₂) And magnesium chloride (MgCl)₂) One kind of (1).

As an embodiment, the aromatic polyamide solution preparation method includes: the aromatic polyamide solution is formed by polymerization. The solvent used in the polymerization reaction is selected from the group consisting of N-methylpyrrolidone (NMP), N-Dimethylacetamide (DMAC), N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), triethyl phosphate (TEP) and concentrated sulfuric acid (H)₂SO₄) At least one of them. The concentrated sulfuric acid (H)₂SO₄) The concentration of (B) is preferably 70 to 80 wt%.

As an embodiment, a porogen is added to the polymerization reaction. The polymerization reaction may be carried out in a twin-screw polymerization or a reaction tank, and is not particularly limited.

As an embodiment, the porogen is selected from at least one of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), and ionic liquid.

In one embodiment, the ionic liquid is at least one selected from the group consisting of quaternary ammonium salts, quaternary phosphonium salts, imidazolium salts, pyridinium salts, piperidine salts, and pyrrolidine salts. Such ionic liquids are more readily soluble in aromatic polyamide solutions and therefore more conveniently formulated into solutions.

As an embodiment, the gel bath includes a first component; the first component is water or dichloromethane. As an embodiment, the gel bath further comprises a second component; the second component is at least one selected from N-methyl pyrrolidone, N-dimethyl acetamide, N-dimethyl formamide, dimethyl sulfoxide and triethyl phosphate. The gel bath component is preferably used primarily to prepare the solvent used for the aromatic polyamide solution. The aromatic polyamide solution is prepared by DMAC solvent, and the components of the gelling bath may be: water, water and DMAC, dichloromethane and DMAC, and the like.

In one embodiment, the mass fraction of water or dichloromethane in the gel bath is 5 to 80%. In one embodiment, the mass fraction of water or dichloromethane in the gel bath is 20 to 60%. In one embodiment, the mass fraction of water or dichloromethane in the gel bath is 30 to 50%.

In one embodiment, the temperature of the gel bath is controlled to be 0 to 80 ℃. In one embodiment, the temperature of the gel bath is controlled to be 10 to 60 ℃.

In one embodiment, the time for forming the film in the gel bath is controlled to be 10 to 300 seconds. In one embodiment, the time for forming the film in the gel bath is controlled to be 30 to 200 seconds.

In one embodiment, the extractant is water and/or dichloromethane. In one embodiment, the temperature of the extracting agent is controlled to be 20-100 ℃. In one embodiment, the temperature of the extracting agent is controlled to be 30-70 ℃.

Under the synergistic effect of the components of the gel bath, the temperature of the gel bath, the components of the extracting agent and the temperature of the extracting agent, the membrane to be treated is easy to form a structure with compact skin and porous inside and form compact skin which is easy to shed. The invention further removes the epidermis by a peeling device to obtain the membrane with the surface layer of micron-sized porous structure and the interior of three-dimensional reticular porous structure.

The preferred temperature and preferred component concentration of the gel bath of the invention are further optimized and form a dense membrane structure with a surface layer and a porous inner part: among these, the preferred gelling bath of the present invention has a water concentration that optimizes the rate of diffusion of the solvent in the film, and the preferred gelling bath of the present invention has a water concentration that provides an optimal concentration difference between the solvent in the gelling bath and the solvent in the film, which allows the film to form an excellent porous structure. The aromatic polyamide-based polymer has a high degree of molecular orientation and very high crystallinity, and an excessively high water content in the gel bath results in an excessively large concentration difference, so that the inside of the film is integrated with the skin, and the skin layer is difficult to separate. Conversely, when the water concentration is too low, the film is difficult to cure. The preferred temperature and preferred component concentration of the gelling bath ensure that the film forms a nano-scale compact skin layer after entering the gelling bath, and the solvent of the film diffuses into the gelling bath relatively quickly to form a good porous structure. After the film is gelled, although a compact skin layer is formed on the surface of the film and the film is completely cured and molded, the interior of the film does not completely complete phase transformation and still exists in a colloidal state. In addition, on the premise that the concentration of water and/or dichloromethane in the gel bath is preferable, if the temperature of the gel bath is too low, the solvent in the colloid which has not completed phase transition in the film diffuses into the gel bath too slowly, so that the film interior is integrated with the skin and the skin layer is difficult to be separated.

Another object of the present invention is to provide a method for preparing an aromatic polyamide porous film, comprising: providing an aromatic polyamide solution; the solution flows out through a slit to form a membrane in a gel bath; the membrane forms a membrane to be treated after the solvent is extracted by the extractant; removing the surface of the film to be treated to form a porous film; and drying the porous film to obtain the aromatic polyamide porous film. The membrane to be treated has a structure with a compact surface and porous inside. The slit flowing out means that the solution is formed into a film through a slit, and therefore any die capable of forming a slit shape can be used, and it is generally preferable to form a slit by using a doctor blade or a slit by using an extrusion die, that is, the solution is formed into a film after flowing out through a slit formed by a doctor blade or the solution is formed into a film after flowing out through a slit of an extrusion die. The peeling device for peeling can adopt a scraper, a brush or a rubber roller with a rough surface. In one embodiment, the porous film is dried and heat-set in sequence to obtain the aromatic polyamide porous film.

As an embodiment, the slit is formed by a doctor blade or an extrusion die. As an embodiment, the drying is infrared drying and/or forced air drying.

In one embodiment, the drying temperature is controlled to be 50 to 150 ℃. In one embodiment, the drying temperature is controlled to be 80-120 ℃.

In one embodiment, the heat setting is infrared heating. In one embodiment, the heat setting temperature is controlled to be 150 to 300 ℃. In one embodiment, the heat setting temperature is controlled to be 200-250 ℃.

Another object of the present invention is to provide a lithium ion secondary battery comprising the above aromatic polyamide porous film.

Drawings

FIG. 1 is an SEM image of the surface of a film to be treated prepared in example 1 of the present invention;

FIG. 2 is an SEM photograph of the surface of an aromatic polyamide porous membrane prepared in example 1 of the present invention;

FIG. 3 is a flow chart showing the production of the aromatic polyamide porous film of the present invention.

In the figure, 1-die head, 2-gel tank, 3-extraction tank, 4-peeling device, 5-dryer, 6-shaping box and 7-winding machine.

Detailed Description

The following specific examples describe the present invention in detail, however, the present invention is not limited to the following examples.

Example 1

Poly (m-phenylene isophthalamide) solution (8000g) is obtained through two-stage screw polymerization, and the solvent is DMAC, wherein the polymer mass percentage concentration is 11.1%. And (2) extruding the solution through a die head by a melt pump after defoaming, and then feeding the solution into a gel bath to form a film, wherein the gel bath comprises water and DMAC, the mass proportion of the water in the gel bath is 30%, the temperature of the gel bath is 30 ℃, and the gel time is 100 seconds. And then, drawing the membrane into an extraction tank, wherein the temperature of the extraction tank is 80 ℃, and extracting the solvent by using water, thereby forming the membrane to be treated with compact skin and porous inside. Removing the epidermis of the film to be treated by a brush, drying by hot air at 100 ℃, and finally entering a high-temperature shaping box at 250 ℃. And finishing rolling after static electricity removal. The air permeability was measured to be 100 seconds/100 CC.

Example 2

A solution of polyphenylsulfone terephthalamide (6000g) was polymerized in a reactor in the solvent DMAC, with a polymer concentration of 33% by weight. Methyltriethylammonium acetate (120g) and the polyphenylsulfone terephthalamide solution prepared above were mixed in a mass ratio of 1: and 5, metering, injecting into a double screw machine, mixing and dispersing, defoaming, extruding in a die head through a melt pump, and then entering into a gel bath to form a film, wherein the gel bath is water and DMAC. The mass of water in the gel bath accounts for 20%, the temperature of the gel bath is 0 ℃, and the gel time is 200 seconds. And then, drawing the membrane into an extraction tank, wherein the temperature of the extraction tank is 20 ℃, and extracting the solvent by using water, thereby forming the membrane to be treated with compact skin and porous inside. Removing the epidermis of the film to be treated by a silica gel scraper, drying by hot air at 100 ℃, and finally entering a high-temperature shaping box at 200 ℃. And finishing rolling after static electricity removal. The air permeability was measured to be 120 seconds/100 CC.

Example 3

Poly (m-phenylene isophthalamide) solution (4000g) was obtained by two-stage screw polymerization in the solvent of DMAC, wherein the polymer mass percentage concentration was 25%. PEG-400 (polyethylene glycol 400, 333g) and the polyisophthaloyl metaphenylene diamine solution prepared in the above are mixed according to a mass ratio of 1: and (3) metering 10, injecting into a double screw machine, mixing and dispersing, defoaming, extruding in a die head through a melt pump, and then entering into a gel bath to form a film, wherein the gel bath is water and DMAC. The mass of water in the gel bath accounts for 36%, the temperature of the gel bath is 15 ℃, and the gel time is 100 seconds. And then, drawing the membrane into an extraction tank, wherein the temperature of the extraction tank is 80 ℃, and extracting the solvent by using water, thereby forming the membrane to be treated with compact skin and porous inside. Removing the epidermis of the film to be treated by a brush, drying by hot air at 120 ℃, and finally entering a high-temperature shaping box at 220 ℃. And finishing rolling after static electricity removal. The air permeability was measured to be 100 seconds/100 CC.

Example 4

In the same manner as in example 2, except that the porogen was added in the polymerization to give PVPK-30 having a mass of 200g, the air permeability was measured to be 80 seconds/100 CC.

Example 5

The same as example 2, except that the porogen was added in the polymerization to give DOP in an amount of 20g by mass. The air permeability was measured to be 50 seconds/100 CC.

Example 6

The same as example 2, except that the gel bath was water, the temperature of the gel bath was 40 ℃, the gel time was 150 seconds, and the drying temperature was 150 ℃. The air permeability was measured to be 280 seconds/100 CC.

Example 7

2000g of polyphenylsulfone terephthalamide solution is obtained by polymerization in a reaction kettle, and the solvent is DMF, wherein the mass percentage concentration of the polymer is 22%. Mixing N-methyl-N-propyl pyrryl onium fluoborate (110g) and the solution of the polyphenylsulfone terephthalamide prepared in the mass ratio of 1: 4, metering and injecting the mixture into a three-screw machine for mixing and dispersing, defoaming, extruding the mixture through a die head by a melt pump, and then entering a gel bath to form a film, wherein the gel bath is dichloromethane and DMF. The mass proportion of the dichloromethane in the gel bath is 20%, the temperature of the gel bath is 20 ℃, and the gel time is 180 seconds. And then, drawing the membrane into an extraction tank, wherein the temperature of the extraction tank is 20 ℃, and extracting the solvent by using dichloromethane, thereby forming the membrane to be treated with compact skin and porous inside. Removing the epidermis of the film to be treated by a brush, drying by hot air at 50 ℃, and finally entering a high-temperature shaping box at 300 ℃. And finishing rolling after static electricity removal. The air permeability was measured to be 150 seconds/100 CC.

Example 8

600g of polyisophthaloyl metaphenylene diamine short fiber is dissolved in 2400g of DMAC solvent to prepare a polymer solution, wherein the mass percentage concentration of the polymer is 20%. Methyl tributylammonium hydrochloride (160g) and the polyisophthaloyl metaphenylene diamine solution prepared above were mixed in a mass ratio of 1: and 5, metering, injecting into a three-screw machine, mixing and dispersing, defoaming, extruding in a die head through a melt pump, and then entering into a gel bath to form a film, wherein the gel bath is water and DMAC. The mass of water in the gel bath accounts for 5%, the temperature of the gel bath is 40 ℃, and the gel time is 80 seconds. And then, drawing the membrane into an extraction tank, wherein the temperature of the extraction tank is 100 ℃, and extracting the solvent by using water, thereby forming the membrane to be treated with compact skin and porous inside. Removing the epidermis of the film to be treated by a brush, drying by hot air at 80 ℃, and finally entering a high-temperature shaping box at 250 ℃. And finishing rolling after static electricity removal. The air permeability was measured to be 60 seconds/100 CC.

Example 9

180g of poly-p-phenylene terephthamide short fiber is dissolved in 1000g of concentrated sulfuric acid solvent, 6g of LiCl is added to be used as a cosolvent to prepare a polymer solution, the polymer solution is uniformly stirred under the negative pressure condition, and is defoamed and extruded out at a die head through a melt pump, and then enters a gel bath to form a film, wherein the gel bath is DMAC and water. The mass of water in the gel bath accounts for 70%, the temperature of the gel bath is 80 ℃, and the gel time is 250 seconds. And then, drawing the film into an extraction tank, wherein the temperature of the extraction tank is 30 ℃, and extracting the solvent by using water, thereby forming the film to be treated with compact skin and porous inner part. Removing the surface of the film to be treated by a brush, drying by hot air at 150 ℃, and finally entering a high-temperature shaping box at 200 ℃. And finishing rolling after static electricity removal. The air permeability was measured to be 470 seconds/100 CC.

Claims

1. A method for producing an aromatic polyamide porous film, comprising: providing an aromatic polyamide solution;

the solution forms a film in a gel bath; the membrane forms a membrane to be treated after the solvent is extracted by the extractant;

removing the surface skin of the film to be treated to form a porous film; removing the surface skin of the film to be treated to form a porous film, wherein the method comprises removing the surface skin of the film to be treated by adopting at least one of a scraper blade, a brush and a rubber roller to form the porous film; the gel bath includes a first component; the first component is water or dichloromethane; the mass fraction of water or dichloromethane in the gel bath is 5-80%; the extractant is water and/or dichloromethane.

2. The process according to claim 1, characterized in that: and drying the porous membrane formed after the surface skin is removed to obtain the aromatic polyamide porous membrane.

3. The process according to claim 2, characterized in that: and drying and heat setting the porous membrane formed after the surface skin is removed in sequence to obtain the aromatic polyamide porous membrane.

4. The process according to claim 1, characterized in that: the thickness of the film to be treated is 10-40 microns; the thickness of the skin is less than 0.1 microns.

5. The process according to claim 1, characterized in that: the preparation method of the aromatic polyamide solution comprises the following steps: the aromatic polyamide fiber and the solvent are mixed to form an aromatic polyamide solution.

6. The process according to claim 5, characterized in that: the preparation method of the aromatic polyamide solution comprises the following steps: mixing aromatic polyamide fiber, solvent, cosolvent and pore-foaming agent to form aromatic polyamide solution.

7. The process according to claim 5 or 6, characterized in that: the aromatic polyamide fiber is selected from aromatic polyamide short fiber and/or aromatic polyamide fibrid.

8. The process according to claim 1, 5 or 6, characterized in that: the solvent is selected from N-methylpyrrolidone (NMP), N-Dimethylacetamide (DMAC), N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), triethyl phosphate (TEP) and concentrated sulfuric acid (H)₂SO₄) At least one of them.

9. The process according to claim 6, characterized in that: the cosolvent is selected from one of sodium chloride, lithium chloride, calcium chloride and magnesium chloride.

10. The process according to claim 1, characterized in that: the preparation method of the aromatic polyamide solution comprises the following steps: the aromatic polyamide solution is formed by polymerization.

11. The process according to claim 10, characterized in that: and adding a pore-foaming agent in the polymerization reaction.

12. The process according to claim 6 or 11, characterized in that: the pore-foaming agent is selected from at least one of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), dibutyl phthalate (DBP), dioctyl phthalate (DOP) and ionic liquid.

13. The method of claim 12, wherein: the ionic liquid is at least one selected from quaternary ammonium salt, quaternary phosphonium salt, imidazolium salt, pyridinium salt, piperidine salt and pyrrolidine salt.

14. The process according to claim 1, characterized in that: the gel bath further comprises a second component; the second component is at least one selected from N-methyl pyrrolidone, N-dimethyl acetamide, N-dimethyl formamide, dimethyl sulfoxide and triethyl phosphate.

15. The process according to claim 1, characterized in that: the mass fraction of water or dichloromethane in the gel bath is 20-60%.

16. The process according to claim 1, characterized in that: the temperature of the gel bath is controlled to be 0-80 ℃.

17. The process according to claim 1, characterized in that: the time for forming the film in the gel bath is controlled to be 10-300 seconds.

18. The process according to claim 1, characterized in that: the temperature of the extracting agent is controlled to be 20-100 ℃.

19. The process according to claim 1, characterized in that: providing an aromatic polyamide solution; the solution flows out through a slit to form a membrane in a gel bath; the membrane forms a membrane to be treated after the solvent is extracted by the extractant; removing the surface of the film to be treated to form a porous film; and drying the porous membrane to obtain the aromatic polyamide porous membrane.

20. The method of claim 19, wherein: and drying and heat setting the porous membrane in sequence to obtain the aromatic polyamide porous membrane.

21. The method of claim 19, wherein: the slit is formed by a doctor blade or an extrusion die.

22. A method of preparation according to claim 2, 3 or 19, characterized in that: the drying is infrared drying and/or forced air drying.

23. The method of claim 22, wherein: the drying temperature is controlled to be 50-150 ℃.

24. The process according to claim 3 or 20, characterized in that: the heat setting is infrared heating.

25. The method of claim 24, wherein: the heat setting temperature is controlled to be 150-300 ℃.