阅读说明：本技术 一种具有交联形貌的聚酰亚胺隔膜及其制备方法 (Polyimide diaphragm with cross-linking morphology and preparation method thereof ) 是由 贾南方 王杰 于 2021-08-27 设计创作，主要内容包括：本发明涉及一种具有交联形貌的聚酰亚胺多孔膜及其制备方法,先利用低温缩合聚合制备聚酰亚胺前驱体聚酰胺酸溶液,通过静电纺丝法得到聚酰胺酸纳米纤维膜,随后将其放入高温热炉进行部分环化处理,再将聚酰胺酸溶液涂覆于部分环化的纳米纤维膜,干燥后将纳米纤维膜进行完全亚胺化处理,制备出含有交联结构的聚酰亚胺纳米纤维膜,其拉伸强度可达40-250MPa,穿刺强度大于4.0N,孔隙率20～95％可调节,厚度为2～30微米。本发明工艺简便,生产效率高,绿色环保,能有效解决纳米纤维膜力学性能不足的缺点,可应用于锂离子电池隔膜、超级电容器隔膜、高温过滤以及吸附等领域。(The invention relates to a polyimide porous membrane with a cross-linking morphology and a preparation method thereof, which comprises the steps of preparing a polyimide precursor polyamide acid solution by low-temperature condensation polymerization, obtaining a polyamide acid nanofiber membrane by an electrostatic spinning method, then placing the polyamide acid nanofiber membrane into a high-temperature heating furnace for partial cyclization treatment, coating the polyamide acid solution on the partially cyclized nanofiber membrane, drying, and then performing complete imidization treatment on the nanofiber membrane to prepare the polyimide nanofiber membrane with the cross-linking structure, wherein the tensile strength of the polyimide nanofiber membrane can reach 40-250MPa, the puncture strength of the polyimide nanofiber membrane is greater than 4.0N, the porosity of the polyimide nanofiber membrane is 20-95%, and the thickness of the polyimide nanofiber membrane is 2-30 micrometers. The method has the advantages of simple and convenient process, high production efficiency, environmental protection, capability of effectively solving the defect of insufficient mechanical property of the nanofiber membrane, and capability of being applied to the fields of lithium ion battery membranes, supercapacitor membranes, high-temperature filtration, adsorption and the like.)

1. The polyimide diaphragm with the cross-linking morphology is characterized in that the thickness of the polyimide diaphragm with the cross-linking morphology is 2-30 μm, preferably 3-10 μm; porosity of 20% to 95%, preferably 30% to 90%; the tensile strength is 40-250MPa, the puncture strength is more than 4.0N, and the transverse and longitudinal thermal shrinkage rates at 300 ℃ are less than 1.5 percent.

2. The polyimide membrane with cross-linked morphology according to claim 1, wherein the diameter of the polyimide fibers in the polyimide membrane with cross-linked morphology is 20-2000nm, preferably 50-1000 nm.

3. The method for preparing the polyimide diaphragm with the cross-linked morphology according to claim 1, characterized by comprising the following steps:

a: preparing a polyamic acid solution by adopting dibasic acid anhydride and diamine, and then preparing a polyamic acid nanofiber membrane by adopting an electrostatic spinning process;

b: carrying out heat treatment on the polyamic acid nanofiber membrane to prepare a partially imidized polyimide nanofiber membrane;

c: coating a polyamic acid solution on the surface of the partially imidized polyimide nanofiber membrane;

d: and D, carrying out heat treatment on the nanofiber membrane obtained in the step C to obtain the polyimide diaphragm with a cross-linking appearance.

4. The preparation method of the polyimide diaphragm with the cross-linking morphology according to claim 3, wherein the solid content of the polyamic acid solution in the step A is 5-30 wt%, preferably 8-20 wt%; the polyamic acid solution is prepared by at least one diamine and at least one dibasic anhydride; the diamine is at least one selected from diaminodiphenyl ether, p-phenylenediamine, 4 ' -diaminodiphenylmethane and 4,4 ' -diamino-2, 2 ' -bis-trifluoromethyl biphenyl, and the dicarboxylic anhydride is at least one selected from biphenyl tetracarboxylic dianhydride, pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, hexafluoro dianhydride and bisphenol A type diether dianhydride; the molar ratio of the dibasic acid anhydride to the diamine is 0.95:1-1.05: 1.

5. The method for preparing a polyimide diaphragm having a crosslinked morphology according to claim 3, wherein the heat treatment in step B is performed in a high temperature furnace under the following conditions: the temperature is 130-260 ℃, the preferable temperature is 140-250 ℃, and the time is 3 s-2 h, the preferable time is 5 s-1 h.

6. The method for preparing a polyimide separator having a crosslinked morphology according to claim 3, wherein the mass fraction of the polyamic acid solution used for coating in step C is 0.05 to 15 wt%, preferably 0.1 to 10 wt%.

7. The method for preparing a polyimide diaphragm with a cross-linking appearance according to claim 3, wherein the composition of the polyamic acid in the polyamic acid solution used for coating in the step C is the same as or different from that of the polyamic acid obtained in the step A.

8. The method of claim 3, wherein the amount of the polyamic acid solution used in step C relative to the partially imidized polyimide nanofiber membrane is 0.0002 to 0.02ml/cm²Preferably 0.0004 to 0.01ml/cm²(ii) a The coating method is one of an electrostatic spraying method, a blade coating method, a transfer coating method, a dipping coating method, a gravure coating method and an extrusion coating method.

Technical Field

The invention belongs to the field of polymer-based porous membrane materials, and particularly relates to a polyimide diaphragm with a cross-linked structure and a preparation method thereof.

Background

With the increasing increase of environmental pollution and the decreasing of fossil energy, it has been an irreversible trend to develop new energy sources that can replace low pollution. With the rapid development of scientific technology, the lithium ion battery greatly improves the life style of people, becomes an indispensable article in daily life, is used as a diaphragm of a key part of the ion battery, the performance and safety of the lithium ion battery are directly affected by the performance of the lithium ion battery, and the recent frequent battery safety accidents cause public attention to the battery safety again. The traditional lithium ion battery diaphragm adopts a polyolefin microporous membrane, such as a polypropylene (PP), Polyethylene (PE) and PP/PE/PP three-layer composite diaphragm, and has the characteristics of low price, good chemical corrosion resistance, excellent mechanical property and the like. However, due to the molecular chain structure and nonpolar nature of the polyolefin diaphragm, the polyolefin diaphragm has poor temperature resistance and poor electrolyte wettability, so that the damage and melting of the diaphragm are easily caused in the use process and the charging and discharging process of the battery, and the battery safety accident is caused. The polyolefin diaphragm can not meet the urgent requirements of people for high specific energy and high power lithium ion batteries. Polyimide has the characteristics of high and low temperature resistance, low dielectric, radiation resistance, high strength and the like due to imide groups and aromatic heterocycles of the main chain of the polyimide, and is widely applied to the fields of aerospace, microelectronics, communication, traffic, advanced composite materials and the like. With the development of material preparation technology, the polyimide nanofiber membrane prepared by an electrostatic spinning method is expected to be used as a lithium battery diaphragm due to excellent comprehensive performance, the polyimide nanofiber membrane prepared by the electrospinning technology has high porosity, high electrolyte wettability, high temperature resistance and excellent thermal dimensional stability, but the polyimide nanofiber non-woven fabric is formed by stacking nanofibers without folding, loose physical lap joints are formed among fibers, so that the mechanical property of the nanofiber membrane is poor, the tensile strength is about 5-10 MPa, and the polyimide nanofiber membrane cannot withstand the winding or laminating process in the battery production process, and the large-scale application of the polyimide nanofiber membrane is seriously hindered. In order to solve the safety problem of the existing polyolefin diaphragm in the use of a high-specific energy and high-power lithium ion battery and actively apply the novel high-temperature-resistant diaphragm to industrial production, a micro-crosslinking structure is introduced among nano fibers to form a simple and efficient technical means for preparing a polyimide nano fiber membrane with crosslinking appearance and high mechanical strength.

Patents CN1042133A and CN102766270A disclose two polyimide nanofiber membranes with cross-linked morphology. In the method disclosed in CN1042133A, a high-temperature thermal crosslinking method is adopted, and a crosslinked structure is obtained by performing high-temperature thermal treatment on the polyimide nanofibers to melt the polyimide nanofibers, so that the mechanical properties are improved. However, the melt crosslinking method has limited applicable systems, and must be thermoplastic polyimide, and the fiber melting during the heat treatment process also causes great shrinkage of the fiber membrane, so that the preparation of the polyimide nanofiber membrane with a crosslinked morphology by the method has limitations. CN102766270A adopts an alkali liquor etching method to form a hydrolytic swelling layer on the surface of a fiber, the fiber dissolves and forms a cross-linking point, the polyimide nanofiber membrane with a cross-linking appearance is obtained by hot cyclization after cleaning, the defect that thermosetting polyimide can not obtain the cross-linking appearance through melting is overcome, the preparation range of the polyimide nanofiber membrane with the cross-linking appearance is widened, but polyimide and precursor polyamic acid are not alkali-resistant, the condition control of the treatment process is extremely difficult, the alkalinity of etching solution is strong and weak, the treatment time can generate great influence on the chemical structure of the fiber membrane and the fiber appearance, the aftertreatment process is complex, a large amount of water resources can be used, and the green environmental protection concept is not met. The two methods have advantages and disadvantages, and further large-scale preparation is difficult.

Disclosure of Invention

The invention aims to provide a preparation method of a polyimide diaphragm with a cross-linking morphology, the method is flexible and simple to operate, the process is simple, the potential of industrial production is realized, the prepared polyimide diaphragm is excellent in comprehensive performance, and the application prospect is good.

The polyimide diaphragm with the cross-linking morphology is characterized in that the porosity is 20% -95%, the tensile strength is 40-250MPa, the puncture strength is greater than 4.0N, and the transverse and longitudinal thermal shrinkage rates at 300 ℃ are less than 1.5%.

Further, the porosity is preferably 30% to 90%;

further, the thickness of the polyimide diaphragm with the cross-linked morphology is 2-50 μm, and preferably 3-10 μm.

Further, the diameter of the polyimide fiber in the polyimide diaphragm with the cross-linked morphology is 20-2000nm, preferably 50-1000 nm.

A preparation method of a polyimide diaphragm with a cross-linking appearance is characterized by comprising the following steps:

a: preparing a polyamic acid solution by adopting at least one dicarboxylic anhydride and at least one diamine, and then preparing a polyamic acid nanofiber membrane by adopting an electrostatic spinning process;

b: carrying out heat treatment on the polyamic acid nanofiber membrane to prepare a partially imidized polyimide nanofiber membrane;

c: applying a polyamic acid solution to the surface of the partially imidized polyimide nanofiber membrane;

d: and D, carrying out heat treatment on the nanofiber membrane obtained in the step C to obtain the polyimide diaphragm with a cross-linking appearance.

Further, the molar ratio of the polyamic acid solution, the dibasic acid anhydride and the diamine in the step A is 0.95:1-1.05: 1.

Further, the dibasic acid anhydride is one or a mixture of more than two of biphenyl tetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), Benzophenone Tetracarboxylic Dianhydride (BTDA), diphenyl ether tetracarboxylic dianhydride (ODPA), hexafluoro dianhydride (6FDA) and bisphenol A type diether dianhydride (BPADA), and the diamine is one or a mixture of more than two of diaminodiphenyl ether (ODA), p-Phenylenediamine (PDA), 4 ' -diaminodiphenylmethane (MDA) and 4,4 ' -diamino-2, 2 ' -bistrifluoromethylbiphenyl (TFDB).

Further, the dicarboxylic anhydride and the diamine are subjected to low-temperature condensation polymerization in a polar aprotic solvent,

the synthesis temperature of the polyamic acid solution is-15 ℃, and preferably-10 ℃.

Further, the polar aprotic solvent is one or more of N, N-Dimethylacetamide (DMAC), N-Dimethylformamide (DMF), N-methylpyrrolidone (NMP), and Dimethylsulfoxide (DMSO).

The solid content of the polyamic acid solution in the step A is 5-30%, and preferably 8-20%.

Further, the heat treatment in the step B is performed in a high temperature furnace, and the heat treatment conditions are as follows: the temperature is 130-260 ℃, the preferable temperature is 140-250 ℃, and the time is 3 s-2 h, the preferable time is 5 s-1 h.

Further, the mass fraction of the polyamic acid solution used for coating in the step C is 0.05-15%, preferably 0.1-10%; the composition of the polyamic acid in the polyamic acid solution used for coating may be the same as or different from that of the polyamic acid obtained in step A.

The coating method includes one of electrostatic spraying, knife coating, transfer coating, dip coating, gravure coating, and extrusion coating.

The amount of polyamic acid solution used relative to the partially imidized polyimide nanofiber membrane is 0.0002 to 0.02ml/cm²Preferably 0.0004 to 0.01ml/cm²。

Further, the heat treatment process adopted in the step D is as follows: the heating rate is 2-30 ℃/min, preferably 5-20 ℃/min, the final temperature is 460 ℃ at 250-.

An article comprising the polyimide separator having a crosslinked morphology.

Compared with the prior art, the method has the following excellent effects:

1. the method of the invention realizes the construction of the cross-linking morphology of the polyimide nanofiber membrane by using a solution coating technology, greatly improves the mechanical strength and the dimensional stability of the polyimide nanofiber membrane, and makes the polyimide nanofiber membrane composite membrane serving as a lithium ion battery membrane possible to be used for the large-scale production of lithium batteries of different processes.

2. The invention adopts the partially cyclized polyimide as the base film, is matched with the polyamic acid coating liquid, has excellent interface bonding performance after complete imidization, and has mechanical property obviously superior to the PI nanofiber composite diaphragm obtained by cyclizing the completely imidized PI nanofiber membrane in the PAA solution coating process.

3. The control of the concentration of the polyamic acid coating solution and the coating amount of the solution can realize the regulation and control of the crosslinking degree of the polyimide nanofiber membrane, the stability of the pore structure and the adjustment of the pore size.

4. Polyimide has various types, almost all systems can be subjected to crosslinking modification by the method, the method has strong universality, and the method can be popularized to application modification of other types of polymer nanofiber membranes.

5. The polyimide nanofiber membrane can realize the function of high-temperature hole closing by coating a precursor polyamic acid solution of soluble polyimide.

Drawings

FIG. 1 is an SEM microtopography of a polyimide separator in example 1;

FIG. 2 is an SEM microtopography of the polyimide separator of example 2;

FIG. 3 is an SEM microtopography picture of the polyimide membrane of example 3;

FIG. 4 is an SEM microtopography picture of the polyimide separator in comparative example 1;

FIG. 5 is an SEM microtopography of the polyimide separator of example 8;

fig. 6 is an SEM micrograph of the polyimide separator after heat treatment in example 8.

Detailed Description

The invention will be further illustrated by the following examples, which should be construed as follows: the following examples are intended to illustrate the invention and are not intended to limit the invention to the embodiments described. Therefore, although the present invention has been described in detail with reference to the following examples, it should be understood by those skilled in the art that any modifications or equivalent substitutions can be made thereto without departing from the spirit and scope of the present invention, and all such modifications and improvements are intended to be included within the scope of the following claims.

Example 1

Preparation of polyimide porous membrane of PMDA/ODA system: the method comprises the following steps of mixing monomer pyromellitic dianhydride (PMDA) and monomer 4, 4' -diaminodiphenyl ether (ODA) according to a molar ratio of 1: weighing 1, reacting in a solvent N, N-dimethylformamide for 10 hours under the condition of ice-water bath at 0 ℃ to obtain a viscous polyamic acid solution with the clear and transparent mass concentration of 12% and the viscosity of 6.5 Pa.s, filling the solution into an injector, performing electrostatic spinning in an electric field with the electric field strength of 1kV/cm, collecting through a stainless steel rotary drum to obtain a polyamic acid porous membrane, stripping the polyamic acid porous membrane, placing the polyamic acid porous membrane in a high-temperature heating furnace for cyclization, and performing temperature rise procedures as follows: heating from room temperature to 180 deg.C at a heating rate of 5 deg.C/min, standing at 180 deg.C for 1h, opening the heating furnace, and naturally cooling to room temperature. Obtaining a partially imidized polyimide porous membrane with a thickness of 10 μm, diluting the previously prepared polyamic acid solution with the same solvent to a mass concentration of 0.1%, and applying the solution to the partially imidized polyimide porous membrane by a dimple coating method in an amount of 0.008ml/cm²After drying, placing the mixture in a high-temperature heating furnace for cyclization, wherein the temperature rise program is as follows: heating from room temperature to 300 deg.C at a rate of 5 deg.C/min, standing at 300 deg.C for 1h, opening the heating furnace, and naturally cooling to room temperature. The polyimide porous membrane with the cross-linking morphology is obtained, the obtained morphology is shown in figure 1, the tensile strength of the composite membrane is 67.5MPa, the puncture strength is 4.7N, the transverse longitudinal heat shrinkage rate is 0.2% at 300 ℃, and the porosity is 69%.

In the comparative example 1,

preparation of polyimide porous membrane of PMDA/ODA system: the method comprises the following steps of mixing monomer pyromellitic dianhydride (PMDA) and monomer 4, 4' -diaminodiphenyl ether (ODA) according to a molar ratio of 1: weighing 1, reacting in a solvent N, N-dimethylformamide for 10 hours under the condition of ice-water bath at 0 ℃ to obtain a viscous polyamic acid solution with the clear and transparent mass concentration of 12% and the viscosity of 6.5 Pa.s, filling the solution into an injector, performing electrostatic spinning in an electric field with the electric field strength of 1kV/cm, collecting through a stainless steel rotary drum to obtain a polyamic acid porous membrane, stripping the polyamic acid porous membrane, placing the polyamic acid porous membrane in a high-temperature heating furnace for cyclization, and performing temperature rise procedures as follows: heating from room temperature to 300 deg.C at a rate of 5 deg.C/min, standing at 300 deg.C for 1h, opening the heating furnace, and naturally cooling to room temperature. The polyimide porous membrane without the cross-linking morphology is obtained, the obtained morphology is shown in figure 4, the tensile strength of the composite diaphragm is 13.4MPa, the puncture strength is 1.5N, the transverse and longitudinal thermal shrinkage rates are 0.8% at 300 ℃, and the porosity is 83%.

Comparative example 2

Preparation of polyimide porous membrane of PMDA/ODA system: the method comprises the following steps of mixing monomer pyromellitic dianhydride (PMDA) and monomer 4, 4' -diaminodiphenyl ether (ODA) according to a molar ratio of 1: weighing 1, reacting in a solvent N, N-dimethylformamide for 10 hours under the condition of ice-water bath at 0 ℃ to obtain a viscous polyamic acid solution with the clear and transparent mass concentration of 12% and the viscosity of 6.5 Pa.s, filling the solution into an injector, performing electrostatic spinning in an electric field with the electric field strength of 1kV/cm, collecting through a stainless steel rotary drum to obtain a polyamic acid porous membrane, stripping the polyamic acid porous membrane, placing the polyamic acid porous membrane in a high-temperature heating furnace for cyclization, and performing temperature rise procedures as follows: heating from room temperature to 300 deg.C at a rate of 5 deg.C/min, standing at 300 deg.C for 1h, opening the heating furnace, and naturally cooling to room temperature. Obtaining a polyimide porous membrane without a cross-linking appearance, diluting a polyamide acid solution prepared previously to the mass concentration of 0.1% by using the same solvent, coating the polyamide acid solution on a partially cyclized polyimide porous membrane, drying the polyimide porous membrane, and then placing the polyimide porous membrane in a high-temperature heating furnace for cyclization, wherein the heating program is as follows: heating from room temperature to 300 deg.C at a rate of 5 deg.C/min, standing at 300 deg.C for 1h, opening the heating furnace, and naturally cooling to room temperature. The polyimide porous membrane with the cross-linking morphology is obtained, the tensile strength of the composite membrane is 47.2MPa, the puncture strength is 2.9N, the transverse and longitudinal thermal shrinkage rates at 300 ℃ are all 0.5%, and the porosity is 67%.

Example 2

Preparing a BPDA/ODA system polyimide porous membrane with a cross-linking morphology: monomers of 3,3 ', 4,4 ' -biphenyltetracarboxylic dianhydride (BPDA) and 4,4 ' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1: weighing 1, reacting for 10 hours in a solvent N, N-Dimethylformamide (DMF) under the condition of ice-water bath at 0 ℃ to obtain a viscous polyamic acid solution with clear and transparent mass concentration of 12%, filling the solution into an injector, performing electrostatic spinning in an electric field with the electric field intensity of 1kV/cm, collecting through a stainless steel rotary drum to obtain a polyamic acid porous membrane, peeling the polyamic acid porous membrane from the rotary drum, and performing imidization treatment in a high-temperature heating furnace, wherein the temperature rise program is as follows: heating from room temperature to 200 deg.C at a heating rate of 5 deg.C/min to 200 deg.CThe resulting mixture was left at room temperature for 30 minutes to obtain a partially imidized polyimide film having a thickness of 15 μm. The previously prepared polyamic acid solution was diluted with the same solvent to a mass concentration of 10%, and applied by extrusion coating to a partially cyclized polyimide porous membrane in an amount of 0.04ml/cm²Placing the dried mixture in a high-temperature heating furnace for cyclization, wherein the temperature rise program is as follows: heating from room temperature to 320 ℃ at a heating rate of 5 ℃/min, staying at 320 ℃ for 1h, opening the heating furnace, and naturally cooling to room temperature. The polyimide porous membrane with the cross-linking morphology is obtained, the obtained morphology is shown in figure 2, the tensile strength of the composite membrane is 120.3MPa, the puncture strength is 5.1N, the transverse and longitudinal heat shrinkage rates at 300 ℃ are both 0.0%, and the porosity is 58%.

Example 3

Preparing a polyimide porous membrane with a cross-linked morphology PMDA/ODA system: the method comprises the following steps of mixing monomer pyromellitic dianhydride (PMDA) and monomer 4, 4' -diaminodiphenyl ether (ODA) according to a molar ratio of 1: weighing 1, reacting for 10 hours in a solvent N, N-Dimethylformamide (DMF) under the condition of ice-water bath at 0 ℃ to obtain a viscous polyamic acid solution with clear and transparent mass concentration of 12%, filling the solution into an injector, performing electrostatic spinning in an electric field with the electric field intensity of 1kV/cm, collecting through a stainless steel rotary drum to obtain a polyamic acid porous membrane, peeling the polyamic acid porous membrane from the rotary drum, and performing imidization treatment in a high-temperature heating furnace, wherein the temperature rise program is as follows: heating to 200 deg.C at a temperature rise rate of 5 deg.C/min, and standing at 200 deg.C for 1 hr to obtain partially imidized polyimide porous membrane with a thickness of 10 μm. The previously prepared polyamic acid solution was diluted with the same solvent to a mass concentration of 0.1%, and then applied to a partially cyclized polyimide porous membrane by dimple coating in an amount of 0.008ml/cm²After drying, placing the mixture in a high-temperature heating furnace for cyclization, wherein the temperature rise program is as follows: heating from room temperature to 300 deg.C at a rate of 5 deg.C/min, standing at 300 deg.C for 15min, opening the heating furnace, and naturally cooling to room temperature. The polyimide porous membrane with the cross-linking morphology is obtained, the obtained morphology is shown in figure 3, the tensile strength of the composite membrane is 89.4MPa, the puncture strength is 5.9N, the transverse and longitudinal thermal shrinkage rates are 0.0% at 300 ℃, and the porosity is 65%.

Example 4

Preparing a polyimide porous membrane with a cross-linked morphology PMDA/ODA system: the method comprises the following steps of mixing monomer pyromellitic dianhydride (PMDA) and monomer 4, 4' -diaminodiphenyl ether (ODA) according to a molar ratio of 1: weighing 1, reacting for 10 hours in a solvent N, N-Dimethylformamide (DMF) under the condition of ice-water bath at 0 ℃ to obtain a viscous polyamic acid solution with clear and transparent mass concentration of 12%, filling the solution into an injector, performing electrostatic spinning in an electric field with the electric field intensity of 1kV/cm, collecting through a stainless steel rotary drum to obtain a polyamic acid porous membrane, peeling the polyamic acid porous membrane from the rotary drum, and performing imidization treatment in a high-temperature heating furnace, wherein the temperature rise program is as follows: the temperature was raised from room temperature to 200 ℃ at a rate of 5 ℃/min, and the film was left at 200 ℃ for 1 hour to obtain a partially imidized polyimide porous film having a thickness of 10 μm. The previously prepared polyamic acid solution was diluted with the same solvent to a mass concentration of 3%, and then applied to a partially cyclized polyimide porous membrane in a dimple coating manner in an amount of 0.008ml/cm²Then coating the partially cyclized polyimide porous membrane on the partially cyclized polyimide porous membrane, drying the partially cyclized polyimide porous membrane, and placing the partially cyclized polyimide porous membrane in a high-temperature heating furnace for cyclization, wherein the temperature-raising program is as follows: heating the composite diaphragm from room temperature to 300 ℃ at the heating rate of 5 ℃/min, standing for 1h at the temperature of 300 ℃, opening a heating furnace, and naturally cooling to the room temperature to obtain the polyimide porous membrane with the cross-linking morphology, wherein the tensile strength of the composite diaphragm is 147.2MPa, the puncture strength is 7.1N, the transverse longitudinal thermal shrinkage rate is 0.0% at the temperature of 300 ℃, and the porosity is 61%.

Example 5

Preparing a BPDA/ODA system polyimide porous membrane with a cross-linking morphology: monomers of 3,3 ', 4,4 ' -biphenyltetracarboxylic dianhydride (BPDA) and 4,4 ' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1: weighing 1, reacting in N, N-Dimethylformamide (DMF) at 0 deg.C in ice-water bath for 10h to obtain clear and transparent viscous polyamic acid solution with mass concentration of 12% and viscosity of 6.1 Pa.s, synthesizing polyamic acid solution of PMDA/ODA system with mass concentration of 12% by the same method, diluting to mass concentration of 1%, filling the solution of BPDA/ODA system into an injector, performing electrostatic spinning in an electric field with electric field strength of 1kV/cm, collecting with a stainless steel drum to obtain polyamic acid porous membrane, peeling the porous membrane of BPDA/ODA system polyamic acid from the drum, and placing in high temperature hot water bathPerforming imidization treatment in a furnace, wherein the temperature rise program comprises the following steps: the temperature was raised from room temperature to 200 ℃ at a rate of 5 ℃/min, and the film was left at 200 ℃ for 1 hour to obtain a partially imidized polyimide porous film having a thickness of 14 μm. The PMDA/ODA system polyamide solution with the mass concentration of 1 percent prepared previously is applied to the partially cyclized polyimide porous membrane by a micro-concave coating method, and the coating amount is 0.01ml/cm²After drying, placing the mixture in a high-temperature heating furnace for cyclization, wherein the temperature rise program is as follows: heating from room temperature to 400 deg.C at a heating rate of 5 deg.C/min, standing at 400 deg.C for 1h, opening the heating furnace, and naturally cooling to room temperature. The polyimide porous membrane with the cross-linking morphology is obtained, the tensile strength of the composite membrane is 83.5MPa, the puncture strength is 5.0N, the transverse and longitudinal thermal shrinkage rates are 0.00% at 300 ℃, and the porosity is 62%.

Example 6

Preparing a BPDA/ODA system polyimide porous membrane with a cross-linking morphology: monomers of 3,3 ', 4,4 ' -biphenyltetracarboxylic dianhydride (BPDA) and 4,4 ' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1: weighing 1, reacting in a solvent N, N-Dimethylformamide (DMF) for 10 hours under the condition of ice-water bath at 0 ℃ to obtain a viscous polyamic acid solution with a clear and transparent mass concentration of 12% and a viscosity of 6.1 Pa.s, synthesizing the polyamic acid solution of a PMDA/ODA system with the mass concentration of 12% by the same method, diluting to a mass concentration of 2%, filling the BPDA/ODA system solution into an injector, performing electrostatic spinning in an electric field with the electric field strength of 1kV/cm, collecting a polyamic acid porous membrane by a stainless steel rotary drum, stripping the BPDA/ODA system porous membrane from the rotary drum, putting the roll in a high-temperature polyamic acid heating furnace for imidization, wherein the heating procedure is as follows: the temperature was raised from room temperature to 200 ℃ at a rate of 5 ℃/min, and the film was left at 200 ℃ for 1 hour to obtain a partially imidized polyimide porous film having a thickness of 14 μm. The PMDA/ODA system polyamide solution with the mass concentration of 2 percent prepared previously is applied to the partially cyclized polyimide porous membrane by a micro-concave coating method, and the coating amount is 0.01ml/cm²After drying, placing the mixture in a high-temperature heating furnace for cyclization, wherein the temperature rise program is as follows: heating from room temperature to 400 deg.C at a heating rate of 5 deg.C/min, standing at 400 deg.C for 1h, opening the heating furnace, and naturally cooling to room temperature. Obtaining the polyimide porous membrane with the cross-linked morphology, and the tensile strength of the composite membrane103.7MPa, puncture strength of 5.6N, transverse and longitudinal thermal shrinkage of 0.0 percent at 300 ℃ and porosity of 58 percent.

Example 7

Preparing a BPDA/PDA system polyimide porous membrane with a cross-linking appearance: monomers of 3,3 ', 4, 4' -biphenyl tetracarboxylic dianhydride (BPDA) and p-Phenylenediamine (PDA) are mixed according to a molar ratio of 1: weighing 1, reacting for 10 hours in a solvent N, N-Dimethylformamide (DMF) under the condition of ice-water bath at 0 ℃ to obtain a viscous polyamic acid solution with a clear and transparent mass concentration of 12% and a viscosity of 6.1 Pa.s, synthesizing the polyamic acid solution of a PMDA/ODA system with the mass concentration of 12% by the same method, diluting to a mass concentration of 3%, filling the BPDA/PDA system solution into an injector, performing electrostatic spinning in an electric field with the electric field strength of 1kV/cm, collecting through a stainless steel rotary drum to obtain a polyamic acid porous membrane, peeling the BPDA/PDA system polyamic acid porous membrane from the roller, and putting the polyamic acid porous membrane into a high-temperature heating furnace for imidization, wherein the heating procedure is as follows: the temperature was raised from room temperature to 200 ℃ at a rate of 5 ℃/min, and the film was left at 200 ℃ for 1 hour to obtain a partially imidized polyimide porous film having a thickness of 14 μm. The PMDA/ODA system polyamide solution with the mass concentration of 3 percent prepared previously is applied to the partially cyclized polyimide porous membrane by a micro-concave coating method, and the coating amount is 0.01ml/cm²The polyimide porous membrane is coated on a partially cyclized BPDA/PDA system, dried and then placed in a high-temperature heating furnace for cyclization, and the temperature-raising program is as follows: heating the composite diaphragm from room temperature to 400 ℃ at the heating rate of 5 ℃/min, standing for 1h at the temperature of 400 ℃, opening a heating furnace, and naturally cooling to the room temperature to obtain the polyimide porous membrane with the cross-linking morphology, wherein the tensile strength of the composite diaphragm is 158.6MPa, the puncture strength is 6.3N, the transverse longitudinal thermal shrinkage rate is 0.0% at the temperature of 300 ℃, and the porosity is 60%.

Example 8

Preparing a polyimide porous membrane with a cross-linked morphology PMDA/ODA system: the monomer biphenyl tetracarboxylic dianhydride (BPDA) and the monomer 4, 4' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1: 1 weighing, reacting in N, N-Dimethylformamide (DMF) at 0 deg.C in ice-water bath for 10h to obtain clear and transparent 15% viscous polyamic acid solution, diluting to appropriate viscosity, placing into a syringe, and subjecting to electric fieldElectrostatic spinning in an electric field with the strength of 1kV/cm, collecting through a stainless steel rotary drum to obtain a polyamide acid porous membrane, peeling the polyamide acid porous membrane from the rotary drum, and performing imidization treatment in a high-temperature heating furnace, wherein the temperature rise program is as follows: the temperature was raised from room temperature to 200 ℃ at a rate of 5 ℃/min, and the film was left at 200 ℃ for 1 hour to obtain a partially imidized polyimide porous film having a thickness of 9 μm. Preparing polyamic acid of a meltable polyimide system 6FDA/ODA system under the same synthesis conditions, diluting the polyamic acid to a mass concentration of 15 percent, applying the polyamic acid to a partially cyclized polyimide porous membrane in a dimple coating mode, wherein the coating dosage is 0.006ml/cm²And after drying, carrying out pretreatment by using a hot press: the temperature is 80 ℃, the pressure is 4MPa, and the time is 1 min. And finally, fully imidizing in a high-temperature heating furnace, wherein the heating procedure is as follows: heating the composite diaphragm from room temperature to 300 ℃ at the heating rate of 5 ℃/min, standing the composite diaphragm at 300 ℃ for 10min, opening a heating furnace, and naturally cooling the composite diaphragm to the room temperature to obtain the polyimide porous membrane with the cross-linking morphology, wherein the tensile strength of the composite diaphragm is 128.7MPa, the puncture strength is 5.9N, the transverse longitudinal thermal shrinkage rate is 0.1% at 300 ℃, and the porosity is 64%. The resulting morphology is shown in fig. 5. After heating the film for half an hour at 350 ℃, a hot hole closing phenomenon appears, and the appearance is shown in figure 6.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.