CN113718536B - Polyimide diaphragm with cross-linked morphology and preparation method thereof - Google Patents
Polyimide diaphragm with cross-linked morphology and preparation method thereof Download PDFInfo
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
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Abstract
The invention relates to a polyimide porous membrane with cross-linking morphology and a preparation method thereof, which comprises the steps of preparing polyimide precursor polyamide acid solution by low-temperature condensation polymerization, obtaining polyamide acid nanofiber membrane by an electrostatic spinning method, then placing the polyamide acid nanofiber membrane into a high-temperature furnace for partial cyclization treatment, coating the polyamide acid solution on the partial cyclization nanofiber membrane, drying, and then carrying out complete imidization treatment on the nanofiber membrane to prepare the polyimide nanofiber membrane with a cross-linking structure, wherein the tensile strength of the polyimide nanofiber membrane can reach 40-250MPa, the puncture strength is greater than 4.0N, the porosity is 20-95% and can be adjusted, and the thickness is 2-30 microns. The invention has simple and convenient process, high production efficiency and environment protection, can effectively solve the defect of insufficient mechanical property of the nanofiber membrane, and can be applied to the fields of lithium ion battery diaphragms, super capacitor diaphragms, high-temperature filtration, adsorption and the like.
Description
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 in environmental pollution and the decreasing fossil energy, the development of new energy sources that can replace low pollution has been an irreversible trend. With the rapid development of science and technology, the lithium ion battery greatly improves our life style, becomes an indispensable article in our daily life, and as a diaphragm of a key component of the lithium ion battery, the performance of the diaphragm directly influences the performance and the safety of the lithium ion battery, and the recent frequent battery safety accidents bring about public concerns about the battery safety again. The traditional lithium ion battery diaphragm adopts polyolefin microporous membranes, such as polypropylene (PP), polyethylene (PE) and PP/PE/PP three-layer composite diaphragms, and has the characteristics of low cost, good chemical corrosion resistance, excellent mechanical properties and the like. However, due to the molecular chain structure and the nonpolar nature of the polyolefin separator, the temperature resistance and electrolyte wettability of the polyolefin separator are poor, so that the separator is easily damaged and melted in the use process and the charge and discharge process of the battery, and the battery safety accident is caused. Polyolefin separators have failed to meet the urgent need for high specific energy, 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 the imide group and aromatic heterocycle of the main chain, 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, polyimide nanofiber membranes prepared by an electrostatic spinning method are expected to be used as lithium battery separators because of the excellent comprehensive performance, and polyimide nanofiber membranes prepared by the electrostatic spinning technology have high porosity, high electrolyte wettability, high temperature resistance and excellent thermal dimensional stability, but because polyimide nanofiber non-woven fabrics are formed by non-return stacking of nanofibers, the fibers are loosely and physically overlapped, so that the mechanical performance of the nanofiber membranes is poor, the tensile strength is about 5-10 MPa, and the polyimide nanofiber membranes cannot withstand winding or lamination processes in the battery production process, so that the large-scale application of the polyimide nanofiber membranes is seriously hindered. In order to solve the safety problem of the prior polyolefin diaphragm in the use of high specific energy and high power lithium ion batteries and actively apply the novel high temperature resistant diaphragm to industrial production, a micro-crosslinking structure is introduced between nanofibers, so that the novel high temperature resistant diaphragm becomes a simple and efficient technical means for preparing polyimide nanofiber membranes with high mechanical strength and crosslinking morphology.
Patent CN1042133a and CN102766270a disclose two kinds of polyimide nanofiber membranes with cross-linked morphology, respectively. 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 polyimide nanofibers to enable the polyimide nanofibers to be fused, so that the mechanical properties are improved. However, the melt crosslinking method has limited applicable systems, thermoplastic polyimide is necessary, and the fiber melt during the heat treatment process also causes great shrinkage of the fiber film, so that the preparation of the polyimide nanofiber film with a crosslinked morphology by the method is limited. CN102766270a adopts an alkali liquor etching method to form a hydrolysis swelling layer on the surface of the fiber, dissolve the fiber and form a crosslinking point, and thermally cyclize after cleaning to obtain the polyimide nanofiber membrane with a crosslinking morphology, so that the defect that thermosetting polyimide can not obtain the crosslinking morphology through melting is overcome, the preparation range of the polyimide nanofiber membrane with the crosslinking morphology 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 liquor is strong and weak, the treatment time can have great influence on the chemical structure and the fiber morphology of the fiber membrane, the post-treatment process is complex, a large amount of water resources can be used, and the environment-friendly concept is not met. Both 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-linked morphology, which has the advantages of flexible and simple operation, simple process, potential of industrial production, excellent comprehensive performance of the prepared polyimide diaphragm and good application prospect.
A polyimide diaphragm with cross-linked morphology is characterized in that the porosity is 20% -95%, the tensile strength is 40-250MPa, the puncture strength is more than 4.0N, and the transverse and longitudinal heat shrinkage rates are all less than 1.5% at 300 ℃.
Further, the porosity is preferably 30% to 90%;
further, the thickness of the polyimide separator having a cross-linked morphology is 2-50 μm, preferably 3-10 μm.
Further, the diameter of the polyimide fiber in the polyimide diaphragm with the cross-linked morphology is 20-2000nm, preferably 50-1000nm.
The preparation method of the polyimide diaphragm with the cross-linked morphology is characterized by comprising the following steps of:
a: preparing polyamic acid solution by adopting at least one dicarboxylic anhydride and at least one diamine, and then preparing polyamic acid nanofiber membrane by adopting an electrostatic spinning process;
b: performing heat treatment on the polyamide 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 C, carrying out heat treatment on the nanofiber membrane obtained in the step C to obtain the polyimide diaphragm with the cross-linked morphology.
Further, the molar ratio of the polyamic acid solution, the dibasic 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 diphenyl tetrahydric dianhydride (BPDA), pyromellitic dianhydride (PMDA), benzophenone Tetrahydric Dianhydride (BTDA), diphenyl ether tetrahydric dianhydride (ODPA), hexafluorodianhydride (6 FDA) 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' -diaminodiphenyl Methane (MDA) and 4,4' -diamino-2, 2' -bistrifluoromethyl biphenyl (TFDB).
Further, the diamine and the dibasic acid anhydride are polymerized in polar aprotic solvent in a low-temperature condensation way,
the synthesis temperature of the polyamic acid solution is-15 to 15 ℃, preferably-10 to 10 ℃.
Further, the polar aprotic solvent is one or more of N, N-Dimethylacetamide (DMAC), N-Dimethylformamide (DMF), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).
The solid content of the polyamic acid solution in the step A is 5 to 30%, preferably 8 to 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 to 260 ℃, preferably 140 to 250 ℃ and the time is 3s to 2 hours, preferably 5s to 1 hour.
Further, the mass fraction of the polyamic acid solution used for coating in the step C is 0.05 to 15%, preferably 0.1 to 10%; the polyamic acid solution used for coating may have the same composition or different composition from the polyamic acid obtained in the step A.
The coating method includes one of electrostatic spraying method, knife coating method, transfer coating method, dip coating method, gravure coating method, and extrusion coating method.
The polyamide acid solution is used in an amount of 0.0002 to 0.02ml/cm relative to the partially imidized polyimide nanofiber membrane 2 Preferably 0.0004-0.01ml/cm 2 。
Further, the heat treatment process adopted in the step D is as follows: the temperature rising rate is 2-30 ℃/min, preferably 5-20 ℃/min, the final temperature is 250-460 ℃, preferably 300-450 ℃, and the residence time is 0.5-70 min, preferably 1-60 min.
An article comprising the polyimide separator having a cross-linked morphology.
Compared with the prior art, the method has the following excellent effects:
1. the method utilizes the solution coating technology to realize the construction of the cross-linked morphology of the polyimide nanofiber membrane, greatly improves the mechanical strength and the dimensional stability of the polyimide nanofiber membrane, and makes the polyimide nanofiber membrane composite membrane as a lithium ion battery membrane possible to be used for the mass production of lithium batteries in different processes.
2. The invention adopts the partially cyclized polyimide as the base film, is matched with the polyamide acid coating liquid, has excellent interface bonding performance after complete imidization, and has mechanical properties obviously superior to those of the PI nanofiber composite membrane obtained by cyclizing the completely imidized PI nanofiber film in the coating of PAA solution.
3. Through the control of the concentration of the polyamide acid coating solution and the coating amount of the solution, the regulation and control of the crosslinking degree of the polyimide nanofiber membrane, the stable pore structure and the adjustment of the pore size can be realized.
4. Polyimide has various types, almost all systems can be crosslinked and modified by the method, the method has strong universality, and the method can be popularized to the application modification of other types of polymer nanofiber membranes.
5. Coating the precursor polyamic acid solution of soluble polyimide can realize the function of polyimide nanofiber membrane height Wen Bikong.
Drawings
FIG. 1 is an SEM micrograph of a polyimide separator membrane of example 1;
FIG. 2 is an SEM micrograph of a polyimide separator membrane of example 2;
FIG. 3 is an SEM micrograph of a polyimide separator of example 3;
FIG. 4 is an SEM micrograph of a polyimide separator of comparative example 1;
FIG. 5 is an SEM micrograph of a polyimide separator membrane of example 8;
fig. 6 is an SEM micrograph of a polyimide separator after heat treatment in example 8.
Detailed Description
The invention will be further elucidated with reference to the following examples, it being noted that: the following examples are only intended to illustrate the invention and not to limit the technical solutions described by the invention. Therefore, although the present invention has been described in detail with reference to the following examples, it will be understood by those skilled in the art that any modifications or equivalent substitutions may be made thereto without departing from the spirit and scope of the present invention, and all such modifications and improvements are intended to be encompassed within the scope of the appended claims.
Example 1
Preparation of polyimide porous membrane of PMDA/ODA system: the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1:1 weighing, reacting in solvent N, N-dimethylformamide in ice water bath at 0 ℃ for 10 hours to obtain a clear transparent viscous polyamic acid solution with mass concentration of 12% and viscosity of 6.5 Pa.s, loading the solution into a syringe, carrying out electrostatic spinning in an electric field with electric field strength of 1kV/cm, collecting a polyamic acid porous membrane through a stainless steel rotary drum, stripping the polyamic acid porous membrane, cyclizing in a high-temperature furnace, and heating to a temperature of the solution: heating from room temperature to 180 ℃ at a heating rate of 5 ℃/min, staying for 1h at 180 ℃, opening a hot furnace, and naturally cooling to room temperature. Obtaining a partially imidized polyimide porous membrane, wherein the thickness is 10 mu m, the polyamic acid solution prepared previously is diluted to a mass concentration of 0.1% by using the same solvent, and then the partially imidized polyimide porous membrane is coated by using a micro-concave coating method, and the coating amount is 0.008ml/cm 2 After drying, placing in a high-temperature furnace for cyclization, and heating up the materials: heating from room temperature to 300 ℃ at a heating rate of 5 ℃/min, staying for 1h at 300 ℃, opening a hot furnace, and naturally cooling to room temperature. Obtaining polyimide porous membrane with cross-linked morphology, and the morphology is shown in figure 1The composite diaphragm has tensile strength of 67.5MPa, puncture strength of 4.7N, transverse and longitudinal heat shrinkage rate of 0.2% at 300 ℃ and porosity of 69%.
In comparative example 1,
preparation of polyimide porous membrane of PMDA/ODA system: the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1:1 weighing, reacting in solvent N, N-dimethylformamide in ice water bath at 0 ℃ for 10 hours to obtain a clear transparent viscous polyamic acid solution with mass concentration of 12% and viscosity of 6.5 Pa.s, loading the solution into a syringe, carrying out electrostatic spinning in an electric field with electric field strength of 1kV/cm, collecting a polyamic acid porous membrane through a stainless steel rotary drum, stripping the polyamic acid porous membrane, cyclizing in a high-temperature furnace, and heating to a temperature of the solution: heating from room temperature to 300 ℃ at a heating rate of 5 ℃/min, staying for 1h at 300 ℃, opening a hot furnace, and naturally cooling to room temperature. The polyimide porous membrane without cross-linking morphology is obtained, the morphology is shown in figure 4, the tensile strength of the composite membrane is 13.4MPa, the puncture strength is 1.5N, the transverse and longitudinal heat 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 monomer pyromellitic dianhydride (PMDA) and the monomer 4,4' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1:1 weighing, reacting in solvent N, N-dimethylformamide in ice water bath at 0 ℃ for 10 hours to obtain a clear transparent viscous polyamic acid solution with mass concentration of 12% and viscosity of 6.5 Pa.s, loading the solution into a syringe, carrying out electrostatic spinning in an electric field with electric field strength of 1kV/cm, collecting a polyamic acid porous membrane through a stainless steel rotary drum, stripping the polyamic acid porous membrane, cyclizing in a high-temperature furnace, and heating to a temperature of the solution: heating from room temperature to 300 ℃ at a heating rate of 5 ℃/min, staying for 1h at 300 ℃, opening a hot furnace, and naturally cooling to room temperature. The polyimide porous membrane without cross-linking morphology is obtained, the polyamide acid solution prepared previously is diluted to the mass concentration of 0.1% by using the same solvent, then the polyamide acid solution is coated on the partially cyclized polyimide porous membrane, and after being dried, the polyimide porous membrane is cyclized in a high-temperature furnace, and the temperature rising program is as follows: heating from room temperature to 300 ℃ at a heating rate of 5 ℃/min, staying for 1h at 300 ℃, opening a hot furnace, and naturally cooling to room temperature. The polyimide porous membrane with cross-linked morphology is obtained, the tensile strength of the composite membrane is 47.2MPa, the puncture strength is 2.9N, the transverse and longitudinal heat shrinkage rates are all 0.5% at 300 ℃, and the porosity is 67%.
Example 2
Preparation of a polyimide porous membrane with a cross-linked morphology BPDA/ODA system: monomers 3,3', 4' -biphenyltetracarboxylic dianhydride (BPDA) and 4,4' -diaminodiphenyl ether (ODA) were mixed in a molar ratio of 1:1 weighing, reacting in solvent N, N-Dimethylformamide (DMF) for 10 hours under the condition of 0 ℃ ice water bath to obtain clear transparent viscous polyamic acid solution with the mass concentration of 12%, loading the solution into a syringe, carrying out electrostatic spinning in an electric field with the electric field strength of 1kV/cm, collecting the solution through a stainless steel rotary drum to obtain a polyamic acid porous membrane, stripping the polyamic acid porous membrane from the roller, and carrying out imidization treatment in a high-temperature furnace, wherein the temperature rise procedure is as follows: the temperature is raised from room temperature to 200 ℃ at a heating rate of 5 ℃/min, and the polyimide film stays at 200 ℃ for 30min, so that the partially imidized polyimide film with the thickness of 15 mu m is obtained. The polyamic acid solution previously prepared was diluted with the same solvent to a mass concentration of 10%, and then applied by extrusion coating to a partially cyclized polyimide porous membrane in an amount of 0.04ml/cm 2 After drying, placing in a high-temperature furnace for cyclization, and heating up the materials: heating from room temperature to 320 ℃ at a heating rate of 5 ℃/min, staying at 320 ℃ for 1h, opening a hot furnace, and naturally cooling to room temperature. The polyimide porous membrane with cross-linked morphology is obtained, the 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 are 0.0% at 300 ℃, and the porosity is 58%.
Example 3
Preparing a polyimide porous membrane with a cross-linked morphology PMDA/ODA system: the monomer pyromellitic dianhydride (PMDA) and the monomer 4,4' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1:1 weighing, reacting in solvent N, N-Dimethylformamide (DMF) at 0deg.C in ice water bath for 10 hr to obtain clear transparent viscous polyamic acid solution with mass concentration of 12%, loading into injector, and electrospinning in electric field with electric field strength of 1kV/cmCollecting the polyamide acid porous membrane through a stainless steel rotary drum, stripping the polyamide acid porous membrane from the roller, and placing the roller in a high-temperature heat furnace for imidization treatment, wherein the temperature rise program is as follows: the temperature is raised from room temperature to 200 ℃ at a heating rate of 5 ℃/min, and the polyimide is kept at 200 ℃ for 1h, so that the partially imidized polyimide porous membrane with the thickness of 10 mu m is obtained. The polyamic acid solution prepared previously was diluted with the same solvent to a mass concentration of 0.1%, and then applied to a partially cyclized polyimide porous membrane by a dimple coating method at a coating amount of 0.008ml/cm 2 After drying, placing in a high-temperature furnace for cyclization, and heating up the materials: heating from room temperature to 300 ℃ at a heating rate of 5 ℃/min, staying at 300 ℃ for 15min, opening a hot furnace, and naturally cooling to room temperature. The polyimide porous membrane with cross-linked morphology is obtained, the 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 heat 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 monomer pyromellitic dianhydride (PMDA) and the monomer 4,4' -diaminodiphenyl ether (ODA) are mixed according to a molar ratio of 1:1 weighing, reacting in solvent N, N-Dimethylformamide (DMF) for 10 hours under the condition of 0 ℃ ice water bath to obtain clear transparent viscous polyamic acid solution with the mass concentration of 12%, loading the solution into a syringe, carrying out electrostatic spinning in an electric field with the electric field strength of 1kV/cm, collecting the solution through a stainless steel rotary drum to obtain a polyamic acid porous membrane, stripping the polyamic acid porous membrane from the roller, and carrying out imidization treatment in a high-temperature furnace, wherein the temperature rise procedure is as follows: the temperature was raised from room temperature to 200℃at a heating rate of 5℃per minute and the reaction was allowed to stand at 200℃for 1 hour to give a partially imidized polyimide porous film having a thickness of 10. Mu.m. The polyamic acid solution prepared previously was diluted with the same solvent to a mass concentration of 3%, and then applied to a partially cyclized polyimide porous membrane by a dimple coating method at a coating amount of 0.008ml/cm 2 Then coating the porous polyimide film on a partially cyclized polyimide porous film, drying the porous polyimide film, and then placing the porous polyimide film in a high-temperature furnace for cyclizing, wherein the temperature-raising program is as follows: heating from room temperature to 300 ℃ at a heating rate of 5 ℃/min, staying for 1h at 300 ℃, opening a hot furnace, and naturally cooling to the roomAnd (3) obtaining the polyimide porous membrane with cross-linked morphology, wherein the tensile strength of the composite membrane is 147.2MPa, the puncture strength is 7.1N, the transverse and longitudinal heat shrinkage rates are 0.0% at 300 ℃, and the porosity is 61%.
Example 5
Preparation of a polyimide porous membrane with a cross-linked morphology BPDA/ODA system: monomers 3,3', 4' -biphenyltetracarboxylic dianhydride (BPDA) and 4,4' -diaminodiphenyl ether (ODA) were mixed in a molar ratio of 1:1 weighing, reacting in 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 percent and a viscosity of 6.1 Pa.s, synthesizing a polyamic acid solution with a PMDA/ODA system with a mass concentration of 12 percent by the same method, diluting to a mass concentration of 1 percent, filling the solution with the BPDA/ODA system into a syringe, carrying out electrostatic spinning in an electric field with an electric field strength of 1kV/cm, collecting the polyamic acid porous membrane through a stainless steel rotary drum, stripping the polyamic acid porous membrane with the BPDA/ODA system from a roller, and carrying out imidization treatment in a high-temperature furnace with a temperature-rise program of: the temperature was raised from room temperature to 200℃at a heating rate of 5℃per minute and the reaction was continued at 200℃for 1 hour to give a partially imidized polyimide porous film having a thickness of 14. Mu.m. The PMDA/ODA system polyamide solution with the mass concentration of 1 percent, which is prepared previously, is coated on the partially cyclized polyimide porous membrane by a micro-concave coating mode, wherein the coating dosage is 0.01ml/cm 2 After drying, placing in a high-temperature furnace for cyclization, and heating up the materials: heating from room temperature to 400 ℃ at a heating rate of 5 ℃/min, staying for 1h at 400 ℃, opening a hot furnace, and naturally cooling to room temperature. The polyimide porous membrane with cross-linked morphology is obtained, the tensile strength of the composite membrane is 83.5MPa, the puncture strength is 5.0N, the transverse and longitudinal heat shrinkage rates are 0.00% at 300 ℃, and the porosity is 62%.
Example 6
Preparation of a polyimide porous membrane with a cross-linked morphology BPDA/ODA system: monomers 3,3', 4' -biphenyltetracarboxylic dianhydride (BPDA) and 4,4' -diaminodiphenyl ether (ODA) were mixed in a molar ratio of 1:1 weighing, reacting in solvent N, N-Dimethylformamide (DMF) for 10h at 0 ℃ in ice water bath to obtain a viscous polyamide acid solution with clear and transparent mass concentration of 12% and viscosity of 6.1 Pa.s,then synthesizing polyamide acid solution with the mass concentration of 12% of the PMDA/ODA system by the same method, diluting to the mass concentration of 2%, filling the solution of the BPDA/ODA system into a syringe, carrying out electrostatic spinning in an electric field with the electric field strength of 1kV/cm, collecting the polyamide acid porous membrane by a stainless steel rotary drum, stripping the polyamide acid porous membrane of the BPDA/ODA system from the drum, and carrying out imidization treatment in a high-temperature furnace, wherein the temperature-rise program is as follows: the temperature was raised from room temperature to 200℃at a heating rate of 5℃per minute and the reaction was continued at 200℃for 1 hour to give a partially imidized polyimide porous film having a thickness of 14. Mu.m. The PMDA/ODA system polyamide solution with the mass concentration of 2 percent, which is prepared previously, is coated on the partially cyclized polyimide porous membrane by a micro-concave coating mode, wherein the coating dosage is 0.01ml/cm 2 After drying, placing in a high-temperature furnace for cyclization, and heating up the materials: heating from room temperature to 400 ℃ at a heating rate of 5 ℃/min, staying for 1h at 400 ℃, opening a hot furnace, and naturally cooling to room temperature. The polyimide porous membrane with cross-linked morphology is obtained, the tensile strength of the composite membrane is 103.7MPa, the puncture strength is 5.6N, the transverse and longitudinal heat shrinkage rates are 0.0% at 300 ℃, and the porosity is 58%.
Example 7
Preparation of a polyimide porous membrane with a cross-linked morphology BPDA/PDA system: monomers 3,3', 4' -biphenyltetracarboxylic dianhydride (BPDA) and p-Phenylenediamine (PDA) in a molar ratio of 1:1 weighing, reacting in solvent N, N-Dimethylformamide (DMF) for 10 hours under the ice water bath condition of 0 ℃ to obtain a viscous polyamide acid solution with a clear and transparent mass concentration of 12 percent and a viscosity of 6.1 Pa.s, synthesizing a polyamide acid solution with a PMDA/ODA system with a mass concentration of 12 percent by the same method, diluting to a mass concentration of 3 percent, filling the solution of the BPDA/PDA system into a syringe, carrying out electrostatic spinning in an electric field with an electric field strength of 1kV/cm, collecting a polyamide acid porous membrane through a stainless steel rotary drum, stripping the polyamide acid porous membrane of the BPDA/PDA system from a roller, and carrying out imidization treatment in a high-temperature furnace, wherein the temperature rise procedure is as follows: the temperature was raised from room temperature to 200℃at a heating rate of 5℃per minute and the reaction was continued at 200℃for 1 hour to give a partially imidized polyimide porous film having a thickness of 14. Mu.m. Application of a previously prepared 3% by mass concentration PMDA/ODA System Polyamide solution to a micro-gravure coatingIs coated on the partially cyclized polyimide porous membrane in a way of 0.01ml/cm 2 The polyimide porous membrane coated on a partial cyclization BPDA/PDA system is dried and then put into a high-temperature furnace for cyclization, and the temperature rise program is as follows: heating from room temperature to 400 ℃ at a heating rate of 5 ℃/min, staying for 1h at 400 ℃, opening a hot furnace, naturally cooling to room temperature to obtain the polyimide porous membrane with cross-linked morphology, wherein the tensile strength of the composite membrane is 158.6MPa, the puncture strength is 6.3N, the transverse and longitudinal heat shrinkage rates are 0.0% at 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 mole ratio of 1:1 weighing, reacting in solvent N, N-Dimethylformamide (DMF) for 10 hours under the condition of ice water bath at 0 ℃ to obtain a clear transparent viscous polyamic acid solution with mass concentration of 15%, diluting the solution to a proper viscosity, loading the solution into a syringe, carrying out electrostatic spinning in an electric field with electric field strength of 1kV/cm, collecting the solution through a stainless steel rotary drum to obtain a polyamic acid porous membrane, stripping the polyamic acid porous membrane from the roller, and carrying out imidization treatment in a high-temperature furnace, wherein the temperature rise procedure is as follows: the temperature was raised from room temperature to 200℃at a heating rate of 5℃per minute and the reaction was allowed to stand at 200℃for 1 hour to give a partially imidized polyimide porous film having a thickness of 9. Mu.m. The same synthesis conditions are used for preparing polyamide acid with mass concentration of 15% of that of a 6FDA/ODA system of a meltable polyimide system, the polyamide acid is diluted to 3% of mass concentration, and the polyamide acid is coated on a partially cyclized polyimide porous membrane in a micro-concave coating mode, wherein the coating dosage is 0.006ml/cm 2 And (3) after drying, carrying out pretreatment by using a hot press: the temperature is 80 ℃, the pressure is 4MPa, and the time is 1min. Finally, for complete imidization in a high temperature furnace, the temperature raising program is as follows: heating from room temperature to 300 ℃ at a heating rate of 5 ℃/min, staying for 10min at 300 ℃, opening a hot furnace, naturally cooling to room temperature to obtain the polyimide porous membrane with cross-linked morphology, wherein the tensile strength of the composite membrane is 128.7MPa, the puncture strength is 5.9N, the transverse and longitudinal heat shrinkage rates are 0.1% at 300 ℃, and the porosity is 64%. The resulting morphology is shown in figure 5. After heating at 350deg.C for half an hour, hot closed pores appearThe morphology is shown in figure 6, for example.
The foregoing description is only illustrative of the preferred embodiments of the present invention and is not to be construed as limiting the scope of the invention, and it will be appreciated by those skilled in the art that equivalent substitutions and obvious variations may be made using the description and illustrations of the present invention, and are intended to be included within the scope of the present invention.
Claims (8)
1. The preparation method of the polyimide diaphragm with the cross-linked morphology is characterized by comprising the following steps of:
a: preparing polyamic acid solution by using binary anhydride and diamine, and preparing polyamic acid nanofiber membrane by using an electrostatic spinning process;
b: performing heat treatment on the polyamide 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 C, carrying out heat treatment on the nanofiber membrane obtained in the step C to obtain the polyimide diaphragm with the cross-linked morphology.
2. The method for preparing a polyimide diaphragm with cross-linked morphology according to claim 1, wherein the solid content of the polyamic acid solution in the step a is 5-30wt%; the polyamic acid solution is prepared from at least one diamine and at least one dicarboxylic anhydride; the diamine is at least one selected from diaminodiphenyl ether, p-phenylenediamine, 4' -diaminodiphenyl methane, 4' -diamino-2, 2' -bistrifluoromethyl biphenyl, and the dicarboxylic anhydride is at least one selected from diphenyl tetraoic acid dianhydride, pyromellitic dianhydride, benzophenone tetraoic acid dianhydride, diphenyl ether tetraoic acid dianhydride, hexafluorodianhydride and bisphenol A type diether dianhydride; the molar ratio of the dicarboxylic anhydride to the diamine is 0.95:1-1.05:1.
3. The method for preparing a polyimide diaphragm with cross-linked morphology according to claim 1, wherein the heat treatment in the step B is performed in a high temperature furnace under the following conditions: the temperature is 130-260 ℃ and the time is 3 s-2 h.
4. The preparation method of the polyimide diaphragm with the cross-linked morphology according to claim 1, wherein the mass fraction of the polyamic acid solution used for coating in the step C is 0.05-15 wt%.
5. The method for producing a polyimide separator having a cross-linked morphology according to claim 1, wherein the polyamic acid solution used in the coating in step C may have the same composition or a different composition from the polyamic acid obtained in step a.
6. The method for producing a polyimide separator having a cross-linked morphology according to claim 1, wherein the polyamic acid solution is used in an amount of 0.0002 to 0.02ml/cm relative to the partially imidized polyimide nanofiber membrane in step C 2 The method comprises the steps of carrying out a first treatment on the surface of the The coating method is one of an electrostatic spraying method, a knife coating method, a transfer coating method, a dipping coating method, a gravure coating method and an extrusion coating method.
7. A polyimide separator with cross-linked morphology prepared according to claim 1, characterized in that the thickness of the polyimide separator with cross-linked morphology is 2-30 μm;
the porosity is 20% -69%; the tensile strength is 67.5-250 MPa, the puncture strength is more than 4.0N, and the transverse and longitudinal heat shrinkage rates at 300 ℃ are all less than 1.5%.
8. A polyimide separator with cross-linked morphology according to claim 7, characterized in that the diameter of the polyimide fibers in the polyimide separator with cross-linked morphology is 20-2000 nm.
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