Fluorinated polyimide separator having semi-interpenetrating network structure, and preparation method therefor and use thereof

Abstract

The present invention belongs to the field of battery materials, and specifically relates to a fluorinated polyimide separator having a semi-interpenetrating network structure, and a preparation method therefor and the use thereof. The preparation method for a fluorinated polyimide separator having a semi-interpenetrating network structure comprises the following steps: forming a mixed slurry comprising fluorinated polyimide fibers, a polyimide having a network structure and a first solvent into a fluorinated polyimide separator having a semi-interpenetrating network structure, wherein the fluorinated polyimide fibers are prepared by reacting a first diamine monomer, a fluorine-free dianhydride monomer and a fluorine-containing dianhydride monomer; and the polyimide having a network structure is prepared by reacting a second diamine monomer, a dianhydride monomer and melamine under the catalysis of a catalyst. The semi-interpenetrating network structure of the separator enhances the overall mechanical strength without depriving the separator of an electrolyte absorption effect, and fluorine effectively improves the compatibility of the separator with an electrolyte while preventing other physical properties from degradation.

Description

Fluorinated polyimide semi-interpenetrating network membrane, its preparation method and application Technical Field

[0001] This invention belongs to the field of battery materials, specifically relating to fluorinated polyimide semi-interpenetrating mesh structure separators, their preparation methods, and applications. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Lithium-ion batteries mainly consist of positive / negative electrode materials, electrolyte, and separator. The separator is a crucial component of lithium-ion batteries, separating the positive and negative electrodes, preventing short circuits, and allowing electrolyte ions to pass freely. There are many types of separators, among which the most commercially available are polyolefin microporous membranes, including PP (polypropylene) / PE (polyethylene) / PP multilayer composite membranes, PP or PE single-layer microporous membranes, and coated membranes. Their main difference lies in the pore-forming mechanism. These membranes offer advantages such as relatively low price, excellent mechanical properties, and high electrochemical stability. However, polyolefin separators have low electrolyte absorption rates, making them prone to electrolyte leakage. Furthermore, the melting temperatures of PE and PP separators are approximately 135°C and 165°C, respectively, leading to thermal contraction and tight contact between the anode and cathode, potentially causing internal short circuits, fires, or even explosions.

[0004] Polyimide (PI) is a high-temperature resistant material. PI films prepared from PI have a significantly higher melting point than PP and PE separators, avoiding separator melting and greatly improving the high-temperature safety performance of batteries. However, PI films have low wettability and low electrolyte absorption rate, which reduces the battery's rate performance. To improve the electrolyte absorption rate of PI films, existing technologies use pore-forming agents to create pores on the PI film. However, pore creation leads to a decrease in the film's mechanical strength and can cause lithium dendrites to puncture the separator, resulting in short circuits and, in severe cases, explosions and fires. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a fluorinated polyimide semi-interpenetrating mesh structure membrane, its preparation method, and its applications. The fluorinated polyimide semi-interpenetrating mesh structure membrane is composed of fluorinated polyimide fibers and a mesh structure of polyimide. The fluorinated polyimide fibers and the mesh structure of polyimide form a semi-interpenetrating mesh structure, enhancing the overall mechanical strength of the membrane without compromising its electrolyte absorption effect. The fluorine element in the fluorinated polyimide fibers effectively improves the membrane's compatibility with the electrolyte while maintaining other physical properties, and the high mechanical strength of the fibers themselves also enhances the mechanical properties of the membrane.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a fluorinated polyimide semi-interpenetrating mesh structure membrane, comprising the following steps:

[0008] A fluorinated polyimide semi-interpenetrating mesh membrane is prepared by coating and soaking a mixed slurry comprising fluorinated polyimide fibers, porous polyimide and a first solvent with an alcohol aqueous solution. The schematic diagram of the structure is shown in Figure 1.

[0009] The fluorinated polyimide fiber is obtained by reacting a first diamine monomer, a fluorine-free dianhydride monomer, and a fluorine-containing dianhydride monomer;

[0010] The network-structured polyimide is prepared by reacting a second diamine monomer, a dianhydride monomer, and melamine under the catalysis of a catalyst.

[0011] The mixed slurry can be obtained by directly mixing fluorinated polyimide fibers and a first solvent, a network structure polyimide, and then forming a porous membrane by coating and soaking in an ethanol aqueous solution.

[0012] Introducing fluorine into the polyimide structure can significantly affect the electrolyte compatibility and mechanical properties of the polyimide separator, thereby improving the performance of lithium metal batteries. This is mainly reflected in the following aspects:

[0013] 1. Improved Electrolyte Compatibility: Fluorine typically exhibits strong electronegativity and hydrophobicity. Introducing fluorine into the polyimide structure may increase the compatibility between the separator and the electrolyte, thereby improving the battery's electrochemical stability. This is particularly important for lithium metal batteries, as these batteries require a very stable electrolyte interface to avoid side reactions.

[0014] 2. Improved interface stability: Fluorinated polyimide separators may help form a stable solid electrolyte interface (SEI) layer on the surface of the lithium metal anode. The stability of the SEI layer is crucial for suppressing the growth of lithium dendrites, which is one of the important causes of short circuits in lithium metal batteries.

[0015] 3. Enhanced Chemical Resistance: Fluorinated polyimide materials typically exhibit higher chemical resistance, which is an advantage in lithium metal batteries because lithium metal is prone to side reactions with the electrolyte, leading to rapid performance degradation. Fluorinated polyimides help suppress these side reactions and extend battery life.

[0016] 4. Reduce byproducts from side reactions: In lithium metal batteries, side reactions may generate byproducts that are detrimental to battery performance. Fluorine can reduce the formation of these byproducts, resulting in more stable battery operation.

[0017] 5. Increased electrolyte permeability: Fluorinated polyimide contains fluorine polar groups, which increase the surface free energy of the membrane and can interact with lithium ions in the electrolyte. This can simultaneously promote the wettability of the electrolyte on the membrane and help the transfer of lithium ions between each other, thereby improving electrochemical performance.

[0018] Optionally, the first diamine monomer or the second diamine monomer includes at least one of 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene, N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-diphenyl]-4,4'-diyl)bis(4-aminobenzamide), and 2,2'-bis(trifluoromethyl)diaminobiphenyl. The fluorine-free dianhydride monomers include at least one of 4,4'-biphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, and pyromellitic dianhydride; the fluorine-containing dianhydride monomers include hexafluorodianhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic acid dianhydride, and N-[4-[4-[(1,3-dioxo-2-benzofuran-5-carbonyl)amino]-2-(trifluoromethyl)phenyl]-3-(trifluoromethyl)phenyl] At least one of -1,3-dioxo-2-benzofuran-5-carboxamide and N,N'-[(perfluoropropane-2,2-diyl)bis(6-hydroxy-3,1-phenylene)]bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxamide), wherein the dianhydride monomer is selected from at least one of non-fluorinated dianhydride monomers and fluorinated dianhydride monomers, and the catalyst comprises at least one of quinoline, triethylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene or 3-methylpyridine.

[0019] The first diamine monomer and the second diamine monomer can be the same substance or different substances. The dianhydride monomers used to prepare the network structure polyimide can be either fluorine-free or fluorine-containing. When using fluorine-containing dianhydride monomers, the fluorine content of the fluorinated polyimide semi-interpenetrating network structure membrane increases, resulting in stronger wettability of the electrolyte and higher electrolyte absorption rate.

[0020] Optionally, the first solvent includes at least one of dimethylacetamide (DMAc), m-cresol, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), chloroform, 3-methoxy-N,N-dimethylpropionamide, and γ-butyrolactone (GBL).

[0021] Optionally, the solvent in the reaction system for preparing fluorinated polyimide fibers can be a first solvent or a second solvent different from the first solvent. The second solvent includes at least one of dimethylacetamide (DMAc), m-cresol, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), chloroform, 3-methoxy-N,N-dimethylpropionamide, and γ-butyrolactone (GBL).

[0022] Optionally, the fluorinated polyimide fiber is obtained by dripping a reaction solution obtained after reacting a first diamine monomer, a non-fluorinated dianhydride monomer, and a fluorinated dianhydride monomer into an antisolvent, wherein the antisolvent includes at least one of methanol, ethanol, and isopropanol.

[0023] Optionally, the solvent in the reaction system for producing fluorinated polyimide fibers can be a first solvent or a third solvent different from the first solvent. The third solvent includes at least one of dimethylacetamide (DMAc), m-cresol, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), chloroform, 3-methoxy-N,N-dimethylpropionamide, and γ-butyrolactone (GBL).

[0024] Optionally, the molar ratio of the first diamine monomer to the total molar ratio of the non-fluorinated dianhydride monomer and the fluorinated dianhydride monomer is 1:(0.8-1.2), and the molar ratio of the non-fluorinated dianhydride monomer to the fluorinated dianhydride monomer is (0.1-0.3):(0.9-0.7).

[0025] Optionally, in step (1), the reaction to produce fluorinated polyimide fibers is divided into two steps: the first step is to react at 80℃~100℃ for 2~4h, and the second step is to react at 170℃~190℃ for 14~18h.

[0026] Optionally, the ratio of the total molar amount of the second diamine monomer and melamine to the molar amount of the dianhydride monomer is 1:(0.8-1.2), and the molar ratio of the second diamine monomer to melamine is (0.9-0.97):(0.1-0.03).

[0027] The higher the proportion of melamine, the higher the degree of mesh in the fluorinated polyimide semi-interpenetrating network structure membrane, and the higher the modulus strength of the membrane. However, the surface wettability and electrolyte absorption rate will decrease.

[0028] Optionally, in step (2), the reaction temperature is 80℃~100℃ and the reaction time is 5~7h.

[0029] Optionally, the mass ratio of fluorinated polyimide fiber to network polyimide is 1:1. In a specific embodiment, the solid content of the fluorinated polyimide fiber slurry is 11.827%, and the solid content of the network polyimide is also 11.827%. The solid content of the two polyimides is initially set to the same solid content ratio during the design, ensuring a mass ratio of 1:1 when they are mixed.

[0030] Optionally, the aqueous alcohol solution includes an aqueous ethanol solution, and the step of preparing the fluorinated polyimide semi-interpenetrating mesh structure membrane further includes peeling and drying, wherein the drying is first performed at 90℃~110℃ for 5~15 min, then at 190℃~210℃ for 5~15 min, and finally at 290℃~310℃ for 5~15 min.

[0031] In a second aspect, the present invention provides a fluorinated polyimide semi-interpenetrating mesh structure membrane, which is prepared by the preparation method described in the first aspect.

[0032] Thirdly, the present invention provides the application of the fluorinated polyimide semi-interpenetrating mesh structure separator as described in the second aspect in batteries.

[0033] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0034] In the preparation method of fluorinated polyimide semi-interpenetrating network structure membrane, fluorinated polyimide fiber slurry is added to porous polyimide slurry to form a semi-interpenetrating network structure, which enhances the overall mechanical strength of the membrane without sacrificing its absorption effect on electrolyte.

[0035] The fluorine in fluorinated polyimide fibers effectively improves the compatibility of the membrane with electrolyte while maintaining other physical properties. The high mechanical strength of the fibers themselves also enhances the mechanical properties of the membrane.

[0036] Compared to membranes without fluorinated polyimide, fluorinated polyimide semi-interpenetrating mesh membranes exhibit significantly improved wettability and absorbance of electrolytes, as well as enhanced mechanical strength. The higher the proportion of fluorinated polyimide added, the more pronounced the mechanical strength and electrolyte absorbance of the membrane become; the absorbance can increase by up to 1.5 times, and the wettability (contact angle) can decrease from 22° to 15°. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0038] Figure 1 is a schematic diagram of the structure of a fluorinated polyimide semi-interpenetrating network film. Detailed Implementation

[0039] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0040] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0041] Unless otherwise specified, the methods used in the embodiments of this application are conventional methods in the prior art.

[0042] The method for testing dry film thickness is as follows: use a micrometer (accuracy 0.01 mm) to test the thickness of different diaphragms, take 5 points on the sample at random, and take the average value.

[0043] The tensile strength test method is as follows: the tensile strength, elongation and modulus of the cross-linked polyimide diaphragm are tested using the ASTM D882-10 tensile test method for plastics.

[0044] The contact angle test method is as follows: using a contact angle measuring instrument, cut the sample into 2*2 cm pieces and fix the four corners flat on a glass slide. Take 10 ml of EC / DEC electrolyte and drop it onto the separator membrane for analysis.

[0045] The method for testing electrolyte absorption rate is as follows: Immerse the diaphragm in the electrolyte (LiPF6EC:DEC (v / v = 50 / 50)) for 2 hours to saturate the diaphragm with electrolyte. Test the mass of the diaphragm before and after absorbing the electrolyte, and calculate it according to the following formula:

[0046] EU = [(W-Wo) / Wo] × 100%, where Wo and W are the masses of the diaphragm before and after absorbing the electrolyte, respectively.

[0047] The porosity test method is as follows: immerse the membrane in n-butanol for 2 hours, and then calculate the porosity according to the formula:

[0048] P(%) = (Mw - Md) / ρVd × 100%; where ρ is the density of n-butanol, Vd is the geometric volume of the membrane, and Mw and Md are the mass of n-butanol absorbed by the membrane and the mass of the membrane itself.

[0049] The method for testing the average pore size is as follows: At least 100 points are taken on both sides of the diaphragm using an electron microscope to test the pore size, and the average pore size of the two sides of the diaphragm is obtained. Then, the average of the average pore sizes of the two sides is taken to obtain the average pore size of the diaphragm as a whole. The formula for calculating the difference between the average pore sizes of the two sides is: (A1-A2) / A1×100%, where A1 is the larger value of the average pore size of the two sides of the diaphragm, and A2 is the smaller value of the average pore size of the two sides of the diaphragm.

[0050] In the examples, the equivalent number is the product of the number of moles and the number of groups, that is, the number of moles of anhydride groups or amino groups.

[0051] Example 1

[0052] Under nitrogen atmosphere, 42.833 g (200 mEq) of 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene and 337 g of m-cresol were added to a reactor and stirred at 22°C until completely dissolved. Then, 5.884 g (40 mEq) of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added and stirred at 22°C for 1 hour. Finally, 35.539 g (160 mEq) of hexafluorodianhydride and 47 g of m-cresol were gradually added and stirred for 1 hour, with the overall anhydride to amine equivalent ratio being 1:1. The temperature was then raised to 90°C and stirred for 3 hours, and finally raised to 180°C and stirred for 16 hours to obtain a slurry. The temperature was then lowered to room temperature, and 180 g of m-cresol solvent was added to the obtained slurry and stirred for 30 minutes. The diluted slurry was gradually added dropwise to 800 mL of methanol solution to form long strips of fluorinated polyimide fibers. The fibers were then thoroughly washed with fresh methanol solution to remove residual m-cresol solvent. Finally, the fibers were dried in an oven at 150°C for 24 hours. 40 g of the dried fluorinated polyimide fibers and 298.2 g of dimethylacetamide were added to a 500 mL beaker and stirred for 12 hours to obtain the fluorinated polyimide fiber slurry (solid content 11.827%), ready for further use.

[0053] Under nitrogen atmosphere, 19.423 g (194 milliequivalents) of 4,4'-diaminodiphenyl ether and 277 g of dimethylacetamide were added to the reactor and stirred at 22°C until completely dissolved. Then, 21.812 g (200 milliequivalents) of pyromellitic dianhydride was gradually added and stirred for 6 hours. After adding 0.252 g (6 milliequivalents) of melamine and stirring for 3 hours (the overall anhydride to amine equivalent ratio was 1:1), 32.29 g of quinoline was added, and the temperature was raised to 90°C and stirred for 6 hours. The temperature was then lowered to room temperature, and the resulting network-structured polyimide slurry (solid content 11.827%) was ready for use.

[0054] Add 50g of a network-structured polyimide slurry to a 100mL glass bottle, then add 5g (10wt% of the network-structured polyimide slurry) of fluorinated polyimide fiber slurry, and stir continuously for 60 minutes to obtain a mixed slurry. Coat the mixed slurry onto a 25μm thick PET substrate. Immerse the coated wet film in an ethanol-water solution (water:ethanol = 3 / 7 by weight) for 10 minutes to obtain a pre-cured polyimide separator at 22℃. Peel the pre-cured polyimide separator off the substrate surface and place it in a tunnel oven. First, dry it at 100℃ for 10 minutes, then at 200℃ for 10 minutes, and finally at 300℃ for 10 minutes to obtain a fluorinated polyimide semi-interpenetrating network structure separator, denoted as SP-POM3-10%.

[0055] Example 2

[0056] Based on Example 1, the difference is that 15g (accounting for 30wt% of the network structure polyimide slurry) of fluorinated polyimide fiber slurry was added, and the final fluorinated polyimide semi-interpenetrating network structure membrane was designated as SP-POM3-30.

[0057] Example 3

[0058] Based on Example 1, the difference is that 25g (accounting for 50wt% of the network structure polyimide slurry) of fluorinated polyimide fiber slurry is added, and the final fluorinated polyimide semi-interpenetrating network structure membrane is denoted as SP-POM3-50.

[0059] Comparative Example 1

[0060] Based on Example 1, the difference is that no fluorinated polyimide fiber slurry is added, and the final polyimide film is denoted as SP-POM3-0.

[0061] The performance of the fluorinated polyimide semi-interpenetrating mesh structure membranes obtained in Examples 1-3 and the polyimide film obtained in Comparative Example 1 were evaluated, and the results are shown in Table 1.

[0062] Table 1

[0063] As shown in Table 1, at the same thickness, with the increase of fluorinated polyimide fibers, the modulus of mechanical strength increases from 2.14 GPa (SP-POM3-0%) to 2.34 GPa (SP-POM3-50%). This is because the added fluorinated polyimide fibers form a semi-interpenetrating network structure in the slurry, thereby enhancing its overall mechanical strength. Furthermore, in addition to the C=O functional groups themselves, the fluorinated polyimide fiber structure is also designed to contain fluorine-containing functional groups. Through the polarity of C=O and fluorine, the wettability of the membrane to the electrolyte decreases from 22 degrees to 15 degrees, and the electrolyte absorption rate increases from 223% (SP-POM3-0%) to 392% (SP-POM3-50%).

[0064] Example 4

[0065] Under nitrogen atmosphere, 42.833 g (200 mEq) of 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene and 337 g of m-cresol were added to a reactor and stirred at 22°C until completely dissolved. Then, 5.884 g (40 mEq) of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added and stirred at 22°C for 1 hour. Finally, 35.539 g (160 mEq) of hexafluorodianhydride and 47 g of m-cresol were gradually added and stirred for 1 hour, with the overall anhydride to amine equivalent ratio being 1:1. The temperature was then raised to 90°C and stirred for 3 hours, and finally raised to 180°C and stirred for 16 hours to obtain a slurry. The temperature was then lowered to room temperature, and 180 g of m-cresol solvent was added to the obtained slurry and stirred for 30 minutes. The diluted slurry was gradually added dropwise to 800 mL of methanol solution to form long strips of fluorinated polyimide fibers. The fibers were then thoroughly washed with fresh methanol solution to remove residual m-cresol solvent. Finally, the fibers were dried in an oven at 150°C for 24 hours. To obtain the fluorinated polyimide fiber slurry, 40 g of the dried fluorinated polyimide fiber and 298.2 g of dimethylacetamide were added to a 500 mL beaker and stirred for 12 hours. This slurry was then ready for further use.

[0066] Under nitrogen atmosphere, 19.423 g (194 milliequivalents) of 4,4'-diaminodiphenyl ether and 277 g of dimethylacetamide were added to a reactor and stirred at 22°C until completely dissolved. Then, 44.422 g (200 milliequivalents) of hexafluorodianhydride was gradually added and stirred continuously for 6 hours. After adding 0.252 g (6 milliequivalents) of melamine and stirring for 3 hours (the overall anhydride to amine equivalent ratio was 1:1), 32.29 g of quinoline was added, and the temperature was raised to 90°C and stirred for 6 hours. The temperature was then lowered to room temperature, and the resulting network-structured polyimide slurry was ready for use.

[0067] Add 50g of a network-structured polyimide slurry to a 100mL glass bottle, then add 5g (10wt% of the network-structured polyimide slurry) of fluorinated polyimide fiber slurry, and stir continuously for 60 minutes to obtain a mixed slurry. Coat the mixed slurry onto a 25μm thick PET substrate. Immerse the coated wet film in an ethanol-water solution (water:ethanol = 3 / 7 by weight) for 10 minutes to obtain a pre-cured polyimide separator at 22℃. Peel the pre-cured polyimide separator off the substrate surface and place it in a tunnel oven. First, dry it at 100℃ for 10 minutes, then at 200℃ for 10 minutes, and finally at 300℃ for 10 minutes to obtain a fluorinated polyimide semi-interpenetrating network structure separator, denoted as SP-6OM3-10%.

[0068] Example 5

[0069] Based on Example 4, the difference is that 15g (30wt% of the network structure polyimide slurry) of fluorinated polyimide fiber slurry was added, and the final fluorinated polyimide semi-interpenetrating network structure membrane was designated as SP-6OM3-30.

[0070] Example 6

[0071] Based on Example 4, the difference is that 25g (50wt% of the network structure polyimide slurry) of fluorinated polyimide fiber slurry was added, and the final fluorinated polyimide semi-interpenetrating network structure membrane was designated as SP-6OM3-50%.

[0072] Comparative Example 2

[0073] Based on Example 4, the difference is that no fluorinated polyimide fiber slurry is added, and the final polyimide film is denoted as SP-6OM3-0.

[0074] The performance of the fluorinated polyimide semi-interpenetrating mesh structure membranes obtained in Examples 4-6 and the polyimide film obtained in Comparative Example 2 was evaluated, and the results are shown in Table 2.

[0075] Table 2

[0076] Table 2 shows that, at the same thickness, with the increase of polyimide fiber, its mechanical strength modulus increases from 1.85 GPa (SP-6OM3-0%) to 2.07 GPa (SP-6OM3-50%), an increase of 11.89% in modulus strength. Besides the fluorinated polyimide fiber structure itself containing fluorinated groups, the 3,3',4,4'-biphenyltetracarboxylic acid dianhydride in the network structure polyimide slurry is replaced with hexafluorodianhydride containing fluorinated groups, increasing the overall fluorine content. The results show that the wettability of the diaphragm to the electrolyte decreased from 18 degrees to 10 degrees, which is better than the wettability of the diaphragms in Examples 1-3. Furthermore, the electrolyte absorption rate increased from 271% (SP-6OM3-0%) to 407% (SP-6OM3-50%), an increase of 50.18%.

[0077] Example 7

[0078] Based on Example 1, the difference from Example 1 is that the milliequivalent of 4,4'-diaminodiphenyl ether is 186 and the milliequivalent of melamine is 14. The resulting fluorinated polyimide semi-interpenetrating network structure membrane is designated as SP-POM7-50.

[0079] Example 8

[0080] Based on Example 1, the difference from Example 1 is that the milliequivalent of 4,4'-diaminodiphenyl ether is 180 and the milliequivalent of melamine is 20. The resulting fluorinated polyimide semi-interpenetrating network structure membrane is designated as SP-POM10-50.

[0081] The performance of the fluorinated polyimide semi-interpenetrating mesh membranes obtained in Examples 7 and 8 was evaluated and compared with that of the fluorinated polyimide semi-interpenetrating mesh membrane obtained in Example 3. The results are shown in Table 3.

[0082] Table 3

[0083] As shown in Table 3, as the milliequivalent of melamine increases from 6 (SP-POM3-50%) to 20 (SP-POM10-50%), its modulus strength gradually increases, indicating a higher degree of network structure, which in turn improves the mechanical strength of the membrane. However, with the increase in the degree of network structure, the electrolyte wettability and electrolyte absorption rate on its surface decrease simultaneously.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a fluorinated polyimide semi-interpenetrating network separator, characterized by, The method comprises the following steps: A mixed slurry comprising fluorinated polyimide fibers, reticular polyimide and a first solvent is coated and soaked in an alcohol aqueous solution to form a fluorinated polyimide semi-interpenetrating reticular membrane; The fluorinated polyimide fibers are prepared by reacting a first diamine monomer, a fluorine-free dianhydride monomer and a fluorine-containing dianhydride monomer; The reticular polyimide is prepared by reacting a second diamine monomer, a dianhydride monomer and melamine under catalysis of a catalyst.

2. The production method according to claim 1, wherein The first diamine monomer or the second diamine monomer comprises at least one of 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene, N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-biphenyl]-4,4'-diyl)bis(4-aminobenzamide), 2,2'-bis(trifluoromethyl)diaminobiphenyl, the fluorine-free dianhydride monomer comprises at least one of 4,4'-diphenyl ether dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, the fluorine-containing dianhydride monomer comprises at least one of hexafluoro dianhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-oxaanthracene tetracarboxylic dianhydride, N-[4-[4-[(1,3-dioxo-2-benzofuran-5-carbonyl)amino]-2-(trifluoromethyl)phenyl]-3-(trifluoromethyl)phenyl]-1,3-dioxo-2-benzofuran-5-carboxamide, N,N'-[(perfluoropropane-2,2-diyl)bis(6-hydroxy-3,1-phenylene)]bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxamide), the dianhydride monomer is selected from at least one of the fluorine-free dianhydride monomer and the fluorine-containing dianhydride monomer, and the catalyst comprises at least one of quinoline, triethylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene or 3-methylpyridine.

3. The production method according to claim 1, wherein The ratio of the molar amount of the first diamine monomer to the total molar amount of the fluorine-free dianhydride monomer and the fluorine-containing dianhydride monomer is 1:(0.8-1.2), and the molar ratio of the fluorine-free dianhydride monomer to the fluorine-containing dianhydride monomer is (0.1-0.3):(0.9-0.7).

4. The production method according to claim 1, wherein The reaction for preparing the fluorinated polyimide fibers is divided into two steps, the first step is performed at 80-100°C for 2-4h, and the second step is performed at 170-190°C for 14-18h.

5. The production method according to claim 1, wherein The ratio of the total molar amount of the second diamine monomer and melamine to the molar amount of the dianhydride monomer is 1:(0.8-1.2), the molar ratio of the second diamine monomer to melamine is (0.9-0.97):(0.1-0.03).

6. The production method according to claim 1, wherein The reaction temperature for preparing the reticular polyimide is 80-100°C, and the reaction time is 5-7h.

7. The production method according to claim 1, wherein The mass ratio of the fluorinated polyimide fibers to the reticular polyimide is 1:

1.

8. The production method according to claim 1, wherein The alcohol aqueous solution comprises an ethanol aqueous solution, and the step of preparing the fluorinated polyimide semi-interpenetrating network diaphragm further comprises peeling and drying, wherein the drying is first carried out at 90-110 ℃ for 5-15 min, then at 190-210 ℃ for 5-15 min, and finally at 290-310 ℃ for 5-15 min.

9. A fluorinated polyimide semi-interpenetrating network separator, characterized in that, Prepared by the preparation method according to any one of claims 1-8.

10. Use of the fluorinated polyimide semi-interpenetrating network diaphragm according to claim 9 in a battery.

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