CN113563619A

CN113563619A - Preparation method of branched-crosslinked sulfonated polyimide membrane

Info

Publication number: CN113563619A
Application number: CN202110969205.0A
Authority: CN
Inventors: 李劲超; 张亚萍; 刘军; 胥文杰; 罗钢; 黄文恒; 龙俊; 罗欢
Original assignee: Sichuan Langsheng New Energy Technology Co ltd; Southwest University of Science and Technology
Current assignee: Sichuan Langsheng New Energy Technology Co ltd; Southwest University of Science and Technology
Priority date: 2021-08-23
Filing date: 2021-08-23
Publication date: 2021-10-29
Anticipated expiration: 2041-08-23
Also published as: CN113563619B

Abstract

The invention discloses a preparation method of a branched-crosslinked sulfonated polyimide film, which is characterized in that a novel branched-crosslinked polyimide film material is obtained by carrying out tape casting film forming and high-temperature polymerization on a Y-type branched triamine monomer, an X-type crosslinked tetramine monomer, a sulfonated diamine monomer, a non-sulfonated diamine monomer and an anhydride monomer. The Y-type branched monomer and the X-type cross-linked tetramine monomer are both synthesized by self. The molar ratio of the cross-linked tetramine, the non-sulfonated diamine, the acid anhydride, the branched triamine, the sulfonated diamine and the benzoic acid is as follows: 0.06-0.14: 0.07-0.23: 1:0.1:0.5:2, and the crosslinking degree of the diaphragm can be controlled by regulating and controlling the proportion of the dosage of the crosslinking monomer. The stability and vanadium resistance of the membrane can be effectively improved by introducing a branched crosslinking structure, and the efficiency, the service life and the like of the all-vanadium redox flow battery can be effectively improved. In conclusion, the branched-crosslinked sulfonated polyimide membrane prepared by the invention has good application prospect in the field of all-vanadium redox flow batteries.

Description

Preparation method of branched-crosslinked sulfonated polyimide membrane

Technical Field

The invention belongs to the field of battery diaphragms, and relates to a preparation method of a branched-crosslinked sulfonated polyimide membrane.

Background

With the continuous development of economy, the utilization problem of renewable energy is more and more emphasized, and therefore, the energy storage and conversion system is required to play a crucial role in energy application. The all-Vanadium Redox Flow Battery (VRFB) is an excellent energy storage system and has the advantages of high response speed, long service life, good reliability, strong deep discharge capability and the like. A Proton Exchange Membrane (PEM), one of the important component materials of VRFB, can separate the positive and negative electrolytes to avoid cross contamination of vanadium ions and conduct protons to complete the cell. Thus, the PEM should have high proton conductivity, excellent vanadium rejection, and outstanding chemical stability. So far, Nafion membranes produced by dupont in the united states have been widely used in VRFB systems due to their high proton conductivity and excellent chemical stability. However, Nafion membrane vanadium permeation is severe, proton selectivity is low and price is expensive, thus limiting its large-scale commercial application in VRFB.

So far, sulfonated aromatic polymer membranes have been of increasing interest to researchers, such as: sulfonated poly (aryl ether sulfones) (SPPES), sulfonated poly (ether ketones) (SPEEK), sulfonated poly (phenylene) oxide (SPPO), Sulfonated Polybenzimidazole (SPBI), and Sulfonated Polyimide (SPI) membranes. Among these membranes, SPI membrane exhibits excellent application potential in VRFB application due to its many advantages of excellent membrane-forming properties, low vanadium ion permeability, low cost, high proton selectivity, etc. However, the study of SPI membrane in VRFB is still preliminary, and its disadvantages mainly lie in the following two aspects: (1) in the strong acid and strong oxidizing electrolyte environment, the SPI film has weak chemical stability, and the service life of the SPI film in the battery is seriously influenced; (2) the unobvious hydrophilic-hydrophobic phase separation structure ensures that the proton conductivity of the SPI membrane is lower, and is not beneficial to obtaining higher voltage efficiency of the battery. Therefore, it is highly desirable to greatly improve the chemical stability and proton conductivity of SPI membrane, making it commercially viable for use in VRFB. To overcome the above problems, many researchers have conducted studies and the prior art (Long J, Xu WJ, Xu SB, Liu J, Wang YL, Luo H, et al, Anovel double branched sulfonated polyimide membrane with ultra-high proton selectivity for a variable redox flow battery, J Membrane Sci 628(2021)119259) has succeeded in producing a double branched sulfonated polyimide (dbSPI) membrane having higher proton conductivity and lower vanadium permeability than a linear sulfonated polyimide (l-SPI) membrane. In addition, when a branched structure is introduced into SPI, the performance of VRFB can be greatly improved, but the chemical stability of SPI membrane materials prepared by the prior art is not excellent enough.

The invention aims to overcome the defects and short plates mentioned in the SPI membrane, prepare a branched-crosslinked SPI membrane with good chemical stability and proton conduction level, and correspondingly provide a preparation method and a main application field thereof.

In the present invention, the "X"

type

4,4',4 ", 4'" (5,5 '-benzimidazole-2, 2') -tetraaniline (BTA) and the "Y"

type

1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene (TFAPOB) are synthesized and introduced into the SPI membrane, so that they simultaneously acquire a cross-linked and branched structure. In addition, the C-F bond contained in the Y-type monomer is very stable, and the attack probability of V (V) can be reduced, so that the chemical stability of the SPI membrane is effectively improved. The branched structure may provide the membrane with a larger free volume, thereby improving its proton conductivity. The introduction of cross-linked structures can also enhance the chemical and dimensional stability of SPI membranes.

Disclosure of Invention

An object of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.

To achieve these objects and other advantages in accordance with the present invention, there is provided a method for preparing a branched-crosslinked sulfonated polyimide membrane, comprising the steps of:

step one, under the protection of nitrogen, adding 1,4,5, 8-naphthalene tetracarboxylic anhydride (NTDA), benzoic acid and m-cresol I into a reactor, and stirring and dissolving at room temperature; adding 2,2' -disulfonic acid Benzidine (BDSA), triethylamine and m-cresol II into a container, stirring at 50-70 ℃ until the mixture is dissolved, sequentially adding 4,4' (5,5' -benzimidazole-2, 2') -tetraaniline (BTA), 4' -diaminodiphenyl ether (ODA) and 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene (TFAPOB) into the container, stirring at 50-70 ℃ until the mixture is dissolved, then placing the materials in the container into a constant-pressure dropping funnel, dropping the materials into a reactor, and stirring at 30-100 ℃ for reaction for 4-8 hours after the dropping is completed to obtain a casting solution; pouring the casting solution on a dry and clean glass plate for casting to form a film, then drying the glass plate for 10-24 hours at the temperature of 60-80 ℃, and then drying the glass plate for 0.5-3 hours at different temperatures of 80-150 ℃ respectively to obtain a triethylamine type branched-crosslinked sulfonated polyimide film;

secondly, the triethylamine type branched-crosslinked sulfonated polyimide membrane is placed in absolute ethyl alcohol to be soaked for 18-48 hours and then placed in 1.0-3.0 mol L^-1Soaking the membrane in the sulfuric acid aqueous solution for 24-48 h, then washing the membrane for 5-10 times by using deionized water to obtain the branched-crosslinked sulfonated polyimide membrane, and soaking the membrane in the deionized water for storage.

Preferably, the molar ratio of 4,4',4 ", 4'" (5,5 '-benzimidazole-2, 2') -tetraaniline, 4 '-diaminodiphenyl ether, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene, 2' -disulfonic acid benzidine and benzoic acid is: 0.06-0.14: 0.07-0.23: 1:0.1:0.5: 2.

Preferably, the volume ratio of the m-cresol I to the m-cresol II is 1: 1; the volume ratio of the total volume of the m-cresol I and the m-cresol II to the triethylamine is as follows: 20-70: 0.5-9.5; the dosage proportion of the triethylamine to the 2,2' -disulfonic acid benzidine is as follows: and adding 0.5-9.5 mL of triethylamine for each 0.4-3.2 mmol of 2,2' -disulfonic acid benzidine.

Preferably, the m-cresol I and the m-cresol II can be replaced by one or a mixture of more than two of N, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone.

Preferably, the thickness range of the cast film is controlled as follows: 25 to 120 μm.

Preferably, the absolute ethyl alcohol can be replaced by one or a mixture of more than two of methanol, acetone and isopropanol; the deionized water can be replaced by distilled water or ultrapure water.

Preferably, in the first step, after the dropwise addition is completed, stirring and reacting for 1-2 hours at 30-100 ℃ to obtain a casting solution, placing the casting solution in a microwave and ultrasonic integrated reactor, and simultaneously starting microwaves and ultrasonic waves for synergistic treatment for 30-45 min, wherein the microwave power is 150-350W; the ultrasonic power is 300-800W, the ultrasonic frequency is 45-65 KHz, and the reaction temperature is 30-100 ℃.

Preferably, in the first step, the casting solution after the synergistic treatment is poured on a dry and clean glass plate for casting film formation, and then electron beam irradiation is carried out, wherein the irradiation dose is 4-10 Gy; then, drying the glass plate in an infrared drying oven for 6-8 hours at the power of 800-1000W and the temperature of 50-60 ℃; and then drying the membrane for 0.5 to 3 hours at different temperatures of between 80 and 150 ℃ to obtain the triethylamine type branched-crosslinked sulfonated polyimide membrane.

The invention at least comprises the following beneficial effects:

compared with the existing sulfonated polyimide membrane technology for VRFB, the invention has the following characteristics and advantages: the invention aims to overcome the defects of weaker chemical stability and insufficient proton conduction capability of sulfonated polyimide membranes for VRFB (falling film transistor), and prepares sulfonated polyimide membranes containing branching-crosslinking by taking fluorine-containing Y-type branched triamine monomers, X-type crosslinked tetramine monomers, non-sulfonated diamine monomers, dianhydride monomers and sulfonated diamine monomers with mass transfer capability as raw materials; the prepared branched-crosslinked sulfonated polyimide membrane can obviously improve the interaction between molecular chains and the space free volume, thereby enhancing the vanadium resistance, the proton conduction capability and the application potential in the VRFB field. Furthermore, by varying the "X" type self-crosslinking tetraamine monomer: 4,4',4 ", 4"' (5,5 '-benzimidazole-2, 2') -tetraaniline and non-sulfonated diamine monomers: the proportion of the 4,4' -diaminodiphenyl ether can effectively regulate and control the degree of crosslinking of the diaphragm, thereby pertinently solving the problems of weak chemical stability and low proton conductivity of the sulfonated polyimide film. The invention prepares the fluorine-containing Y-type branched triamine monomer required by the branched-crosslinked sulfonated polyimide film: 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene and "X" type self-crosslinking tetraamine monomer: the synthesis of 4,4',4 ", 4'" (5,5 '-benzimidazole-2, 2') -tetraaniline is shown in FIGS. 2 and 3, respectively.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Description of the drawings:

FIG. 1 is a reaction scheme for preparing a branched-crosslinked sulfonated polyimide membrane according to the present invention;

FIG. 2 is a reaction scheme for the synthesis of 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene (TFAPOB) according to the present invention;

FIG. 3 is a reaction scheme for the synthesis of 4,4' (5,5' -benzimidazole-2, 2') -tetraaniline (BTA) according to the invention;

FIG. 4 is an FTIR spectrum of 4,4' (5,5' -benzimidazole-2, 2') -tetraaniline (BTA) of the present invention;

FIG. 5 shows the preparation of 4,4' (5,5' -benzimidazole-2, 2') -tetraaniline (BTA) according to the invention¹H NMR spectrum;

FIG. 6 is an FTIR spectrum of an sc-bSPI film of the invention;

FIG. 7 shows sc-bSPI-14 membranes of the invention¹H NMR spectrum;

FIG. 8 shows VO passing through sc-bSPI membrane according to the invention²⁺An ion concentration curve;

FIG. 9 is an open circuit voltage curve for the sc-bSPI-14 film of the present invention;

FIG. 10 is a coulombic efficiency curve for the sc-bSPI-14 membrane of the invention;

FIG. 11 is a voltage efficiency curve for the sc-bSPI-14 film of the invention;

FIG. 12 is an energy efficiency curve for sc-bSPI-14 membranes of the invention;

FIG. 13 is a cycle test curve for sc-bSPI-14 membranes of the invention.

The specific implementation mode is as follows:

the present invention is further described in detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description text.

It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.

Example 1:

a method for preparing a branched-crosslinked sulfonated polyimide membrane, comprising the steps of:

step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-neck flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, stirred at 60 ℃ until the solid is completely dissolved, then 0.4mmol TFAPOB, 0.92mmol ODA and 0.24mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-neck flask by using a constant pressure funnel, and stirred at 60 ℃ for reaction for 15 hours, thus obtaining the branched-crosslinked sulfonated polyimide casting solution; pouring the casting solution on a dry and clean glass plate for casting to form a film, and drying at 60 ℃ for 15 hours; drying at 80 ℃, 100 ℃, 120 ℃ and 150 ℃ for 1 hour respectively to obtain the triethylamine salt type branched-crosslinked sulfonated polyimide membrane;

step two, placing the obtained triethylamine salt type branched-crosslinked sulfonated polyimide membrane in absolute ethyl alcohol for soaking for 24 hours to remove residual solvent and unreacted monomer(ii) a Then, the mixture was immersed in 1.0mol L^-1The protonation process is finished in sulfuric acid solution for 24 hours; finally, washing with deionized water for 7 times to obtain a branched-crosslinked sulfonated polyimide film (sc-bSPI-6);

the branched-crosslinked sulfonated polyimide membrane prepared in this example had a thickness of 51 μm; ion Exchange Capacity (IEC) of 1.65mmol g^-1dry。

Example 2:

step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-neck flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, stirred at 60 ℃ until the solid is completely dissolved, then 0.4mmol TFAPOB, 0.76mmol ODA and 0.32mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-neck flask by using a constant pressure funnel, and stirred at 60 ℃ for reaction for 12 hours, thus obtaining the branched-crosslinked sulfonated polyimide casting solution; pouring the casting solution on a dry and clean glass plate for casting to form a film, and drying at 60 ℃ for 15 hours; drying at 80 ℃, 100 ℃, 120 ℃ and 150 ℃ for 1 hour respectively to obtain the triethylamine salt type branched-crosslinked sulfonated polyimide membrane;

step two, placing the obtained triethylamine salt type branched-crosslinked sulfonated polyimide membrane in absolute ethyl alcohol to be soaked for 24 hours so as to remove residual solvent and unreacted monomers; then, the mixture was immersed in 1.0mol L^-1The protonation process is finished in sulfuric acid solution for 24 hours; finally, washing with deionized water for 7 times to obtain a branched-crosslinked sulfonated polyimide film (sc-bSPI-8);

the branched-crosslinked sulfonated polyimide membrane prepared in this example had a thickness of 50 μm; ion Exchange Capacity (IEC) of 1.60mmol g^-1dry。

Example 3:

step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-neck flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, stirred at 60 ℃ until the solid is completely dissolved, then 0.4mmol TFAPOB, 0.6mmol ODA and 0.4mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-neck flask by using a constant pressure funnel, and stirred at 60 ℃ for reaction for 10 hours, thus obtaining the branched-crosslinked sulfonated polyimide casting solution; pouring the casting solution on a dry and clean glass plate for casting to form a film, and drying at 60 ℃ for 15 hours; drying at 80 ℃, 100 ℃, 120 ℃ and 150 ℃ for 1 hour respectively to obtain the triethylamine salt type branched-crosslinked sulfonated polyimide membrane;

step two, placing the obtained triethylamine salt type branched-crosslinked sulfonated polyimide membrane in absolute ethyl alcohol to be soaked for 24 hours to remove residual solvent and unreacted monomers, and then soaking in 1.0mol L^-1The protonation process is finished after 24 hours in sulfuric acid solution, and finally the branched-crosslinked sulfonated polyimide film (sc-bSPI-10) is obtained after 7 times of washing by deionized water;

the branched-crosslinked sulfonated polyimide membrane prepared in this example had a thickness of 51 μm; ion Exchange Capacity (IEC) of 1.51mmol g^-1dry。

Example 4:

step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-neck flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, stirred at 60 ℃ until the solid is completely dissolved, then 0.4mmol TFAPOB, 0.44mmol ODA and 0.48mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-neck flask by using a constant pressure funnel, and stirred at 60 ℃ for reaction for 8 hours, thus obtaining the branched-crosslinked sulfonated polyimide casting solution; pouring the casting solution on a dry and clean glass plate for casting to form a film, and drying at 60 ℃ for 15 hours; drying at 80 ℃, 100 ℃, 120 ℃ and 150 ℃ for 1 hour respectively to obtain the triethylamine salt type branched-crosslinked sulfonated polyimide membrane;

step two, placing the obtained triethylamine salt type branched-crosslinked sulfonated polyimide membrane in absolute ethyl alcohol to be soaked for 24 hours to remove residual solvent and unreacted monomers, and then soaking in 1.0mol L^-1The protonation process is finished after 24 hours in sulfuric acid solution, and finally the branched-crosslinked sulfonated polyimide film (sc-bSPI-12) is obtained after 7 times of washing by deionized water;

the branched-crosslinked sulfonated polyimide membrane prepared in this example had a thickness of 51 μm; ion Exchange Capacity (IEC) of 1.42mmol g^-1dry。

Example 5:

step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-neck flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, stirred at 60 ℃ until the solid is completely dissolved, then 0.4mmol TFAPOB, 0.28mmol ODA and 0.56mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-neck flask by using a constant pressure funnel, and stirred at 40 ℃ for reaction for 6 hours, thus obtaining the branched-crosslinked sulfonated polyimide casting solution; pouring the casting solution on a dry and clean glass plate for casting to form a film, and drying at 60 ℃ for 15 hours; drying at 80 ℃, 100 ℃, 120 ℃ and 150 ℃ for 1 hour respectively to obtain the triethylamine salt type branched-crosslinked sulfonated polyimide membrane;

step two, placing the obtained triethylamine salt type branched-crosslinked sulfonated polyimide membrane in absolute ethyl alcohol to be soaked for 24 hours to remove residual solvent and unreacted monomers, and then soaking in 1.0mol L^-1The protonation process is finished after 24 hours in sulfuric acid solution, and finally the branched-crosslinked sulfonated polyimide film (sc-bSPI-14) is obtained after 7 times of washing by deionized water;

the branched-crosslinked sulfonated polyimide membrane prepared in this example had a thickness of 50 μm; ion Exchange Capacity (IEC) of 1.36mmol g^-1dry; thickness of commercial Nafion 212 film thereinIs 51 μm; ion Exchange Capacity (IEC) of 0.92mmol g^-1dry; has higher ion exchange capacity and is beneficial to proton transfer.

Example 6:

step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-neck flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, stirred at 60 ℃ until the solid is completely dissolved, then 0.4mmol TFAPOB, 0.28mmol ODA and 0.56mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-neck flask by using a constant pressure funnel, and stirred at 40 ℃ for 2 hours to react, thus obtaining the branched-crosslinked sulfonated polyimide casting solution; placing the casting solution in a microwave and ultrasonic integrated reactor, and simultaneously starting microwaves and ultrasonic waves for synergistic treatment for 45min, wherein the microwave power is 350W; the ultrasonic power is 800W, the ultrasonic frequency is 45KHz, and the reaction temperature is 50 ℃; pouring the treated casting solution on a dry and clean glass plate for casting to form a film, and drying at 60 ℃ for 15 hours; drying at 80 ℃, 100 ℃, 120 ℃ and 150 ℃ for 1 hour respectively to obtain the triethylamine salt type branched-crosslinked sulfonated polyimide membrane;

step two, placing the obtained triethylamine salt type branched-crosslinked sulfonated polyimide membrane in absolute ethyl alcohol to be soaked for 24 hours to remove residual solvent and unreacted monomers, and then soaking in 1.0mol L^-1The protonation process is finished after 24 hours in sulfuric acid solution, and finally the branched-crosslinked sulfonated polyimide film is obtained after 7 times of washing by deionized water; the branched-crosslinked sulfonated polyimide membrane prepared in this example had a thickness of 50 μm;

the branched-crosslinked sulfonated polyimide membrane prepared in this example was tested in an all-vanadium redox flow battery (test method was consistent with sc-bSPI-14 membrane), and was measured at 200mA cm^-2The coulombic efficiency CE at high current density of 99.42%, the voltage efficiency VE of 66.31% and the energy efficiency EE of 66.82%; sc-bSPI-14 film at 200mA cm^-2The coulombic efficiency CE at high current density of 99.22%, the voltage efficiency VE of 64.14% and the energy efficiency EE of 64.44%; the branched-crosslinked sulfonated polyimide film prepared in this example was immersed in 0.1mol L of 40 deg.C^-1VO₂ ⁺+3.0mol L^-1H₂SO₄VO was recorded every 3 days in solution for 15 days with a spectrophotometer²⁺Concentration of (b), the branched-crosslinked sulfonated polyimide membrane produced 0.39mol L during the 15 day soaking due to the strong acid and strong oxidizing environment^-1g^-1VO (a) of²⁺(ii) a And sc-bSPI-14 film was 0.41mol L^-1g^-1VO (a) of²⁺。

Example 7:

step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-neck flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, stirred at 60 ℃ until the solid is completely dissolved, then 0.4mmol TFAPOB, 0.28mmol ODA and 0.56mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-neck flask by using a constant pressure funnel, and stirred at 40 ℃ for 2 hours to react, thus obtaining the branched-crosslinked sulfonated polyimide casting solution; placing the casting solution in a microwave and ultrasonic integrated reactor, and simultaneously starting microwaves and ultrasonic waves for synergistic treatment for 45min, wherein the microwave power is 350W; the ultrasonic power is 800W, the ultrasonic frequency is 45KHz, and the reaction temperature is 50 ℃; pouring the casting solution subjected to the synergistic treatment onto a dry and clean glass plate for casting film formation, and then performing electron beam irradiation with the irradiation dose of 8 Gy; then, drying the glass plate in an infrared drying oven for 6 hours at the power of 1000W and the temperature of 60 ℃; then drying the membrane for 1h at the temperature of 80 ℃, 100 ℃, 120 ℃ and 150 ℃ respectively to obtain a triethylamine type branched-crosslinked sulfonated polyimide membrane;

step two, placing the obtained triethylamine salt type branched-crosslinked sulfonated polyimide membrane in absolute ethyl alcohol to be soaked for 24 hours to remove residual solventAnd unreacted monomer, and soaking in 1.0mol L^-1The protonation process is finished after 24 hours in sulfuric acid solution, and finally the branched-crosslinked sulfonated polyimide film is obtained after 7 times of washing by deionized water; the branched-crosslinked sulfonated polyimide membrane prepared in this example had a thickness of 50 μm;

the branched-crosslinked sulfonated polyimide membrane prepared in this example was tested in an all-vanadium redox flow battery (test method was consistent with sc-bfspi-14 membrane), and the branched-crosslinked sulfonated polyimide membrane prepared in this example was tested at 200mAcm^-2The coulombic efficiency CE at high current density of 99.78%, the voltage efficiency VE of 67.45% and the energy efficiency EE of 67.78%; sc-bSPI-14 film at 200mA cm^-2The coulombic efficiency CE at high current density of 99.22%, the voltage efficiency VE of 64.14% and the energy efficiency EE of 64.44%. The branched-crosslinked sulfonated polyimide film prepared in this example was immersed in 0.1mol L of 40 deg.C^-1VO₂ ⁺+3.0mol L^-1H₂SO₄VO was recorded every 3 days in solution for 15 days with a spectrophotometer²⁺Concentration of (a), the branched-crosslinked sulfonated polyimide membrane produced 0.37mol L during the 15 day soaking due to the strong acid and strong oxidizing environment^-1g^-1VO (a) of²⁺(ii) a And sc-bSPI-14 film was 0.41mol L^-1g^-1VO (a) of²⁺。

The FTIR spectrum of BTA in the present invention is shown in FIG. 4, and the BTA is 3203cm^-1And 3315cm^-1The peak of (A) belongs to-NH₂Stretching vibration of 1780cm^-1There was no absorption peak, which means that-COOH in DBA had been consumed, 1446cm^-1The peak at (a) can be attributed to the symmetric oscillation of the imidazole ring, demonstrating the successful synthesis of BTA monomer.

The BTA was also analyzed¹The H NMR spectrum was used to confirm the structure, and the results are shown in FIG. 5. The peak in FIG. 5 is at 4.95ppm (H)₁)、5.97ppm(H₂)、6.64ppm(H₃)、7.49ppm(H₄)、7.66ppm(H₅)、7.84ppm(H₆)、12.58ppm(H₇). Actual peak area ratio (H)₁:H₂:H₃:H₄:H₅:H₆:H₇2.09:0.48:1.05:0.52:0.56:0.45:0.46) is very close to the theoretical value (H)₁:H₂:H₃:H₄:H₅:H₆:H₇The exact synthesis of BTA was verified as 4:1:2:1:1: 1).

The chemical structures of the branched-crosslinked sulfonated polyimide membranes prepared in examples 1 to 5 were characterized by FTIR spectra, and the results are shown in FIG. 6. Characteristic peak 1710cm^-1And 1667cm^-1Can belong to the asymmetric and symmetric stretching vibration of carbonyl. 1450cm^-1The peak at (A) is due to the symmetric vibration of the imidazole ring on BTA monomer, and the asymmetric vibration of C-N on the imide ring is located at 1351cm^-1。1249cm^-1Is attributed to vibration of-O-. Furthermore, 1135cm^-1The characteristic absorption peak at (A) is attributed to-CF on TFAPOB monomer₃Vibration of the radicals. -SO₃Characteristic absorption peaks for the H group appear at 1196, 1098 and 1028cm^-1. In addition, at 1780cm^-1No significant polyimide acid absorption peak was present nearby, indicating that the branched-crosslinked sulfonated polyimide membrane was fully imidized. Thus, FTIR spectra indicate that branched-crosslinked sulfonated polyimide membranes have been successfully prepared from NTDA, BDSA, TFAPOB, ODA, and BTA monomers.

Of sc-bSPI-14 membranes¹The H NMR spectrum is shown in FIG. 7. Chemical shifts at 8.79ppm (He) and 8.61ppm (Hf) correspond to protons of the NTDA naphthalene ring. The peaks at 8.24ppm (Hg) and 7.77ppm (Hh) are attributable to the benzene hydrogen of ODA. Chemical shifts at 8.14ppm, 7.95ppm, and 7.79ppm were derived from Hi, Hk, and Hj on BDSA. Chemical shifts of 6.59ppm (Hd), 7.58ppm (Ha), 7.60ppm (Hb), and 7.64ppm (Hc) are attributable to benzene hydrogen of TFAPOB. Signals at 6.54(Hm), 6.57(Hl), 7.74(Hn), 8.02(Hp), 8.24(Hq) are H shifts on the BTA. These characteristic peaks also confirm the successful synthesis of sc-bSPI-14 membranes.

The following performance tests were performed on the branched-crosslinked sulfonated polyimide membranes prepared in the examples, respectively, as follows:

(1) and (3) vanadium ion permeability test:

the prepared branched-crosslinked sulfonated polyimide membrane is clamped between two diffusion cells, and 1.0mol L of the branched-crosslinked sulfonated polyimide membrane is respectively filled in the left side and the right side of the membrane^-1VO²⁺+2.0mol L^-1H₂SO₄Solution and 1.0mol L^-1MgSO₄+2.0mol L^-1H₂SO₄A solution; at regular intervals, the sample solution was taken out of the cell on the right side of the membrane, and VO was measured with an ultraviolet-visible spectrophotometer²⁺The absorbance of the ions, and the VO passing through the membrane at that moment is calculated by using a standard curve²⁺Ion concentration (as shown in fig. 8); pouring the sample solution back to the right cell after each test; the vanadium ion permeability of the membrane is calculated according to the following formula:

wherein V is the volume (cm) of the solution on the left and right sides of the membrane³)；C_tVO in the solution on the right side of the membrane at time t (min)²⁺Concentration of ions (mol L)^-1)；C_LIs VO in the solution on the left side of the membrane²⁺Initial concentration of ions (mol L)^-1) (ii) a A is the effective area (cm) of the diaphragm²) (ii) a VO with P as diaphragm²⁺Ion permeability (cm)²min^-1) (ii) a The branched-crosslinked sulfonated polyimide membranes of each example were tested 3 times under the same conditions, and the results were averaged;

the vanadium ion permeability of the branched-crosslinked sulfonated polyimide membranes of examples 1 to 7 is shown in table 1.

(2) Proton conductivity test:

the conductivity cell was partitioned into two compartments using a soaked septum, both compartments being filled with solution. Finally, the impedance of the conductivity cell with the membrane (R) was measured at a constant current of 5.0mA and a frequency of 1.0Hz to 100kHz using an electrochemical workstation model CHI660E, manufactured by Shanghai Chenghua instruments, Inc. (R)₁). The same conductivity cell, the same distance between two electrodes and the same volume of electrolyte in two compartments are used to measure the impedance (R) of the conductivity cell without membrane by the same test method₀). The proton conductivity of the membrane is calculated as follows:

where σ is the proton conductivity (S cm) of the membrane^-1)，R₀And R₁The impedance of the cell without and with membrane, respectively, and A is the effective area (cm) of the membrane²) And d is the thickness (cm) of the separator;

the proton conductivity of the branched-crosslinked sulfonated polyimide membranes of examples 1 to 7 is shown in Table 1.

(3) Proton selectivity:

the Proton Selectivity (PS) of the membrane is defined as the ratio of proton conductivity to vanadium ion permeability, and can be used to evaluate the overall performance of the membrane, and is calculated as follows:

proton selectivities of the branched-crosslinked sulfonated polyimide membranes of examples 1 to 7 are shown in table 1:

TABLE 1

As can be seen from Table 1 and FIG. 8, the branched-crosslinked sulfonated polyimide membranes of examples 1 to 5 have vanadium ion permeability (1.0 to 2.31X 10)^-7cm² min^-1) Are all lower than Nafion 212(7.48 multiplied by 10)^-7cm²min^-1) The prepared branched-crosslinked sulfonated polyimide film is proved to have excellent vanadium resistance. The reason is attributable to the strong Donna repelling effect of the BTA monomer on vanadium ions by the imidazole group. Secondly, the membrane is crosslinked, and the intermolecular interaction is enhanced, so that a more compact structure is formed, and the migration of vanadium is effectively resisted. To sum up, the following steps are carried out: the cross-linked membrane can effectively prevent the cross permeation of vanadium ions.

The σ of the branched-crosslinked sulfonated polyimide membranes and Nafion 212 membranes of examples 1 to 5 is shown in Table 1. The σ of sc-bSPI-14 membrane is very close to that of Nafion 212 membrane.

Finally, the branched-crosslinked sulfonated polyimide membranes should have a higher σ and lower P, and therefore a high PS can be achieved, thus promoting improved VRFB performance. The sc-bSPI-14 membrane had the highest PS (2.78X 10) of all membranes⁵S min cm^-3) And is a Nafion 212 membrane (0.43X 10)⁵S min cm^-3) About 6 times of the total weight of the product.

To further characterize the vanadium-rejection performance of sc-bSPI-14 and Nafion 212 membranes, the self-discharge behavior of VRFB using sc-bSPI-14 and Nafion 212 membranes was studied and the results are shown in FIG. 9. The OCV of sc-bfspi-14 and Nafion 212 membranes showed similar trend of change, the open circuit voltage slowly dropped before 1.3V and then rapidly dropped to 0.8V. The self-discharge life (defined as the time until the OCV remained above 0.8V) of the sc-bSPI-14 film was 46 h. The OCV of sc-bSPI-14 is approximately four times that of Nafion 212(11 h). The results show that: compared with Nafion 212, sc-bSPI-14 with a branched and cross-linked structure has stronger vanadium resistance.

Since the sc-bsspi-14 membrane of all membranes showed the highest proton selectivity, the sc-bsspi-14 membrane was selected for testing cell performance (the membranes prepared by the present invention were tested in an all vanadium redox flow battery and compared with the performance of the all vanadium redox flow battery using a commercial Nafion 212 membrane). The sc-bSPI-14 membrane prepared in the invention example 5 and a commercial Nafion 212 membrane are used for assembling an all-vanadium redox flow battery, and the battery performance of the membrane is verified. 1.7mol L of solution storage tanks are respectively arranged in the positive and negative electrode solution storage tanks^-1VO^3.5++4.7mol L^-150mL of sulfuric acid solution, and conveying the electrolyte into the battery through a magnetic pump. And a Xinwei battery detection system (CT-4008T-5V/12A-204n-F) is used for carrying out constant-current charging and discharging tests on the battery (the current density is 200-80 mA cm)^-2) The voltage range is 0.8-1.65V. Coulombic efficiency, energy efficiency and voltage efficiency can be calculated by using the formula as follows:

coulombic efficiency ═ discharge capacity/charge capacity × 100%

Energy efficiency ═ discharge energy/charge energy × 100%

Voltage efficiency ═ energy efficiency/coulombic efficiency × 100%

The results of coulombic efficiency CE, voltage efficiency VE and energy efficiency EE are shown in FIGS. 10 to 11. The CE of sc-bSPI-14 (99.2-97.1%) is higher than that of Nafion 212 (94.5-86.5%). Such results indicate that sc-bSPI-14 has lower vanadium ion permeability. When the current density is from 80mA cm^-2Rise to 200mA cm^-2At high current densities, both the CE of the sc-bSPI-14 and Nafion 212 films became higher. At 80 to 200mA cm^-2In the following, the VE of the Nafion 212 membrane was higher than that of the sc-bSPI-14 membrane because Nafion 212 has higher proton conductivity. This is because the Nafion 212 membrane contains a hydrophobic polytetrafluoroethylene backbone and hydrophilic perfluoroalkyl perfluorosulfonate side chains, which greatly improves its proton conductivity. Thus, sc-bSPI-14 membrane VE is lower than Nafion 212. As the current density increased, both the VE of the sc-bSPI-14 and Nafion 212 films decreased. However, the Nafion 212 membrane exhibited a faster VE drop rate than the sc-bSPI-14 membrane, indicating a better balance between σ and P for the sc-bSPI-14 membrane. Furthermore, EE is the most important indicator for measuring VRFB energy conversion and storage capacity. sc-bSPI-14 membranes at 200 to 80mA cm^-2Shows higher EE values (64.6-82.8%) than Nafion 212 membranes (60.5-78.5%), which is the same as the proton selectivity results. The results show that: the sc-bSPI-14 film has excellent VRFB application prospect.

To evaluate the stability of sc-bSPI-14 membranes in VRFB, sc-bSPI-14 membranes were tested at 140mA cm^-2Next, 1000 cycles of testing were performed as shown in fig. 13. sc-bSPI-14 shows good cell stability in 1000 cycles of VRFB tests (CE ≈ 98.4%, VE ≈ 76.8% and EE ≈ 75.6%), which proves its excellent cycling stability.

To investigate the chemical stability of the membranes, sc-bSPI-14 films were immersed in 0.1mol L at 40 deg.C^-1VO₂ ⁺+3.0mol L^-1H₂SO₄VO was recorded every 3 days in solution for 15 days with a spectrophotometer²⁺The concentration of (c). Over the course of a 15-day soak, the sc-bSPI-14 film produced 0.41mol L due to the strong acid and strong oxidizing environment^-1g^-1VO (a) of²⁺And with the prior art (Long J, Xu WJ, Xu SB, Liu J, Wang YL, Luo H, et al. AComparison of dbSPI50 membranes in novel double branched sulfonated polyimide membranes with ultra-high proton selectivity for a variable redox flow battery, J Membr Sci 628(2021)119259, resulted in 0.44mol L of dbSPI50 membrane^-1g^-1VO (a) of²⁺(ii) a Whereas the sc-bSPI-14 membrane produced a lower VO²⁺Concentration of (0.41mol L)^-1g^-1) The sc-bSPI-14 film is proved to have more excellent chemical stability.

In the above examples, the starting materials were all commercially available products, except that 4,4',4 ", 4'" (5,5 '-benzimidazole-2, 2') -tetraaniline and 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene were synthesized autonomously in the laboratory.

Wherein, the fluorine-containing Y-type branched triamine monomer: the synthesis procedure of TFAPOB is as follows:

(1) under a nitrogen blanket, 4.2g of phloroglucinol, 20.73g of potassium carbonate, 22.55g of 2-chloro-5-nitrobenzotrifluoride, 200mL of DMAc and 20mL of toluene were added in this order to a 500mL three-necked flask. The reaction system is stirred for 0.5h at normal temperature to fully dissolve solid substances, and then the temperature is increased to 80 ℃ for reaction for 12 h. And after the reaction is finished, pouring the liquid into deionized water, precipitating, washing the precipitate by using the deionized water, and placing the precipitate at 80 ℃ for vacuum drying for 24 hours to obtain 1,3, 5-tris (2-trifluoromethyl-4-nitrophenoxy) benzene solid powder.

(2) 16.35g of 1,3, 5-tris (2-trifluoromethyl-4-nitrophenoxy) benzene, 3.77g of activated carbon, 0.37g of FeCl₃·6H₂O and 150mL of absolute ethanol were sequentially added to a 500mL three-necked flask. Firstly, heating a reaction system to 80 ℃, stirring and reacting for 0.5h to activate the activated carbon, and then cooling the reaction system to 70 ℃. Subsequently, 50mL of hydrazine hydrate was slowly added dropwise to the reaction system using a constant pressure dropping funnel, and the reaction was continued for 12 hours. After the reaction is finished, repeatedly filtering while the solution is hot to completely remove the active carbon, pouring the obtained filtrate into deionized water, and standing for two days to generate a precipitate. Finally, the precipitate is collected by filtration, washed by deionized water and dried in vacuum at 60 ℃ for 24h to obtain white fluorine-containing Y-type branched triamine monomer: TFAPOB.

The synthesis steps of 4,4',4 ", 4'" (5,5 '-benzimidazole-2, 2') -tetraaniline are as follows:

14.02g P₂O₅And 50g of polyphosphoric acid are poured into a mechanically stirred three-necked bottle, the temperature is increased to 180 ℃, and P is completely dissolved₂O₅. Then cooling the three-necked bottle to 80 ℃, adding 8.57g of 3,3 '-diaminobenzidine into the three-necked bottle, heating to 120 ℃ until the 3,3' -diaminobenzidine is completely dissolved, then cooling to 80 ℃, finally adding 12.17g of 3, 5-diaminobenzoic acid into the three-necked bottle, respectively stirring for 2,4 and 24 hours at 120,150 and 180 ℃, cooling to 80 ℃ after the reaction is finished, finally pouring the mixture into deionized water, and adjusting the pH value to 8.0 to remove polyphosphoric acid; filtering the solid, washing the solid for multiple times by deionized water, and drying the solid in vacuum at 40 ℃ to obtain the X-type tetramine monomer containing the imidazole group: a BTA.

In the above examples, the amount of the substance may be converted to mass; the mass unit may be grams or kilograms.

The present invention and those not specifically described in the above embodiments are the prior art.

In the above embodiments, the process parameters (temperature, time, concentration, etc.) and the amounts of the components in each step are all applicable.

While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable in various fields of endeavor to which the invention pertains, and further modifications may readily be made by those skilled in the art, it being understood that the invention is not limited to the details shown and described herein without departing from the general concept defined by the appended claims and their equivalents.

Claims

1. A preparation method of a branched-crosslinked sulfonated polyimide membrane is characterized by comprising the following steps:

step one, under the protection of nitrogen, adding 1,4,5, 8-naphthalene tetracarboxylic anhydride, benzoic acid and m-cresol I into a reactor, and stirring and dissolving at room temperature; adding 2,2' -disulfonic acid benzidine, triethylamine and m-cresol II into a container, stirring at 50-70 ℃ until the mixture is dissolved, sequentially adding 4,4' (5,5' -benzimidazole-2, 2') -tetraaniline, 4' -diaminodiphenyl ether and 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene into the container, stirring at 50-70 ℃ until the mixture is dissolved, then placing the materials in the container into a constant-pressure dropping funnel, dropwise adding the materials into a reactor, and stirring and reacting at 30-100 ℃ for 4-8 hours after the dropwise adding is completed to obtain a casting solution; pouring the casting solution on a dry and clean glass plate for casting to form a film, then drying the glass plate for 10-24 hours at the temperature of 60-80 ℃, and then drying the glass plate for 0.5-3 hours at different temperatures of 80-150 ℃ respectively to obtain a triethylamine type branched-crosslinked sulfonated polyimide film;

step two, soaking the triethylamine type branched-crosslinked sulfonated polyimide membrane in absolute ethyl alcohol for 18-48 h, and then placing the membrane in 1.0-3.0 mol of L-¹Soaking the membrane in the sulfuric acid aqueous solution for 24-48 h, then washing the membrane for 5-10 times by using deionized water to obtain the branched-crosslinked sulfonated polyimide membrane, and soaking the membrane in the deionized water for storage.

2. The method of preparing a branched-crosslinked sulfonated polyimide membrane according to claim 1, wherein the molar ratio of 4,4',4 ", 4'" (5,5 '-benzimidazole-2, 2') -tetraaniline, 4 '-oxydianiline, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene, 2' -disulfonic acid benzidine and benzoic acid is: 0.06-0.14: 0.07-0.23: 1:0.1:0.5: 2.

3. The method of preparing a branched-crosslinked sulfonated polyimide film according to claim 1, wherein the volume ratio of m-cresol i to m-cresol ii is 1: 1; the volume ratio of the total volume of the m-cresol I and the m-cresol II to the triethylamine is as follows: 20-70: 0.5-9.5; the dosage proportion of the triethylamine to the 2,2' -disulfonic acid benzidine is as follows: and adding 0.5-9.5 mL of triethylamine for each 0.4-3.2 mmol of 2,2' -disulfonic acid benzidine.

4. The method of preparing a branched-crosslinked sulfonated polyimide membrane according to claim 1, wherein both of m-cresol i and m-cresol ii can be replaced with one or a mixture of two or more of N, N-dimethylformamide, N-dimethylacetamide, dimethylsulfoxide, and N-methylpyrrolidone.

5. The method of preparing a branched-crosslinked sulfonated polyimide membrane according to claim 1, wherein the thickness range of the cast membrane is controlled to be: 25 to 120 μm.

6. The method for preparing a branched-crosslinked sulfonated polyimide membrane according to claim 1, wherein the absolute ethanol may be replaced with one or a mixture of two or more of methanol, acetone, and isopropyl alcohol; the deionized water can be replaced by distilled water or ultrapure water.

7. The method for preparing the branched-crosslinked sulfonated polyimide membrane according to claim 1, wherein in the first step, after the dropwise addition is completed, the reaction is carried out for 1 to 2 hours under stirring at 30 to 100 ℃ to obtain a membrane casting solution, the membrane casting solution is placed in a microwave and ultrasonic integrated reactor, the microwave and the ultrasonic are started simultaneously for carrying out the synergistic treatment for 30 to 45 minutes, and the microwave power is 150 to 350W; the ultrasonic power is 300-800W, the ultrasonic frequency is 45-65 KHz, and the reaction temperature is 30-100 ℃.

8. The method for preparing the branched-crosslinked sulfonated polyimide membrane according to claim 7, wherein in the first step, the casting solution after the synergistic treatment is poured on a dry and clean glass plate for casting to form a membrane, and then electron beam irradiation is performed, wherein the irradiation dose is 4-10 Gy; then, drying the glass plate in an infrared drying oven for 6-8 hours at the power of 800-1000W and the temperature of 50-60 ℃; and then drying the membrane for 0.5 to 3 hours at different temperatures of between 80 and 150 ℃ to obtain the triethylamine type branched-crosslinked sulfonated polyimide membrane.