Preparation and application of high-selectivity composite ion conduction membrane

Abstract

The invention discloses preparation and application of a high-selectivity composite ion conduction membrane, and a preparation method comprises the following steps: dissolving PVDF powder in an organic solvent, adding a pore-forming agent, carrying out film casting, immersing into water for conversion, taking out the membrane, and drying to obtain a porous substrate; mixing an HPA solution with the MXene dispersion liquid, then adjusting the pH value to be acidic, and heating and stirring for reaction to obtain an MXene-HPA compound; dispersing sulfonated polyetheretherketone and the MXene-HPA compound in an organic solvent to obtain a third mixed solution, coating the surface of a porous substrate with the third mixed solution, and drying to obtain an intermediate; and immersing the intermediate in a PEI cross-linking solution for reaction to obtain the composite ion conduction membrane. The composite ion conduction membrane prepared on the basis of SPEEK has relatively low vanadium permeability, and meanwhile, the problem of relatively low proton conduction capability of an SPEEK membrane is solved. The all-vanadium redox flow battery assembled based on the composite ion conduction membrane has excellent cycle capacity retention rate.

Description

Technical Field

[0001] The invention relates to the preparation and application of an ion conduction membrane, and in particular to the preparation of a highly selective composite ion conduction membrane and the application of the membrane in an all-vanadium liquid flow battery. Background Art

[0002] Sulfonated polyether ether ketone (SPEEK) is a commonly used ion exchange membrane material, which has attracted attention in the field of fuel cells due to its good chemical stability and thermal stability. However, when SPEEK membrane is used as an ion exchange membrane in all-vanadium liquid flow batteries, vanadium ions easily pass through the SPEEK membrane and migrate from one electrolyte chamber to another, resulting in a high vanadium permeability problem. High vanadium permeability will directly lead to many problems such as capacity decay of liquid flow batteries, increased self-discharge rate, and significantly reduced coulombic efficiency and energy efficiency. In addition, although the SPEEK membrane has a certain proton conduction capacity, its ion conductivity is still lower than that of other special ion exchange membranes (such as Nafion membrane). SPEEK membrane also has many problems such as insufficient mechanical strength and poor selectivity. These problems seriously hinder the large-scale application of SPEEK membrane in the field of all-vanadium liquid flow batteries. How to prepare a highly selective composite ion conduction membrane suitable for all-vanadium liquid flow batteries based on SPEEK has become a technical problem that needs to be solved urgently. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a method for preparing a highly selective composite ion conducting membrane, so as to solve the problem of how to prepare a highly selective composite ion conducting membrane with low vanadium permeability. Another purpose of the present invention is to propose the application of a highly selective composite ion conducting membrane in the preparation of an all-vanadium redox flow battery, so as to solve the problem of how to prepare an all-vanadium redox flow battery.

[0004] Technical solution: A method for preparing a highly selective composite ion conducting membrane according to the present invention comprises the following steps:

[0005] (1) dissolving PVDF powder in an organic solvent, adding a pore-forming agent and mixing to obtain a first mixed solution, casting the first mixed solution into a film, and then immersing the film in water for conversion, taking out the film after conversion and drying it to obtain a porous substrate;

[0006] (2) dissolving phosphotungstic acid in an ethanol aqueous solution to obtain an HPA solution, dispersing MXene in an ethanol aqueous solution to obtain a MXene dispersion, mixing the HPA solution and the MXene dispersion to obtain a second mixed solution, adjusting the pH of the second mixed solution to acidic, heating and stirring the reaction, centrifuging to obtain a precipitate, and drying the precipitate to obtain a MXene-HPA composite;

[0007] (3) dispersing the sulfonated polyetheretherketone and the MXene-HPA composite in an organic solvent to obtain a third mixed solution, coating the third mixed solution on the surface of the porous substrate, and drying to obtain an intermediate;

[0008] (4) Immersing the intermediate in a PEI cross-linking solution for reaction, taking out the intermediate after the reaction and subjecting the intermediate to vacuum heat treatment to obtain a composite ion conductive membrane.

[0009] The present invention anchors HPA on the surface of MXene through electrostatic adsorption and hydrogen bonding. MXene has a two-dimensional layered structure with a certain distance between its layers. When MXene and HPA (heteropoly acid) form a complex, HPA can be embedded in the interlayer of MXene to further adjust the interlayer distance. This interlayer structure physically hinders the penetration of vanadium ions, and vanadium ions need to diffuse through narrow channels between layers, increasing the difficulty of their penetration. At the same time, the layered structure of the MXene-HPA complex can provide a larger specific surface area, making the adsorption and diffusion process of vanadium ions between layers more complicated, extending the penetration path of vanadium ions, thereby reducing the penetration amount of vanadium ions.

[0010] Preferably, in step (1), the organic solvent includes at least one of N-methyl-2-pyrrolidone, dimethylacetamide, dimethyl sulfoxide, cyclopentane, and hexafluoroisopropanol, and the pore-forming agent is LiCl.

[0011] Preferably, in step (1), the mass ratio of PVDF powder, organic solvent and pore-forming agent is 10-15:85-90:3-7, and the thickness of the porous substrate is 10-50 mm.

[0012] Preferably, in step (2), the volume ratio of ethanol to water in the ethanol aqueous solution is 1-2:1-2, the concentration of phosphotungstic acid in the HPA solution is 0.05-0.15M, and the molar ratio of phosphotungstic acid to MXene is 1-4:1-4.

[0013] Preferably, in step (2), the pH value of the second mixed solution is adjusted to 2-4, the heating and stirring reaction conditions are heating to 50-70° C. and stirring the reaction for 6-24 hours, and the drying method is vacuum drying.

[0014] Preferably, in step (3), the organic solvent comprises at least one of dimethylacetamide, N-methyl-2-pyrrolidone and dimethyl sulfoxide.

[0015] Preferably, in step (3), the mass ratio of the sulfonated polyetheretherketone, the MXene-HPA composite and the organic solvent is 8-12:1-2:80-120, and the coating amount of the third mixed solution on the surface of the porous substrate is 10-50 g / m 2, the drying temperature is 50-70℃.

[0016] Preferably, in step (4), the PEI cross-linking solution is a polyethyleneimine aqueous solution with a concentration of 2-5 wt % and a pH of 8-10.

[0017] Preferably, in step (4), the reaction time is at least 20 minutes, and the vacuum heat treatment is performed at 60-100° C. under vacuum conditions for 1-3 hours.

[0018] Another aspect of the present invention discloses the use of the composite ion conductive membrane prepared by the above preparation method in the preparation of an all-vanadium liquid flow battery.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0020] The composite ion conducting membrane prepared based on SPEEK has a low vanadium permeability, which can be as low as 1.3×10 -6 cm 2 ·h -1 At the same time, it overcomes the problem of low proton conductivity of SPEEK membrane, and the proton conductivity can reach 63mS·cm -1 The composite ion-conducting membrane also has high strength and has good application prospects in the field of all-vanadium redox flow batteries. The all-vanadium redox flow battery assembled based on the composite ion-conducting membrane has excellent cycle capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a TEM image of the composite ion conductive membrane prepared in Example 1. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0023] Example 1: A method for preparing a highly selective composite ion conducting membrane is as follows:

[0024] (1) PVDF powder, N-methyl-2-pyrrolidone and LiCl were weighed in a mass ratio of 10:90:5, the PVDF powder was dissolved in N-methyl-2-pyrrolidone at 160° C., and LiCl was added and mixed to obtain a first mixed solution, the first mixed solution was cast into a film and then immersed in deionized water for conversion at room temperature for 10 hours, and the film was taken out after conversion and dried to obtain a porous substrate with a thickness of 50 mm; the porosity of the porous substrate was about 70% and the average pore size was 147 nm.

[0025] (2) Ethanol and water are mixed in a volume ratio of 1:1 to obtain an ethanol aqueous solution, phosphotungstic acid is dissolved in the ethanol aqueous solution to obtain an HPA solution with a phosphotungstic acid concentration of 0.1 M, titanium carbide MXene (CAS No.: 12363-89-2) is dispersed in the ethanol aqueous solution to obtain a MXene dispersion with a MXene concentration of 0.1 M, the HPA solution and the MXene dispersion are mixed in a volume ratio of 2:1 to obtain a second mixed solution, the pH of the second mixed solution is adjusted to 3, and then heated to 60°C and stirred for reaction for 12 hours, and then centrifuged to obtain a precipitate, and the precipitate is vacuum dried to obtain a MXene-HPA composite;

[0026] (3) Sulfonated polyetheretherketone with a sulfonation degree of 70% was dissolved in dimethylacetamide at a mass ratio of 1:9, and then the MXene-HPA complex was added at a mass ratio of 10:1 to the sulfonated polyetheretherketone and the MXene-HPA complex. After ultrasonic dispersion for 2 hours, the third mixed solution was obtained. The coating amount was 30 g / m 2 The third mixed solution is coated on the surface of the porous substrate by a doctor blade coating method, and dried at 60° C. to obtain an intermediate;

[0027] (4) The intermediate is immersed in a PEI crosslinking solution for reaction for 30 minutes, then the intermediate is taken out and heat treated at 80° C. under vacuum for 2 hours to obtain a composite ion conducting membrane. The PEI crosslinking solution is a polyethyleneimine aqueous solution with a concentration of 3 wt % and a pH of 9.

[0028] Example 2: A method for preparing a highly selective composite ion conducting membrane is as follows:

[0029] (1) PVDF powder, dimethylacetamide and LiCl were weighed in a mass ratio of 15:85:3, the PVDF powder was dissolved in dimethylacetamide at 140°C, and LiCl was added and mixed to obtain a first mixed solution, the first mixed solution was cast into a film and then immersed in deionized water for conversion at room temperature for 10 hours, and the film was taken out after conversion and dried to obtain a porous substrate with a thickness of 50 mm; the porosity of the porous substrate was about 68% and the average pore size was 153 nm.

[0030] (2) Ethanol and water are mixed in a volume ratio of 2:1 to obtain an ethanol aqueous solution, phosphotungstic acid is dissolved in the ethanol aqueous solution to obtain an HPA solution with a phosphotungstic acid concentration of 0.05 M, titanium carbide MXene (CAS No.: 12363-89-2) is dispersed in the ethanol aqueous solution to obtain a MXene dispersion with a MXene concentration of 0.1 M, the HPA solution and the MXene dispersion are mixed in a volume ratio of 2:1 to obtain a second mixed solution, the pH of the second mixed solution is adjusted to 2, and then heated to 50°C and stirred for reaction for 24 hours, and then centrifuged to obtain a precipitate, and the precipitate is vacuum dried to obtain a MXene-HPA composite;

[0031] (3) Sulfonated polyetheretherketone with a sulfonation degree of 80% was dissolved in dimethylacetamide at a mass ratio of 1:9, and then the MXene-HPA complex was added at a mass ratio of 8:1 to the sulfonated polyetheretherketone and the MXene-HPA complex. After ultrasonic dispersion for 2 hours, the third mixed solution was obtained. The coating amount was 10 g / m 2 The third mixed solution is coated on the surface of the porous substrate by a doctor blade coating method, and dried at 50° C. to obtain an intermediate;

[0032] (4) The intermediate is immersed in a PEI crosslinking solution for reaction for 20 minutes, then the intermediate is taken out and heat treated at 60° C. under vacuum conditions for 3 hours to obtain a composite ion conductive membrane. The PEI crosslinking solution is a polyethyleneimine aqueous solution with a concentration of 2 wt % and a pH of 8.

[0033] Example 3: A method for preparing a highly selective composite ion conducting membrane is as follows:

[0034] (1) PVDF powder, dimethyl sulfoxide and LiCl were weighed in a mass ratio of 12:88:7, the PVDF powder was dissolved in dimethyl sulfoxide at 100°C, and LiCl was added and mixed to obtain a first mixed solution, the first mixed solution was cast into a film and then immersed in deionized water for conversion at room temperature for 10 hours, and the film was taken out after conversion and dried to obtain a porous substrate with a thickness of 50 mm; the porosity of the porous substrate was about 73% and the average pore size was 166 nm.

[0035] (2) Ethanol and water are mixed in a volume ratio of 1:2 to obtain an ethanol aqueous solution, phosphotungstic acid is dissolved in the ethanol aqueous solution to obtain an HPA solution with a phosphotungstic acid concentration of 0.15 M, titanium carbide MXene (CAS No.: 12363-89-2) is dispersed in the ethanol aqueous solution to obtain a MXene dispersion with a MXene concentration of 0.075 M, the HPA solution and the MXene dispersion are mixed in a volume ratio of 2:1 to obtain a second mixed solution, the pH of the second mixed solution is adjusted to 4, and then heated to 70°C and stirred for reaction for 6 hours, and then centrifuged to obtain a precipitate, and the precipitate is vacuum dried to obtain a MXene-HPA composite;

[0036] (3) Sulfonated polyetheretherketone with a sulfonation degree of 60% was dissolved in N-methyl-2-pyrrolidone at a mass ratio of 1:9, and then the MXene-HPA complex was added at a mass ratio of 6:1 to the sulfonated polyetheretherketone and the MXene-HPA complex. After ultrasonic dispersion for 2 hours, the third mixed solution was obtained. The coating amount was 10 g / m 2 The third mixed solution is coated on the surface of the porous substrate by a doctor blade coating method, and dried at 70° C. to obtain an intermediate;

[0037] (4) The intermediate is immersed in a PEI crosslinking solution and reacted for 40 minutes, then the intermediate is taken out and heat treated at 100° C. under vacuum for 1 hour to obtain a composite ion conductive membrane. The PEI crosslinking solution is a polyethyleneimine aqueous solution with a concentration of 5 wt % and a pH of 10.

[0038] Example 4: A method for preparing a highly selective composite ion conducting membrane is as follows:

[0039] (1) PVDF powder, sulfolane and LiCl were weighed in a mass ratio of 14:86:5, the PVDF powder was dissolved in sulfolane at 130°C, and LiCl was added and mixed to obtain a first mixed solution, the first mixed solution was cast into a membrane and then immersed in deionized water for conversion at room temperature for 10 hours, and the membrane was taken out after conversion and dried to obtain a porous substrate with a thickness of 50 mm; the porosity of the porous substrate was about 64% and the average pore size was 123 nm.

[0040] (2) Ethanol and water are mixed in a volume ratio of 1:1 to obtain an ethanol aqueous solution, phosphotungstic acid is dissolved in the ethanol aqueous solution to obtain an HPA solution with a phosphotungstic acid concentration of 0.05 M, titanium carbide MXene (CAS No.: 12363-89-2) is dispersed in the ethanol aqueous solution to obtain a MXene dispersion with a MXene concentration of 0.4 M, the HPA solution and the MXene dispersion are mixed in a volume ratio of 2:1 to obtain a second mixed solution, the pH of the second mixed solution is adjusted to 3, and then heated to 60°C and stirred for reaction for 12 hours, and then centrifuged to obtain a precipitate, and the precipitate is vacuum dried to obtain a MXene-HPA composite;

[0041] (3) Sulfonated polyetheretherketone with a sulfonation degree of 70% was dissolved in dimethyl sulfoxide at a mass ratio of 1:9, and then the MXene-HPA complex was added at a mass ratio of 10:1 to the sulfonated polyetheretherketone and the MXene-HPA complex. After ultrasonic dispersion for 2 hours, the third mixed solution was obtained. The coating amount was 50 g / m 2 The third mixed solution is coated on the surface of the porous substrate by a doctor blade coating method, and dried at 60° C. to obtain an intermediate;

[0042] (4) The intermediate is immersed in a PEI crosslinking solution for reaction for 30 minutes, then the intermediate is taken out and heat treated at 90° C. under vacuum conditions for 2 hours to obtain a composite ion conductive membrane. The PEI crosslinking solution is a polyethyleneimine aqueous solution with a concentration of 3 wt % and a pH of 9.

[0043] Comparative Example 1: The rest is the same as Example 1, except that:

[0044] In step (3), no MXene-HPA composite is added, and the dimethylacetamide solution of sulfonated polyetheretherketone is directly coated on the surface of the porous substrate.

[0045] Comparative Example 2: The rest is the same as Example 1, except that:

[0046] In step (3), the MXene-HPA composite is replaced with titanium carbide MXene (CAS No.: 12363-89-2).

[0047] Comparative Example 3: The rest is the same as Example 1, except that:

[0048] In step (3), the MXene-HPA complex is replaced with phosphotungstic acid.

[0049] Comparative Example 4: The rest is the same as Example 1, except that:

[0050] The phosphotungstic acid in step (2) is replaced by phosphomolybdic acid.

[0051] Comparative Example 5: The rest is the same as Example 1, except that:

[0052] To prepare the MXene-HPA composite, phosphotungstic acid and MXene were directly added to the dimethylacetamide solution of sulfonated polyetheretherketone.

[0053] Comparative Example 6: The rest is the same as Example 1, except that:

[0054] In step (3), the porous substrate is replaced with a PVDF membrane of the same material and thickness.

[0055] The composite ion conducting membranes prepared in Examples 1-4 and Comparative Examples 1-6 were subjected to the following performance tests:

[0056] Diffusion cell method for testing vanadium permeability: using a diffusion cell device, the composite ion conduction membrane is placed between two compartments, one compartment is filled with a solution containing vanadium ions, and the other compartment is a blank solution or a specific receiving solution. Under certain temperature and stirring conditions, the vanadium ions are allowed to diffuse through the membrane. After a period of time, the concentration of vanadium ions in the receiving solution is determined by analytical methods such as atomic absorption spectroscopy (AAS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), thereby calculating the amount of vanadium ions that penetrate through the membrane per unit area per unit time, i.e., the vanadium permeability.

[0057] Proton conductivity test method: DC polarization method, a stable DC voltage is applied between two electrodes to make protons conduct in the membrane to form current. The steady-state current passing through the membrane is measured, and the proton conductivity is calculated according to Ohm's law based on the area and thickness of the membrane and the applied voltage. This method needs to be careful to avoid the influence of electrode reaction on the measurement results. It is usually necessary to select suitable electrode materials and electrolytes, and perform sufficient pretreatment.

[0058] Cyclic capacity retention rate test method simulates battery cycle test: the composite ion conductive membrane is applied to the all-vanadium liquid flow battery simulation system and assembled into a battery. The charge and discharge cycle is carried out at a certain current density, and the capacity during each charge and discharge process is recorded (calculated by measuring the charge and discharge time and current). After 100 cycles, the capacity retention rate of the battery is calculated. The formula is: Capacity retention rate = (Cn / C1) * 100%, where Cn is the capacity of the nth cycle and C1 is the capacity of the first cycle.

[0059] Tensile strength test method Universal material testing machine test: The composite ion conductive membrane is made into a standard size specimen, generally rectangular or dumbbell-shaped. The specimen is mounted on the fixture of the universal material testing machine, and a tensile force is applied to the specimen at a constant rate until the specimen breaks. The testing machine can automatically record the force-displacement curve during the stretching process, and the maximum tensile force F when the specimen breaks is obtained based on the curve. Then, based on the initial cross-sectional area S of the specimen, the formula tensile strength = F / S is used for calculation.

[0060] The results are as follows:

[0061] Table 1 Performance test results of different ion conduction membranes

[0062]

[0063]

[0064] The results in Table 1 show that neither phosphotungstic acid nor MXene alone, or a direct mixture of the two, can effectively inhibit the increase in vanadium permeability, and the proton conductivity is low. Only the MXene-HPA complex obtained by anchoring phosphotungstic acid on the MXene surface through electrostatic adsorption and hydrogen bonding can effectively reduce the vanadium permeability of the ion conduction membrane, while improving the proton conductivity of the sPEEK membrane, with excellent ion selectivity, and effectively improving the cycle capacity of the all-vanadium liquid flow battery. In addition, Comparative Example 6 shows that the inhibitory effect of the MXene-HPA complex on vanadium permeability also depends on the numerous pores on the porous base membrane.

Claims

1. A method for preparing a highly selective composite ion conducting membrane, characterized in that: The steps include: (1) dissolving PVDF powder in an organic solvent, adding a pore-forming agent and mixing to obtain a first mixed solution, casting the first mixed solution into a film, and then immersing the film in water for conversion, taking out the film after conversion and drying it to obtain a porous substrate; (2) dissolving phosphotungstic acid in an ethanol aqueous solution to obtain an HPA solution, dispersing MXene in an ethanol aqueous solution to obtain a MXene dispersion, mixing the HPA solution and the MXene dispersion to obtain a second mixed solution, adjusting the pH of the second mixed solution to acidic, heating and stirring the reaction, centrifuging to obtain a precipitate, and drying the precipitate to obtain a MXene-HPA composite; (3) dispersing the sulfonated polyetheretherketone and the MXene-HPA composite in an organic solvent to obtain a third mixed solution, coating the third mixed solution on the surface of the porous substrate, and drying to obtain an intermediate; (4) Immersing the intermediate in a PEI cross-linking solution for reaction, taking out the intermediate after the reaction and subjecting the intermediate to vacuum heat treatment to obtain a composite ion conductive membrane.

2. The method for preparing a highly selective composite ion conducting membrane according to claim 1, characterized in that: In step (1), the organic solvent includes at least one of N-methyl-2-pyrrolidone, dimethylacetamide, dimethyl sulfoxide, cyclopentane, and hexafluoroisopropanol, and the pore-forming agent is LiCl.

3. The method for preparing a highly selective composite ion conducting membrane according to claim 1, characterized in that: In step (1), the mass ratio of PVDF powder, organic solvent and pore-forming agent is 10-15:85-90:3-7, and the thickness of the porous substrate is 10-50 mm.

4. The method for preparing a highly selective composite ion conducting membrane according to claim 1, characterized in that: In step (2), the volume ratio of ethanol to water in the ethanol aqueous solution is 1-2:1-2, the concentration of phosphotungstic acid in the HPA solution is 0.05-0.15M, and the molar ratio of phosphotungstic acid to MXene is 1-4:1-4.

5. The method for preparing a highly selective composite ion conducting membrane according to claim 1, characterized in that: In step (2), the pH value of the second mixed solution is adjusted to 2-4, and the heating and stirring reaction conditions are heating to 50-70° C. and stirring the reaction for 6-24 hours. The drying method is vacuum drying.

6. The method for preparing a highly selective composite ion conducting membrane according to claim 1, characterized in that: In step (3), the organic solvent includes at least one of dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide.

7. The method for preparing a highly selective composite ion conducting membrane according to claim 1, characterized in that: In step (3), the mass ratio of the sulfonated polyetheretherketone, the MXene-HPA composite and the organic solvent is 8-12:1-2:80-120, and the coating amount of the third mixed solution on the surface of the porous substrate is 10-50 g / m 2 , the drying temperature is 50-70℃.

8. The method for preparing a highly selective composite ion conducting membrane according to claim 1, characterized in that: In step (4), the PEI cross-linking solution is a polyethyleneimine aqueous solution with a concentration of 2-5wt% and a pH of 8-10.

9. The method for preparing a highly selective composite ion conducting membrane according to claim 1, characterized in that: In step (4), the reaction time is at least 20 minutes, and the vacuum heat treatment condition is heat treatment at 60-100° C. under vacuum conditions for 1-3 hours.

10. Use of the composite ion conductive membrane prepared by the preparation method according to any one of claims 1 to 9 in the preparation of all-vanadium redox flow batteries.

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