Preparation method of in-situ growth ZIF-71 polypropylene composite membrane and application of in-situ growth ZIF-71 polypropylene composite membrane in non-aqueous flow battery

Abstract

The invention relates to a composite membrane of a zeolite imidazate framework (ZIF-71) and a polypropylene (PP) membrane in a metal organic framework, a preparation method of the composite membrane and application of the composite membrane in a non-aqueous flow battery, belongs to the technical field of flow batteries, and provides a ZIF-71 / PP composite membrane which is prepared through different in-situ growth methods and has different surface appearances. The in-situ grown 2-nitroimidazole zinc zeolite imidazate framework layer with different morphologies can effectively prevent active substances from crossing and crossing in the non-aqueous flow battery. In addition, the excellent performance of the non-aqueous flow battery verifies that the composite diaphragm of the metal organic framework and the polypropylene can still keep the structural integrity during long-term operation in an organic medium.

Description

Technical Field

[0001] This invention relates to two zeolite imidazole ester framework (ZIF-71) polypropylene composite membranes with different morphologies grown in situ, their preparation methods, and their applications in non-aqueous flow batteries, belonging to the field of flow battery technology. Background Technology

[0002] The large-scale utilization of intermittent energy sources such as solar and wind power urgently requires supporting high-capacity energy storage technologies to achieve supply and demand balance. Flow batteries, especially vanadium redox flow batteries (VFBs), are highly promising grid-scale energy storage technologies. However, the development of vanadium redox flow batteries is limited by high material costs and relatively low energy density (typically 25-30 Wh·L−1). In contrast, non-aqueous flow batteries (NAFBs) have a wider electrochemical stability window (up to 4V, far exceeding the 1.5V of aqueous systems) and a richer selection of materials, giving them significant advantages in the field of high-energy-density energy storage.

[0003] As a core component of flow batteries, the separator has become a research hotspot due to its dual function of inhibiting cross-permeation of active materials and promoting rapid charge carrier transport. However, the development of non-aqueous flow battery separators faces numerous challenges. These separators must simultaneously meet stringent requirements such as excellent resistance to organic solvents, high ionic conductivity in the organic solvent phase, and low permeability of active materials. Furthermore, the inherent defects of non-aqueous electrolytes, such as high viscosity and poor ionic conductivity, further exacerbate the difficulty of achieving these requirements. Currently, commercially available polyolefin separators such as Celgard and Fumasep are widely used in non-aqueous systems, but these separators generally suffer from insufficient ion selectivity or easy swelling in organic solvents. Therefore, the preparation of separators with both excellent resistance to organic solvents and low permeability of active materials is crucial for advancing the technology of non-aqueous flow batteries. Summary of the Invention

[0004] Non-aqueous flow batteries (NAFBs) require separators with excellent resistance to organic solvents and high permeability of active materials in the organic solvent phase to withstand the inherent corrosive effects of non-aqueous electrolytes. Addressing the technical problem of low selectivity caused by severe cross-contamination of active materials in NAFB separators, this invention designs a ZIF-71 / PP composite membrane with an in-situ grown ZIF-71 selective layer, exhibiting excellent resistance to organic solvents and low permeability of active materials. The dense selective layer of ZIF-71 effectively achieves efficient sieving of active materials, and the organic solvent-loving ZIF-71 layer formed on the PP surface provides excellent electrolyte wettability, significantly improving battery life.

[0005] An in-situ grown ZIF-71 / polypropylene composite membrane, the composite membrane comprising a porous polypropylene base membrane and a ZIF-71 selective layer grown in situ at the interface of the porous polypropylene base membrane; the ZIF-71 selective layer is composed of dense ZIF-71 and the thickness of the ZIF-71 selective layer is 1-2 μm.

[0006] The microstructure of the ZIF-71 selective layer is blocky or spherical.

[0007] The electrolyte contact angle of the composite membrane is 20-40°, preferably 20-30°; the swelling rate of the composite membrane in organic solvent is 3-10%, preferably 3-6%.

[0008] The composite membrane has a permeability of less than 7.78 × 10⁻⁶ for 10-methylphenthiazide. -10 cm 2·s-1 And / or the permeability to 2,1,3-benzothiadiazole is less than 1.61 × 10⁻⁶. -9 cm 2·s-1 .

[0009] The preparation method of the in-situ grown ZIF-71 / polypropylene composite membrane includes the following steps: Step 1: Prepare zinc source solution and ligand solution respectively; Step 2: Immerse the polypropylene porous base membrane in the solvent for pretreatment; Step 3: Place the pretreated polypropylene porous base membrane in a diffusion device, add the zinc source solution and the ligand solution to the two spaces separated by the diffusion device respectively, and carry out a diffusion reaction under controlled temperature and humidity conditions to grow a ZIF-71 selective layer in situ on the surface of the polypropylene porous base membrane; Step 4: After the reaction is completed, remove the membrane and dry it to obtain the in-situ grown ZIF-71 / polypropylene composite membrane.

[0010] In step one: the zinc source solution is a methanol solution of anhydrous zinc acetate; the ligand solution is a methanol solution of 4,5-dichloroimidazole; in step two: the solvent is anhydrous methanol.

[0011] In step one: the concentration of the methanol solution of anhydrous zinc acetate is 0.9-1.8 mg / mL, or 0.005-0.01 mol / L; the concentration of the methanol solution of 4,5-dichloroimidazole is 1.4-6.8 mg / mL, or 0.01-0.05 mol / L; the molar ratio of anhydrous zinc acetate to 4,5-dichloroimidazole is 1:(2-5), preferably 1:(3.5-4.5).

[0012] In step three: the diffusion device is an H-type diffusion tank; the ambient temperature of the diffusion reaction is 20-40℃, preferably 25-30℃; the ambient humidity of the diffusion reaction is 30-70%RH, preferably 35-50%RH; and the diffusion reaction time is 12-48h.

[0013] Step three also includes stirring the solution at a rotation speed of 100-300 r / min; the drying temperature in step four is 60-80℃, preferably 60-65℃.

[0014] Application of the in-situ grown ZIF-71 / polypropylene composite membrane in non-aqueous flow batteries.

[0015] The beneficial effects of this invention are: A dense ZIF-71 / PP composite membrane with both blocky and flower-like structures was successfully constructed using an in-situ growth strategy. A highly efficient selective layer was constructed through precise control of the membrane's pore structure and surface properties. The resulting membrane exhibits extremely low active material permeability, as low as 7.78 × 10⁻⁶. −10 cm 2 ·s −1 It exhibits excellent electrolyte wettability. In DMF-based non-aqueous flow battery systems, the performance of this separator far surpasses that of the commercially available Celgard 2500 separator, with an average energy efficiency improvement of approximately 27% and an average coulombic efficiency improvement of approximately 7%, while maintaining stable cycling performance for over 75 cycles. Attached Figure Description

[0016] Figure 1 SEM images of the original PP film and the in-situ grown ZIF-71 / PP composite film. (a) Surface morphology of the blocky ZIF-71 / PP composite film. (b) Surface morphology of the flower-shaped ZIF-71 / PP composite film. (c) Cross-sectional morphology of the blocky ZIF-71 / PP composite film. (d) Cross-sectional morphology of the flower-shaped ZIF-71 / PP composite film.

[0017] Figure 2 Digital photographs of in-situ grown ZIF-71 / PP composite films. (a) Block-shaped ZIF-71 / PP composite film. (b) Flower-shaped ZIF-71 / PP composite film.

[0018] Figure 3 Digital photographs of in-situ grown ZIF-71 / PP composite membranes after immersion in DMF for 5 days. (a) Block-shaped ZIF-71 / PP composite membrane. (b) Flower-shaped ZIF-71 / PP composite membrane.

[0019] Figure 4 Electrolyte contact angle diagrams for the original PP membrane and the in-situ grown block ZIF-71 / PP composite membrane and flower-shaped ZIF-71 / PP composite membrane.

[0020] Figure 5 The swelling ratios are those of in-situ grown block ZIF-71 / PP composite films and flower-shaped ZIF-71 / PP composite films.

[0021] Figure 6 Electrolyte absorption rates for in-situ grown block ZIF-71 / PP composite membranes and flower-shaped ZIF-71 / PP composite membranes.

[0022] Figure 7 The permeability of the original PP membrane, the in-situ grown block ZIF-71 / PP composite membrane, and the flower-shaped ZIF-71 / PP composite membrane in DMF electrolyte was measured.

[0023] Figure 8 The battery performance of the separator in a non-aqueous flow battery (NAFB). (a) In-situ grown bulk ZIF-71 / PP composite membrane and flower-shaped ZIF-71 / PP composite membrane at 5 mA cm⁻¹. −2 (a) Coulombic efficiency (CE), (b) voltage efficiency (VE), and (c) energy efficiency (EE) at current density.

[0024] Figure 9 The variable current performance of NAFB using a flower-shaped ZIF-71 / PP composite diaphragm. Detailed Implementation

[0025] This invention proposes ZIF-71 / PP composite membranes with different surface morphologies prepared by different in-situ growth methods. The in-situ grown 2-nitroimidazole zinc zeolite imidazole ester framework layers with different morphologies effectively block cross-contamination of active materials in non-aqueous flow batteries. Furthermore, the excellent performance of the non-aqueous flow battery verifies that the composite membrane of metal-organic framework and polypropylene can maintain structural integrity even during long-term operation in organic environments.

[0026] Some embodiments of this patent include the following technical solutions:

[0027] In-situ grown ZIF-71 / PP composite membranes with different morphologies were constructed using an in-situ growth method. A dense ZIF-71 selective layer was built on the PP interface via diffusion. The ZIF-71 / PP composite membrane is composed of three-dimensional ZIF-71 in-situ grown on the surface of a PP membrane, including: a base membrane made of polypropylene (PP) and a dense ZIF-71 selective layer prepared by in-situ growth. The ZIF-71 selective layer was prepared by interfacial diffusion, and its selective layer thickness was 1-2 μm, while the PP membrane thickness was 25 μm.

[0028] The two different morphologies of ZIF-71 are blocky and flower-shaped.

[0029] A method for preparing an in-situ grown ZIF-71 / PP composite membrane includes the following steps:

[0030] Step 1: Accurately weigh out a certain amount of anhydrous zinc acetate (Zn(CH3COOH)2) and 4,5-dichloroimidazole, and dissolve them separately in methanol. Stir thoroughly for 10-30 min until Zn(CH3COOH)2 and 4,5-dichloroimidazole are completely dissolved to form a homogeneous mixed solution. The molar ratio of anhydrous zinc acetate to 4,5-dichloroimidazole is 1:(2-5).

[0031] Step 2: Cut the PP film to a suitable size and soak it in a certain amount of anhydrous methanol for 1-2 hours to ensure that the PP film is fully wetted by methanol.

[0032] Step 3: The PP membrane obtained in Step 2 is sandwiched between the annular gasket of polytetrafluoroethylene rubber and assembled in the middle of the H-type counter-diffusion cell, and fixed with a clamp. 20-200 mL of each of the two raw material solutions prepared in Step 1 is added to both sides of the H-type counter-diffusion cell, and the cell is placed under conditions of 20-40℃ and 30-70%RH. After diffusion for a period of time, the membrane is removed and dried at 60-80℃ to obtain the in-situ grown ZIF-71 / PP composite membrane.

[0033] Preferably, in step one, the concentration of the methanol solution of anhydrous zinc acetate (Zn(CH3COOH)2) is 0.005~0.01 mol / L, the concentration of 4,5-dichloroimidazole is 0.01~0.05 mol / L, and the molar ratio of anhydrous zinc acetate to 4,5-dichloroimidazole is 1:(3.5~4.5).

[0034] Preferably, the environmental conditions in step three are 25~30℃ and 35-50%RH.

[0035] Preferably, in step three, the volume of the raw material solution is 50-70 mL; and the drying temperature is 60-65 °C.

[0036] The composite membrane has good electrolyte wettability, and its contact angle is 20~40°, preferably 20~30°.

[0037] The composite membrane has a low swelling rate of 3-10%, preferably 3-6%.

[0038] The permeability of the anion exchange membrane to 10-methylphenthiazide is less than 7.78 × 10⁻⁶. −10 cm 2 ·s −1 And / or the permeability to 2,1,3-benzothiadiazole is less than 1.61 × 10⁻⁶. −9 cm 2·s −1 .

[0039] The application of any of the methods described herein in non-aqueous flow batteries is intended to improve the coulombic efficiency and energy efficiency of the battery.

[0040] Example 1: Block ZIF-71 / PP Composite Film

[0041] (1) A method for preparing an in-situ grown ZIF-71 / PP composite membrane, the specific steps of which are as follows: Weigh 0.0573g Zn(CH3COOH)2 and dissolve it in 40mL methanol. Stir thoroughly for 10min until Zn(CH3COOH)2 is completely dissolved, forming a clear solution. Weigh 0.1712g 4,5-dichloroimidazole and dissolve it in 40mL methanol. Stir thoroughly for 10min until 4,5-dichloroimidazole is completely dissolved, forming a clear solution.

[0042] (2) Cut the PP film into squares with a side length of 5cm and soak them in methanol for 2 hours.

[0043] (3) The PP membrane was placed in the middle of the H-type diffusion cell, and Zn(CH3COOH)2 solution and 4,5-dichloroimidazole solution were added to both sides of the H-type diffusion cell respectively. The diffusion time was 24 h. After the diffusion was completed, the membrane was taken out and dried at 60 °C to obtain the in-situ grown ZIF-71 / PP composite membrane.

[0044] Example 2: Flower-shaped ZIF-71 / PP composite film

[0045] (1) A method for preparing an in-situ grown ZIF-71 / PP composite membrane, the specific steps of which are as follows: Weigh 0.0573g Zn(CH3COOH)2 and dissolve it in 40mL methanol. Stir thoroughly for 10min until Zn(CH3COOH)2 is completely dissolved, forming a clear solution. Weigh 0.1712g 4,5-dichloroimidazole and dissolve it in 40mL methanol. Stir thoroughly for 10min until 4,5-dichloroimidazole is completely dissolved, forming a clear solution.

[0046] (2) Cut the PP film into squares with a side length of 5cm and soak them in methanol for 2 hours.

[0047] (3) The PP membrane was placed in the middle of the H-type diffusion cell. Zn(CH3COOH)2 solution and 4,5-dichloroimidazole solution were added to both sides of the H-type diffusion cell, and a polytetrafluoroethylene rotor was added. The stirring speed was set to 200 r / min and the diffusion time was 24 h. After the diffusion was completed, the membrane was removed and dried at 60 °C to obtain the in-situ grown ZIF-71 / PP composite membrane.

[0048] The main testing methods are as follows:

[0049] The electrolyte absorbance and swelling degree of the membrane were tested according to standard methods. The membrane was immersed in 1 MTEABF4 / DMF solution at room temperature for 24 hours. After immersion, excess solution on the surface of the wet membrane was gently blotted with lint-free paper, and its wet doping weight was recorded immediately. Subsequently, the diaphragm was vacuum dried at 120°C for 24 hours, and its dry weight was measured. Then, the dried membrane was thoroughly cleaned repeatedly with DMF to remove residual TEABF4, followed by vacuum drying at 120°C for 24 hours to obtain the dedoped dry weight. DMF , and polymers ( The mass fraction is calculated using the following formula:

[0050]

[0051]

[0052]

[0053] For swelling degree measurement, the diaphragm was cut into 2×2cm square samples. First, its dry length was measured and recorded. The dry film was then immersed in pure DMF at room temperature until swelling equilibrium was reached. After immersion, excess solution was gently blotted from the surface of the wet film with lint-free paper, and its wet length was immediately measured. The degree of swelling of the diaphragm is calculated using the appropriate formula. Degree of swelling

[0054]

[0055] in and These are the lengths of the wet film and the dry film, respectively.

[0056] Permeability of active substances

[0057] The permeability of the active material through the membrane was determined using a diffusion cell apparatus. The diffusion cell consisted of two chambers: the left chamber contained 50 mL of 0.1 M active material + 1.0 MTEABF4 solution (50 mL), while the right chamber contained 50 mL of blank 1.0 MTEABF4 / DMF solution. To minimize the effects of concentration polarization, magnetic stir bar was placed in both chambers for continuous stirring throughout the test. Every 5 hours, 4 mL of solution was sampled from the right chamber and immediately replenished with an equal volume of fresh 1.0 MTEABF4 / DMF solution to maintain a constant volume. The concentration of the permeated active material in the sampled solution was quantitatively analyzed using a UV-Vis spectrophotometer. The permeability of the active material was calculated using the following formula:

[0058]

[0059] Among them, V R This indicates the constant volume of the solution in the right chamber (50 mL in this work); C R (t) represents the concentration (mol / L) of the active substance in the right chamber at time t; C L is the initial concentration (mol / L) of the active material in the left chamber, which is considered a constant during the test period for simplified calculation; A and L are the effective permeation area (cm²) and thickness (cm) of the membrane, respectively; P is the permeability coefficient (cm²) of the active material. 2 s −1 ).

[0060] Non-aqueous flow battery (NAFB) single cell performance

[0061] The separator was sandwiched between two carbon felt (SGL) electrodes and secured by two graphite plates. The entire electrode-separator assembly was then fixed between two polytetrafluoroethylene (PTFE) plates to ensure structural stability. Both positive and negative electrode electrolytes were 10 mL of a DMF-based mixed solution containing 1 MTEABF4, 0.1 MBTD, and 0.1 MMPT. The SGL graphite felt (area: 2 cm × 2 cm) served as the positive and negative electrodes, while the graphite plates acted as current collectors for both electrodes. During battery testing, the anolyte was purged with nitrogen to eliminate oxygen interference, and the flow rate of both electrolytes was set to 50 mL / min. −1 Coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) are calculated using the following formulas:

[0062]

[0063]

[0064]

[0065] The membrane characterization and test results are as follows:

[0066] Both the bulk ZIF-71 / PP composite film and the flower-shaped ZIF-71 / PP composite film prepared by in-situ growth method grew densely on the PP surface without obvious defects. Figure 1 , Figure 2 ).

[0067] The resulting ZIF-71 / PP composite films all exhibited excellent organic solvent stability. Figure 3 The in-situ grown ZIF-71 selective layer not only gives the composite membrane excellent electrolyte absorption rate (…). Figure 4 ), wettability ( Figure 5Low swelling ratio ( Figure 6 ) and extremely low active substance penetration ( Figure 7 ).

[0068] This membrane exhibits excellent barrier properties, with permeability to the positive electrolyte 2,1,3-benzothiadiazole and the negative electrolyte 10-methylphenthiazide as low as 1.61 × 10⁻⁶. −9 cm 2 ·s −1 With 7.78×10 −10 cm 2 ·s −1 Furthermore, this membrane exhibits excellent stability in strongly polar organic solvents, maintaining a stability of 5 mA·cm⁻¹ in non-aqueous flow battery systems. −2 After 75 cycles at a given current density, the block ZIF-71 / PP composite membrane exhibited an average coulombic efficiency (CE) of 91.3% and an average energy efficiency (EE) exceeding 54.1%, while the flower-shaped ZIF-71 / PP composite membrane achieved an average CE of 94.9% and an average EE exceeding 59.4%. Both significantly outperformed the commercially available Celgard membrane (which, after only 70 cycles, had an average coulombic efficiency of 88.7% and an average energy efficiency of 48.8%). This provides an innovative strategy for the design of next-generation non-aqueous flow battery membranes, and the prepared membrane combines excellent resistance to organic solvents with high sieving capacity.

Claims

1. An in-situ grown ZIF-71 / polypropylene composite membrane, characterized in that, The composite membrane comprises a polypropylene porous base membrane and a ZIF-71 selective layer grown in situ at the interface of the polypropylene porous base membrane; the ZIF-71 selective layer is composed of dense ZIF-71 and the thickness of the ZIF-71 selective layer is 1-2 μm.

2. The in-situ grown ZIF-71 / polypropylene composite membrane according to claim 1, characterized in that, The microstructure of the ZIF-71 selective layer is blocky or spherical.

3. The in-situ grown ZIF-71 / polypropylene composite membrane according to claim 1, characterized in that, The electrolyte contact angle of the composite membrane is 20-40°, preferably 20-30°; the swelling rate of the composite membrane in organic solvent is 3-10%, preferably 3-6%.

4. The in-situ grown ZIF-71 / polypropylene composite membrane according to claim 1, characterized in that, The composite membrane has a permeability of less than 7.78 × 10⁻⁶ for 10-methylphenthiazide. -10 cm 2·s-1 And / or the permeability to 2,1,3-benzothiadiazole is less than 1.61 × 10⁻⁶. -9 cm 2·s-1 .

5. A method for preparing an in-situ grown ZIF-71 / polypropylene composite membrane as described in any one of claims 1-4, characterized in that, The process includes the following steps: Step 1: Prepare zinc source solution and ligand solution separately; Step 2: Pre-treat the polypropylene porous membrane by immersing it in the solvent; Step 3: Place the pre-treated polypropylene porous membrane in a diffusion device, add the zinc source solution and the ligand solution to the two spaces separated by the diffusion device, and carry out the diffusion reaction under controlled temperature and humidity conditions to grow a ZIF-71 selective layer in situ on the surface of the polypropylene porous membrane; Step 4: After the reaction is completed, remove the membrane and dry it to obtain the in-situ grown ZIF-71 / polypropylene composite membrane.

6. The preparation method according to claim 5, characterized in that, In step one: the zinc source solution is a methanol solution of anhydrous zinc acetate; The ligand solution is a methanol solution of 4,5-dichloroimidazole; in step two, the solvent is anhydrous methanol.

7. The preparation method according to claim 6, characterized in that, In step one: the concentration of the methanol solution of anhydrous zinc acetate is 0.9-1.8 mg / mL, or 0.005-0.01 mol / L; the concentration of the methanol solution of 4,5-dichloroimidazole is 1.4-6.8 mg / mL, or 0.01-0.05 mol / L; the molar ratio of anhydrous zinc acetate to 4,5-dichloroimidazole is 1:(2-5), preferably 1:(3.5-4.5).

8. The preparation method according to claim 5, characterized in that, In step three: the diffusion device is an H-type diffusion tank; the ambient temperature of the diffusion reaction is 20-40℃, preferably 25-30℃; the ambient humidity of the diffusion reaction is 30-70%RH, preferably 35-50%RH; and the diffusion reaction time is 12-48h.

9. The preparation method according to claim 5, characterized in that, Step three also includes stirring the solution at a rotation speed of 100-300 r / min; the drying temperature in step four is 60-80℃, preferably 60-65℃.

10. The application of an in-situ grown ZIF-71 / polypropylene composite membrane as described in any one of claims 1-4 in a non-aqueous flow battery.

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