Metal organic framework film as well as preparation method and application thereof

Abstract

The invention discloses a metal organic framework membrane and a preparation method thereof, and belongs to the technical field of membrane preparation. The metal organic framework film includes a metal organic framework material and a binder. The adhesive is composed of an adhesive A and an adhesive B; the adhesive A is selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene, polyvinyl alcohol, polyvinyl ether, polyethylene glycol, polyethylene glycol terephthalate, polyethylene oxide, polypropylene, polyacrylonitrile, polymethyl methacrylate, polyimide, polyamide, polyamide-imide and sodium carboxymethyl cellulose; and one or more of sodium alginate. And the adhesive B is selected from one or more of polytetrafluoroethylene, an ethylene-tetrafluoroethylene copolymer and a hexafluoropropylene-tetrafluoroethylene copolymer. The preparation method does not need a solvent and has the advantages of being low in cost, short in process, easy to operate and environmentally friendly, and the obtained metal organic framework film can be applied to different fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane preparation, and relates to a preparation method and application of a metal-organic framework membrane. Background Art

[0002] Due to the characteristics of large specific surface area, high porosity, regular and easily adjustable pore structure, and easy functionalization, metal-organic framework materials are widely used in the fields of energy storage, catalysis, separation, adsorption, etc. In the field of energy storage, metal-organic framework materials are usually prepared into composite diaphragms, or mixed with active electrode materials to prepare composite electrode materials, or prepared into composite solid electrolyte materials. Regarding the above applications, the currently published technical means include: 1) preparing a slurry containing metal-organic framework materials by a wet process, and then coating it on the surface of a base membrane; 2) preparing a composite / mixed matrix membrane by in-situ synthesis on the surface of the base membrane or by means of electrospinning. In the field of adsorption separation, metal-organic framework materials can be used to prepare mixed matrix membranes by introducing a polymer matrix, or directly prepared into self-supporting membranes by in-situ synthesis. The main problems faced by the above technical means are: 1) long preparation process and complex operation; 2) the use of organic solvents is involved in the wet pulping process, resulting in high costs, some of the organic solvents being toxic, and subsequent recovery further increasing the preparation cost and environmental pressure; 3) there are poor interfacial compatibility between metal-organic framework particles and the matrix and easy agglomeration of metal-organic framework particles in the mixed matrix membrane, resulting in a decline in mechanical properties and mass transfer performance; 4) the large-scale preparation and quality control of membranes involved in in-situ synthesis are too difficult, with high technical barriers and not being easily promoted industrially.

[0003] In summary, it is crucial to develop a green, safe, low-cost, and short-process membrane preparation technology to solve the above problems. Summary of the Invention

[0004] The present invention proposes a metal-organic framework membrane and a preparation method thereof, which is a solvent-free, low-cost, short-process, safe and efficient metal-organic framework membrane preparation technology. By mixing metal-organic framework materials and a specific binder, applying shear force to promote the fibrillation of the binder, the purpose of bonding and fixing metal-organic framework particles is achieved, and then a membrane is prepared through the action of mechanical force. The whole process is simple and efficient, and is suitable for industrial promotion.

[0005] To achieve the above object, the present invention adopts the following technical solutions.

[0006] The present invention discloses a metal-organic framework membrane, and the metal-organic framework membrane comprises metal-organic framework materials and a binder.

[0007] Further, the porosity of the metal-organic framework materials is greater than 40%, and the specific surface area is greater than 200m 2 / g, with a pore size less than 10 nm. The selection of pore characteristics such as the porosity and pore size of the metal-organic framework material provides channels for mass transfer in the application scenario of the finally formed product film. Preferably, the metal-organic framework material is selected from magnesium-based metal-organic framework materials, calcium-based metal-organic framework materials, zinc-based metal-organic framework materials, aluminum-based metal-organic framework materials, zirconium-based metal-organic framework materials, chromium-based metal-organic framework materials, iron-based metal-organic framework materials, copper-based metal-organic framework materials, lanthanum-based metal-organic framework materials, or cerium-based metal-organic framework materials. While ensuring the above pore structure characteristics of the material such as porosity and pore size, the cost of the material is also taken into account.

[0008] Furthermore, the binder is composed of binder A and binder B. Binder A is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene, polyvinyl alcohol, polyvinyl ethyl ether, polyethylene glycol, polyethylene terephthalate, polyethylene oxide, polypropylene, polyacrylonitrile, polymethyl methacrylate, polyimide, polyamide, polyamide-imide, sodium carboxymethyl cellulose, and sodium alginate; Binder B is selected from one or more of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, and hexafluoropropylene-tetrafluoroethylene copolymer.

[0009] Among the two binders, binder A plays a binding role and does not have a fibrillating effect. By adding binder A, the MOF powder can be better and more uniformly mixed, so that the MOF powder particles can be better and more uniformly adhered to the fibrillar network structure formed by binder B. Binder B is a binder that can be fibrillated. Through the fibrillation of binder B, a network structure is formed, and the metal-organic framework material is uniformly adhered to this network structure under the action of binder A, forming a metal-organic framework membrane with high porosity, good pore connectivity, and good air permeability. Binder A and binder B are both indispensable. If only binder B, that is, the fibrillatable binder, is used to form a 3D network structure to bond the whole MOF material together, there will be a situation where the local adhesion strength is insufficient and it will fall off; in addition, the fibrillatable binder B cannot be fully premixed with the metal-organic framework material, because excessive stirring and mixing will cause binder B to agglomerate and lose the ability to form a 3D network structure. Therefore, it is necessary to add binder A that does not have a fibrillating effect, which can be fully premixed with the metal-organic framework material and help it to be uniformly adhered to the fibrillar 3D network structure formed by binder B; in addition, binder A can increase the local adhesion ability and enable the fibrillatable binder B to form an overall adhesion ability.

[0010] Furthermore, the surface of the metal-organic framework membrane is smooth and flat, with uniform thickness, and the average thickness is 2 - 50 μm. Preferably, the thickness of the metal-organic framework membrane is 5 - 30 μm.

[0011] Furthermore, the microscopic morphology of the metal-organic framework membrane shows that: the binder B fibrillates to form a 3D dendritic network structure, and several dense solid particles are uniformly and densely adhered to the 3D dendritic network structure, and the solid particles therein are formed by uniformly mixing the metal-organic framework material and the binder A into one body.

[0012] Furthermore, the air permeability test of the metal-organic framework membrane shows that its Gurley value is between 85 - 155 s / 100 mL, which confirms that the metal-organic framework membrane of the present invention has good air permeability, high porosity and good pore connectivity, and is beneficial to applications in different scenarios.

[0013] Furthermore, the preparation method of the metal-organic framework membrane is as follows:

[0014] 1) Premix the metal-organic framework material and the binder A to make them fully contact and mix evenly to obtain a premix.

[0015] 2) Fully mix the premix obtained in step 1) and the binder B to form a mixture.

[0016] 3) Under the action of shear force, fibrillate the binder B in the above mixture so that the fibrillated binder B forms a 3D network structure, and the metal-organic framework material adheres to the 3D network structure.

[0017] 4) Press the mixture sheared in step 3) into a membrane.

[0018] Furthermore, the total mass of the binder is less than 20% of the total mass of the mixture; the binder A:binder B = 0 - 1:1 (excluding 0) (mass ratio); the mixing method is not limited, and ball milling mixing, mechanical shear mixing, ribbon mixing, and double cone mixing are preferred. The mixing time varies according to the composition of the mixture and only needs to achieve sufficient mixing. Preferably, the mixing time is 0.1 - 2 h.

[0019] Furthermore, the method for realizing fibrillation is not limited. Under shear force, as long as the binder B fibrillates to a microscopic morphology showing a fiber distribution forming a 3D network structure, the object of the present invention can be achieved. Preferably, the method for realizing fibrillation adopts an air flow shear method such as Example 9 in the present invention, or a mechanical extrusion shear method such as high-speed mechanical mixing in Example 1.

[0020] Furthermore, the method for pressing into a membrane is not limited, and common methods in the film-making field can be selected. Preferably, the method for pressing into a membrane can adopt cold pressing, hot pressing, or roll pressing. Among them, when adopting the hot pressing method, preferably, the temperature range is 20 - 120 °C.

[0021] Furthermore, the metal-organic framework membrane can be applied as a battery separator, an electrode sheet protective film, an electrolyte base film, and a separation membrane.

[0022] The beneficial effects of the present invention are reflected in:

[0023] The present invention does not use solvents. By using two adhesives in combination and with process coordination, the metal-organic framework material is uniformly distributed on the dendritic network structure formed by the adhesives, forming a thin film with a high porosity, good pore connectivity, and good air permeability. When applied to the separator, it exhibits excellent ion transport performance, and the battery has a high ionic conductivity.

[0024] Compared with the wet method for preparing metal-organic framework membranes and the in-situ synthesis method for preparing metal-organic framework membranes, the method for preparing the metal-organic framework membrane of the present invention does not use solvents throughout the process, does not require subsequent coating, drying, solvent recovery, etc. It has the advantages of a short process, simple operation, low cost, environmental friendliness, and safety and high efficiency. Description of the Drawings

[0025] Figure 1 This is a physical picture of the ZIF-8 membrane prepared in Example 1 of the present invention.

[0026] Figure 2 This is a scanning electron microscope picture of the ZIF-8 membrane prepared in Example 1 of the present invention.

[0027] Figure 3 This is the linear sweep voltammogram measured after assembling the battery with the metal-organic framework membrane prepared in Example 1 of the present invention.

[0028] Figure 4 This is the linear sweep voltammogram measured after assembling the battery with the metal-organic framework membrane prepared in Example 2 of the present invention.

[0029] Figure 5 This is the linear sweep voltammogram measured after assembling the battery with the metal-organic framework membrane prepared in Example 3 of the present invention.

[0030] Figure 6 This is the linear sweep voltammogram measured after assembling the battery with the metal-organic framework membrane prepared in Example 5 of the present invention.

[0031] Figure 7 This is the linear sweep voltammogram measured after assembling the battery with the metal-organic framework membrane prepared in Example 6 of the present invention.

[0032] Figure 8 This is the linear sweep voltammogram measured after assembling the battery with the metal-organic framework membrane prepared in Example 7 of the present invention. Detailed Embodiments

[0033] The following examples further illustrate the content of the present invention, but should not be construed as limiting the present invention. Without departing from the spirit and essence of the present invention, all other contents obtained by making several equivalent improvements and simple modifications to the present invention belong to the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well-known to those skilled in the art. Other preparation methods that can achieve the preparation of the metal-organic framework film also belong to the scope of the present invention.

[0034] Example 1

[0035] (1) Weigh 95 g of ZIF-8 and place it in a drying oven. Set the temperature to 80 °C and dry it to a constant weight for later use.

[0036] (2) Mix the dried ZIF-8 powder above with 0.5 g of polyvinylidene fluoride PVDF. Set the rotation speed to 500 - 2000 rpm and the mixing time to 30 - 120 min to obtain a premix. Here, the rotation speed and mixing time are selected according to the powder properties to ensure sufficient mixing; the set rotation speed and mixing time here are preferred choices.

[0037] (3) Mix the premix obtained in step (2) with 4.5 g of polytetrafluoroethylene powder PTFE (molecular weight greater than 5 million). The rotation speed can be set at 50 - 300 rpm and the time at 5 - 20 min.

[0038] (4) In this example, high-speed mechanical mixing is used. Set the rotation speed to 1000 - 5000 rpm and process for 5 - 60 min at high rotation speed to fibrillate the PTFE in the mixture in step (3) and adhere the metal-organic framework material. Here, the mixing rotation speed and time are selected according to the different adhesives B. As long as it is determined that under high-speed mechanical shear force, the adhesive B fibrillates to a fiber distribution with a microscopic morphology showing a 3D network structure; the above rotation speed and time ranges provided in this example are preferred ranges.

[0039] (5) Put the mixture obtained in step (4) into a roller press. Set the temperature to 60 °C, adjust the roller gap, and press it into a ZIF-8 film with a predetermined thickness. According to the usage requirements of the film, the thickness of the formed finished film can be set at 2 - 50 microns, and the roller gap is adjusted according to this predetermined thickness.

[0040] Example 2

[0041] Set the total mass ratio of the adhesive in Example 1 to 8%. Among them, 92 g of ZIF-8, the metal-organic framework material, is added in steps (1) and (2), 0.8 g of PVDF as adhesive A, and 7.2 g of PTFE as adhesive B. The remaining steps and parameters are the same as those in Example 1.

[0042] Example 3

[0043] Set the mass ratio of the binder in Example 1 to 12%. Among them, 88 g of ZIF-8 of the metal-organic framework material is added in steps (1) and (2), 1.2 g of PVDF as binder A, and 10.8 g of PTFE as binder B. The remaining steps and parameters are the same as those in Example 1.

[0044] Example 4

[0045] Set the rolling temperature in step 5 of Example 2 to 120 °C, and keep the remaining steps unchanged.

[0046] Example 5

[0047] Replace ZIF-8 in Example 2 with MIL-53, and keep the remaining steps unchanged.

[0048] (1) Weigh 92 g of MIL-53, put it into a drying oven, set the temperature to 80 °C, and dry it to constant weight for later use.

[0049] (2) Mix the above dried MIL-53 powder with 0.8 g of polyvinylidene fluoride PVDF, set the rotation speed to 500 rpm, and the time to 60 min to obtain a premix.

[0050] (3) Mix the premix obtained in step (2) with 7.2 g of polytetrafluoroethylene powder PTFE (molecular weight greater than 5 million), set the rotation speed to 100 rpm, and the time to 10 min.

[0051] (4) Set the rotation speed to 2500 rpm, and process for 30 min at high speed, so as to fibrillate the PTFE in the mixture in step (3) and adhere the metal-organic framework material.

[0052] (5) Put the mixture obtained in step (4) into a rolling press, set the temperature to 60 °C, adjust the roller spacing, and press it into a MIL-53 film with a predetermined thickness.

[0053] Example 6

[0054] Set the mass ratio of the binder in Example 5 to 12%. Among them, 88 g of MIL-53 of the metal-organic framework material is added in steps (1) and (2), 1.2 g of PVDF as binder A, and 10.8 g of PTFE as binder B. The remaining steps and parameters are the same as those in Example 5.

[0055] Example 7

[0056] Set the mass ratio of the binder in Example 5 to 18%. Among them, 82 g of MIL-53 of the metal-organic framework material was added in steps (1) and (2), 1.8 g of PVDF as binder A, and 16.2 g of PTFE as binder B. The remaining steps and parameters are the same as those in Example 5.

[0057] Example 8

[0058] Set the mass ratio of the binder in Example 5 to 18%. Among them, 82 g of MIL-53 of the metal-organic framework material was added in steps (1) and (2), 9.0 g of PVDF as binder A, and 9.0 g of PTFE as binder B. The remaining steps and parameters are the same as those in Example 5.

[0059] Example 9

[0060] (1) Weigh 92 g of MIL-53, put it into a drying oven, set the temperature to 80 °C, and dry it to a constant weight for later use.

[0061] (2) Mix the above-mentioned dried MIL-53 powder with 0.8 g of polyvinylidene fluoride PVDF, set the rotation speed to 500 rpm, and the time to 60 min to obtain a premix.

[0062] (3) Mix the premix obtained in step (2) with 7.2 g of polytetrafluoroethylene powder PTFE (molecular weight greater than 5 million), set the rotation speed to 100 rpm, and the time to 10 min.

[0063] (4) Carry out gas flow crushing on the mixture obtained in step (3), and set the gas flow pressure to 0.2 - 1.0 MPa. The gas flow pressure here is selected according to the different binder B, as long as it is determined that under the shear force formed by the gas flow, the binder B is fibrillated to a fiber distribution with a 3D network structure in the microscopic morphology; the above gas flow pressure range provided in this example is a preferred range.

[0064] (5) Put the mixture obtained in step (4) into a roll press, set the temperature to 90 °C, adjust the roller spacing, and press it into a MIL53 film with a predetermined thickness.

[0065] Among them, the MOF materials selected in each example are metal-organic framework materials, and their pore structures all meet the requirements of porosity greater than 40%, specific surface area greater than 200 m 2 / g, pore diameter less than 10 nm; for example, ZIF-8 used in Examples 1 - 4 has a specific surface area of about 1600 m 2 / g, pore diameters of about 0.34 nm and 1.1 nm, and porosity of about 65%; MIL-53 used in Example 5 has a specific surface area of about 1100 m 2 / g, with a pore diameter of about 0.6 nm and a porosity of about 60%.

[0066] As Figure 1 Shown in the figure is the ZIF-8 membrane prepared in Example 1. Its surface is smooth and flat, and the thickness is uniform. The measured thickness is about 25 μm, indicating that the preparation technology of the present invention has strong operability. Figure 2 This is an electron microscope picture of the ZIF-8 membrane prepared by the present invention. It can be confirmed from the picture that the adhesive PTFE has fibrillated and formed a dendritic network structure. The dendritic network structure of the adhesive PTFE adheres the solid particles formed by uniformly mixing the metal-organic framework material and the adhesive PVDF into one body. Under the action of rolling, a smooth, flat and densely bonded film is formed. The dense bonding is conducive to the connection of the pores in each metal-organic framework material particle, so that the formed film can have good gas permeability. The metal-organic framework membranes prepared in each example were subjected to gas permeability tests (PAPB-B01 type diaphragm gas permeability tester), and the time required to pass 100 mL of gas, that is, the Gurley value, was measured. The results showed that the Gurley value of the metal-organic framework membrane was between 85 - 155 s / 100 mL, indicating that the obtained metal-organic framework membrane has good gas permeability, high porosity and good pore connectivity, which is beneficial to applications in different scenarios.

[0067] Application Example 1

[0068] In order to demonstrate the application potential of the metal-organic framework membrane obtained by the present invention, the metal-organic framework membrane prepared in the example is now applied as a battery separator, and then relevant electrochemical performance tests are carried out. The metal-organic framework membrane obtained in the example was cut into several thin slices with a diameter of 0.8 cm, and then a symmetric cell was composed with an electrolyte (1 M LiPF6 in EC:EMC:DMC = 1:1:1 vol.%) and a stainless steel electrode sheet to conduct an electrochemical impedance test, so as to obtain the ionic conductivity. The battery separator, the electrolyte (1 M LiPF6 in EC:EMC:DMC = 1:1:1 vol.%), the stainless steel electrode sheet and the Li electrode sheet were composed into a battery, and then a linear sweep voltammetry test (LSV) was carried out, and the electrochemical stability window value was obtained through the test results. It should be particularly noted that the above applications and tests are all in a lean electrolyte state, that is, the amount of electrolyte used during the injection process is small (the amount of electrolyte used in the above tests is 5 μL, only to wet the separator and the electrode interface); to verify the application of the metal-organic framework membrane of the present invention in semi-solid batteries. The test results are shown as follows.

[0069] Table 1 shows the test results of the ionic conductivity obtained after assembling the symmetric cells with the metal-organic framework membranes prepared in each example. It can be seen that the ionic conductivity is in the range of 0.3 - 0.7 mS·cm -1Within a certain range, it exhibits relatively excellent ion transport performance. This is because the obtained metal-organic framework membrane has a high porosity, can store the electrolyte well, and is conducive to the transport of ions in the pores.

[0070] Table 1 Ion conductivity results obtained from testing the batteries assembled with the metal-organic framework membranes obtained in each example

[0071]

[0072] Figures 3 - 8 They are the LSV spectra of the batteries assembled with the metal-organic framework membranes prepared in Examples 1-3 and Examples 5-7 respectively. From the results, it can be seen that when the voltage is less than 4.8 V, the LSV curve has a flat platform and no obvious redox peaks, indicating that the prepared metal-organic framework membrane has extremely high electrochemical stability, and the electrochemical stability window is above 4.8 V, which can match the usage scenarios of high-voltage cathode materials.

[0073] In summary, the metal-organic framework membrane provided by this application can obtain a relatively high ion conductivity. In addition, since the metal-organic framework material itself is an organic-inorganic coordination compound, the material properties are stable, and it exhibits extremely high electrochemical stability. The electrochemical stability window can reach 5 V, which can match high-voltage electrode materials. Considering comprehensively, the metal-organic framework membrane disclosed in this patent has a stable structure and a simple and easy-to-operate preparation process, endowing it with good potential for application in different scenarios.

Claims

1. A metal-organic framework membrane, characterized in that: The metal-organic framework membrane comprises a metal-organic framework material and an adhesive; wherein the adhesive consists of at least two adhesives; wherein at least one adhesive is in a fibrous state and has a fibrous 3D network structure; at least one adhesive is not in a fibrous state.

2. The metal-organic framework membrane according to claim 1, wherein: The metal-organic framework membrane comprises a metal-organic framework material, adhesive A and adhesive B; The microscopic morphology of the metal-organic framework membrane shows that: adhesive B fibrates to form a 3D dendritic network structure, and a number of dense solid particles are uniformly and densely adhered to the 3D dendritic network structure; wherein the solid particles are formed by uniformly mixing the metal-organic framework material and adhesive A into one body.

3. The metal-organic framework film according to claim 2, wherein: The total mass of the adhesive is less than 20% of the total mass of the metal-organic framework membrane; and the mass ratio of adhesive A:adhesive B is 0 to 1:1, where 0:1 is not included.

4. The metal-organic framework membrane according to claim 3, characterized in that: Adhesive A is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene, polyvinyl alcohol, polyvinyl ethyl ether, polyethylene glycol, polyethylene terephthalate, polyethylene oxide, polypropylene, polyacrylonitrile, polymethyl methacrylate, polyimide, polyamide, polyamide-imide, sodium carboxymethyl cellulose, sodium alginate; Adhesive B is selected from one or more of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, hexafluoropropylene-tetrafluoroethylene copolymer.

5. The metal-organic framework film according to claim 2, wherein: The porosity of the metal-organic framework material is greater than 40%, the specific surface area is greater than 200 m 2 / g, and the pore diameter is less than 10 nm.

6. The metal-organic framework film according to claim 2, characterized in that: The metal-organic framework material is selected from magnesium-based metal-organic framework materials, calcium-based metal-organic framework materials, zinc-based metal-organic framework materials, aluminum-based metal-organic framework materials, zirconium-based metal-organic framework materials, chromium-based metal-organic framework materials, iron-based metal-organic framework materials, copper-based metal-organic framework materials, lanthanum-based metal-organic framework materials, or cerium-based metal-organic framework materials.

7. The metal-organic framework membrane according to claim 2, wherein: The surface of the metal-organic framework membrane is smooth and flat, and the average thickness is 2 - 50 μm; the air permeability test value of the metal-organic framework membrane, i.e., the Gurley value, is between 85 - 155 s / 100 mL.

8. A method for preparing a metal-organic framework membrane according to any one of claims 2-7, characterized in that, Comprising the following steps: 1) Premix the metal-organic framework material and adhesive A to make them fully mixed and uniformly mixed to obtain a premix; 2) Fully mix the premix obtained in step 1) with adhesive B to form a mixture; 3) Under the action of shear force, fibrate adhesive B in the mixture so that the fibrated adhesive B forms a fibrous 3D network structure; 4) Press the mixture sheared in step 3) into a membrane.

9. The preparation method of a metal-organic framework film according to claim 8, characterized in that: The fibrating method in step 3) adopts an air shear method of air breaking, and the air pressure is 0.2 - 1.0 MPa.

10. The preparation method of a metal-organic framework film according to claim 8, characterized in that: The fibrating method in step 3) adopts a mechanical extrusion shear method of high-speed mechanical mixing, and its rotation speed is 1000 - 5000 rpm, and it is mixed at this rotation speed for 5 - 60 min.

11. A battery assembly, wherein the battery assembly uses the metal-organic framework membrane according to any one of claims 1 - 7 as a battery separator, an electrolyte base film or an electrode sheet protective film.

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