A method of preparing a metal organic framework membrane

Abstract

The application belongs to the technical field of sodium ion battery separators, and specifically discloses a preparation method of a metal organic framework separator, which comprises the following steps: S1: preparing a hierarchical pore MIL-101-Fe; and S2: preparing a MIL-101-Fe / PP separator. The application provides a preparation method of a metal organic framework separator, and the prepared metal organic framework separator is applied to a sodium ion battery, so that the ion migration rate and ion conductivity can be improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery separator technology, and particularly relates to a method for preparing a metal-organic framework separator. Background Technology

[0002] Sodium-ion batteries are a type of rechargeable battery. Their working principle is similar to that of lithium-ion batteries, primarily relying on the movement of sodium ions between the positive and negative electrodes. Sodium-ion batteries mainly consist of positive and negative electrode materials, an electrolyte, a separator, and positive and negative electrode casings.

[0003] With the rapid development of sodium battery technology, the development of sodium-ion batteries with higher energy density is imperative. High-energy-density sodium-ion batteries require higher ion transport rates; the sodium-ion migration rate and ionic conductivity of the sodium battery separator directly affect the electrochemical and safety performance of the battery. However, the sodium-ion migration rate and ionic conductivity of current sodium battery separators are not ideal. Therefore, there is an urgent need for a separator with high ion migration rate and ionic conductivity, while also meeting requirements for thermal stability, corrosion resistance, and good electrolyte wettability. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned problems in the prior art and provide a method for preparing a metal-organic framework membrane. The prepared metal-organic framework membrane can be used in sodium-ion batteries to improve ion migration rate and ion conductivity.

[0005] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0006] A method for preparing a metal-organic framework membrane, the method comprising the following steps:

[0007] S1: Preparation of hierarchical porous MIL-101-Fe

[0008] Iron salt and terephthalic acid were added to N,N-dimethylformamide, followed by deionized water. After stirring until homogeneous, a mixture was prepared. The mixture was then transferred to a microwave reactor for crystallization for 8-24 hours to obtain a brownish-yellow gel. The microwave reactor was cooled to room temperature, and the brownish-yellow gel was removed from the reactor. It was washed with N,N-dimethylformamide solution and methanol solution, respectively. After washing, it was transferred to a constant temperature oven for drying. After drying, multi-level porous MIL-101-Fe was obtained.

[0009] S2: Preparation of MIL-101-Fe / PP membrane

[0010] Multi-level porous MIL-101-Fe was placed in a PVDF-HFP / NMP solution and stirred thoroughly to form a homogeneous mixture. This homogeneous mixture was then coated onto a polypropylene membrane and dried to prepare the MIL-101-Fe / PP membrane.

[0011] Further, in step S1, the iron salt is any one or more of FeCl3·6H2O, Fe2(SO4)3·9H2O, Fe(NO3)3·9H2O and Fe(CH3COO)2·4H2O mixed in any proportion.

[0012] Furthermore, in the mixture, the molar concentration ratio of iron salt to terephthalic acid is 2:(1-2);

[0013] The molar concentration of terephthalic acid in the mixture is 0.10-0.20 mol / L.

[0014] Furthermore, in the mixture, the volume ratio of deionized water to N,N-dimethylformamide is (0.05-0.67):1.

[0015] Furthermore, during the crystallization process in the microwave reactor, the crystallization temperature is 120-200℃.

[0016] Further, in step S1, the specific process of washing the brownish-yellow gelatinous substance with N,N-dimethylformamide solution and methanol solution is as follows: first, wash the brownish-yellow gelatinous substance with N,N-dimethylformamide solution three times, and then wash it with methanol solution three times.

[0017] Furthermore, in step S1, during the drying process in the constant temperature oven, the drying temperature is 100-150℃ and the drying time is 8-12h.

[0018] Further, in step S2, the mass ratio of the hierarchical porous MIL-101-Fe to the PVDF-HFP / NMP solution in the mixed homogeneous liquid is (1-3):(0.5-2).

[0019] Furthermore, the mass concentration of the PVDF-HFP / NMP solution is 5-10%.

[0020] Furthermore, in step S2, the drying temperature is 50-70℃.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. The present invention provides a method for preparing a metal-organic framework (MOF) separator, wherein a functional coating containing a multi-level porous MOF structure, MIL-101-Fe, is coated on the surface of a polypropylene separator. Since the nanochannels and negatively charged interparticle channels inside the MOF restrict the migration of anions, the migration number of sodium ions in the prepared separator is increased, thereby improving the sodium ion migration rate and ionic conductivity, and improving the rate performance of the battery.

[0023] 2. The present invention provides a method for preparing a metal-organic framework membrane. During the preparation process, a microwave-assisted reaction vessel is used for crystallization. The non-contact heating characteristics of microwave radiation help achieve uniform heating of the reaction system, thereby improving the quality and crystallinity of the product. Microwave heating can complete the synthesis reaction at a lower temperature and in a shorter time. Compared with traditional hydrothermal or solvothermal methods, microwave-assisted synthesis is more efficient and energy-saving. The product synthesized by microwave assistance can be more easily separated from the reaction system, and there are almost no byproducts, thus simplifying the processing steps.

[0024] 3. The present invention provides a method for preparing a metal-organic framework membrane. The prepared membrane has the characteristics of good thermal stability and good corrosion resistance, and also has good electrolytic wettability. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a method for preparing a metal-organic framework membrane, the method comprising the following steps:

[0027] S1: Preparation of hierarchical porous MIL-101-Fe

[0028] Iron salt and terephthalic acid were added to N,N-dimethylformamide, and then deionized water was added. After stirring evenly, a mixture was prepared. The molar ratio of iron salt to terephthalic acid in the mixture was 2:(1-2).

[0029] The molar concentration of terephthalic acid in the mixture is 0.10-0.20 mol / L;

[0030] In the mixture, the volume ratio of deionized water to N,N-dimethylformamide is (0.05-0.67):1;

[0031] The iron salt is any one or more of FeCl3·6H2O, Fe2(SO4)3·9H2O, Fe(NO3)3·9H2O and Fe(CH3COO)2·4H2O mixed in any proportion;

[0032] The mixture was transferred to a microwave reactor and crystallized at 120-200℃ for 8-24 hours to obtain a brownish-yellow gel-like substance.

[0033] After the microwave reactor is cooled to room temperature, the brownish-yellow gel-like substance inside the microwave reactor is removed. First, the brownish-yellow gel-like substance is washed with N,N-dimethylformamide solution three times, and then washed with methanol solution three times.

[0034] After washing, the sample was transferred to a constant temperature oven and dried at 100-150℃ for 8-12 hours to obtain multi-level porous MIL-101-Fe.

[0035] S2: Preparation of MIL-101-Fe / PP membrane

[0036] The multi-level porous MIL-101-Fe was placed in a PVDF-HFP / NMP solution with a mass concentration of 5-10% and stirred thoroughly to form a homogeneous mixture.

[0037] In the homogeneous mixture, the mass ratio of the hierarchical porous MIL-101-Fe to the PVDF-HFP / NMP solution is (1-3):(0.5-2), preferably (0.55-0.60):1;

[0038] The uniformly mixed liquid was coated onto a polypropylene membrane and dried at 50-70℃ to prepare the MIL-101-Fe / PP membrane.

[0039] The following are specific embodiments. Unless otherwise specified, all raw materials in the following embodiments can be obtained commercially.

[0040] Example 1

[0041] This embodiment provides a method for preparing a metal-organic framework membrane, which includes the following steps:

[0042] S1: Preparation of hierarchical porous MIL-101-Fe

[0043] 2.5 mmol FeCl3·6H2O and 2.5 mmol terephthalic acid were added to 15 ml N,N-dimethylformamide, followed by 5 ml deionized water. After stirring evenly, the mixture was transferred to a microwave-assisted reaction vessel and crystallized at 120 °C for 24 h to obtain a brownish-yellow gel. After the reaction vessel cooled to room temperature, the brownish-yellow gel was washed three times each with N,N-dimethylformamide solution and methanol solution, and then transferred to a 100 °C constant temperature oven and dried for 12 h to obtain hierarchical porous MIL-101-Fe.

[0044] S2: Preparation of MIL-101-Fe / PP membrane

[0045] Multi-level porous MIL-101-Fe was placed in a 7% (w / w) PVDF-HFP / NMP solution, wherein the weight ratio of multi-level porous MIL-101-Fe to PVDF-HFP / NMP solution was 55%. The mixture was stirred thoroughly to form a homogeneous liquid, which was then coated onto a PP membrane using a coating machine. After being thoroughly dried at 50°C, the MIL-101-Fe / PP membrane was prepared.

[0046] Example 2

[0047] This embodiment provides a method for preparing a metal-organic framework membrane, which includes the following steps:

[0048] S1: Preparation of hierarchical porous MIL-101-Fe

[0049] 20 mmol Fe(NO3)3·9H2O and 15 mmol terephthalic acid were added to 60 ml N,N-dimethylformamide, followed by 10 ml deionized water. After stirring evenly, the mixture was transferred to a microwave-assisted reaction vessel and crystallized at 140 °C for 24 h to obtain a brownish-yellow gel. After the reaction vessel cooled to room temperature, the brownish-yellow gel was washed three times each with N,N-dimethylformamide solution and methanol solution, and then transferred to a 100 °C constant temperature oven and dried for 6 h to obtain hierarchical porous MIL-101-Fe.

[0050] S2: Preparation of MIL-101-Fe / PP membrane

[0051] Multi-level porous MIL-101-Fe was placed in a 7% (w / w) PVDF-HFP / NMP solution, wherein the weight ratio of multi-level porous MIL-101-Fe to PVDF-HFP / NMP solution was 58%. The mixture was stirred thoroughly to form a homogeneous liquid, which was then coated onto a PP membrane using a coating machine. After being thoroughly dried at 50°C, the MIL-101-Fe / PP membrane was prepared.

[0052] Example 3

[0053] This embodiment provides a method for preparing a metal-organic framework membrane, which includes the following steps:

[0054] S1: Preparation of hierarchical porous MIL-101-Fe

[0055] 30 mmol Fe(NO3)3·9H2O and 15 mmol terephthalic acid were added to 100 ml N,N-dimethylformamide, followed by 10 ml deionized water. After stirring evenly, the mixture was transferred to a microwave-assisted reaction vessel and crystallized at 130 °C for 10 h to obtain a brownish-yellow gel. After the reaction vessel cooled to room temperature, the brownish-yellow gel was washed three times each with N,N-dimethylformamide solution and methanol solution, and then transferred to a 100 °C constant temperature oven and dried for 6 h to obtain multi-level porous MIL-101-Fe.

[0056] S2: Preparation of MIL-101-Fe / PP membrane

[0057] Multi-level porous MIL-101-Fe was placed in a PVDF-HFP / NMP solution with a mass concentration of 8%, wherein the weight ratio of multi-level porous MIL-101-Fe to PVDF-HFP / NMP solution was 56%. The mixture was stirred thoroughly to form a homogeneous liquid, which was then coated onto a PP membrane using a coating machine. After being thoroughly dried at 50°C, the MIL-101-Fe / PP membrane was prepared.

[0058] Example 4

[0059] This embodiment provides a method for preparing a metal-organic framework membrane, which includes the following steps:

[0060] S1: 40 mmol FeCl3·6H2O and 30 mmol terephthalic acid were added to 150 ml N,N-dimethylformamide, followed by 50 ml deionized water. After stirring evenly, the mixture was transferred to a microwave-assisted microwave reactor and crystallized at 160 °C for 16 h to obtain a brownish-yellow gel. After the reactor cooled to room temperature, the brownish-yellow gel was washed three times each with N,N-dimethylformamide solution and methanol solution, and then transferred to a 120 °C constant temperature oven and dried for 10 h to obtain hierarchical porous MIL-101-Fe.

[0061] S2: Preparation of MIL-101-Fe / PP membrane

[0062] Multi-level porous MIL-101-Fe was placed in a PVDF-HFP / NMP solution with a mass concentration of 8%, wherein the weight ratio of multi-level porous MIL-101-Fe to PVDF-HFP / NMP solution was 60%. The mixture was stirred thoroughly to form a homogeneous liquid, which was then coated onto a PP membrane using a coating machine. After being thoroughly dried at 60°C, the MIL-101-Fe / PP membrane was prepared.

[0063] Example 5

[0064] This embodiment provides a method for preparing a metal-organic framework membrane, which includes the following steps:

[0065] S1: 21 mmol FeCl3·6H2O and 21 mmol terephthalic acid were added to 200 ml N,N-dimethylformamide, followed by 10 ml deionized water. After stirring evenly, the mixture was transferred to a microwave-assisted microwave reactor and crystallized at 120 °C for 24 h to obtain a brownish-yellow gel. After the reactor cooled to room temperature, the brownish-yellow gel was washed three times each with N,N-dimethylformamide solution and methanol solution, and then transferred to a 100 °C constant temperature oven and dried for 12 h to obtain a hierarchical porous MIL-101-Fe.

[0066] S2: Preparation of MIL-101-Fe / PP membrane

[0067] Multi-level porous MIL-101-Fe was placed in a 5% (w / w) PVDF-HFP / NMP solution, wherein the weight ratio of multi-level porous MIL-101-Fe to PVDF-HFP / NMP solution was 60%. The mixture was stirred thoroughly to form a homogeneous liquid, which was then coated onto a PP membrane using a coating machine. After being thoroughly dried at 50°C, the MIL-101-Fe / PP membrane was prepared.

[0068] Example 6

[0069] This embodiment provides a method for preparing a metal-organic framework membrane, which includes the following steps:

[0070] S1: 66.8 mmol FeCl3·6H2O and 33.4 mmol terephthalic acid were added to 100 ml N,N-dimethylformamide, followed by 67 ml deionized water. After stirring evenly, the mixture was transferred to a microwave-assisted reaction vessel and crystallized at 200 °C for 8 h to obtain a brownish-yellow gel. After the reaction vessel cooled to room temperature, the brownish-yellow gel was washed three times each with N,N-dimethylformamide solution and methanol solution, and then transferred to a constant temperature oven at 150 °C for drying for 8 h to obtain hierarchical porous MIL-101-Fe.

[0071] S2: Preparation of MIL-101-Fe / PP membrane

[0072] Multi-level porous MIL-101-Fe was placed in a 10% (w / w) PVDF-HFP / NMP solution, with a weight ratio of 1:2 between the multi-level porous MIL-101-Fe and the PVDF-HFP / NMP solution. The mixture was stirred thoroughly to form a homogeneous liquid, which was then coated onto a PP membrane using a coating machine. After thorough drying at 70°C, the MIL-101-Fe / PP membrane was prepared.

[0073] Comparative Example 1

[0074] This comparative example provides a method for preparing a metal-organic framework membrane, which includes the following steps:

[0075] S1: 40 mmol FeCl3·6H2O and 30 mmol terephthalic acid were added to 150 ml N,N-dimethylformamide, followed by 50 ml deionized water. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene liner and crystallized at 160 °C for 16 h using a hydrothermal method to prepare a brownish-yellow gel. After the reaction vessel cooled to room temperature, the brownish-yellow gel was washed three times each with N,N-dimethylformamide solution and methanol solution, and then transferred to a 120 °C constant temperature oven and dried for 10 h to obtain a hierarchical porous MIL-101-Fe.

[0076] S2: Preparation of MIL-101-Fe / PP membrane

[0077] Multi-level porous MIL-101-Fe was placed in a PVDF-HFP / NMP solution with a mass concentration of 8%, wherein the weight ratio of multi-level porous MIL-101-Fe to PVDF-HFP / NMP solution was 60%. The mixture was stirred thoroughly to form a homogeneous liquid, which was then coated onto a PP membrane using a coating machine. After being thoroughly dried at 60°C, the MIL-101-Fe / PP membrane was prepared.

[0078] Comparative Example 2

[0079] The comparative example provided is a conventional polymer base membrane material PP membrane with a pore size of 0.2, a porosity of 32%, and a base membrane thickness of 16μm.

[0080] Experimental Example

[0081] The ion migration rate of the MIL-101-Fe / PP membranes prepared in the above examples and comparative examples was evaluated by electrochemical methods. The ion transference number was calculated by the classic Bruce-Vincent method, and the conductivity was measured by impedance testing. The results are shown in Table 1.

[0082] Table 1

[0083]

[0084]

[0085] Compared with existing technologies, the ion transference number of the membranes in existing technologies is 0.25-0.40, and the conductivity is 0.5-0.8 mS / cm;

[0086] As can be seen from the data in Table 1, the MIL-101-Fe / PP membrane prepared in the examples has significantly improved ion transference number and conductivity compared with the prior art.

[0087] Specifically, as can be seen from Example 4 and Comparative Example 1, Comparative Example 1 uses a hydrothermal method to prepare hierarchical porous MIL-101-Fe, while Example 4 uses a microwave-assisted heating method. The ion transport number and conductivity of Example 4 are improved compared to Comparative Example 1, indicating that the microwave-assisted heating method can not only shorten the crystallization time and improve the crystallization efficiency, but also improve the thermal stability of the prepared membrane. Moreover, microwave-assisted heating also has the advantages of high efficiency and energy saving.

[0088] This invention provides a method for preparing a metal-organic framework (MOF) separator. A functional coating containing a hierarchical porous MOF structure, MIL-101-Fe, is coated on the surface of a polypropylene separator. Since the nanochannels and negatively charged interparticle channels inside the MOF restrict the migration of anions, the migration number of sodium ions in the prepared separator is increased, thereby improving the sodium ion migration rate and ionic conductivity, and improving the rate performance of the battery.

[0089] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0090] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a metal-organic framework membrane, characterized in that, The preparation method includes the following steps: S1: Preparation of hierarchical porous MIL-101-Fe Iron salt and terephthalic acid were added to N,N-dimethylformamide, followed by deionized water. After stirring until homogeneous, a mixture was prepared. The mixture was then transferred to a microwave reactor for crystallization for 8-24 hours to obtain a brownish-yellow gel. The microwave reactor was cooled to room temperature, and the brownish-yellow gel was removed from the reactor. It was washed with N,N-dimethylformamide solution and methanol solution, respectively. After washing, it was transferred to a constant temperature oven for drying. After drying, multi-level porous MIL-101-Fe was obtained. S2: Preparation of MIL-101-Fe / PP membrane Multi-level porous MIL-101-Fe was placed in a PVDF-HFP / NMP solution and stirred thoroughly to form a homogeneous mixture. This homogeneous mixture was then coated onto a polypropylene membrane and dried to prepare a MIL-101-Fe / PP membrane. In step S1, the iron salt is any one or more of FeCl3·6H2O, Fe2(SO4)3·9H2O, Fe(NO3)3·9H2O and Fe(CH3COO)2·4H2O mixed in any proportion; In the mixture, the molar ratio of iron salt to terephthalic acid is 2:(1-2). The molar concentration of terephthalic acid in the mixture is 0.10-0.20 mol / L; In the mixture, the volume ratio of deionized water to N,N-dimethylformamide is (0.05-0.67):1; During the crystallization process in the microwave reactor, the crystallization temperature is 120-200℃; In step S2, the mass ratio of the hierarchical porous MIL-101-Fe to the PVDF-HFP / NMP solution in the homogeneous mixture is (1-3):(0.5-2).

2. The method for preparing a metal-organic framework membrane according to claim 1, characterized in that, In step S1, the specific process of washing the brownish-yellow gelatinous substance with N,N-dimethylformamide solution and methanol solution is as follows: first, wash the brownish-yellow gelatinous substance with N,N-dimethylformamide solution three times, and then wash it with methanol solution three times.

3. The method for preparing a metal-organic framework membrane according to claim 1, characterized in that, In step S1, during the drying process in the constant temperature oven, the drying temperature is 100-150℃ and the drying time is 8-12h.

4. The method for preparing a metal-organic framework membrane according to claim 1, characterized in that, The mass concentration of the PVDF-HFP / NMP solution is 5-10%.

5. The method for preparing a metal-organic framework membrane according to claim 1, characterized in that, In step S2, the drying temperature is 50-70℃.

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