CN111192991A

CN111192991A - MFI-PAN (melt flow index-Polyacrylonitrile) diaphragm and preparation method and application thereof

Info

Publication number: CN111192991A
Application number: CN202010020194.7A
Authority: CN
Inventors: 刘海清; 吴云琴; 翟云云; 戴文琪; 孙良钰; 李蕾; 王晓雅; 刘冰冰
Original assignee: Jiaxing University
Current assignee: Jiaxing University
Priority date: 2020-01-08
Filing date: 2020-01-08
Publication date: 2020-05-22
Anticipated expiration: 2040-01-08
Also published as: CN111192991B

Abstract

The invention discloses an MFI-PAN membrane and a preparation method and application thereof. The preparation method comprises the following steps: (1) preparing MFI zeolite with a multilayer structure; (2) removing the organic structure directing agent in the MFI zeolite with the multilayer structure prepared in the step (1) to obtain an open-pore two-dimensional MFI type zeolite nanosheet; (3) dissolving polyacrylonitrile in an organic solvent to be used as a spinning solution, and preparing a PAN (polyacrylonitrile) base membrane through electrostatic spinning; (4) and (3) dispersing the two-dimensional MFI type zeolite nanosheets with the holes prepared in the step (2) in water, adding a cross-linking agent, dropwise adding the cross-linking agent to the PAN base film prepared in the step (3), and assembling the two-dimensional MFI type zeolite nanosheets with the holes to the PAN base film to prepare the MFI-PAN diaphragm. The MFI-PAN lithium ion battery diaphragm prepared by the method has good contact between the two-dimensional MFI type zeolite nanosheet and the PAN base film, has high porosity and Li < + > migration number, and has wide application prospect in the aspects of electronic equipment, catalysis, gas separation and the like.

Description

MFI-PAN (melt flow index-Polyacrylonitrile) diaphragm and preparation method and application thereof

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to an MFI-PAN diaphragm and a preparation method and application thereof.

Background

With the increasing prominence of the problems of energy crisis, environmental pollution and the like, the development of new energy sources for sustainable development to replace fossil fuels becomes an urgent task. Lithium ion batteries are receiving much attention as a new type of high-energy green batteries. The diaphragm is used as one of core materials of the lithium ion battery, can prevent direct contact of a positive electrode and a negative electrode, allows lithium ions in electrolyte to freely pass through, and plays roles in electronic isolation and safety guarantee in the lithium ion battery. Currently, Polyethylene (PE), polypropylene (PP) and PP-PE-PP three-layer polymer separators have been widely used in commercial lithium ion battery separators because of their lower cost, excellent chemical stability and good mechanical properties. However, polyolefin separators have poor thermal stability and electrochemical properties, and often present safety hazards. In order to further improve the safety and the cycle performance of the lithium ion battery, researchers develop a plurality of functional novel diaphragms on the basis of the traditional polyolefin membranes.

Since the polyolefin material has a low heat distortion temperature and the separator undergoes severe heat shrinkage at an excessively high temperature, such a separator is not suitable for use in a high-temperature environment. The inorganic material with high thermal resistance is coated on the surface of the diaphragm, so that the expansion of thermal runaway at high temperature can be prevented, and the thermal stability of the diaphragm is effectively improved.

SiO with large thermal resistance is treated by Kim project group (Journal of Membrane Science, 2017, 535, 151-157.) of Korean Hanyang university in 2017₂The ceramic particles are coated on the surface of the PE diaphragm after amination, so that the compound effect is further improvedThe stability and mechanical properties of the composite membrane at high temperature.

In order to improve the ceramic loading of the composite membrane, the problem group of the university of east China science and Technology (2017, 144, 178-.

Due to the fact that the ceramic ions are large in size, the contact between the surface of the diaphragm and electrolyte is limited due to the fact that the diaphragm is coated with the small specific surface area of the surface of the diaphragm, and the ionic conductivity of the ceramic composite diaphragm is not obviously improved.

A Yuan Shuai topic group of Shanghai university in 2017 (Journal of Power Sources, 2017, 342, 816 and 824.) proposes that an MFI type zeolite molecular sieve (ZSM-5) is coated on the surface of a PE diaphragm in a dip coating mode, and compared with the original PE diaphragm, the ion conductivity of the modified diaphragm is from 0.30mS cm^-1To be improved by 0.54mS cm^-1，Li⁺The transport number increases greatly from 0.28 to 0.44 due to the specific pore structure of the ZSM-5 zeolite molecular sieve and its interaction with the electrolyte.

Compared with granular MFI type zeolite molecular sieve, the inorganic coating adopting two-dimensional MFI type zeolite nanosheets with large specific surface area and high porosity as the lithium ion battery diaphragm can be Li⁺Providing selective migration channels, beneficial to enhance Li⁺The number of migrations. The inorganic open-pore two-dimensional MFI type zeolite nanosheet is used as a modification material of a lithium battery diaphragm and is not reported in the published technology.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the MFI-PAN membrane, the preparation method and the application thereof⁺The transference number is increased, and the performance of the lithium ion battery is improved.

A preparation method of an MFI-PAN membrane comprises the following steps:

(1) preparing MFI zeolite with a multilayer structure;

(2) removing the organic structure directing agent in the MFI zeolite with the multilayer structure prepared in the step (1) to obtain an open-pore two-dimensional MFI type zeolite nanosheet;

(3) dissolving polyacrylonitrile in an organic solvent to be used as a spinning solution, and preparing a PAN (polyacrylonitrile) base membrane through electrostatic spinning;

(4) and (3) dispersing the two-dimensional MFI type zeolite nanosheets with the holes prepared in the step (2) in water, adding a cross-linking agent, dropwise adding the cross-linking agent to the PAN base film prepared in the step (3), and assembling the two-dimensional MFI type zeolite nanosheets with the holes to the PAN base film to prepare the MFI-PAN diaphragm.

Conventional methods can be selected for the synthesis of MFI zeolite (ML-MFI) having a multilayer structure. Preferably, the method for preparing the MFI zeolite with a multilayer structure in the step (1) is as follows: adding organic structure directing agent into water, adding alkali liquor and ethyl orthosilicate, hydrolyzing, crystallizing, and separating to obtain MFI zeolite with multilayer structure. The alkali liquor can be prepared from the following components: NaOH and Na₂SO₄Dissolved in water, such as: 1.4g NaOH, 3.8g anhydrous Na₂SO₄Dissolved in 33g of deionized water, the NaOH mass concentration is about 3.67 percent, and Na is added₂SO₄The mass concentration is about 10%.

The preparation method of the organic structure directing agent comprises the following steps: mixing NDDA and 1-bromohexane, carrying out alkylation reaction of the 1-bromohexane under the protection of inert gas, and drying a product to obtain the organic structure directing agent. In the reaction process, the mixture can be stirred magnetically for 30min and mixed uniformly, then is subjected to oil bath at 85 ℃, and is condensed and refluxed for 10h, and then the product is dried after the reaction is finished.

The preparation method of the NDDA comprises the following steps: reacting the reactants N, N, N, N-tetramethyl-1, 6-hexanediamine and C₂₂H₄₅And after mixing Br and the solvent, stirring for 10h at 65 ℃, cooling and crystallizing, and washing a product to obtain the NDDA. The solvent used in the reaction can be acetonitrile and toluene which are mixed evenly according to the volume ratio of 1: 1.

The method for removing the organic structure directing agent in the step (2) comprises the following steps: adding concentrated sulfuric acid into the MFI zeolite with the multilayer structure prepared in the step (1), then adding hydrogen peroxide, treating at 80 ℃ for 24 hours to remove the organic structure directing agent, and centrifugally collecting bottom-layer wet mud; the stripping step was repeated several times.

In the step (3), the electrostatic spinning voltage is 20-30kV, the perfusion speed of the spinning solution is 1-2.5mL/h, and the spinning temperature and the spinning humidity are respectively 24 ℃ and 40%. The temperature and the humidity of electrostatic spinning are controlled under the conditions, and the spinning effect is good.

Preferably, the PAN base film prepared by electrostatic spinning in the step (3) has a porosity of 70-90% and a pore diameter of 1-2 μm.

In the step (4), after the two-dimensional MFI-type zeolite nanosheets with the holes are assembled on the PAN base film, the assembling thickness of the two-dimensional MFI-type zeolite nanosheets with the holes is 0.058-0.23 mg/cm². During assembly, in order to ensure uniform assembly, the two-dimensional MFI-type zeolite nanosheets with the holes are dispersed in water, water penetrates through the PAN base film after suction filtration, and the two-dimensional MFI-type zeolite nanosheets with the holes are intercepted by the PAN base film, so that the amount of water used during dispersion can be used as required, and the nanosheets can be uniformly assembled.

Polyvinylpyrrolidone (PVP) can be used as the cross-linking agent, and the addition amount of the cross-linking agent can be 0.1mg for every 5mg of the two-dimensional MFI-type zeolite nanosheets with open pores.

And (4) after the dropwise addition is completed in the step (4), performing suction filtration, wherein the suction filtration pressure is less than 0.0005Mpa, and the suction filtration time is more than 2 hours, so that the performance of the product obtained by suction filtration is better.

The invention also provides the MFI-PAN membrane prepared by the preparation method.

The invention also provides application of the MFI-PAN diaphragm in preparation of a lithium ion battery diaphragm.

The MFI-PAN lithium ion battery diaphragm prepared by the method has good contact between the two-dimensional MFI type zeolite nanosheet and the PAN base film, high porosity and Li⁺The transference number has wide application prospect in the aspects of electronic equipment, catalysis, gas separation and the like.

Drawings

FIG. 1 is an SEM image of a prepared ML-MFI type zeolite molecular sieve.

Fig. 2 is an SEM image of the prepared two-dimensional MFI-type zeolite nanosheets.

Fig. 3 is a TEM image of the prepared two-dimensional MFI-type zeolite nanosheets.

FIG. 4 is N of two-dimensional MFI type zeolite nanosheets under 77K₂Adsorption and desorption isotherms.

Fig. 5 is a pore size distribution diagram of a two-dimensional MFI-type zeolite nanosheet.

Fig. 6 is an SEM image of the PAN membrane prepared.

FIG. 7 is a schematic structural diagram of a self-made simple vacuum filtration device.

Fig. 8 is a schematic process diagram of preparing an inorganic two-dimensional zeolite nanosheet modified lithium ion battery separator.

Fig. 9 is an SEM image of the MFI-PAN1(1mg MFI nanosheet) separator prepared in example.

Fig. 10 is an SEM image of the MFI-PAN4(4mg MFI nanosheet) separator prepared in example.

Fig. 11 is a discharge curve of the separator prepared in example at different rates.

Fig. 12 is a cycle curve of the separator prepared in example at a 2C rate.

Fig. 13 is a discharge curve of the separators with different MFI nanosheet contents prepared in the example at different rates.

Fig. 14 is a cycle curve of the diaphragms with different MFI nanosheet contents prepared in the examples at a 2C rate.

Detailed Description

Example 1

Preparing an open-pore two-dimensional MFI type zeolite nanosheet (nanosheet for short):

a template agent consisting of long-chain alkyl and biquaternary ammonium salt is adopted to synthesize MFI zeolite (ML-MFI) with a multilayer structure, and the specific synthesis steps are as follows:

mixing 51.696g N, N, N, N-tetramethyl-1, 6-hexanediamine and 11.694g C₂₂H₄₅Br was dissolved in 150mL acetonitrile and 150mL toluene. Stirring at normal temperature for 30min, and then stirring in oil bath at 65 ℃ for 10 h. Cooling in ice bath, filtering and recovering precipitated solid, and recovering the filtrate for recycling. The precipitate was washed with diethyl ether several times and allowed to stand until the precipitate was dried to give NDDA. 10.045g NDDA, 3.100g 1-bromohexane and 150mL acetonitrile were added to a three-necked flask, and after magnetically stirring at room temperature for 30min under nitrogen protection, the mixture was oiled at 85 DEG CAnd (3) stirring in a bath, condensing and refluxing for 10h, finishing the reaction, washing, and then drying in a vacuum oven at 80 ℃ for 12 h. Obtaining the Organic Structure Directing Agent (OSDA), the molecular formula of which is C₃₈H₈₂Br₂N₂The template agent consists of long-chain alkane and biquaternary ammonium salt.

Preparing alkali liquor in advance: 1.4g NaOH and 3.8g anhydrous Na were weighed₂SO₄And 33g of deionized water are put into a centrifuge tube, dissolved and covered for standby.

1.6g of OSDA was weighed, 15g of deionized water was added, 7.6g of the above prepared lye and 6.2g of TEOS (tetraethylorthosilicate) were added to the centrifuge tube, and the lid was closed. The solution was magnetically stirred at room temperature for 10min and then hydrolyzed in an oil bath at 60 ℃ for 6 h. Transferring the gel mixture into a reaction kettle, and placing small-size magnetons in the reaction kettle. Symmetrically fixed at 150 deg.C in a 60r.p.m rotary oven, and crystallized for 7 days. After crystallization, the reaction vessel was immediately taken out and cooled with cold water. 20000g of crystallized product is centrifuged, washed for more than 3 times, and the filter cake is dried at 80 ℃ overnight to obtain the petal-shaped ML-MFI zeolite formed by the interactive growth of a plurality of MFI nano sheets. And weighing and packing the obtained product. The SEM image of the prepared ML-MFI zeolite is shown in FIG. 1.

Preparing an open-pore two-dimensional MFI type zeolite nanosheet: adding 0.050g of ML-MFI zeolite into a high-temperature glass bottle, adding 12mL of concentrated sulfuric acid with the mass concentration of 98%, stirring for 30min, adding 4mL of 30% hydrogen peroxide, uniformly mixing, placing the dispersion into an oven with the temperature of 80 ℃ for treatment for 24h, and centrifugally washing to leave bottom-layer wet mud. And adding 12mL of 98% concentrated sulfuric acid into the bottom layer wet mud, stirring for 30min, adding 4mL of 30% hydrogen peroxide, uniformly mixing, placing the dispersion in an oven at 80 ℃ for treating for 24h, centrifugally washing, and repeating the step for 3 times. And (3) centrifugally washing the wet mud for the last time to be neutral to obtain the MFI zeolite basically without the template agent, dispersing the zeolite in an aqueous solution, and stripping and purifying to obtain the two-dimensional MFI type zeolite nanosheet basically without impurity particles and open pores. And adding 5mg of the obtained two-dimensional MFI-type zeolite nanosheet with the open pores into 10g of water to obtain a two-dimensional MFI-type zeolite nanosheet dispersion with the open pores for later use.

SEM image, TEM image and N under 77K of prepared two-dimensional MFI type zeolite nanosheet₂The adsorption-desorption isotherms and the pore size distribution diagrams are respectively shown in fig. 2, fig. 3, fig. 4 and fig. 5, and the combination of the graphs shows that the prepared two-dimensional MFI-type zeolite nanosheet has high surface-thickness ratio and porosity, micropores are almost completely opened, and the specific surface area is 376m²Both of these conditions favor the migration of Li +.

Example 2

Preparation of PAN nanofiber-based membrane:

taking 92g N, N-Dimethylformamide (DMF) in a high-temperature glass bottle, slowly adding 8g of PAN powder into the high-temperature glass bottle while stirring, and then stirring for 24 hours at normal temperature to obtain a clear 8 wt.% PAN spinning solution. The PAN fiber base membrane is prepared by utilizing an electrostatic spinning technology under the high-voltage electric field force, the electrostatic spinning voltage is 25kV, the filling speed of a spinning solution is 2.5mL/h, and the spinning temperature and the spinning humidity are respectively 24 ℃ and 40%. Fig. 6 is an SEM image of the prepared PAN basement membrane, and it can be seen from the figure that the prepared PAN nanofiber membrane has a small diameter, so that it has good electrolyte wettability, which is beneficial for making basement membrane.

The porosity of the prepared electrostatic spinning PAN nanofiber membrane is 70-90%, and the pore diameter is 1-2 mu m.

Example 3

Preparing a vacuum decompression suction filtration device:

as shown in fig. 7, two stop valves are installed on the rubber tube, one stop valve is connected with the vacuum pump to reduce the inlet pressure, the other stop valve is connected with the rubber tube with the vacuum meter to control the suction filtration speed, and the two stop valves are connected with the suction filtration bottle by the three-way valve to form the vacuum pressure reduction suction filtration device. The device can control the speed of suction filtration and can also be used for preparing compact films.

Example 4

Preparing an MFI-PAN membrane:

10g of the two-dimensional MFI-type zeolite nanosheet dispersion obtained in example 1, which had openings, was placed in a glass bottle (containing 5mg of nanosheet), 0.0001g (0.1mg) of polyvinylpyrrolidone (PVP) was added as a crosslinking agent, the mixture was stirred until the PVP was dissolved, and the dispersion was homogenized by sonication for 30min, 2g of the mixture was addedUniformly dripping two-dimensional MFI zeolite nanosheet dispersion (containing 1mg of nanosheets) of a cross-linking agent on the PAN-based diaphragm (with the diameter of 4cm and the thickness of 10 microns) prepared in example 2, utilizing the reduced-pressure vacuum filtration device in example 3 to open the pressure reduction valve to the maximum, utilizing the speed control valve to adjust the filtration pressure to be less than 0.005MPa, and obtaining the compact MFI-PAN diaphragm when the filtration time is 2 hours, wherein the dosage ratio of the two-dimensional MFI (nanosheets) to the base film is 0.08mg/cm²And standing at room temperature for later use. Fig. 8 is a schematic diagram of a process for preparing an inorganic two-dimensional MFI zeolite nanosheet modified lithium ion battery diaphragm (MFI-PAN diaphragm), wherein the two-dimensional MFI type zeolite nanosheet with the opening is assembled on a PAN base film prepared by electrostatic spinning through a reduced-pressure vacuum filtration device to prepare the MFI-PAN diaphragm named MFI-PAN 1. Fig. 9 is an SEM image of the prepared lithium ion battery separator MFI-PAN1, from which it can be seen that MFI nanosheets can be uniformly laid on the PAN-based membrane to form a dense thin film.

Example 5

Taking 10g of the two-dimensional MFI type zeolite nanosheet dispersion (containing 5mg of nanosheet) with the opening obtained in the example 1, adding 0.0001g (0.1mg) of polyvinylpyrrolidone (PVP) serving as a cross-linking agent, stirring until the PVP is dissolved, ultrasonically dispersing uniformly for 30min, then taking 8g of the two-dimensional MFI zeolite nanosheet dispersion (containing 4mg of nanosheet) with the cross-linking agent to be uniformly dripped on the PAN-based diaphragm (with the diameter of 4cm and the thickness of 10 mu m) prepared in the example 2, using the reduced-pressure vacuum filtration device in the example 3 to open the pressure-reducing valve to the maximum, using the speed-controlling valve to adjust the filtration pressure to be less than 0.005MPa, and using the filtration time to be 2 hours to obtain the compact MFI-PAN diaphragm, wherein the dosage ratio of the two-dimensional MFI to the base membrane is 0.32mg/cm²And standing at room temperature for later use. Fig. 8 is a schematic diagram of a process for preparing an inorganic two-dimensional MFI zeolite nanosheet modified lithium ion battery diaphragm (MFI-PAN diaphragm), wherein the two-dimensional MFI type zeolite nanosheet with the opening is assembled on a PAN base film prepared by electrostatic spinning through a reduced-pressure vacuum filtration device to prepare the MFI-PAN diaphragm named MFI-PAN 4. Fig. 10 is an SEM image of the prepared lithium ion battery separator MFI-PAN4, from which it can be seen that MFI nanosheets can be uniformly laid on the PAN-based membrane to form a dense thin film.

Example 6

Electrochemical performance tests were then performed on lithium ion batteries prepared from MFI-PAN membranes, PAN-based membranes (spectra, P1361), and commercial Celgard membranes (Celgard, 2320).

Fig. 11 and 12 show the discharge curves of the lithium ion batteries assembled by the MFI-PAN separator (prepared in example 4), the PAN-based membrane and the Celgard separator at different rates (0.5C, 1C, 2C, 5C and 10C) and the cycle performance curve at the rate of 2C, and it can be seen from fig. 11 that as the rate increases, the discharge plateaus of the lithium ion batteries assembled by the MFI-PAN separator, the PAN-based membrane and the Celgard separator decrease, the specific discharge capacity decreases, and the reason for this phenomenon is related to the polarization of the batteries. The specific discharge capacity of the lithium ion battery assembled by the MFI-PAN diaphragm is respectively 150mAh/g, 146mAh/g, 141mAh/g, 133mAh/g and 126mAh/g under the multiplying power of 0.5C, 1C, 2C, 5C and 10C, and the battery assembled by the MFI-PAN diaphragm shows more specific discharge capacity than the battery assembled by the Celgard diaphragm and the PAN base film, which shows that the electrochemical performance of the PAN base film only modifying a small amount of two-dimensional MFI type zeolite nanosheets is obviously superior to that of the original PAN base film and the commercialized Celgard diaphragm. As can be seen from fig. 12, their performances at 2C rate are relatively stable.

Example 7

And then, the electrochemical performance of the lithium ion battery prepared by the MFI-PAN1 diaphragm, the MFI-PAN4 diaphragm and the PAN basal membrane (Spectrure, P1361) is tested.

Fig. 13 and 14 show the discharge curves of the lithium ion battery assembled by the MFI-PAN1 diaphragm, the MFI-PAN4 diaphragm and the PAN diaphragm at different magnifications (0.5C, 1C, 2C, 5C, 10C and 20C) and the cycle performance curve at the magnifications of 2C, and it can be seen from fig. 13 that as the magnifications increase, the discharge platforms of the lithium ion battery assembled by the MFI-PAN1 diaphragm, the MFI-PAN4 diaphragm and the PAN diaphragm all decrease, the specific discharge capacity all decreases, and the reasons for this phenomenon are all related to the polarization of the battery. Under the 20C multiplying power, the specific discharge capacity of the lithium ion battery assembled by the MFI-PAN4 diaphragm is 104mAh/g, which is higher than that of the lithium ion battery assembled by the MFI-PAN1 diaphragm and the PAN diaphragm, while the specific discharge capacity of the lithium ion battery assembled by the MFI-PAN1 diaphragm is smaller than that of the PAN diaphragm under the 20C multiplying power. Under the 2C multiplying power, the specific discharge capacity of the lithium ion battery assembled by the MFI-PAN1 diaphragm is 136mAh/g, while the specific discharge capacities of the lithium ion battery assembled by the MFI-PAN4 diaphragm and the PAN diaphragm are 133mAh/g and 130mAh/g respectively, and as can be seen from the graph of FIG. 13, under the high multiplying power, the diaphragm (MFI-PAN4 diaphragm) with high MFI nano-sheet content is large in specific discharge capacity. Under low multiplying power, the diaphragm (MFI-PAN1 diaphragm) with low MFI nano-sheet content has large specific discharge capacity. It can be seen from fig. 14 that the performance of all 3 separators is relatively stable at 2C rate.

Claims

1. A preparation method of an MFI-PAN membrane is characterized by comprising the following steps:

(1) preparing MFI zeolite with a multilayer structure;

2. The production method according to claim 1, wherein the MFI zeolite of the multilayer structure produced in step (1) is produced by:

adding organic structure directing agent into water, adding alkali liquor and ethyl orthosilicate, hydrolyzing, crystallizing, and separating to obtain MFI zeolite with multilayer structure.

3. The method of claim 2, wherein the organic structure directing agent is prepared by: mixing NDDA and 1-bromohexane, carrying out alkylation reaction of the 1-bromohexane under the protection of inert gas, and drying a product to obtain the organic structure directing agent.

4. The method of claim 3, wherein the NDDA is prepared by: reacting the reactants N, N, N, N-tetramethyl-1, 6-hexanediamine and C₂₂H₄₅And after mixing Br and the solvent, stirring for 10h at 65 ℃, cooling and crystallizing, and washing a product to obtain the NDDA.

5. The method of claim 1, wherein the organic structure directing agent is removed in step (2) by: adding concentrated sulfuric acid into the MFI zeolite with the multilayer structure prepared in the step (1), then adding hydrogen peroxide, treating at 80 ℃ for 24 hours to remove the organic structure directing agent, and centrifugally collecting bottom-layer wet mud; the stripping step was repeated several times.

6. The preparation method according to claim 1, wherein the electrospinning voltage in the step (3) is 20-30kV, the perfusion speed of the spinning solution is 1-2.5mL/h, and the spinning temperature and humidity are 24 ℃ and 40%, respectively.

7. The method according to claim 1, wherein the PAN-based film prepared by electrospinning in step (3) has a porosity of 70% to 90% and a pore size of 1 to 2 μm.

8. The preparation method of claim 1, wherein in the step (4), after the two-dimensional MFI-type zeolite nanosheets with the openings are assembled on the PAN base film, the assembled thickness of the two-dimensional MFI-type zeolite nanosheets with the openings is 0.08-0.32 mg/cm²。

9. An MFI-PAN membrane prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the MFI-PAN separator of claim 11 in the preparation of a lithium ion battery separator.