Composite electromagnetic shielding material and preparation method thereof

Abstract

The invention relates to the technical field of electromagnetic shielding materials, in particular to a composite electromagnetic shielding material and a preparation method thereof. The composite electromagnetic shielding material comprises a multi-layer film structure, and the multi-layer film structure comprises a PVDF / MXene single-layer film and a PVDF single-layer film which are sequentially stacked. The composite electromagnetic shielding material provided by the invention has good flexibility and electromagnetic shielding performance, and is an excellent flexible electromagnetic shielding material.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding materials, and in particular to a composite electromagnetic shielding material and a preparation method thereof. Background Art

[0002] Current sensors detect the power consumption status of electronic devices by acquiring characteristic parameters of current to ensure safe operation of the equipment. High-precision current sensors based on the principle of magnetic field induction, such as tunnel magnetoresistance sensors, giant magnetoresistance sensors, Hall effect sensors, fluxgate sensors, etc., need to be equipped with electromagnetic shielding materials to achieve resistance to electromagnetic field interference in order to ensure measurement accuracy. However, traditional metal-based (such as silver, copper, iron and aluminum) electromagnetic shielding materials have defects such as poor flexibility, easy corrosion and high cost, which makes it difficult to meet market demand.

[0003] Filling conductive materials into flexible matrices is considered a way to obtain flexible electromagnetic shielding composite materials. So far, polystyrene, polymethyl methacrylate, polyvinyl alcohol, polyimide, polyurethane, polypropylene, epoxy resin and polyvinylidene fluoride (PVDF) are often used as flexible matrices. Among them, polyvinylidene fluoride has attracted widespread attention due to its excellent flexibility, light weight, processability and dielectric properties.

[0004] Yanli Li published “Scalable manufacturing of flexible, durable Ti” in Composites Part B: Engineering in April 2021. 3 C 2 T x MXene / Polyvinylidene fluoride filmfor multifunctional electromagnetic interference shielding and electro / photo-thermal conversion applications", they prepared flexible PVDF / MXene films by blade coating. The ordered arrangement of MXene nanosheet structures effectively improved the conductivity of the composite film and formed multiple reflection planes and interface polarization. The PVDF / MXene film (thickness of 17μm) showed excellent electromagnetic shielding performance of 42.9dB, resistance to mechanical strain (tensile strength of 23MPa) and chemical ability. However, the films prepared by the blade coating method are generally of poor quality and the coating thickness is difficult to be uniform. In addition, considering the high electromagnetic shielding properties of pure MXene (over 100dB), further exploration is needed to improve its electromagnetic shielding performance while ensuring the flexibility of MXene-based composites.

[0005] Therefore, there is an urgent need to provide a composite electromagnetic shielding material with high electromagnetic shielding properties, good flexibility and high tensile strength and a preparation method thereof. Summary of the invention

[0006] The purpose of the present invention is to solve the problems of poor flexibility of existing electromagnetic shielding materials and the need to further improve the battery shielding performance, and to provide a composite electromagnetic shielding material and a preparation method thereof.

[0007] In order to achieve the above-mentioned object, a first aspect of the present invention provides a composite electromagnetic shielding material, wherein the multilayer film structure comprises a PVDF / MXene single-layer film and a PVDF single-layer film stacked in sequence.

[0008] A second aspect of the present invention provides a method for preparing a composite electromagnetic shielding material, wherein the method comprises the following steps:

[0009] (1) evaporating a dispersion containing MXene, PVDF and a solvent into a film to obtain a PVDF / MXene evaporated film;

[0010] (2) subjecting the PVDF / MXene evaporated film to a first hot pressing to obtain a PVDF / MXene single-layer film;

[0011] (3) The PVDF / MXene single-layer film and the PVDF single-layer film are alternately stacked multiple times and then hot-pressed for a second time to obtain a composite electromagnetic shielding material.

[0012] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0013] 1) The composite electromagnetic shielding material provided in the present invention has both good flexibility and electromagnetic shielding performance, and is an excellent flexible electromagnetic shielding material;

[0014] 2) The preparation method of the composite electromagnetic shielding material provided in the present invention uses MXene as a conductive filler and PVDF as a flexible matrix, and adopts evaporation film forming and hot pressing molding to prepare the composite electromagnetic shielding material. The film forming quality is high, the process flow is simple, and it is suitable for industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1-5 is a scanning electron microscope image of a cross section of the composite electromagnetic shielding material prepared in Example 1-5;

[0016] Figure 6 is a graph showing the electromagnetic shielding test results of the composite electromagnetic shielding material prepared in Examples 1-5;

[0017] Figure 7This is a tensile strength test chart of the composite electromagnetic shielding material prepared in Example 1-5. DETAILED DESCRIPTION

[0018] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0019] A first aspect of the present invention provides a composite electromagnetic shielding material, wherein the material includes a multilayer film structure; wherein the multilayer film structure includes a PVDF / MXene single-layer film and a PVDF single-layer film stacked in sequence.

[0020] In a preferred embodiment of the present invention, the total number of layers of the multilayer film structure is N, where N is an integer between 3-25, preferably an integer between 10-18.

[0021] Among them, in the present invention, the total number of layers N of the multilayer film structure can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, etc. When N is an odd number, it is preferred that the PVDF / MXene monolayer film has one more layer than the PVDF monolayer film. By controlling the total number of layers, it is helpful to make the composite electromagnetic shielding material further obtain excellent electromagnetic shielding performance on the basis of maintaining good flexibility.

[0022] In a preferred embodiment of the present invention, in the PVDF / MXene single-layer membrane, the mass ratio of PVDF to MXene is 1:0.2-2, preferably 1:0.5-1.5.

[0023] In a preferred embodiment of the present invention, the thickness of the composite electromagnetic shielding material is 0.3-2 mm, preferably 0.5-1.5 mm.

[0024] In the present invention, if the thickness of the composite electromagnetic shielding material is too large, the flexibility will be reduced, and if the thickness of the composite electromagnetic shielding material is too small, the shielding performance will be reduced. When the thickness of the composite electromagnetic shielding material is within the preferred range, the comprehensive performance of the composite electromagnetic shielding material is better.

[0025] In a preferred embodiment of the present invention, within the range of 8.2-12.4 GHz, the electromagnetic shielding performance of the composite electromagnetic shielding material is between 59-74 dB.

[0026] Among them, in the present invention, the inventors have found through research that multiple stacking of PVDF / MXene single-layer films and PVDF single-layer films can not only significantly improve the electromagnetic shielding performance of the composite electromagnetic shielding material, but also greatly improve the tensile strength of the composite electromagnetic shielding material, which helps to improve the flexibility of the composite electromagnetic shielding material.

[0027] A second aspect of the present invention provides a method for preparing a composite electromagnetic shielding material, wherein the method comprises the following steps:

[0028] (1) evaporating a dispersion containing MXene, PVDF and a solvent into a film to obtain a PVDF / MXene evaporated film;

[0029] (2) subjecting the PVDF / MXene evaporated film to a first hot pressing to obtain a PVDF / MXene single-layer film;

[0030] (3) The PVDF / MXene single-layer film and the PVDF single-layer film are alternately stacked multiple times and then hot-pressed for a second time to obtain a composite electromagnetic shielding material.

[0031] Among them, in the present invention, the inventors have discovered through research that by modifying the PVDF single-layer film with MXene and alternately stacking the PVDF / MXene single-layer film and the PVDF single-layer film multiple times and then hot-pressing them, the composite electromagnetic shielding material can have both good flexibility and excellent electromagnetic shielding properties.

[0032] In step (1):

[0033] In a preferred embodiment of the present invention, the solvent is selected from one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, tetrahydrofuran, dimethyl sulfoxide, and N-methylpyrrolidone, preferably N,N-dimethylformamide and / or N,N-dimethylacetamide.

[0034] In a preferred embodiment of the present invention, the mass ratio of PVDF to MXene is 1:0.2-2, preferably 1:0.5-1.5.

[0035] Among them, in the present invention, the inventors have found through research that when the mass ratio of MXene to PVDF is too large, it is difficult to form a film; when the mass ratio of MXene to PVDF is too small, the shielding performance is difficult to meet the requirements. When the mass ratio of MXene to PVDF is within the above-defined range, the shielding performance of the prepared composite electromagnetic shielding material is better.

[0036] In a preferred embodiment of the present invention, the concentration of PVDF in the dispersion is 10-70 mg / mL, preferably 30-50 mg / mL.

[0037] Among them, in the present invention, the concentration of PVDF in the dispersion is too high, the dispersion is relatively viscous and has poor fluidity, resulting in poor dispersibility of MXene in the dispersion, and poor uniformity of the prepared composite electromagnetic shielding material; the concentration of PVDF in the dispersion is too low, the evaporation time is too long, and the toughness of the prepared composite electromagnetic shielding material is low.

[0038] In a preferred embodiment of the present invention, in order to improve the dispersibility of MXene and PVDF in the solvent, PVDF can be first added to the solvent for ultrasonic treatment, and then MXene is added under stirring and ultrasonic treatment is continued. Preferably, the ultrasonic power of the ultrasonic treatment is 300-500W, and the ultrasonic time is 0.5-2.5h.

[0039] In a preferred embodiment of the present invention, the operating conditions of the evaporation film formation include: the evaporation temperature is 35-55°C, preferably 40-50°C.

[0040] Among them, in the present invention, by controlling the evaporation temperature, the evaporation rate can be controlled, which in turn helps to improve the flexibility of the PVDF / MXene single-layer film and improve the film quality.

[0041] In step (2):

[0042] In a preferred embodiment of the present invention, the operating conditions of the first hot pressing include: hot pressing temperature of 140-220°C, preferably 160-200°C; hot pressing pressure of 5-20MPa, preferably 10-15MPa; hot pressing time of 5-30s, preferably 10-20s.

[0043] Among them, in the present invention, by controlling the operating conditions of the first hot pressing, it is helpful to obtain a PVDF / MXene single-layer film with high flatness and high density.

[0044] In step (3):

[0045] In a preferred embodiment of the present invention, the PVDF single-layer membrane may be a commercially available product, or may be prepared according to the preparation method of the PVDF / MXene single-layer membrane of the present invention after omitting MXene.

[0046] In a preferred embodiment of the present invention, the operating conditions of the second hot pressing include: hot pressing temperature of 140-220°C, preferably 160-200°C; hot pressing pressure of 5-20MPa, preferably 10-15MPa; hot pressing time of 5-30s, preferably 10-20s.

[0047] In the present invention, the purpose of the second hot pressing is to compound the PVDF / MXene monolayer film with the PVDF monolayer film. In order to prevent the PVDF / MXene monolayer film from deforming again during the second hot pressing process, preferably, the operating conditions of the first hot pressing and the second hot pressing are the same.

[0048] In a preferred embodiment of the present invention, the number of layers of the PVDF / MXene single-layer membrane is 2-14 layers, preferably 5-9 layers; the number of layers of the PVDF single-layer membrane is the same as the number of layers of the PVDF / MXene single-layer membrane or one layer less than the number of layers of the PVDF / MXene single-layer membrane.

[0049] The present invention will be described in detail below through examples.

[0050] Example 1

[0051] (1) PVDF was added to DMF for ultrasonic treatment at an ultrasonic power of 400 W and an ultrasonic time of 1 h. Then, MXene was added under magnetic stirring at a mass ratio of PVDF to MXene of 1:0.5, and then ultrasonic treatment was continued for 1.5 h to obtain a dispersion with a PVDF concentration of 40 mg / mL. The dispersion was poured into a glass dish and heated at a constant temperature of 40°C. After DMF evaporated, a PVDF / MXene evaporated film was obtained.

[0052] (2) Peeling the PVDF / MXene evaporated film from the glass dish, placing it in a steel plate mold, and performing the first hot pressing at 15 MPa and 180 °C for 15 s to obtain a PVDF / MXene single-layer film;

[0053] (3) adding PVDF to DMF and subjecting it to ultrasonic treatment at an ultrasonic power of 400 W and an ultrasonic time of 1 h to obtain a PVDF / DMF solution with a concentration of 40 mg / mL; then pouring the PVDF / DMF solution into a glass dish and heating it at a constant temperature of 40° C. to obtain a PVDF evaporated film after DMF evaporates; peeling off the PVDF evaporated film from the glass dish, placing it in a steel plate mold, and hot pressing it at 15 MPa and 180° C. for 15 s to obtain a PVDF monolayer film;

[0054] First, place a layer of PVDF / MXene single-layer membrane in the steel plate mold, and then place another layer of PVDF single-layer membrane, and then repeat the operation, placing a total of 7 layers of PVDF / MXene single-layer membrane and 7 layers of PVDF single-layer membrane. Perform a second hot pressing at 15 MPa and 180°C for 15 seconds to obtain a 14-layer composite electromagnetic shielding material with a total thickness of 1.0 mm.

[0055] Example 2

[0056] (1) PVDF was added to DMF for ultrasonic treatment at an ultrasonic power of 400 W and an ultrasonic time of 1 h. Then, MXene was added under magnetic stirring at a mass ratio of PVDF to MXene of 1:1, and then the ultrasonic treatment was continued for 1.5 h to obtain a dispersion with a PVDF concentration of 30 mg / mL. The dispersion was poured into a glass dish and heated at a constant temperature of 50°C. After DMF evaporated, a PVDF / MXene evaporated film was obtained.

[0057] (2) Peeling the PVDF / MXene evaporated film from the glass dish, placing it in a steel plate mold, and performing the first hot pressing at 12 MPa and 160°C for 10 seconds to obtain a PVDF / MXene single-layer film;

[0058] (3) adding PVDF to DMF and subjecting it to ultrasonic treatment at an ultrasonic power of 400 W and an ultrasonic time of 1 h to obtain a PVDF / DMF solution with a concentration of 30 mg / mL; then pouring the PVDF / DMF solution into a glass dish and heating it at a constant temperature of 50° C. to obtain a PVDF evaporated film after DMF evaporates; peeling off the PVDF evaporated film from the glass dish, placing it in a steel plate mold, and hot pressing it at 12 MPa and 160° C. for 10 s to obtain a PVDF monolayer film;

[0059] First, place a layer of PVDF / MXene single-layer membrane in the steel plate mold, and then place another layer of PVDF single-layer membrane, and then repeat the operation, placing a total of 6 layers of PVDF / MXene single-layer membrane and 5 layers of PVDF single-layer membrane. Perform a second hot pressing at 12 MPa and 160°C for 10 seconds to obtain 11 layers of composite electromagnetic shielding material with a total thickness of 0.8 mm.

[0060] Example 3

[0061] (1) PVDF was added to N,N-dimethylacetamide for ultrasonic treatment at an ultrasonic power of 400 W and an ultrasonic time of 1 h. Then, MXene was added under magnetic stirring at a mass ratio of PVDF to MXene of 1:1.5, and then ultrasonic treatment was continued for 1.5 h to obtain a dispersion with a PVDF concentration of 50 mg / mL. The dispersion was poured into a glass dish and heated at a constant temperature of 45°C. After N,N-dimethylacetamide evaporated, a PVDF / MXene evaporated film was obtained.

[0062] (2) Peeling the PVDF / MXene evaporated film from the glass dish, placing it in a steel plate mold, and performing the first hot pressing at 10 MPa and 200 °C for 13 seconds to obtain a PVDF / MXene single-layer film;

[0063] (3) adding PVDF to N,N-dimethylacetamide and subjecting it to ultrasonic treatment at an ultrasonic power of 400 W and an ultrasonic time of 1 h to obtain a PVDF / N,N-dimethylacetamide solution with a concentration of 50 mg / mL; then pouring the PVDF / N,N-dimethylacetamide solution into a glass dish and heating it at a constant temperature of 45° C. to obtain a PVDF evaporated film after N,N-dimethylacetamide evaporates; peeling off the PVDF evaporated film from the glass dish, placing it in a steel plate mold, and hot pressing it at 10 MPa and 200° C. for 13 seconds to obtain a PVDF monolayer film;

[0064] First, place a layer of PVDF / MXene single-layer membrane in the steel plate mold, and then place another layer of PVDF single-layer membrane, and then repeat the operation, placing a total of 9 layers of PVDF / MXene single-layer membrane and 9 layers of PVDF single-layer membrane. Perform a second hot pressing at 10 MPa and 200°C for 13 seconds to obtain 18 layers of composite electromagnetic shielding material with a total thickness of 1.3 mm.

[0065] Example 4

[0066] (1) PVDF was added to tetrahydrofuran for ultrasonic treatment at an ultrasonic power of 300 W and an ultrasonic time of 2 h. Then, MXene was added under magnetic stirring at a mass ratio of PVDF to MXene of 1:0.2, and then the ultrasonic treatment was continued for 2 h to obtain a dispersion with a PVDF concentration of 20 mg / mL. The dispersion was poured into a glass dish and heated at a constant temperature of 35°C. After the tetrahydrofuran evaporated, a PVDF / MXene evaporated film was obtained.

[0067] (2) Peeling the PVDF / MXene evaporated film from the glass dish, placing it in a steel plate mold, and performing the first hot pressing at 7 MPa and 220 °C for 25 seconds to obtain a PVDF / MXene single-layer film;

[0068] (3) adding PVDF to tetrahydrofuran and subjecting it to ultrasonic treatment at an ultrasonic power of 300 W for 2 h to obtain a PVDF / tetrahydrofuran solution with a concentration of 20 mg / mL; then pouring the PVDF / tetrahydrofuran solution into a glass dish and heating it at a constant temperature of 35° C. to obtain a PVDF evaporated film after the tetrahydrofuran evaporates; peeling off the PVDF evaporated film from the glass dish, placing it in a steel plate mold, and hot pressing it at 7 MPa and 220° C. for 25 s to obtain a PVDF monolayer film;

[0069] First, place a layer of PVDF / MXene single-layer membrane in the steel plate mold, and then place another layer of PVDF single-layer membrane, and then repeat the operation, placing a total of 3 layers of PVDF / MXene single-layer membrane and 3 layers of PVDF single-layer membrane. Perform a second hot pressing at 7MPa and 220°C for 25s to obtain a 6-layer composite electromagnetic shielding material with a total thickness of 0.4mm.

[0070] Example 5

[0071] (1) PVDF was added to dimethyl sulfoxide for ultrasonic treatment at an ultrasonic power of 500 W and an ultrasonic time of 0.5 h. Then, MXene was added under magnetic stirring at a mass ratio of PVDF to MXene of 1:2, and then the ultrasonic treatment was continued for 0.5 h to obtain a dispersion with a PVDF concentration of 60 mg / mL. The dispersion was poured into a glass dish and heated at a constant temperature of 55°C. After the dimethyl sulfoxide evaporated, a PVDF / MXene evaporated film was obtained.

[0072] (2) Peeling the PVDF / MXene evaporated film from the glass dish, placing it in a steel plate mold, and performing the first hot pressing at 18 MPa and 140 °C for 5 seconds to obtain a PVDF / MXene single-layer film;

[0073] (3) adding PVDF to dimethyl sulfoxide and subjecting it to ultrasonic treatment at an ultrasonic power of 500 W and an ultrasonic time of 0.5 h to obtain a PVDF / dimethyl sulfoxide solution with a concentration of 60 mg / mL; then pouring the PVDF / dimethyl sulfoxide solution into a glass dish and heating it at a constant temperature of 55° C. to obtain a PVDF evaporated film after the dimethyl sulfoxide evaporates; peeling off the PVDF evaporated film from the glass dish, placing it in a steel plate mold, and hot pressing it at 18 MPa and 140° C. for 5 seconds to obtain a PVDF monolayer film;

[0074] First, place a layer of PVDF / MXene single-layer film in the steel plate mold, and then place another layer of PVDF single-layer film, and then repeat the operation, placing a total of 12 layers of PVDF / MXene single-layer film and 12 layers of PVDF single-layer film. Perform a second hot pressing at 18 MPa and 140°C for 5 seconds to obtain 24 layers of composite electromagnetic shielding material with a total thickness of 2.0 mm.

[0075] Test Example 1

[0076] The cross section of the composite electromagnetic shielding material prepared in Examples 1-5 was partially scanned by electron microscope. The scanning results are as follows: Figure 1-5 shown.

[0077] Depend on Figure 1-5It can be seen that the composite electromagnetic shielding material prepared in the present invention has an obvious and clear layered structure, which can reflect alternating electromagnetic waves multiple times, increase the propagation path of electromagnetic waves and form a reflection-absorption-re-reflection shielding mechanism, thereby improving the electromagnetic shielding performance of the composite material.

[0078] Test Example 2

[0079] The electromagnetic shielding performance of the composite electromagnetic shielding materials prepared in Examples 1-5 was tested using a vector network analyzer (Keysight N5247B, USA) in the 8.2-12.4 GHz frequency band (X band). The test results are shown in FIG. Figure 6 shown.

[0080] Depend on Figure 6 It can be seen that within the range of 8.2-12.4 GHz, the electromagnetic shielding performance of the composite electromagnetic shielding material is basically stable, between 59-74 dB, and increases with the increase of frequency.

[0081] Test Example 3

[0082] The tensile properties of the composite electromagnetic shielding materials prepared in Examples 1-5 were tested using a universal material testing machine (INSTRON 5943). The test results are as follows: Figure 7 shown.

[0083] Depend on Figure 7 It can be seen that the ultimate stress of the composite electromagnetic shielding material prepared in the present invention is between 35-50 MPa, and the increase in the ultimate stress indicates that the multi-layer design strategy in the present invention is helpful to improve the mechanical tensile properties of the composite electromagnetic shielding material.

[0084] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A composite electromagnetic shielding material, characterized in that: The material includes a multilayer film structure, wherein the multilayer film structure includes a PVDF / MXene single-layer film and a PVDF single-layer film stacked in sequence.

2. The composite electromagnetic shielding material according to claim 1, wherein: The total number of layers of the multilayer film structure is N, where N is an integer between 3-25, preferably an integer between 10-18.

3. The composite electromagnetic shielding material according to claim 1 or 2, wherein: In the PVDF / MXene single-layer film, the mass ratio of PVDF to MXene is 1:0.2-2, preferably 1:0.5-1.

5.

4. The composite electromagnetic shielding material according to any one of claims 1 to 3, wherein: The thickness of the composite electromagnetic shielding material is 0.3-2 mm, preferably 0.5-1.5 mm.

5. The composite electromagnetic shielding material according to any one of claims 1 to 4, wherein: In the range of 8.2-12.4 GHz, the electromagnetic shielding performance of the composite electromagnetic shielding material is between 59-74 dB.

6. A method for preparing a composite electromagnetic shielding material, characterized in that: The method comprises the following steps: (1) evaporating a dispersion containing MXene, PVDF and a solvent into a film to obtain a PVDF / MXene evaporated film; (2) subjecting the PVDF / MXene evaporated film to a first hot pressing to obtain a PVDF / MXene single-layer film; (3) The PVDF / MXene single-layer film and the PVDF single-layer film are alternately stacked multiple times and then hot-pressed for a second time to obtain a composite electromagnetic shielding material.

7. The preparation method according to claim 6, wherein: The solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, dimethyl sulfoxide, and N-methylpyrrolidone; Preferably, the mass ratio of PVDF to MXene is 1:0.2-2, preferably 1:0.5-1.5; Preferably, in the dispersion, the concentration of PVDF is 10-70 mg / mL, preferably 30-50 mg / mL; Preferably, the operating conditions of the evaporation film formation include: an evaporation temperature of 35-55°C, preferably 40-50°C.

8. The preparation method according to claim 6 or 7, wherein: The operating conditions of the first hot pressing include: hot pressing temperature of 140-220° C., preferably 160-200° C.; hot pressing pressure of 5-20 MPa, preferably 10-15 MPa; hot pressing time of 5-30 s, preferably 10-20 s.

9. The preparation method according to any one of claims 6 to 8, wherein: The operating conditions of the second hot pressing include: hot pressing temperature of 140-220° C., preferably 160-200° C.; hot pressing pressure of 5-20 MPa, preferably 10-15 MPa; hot pressing time of 5-30 s, preferably 10-20 s.

10. The preparation method according to any one of claims 6 to 9, wherein: The number of layers of the PVDF / MXene single-layer membrane is 2-14 layers, preferably 5-9 layers; the number of layers of the PVDF single-layer membrane is the same as the number of layers of the PVDF / MXene single-layer membrane or one layer less than the number of layers of the PVDF / MXene single-layer membrane.

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