Method for preparing mxene / liquid metal-based flexible composite film and application thereof

Abstract

The application discloses a preparation method of a MXene / liquid metal-based flexible composite film and application thereof, and belongs to the technical field of nanocomposites. The method is as follows: a first dispersion liquid is prepared by mixing a MXene water dispersion liquid and a bacterial cellulose water dispersion liquid; a second dispersion liquid is prepared by mixing a PEDOT:PSS water-based diluent and liquid metal and then performing ice water bath ultrasonic crushing; an intermediate film is obtained by alternately using the first dispersion liquid and the second dispersion liquid to perform vacuum filtration; and the composite film is prepared by performing heat pressing and shaping on the intermediate film. The composite film is constructed by a layered heterostructure to form a continuous conductive network, and has energy storage and sensing functions. The preparation process is simple and has good repeatability. The micro supercapacitor prepared based on the composite film can realize high-voltage output, the flexible pressure sensor prepared has a wide detection range and high sensitivity, and the application prospect of the composite film in the field of flexible electronics is wide.

Description

Technical Field

[0001] This invention relates to the field of nanocomposite materials technology, specifically to a method for preparing an MXene / liquid metal-based flexible composite membrane and its application. Background Technology

[0002] With the rapid development of flexible electronics technology, wearable health monitoring devices, bionic electronic skin, flexible energy storage devices, and other products are emerging. The market demand for core materials that combine high flexibility, high conductivity, and multifunctional integration is becoming increasingly urgent. These flexible electronic devices not only require materials to maintain stable electrical properties under repeated bending, stretching, and other deformations, but also need to integrate multiple functions such as sensing, energy storage, and anti-interference to meet the needs of complex application scenarios. Existing single-function materials are no longer sufficient to meet this development trend.

[0003] MXene, a novel two-dimensional layered material that has attracted much attention in recent years, has shown broad application prospects in the field of flexible electronics due to its high conductivity and rich surface chemical properties. Assembling MXene nanosheets into macroscopic thin films is a prerequisite for its application. However, MXene nanosheets are prone to stacking and agglomeration due to van der Waals forces, and the functions of a single MXene thin film are relatively limited, making it difficult to achieve synergistic effects of multiple properties.

[0004] Liquid metals (such as Ga, In, and their alloys) exhibit unique advantages: their fluid dynamic properties at room temperature endow them with excellent deformation adaptability, while also possessing high electrical and thermal conductivity and good biocompatibility. These properties make them ideal choices for flexible conductive materials. Currently, liquid metals have been applied in various scenarios in the field of flexible electronics, such as the fabrication of stretchable conductors, flexible sensors, energy storage devices, and reconfigurable antennas, effectively solving the problems of easy breakage and unstable performance of traditional rigid conductive materials in flexible devices.

[0005] To combine the highly conductive framework properties of MXene with the flexible conductivity of liquid metals, researchers have conducted extensive studies on composite modification in recent years. For example, liquid metals have been encapsulated within MXene networks through coordination induction (EnergyEnviron. Sci., 2022, 15, 5240), or liquid metals have been introduced into MXene / AgNW (silver nanowire) structures as bridges to enhance interfacial interactions (Adv. Funct. Mater. 2023, 33, 2301587). While these methods have improved specific properties of the materials to some extent, they still have significant limitations.

[0006] From the perspective of existing technological achievements, current research on MXene and liquid metal composite materials is mostly focused on single-function development or specific morphology preparation. On the one hand, patented technologies mainly focus on the development of composite hydrogels (such as patents CN119684737A and CN119490699A), or design for single functions such as electromagnetic shielding (CN119306973A), thermal conductivity (CN120193192A), and sensing (CN120289938A), lacking multi-functional integrated design and failing to meet the demand for multi-functional synergy of materials in flexible electronic devices. On the other hand, in existing composite processes, liquid metal is prone to agglomeration due to surface tension, and the interfacial bonding force between MXene nanosheets and liquid metal is weak, resulting in poor structural uniformity and insufficient long-term stability of the composite material, which limits its industrial application.

[0007] Therefore, developing a simple, low-cost, and multifunctional integrated method for preparing MXene / liquid metal-based composite membranes has significant research value and application prospects. Summary of the Invention

[0008] To address the problems of limited functionality, poor structural uniformity, and complex fabrication processes in existing MXene / liquid metal composite materials, this invention aims to provide a method for preparing an MXene / liquid metal-based flexible composite membrane and its applications. Specifically, the first objective of this invention is to simplify the fabrication process. MXene nanosheets and liquid metal nanoparticles are composited using a vacuum filtration layer-by-layer assembly combined with hot-pressing to create an integrated flexible composite membrane with both high energy storage and high-sensitivity sensing capabilities. Simultaneously, the dispersion of the liquid metal is controlled by PEDOT:PSS, the interlayer spacing of MXene is controlled by bacterial cellulose (BC) to improve the mechanical flexibility of the composite membrane, and a continuous conductive network is constructed using hot-pressing to optimize the microstructure of the composite material, thereby enhancing the structural uniformity and mechanical-electrical stability of the composite membrane. Furthermore, the second objective of this invention is to develop high-performance application devices based on this composite membrane, particularly enabling the fabricated micro-supercapacitor to possess excellent specific capacitance and high voltage output performance, and enabling the fabricated flexible pressure sensor to have a wide detection range and high sensitivity.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] I. Preparation of MXene / Liquid Metal-based Flexible Composite Membranes

[0011] This invention first discloses a method for preparing an MXene / liquid metal-based flexible composite film, comprising the following steps:

[0012] Step 1: Prepare the first dispersion (MXene / bacterial cellulose (BC) mixture)

[0013] Monolayer or few-layer MXene nanosheets were added to deionized water and stirred to disperse, resulting in an MXene aqueous dispersion with a concentration of 1-20 mg / mL. A bacterial cellulose (BC) aqueous dispersion with a concentration of 1-8 mg / mL was prepared. The bacterial cellulose aqueous dispersion was added to the MXene aqueous dispersion and mixed thoroughly to obtain a first dispersion, wherein the mass ratio of MXene to bacterial cellulose was 0.1-10:1.

[0014] Step 2: Prepare the second dispersion (a mixture of PEDOT:PSS / liquid metal nanoparticles).

[0015] Prepare an aqueous dilution of PEDOT:PSS with a concentration of 0.3~5 mg / mL; add liquid metal to the aqueous dilution of PEDOT:PSS, and place the resulting mixed solution in an ice-water bath at 0~10℃. Perform ultrasonic cavitation treatment using an ultrasonic cell disruptor with an ultrasonic power ≥200W and an ultrasonic time of 10~30 min to break the bulk liquid metal into nanoparticles with a diameter of 100~800 nm, thus obtaining an aqueous dispersion in which PEDOT:PSS and liquid metal nanoparticles are uniformly mixed, i.e., the second dispersion, wherein the concentration of liquid metal is 0.5~15 mg / mL.

[0016] Step 3: Layer-by-layer assembly to prepare the intermediate membrane

[0017] A layered intermediate membrane is obtained by alternating the use of a first dispersion and a second dispersion through vacuum filtration. Specifically, the first and second dispersions are alternately added to a vacuum filtration device equipped with a microporous membrane. After the previous dispersion is completely filtered and no obvious residual solution remains on the membrane, the next dispersion is added. This process is repeated until a preset number of layers is reached, forming a layered intermediate membrane. During the alternating filtration process, the volume ratio of the first dispersion to the second dispersion used in each layer is 0.5 to 2:1, and the total number of composite membrane layers can be set according to actual needs.

[0018] Step 4: Hot pressing and shaping to prepare composite film

[0019] The intermediate membrane obtained in step 3 is subjected to hot pressing treatment, with the hot pressing temperature set at 30~60℃, the pressure at 0.5~3MPa, and the time at 5~15min. After hot pressing, it is dried at room temperature to obtain the MXene / liquid metal-based flexible composite membrane.

[0020] Furthermore, the liquid metal includes Ga. 74.5 In 25.5 Ga 68.5 In 21.5 Sn1, Ga 21 In 64 Zn 15At least one of them.

[0021] Furthermore, MXene nanosheets can be obtained by chemically etching the MAX phase, for example, by using HCl+LiF etching to remove the Al phase of the Ti3AlC2 intermediate layer, followed by ultrasonic exfoliation to obtain MXene nanosheets.

[0022] II. Fabrication of Micro Supercapacitors Based on Composite Films

[0023] The present invention further provides a high-performance micro supercapacitor, which is made of the aforementioned MXene / liquid metal-based flexible composite film, and the specific preparation process is as follows:

[0024] Substrate adhesion: The MXene / liquid metal-based flexible composite film is adhered to a single-sided adhesive tape. The single-sided adhesive tape is preferably a polyethylene terephthalate (PET) tape with a thickness of 100μm~200μm.

[0025] Sputtered current collector layer: A current collector layer is sputtered onto the surface of the composite film using magnetron sputtering technology. The current collector layer is preferably an Au layer with a thickness of 50~500nm.

[0026] Laser-marked interdigitated electrodes: Interdigitated patterns are etched on a composite film with a current collector layer using a laser marking method to obtain interdigitated electrodes; wherein the laser marking power is 300mW~5000mW, the marking speed is 3mm / s~30mm / s, the interdigitated electrode interdigitated width is 100~1000μm, the interdigitated spacing is 100~500μm, and the interdigitated length is 8~10mm.

[0027] Coating with gel electrolyte: A layer of gel electrolyte is uniformly coated on the surface of the interdigitated electrode. The gel electrolyte is preferably a polyvinyl alcohol (PVA) / ionic liquid conductive gel; wherein the PVA concentration is 0.1~0.4 g / mL, and the ionic liquid is selected from PYR. 14 One of TFSI (N-butyl-N-methylpyrrolidone bis(trifluoromethanesulfonyl)imide), EMIM:TFSI (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide), and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), with a concentration of 1~21 mol / L.

[0028] Encapsulation and molding: Wires are connected to both ends of the electrodes, and then the entire structure is encapsulated using a polymer film to obtain a miniature supercapacitor.

[0029] III. Fabrication of Flexible Pressure Sensors Based on Composite Membranes

[0030] This invention further provides a flexible pressure sensor, which uses the aforementioned MXene / liquid metal-based flexible composite film as the sensitive layer. The specific preparation process is as follows:

[0031] Preparation of a polymer substrate with a conductive layer: A polymer film is selected as the substrate material, preferably a polyimide (PI) film or a polyethylene terephthalate (PET) film, with a thickness preferably of 50-200 μm. A conductive layer is prepared on one side of the polymer film using methods such as magnetron sputtering, electron beam evaporation, or sputtering deposition to form a polymer substrate with a conductive layer. The conductive layer is selected from either an Au layer or an ITO (indium tin oxide) layer, with a thickness controlled to be 100-500 nm.

[0032] Assemble the sensor sandwich structure: Take two polymer substrates with conductive layers and place them opposite each other. Cut the MXene / liquid metal-based flexible composite film into a shape that matches the size of the substrate and place it between the conductive layers of the two substrates to form a sandwich structure of "polymer substrate-conductive layer-composite film-conductive layer-polymer substrate".

[0033] Leading out electrode wires: Leading out electrode wires from the edges of the upper and lower conductive layers respectively, thus obtaining a flexible pressure sensor.

[0034] This invention involves adding bulk liquid metal to a PEDOT:PSS aqueous dilution solution and subjecting it to ultrasonic cavitation. During this process, PEDOT:PSS can form a cross-linked structure with the liquid metal nanoparticles, thereby inhibiting nanoparticle aggregation and improving their dispersion stability. Simultaneously, the inherent conductivity of PEDOT:PSS provides additional conductive pathways between the liquid metal nanoparticles. After uniformly mixing with bacterial cellulose in the MXene nanosheet system, the bacterial cellulose can insert into the MXene interlayers, further expanding the interlayer spacing and providing more active sites, thus enhancing the material's energy storage performance. The addition of bacterial cellulose also effectively improves the mechanical flexibility of the composite membrane. Furthermore, the composite membrane, formed through vacuum filtration, layer-by-layer assembly, and hot pressing, provides greater compression space under external pressure. When pressure is applied, the interlayer gaps shrink, and the conductive network contact between MXene nanosheets and liquid metal nanoparticles becomes more complete. This results in a pressure sensor based on this composite membrane exhibiting advantages such as wide measurement range and high sensitivity.

[0035] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0036] The MXene / liquid metal-based flexible composite membrane provided by this invention can simultaneously realize multiple functions such as energy storage and sensing. It is formed by layering MXene nanosheets, bacterial cellulose, and PEDOT:PSS dispersed liquid metal nanoparticles to create a layered heterostructure, resulting in a continuous variable conductive network within the structure. This significantly enhances energy storage characteristics while endowing it with excellent sensing performance. Furthermore, the composite membrane provided by this invention has advantages such as simple preparation method and good reproducibility. Moreover, the micro supercapacitor assembled from interdigitated electrodes prepared based on this composite membrane can achieve high-voltage output, demonstrating significant comprehensive application advantages. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the preparation process of the MXene / liquid metal-based flexible composite membrane in Example 1.

[0038] Figure 2 The EGaIn liquid metal in Example 1 in deionized water ( Figure 2 a) and PEDOT:PSS aqueous dilution ( Figure 2 Optical photograph of (b) after ultrasonic dispersion and standing for 24 hours.

[0039] Figure 3 This is an optical photograph of the MXene / liquid metal-based flexible composite film prepared in Example 1 under bending conditions.

[0040] Figure 4 This is an electron microscope image of the multilayer microstructure of the cross-section of the MXene / liquid metal-based flexible composite membrane prepared in Example 1.

[0041] Figure 5 This is a schematic diagram of the fabrication process for a micro supercapacitor based on an MXene / liquid metal-based flexible composite film in Example 2.

[0042] Figure 6 The graph shows the cyclic volt-ampere characteristics of the micro supercapacitor prepared in Example 2 within a voltage window of 0-2V.

[0043] Figure 7 The figure shows the AC impedance spectrum of the micro supercapacitor prepared in Example 2, with the inset being a magnified view of a portion thereof.

[0044] Figure 8 This is a schematic diagram of the pressure sensor prepared in Example 3.

[0045] Figure 9 The graph shows the relationship between the relative change in current (i.e., the ratio of the change in current to the initial value of current) of the pressure sensor prepared in Example 3 and the pressure. The red line in the graph is a piecewise linear fitting line, and the slope represents the response sensitivity of the relative change in current to pressure within that interval.

[0046] Figure 10 An optical photograph of the MXene / liquid metal-based flexible composite membrane prepared using a pure MXene aqueous dispersion without bacterial cellulose as the first dispersion in Comparative Example 1, showing the membrane breaking under slight bending. Detailed Implementation

[0047] 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.

[0048] Example 1

[0049] like Figure 1 As shown, an MXene / liquid metal-based flexible composite membrane was prepared by vacuum filtration using a layer-by-layer assembly strategy. The specific steps are as follows:

[0050] Step 1: Preparation of the first dispersion

[0051] Prepare 8 mL of MXene aqueous dispersion with a concentration of 5 mg / mL, add 8.9 mL of BC aqueous dispersion with a concentration of 3 mg / mL to the MXene aqueous dispersion, and stir well to obtain the first dispersion.

[0052] Step 2: Preparation of the second dispersion

[0053] Add 3 mL of a 1.3% (w / w) PEDOT:PSS aqueous solution to 40 mL of deionized water to prepare a 1 mg / mL PEDOT:PSS aqueous dilution. Then add 320 mg of EGaIn (eutectic gallium indium alloy, i.e., Ga) to the PEDOT:PSS aqueous dilution. 74.5 In 25.5 The resulting mixed solution was placed in an ice-water bath at 4°C and subjected to ultrasonic cavitation treatment using an ultrasonic cell disruptor. The ultrasonic power was set to 300W and the ultrasonic time to 15min, which caused the blocky EGaIn to split into nanoparticles, thus obtaining an aqueous dispersion in which PEDOT:PSS and EGaIn liquid metal nanoparticles were uniformly mixed, i.e., the second dispersion. Figure 2 Demonstrates the role of EGaIn liquid metal in deionized water ( Figure 2 a) and PEDOT:PSS aqueous dilution ( Figure 2 In b), the dispersibility of EGaIn liquid metal nanoparticles after ultrasonic dispersion and standing for 24 hours was compared, and EGaIn liquid metal nanoparticles could maintain better dispersion in PEDOT:PSS aqueous dilution.

[0054] Step 3: Layer-by-layer assembly to prepare the intermediate membrane

[0055] A layered intermediate membrane was obtained by alternating the use of a first dispersion and a second dispersion for vacuum filtration. Specifically, the first and second dispersions were alternately added to a vacuum filtration device equipped with a microporous filter membrane. After the previous dispersion was completely filtered and there was no obvious residual solution on the filter membrane, the next dispersion was added. This process was repeated until seven intermediate membranes were formed. The specific number of layers and the amounts used were as follows: first layer, 2 mL of the first dispersion; second layer, 1.5 mL of the second dispersion; third layer, 2 mL of the first dispersion; fourth layer, 1.5 mL of the second dispersion; fifth layer, 2 mL of the first dispersion; sixth layer, 1.5 mL of the second dispersion; and seventh layer, 2 mL of the first dispersion.

[0056] Step 4: Hot pressing and shaping to prepare composite film

[0057] The intermediate membrane obtained in step 3 was subjected to hot pressing at a pressure of 0.5 MPa, a temperature of 40°C, and a time of 15 min. After hot pressing, it was dried at room temperature to obtain the MXene / liquid metal-based flexible composite membrane. The conductivity of this composite membrane is 640 S / cm. A photograph of the actual product is shown below. Figure 3 As shown, the cross-sectional electron microscope image of the composite membrane is as follows. Figure 4 As shown.

[0058] Example 2

[0059] like Figure 5 As shown, this embodiment utilizes the MXene / liquid metal-based flexible composite film (MXene / EGaIn composite film) from Example 1 to fabricate a flexible micro supercapacitor. The steps are as follows:

[0060] First, the MXene / EGaIn composite film obtained in Example 1 was cut into squares with a side length of 15 mm and adhered to a single-sided PET tape with a thickness of 150 μm. Then, a 150 nm thick Au layer was sputtered onto the surface of the composite film as a current collector layer using magnetron sputtering. Subsequently, interdigitated patterns were etched on the composite film with the current collector layer using femtosecond laser marking (laser marking power of 350 mW, marking speed of 4 mm / s, marking times of 4 times) to obtain interdigitated electrodes. The interdigitated electrodes had an interdigitated width of 600 μm, an interdigitated spacing of 150 μm, and an interdigitated length of 10 mm. Then, LiTFSi (18.09 g) was dissolved in deionized water (3 mL) to form a 21 mol / L LiTFSi solution. Under heating at 95 °C and magnetic stirring, 1.2 g of PVA was slowly added, and stirring was continued until a clear PVA / LiTFSi gel electrolyte was obtained. Finally, PVA / LiTFSI gel electrolyte is coated on the surface of the interdigitated electrodes, wires are connected to both ends of the electrodes, and the entire structure is encapsulated with PET film to obtain a micro supercapacitor.

[0061] The prepared micro-supercapacitor was connected to a CHI660E electrochemical workstation at room temperature for cyclic voltammetry testing. The operating voltage window was set to 0.2 V. The obtained voltammetric characteristic curve is shown below. Figure 6 As shown in the figure. Experimental results show that the areal capacitance of the micro supercapacitor is 66.78 mF / cm². 2 The AC impedance spectrum obtained from the test is as follows: Figure 7 As shown, the equivalent resistance is 7Ω.

[0062] Example 3

[0063] This embodiment utilizes the MXene / liquid metal-based flexible composite membrane (MXene / EGaIn composite membrane) from Example 1 to fabricate a flexible pressure sensor. The steps are as follows:

[0064] First, a 200 nm Au layer is sputtered onto a 200 μm thick PI film using a magnetron sputtering machine to form a PI substrate with a conductive layer for electrical signal transmission in the pressure sensor.

[0065] Two PI substrates (1cm × 1cm square) with conductive layers were prepared and placed opposite each other. The MXene / EGaIn composite film obtained in Example 1 was cut into a shape matching the substrate size and placed between the conductive layers of the two substrates, forming a sandwich structure of "polymer substrate-conductive layer-composite film-conductive layer-polymer substrate". Copper wires were led out from the edges of the upper and lower conductive layers respectively to obtain a flexible pressure sensor, the structure of which is as follows. Figure 8 As shown.

[0066] When pressure is applied to the upper surface of the flexible pressure sensor, the thickness of the MXene / EGaIn composite film and the contact pathways between the internal MXene nanosheets and EGaIn liquid metal particles will change. The greater the pressure, the smaller the thickness of the composite film, the more internal conductive pathways, the smaller the resistance value, resulting in a larger output current value. Figure 9 The figure shows the relative change of current in a flexible pressure sensor as a function of pressure. This flexible pressure sensor has a wide detection range and high sensitivity.

[0067] Comparative Example 1

[0068] A pure MXene aqueous dispersion without bacterial cellulose was used as the first dispersion to compare the effect of mixed bacterial cellulose on improving the mechanical flexibility of MXene / liquid metal-based multifunctional flexible composite membranes. The specific steps are as follows:

[0069] Step 1: Preparation of the first dispersion

[0070] Prepare 8 mL of MXene aqueous dispersion with a concentration of 5 mg / mL to obtain the first dispersion.

[0071] Step 2: Preparation of the second dispersion

[0072] Same as step 2 in Example 1.

[0073] Step 3: Layer-by-layer assembly to prepare the intermediate membrane

[0074] Same as step 3 in Example 1.

[0075] Step 4: Hot pressing and shaping to prepare composite film

[0076] Same as step 4 in Example 1.

[0077] The BC-free MXene / liquid metal-based flexible composite membrane prepared in this comparative example is prone to fracture under bending, exhibiting poor mechanical flexibility. A photograph of the membrane showing fracture under slight bending is shown below. Figure 10 As shown.

[0078] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an MXene / liquid metal-based flexible composite membrane, characterized in that, Includes the following steps: Step 1: Preparation of the first dispersion: Prepare an aqueous dispersion of MXene and an aqueous dispersion of bacterial cellulose, and mix them evenly to obtain a first dispersion. Step 2: Preparation of the second dispersion Prepare an aqueous diluent for PEDOT:PSS; add liquid metal to the aqueous diluent for PEDOT:PSS, and in an ice-water bath, use ultrasonic cavitation to break down the liquid metal to form an aqueous dispersion in which PEDOT:PSS and liquid metal nanoparticles are uniformly mixed, i.e., the second dispersion. Step 3: Layer-by-layer assembly to prepare the intermediate membrane A layer-by-layer assembled intermediate membrane was obtained by vacuum filtration using alternating first and second dispersions. Step 4: Hot pressing and shaping to prepare composite film The intermediate film obtained in step 3 is subjected to hot pressing; after hot pressing, it is dried at room temperature to obtain an MXene / liquid metal-based flexible composite film.

2. The method for preparing the MXene / liquid metal-based flexible composite membrane according to claim 1, characterized in that: In step 1, the concentration of the MXene aqueous dispersion is 1-20 mg / mL, the concentration of the bacterial cellulose aqueous dispersion is 1-8 mg / mL, and the mass ratio of MXene to bacterial cellulose in the first dispersion is 0.1-10:1; in step 2, the concentration of the PEDOT:PSS aqueous dilution is 0.3-5 mg / mL, and the liquid metal includes Ga. 74.5 In 25.5 Ga 68.5 In 21.5 Sn1, Ga 21 In 64 Zn 15 At least one of the following, the concentration of liquid metal in the resulting second dispersion is 0.5~15 mg / mL.

3. The method for preparing the MXene / liquid metal-based flexible composite film according to claim 1, characterized in that, In step 2, the temperature of the ice-water bath is 0~10℃, the ultrasonic power of the ultrasonic cavitation is ≥200W, the ultrasonic time is 10~30min, and the diameter of the liquid metal nanoparticles obtained after ultrasonic cavitation is 100~800nm; in step 4, the temperature of the hot pressing treatment is 30~60℃, the pressure is 0.5~3MPa, and the time is 5~15min.

4. The method for preparing the MXene / liquid metal-based flexible composite film according to claim 1, characterized in that, The preparation method of the intermediate membrane in step 3 is as follows: the first dispersion and the second dispersion are alternately added to a vacuum filtration device equipped with a microporous filter membrane. After the previous dispersion is completely filtered and there is no obvious residual solution on the filter membrane, the next dispersion is added. The operation is repeated until the preset number of layers is reached to form a layer-by-layer assembled intermediate membrane. In the process of alternating filtration, the mass ratio of the first dispersion to the second dispersion used in a single layer is 0.5 to 2:

1. The total number of composite membrane layers is set according to actual needs.

5. An MXene / liquid metal-based flexible composite membrane prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the MXene / liquid metal-based flexible composite membrane of claim 5 in a micro supercapacitor or flexible pressure sensor.

7. A miniature supercapacitor, characterized in that: The MXene / liquid metal-based flexible composite film described in claim 5 is used as the core electrode material.

8. The micro supercapacitor according to claim 7, characterized in that, The fabrication process of the micro supercapacitor is as follows: the MXene / liquid metal-based flexible composite film is adhered to a single-sided adhesive tape; a current collector layer is sputtered on the surface of the composite film using magnetron sputtering technology; interdigitated patterns are etched on the composite film with the current collector layer using laser marking to obtain interdigitated electrodes; a gel electrolyte is coated on the surface of the interdigitated electrodes, wires are connected to both ends of the electrodes, and the overall structure is encapsulated using a polymer film to obtain the micro supercapacitor.

9. A flexible pressure sensor, characterized in that: The MXene / liquid metal-based flexible composite membrane described in claim 5 is used as the sensitive layer.

10. The flexible pressure sensor according to claim 9, characterized in that, The fabrication process of the flexible pressure sensor is as follows: a polymer film is selected as the substrate material, and a conductive layer is prepared on one side of the polymer film to form a polymer substrate with a conductive layer; two polymer substrates with conductive layers are taken and their conductive layers are placed opposite each other, and an MXene / liquid metal-based flexible composite film is placed between the conductive layers of the two substrates; electrode wires are led out from the edges of the upper and lower conductive layers respectively to obtain the flexible pressure sensor.

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