Electromagnetic shielding composite film with controllable electric-magnetic gradient, preparation method and application thereof

Abstract

The invention discloses an electromagnetic shielding composite film with controllable electric-magnetic gradient, a preparation method and application thereof. The electromagnetic shielding composite film with a controllable electric-magnetic double-gradient structure is prepared through a height-controllable vacuum-assisted suction filtration method, the upper layer of the electric-magnetic double-gradient network structure is composed of a magnetic double-metal hydroxide nanosheet (at) MXene compound, the part provides electric-magnetic synergistic loss, an impedance matching layer is formed, and the electromagnetic shielding composite film is used for conducting electromagnetic shielding on the magnetic double-metal hydroxide nanosheet (at) MXene compound. And the lower layer is formed by pure MXene with high conductivity and is used as an efficient shielding layer. An electric-magnetic dual-gradient network formed by the impedance matching layer and the conductive shielding layer and a large number of electromagnetic heterogeneous interfaces can construct an electric-magnetoelectric-magnetic loss synergistic loss effect and induce polarization loss. The impedance matching layer and the efficient shielding layer in the electric-magnetic double-gradient structure effectively construct an absorption-reflection-reabsorption electromagnetic wave loss mechanism. The obtained composite film shows ultrahigh electromagnetic interference shielding effectiveness (EMI SE) and low electromagnetic wave reflectivity at the same time.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding materials technology, and in particular to an electromagnetic shielding composite film with a controllable electromagnetic gradient, its preparation method, and its application. Background Technology

[0002] With the rapid development of 5G, the Internet of Things, and high-density integrated electronic technologies, electromagnetic interference and electromagnetic radiation pollution have become significant factors affecting the reliability of electronic devices, information security, and human health. Developing high-performance electromagnetic shielding materials is crucial to addressing these challenges.

[0003] Traditional metal-based shielding materials (such as copper, silver, nickel, and their alloys) rely on their high conductivity, primarily using reflection mechanisms to shield electromagnetic waves. However, these materials suffer from inherent drawbacks such as high density, susceptibility to corrosion, poor flexibility, and complex processing, making it difficult to meet the urgent need for lightweight, ultra-thin, and bendable shielding materials in modern flexible electronic devices. In recent years, novel two-dimensional materials like MXene (such as Ti3C2T) have emerged as promising alternatives. x Due to its excellent intrinsic conductivity and abundant surface functional groups, MXene has shown great potential in the preparation of thin, high-performance electromagnetic shielding composite materials. However, single MXene-based materials typically exhibit excessively high dielectric constants and conductivity, leading to a severe impedance mismatch between them and free space. This causes most incident electromagnetic waves to be reflected from their surface, generating strong secondary electromagnetic pollution and limiting their application in scenarios requiring low-reflection shielding.

[0004] The prior art CN202122402697.1 discloses an MXene-based electromagnetic shielding composite film with a conductive gradient structure and its preparation method, and CN202311382518.1 discloses an electromagnetic shielding composite material and its preparation method. However, the above prior art does not explain the dual gradient.

[0005] To overcome the limitations of a single electrical loss mechanism, researchers have attempted to combine MXene with magnetic components (such as ferrite and metallic magnetic powder) to construct an electromagnetic synergistic loss mechanism within the material and optimize impedance matching. Studies have shown that this electro / magnetic composite strategy effectively enhances electromagnetic wave attenuation and reduces reflection. However, in most reported composite systems, conductive and magnetic fillers are typically dispersed randomly and homogeneously, resulting in a spatially uniform distribution of their electromagnetic parameters. This homogeneous structure makes it difficult to finely and continuously control impedance, often sacrificing some overall shielding effectiveness while enhancing absorption. Achieving both high shielding effectiveness and low reflectivity simultaneously in ultrathin materials remains a significant challenge. Material structure design is considered crucial to reconcile the contradiction between efficient electromagnetic shielding and low reflection characteristics. Currently, various structures (such as isolation structures, porous structures, and layered structures) have been designed to reconcile the conflict between efficient EMI shielding and low reflection. While isolation and porous structures can effectively reduce electromagnetic wave reflection, they generally suffer from insufficient mechanical strength and excessive shielding thickness (typically >2.0 mm), making them unsuitable for flexible devices with stringent requirements for thickness and flexibility. Porous foam structures also face the challenge of balancing high electromagnetic shielding effectiveness with ultra-thin thickness. The design concept of a controllable electro-magnetic dual gradient structure offers a new approach to solving these problems. By precisely controlling the type and distribution of fillers in different functional layers, it can integrate the advantages of each component and achieve functional gradients. Nevertheless, existing research on constructing controllable, continuous electromagnetic gradients within thin films and using these gradients to regulate electromagnetic wave dissipation paths and reflection behavior is still insufficient. In particular, methods for integrating highly conductive MXene, tunable magnetic layered double hydroxides, and nanofiber network bacterial cellulose into a gradient design, and their applications in electromagnetic shielding, have not yet been reported. Summary of the Invention

[0006] To address the problems in existing technologies, this invention provides an electromagnetic shielding composite film material with a controllable electromagnetic gradient, its preparation method, and its applications. A series of magnetic bimetallic hydroxide nanosheet@MXene composite materials with different magnetic properties and conductivity were synthesized by in-situ growth of magnetic bimetallic hydroxide nanosheets on MXene nanosheets. This successfully constructed abundant electromagnetic heterogeneous interfaces within the materials, endowing the composite film with electromagnetic double-loss functionality.

[0007] A composite membrane with a rich porous structure and an electromagnetic dual-gradient structure was successfully constructed using a layer-by-layer filtration followed by freeze-drying. This effectively extended the electromagnetic wave transmission path, reduced the proportion of electromagnetic wave reflection in the electromagnetic shielding effectiveness, and improved the electromagnetic shielding performance of the composite membrane. The introduction of magnetic materials and the construction of the electromagnetic dual-gradient structure enriched the electromagnetic wave loss mechanism of the composite membrane. Simultaneously, it optimized the impedance matching of the composite membrane, reduced the surface reflectivity of electromagnetic waves, and avoided impedance mismatch caused by the high conductivity of MXene and secondary electromagnetic pollution caused by electromagnetic wave reflection. The gradient structure effectively enhanced interfacial polarization and established an absorption-reflection-reabsorption electromagnetic wave loss mechanism, thus significantly improving the electromagnetic shielding effectiveness.

[0008] In the first aspect, the present invention proposes an electromagnetic shielding composite membrane with a controllable electromagnetic gradient, the composite membrane being composed of MXene nanosheets, magnetic bimetallic hydroxide nanosheets@MXene composite material (NFMx), and bacterial cellulose (BC).

[0009] Furthermore, the magnetic bimetallic hydroxide nanosheets can be selected from one or more of Mg-Fe bimetallic hydroxide nanosheets, Ni-Fe bimetallic hydroxide nanosheets, Ni-Al bimetallic hydroxide nanosheets, Co-Fe bimetallic hydroxide nanosheets, Ni-Fe bimetallic hydroxide nanosheets, and Ni-Co bimetallic hydroxide nanosheets. This selection breaks the single electrical loss mechanism of MXene and constructs an electromagnetic double loss mechanism.

[0010] Furthermore, the composite film has an electromagnetic shielding performance of 50-70 dB.

[0011] Furthermore, the MXene nanosheets have a size of 0.5 μm-10 μm and a thickness of 1.5 nm-10 nm.

[0012] In the second aspect, this application proposes a method for preparing an electromagnetic shielding composite film material with a controllable electromagnetic gradient, (1) preparing n parts of magnetic bimetallic hydroxide nanosheets@MXene composite materials with different magnetic properties and conductivity and dispersing them in a solvent to obtain n parts of different magnetic bimetallic hydroxide nanosheets@MXene composite material dispersions; (2) Add n portions of the same bacterial cellulose dispersion to the n portions of magnetic bimetallic hydroxide nanosheets@MXene composite material dispersion described in step (1), disperse evenly, and obtain n portions of different magnetic bimetallic hydroxide nanosheets@MXene composite material / bacterial cellulose dispersion. (3) The magnetic bimetallic hydroxide nanosheets@MXene composite material / bacterial cellulose dispersion obtained in step (2) are deposited on the filter membrane in order of magnetic strength from strong to weak to obtain an impedance matching layer of magnetic bimetallic hydroxide nanosheets@MXene / bacterial cellulose electromagnetic shielding composite membrane with controllable electromagnetic gradient. (4) On the basis of the impedance matching layer obtained in step (3), another pure MXene layer is filtered, and after filtration, it is dried to separate the magnetic bimetallic hydroxide nanosheets@MXene / bacterial cellulose electromagnetic shielding composite membrane with controllable electromagnetic gradient.

[0013] Furthermore, the MXene nanosheets are dispersed in a solvent to obtain a dispersion, wherein the solvent is water, and the concentration of the MXene nanosheets is 1-30 mg / ml.

[0014] Furthermore, the bacterial cellulose dispersion has a solid content of 0.6-1%.

[0015] Furthermore, the mass percentage of MXene in the magnetic bimetallic hydroxide nanosheet@MXene composite material is 10-90 wt%.

[0016] Furthermore, the mass percentages of each layer of magnetic bimetallic hydroxide nanosheets@MXene composite material and bacterial cellulose in the impedance matching layer are 50 wt%.

[0017] Thirdly, this application also claims protection for an application in electromagnetic shielding, wherein the electromagnetic shielding employs the composite film described in the first aspect, or the composite film obtained by the preparation method described in the second aspect.

[0018] Furthermore, the electromagnetic shielding composite film is used in wearable electronic devices, communication equipment, computers, consumer electronics, automotive electronics, stealth technology, and defense industries.

[0019] This application has the following beneficial effects: A series of NFMx composite materials with different magnetic properties and conductivity were prepared by in-situ growth of magnetic bimetallic hydroxide nanosheets on MXene nanosheets. Using these materials, an electromagnetic dual-gradient structure composite film was constructed. The growth of magnetic bimetallic hydroxide nanosheets introduced a large number of electromagnetic heterogeneous interfaces into the composite film, which can construct a synergistic loss effect of electromagnetic and electromagnetic losses and induce polarization loss. The successful construction of the electromagnetic dual-gradient structure and impedance matching layer effectively avoided the impedance mismatch caused by the high conductivity of MXene and the secondary pollution caused by reflection. An electromagnetic shielding composite film dominated by absorption loss was successfully prepared.

[0020] The film-forming method of layer-by-layer filtration followed by freeze-drying successfully created a rich porous structure in the composite membrane, which effectively increased the multiple reflections of electromagnetic waves within the membrane, extended the electromagnetic wave transmission path, and enhanced the material's ability to dissipate electromagnetic waves.

[0021] The design of the electromagnetic dual gradient structure endows the material with a loss mechanism of "absorption-reflection-reabsorption", which enables the prepared thin film to have high electromagnetic shielding effectiveness (65.38 dB) and high absorption (60.75 dB), effectively reducing secondary electromagnetic pollution to the environment. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the upper surface of the magnetic Ni-Fe bimetallic hydroxide nanosheets@MXene / bacterial cellulose electromagnetic shielding composite film in Example 1.

[0023] Figure 2 This is a scanning electron microscope image of the lower surface of the magnetic Ni-Fe bimetallic hydroxide nanosheets@MXene / bacterial cellulose electromagnetic shielding composite film in Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described in this specification are merely for explaining the invention and are not intended to limit the invention. The parameters, proportions, etc., of the embodiments can be selected according to local conditions without substantially affecting the results. Unless otherwise specified, the reagents and methods used in the embodiments are conventional in the art.

[0025] The bacterial cellulose used in this embodiment of the invention was purchased from Foshan Sailuna Technology Co., Ltd., and its specification is BCS60N.

[0026] The MXene in this embodiment of the invention is prepared by the following method: First, take 15 mL of deionized water at 50°C. o Preheat at C. Once the preheating temperature is reached, add 50 ml of concentrated hydrochloric acid. Then, weigh 2.5 g of LiF and slowly add it to the solution, stirring for 10 min. Next, weigh 2 g of Ti3AlC2 powder and slowly add it to the mixture, stirring at 50°C. oThe mixture was stirred continuously at C for 24 hours. Afterward, the obtained mixture was repeatedly washed by centrifugation with deionized water (DI) until the pH of the supernatant was greater than 6. This was followed by several more centrifugation washes, with the rotation speed gradually increasing from 3500 rpm to 6000 rpm, resulting in a clay-like precipitate. The precipitate was then dispersed in deionized water and sonicated for 10 minutes to separate the MXene sheets. The resulting MXene solution had a concentration of approximately 1-30 mg / mL, with MXene nanosheets ranging in size from 0.5 μm to 10 μm and a thickness from 1.5 nm to 10 nm. The dispersion was then stored under vacuum for long-term preservation.

[0027] The magnetic Ni-Fe LDH @ MXene composite material in this embodiment of the invention is prepared by the following method: Magnetic Ni-Fe LDH @ MXene composite material was prepared via a simple co-precipitation method. First, 10 mL of a metal salt solution containing Ni(NO3)2·6H2O (0.056 g) and Fe(NO3)3·9H2O (0.052 g) was prepared. Then, 30 mL of a dispersion of MXene nanosheets containing 0.3 g of MXene was slowly added to the above solution under ultrasonication, along with 0.036 g of NH4F, and the mixture was stirred vigorously for 1 hour. Then, over 3 hours, 15 mL of a solution containing NaOH (0.026 g) and Na2CO3 (0.171 g) was added to the above mixed solution. After aging the suspension at room temperature for 24 hours, the mixture was centrifuged, washed, and freeze-dried to obtain the Ni-Fe LDH @ MXene composite material (NFMx), denoted as NFM1. By adjusting the mass ratios of Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, NH4F, NaOH, and Na2CO3 in the reaction, NFM composites with different Ni-Fe LDH mass ratios of 1:9, 3:7, 5:5, 7:3, and 9:1 were prepared. For convenience, the Ni-FeLDH@MXene composites with different mass ratios (1:9, 3:7, 5:5, 7:3, and 9:1) were labeled as NFM1, NFM2, NFM3, NFM4, and NFM5, respectively. In addition, pure Ni-FeLDH was prepared for comparison; the pure Ni-Fe LDH was synthesized using the same room-temperature co-precipitation method.

[0028] The nylon 6 filter membrane used in this invention was purchased from Tianjin Jinteng Experimental Equipment Co., Ltd. It has a diameter of 55 mm, a pore size of 0.22 μm, and an inner diameter of 42 mm at the mouth of the filtration flask. Therefore, the effective filtration area is 13.85 cm². 2 .

[0029] Furthermore, for clarity, the prepared gradient structure composite membrane is named NFM(X1-X2-X3-…Xn) / BC. The naming rules for the composite membrane are as follows: n is the number of layers in the composite membrane, and Xn represents the mass fraction of MXene in the Ni-Fe LDH@MXene composite material in the nth layer.

[0030] Taking NFM(10-50-90-100) / BC as an example, the gradient composite membrane has four layers. The first layer is an NFM5 / BC layer containing 50 wt% NFM5 and BC respectively. The second layer is an NFM3 / BC layer containing 50 wt% NFM3 and BC respectively. The third layer is an NFM1 / BC layer containing 50 wt% NFM1 and BC respectively. The fourth layer is a pure MXene layer containing 15 mg MXene. Example 1

[0031] Weigh out 30 mg of NFM1, NFM3, and NFM5 and disperse them in 20 mL of deionized water. Sonicate at 200 W for 30 min to disperse them evenly. Then add bacterial cellulose dispersion containing 30 mg of BC to each of the above three dispersions. Sonicate at 200 W for 30 min and stir to disperse them evenly to obtain NFM1 / BC, NFM3 / BC, and NFM5 / BC. Take MXene nanosheet dispersion containing 15 mg of MXene and denote it as MX.

[0032] A gradient composite membrane was prepared by sequential filtration of the mixed dispersion in the order of NFM5 / BC, NFM3 / BC, NFM1 / BC, and MX, using Nylon 6 as the filter membrane and the vacuum degree was controlled at -0.1 MPa. After filtration, the composite membrane is rapidly freeze-dried for 48 hours to obtain an MXene (10-50-90-100) / BC gradient composite membrane with a total shielding effectiveness of 65.38 dB. Example 2

[0033] Weigh out 30 mg of NFM2, NFM3, and NFM4 respectively and disperse them in 20 mL of deionized water. Sonicate at 200 W for 30 min to disperse them evenly. Then add bacterial cellulose dispersion containing 30 mg of BC to the above three dispersions, sonicate at 200 W for 30 min and stir to disperse them evenly to obtain NFM2 / BC, NFM3 / BC, and NFM4 / BC. Then take the MXene nanosheet dispersion containing 15 mg of MXene and denote it as MX.

[0034] A gradient composite membrane was prepared by sequentially filtering the mixed dispersion in the order of NFM4 / BC, NFM3 / BC, NFM2 / BC, and MX, using Nylon 6 as the filter membrane and controlling the vacuum degree at -0.1 MPa. After filtration, the composite membrane is rapidly freeze-dried for 48 hours to obtain an MXene (30-50-70-100) / BC gradient composite membrane with a total shielding effectiveness of 60.53 dB. Example 3

[0035] Weigh 30 mg of pure Ni-Fe LDH and NFM3 and disperse them in 20 mL of deionized water. Sonicate at 200 W for 30 min to ensure uniform dispersion. Dilute the MXene nanosheet dispersion containing 30 mg of MXene to 20 mL and sonicate at 200 W for 30 min to ensure uniform dispersion. Add bacterial cellulose dispersion containing 30 mg of BC to the above three dispersions and sonicate at 200 W for 30 min. Stir to ensure uniform dispersion to obtain Ni-Fe LDH / BC, NFM3 / BC, and MXene / BC. Take the MXene nanosheet dispersion containing 15 mg of MXene and denote it as MX.

[0036] A gradient composite membrane was prepared by sequentially filtering the mixed dispersion in the order of Ni-Fe LDH / BC, NFM3 / BC, MXene / BC, and MX, using Nylon 6 as the filter membrane and controlling the vacuum degree at -0.1 MPa. After filtration, the composite membrane is rapidly freeze-dried for 48 hours to obtain an MXene (0-50-100-100) / BC gradient composite membrane with a total shielding effectiveness of 64.17 dB. Comparative Example 1

[0037] Weigh 90 mg NFM3 and disperse it in 60 mL of deionized water. Sonicate at 200 W for 30 min to disperse it evenly. Then add bacterial cellulose dispersion containing 90 mg BC to the above dispersion. Sonicate at 200 W for 30 min and stir to disperse it evenly to obtain NFM3 / BC. Then take MXene nanosheet dispersion containing 15 mg MXene and denote it as MX.

[0038] A gradient composite membrane was prepared by sequentially filtering NFM3 / BC and MX in the mixed dispersion, using Nylon 6 as the filter membrane and controlling the vacuum degree at -0.1 MPa. After filtration, the composite membrane is rapidly freeze-dried for 48 hours to obtain an MXene (50-50-50-100) / BC gradient composite membrane with a total shielding effectiveness of 54.36 dB. Comparative Example 2

[0039] Mix a BC dispersion containing 57 mg BC with an MXene dispersion containing 3 mg MXene, sonicate at 200 W for 30 min, and then stir to ensure uniform dispersion; mix a BC dispersion containing 45 mg BC with an MXene dispersion containing 15 mg MXene, sonicate at 200 W for 30 min, and then stir to ensure uniform dispersion; mix a BC dispersion containing 33 mg BC with an MXene dispersion containing 27 mg MXene, sonicate at 200 W for 30 min, and then stir to ensure uniform dispersion; thus obtaining MX-5 / BC, MX-25 / BC, and MX-45.

[0040] A gradient composite membrane was prepared by sequentially filtering the mixed dispersions MX-5 / BC, MX-25 / BC, MX-45, and MX, using nylon 6 as the filter membrane and controlling the vacuum degree at -0.1 MPa. After filtration, the composite membrane is rapidly freeze-dried for 48 hours to obtain an MXene (5-25-45-100) / BC gradient composite membrane with a total shielding effectiveness of 61.28 dB. Comparative Example 3

[0041] Mix a BC dispersion containing 54 mg BC with an MXene dispersion containing 6 mg MXene, sonicate at 200 W for 30 min, and then stir to ensure uniform dispersion; mix a BC dispersion containing 45 mg BC with an MXene dispersion containing 15 mg MXene, sonicate at 200 W for 30 min, and then stir to ensure uniform dispersion; mix a BC dispersion containing 39 mg BC with an MXene dispersion containing 21 mg MXene, sonicate at 200 W for 30 min, and then stir to ensure uniform dispersion; thus obtaining MX-15 / BC, MX-25 / BC, and MX-35.

[0042] A gradient composite membrane was prepared by sequentially filtering the mixed dispersions MX-5 / BC, MX-25 / BC, MX-45, and MX, using nylon 6 as the filter membrane and controlling the vacuum degree at -0.1 MPa. After filtration, the composite membrane is rapidly freeze-dried for 48 hours to obtain an MXene (15-25-35-100) / BC gradient composite membrane with a total shielding effectiveness of 56.35 dB. Comparative Example 4

[0043] An MXene dispersion containing 45 mg MXene was prepared. A bacterial cellulose dispersion containing 135 mg BC was added to the above dispersion. The mixture was ultrasonically dispersed at 200 W for 30 min and then stirred to ensure uniform dispersion, resulting in MX-25 / BC. An MXene nanosheet dispersion containing 15 mg MXene was then taken and denoted as MX.

[0044] A gradient composite membrane was prepared by sequentially filtering the mixed dispersions MX-25 / BC and MX, using nylon 6 as the filter membrane and controlling the vacuum degree at -0.1 MPa. After filtration, the composite membrane is rapidly freeze-dried for 48 hours to obtain an MXene (25-25-25-100) / BC gradient composite membrane with a total shielding effectiveness of 50.89 dB.

[0045] The electromagnetic shielding performance of the obtained composite film is shown in Table 1.

[0046] Table 1 serial number Thickness (μm) Overall shielding effectiveness (dB) Absorption efficiency (dB) Absorption efficiency ratio Example 1 328 65.38 60.75 92.92% Example 2 326 60.53 55.42 91.56% Example 3 320 64.17 57.92 90.26% Comparative Example 1 330 54.36 48.67 89.53% Comparative Example 2 300 61.28 54.96 89.68% Comparative Example 3 303 56.35 49.78 88.34% Comparative Example 4 307 50.89 44.63 87.70% The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. An electromagnetic shielding composite film with a controllable electromagnetic gradient, characterized in that, The composite membrane is composed of MXene nanosheets, magnetic bimetallic hydroxide nanosheets@MXene composite material, and bacterial cellulose, wherein the MXene nanosheets are Ti3C2T. x MXene, Ta4C3T x MXene, Ti2CT x MXene, Nb4C3T x MXene, Nb2CT x One or more of MXene.

2. The electromagnetic shielding composite film with a controllable electromagnetic gradient according to claim 1, characterized in that, The magnetic bimetallic hydroxide nanosheets are one or more of the following: Mg-Fe bimetallic hydroxide nanosheets, Ni-Fe bimetallic hydroxide nanosheets, Ni-Al bimetallic hydroxide nanosheets, Co-Fe bimetallic hydroxide nanosheets, Ni-Fe bimetallic hydroxide nanosheets, and Ni-Co bimetallic hydroxide nanosheets.

3. The electromagnetic shielding composite film with a controllable electromagnetic gradient according to claim 1, characterized in that, The composite membrane has an electromagnetic shielding performance of 50-70 dB.

4. The electromagnetic shielding composite film with a controllable electromagnetic gradient according to claim 1, characterized in that, The MXene nanosheets have a size of 0.5 μm-10 μm and a thickness of 1.5 nm-10 nm.

5. A method for preparing an electromagnetic shielding composite film with a controllable electromagnetic gradient according to any one of claims 1-4, characterized in that, (1) Prepare n magnetic bimetallic hydroxide nanosheets@MXene composite materials with different magnetic properties and conductivity, and disperse them in solvents respectively to obtain n different magnetic bimetallic hydroxide nanosheets@MXene composite material dispersions; (2) Add n portions of the same bacterial cellulose dispersion to the n portions of magnetic bimetallic hydroxide nanosheets@MXene composite material dispersion described in step (1), disperse evenly, and obtain n portions of different magnetic bimetallic hydroxide nanosheets@MXene composite material / bacterial cellulose dispersion. (3) The magnetic bimetallic hydroxide nanosheets@MXene composite material / bacterial cellulose dispersion obtained in step (2) are deposited on the filter membrane in order of magnetic strength from strong to weak to obtain an impedance matching layer of magnetic bimetallic hydroxide nanosheets@MXene / bacterial cellulose electromagnetic shielding composite membrane with controllable electromagnetic gradient. (4) On the basis of the impedance matching layer obtained in step (3), another pure MXene layer is filtered, and after filtration, it is dried to separate the magnetic bimetallic hydroxide nanosheets@MXene / bacterial cellulose electromagnetic shielding composite membrane with controllable electromagnetic gradient.

6. A method for preparing an electromagnetic shielding composite film with a controllable electromagnetic gradient according to claim 5, characterized in that, The MXene nanosheets are dispersed in a solvent, namely water, to obtain a dispersion, and the concentration of the MXene nanosheets is 1-30 mg / ml.

7. The method for preparing an electromagnetic shielding composite film with a controllable electromagnetic gradient according to claim 5, characterized in that, The bacterial cellulose dispersion has a solid content of 0.6-1%.

8. A method for preparing an electromagnetic shielding composite film with a controllable electromagnetic gradient according to claim 5, characterized in that, The MXene content in the magnetic bimetallic hydroxide nanosheets@MXene composite material is 10-90 wt%.

9. A method for preparing an electromagnetic shielding composite film with a controllable electromagnetic gradient according to claim 5, characterized in that, In the impedance matching layer, each layer of magnetic bimetallic hydroxide nanosheets@MXene composite material and bacterial cellulose has a mass ratio of 50 wt%.

10. An application characterized in that, The application is in electromagnetic shielding, wherein the electromagnetic shielding adopts the composite film according to any one of claims 1-4, or the composite film obtained by the preparation method according to any one of claims 5-9.

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