An electromagnetic shielding material, its preparation method and application

Abstract

This invention discloses an electromagnetic shielding material, its preparation method, and its application. The electromagnetic shielding material is a bilayer structure formed by bonding a composite aerogel and a composite hydrogel. The composite aerogel is prepared by carbonizing a composite aerogel material obtained from precursor solution A through directional freezing and freeze-drying, followed by heat treatment. The composite hydrogel is prepared by a cyclic freeze-thaw process involving multiple directional freezing and dissolution cycles from precursor solution B. This invention effectively improves the electromagnetic shielding material's absorption capacity by using the aerogel as the absorbing layer and the hydrogel as the shielding layer. Furthermore, the hygroscopic hydrogel absorbs ambient moisture, while the porous aerogel continuously evaporates moisture, achieving a continuous humidity gradient and thus enhancing the system's self-powering capability.

Description

Technical Field

[0001] This invention relates to electromagnetic shielding materials, specifically to an electromagnetic shielding material, its preparation method, and its application. Background Technology

[0002] With the rapid development of information technology and the electronics industry, electronic devices have been widely used in communications, medical devices, aerospace, military protection, and emerging smart wearables. At the same time, electronic devices generate a large amount of electromagnetic radiation during operation and are susceptible to external electromagnetic interference in complex electromagnetic environments. Electromagnetic interference not only affects the operational stability and lifespan of precision electronic components but can also lead to signal distortion or even failure in communication systems, posing serious safety hazards in critical scenarios such as military and aerospace applications. Therefore, the development of highly efficient electromagnetic shielding materials has become a key research direction in the fields of materials science and engineering.

[0003] Currently, commonly used electromagnetic shielding materials mainly include metallic materials, carbon-based materials, and conductive polymer materials. However, most existing electromagnetic shielding materials only possess a single passive shielding function. With the increasing miniaturization, integration, and intelligence of electronic devices, this limitation of traditional electromagnetic shielding materials is no longer sufficient to meet emerging demands. Especially in portable electronic devices, intelligent protective equipment, and IoT terminals, if shielding materials could simultaneously provide electromagnetic protection and energy harvesting and conversion capabilities, it would not only significantly improve the system's energy self-sufficiency and reduce dependence on external power sources, but also provide new solutions for adaptive and sustainable electromagnetic protection systems.

[0004] In recent years, moisture, as a ubiquitous form of water in the environment, has been widely explored for energy harvesting. Under moisture stimulation, materials need to generate a directional diffusion current of ions, while the external circuit generates a directional migration current of electrons, to ensure that moisture-powered materials can output electrical energy. However, existing moisture-powered materials still face several challenges in practical applications: First, most materials have uniform ion distribution or limited migration channels, making it difficult to form a sufficient ion concentration gradient, resulting in limited output voltage and current. Second, the moisture absorption and ion migration processes of materials in humid environments are often unsustainable, and the electrical output easily decays over time, failing to meet the needs of long-term operation. Third, existing moisture-powered devices are mostly single-function materials, possessing only energy harvesting capabilities and lacking coupling designs with other functions, limiting their promotion and practical application value in smart portable devices and multi-scenario applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the deficiencies in the prior art and provide an electromagnetic shielding material, its preparation method and application, which can effectively improve the self-powering capability of electromagnetic shielding materials.

[0006] To achieve the above objectives, the present invention provides an electromagnetic shielding material, which is a bilayer structure formed by bonding composite aerogel and composite hydrogel. The composite aerogel is prepared by directional freezing and freeze-drying of precursor solution A, followed by heat treatment and carbonization. The composite hydrogel is prepared by a cyclic freeze-thaw process involving multiple directional freezing and dissolution of precursor solution B. Precursor solution A is prepared by mixing any one or more of MXene (two-dimensional transition metal carbon / nitride) aqueous solution, graphene oxide (GO) aqueous solution, and aramid nanofiber (ANF) aqueous solution with a crosslinking agent. Precursor solution B is prepared by dispersing and dissolving a mixture of phytic acid (PA) aqueous solution, hygroscopic salt, and polyvinyl alcohol (PVA) aqueous solution or a mixture of polyvinyl alcohol aqueous solution and polymer aqueous solution.

[0007] This invention effectively improves the absorption capacity of electromagnetic shielding materials by using aerogel as an absorbing layer and hydrogel as a shielding layer. Furthermore, the hygroscopic hydrogel absorbs ambient moisture while the porous aerogel continuously evaporates moisture, creating a sustained humidity gradient and thus enhancing the system's self-powering capability.

[0008] Furthermore, the aerogel is subjected to directional freezing and heat treatment processes to form an absorbing layer with ordered porous characteristics, which enhances dielectric loss and multiple reflection / scattering effects under the action of electromagnetic waves, thereby improving the material's ability to absorb electromagnetic waves. At the same time, the hydrogel is cross-linked with phytic acid and PVA to form a hygroscopic ion hydrogel, and combined with freeze-thaw processes to construct a loose and continuous ion transport network. Under the action of hygroscopic salts, a moisture gradient and ion concentration gradient can be continuously formed, which significantly improves the ion migration rate and charge separation efficiency, thereby achieving stable and continuous high-performance moisture-driven power generation output.

[0009] The composite aerogel has a thickness of 1.5–5 mm, and the composite hydrogel has a thickness of 1.5–5 mm.

[0010] In some embodiments, preferably, the crosslinking agent is an aqueous solution of sodium alginate or an aqueous solution of polyvinyl alcohol; the polymer is chitosan or sodium alginate; and the hygroscopic salt is lithium chloride, lithium bromide, potassium bromide, or calcium chloride.

[0011] In some embodiments, preferably, the concentrations of the MXene aqueous solution, graphene oxide aqueous solution, and aramid nanofiber aqueous solution used in the precursor solution A are all controlled within the range of 2 to 20 mg / mL. The preferred concentration of the MXene aqueous solution is 10 mg / mL, the preferred concentration of the graphene oxide aqueous solution is 10 to 15 mg / mL, and the preferred concentration of the aramid nanofiber aqueous solution is 4 mg / mL.

[0012] The crosslinking agent is a polymer solution with a mass fraction of 5-20 wt%, and the amount added accounts for 10-40% of the total volume of the precursor solution A; the crosslinking agent is preferably a sodium alginate aqueous solution with a mass fraction of 20 wt%, and the amount added accounts for 12.5-25% of the total volume of the precursor solution A.

[0013] The precursor solution B comprises a polyvinyl alcohol aqueous solution with a concentration of 5–20 wt%, a polymer aqueous solution with a concentration of 5–20 wt%, and a phytic acid aqueous solution with a concentration of 50 wt%. The mass ratio of the polyvinyl alcohol aqueous solution or a mixture of polyvinyl alcohol aqueous solution and polymer aqueous solution, the phytic acid aqueous solution, and the hygroscopic salt is (8–12):(4–6):(2–4). Preferably, the polyvinyl alcohol aqueous solution has a concentration of 10 wt%, the polymer aqueous solution has a concentration of 5–10 wt%, and the hygroscopic salt is preferably lithium chloride or lithium bromide.

[0014] More preferably, precursor solution A is prepared by mixing graphene oxide aqueous solution and crosslinking agent, wherein the concentration of graphene oxide aqueous solution is 15 mg / mL, and the crosslinking agent is sodium alginate aqueous solution with a mass fraction of 20 wt%, and the amount added accounts for 25% of the total volume of precursor solution A; precursor solution B is prepared by dispersing and dissolving polyvinyl alcohol aqueous solution, phytic acid aqueous solution and hygroscopic salt, wherein the concentration of polyvinyl alcohol aqueous solution is 10 wt%, the hygroscopic salt is lithium chloride, and the mass ratio of polyvinyl alcohol aqueous solution, phytic acid aqueous solution and hygroscopic salt is 12:6:3.

[0015] The present invention also provides a method for preparing the above-mentioned electromagnetic shielding material, comprising the following steps: (1) Mix one or more of MXene aqueous solution, graphene oxide aqueous solution and aramid nanofiber aqueous solution with a crosslinking agent and stir evenly to obtain precursor solution A; (2) The precursor solution A was poured into a mold for directional freezing and freeze-drying to obtain a composite aerogel material. The directional freezing was carried out at -50℃ to -100℃, the freezing rate was controlled at 2 to 15℃ / min, and the freezing process lasted for 0.5 to 2h. The freeze-drying was carried out at -50℃ to -80℃ and a vacuum of 1 to 50Pa for 24 to 72h. (3) The composite aerogel material is heat-treated in an inert atmosphere to obtain carbonized composite aerogel; the heat treatment temperature range is 200-800℃, the heating rate is 1-10℃ / min, and the holding time is 1-3h. (4) Mix the phytic acid aqueous solution, hygroscopic salt, and polyvinyl alcohol aqueous solution or a mixture of polyvinyl alcohol aqueous solution and polymer aqueous solution, and then stir under heating conditions until completely dissolved to obtain precursor solution B; (5) Pour the precursor solution B into the mold and carry out a cyclic freeze-thaw process of multiple directional freezing and dissolution to obtain a composite hydrogel; wherein, the number of cyclic freeze-thaw processes of directional freezing and dissolution is 1 to 5 times, the freezing temperature is -80℃ to -100℃, and the cooling rate is controlled at 2 to 6℃ / min. (6) The composite aerogel obtained in step (3) is brought into contact with the composite hydrogel obtained in step (5) and a firm bond is achieved through interfacial adhesion, thus obtaining the electromagnetic shielding material.

[0016] In step (2), preferably, directional freezing is carried out at -80℃ to -100℃, and the freezing rate is controlled at 4 to 10℃ / min; More preferably, directional freezing is carried out at -80°C with a freezing rate controlled at 5°C / min; freeze drying is carried out at -60°C and a vacuum of 10 Pa for 48 hours.

[0017] In step (3), preferably, the heat treatment temperature range is 300 to 600°C; More preferably, the heat treatment temperature is 300℃, the heating rate is 5℃ / min, and the holding time is 2h.

[0018] In step (4), the heating temperature is 70-80℃.

[0019] In step (5), preferably, the number of cycles of directional freezing and thawing is 2 to 4. More preferably, the directional freezing and thawing cycle is repeated 3 times, the thawing temperature is controlled between 25℃ and -100℃, and the cooling rate is controlled at 4℃ / min.

[0020] This invention utilizes process control of directional freezing and heat treatment during the preparation of composite aerosols to form an ordered porous structure and gradient pore size distribution along the freezing direction in the resulting composite aerogel material. After heat treatment, a carbon skeleton with a moderate conductive network and defect structure coexisting is obtained, thereby generating significant dielectric loss, multiple reflection / scattering loss, and impedance matching enhancement effect under the action of electromagnetic waves, thus achieving higher electromagnetic wave absorption capability.

[0021] By optimizing the freeze-thaw process parameters and coordinating the selection and matching of composite hydrogel raw material components, the resulting composite hydrogel forms a porous network structure with moderate cross-linking density and continuous ion channels. Under the action of hygroscopic salt, it can continuously absorb environmental moisture and build a stable ion concentration gradient and moisture gradient inside the material, thereby significantly improving the ion migration rate and charge separation efficiency, and realizing continuous and stable moisture-driven power generation output.

[0022] The present invention also provides the application of the above-mentioned electromagnetic shielding material in self-generating shielding materials.

[0023] Specifically, it can be used in portable electronic devices, smart protection, and wearable systems.

[0024] The present invention has the following advantages over the prior art: This invention's electromagnetic shielding material employs a water / aerogel dual-layer structure design. On one hand, by using aerogel as the absorbing layer and hydrogel as the shielding layer, the absorption capacity of the electromagnetic shielding material for electromagnetic waves can be effectively improved. On the other hand, the hygroscopic hydrogel can absorb ambient moisture while the porous aerogel can continuously evaporate moisture, achieving a continuous humidity gradient. This enhances the system's self-powering capability, reduces dependence on external power sources, and provides a new electromagnetic protection solution for applications such as portable electronic devices, intelligent protection, and wearable systems.

[0025] Simultaneously, by controlling the pore orientation and carbon skeleton structure of the aerogel through directional freezing and heat treatment processes, an absorbing layer with ordered porous characteristics is formed. Under the action of electromagnetic waves, the dielectric loss and multiple reflection / scattering effects are enhanced, thereby improving the material's ability to absorb electromagnetic waves. By controlling the type and content of hygroscopic salts in the hydrogel, the ionic conductivity and interfacial reflection loss of the system are significantly improved, enabling the hydrogel layer to function as a highly efficient electromagnetic shielding layer. By introducing phytic acid-crosslinked hygroscopic ion hydrogels and combining them with freeze-thaw processes to construct a loose and continuous ion transport network, a moisture gradient and ion concentration gradient are continuously formed under the action of hygroscopic salts, significantly improving ion migration rate and charge separation efficiency, thereby achieving stable and continuous high-performance moisture-driven power generation output. Attached Figure Description

[0026] Figure 1 The image shows the actual composite hydrogel prepared in Example 1. Figure 2 Here is a photograph of the electromagnetic shielding material prepared in Example 2; Figure 3 SEM image of the composite aerogel prepared in Example 3; Figure 4 The image shows the test results of the shielding coefficient and shielding effectiveness of the electromagnetic shielding material prepared in Example 3 (electromagnetic waves are incident from the direction of the hydrogel). Figure 5 The image shows the test results of the shielding coefficient and shielding effectiveness of the electromagnetic shielding material prepared in Example 3 (electromagnetic waves are incident from the direction of the aerogel). Figure 6 The graph shows the open-circuit voltage and short-circuit current curves of the electromagnetic shielding material prepared in Example 4. Figure 7 The open-circuit voltage curve of the electromagnetic shielding material prepared in Example 1 during operation is shown in the figure. Figure 8The graph shows the open-circuit voltage curve of the electromagnetic shielding material prepared in Example 2 during operation. Figure 9 The graph shows the open-circuit voltage curve of the electromagnetic shielding material prepared in Example 3 during operation. Figure 10 The image shows the electromagnetic shielding material prepared in Example 1 and the test results of its shielding effectiveness (electromagnetic waves are incident from the direction of the aerogel). Detailed Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments.

[0028] Experimental materials: MXene aqueous solution was purchased from Jilin Yiyi Technology Co., Ltd., GO aqueous solution was purchased from Hangzhou Gaoxi Technology Co., Ltd., aramid fiber (Kevlar) was purchased from Taihe New Materials Co., Ltd. (Yantai, China), and phytic acid aqueous solution was purchased from Aladdin. The remaining aqueous solutions (sodium alginate aqueous solution, PVA aqueous solution, and chitosan aqueous solution) were obtained by dispersing the raw materials purchased by Aladdin.

[0029] Example 1

[0030] This embodiment describes an electromagnetic shielding material, prepared using the following method: Step 1: Mix MXene aqueous solution (10 mg / mL), GO aqueous solution (10 mg / mL), ANF aqueous solution (4 mg / mL) and sodium alginate aqueous solution (20 wt%) in a volume ratio of 2:1:0.5:0.5 and stir until homogeneous to obtain precursor solution A.

[0031] Step 2: Pour the precursor solution A into a mold and perform directional freezing (-60℃, freezing rate 5℃ / min, freezing for 1h) and freeze drying (-60℃, vacuum 10Pa, drying for 48h) to obtain the composite aerogel material.

[0032] Step 3: The composite aerogel material is heat-treated in a nitrogen atmosphere (heating rate 5℃ / min, holding time 2h, temperature 200℃) to obtain a carbonized composite aerogel with a thickness of 2mm.

[0033] Step 4: Mix PVA aqueous solution (10wt%), chitosan aqueous solution (5wt%), phytic acid aqueous solution (50wt%) and lithium chloride in a mass ratio of 6:2:4:2, heat and stir at 75°C until completely dissolved to obtain precursor solution B.

[0034] Step 5: Pour precursor solution B into a mold and perform one directional freeze / thaw cycle (-100℃ to 25℃, freezing rate 4℃ / min) to obtain the following... Figure 1The composite hydrogel shown has a thickness of 5 mm. PA can react with the hydroxyl groups on the polymer chains, serving as crosslinking points and forming the polymer backbone through hydrogen bonding. The introduction of inorganic hygroscopic salts weakens the hydrogen bonds in the hydrogel, resulting in an ionic hydrogel with a loose crosslinked structure.

[0035] Step 6: Contact the composite aerogel obtained in Step 3 with the composite hydrogel obtained in Step 5 to achieve a firm bond through interfacial adhesion, thereby obtaining a self-generating hydrogel electromagnetic shielding material.

[0036] The electromagnetic shielding material obtained above was tested in an environment with a humidity difference. The hygroscopic hydrogel exhibited ion migration and output a potential difference under the influence of ambient humidity. Test results showed that the open-circuit voltage output by this material during operation exceeded 0.5V (see...). Figure 7 ).

[0037] Example 2

[0038] This embodiment describes an electromagnetic shielding material, prepared using the following method: Step 1: Mix MXene aqueous solution (10 mg / mL), GO aqueous solution (10 mg / mL) and sodium alginate aqueous solution (20 wt%) in a volume ratio of 2:1:1 and stir until homogeneous to obtain precursor solution A.

[0039] Step 2: Pour the precursor solution A into a mold and perform directional freezing (-60℃, freezing rate 5℃ / min, freezing for 1h) and freeze drying (-60℃, vacuum 10Pa, drying for 48h) to obtain the composite aerogel material.

[0040] Step 3: Heat-treat the composite aerogel material in a nitrogen atmosphere (heating rate 5℃ / min, holding for 2h, temperature 400℃) to obtain a carbonized composite aerogel with a thickness of 3mm.

[0041] Step 4: Mix PVA aqueous solution (10wt%), chitosan aqueous solution (5wt%), phytic acid aqueous solution (50wt%) and lithium bromide in a mass ratio of 5:5:5:2, heat and stir until completely dissolved to obtain precursor solution B.

[0042] Step 5: Pour the precursor solution B into the mold and perform 3 directional freeze / thaw cycles (-100℃ to 25℃, freezing rate 4℃ / min) to obtain a composite hydrogel with a thickness of 5mm.

[0043] Step 6: Contact the composite aerogel obtained in Step 3 with the composite hydrogel obtained in Step 5. A strong bond is achieved through interfacial adhesion, resulting in the composite aerogel obtained in Step 5. Figure 2 The electromagnetic shielding material shown.

[0044] The electromagnetic shielding material prepared above was tested in an environment with a humidity difference. The hygroscopic hydrogel exhibited ion migration and output a potential difference under the influence of ambient humidity. Test results showed that the open-circuit voltage output by this material during operation exceeded 1.15V (see...). Figure 8 ).

[0045] Example 3

[0046] This embodiment describes an electromagnetic shielding material, which is prepared using the following steps: Step 1: Mix GO aqueous solution (15 mg / mL) and sodium alginate aqueous solution (20 wt%) at a volume ratio of 3:1 and stir until homogeneous to obtain precursor solution A.

[0047] Step 2: Pour the precursor solution A into a mold and perform directional freezing (-60℃, freezing rate 5℃ / min, freezing for 1h) and freeze drying (-60℃, vacuum 10Pa, drying for 48h) to obtain the composite aerogel material.

[0048] Step 3: The composite aerogel material is heat-treated in a nitrogen atmosphere (heating rate 5℃ / min, holding time 2h, temperature 300℃) to obtain the following result. Figure 3 The carbonized composite aerogel shown has a thickness of 5 mm. This composite aerogel has an ordered porous structure, which is beneficial for the directional transport of moisture and the multiple reflection losses of electromagnetic waves.

[0049] Step 4: Mix PVA aqueous solution (10wt%), phytic acid aqueous solution (50wt%) and lithium chloride in a mass ratio of 12:6:3, heat and stir until completely dissolved to obtain precursor solution B.

[0050] Step 5: Pour the precursor solution B into the mold and perform 3 directional freeze / thaw cycles (-100℃ to 25℃, freezing rate 2℃ / min) to obtain a composite hydrogel with a thickness of 5mm.

[0051] Step 6: Contact the composite aerogel obtained in Step 3 with the composite hydrogel obtained in Step 5 to achieve a firm bond through interfacial adhesion, thereby obtaining the electromagnetic shielding material of the present invention.

[0052] Composite hydrogels, due to their high ionic conductivity, can serve as electromagnetic shielding layers, while composite aerogels, acting as electromagnetic wave absorbing layers, can dissipate electromagnetic waves through dielectric loss and multiple reflections / scattering. For example... Figure 4 As shown (a is the shielding coefficient, b is the shielding effectiveness), when electromagnetic waves are incident from one side of the composite aerogel, the absorption coefficient of this electromagnetic shielding material can reach as high as 0.9; Figure 5As shown (a is the shielding coefficient, b is the shielding effectiveness), when electromagnetic waves are incident from one side of the composite hydrogel, the absorption coefficient of this electromagnetic shielding material is less than 0.5.

[0053] Meanwhile, the electromagnetic shielding material was tested in an environment with a humidity difference. The hygroscopic hydrogel continuously absorbs ambient moisture, while the porous aerogel promotes moisture evaporation, forming a stable humidity gradient at the water / aerogel interface. This drives the directional migration of ions within the hydrogel and generates a potential difference in the external circuit. Test results show that the material can output an open-circuit voltage of over 1.3V during operation, demonstrating excellent moisture-driven self-generating performance (see...). Figure 9 ).

[0054] Compared with the electromagnetic shielding material prepared in Example 1 (e.g.) Figure 10 As shown in Example 3, the electromagnetic shielding performance of the material obtained is improved due to the higher degree of carbonization of the absorbing layer and the higher ion content in the hydrogel. At the same time, the open-circuit voltage and short-circuit current output driven by moisture are improved and the stability is increased, indicating that the preparation process conditions of aerogel and hydrogel play an important role in obtaining better overall performance.

[0055] Example 4

[0056] This embodiment describes an electromagnetic shielding material, prepared using the following method: Step 1: Mix MXene aqueous solution (10 mg / mL) and sodium alginate aqueous solution (20 wt%) at a volume ratio of 3:1 and stir until homogeneous to obtain precursor solution A.

[0057] Step 2: Pour the precursor solution A into a mold and perform directional freezing (-60℃, freezing rate 8℃ / min, freezing for 1h) and freeze drying (-60℃, vacuum 10Pa, drying for 48h) to obtain the composite aerogel material.

[0058] Step 3: Heat-treat the composite aerogel material in a nitrogen atmosphere (heating rate 5℃ / min, holding for 2h, temperature 300℃) to obtain a carbonized composite aerogel with a thickness of 3mm.

[0059] Step 4: Mix PVA aqueous solution (10wt%), sodium alginate aqueous solution (10wt%), phytic acid aqueous solution (50wt%) and lithium chloride in a mass ratio of 9:3:6:4, heat and stir until completely dissolved to obtain precursor solution B.

[0060] Step 5: Pour the precursor solution B into the mold and perform 3 directional freeze / thaw cycles (-100℃ to 25℃, freezing rate 6℃ / min) to obtain a composite hydrogel with a thickness of 3mm.

[0061] Step 6: Contact the composite aerogel obtained in Step 3 with the composite hydrogel obtained in Step 5 to achieve a firm bond through interfacial adhesion, thereby obtaining the electromagnetic shielding material.

[0062] like Figure 6 As shown (a is the open-circuit voltage, b is the short-circuit current), when the electromagnetic shielding material is placed in an environment with 70% humidity, the hygroscopic hydrogel continuously absorbs moisture, thus forming a continuous moisture gradient between the water and aerogel. For more than 800 minutes, its open-circuit voltage remains above 1.15V, while its instantaneous short-circuit current exceeds 900µA.

[0063] As can be seen from the above embodiments, the electromagnetic shielding material prepared by the present invention has excellent moisture-driven self-generating performance, improves self-powering capability, reduces dependence on external power source, and can provide a new electromagnetic protection solution for applications such as portable electronic devices, intelligent protection and wearable systems.

Claims

1. An electromagnetic shielding material, characterized in that, The electromagnetic shielding material is a double-layer structure formed by bonding composite aerogel and composite hydrogel. The composite aerogel is prepared by directional freezing and freeze-drying of precursor solution A, followed by heat treatment and carbonization. The composite hydrogel is prepared by a cyclic freeze-thaw process involving multiple directional freezing and dissolution of precursor solution B. Precursor solution A is prepared by mixing any one or more of MXene aqueous solution, graphene oxide aqueous solution, and aramid nanofiber aqueous solution with a crosslinking agent. Precursor solution B is prepared by dispersing and dissolving a mixture of phytic acid aqueous solution, hygroscopic salt, and polyvinyl alcohol aqueous solution or a mixture of polyvinyl alcohol aqueous solution and polymer aqueous solution.

2. The electromagnetic shielding material according to claim 1, characterized in that, The composite aerogel has a thickness of 1.5–5 mm, and the composite hydrogel has a thickness of 1.5–5 mm.

3. The electromagnetic shielding material according to claim 2, characterized in that, The concentrations of MXene aqueous solution, graphene oxide aqueous solution, and aramid nanofiber aqueous solution in precursor solution A are all 2–20 mg / mL; the crosslinking agent is a polymer solution with a mass fraction of 5–20 wt%, and the amount added accounts for 10–40% of the total volume of precursor solution A; the concentrations of polyvinyl alcohol aqueous solution, polymer aqueous solution, and phytic acid aqueous solution used in precursor solution B are 5–20 wt%, 5–20 wt%, and 50 wt%, and the mass ratio of polyvinyl alcohol aqueous solution or a mixture of polyvinyl alcohol aqueous solution and polymer aqueous solution, phytic acid aqueous solution, and hygroscopic salt is (8–12):(4–6):(2–4).

4. The electromagnetic shielding material according to claim 3, characterized in that, The crosslinking agent is an aqueous solution of sodium alginate or an aqueous solution of polyvinyl alcohol; the polymer is chitosan or sodium alginate; and the hygroscopic salt is lithium chloride, lithium bromide, potassium bromide, or calcium chloride.

5. The electromagnetic shielding material according to claim 4, characterized in that, The precursor solution A contains MXene aqueous solution with a concentration of 10 mg / mL, graphene oxide aqueous solution with a concentration of 10-15 mg / mL, and aramid nanofiber aqueous solution with a concentration of 4 mg / mL. The crosslinking agent is sodium alginate aqueous solution with a mass fraction of 20 wt%, and the amount added accounts for 12.5-25% of the total volume of the precursor solution A. The precursor solution B contains polyvinyl alcohol aqueous solution with a concentration of 10 wt%, polymer aqueous solution with a concentration of 5-10 wt%, and lithium chloride or lithium bromide is used as the hygroscopic salt.

6. The electromagnetic shielding material according to claim 5, characterized in that, The precursor solution A is prepared by mixing an aqueous solution of graphene oxide with a crosslinking agent. The concentration of the aqueous solution of graphene oxide is 15 mg / mL, and the crosslinking agent is a sodium alginate aqueous solution with a mass fraction of 20 wt%, which accounts for 25% of the total volume of the precursor solution A. The precursor solution B is prepared by dispersing and dissolving a mixture of an aqueous solution of polyvinyl alcohol, an aqueous solution of phytic acid, and a hygroscopic salt. The concentration of the aqueous solution of polyvinyl alcohol is 10 wt%, and the hygroscopic salt is lithium chloride. The mass ratio of the aqueous solution of polyvinyl alcohol, the aqueous solution of phytic acid, and the hygroscopic salt is 12:6:

3.

7. A method for preparing the electromagnetic shielding material according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: (1) Mix one or more of MXene aqueous solution, graphene oxide aqueous solution and aramid nanofiber aqueous solution with a crosslinking agent and stir evenly to obtain precursor solution A; (2) The precursor solution A is poured into a mold for directional freezing and freeze-drying to obtain a composite aerogel material; the directional freezing is carried out at -50℃ to -100℃, the freezing rate is controlled at 2 to 15℃ / min, and the freezing process lasts for 0.5 to 2h; the freeze-drying is carried out at -50℃ to -80℃ and a vacuum degree of 1 to 50Pa, and the drying time is 24 to 72h. (3) The composite aerogel material is heat-treated in an inert atmosphere to obtain carbonized composite aerogel; the heat treatment temperature range is 200 to 800℃, the heating rate is 1 to 10℃ / min, and the holding time is 1 to 3h. (4) Mix the phytic acid aqueous solution, hygroscopic salt, and polyvinyl alcohol aqueous solution or a mixture of polyvinyl alcohol aqueous solution and polymer aqueous solution, and then stir under heating conditions until completely dissolved to obtain precursor solution B; (5) Pour the precursor solution B into the mold and carry out a cyclic freeze-thaw process of multiple directional freezing and dissolution to obtain a composite hydrogel; wherein, the number of cyclic freeze-thaw processes of directional freezing and dissolution is 1 to 5 times, the freezing temperature is -80℃ to -100℃, and the cooling rate is controlled at 2 to 6℃ / min. (6) The composite aerogel obtained in step (3) is brought into contact with the composite hydrogel obtained in step (5) and a firm bond is achieved through interfacial adhesion to obtain the electromagnetic shielding material.

8. The application of the electromagnetic shielding material according to any one of claims 1 to 6 in the application of self-generating shielding materials.

9. The application of the electromagnetic shielding material according to any one of claims 1 to 6 in portable electronic devices, smart protection and wearable systems.

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