Electromagnetic interference shielding nanocomposite film with asymmetric alternating multilayer structure and its preparation method

Abstract

The invention discloses an electromagnetic interference shielding nanocomposite film with an asymmetric alternating multilayer structure and a preparation method thereof. The nanocomposite film comprises an absorption layer nanofilm and a reflection layer nanofilm. The composition of the single-layer absorption layer nanofilm comprises 1-40 parts of cellulose nanofibers and 1-50 parts of magnetic nanoparticles by weight; the composition of the reflection layer nanofilm comprises 1-25 parts of cellulose nanofibers and 1-66 parts of conductive nanoparticles; the asymmetric alternation means that the absorption layer nanofilms and the reflection layer nanofilms of different thicknesses are alternately stacked. In the present invention, compared with a cellulose nanofiber / reduced graphene oxide loaded ferroferric oxide / silver nanowire blended nanocomposite film with the same component content, the nanocomposite film with an asymmetric alternating multilayer structure shows ultra-high electromagnetic interference shielding performance and outstanding mechanical properties.

Description

Technical Field

[0001] The invention relates to the field of high-performance electromagnetic interference shielding materials, in particular to an electromagnetic interference shielding nano-composite film with an asymmetric alternating multi-layer structure and a preparation method thereof. Background Art

[0002] With the rapid development of communication technology, it is very urgent to develop electromagnetic interference shielding materials with high electromagnetic interference shielding performance, outstanding mechanical properties and excellent thermal conductivity to solve the increasing electromagnetic radiation pollution and heat accumulation problems. In particular, in recent years, with the rapid popularization of portable and wearable electronic products, the requirements for electromagnetic interference shielding materials to be lighter, thinner and more flexible have been put forward. Metal-based materials are widely used in multifunctional electromagnetic interference shielding materials due to their excellent thermal and electrical conductivity, but their application is limited by their disadvantages such as difficult processing, low flexibility, high density and poor chemical corrosion resistance. Conductive polymer composites composed of conductive nanofillers and polymers have attracted widespread attention from researchers due to their advantages such as light weight, corrosion resistance and easy processing. However, due to the percolation threshold of conductive polymer materials, a high load of fillers is often required to achieve good electromagnetic interference shielding performance, but this will lead to a serious reduction in the flexibility and mechanical properties of conductive polymer composites, and the conductive polymer composites have a large thickness, which greatly limits their practical application. Therefore, the development of ultra-thin flexible materials with high electromagnetic interference shielding performance, high thermal conductivity and excellent mechanical properties is still a huge challenge. Summary of the invention

[0003] The purpose of the present invention is to provide an electromagnetic interference shielding nanocomposite film with an asymmetric alternating multilayer structure, which can significantly improve the electromagnetic interference shielding performance and mechanical properties of the nanocomposite film at the same time, solving the contradiction that the increase of the electromagnetic interference shielding performance of polymer-based electromagnetic interference shielding materials leads to the decrease of mechanical properties.

[0004] The technical solution of the present invention is: an electromagnetic interference shielding nano-composite film with an asymmetric alternating multilayer structure, including an absorption layer nano-film and a reflection layer nano-film. Calculated by weight, the composition of the single-layer absorption layer nano-film includes 1-40 parts of cellulose nano-fibers and 1-50 parts of magnetic nano-particles; the composition of the reflection layer nano-film includes 1-25 parts of cellulose nano-fibers and 1-66 parts of conductive nano-particles; the asymmetric alternation means that the absorption layer nano-films and the reflection layer nano-films of different thicknesses are alternately stacked.

[0005] The magnetic nanoparticles are carbon nanotubes loaded with ferroferric oxide, titanium carbide loaded with ferroferric oxide or titanium carbide loaded with nickel; the conductive nanoparticles are silver nanowires, carbon nanotubes or graphene.

[0006] Preparation method of electromagnetic interference shielding nano-composite film with asymmetric alternating multi-layer structure, characterized by comprising the following steps:

[0007] 1) Take each component according to the above mass parts, mix and stir the conductive nanoparticle dispersion liquid and the cellulose nanofiber dispersion liquid to make them fully mixed, forming a uniform cellulose nanofiber / conductive nanoparticle dispersion liquid, and perform vacuum-assisted filtration on the cellulose nanofiber / silver nanowire dispersion liquid to obtain a reflective layer nano-film;

[0008] 2) Take each component according to the above mass parts, mix the cellulose nanofiber aqueous dispersion liquid and the magnetic nanoparticles and perform ultrasonic dispersion to form a uniform cellulose nanofiber / magnetic nanoparticle dispersion liquid; on the basis of step 1), add the cellulose nanofiber / magnetic nanoparticle dispersion liquid to the surface of the reflective layer nano-film obtained in step 1) and continue vacuum-assisted filtration to form an asymmetric double-layer nano-composite film;

[0009] 3) Repeat the above steps 1) and 2) to prepare an electromagnetic interference shielding nano-composite film with an asymmetric alternating multi-layer structure of 2 layers or more.

[0010] The thickness of the absorption layer nano-film is 8 - 50 μm, and the thickness of the reflective layer nano-film is 6 - 50 μm.

[0011] In the present invention, compared with the cellulose nanofiber / reduced graphene oxide loaded with magnetite / silver nanowire blend nano-composite film with the same component content, the nano-composite film with an asymmetric alternating multi-layer structure shows ultra-high electromagnetic interference shielding performance and excellent mechanical properties. Taking the electromagnetic interference shielding film with an asymmetric alternating 6-layer structure prepared by the present invention as an example, its average electromagnetic shielding effectiveness and tensile strength are respectively increased by 64.8% and 68.9% compared with the products of the prior art. Description of the Drawings

[0012] Figure 1 Cross-sectional scanning electron microscope image comparison of the embodiments of the present invention;

[0013] (a) Control; (b) Asymmetric 2-layer nano-composite film; (c) Asymmetric gradient alternating 4-layer nano-composite film; (d) Asymmetric gradient alternating 6-layer nano-composite film;

[0014] Figure 2 Tensile strength and elongation at break comparison chart of the asymmetric alternating multi-layer nano-composite film of the embodiments of the present invention and the blend nano-composite film with the same component content;

[0015] Figure 2Among them, 1: Tensile strength and elongation at break of the cellulose nanofiber / reduced graphene oxide supported iron oxide / silver nanowire blended nanocomposite film; 2: Tensile strength and elongation at break of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric bilayer nanocomposite film; 3: Tensile strength and elongation at break of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric gradient alternating 4-layer nanocomposite film; 4: Tensile strength and elongation at break of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric gradient alternating 6-layer nanocomposite film.

[0016] Figure 3 Conductivity comparison chart of the asymmetric alternating multi-layer nanocomposite film of the embodiment of the present invention and the blended nanocomposite film with the same composition content;

[0017] Figure 3 Among them, 1: Conductivity of the cellulose nanofiber / reduced graphene oxide supported iron oxide / silver nanowire blended nanocomposite film; 2: Conductivity of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric bilayer nanocomposite film; 3: Conductivity of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric gradient alternating 4-layer nanocomposite film; 4: Conductivity of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric gradient alternating 6-layer nanocomposite film.

[0018] Figure 4 Electromagnetic interference shielding performance comparison chart of the asymmetric alternating multi-layer nanocomposite film of the embodiment of the present invention and the blended nanocomposite film with the same composition content;

[0019] Figure 4 Among them, 1: Electromagnetic interference shielding effectiveness of the cellulose nanofiber / reduced graphene oxide supported iron oxide / silver nanowire blended nanocomposite film; 2: Electromagnetic interference shielding effectiveness of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric bilayer nanocomposite film; 3: Electromagnetic interference shielding effectiveness of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric gradient alternating 4-layer nanocomposite film; 4: Electromagnetic interference shielding effectiveness of the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric gradient alternating 6-layer nanocomposite film. Detailed implementation mode

[0020] The present invention will be further described below in conjunction with embodiments, but it is not used as a basis for limiting the present invention.

[0021] Example 1: Preparation of an electromagnetic interference shielding nanocomposite film with an asymmetric alternating multilayer structure, the steps are as follows:

[0022] 1) First, weigh 5 g of cellulose nanofiber aqueous dispersion (1.25 wt%), and then add water for dilution to form 42 mL of cellulose nanofiber aqueous dispersion. Secondly, add 10 mL of reduced graphene oxide loaded with iron tetroxide (5 mg∙mL -1 ) aqueous dispersion, manually stir and sonicate for 15 minutes to form 52 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide aqueous dispersion. Finally, add 30 mL of silver nanowire (2.2 mg∙mL -1 ) aqueous dispersion to 52 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide aqueous dispersion, manually stir for 10 min to form 82 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide / silver nanowire aqueous dispersion, and then obtain a cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide / silver nanowire blend nanocomposite film through vacuum-assisted filtration.

[0023] 2) Preparation of cellulose nanofiber / silver nanowire dispersion: Weigh 2 g of cellulose nanofiber aqueous dispersion (1.25 wt%), add water for dilution to form 10 mL of cellulose nanofiber dispersion. Then add 30 mL of silver nanowire (2.2 mg∙mL -1 ) dispersion to 10 mL of cellulose nanofiber dispersion under magnetic stirring and stir for 15 minutes to form a uniform 40 mL of cellulose nanofiber / silver nanowire dispersion (2.275 mg∙mL -1 ).

[0024] 3) Preparation of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion: Weigh 3 g of cellulose nanofiber (1.25 wt%) aqueous dispersion, add water for dilution to form 32 mL of cellulose nanofiber dispersion. Then add 10 mL of reduced graphene oxide loaded with iron tetroxide (5 mg∙mL -1 ) dispersion to 32 mL of cellulose nanofiber dispersion and sonicate for 15 minutes to form a uniform 42 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion (2.08 mg∙mL -1 ).

[0025] 4) Preparation of asymmetric bilayer nanocomposite film: First, 40 mL of cellulose nanofiber / silver nanowire dispersion was subjected to vacuum-assisted filtration to construct a cellulose nanofiber / silver nanowire layer. Second, 42 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion was added to the surface of the cellulose nanofiber / silver nanowire layer and continued to be vacuum-assisted filtered to obtain an asymmetric bilayer nanocomposite film (the absorption layer thickness is 30 μm, and the reflection layer thickness is 20 μm).

[0026] 5) Preparation of asymmetric gradient alternating 4-layer nanocomposite film: 40 mL of cellulose nanofiber / silver nanowire dispersion was divided into 30 mL of cellulose nanofiber / silver nanowire dispersion and 10 mL of cellulose nanofiber / silver nanowire dispersion, and 42 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion was divided into 32 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion and 10 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion. Vacuum-assisted filtration was carried out in the order of 30 mL of cellulose nanofiber / silver nanowire, 10 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide, 10 mL of cellulose nanofiber / silver nanowire, and 32 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion to obtain an asymmetric gradient alternating 4-layer nanocomposite film (the absorption layer thicknesses are 18 μm and 8 μm respectively; the reflection layer thicknesses are 16 μm and 6 μm respectively).

[0027] 6) Preparation of asymmetric gradient alternating 6-layer nanocomposite film: Divide 40 mL of cellulose nanofiber / silver nanowire dispersion into 20 mL of cellulose nanofiber / silver nanowire dispersion, 12.5 mL of cellulose nanofiber / silver nanowire dispersion, and 7.5 mL of cellulose nanofiber / silver nanowire dispersion; divide 42 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion into 22 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion, 12.5 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion, and 7.5 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion; successively perform vacuum-assisted filtration in the order of 20 mL of cellulose nanofiber / silver nanowire, 7.5 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide, 12.5 mL of cellulose nanofiber / silver nanowire, 12.5 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide, 7.5 mL of cellulose nanofiber / silver nanowire, and 22 mL of cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide dispersion to obtain an asymmetric gradient alternating 6-layer nanocomposite film (the absorption layer thicknesses are 16 μm, 10 μm, 5 μm respectively; the reflection layer thicknesses are 12 μm, 7 μm, 4 μm respectively).

[0028] The cross-sections of the cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide / silver nanowire blend nanocomposite film, the cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide & cellulose nanofiber / silver nanowire asymmetric 2-layer nanocomposite film, the asymmetric gradient alternating 4-layer nanocomposite film, and the asymmetric gradient alternating 6-layer nanocomposite film obtained in the above steps are as Figure 1 shown. It can be seen from the figure that the cross-section of the blend nanocomposite film is irregular and has many defects, while the cross-section of the asymmetric two-layer nanocomposite film is relatively regular and exhibits asymmetric and gradient alternating structural characteristics.

[0029] The tensile strength and elongation at break of the cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide / silver nanowire blend nanocomposite film, the cellulose nanofiber / reduced graphene oxide loaded with iron tetroxide & cellulose nanofiber / silver nanowire asymmetric 2-layer nanocomposite film, the asymmetric gradient alternating 4-layer nanocomposite film, and the asymmetric gradient alternating 6-layer nanocomposite film obtained in the above steps are as Figure 2As shown in the figure, compared with the cellulose nanofiber / reduced graphene oxide loaded ferric oxide / silver nanowire blended nanocomposite membrane with the same content of components, the cellulose nanofiber / reduced graphene oxide loaded ferric oxide & cellulose nanofiber / silver nanowire asymmetric 2-layer nanocomposite membrane, asymmetric gradient alternating 4-layer nanocomposite membrane, and asymmetric gradient alternating 6-layer nanocomposite membrane showed higher mechanical properties. For example, the tensile strength and elongation at break of the cellulose nanofiber / reduced graphene oxide loaded ferric oxide / silver nanowire blended nanocomposite membrane were 68.2 MPa and 6.0%, respectively, while the tensile strength and elongation at break of the cellulose nanofiber / reduced graphene oxide loaded ferric oxide & cellulose nanofiber / silver nanowire asymmetric gradient alternating 6-layer nanocomposite membrane were 115.2 MPa and 8.1%, respectively. The analysis believes that this is mainly attributed to the asymmetric gradient alternating multilayer structure design, which first reduces the agglomeration phenomenon between nanomaterials, maximizes the hydrogen bonding between the components and the interlayer hydrogen bonding, and secondly forms the micro-scale zigzag crack path. The large amount of hydrogen bonding in the material is conducive to load transfer and energy dissipation. The Z-shaped crack can absorb a large amount of fracture energy during crack growth, resulting in a significant improvement in the mechanical properties of the material.

[0030] The conductivity of the cellulose nanofiber / reduced graphene oxide loaded ferroferric oxide / silver nanowire blended nanocomposite membrane, the cellulose nanofiber / reduced graphene oxide loaded ferroferric oxide & cellulose nanofiber / silver nanowire asymmetric 2-layer nanocomposite membrane, the asymmetric gradient alternating 4-layer nanocomposite membrane, and the asymmetric gradient alternating 6-layer nanocomposite membrane obtained in the above steps is as follows: Figure 3 As shown, compared with the cellulose nanofiber / reduced graphene oxide loaded ferroferric oxide / silver nanowire blended nanocomposite membrane with the same content of ingredients, the cellulose nanofiber / reduced graphene oxide loaded ferroferric oxide & cellulose nanofiber / silver nanowire asymmetric 2-layer nanocomposite membrane, asymmetric gradient alternating 4-layer nanocomposite membrane, and asymmetric gradient alternating 6-layer nanocomposite membrane showed higher conductivity. This is mainly due to the asymmetric gradient alternating multilayer structure design, and the overlap between the silver nanowires is closer to form an ultra-efficient conductive network. Interestingly, the conductivity of the asymmetric 2-layer nanocomposite membrane, the asymmetric gradient alternating 4-layer nanocomposite membrane, and the asymmetric gradient alternating 6-layer nanocomposite membrane decreases with the increase in the number of layers. This may be because after a layer of cellulose nanofiber / silver nanowire is divided into multiple layers, the conductive network of the silver nanowire is weakened, and the conductivity of the nanocomposite membrane is reduced.

[0031] The electromagnetic interference shielding performance of the cellulose nanofiber / reduced graphene oxide supported iron oxide / silver nanowire blended nanocomposite film, the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric bilayer nanocomposite film, the asymmetric gradient alternating four-layer nanocomposite film, and the asymmetric gradient alternating six-layer nanocomposite film obtained in the above appeal steps is as follows Figure 4 As shown, compared with the cellulose nanofiber / reduced graphene oxide supported iron oxide / silver nanowire blended nanocomposite film with the same composition content, the cellulose nanofiber / reduced graphene oxide supported iron oxide & cellulose nanofiber / silver nanowire asymmetric bilayer nanocomposite film, the asymmetric gradient alternating four-layer nanocomposite film, and the asymmetric gradient alternating six-layer nanocomposite film show higher electromagnetic interference shielding performance. In particular, the average electromagnetic shielding effectiveness of the asymmetric gradient alternating six-layer nanocomposite film is 104 dB (up to 112.9 dB), while the average electromagnetic interference shielding effectiveness of the cellulose nanofiber / reduced graphene oxide supported iron oxide / silver nanowire blended nanocomposite film is only 63.1 dB. This is firstly due to the fact that the asymmetric gradient alternating multi-layer structure greatly improves the conductivity of the nanocomposite film; secondly, the conductivity of the asymmetric bilayer nanocomposite film, the asymmetric gradient alternating four-layer nanocomposite film, and the asymmetric gradient alternating six-layer nanocomposite film decreases with the increase in the number of layers, but the electromagnetic shielding effectiveness shows a significant increase, which is attributed to the fact that the asymmetric gradient alternating multi-layer structure design forms a new electromagnetic interference shielding mechanism of gradient absorption and gradient reflection of electromagnetic waves in the nanocomposite film, increasing the absorption of electromagnetic waves and resulting in an increase in electromagnetic effectiveness.

[0032] The electromagnetic interference shielding mechanism of gradient absorption and gradient reflection described in the above steps refers to: when electromagnetic waves strike the absorption layer (16 μm) of the asymmetric gradient alternating 6-layer nanocomposite film, due to the dielectric loss and magnetic loss of the magnetic hybrid nanoparticles, a part of the electromagnetic waves is absorbed, and only a very small amount of electromagnetic waves are reflected. When the electromagnetic waves passing through the absorption layer (16 μm) encounter the reflection layer (4 μm), due to impedance mismatch, a small amount of electromagnetic waves are reflected at the interface between the absorption layer (16 μm) and the reflection layer (4 μm) and enter the absorption layer (16 μm) again. A small part of the electromagnetic waves entering the reflection layer (4 μm) interacts with high-density carriers (such as electrons, holes, and dipoles), resulting in the attenuation of electromagnetic wave energy due to ohmic loss and induced current, and the electromagnetic waves are absorbed. When the electromagnetic waves passing through the reflection layer (4 μm) encounter the absorption layer (10 μm), less electromagnetic waves are absorbed due to magnetic loss and dielectric loss. When the electromagnetic waves passing through the absorption layer (10 μm) encounter the reflection layer (7 μm), due to impedance mismatch, a part of the electromagnetic waves is reflected back to the absorption layer (10 μm), and the reflection layer (4 μm) and the absorption layer (16 μm) are absorbed again. A part of the electromagnetic waves entering the reflection layer (7 μm) is absorbed due to the attenuation of electromagnetic wave energy by ohmic loss and induced current. When the electromagnetic waves passing through the reflection layer (7 μm) encounter the absorption layer (5 μm), a very small amount of electromagnetic waves are absorbed due to magnetic loss and dielectric loss. When the electromagnetic waves passing through the absorption layer (5 μm) encounter the reflection layer (12 μm), a considerable part of the electromagnetic waves are reflected back to the absorption layer (5 μm), the reflection layer (7 μm), the absorption layer (10 μm), the reflection layer (4 μm), and the absorption layer (16 μm) and are reflected and absorbed multiple times. The electromagnetic waves entering the reflection layer (12 μm) are absorbed due to a large amount of ohmic loss and the attenuation of electromagnetic wave energy by induced current. This unique gradient absorption and gradient reflection electromagnetic interference shielding mechanism of the asymmetric gradient alternating 6-layer nanostructured composite film enables the electromagnetic waves to be gradient-reflected and gradient-absorbed back and forth within the nanocomposite film, resulting in a great improvement in the electromagnetic shielding effectiveness of the nanocomposite film, providing an effective strategy for preparing electromagnetic shielding materials with ultra-high electromagnetic shielding performance.

Claims

1. An electromagnetic interference shielding nanocomposite film with an asymmetric alternating multilayer structure, characterized in that: It includes an absorption layer nanofilm and a reflection layer nanofilm. Calculated by mass fraction, the composition of a single-layer absorption layer nanofilm includes 1 - 40 parts of cellulose nanofibers and 1 - 50 parts of magnetic nanoparticles; the composition of the reflection layer nanofilm includes 1 - 25 parts of cellulose nanofibers and 1 - 66 parts of conductive nanoparticles; the so-called asymmetric alternation means that the absorption layer nanofilm and the reflection layer nanofilm with different thicknesses are alternately laminated.

2. The electromagnetic interference shielding nano-composite film with an asymmetric alternating multi-layer structure according to claim 1, characterized in that: The magnetic nanoparticles are carbon nanotube-supported iron tetroxide, titanium carbide-supported iron tetroxide or titanium carbide-supported nickel; the conductive nanoparticles are silver nanowires, carbon nanotubes or graphene.

3. The preparation method of the electromagnetic interference shielding nanocomposite film with an asymmetric alternating multi-layer structure according to claim 1 or 2, characterized in that, It includes the following steps: 1) Take each component according to the above mass fraction, mix and stir the conductive nanoparticle dispersion liquid and the cellulose nanofiber dispersion liquid to make them fully mixed, forming a uniform cellulose nanofiber / conductive nanoparticle dispersion liquid, and perform vacuum-assisted filtration on the cellulose nanofiber / silver nanowire dispersion liquid to obtain the reflection layer nanofilm; 2) Take each component according to the above mass fraction, mix and ultrasonically disperse the cellulose nanofiber aqueous dispersion liquid and the magnetic nanoparticles to form a uniform cellulose nanofiber / magnetic nanoparticle dispersion liquid; on the basis of step 1), add the cellulose nanofiber / magnetic nanoparticle dispersion liquid to the surface of the reflection layer nanofilm obtained in step 1) and continue vacuum-assisted filtration to form an asymmetric double-layer nanocomposite film; 3) Repeat the above steps 1) and 2) to prepare an electromagnetic interference shielding nanocomposite film with a multi-layer structure of more than 2 layers of asymmetric alternation.

4. The preparation method according to claim 3, characterized in that: The thickness of the absorption layer nanofilm is 8 - 50 μm, and the thickness of the reflection layer nanofilm is 6 - 50 μm.

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