Preparation method of a biomass carbon-based ultra-light insulating electromagnetic shielding material

Abstract

The present invention discloses a preparation method of a biomass carbon-based ultra-light insulating electromagnetic shielding material. By means of designing the critical size of biomass carbon, modulating the core conductivity, insulating coating of the interface, etc., the material can be integrated with the device matrix, and while electromagnetic induction shielding is generated therein, the insulating shell layer between particles effectively blocks the transport of electrons, forming a relatively high volume resistivity to ensure the electrical safety and performance of surrounding connectors. The present invention can be widely applied to direct injection molding, extrusion molding, hot pressing, coating and other forming and in-situ electromagnetic shielding of various devices such as connectors, controllers, switches, motors, etc. in a wide range of fields including new energy vehicles, electronic and electrical products, communication and Internet of Things products, aircrafts, aerospace spacecrafts, etc., and is applicable to electromagnetic wave shielding of devices and products in the frequency band of 1 Hz to 42.5 GHz.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic functional materials, and particularly relates to a preparation method of a biomass carbon-based ultra-light insulating electromagnetic shielding material. Background Art

[0002] With the advent of the carbon neutral and carbon peak era, new energy vehicles are considered the first choice to replace fuel vehicles. However, in the three-electricity system, electromagnetic interference (EMI) and electromagnetic radiation (EMR) generated by high-voltage line power transmission, data signal transmission, network communication, instantaneous start and stop of devices, wireless charging, wire harness and battery pack layout, etc., will cause signal distortion and even failure of in-vehicle sensors, driverless systems, cameras, controllers, etc., seriously threatening driving safety, and also threatening the physical and mental health of drivers and passengers. Such problems are not limited to new energy vehicle products. The huge impact of electromagnetic compatibility (EMC) on the operation of electronic and communication devices widely exists in various industries and products such as consumer electronics, 5G, intelligent Internet of Things, aviation, and aerospace, and has become a pain point in the industry and has successively formed mandatory standards in various countries. Electromagnetic shielding materials that can be integrated into devices and products are considered a very effective way to solve this problem.

[0003] At present, most of the electromagnetic shielding materials used in the industry are for the high-frequency microwave range around 8-12 GHz (X-band), mainly metal or conductive non-metal materials with good conductivity and their composite matrices. For example: Chinese Patent CN202111331937.3, an electromagnetic shielding paper based on conductive MOF material modification and its preparation method, uses MOF material with excellent conductivity to modify PI fiber to obtain a continuously conductive skeleton shielding paper structure; Chinese Patent CN201820797508.2, a double-layer conductive structure electromagnetic shielding material, adopts a double-layer structure of copper foil and foamed iron-nickel alloy, and is supplemented with conductive rubber and copper powder adhesive to form a continuously conductive electromagnetic shielding matrix; Chinese Patent CN201410692427.2, an application of graphene composite material as an electromagnetic shielding material, uses graphene to coat the surface of a foam sponge skeleton to form a three-dimensional connected conductive skeleton shielding material. However, with the increasing complexity of the internal electrical structure of devices and the requirement of device miniaturization, the integration of such conductive shielding materials with the device body will cause short circuits in electrical structures such as internal connectors and circuits, affecting the safety and reliability of the devices. Therefore, the current conductive shielding materials can only shield the electromagnetic waves generated by the device itself and incident from the outside in the form of a shell, shielding cover, external coating, etc. How to integrate the shielding material with the device matrix and effectively shield electromagnetic waves without affecting the internal electrical safety and performance of the device is the key to solving the electromagnetic compatibility problem of future miniaturized and integrated devices. Summary of the Invention

[0004] Aiming at the problems existing in the application of existing large-area continuous conductive shielding materials, the present invention aims to provide a preparation method of a biomass carbon-based ultra-light insulating electromagnetic shielding material. By designing the critical size of biomass carbon, modulating the core conductivity, and insulating coating the interface, etc., the material can be integrated with the device matrix, and while generating electromagnetic induction shielding therein, the insulating shell layer between particles effectively blocks the transport of electrons, forming a relatively high volume resistivity to ensure the electrical safety and performance of surrounding connectors. The present invention can be widely applied to direct injection molding, extrusion molding, hot pressing, coating and other forming and in-situ electromagnetic shielding of various devices such as connectors, controllers, switches, motors, etc. in a wide range of fields including new energy vehicles, electronic and electrical products, communication and Internet of Things products, aircraft, aerospace spacecraft, etc., and is applicable to electromagnetic wave shielding of devices and products in the frequency band of 1 Hz to 42.5 GHz.

[0005] The preparation method of the biomass carbon-based ultra-light insulating electromagnetic shielding material of the present invention is to in-situ coat particles with amorphous oxides or insulating polymers with high resistivity under good dispersion conditions to block the conductive channels between particles, and specifically includes the following steps:

[0006] Step 1: Sufficiently dry and dehydrate the biomass raw material, and then, in an inert protective atmosphere or in vacuum, heat it to 600 - 2300 °C at a rate of 2 °C - 5 °C / min, keep it warm for 1 - 8 h for high-temperature carbonization operation, and after natural cooling, grind the obtained product into biomass carbon powder with a particle size of 8 - 150 μm, and then separate biomass carbon powder with different particle sizes through sieve meshes of different mesh numbers.

[0007] Step 2: Disperse 0.5 - 3 g of the biomass carbon powder obtained in Step 1 in 20 ml of water or absolute ethanol, add a certain amount of dispersant, and continuously perform ultrasonic treatment or high-speed stirring at room temperature (25 °C) for 0.5 - 6 h for interfacial functional group modification and modification to make the powder evenly dispersed and reduce the agglomeration between particles; perform suction filtration or centrifugal separation on the obtained product to obtain modified biomass carbon powder with good water solubility and dispersibility;

[0008] Step 3: Redisperse 0.01 - 3 g of the modified biomass carbon powder obtained in Step 2 in 10 mL - 50 mL of an aqueous solution of a conductive polymer monomer with a concentration of 0.0001 - 0.5 g / mL, continuously perform ultrasonic treatment or stirring to obtain a precursor solution, and adjust the pH value of the system ≤ 5;

[0009] Step 4: Drop a certain amount of initiator into the precursor solution obtained in Step 3, continuously stir it under ice bath conditions for 1 - 8 h, wash the obtained product successively with water and absolute ethanol until the washing waste liquid is clear and the pH value is neutral, and perform suction filtration or centrifugal separation to obtain biomass carbon particles coated with a conductive polymer;

[0010] Step 5: Coating the biomass carbon particles obtained in Step 4 with an insulating amorphous silica or insulating polymer shell layer respectively by the method of Step 5a or 5b:

[0011] 5a: Uniformly disperse the biomass carbon particles coated with a conductive polymer in a mixed solution composed of water, alcohol, and ammonia water, stir at room temperature for 0.5 - 2 h, slowly drop tetraethyl orthosilicate (TEOS) into the system, and continue to stir at room temperature for 1 - 20 h. After the reaction product is washed with water and ethanol, it is separated by suction filtration or centrifugation and dried to obtain the powder of the biomass carbon-based shielding material coated with insulating amorphous SiO2;

[0012] 5b: Uniformly disperse the biomass carbon particles coated with a conductive polymer in an aqueous solution of an insulating polymer monomer with a concentration of 0.05 - 8 mol / L, stir at room temperature for 0.5 - 5 h, slowly add an initiator to the solution, and continuously stir at 0 - 90 °C for 1 - 20 h. After the reaction product is washed with water and ethanol, it is separated by suction filtration or centrifugation and dried to obtain the powder of the biomass carbon-based shielding material coated with an insulating polymer;

[0013] Step 6: Mix the insulating coated biomass carbon-based powder obtained in Step 5 with the device matrix raw materials, and after molding, obtain the insulating electromagnetic shielding material and device with particle-level coating and high resistivity.

[0014] The device matrix includes resin, rubber, coating, colloid, paraffin, etc.

[0015] The added mass of the insulating coated biomass carbon-based powder is 10 - 35% of the mass of the device matrix raw materials.

[0016] The mixing methods include direct mixing, internal mixing, open mixing, etc.

[0017] The molding methods include injection molding, extrusion molding, compression molding, blow molding, extrusion, rotational molding, coating, etc.

[0018] In Step 1, the biomass raw materials include various plants or agricultural and forestry wastes such as straw, trees, rhizomes, peels, fibers, seeds, etc. The mesh numbers of the sieve are 900 mesh, 1600 mesh, and 1800 mesh.

[0019] In Step 2, the dispersant can be one or several of polyvinylpyrrolidone (PVP), sodium dodecylbenzenesulfonate (SDS), sodium dodecylbenzenesulfonate (SDBS), KH550, cetyltrimethylammonium bromide (CTAB), oleic acid, Tween, sodium citrate, etc., or other types that are affinity with the surface of biomass carbon; the addition ratio of the dispersant is 0.001 - 3 mol / L.

[0020] In Step 3, the conductive polymer monomer is one or several of aniline, thiophene, and pyrrole.

[0021] In Step 3, the pH value of the system is adjusted with hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, etc.

[0022] In Step 4, the initiator is an aqueous solution or an alcohol solution of persulfate, and the addition amount is 0.02 - 4 mol / L.

[0023] In Step 5a, in the mixed solution composed of water, alcohol, and ammonia water, the volume ratio of ammonia water (with a concentration of 25 - 28%), water, and alcohol is 1:2 - 30:25 - 60.

[0024] In Step 5a, the proportion of the biomass carbon particles coated with the conductive polymer dispersed in the mixed solution is 0.01 - 0.075 g / mL.

[0025] In Step 5a, the addition proportion of tetraethyl orthosilicate accounts for 2 - 20% of the total solution volume.

[0026] In Step 5b, the insulating polymer monomer is selected from the monomers that constitute polymers with high resistivity such as polystyrene (PS), polymethyl methacrylate (PMMA), polyphenylene sulfide (PPS), polyamide (PA), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), polycarbonate (PC), polyoxymethylene (POM), polyethylene (PE), polyvinyl chloride (PVC), polylactic acid (PLA), etc., and the precursor monomers of their doping or derivatives.

[0027] In Step 5b, the proportion of the biomass carbon particles coated with the conductive polymer dispersed in the aqueous solution of the insulating polymer monomer is 0.01 - 0.075 g / mL.

[0028] In Step 5b, the initiator is persulfate and a reagent that can polymerize the above monomers, and the addition proportion is 1 - 12% of the total solution volume.

[0029] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0030] 1. By shielding the eddy current effect of the conductive core of the material, the present invention can still form a reverse magnetic field and strong electromagnetic shielding performance through the electromagnetic induction effect in the microwave electromagnetic field, and at the same time avoids the formation of an overall large - area conductive network;

[0031] 2. The present invention uses a conductive polymer to coat and modulate the interfacial conductivity of the porous biomass core, and enhances the eddy current effect and improves the electromagnetic shielding efficiency by means of multiple scattering and reverse magnetic field enhancement;

[0032] 3. In the present invention, a high-resistivity amorphous oxide or polymer shell tightly coats the biomass carbon-based conductive core particles, forming an insulating interface of the particles at the micron scale, effectively blocking the conductive connection between the particles, increasing the overall resistivity, and while ensuring the shielding performance, improving the insulating electrical properties of the material, even integrating the shielding layer and the electrical layer into one.

[0033] 4. The insulating shielding material involved in the present invention can be combined with a matrix as a polymer raw material and directly used for the processing and coating molding of various devices or product components such as connectors, controllers, switches, etc., eliminating the existing external conductive shielding housing and not affecting the electrical safety of the internal plug electrodes and circuits.

[0034] 5. The biomass raw materials used in the present invention can be widely obtained at extremely low costs. The preparation does not require expensive equipment and energy consumption, has a short production cycle, large output, good repeatability, adjustable size and performance, and at the same time solves the problem of the treatment of agricultural and forestry waste such as straw, being economical and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the SEM image of the biomass carbon / SiO2 prepared in Example 2. The SEM morphology image shows that the biomass carbon / SiO2 particles are irregular in shape, with relatively uniform sizes, averaging about 8 - 10 μm, and the surface roughness of the particles is relatively large, indicating the dense insulating coating of SiO2, good dispersion between the particles, and no obvious agglomeration.

[0036] Figure 2 It is the SEM image of the biomass carbon / PANI / PS prepared in Example 4. The SEM morphology image shows that the biomass carbon / PANI / PS particles are irregular in shape, with relatively uniform sizes, averaging about 10 - 12 μm, and the surface roughness of the particles increases, indicating the double-layer dense insulating coating of PANI / PS, good dispersion between the particles, no obvious agglomeration, and the smaller particle fragments should be a small amount of PS that is not interfacially polymerized.

[0037] Figure 3 For Examples 1 - 5, the real part of the dielectric constant of the samples in the frequency bands of (a) 1 - 18 GHz, (b) 18 - 26.5 GHz, and (c) 26.5 - 40 GHz respectively. The ε' of the corresponding samples in Examples 1 - 5 is at a relatively high level in the range of 1 - 40 GHz, and in some frequency bands of 1 - 18 GHz, it can reach more than 20, indicating that although there is an insulating shell coating, there are a large number of dielectric dipoles in the biomass carbon and the biomass carbon / PANI conductive cores.

[0038] Figure 4For Examples 1-5, the imaginary parts of the dielectric constants of the samples in the frequency bands of (a) 1-18 GHz, (b) 18-26.5 GHz, and (c) 26.5-40 GHz are respectively. The values of ε" of the corresponding samples in Examples 1-5 are also relatively large in the range of 1-40 GHz. In some frequency bands of 1-18 GHz and 18-26.5 GHz, they can reach more than 8, indicating that although coated with an insulating shell, the biomass carbon and the biomass carbon / PANI conductive core still have good dielectric loss performance.

[0039] Figure 5 For Examples 1-5, the shielding effectiveness of the samples in the frequency bands of (a) 1-18 GHz, (b) 18-26.5 GHz, and (c) 26.5-40 GHz are respectively. The SE of the high-resistivity insulating samples in Examples 1-5 has exceeded 5 dB in the C-Ku frequency band of 1-18 GHz and the entire frequency band of 18-26.5 GHz, and the SE in some frequency bands of 26.5-40 GHz has exceeded 10 dB. Combining with the relatively high resistivity (greater than 10 9 Ω·m) of the samples in Examples 1-5, it shows that the biomass carbon and the biomass carbon / PANI conductive core have relatively high dielectric properties, so that even without conductive connection between particles and coated with an insulating shell, they can still effectively shield electromagnetic waves in the frequency band of 1-40 GHz. Among them, in Figure (a), Example 6 is the shielding effectiveness of biomass carbon without coating the conductive core and insulating material. Comparing with Examples 1-5, it can be seen that the double-layer coating of the conductive core / insulating material will not reduce the shielding effectiveness of the material. Comparing Figure 1 、 Figure 2 the average particle size, the prepared biomass carbon / SiO2 particles in the examples may be partially smaller than the critical size, resulting in the inability to generate the eddy current effect, thus reducing the shielding effectiveness. Specific embodiments

[0040] Example 1:

[0041] 1. The straw crushing raw materials are fully dehydrated and dried, and then carbonized and sintered at 800 °C for 18 h in an argon atmosphere. The obtained product is ground into powder, and the biomass carbon powder with an average particle size of 11 μm is obtained by sieving;

[0042] 2. 0.5 g of the biomass carbon powder obtained in step 1 is dispersed in 20 mL of absolute ethanol, and 1 g of PVP is added as a dispersant, and ultrasonic treatment is continuously carried out for 1 h until the powder is evenly dispersed; the obtained product is separated by suction filtration;

[0043] 3. Redisperse the biomass carbon-based powder obtained in step 2 in 20 mL of 5 mol / L styrene aqueous solution, mix evenly at 70 °C, then slowly add 0.5 mL of 0.15 mol / L ammonium persulfate aqueous solution, and continuously stir for 3 h; after the reaction product is washed three times with water and anhydrous ethanol respectively, it is dried for 8 h to obtain biomass carbon / PS particle powder;

[0044] 4. Mix the insulated coated biomass carbon / PS powder obtained in step 3 with epoxy resin in a proportion of 30% and fully mix and mold it, and respectively test its electromagnetic parameters and shielding effectiveness at 1 - 18 GHz, 18 - 26.5 GHz, and 26.5 - 40 GHz.

[0045] Example 2:

[0046] 1. Thoroughly dehydrate and dry the crushed straw raw material, then sinter it at 600 °C for 18 h in an argon atmosphere, grind the obtained product into powder, and sieve it to obtain biomass carbon powder with an average particle size of 9 μm;

[0047] 2. Disperse 0.5 g of the biomass carbon powder obtained in step 1 in 20 mL of anhydrous ethanol, add 1 g of PVP as a dispersant, and continuously perform ultrasonic treatment for 1 h until the powder is evenly dispersed; filter and separate the obtained product;

[0048] 3. Redisperse the biomass carbon-based powder obtained in step 2 in 20 mL of anhydrous ethanol, add 0.2 g of PVP and 0.8 mL of ammonia water, and stir at room temperature for 0.5 h; then, while maintaining the stirring speed, slowly add 0.3 mL of tetraethyl orthosilicate (TEOS) to the solution, and continue to stir for 5 h; after the reaction product is washed three times with water and anhydrous ethanol respectively, it is dried for 8 h to obtain biomass carbon / SiO2 particle powder;

[0049] 4. Mix the insulated coated biomass carbon / SiO2 powder obtained in step 3 with paraffin in a proportion of 30% and fully mix and mold it, and respectively test its electromagnetic parameters and shielding effectiveness at 1 - 18 GHz, 18 - 26.5 GHz, and 26.5 - 40 GHz.

[0050] Example 3:

[0051] 1. Thoroughly dehydrate and dry the crushed straw raw material, then sinter it at 800 °C for 18 h in an argon atmosphere, grind the obtained product into powder, and sieve it to obtain biomass carbon powder with an average particle size of 11 μm;

[0052] 2. Disperse 0.5 g of the biomass carbon powder obtained in step 1 in 20 mL of anhydrous ethanol, add 1 g of PVP as a dispersant, and continuously perform ultrasonic treatment for 1 h until the powder is evenly dispersed; filter and separate the obtained product;

[0053] 3. Redisperse the biomass carbon-based powder obtained in step 2 in 30 mL of 1 mol / L aniline aqueous solution, and add 5 mL of 0.1 mol / L hydrochloric acid solution dropwise thereto, and continuously perform ultrasonic treatment for 1 h;

[0054] 4. Under the condition of an ice bath at 0 °C, slowly add 5 mL of 1 mol / L ammonium persulfate aqueous solution dropwise to the solution, and continuously stir for 3 h; After the reaction product is washed three times each with water and absolute ethanol, it is centrifuged and dried to obtain the biomass carbon / PANI particle powder;

[0055] 5. Redisperse the biomass carbon / PANI powder obtained in step 4 in a mixed solution composed of 2 mL of MMA, 18 mL of distilled water and 55 mL of absolute ethanol. After mixing evenly, add 0.02 g of ammonium persulfate to the solution, and continuously stir at 70 °C for 10 h; After the reaction product is washed three times each with water and ethanol, it is vacuum dried for 8 h to obtain the biomass carbon / PANI / PMMA powder.

[0056] 6. Mix the insulated coated biomass carbon / PANI / PMMA powder obtained in step 5 with epoxy resin in a proportion of 30% and fully mold it, and test its electromagnetic parameters and shielding effectiveness at 1 - 18 GHz, 18 - 26.5 GHz, and 26.5 - 40 GHz respectively.

[0057] Example 4:

[0058] 1. Thoroughly dehydrate and dry the crushed straw raw material, and then perform carbonization sintering at 700 °C for 10 h in an argon atmosphere. The obtained product is ground into powder and sieved to obtain biomass carbon powder with an average particle size of 11 μm;

[0059] 2. Disperse 0.5 g of the biomass carbon powder obtained in step 1 in 20 mL of absolute ethanol, and add 1 g of PVP as a dispersant, and continuously perform ultrasonic treatment for 1 h until the powder is evenly dispersed; The obtained product is separated by filtration;

[0060] 3. Redisperse the biomass carbon-based powder obtained in step 2 in 30 mL of 1 mol / L aniline aqueous solution, and add 5 mL of 0.1 mol / L hydrochloric acid solution dropwise thereto, and continuously perform ultrasonic treatment for 1 h;

[0061] 4. Under the condition of an ice bath at 0 °C, slowly add 5 mL of 1 mol / L ammonium persulfate aqueous solution dropwise to the solution, and continuously stir for 3 h; After the reaction product is washed three times each with water and absolute ethanol, it is centrifuged and dried to obtain the biomass carbon / PANI particle powder;

[0062] 5. Redisperse the biomass carbon / PANI powder obtained in step 4 in an aqueous solution of 5 mol / L styrene. After mixing evenly, add 0.5 ml of ammonium persulfate with a concentration of 0.15 mol / L to the solution, and continuously stir at 70 °C for 3 h. After the reaction product is washed three times with water and ethanol respectively, it is dried in vacuum for 8 h to obtain biomass carbon / PANI / PS powder.

[0063] 6. Mix the insulated coated biomass carbon / PANI / PS powder obtained in step 5 with epoxy resin in a proportion of 30% and fully mold it, and test its electromagnetic parameters and shielding effectiveness at 1 - 18 GHz, 18 - 26.5 GHz, and 26.5 - 40 GHz respectively.

[0064] Example 5:

[0065] 1. Thoroughly dehydrate and dry the crushed straw raw material, and then sinter it at 800 °C in an argon atmosphere for 18 h. Grind the obtained product into powder and sieve it to obtain biomass carbon powder with an average particle size of 9 μm.

[0066] 2. Disperse 0.5 g of the biomass carbon powder obtained in step 1 in 20 mL of absolute ethanol, add 1 g of PVP as a dispersant, and continuously perform ultrasonic treatment for 1 h until the powder is evenly dispersed. Filter and separate the obtained product.

[0067] 3. Redisperse the biomass carbon-based powder obtained in step 2 in 30 mL of 1 mol / L aniline aqueous solution, and dropwise add 5 ml of hydrochloric acid solution with a concentration of 0.1 mol / L to it, and continuously perform ultrasonic treatment for 1 h.

[0068] 4. Under the condition of an ice bath at 0 °C, slowly dropwise add 5 ml of ammonium persulfate aqueous solution with a concentration of 1 mol / L to the solution, and continuously stir for 3 h. After the reaction product is washed three times with water and absolute ethanol respectively, it is centrifuged and separated and dried to obtain biomass carbon / PANI particle powder.

[0069] 5. Redisperse the biomass carbon / PANI powder obtained in step 4 in 20 mL of absolute ethanol, add 0.2 g of PVP and 0.8 ml of ammonia water, and stir at room temperature for 0.5 h. Then, while maintaining the stirring speed, slowly dropwise add 0.3 ml of tetraethyl orthosilicate (TEOS) to the solution, and continue to stir for 5 h. After the reaction product is washed three times with water and absolute ethanol respectively, it is dried for 8 h to obtain biomass carbon / PANI / SiO2 particle powder.

[0070] 6. Mix the insulated coated biomass carbon / PANI / SiO2 powder obtained in step 5 with paraffin in a proportion of 30% and fully mold it, and test its electromagnetic parameters and shielding effectiveness at 1 - 18 GHz, 18 - 26.5 GHz, and 26.5 - 40 GHz respectively.

Claims

1. A preparation method of a biomass carbon-based ultra-light insulating electromagnetic shielding material, characterized in that It includes the following steps: Step 1: Sufficiently dry and dehydrate the biomass raw material, and then carry out high-temperature carbonization operation in an inert protective atmosphere or in vacuum. After natural cooling, grind the obtained product into biomass carbon powder with a particle size of 8 - 150 μm; Step 2: Disperse 0.5 - 3 g of the biomass carbon powder obtained in Step 1 in 20 ml of water or absolute ethanol, add a dispersant, and continuously carry out ultrasonic treatment or high-speed stirring at room temperature for 0.5 - 6 h for interfacial functional group modification and modification to make the powder evenly dispersed and reduce the agglomeration between particles; Carry out suction filtration or centrifugal separation on the obtained product to obtain a modified biomass carbon powder with good water solubility and dispersibility; Step 3: Redisperse 0.01 - 3 g of the modified biomass carbon powder obtained in Step 2 in 10 mL - 50 mL of an aqueous solution of a conductive polymer monomer with a concentration of 0.0001 - 0.5 g / mL, continuously carry out ultrasonic treatment or stirring to obtain a precursor solution, and adjust the pH value of the system ≤ 5; Step 4: Dropwise add an initiator to the precursor solution obtained in Step 3, continuously stir under ice bath conditions for 1 - 8 h, wash the obtained product with water and absolute ethanol in sequence until the washing waste liquid is clear and the pH value is neutral, carry out suction filtration or centrifugal separation, and then conductive polymer-coated biomass carbon particles can be obtained; Step 5: For the conductive polymer-coated biomass carbon particles obtained in Step 4, use the method of Step 5a or 5b to coat the particles with an insulating amorphous silica or insulating polymer shell layer: 5a: Uniformly disperse the conductive polymer-coated biomass carbon particles in a mixed solution composed of water, alcohol, and ammonia water, stir at room temperature for 0.5 - 2 h, slowly dropwise add tetraethyl orthosilicate to the system, and continue to stir at room temperature for 1 - 20 h. After the reaction product is washed with water and ethanol, carry out suction filtration or centrifugal separation and drying to obtain an insulating amorphous SiO2-coated biomass carbon-based shielding material powder; 5b: Uniformly disperse the conductive polymer-coated biomass carbon particles in an aqueous solution of an insulating polymer monomer with a concentration of 0.05 - 8 mol / L, stir at room temperature for 0.5 - 5 h, slowly add an initiator to the solution, and continuously stir at 0 - 90 °C for 1 - 20 h. After the reaction product is washed with water and ethanol, carry out suction filtration or centrifugal separation and drying to obtain an insulating polymer-coated biomass carbon-based shielding material powder; Step 6: Mix the insulating-coated biomass carbon-based powder obtained in Step 5 with the device matrix raw material, and after molding, obtain an insulating electromagnetic shielding material or device with particle-level coating and high resistivity; In Step 2, the dispersant is one or more of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, KH550, cetyltrimethylammonium bromide, oleic acid, Tween, sodium citrate; The addition ratio of the dispersant is 0.001 - 3 mol / L; In Step 3, the conductive polymer monomer is one or more of aniline, thiophene, and pyrrole.

2. The preparation method according to claim 1, wherein: In Step 1, the high-temperature carbonization is carried out by heating to 600 - 2300 °C at a rate of 2 °C - 5 °C / min and holding for 1 - 8 h.

3. The preparation method according to claim 1, characterized in that: In step 4, the initiator is an aqueous solution or an alcohol solution of persulfate, and the addition amount is 0.02 - 4 mol / L.

4. The preparation method according to claim 1, characterized in that: In step 5a, in the mixed solution composed of water, alcohol, and ammonia water, the volume ratio of ammonia water, water, and alcohol is 1:2 - 30:25 - 60; the addition ratio of tetraethyl orthosilicate accounts for 2 - 20% of the total solution volume; the proportion of the biomass carbon particles coated with the conductive polymer dispersed in the mixed solution is 0.01 - 0.075 g / mL.

5. The preparation method according to claim 1, characterized in that: In step 5b, the insulating polymer monomer is selected from the monomers that constitute polymers with high resistivity such as polystyrene, polymethyl methacrylate, polyphenylene sulfide, polyamide, polypropylene, polybutylene terephthalate, polyimide, polycarbonate, polyoxymethylene, polyethylene, polyvinyl chloride, or polylactic acid, and the precursor monomers of their doping or derivatives.

6. The preparation method according to claim 1, characterized in that: In step 5b, the proportion of the biomass carbon particles coated with the conductive polymer dispersed in the aqueous solution of the insulating polymer monomer is 0.01 - 0.075 g / mL.

7. The preparation method according to claim 1, characterized in that: In step 5b, the initiator is persulfate, and the addition ratio is 1 - 12% of the total solution volume.

8. The preparation method according to claim 1, characterized in that: The added mass of the insulated biomass carbon-based powder is 10 - 35% of the mass of the device matrix raw material.

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