Millimeter-level heat-conducting flexible graphite plate, preparation method and application thereof

Abstract

The application discloses a preparation method of a millimeter-level heat-conducting flexible graphite plate, and the method comprises the following steps: stacking artificial graphite films (4-20 mu m) and PS small balls (10-1000 nm) layer by layer to a certain thickness (0.1-0.5 mm); micro-thermal bonding and fixing at 100-150 degrees to form a multi-level structure material with gaps, facilitating the exchange of electrolytes; using the above assembled material as an electrode, cooperating with a copper sulfate solution (0.1-2 mol / L) to carry out water electroplating, electroplating copper in the narrow gap between the flexible graphite films (the electroplating time is 4-20 min), and the average thickness of the metal layer is 20-100 nm; drying and hot pressing, the pressure is 0.5-5 MPa, the temperature is (800-1000 DEG C), and the high-temperature maintaining time is 3-20 min. After the electroplating is completed, the repulsion of the copper atoms to the wrinkle is driven by high temperature (the temperature is 800-1000 DEG C), so that a certain gap is generated at the wrinkle, a movement space of the wrinkle is formed, and the flexible problem of the wrinkled graphene after electroplating is solved.

Description

Technical Field

[0001] This invention relates to the field of thermal conductivity, and more particularly to a millimeter-scale thermally conductive flexible graphite plate, its preparation method, and its application. Background Technology

[0002] Flexible graphite sheets are materials with good electrical conductivity, thermal stability, and flexibility, and are widely used in electronics, new energy, aerospace, and other fields. However, large-scale fabrication of flexible graphite sheets is currently a major research focus. Existing methods for fabricating flexible graphite sheets mainly suffer from the following problems: 1. Cost: The high price of high-performance graphite materials increases the manufacturing cost of flexible graphite sheets, limiting their application in cost-sensitive fields. 2. Process complexity: Maintaining flexibility requires complex fabrication processes, such as multilayer structure design and composite materials. These processes are complex and difficult to mass-produce. 3. Balancing electrical conductivity, thermal stability, and flexibility: Achieving a balance between the flexibility, mechanical properties, and thermal conductivity of graphite sheets is a challenge.

[0003] To address the aforementioned issues, flexible graphite sheets can currently be fabricated by combining flexible graphite with other metallic materials to reduce manufacturing costs and achieve high thermal conductivity, thus balancing mechanical and thermal properties. However, flexible graphite films are smooth, have low surface energy, and poor solution affinity, making it difficult for metal atoms to adhere. Furthermore, maintaining flexibility in the layer-by-layer composite of flexible graphite films and metallic copper is a problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing and applying millimeter-scale thermally conductive flexible graphite plates.

[0005] The objective of this invention is achieved through the following technical solution: a method for preparing a millimeter-scale thermally conductive flexible graphite plate, comprising the following steps:

[0006] (1) Flexible artificial graphite film and PS layer are stacked alternately and then bonded and fixed by micro-heating at 100-150℃ to form a multi-level structural material; the PS layer is composed of PS microspheres; the flexible artificial graphite film contains wrinkles, and the surface wrinkle density is 200-800 mm / cm. 2 ;

[0007] (2) The multi-level structure material prepared in step (1) is used as the cathode, and a mixed solution of copper sulfate and sulfuric acid is used as the electrolyte for electroplating. Copper is electroplated in the slits between the graphite films of the multi-level structure material. The slit effect and polarization effect of the material greatly promote the rapid growth of copper atoms.

[0008] (3) After the multi-level structural material completed by electroplating in step (2) is dried, it is hot-pressed at a pressure of 0.5-5 MPa and a temperature of 800-1000℃ for 3-20 minutes to obtain a millimeter-scale thermally conductive graphite plate. Under hot pressing, amorphous copper rapidly crystallizes and grows to form a uniform thickness of highly thermally conductive single crystal, thereby reducing the interlayer thermal resistance of the graphite film and increasing the thermal conductivity of the material.

[0009] This invention first utilizes PS microspheres to form slits, ensuring sufficient wetting and exchange of electrolytes. The resulting current polarization effect, along with the confinement and template effect of the slits, greatly promotes metal electroplating on the smooth artificial graphite film surface. This eliminates the surface activity requirements of conventional graphite electroplating and solves the problem of difficult copper atom electroplating on smooth graphite surfaces, especially for batch intercalation electroplating. Secondly, after electroplating, high temperature (800-1000℃) drives the repulsive effect of the wrinkles on the copper atoms, creating gaps at the wrinkles and forming a movement space for the wrinkles. This solves the problem of flexibility in the wrinkled graphene after electroplating, resulting in an integrated millimeter-scale thermally conductive flexible graphite plate using a high thermal conductivity copper single-crystal thin film as a binder. The final millimeter-scale thermally conductive flexible graphite plate is connected by single-crystal copper (copper is the metal most compatible with the graphite lattice structure) nanofilms, exhibiting low thermal resistance and a stable interface. It can be widely used in high-throughput thermal management, such as heat dissipation in ultra-high frequency mobile phones, computers, and tablets.

[0010] In some embodiments of the present invention, the PS layer is prepared by spin coating.

[0011] In some embodiments of the present invention, the PS microspheres have a particle size ranging from 50 to 1000 nm. Microspheres of varying sizes are more conducive to solution penetration.

[0012] In some embodiments of the present invention, the thickness of the graphite film is 4-20 μm, and the thickness formed by the staggered stacking of the graphite film and the PS layer is 0.1-0.5 mm.

[0013] In some embodiments of the present invention, in step (3), the average thickness of the copper metal layer in the millimeter-scale thermally conductive graphite plate is 20-100 nm. The nanometer thickness of the metal binder reduces the atomic mobility barrier, thereby greatly reducing the crystallization temperature of the metal. On the one hand, it saves energy consumption costs in the hot pressing process, and on the other hand, the high thermal conductivity of highly crystalline copper can greatly reduce the interfacial thermal resistance between graphite films.

[0014] In some embodiments of the present invention, in step (2), the concentration of the copper sulfate solution is 0.1-2 mol / L, the concentration of the sulfuric acid solution is 0.3-6 mol / L, the electroplating voltage range is 4-5V, and the current density is 10-25 A / dm³. 2 The electroplating time is 4-20 minutes.

[0015] The present invention also relates to millimeter-scale flexible thermally conductive graphite plates prepared by the above-described preparation method.

[0016] This invention utilizes a high thermal conductivity single-crystal copper film as an adhesive to bond high thermal conductivity artificial graphite together at low cost. Copper itself has high thermal conductivity and excellent lattice matching with the graphene surface, enabling excellent interfacial heat transport. Furthermore, the nanometer-thickness of the metal layer lowers its crystallization temperature and significantly reduces its volume fraction, without significantly reducing the thermal conductivity of the graphite film, thus ensuring the material's thermal conductivity. Simultaneously, the flexible graphite film and copper can be layered, allowing for arbitrary control of the composite material thickness or improvement in thermal flux. Through the synergistic effect of these three factors, high thermal conductivity and high flux thermal management can ultimately be achieved.

[0017] The beneficial effects of this invention are as follows: It avoids the surface activation process of hydrophobic graphite films in conventional electroplating. The electric heating and the nano-thickness of the copper significantly reduce material processing time and temperature, thereby lowering costs and laying a material and technological foundation for heat dissipation in future high-frequency electronic devices. The thermal conductivity is close to 1500 W / mK, and the thickness reaches 0.1-0.5 mm; it can be used continuously for 10,000 hours without thermal conductivity loss. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the slit stacking of flexible artificial graphite films.

[0019] Figure 2 This is a surface morphology diagram of the flexible artificial graphite film in Example 1.

[0020] Figure 3 The bonding interface between the flexible artificial graphite film prepared in Example 1 and the 40nm metal is shown in the high-resolution TEM image.

[0021] Figure 4 An optical photograph of the 1 mm thick bonded flexible graphite plate prepared in Example 1.

[0022] Figure 5 The images show bending test photos of the 1mm thick bonded flexible graphite plate prepared in Example 1, where a is a photo of the bending process and b is a photo after 100,000 bends. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0024] In the following embodiments, the thermal conductivity test method uses the laser flash method. Specifically, a heat source is injected from the bottom of the heat-conducting plate, and an infrared detector is used to detect the heat at the top. Figure 1 As shown.

[0025] The heat flux of a material is directly proportional to the product of its thickness and thermal conductivity. Therefore, the following examples will directly show the thickness and thermal conductivity values ​​of the material.

[0026] Example 1

[0027] A method for preparing a millimeter-scale thermally conductive flexible graphite plate includes the following steps:

[0028] (1) Mix 50nm PS microspheres, 100nm PS microspheres, 500nm PS microspheres, and 1μm PS microspheres (Transgene Biotechnology) in equal mass ratio, disperse them in water to form a 1% mass fraction dispersion, and spin-coat it onto a 20μm thick flexible artificial graphite film (surface wrinkle density of 200mm / cm). 2 A PS layer is formed on a substrate with a thermal conductivity of approximately 1670 W / mK, and the PS coverage is maintained at 25% (coverage area) by controlling the rotation speed and time. Then, a 20 μm thick flexible artificial graphite film is deposited on top of the PS layer, and this process is repeated, resulting in a total of 25 layers of flexible artificial graphite film and 24 layers of PS layers stacked alternately. Figure 1 Then, it is bonded and fixed at 100℃ with slight heat to form a multi-level structural material;

[0029] (2) Using the multi-level structure material obtained in step (1) as the cathode, and copper sulfate solution as the electrolyte, electroplating was performed. The concentration of the copper sulfate solution was 1 mol / L, the concentration of the sulfuric acid solution was 3 mol / L, the electroplating voltage range was 4.5 V, and the current density was 15 A / dm³. 2 The electroplating time is 20 minutes. After electroplating, the image is analyzed using SEM (Selenium Electron Microscopy). Figure 3 It can be seen that Cu has formed a single crystal with a thickness of 40 nm.

[0030] (3) After the multi-level structural material is dried after electroplating in step (2), it is hot-pressed at a pressure of 0.5 MPa and a temperature of 1000℃ for 20 minutes to completely decompose the PS microspheres and allow the metal to crystallize and homogenize the metal into a metal layer with an average thickness of 20 nm. Finally, a millimeter-level thermally conductive flexible graphite plate is obtained.

[0031] Figure 2 The image shown is a surface morphology diagram of a single flexible graphite film. Figure 2 As shown, the surface of a single graphite film is smooth and flat, making it difficult to electroplate a composite copper metal layer on the surface. Figure 3 The sub-millimeter thick (approximately 0.5 mm) thermally conductive graphite plate prepared in this embodiment ( Figure 4A high-resolution TEM image of the interface between a graphite film and a copper metal layer is shown. The image shows that the copper and graphene are bonded at the atomic level, and the copper exhibits single-crystal characteristics, which lays the structural foundation for the subsequent high thermal conductivity. The metal density is relatively low at the bends in the image, indicating that after electroplating, the high temperature (800-1000℃) drives the repulsion of copper atoms by the wrinkles, creating voids at the original wrinkles and forming the movement space of the wrinkles, thus giving the material good flexibility.

[0032] Thermal conductivity tests showed that the prepared graphite plate had a horizontal thermal conductivity of 1460 W / mK. Furthermore... Figure 5 As shown, there was no obvious damage after 100,000 bends.

[0033] Example 2

[0034] A method for preparing a millimeter-scale thermally conductive flexible graphite plate includes the following steps:

[0035] (1) Mix 100nm PS microspheres, 500nm PS microspheres, and 800nm ​​PS microspheres (Transgene Biotechnology) in equal mass ratio, disperse them in water to form a 2% mass fraction dispersion, and spin-coat it onto a 4μm thick flexible artificial graphite film (surface wrinkle density of 340mm / cm²). 2 A PS layer is formed on the surface of a material with a thermal conductivity of about 1530 W / mK. The PS coverage is controlled by adjusting the rotation speed and time to achieve a coverage of 20% to 30% (coverage area). A 4 μm thick flexible artificial graphite film is then placed on top of the PS layer. This process is repeated, with the layers stacked alternately to a thickness of 0.12 mm. The material is then bonded and fixed by micro-thermal bonding at 150°C to form a multi-level structural material.

[0036] (2) Using the multi-level structure material prepared in step (1) as the cathode, and copper sulfate solution as the electrolyte, electroplating was performed. The concentration of the copper sulfate solution was 2 mol / L, the concentration of the sulfuric acid solution was 0.5 mol / L, the electroplating voltage range was 5V, and the current density was 25A / dm³. 2 The electroplating time was 4 minutes. After electroplating, SEM showed that Cu had formed a single crystal with a thickness of 20 nm.

[0037] (3) After the multi-level structural material completed in step (2) by electroplating is dried, it is hot-pressed at a pressure of 0.5 MPa and a temperature of 900 °C for 15 min to completely decompose the PS microspheres and allow the metal to crystallize, homogenizing the metal into a metal layer with an average thickness of 100 nm; finally, a millimeter-scale flexible thermally conductive graphite plate is obtained. The thickness of the millimeter-scale thermally conductive graphite plate obtained in this embodiment is approximately 0.112 mm.

[0038] Thermal conductivity tests showed that the prepared graphite plate had a horizontal thermal conductivity of 1390 W / mK. Furthermore, it showed no significant damage after being bent 100,000 times.

[0039] Example 3

[0040] A method for preparing a millimeter-scale thermally conductive flexible graphite plate includes the following steps:

[0041] (1) Mix 100nm PS microspheres, 500nm PS microspheres, and 800nm ​​PS microspheres (Transgene Biotechnology) in equal mass ratios and spin-coat them onto a 15μm thick flexible artificial graphite film (surface wrinkle density of 430mm / cm²). 2 A PS layer is formed on the surface of a material with a thermal conductivity of about 1500 W / mK. The PS coverage is controlled by adjusting the rotation speed and time to achieve a coverage area of ​​20% to 30%. A 15 μm thick flexible artificial graphite film is then placed on top of the PS layer. This process is repeated, with the layers stacked alternately to a thickness of 0.33 mm. The material is then bonded and fixed at 120°C using a micro-thermal bonding method to form a multi-level structural material.

[0042] (2) Using the multi-level structure material obtained in step (1) as the cathode, and copper sulfate solution as the electrolyte, water electroplating is performed. The concentration of the copper sulfate solution is 0.1 mol / L, the electroplating voltage range is 4V, and the current density is 10A / dm³. 2 The electroplating time was 20 minutes. After electroplating, SEM analysis showed that Cu had formed a single crystal with a thickness of 67 nm.

[0043] (3) After the multi-level structural material is dried after electroplating in step (2), it is hot-pressed at a pressure of 5 MPa and a temperature of 800℃ for 3 minutes to completely decompose the PS microspheres and allow the metal to crystallize and homogenize the metal into a metal layer with an average thickness of 20 nm. Finally, a millimeter-level thermally conductive graphite plate is obtained.

[0044] The thickness of the millimeter-scale thermally conductive graphite plate obtained in this embodiment is approximately 0.3 mm.

[0045] Thermal conductivity tests showed that the prepared graphite plate had a horizontal thermal conductivity of 1210 W / mK. Furthermore, it showed no significant damage after being bent 100,000 times.

[0046] Comparative Example 1

[0047] A method for preparing a millimeter-scale thermally conductive flexible graphite plate includes the following steps:

[0048] (1) A 20μm thick flexible artificial graphite film (with a surface wrinkle density of 200mm / cm²) is applied. 2 (with a thermal conductivity of approximately 1670 W / mK), until its thickness is consistent with the thickness of the composite film obtained in step 1 of Example 1, and then it is micro-heat treated at 100°C.

[0049] (2) Using the stacked film obtained in step (1) as the cathode, electroplating was performed with copper sulfate solution as the electrolyte. The concentration of the copper sulfate solution was 1 mol / L, the concentration of the sulfuric acid solution was 3 mol / L, the electroplating voltage range was 4.5 V, and the current density was 15 A / dm³. 2 The electroplating time was 20 minutes. After electroplating, Cu could not be observed using SEM.

[0050] (3) After the multi-level structural material completed by electroplating in step (2) is dried, it is hot-pressed at a pressure of 0.2 MPa and a temperature of 700 °C for 30 min; finally, a thermally conductive graphite plate is obtained.

[0051] After thermal conductivity testing, the horizontal thermal conductivity of the prepared graphite plate was found to be only 340 W / mK, and there was no significant damage after 100,000 bends.

[0052] Comparative Example 2

[0053] Other conditions are the same as in Example 1, except that in step (3), the multi-level structural material after electroplating in step (2) is dried and then hot-pressed at a pressure of 0.05 MPa and a temperature of 700°C for 10 minutes.

[0054] After thermal conductivity testing, the prepared graphite plate had a horizontal thermal conductivity of 1270 W / mK, but it suffered significant damage and lost its flexibility after being bent 10,000 times.

Claims

1. A method for producing a millimeter-scale thermally conductive flexible graphite sheet, characterized by, The method comprises the following steps: (1) interlaced stacking of flexible artificial graphite film and PS layer, then micro-heat bonding and fixing at 100-150℃ to form a multi-level structure material; wherein the PS layer is composed of PS small balls; the flexible artificial graphite film contains surface folds, and the surface fold density is 200-800mm / cm 2 ; (2) using the multi-level structure material prepared in step (1) as a cathode and a copper sulfate solution as an electrolyte, water electroplating copper in the interlayer gap of the graphite film of the multi-level structure material; (3) drying the multi-level structure material after the water electroplating in step (2) and hot-pressing the multi-level structure material at a pressure of 0.5-5 MPa and a temperature of 800-1000 ℃ for 3-20 min to obtain a millimeter-level thermal conductive graphite plate.

2. The method of claim 1, wherein, In step (1), the PS layer is prepared by spin coating.

3. The method of claim 1, wherein, In step (1), the particle size of the PS balls is 50-1000 nm.

4. The method of claim 1, wherein, In step (1), the thickness of the flexible artificial graphite film is 4-20 μm.

5. The method of claim 1, wherein, In step (1), the thickness of the flexible artificial graphite film and the PS layer stacked alternately is 0.1-0.5 mm.

6. The method of claim 1, wherein, In step (3), the average thickness of the copper metal layer in the millimeter-level thermal conductive graphite plate is 20-100 nm.

7. The method of claim 1, wherein, In the step (2), the concentration of the copper sulfate solution is 0.1-2 mol / L, the voltage range for electroplating is 4-5 V, the current density is 10-25 A / dm 2 , the concentration of the sulfuric acid solution is 0.3-6 mol / L, and the electroplating time is 4-20 min.

8. A millimeter-level thermal conductive graphite plate prepared by the method of any one of claims 1-7.

9. Application of the millimeter-level thermal conductive graphite plate of claim 8 as a heat dissipation material.

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