Graphene thermal interface material and preparation method thereof

Abstract

The invention discloses a graphene thermal interface material and a preparation method thereof.The preparation method comprises the steps that 1, the upper surface and the lower surface of an original graphene film are coated with graphene oxide slurry respectively and dried, and a sandwich structure composite film is formed; (2) coating the surface of the sandwich structure composite film with graphene oxide slurry; and (3) stacking a plurality of sandwich structure composite films with the surfaces coated with the graphene oxide slurry, then drying under the pressure of 0.1-20 MPa, performing thermal reduction under the protective atmosphere, and finally cutting along the direction perpendicular to the surface of the original graphene film to obtain the graphene thermal interface material. According to the preparation method, the use of a traditional adhesive is avoided, and the out-of-plane thermal conductivity of the graphene thermal interface material is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of thermal interface materials technology, specifically relating to a graphene thermal interface material and its preparation method. Background Technology

[0002] With the rapid advancements in 5G communication, artificial intelligence, high-performance computing, and new energy vehicles, the heat flux density of core chips and power devices has increased dramatically. Meanwhile, the increasingly compact structure of equipment has resulted in extremely limited heat dissipation space. If heat cannot be dissipated in time, it will accumulate in the confined space, leading to thermal runaway, affecting the reliability of electronic devices and reducing their lifespan. Traditional thermal conductive materials (such as silicone grease and silicone pads) are no longer sufficient to meet the increasingly stringent heat dissipation requirements due to their low thermal conductivity and poor long-term reliability.

[0003] Against this backdrop, graphene has emerged as a key breakthrough due to its exceptional properties, including extremely high intrinsic thermal conductivity (theoretical value of 5300 W / (m·K)), ultra-thinness and flexibility, lightweight nature, and chemical stability. It is widely used in various forms such as thermally conductive films and pads in applications including smartphones, 5G base stations, data center servers, new energy vehicle electronic control systems, and power batteries. It efficiently acts as a "thermal bridge" between heat sources and heat sinks, significantly improving heat dissipation efficiency, equipment performance, and reliability. Graphene has become a crucial cutting-edge material for solving the "thermal bottleneck" of modern electronic devices and driving the sustainable development of the industry.

[0004] Typically, graphene materials exhibit significant anisotropic thermal conductivity: their in-plane thermal conductivity can exceed 1500 W / (m·K), while their out-of-plane thermal conductivity is generally below 8 W / (m·K). This huge difference makes it difficult for traditional graphene materials to meet the high-efficiency heat dissipation requirements of high-power devices in the vertical direction. To improve the out-of-plane thermal conductivity of graphene, the key lies in overcoming its inherent two-dimensional limitations and constructing efficient heat conduction pathways in the vertical out-of-plane direction.

[0005] Currently, common methods for constructing three-dimensional heat conduction networks each have their limitations: for example, the ice template method is complex and difficult to mass-produce; or the method involves building "vertical thermal bridges" by doping with other materials.

[0006] For example, the invention patent application with publication number CN115724424A discloses an all-carbon material based on graphene-oriented carbon nanotube arrays that integrates directional thermal conduction and heat dissipation. The preparation method of the carbon material is as follows: spin-coating a xylene solution of polycarbosilane onto the surface of a reduced graphene oxide film, drying, and high-temperature calcination to obtain a reduced graphene oxide film with silicon carbide etched on the surface. Then, the temperature is raised to 860°C, and carbon nanotube arrays are grown by a floating catalytic method to obtain a reduced graphene oxide film with carbon nanotube arrays on the surface. Although it can improve out-of-plane thermal conductivity to a certain extent, the improvement effect is limited.

[0007] Patent application CN111484832A discloses a graphene / silicon carbide nanowire composite thermal interface material. This material comprises graphene sheets and silicon carbide nanowires, which are interwoven. The thermal interface material is grown in situ between the graphene sheets using a high-frequency heating method, forming interlayer thermal conductivity pathways and addressing the issue of low out-of-plane thermal conductivity. However, the out-of-plane thermal conductivity of the resulting material is only 10 W / (m·K), requiring further improvement.

[0008] Furthermore, the lamination hot pressing and flip-cutting technologies that have emerged in recent years can convert the high in-plane thermal conductivity of graphene into out-of-plane thermal conductivity. However, this process typically relies on low thermal conductivity polymers such as rubber and epoxy resin as binders. These polymers not only reduce the overall thermal conductivity of the material, affecting the final heat dissipation effect, but their limited temperature resistance also restricts the application range of the product in high-temperature environments.

[0009] Therefore, developing a graphene thermal interface material that requires no adhesive and has excellent out-of-plane thermal conductivity has become an urgent need in the field of advanced thermal management. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the first aspect of this invention provides a method for preparing graphene thermal interface materials, which yields graphene thermal interface materials with excellent out-of-plane thermal conductivity.

[0011] This invention provides a method for preparing a graphene thermal interface material, comprising: (1) Graphene oxide slurry was coated on the upper and lower surfaces of the original graphene film and dried to form a sandwich structure composite film; (2) Coating the surface of the sandwich structure composite membrane with graphene oxide slurry; (3) Stack multiple sandwich-structured composite films coated with graphene oxide slurry on their surfaces, then dry them under a pressure of 0.1~20 MPa, perform thermal reduction under a protective atmosphere, and finally cut them along a direction perpendicular to the surface of the original graphene film to obtain the graphene thermal interface material.

[0012] During the drying process, the graphene oxide film attached to the surface of the original graphene film will evaporate with the solvent to form a film, which promotes the close bonding of the graphene oxide film and the original graphene film. With the π-π conjugation effect between the two, a structurally stable sandwich structure composite film of "graphene oxide film / original graphene film / graphene oxide film" is formed.

[0013] To achieve stable stacking of multilayer graphene structures and further enhance the bonding strength between graphene film layers, the present invention coats the surface of the sandwich structure composite film obtained in step (1) with graphene oxide slurry, then stacks multiple sandwich structure composite films coated with graphene oxide slurry, and then applies pressure to dry them.

[0014] During the pressure drying process, the newly coated graphene oxide slurry induces swelling in the underlying dried graphene oxide film. Water molecules in the graphene oxide slurry penetrate into the interior of the underlying graphene oxide film, activating its surface oxygen-containing groups and providing space for the graphene oxide sheets to move laterally. This increases the contact area of ​​oxygen-containing functional groups on the surfaces of the upper and lower graphene oxide layers, promotes the formation of hydrogen bonds and π-π conjugated bonds, and achieves mutual fusion between the graphene oxide layers.

[0015] Graphene oxide slurry, as a highly efficient adhesive medium, not only avoids the use of traditional polymer adhesives but also ensures tight adhesion between the original graphene films in each sandwich-structured composite film under appropriate pressure. As the solvent further evaporates during the drying process, the originally separated graphene sheets are firmly connected into a structurally stable whole. Subsequent thermal reduction and cutting processes yield a graphene thermal interface material containing only graphene, which is less prone to cracking and breakage during cutting. Based on the stablely connected graphene sheets, the out-of-plane thermal conductivity of the graphene thermal interface material is significantly improved.

[0016] Furthermore, this invention controls the drying pressure after stacking to ensure that the thickness of the graphene oxide film between the two stacked sandwich-structured composite films is moderate, thus fully utilizing the graphene oxide film as an adhesive. If the drying pressure is too low, air will exist between the two graphene oxide films, preventing tight adhesion and causing the structure to become loose or crack. If the drying pressure is too high, the graphene oxide film will become too thin, or even overflow between the two sandwich-structured composite films, losing its adhesive function.

[0017] Preferably, in step (1), the original graphene film is a reduced graphene oxide film, a graphite film, or a graphene film, the thickness of the original graphene film is 20~1000 μm, and the in-plane thermal conductivity of the original graphene film is 10~2000 W / (m·K).

[0018] Preferably, in step (1), the concentration of the graphene oxide slurry is 0.5~20 mg / mL. The appropriate concentration of the graphene oxide slurry can form a graphene oxide film of moderate thickness and uniformity on the surface of the graphene film, giving full play to the π-π conjugation effect between graphene oxide and graphene, and preparing a sandwich structure composite film with stable bonding. Moreover, the appropriate concentration makes the coating operation convenient and improves the coating efficiency.

[0019] Preferably, the coating process of the graphene oxide slurry is scraping or dipping, and the coating thickness of the graphene oxide slurry is 0.1 mm to 1 cm. A suitable coating process can accelerate the coating efficiency, and a suitable coating thickness can make the graphene oxide slurry coating more uniform. In turn, by means of the π-π conjugation effect between the graphene oxide film and the original graphene film, the two are more closely bonded, resulting in a more stable sandwich structure composite film.

[0020] Preferably, in step (1), the drying temperature is 20~200℃, and the drying method is natural drying or forced air drying.

[0021] This invention provides a suitable drying temperature to ensure that the graphene oxide slurry attached to the surface of the original graphene evaporates the solvent at the appropriate temperature, thereby improving the evaporation efficiency. This provides the necessary evaporation conditions for the graphene oxide sheets to be tightly bonded to the original graphene film through π-π conjugation. At the same time, it avoids premature thermal reduction of the graphene oxide, which would cause it to lose its adhesive properties and affect the swelling effect in the subsequent lamination process.

[0022] Preferably, in step (2), the concentration of the graphene oxide slurry is 0.1~20 mg / mL. The concentration of the graphene oxide slurry in this step is even lower because the graphene oxide slurry in the lamination process needs a sufficient amount of water to wet the dried graphene oxide film in the sandwich structure composite film, thereby accelerating the swelling rate and improving the bonding effect.

[0023] Preferably, in step (3), the drying process is carried out directly under the pressure, or the drying process is carried out after the pressure is maintained and shaped under the pressure.

[0024] Preferably, in step (3), the drying temperature is 20~200ºC.

[0025] This invention controls the drying temperature to ensure that the coated graphene oxide slurry and the graphene oxide layers in the sandwich structure have sufficient time to swell, come into contact, and react. After the reaction is complete, the water molecules in the graphene oxide slurry can completely evaporate, stabilizing the laminated structure.

[0026] More preferably, in step (3), the drying is a step drying, which is maintained at 20~60ºC for 5~72 h, and then maintained at 60~200ºC for 12~240 h.

[0027] This invention first dries the graphene oxide slurry at a low temperature, allowing water molecules in the slurry to fully penetrate into the lower dried graphene oxide film, thus providing sufficient time for a swelling reaction. Subsequently, the temperature is moderately increased to allow the water molecules to evaporate, resulting in a tightly bonded graphene mass. During the drying process, if the mass of the graphene mass stabilizes and no longer changes, it can be determined that the water has completely evaporated, and the drying process is complete. This stepped drying method minimizes the risk of excessively high drying temperatures, which would accelerate water evaporation, preventing the graphene oxide slurry from undergoing a sufficient swelling reaction with the lower dried graphene oxide film, resulting in a weak bond between the graphene films. Furthermore, excessively high temperatures can cause violent vaporization of water molecules in the graphene oxide slurry, and excessive water vapor can damage the stable graphene structure.

[0028] Preferably, the temperature of the thermal reduction is 200~3000℃, and the heating rate is 0.5~10℃ / min.

[0029] This invention aims to control the thermal reduction temperature to ensure a high temperature that effectively decomposes the hydrogen bonds and oxygen-containing groups inside the graphene oxide film, reducing it to graphene and thus improving the out-of-plane thermal conductivity. Simultaneously, a moderate heating rate avoids excessively rapid heating that could cause the oxygen-containing groups inside the graphene oxide film to decompose violently, generating large amounts of gas and leading to film breakage or cracking.

[0030] Preferably, the holding time at the highest temperature during thermal reduction is 0.5 to 24 hours. A suitable holding time can ensure that graphene oxide is fully reduced to graphene, restoring the high thermal conductivity of graphene.

[0031] Preferably, the protective atmosphere is a vacuum, an inert gas, or a mixture of inert gases containing reducing gases, which enables the graphene oxide to be efficiently reduced.

[0032] Preferably, the cutting process is wire cutting, internal circle cutting, ultrasonic scalpel cutting, or laser cutting, and the cutting thickness is 0.2~2 mm.

[0033] On the other hand, the present invention provides a method for preparing the graphene thermal interface material and a graphene thermal interface material obtained therefrom.

[0034] Preferably, the graphene thermal interface material contains only graphene, and the out-of-plane thermal conductivity of the graphene thermal interface material is 50~1500 W / mk.

[0035] Compared with the prior art, the present invention has the following beneficial effects: This invention first utilizes the π-π conjugation effect between graphene oxide and graphene to construct a stable sandwich-structured composite film of "graphene oxide film / original graphene film / graphene oxide film". Then, a graphene oxide slurry is layered and coated, and pressure drying is applied to induce water molecules in the slurry to permeate into the underlying graphene oxide film and swell, thereby activating the oxygen-containing functional groups within the graphene oxide film and forming strong hydrogen bonds between the graphene oxide layers. This invention also ensures that the graphene oxide film fully utilizes its adhesive properties by providing appropriate pressure during drying, allowing the graphene layers to adhere tightly. Subsequent thermal reduction and cutting yield a structurally stable graphene-only thermal interface material with high out-of-plane thermal conductivity. Attached Figure Description

[0036] Figure 1 A photograph of a graphene thermal interface material prepared in Example 1 of this invention; Figure 2 This is a photograph of a graphene thermal interface material prepared in Comparative Example 1 of this invention. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1 1) Take a 300-micrometer-thick graphene film (original film thermal diffusivity: 600 mm). 2 A graphene film with a thermal conductivity of 70 W / m·K (with a surface thermal conductivity of 70 W / m·K) was used as the initial graphene film. A 10 mg / mL graphene oxide film was then used, with the doctor blade thickness adjusted to 5 mm. Graphene oxide was sequentially coated onto the upper and lower surfaces of the graphene film and allowed to air dry. This resulted in a sandwich-structured composite film of "graphene oxide film / graphene film / graphene oxide film". 2) Coat the surface of the composite membrane in step 1) with 5 mg / mL graphene oxide slurry and stack it into a mold.

[0039] 3) Apply a force of 10 MPa to the sample and maintain it at room temperature for 24 h, then at 80℃ for 48 h. Next, place the sample in a vacuum press and heat it to 500℃ (heating rate 1℃ / min), maintaining it at 500℃ for 1 h for high-temperature thermal reduction. Finally, use an internal circular cutter to cut the sample (perpendicular to the original graphene film surface). After cutting, the graphene thermal interface material is obtained.

[0040] Images of the graphene thermal interface material prepared in Example 1 of this invention are shown below. Figure 1 As shown, the graphene thermal interface material obtained after flipping and cutting exhibits a highly regular vertical orientation and a stable structure without breakage.

[0041] Test results show that the out-of-plane thermal diffusivity of the graphene thermal interface material described in Example 1 of this invention is 565 mm. 2 / s, with an out-of-plane thermal conductivity of 269 W / m·K.

[0042] Example 2 The only difference from Example 1 is that the thermal reduction temperature of Example 2 of the present invention is 200 °C.

[0043] The test results show that the out-of-plane thermal diffusivity of the graphene film obtained in Example 2 of this invention is 400 mm. 2 / s, with an out-of-plane thermal conductivity of 190 W / m·K.

[0044] Comparative Example 1 The only difference from Example 1 is that the drying pressure in step (3) of Comparative Example 1 of the present invention is 40 MPa. After drying and demolding under the pressure, some graphene sheets delaminate and cannot be assembled into a complete block.

[0045] Comparative Example 2 The only difference from Example 1 is that no pressure was applied in step (3) of Comparative Example 1 of the present invention. After drying and demolding, some graphene sheets that are not in close contact are prone to delamination and cannot be assembled into a complete block.

[0046] Comparative Example 3 1) Take a 300-micrometer-thick graphene film (original film thermal diffusivity: 600 mm). 2 The original graphene film (with a thermal conductivity of 70 W / m·K) was used as the original graphene film. A 5 mg / mL graphene oxide slurry was directly coated onto the surface of the original graphene film and then stacked into a mold. 2) Apply a force of 10 MPa to the sample and maintain it at room temperature for 24 h, then maintain it at 80℃ for 48 h. Place the sample in a vacuum press and heat it to 500℃ (heating rate of 1℃ / min) for 1 h for high-temperature thermal reduction. Cut the sample using an internal circular cutter (perpendicular to the surface of the original graphene film).

[0047] Images of the graphene thermal interface material prepared in Comparative Example 3 of this invention are shown below. Figure 2 As shown, the graphene film is easily broken and loses its shape after being flipped and cut.

[0048] Results Analysis As seen in Comparative Example 1, due to the excessive drying pressure applied in step (3), a large amount of graphene oxide slurry, along with water, was rapidly extruded from the mold. The dried graphene oxide did not have time to undergo a swelling reaction, and the small amount of residual graphene slurry could not provide sufficient reactive groups, resulting in weak bonding between some graphene films and the inability to form graphene blocks.

[0049] As seen in Comparative Example 2, due to the application of too little drying pressure in step (3), the contact between some graphene films is not tight, and the residual air weakens the interaction between graphene oxides, resulting in the delamination of graphene films.

[0050] Comparative Example 3 shows that if only a sandwich-structured composite film of "graphene oxide film / original graphene film / graphene oxide film" is prepared, but graphene oxide slurry is not coated on its surface before direct lamination, drying, and thermal reduction, the lack of graphene oxide slurry as an adhesive layer between the sandwich-structured composite films will result in poor interlayer adhesion. After flipping and cutting, the material is prone to breakage and loss of shape, making it impossible to obtain a graphene thermal interface material with high out-of-plane thermal conductivity.

[0051] In Embodiment 1 of the present invention, graphene oxide slurry is used as an adhesive during the graphene bonding and stacking process. The graphene oxide film undergoes subsequent lamination under appropriate pressure, causing it to swell with the graphene oxide slurry and subsequently fuse with each other through hydrogen bonding, ensuring tight contact between the layers of the sandwich-structured composite film. This significantly enhances the bonding strength between graphene films and the overall structural stability. Furthermore, after subsequent thermal reduction treatment, the entire graphene thermal interface material contains only graphene material, avoiding the use of other polymer adhesives. This not only improves the out-of-plane thermal conductivity of the material but also extends the operating temperature range of the product.

Claims

1. A method for preparing a graphene thermal interface material, characterized in that, include: (1) Graphene oxide slurry was coated on the upper and lower surfaces of the original graphene film and dried to form a sandwich structure composite film; (2) Coating the surface of the sandwich structure composite membrane with graphene oxide slurry; (3) Stack multiple sandwich-structured composite films coated with graphene oxide slurry on their surfaces, then dry them under a pressure of 0.1~20MPa, perform thermal reduction under a protective atmosphere, and finally cut them along a direction perpendicular to the surface of the original graphene film to obtain the graphene thermal interface material.

2. The method for preparing the graphene thermal interface material according to claim 1, characterized in that, In step (1), the concentration of the graphene oxide slurry is 0.5~20 mg / mL.

3. The method for preparing the graphene thermal interface material according to claim 1, characterized in that, The coating process of the graphene oxide slurry is by scraping or dipping, and the coating thickness of the graphene oxide slurry is 0.1 mm to 1 cm.

4. The method for preparing the graphene thermal interface material according to claim 1, characterized in that, In step (1), the drying temperature is 20~200℃, and the drying method is natural drying or forced air drying.

5. The method for preparing the graphene thermal interface material according to claim 1, characterized in that, In step (2), the concentration of the graphene oxide slurry is 0.1~20 mg / mL.

6. The method for preparing the graphene thermal interface material according to claim 1, characterized in that, In step (3), the drying temperature is 20~200 ºC.

7. The method for preparing the graphene thermal interface material according to claim 6, characterized in that, In step (3), the drying is a step drying process, which involves maintaining the temperature at 20~60 ºC for 5~72 h and then maintaining it at 60~200 ºC for 12~240 h.

8. The method for preparing the graphene thermal interface material according to claim 1, characterized in that, The temperature for thermal reduction is 200~3000℃, and the heating rate is 0.5~10℃ / min.

9. The graphene thermal interface material prepared by the method according to any one of claims 1-8.

10. The graphene thermal interface material according to claim 9, characterized in that, The graphene thermal interface material contains only graphene, and its out-of-plane thermal conductivity is 50~1500 W / (m·K).

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