A structural liquid metal composite sheet, and a preparation method and application thereof

Abstract

The application provides a structural liquid metal composite sheet and a preparation method and application thereof, and belongs to the technical field of thermal interface materials. The preparation method comprises the following steps: performing surface functionalization treatment on a high-thermal-conductivity structural substrate; coating a low-melting-point liquid metal material on the surface of the modified high-thermal-conductivity structural substrate to obtain a coated composite substrate; performing vacuum interface enhancement treatment on the coated composite substrate to strengthen the interfacial bonding force between the liquid metal material and the structural substrate, thereby obtaining a composite sheet; and performing anti-oxidation treatment on the liquid metal on the surface layer of the composite sheet, thereby obtaining a structural liquid metal composite sheet. The application adopts a dual synergistic mechanism of a skeleton structure physical restraint and interface chemical modification, effectively improves the interfacial wettability of the liquid metal and the graphene substrate, solves the industry pain points of easy agglomeration, overflow and leakage of the liquid metal, and the finished product has excellent anti-leakage and anti-pumping-out performances, can be adapted to complex service conditions of electronic devices for a long time, and the structural stability is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of thermal interface materials technology, and in particular to a structural liquid metal composite sheet, its preparation method, and its application. Background Technology

[0002] With the rapid development of semiconductor technology, the integration and power density of electronic devices such as CPUs, GPUs, and AI chips are continuously increasing, leading to a sharp increase in the heat generated during operation. If this heat cannot be dissipated in a timely and efficient manner, it will seriously affect the working performance, operational stability, and overall lifespan of electronic devices. Thermal interface materials (TIMs), as the core key materials connecting heat-generating chips and heat sinks, directly determine the working efficiency and reliability of the overall heat dissipation system of electronic devices through their thermal conductivity, interface adhesion, and long-term stability.

[0003] Currently, the mainstream thermal interface materials in the industry mainly include silicone grease, thermal pads, and phase change thermal conductive materials. Among them, traditional silicone grease and phase change pads generally have thermal conductivity below 10 W / (m·K), with limited thermal conductivity, and are prone to problems such as drying out, pumping out, and aging failure during long-term use, resulting in poor long-term service stability. Conventional thermal pads are limited by defects such as uneven dispersion of thermally conductive fillers and insufficient interface adhesion, and the interface thermal resistance is usually maintained at 0.1~0.2 cm. 2 ·K / W, which cannot meet the high-intensity heat dissipation requirements of high-power, high-heat-flux-density electronic devices.

[0004] Gallium-based low-melting-point liquid metal alloys possess high thermal conductivity of 20–40 W / (m·K) and low thermal density of 0.01–0.02 cm⁻¹. 2 The ultra-low interfacial thermal resistance and other excellent properties of liquid metals have made them a key research direction and application hotspot in the field of high-end electronic heat dissipation. However, pure liquid metal materials have many inherent defects that seriously restrict their large-scale commercial use: First, there is a high risk of overflow. Pure liquid metals have extremely high fluidity at room temperature, making them difficult to encapsulate. During long-term thermal cycling of electronic devices, leakage and overflow are very likely to occur, which can corrode surrounding precision electronic components and cause equipment failure. Second, they are prone to oxidation failure. A dense oxide film can easily form on the surface of liquid metals, which can significantly increase interfacial thermal resistance, reduce overall thermal conductivity, and shorten product lifespan. Third, there is a serious risk of pumping out. Under long-term hot and cold cycling conditions, liquid metals are prone to displacement and loss, leading to a continuous decline in heat dissipation performance. Fourth, the material has a high surface energy and poor wettability at the interface with conventional thermal conductive substrates, which can easily lead to agglomeration and droplet formation, further aggravating leakage and overflow problems.

[0005] To overcome the aforementioned shortcomings of liquid metals, existing technologies often employ modification schemes such as combining liquid metals with polymers, encapsulating them in metal shells, and filling porous frameworks with liquid metals. However, existing composite technologies still have significant technical limitations, failing to fundamentally achieve excellent interfacial bonding performance, overflow control, ultra-low thermal resistance, and oxidation resistance. Furthermore, existing preparation processes are incomplete and fragmented, making it difficult to achieve standardization and large-scale mass production.

[0006] In summary, developing a structural liquid metal composite sheet with low interfacial thermal resistance, high structural stability, excellent oxidation resistance, and scalable mass production, as well as its preparation method, is a technical problem that urgently needs to be solved by those skilled in the art, and has extremely high engineering application value and market promotion value. Summary of the Invention

[0007] The purpose of this invention is to address the problems of existing technologies, such as easy leakage and oxidation of liquid metal, poor interfacial wettability, easy pumping out during long-term service, high thermal resistance of composite products, and difficulty in large-scale preparation. This invention provides a structural liquid metal composite sheet, its preparation method, and its application, aiming to take into account multiple properties such as ultra-high thermal conductivity, low interfacial thermal resistance, leakage prevention, pumping resistance, and oxidation resistance, while simplifying the process flow and adapting to the needs of industrial mass production.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a structural liquid metal composite sheet, comprising the following steps: 1) Surface functionalization treatment is performed on a high thermal conductivity structural substrate to obtain a modified high thermal conductivity structural substrate; 2) A low-melting-point liquid metal material is coated onto the surface of a modified high thermal conductivity structural substrate to obtain a coated composite substrate; 3) The composite substrate after vacuum interface enhancement treatment strengthens the interfacial bonding between the liquid metal material and the structural substrate, resulting in a composite sheet; 4) The liquid metal on the surface of the composite sheet is subjected to anti-oxidation treatment to obtain a structural liquid metal composite sheet.

[0009] Preferably, the high thermal conductivity structural substrate in step 1) is a sheet or foam material, the structure of the high thermal conductivity structural substrate is an oriented structure or a porous structure, and the material of the high thermal conductivity structural substrate is metal or non-metal.

[0010] Preferably, the low-melting-point liquid metal material in step 2) comprises one or more of gallium, gallium-based alloys, and bismuth-based alloys; the gallium-based alloy is a gallium-indium alloy, a gallium-indium-tin alloy, or a gallium-indium-tin-zinc alloy, the bismuth-based alloy is a bismuth-indium alloy or a bismuth-indium-tin alloy, and the melting point of the low-melting-point liquid metal material is ≤150℃.

[0011] Preferably, the high thermal conductivity structural substrate is a graphene oriented sheet or graphene foam material, and the out-of-plane thermal conductivity of the high thermal conductivity structural substrate is >70W / (m). K); The low-melting-point liquid metal material is a gallium-based alloy or a bismuth-based alloy, and the melting point of the low-melting-point liquid metal material is ≤80℃.

[0012] Preferably, the surface functionalization treatment in step 1) includes one or more of the following: chemical etching, plasma treatment, ozone treatment, mechanical polishing, and silane coupling agent treatment; the coating in step 2) is applied by brushing or spraying.

[0013] Preferably, the vacuum interface enhancement treatment in step 3) is vacuum impregnation. The vacuum impregnation method is as follows: the coated composite substrate is placed in a vacuum system and impregnated under the conditions of vacuum degree ≤1Pa and temperature higher than the melting point of liquid metal material, so that liquid metal completely fills the pore structure of the substrate.

[0014] Preferably, after the vacuum interface enhancement treatment is completed, the excess liquid metal on the surface and in the pores of the composite sheet is removed. The methods for removing the excess liquid metal are wiping, scraping, rolling or centrifuging.

[0015] Preferably, the antioxidant treatment in step 4) includes one or more of the following: passivation treatment, ultrathin polymer coating treatment, and inert gas sealing treatment.

[0016] The present invention also provides a structural liquid metal composite sheet prepared by the aforementioned preparation method.

[0017] The present invention also provides the application of the aforementioned structural liquid metal composite sheet in high heat flux density electronic devices.

[0018] The beneficial effects of this invention are: 1) This invention adopts a dual synergistic mechanism of physical constraint of skeleton structure and chemical modification of interface to effectively improve the interfacial wettability of liquid metal and graphene substrate, solve the industry pain points of easy agglomeration, overflow and leakage of liquid metal, and the finished product has excellent anti-leakage and anti-pumping performance, and can be adapted to the complex service conditions of cold and hot cycles of electronic devices for a long time, and the structural stability is greatly improved.

[0019] 2) This invention fully combines the dual advantages of high thermal conductivity of graphene substrate and ultra-low interfacial thermal resistance of liquid metal. By strengthening the interface to eliminate contact voids, the overall interfacial contact thermal resistance is significantly reduced. The overall heat dissipation performance of the composite sheet is far superior to that of traditional thermal grease, phase change sheet and conventional polymer thermal pads, which can meet the extreme heat dissipation requirements of high heat flux density electronic devices such as AI chips, GPUs and high-end servers.

[0020] 3) This invention innovatively constructs a monolayer anti-oxidation protective structure, which effectively blocks the contact between liquid metal and air without affecting the interfacial thermal conductivity, inhibits the formation and diffusion of oxide film, and completely solves the defects of traditional liquid metal materials that are easy to oxidize and have rapid performance degradation, greatly improving the long-term service stability and service life of the composite heat-conducting sheet.

[0021] 4) The preparation method of the present invention has a continuous process, precise and controllable parameters, high degree of standardization, and good batch consistency of products. It breaks through the technical bottlenecks of traditional liquid metal composite material preparation, which is cumbersome, unstable and difficult to mass-produce. It has a strong industrialization capability and broad market application prospects. Detailed Implementation

[0022] This invention provides a method for preparing a structural liquid metal composite sheet, comprising the following steps: 1) Surface functionalization treatment is performed on a high thermal conductivity structural substrate to obtain a modified high thermal conductivity structural substrate; 2) A low-melting-point liquid metal material is coated onto the surface of a modified high thermal conductivity structural substrate to obtain a coated composite substrate; 3) The composite substrate after vacuum interface enhancement treatment strengthens the interfacial bonding between the liquid metal material and the structural substrate, resulting in a composite sheet; 4) The liquid metal on the surface of the composite sheet is subjected to anti-oxidation treatment to obtain a structural liquid metal composite sheet.

[0023] In this invention, the high thermal conductivity structural substrate mentioned in step 1) is preferably a sheet or foam material, the structure of the high thermal conductivity structural substrate is preferably an oriented structure or a porous structure, and the material of the high thermal conductivity structural substrate is preferably metal or non-metal; the high thermal conductivity structural substrate is further preferably graphene oriented sheet or graphene foam material, and the out-of-plane thermal conductivity of the high thermal conductivity structural substrate is preferably >70W / (m K), further optimized for >80W / (m K).

[0024] In this invention, the thermal resistance of the graphene oriented sheet is ≤0.12cm under a standard thickness of 0.3mm. 2 • K / W, with excellent axial thermal conductivity and interface bonding capabilities.

[0025] In this invention, the low-melting-point liquid metal material in step 2) preferably includes one or more of gallium, gallium-based alloys, and bismuth-based alloys, and more preferably gallium-based alloys or bismuth-based alloys; the gallium-based alloy is preferably gallium-indium alloy, gallium-indium-tin alloy, or gallium-indium-tin-zinc alloy, the bismuth-based alloy is preferably bismuth-indium alloy or bismuth-indium-tin alloy, and the melting point of the low-melting-point liquid metal material is preferably ≤150℃, and more preferably ≤80℃.

[0026] In this invention, the preferred mass fraction of the gallium-indium-tin alloy is 65-75% gallium, 15-25% indium, and 5-15% tin; more preferably, 67-73% gallium, 17-23% indium, and 7-12% tin; even more preferably, 68.5-70% gallium, 20-21.5% indium, and 10% tin. The gallium-indium-tin alloy has a melting point ≤10℃ and is liquid at room temperature. The preferred mass fraction of the bismuth-indium-tin alloy is 30-60% bismuth, 25-60% indium, and 10-20% tin; more preferably, 40-50% bismuth, 30-50% indium, and 12-18% tin; even more preferably, 45% bismuth, 40% indium, and 15% tin. The bismuth-indium-tin alloy is solid at room temperature, has a melting point ≤80℃, and needs to be heated above the melting point to complete melting before coating and lamination.

[0027] In this invention, the surface functionalization treatment in step 1) preferably includes one or more of the following: chemical etching, plasma treatment, ozone treatment, mechanical polishing, and silane coupling agent treatment; the coating in step 2) is preferably applied by brushing or spraying.

[0028] In this invention, surface functionalization treatment improves the physicochemical properties of the substrate surface, reduces interfacial energy mismatch between the substrate and liquid metal, and enhances interfacial wettability and bonding consistency. The plasma treatment uses an oxygen atmosphere, with a vacuum level preferably -0.4 to -0.2 mbar, more preferably -0.3 mbar, a treatment power preferably 45 to 55 W, more preferably 50 W, and a treatment time preferably 3 to 10 min, more preferably 5 to 6 min. The silane coupling agent is preferably a silane coupling agent containing polar groups, such as KH550, KH560, or KH570. The silane coupling agent treatment method employs vacuum vapor deposition, with the treatment temperature selected according to the type of coupling agent, preferably in the range of 60 to 120°C. The vacuum level of vacuum vapor deposition is preferably -1 kPa, and the deposition time is preferably 1 to 3 h, more preferably 2 h. This process constructs active functional groups on the substrate surface, achieving interfacial modification.

[0029] In this invention, the low-melting-point liquid metal material described in step 2) is uniformly coated on the surface of the modified high thermal conductivity structural substrate to achieve initial bonding and filling between the liquid metal and the substrate, ensuring the uniformity and thickness consistency of the liquid metal coating.

[0030] In this invention, the vacuum interface enhancement treatment in step 3) is preferably vacuum impregnation. The vacuum impregnation method is as follows: the coated composite substrate is placed in a vacuum system and impregnated under the conditions of vacuum degree ≤1Pa and temperature higher than the melting point of liquid metal material, so that liquid metal completely fills the pore structure of the substrate.

[0031] In this invention, the vacuum impregnation temperature is preferably 80~120℃, more preferably 90~110℃, and even more preferably 100℃. It is preferably maintained at 80~120℃ for 2~4 hours, more preferably for 3 hours, and the overall vacuum impregnation time is preferably ≥8 hours. This promotes the liquid metal to fully wet and penetrate into the microstructure of the substrate, strengthens the bonding strength of the two-phase interface, and eliminates interface voids and air gaps.

[0032] In this invention, after the vacuum interface enhancement treatment is completed, it is preferable to remove the free excess liquid metal on the surface and in the pores of the composite sheet. The preferred methods for removing the free excess liquid metal are wiping, scraping, rolling or centrifuging.

[0033] In this invention, excess liquid metal on the surface and in shallow pores of the composite sheet is preferably removed by roller pressing or centrifugation, thereby reducing the risk of overflow and pumping out from the source. The centrifugation speed is preferably 1000~5000 rpm, more preferably 2000~4000 rpm, and more preferably 3000 rpm. The centrifugation time is preferably 1~10 min, more preferably 3~7 min, and more preferably 5~6 min. The roller pressing process sets the roller spacing based on the measured thickness of the graphene thermal conductive sheet to accurately control the pressing amount and ensure the structural regularity of the finished product.

[0034] In this invention, the antioxidant treatment in step 4) preferably includes one or more of the following: passivation treatment, ultrathin polymer coating treatment, and inert gas sealing treatment.

[0035] In this invention, the ultrathin polymer coating treatment is preferably a monolayer coating treatment, which isolates the material from air and moisture, inhibits the formation of liquid metal oxide film, and improves the long-term stability of the material. Preferably, a monolayer protective layer is constructed using methyltrimethoxysilane (MTMS), a strongly hydrophobic nonpolar molecule. The coating treatment method is preferably chemical vapor deposition (CVD). The coating treatment temperature is preferably 60~70℃, more preferably 65℃. The coating treatment time is preferably 1.5~2.5h, more preferably 2h. The vacuum degree of the coating treatment is preferably ≤-1kPa, more preferably ≤-1.2kPa, forming a uniform, dense, and ultrathin antioxidant protective layer.

[0036] The method for preparing the structural liquid metal composite sheet of the present invention completely solves the technical problems of poor interfacial wettability, easy agglomeration and leakage, cold and hot cycle pumping out, and easy oxidation failure of traditional liquid metal composite materials through an integrated process of precise interface modification, vacuum uniform compounding, interface strengthening, residual material removal and surface anti-oxidation protection. At the same time, the process flow is standardized and the parameters are controllable, which can stably prepare liquid metal composite heat-conducting sheets with low interfacial thermal resistance and high structural stability.

[0037] The present invention also provides a structural liquid metal composite sheet prepared by the aforementioned preparation method.

[0038] The structural liquid metal composite sheet of the present invention mainly consists of two functional structures: one is a thermally conductive skeleton substrate made of sheet / foam material with high thermal conductivity orientation or porous structure, which has high thermal conductivity and porous structure, and can form a stable physical bond for liquid metal; the other is a thermal interface functional layer made of low melting point liquid metal material, which fills and loads the internal pores and surface microstructure of the high thermal conductivity structural substrate, and is used to significantly reduce the interfacial contact thermal resistance.

[0039] The present invention also provides the application of the aforementioned structural liquid metal composite sheet in high heat flux density electronic devices.

[0040] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0041] All embodiments use a uniform substrate: a 0.3mm thick graphene heat-conducting sheet with a thermal conductivity of 90 W / (m·K) and an initial thermal resistance of 0.08 cm. 2 ·K / W.

[0042] Example 1

[0043] In this embodiment, a gallium-indium-tin alloy is used as the thermal interface layer. The mass fraction of each component in the alloy is: gallium 68.5%, indium 21.5%, and tin 10%. The alloy has a melting point of 10°C and remains liquid at room temperature.

[0044] The preparation steps for the structural liquid metal composite sheet are as follows: 1) Substrate surface functionalization treatment: oxygen plasma treatment is used with a vacuum degree of -0.3mbar, a power of 50W, and a treatment time of 5min to complete the surface activation and modification of the graphene heat conduction sheet, thereby obtaining a modified graphene sheet and improving the wettability of liquid metal.

[0045] 2) Liquid metal coating composite: Molten gallium indium tin alloy is uniformly coated onto the surface of modified graphene sheets using a brush coating method. The coating thickness is 10μm to ensure uniform coating without blank areas, resulting in a coated composite substrate.

[0046] 3) Vacuum interface enhancement treatment: The coated composite substrate is placed in a vacuum system and kept at a vacuum of 0.5 Pa and a temperature of 100 °C for 3 hours. Then, the temperature is lowered while maintaining the vacuum during the cooling process. The overall vacuum maintenance time is 8.5 hours, which allows the liquid metal to fully wet and penetrate into the interior of the graphene microstructure and eliminate the interfacial air layer.

[0047] 4) Removal of excess liquid metal: Centrifugation is used to remove excess liquid metal from the surface and pores of the composite sheet by centrifugation at 3000 rpm for 5 minutes.

[0048] 5) Liquid metal anti-oxidation treatment on the surface: MTMS monolayer is coated by chemical vapor deposition at a temperature of 65℃, a vacuum of -1.2kPa, and a coating time of 2h to form a dense hydrophobic anti-oxidation monolayer, thus obtaining the finished structural liquid metal composite sheet.

[0049] Example 2

[0050] In this embodiment, the substrate surface functionalization process uses KH550 silane coupling agent for vacuum vapor deposition. KH550 silane coupling agent is selected, and the vacuum vapor deposition temperature is 90℃, the vacuum degree is -1kPa, and the deposition time is 2h. Other steps and parameters are the same as in Example 1.

[0051] Example 3

[0052] This embodiment uses a bismuth-indium-tin alloy. The mass fractions of each component in the alloy are: bismuth 35%, indium 45%, and tin 20%. The alloy has a melting point of 60°C and remains solid at room temperature. It needs to be preheated to 70°C to be completely melted before brush coating. The surface functionalization process of the substrate uses KH570 silane coupling agent for vacuum vapor deposition. The vacuum vapor deposition temperature is 100℃, the vacuum degree is -1kPa, and the deposition time is 1.5h. The vacuum interface enhancement treatment is held at 110℃ for 2.5h. The removal of excess liquid metal is carried out by a roll pressing process, and the roll gap is precisely set according to the actual measured thickness of graphene of 0.3mm. The other process steps and parameters are the same as in Example 1.

[0053] Comparative Example 1

[0054] Using the same graphene heat-conducting sheet as in Example 1, steps 2) liquid metal coating and composite, 4) removal of excess liquid metal, 3) vacuum interface enhancement treatment and 5) surface liquid metal anti-oxidation treatment in Example 1 are omitted. The graphene heat-conducting sheet is directly used as the thermal interface material for testing.

[0055] Comparative Example 2

[0056] The same gallium indium tin alloy as in Example 1 is used and directly coated on the heat dissipation interface; there is no graphene-free heat conduction sheet structure support, which eliminates the need for step 1) substrate surface functionalization treatment, step 3) vacuum interface enhancement treatment, and step 5) liquid metal anti-oxidation treatment of the surface layer in Example 1.

[0057] Comparative Example 3

[0058] The graphene structure + liquid metal composite structure is adopted, and the functional treatment of the substrate surface in step 1) and the liquid metal anti-oxidation treatment of the surface layer in step 5) of Example 1 are omitted. Other process steps and parameters are the same as those in Example 1.

[0059] The key properties of the structural liquid metal composite sheets prepared in Examples 1-3 and Comparative Examples 1-3 were tested using the following standard test methods: (1) Thermal resistance test: According to ASTM-D5470 standard, the interfacial thermal resistance of the material was tested using an LW-9389 thermal conductivity meter at 80℃ and 40psi pressure.

[0060] (2) Thermal resistance deterioration rate test: The material was placed in a 500-hour aging test in a -40~125℃ cyclic temperature change chamber. The long-term thermal stability of the material was characterized by comparing the thermal resistance change rate before and after the test.

[0061] (3) Liquid metal spill test: The material is sandwiched between two transparent glass plates and observed under a 30% compression rate to see if there is any liquid metal spill. The leak prevention and structural restraint performance of the material are evaluated.

[0062] Table 1 Summary data of key performance tests for the examples and comparative examples

[0063] As can be seen from the test data in Table 1, the structural liquid metal composite sheet of the present invention exhibits significant comprehensive performance advantages: (1) Ultra-low interfacial thermal resistance: The thermal resistance of the composite sheets in Examples 1-3 is consistently around 0.05 cm. 2 The thermal resistance is around K / W, compared to the graphene substrate without liquid metal composite (Comparative Example 1 has an interfacial thermal resistance of 0.12 cm). 2 The thermal resistance reduction of more than 50% (K / W) indicates that through the interface modification and graphene composite process of the present invention, liquid metal can effectively fill the interface gaps and significantly reduce the contact thermal resistance.

[0064] (2) Excellent leakage prevention and structural stability: The composite sheets of Examples 1 to 3 showed no liquid metal overflow at a compression rate of 30%, indicating that the physical constraint of the graphene framework structure and the interface combination of surface modification worked synergistically to significantly reduce the overflow risk of pure liquid metal (Comparative Example 2) and unmodified composite system (Comparative Example 3).

[0065] (3) Excellent long-term thermal stability: The thermal resistance deterioration rate of the composite sheets in Examples 1-3 is only 5-6%, which is much lower than that of Comparative Example 2 (56%) and Comparative Example 3 (15%). This indicates that the surface anti-oxidation treatment of the present invention effectively inhibits the oxidation of liquid metal and significantly improves the long-term service stability of the material under cold and hot cycling conditions.

[0066] The examples and comparative examples demonstrate that this invention, through a synergistic technical solution of "microstructure physical confinement + interface chemical modification + surface anti-oxidation protection," achieves a unified performance of ultra-low thermal resistance, leak prevention, pump-out resistance, and long-term stability, overcoming the technical bottleneck of "difficulty in simultaneously achieving low thermal resistance and high stability" in existing technologies. This invention reduces interfacial energy mismatch through surface modification, achieving an interfacial thermal resistance as low as 0.05 cm⁻¹. 2 With a heat flux density of less than K / W, it combines high thermal conductivity with long-term stability. The manufacturing process is simple and controllable, and it is easy to scale up for mass production. It can be widely used in heat dissipation scenarios of high-heat-flux-density electronic devices such as high-power CPUs, GPUs and AI computing chips.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a structural liquid metal composite sheet, characterized in that, It includes the following steps: 1) Surface functionalization treatment is performed on a high thermal conductivity structural substrate to obtain a modified high thermal conductivity structural substrate; 2) A low-melting-point liquid metal material is coated onto the surface of a modified high thermal conductivity structural substrate to obtain a coated composite substrate; 3) The composite substrate after vacuum interface enhancement treatment strengthens the interfacial bonding between the liquid metal material and the structural substrate, resulting in a composite sheet; 4) The liquid metal on the surface of the composite sheet is subjected to anti-oxidation treatment to obtain a structural liquid metal composite sheet.

2. The preparation method according to claim 1, characterized in that, Step 1) The high thermal conductivity structural substrate is a sheet or foam material, the structure of the high thermal conductivity structural substrate is an oriented structure or a porous structure, and the material of the high thermal conductivity structural substrate is metal or non-metal.

3. The preparation method according to claim 1 or 2, characterized in that, Step 2) The low-melting-point liquid metal material includes one or more of gallium, gallium-based alloys and bismuth-based alloys; the gallium-based alloy is gallium-indium alloy, gallium-indium-tin alloy or gallium-indium-tin-zinc alloy, the bismuth-based alloy is bismuth-indium alloy or bismuth-indium-tin alloy, and the melting point of the low-melting-point liquid metal material is ≤150℃.

4. The preparation method according to claim 3, characterized in that, The high thermal conductivity structural substrate is a graphene-oriented sheet or graphene foam material, and the out-of-plane thermal conductivity of the high thermal conductivity structural substrate is >70W / (m). K); The low-melting-point liquid metal material is a gallium-based alloy or a bismuth-based alloy, and the melting point of the low-melting-point liquid metal material is ≤80℃.

5. The preparation method according to claim 1 or 4, characterized in that, Step 1) The surface functionalization treatment includes one or more of the following: chemical etching, plasma treatment, ozone treatment, mechanical polishing, and silane coupling agent treatment; Step 2) The coating is applied by brushing or spraying.

6. The preparation method according to claim 5, characterized in that, Step 3) The vacuum interface enhancement treatment is vacuum impregnation. The vacuum impregnation method is as follows: the coated composite substrate is placed in a vacuum system and impregnated under the conditions of vacuum degree ≤1Pa and temperature higher than the melting point of liquid metal material, so that liquid metal completely fills the pore structure of the substrate.

7. The preparation method according to claim 5, characterized in that, After the vacuum interface enhancement treatment is completed, the excess liquid metal on the surface and in the pores of the composite sheet is removed. The methods for removing the excess liquid metal are wiping, scraping, rolling or centrifuging.

8. The preparation method according to claim 6, characterized in that, Step 4) The antioxidant treatment includes one or more of the following: passivation treatment, ultrathin polymer coating treatment, and inert gas sealing treatment.

9. The structural liquid metal composite sheet prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the structural liquid metal composite sheet of claim 9 in high heat flux density electronic devices.

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