A high-thermal-conductivity graphene film, a preparation method and application thereof

Abstract

This invention discloses a graphene film with high thermal conductivity, its preparation method, and its applications. By designing a synergistic processing mechanism that dynamically and synchronously increases temperature and pressure, this invention suppresses the nucleation and growth of pores throughout the entire process from low to high temperatures. This provides a consistently high-pressure, dense environment for carbon atom diffusion and rearrangement, creating a lower-energy rearrangement pathway. As the temperature increases, the synchronously increasing pressure provides an additional, uniformly oriented driving force. The precise coupling of these two forces allows graphite microcrystals to achieve the crystallinity and orientation required by traditional processes at a lower peak temperature. The graphene film prepared by this invention exhibits significantly improved performance, with an in-plane thermal conductivity reaching 1500 W / m². ‑1 K ‑1 The density can reach 2.1 g / cm³. ‑3 above.

Description

Technical Field

[0001] This invention belongs to the field of advanced carbon material preparation technology, specifically relating to a graphene film with high thermal conductivity, its preparation method, and its application. Background Technology

[0002] The preparation of high thermal conductivity graphene films typically requires heat treatment of the graphene-based precursor film, including low-temperature pre-reduction and high-temperature graphitization. Graphitization, in essence, is the process by which carbon atoms rearrange themselves at high temperatures, transforming the disordered layer structure into an ideal graphite crystal structure. This process directly determines the film's thermal and electrical conductivity properties. Currently, the mainstream process involves high-temperature graphitization of the graphene-based precursor film in a graphitization furnace under atmospheric or low-pressure inert atmosphere. However, achieving high thermal conductivity often faces two challenges: 1. Requires extremely high graphitization temperature: Under normal pressure, the furnace temperature needs to be at least 2800~3150 °C to achieve a high degree of graphitization in graphene films. This places extremely high demands on equipment, consumes a lot of energy, and can easily lead to abnormal growth of grains or cracking of the film.

[0003] 2. Requires multiple graphitization cycles: To gradually improve performance at relatively feasible temperatures, the industry often employs a multiple graphitization process. This method has a long production cycle, high energy consumption, and low efficiency, and repeated thermal shocks may introduce new defects or cause mechanical damage. Summary of the Invention

[0004] To address the issue of incomplete structure in graphene films prepared by existing technologies, this invention provides a high thermal conductivity graphene film, its preparation method, and its applications. This invention employs a synergistic processing mechanism involving dynamic and synchronous increases in temperature and pressure. This mechanism dynamically suppresses pore nucleation and growth throughout the entire process from low to high temperatures, providing a consistently high-pressure and dense environment for carbon atom diffusion and rearrangement. This creates a lower-energy rearrangement pathway: as the temperature increases, the synchronously increasing pressure provides an additional, uniformly oriented driving force. The precise coupling of these two forces allows graphite microcrystals to achieve the crystallinity and orientation required by traditional processes at a lower peak temperature. The graphene film prepared by this invention exhibits significantly improved performance, with an in-plane thermal conductivity reaching 1500 W / m². -1 K -1 The density can reach 2.1 g / cm³. -3 above.

[0005] One of the technical solutions of this invention is to provide a method for preparing a graphene film with high thermal conductivity, wherein a graphene-based precursor film is heat-treated under dynamic pressurization conditions; the dynamic pressurization process adopts a segmented coupling method: Phase 1: From room temperature to the first transition temperature (T1), the pressure increases from the initial pressure (P0) to the intermediate pressure (P1). Second stage: From T1 to the target peak temperature (Tp), the pressure increases from P1 to the peak pressure (Pp). Wherein, T1 is 600~1200 °C, P0 is 1.0~3.0 MPa, P1 is 2.0~4.0 MPa, Tp is 1600~2100 °C, and Pp is 5.0~10.0 MPa.

[0006] The pressure-temperature relationship satisfies: dP / dT ≥ 0.005 MPa / °C, and there is no plateau period where the pressure remains constant throughout the entire heating range from room temperature to peak temperature.

[0007] Preferably, the dynamic pressurization process is as follows: in the first stage, the pressure increases from the initial pressure of 2.0 MPa to 3.5 MPa from room temperature to 1000 °C; in the second stage, the pressure increases linearly from 1000 °C to the target peak temperature of 2000 °C to 8.5~9.5 MPa, with a pressurization rate of not less than 0.005 MPa / °C.

[0008] During the heating process, the oxygen-containing functional groups remaining inside the graphene-based precursor film continuously decompose and attempt to form micropores or gas molecules. In traditional constant-pressure schemes, as the temperature rises, the thermal motion of gas molecules intensifies, and their suppressive effect on pores relatively weakens. This invention, through synchronous pressurization, enables the chemical potential and pressure of the inert gas inside the furnace to increase synchronously with the temperature, thereby suppressing the nucleation and growth of pores in real time and dynamically throughout the entire process from low to high temperature, providing a consistently high-pressure and dense environment for the diffusion and rearrangement of carbon atoms.

[0009] The slippage, rotation, and rearrangement of graphene sheets at high temperatures require overcoming enormous interlayer van der Waals forces and lattice barriers. In this invention, the simultaneous increase in pressure and temperature creates a rearrangement path with lower energy: as the temperature rises, the synchronously increasing pressure provides an additional, uniformly oriented driving force. The precise coupling of the two allows graphite crystallites to achieve the crystallinity and orientation required by traditional processes at a lower peak temperature.

[0010] Between room temperature and 1000 °C, functional group removal primarily occurs, requiring moderate pressure to prevent interlayer cracking caused by excessively rapid decomposition; between 1000 and 1600 °C, initial carbon atom rearrangement primarily occurs, requiring gradually increasing pressure to guide orientation; between 1600 and 2100 °C, grain growth and defect healing primarily occur, requiring the highest pressure to provide maximum driving force. The dynamic synchronous pressure-boosting scheme of this invention achieves this optimization across the entire temperature range, rather than relying on a single pressure.

[0011] Furthermore, the graphene-based precursor film is a reduced graphene oxide film; the carbon-oxygen atom ratio of the graphene-based precursor film is greater than 5:1.

[0012] Furthermore, the highest temperature for graphitization treatment is 2800~3150 °C.

[0013] Furthermore, it includes the following steps: a) Place the graphene-based precursor film between two high-temperature resistant substrates and load it into the homogenization zone of a high-temperature and high-pressure furnace. b) After evacuating the furnace, fill it with high-purity inert gas to the initial pressure (P0). c) Start heating and heat up to the target peak temperature (T) according to the preset program. p Simultaneously, throughout the entire heating process, the gas pressure inside the furnace is increased synchronously and continuously as the temperature rises through dynamic pressurization. When the temperature reaches T... p At that time, the pressure inside the furnace simultaneously reaches the peak pressure (P). p Its pressure-temperature curve is linear, step-like, or exponential, and the time synchronization error between pressure change and temperature change does not exceed 5% of the total heating time.

[0014] d) In T p and P p Under the specified conditions, maintain heat and pressure for 60~600 min; e) After the heat preservation is completed, stop heating and cool the furnace body to below the specified temperature while maintaining the pressure at a value not lower than the set value; f) Depressurize to atmospheric pressure and remove the graphene film after steps a~e; g) The graphene film obtained in step f is subjected to high-temperature graphitization treatment to obtain the final high thermal conductivity graphene film.

[0015] Furthermore, the high-temperature resistant substrate is a high-purity graphite plate, a graphite plate with pyrolytic carbon deposited on its surface, or a graphite plate with boron nitride sprayed on its surface.

[0016] Further, in step (b), after evacuating to a pressure below 10 Pa, argon or nitrogen is introduced to an initial pressure of 1.0~3.0 MPa. Argon is preferred when the processing temperature exceeds 1900 °C.

[0017] The second technical solution of the present invention is to provide a graphene film with high thermal conductivity prepared by the above method.

[0018] The third technical solution of the present invention is to provide the application of the above-mentioned graphene film with high thermal conductivity.

[0019] The advantages of this invention are: dynamic synchronous pressurization avoids the internal stress concentration and structural damage caused by the partial disordered expansion or microcracks of the material under high temperature and low pressure in the process of heating first and then pressurizing, which is then pressed back under high pressure. The process of this invention is smoother, and the material structure is always in a state of pressure equilibrium. The graphene film prepared by this invention has significant structural advantages, with a dense and uniform microstructure, highly consistent graphene sheet orientation, significantly increased grain size, and low defect density. In the pressure furnace, the isostatic pressure of the gas is isotropic, avoiding stress unevenness and damage caused by mechanical hot pressing. It is suitable for processing brittle films or large-area films, and integrates densification and orientation optimization into one graphitization cycle, resulting in high efficiency. In particular, compared with non-cooperative processes that only change the pressure application method under the same peak temperature, peak pressure, and holding time, the graphene film prepared by the method of this invention has significantly improved performance, with an in-plane thermal conductivity of up to 1500 W / m. -1 K -1 The above results show an improvement of 15% to 25% or more compared to films treated with traditional atmospheric pressure graphitization, with a density reaching 2.1 g / cm³. -3 This represents a relative increase of 5% to 10%. Attached Figure Description

[0020] Figure 1 This is a diagram showing the heating and cooling curves of the core process steps of this invention.

[0021] Figure 2 The images show a comparison of the SEM structures of the graphene film before and after treatment. a) is before treatment, and b) is after treatment. Detailed Implementation

[0022] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0023] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0024] The embodiments of the present invention will be further described below with reference to several examples.

[0025] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0026] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0027] Example 1

[0028] In this embodiment, a reduced graphene oxide film with a carbon-to-oxygen atomic ratio of 8:1 and a thickness of 100 μm was used as the raw material. It was sandwiched between two high-purity graphite plates and placed in a high-temperature pressure furnace. First, the furnace chamber was evacuated to a pressure below 5 Pa, then high-purity argon was introduced to an initial pressure of 2.0 MPa. Heating was initiated and a dynamic pressurization program was executed: in the first stage, the temperature was increased from room temperature to 1000°C, and the pressure simultaneously increased to 3.5 MPa; in the second stage, the temperature was increased to the target peak temperature of 2000°C, and the pressure simultaneously and linearly increased to the peak pressure of 8.5 MPa. Under these conditions, the temperature and pressure were maintained for 180 min. Afterward, the pressure was maintained at no less than 4.3 MPa, and the furnace was cooled to 200°C. Finally, the pressure was released and the sample was removed. After graphitization treatment at 3000°C, the in-plane thermal conductivity of the obtained graphene film reached 1750 W / m². -1 K -1 Its density is 2.1 g / cm³. -3 .

[0029] Example 2

[0030] In this embodiment, a reduced graphene oxide film with a carbon-to-oxygen atomic ratio of 10.3:1 and a thickness of 50 μm was used as raw material. It was sandwiched between two high-purity graphite plates and placed in the homogenization zone of a high-temperature pressure furnace. The furnace chamber was evacuated to a pressure of 5 Pa and then filled with high-purity argon gas to an initial pressure of 2.0 MPa. Heating was initiated. In the first stage, the temperature was increased from room temperature to 1000 °C, with the pressure simultaneously increasing to 3.5 MPa. In the second stage, the temperature was increased to the target peak temperature of 2000 °C, with the pressure simultaneously and linearly increasing to the peak pressure of 8.5 MPa. The temperature and pressure were maintained at 2000 °C and 8.5 MPa for 300 min. Heating was stopped, and the pressure was maintained at no less than 4.3 MPa while the furnace was programmed to cool to 200 °C. The pressure was then slowly released to atmospheric pressure, and the graphene film was removed from the furnace. After high-temperature graphitization treatment, the surface thermal conductivity of the film was 1720 W / m. -1 K -1 Its bulk density is 2.12 g / cm³. -3 Compared with Example 1, although the holding time was extended, the thermal conductivity was similar, indicating that under the conditions of 2000 °C and 8.5 MPa, 180 min was sufficient to saturate the graphitization degree. Extending the holding time did not significantly improve the performance, but it ensured the stability of the process.

[0031] Example 3

[0032] In this embodiment, a reduced graphene oxide film with a carbon-to-oxygen atomic ratio of 5.8:1 and a thickness of 50 μm was sandwiched between two high-purity graphite plates and placed in the homogenization zone of a high-temperature pressure furnace. The furnace chamber was evacuated to a pressure of 5 Pa and then filled with high-purity argon gas to an initial pressure of 2.0 MPa. Heating was initiated, with the first stage increasing the temperature from room temperature to 1000 °C, and the pressure simultaneously increasing to 3.5 MPa; the second stage increased the temperature to the target peak temperature of 2000 °C, and the pressure simultaneously and linearly increased to the peak pressure of 9.5 MPa. The temperature and pressure were maintained at 2000 °C and 9.5 MPa for 120 min. Heating was stopped, and the pressure was maintained at no less than 4.8 MPa while the furnace was programmed to cool to 200 °C. The pressure was then slowly released to atmospheric pressure, and the graphene film was removed from the furnace. After high-temperature graphitization treatment, the in-surface thermal conductivity of the film was 1850 W / m. - 1 K -1 Its bulk density is 2.16 g / cm³. -3 Compared to Example 1, treatment at a higher pressure of 9.5 MPa, even with a shorter holding time of 120 min, resulted in a lower thermal conductivity, decreasing from 1750 W / m². -1 K -1 Increased to 1850 W m -1 K -1 This fully demonstrates the significant promoting effect of high pressure on the graphitization process.

[0033] To fully demonstrate the innovation and superiority of the dynamic synergistic effect of temperature and pressure in this invention, the following three comparative examples are provided. All comparative examples use the exact same precursor film, high-purity graphite substrate, high-temperature and high-pressure furnace equipment, and graphitization process (2800~3150 °C) as Example 1. The only difference lies in the coupling method of pressure and temperature during the high-temperature and high-pressure treatment stage.

[0034] Comparative Example 1 After evacuating to a pressure below 5 Pa, high-purity argon gas was introduced to a pressure of 2.0 MPa. Throughout the heating process from room temperature to 2000 °C, the furnace pressure was maintained at a constant 2.0 MPa. The heating rate was the same as in Example 1. The furnace was held at 2000 °C and 2.0 MPa for 180 min. After the holding period, heating was stopped, and the furnace was cooled to 200 °C while maintaining a pressure not lower than 2.0 MPa. The pressure was then slowly released to atmospheric pressure, and the sample was removed. Subsequent high-temperature graphitization treatment was exactly the same as in Example 1. The resulting graphene film had an in-plane thermal conductivity of 1380 W / m. -1 K -1 Its bulk density is 1.78 g / cm³. -3Scanning electron microscopy revealed that the membrane cross-section was porous and the graphene sheets were randomly oriented.

[0035] Comparative Example 2 The heating procedure was exactly the same as in Example 1, i.e., heating from room temperature to 2000 °C. Pressure control was changed to a stepped approach: at five temperature points—room temperature, 500 °C, 1000 °C, 1500 °C, and 2000 °C—the pressure was stepped up to 2.0 MPa, 3.5 MPa, 5.0 MPa, 7.0 MPa, and 8.5 MPa, respectively, with the pressure remaining constant between any two step points. The temperature was held at 2000 °C and 8.5 MPa for 180 min. After holding, heating was stopped, and the furnace was cooled to 200 °C while maintaining a pressure not lower than 4.3 MPa. The pressure was then slowly released to atmospheric pressure, and the sample was removed. Subsequent high-temperature graphitization treatment was exactly the same as in Example 1. The resulting graphene film had an in-plane thermal conductivity of 1510 W / m. -1 K -1 Its bulk density is 2.01 g / cm³. -3 Scanning electron microscopy revealed that the membrane cross-section was relatively dense, but a small number of micropores and disordered orientation regions were visible within the temperature range corresponding to the pressure plateau period.

[0036] Comparative Example 3 After evacuating to a pressure below 5 Pa, high-purity argon gas was introduced to an initial pressure of 2.0 MPa. Throughout the heating process from room temperature to 2000 °C, the furnace pressure was maintained constant at 2.0 MPa. Once the temperature reached 2000 °C, the pressurization program was initiated, linearly increasing the pressure from 2.0 MPa to 8.5 MPa at the same rate as the second stage of Example 1. The furnace was then held at 2000 °C and 8.5 MPa for 180 min. After the holding period, heating was stopped, and the furnace was cooled to 200 °C while maintaining a pressure not lower than 4.3 MPa. The pressure was then slowly released to atmospheric pressure, and the sample was removed. Subsequent high-temperature graphitization treatment was identical to that in Example 1. The resulting graphene film had an in-plane thermal conductivity of 1410 W / m. -1 K -1 Its bulk density is 1.97 g / cm³. -3 Scanning electron microscopy revealed obvious micropores in the cross-section of the film, and some graphene sheets showed disordered orientation.

[0037] A comparison of Example 1 with Comparative Examples 1-3 shows that the thermal conductivity at constant low pressure is only 1380 W / m. - 1 K -1 This indicates that high pressure is necessary; the thermal conductivity of heating before pressurization is 1410 W / m. -1 K -1This indicates that delayed pressurization cannot repair existing defects; the thermal conductivity of stepped pressurization is 1510 W / m. -1 K -1 This indicates that the pressure plateau period provides time for defect growth. Only Example 1, which used continuous synchronous pressure increase, achieved a thermal conductivity of 1750 W / m². -1 K -1 This demonstrates that continuous synchronous voltage boosting is a key technological feature of this invention.

[0038] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing a graphene film with high thermal conductivity, characterized in that, The graphene-based precursor film was heat-treated under dynamic pressurization conditions; the dynamic pressurization process employed a segmented coupling method. Phase 1: From room temperature to the first transition temperature (T1), the pressure increases from the initial pressure (P0) to the intermediate pressure (P1). Second stage: From T1 to the target peak temperature (Tp), the pressure increases from P1 to the peak pressure (Pp). Wherein, T1 is 600~1200 °C, P0 is 1.0~3.0 MPa, P1 is 2.0~4.0 MPa, Tp is 1600~2100 °C, and Pp is 5.0~10.0 MPa.

2. The method according to claim 1, characterized in that, The pressure-temperature relationship in the second stage satisfies: dP / dT ≥ 0.005 MPa / °C, and there is no plateau period where the pressure remains constant.

3. The method according to claim 1, characterized in that, The graphene-based precursor film is a reduced graphene oxide film; the carbon-oxygen atom ratio of the graphene-based precursor film is greater than 5:

1.

4. The method according to claim 1, characterized in that, The highest temperature for graphitization is 2800~3150 °C.

5. The method according to claim 1, characterized in that, Includes the following steps: a) Place the graphene-based precursor film between two high-temperature resistant substrates; b) After evacuation, fill with inert gas to the initial pressure (P0); c) Start heating and program the temperature up to the target peak temperature (Tp). At the same time, the gas pressure is increased synchronously and continuously as the temperature rises through dynamic pressurization. When the temperature reaches Tp, the pressure inside the furnace reaches the peak pressure (Pp) synchronously. d) Hold at Tp and Pp for 60~600 min; e) After the heat preservation is completed, stop heating and cool the furnace body to below 200 °C while maintaining the pressure at no less than half of the peak pressure; f) Depressurize to atmospheric pressure and remove the graphene film after steps a~e; g) The graphene film obtained in step f is graphitized to obtain the final high thermal conductivity graphene film.

6. The method according to claim 5, characterized in that, The high-temperature resistant substrate is a high-purity graphite plate, a graphite plate with pyrolytic carbon deposited on its surface, or a graphite plate with boron nitride sprayed on its surface.

7. The method according to claim 5, characterized in that, The inert gas is argon or nitrogen.

8. A graphene film with high thermal conductivity prepared by the method described in claim 1.

9. An application of the high thermal conductivity graphene film as described in claim 8.

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