Three-dimensional continuous graphite network structure material and preparation method and device thereof

Abstract

The invention discloses a three-dimensional continuous graphite network structure material and a preparation method and device thereof. The preparation method comprises the following steps: S1, introducing carbon source gas into a reactor filled with a carbon fiber skeleton, carrying out pyrolytic reaction on the carbon source gas at 1100-1500 DEG C, and growing pyrolytic carbon generated by the reaction on the carbon fiber skeleton to obtain a pyrolytic carbon coated carbon fiber structure; s2, in an inert atmosphere, performing graphitization treatment on the carbon fiber structure to form a three-dimensional continuous graphite network structure material; the graphitization treatment temperature is greater than or equal to 2500 DEG C. Different from a traditional CVI densification process, the preparation method has the advantages that a carbon fiber skeleton with a low volume fraction is used as a growth template instead of a reinforced phase, the isotropic (quasi-isotropic), high-thermal-conductivity, high-electric-conductivity and density-adjustable continuous graphite network material is obtained by accurately controlling growth space and conditions, and the preparation method is suitable for the fields of thermal management, electrodes and the like.

Description

Technical Field

[0001] This invention belongs to the field of carbon material preparation technology, specifically relating to a three-dimensional continuous graphite network structure material and its preparation method and device. Background Technology

[0002] With the advancement of technology, the integration of electronic and industrial equipment is increasing, leading to a corresponding increase in power density and heat generation. Especially for high-precision instruments, internal heat accumulation directly reduces the reliability of electronic components, thus affecting the measurement accuracy and operational stability of the equipment. Therefore, developing high-performance thermally conductive materials is key to efficiently dissipating accumulated heat. Graphene, as a highly promising thermally conductive material, boasts a thermal conductivity as high as 5300 W / (m·K), making it one of the best-known thermally conductive materials.

[0003] Existing technologies disclose the preparation of three-dimensional graphene networks using a metal template method. The product obtained by this method is a low-density, thin-walled graphene aerogel / foam. Although it has a high specific surface area and electrical conductivity, it has low mechanical strength and poor absolute thermal conductivity, making it unsuitable as a load-bearing structure or an efficient heat sink.

[0004] Existing technologies disclose the preparation of C / C composite materials using the traditional CVI (chemical vapor infiltration) method. This method uses a high volume fraction (>20%) fiber preform as the reinforcing phase and aims at complete densification (filling the pores). The product is a two-phase composite material of fiber and matrix carbon. The performance of this composite material is limited by the interface and grain boundaries, making it difficult to obtain an isotropic single crystal / quasi-single crystal continuum, thus affecting its thermal conductivity.

[0005] Therefore, there is an urgent need to provide an isotropic graphite material with high thermal conductivity and high electrical conductivity. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a three-dimensional continuous graphite network structure material, its preparation method, and a device thereof. The three-dimensional continuous graphite network structure material prepared by this invention is isotropic, meaning that its performance is essentially the same in different directions (e.g., the three vector directions of the spatial coordinate axes x, y, and z). It also possesses high thermal conductivity and high electrical conductivity, and its density is adjustable, making it suitable for applications such as thermal management and electrodes, and enabling the fabrication of related devices.

[0007] Prior to this application, existing methods for preparing graphite materials typically employ woven carbon fibers as a reinforcing phase, which are then combined with a matrix carbon to form graphite materials. However, woven carbon fibers are obtained by weaving bundles of carbon fibers into two- or three-dimensional bundles, which results in insufficient deposition space within the bundles and severely reduces surface utilization. Furthermore, the thermal and electrical conductivity of the product is affected by the weaving method, making it impossible to achieve isotropic properties. Additionally, the web structure of woven carbon fibers has a high volume ratio and weight ratio.

[0008] The present invention solves the above problems through the following technical solution: This invention provides a method for preparing a three-dimensional continuous graphite network structure material, which includes the following steps: S1. A carbon source gas is introduced into a reactor filled with a carbon fiber skeleton. The carbon source gas undergoes a pyrolysis reaction, and the pyrolytic carbon generated by the reaction grows on the carbon fiber skeleton to obtain a carbon fiber structure coated with pyrolytic carbon. The temperature of the pyrolysis reaction is 1100-1500℃. The carbon fiber skeleton is a non-woven carbon fiber skeleton, and the average spacing between the carbon fibers in the carbon fiber skeleton is 20-500μm; the initial volume fraction of the carbon fiber skeleton is less than 10%; wherein, the initial volume fraction is the ratio of the carbon fiber volume to the carbon fiber packing volume. S2. Under an inert atmosphere, the carbon fiber structure is graphitized to form a three-dimensional continuous graphite network structure material; the graphitization temperature is greater than or equal to 2500℃.

[0009] Unlike the densification process of the traditional CVI (chemical vapor infiltration) method, this invention uses a low volume fraction of non-woven carbon fiber skeleton as a growth template rather than a reinforcing phase. It employs a medium-temperature CVD (chemical vapor deposition method to suppress homogeneous nucleation) to precisely control the growth space and conditions of pyrolytic carbon. Combined with an ultra-high temperature graphitization process (to promote crystal fusion), the traditional "filling densification" is adjusted to "space-guided epitaxial growth" to obtain high-quality layered carbon deposition products, namely, three-dimensional continuous graphite network structure materials.

[0010] In this invention, the carbon fibers in the carbon fiber skeleton need to meet specific spacing requirements to achieve a loose effect; wherein, the spacing can be understood as the free distance between the carbon fibers in the carbon fiber skeleton.

[0011] In this invention, the initial volume fraction is calculated by dividing the carbon fiber volume by the carbon fiber stacked volume; wherein, the carbon fiber stacked volume is the sum of the carbon fiber volume and the free space volume, and the free space refers to the gap formed by the mutual support between the carbon fibers.

[0012] In step S1 of the present invention, the reactor filled with carbon fiber skeleton can be a chemical vapor deposition reactor.

[0013] In this invention, the "average spacing between carbon fibers in the carbon fiber skeleton" and the "temperature of the pyrolysis reaction" are optimal balance points derived from extensive experiments and theoretical analysis, rather than simple superpositions of conventional choices. Within the limited space formed by the carbon fiber skeleton, the residence time of gas molecules in the pyrolysis reaction region is greatly shortened due to the restricted fluid path; this results in insufficient time for homogeneous nucleation to complete complex chain reactions and carbon cluster growth, effectively suppressing it kinetically. In contrast, heterogeneous deposition involves molecules directly impacting surfaces with higher energy and rapidly dissociating and depositing, a much faster process; the above conditions, by controlling the residence time, kinetically "kill" the possibility of homogeneous nucleation. Therefore, in step S1, the probability of reactant molecules (such as methane) encountering a solid surface (such as a carbon bed) during diffusion is much higher than the probability of encountering another molecule in the free gas phase and undergoing a homogeneous reaction. From a kinetic perspective, the reactant supply rate and reaction opportunities are significantly improved in heterogeneous deposition.

[0014] In some embodiments, in step S1, the average spacing between the carbon fibers in the carbon fiber skeleton is 50-300 μm.

[0015] In some embodiments, in step S1, the carbon fiber skeleton is prepared by randomly stacking carbon fibers or by controlling the orientation of carbon fibers; wherein, by random stacking and controlled orientation stacking, carbon fibers can form a skeleton structure in a non-woven state.

[0016] In some embodiments, in step S1, the raw material of the carbon fiber skeleton includes chopped carbon fiber or continuous carbon fiber. Since the carbon fiber skeleton of this application is in a non-woven state, its raw material is preferably chopped carbon fiber, which cannot be woven; wherein, the length of the chopped carbon fiber is 1-50mm.

[0017] In some implementations, in step S1, the initial volume fraction of the carbon fiber skeleton is 0.1%-5%.

[0018] In a specific implementation, the preparation process of the carbon fiber skeleton includes: using a mechanical needle roller to loosen the carbon fiber and supplying gas into the carbon fiber to form a three-dimensional network structure; this preparation process is similar to the process of "fluffing cotton". By mechanically loosening and introducing gas, there are random contact points between the carbon fibers. In addition to the contact points, there are gaps. The spacing is formed by bending, overlapping and supporting the carbon fibers, thereby forming a fluffy carbon fiber skeleton.

[0019] In step S1 of the present invention, there is no adhesive between the carbon fibers in the carbon fiber skeleton.

[0020] In step S1 of the present invention, when the carbon fiber skeleton is made of organic fiber, the carbon fiber skeleton can be carbonized before it is filled into the reactor; if the carbon fiber skeleton is already carbonized fiber, this step can be omitted.

[0021] In some embodiments, in step S1, the carbon source gas is selected from one or more of methane, ethane, ethylene, propylene, and natural gas.

[0022] In step S1 of the present invention, the growth of pyrolytic carbon on the carbon fiber skeleton is heterogeneous epitaxial growth (heterogeneous deposition). During this growth process, the homogeneous nucleation of carbon source gas (homogeneous nucleation) can be suppressed to produce carbon black. The crystal form obtained by pyrolytic carbon after heterogeneous deposition is better than the crystal form of carbonized or graphitized carbon fiber itself, which is beneficial to improving the electrical and thermal conductivity of the product.

[0023] In some implementations, the growth time in step S1 is 1-10 h.

[0024] In some embodiments, in step S1, the growth rate is 5-50 μm / h; wherein the growth rate control process is as follows: based on the cavity size and the filling amount of the carbon fiber skeleton, the sum of all surface areas involved in deposition within the reactor is calculated, and then the growth rate of pyrolytic carbon on the carbon fiber skeleton is controlled by the flow rate of the carbon source gas. For example: in a cross-sectional area of ​​1.5 m... 2 In the reactor, the flow rate of the carbon source gas (methane) is 8 Nm³. 3 / min, for example: in a tube furnace with a diameter of 50 mm, the flow rate of the carbon source gas (methane) is 4 SLM.

[0025] In some embodiments, the pressure condition for the pyrolysis reaction in step S1 is atmospheric pressure.

[0026] In step S2 of the present invention, during the graphitization process, pyrolytic carbon is converted into graphite crystals and fused with carbon fibers to form a three-dimensional continuous graphite network structure material.

[0027] In some embodiments, the temperature of the graphitization treatment in step S2 is 2500-3000°C.

[0028] In some embodiments, the graphitization process in step S2 takes 1-10 hours.

[0029] The present invention also provides a three-dimensional continuous graphite network structure material, which is prepared by the preparation method described above.

[0030] In some embodiments, the density of the three-dimensional continuous graphite network structure material is 0.1-1.7 g / cm³. 3 .

[0031] In a specific implementation, when the density of the three-dimensional continuous graphite network structure material is greater than 1 g / cm³ 3 At that time, the thermal conductivity in at least one direction of the three-dimensional continuous graphite network structure material is greater than 200 W / (m·K), and the resistivity is less than 8×10⁻⁶. -4 Ω·cm.

[0032] The present invention also provides a thermal management device comprising the three-dimensional continuous graphite network structure material as described above.

[0033] In this invention, the three-dimensional continuous graphite network structure material possesses three major characteristics: "isotropy", "high thermal conductivity", and "continuum".

[0034] Preferably, the thermal management device includes a thermal interface material, a heat sink, a vapor chamber, or a heat sink.

[0035] The present invention also provides an electrode device comprising the three-dimensional continuous graphite network structure material as described above.

[0036] Preferably, the electrode device includes a fuel cell bipolar plate, an electrolytic electrode, or a supercapacitor electrode.

[0037] Compared with the prior art, the present invention has the following significant advantages: Unlike traditional CVI densification processes, this invention uses a low-volume-fraction carbon fiber skeleton as a growth template rather than a reinforcing phase. By precisely controlling the growth space and conditions, an isotropic (quasi-isotropic), high thermal conductivity, high electrical conductivity, and density-adjustable three-dimensional continuous graphite network structure material is obtained, which is suitable for thermal management, electrodes, and other fields. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of the preparation method in Example 1 of the present invention; Figure 2 This is a SEM image of the carbon fiber skeleton of Embodiment 1 of the present invention; Figure 3 These are low-magnification and high-magnification SEM images of the three-dimensional continuous graphite network structure material of Embodiment 1 of the present invention; Figure 4 This is a bar chart comparing the thermal conductivity of the products of Example 1 of the present invention with those of Comparative Examples 1, 2, and 3. Figure 5 This is a schematic diagram of the three-dimensional continuous graphite network structure material, the traditional C / C composite material, and the skeleton of graphene foam in Embodiment 1 of the present invention; Figure 6 The XRD patterns are those of the products of Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0039] The present invention will be further described in detail below through preferred embodiments, but the scope of protection of the present invention is not limited thereto.

[0040] Example 1 This embodiment discloses a three-dimensional continuous graphite network structure material and its preparation method.

[0041] Figure 1 This is a process flow diagram of the preparation method in this embodiment, as shown below. Figure 1 As shown, the preparation method includes the following steps: S0. T300 chopped carbon fiber is selected as the non-woven carbon fiber skeleton. Figure 2 The following are SEM images of the carbon fiber skeleton in this embodiment: Image a is an SEM image of a certain location of the material at a resolution of 20 μm; Image b is an SEM image of another location of the material at a resolution of 20 μm; Image c is an SEM image of the material at a resolution of 50 μm; Image b is an SEM image of the material at a resolution of 200 μm; The cross-section of the carbon fiber skeleton is non-circular to form a curled carbon fiber structure. First, a three-dimensional network is formed by mechanical needle roller opening and gas conveying. The average spacing between carbon fibers in the carbon fiber skeleton is 150μm, the initial volume fraction of the carbon fiber skeleton (the ratio of carbon fiber volume to carbon fiber packing volume) is about 3%, and the porosity is 97%. After the above treatment, a carbon fiber skeleton with low density is formed. Then, the carbon fiber skeleton was pretreated under an argon atmosphere at a temperature of 1200℃ and a time of 2h to carbonize the organic fibers. S1. Methane is introduced into a reactor filled with a carbon fiber skeleton. The methane undergoes a pyrolysis reaction at 1250°C and atmospheric pressure. The flow rate of methane is 1000 sccm, and the introduction time (i.e., the growth time of pyrolytic carbon on the carbon fiber skeleton) is 8 hours. The pyrolytic carbon generated by the reaction grows on the carbon fiber skeleton to obtain a carbon fiber structure coated with pyrolytic carbon. No carbon black is generated in this process. S2. Under an argon atmosphere, the carbon fiber structure is graphitized at 2800℃ for 3 hours to form a three-dimensional continuous graphite network structure material.

[0042] Figure 3The images show low-magnification and high-magnification SEM images of the three-dimensional continuous graphite network structure material in this embodiment; Image a shows the three-dimensional network structure formed after deposition on the carbon fiber surface; it can be seen that, except for the heterogeneous deposition products, other locations are very clean and there is no homogeneous nucleation carbon black; Image b shows the regular layered structure formed by heterogeneous deposition at a resolution of 20 μm; Images c and d show different cross-sections of the graphite powder after crushing.

[0043] Figure 5 Figure 1 shows a schematic diagram of the three-dimensional continuous graphite network structure material, the traditional C / C composite material, and the graphene foam skeleton in this embodiment; Figure 2a shows a schematic diagram of the three-dimensional continuous graphite network structure material, Figure 3b shows a schematic diagram of the graphene foam skeleton, and Figure 4c shows a schematic diagram of the traditional C / C composite material.

[0044] Example 1 This embodiment discloses the characterization results of the three-dimensional continuous graphite network structure material of Example 1.

[0045] (1) Scanning electron microscopy Test instrument name: Field emission scanning electron microscope; Manufacturer: FEI, USA; Instrument model: NovaNanoSEM450; The density of the three-dimensional continuous graphite network structure material was determined to be 1.1 g / cm³ using scanning electron microscopy.

[0046] (2) X-ray diffraction method Test instrument name: X-ray diffractometer; Manufacturer: Rigaku, Japan; Instrument model: SmartLabSE; The microstructure of the product was determined using X-ray diffraction (SEM); the results are as follows. Figure 3 As shown, the product has a continuous network structure and no clear grain boundaries; (3) Raman spectroscopy Testing instrument: Laser Raman spectrometer; Manufacturer: Renishaw, UK; Instrument model: inVia Reflex; The crystal structure of the product was determined by Raman spectroscopy (XRD); the results are as follows. Figure 6 As shown, Figure 6 The black line in the figure represents the product of Example 1, with ID / IG (intensity ratio of D peak to G peak) << 0.1 and grain size > 100 nm; the graphitization degree of the product of Example 1 is 95.31%; (4) Laser flash method Test instrument: Laser thermal conductivity meter; Manufacturer: Netzsch, Germany; Instrument model: LFA467; The thermal conductivity of the product was detected by laser flare method, and the average value of the product in the three directions of x, y and z was 850 W / (m·K), and the anisotropy ratio was 1.1.

[0047] (5) Resistivity test method Testing instrument: Intelligent computer resistivity meter; Manufacturer: Xiangtan Xiangyi; Instrument model: CDZL; The resistivity of the product was measured using a resistivity test method, and the average resistivity of the product in the x, y, and z axes was found to be 3 × 10⁻⁶. -4 Ω·cm.

[0048] Comparative Example 1 This comparative example discloses a graphite material and its preparation method.

[0049] In step S0 of this comparative example, the average spacing between carbon fibers in the carbon fiber skeleton is too small, at 10 μm (which is a dense carbon felt). The other steps and conditions are the same as in Example 1.

[0050] Comparative Example 2 This comparative example discloses a graphite material and its preparation method.

[0051] In step S0 of this comparative example, the average spacing of the carbon fibers in the carbon fiber skeleton is too large, which is 1 mm. The other steps and conditions are the same as in Example 1.

[0052] Comparative Example 3 This comparative example discloses a method for preparing conventional graphite materials in the art.

[0053] A 40% volume fraction 2D woven carbon cloth preform was selected, and the CVI (vapor phase infiltration) process, a standard technique in the art, was employed. During this process, conventional isothermal and multi-cycle operating conditions were used to densify the product to 1.8 g / cm³. 3 .

[0054] Example 2 This effective example tested the thermal conductivity of the products of Comparative Examples 1-3 and compared it with the thermal conductivity of the product of Example 1. Figure 4 This is a bar chart comparing the thermal conductivity of the products from Example 1 and Comparative Examples 1, 2, and 3. The graphite material prepared in Comparative Example 1 has a small average spacing between carbon fibers, resulting in rapid deposition, severe surface crusting, and insufficient internal growth. The final material is dense but has a thermal conductivity of only 20 W / (m·K), and the product exhibits significant anisotropy.

[0055] Comparative Example 2 exhibited a large amount of carbon black fumes during the CVD (chemical vapor deposition) process in step S1, resulting in a loose and uneven deposit with a fragile structure and low performance after graphitization; the thermal conductivity of this product was 5 W / (m·K). Furthermore, as... Figure 6 As shown, Figure 6 The red line represents the XRD results of the product of Comparative Example 2, which has a graphitization degree of only 36.33%.

[0056] The product of Comparative Example 3 has high strength, but its thermal conductivity is much lower than that of Example 1. Its in-plane thermal conductivity is about 120 W / (m·K), and its interlayer thermal conductivity is about 50 W / (m·K). The product exhibits significant anisotropy.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a three-dimensional continuous graphite network structure material, characterized in that, It includes the following steps: S1. A carbon source gas is introduced into a reactor filled with a carbon fiber skeleton. The carbon source gas undergoes a pyrolysis reaction, and the pyrolytic carbon generated by the reaction grows on the carbon fiber skeleton to obtain a carbon fiber structure coated with pyrolytic carbon. The temperature of the pyrolysis reaction is 1100-1500℃. The carbon fiber skeleton is a non-woven carbon fiber skeleton, and the average spacing between the carbon fibers in the carbon fiber skeleton is 20-500μm; the initial volume fraction of the carbon fiber skeleton is less than 10%; wherein, the initial volume fraction is the ratio of the carbon fiber volume to the carbon fiber packing volume. S2. Under an inert atmosphere, the carbon fiber structure is graphitized to form a three-dimensional continuous graphite network structure material; the graphitization temperature is greater than or equal to 2500℃.

2. The preparation method according to claim 1, characterized in that, Step S1 satisfies at least one of the following conditions: i. The average spacing between carbon fibers in the carbon fiber skeleton is 50-300μm; ii. The carbon fiber skeleton is prepared by randomly stacking carbon fibers or by stacking carbon fibers in a controlled orientation. iii. The raw materials for the carbon fiber skeleton include chopped carbon fibers or continuous carbon fibers; iv. The initial volume fraction of the carbon fiber skeleton is 0.1%-5%.

3. The preparation method according to claim 2, characterized in that, In step S1, the method for preparing the carbon fiber skeleton includes: using a mechanical needle roller to loosen the carbon fiber and supplying gas into the carbon fiber to form a three-dimensional network structure.

4. The preparation method according to claim 1, characterized in that, In step S1, the carbon source gas is selected from one or more of methane, ethane, ethylene, propylene, and natural gas.

5. The preparation method according to claim 1, characterized in that, Step S1 satisfies at least one of the following conditions: i. The growth time is 1-10 h; ii. The growth rate is 5-50 μm / h; iii. The pressure condition for the pyrolysis reaction is atmospheric pressure.

6. The preparation method according to claim 1, characterized in that, Step S2 satisfies at least one of the following conditions: i. The temperature of the graphitization treatment is 2500-3000℃; ii. The graphitization treatment time is 1-10 h.

7. A three-dimensional continuous graphite network structure material, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. The three-dimensional continuous graphite network structure material as described in claim 7, characterized in that, The density of the three-dimensional continuous graphite network structure material is 0.1-1.7 g / cm³. 3 ; When the density of the three-dimensional continuous graphite network structure material is greater than 1 g / cm³ 3 At that time, the thermal conductivity in at least one direction of the three-dimensional continuous graphite network structure material is greater than 200 W / (m·K), and the resistivity is less than 8×10⁻⁶. -4 Ω·cm.

9. A thermal management device, characterized in that, It includes the three-dimensional continuous graphite network structure material as described in claim 7 or 8.

10. An electrode device, characterized in that, It includes the three-dimensional continuous graphite network structure material as described in claim 7 or 8.

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