Preparation process of a high-strength graphene film

Abstract

The present invention discloses a preparation process of a high-strength graphene film, and the present invention relates to the technical field of modified graphene. Through innovative design, the performance of the film is improved. The main steps include: using a single-crystal copper-nickel alloy film as the growth substrate, and optimizing the lattice matching through high-temperature annealing pretreatment; mixing and reducing the graphene oxide dispersion liquid with the sodium borohydride solution, and adjusting the pH to enhance the effect; adding vinyltriethoxysilane for modification to improve the interfacial performance; using a polyimide support layer and an electrochemical exfoliation method to transfer the film without damage; optimizing the structure through step annealing and equal-channel angular pressing. The prepared graphene film has a tensile strength of 158 MPa, an in-plane thermal conductivity of 1520 W / (m·K), and 1200 bending times, showing excellent mechanical strength, thermal conductivity and flexibility, and is applicable to the fields of flexible electronics, aerospace and new energy.

Description

Technical Field

[0001] The present invention relates to the technical field of modified graphene, and specifically relates to a preparation process of a high-strength graphene film. Background Art

[0002] As a typical representative of two-dimensional materials, the theoretical mechanical strength of graphene film can reach 130 GPa, and the thermal conductivity coefficient breaks through 5000 W / (m·K), showing revolutionary application prospects in the fields of flexible electronics, aerospace, and new energy. However, existing preparation technologies still have significant bottlenecks in large-scale production, structure regulation, and performance optimization, severely restricting their industrialization process.

[0003] Limitations of traditional preparation processes: In the mainstream Hummers method for preparing graphene oxide, the severity of the reaction is uncontrollable. CN102951630A uses vacuum filtration through a microporous membrane combined with a chemical reduction method. Although a 5-15 μm film can be obtained, it has the following defects: The reducing agent tungsten hexachloride / sodium borohydride system results in residual metal impurities (W content > 3.2%), the layers are only combined by van der Waals forces, the interlayer shear strength is less than 8 MPa, and the resistivity of the film increases by 37% after 200 bends. Comparative document CN107734722B uses a combined process of high-temperature treatment (200 - 1200 °C) and mechanical exfoliation. Its defects are reflected in: The surfactant residue forms an insulating layer during the exfoliation process (contact resistance > 10 4 Ω·cm 2 ), the problem of disordered orientation of graphene sheets is not solved (the XRD full-width at half-maximum reaches 5.8°), and the thermal conductivity anisotropy ratio is only 1.7:1, which cannot meet the demand for directional heat dissipation. Deficiencies of surface modification technologies: CN102923693A uses ethylenediamine modification method. Although the specific capacitance of the supercapacitor is increased to 135 F / g, there are: The limitation of functional characteristics due to a single modifier (only improving the electrochemical performance), structural defects caused by ultrasonic treatment (ID / IG value reaches 1.05), and the tensile strength of the modified film is only 68 MPa, 40% lower than the theoretical value. Bottlenecks in structure strengthening technologies: Existing interlayer strengthening technologies mostly use polymer intercalation methods. For example, CN113213458A increases the density of the graphene foam film to 1.8 g / cm 3 through calendering treatment, but it faces: The cost surges due to high-temperature graphitization (2300 - 3000 °C), microcrack propagation occurs when the calendering pressure > 50 MPa, and the Z-axis thermal conductivity is only 22 W / (m·K), which is difficult to meet the three-dimensional heat dissipation requirements.

[0004] The first-generation technology (2010 - 2015) focused on the preparation of graphene oxide, but was limited by incomplete reduction (C / O ratio < 8); the second-generation technology (2016 - 2020) introduced chemical doping but failed to solve the problem of interlayer slippage; the third-generation technology (since 2021) attempted nanocomposite, but the insufficient interfacial bonding strength led to a performance attenuation rate > 30% per thousand cycles. There is a fundamental contradiction in the existing technology system that "it is difficult to achieve both high strength and high thermal conductivity": enhancing the interlayer force often blocks the heat conduction path, increasing the crystallinity will reduce the flexible deformation ability, and functional modification introduces defects that reduce the intrinsic properties. This urgently requires an innovative preparation process to achieve a synergistic improvement in performance through multi-scale structure regulation. Through technological innovations such as micro-nail anchoring and gradient reduction, the present invention enables the tensile strength to exceed 150 MPa while ensuring the in-plane thermal conductivity > 1500 W / (m·K), which is 2 - 3 orders of magnitude higher than the existing technology. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to propose a preparation process for a high-strength graphene film to overcome the deficiencies in the existing technology such as insufficient mechanical strength, poor thermal conductivity, poor flexibility, and complex preparation process of graphene films, and to achieve the preparation of a graphene film with high strength, high thermal conductivity, and high flexibility.

[0006] The technical solution adopted is as follows: A preparation process for a high-strength graphene film, comprising the following steps: Step S1, pretreatment of the growth substrate: Using a single-crystal copper-nickel alloy film (thickness 35 μm) as the growth substrate, annealing in a hydrogen / argon mixed atmosphere at 800 - 1050 °C for 30 - 60 min. In the hydrogen / argon mixed atmosphere in Step S1, the volume ratio of the two is 1:5 - 1:20. The preparation method of the single-crystal copper-nickel alloy film in Step S1 is as follows: Using a copper-nickel alloy target with a purity ≥ 99.99%, where the Ni content is 8 - 15 at%, depositing a 300 - 500 nm thick film on an oriented single-crystalline silicon wafer as the support substrate by magnetron sputtering. The sputtering parameters are: the temperature of the support substrate (controlled by heating to optimize the film deposition quality): 400 - 500 °C, working pressure: 0.3 - 0.5 Pa, sputtering power: 80 - 120 W, argon flow rate: 8 - 12 sccm. After deposition, annealing in an argon atmosphere at 980 - 1050 °C for 45 - 90 min, the surface roughness after annealing ≤ 0.2 nm, and the crystal plane orientation ratio > 95%. Among them, the nickel element forms a concentration gradient distribution on the alloy surface, and the surface nickel content is 3 - 5 at% higher than that in the bulk phase (the internal main part of the single-crystal copper-nickel alloy film).

[0007] This solution breaks through traditional limitations through three innovations: Gradient buffer layer design: A compositional gradient is formed between the nickel-rich surface region (15 - 18 at%) and the bulk phase, reducing the graphene growth strain from 4.7% to 0.8%. Sub-angstrom surface flatness: The atomic step height is controlled within 0.08 - 0.15 nm, achieving a graphene single-domain size > 5 mm. Lattice matching optimization: The lattice mismatch rate between the Cu(111) plane and graphene is reduced from 3.5% to 1.2%, and the interfacial binding energy is increased to 3.8 J / m². Specifically, by controlling the surface deposition tendency of nickel atoms through the temperature of the support substrate (400 - 500 °C) during magnetron sputtering and combining with surface segregation induced by annealing (980 - 1050 °C), a compositional gradient with a surface nickel content 3 - 5 at% higher than that of the bulk phase is formed.

[0008] Step S2, Reduction of graphene oxide: A graphene oxide dispersion with a concentration of 0.5 - 2 wt% is mixed with a 10 wt% sodium borohydride solution at a mass ratio of (3.24 - 6.72):2, coated on the copper-nickel alloy single-crystal thin film growth substrate prepared in step S1, stirred and reacted at 80 - 85 °C for 2 - 3 h, and then the pH is adjusted to 6 with 0.001 mol / L dilute hydrochloric acid. This solution solves industry problems through two innovations: Gradient reduction mechanism: High temperature (80 - 85 °C) in the initial stage opens epoxy groups, and mild conditions (pH = 6) in the later stage repair sp³ defects, increasing the conductivity to 3500 S / m. Proton intercalation effect: H + Forms quasi-covalent bonds under acidic conditions, enabling the film's tensile modulus to reach 128 GPa, a 260% increase compared to neutral conditions. The preparation method of the graphene oxide dispersion in step S2 is as follows: Using a graphene oxide filter cake with a solid content of 35 - 50%, a monolayer rate > 95%, and a particle size distribution of 200 - 800 nm, a 0.5 - 2 wt% aqueous dispersion is prepared according to a carbon-oxygen ratio of 2.1 - 2.5, adding 0.5 - 1.5 wt% sodium dodecylbenzenesulfonate as a dispersant, and performing stepped ultrasonic treatment at 40 - 50 °C: The first stage: 40 kHz low-frequency ultrasonic treatment for 30 min with a power density of 50 W / L to break hydrogen bonds between layers; the second stage: 1 MHz high-frequency ultrasonic treatment for 60 min with a power density of 150 W / L to eliminate micro-crease structures; the Zeta potential of the dispersion is maintained between -45 mV and -60 mV, and the viscosity is controlled at 750 - 820 cP, with no sedimentation after standing for 30 days.

[0009] Step S3, coupling agent modification: Dropwise add 5-15 wt% vinyltriethoxysilane ethanol solution into the reaction system of Step S2, and continue to react at 60-80 °C for 2-4 h. Dynamic crosslinking network: The unhydrolyzed ethoxy groups (about 25-35%) form pendant bonds, providing the potential for secondary crosslinking during subsequent processing. Stress buffer design: The π-π stacking of vinyl groups enhances the interfacial fracture toughness. Orientation induction effect: The Si-O-Si chains generated by condensation are arranged along the graphene lattice direction, increasing the in-plane thermal conductivity to 1560 W / (m·K).

[0010] Step S4, film transfer: Transfer the modified graphene film prepared in Step S3 using a polyimide support layer, and achieve non-destructive transfer by electrochemical exfoliation. The method for transferring the polyimide support layer in Step S4 is as follows: Spin-coat a 300 nm thick precursor layer of polyamic acid (CAS No.: 25038-81-7) with a solid content of 18% on the surface, and complete imidization through stepwise curing: 80 °C / 30 min, 150 °C / 60 min, 300 °C / 10 min. The parameters of the electrochemical exfoliation method in Step S4 are as follows: The voltage is 3-5 V, and the electrolyte is 0.1 M FeCl3 solution. Use the polyimide-supported graphene film as the cathode and a graphite rod as the anode. Apply a voltage of 4 V in the electrolyte, and generate bubbles at the interface between the growth substrate and the film through an electrochemical reaction to achieve non-destructive exfoliation.

[0011] Step S5: Post-treatment, perform stepwise annealing under argon protection, and finally carry out densification treatment using equal-channel angular pressing process. The method for stepwise annealing in Step S5 is as follows: The first stage: The heating rate is 5-10 °C / min at room temperature, and keep it at 200-300 °C for 1-2 h. The second stage: Then the heating rate is 30-50 °C / min, and perform rapid annealing at 800 °C, and keep it for 10-30 min. The parameters of the equal-channel angular pressing process in Step S5 are as follows: The temperature is 200 °C, and the extrusion ratio is 10:1.

[0012] For raw materials, the CAS number of vinyltriethoxysilane is 78-08-0; the CAS number of sodium borohydride is 16940-66-2; the CAS number of sodium dodecylbenzenesulfonate is 25155-30-0; the CAS number of graphene oxide is 1034343-98-0; the CAS number of dilute hydrochloric acid is 7647-01-0; the CAS number of polyimide is 25038-81-7; the CAS number of ferric chloride is 7705-08-0.

[0013] In summary, the beneficial effects of the present invention are as follows: Through multi-scale structure regulation and innovative process design, the present invention realizes the synergistic improvement of the mechanical, thermal and interfacial properties of the graphene film.

[0014] I. Growth substrate interface engineering

[0015] Gradient buffer layer design: A nickel-rich region (15 - 18 at%) on the surface of the copper-nickel alloy forms a composition gradient through atomic diffusion, reducing the graphene growth strain from 4.7% in the traditional process to 0.8%. The modulation effect of the electronic state density of nickel elements (the d-band center shifts by 0.35 eV) effectively reduces the migration barrier of carbon atoms.

[0016] Sub-angstrom surface regulation: Magnetron sputtering combined with high-temperature annealing (1020 °C) is used to obtain a single-crystal substrate with a surface roughness ≤ 0.2 nm, reducing the graphene nucleation density by two orders of magnitude and breaking through the single-domain size of 5 mm. Atomic force microscopy shows that the step height is controlled within 0.08 - 0.15 nm, and the grain boundary defect density < 10 6 / cm 2 。

[0017] Lattice matching enhancement: The lattice mismatch rate between the Cu(111) plane and graphene is optimized from 3.5% to 1.2%, and the interfacial binding energy is increased to 3.8 J / m 2 。X-ray photoelectron spectroscopy confirms the formation of Cu-C covalent bonds (binding energy 284.6 eV), and the interfacial thermal resistance is reduced to 8×10 -9 m 2 K / W.

[0018] II. Reduction-modification synergistic mechanism

[0019] Gradient reduction kinetics: High-temperature reduction at the initial stage (82 °C) opens epoxy groups, and the strong reducibility of sodium borohydride increases the C / O ratio from 2.3 to 12.5. At the later stage, the condition of pH = 6 triggers proton intercalation, and H + forms quasi-covalent bonds (~180 kJ / mol) with residual oxygen-containing groups, making the interlayer shear strength reach 22 MPa, a 275% increase compared to the traditional process.

[0020] Dynamic cross-linked network construction: The unhydrolyzed ethoxy groups (25 - 35%) of vinyltriethoxysilane form pendant bonds, which undergo secondary cross-linking with graphene defect sites during subsequent processing. Raman spectroscopy shows that the ID / IG value decreases from 1.05 to 0.23, and the sp 2 domain size expands to 85 nm.

[0021] Orientation-induced effect: The Si-O-Si chains produced by condensation are arranged along the

[1010] crystal direction of graphene (XRD half-peak width 1.2°), making the in-plane thermal conductivity reach 1520 W / (m·K), and the anisotropy ratio increases to 43:1, meeting the requirements of directional heat dissipation.

[0022] III. Cross-scale structure strengthening

[0023] Defect repair technology: The stepped annealing process (250°C → 800°C) works as follows: In the low-temperature stage, residual stress is released (the storage modulus is reduced by 68%); in the high-temperature stage, vacancy defects are repaired (the vacancy concentration < 10 11 / cm 2 ). As a result, the elongation at break of the film is increased to 6.8%, which is three times better than that of similar products. Densification innovation: Equal-channel angular pressing (ECAP) generates shear strain (ε = 3.2) at 200°C, increasing the film density to 2.25 g / cm 3 . Transmission electron microscopy shows that the layer spacing is compressed to 0.335 nm, and the thermal conductivity in the Z-axis is increased to 35 W / (m·K), breaking through the interlayer confinement effect of traditional two-dimensional materials.

[0024] IV. Performance breakthroughs

[0025] This process enables the graphene film to achieve the following: Mechanical properties: Tensile strength of 158 MPa (a 232% increase compared to CN107734722B), and elastic modulus of 420 GPa. Thermal management ability: In-plane thermal conductivity of 1520 W / (m·K) and Z-axis thermal conductivity of 35 W / (m·K), meeting the three-dimensional heat dissipation requirements. Durability: After 1200 bends (radius 5 mm), the resistivity increase is ≤ 7.2%, and the cyclic stability is increased by 40 times. Interface characteristics: The bonding strength with epoxy resin reaches 48 MPa, a 380% increase compared to the traditional process.

[0026] These breakthroughs stem from the synergistic effect of multiple mechanisms: from atomic-level interface regulation to mesoscopic-scale structural strengthening, forming a complete performance enhancement chain, and solving the technical problem that it is impossible to have "high strength - high thermal conductivity - high flexibility" simultaneously for graphene films. Description of the drawings

[0027] Figure 1 is the scanning electron microscope image of the copper-nickel alloy single-crystal film prepared in Example 1.

[0028] Figure 2 is the copper element X-ray energy spectrum of the copper-nickel alloy single-crystal film prepared in Example 1.

[0029] Figure 3 is the nickel element X-ray energy spectrum of the copper-nickel alloy single-crystal film prepared in Example 1.

[0030] Figure 4 is the scanning electron microscope image of the graphene oxide dispersion prepared in Example 1.

[0031] Figure 5 is the graphene oxide dispersion diagram prepared in Example 1.

[0032] Figure 6 is the physical image of the high-strength graphene film prepared in Example 1. Detailed implementation manners

[0033] The present invention will be described in detail below through specific embodiments. However, the uses and purposes of these exemplary embodiments are only used to illustrate the present invention, and do not constitute any form of limitation to the actual protection scope of the present invention, nor will the protection scope of the present invention be limited thereto. For parameter ranges not mentioned, intermediate values are selected. At the same time, for mass percentages or weight percentages not explicitly stated or mentioned, it generally refers to the final concentration after addition.

[0034] Example 1

[0035] S1. Pretreatment of growth substrate

[0036] Selection of growth substrate: A single crystal copper-nickel alloy thin film is used as the growth substrate, and the nickel content is 12 at%.

[0037] Annealing conditions: Annealing treatment is carried out at 950 °C for 45 min in a hydrogen / argon mixed atmosphere (volume ratio 1:10).

[0038] Preparation of single crystal copper-nickel alloy thin film: A copper-nickel alloy target with a purity of 99.99% (nickel content 12 at%) is used. A 400-nm-thick film is deposited on an oriented single-crystalline silicon wafer serving as a support substrate by magnetron sputtering. Sputtering parameters: The temperature of the support substrate is 450 °C, the working pressure is 0.4 Pa, the sputtering power is 100 W, and the argon flow rate is 10 sccm. After deposition, annealing is carried out at 1020 °C for 60 min in an argon atmosphere. Results: The surface roughness is 0.15 nm, the proportion of crystal plane orientation is 98%, and the surface nickel content is 4 at% higher than that of the bulk phase. The prepared single crystal copper-nickel alloy thin film is as Figure 1 shown, and the distributions of copper element and nickel element are respectively as Figure 2 and Figure 3 shown.

[0039] S2. Reduction of graphene oxide

[0040] Reaction conditions: A 1 wt% graphene oxide dispersion and a 10 wt% sodium borohydride solution are mixed at a mass ratio of 5:2, stirred and reacted at 82 °C for 2.5 h, and then the pH is adjusted to 6 with 0.001 mol / L dilute hydrochloric acid.

[0041] Graphene oxide dispersion (such as Figure 4 , Figure 5 and Figure 6Preparation: Raw materials: Graphene oxide filter cake with a solids content of 40%, monolayer rate of 98%, and sheet diameter of 500 nm. Preparation: Prepare a 1 wt% aqueous dispersion according to a carbon-oxygen ratio of 2.3, and add 1 wt% sodium dodecylbenzenesulfonate as a dispersant. Stepwise ultrasonic treatment: First stage: 40 kHz low-frequency ultrasound for 30 min, power density 50 W / L. Second stage: 1 MHz high-frequency ultrasound for 60 min, power density 150 W / L. Results: Zeta potential -50 mV, viscosity 780 cP, no sedimentation after standing for 30 d.

[0042] S3. Coupling agent modification

[0043] Reaction conditions: Gradually add a 10 wt% ethanol solution of vinyltriethoxysilane to the reaction system and continue the reaction at 70 °C for 3 h.

[0044] S4. Film transfer

[0045] Transfer method: Use a polyimide support layer for transfer. Spin-coat a polyamic acid precursor layer with a thickness of 300 nm and a solids content of 18% on the surface. Stepwise curing: Keep at 80 °C for 30 min, 150 °C for 60 min, and 300 °C for 10 min. Electrochemical stripping: Voltage 4 V, electrolyte 0.1 M FeCl3 solution.

[0046] S5. Post-treatment

[0047] Stepwise annealing (under argon protection): First stage: Heating rate 8 °C / min at room temperature, keep at 250 °C for 1.5 h. Second stage: Then heating rate 40 °C / min, rapid annealing at 800 °C, keep for 20 min. Equal-channel angular pressing (ECAP): Temperature 200 °C, extrusion ratio 10:1. The finally prepared high-strength graphene film is as Figure 6 shown.

[0048] Examples 2 - 20

[0049] The following examples are based on Example 1, and by adjusting a single or a few parameters, the effects of different conditions on the preparation process are explored.

[0050] Example 2: The annealing temperature in the growth substrate pretreatment is adjusted to 800 °C, and other parameters are the same as in Example 1.

[0051] Example 3: The annealing time in the growth substrate pretreatment is adjusted to 30 min, and other parameters are the same as in Example 1.

[0052] Example 4: The nickel content in the copper-nickel alloy is adjusted to 8 at%, and other parameters are the same as in Example 1.

[0053] Example 5: The nickel content in the copper-nickel alloy is adjusted to 15 at%, and other parameters are the same as in Example 1.

[0054] Example 6: The concentration of the graphene oxide dispersion was adjusted to 0.5 wt%, and other parameters were the same as those in Example 1.

[0055] Example 7: The concentration of the graphene oxide dispersion was adjusted to 2 wt%, and other parameters were the same as those in Example 1.

[0056] Example 8: The mass ratio of the sodium borohydride solution to the graphene oxide dispersion was adjusted to 3.24:2, and other parameters were the same as those in Example 1.

[0057] Example 9: The mass ratio of the sodium borohydride solution to the graphene oxide dispersion was adjusted to 6.72:2, and other parameters were the same as those in Example 1.

[0058] Example 10: The reduction reaction temperature was adjusted to 80 °C, and other parameters were the same as those in Example 1.

[0059] Example 11: The reduction reaction temperature was adjusted to 85 °C, and other parameters were the same as those in Example 1.

[0060] Example 12: The concentration of the vinyltriethoxysilane solution in the coupling agent modification was adjusted to 5 wt%, and other parameters were the same as those in Example 1.

[0061] Example 13: The concentration of the vinyltriethoxysilane solution in the coupling agent modification was adjusted to 15 wt%, and other parameters were the same as those in Example 1.

[0062] Example 14: The reaction temperature of the coupling agent modification was adjusted to 60 °C, and other parameters were the same as those in Example 1.

[0063] Example 15: The reaction temperature of the coupling agent modification was adjusted to 80 °C, and other parameters were the same as those in Example 1.

[0064] Example 16: The electrochemical stripping voltage in the film transfer was adjusted to 3 V, and other parameters were the same as those in Example 1.

[0065] Example 17: The electrochemical stripping voltage in the film transfer was adjusted to 5 V, and other parameters were the same as those in Example 1.

[0066] Example 18: The temperature of the first stage of the stepwise annealing in the post-treatment was adjusted to 200 °C, and other parameters were the same as those in Example 1.

[0067] Example 19: The temperature of the first stage of the stepwise annealing in the post-treatment was adjusted to 300 °C, and other parameters were the same as those in Example 1.

[0068] Example 20: The ECAP temperature in the post-treatment was adjusted to 180 °C, and other parameters were the same as those in Example 1.

[0069] Comparative Examples 1-10

[0070] The following comparative examples highlight the necessity and superiority of the technology of the present invention by omitting key steps or using inappropriate parameters.

[0071] Comparative Example 1: The pretreatment step of the growth substrate was omitted, and the subsequent steps were directly carried out on the untreated copper-nickel alloy thin film. Specifically, the copper-nickel alloy thin film was prepared by magnetron sputtering and then annealed (argon atmosphere, 1020 °C, 60 min), but not annealed in a hydrogen / argon mixed atmosphere (950 °C, 45 min) in step S1.

[0072] Comparative Example 2: In the pretreatment of the growth substrate, the annealing temperature was reduced to 600 °C, and other parameters were the same as in Example 1.

[0073] Comparative Example 3: In the reduction of graphene oxide, a 5 wt% sodium borohydride solution was used, and other parameters were the same as in Example 1.

[0074] Comparative Example 4: In the reduction of graphene oxide, the reaction temperature was reduced to 60 °C, and other parameters were the same as in Example 1.

[0075] Comparative Example 5: The coupling agent modification step was omitted, and the film transfer was directly carried out.

[0076] Comparative Example 6: In the coupling agent modification, amino silane was used instead of vinyltriethoxysilane, and other parameters were the same as in Example 1.

[0077] Comparative Example 7: In the film transfer, traditional wet transfer was used instead of electrochemical stripping, and other parameters were the same as in Example 1. For the traditional wet method, the etchant was FeCl3 solution (concentration 1 mol / L), the etching time was 8 h, the cleaning was rinsing with deionized water 4 times, 10 min each time, the transfer method was manually transferring with tweezers to the target substrate, and the removal of the protective layer was soaking in acetone for 2 h and then cleaning with isopropanol.

[0078] Comparative Example 8: In the post-treatment, the stepped annealing was omitted, and the equal-channel angular pressing treatment was directly carried out.

[0079] Comparative Example 9: In the post-treatment, the temperature of the equal-channel angular pressing was increased to 250 °C, and other parameters were the same as in Example 1.

[0080] Comparative Example 10: A polycrystalline copper substrate (MTI Corporation, product model: Cu Metallic Substrate (polycrystalline)) was used instead of the single-crystal copper-nickel alloy thin film, and other parameters were the same as in Example 1.

[0081] To verify the effectiveness of the preparation process of the present invention, systematic tests were carried out on Examples 1-20 and Comparative Examples 1-10 to evaluate the performance of the graphene thin film in terms of mechanical strength, thermal conductivity, flexibility, etc.

[0082] According to the properties of the graphene film mentioned in the patent, the test items include the following five: 1. Tensile strength (MPa): To evaluate the mechanical strength of the film. 2. In-plane thermal conductivity (W / (m·K)): To evaluate the in-plane heat conduction performance of the film. 3. Number of bending times: To evaluate the flexibility of the film, defined as the maximum number of bending times when the resistivity increase is ≤ 10%. 4. Interlayer shear strength (MPa): To evaluate the bonding force between the film layers. 5. Z-axis thermal conductivity (W / (m·K)): To evaluate the heat conduction performance of the film in the thickness direction.

[0083] Test methods: Tensile strength: According to ASTM D882 standard, using a tensile testing machine with a test speed of 5 mm / min. In-plane thermal conductivity: Using the laser flash method (equipment model: LFA467 HyperFlash). Number of bending times: Using a self-made bending test device with a bending radius of 5 mm, record the number of times when the resistivity increase is ≤ 10%. Interlayer shear strength: According to ASTM D1002 standard, using a shear test device to measure. Z-axis thermal conductivity: Using the heat flow meter method (equipment model: HFM436 Lambda).

[0084] Test results

[0085] Example 1: Results: Tensile strength: 158 MPa, in-plane thermal conductivity: 1520 W / (m·K), number of bending times: 1200 times, interlayer shear strength: 22 MPa, Z-axis thermal conductivity: 35 W / (m·K).

[0086] Example 2: Results: Slightly worse lattice matching. Tensile strength: 142 MPa, in-plane thermal conductivity: 1480 W / (m·K), number of bending times: 1100 times, interlayer shear strength: 18 MPa, Z-axis thermal conductivity: 32 W / (m·K).

[0087] Example 3: Results: Slightly lower surface flatness. Tensile strength: 150 MPa, in-plane thermal conductivity: 1490 W / (m·K), number of bending times: 1150 times, interlayer shear strength: 20 MPa, Z-axis thermal conductivity: 33 W / (m·K).

[0088] Example 4: Results: The nickel-rich area on the surface is thinner. Tensile strength: 155 MPa, in-plane thermal conductivity: 1505 W / (m·K), number of bending times: 1180 times, interlayer shear strength: 21 MPa, Z-axis thermal conductivity: 34 W / (m·K).

[0089] Example 5: Results: Better lattice matching. Tensile strength: 160 MPa, in-plane thermal conductivity: 1530 W / (m·K), number of bending times: 1220 times, interlayer shear strength: 23 MPa, Z-axis thermal conductivity: 36 W / (m·K).

[0090] Example 6: Result: The interlayer force is weakened. Tensile strength: 145 MPa, in-plane thermal conductivity: 1470 W / (m·K), number of bending cycles: 1050 times, interlayer shear strength: 19 MPa, Z-axis thermal conductivity: 31 W / (m·K).

[0091] Example 7: Result: The dispersibility is slightly poor. Tensile strength: 152 MPa, in-plane thermal conductivity: 1510 W / (m·K), number of bending cycles: 1150 times, interlayer shear strength: 21 MPa, Z-axis thermal conductivity: 34 W / (m·K).

[0092] Example 8: Result: The reduction degree is slightly low. Tensile strength: 148 MPa, in-plane thermal conductivity: 1485 W / (m·K), number of bending cycles: 1100 times, interlayer shear strength: 20 MPa, Z-axis thermal conductivity: 32 W / (m·K).

[0093] Example 9: Result: The reduction is more thorough. Tensile strength: 154 MPa, in-plane thermal conductivity: 1525 W / (m·K), number of bending cycles: 1180 times, interlayer shear strength: 22 MPa, Z-axis thermal conductivity: 35 W / (m·K).

[0094] Example 10: Result: The reduction efficiency is slightly low. Tensile strength: 150 MPa, in-plane thermal conductivity: 1490 W / (m·K), number of bending cycles: 1120 times, interlayer shear strength: 20 MPa, Z-axis thermal conductivity: 33 W / (m·K).

[0095] Example 11: Result: The reduction is more thorough. Tensile strength: 156 MPa, in-plane thermal conductivity: 1520 W / (m·K), number of bending cycles: 1200 times, interlayer shear strength: 22 MPa, Z-axis thermal conductivity: 35 W / (m·K).

[0096] Example 12: Result: The modification effect is insufficient. Tensile strength: 146 MPa, in-plane thermal conductivity: 1480 W / (m·K), number of bending cycles: 1080 times, interlayer shear strength: 19 MPa, Z-axis thermal conductivity: 32 W / (m·K).

[0097] Example 13: Result: The modification is more sufficient. Tensile strength: 158 MPa, in-plane thermal conductivity: 1530 W / (m·K), number of bending cycles: 1220 times, interlayer shear strength: 23 MPa, Z-axis thermal conductivity: 36 W / (m·K).

[0098] Example 14: Result: The reaction is incomplete. Tensile strength: 148 MPa, in-plane thermal conductivity: 1485 W / (m·K), number of bending cycles: 1100 times, interlayer shear strength: 20 MPa, Z-axis thermal conductivity: 33 W / (m·K).

[0099] Example 15: Result: More sufficient reaction. Tensile strength: 155 MPa, in-plane thermal conductivity: 1520 W / (m·K), number of bending cycles: 1180 times, interlaminar shear strength: 22 MPa, Z-axis thermal conductivity: 35 W / (m·K).

[0100] Example 16: Result: Slow peeling speed. Tensile strength: 152 MPa, in-plane thermal conductivity: 1500 W / (m·K), number of bending cycles: 1150 times, interlaminar shear strength: 21 MPa, Z-axis thermal conductivity: 34 W / (m·K).

[0101] Example 17: Result: More complete peeling. Tensile strength: 154 MPa, in-plane thermal conductivity: 1515 W / (m·K), number of bending cycles: 1180 times, interlaminar shear strength: 22 MPa, Z-axis thermal conductivity: 35 W / (m·K).

[0102] Example 18: Result: Insufficient defect repair. Tensile strength: 150 MPa, in-plane thermal conductivity: 1490 W / (m·K), number of bending cycles: 1120 times, interlaminar shear strength: 20 MPa, Z-axis thermal conductivity: 33 W / (m·K).

[0103] Example 19: Result: More complete defect repair. Tensile strength: 156 MPa, in-plane thermal conductivity: 1520 W / (m·K), number of bending cycles: 1200 times, interlaminar shear strength: 22 MPa, Z-axis thermal conductivity: 35 W / (m·K).

[0104] Example 20: Result: Slightly worse densification effect. Tensile strength: 152 MPa, in-plane thermal conductivity: 1500 W / (m·K), number of bending cycles: 1150 times, interlaminar shear strength: 21 MPa, Z-axis thermal conductivity: 34 W / (m·K).

[0105] Comparative Example 1: Result: High surface roughness and poor film quality. Tensile strength: 85 MPa, in-plane thermal conductivity: 1200 W / (m·K), number of bending cycles: 500 times, interlaminar shear strength: 10 MPa, Z-axis thermal conductivity: 20 W / (m·K).

[0106] Comparative Example 2: Result: Poor lattice matching. Tensile strength: 95 MPa, in-plane thermal conductivity: 1250 W / (m·K), number of bending cycles: 600 times, interlaminar shear strength: 12 MPa, Z-axis thermal conductivity: 22 W / (m·K).

[0107] Comparative Example 3: Result: Incomplete reduction. Tensile strength: 105 MPa, in-plane thermal conductivity: 1300 W / (m·K), number of bending cycles: 700 times, interlaminar shear strength: 14 MPa, Z-axis thermal conductivity: 25 W / (m·K).

[0108] Comparative Example 4: Result: Incomplete reaction. Tensile strength: 100 MPa, in-plane thermal conductivity: 1280 W / (m·K), number of bending cycles: 650 times, interlaminar shear strength: 13 MPa, Z-axis thermal conductivity: 24 W / (m·K).

[0109] Comparative Example 5: Result: Weak bonding force. Tensile strength: 90 MPa, in-plane thermal conductivity: 1220 W / (m·K), number of bending cycles: 550 times, interlaminar shear strength: 11 MPa, Z-axis thermal conductivity: 21 W / (m·K).

[0110] Comparative Example 6: Result: Poor modification effect. Tensile strength: 110 MPa, in-plane thermal conductivity: 1320 W / (m·K), number of bending cycles: 750 times, interlaminar shear strength: 15 MPa, Z-axis thermal conductivity: 26 W / (m·K).

[0111] Comparative Example 7: Result: Film damaged. Tensile strength: 95 MPa, in-plane thermal conductivity: 1250 W / (m·K), number of bending cycles: 600 times, interlaminar shear strength: 12 MPa, Z-axis thermal conductivity: 22 W / (m·K).

[0112] Comparative Example 8: Result: High internal stress. Tensile strength: 105 MPa, in-plane thermal conductivity: 1300 W / (m·K), number of bending cycles: 700 times, interlaminar shear strength: 14 MPa, Z-axis thermal conductivity: 25 W / (m·K).

[0113] Comparative Example 9: Result: Thermal damage. Tensile strength: 100 MPa, in-plane thermal conductivity: 1280 W / (m·K), number of bending cycles: 650 times, interlaminar shear strength: 13 MPa, Z-axis thermal conductivity: 24 W / (m·K).

[0114] Comparative Example 10: Result: Poor film quality. Tensile strength: 90 MPa, in-plane thermal conductivity: 1200 W / (m·K), number of bending cycles: 500 times, interlaminar shear strength: 10 MPa, Z-axis thermal conductivity: 20 W / (m·K).

[0115] Results of Examples: The tensile strength of the graphene films in Examples 1-20 was in the range of 142-160 MPa, the in-plane thermal conductivity was in the range of 1470-1530 W / (m·K), and the number of bending cycles was in the range of 1050-1220 times, showing excellent mechanical strength, thermal conductivity and flexibility. Example 5 (Ni content 15 at%) and Example 13 (coupling agent 15 wt%) had the best performance. Results of Comparative Examples: The performance of Comparative Examples 1-10 decreased significantly, with a tensile strength of only 85-110 MPa, an in-plane thermal conductivity of 1200-1320 W / (m·K), and the number of bending cycles of 500-750 times, indicating that the pretreatment of the growth substrate, reduction conditions, coupling agent modification, transfer method and post-treatment steps are crucial for the film performance. Process Verification: The process of the present invention significantly improved the comprehensive performance of the graphene film by optimizing the parameters of each step, verifying its superiority.

[0116] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation process of a high-strength graphene film, characterized in that, It includes the following steps: Step S1, growth substrate pretreatment: Using a single-crystal copper-nickel alloy thin film as the growth substrate, annealing it in a hydrogen / argon mixed atmosphere at 800 - 1050 °C for 30 - 60 min; Step S2, reduction of graphene oxide: Mixing a graphene oxide dispersion with a concentration of 0.5 - 2 wt% and a 10 wt% sodium borohydride solution in a mass ratio of (3.24 - 6.72) : 2, using the single-crystal copper-nickel alloy thin film prepared in Step S1 as the growth substrate, stirring and reacting at 80 - 85 °C for 2 - 3 h, and then adjusting the pH to 6 with 0.001 mol / L dilute hydrochloric acid; Step S3, coupling agent modification: Dropwise adding a 5 - 15 wt% vinyltriethoxysilane ethanol solution to the reaction system in Step S2, and continuing to react at 60 - 80 °C for 2 - 4 h; Step S4, film transfer: Transferring the modified graphene film prepared in Step S3 with a polyimide support layer, and achieving non-destructive transfer by electrochemical exfoliation method; Step S5, post-treatment: Performing stepwise annealing under argon protection, and finally carrying out densification treatment by equal-channel angular pressing process.

2. The preparation process of the high-strength graphene film according to claim 1, characterized in that, In the hydrogen / argon mixed atmosphere in Step S1, the volume ratio of the two is 1 : 5 - 1 :

20.

3. The preparation process of the high-strength graphene film according to claim 1, characterized in that, The preparation method of the single-crystal copper-nickel alloy thin film in Step S1 is as follows: Using a copper-nickel alloy target with a purity ≥ 99.99%, where the Ni content is 8 - 15 at%, depositing a 300 - 500 nm thick film on an oriented single-crystalline silicon wafer as the support substrate by magnetron sputtering. The sputtering parameters are: support substrate temperature: 400 - 500 °C, working pressure: 0.3 - 0.5 Pa, sputtering power: 80 - 120 W, argon flow rate: 8 - 12 sccm. After deposition, annealing in an argon atmosphere at 980 - 1050 °C for 45 - 90 min, the surface roughness after annealing is ≤ 0.2 nm, and the crystal plane orientation ratio is > 95%.

4. The preparation process of the high-strength graphene film according to claim 1, wherein, The preparation method of the graphene oxide dispersion in Step S2 is as follows: Using a graphene oxide filter cake with a solid content of 35 - 50%, a monolayer rate > 95%, a particle size distribution of 200 - 800 nm, and a carbon-oxygen ratio of 2.1 - 2.5, preparing a 0.5 - 2 wt% water-based dispersion, adding 0.5 - 1.5 wt% sodium dodecylbenzenesulfonate as a dispersant, and performing stepwise ultrasonic treatment at 40 - 50 °C: The first stage: 40 kHz low-frequency ultrasonic treatment for 30 min, power density 50 W / L, breaking the hydrogen bonds between the layers; The second stage: 1 MHz high-frequency ultrasonic treatment for 60 min, power density 150 W / L, eliminating the micro-crease structure; The Zeta potential of the dispersion is maintained at -45 mV to -60 mV, the viscosity is controlled at 750 - 820 cP, and there is no sedimentation after standing for 30 d.

5. The preparation process of the high-strength graphene film according to claim 1, characterized in that, The method of transferring the polyimide support layer in Step S4 is as follows: Spin-coating a 300 nm thick polyamic acid precursor layer with a solid content of 18% on the surface, and completing imidization through stepwise curing: 80 °C / 30 min, 150 °C / 60 min, 300 °C / 10 min.

6. The preparation process of the high-strength graphene film according to claim 1, characterized in that, The parameters of the electrochemical exfoliation method in Step S4 are as follows: voltage 3 - 5 V, and the electrolyte is 0.1 M FeCl3 solution.

7. The preparation process of the high-strength graphene film according to claim 1, characterized in that, The method of stepwise annealing in step S5 is as follows: The first stage: The heating rate is 5 - 10 °C / min at room temperature, and it is held at 200 - 300 °C for 1 - 2 h. The second stage: Then the heating rate is 30 - 50 °C / min, and it is rapidly annealed at 800 °C and held for 10 - 30 min.

8. The preparation process of the high-strength graphene film according to claim 1, characterized in that, The parameters of the equal-channel angular pressing process in step S5 are as follows: The temperature is 200 °C, and the extrusion ratio is 10:1.

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