Nanomortise and tenon structure carbon nanofiber heating film and preparation method thereof

Abstract

The present application relates to the field of nanomaterials and heat management, in particular to a preparation method of a nano-mortise and tenon structure carbon nanofiber heating film, a secondary mortise and tenon structure is formed by in-situ growth of carbon nanotubes through metal catalysis, and a three-dimensional interpenetrating network between fibers is realized. Specifically, a polymer precursor fiber film containing a transition metal salt is prepared by using a free surface electrospinning technology, after pre-oxidation, through melamine assisted high temperature carbonization, a 'pod-shaped' carbon nanotube branch is catalytically grown on the surface of the carbon nanofiber, and a mortise and tenon type mechanical interlocking and chemical bonding synergistic interface is formed. The structure increases the contact area between the fibers, the thickness direction thermal conductivity coefficient and the transverse electrical conductivity are improved, and at the same time, high mechanical strength is also possessed. The present application does not need to introduce an insulating adhesive, the process is compatible with the existing production line, and can be widely applied to high-power electronic heat dissipation, flexible device heat management and energy field.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials and thermal management technology, specifically to a carbon nanofiber heating film with a nano-mortise and tenon structure and its preparation method. Background Technology

[0002] Carbon nanofibers exhibit extremely high axial thermal conductivity; for example, pitch-based carbon fibers can achieve axial thermal conductivity exceeding 1000 W / m·K, approaching the level of single-crystal graphite. Their dense structure and low-defect characteristics (such as the ordered arrangement of multiple graphite sheets) effectively reduce phonon scattering and improve heat transfer efficiency. In terms of electrical conductivity, carbon nanofibers can exhibit resistivity as low as 0.1–0.37 Ω·cm and conductivity as high as 200 S / m, thanks to their highly graphitized carbon framework and three-dimensional conductive network structure. By doping with materials such as graphene or carbon nanotubes, their conductivity can be further enhanced, for example, achieving shielding effectiveness of up to 84.5 dB in electromagnetic shielding materials. Their high specific surface area and tight interfiber contacts also reduce interfacial resistance, making them suitable for flexible electronic devices and lithium-ion battery electrodes.

[0003] However, thin films made from carbon nanofibers face the following bottlenecks in practical applications: First, the electrical and thermal conductivity of carbon nanofibers exhibits significant directionality. In macroscopic materials, carbon nanofibers rely solely on van der Waals forces for inter-fiber contact, resulting in high interfacial thermal resistance. The thermal conductivity along the fiber axis can reach over 1000 W / m·K, but the thermal conductivity perpendicular to the fiber is only 8-15 W / m·K. Similarly, its electrical conductivity is prone to high interfacial resistance in the fiber contact region, with the lateral conductivity less than 1% of the axial conductivity.

[0004] Furthermore, the high aspect ratio and surface energy of carbon nanofibers make them prone to entanglement and aggregation, making it difficult to disperse uniformly in the polymer matrix, thus limiting the thermal / electrical conductivity of the composite material. For example, adding 3% carbon nanofibers to epoxy resin increases the thermal conductivity of the composite material from 0.2 W / m·K to 0.6 W / m·K, but this is still far below the theoretical value of a single carbon nanofiber.

[0005] Meanwhile, the diameter, density, and defects of carbon nanofibers directly affect the uniformity of electrical and thermal conductivity. Carbon nanofiber membranes face the problem of performance differences due to structural heterogeneity; for example, disordered fiber networks may form localized electrical / thermal bottlenecks, reducing overall efficiency. Finally, traditional carbon nanofiber membranes lack physical interlocking between layers, have a shear strength of less than 30 MPa, and are prone to slippage under dynamic loads, affecting long-term reliability. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a carbon nanofiber heating film with a nano-mortise and tenon structure and its preparation method, which solves the problems of high interfacial thermal resistance of carbon nanofiber films and difficulty in uniformly dispersing carbon nanofibers in polymer matrices.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a carbon nanofiber heating film with a nano-mortise and tenon structure, comprising the following steps: S1. Preparation of precursor solution First, polyacrylonitrile and cellulose acetate are dissolved in DMF solvent, then metal acetylacetone salt is added. The mixture is stirred at 60°C to promote polymer chain decomposition and form a homogeneous solution. The solution viscosity is then tested using a rotational rheometer and controlled at around 3000 mPa·s to ensure stable jet during spinning.

[0008] S2. Free Surface Electrospinning A multi-hole stepped spinneret is used to generate multiple jets by utilizing liquid surface tension. The spinneret is made of stainless steel. The nonwoven fabric collector uses a high-speed rotating roller with a linear velocity of 10 m / s to randomly stack the fibers, forming a three-dimensional fluffy structure, which is beneficial for gas diffusion during subsequent carbonization. The spinning voltage is 85-90 kV, and the ultra-high electric field stretches and refines the solution jet, reducing the diameter from the millimeter level to the nanometer level. The distance between the spinneret and the collector is 20-30 cm to ensure sufficient jet stretching and solvent evaporation. The flow rate is 60 mL / h, matched with the electric field strength; too high a flow rate will form droplets, while too low a flow rate will reduce the yield.

[0009] S3. Pre-oxidation treatment The fiber membrane is pre-oxidized in a pre-oxidation furnace by introducing an air atmosphere. The heating rate is 1-3℃ / min, and the final temperature is 250-300℃. In this high-temperature environment, the cyano groups of polyacrylonitrile undergo a cyclization reaction, forming a ladder-like structure and improving thermal stability. The acetyl groups in cellulose acetate undergo thermal decomposition to generate CO2 and H2O, while simultaneously forming micropores on the fiber surface. At the same time, some metals (such as Fe) are oxidized to Fe2O3, providing a precursor for subsequent carbonization to generate Fe3C.

[0010] S4. In-situ carbonization The pre-oxidized fiber membrane and melamine were carbonized together in an inert atmosphere at a temperature of 700-900℃, a heating rate of 5-10℃ / min, and a holding time of 1-3 hours, to catalyze the in-situ growth of branched carbon nanotubes. Melamine decomposes above 600℃ into gases such as NH3, HCN, and C2N2, providing nitrogen and carbon sources. NH3 reacts with the carbon skeleton to form active sites such as pyridine nitrogen (N-6) and pyrrole nitrogen (N-5), enhancing the ORR / OER catalytic activity. HCN cleavage provides carbon atoms, which are then catalyzed by metal particles to grow along specific crystal orientations into CNTs. During the heating phase, N2 protection prevents fiber oxidation. The N2 flow rate is controlled within the range of 200-500 sccm to ensure a stable reducing environment for the metal particles. Melamine begins to decompose at 300-500℃, releasing gases. At 700℃, Fe₂O₃ is reduced to Fe by carbon, and some Fe reacts with C to form Fe₃C. The Fe / Fe₃C interface acts as a catalyst for CNT growth. At 800℃, CNT growth begins, with Fe particles encapsulated by a graphite layer to prevent oxidative deactivation. Carbon atoms adsorb, diffuse, and precipitate on the metal surface to form CNTs. Simultaneously, gases produced by the decomposition of cellulose acetate create pores within the fibers, with pore sizes ranging from 10 to 100 nm, increasing the exposure of active sites and forming a pod-like structure.

[0011] This invention provides a carbon nanofiber heating film with a nano-mortise and tenon structure and its preparation method. It has the following beneficial effects: This invention utilizes carbon nanotube synapses embedded in the surface of adjacent fibers in a tenon-and-mortise manner, increasing the contact area by 5-10 times. Synapse length and density are synergistically optimized, resulting in an interfacial contact resistance of 0.05-0.1 Ω·cm as tested using the four-probe method. 2 .

[0012] This invention utilizes a novel strategy combining free-surface electrospinning with in-situ carbonization growth to prepare on a large scale a freestanding bifunctional catalyst (MNO-CNT-CNFFs) composed of non-noble metal transition metal-based nitrogen / oxygen co-doped carbon nanotubes (CNTs) and carbon nanofiber membranes.

[0013] This invention involves encapsulating Fe nanoparticles within a graphite layer at a carbonization temperature of 800°C, resulting in in-situ grown CNTs forming a "pod-like" structure, which increases the exposure of active sites and specific surface area. Attached Figure Description

[0014] Figure 1 The image shows an SEM image of the carbon nanofiber heating film prepared according to the present invention, where a is a schematic diagram of carbon nanotube synapses embedded in the surface of adjacent fibers in a tenon-and-mortise manner, and b is a magnified schematic diagram of a single fiber. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0016] This invention provides a method for preparing an iron-based nano-mortise and tenon structure carbon nanofiber heating film, comprising the following steps: S1. Preparation of precursor solution Dissolve 6g of polyacrylonitrile and 6g of cellulose acetate in 100mL of DMF solvent and stir at 60℃ for 4 hours until completely dissolved. Add 5g of acetylacetone iron and continue stirring for 12 hours to form a homogeneous spinning solution.

[0017] S2. Free Surface Electrospinning A stepped spinneret was used, with a high voltage of 85-90kV applied, a spinning solution flow rate of 60mL / h, and a distance of 25cm between the spinneret and the grounded nonwoven fabric collector. Continuous spinning for 60 minutes yielded an Fe-enriched nanofiber membrane with dimensions of 180cm×80cm.

[0018] S3. Stabilization treatment Fe-enriched nanofiber membranes were placed in an air oven and heated to 280°C at a rate of 1°C / min, and held at that temperature for 2 hours to obtain pre-oxidized fiber membranes.

[0019] S4. In-situ carbonization and CNT growth The pre-oxidized film was placed in a ceramic boat, with 1g of melamine laid at the bottom. The mass ratio of the pre-oxidized film to melamine was 1:5. Under N2 protection, the temperature was increased to 800℃ at 5℃ / min and held at that temperature for 2 hours. After cooling to room temperature, FeNO-CNT-CNFF-800 was obtained, with uniformly grown "pod-shaped" carbon nanotubes (Fe nanoparticles encapsulated in 4-6 layers of graphite shell) with a diameter of 10-30nm on the surface.

[0020] Measured data: Thermal conductivity: The thermal conductivity in the thickness direction is 25 W / m·K, which is 80% higher than that of traditional films, indicating that the three-dimensional heat transfer network is more uniform.

[0021] Electrical conductivity: The resistivity using the four-probe method is 5.2 × 10⁻⁶. -3 Ω·cm, compared to the unmodified film (1×10 -2 The current density (Ω·cm) is reduced by about one order of magnitude; at a current density of 10A / cm², the temperature rise is less than 5℃, making it more stable and having a stronger current carrying capacity compared to traditional membranes.

[0022] Mechanical properties: After 2000 bending cycles with a curvature radius of 0.5 mm, the rate of change in electrical resistance is less than 2%. Example

[0023] This invention provides a method for preparing a cobalt-based nano-mortise and tenon structure carbon nanofiber heating film, comprising the following steps: S1. Preparation of precursor solution Referring to Example 1, the difference is that 5g of cobalt acetylacetone was added and the mixture was stirred for 12 hours to form a uniform spinning solution.

[0024] S2. Electrospinning and Stabilization Referring to Example 1, the difference lies in the preparation of a Co-enriched nanofiber membrane followed by pre-oxidation.

[0025] S3. Carbonization process optimization The pre-oxidized film was placed in a ceramic boat, with 1g of melamine laid at the bottom. The mass ratio of pre-oxidized film to melamine was 1:5. Under a nitrogen atmosphere, the temperature was increased to 700℃ at 5℃ / min and held at this temperature for 2 hours. CoNO-CNT-CNFF-700 was obtained, with relatively short CNT growth (length <100nm), but its surface was enriched with Co-N. x Active site (N content detected by XPS: 4.8 at.%).

[0026] Measured data: Thermal conductivity: The thermal conductivity in the thickness direction is 20 W / m·K, which is 50%-70% higher than that of traditional heating films, indicating that the Co-based material optimizes the interfacial heat transfer path through pyridine nitrogen doping.

[0027] Conductivity: The transverse conductivity measured by the four-probe method is 1.5×10³S / m, which is an order of magnitude higher than that of the unmodified film; at a current density of 5A / cm², the temperature rise is 8-10℃, and the stability is better than that of traditional heating films. Example

[0028] This invention provides a method for preparing a nickel-based nano-mortise and tenon structure carbon nanofiber heating film, comprising the following steps: S1. Precursor solution and spinning Referring to Example 1, the difference is that 5g of nickel acetylacetone was added and the mixture was stirred for 12 hours to form a uniform spinning solution.

[0029] S2. Electrospinning and Stabilization Referring to Example 1, the difference lies in the preparation of a Ni-enriched nanofiber membrane followed by pre-oxidation.

[0030] S3. High-temperature carbonization regulation The pre-oxidized film was placed in a ceramic boat, and 2g of melamine was laid at the bottom. The mass ratio of the pre-oxidized film to melamine was 1:10. Under N2 protection, the temperature was increased to 900℃ at 5℃ / min and kept at the temperature for 2 hours.

[0031] The obtained NiNO-CNT-CNFF-900 showed a significant increase in CNT length of 500 nm and improved graphitization (Raman ID / IG=1.139), with a Ni-N surface. x It accounted for 9.0% (XPS analysis).

[0032] Measured data: Thermal conductivity: The thermal conductivity in the thickness direction is 32 W / m·K.

[0033] Electrical conductivity: The transverse conductivity measured by the four-probe method reached 1×10⁻⁶. 4 The S / m ratio is two orders of magnitude higher than that of the unmodified film.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A carbon nanofiber heating film with a nano-mortise and tenon structure, characterized in that: include: A carbon nanofiber matrix, wherein the carbon nanofiber matrix is ​​formed by carbonization of a blend of polyacrylonitrile and cellulose acetate, and the fiber diameter is 100-500 nm; A branched carbon nanotube structure is generated in situ on the surface of carbon nanofibers, forming an interlocking network. The length of the carbon nanotube branches is 50-200 nm, and the density is 10. 5 -10 7 / cm 2 ; Metal nanoparticles, wherein the metal nanoparticles are selected from at least one of Fe, Co, and Ni, and the particle size is 10-50 nm, and the metal nanoparticles are embedded at the ends of carbon nanotubes or on the surface of carbon nanofibers. A nitrogen-oxygen co-doped carbon framework, wherein the nitrogen content of the nitrogen-oxygen co-doped carbon framework is 4.8-9.0 at.% and the oxygen content is 2.5-5.3 at.%, forms a three-dimensional conductive / thermal conductive network.

2. The nano-mortise and tenon structure carbon nanofiber heating film according to claim 1, characterized in that: The interface between the carbon nanotube branches and adjacent carbon nanofibers involves a synergistic effect of chemical bonding and mechanical interlocking, with an interfacial contact resistance of 0.05-0.1 Ω·cm. 2 The thermal conductivity in the thickness direction is 20-30 W / m·K.

3. The method for preparing the nano-mortise and tenon structure carbon nanofiber heating film according to claim 1, characterized in that: Includes the following steps: S1. Dissolve polyacrylonitrile, cellulose acetate and metal acetylacetonate in DMF solvent to prepare a spinning precursor solution; S2. Nanofiber membranes were prepared by free surface electrospinning technology, with an electrospinning voltage of 85-90 kV and a distance of 20-30 cm between the spinneret and the collector. S3. The fiber membrane is pre-oxidized by introducing air into the pre-oxidation furnace at a heating rate of 1-3℃ / min and a final temperature of 250-300℃. S4. The pre-oxidized fiber membrane and melamine are placed together in an inert atmosphere for carbonization at a temperature of 700-900℃, a heating rate of 5-10℃ / min, and a holding time of 1-3 hours to catalyze the growth of carbon nanotube branches in situ.

4. The method for preparing the nano-mortise and tenon structure carbon nanofiber heating film according to claim 3, characterized in that: In step S1, the metal acetylacetonate is at least one of Fe(Acac)3, Co(Acac)2, and Ni(Acac)2, and its addition amount is 10-30% of the total polymer mass.

5. The method for preparing the nano-mortise and tenon structure carbon nanofiber heating film according to claim 3, characterized in that: In step S4, the mass ratio of melamine to pre-oxidized fiber membrane is 1:(5-10), and the NH3 and HCN gases generated by the decomposition of melamine during carbonization are used as nitrogen and carbon sources, respectively.

6. The method for preparing the nano-mortise and tenon structure carbon nanofiber heating film according to claim 3, characterized in that: In step S2, electrospinning uses a stepped multi-hole spinneret with an orifice diameter of 0.5-1.0 mm, a spinning solution flow rate of 50-80 mL / h, and a collector linear velocity ≥10 m / s.

7. The method for preparing the nano-mortise and tenon structure carbon nanofiber heating film according to claim 3, characterized in that: In step S4, the metal nanoparticles formed after carbonization are encapsulated by 4-6 layers of graphite shell, and the graphitization degree ID / IG value of the carbon nanotube branches is 1.0-1.

2.

8. The application of the nano-mortise and tenon structure carbon nanofiber heating film according to any one of claims 1-2 in heating sheets, flexible circuit boards or lithium-ion battery electrodes, wherein the resistance change rate of the carbon nanofiber heating film is ≤2% after 2000 bending cycles.

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