Highly conductive graphitized nanofiber aerogel and preparation method and application thereof

Abstract

The application relates to a high-conductivity graphitized nanofiber aerogel and a preparation method and application thereof, and comprises the following steps: dissolving a polymer in an organic solvent to obtain a spinning solution by stirring; performing electrostatic spinning on the spinning solution in S1 to deposit a polymer nanofiber film; performing carbonization on the polymer nanofiber film in S2 after pre-oxidation to obtain a pre-carbonized fiber film; dispersing the pre-carbonized fiber film in S3 in an aqueous solution containing graphene oxide and a cationic dispersant, and then performing shearing dispersion and ultrasonic dispersion to obtain a dispersed fiber solution; performing directional freezing and drying on the dispersed fiber solution in S4, and then performing graphitization to obtain the high-conductivity graphitized nanofiber aerogel. Compared with the prior art, the high-conductivity graphitized nanofiber aerogel prepared by the application not only has high elasticity, but also has low vertical resistance, so that the mechanical properties of the aerogel are ensured and the conductivity is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-conductivity aerogels, and particularly relates to a high-conductivity graphitized nanofiber aerogel and a preparation method and application thereof. BACKGROUND

[0002] Aerogels are known as "miraculous materials that can change the world", and are the smallest solid in the world, having extremely small bulk density, super large specific surface area and extremely high porosity. Compared with ordinary conductive materials, conductive aerogels have a more abundant internal conductive network, can generate more contact sites when deformed, and have the characteristics of being more sensitive to external stimuli, and have been widely used in sensors, energy storage, catalysis, wastewater treatment, electromagnetic shielding and other fields. Traditional conductive aerogels are generally carbon nanofiber aerogels, graphene aerogels, MXene aerogels, nanowire aerogels and the like. Carbon nanofiber aerogels have high mechanical properties, but have the defect of poor conductivity due to low carbonization temperature; graphene and MXene aerogels have good conductivity, but have the problems of high price and poor mechanical properties; the preparation method of nanowire aerogels (such as silver nanowires and copper nanowires) is complex, the reaction conditions are harsh, the aspect ratio is mostly within 1000, which leads to limited improvement of the mechanical properties of the material, and the material is not corrosion-resistant. Therefore, how to realize the synergistic optimization of the mechanical properties and the conductivity of the aerogel has become the research focus today.

[0003] In recent years, researchers have prepared a series of elastic carbon nanofiber composite aerogel materials with excellent mechanical properties and good conductivity by using graphene oxide, carbon nanotubes, MXene and carbon nanofiber as raw materials. Fudan University uses pre-oxidized polyacrylonitrile nanofiber and graphene oxide as raw materials, realizes efficient compounding and synergistic assembly between graphene and nanofiber through homogenization dispersion, freeze-drying and carbonization at 800 DEG C, and is used for efficient energy storage / conversion. Auburn University in the United States uses cellulose nanofiber, graphene oxide and carbon nanotube as raw materials to prepare aerogel, and then carbonizes at 800 DEG C to obtain a conductive aerogel material with a honeycomb structure, and applies it to the field of intelligent wearable devices. Patent CN113233466A discloses a 3D super-elastic electrospun carbon nanofiber / MXene composite aerogel material, which solves the problem of interface contact resistance between fibers through the synergistic effect of one-dimensional and two-dimensional materials. However, the above-mentioned prior art is limited by the properties of carbon fiber, and the conductivity has not been greatly improved, which is not conducive to practical application.

[0004] After the nanofiber is treated at a higher temperature (2600-3000 DEG C), the microcrystalline structure becomes a regular and long-range graphite sheet structure, which is more conducive to the free movement of non-local pi bond electrons in the lattice, thereby causing the improvement of the electrical conductivity. However, under the treatment of ultra-high temperature, the nanofiber aerogel will collapse due to the problems such as uneven dispersion, thermal shrinkage change of the fiber, and weak bonding force of the fiber lap joint.

[0005] Therefore, it is urgent to develop a nanofiber aerogel with stable structure, excellent mechanical properties and good electrical conductivity. SUMMARY

[0006] The purpose of the present application is to provide a high-conductivity graphitized nanofiber aerogel and its preparation method and application, so as to solve the defects that the mechanical properties and electrical conductivity of the existing nanofiber aerogel cannot be optimized simultaneously.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] A preparation method of a high-conductivity graphitized nanofiber aerogel, comprising the following steps:

[0009] S1: dissolving a polymer in an organic solvent to obtain a spinning solution by stirring;

[0010] S2: electrospinning the spinning solution in S1 to deposit a polymer nanofiber membrane;

[0011] S3: pre-oxidizing the polymer nanofiber membrane in S2 and then carbonizing to obtain a pre-carbonized fiber membrane;

[0012] S4: dispersing the pre-carbonized fiber membrane in S3 in an aqueous solution containing graphene oxide and a cationic dispersant, and then performing shear dispersion and ultrasonic dispersion to obtain a dispersed fiber solution;

[0013] S5: performing directional freezing and drying on the dispersed fiber solution in S4, and then graphitizing to obtain a high-conductivity graphitized nanofiber aerogel.

[0014] Further, in step S1, the polymer includes one of polyacrylonitrile or polyvinylpyrrolidone.

[0015] Further, the molecular weight of the polyacrylonitrile is 50000-150000 g / mol, and the molecular weight of the polyvinylpyrrolidone is 8000-700000 g / mol.

[0016] Further, in step S1, the organic solvent includes one of dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF), preferably DMF.

[0017] Further, in step S1, the stirring time is 2-12h, preferably 5-10h.

[0018] Further, in step S1, the stirring rate is 300-500rpm, preferably 400rpm.

[0019] Further, in step S1, the concentration of the polymer in the spinning solution is 5-12wt%.

[0020] Further, in step S1, the stirring is carried out at room temperature, and the stirring obtains a homogeneous system of the spinning solution.

[0021] Further, in step S2, the spinning solution is stretched to form a jet under the action of a high-voltage electric field, and the jet is deposited on a receiving device to obtain a polymer nanofiber membrane with uniform morphology and no adhesion.

[0022] Further, in step S2, the electrospinning temperature is 15-35℃.

[0023] Further, in step S2, the air humidity during electrospinning is 20-80%, preferably 30-50%.

[0024] Further, in step S2, the electrospinning voltage is 10-50kV, preferably 15-25kV.

[0025] Further, in step S2, the electrospinning infusion speed is 0.5-15mL / h, preferably 1-2mL / h.

[0026] Further, in step S2, the electrospinning spinning distance is 15-60cm, preferably 15-25cm.

[0027] Further, in step S2, the electrospinning slide speed is 1-200cm / min, preferably 30-100cm / min.

[0028] Further, in step S2, the receiving device drum speed during electrospinning is 10-100r / min, preferably 50-100r / min.

[0029] Further, in step S3, the pre-oxidation temperature is 250-300℃.

[0030] Further, in step S3, the pre-oxidation temperature is 250-300℃.

[0031] Further, in step S3, the pre-oxidation time is 1-3h.

[0032] Further, in step S3, the pre-oxidation atmosphere is air.

[0033] Further, in step S3, the carbonization is performed in an inert gas atmosphere, preferably argon.

[0034] Further, in step S3, the carbonization temperature increasing rate is 5-20℃ / min, preferably 7-15℃ / min.

[0035] Further, in step S3, the highest temperature after the carbonization temperature increasing is 800-1200℃, preferably 1000℃.

[0036] Further, in step S3, the carbonization time is 1-3h.

[0037] Further, in step S4, the mass ratio of the pre-carbonized fiber membrane, graphene oxide and cationic dispersant is 4:(0.5-4):(0.02-0.1), preferably 4:(0.8-2):(0.05-0.08).

[0038] Further, in step S4, the cationic dispersant includes one or more of polyacrylamide, dodecyl ammonium acetate, octadecyl ammonium acetate, sodium dodecyl benzene sulfonate, dodecyl trimethyl ammonium chloride, dodecyl trimethyl ammonium bromide or polydimethyl diallyl ammonium chloride.

[0039] Further, in step S4, the graphene oxide wrapping on the fiber surface endows it with hydrophilicity, and the cationic dispersant endows the fiber with positive charge, so that a stable dispersion system can be finally obtained.

[0040] Further, in step S4, the shear dispersion adopts a high-temperature assisted micro-jet high-pressure homogenization method, the shear dispersion time is 1-10min, and the aspect ratio of the pre-carbonized fiber after shear dispersion is maintained above 10000.

[0041] Further, the high-temperature assisted micro-jet high-pressure homogenization method refers to setting 3-10 high-temperature nano mixing sources in the solution, and utilizing the high-temperature nano mixing sources to generate multiple active turbulent flow regions.

[0042] Further, in step S4, the ultrasonic dispersion is specifically intermittent high-frequency ultrasonic magnetic stirring, so as to obtain a homogeneous and stable fiber dispersion solution.

[0043] Further, the ultrasonic dispersion is that the pre-dispersion solution after shear dispersion is placed in a water bath to alternately perform high-frequency ultrasonic and magnetic stirring, the alternating times are 5-10 times, and the duration time is 0.5-4h.

[0044] Further, in step S5, the directional freezing is specifically that the ultrasonic dispersed fiber dispersion liquid is placed in an aerogel mold with a directional temperature gradient for directional freezing, and through gas-liquid nondestructive displacement drying, a pre-carbonized aerogel is obtained.

[0045] Further, the gas-liquid nondestructive displacement drying is performed in a vacuum freeze dryer.

[0046] Further, in step S5, the temperature gradient range of the directional freezing is a temperature range between the bottom surface in contact with the cold source and the upper surface of the mold, and the temperature gradient range is -196 to 30 DEG C.

[0047] Further, in step S5, the cold plate temperature during the drying is -50 to -10 DEG C, and preferably -40 to -20 DEG C.

[0048] Further, in step S5, the drying time is 10 to 48 h, and preferably 10 to 30 h.

[0049] Further, in step S5, the graphitization is specifically performed in a graphite furnace with a suspended porous sample tank.

[0050] Further, in step S5, the heating rate of the graphitization is 20 to 100 DEG C / min.

[0051] Further, in step S5, the highest temperature after the graphitization heating is 2600 to 3000 DEG C.

[0052] Further, in step S5, the graphitization time is 1 to 4 h.

[0053] The application also provides a high-conductivity graphitized nanofiber aerogel prepared by the above preparation method.

[0054] The application also provides an application of the high-conductivity graphitized nanofiber aerogel in energy storage and conversion.

[0055] Compared with the prior art, the application has the following beneficial effects:

[0056] (1) The application uses graphite nanofiber as a building block, uses graphene as a conjugated binder, uses a carbon source complementary homogeneous dispersion method, a vertical directional freezing technology, and a suspended high-precision temperature control graphitization process for aerogel, and a composite aerogel material prepared by the method has high elasticity, will not collapse, and has low vertical resistance, so that the mechanical properties of the aerogel are ensured and the conductivity is improved.

[0057] (2) The preparation method of highly conductive graphitized nanofiber aerogel provided by the present invention is a continuous process, which is different from the traditional method that uses pre-oxidized polyacrylonitrile nanofibers as aerogel precursor. This method directly uses pre-carbonized nanofibers as aerogel precursor, adds graphene oxide as a complementary carbon source to the fiber dispersion, and uses the π-π interaction and π-hydrogen interaction between graphene oxide and carbon fiber to wrap graphene oxide on the surface of carbon fiber. The hydrophilic groups such as hydroxyl and carboxyl groups on the graphene oxide molecular chain are used to achieve uniform wetting of hydrophobic carbon fiber in the aqueous phase. At the same time, a cationic dispersant is added to give the fiber a positive charge and obtain a stable dispersion system.

[0058] (3) The present invention sets up multiple high-temperature and high-pressure micro-jet nano-mixing sources in the solution to generate multiple active turbulent zones, thereby accelerating the directional migration and stabilization of each component in the solution during the dispersion process; it uses high-frequency ultrasound to generate permanent structural defects in carbon fibers, derives structural charges, and generates electrostatic repulsion between them to avoid agglomeration; at the same time, it uses intermittent alternating ultrasound and stirring to maximize dispersion efficiency.

[0059] (4) The present invention performs directional freezing and low-damage drying of the dispersion to construct an aerogel cell structure with a vertically oriented continuous conductive network.

[0060] (5) In this invention, the aerogel is placed in a suspended high-precision temperature-controlled graphite furnace for ultra-high temperature graphitization treatment. The graphite furnace sample tank is designed as a suspended porous structure to achieve uniform heating of the upper and lower surfaces of the aerogel and avoid structural collapse. Attached Figure Description

[0061] Figure 1 This is a diagram illustrating the multi-scale conductivity mechanism of the highly conductive graphitized nanofiber aerogel of this invention.

[0062] Figure 2 The image shows a scanning electron microscope and physical image of the highly conductive graphitized nanofiber aerogel in Example 1.

[0063] Figure 3 The graph shows a comparison of the vertical resistance values ​​of the highly conductive graphitized nanofiber aerogels of Examples 1-3 and the ordinary carbonized nanofiber aerogel of Comparative Example 1. Detailed Implementation

[0064] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0065] Unless otherwise indicated, the reagents, methods, instruments and apparatus employed in the present application are those conventional in the art. Unless otherwise indicated, the reagents and materials used in the following examples are commercially available and of the highest grade of purity available.

[0066] Example 1:

[0067] The preparation method of the high-conductivity graphitized nanofiber aerogel in this embodiment comprises the following steps:

[0068] S1, 3.6 g of PAN (molecular weight 120000 g / mol) was added to 26.4 g of DMF, stirred at room temperature for 5 h at 400 rpm, and prepared into a 12 wt% homogeneous spinning solution;

[0069] S2, the spinning solution obtained in S1 was injected into a syringe, and electrospinning was carried out under the process parameter conditions of air humidity of 30%, temperature of 20±2℃, voltage of 25kV, perfusion speed of 1mL / h, spinning distance of 20cm, receiving device roller speed of 50r / min, and slide speed of 30cm / min. Under the action of high-voltage electric field, the spinning solution was stretched to form a jet, and the jet was deposited on the receiving device to obtain a PAN nanofiber membrane with a diameter of 200-800nm;

[0070] S3, the PAN nanofiber membrane obtained in S2 was placed in a muffle furnace, and heated at a rate of 1℃ / min, and kept at 155℃ for 60 min, and then heated at a rate of 1℃ / min to a pre-oxidation temperature of 280℃, and kept for 80 min to obtain a pre-oxidized nanofiber membrane with a fiber diameter of 100-600nm;

[0071] S4, the pre-oxidized nanofiber membrane obtained in S3 was placed in a tube furnace with argon flowing, and heated at a rate of 10℃ / min, and kept at 1000℃ for 2h to obtain a pre-carbonized nanofiber membrane with a fiber diameter of 80-400nm;

[0072] S5, 4g of the pre-carbonized nanofiber membrane obtained in S4 was cut into a 1cm×1cm block and added to water, and 1g of graphene oxide and 0.05g of polyacrylamide were added to obtain a dispersion system;

[0073] S6, the dispersion system of S5 was placed in an Eca microjet high-pressure homogenizer, and 5 high-temperature nanometer mixing sources were set to heat to 80℃, and the dispersion system obtained in S5 was sheared and dispersed for 5 min, and the flow rate of the dispersion system during shearing was 1000m / s, so that the aspect ratio of the pre-carbonized fiber was maintained at more than 10000, and a pre-dispersion solution was obtained;

[0074] S7, the pre-dispersed solution obtained in S6 is placed in a water bath and subjected to high-frequency ultrasonic waves (12 MHz) and magnetic stirring alternately for 6 times, and the duration is 3 h, to obtain a homogeneous fiber dispersion liquid;

[0075] S8, the fiber dispersion liquid obtained in S7 is placed in an aerogel mold with a directional temperature gradient, and then subjected to directional freezing in a vacuum freeze dryer, the bottom surface temperature of the contact cold source is -196℃, the upper surface temperature of the mold is 30℃, the cold plate temperature during drying is -40℃, the vacuum degree is 50 Pa, and the drying time is 24 h, to obtain a pre-carbonized aerogel through gas-liquid nondestructive replacement drying;

[0076] S9, the pre-carbonized aerogel obtained in S8 is placed in a graphite furnace sample groove with a suspended porous structure for suspended high-precision temperature-controlled graphitization, the temperature is raised at a rate of 60℃ / min, and the temperature is kept at 2800℃ for 1.5 h, to finally obtain a high-elasticity high-conductivity graphitized nanofiber aerogel.

[0077] Example 2:

[0078] The preparation method of the high-conductivity graphitized nanofiber aerogel in this embodiment comprises the following steps:

[0079] S1, 3 g of PAN (molecular weight 150000 g / mol) is added to 27 g of DMF, and stirred at room temperature for 10 h to prepare a 10 wt% homogeneous spinning solution;

[0080] S2, the spinning solution obtained in S1 is injected into a syringe, and electrospinning is carried out under the following process parameter conditions: air humidity is 40%, temperature is 25±2℃, voltage is 18 kV, perfusion speed is 1.2 mL / h, spinning distance is 15 cm, receiving device roller speed is 100 r / min, and sliding table speed is 50 cm / min. Under the action of a high-voltage electric field, the spinning solution is stretched to form a jet, and the jet is deposited on the receiving device to obtain a PAN nanofiber membrane with a diameter of 300-900 nm;

[0081] S3, the PAN nanofiber membrane obtained in S2 is placed in a muffle furnace, the temperature is raised at a rate of 2℃ / min, and the temperature is kept at 155℃ for 120 min, and then the temperature is raised to the pre-oxidation temperature of 300℃ at a rate of 2℃ / min, and the temperature is kept for 120 min to obtain a pre-oxidized nanofiber membrane with a fiber diameter of 200-700 nm;

[0082] S4, the pre-oxidized nanofiber membrane obtained in S3 is placed in a tube furnace with argon, the temperature is raised at a rate of 8℃ / min, and the temperature is kept at 1000℃ for 1.5 h to obtain a pre-carbonized nanofiber membrane with a fiber diameter of 100-400 nm;

[0083] S5, 4 g of the pre-carbonized nanofiber membrane obtained in S4 was cut into 1 cm x 1 cm blocks and added to water, and 0.8 g of graphene oxide and 0.06 g of dodecylammonium acetate were added to obtain a dispersion system;

[0084] S6, the dispersion system of S5 was placed in an Eca microfluidic high-pressure homogenizer, and 8 high-temperature nanometer mixing sources were set to heat to 80°C. The pre-dispersed solution obtained in S5 was sheared and dispersed for 8 min, and the flow rate of the dispersion system during shearing was 1000 m / s, so that the aspect ratio of the pre-carbonized fiber was maintained at more than 10000, to obtain a pre-dispersed solution;

[0085] S7, the pre-dispersed solution obtained in S6 was placed in a water bath and alternately subjected to high-frequency ultrasonic (12 MHz) and magnetic stirring, with a rotation frequency of 6 times and a duration of 3 h, to obtain a homogeneous fiber dispersion liquid;

[0086] S8, the fiber dispersion liquid obtained in S7 was placed in an aerogel mold with a directional temperature gradient, and then subjected to directional freezing in a vacuum freeze dryer, with a bottom surface temperature of the contact cold source of -80°C, a top surface temperature of the mold of 30°C, a cold plate temperature of -30°C during drying, a vacuum degree of 30 Pa, and a drying time of 30 h. After gas-liquid non-destructive replacement drying, a pre-carbonized aerogel was obtained.

[0087] S9, the pre-carbonized aerogel obtained in S8 was placed in a graphite furnace sample groove with a suspended porous structure, and was heated at a rate of 40°C / min, and maintained at 2600°C for 2 h, to obtain a high-elasticity high-conductivity graphitized nanofiber aerogel.

[0088] Example 3

[0089] The preparation method of a high-conductivity graphitized nanofiber aerogel in this embodiment comprises the following steps:

[0090] S1, 1 g of PVP (molecular weight 100000 g / mol) was added to 19 g of DMF, and stirred at room temperature for 6 h to prepare a 5 wt% homogeneous spinning solution;

[0091] S2, the spinning solution obtained in S1 was injected into a syringe, and electrospinning was carried out under the following process parameter conditions: air humidity of 35%, temperature of 30±2°C, voltage of 15 kV, perfusion speed of 1.2 mL / h, spinning distance of 15 cm, receiving device roller speed of 100 r / min, and slide speed of 80 cm / min. Under the action of a high-voltage electric field, the spinning solution was stretched to form a jet, which was deposited on the receiving device to obtain a PVP nanofiber membrane with a diameter of 200-500 nm;

[0092] S3, the PVP nanofiber membrane obtained in S2 was placed in a muffle furnace, and heated at a rate of 5℃ / min, and kept at 150℃ for 60min, and then heated at a rate of 3℃ / min to 250℃, and kept at 250℃ for 120min to obtain a pre-oxidized nanofiber membrane with a fiber diameter of 150-400nm;

[0093] S4, the pre-oxidized nanofiber membrane obtained in S3 was placed in a tube furnace with argon, and heated at a rate of 7℃ / min, and kept at 1000℃ for 3h to obtain a pre-carbonized nanofiber membrane with a fiber diameter of 100-300nm;

[0094] S5, 4g of the pre-carbonized nanofiber membrane obtained in S4 was cut into a 2cm×2cm block and added to water, and 2g of graphene oxide, 0.04g of sodium dodecyl benzene sulfonate, and 0.04g of polydimethyl diallyl ammonium chloride were added to obtain a dispersion system;

[0095] S6, the dispersion system of S5 was placed in an Eca micro-jet high-pressure homogenizer, and 8 high-temperature nanometer mixing sources were set to heat to 80℃, and the dispersion system obtained in S5 was sheared and dispersed for 8min, and the flow rate of the dispersion system during shearing was 1000m / s, so that the aspect ratio of the pre-carbonized fiber was maintained at more than 10000, to obtain a pre-dispersion solution;

[0096] S7, the pre-dispersion solution obtained in S6 was placed in a water bath and subjected to high-frequency ultrasonic (12MHz) and magnetic stirring alternately, the number of alternations was 6 times, and the duration was 3h, to obtain a homogeneous fiber dispersion liquid;

[0097] S8, the fiber dispersion liquid obtained in S7 was placed in an aerogel mold with a directional temperature gradient for directional freezing, the bottom surface temperature of the contact cold source was 0℃, the upper surface temperature of the mold was 30℃, the cold plate temperature during drying was -20℃, the vacuum degree was 5Pa, and the drying time was 10h, to obtain a pre-carbonized aerogel through gas-liquid lossless replacement drying;

[0098] S9, the pre-carbonized aerogel obtained in S8 was placed in a graphite furnace sample groove with a suspended porous structure, and heated at a rate of 100℃ / min, and kept at 3000℃ for 4h to obtain a high-elasticity high-conductivity graphitized nanofiber aerogel.

[0099] Comparative Example 1:

[0100] The present embodiment provides a common carbonized nanofiber aerogel, and the specific steps are as follows:

[0101] S1, 3.6g of PAN (molecular weight 120000g / mol) was added to 26.4g of DMF, and stirred at room temperature at 400rpm for 5h to prepare a 12wt% homogeneous spinning solution;

[0102] S2, the spinning dope obtained in S1 is injected into a syringe, electrospinning is carried out under the process parameter conditions that the air humidity is 30%, the temperature is 20±2℃, the voltage is 25kV, the perfusion speed is 1mL / h, the spinning distance is 20cm, the receiving device roller speed is 50r / min, and the slide speed is 30cm / min in an environment with a temperature of 20±2℃, to obtain PAN nanofiber membranes with a diameter of 200-800nm;

[0103] S3, the PAN nanofiber membrane obtained in S2 is placed in a muffle furnace, heated at a rate of 1℃ / min, kept at 155℃ for 60min, then heated at a rate of 1℃ / min, and kept at 280℃ for 80min, to obtain a pre-oxidized nanofiber membrane with a fiber diameter of 100-600nm;

[0104] S4, 4g of the pre-oxidized nanofiber membrane obtained in S3 is cut into 1cm×1cm blocks and added to water, and 1g of graphene oxide is added to obtain a dispersion system;

[0105] S5, the dispersion system obtained in S4 is subjected to rapid shear dispersion for 5min using an IKA homogenizing disperser, so that the aspect ratio of the pre-oxidized fibers is maintained at more than 10000, to obtain a homogeneous fiber dispersion liquid;

[0106] S6, the fiber dispersion liquid obtained in S5 is placed in an aerogel mold, randomly isotropically frozen in liquid nitrogen, and then placed in a vacuum drying machine for drying, with a cold plate temperature of-40℃, a vacuum degree of 50Pa, and a drying time of 24h, to obtain a pre-oxidized nanofiber aerogel through gas-liquid non-destructive replacement drying;

[0107] S7, the pre-oxidized nanofiber aerogel obtained in S6 is placed in a tube furnace with argon flowing, heated at a rate of 10℃ / min, and kept at 1000℃ for 2h to obtain a carbon nanofiber aerogel. When the heating temperature is increased to the graphitization temperature of 2800℃, the carbon nanofiber aerogel of the present embodiment will obviously shrink and collapse, and it is impossible to successfully prepare a carbon nanofiber aerogel that maintains high elastic mechanical properties.

[0108] The following tests are carried out on Examples 1-3 and Comparative Examples:

[0109] (1) The cross section and longitudinal section of Example 1 are characterized using a scanning electron microscope.

[0110] (2) Vertical resistance test: the vertical resistance refers to the resistance of the conductive material in the vertical direction under certain conditions. The sample is placed between two measuring electrodes in the vertical resistance test device; the measuring electrodes are gold-plated electrodes; for every increase of 0.05 MPa, the resistance value between the two electrodes is measured by a low resistance tester; the resistance values under different pressures are recorded until the change rate of the current resistance value and the previous resistance test value is not greater than 5%, then it is considered that the minimum resistance value is reached, and the test is stopped.

[0111] Figure 1 The above is the description of the comparative examples for the convenience of the ordinary skilled in the art to understand and use the invention. Those skilled in the art can easily make various modifications to these examples, and apply the general principles described herein to other examples without creative labor. Therefore, the present application is not limited to the above examples, and the improvements and modifications made by those skilled in the art without departing from the scope of the present application should be within the scope of protection of the present application.

[0112] Figure 2 The cross-section and longitudinal section morphology of the high-conductive graphitized nanofiber aerogel of Example 1 are characterized, and it can be seen from the figure that the cross-section is a uniform honeycomb porous structure, and the longitudinal section is a long-range continuous sheet structure. From the physical picture, it can be seen that the high-conductive graphitized nanofiber aerogel prepared by the present application will not collapse and shrink, and can maintain good morphology.

[0113] Figure 3 The vertical resistance of Examples 1-3 and Comparative Example is shown. As can be seen from the figure, under a pressure of 0.5 MPa, the vertical resistance of Examples 1-3 is as low as 0.133 mΩ, 0.125 mΩ and 0.142 mΩ respectively, while the vertical resistance of Comparative Example 1 is one order of magnitude higher than that of the examples. Therefore, under the premise of ensuring the mechanical strength, the resistance value of the examples in the vertical direction is significantly reduced, the conductivity is significantly improved, and the conductivity changes with the size of the applied pressure and has controllability, which is more conducive to its application in the field of energy storage and conversion.

[0114] The above description of the comparative examples is for the convenience of the ordinary skilled in the art to understand and use the invention. Those skilled in the art can easily make various modifications to these examples, and apply the general principles described herein to other examples without creative labor. Therefore, the present application is not limited to the above examples, and the improvements and modifications made by those skilled in the art without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A method for preparing a highly conductive graphitized nanofiber aerogel, characterized in that, Includes the following steps: S1: Dissolve the polymer in an organic solvent and stir to obtain a spinning solution; S2: Electrospinning the spinning solution in S1 to deposit a polymer nanofiber membrane; S3: The polymer nanofiber membrane in S2 is pre-oxidized and then carbonized to obtain a pre-carbonized fiber membrane; S4: The pre-carbonized fiber membrane in S3 is dispersed in an aqueous solution containing graphene oxide and a cationic dispersant, and then sheared and ultrasonically dispersed to obtain a dispersed fiber solution. S5: The dispersed fiber solution in S4 is directionally frozen and dried, and then graphitized to obtain a highly conductive graphitized nanofiber aerogel.

2. The method for preparing a highly conductive graphitized nanofiber aerogel according to claim 1, characterized in that, In step S1, the polymer includes either polyacrylonitrile or polyvinylpyrrolidone; The stirring time is 2-12 hours, and the stirring speed is 300-500 rpm. The concentration of the polymer in the spinning solution is 5-12 wt%.

3. The method for preparing a highly conductive graphitized nanofiber aerogel according to claim 1, characterized in that, In step S2, the temperature of electrospinning is 15-35℃, and the air humidity during electrospinning is 20-80%. The electrospinning voltage is 10-50kV, the electrospinning injection rate is 0.5-15mL / h, the electrospinning distance is 15-60cm, the electrospinning slide speed is 1-200cm / min, and the receiving device roller speed is 10-100r / min.

4. The method for preparing a highly conductive graphitized nanofiber aerogel according to claim 1, characterized in that, In step S3, the heating rate of the pre-oxidation is 0.5-5℃ / min, the pre-oxidation temperature is 250-300℃, and the pre-oxidation time is 1-3h.

5. The method for preparing a highly conductive graphitized nanofiber aerogel according to claim 1, characterized in that, In step S3, the carbonization is carried out in an inert gas atmosphere, the heating rate of the carbonization is 5-20℃ / min, the highest temperature after carbonization is 800-1200℃, and the carbonization time is 1-3h.

6. The method for preparing a highly conductive graphitized nanofiber aerogel according to claim 1, characterized in that, In step S4, the mass ratio of the pre-carbonized fiber membrane, graphene oxide, and cationic dispersant is 4:(0.5-4):(0.02-0.1). The cationic dispersant includes one or more of polyacrylamide, dodecylammonium acetate, octadecylammonium acetate, sodium dodecylbenzenesulfonate, dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, or polydimethyldiallylammonium chloride.

7. The method for preparing a highly conductive graphitized nanofiber aerogel according to claim 1, characterized in that, In step S5, the temperature gradient range of the directional freezing is -196 to 30°C; The vacuum degree during drying is 5-100 Pa, and the drying time is 10-48 h.

8. The method for preparing a highly conductive graphitized nanofiber aerogel according to claim 1, characterized in that, In step S5, the graphitization heating rate is 20-100℃ / min, the highest graphitization temperature after heating is 2600-3000℃, and the graphitization time is 1-4h.

9. A highly conductive graphitized nanofiber aerogel, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. An application of the highly conductive graphitized nanofiber aerogel as described in claim 9 in energy storage and conversion.

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