Carbon aerogel fiber and preparation method and application thereof

Abstract

The present application relates to a kind of carbon aerogel fibers and its preparation method and application, belong to carbon aerogel technical field.Preparation method includes the following steps, S1, to core layer spinning solution and sheath layer spinning solution is carried out coaxial wet spinning, after being immersed in coagulation bath, after washing, dry and obtain hydrogel fiber;The core layer spinning solution is the mixed solution of polymethyl methacrylate, polyacrylonitrile and solvent;The sheath layer spinning solution is obtained by mixing MXene solution and cellulose solution according to mass ratio 5-12:100;S2, to hydrogel fiber is frozen, dry and obtain aerogel fiber;S3, to aerogel fiber is pre-oxidized, once carbonization treatment, activation treatment and secondary carbonization treatment and obtain the carbon aerogel fiber of the present application.The carbon aerogel fiber of the present application uses cellulose nanofiber as the skeleton of aerogel fiber, two-dimensional material MXene with rich surface active site is used as stabilizer and conductive agent of aerogel fiber skeleton, and one-dimensional, two-dimensional material synergistic effect is fully played.

Description

Technical Field

[0001] This invention belongs to the field of carbon aerogel technology, and particularly relates to a carbon aerogel fiber, its preparation method and application. Background Technology

[0002] With social development and the progress of the times, people's demand for flexible soft and electronic devices is increasing day by day. The development of new energy sources and the exploration of new devices are severe challenges facing mankind. At the same time, the rapid development of science and technology has brought us many intelligent flexible soft and electronic devices, such as flexible sensors.

[0003] Currently, flexible gel fiber sensors suffer from drawbacks such as complex fabrication, low conductivity, low sensitivity, poor flexibility, weak mechanical properties, and significant environmental pollution. Chinese patent CN 112403406A discloses an MXene fiber aerogel, its preparation, and its application in a pressure sensor. The pressure sensor's sensitive material is composed of MXene fiber aerogel, which exhibits poor mechanical flexibility. Chinese patent CN 109898176A discloses a flexible, stretchable hydrogel optical fiber sensor, its preparation, and its application. The optical fiber has a core-sheath structure, with a transparent silicone capillary skin and a lithium bromide-containing polyacrylamide hydrogel core. This sensor causes significant environmental pollution and has poor conductivity. Chinese patent CN 110776667A discloses a piezoresistive sensor material, its preparation method, and its application. This sensor exhibits poor flexibility and low sensitivity. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides carbon aerogel fibers, their preparation methods, and applications. The prepared carbon aerogel fibers possess high conductivity, good flexibility, and a porous three-dimensional network carbon-based structure. Due to their high specific surface area and porous structure, they offer higher energy density and power density. They can be applied to yarn-like supercapacitors, exhibiting environmental friendliness, mechanical flexibility, excellent conductivity, and electrochemical performance. This provides new ideas for flexible intelligent wearable electronic devices and fabrics, and can be applied in the fields of energy storage and conversion.

[0005] The first objective of this invention is to provide a method for preparing carbon aerogel fibers, comprising the following steps:

[0006] S1. The core spinning solution and the sheath spinning solution are coaxially wet spun, and after soaking in a coagulation bath, they are washed and dried to obtain hydrogel fibers; the core spinning solution is a mixture of polymethyl methacrylate, polyacrylonitrile and solvent; the sheath spinning solution is obtained by mixing MXene solution and cellulose solution at a mass ratio of 5-12:100.

[0007] S2. Freeze and dry the hydrogel fiber described in S1 to obtain aerogel fiber;

[0008] S3. The aerogel fiber described in S2 is subjected to pre-oxidation treatment, primary carbonization treatment, activation treatment and secondary carbonization treatment to obtain the carbon aerogel fiber.

[0009] In one embodiment of the present invention, in S1, the MXene solution is MXene nanosheets dissolved in water; the concentration of the MXene solution is 20wt%-30wt%.

[0010] The cellulose solution is prepared by dissolving microcrystalline cellulose, sodium hydroxide, and urea in water; the temperature of the cellulose solution is below -12°C; the concentration of microcrystalline cellulose in the cellulose solution is 1.5wt%-2.5wt%, the concentration of sodium hydroxide is 6wt%-8wt%, and the concentration of urea is 11wt%-13wt%.

[0011] The concentration of polyacrylonitrile in the core spinning solution is 125 mg / mL-185 mg / mL; the mass ratio of polyacrylonitrile to polymethyl methacrylate is 1-4:1-4.

[0012] Furthermore, the mass ratio of polyacrylonitrile (PAN) to polymethyl methacrylate (PMMA) is (4:1), (3:2), (2:3), or (1:4).

[0013] Preferably, the mass ratio of polyacrylonitrile (PAN) to polymethyl methacrylate (PMMA) is 4:1.

[0014] In one embodiment of the present invention, in S1, during the coaxial wet spinning process, the sizes of the coaxial spinning heads corresponding to the core layer and the sheath layer are 17G-18G and 22G-25G, respectively; the advancing speeds of the core layer and the sheath layer are 0.2mL / min-0.3mL / min and 0.6mL / min-0.9mL / min, respectively.

[0015] In one embodiment of the present invention, in S1, the drying is performed at 82°C-88°C for 4.5-5.5 hours.

[0016] In one embodiment of the present invention, in S1, the coagulation bath is composed of an ethanol solution containing 5 wt% calcium chloride and deionized water (the volume ratio of deionized water to ethanol is 3:1). During this process, the solvent in the core spinning solution diffuses into the coagulation bath, while the non-solvent (water) in the coagulation bath rapidly diffuses into the fiber interior. When the mass transfer process proceeds to a certain extent, and the non-solvent content in the spinning solution stream reaches a certain amount, PAN begins to undergo phase separation, forming a polymer-rich phase and a polymer-poor phase, which, after solidification, form the fiber skeleton and internal pores, respectively.

[0017] In one embodiment of the present invention, in S1, the solvent is selected from dimethyl sulfoxide and / or N-dimethylformamide.

[0018] In one embodiment of the present invention, in S2, the freezing is performed at -82°C to -88°C for 0.5h to 1.5h; the drying is performed at -62°C to -68°C under vacuum for 40h to 50h.

[0019] In one embodiment of the present invention, in S3, the pre-oxidation treatment is divided into four stages: the first stage is to heat to 140℃-160℃ at a rate of 1.8℃ / min-2.2℃ / min and hold for 1h-1.5h; the second stage is to heat to 190℃-210℃ at a rate of 1.8℃ / min-2.2℃ / min and hold for 1h-1.5h; the third stage is to heat to 240℃-260℃ at a rate of 1.8℃ / min-2.2℃ / min and hold for 1h-1.5h; and the fourth stage is to air cool to 20℃-30℃.

[0020] In one embodiment of the present invention, in S3, the primary carbonization treatment involves heating to 500℃-1000℃ in a nitrogen or argon atmosphere at a rate of 3.8℃ / min-4.2℃ / min and holding for 1-2 hours to further remove organic components, but without forming the final carbon fiber structure. The secondary carbonization treatment involves heating to 1000℃-2000℃ in a nitrogen or argon atmosphere at a rate of 3.8℃ / min-4.2℃ / min and holding for 1-2 hours. This is crucial for forming the carbon fiber structure, where most of the organic components are removed, and the crystallinity of the fiber increases.

[0021] In one embodiment of the present invention, in step S3, the activation treatment involves immersing the carbonized fibers in a 1.8 mol / L-2.2 mol / L potassium hydroxide solution for 2.5 h-3.5 h; the temperature of the potassium hydroxide solution is 95 °C-100 °C. Introducing chemically active substances (alkaline compounds, such as potassium hydroxide or sodium hydroxide) into the carbon material allows the active substances to react with the carbon material, triggering a chemical change and forming a porous structure.

[0022] A second objective of this invention is to provide a carbon aerogel fiber prepared by the method described above.

[0023] In one embodiment of the present invention, polyacrylonitrile is used as the core layer to prepare carbon fibers due to its high carbonization rate and good spinnability. Polymethyl methacrylate is selected to act as a pore-forming agent by utilizing its high-temperature decomposition properties, shaping a porous carbon structure in the skin layer to form internal and external pathways in the coaxial fiber, which can enhance the adsorption and permeation of electrolytes. Cellulose CNF and MXene (Ti3C2T) are also used. xThe preparation of aerogels as sheaths utilizes CNFs with high aspect ratios to entangle and assemble into an interconnected framework. MXene sheets enhance the structural stability of the CNF framework and give the aerogel a porous three-dimensional network structure with high conductivity.

[0024] A third objective of this invention is to provide an application of the aforementioned carbon aerogel fiber in a capacitor.

[0025] The technical solution of the present invention has the following advantages compared with the prior art:

[0026] (1) The preparation method described in this invention uses coaxial wet spinning technology to construct carbon aerogel fibers with a core-sheath structure. The cellulose base is environmentally friendly and biodegradable, and the conductivity of the carbonized aerogel fibers is improved by loading MXene. It is selected to be combined with polyacrylonitrile in the core layer. Carbon aerogel fibers with a three-dimensional structure are obtained through freeze drying, carbonization and other processes. It has a high specific surface area and a porous three-dimensional network carbon-based structure. Due to the porous structure, it provides higher energy density and power density, and also has excellent conductivity and electrochemical performance. It is widely applicable to piezoelectric sensors and solves the problems of poor mechanical strength and poor signal transmission of existing wearable aerogel sensors, thereby improving the sensitivity and stability of wearable flexible sensors.

[0027] (2) The preparation method described in this invention is simple and easy to control. From the use of raw materials to the preparation process, it is green and pollution-free, which is conducive to large-scale industrial production.

[0028] (3) The carbon aerogel fiber of the present invention uses cellulose nanofibers as the skeleton of aerogel fiber and MXene, a two-dimensional material with abundant surface active sites, as a stabilizer and conductive agent of aerogel fiber skeleton. It fully leverages the synergistic effect of one-dimensional and two-dimensional materials. On the one hand, it solves the problem of interfacial contact resistance between fibers, making aerogel a suitable sensor material with appropriate conductivity. On the other hand, it endows aerogel fiber with good elasticity and flexibility. Attached Figure Description

[0029] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0030] Figure 1 This is a process flow diagram of the carbon aerogel fiber of the present invention;

[0031] Figure 2 This is a schematic diagram of the coaxial wet spinning structure of the present invention;

[0032] Explanation of reference numerals in the attached drawings: 201-microflow pump, 202-syringe, 203-aerogel fiber, 204-coagulation bath, 205-winding device. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0034] In this invention, unless otherwise stated, the Ti3C2T used in the embodiments and comparative examples is... x The preparation of (MXene) nanosheets specifically includes the following steps: LiF is dissolved in HCl in a polytetrafluoroethylene container under magnetic stirring, and then Ti3AlC2 powder is gradually added. The mixture is then stirred at 32°C for 24 hours to etch an aluminum layer. After ultrasonic treatment for 1 hour, the pH of the suspension is adjusted to above 6.0 by washing with water, resulting in a dark green solution. Finally, the mixture is centrifuged at 3800 rpm to collect the precipitate and obtain Ti3C2T. x Nanosheets.

[0035] In this invention, unless otherwise stated, the coagulation bath used in the examples and comparative examples consists of an ethanol solution containing 5 wt% calcium chloride and deionized water (the volume ratio of deionized water to ethanol is 3:1).

[0036] Example 1

[0037] Reference Figure 1-2 As shown, the carbon aerogel fiber and its preparation method of the present invention specifically include the following steps:

[0038] S1, Solution preparation

[0039] S11, sheath Ti3C2T x Preparation of CNF solution

[0040] Cellulose CNF solution: Disperse microcrystalline cellulose in a 7wt% NaOH / 12wt% urea aqueous solution pre-cooled to -12℃, and stir rapidly to dissolve, to obtain a clear and transparent cellulose solution with a cellulose concentration of 2wt%.

[0041] Ti3C2T x (MXene) solution: Ti3C2T x Nanosheets were dispersed in deionized water under ultrasonic treatment for 1 hour to obtain Ti3C2T with a concentration of 25 wt%. x Solution;

[0042] Ti3C2T x / CNF solution: Mix CNF solution and Ti3C2T x The solution was mixed at a mass ratio of 10:100 under magnetic stirring for 30 min, and then sonicated for 1 h to form a homogeneous Ti3C2T solution.x / CNF solution;

[0043] S12. Preparation of the core layer PAN / PMMA spinning solution: First, a certain amount of PMMA is dissolved in 4 mL of DMSO solution and stirred for 30 min in a 60℃ water bath. Then, white polyacrylonitrile powder is added to the PMMA / DMSO solution and stirred for about 2 h. After stirring, the solution is taken out and ultrasonically vibrated for 15 min. Then, the solution is allowed to stand until the bubbles inside the spinning solution are eliminated to obtain the PAN / PMMA spinning solution. The concentration of PAN is 165 mg / mL, and the mass ratio of PAN to PMMA is set to 4:1.

[0044] S2. The core spinning solution and sheath spinning solution are transferred to the corresponding spinning injectors 202 respectively. The coaxial spinning solution is introduced into the coagulation bath 204 through the coaxial spinning heads of 17G and 22G. The core and sheath advance speeds are 0.25mL / min and 0.75mL / min respectively. The advance speed is precisely controlled by the micro-flow pump 201. After soaking in the coagulation bath for 30min, the solution is taken out, washed and placed in an oven at 85℃ for 5h to dry. The fiber is kept stretched throughout the process to obtain hydrogel fiber. The fiber is then wound and collected in the winding device 205.

[0045] S3. Hydrogel fibers were frozen at -85℃ for 1 hour and then vacuum dried at -65℃ for 45 hours to obtain aerogel fibers 203.

[0046] S4. The aerogel fibers are placed in a tube furnace under a tension of 50N for heat treatment. First, the temperature is increased from 20℃ to 150℃ at a heating rate of 2℃ / min and held for 1 hour. Then, the temperature is increased from 150℃ to 200℃ and held for 1 hour. Finally, the temperature is increased to 250℃ and held for 1 hour. The temperature is then reduced to room temperature to complete the pre-oxidation process. Subsequently, the pre-oxidized fibers are placed in a high-temperature tube furnace for primary carbonization. During carbonization, high-purity nitrogen is introduced and the temperature is increased from room temperature to 800℃ at a heating rate of 4℃ / min and held for 1 hour. Nitrogen is continuously introduced during the cooling process to ensure that all residual waste gas in the tube furnace is discharged and to prevent it from condensing and depositing on the carbonized material due to cooling. Next, the carbonized fibers are soaked in a 2mol / L KOH aqueous solution at 100℃ for 3 hours. Finally, the activated fibers are washed, dried, and then subjected to secondary carbonization according to the above primary carbonization steps to obtain carbon aerogel fibers.

[0047] Example 2

[0048] The carbon aerogel fiber and its preparation method of the present invention specifically include the following steps:

[0049] Basically the same as Example 1, except that: the concentration of the cellulose solution is 1.5 wt%; Ti3C2T xThe concentration of the solution was 20 wt%; the concentration of PAN in the PAN / PMMA spinning solution was 125 mg / mL, and the mass ratio of PAN to PMMA was set to 3:2; the propulsion speeds of the core layer and the sheath layer were 0.2 mL / min and 0.6 mL / min, respectively.

[0050] Example 3

[0051] The carbon aerogel fiber and its preparation method of the present invention specifically include the following steps:

[0052] Basically the same as Example 1, except that: the concentration of the cellulose solution is 2.5 wt%; Ti3C2T x The concentration of the solution was 30 wt%; the concentration of PAN in the PAN / PMMA spinning solution was 185 mg / mL, and the mass ratio of PAN to PMMA was set to 2:3; the propulsion speeds of the core layer and the sheath layer were 0.3 mL / min and 0.9 mL / min, respectively.

[0053] Comparative Example 1

[0054] It is basically the same as Example 1, except that the core layer PAN / PMMA spinning solution is not used.

[0055] Comparative Example 2

[0056] Basically the same as Example 1, except that: a sheath layer of Ti3C2T is not used. x / CNF solution.

[0057] Comparative Example 3

[0058] It is basically the same as Example 1, except that no activation treatment is performed.

[0059] Comparative Example 4

[0060] The process is basically the same as in Example 1, except that the core spinning solution contains only PAN and no PMMA.

[0061] Comparative Example 5

[0062] It is basically the same as Example 1, except that no carbonization treatment is performed.

[0063] Comparative Example 6

[0064] First, carbon nanofibers were prepared by carbonizing the PAN / PMMA spinning solution, and then mixed with MXene nanosheets to obtain a uniformly dispersed suspension. Subsequently, the prepared carbon nanofibers / MXene were placed in a freeze dryer for freeze drying for more than 48 hours to obtain carbon nanofibers / MXene composite aerogel.

[0065] Test case

[0066] The fibers prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to mechanical, electrochemical, and sensitivity tests. The test methods or standards are as follows:

[0067] (1) Mechanical properties: The mechanical properties of the fiber before and after carbonization were tested using a single-fiber tensile strength tester. The fiber length was 80 mm, and the tensile rate was 10 mm / min. In the subsequent loading and unloading tests, the maximum tensile strain was first stretched to 50%, and then unloaded at a rate of 10 mm / min. Since the mechanical property data are related to the ambient temperature and humidity, these data were measured under the same conditions: 23℃ and 50% relative humidity.

[0068] (2) Electrochemical properties: Conductivity is a parameter used to describe the ease with which charge flows in a substance. The conductivity of the fibers was tested using a four-probe system (RTS-8, Guangzhou Four-Probe Technology). Five measurements were taken on each side of each material, and the average value was used for calculation. The experiment was conducted at room temperature. To study the effect on fiber conductivity, the fiber resistance was measured using a multimeter, and the fiber conductivity was calculated using a formula.

[0069] (3) Sensitivity test: Sensitivity is an important standard for measuring electronic instruments. Sensitivity refers to the sensor’s response to a unit current change under pressure. The sensitivity is tested under 40 kPa pressure.

[0070] The performance test results are shown in Table 1 below:

[0071] Table 1

[0072] Fracture strength (CN) Elongation at break (%) Electrical conductivity (S / m) Sensitivity (K / Pa) Example 1 2736 3.7 298.43 156.47 Example 2 2192 2.4 226.64 - Example 3 2247 2.6 219.72 - Comparative Example 1 1118 0.8 105.91 24.74 Comparative Example 2 1867 1.9 123.74 - Comparative Example 3 852 1.2 154.12 - Comparative Example 4 2042 2.7 178.28 - Comparative Example 5 735 1.4 87.49 31.89 Comparative Example 6 653 0.7 74.83 54.71

[0073] As shown in Table 1, with the increase of MXene content, the fiber strength, conductivity, and specific capacitance all show a trend of first increasing and then decreasing, reaching a peak at an MXene content of 25 wt%. With the addition of MXene, the discharge time of the hybrid fiber gradually increases, showing the highest charge storage capacity at a content of 25 wt%. When the MXene content continues to increase, the electrode energy storage capacity decreases because the two-dimensional sheets are prone to stacking, and when the content is too high, it will cause MXene agglomeration. With the increase of PAN solid content, the conductivity shows a trend of first increasing and then decreasing. The higher the solid content of the spinning solution, the higher the polymer matrix content per unit length of fiber, and the easier it is to form a continuous and rich conductive network after carbonization, thus increasing the conductivity accordingly. However, when the concentration of the spinning solution further increases, with the further increase of PAN solid content, the fiber exhibits a "void" porous structure after high-temperature carbonization, which will affect the conductive network and thus affect the electron transport efficiency. The propulsion speed corresponds to the volume of the injected spinning solution, and therefore the propulsion speed is related to the needle area. A mismatch between these two speeds can cause fiber splitting or structural discontinuity. Based on the cross-sectional structure of the coaxial spinneret, the cross-sectional area ratio of the sheath to the core layer is approximately 3:1. It was found that the hydrogels and aerogels prepared with cellulose concentrations of 2.5 wt% and 1.5 wt% exhibited generally poor structural formation, with the material appearing as flocculent material during regeneration. The hydrogen bonding between cellulose fibers was low, resulting in an interwoven, porous aerogel material. However, the aerogel exhibited better formability when the cellulose concentration was 2 wt%.

[0074] As can be seen from Example 1 and Comparative Example 1, the use of a core layer PAN / PMMA spinning solution and this core-sheath structure can increase its sensitivity in sensing applications.

[0075] As can be seen from Example 1 and Comparative Example 2, MXene is pre-dispersed through hydrogen bonding and electrostatic interaction, which effectively avoids the self-stacking of MXene. The ordered interconnected MXene sheets improve the electrical conductivity of aerogel fibers.

[0076] As can be seen from Example 1 and Comparative Example 4, after introducing PMMA, the modulus of the hybrid fiber before and after carbonization is higher than that of pure PAN, especially the carbonized sample, which shows that the rigidity of the PAN / PMMA hybrid fiber has increased.

[0077] As can be seen from Example 1 and Comparative Example 5, the strength of the carbonized fibers is further improved compared to the nascent fibers after carbonization treatment. This is because carbonization removes non-carbon components, gradually increases the C-C spacing, increases the crystal size, and shapes a graphite-like structure (hexagonal layered structure), thus improving fiber strength. Carbonized PAN fibers also exhibit better conductivity, making them more sensitive in certain sensing applications. Carbon fibers have high electrical conductivity, enabling them to better sense and conduct electronic signals.

[0078] As can be seen from Example 1 and Comparative Example 6, the coaxial wet core-sheath structure exhibits better mechanical properties and electrical conductivity than a single hybrid composite. Aerogel fibers typically possess a very high specific surface area due to their porous structure with numerous micropores, making them more sensitive in adsorbing gases, liquids, or other molecules.

[0079] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for producing a carbon aerogel fiber, characterized by, Comprising the following steps, S1, coaxial wet spinning of core layer spinning solution and sheath layer spinning solution, after immersion in coagulation bath, washing and drying to obtain hydrogel fiber; the core layer spinning solution is a mixture of polymethyl methacrylate, polyacrylonitrile and solvent; the sheath layer spinning solution is obtained by mixing MXene solution and cellulose solution according to a mass ratio of 5-12:100; the MXene solution is MXene nanosheet dissolved in water; the cellulose solution is microcrystalline cellulose, sodium hydroxide and urea dissolved in water; S2, freezing and drying the hydrogel fiber of S1 to obtain aerogel fiber; S3, pre-oxidation treatment, first carbonization treatment, activation treatment and second carbonization treatment of the aerogel fiber of S2 to obtain the carbon aerogel fiber; the first carbonization treatment is to heat to 500-1000℃ at a rate of 3.8-4.2℃ / min in nitrogen or argon atmosphere for 1-2h; the activation treatment is to immerse the carbonized fiber in 1.8-2.2mol / L potassium hydroxide solution for 2.5-3.5h; the temperature of the potassium hydroxide solution is 95-100℃; the second carbonization treatment is to heat to 1000-2000℃ at a rate of 3.8-4.2℃ / min in nitrogen or argon atmosphere for 1-2h.

2. The method for preparing a carbon aerogel fiber according to claim 1, characterized by, In S1, the concentration of the MXene solution is 20-30wt%; The temperature of the cellulose solution is below-12℃; the concentration of microcrystalline cellulose in the cellulose solution is 1.5-2.5wt%, the concentration of sodium hydroxide is 6-8wt%, and the concentration of urea is 11-13wt%; The concentration of polyacrylonitrile in the core layer spinning solution is 125-185mg / mL; the mass ratio of polyacrylonitrile to polymethyl methacrylate is 1-4:1-4.

3. The method for preparing a carbon aerogel fiber according to claim 1, characterized by, In S1, during the coaxial wet spinning process, the sizes of the coaxial spinning heads corresponding to the core layer and the sheath layer are 17-18G and 22-25G respectively; the advancing speeds of the core layer and the sheath layer are 0.2-0.3mL / min and 0.6-0.9mL / min respectively.

4. The method for preparing a carbon aerogel fiber according to claim 1, characterized by, In S1, the drying is at 82-88℃ for 4.5-5.5h.

5. The method of claim 1, wherein the carbon aerogel fiber is prepared by the steps of: In S2, the freezing is at-82 to-88℃ for 0.5-1.5h; the drying is vacuum drying at-62 to-68℃ for 40-50h.

6. The method of claim 1, wherein the carbon aerogel fiber is prepared by the steps of: In S3, the pre-oxidation treatment is divided into four stages, the first stage is to heat to 140-160℃ at a rate of 1.8-2.2℃ / min for 1-1.5h; the second stage is to heat to 190-210℃ at a rate of 1.8-2.2℃ / min for 1-1.5h; the third stage is to heat to 240-260℃ at a rate of 1.8-2.2℃ / min for 1-1.5h; the fourth stage is air cooling to 20-30℃.

7. A carbon aerogel fiber produced by the process of any one of claims 1-6.

8. Use of a carbon aerogel fiber according to claim 7 in a capacitor.

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