CN111535011A

CN111535011A - Method for preparing graphene fibers through joule heat flash evaporation

Info

Publication number: CN111535011A
Application number: CN202010511161.2A
Authority: CN
Inventors: 刘忠范; 程熠; 亓月; 王坤; 李隽良
Original assignee: Peking University; Beijing Graphene Institute BGI
Current assignee: Peking University; Beijing Graphene Institute BGI
Priority date: 2020-06-08
Filing date: 2020-06-08
Publication date: 2020-08-14

Abstract

The present disclosure provides a method for preparing graphene fiber by joule heating flash evaporation, comprising providing a carbon-containing fiber with conductivity; and applying voltage to the carbon-containing fibers to generate Joule heat to graphitize the carbon-containing fibers to obtain the graphene fibers. The method disclosed by the invention utilizes the Joule heat generated by applying voltage to enable the fiber to reach high temperature quickly, and graphitization of the fiber can be realized in a short time. The method can effectively realize the rapid and continuous preparation of the graphene fiber, and greatly reduces the production cost of the graphene fiber. The obtained graphene fiber has a compact cross section, high graphitization degree, excellent electric and heat conducting properties and important application value.

Description

Method for preparing graphene fibers through joule heat flash evaporation

Technical Field

The disclosure relates to the field of material preparation, in particular to a method for preparing graphene fibers by joule heating flash evaporation.

Background

The graphene has the characteristics of excellent electric conductivity, heat conductivity, mechanical strength, chemical stability and the like, and shows wide application value in the aspects of energy, electronic circuits, biological medicines and the like. The development of a convenient and effective preparation method of the graphene fiber is helpful for promoting industrial production and commercial application of the graphene fiber, and is one of the research hotspots in the field of current carbon nano materials.

The traditional method for preparing graphene fibers is a wet spinning method based on Graphene Oxide (GO). The method mainly comprises the steps of injecting liquid crystal phase GO into a coagulating bath to form GO gel fibers, and then carrying out water washing, drying, stretching, reducing and the like to obtain the target graphene fibers (Gao C.et al. nat. Commun.2011,2: 571). However, the subsequent GO reduction process in the graphene preparation process is complicated. For the methods of chemical reduction (Gao, c.et al. acs Nano 2012,6,7103.) and laser reduction (Qu, l.et al. angelw.chem.int.ed.2013, 52,10482.), the reduction degree is limited, and the surface of the fiber after reduction inevitably has defect sites such as oxidation functional groups, cracks, folds and the like, which adversely affects the electrical conductivity, thermal conductivity and mechanical properties of the fiber. The subsequent development of high-temperature (3000 ℃) reduction method greatly reduces the surface defects of the fiber and improves the graphitization degree of the fiber (Gao, C.et al.adv.Mater.2016,28,6449.). But the energy consumption brought by the lifting temperature and the long-time high-temperature treatment greatly increases the preparation cost of the fiber.

A method of preparing graphene fibers by Chemical Vapor Deposition (CVD) is considered to be a convenient method of preparing graphene fibers, but it often requires graphene growth by means of a template. Dai et al grow multilayer graphene on the surface of a copper wire under a controlled condition by using a CVD method, and etch and remove the copper wire to obtain corresponding graphene fiber (Dai L.et. Angew.chem.int.Ed.2015,54,14947.). Using a similar method, Zhu et al grows graphene on a metal mesh woven from copper wires, and after etching away the copper mesh, a fabric woven from graphene fibers is obtained (Zhu h.et al sci.rep.2012,2, 395). However, the fibers need to undergo etching in an etching solution, fiber transfer and other processes, and the graphene fibers are inevitably wrinkled, damaged and the like under the surface tension of water, so that the obtained fibers have poor performance.

Therefore, a new method for preparing graphene fiber is needed to solve the problems of the existing methods.

It is noted that the information disclosed in the foregoing background section is only for enhancement of background understanding of the present disclosure and therefore it may contain information that does not constitute prior art that is known to a person of ordinary skill in the art.

Disclosure of Invention

The main purpose of the present disclosure is to overcome at least one of the above drawbacks of the prior art, and to provide a method for preparing graphene fiber by joule heating flash evaporation, so as to solve the problems of high preparation cost, poor product performance, difficulty in mass production, and the like of the existing graphene fiber.

In order to achieve the purpose, the following technical scheme is adopted in the disclosure:

the present disclosure provides a method for preparing graphene fibers by joule heating flash evaporation, comprising: providing a carbon-containing fiber with conductivity; and applying voltage to the carbon-containing fibers to generate Joule heat to graphitize the carbon-containing fibers to obtain the graphene fibers.

According to one embodiment of the present disclosure, the carbon-containing fiber having electrical conductivity is obtained by: spinning the carbon-containing precursor to obtain precursor fiber; and the precursor fiber is at 10 Pa-10 Pa⁵Heating to 200-500 ℃ under Pa pressure, and keeping the temperature for 10-300 min to obtain the conductive carbon-containing fiber.

According to one embodiment of the present disclosure, the carbon-containing precursor is selected from one or more of polyacrylonitrile, pitch, polyvinylpyrrolidone, polybenzimidazole, polyparaphenylene benzobisoxazole, polyethylene, polypropylene, aramid, viscose, and graphene oxide; the precursor fiber is placed in one or more of argon, hydrogen, nitrogen and argon-oxygen mixed gas for heating.

According to one embodiment of the present disclosure, the method of the spinning process is selected from one or more of a melt spinning method, a dry spinning method, a wet spinning method, and an electrospinning method.

According to one embodiment of the present disclosure, the carbon-containing fiber having conductivity is a graphene oxide fiber after a pre-reduction treatment, the pre-reduction treatment including: and placing the graphene oxide fiber in a reducing agent solution for reduction reaction to obtain the conductive graphene oxide fiber.

According to one embodiment of the present disclosure, the applied voltage is 20V to 380V, the time of the applied voltage is 0.05s to 30s, and the temperature reached after the applied voltage is 2000 ℃ to 3000 ℃.

According to one embodiment of the present disclosure, a voltage is applied by connecting respective electrodes to both ends of a carbon-containing fiber, wherein a distance between potential connection points of the electrodes to both ends of the carbon-containing fiber is 0.5cm to 20 cm.

According to one embodiment of the disclosure, the method further comprises placing the carbon-containing fibers on a conveying device to apply voltage, so as to realize continuous preparation of the graphene fibers, wherein the conveying speed of the conveying device is 0.1-20 cm/s.

According to one embodiment of the present disclosure, the voltage is applied under a low vacuum condition with a pressure <10Pa or under protection of inert gas, wherein the inert gas used when applying the voltage is selected from one or more of nitrogen and argon.

According to one embodiment of the present disclosure, the method further comprises doping the carbon-containing fiber by introducing one or more of a nitrogen-containing precursor and a boron-containing precursor when the voltage is applied, wherein the nitrogen-containing precursor is selected from one or more of ammonia gas, acetonitrile, pyridine, pyrrole and methylamine, and the boron-containing precursor is selected from one or more of phenylboronic acid, diborane, boron powder and triethylborane.

The disclosure also provides a graphene fiber prepared by the method.

According to the technical scheme, the beneficial effects of the disclosure are as follows:

according to the method for preparing the graphene fiber by the Joule heat flash evaporation, the specific voltage is applied to the carbon-containing fiber with conductivity, the Joule heat is generated by the carbon-containing fiber, so that the fiber can reach high temperature quickly, graphitization of the fiber can be realized in a short time, the method can effectively realize quick and continuous preparation of the graphene fiber, and the production cost of the graphene fiber is greatly reduced. The obtained graphene fiber has more excellent electric conductivity and thermal conductivity, the fiber section is compact, the graphitization degree is high, and the method has important significance for expanding the industrial production application of the graphene fiber.

Drawings

The following drawings are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description serve to explain the principles of the disclosure and not to limit the disclosure.

Fig. 1 is an apparatus for preparing graphene fibers according to an embodiment of the present disclosure;

FIG. 2 is a top view of the apparatus shown in FIG. 1;

FIG. 3 is a comparison of Raman spectra of fibers before and after Joule thermal flash evaporation of example 1;

fig. 4 is a scanning electron micrograph of the graphene fiber prepared in example 1;

fig. 5 is an electrical test result of the graphene fiber prepared in example 1;

FIG. 6 is a comparison of Raman spectra of graphene fibers before and after Joule thermal flash evaporation in example 2;

fig. 7 and 8 are graphs comparing the element contents of the graphene fibers before and after joule heat flash evaporation in example 2, respectively.

Wherein the reference numerals are as follows:

100: shell body

101: air inlet

102: air outlet

103: cavity body

210: filament-releasing rotating wheel

211. 221: groove

212. 222: supporting frame

220: filament collecting rotating wheel

310: first fixed pulley

320: a first electrode

330: second fixed pulley

340: second electrode

400: horizontal plate

Detailed Description

The following presents various embodiments or examples in order to enable those skilled in the art to practice the invention with reference to the description herein. These are, of course, merely examples and are not intended to limit the present disclosure. The endpoints of the ranges and any values disclosed in the present disclosure are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to yield one or more new ranges of values, which ranges of values should be considered as specifically disclosed herein.

According to the invention, the existing method for preparing the graphene fiber has the problems of high preparation cost, poor product performance, difficulty in batch production and the like. Therefore, the invention realizes a novel method for preparing graphene fibers by Joule thermal flash evaporation in combination with a specific device. According to the method, voltage is applied to the fibers, and the fibers are rapidly graphitized by using high temperature generated by Joule heat, so that a fussy template etching step is effectively avoided, rapid and continuous preparation of the graphene fibers is realized, and the production cost of the graphene fibers is greatly reduced.

Referring to fig. 1, which representatively illustrates an apparatus for preparing graphene fibers according to an exemplary embodiment of the present disclosure, fig. 2 representatively illustrates a top view of the apparatus for preparing graphene fibers, which can embody principles of the present disclosure. A method for preparing graphene fibers according to the present disclosure will be described in detail with reference to fig. 1 and 2. The method provided by the present disclosure is exemplified by being applied to the preparation of graphene fibers. Those skilled in the art will readily appreciate that numerous modifications, additions, substitutions, deletions, or other changes may be made to the specific embodiments described below in order to apply the relevant designs of the present disclosure to other types of graphene composite materials, and such changes are within the scope of the principles of the devices presented in the present disclosure.

As shown in fig. 1, in the present embodiment, the apparatus for preparing graphene fibers mainly includes a housing 100, a wire winding and unwinding assembly, and a voltage applying assembly. It should be noted that fig. 1 is only a partial schematic view of the apparatus for preparing graphene fibers according to the present disclosure, and does not show structures such as a motor, a vacuum pump, and the like. Referring to fig. 2 in combination, fig. 2 representatively illustrates a top view of an apparatus for preparing graphene fibers, which can embody principles of the present disclosure. The structure, connection manner and functional relationship of each main component of an exemplary embodiment of the apparatus for manufacturing graphene fibers proposed by the present disclosure will be described in detail below with reference to fig. 1 and 2.

With reference to fig. 1 and fig. 2, in this embodiment, the apparatus for preparing graphene fibers includes a housing 100, a wire winding and unwinding assembly, and a voltage applying assembly, wherein the housing 100 encloses a cavity 103, and a horizontal plate 400 is disposed inside the housing, and the horizontal plate 400 is used for placing the wire winding and unwinding assembly and the voltage applying assembly. The wire releasing and collecting assembly comprises a wire releasing rotating wheel 210 and a wire collecting rotating wheel 220, wherein the wire releasing rotating wheel 210 and the wire collecting rotating wheel 220 are fixedly connected to two ends of the horizontal plate 400 through supporting

frames

212 and 222 respectively.

As shown in fig. 2, the voltage applying assembly includes a first electrode 320 and a second electrode 340, a first fixed pulley 310 is connected to one end of the first electrode 320, and a second fixed pulley 330 is connected to one end of the second electrode 340. Generally, the axes of the first fixed pulley 310 and the second fixed pulley 330 are required to be on the same horizontal line with the axes of the wire releasing wheel 210 and the wire collecting wheel 220, and the first fixed pulley 310 and the second fixed pulley 330 are arranged between the wire releasing wheel 210 and the wire collecting wheel 220.

The process flow for preparing graphene fiber according to the present disclosure is specifically described below with reference to the apparatus of fig. 1 and 2.

First, a conductive carbon-containing fiber is provided. The conductive carbon-containing fiber is wound on the wire take-up and pay-off assembly, and a part of the carbon-containing fiber between the wire pay-off rotating wheel 210 and the wire take-up rotating wheel 220 is placed on the first fixed pulley 310 and the second fixed pulley 330, so that the conductive carbon-containing fiber is directly in surface contact with the first fixed pulley 310 and the second fixed pulley 330 to be connected into a circuit. In some embodiments, the filament releasing wheel 210 and the filament collecting wheel 220 are respectively provided with a

groove

211, 221, and the carbon fiber is disposed in the

groove

211, 221 to prevent the carbon fiber from falling off when the filament releasing wheel 210 and the filament collecting wheel 220 rotate.

According to the present disclosure, the aforementioned carbon-containing fiber having electrical conductivity can be obtained by: spinning the precursor containing carbon to obtain precursor fiber, and setting the precursor fiber in certain atmosphere, such as one or several of argon, hydrogen, nitrogen and mixed argon-oxygen gas, at 10-10 Pa⁵Pa, e.g. 10Pa, 100Pa, 1000Pa, 10Pa⁴Heating to 200-500 deg.C (such as 200 deg.C, 250 deg.C, 300 deg.C, 320 deg.C, 400 deg.C) under Pa, etc., and maintaining for 10-300 min (such as 10min, 50min, 70min, 100min, 120min, 180min, 200min, etc.) to obtain conductive carbon-containing fiber.

In some embodiments, the carbon-containing precursor may be one or more of polyacrylonitrile, pitch, polyvinylpyrrolidone, polybenzimidazole, Polyparaphenylene Benzobisoxazole (PBO), polyethylene, polypropylene, aramid, viscose, and Graphene Oxide (GO). The spinning process includes, but is not limited to, one or more of melt spinning, dry spinning, wet spinning, and electrospinning.

The foregoing operation is performed to enable the carbon-containing fibers to have appropriate conductivity, so that graphene can be generated at a high temperature by generating sufficient joule heat when a voltage is applied thereto. If the conductivity is too poor and the current is small, the corresponding temperature cannot be reached if the heat generation is small, so that the graphene fiber cannot be obtained. Of course, if the precursor fiber itself already has good conductivity, this step can also be omitted and the voltage applied directly to the fiber, without the disclosure being limited thereto.

In addition, in some embodiments, the carbon-containing fiber with conductivity may also be a graphene oxide fiber subjected to pre-reduction treatment, and a part of graphene oxide in the graphene oxide fiber may be reduced to graphene by performing the pre-reduction treatment on the graphene oxide fiber, so that the fiber is endowed with conductivity to a certain extent, and then the subsequent voltage application treatment may be performed on the fiber, so as to obtain a graphene fiber with excellent performance. The pre-reduction treatment comprises the step of placing the graphene oxide fibers in a reducing agent solution to perform a reduction reaction. Wherein the reducing agent may be a reducing agent such as Hydrogen Iodide (HI), the present disclosure is not limited thereto.

Then, a voltage is applied to the conductive carbon-containing fiber to generate joule heat to graphitize the carbon-containing fiber to obtain the graphene fiber.

Specifically, in operation, the chamber 103 is evacuated by an evacuation device connected to the apparatus, such as a vacuum pump, vacuum generator, or the like, so that the system is in a low vacuum (pressure <10Pa) or inert gas (e.g., nitrogen, argon) protective state. In some embodiments, other element-containing precursors may also be introduced to dope the carbon-containing fiber, such as one or more of nitrogen-containing precursors including, but not limited to, one or more of ammonia, acetonitrile, pyridine, pyrrole, and methylamine, and boron-containing precursors including, but not limited to, one or more of phenylboronic acid, diborane, boron powder, and triethylborane. By doping the fibers when voltage is applied, the conductivity, catalytic performance or other performances of the obtained product can be improved to different degrees according to different doping elements and actual requirements.

The filament releasing rotating wheel 210 and the filament collecting rotating wheel 220 are generally connected with a driving motor, the filament releasing rotating wheel 210 and the filament collecting rotating wheel 220 are driven to rotate, fibers wound on the filament releasing rotating wheel 210 and the filament collecting rotating wheel 220 continuously pass through the surfaces of the first fixed pulley 310 and the second fixed pulley 330 through the rotation of the filament releasing rotating wheel and the filament collecting rotating wheel, at the moment, a certain voltage is applied to the fibers passing through the surface contact of the first fixed pulley 310 and the second fixed pulley 330 through the first electrode 320 and the second electrode 340, the generated joule heat can promote the high-temperature graphitization of the fibers, and the fibers passing through the first fixed pulley 310 and the second fixed pulley 330 can also be continuously graphitized along with the continuous rotation of the filament releasing rotating wheel 210 and the filament collecting rotating wheel 220, so. Generally, the graphitization time of the fibers can be controlled by adjusting the rotation speed of the filament pay-off wheel 210 and the filament take-up wheel 220 to 0.1cm/s to 20cm/s, for example, 0.1cm/s, 1cm/s, 2cm/s, 6cm/s, 10cm/s, 16cm/s, etc. It should be noted that, according to actual needs, the apparatus may also implement static or intermittent preparation of graphene fibers, for example, a voltage is directly applied to the fibers between the filament unwinding wheel 210 and the filament winding wheel 220 without rotating the filament unwinding wheel 210 and the filament winding wheel 220, and the disclosure is not limited thereto.

In some embodiments, the voltage applied is 20V to 380V, for example, 20V, 40V, 45V, 50V, 70V, 100V, 120V, 200V, 300V, 350V, etc., preferably 100V to 220V, and the voltage is applied for 0.05s to 30s, for example, 0.05s, 0.1s, 1s, 2s, 5s, 10s, 13s, 19s, 25s, 27s, etc., preferably 1s to 10s, so that the temperature reaches a high temperature of about 2000 ℃ to 3000 ℃. Further, when a voltage is applied, the distance between the potential connection points of the electrodes connected to both ends of the carbon-containing fiber, that is, the distance between the first fixed pulley 310 and the second fixed pulley 330 has a certain influence on the graphitization of the fiber, and preferably, the distance is 0.5cm to 20cm, for example, 0.5cm, 1cm, 4cm, 10cm, 15cm, 18cm, and the like, and preferably 1cm to 5 cm. The fiber defects are not completely repaired and the graphitization degree is not high due to factors such as too low voltage, too short pulley distance, too short voltage application time and the like; conversely, too high a voltage, too high a pulley distance, too long a voltage application time, etc., may cause the entire circuit to be short-circuited.

The invention will be further illustrated by the following examples, but is not to be construed as being limited thereto. Unless otherwise specified, reagents, materials and the like used in the present invention are commercially available.

Example 1

1) PAN (Alfa Aesar, average molecular weight Mw 150000) is dissolved in Dimethylformamide (DMF) solution to prepare spinning solution with the mass fraction of 10 wt%, and precursor fibers (the diameter of a spinning nozzle is 100 μm, the spinning voltage is 10kV, a receiver is graphene paper, the distance between an injector and the receiver is 10cm, and the spinning time is 6min) are prepared by electrostatic spinning.

2) And (3) placing the PAN fiber obtained by spinning into a tubular furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the atmosphere of normal pressure, 200sccm argon and 10sccm hydrogen, preserving the temperature for 30min, and then cooling with the furnace and taking out.

3) Installing the fiber obtained in the step 2) on a device shown in figure 1, opening a vacuum pump to keep the system pressure less than 10Pa, applying 150V voltage to two ends of the fiber, and starting rotating wheels at two ends to keep the rotating speed at 0.5 cm/s. And after the fiber is completely reacted, closing the voltage source and the roller driving button, and taking out a target fiber sample after the sample is cooled to obtain the graphene fiber.

Fig. 3 is a comparison graph of raman spectra of the fiber before and after joule heat flash evaporation in example 1, and it can be seen from fig. 3 that graphene grows in the fiber after joule heat flash evaporation treatment. Fig. 4 is a scanning electron microscope image of the graphene fiber prepared in example 1, and it can be observed that the fiber section is dense; fig. 5 shows the electrical test results of the graphene fiber prepared in example 1 (the length of the test fiber is 10cm, and the diameter is about 60 μm), and it can be seen from fig. 5 that the prepared graphene fiber has excellent conductivity.

Example 2

1) Dispersing Graphene Oxide (GO) powder (Nanjing Xiapong nanometer material Co., Ltd.) in water solution, performing ultrasonic treatment for 1h to obtain uniform dispersion liquid, and performing wet spinning to obtain corresponding GO fiber, wherein the diameter of a spinning nozzle is 50 μm, the extrusion rate is 5mm/min, and a coagulating bath is CaCl₂The prepared GO fiber needs to be subjected to water washing, drying and other treatment steps in the following process, namely washing with deionized water for 3 times, and then drying in a 70 ℃ oven for 2 hours in vacuum.

2) Mounting the GO fibers obtained in step 1) on a device as shown in fig. 1. Then, the vacuum pump was turned on, the system was kept at a low pressure, and 100sccm of nitrogen gas was introduced. After 10min, sequentially opening the voltage and the rotating system, keeping the voltage at 220V, and enabling the rotating speed of the rotating system to be 1 cm/s. And after the fiber is completely reacted, closing the voltage source and the roller driving button, and taking out a target fiber sample after the sample is cooled to obtain the graphene fiber.

Fig. 6 is a comparison graph of raman spectra of graphene fibers before and after joule heat flash evaporation in example 2, and it can be seen from fig. 6 that defect sites in the fibers subjected to joule heat flash evaporation treatment are significantly reduced, and the graphitization degree is significantly improved. Fig. 7 and 8 are element content comparison graphs of the graphene fibers before and after joule heating flash evaporation in example 2, respectively, and it can be seen that the oxygen element content in the fibers is significantly reduced after joule heating flash evaporation, which indicates that the GO fibers are effectively reduced.

Compared with other methods for preparing the graphene fiber, the method for preparing the graphene fiber has the advantages of simple steps, high controllability, capability of realizing rapid, low-cost and batch preparation of the graphene fiber, and more excellent electric conductivity and thermal conductivity of the prepared graphene fiber compared with the existing method, compact fiber section of the obtained graphene fiber, high graphitization degree and fiber conductivity of 5.5 × 10⁵S/m, the fiber yield can reach 30m/h, and the application prospect is good.

It should be noted by those skilled in the art that the described embodiments of the present disclosure are merely exemplary, and that various other substitutions, alterations, and modifications may be made within the scope of the present disclosure. Accordingly, the present disclosure is not limited to the above-described embodiments, but is only limited by the claims.

Claims

1. A method for preparing graphene fibers by Joule thermal flash evaporation is characterized by comprising the following steps:

providing a carbon-containing fiber with conductivity; and

and applying a voltage to the carbon-containing fibers to generate Joule heat to graphitize the carbon-containing fibers to obtain the graphene fibers.

2. The method according to claim 1, wherein the carbon-containing fibers having electrical conductivity are obtained by:

spinning the carbon-containing precursor to obtain precursor fiber; and

the precursor fiber is at 10 Pa-10 Pa⁵Heating to 200-500 ℃ under Pa pressure, and keeping the temperature for 10-300 min to obtain the conductive carbon-containing fiber.

3. The method of claim 2, wherein the carbon-containing precursor is selected from one or more of polyacrylonitrile, pitch, polyvinylpyrrolidone, polybenzimidazole, polyparaphenylene benzobisoxazole, polyethylene, polypropylene, aramid, viscose, and graphene oxide; the precursor fiber is placed in one or more gases of argon, hydrogen, nitrogen and argon-oxygen mixed gas for heating; the spinning treatment method is one or more selected from a melt spinning method, a dry spinning method, a wet spinning method and an electrostatic spinning method.

4. The method according to claim 1, wherein the carbon-containing fiber having conductivity is a graphene oxide fiber after a pre-reduction treatment, and the pre-reduction treatment comprises: and placing the graphene oxide fiber in a reducing agent solution for reduction reaction to obtain the conductive graphene oxide fiber.

5. The method according to claim 1, wherein the applied voltage is 20V to 380V, the time of the applied voltage is 0.05s to 30s, and the temperature reached after the applied voltage is 2000 ℃ to 3000 ℃.

6. The method according to claim 1, wherein the voltage is applied by connecting respective electrodes to both ends of the carbon-containing fiber, wherein a distance between potential connection points of the electrodes to both ends of the carbon-containing fiber is 0.5cm to 20 cm.

7. The method of claim 1, further comprising applying a voltage to the carbon-containing fibers on a conveyor to achieve continuous production of the graphene fibers, wherein the conveyor has a conveying speed of 0.1cm/s to 20 cm/s.

8. The method according to claim 1, wherein the voltage is applied under low vacuum conditions at a pressure <10Pa or under inert gas protection, wherein the inert gas used in applying the voltage is selected from one or more of nitrogen, argon.

9. The method of claim 1, further comprising doping the carbon-containing fiber by introducing one or more of a nitrogen-containing precursor selected from one or more of ammonia, acetonitrile, pyridine, pyrrole, and methylamine and a boron-containing precursor selected from one or more of phenylboronic acid, diborane, boron powder, and triethylborane while applying the voltage.

10. A graphene fiber prepared by the method of any one of claims 1 to 9.