CN115262035A

CN115262035A - Graphene nanofiber material and preparation method and application thereof

Info

Publication number: CN115262035A
Application number: CN202110481061.4A
Authority: CN
Inventors: 何海勇; 王键; 王德宇
Original assignee: Ningbo Institute of Material Technology and Engineering of CAS
Current assignee: Ningbo Institute of Material Technology and Engineering of CAS
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2022-11-01

Abstract

The application discloses a graphene nanofiber material and a preparation method and application thereof, wherein the diameter of the graphene nanofiber is 100-900 nm, and the length of the graphene nanofiber is more than or equal to 10 micrometers. When the material is used as a potassium ion battery cathode, the electrolyte is filled in macropores among the graphene nanofibers to form an ion channel, so that the diffusion distance and resistance of ions in the electrode are reduced, and the specific capacity and the rate capability of the potassium ion battery can be improved.

Description

Graphene nanofiber material and preparation method and application thereof

Technical Field

The application relates to a graphene nanofiber material and a preparation method and application thereof, and belongs to the field of nanomaterials.

Background

Based on the advantages of low cost (only 13 percent of lithium), abundant reserves (the earth crust abundance is 2.09wt percent), low reduction potential (-2.93V vs. SHE) and the like of potassium, and can also form an intercalation compound KC with graphite₈The reversible reaction of (a), potassium ion batteries are promising as one of the most potential alternatives of lithium ion batteries. However, the volume expansion rate of graphite intercalated with potassium is as high as 60%, wherebyThe internal stress generated easily causes the material to crack and fail, and also causes the electrochemical dynamic process to be slow. Thus, in potassium ion batteries, the rate capability and cycling stability of graphite anodes is far less than that of lithium ion batteries. The graphene nanofiber serving as a flexible material can better resist the pulverization effect generated by expansion, and meanwhile, the fiber gaps of the graphene nanofiber serving as ion channels can effectively shorten the migration distance of potassium in the material after the graphene nanofiber is filled with electrolyte, so that the multiplying power performance is improved. Meanwhile, the foam graphene is a flexible material, and the foam graphene contains excessive macropores to cause spatial waste, so that the volume energy density is poor; the graphene film has poor rate capability because of the difficulty in potassium ion transport due to its layered structure.

The preparation method of the fiber is wet spinning and a limited-area hydrothermal method. The diameters of the fibers prepared by the two are micron-sized, so that the requirements are difficult to meet. Among them, the carbon electrode double layer capacitor is a capacitor using a carbon material as an electrode, and electrostatic spinning is undoubtedly a relatively convenient means for mass production of nanofibers. Electrospinning is a special fiber manufacturing process, where polymer solutions or melts are jet spun in a strong electric field. Under the action of the electric field, the liquid drop at the needle head changes from a spherical shape to a conical shape (i.e. a Taylor cone) and extends from the tip of the cone to obtain a fiber filament. In this way, polymer filaments of nanometer diameter can be produced. However, graphene oxide nanosheets in the graphene oxide liquid crystal cannot be crosslinked with each other like polymer chains, and therefore cannot be directly stretched into nanofibers under the action of an electric field.

Disclosure of Invention

In order to solve the problems, the coaxial electrostatic spinning technology is adopted in the application. The coaxial electrostatic spinning is different from the common electrostatic spinning which needs to be a single system, wherein the coaxial electrostatic spinning is to inject an inner fluid and an outer fluid solution into two capillaries with different inner diameters and coaxial, the inner fluid and the outer fluid are converged at the tail end of a spray head, and the inner fluid and the outer fluid are solidified into the composite nanofiber under the action of an electric field force. Even non-spinnable liquid such as graphene oxide liquid crystal can still be filled in the inner cavity of the tubular nanofiber constructed by the outer fluid under the drive of the shearing force between the inner fluid and the outer fluid. And then removing the outer-layer polymer, and reducing and curing the graphene oxide on the inner layer to obtain the graphene nanofiber.

According to the first aspect of the application, the graphene nanofiber material is provided, graphene is directionally arranged in a domain-limited space to form a compact structure, so that the graphene nanofiber material has higher energy density, and meanwhile, when the graphene nanofiber material is applied as a potassium ion battery electrode, an electrolyte is filled in macropores between graphene nanofibers to form an ion channel, so that the diffusion distance and resistance of ions in the electrode are reduced, and the rate capability and the cycle stability of the battery can be improved.

The diameter of the graphene nanofiber material is 100-900 nm, and the length of the graphene nanofiber material is greater than or equal to 10 micrometers.

Optionally, the graphene nanofiber material is formed by crosslinking reduced graphene oxide nanosheets with each other.

Optionally, the graphene nanofiber material is completely cross-linked from reduced graphene oxide nanoplatelets to each other without any cross-linking agent.

Optionally, the graphene nanofiber material has a diameter of 300 to 900nm.

Optionally, the graphene nanofiber material has a diameter independently selected from any value of 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, or a range value between any two.

Optionally, the graphene nanofiber material has a length of 10 to 50 μm.

Optionally, the length of the graphene nanofiber material is 10 to 30 μm.

Optionally, the graphene nanofiber material has a length independently selected from any of 10 μ ι η, 15 μ ι η, 20 μ ι η, 25 μ ι η, 30 μ ι η, 35 μ ι η, 40 μ ι η, 45 μ ι η, 50 μ ι η, or a range of values between any two.

According to a second aspect of the present application, there is provided a method for preparing a graphene nanofiber material, comprising at least the following steps:

obtaining the composite nanofiber with a core-shell structure by using a coaxial electrostatic spinning method by using a spinnable high-molecular solution as an outer-layer fluid and a graphene oxide dispersion liquid as an inner-layer fluid;

and reducing, and removing the shell of the composite nanofiber to obtain the graphene nanofiber material.

Optionally, the solvent in the spinnable polymer solution is at least one selected from water, dimethylformamide DMF, ethanol and acetone;

optionally, the solute in the spinnable polymer solution is selected from at least one of polyvinylpyrrolidone PVP, polyethylene oxide PEO, sodium polyacrylate PAAS, polyacrylonitrile PAN, polyvinyl alcohol PVA, polyvinylidene fluoride PVDF, polymethyl methacrylate PMMA, polylactic acid PLA;

optionally, the mass concentration of the spinnable polymer solution is 1 to 30%.

Optionally, the upper limit of the mass concentration of the spinnable polymer solution is selected from 30%, 25%, 23%, 20%, 15%, 10%, 7.4% or 5%, and the lower limit is selected from 25%, 23%, 20%, 15%, 10%, 7.4%, 5% or 1%.

Optionally, the solvent in the graphene oxide dispersion liquid is selected from at least one of deionized water, N dimethylformamide DMF, and ethanol.

Optionally, the oxygen content of the graphene oxide is 30 to 50wt%.

Optionally, the mass concentration of the graphene oxide dispersion is 0.1 to 0.75wt.%.

Optionally, the mass concentration of the graphene oxide dispersion is independently selected from any of 0.1wt.%, 0.15wt.%, 0.2wt.%, 0.25wt.%, 0.3wt.%, 0.35wt.%, 0.4wt.%, 0.45wt.%, 0.5wt.%, 0.55wt.%, 0.6wt.%, 0.65wt.%, 0.7wt.%, 0.75wt.%, or a range value therebetween.

Optionally, the diameter of the composite nanofiber with the core-shell structure is greater than or equal to 1 μm.

Optionally, the diameter of the composite nanofiber with the core-shell structure is greater than or equal to 800nm.

Optionally, the diameter of the composite nanofiber with the core-shell structure is 800-2000 nm.

Optionally, the diameter of the composite nanofibers of the core-shell structure is independently selected from any value of 800nm, 850nm, 900nm, 950nm, 1000nm, 1050nm, 1100nm, 1150nm, 1200nm, 1300nm, 1400nm, 1500nm, 1600nm, 1700nm, 1800nm, 1900nm, 2000nm or a range value between any two.

Optionally, the reducing comprises chemical reducing or thermal reducing.

Optionally, the chemical reduction comprises:

and adding the composite nano-fiber into a reducing agent solution for reaction.

Optionally, the reducing agent is selected from at least one of hydrazine hydrate, hydrogen iodide, sodium borohydride, ascorbic acid.

Optionally, the solvent of the reducing agent is selected from at least one of deionized water, ethanol, ethylene glycol, glycerol, diethylene glycol, and aliphatic hydrocarbon.

Optionally, the mass concentration of the reducing agent solution is 1 to 50%.

Optionally, the conditions of the reaction include:

the reaction form is hydrothermal reaction;

the hydrothermal reaction temperature is 90-180 ℃;

the hydrothermal reaction time is 1-12 h.

Optionally, the conditions of the reaction include:

the reaction form is hydrothermal reaction;

the hydrothermal reaction temperature is 95-180 ℃;

the hydrothermal reaction time is 1-12 h.

Alternatively, the reaction may also take the form of rotary evaporation.

Optionally, the thermal reduction comprises:

keeping the temperature for 1-6 h at 600-2800 ℃ in an inert atmosphere.

Optionally, removing the outer shell of the composite nanofiber comprises washing or heat removal.

Optionally, the cleaning removal comprises:

cleaning the reduced composite nanofiber by using a solvent;

optionally, the heat removal comprises:

keeping the temperature for 1-6 h at 600-2800 ℃ in an inert atmosphere.

Optionally, the inactive gas of the inactive atmosphere is selected from at least one of nitrogen, argon, helium.

In the application, the composite nano-fiber is subjected to heat preservation for 1-6 hours at 600-2800 ℃ in an inert atmosphere, and thermal reduction and thermal removal can be simultaneously realized. Namely, the reduction of the graphene oxide of the core layer and the outer shell of the composite nanofiber can be simultaneously achieved through high-temperature heat treatment. Optionally, the conditions of the high-temperature heat treatment are as follows: keeping the temperature for 1 to 6 hours at the temperature of 600 to 2800 ℃ in an inert atmosphere.

Optionally, the temperature of the high-temperature heat treatment is 800 to 1500 ℃.

Optionally, the temperature of the high temperature heat treatment is independently selected from any value or a range value between any two of 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃, 1500 ℃, 1600 ℃, 1700 ℃, 1800 ℃, 1900 ℃, 2000 ℃, 2100 ℃, 2200 ℃, 2400 ℃, 2600 ℃, 2800 ℃.

In the application, when the composite nano fiber with the core-shell structure is reduced, the solidification of the core layer graphene oxide fiber is realized. The reduction mode can be chemical reduction or hydrothermal reduction. In the reduced core-shell structure composite nanofiber, the graphene oxide nanofiber on the inner layer is reduced to be solidified, meanwhile, the polymer on the outer layer cannot be changed, and the shell layer can be cleaned by adopting a solvent.

Optionally, specific conditions of the coaxial electrospinning method include:

the spinning voltage is 10-25 KV;

the working distance is 10-25 cm;

the flow rate of the outer layer fluid is 0.06-0.21 ml/min;

the flow rate of the inner layer fluid is 0.03-0.09 ml/min.

Optionally, the spinning voltage is 15KV;

the working distance was 23cm.

Optionally, the ratio of the flow rate of the inner layer fluid to the flow rate of the outer layer fluid is 1.

Optionally, the flow rate of the inner layer fluid is independently selected from any of 0.03ml/min, 0.04ml/min, 0.05ml/min, 0.06ml/min, 0.07ml/min, 0.08ml/min, 0.09ml/min, or a range between any two.

Optionally, the flow rate of the sheath fluid is independently selected from any of 0.06ml/min, 0.08ml/min, 0.1ml/min, 0.12ml/min, 0.14ml/min, 0.15ml/min, 0.16ml/min, 0.18ml/min, 0.20ml/min, 0.21ml/min, or a range between any two.

Optionally, the ratio of the flow rate of the inner layer fluid and the flow rate of the outer layer fluid is independently selected from any or a range of values between 1.

Too high a ratio of internal to external flow rates can result in spinning failures, and too low a ratio can result in too short fibers. During spinning, the flow rate of the inner fluid needs to be adjusted according to the flow rate ratio and by taking the flow rate of the outer fluid as a reference.

According to a third aspect of the present application, there is provided a use of at least one of the graphene nanofiber material described in any one of the above and the graphene nanofiber material prepared by the preparation method described in any one of the above in a potassium ion battery or a nanofiber sensor.

The spinnable polymer as used herein refers to a polymer compound having spinnability.

The beneficial effects that this application can produce include:

this application makes it have higher energy density through arranging graphite alkene orientation in the confined space to compact structure, simultaneously, when this material was used as potassium ion battery electrode, the electrolyte filled forms ion channel behind the macropore between graphite alkene nanofiber, has reduced the diffusion distance and the resistance of ion in the inside of electrode to promote potassium ion battery's power density.

Because the material is reduced from graphene oxide, the surface of the material is provided with a large number of active groups and defect sites. Therefore, the material has certain mechanical strength, good conductivity and chemical stability, and is an excellent material for preparing a sensor.

Drawings

FIG. 1 is a schematic view of a process for preparing core-shell fibers;

FIG. 2 is an SEM image of GO @ PEO composite nanofibers provided in example 1;

fig. 3 is an SEM image of graphene nanofibers provided in example 1;

FIG. 4 is an SEM image of GO @ PVP composite nanofibers provided in example 2;

fig. 5 is an SEM image of graphene nanofibers provided in example 2;

FIG. 6 is an SEM image of GO @ PMMA composite nanofibers provided in example 3;

fig. 7 is an SEM image of graphene nanofibers provided in example 3;

FIG. 8 shows five graphene fibers prepared according to the method of example 1 at 50mA g^-1Comparing the lower constant current charging and discharging curve;

FIG. 9 is a graph comparing rate performance of five graphene fibers prepared according to the method of example 1;

fig. 10 is a SEM of micron-sized graphene fibers provided in comparative example 1;

fig. 11 is a SEM of micron-sized graphene fibers provided in comparative example 2;

fig. 12 is a micron-sized graphene fiber SEM provided in comparative example 3.

Detailed Description

The present application will be described in detail with reference to examples, but the present application is not limited to these examples.

Unless otherwise specified, the raw materials such as PEO, PVP, PMMA, DMF, graphene oxide, etc. described in the present application are purchased from alatin corporation or national institutes of chemicals limited.

Wherein the oxygen content of the graphene oxide is 30-50wt.%.

The analysis method in the examples of the present application is as follows:

SEM analysis was performed using a field emission scanning electron microscope thermal field Sirion200 (SEM 5) from FEI corporation, USA;

and (3) carrying out electrochemical performance test by using a Wuhan blue electric test system.

FIG. 1 is a schematic view of a process for preparing core-shell fibers.

Example 1

Preparation of the outer layer fluid: 1.6g of PEO (Mw: 300000) was weighed out, dissolved in 18.4g of water and stirred at 50 ℃ for 6h to give a clear viscous solution, i.e. a PEO solution (solids ≈ 8 wt.%).

Preparation of inner layer fluid: 48mg of graphene oxide is weighed, 8g of water is added, the mixture is stirred for 6 hours at room temperature and then subjected to ultrasonic dispersion for 3 hours, and a stable graphene oxide dispersion liquid (the solid content is approximately equal to 0.6 wt.%) is obtained.

Coaxial electrostatic spinning: and respectively taking the prepared graphene oxide dispersion liquid as an inner layer fluid and a PEO solution as an outer layer fluid to carry out coaxial electrostatic spinning. The specific spinning operation is as follows: the spinning voltage is set to be 15Kv, and the working distance is 23cm; adjusting the flow rates of the inner layer fluid and the outer layer fluid to be 0.07ml/min and 0.21ml/min respectively; the GO @ PEO composite nanofiber with the core-shell structure and the diameter of about 1 mu m is obtained (the microstructure is shown in figure 2).

Removing outer layer polymers and reducing graphene oxide fibers: the GO @ PEO composite nanofiber is placed in a tubular furnace and treated for 3h under the argon atmosphere (argon flow rate: 105sccm; heating rate: 1 ℃/min; heat preservation temperature: 1000 ℃). The outer layer of polymer PEO is completely decomposed, and the remaining graphene oxide nano-fibers are reduced at high temperature to obtain graphene nano-fibers (the micro-morphology is shown in figure 3), the diameter of which is 300-900nm and the length of which is 10-30 μm.

Example 2

Preparation of outer layer fluid of outer fluid: 1.6g of PVP (Mw: 1300000) were weighed out, dissolved in 18.4g of ethanol and stirred at 60 ℃ for 6h to obtain a clear viscous solution, i.e. a PVP solution (solids content ≈ 8 wt.%).

Preparation of inner fluid and inner fluid: weighing 48mg of graphene oxide, adding 8g of ethanol, stirring for 6 hours at room temperature, and performing ultrasonic dispersion for 3 hours to obtain a stable graphene oxide dispersion liquid (with solid content of 0.6 wt.%).

Coaxial electrostatic spinning: and respectively taking the prepared graphene oxide dispersion liquid as an inner layer fluid and PVP solution as an outer layer fluid to carry out coaxial electrostatic spinning. The specific spinning operation is as follows: the spinning voltage is set to be 15Kv, and the working distance is 23cm; adjusting the flow rates of the inner layer fluid and the outer layer fluid to be 0.05ml/min and 0.15ml/min respectively; the GO @ PVP composite nanofiber with a core-shell structure and the diameter of about 1 mu m is obtained (the microstructure is shown in figure 4).

Removing outer-layer polymers and reducing graphene oxide fibers: the GO @ PVP composite nano-fiber is put into a tubular furnace and treated for 3 hours under the argon atmosphere (argon flow rate: 105sccm; heating rate: 1 ℃/min; heat preservation temperature: 1000 ℃). The outer layer polymer PVP is completely decomposed, and the remained graphene oxide nano-fiber is reduced at high temperature to obtain the graphene nano-fiber (the microstructure is shown in figure 5), the diameter is 300-900nm, and the length is 10-30 μm.

Example 3

Preparation of outer fluid layer fluid: 6g of PMMA (Mw: 120000) was weighed out, dissolved in 14g of DMF and stirred at 50 ℃ for 6h to obtain a clear viscous solution, i.e. a PMMA solution (solids content ≈ 30 wt.%).

Preparing inner fluid and inner layer fluid: weighing 48mg of graphene oxide, adding 8g of DMF, stirring for 6h at room temperature, and performing ultrasonic dispersion for 3h to obtain a stable graphene oxide dispersion liquid (with the solid content of 0.6 wt.%).

Coaxial electrostatic spinning: when the static electric field is 15Kv and the working distance is 23cm; adjusting the flow rate of the inner layer fluid to be 0.06ml/min and the flow rate of the outer layer fluid to be 0.20ml/min; composite nano-fiber GO @ PMMA with a core-shell structure and a diameter of about 1 mu m can be continuously and stably obtained (the micro-morphology is shown in figure 6).

Removing outer layer high polymer and reducing graphene oxide fiber: the GO @ PMMA composite nano-fiber is placed into a 95 ℃ ethylene glycol solution (0.5 g/ml) of hydrazine hydrate to be soaked for 12 hours to complete the reduction and solidification of the inner layer graphene oxide fiber, and then the inner layer graphene oxide fiber is repeatedly washed in DMF for a plurality of times and fully dried. Finally, the sample is placed into a tube furnace and treated for 3 hours under the argon atmosphere (argon flow rate: 105sccm; heating rate: 1 ℃/min; holding temperature: 1000 ℃). The residual outer polymer PMMA is completely decomposed, and the remaining graphene oxide nano-fibers are further reduced at high temperature to obtain graphene nano-fibers (the micro-morphology is shown in figure 7), wherein the diameter is 300-900nm, and the length is 10-30 μm.

Example 4

The internal and external fluid configurations and the coaxial electrospinning process were the same as in example 3, except that the outer polymer was removed and the graphene oxide fibers were reduced:

putting the GO @ PMMA composite nano fiber into deionized water, carrying out hydrothermal treatment at 180 ℃ for 12h to complete reduction and solidification of the inner layer graphene oxide fiber, and then repeatedly washing in DMF for several times and fully drying. Finally, the sample is placed into a tube furnace and treated for 3 hours under the argon atmosphere (argon flow rate: 105sccm; heating rate: 1 ℃/min; holding temperature: 1000 ℃). And (3) completely decomposing the residual outer-layer polymer PMMA, and further reducing the remained graphene oxide nano-fibers at high temperature to obtain the graphene nano-fibers with the diameter of 300-900nm and the length of 10-30 mu m.

Example 5

The internal and external fluid configurations and the coaxial electrospinning process are the same as those in example 1, except that the outer polymer is removed and the graphene oxide fiber is reduced: putting the GO @ PEO composite nanofiber into a sealed container containing saturated hydrogen iodide steam, heating to 100 ℃ and keeping for 12 hours to complete reduction and solidification of the inner layer graphene oxide fiber, and then repeatedly washing in deionized water for several times and fully drying. Finally, the sample is placed into a tube furnace and treated for 3 hours under the argon atmosphere (argon flow rate: 105sccm; heating rate: 1 ℃/min; holding temperature: 1000 ℃). And (3) completely decomposing the residual outer-layer polymer PMMA, and further reducing the remained graphene oxide nano-fibers at high temperature to obtain the graphene nano-fibers with the diameter of 300-900nm and the length of 10-30 mu m.

Example 6

The internal and external fluid configurations and the coaxial electrospinning process are the same as those in example 3, except that the removal of the outer polymer and the reduction of the graphene oxide fiber:

putting the GO @ PMMA composite nano fiber into an aqueous solution of iohydric acid (the mass concentration of the iohydric acid is 5%) at 95 ℃ for hydrothermal reaction for 6h to complete reduction and solidification of the inner-layer graphene oxide fiber, and then repeatedly washing in deionized water for several times and fully drying. Finally, the sample is placed into a tube furnace and treated for 3 hours under the argon atmosphere (argon flow rate: 105sccm; heating rate: 1 ℃/min; holding temperature: 1000 ℃). And (3) completely decomposing the residual outer-layer polymer PMMA, and further reducing the remained graphene oxide nano-fibers at high temperature to obtain the graphene nano-fibers with the diameter of 300-900nm and the length of 10-30 mu m.

Comparative example

Comparative example 1: method for preparing graphene fiber by limited-area hydrothermal method

Such as, for example, the simple furniture of Light, flexible and Multifunctional Graphene fibers, DOI:10.1002/adma.201200170: injecting the graphene oxide dispersion liquid into a glass tube, sealing, and carrying out hydrothermal treatment at 230 ℃ for 2h to obtain the continuous graphene fiber (the diameter is about 30 mu m).

Comparative example 2: wet spinning method for preparing graphene fiber

Wet-spinning of tertiary synthetic coaxial fibers for high performance yarn. DOI:10.1039/c7ta07937k: preparing liquid crystal spinning solution of graphene oxide, and preparing graphene fibers (with the diameter of about 100 microns) by using a wet spinning technology and a chemical reduction mode by using a sodium hydroxide/methanol solution as a coagulating bath.

Comparative example 3: a graphene film grown by Chemical Vapor Deposition (CVD) is transferred into an organic solvent (such as ethanol, acetone and the like) by using a direct drawing self-assembled, porous and monolithic graphene fiber displacement DOI of 10.1021/la202380g, the film is curled and shrunk, and the film is extracted from the solvent by using tweezers, and finally, graphene fibers (the diameter is 20-50 mu m) with a loose porous structure are obtained.

The graphene nanofiber materials provided by the embodiments and the comparative examples of the present application are subjected to morphology characterization:

as shown in fig. 3, 5 and 7, the graphene nanofibers provided in the embodiments 1, 2 and 3 of the present application have a diameter of 300-900nm and a length of 10-30 μm, and other embodiments have the same characteristics;

as shown in FIGS. 10, 11 and 12, the graphene nanofiber material provided by the comparative example has a diameter of 20-100 μm and a length of 1-10cm.

Electrochemical performance tests are performed on the graphene nanofiber materials provided in the embodiments and comparative examples of the present application:

preparation of a test sample:

reduced graphene oxide fibers, designated 600-rGONFs, 800-rGONFs, 1000-rGONFs, 1400-rGONFs, 2800-rGONFs, and the like, after thermal treatment at 600 ℃/800 ℃/1000 ℃/1400 ℃/2800 ℃ were prepared as in example 1. Mixing the prepared reduced graphene oxide fibers, a conductive agent (super-P) and a binder (CMC) according to the mass ratio of 8. The slurry is evenly coated on the surface of a copper foil and dried for 12 hours in vacuum at 120 ℃. Then cutting the copper foil into pole pieces with the diameter of 12mm to obtain test electrodes;

the test method comprises the following steps:

in an argon glove box (H)₂O and O₂All volume fractions of (A) are less than 1X 10^-7) In assembling the CR2016 half-cell. The self-made metal potassium sheet is used as a counter electrode and contains 0.8 mol.L^-1KPF₆EC/DEC (ethylene carbonate/diethyl carbonate =1,v/v) electrolyte and a glass fiber separator. After assembly, the plates were allowed to stand for 12 hours and then tested for electrochemical performance using a blue cell test system.

The prepared button type half cell is tested for specific capacity and rate capability by adopting constant current charging and discharging, and the method specifically comprises the following steps:

(1)50mA·g^-1and (3) testing specific capacity under low current:

at 50mA g on a blue battery test system^-1The current density of the voltage-current constant current charge-discharge long-cycle test is carried out on the button half-cell sample to be tested, the cut-off voltage interval is 0-3V, and as shown in figure 8, the current density is a charge-discharge curve comparison graph. According to the formula: c_ThanSpecific capacity C of sample under the current density can be obtained by = I multiplied by t divided by M_ThanWherein I is the test current, t is the charge/discharge time, and M is the pole piece load mass80% of the total.

(2)800mA·g^-1And (3) testing the specific capacity under large current:

the test method was substantially the same as in (1), except that the test current was 800mA · g^-1。

(3) Rate capability test

Respectively takes 50, 100, 200, 400, 800, 1600, 3200 and 6400 mA.g^-1The current density of the battery is tested for 5 circles of constant current charge and discharge circulation of the button half cell. As shown in fig. 9, a graph comparing the rate performance is shown.

The test results are shown in Table 1

Table 1 is a table of performance parameters of the graphene nanofiber materials prepared into electrodes in each example and comparative example

As can be seen from Table 1, the reduced graphene oxide fibers provided by the present application can provide 345mAh g after reduction at 1400 ℃^-1The specific capacity of (2) is 279mAh & g which exceeds the theoretical capacity^-1. It can be seen that when the electrolyte is filled in the macropores between the graphene nanofibers, an ion channel is formed, and the diffusion distance and resistance of ions in the electrode are reduced, so that the specific capacity and the rate capability of the potassium ion battery are improved.

Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

Claims

1. The graphene nanofiber material is characterized in that the diameter of the graphene nanofiber material is 100-900 nm, and the length of the graphene nanofiber material is greater than or equal to 10 micrometers.

2. The graphene nanofiber material according to claim 1, wherein the graphene nanofiber material is formed by cross-linking reduced graphene oxide nanosheets with each other.

3. The method for preparing the graphene nanofiber material as claimed in claim 1 or 2, characterized by comprising at least the following steps:

obtaining the composite nanofiber with a core-shell structure by using a coaxial electrostatic spinning method by using a spinnable high-molecular solution as an outer-layer fluid and a graphene oxide dispersion liquid as an inner-layer fluid; and reducing, and removing the shell of the composite nanofiber to obtain the graphene nanofiber material.

4. The method according to claim 3, wherein the solvent in the spinnable polymer solution is at least one selected from the group consisting of water, dimethylformamide, ethanol, and acetone;

the solute in the spinnable polymer solution is at least one selected from polyvinylpyrrolidone, polyethylene oxide, sodium polyacrylate, polyacrylonitrile, polyvinyl alcohol, polyvinylidene fluoride, polymethyl methacrylate and polylactic acid;

the mass concentration of the spinnable polymer solution is 1-30%.

5. The preparation method according to claim 3, wherein the solvent in the graphene oxide dispersion liquid is at least one selected from water, N-dimethylformamide, and ethanol;

the mass concentration of the graphene oxide dispersion liquid is 0.1-0.75%.

6. The preparation method according to claim 3, wherein the diameter of the composite nanofiber with the core-shell structure is greater than or equal to 800nm.

7. The production method according to claim 3, wherein the reduction includes chemical reduction or thermal reduction;

preferably, the chemical reduction comprises:

adding the composite nano-fiber into a reducing agent solution for reaction;

preferably, the reducing agent is selected from at least one of hydrazine hydrate, hydrogen iodide, sodium borohydride and ascorbic acid;

preferably, the solvent of the reducing agent solution is at least one selected from deionized water, ethylene glycol, glycerol, diethylene glycol, aliphatic hydrocarbon;

preferably, the mass concentration of the reducing agent solution is 1-50%;

preferably, the conditions of the reaction include:

the reaction form is hydrothermal reaction;

the hydrothermal reaction temperature is 95-200 ℃;

the hydrothermal reaction time is 1-12 h;

preferably, the thermal reduction comprises:

keeping the temperature for 1 to 6 hours at the temperature of 600 to 2800 ℃ in an inert atmosphere.

8. The method according to claim 3, wherein the removing of the outer shell of the composite nanofiber comprises washing removal or heat removal;

preferably, the cleaning removal comprises:

cleaning the reduced composite nanofiber by using a solvent;

preferably, the heat removal comprises:

keeping the temperature for 1-6 h at 600-2800 ℃ in an inert atmosphere.

9. The method for preparing the copolymer according to claim 3, wherein the specific conditions of the coaxial electrospinning method include:

the spinning voltage is 10-25 KV;

the working distance is 10-25 cm;

the flow rate of the outer layer fluid is 0.06-0.21 ml/min;

the flow rate of the inner layer fluid is 0.02-0.10 ml/min;

the ratio of the flow rate of the inner layer fluid to the flow rate of the outer layer fluid is 1 to 1.

10. Use of at least one of the graphene nanofiber material as defined in claim 1 or 2 and the graphene nanofiber material prepared by the preparation method as defined in any one of claims 3 to 9 in a potassium ion battery or a nanofiber sensor.