CN115262035B

CN115262035B - Graphene nanofiber material and preparation method and application thereof

Info

Publication number: CN115262035B
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: 2024-06-04
Anticipated expiration: 2041-04-30
Also published as: CN115262035A

Abstract

The application discloses a graphene nanofiber material, 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 mu m. When the material is used as a negative electrode of a potassium ion battery, an ion channel is formed after electrolyte is filled in a large hole between graphene nanofibers, so that the diffusion distance and resistance of ions in the electrode are reduced, and the specific capacity and rate performance 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 about 13% of lithium), rich reserve (crust abundance of 2.09 wt%), low reduction potential (-2.93V vs. SHE) and the like of potassium, the potassium ion battery is one of the most potential alternatives for lithium ion batteries, and can also form a reversible reaction of intercalation compound KC ₈ with graphite. However, the volume expansion rate of graphite embedded in potassium is as high as 60%, and the internal stress generated by the graphite embedded in potassium is easy to cause cracking and failure of materials, and slow electrochemical dynamic process is caused. Therefore, in potassium ion batteries, the rate capability and cycling stability of graphite negative electrodes are far less than they perform in lithium ion batteries. The graphene nanofiber can better resist the pulverization effect generated by expansion as a flexible material, and meanwhile, the fiber gaps of the graphene nanofiber are used as ion channels after electrolyte is filled, so that the migration distance of potassium in the material can be effectively shortened, and the multiplying power performance is improved. The foam graphene is made of flexible materials, and excessive macropores are contained in the foam graphene to cause space waste, so that the volume energy density is poor; however, the graphene film has poor rate performance because the layered structure thereof causes difficult potassium ion transmission.

The fiber preparation method is wet spinning and a domain-limited hydrothermal method. The diameters of the fibers prepared by the two are in the micron order, and the requirements are difficult to meet. Among them, the carbon electrode double-layer capacitor is a capacitor using carbon material as electrode, and electrostatic spinning is certainly a relatively convenient means for preparing nanofibers on a large scale. Electrospinning is a special fiber manufacturing process in which a polymer solution or melt is spun by spraying in a strong electric field. Under the action of the electric field, the droplet at the needle will change from a sphere to a cone shape (i.e. "taylor cone") and extend from the tip of the cone to obtain a fiber filament. In this way, polymer filaments of nanoscale diameter can be produced. However, graphene oxide nanoplatelets in graphene oxide liquid crystals cannot be crosslinked with each other like a polymer chain, and thus cannot be stretched directly into nanofibers under the action of an electric field.

Disclosure of Invention

In order to solve the problems, the application adopts the coaxial electrostatic spinning technology. Unlike common electrostatic spinning, which is a single system, the coaxial electrostatic spinning is to inject inner fluid and outer fluid solution into two capillaries with different inner diameters and coaxial, which are converged at the end of the nozzle and solidified into composite nano fiber under the action of electric field force. Even though the liquid is non-spinnable liquid such as graphene oxide liquid crystal, the liquid can still be filled in the inner cavity of the tubular nanofiber constructed by the external fluid under the drive of the shearing force between the internal fluid and the external fluid. And then removing the outer polymer, and reducing and solidifying the graphene oxide of the inner layer to obtain the graphene nanofiber.

According to the first aspect of the application, the graphene nanofiber material is provided, and graphene is arranged in a dense structure in a limited space in an oriented manner, 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 ion channel is formed after electrolyte is filled in macropores among graphene nanofibers, so that the diffusion distance and resistance of ions in the electrode are reduced, and the rate performance and the cycling stability of the battery can be improved.

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

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

Optionally, the graphene nanofiber material is formed by completely crosslinking reduced graphene oxide nanoplatelets with each other without any crosslinking agent.

Optionally, the diameter of the graphene nanofiber material is 300-900 nm.

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

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

Optionally, the graphene nanofiber material has a length of 10-30 μm.

Alternatively, the graphene nanofiber material is independently selected from any value or range of values between any two of 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm in length.

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

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

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 at least one selected from polyvinylpyrrolidone PVP, polyethylene oxide PEO, sodium polyacrylate PAAS, polyacrylonitrile PAN, polyvinyl alcohol PVA, polyvinylidene fluoride PVDF, polymethyl methacrylate PMMA and polylactic acid PLA;

optionally, the mass concentration of the spinnability high polymer solution is 1-30%.

Optionally, the upper limit of the mass concentration of the spinnability 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 is at least one selected from deionized water, N dimethylformamide DMF and ethanol.

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

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

Alternatively, the mass concentration of the graphene oxide dispersion is independently selected from any value or range of values between any two 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.％.

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

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

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

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

Optionally, the reduction comprises chemical reduction or thermal reduction.

Optionally, the chemical reduction comprises:

And adding the composite nanofiber into a reducing agent solution for reaction.

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

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

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

Optionally, the reaction conditions include:

the reaction mode is hydrothermal reaction;

The hydrothermal reaction temperature is 90-180 ℃;

the hydrothermal reaction time is 1-12 h.

Optionally, the reaction conditions include:

the reaction mode is hydrothermal reaction;

the hydrothermal reaction temperature is 95-180 ℃;

the hydrothermal reaction time is 1-12 h.

Alternatively, the reaction may also be in the form of rotary evaporation.

Optionally, the thermal reduction comprises:

Under the inactive atmosphere, the temperature is kept between 600 and 2800 ℃ for 1 to 6 hours.

Optionally, the removing the outer shell of the composite nanofiber comprises cleaning or thermal removal.

Optionally, the cleaning and removing includes:

Cleaning the reduced composite nanofiber by using a solvent;

optionally, the heat removal comprises:

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

In the application, the composite nanofiber is subjected to heat preservation for 1-6 hours at 600-2800 ℃ under the inactive atmosphere, so that heat reduction and heat removal can be realized simultaneously. Namely, the reduction of the graphene oxide of the core layer and the shell of the composite nanofiber can be simultaneously realized through high-temperature heat treatment. Optionally, the conditions of the high temperature heat treatment are: under the inactive atmosphere, the temperature is kept between 600 and 2800 ℃ for 1 to 6 hours.

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

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

According to the application, when the composite nanofiber with the core-shell structure is reduced, the solidification of the core-layer graphene oxide fiber is realized. The manner of reduction may be chemical reduction or hydrothermal reduction. The reduced composite nanofiber with the core-shell structure has the advantages that the graphene oxide nanofiber on the inner layer is reduced to be solidified, meanwhile, the polymer on the outer layer cannot be changed, and at the moment, the shell can be cleaned by adopting a solvent.

Optionally, the specific conditions of the coaxial electrospinning method include:

the spinning voltage is 10 KV to 25KV;

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 fluid in the inner layer 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 1:1-1:5.

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

Alternatively, the flow rate of the sheath fluid is independently selected from any value or range of values between any two 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.

Optionally, the ratio of the flow rate of the inner layer fluid to the flow rate of the outer layer fluid is independently selected from any of 1:1, 1:2, 1:3, 1:4, 1:5 or a range of values therebetween.

An excessively large internal-external flow rate ratio may cause spinning failure, and an excessively small internal flow rate ratio may cause fiber to be excessively short. During spinning, the flow rate of the inner fluid needs to be adjusted according to the flow rate ratio by taking the flow rate of the outer fluid as a reference.

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

The spinnability polymer in the present application refers to a polymer compound having spinnability.

The application has the beneficial effects that:

according to the application, the graphene is arranged in a dense structure in a limited space in a directional manner, so that the material has higher energy density, and meanwhile, when the material is applied as a potassium ion battery electrode, an ion channel is formed after electrolyte is filled in macropores among graphene nanofibers, so that the diffusion distance and resistance of ions in the electrode are reduced, and the power density of the potassium ion battery is improved.

Because the material is reduced by 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 the sensor.

Drawings

FIG. 1 is a schematic illustration of a core-shell fiber preparation process;

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 by example 3;

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

FIG. 8 is a graph showing comparison of constant current charge and discharge curves of five graphene fibers prepared according to the method of example 1 at 50mA.g ^-1;

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

FIG. 10 is a SEM of the micro-scale graphene fibers provided by comparative example 1;

FIG. 11 is a SEM of the micro-scale graphene fibers provided by comparative example 2;

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

Detailed Description

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

Unless specifically stated, the raw materials such as PEO, PVP, PMMA, DMF, graphene oxide, and the like in the present application are purchased from Allatin corporation or national pharmaceutical chemicals Co., ltd.

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

The analysis method in the embodiment of the application is as follows:

SEM analysis was performed using a FEI company Sirion, usa, field emission scanning electron microscope thermal field Sirion (SEM 5);

Electrochemical performance testing was performed using the martial blue electric testing system.

FIG. 1 is a schematic illustration of a core-shell fiber preparation flow.

Example 1

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

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

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

Removing outer polymer and reducing graphene oxide fiber: the GO@PEO composite nanofiber is placed into a tube furnace and treated for 3 hours under an argon atmosphere (argon flow rate: 105sccm; heating rate: 1 ℃/min; heat preservation temperature: 1000 ℃). The outer polymer PEO is completely decomposed, and the remained graphene oxide nanofiber is reduced at high temperature to obtain the graphene nanofiber (the microstructure is shown as figure 3), the diameter is 300-900nm, and the length is 10-30 mu m.

Example 2

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

Preparing inner fluid and inner layer fluid: 48mg of graphene oxide was weighed, 8g of ethanol was added and stirred at room temperature for 6 hours, followed by ultrasonic dispersion for 3 hours, to obtain a stable graphene oxide dispersion (solid content 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 15Kv, and the working distance is 23cm; adjusting the flow velocity of the inner and outer fluid to be 0.05ml/min and 0.15ml/min respectively; the GO@PVP composite nanofiber with a core-shell structure and a diameter of about 1 μm is obtained (the microstructure is shown in figure 4).

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

Example 3

Preparing an outer fluid layer fluid: 6g of PMMA (Mw: 120000) was weighed out, dissolved in 14g of DMF and stirred at 50℃for 6 hours to obtain a clear viscous solution, namely PMMA solution (solid content. Apprxeq.30 wt.%).

Preparing inner fluid and inner layer fluid: 48mg of graphene oxide was weighed, 8g of DMF was added and stirred at room temperature for 6 hours, followed by ultrasonic dispersion for 3 hours, to obtain a stable graphene oxide dispersion (solid content 0.6 wt.%).

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

Removing the reduction of the outer layer macromolecule and the graphene oxide fiber: the GO@PMMA composite nanofiber was immersed in a glycol solution (0.5 g/ml) of hydrazine hydrate at 95℃for 12 hours to complete the reduction solidification of the inner graphene oxide fiber, followed by repeated washing in DMF for several times and sufficient 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; heat preservation temperature: 1000 ℃). The residual outer polymer PMMA is completely decomposed, and the remained graphene oxide nanofiber is further reduced at high temperature to obtain the graphene nanofiber (the microstructure is shown in figure 7), wherein the diameter is 300-900nm, and the length is 10-30 mu m.

Example 4

The internal and external fluid configurations and coaxial electrospinning flows were exactly the same as in example 3, except for the removal of the external polymer and reduction of the graphene oxide fibers:

And putting the GO@PMMA composite nanofiber into deionized water, and carrying out hydrothermal treatment at 180 ℃ for 12 hours to finish 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; heat preservation temperature: 1000 ℃). The residual outer polymer PMMA is completely decomposed, and the remained graphene oxide nanofiber is further reduced at high temperature to obtain the graphene nanofiber with the diameter of 300-900nm and the length of 10-30 mu m.

Example 5

The internal and external fluid configurations and coaxial electrospinning flows were exactly the same as in example 1, except for the removal of the external polymer and reduction of the graphene oxide fibers: the GO@PEO composite nanofiber is placed in a sealed container containing saturated hydrogen iodide steam, heated to 100 ℃ and maintained for 12 hours to complete the reduction and solidification of the inner layer graphene oxide fiber, and then repeatedly washed in deionized water 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; heat preservation temperature: 1000 ℃). The residual outer polymer PMMA is completely decomposed, and the remained graphene oxide nanofiber is further reduced at high temperature to obtain the graphene nanofiber with the diameter of 300-900nm and the length of 10-30 mu m.

Example 6

And (3) putting the GO@PMMA composite nanofiber into a 95 ℃ aqueous solution of iodic acid (the mass concentration of the iodic acid is 5%) to perform hydrothermal reaction for 6 hours so as to finish reduction and solidification of the inner-layer graphene oxide fiber, and then repeatedly washing in deionized water for a plurality of 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; heat preservation temperature: 1000 ℃). The residual outer polymer PMMA is completely decomposed, and the remained graphene oxide nanofiber is further reduced at high temperature to obtain the graphene nanofiber with the diameter of 300-900nm and the length of 10-30 mu m.

Comparative example

Comparative example 1: preparation of graphene fiber by finite field hydrothermal method

If Facile Fabrication of Light,Flexible and Multifunctional Graphene Fibers.DOI:10.1002/adma.201200170：, injecting the graphene oxide dispersion liquid into a glass tube, sealing, and performing hydrothermal treatment at 230 ℃ for 2 hours to obtain continuous graphene fibers (with the diameter of about 30 μm).

Comparative example 2: preparation of graphene fiber by wet spinning method

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

Comparative example 3：Directly drawing self-assembled,porous,and monolithic graphene fiber from chemical vapor deposition.DOI:10.1021/la202380g a graphene film grown by Chemical Vapor Deposition (CVD) was transferred to an organic solvent (e.g., ethanol, acetone, etc.), the film was curled and shrunk, and the film was extracted from the solvent with tweezers, finally obtaining graphene fibers (20-50 μm in diameter) having a loose porous structure.

The morphology of the graphene nanofiber material provided by each embodiment and the comparative example is characterized:

As shown in fig. 3, 5 and 7, the graphene nanofibers provided in 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 also have the same characteristics;

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

Electrochemical performance test was performed on graphene nanofiber materials provided in each example and comparative example of the present application:

Test sample preparation:

Reduced graphene oxide fibers after heat treatment at 600 ℃/800 ℃/1000 ℃/1400 ℃/2800 ℃ were prepared as in example 1, and were designated 600-rGONFs, 800-rGONFs, 1000-rGONFs, 1400-rGONFs, 2800-rGONFs, respectively. And mixing the prepared reduced graphene oxide fibers with a conductive agent (super-P) and a binder (CMC) according to a mass ratio of 8:1:1, adding a small amount of deionized water, and fully grinding into slurry. The slurry was uniformly coated on the surface of copper foil and dried in vacuum at 120 ℃ for 12 hours. Then cutting the copper foil into pole pieces with the diameter of 12mm to obtain a test electrode;

The testing method comprises the following steps:

CR2016 half-cells were assembled in an argon glove box (volume fractions of both H ₂ O and O ₂ were lower than 1 x 10 ^-7). The self-made metallic potassium sheet was used as a counter electrode, using an electrolyte containing 0.8 mol.L ^-1KPF₆ of EC/DEC (ethylene carbonate/diethyl carbonate =1:1, v/v) and a glass fiber separator. After assembly, the mixture was allowed to stand for 12 hours and then subjected to electrochemical performance testing using a blue cell testing system.

The specific capacity and the multiplying power performance of the prepared button half battery are tested by adopting constant current charge and discharge, and the method specifically comprises the following steps:

(1) Specific capacity test at 50 mA.g ^-1 small current:

And (3) carrying out constant-current charge-discharge long-cycle test on the button half-cell sample to be tested on the blue-cell test system at the current density of 50mA g ^-1, wherein the cut-off voltage interval is 0-3V, and the cut-off voltage interval is a charge-discharge curve comparison chart as shown in figure 8. According to the formula: c _{Ratio of} = I x t/M the specific capacity of the sample at this current density C _{Ratio of} is obtained where I is the test current, t is the charge/discharge time and M is 80% of the pole piece load mass.

(2) Specific capacity test at 800 mA.g ^-1 high current:

The test method was substantially the same as (1) except that the test current was 800 mA.g ^-1.

(3) Rate capability test

The half-cell was tested for 5 cycles of constant current charge and discharge cycles at current densities of 50, 100, 200, 400, 800, 1600, 3200, 6400 mA.g ^-1, respectively. As shown in fig. 9, a ratio performance comparison chart is shown.

The test results are shown in Table 1

Table 1 shows the performance parameters of the graphene nanofiber materials prepared into electrodes according to the examples and comparative examples

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

While the application has been described in terms of preferred embodiments, it will be understood by those skilled in the art that various changes and modifications can be made without departing from the scope of the application, and it is intended that the application is not limited to the specific embodiments disclosed.

Claims

1. The preparation method of 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 more than or equal to 10 mu m;

The preparation method at least comprises the following steps:

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

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

3. The method according to claim 1, 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 spinnability high 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 spinnability high polymer solution is 1-30%.

4. The method according to claim 1, wherein the solvent in the graphene oxide dispersion is at least one selected from the group consisting of water, N dimethylformamide, and ethanol;

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

5. The method according to claim 1, wherein the diameter of the composite nanofiber of the core-shell structure is 800nm or more.

6. The method of claim 1, wherein the reduction comprises chemical reduction or thermal reduction.

7. The method of preparing according to claim 6, wherein the chemical reduction comprises:

And adding the composite nanofiber into a reducing agent solution for reaction.

8. The method according to claim 7, wherein the reducing agent is at least one selected from hydrazine hydrate, hydrogen iodide, sodium borohydride, and ascorbic acid.

9. The method according to claim 7, wherein the solvent of the reducing agent solution is at least one selected from deionized water, ethylene glycol, glycerin, diethylene glycol, and aliphatic hydrocarbons.

10. The method according to claim 7, wherein the mass concentration of the reducing agent solution is 1 to 50%.

11. The method of claim 7, wherein the reaction conditions include:

the reaction mode is hydrothermal reaction;

The hydrothermal reaction temperature is 95-200 ℃;

the hydrothermal reaction time is 1-12 h.

12. The method of preparing according to claim 6, wherein the thermal reduction comprises:

13. The method of claim 1, wherein the removing the outer shell of the composite nanofiber comprises a cleaning removal or a thermal removal.

14. The method of claim 13, wherein the cleaning and removing comprises:

and cleaning the reduced composite nanofiber by using a solvent.

15. The method of manufacturing according to claim 13, wherein the heat removal comprises:

16. The method according to claim 1, wherein the specific conditions of the coaxial electrospinning method include:

the spinning voltage is 10 KV to 25KV;

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 fluid in the inner layer is 0.02-0.10 ml/min;

The ratio of the flow velocity of the inner layer fluid to the flow velocity of the outer layer fluid is 1:1-1:5.

17. Use of at least one of the graphene nanofiber materials prepared by the preparation method of any one of claims 1-16 in potassium ion batteries and nanofiber sensors.