CN116639682B

CN116639682B - Porous carbon fiber-carbon nanotube three-dimensional network skeleton film and preparation method thereof

Info

Publication number: CN116639682B
Application number: CN202310525225.8A
Authority: CN
Inventors: 张垠; 石倩; 曹坤; 韩锐; 曹开颜; 周超; 王文燕; 杨森
Original assignee: Xian Jiaotong University; Xihua University
Current assignee: Xian Jiaotong University; Xihua University
Priority date: 2023-05-11
Filing date: 2023-05-11
Publication date: 2025-05-06
Anticipated expiration: 2043-05-11
Also published as: CN116639682A

Abstract

The present invention discloses a porous carbon fiber-carbon nanotube three-dimensional network skeleton film and a preparation method thereof, wherein a polyacrylonitrile nanofiber film is prepared by electrostatic spinning, metal ions are adsorbed onto the surface of the polyacrylonitrile nanofiber film, and then the film is pyrolyzed with melamine to obtain the film. The method prepares a porous carbon nanofiber film with multi-walled carbon nanotubes uniformly grown on the surface by electrostatic spinning combined with pyrolysis, and the finally obtained porous carbon fiber-carbon nanotube three-dimensional network skeleton film has a larger specific surface area and excellent electrical properties; the method has the advantages of simple operation, high safety, and low cost, and has good application prospects.

Description

Porous carbon fiber-carbon nanotube three-dimensional network skeleton film and preparation method thereof

Technical Field

The invention belongs to the technical field of nano composite material preparation, and relates to a porous carbon fiber-carbon nano tube three-dimensional network skeleton film and a preparation method thereof.

Background

The portable electronic product has the trend of light weight, thin thickness and flexibility, and the development of the flexible electrode material which has high multiplying power performance, high energy density, light weight, thinness and flexibility is urgent in order to meet the energy storage requirement of the portable electronic product.

The most typical flexible electrode material is carbon nanofiber, and the carbon nanofiber has the advantages of large specific surface area, simple preparation method, good mechanical property, low production cost and the like, and has wide application in the fields of electrode materials, sensors, fiber composite reinforced materials, catalyst carriers, hydrogen storage and the like. The three-dimensional network structure formed by interweaving the carbon nanofibers improves the flexibility of the electrode, can be directly used as a negative electrode of a lithium ion battery, does not need to be added with a binder, and is beneficial to improving the quality of an active material. In addition, carbon nanofibers have low crystallinity and many defects and functional groups, and can provide sufficient reactive sites for adsorption of lithium ions. However, the presence of defects also inevitably reduces the initial coulombic efficiency and conductivity of the carbon nanofibers.

Compared with carbon nano-fibers, the carbon nano-tubes have high graphitization degree, higher conductivity and structural stability, and can accelerate the transmission of electrons. In addition, the large specific surface area of the carbon nano tube is also beneficial to diffusion and permeation of the electrolyte. Therefore, if the combined carbon nanofibers have sufficient reactive site characteristics and high conductivity of the carbon nanotubes, it would be expected to obtain a flexible carbon negative electrode material having excellent lithium ion storage properties. At present, concentrated acid is often used for carrying out surface treatment on carbon fibers, the specific surface area is increased so as to deposit a catalyst for carbon nanotube growth, and the method is tedious and has poor safety. In addition, toxic liquid carbon sources and catalyst precursor solutions are generally used when carbon nanotubes are grown on the surfaces of carbon fibers in situ, and health risks exist. Therefore, it is important to develop a simple method for in-situ growth of carbon nanotubes on the surface of carbon fibers.

Disclosure of Invention

In order to overcome the problems, the inventor has conducted intensive researches and researches on a porous carbon fiber-carbon nano tube three-dimensional network skeleton film and a preparation method thereof, wherein a polyacrylonitrile nano fiber film is prepared through electrostatic spinning, metal ions are adsorbed to the surface of the polyacrylonitrile nano fiber film, and then the polyacrylonitrile nano fiber film and melamine are subjected to pyrolysis to prepare the polyacrylonitrile nano fiber film. The method prepares the porous carbon nanofiber membrane with the surface uniformly growing the multi-wall carbon nanotubes by combining an electrostatic spinning method with pyrolysis, particularly the treatment of a metal salt solution, so that the prepared porous carbon fiber-carbon nanotube three-dimensional network skeleton membrane has larger specific surface area and excellent electrical performance,

The method has the advantages of simple operation, high safety and low cost, and has good application prospect, thereby completing the invention.

In particular, it is an object of the present invention to provide the following aspects:

in a first aspect, a method for preparing a porous carbon fiber-carbon nanotube three-dimensional network skeleton film is provided, the method comprising:

Step 1, preparing a polyacrylonitrile nanofiber film;

Step 2, modifying the polyacrylonitrile nanofiber membrane by utilizing metal ions to obtain a modified polyacrylonitrile nanofiber membrane;

And step 3, pyrolyzing the modified polyacrylonitrile nanofiber membrane to obtain the porous carbon fiber-carbon nanotube three-dimensional network skeleton membrane.

Wherein in step 1, the polyacrylonitrile nanofiber membrane contains zinc salt.

Wherein, the step1 comprises the following substeps:

step 1-1, adding zinc salt and polyacrylonitrile into a polar solution, and stirring to obtain a spinning precursor;

Step 1-2, carrying out electrostatic spinning on the spinning precursor to obtain a pretreated polyacrylonitrile nanofiber film;

And step 1-3, performing pre-oxidation treatment on the pre-treated polyacrylonitrile nanofiber membrane to obtain the polyacrylonitrile nanofiber membrane.

In the step 1-1, the polar solvent is any one or more of dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide, sodium thiocyanate and sulfolane, preferably dimethyl sulfoxide, N-dimethylformamide or N, N-dimethylacetamide.

In the step 1-3, the pre-oxidation temperature is 200-300 ℃, and the pre-oxidation time is 0.5-3 h.

In step2, the metal ion is a transition metal ion, preferably one or more selected from cobalt ion, iron ion and nickel ion.

In the step 3, the pyrolysis temperature is 800-1200 ℃, and the pyrolysis time is 1-5 h.

In a second aspect, there is provided a porous carbon fiber-carbon nanotube three-dimensional network skeletal film produced according to the method of the first aspect.

The thickness of the film is 400-900 mu m, the specific surface area is 450-520 m ²/g, and the diameter of the carbon nano tube in the film is 24-35 nm.

In a third aspect, a flexible electrode material is provided, which comprises the porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared by the method in the first aspect.

The invention has the beneficial effects that:

(1) The preparation method of the porous carbon fiber-carbon nanotube three-dimensional network skeleton film is simple and high in safety, and the porous carbon nanofiber with the surface uniformly growing with the multi-wall carbon nanotubes is prepared by pyrolyzing the melamine and the modified polyacrylonitrile nanofiber film, so that the porous carbon fiber has a larger specific surface area and a more excellent specific capacity.

(2) According to the preparation method of the porous carbon fiber-carbon nanotube three-dimensional network skeleton film, the lithium ion storage performance is remarkably improved, and the specific charge capacity reaches 240-290 mAh g ^-1 after 100 cycles under the current of 2A g ^-1.

(3) The porous carbon fiber-carbon nanotube three-dimensional network skeleton film provided by the invention has the advantages of high reliability, strong repeatability, good application prospect and environment friendliness.

Drawings

Various other advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. It is evident that the figures described below are only some embodiments of the invention, from which other figures can be obtained without inventive effort for a person skilled in the art.

In the drawings:

FIG. 1 (a) is a SEM image of a polyacrylonitrile nanofiber membrane prepared in example 1;

FIG. 1 (b) shows an SEM image of CFs@CNT-1 of example 1;

FIG. 2 shows an SEM image of a modacrylic nanofiber film of example 1;

FIG. 3 shows a TEM image of a carbon nanotube at the surface of CFs@CNT-1 of example 1;

FIG. 4 shows a BET-isothermal adsorption/desorption graph of CFs@CNT-1 in example 1;

FIG. 5 shows a graph of the specific capacity of CFs@CNT-1 over 100 cycles in example 1.

Detailed Description

Specific embodiments of the present invention will be described in more detail below with reference to fig. 1 (a) to 5. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

It should be noted that certain terms are used throughout the description and claims to refer to particular components. Those of skill in the art will understand that a person may refer to the same component by different names. The description and claims do not identify differences in terms of components, but rather differences in terms of the functionality of the components. As used throughout the specification and claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. The description hereinafter sets forth a preferred embodiment for practicing the invention, but is not intended to limit the scope of the invention, as the description proceeds with reference to the general principles of the description. The scope of the invention is defined by the appended claims.

For the purpose of facilitating an understanding of the embodiments of the present invention, reference will now be made to the drawings, by way of example, and specific examples of which are illustrated in the accompanying drawings.

In a first aspect, the present invention provides a method for preparing a porous carbon fiber-carbon nanotube three-dimensional network skeleton film, the method comprising:

and step 1, preparing the polyacrylonitrile nanofiber membrane.

According to a preferred embodiment, the polyacrylonitrile nanofiber membrane contains zinc salt, and further, the step 1 comprises the following substeps:

Wherein in step 1-1 the zinc salt is preferably selected from zinc acetate and/or zinc nitrate, more preferably zinc acetate. When zinc acetate and zinc nitrate react at a certain temperature, other ions which affect the reaction are not generated.

In the invention, the micro-size of the polyacrylonitrile nanofiber membrane prepared from zinc salt is more uniform, and the size is easy to regulate and control. The inventors have found that zinc salts have a large effect on the diameter of polyacrylonitrile nanofiber membranes. While the amount of zinc salt is increased, the diameter of the prepared polyacrylonitrile nanofiber membrane is reduced, and the inventor believes that the diameter of the prepared polyacrylonitrile nanofiber membrane is increased due to the fact that the added zinc salt such as zinc acetate increases, the conductivity of the solution is increased, the electrostatic repulsive force acting on the solution is increased, and as the amount of zinc salt is continuously increased, the viscosity of a spinning precursor is increased due to the fact that the viscosity of the spinning precursor is increased, the surface tension is increased due to the increase of the viscosity, the instability of jet flow is reduced, and the diameter of the prepared polyacrylonitrile nanofiber membrane is increased.

Preferably, the addition amount of the zinc salt is 0.1-0.4 mol/L, more preferably, the addition amount of the zinc salt is 0.2-0.3 mol/L, for example, the addition amount of the zinc salt is 0.23mol/L.

In the invention, the concentration of the polyacrylonitrile is too high, so that the viscosity of the solution is too high, the spinneret orifices are easily blocked in the later electrostatic spinning process to interrupt the electrostatic spinning process, the concentration of the polyacrylonitrile is low, the sprayed spinning trickle is easily interrupted or adhered, and the compactness of the generated polyacrylonitrile nanofiber film is poor. The polyacrylonitrile with proper concentration can increase the viscosity of the spinning precursor, so that the precursor can bear larger tensile strength, the crystallinity is improved, and the performance of the obtained polyacrylonitrile nanofiber film is better.

Wherein the concentration of the polyacrylonitrile is 8wt% to 15wt%, preferably 9wt% to 12wt%, for example 10wt%, and the average molecular weight of the polyacrylonitrile is 90000 to 150000, for example 130000.

In step 1-1, the polar solvent is any one or more of dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide, sodium thiocyanate and sulfolane, preferably dimethyl sulfoxide, N-dimethylformamide or N, N-dimethylacetamide, more preferably N, N-dimethylformamide.

In the step 1-1, polyacrylonitrile is dissolved in a polar solvent to obtain a uniform solution, which is favorable for obtaining the uniformly spun polyacrylonitrile nanofiber thin. The polar solvent content is required to be relatively low, and the volatilization speed is high in the electrostatic spinning process, so that the subsequent solidification and filament forming speed is increased. The polyacrylonitrile is dissolved in the polar solvent with the concentration range, so that the effect is better.

In step 1-1, stirring is performed at a certain temperature, so that stirring time can be shortened, and a uniform solution can be obtained. The stirring temperature is 50-80 ℃, preferably 60-75 ℃, such as 70 ℃, and the stirring time is 1-3 h, preferably 1.5-2.5 h, such as 2h.

In the invention, electrostatic spinning has become one of the main ways to effectively prepare nanofiber materials because of the advantages of simple manufacturing device, low spinning cost, various spinnable substances, controllable process and the like. The parameters of electrostatic spinning have certain influence on the diameter, morphology and structure of the pretreated polyacrylonitrile nanofiber membrane, and the preparation of the pretreated polyacrylonitrile nanofiber membrane with good morphology becomes one of factors for the subsequent preparation of the porous carbon fiber-carbon nanotube three-dimensional network skeleton membrane.

In the step 1-2, the electrostatic spinning process conditions are that the voltage is 9-15 kV, preferably 11kV, and the receiving distance (the distance between the needle head and the collecting plate) is 10-15 cm, preferably 12cm.

In the step 1-3, in the preoxidation process, a series of cyclization, oxidation, dehydrogenation and other reactions are carried out on the polyacrylonitrile molecular chain to form a cyclization structure, so that the linear macromolecular chain of the thermoplastic polyacrylonitrile is converted into the polyacrylonitrile-based carbon fiber preoxidized yarn with a non-plastic heat-resistant trapezoid structure. The non-plastic heat-resistant trapezoid structure ensures that the obtained pre-oxidized fiber is not melted and not burnt in the subsequent high-temperature carbonization, keeps the fiber form and is in a stable state in thermodynamics, plays a role in fixing oxygen and carbon for the carbonization process, and is beneficial to improving the mechanical property of the carbon fiber. Preoxidation is a process for determining the performance of the polyacrylonitrile nanofiber membrane, and is also an important step for evaluating the quality of the polyacrylonitrile nanofiber membrane, so that the preoxidation is very important.

When the oxidation temperature is higher, the oxidation degree of the fiber of the prepared polyacrylonitrile nanofiber film is higher, the skin-core structure of the fiber of the polyacrylonitrile nanofiber film is easy to cause the formation of defects, and the strength of the carbon fiber is reduced.

Wherein the pre-oxidation temperature is 200-300 ℃, preferably 230-280 ℃, such as 250 ℃, the pre-oxidation time is 0.5-3 h, preferably 1-2.5 h, such as 2h, and the pre-oxidation heating rate is 2-10 ℃, preferably 3-7 ℃, such as 5 ℃.

And 2, modifying the polyacrylonitrile nanofiber membrane by utilizing metal ions to obtain the modified polyacrylonitrile nanofiber membrane.

In the step 2, metal ions are adsorbed to the surface of the polyacrylonitrile nanofiber membrane, so that the modified polyacrylonitrile nanofiber membrane is obtained. The metal ion is a transition metal ion, preferably one or more selected from cobalt ion, iron ion and nickel ion, more preferably cobalt ion and/or iron ion, for example cobalt ion.

In step 2, a metal salt is dissolved in the solution to obtain a metal salt solution, and metal ions in the metal salt solution are further adsorbed on the surface of the polyacrylonitrile nanofiber membrane, wherein the metal salt is a transition metal salt, preferably one or more selected from cobalt salts such as cobalt acetate and cobalt nitrate, iron salts such as ferric nitrate and ferric acetate, nickel salts such as nickel nitrate and nickel acetate, more preferably cobalt salt or iron salt, and most preferably cobalt salt, for example cobalt acetate. The concentration of the metal salt in the metal salt solution is 0.04-2 mol/L, preferably 0.05-1.5 mol/L, and more preferably 0.05mol/L.

According to the invention, when the concentration of the metal salt in the metal salt solution is too high, the metal ions and/or the metal salt attached to the surface can cause excessive growth of the carbon nano tube so as to damage the original three-dimensional network structure inside the polyacrylonitrile nano fiber, and when the concentration is too low, the internal fiber of the polyacrylonitrile nano fiber cannot be connected through the nano tube, or the finally generated carbon nano tube is sparse, so that the density of the finally prepared porous carbon fiber-carbon nano tube three-dimensional network skeleton film is influenced.

In the present invention, the inventors have found that, after the polyacrylonitrile nanofiber membrane is modified with a metal salt solution, metal ions such as iron ions, cobalt ions, etc. are uniformly attached to the surface of the polyacrylonitrile nanofiber membrane, and the metal ions form metal nanoparticles such as iron nanoparticles, cobalt nanoparticles, etc. during the later pyrolysis process, which not only play a role of a catalyst such as accelerating the reaction, but also more particularly promote the growth of carbon nanotubes, thereby imparting excellent electrical properties to the porous carbon fiber-carbon nanotube three-dimensional network skeleton membrane, but also do not naturally have electrical properties, or are not suitable for use as a negative electrode material for lithium ion storage, if the polyacrylonitrile nanofiber membrane is not subjected to the modification treatment.

Further, the solvent used for dissolving the metal salt may be water which is inexpensive and easily available.

In the step 2, the modification treatment comprises soaking, the longer the soaking time is, the more metal ions are adsorbed on the polyacrylonitrile nanofiber membrane, but the longer the soaking time is, the less the influence on the amount of the metal ions adsorbed on the polyacrylonitrile nanofiber membrane is. The soaking time is 12-48 hours, preferably 18-36 hours, and more preferably 24 hours.

In step 2, according to a preferred embodiment, the soaked polyacrylonitrile nanofiber membrane is further dried to facilitate carbonization of the post-modified polyacrylonitrile nanofiber membrane. The drying may be carried out at 50-100 ℃ for 12-24 hours, for example at 50 ℃ for 24 hours.

In step 3, one or more of melamine, glucose and polystyrene are also added during pyrolysis, preferably melamine.

In step 3, the fiber internal structure of the modified polyacrylonitrile nanofiber membrane is subjected to pyrolysis or carbonization, so that a layered graphite-like structure is formed, and the fiber is greatly contracted. The melamine melt decomposition causes shrinkage and collapse of the nano carbon fiber, so that the nano fiber is flattened, bonded and crosslinked to form a three-dimensional network structure, various mesoporous and macroporous with different sizes are generated, meanwhile, as metal ions form metal nano particles in the pyrolysis process, the growth of the carbon nano tube is promoted, the overlap area of the nano fiber in the network is further promoted to be increased, the contact resistance is reduced, the contact passage is increased, a good continuous conductive network structure is provided, the electron conductivity is enhanced, and finally the resistance of the porous carbon fiber-carbon nano tube three-dimensional network skeleton film is greatly reduced, so that the electrochemical characteristics of the electrode are improved.

In step3, the melamine is pyrolyzed under the protection of an inert gas such as argon, and the melamine is placed upstream of the inert gas, and the modified polyacrylonitrile nanofiber membrane is placed downstream.

In the step 3, the polymer which is not cyclized in the pre-oxidation process is cyclized continuously or pyrolyzed to release small molecular gas products such as HCN, NH ₃、H₂、H₂O、CH₄、CO₂ and the like in the initial carbonization stage, along with the rising of the temperature, the structural unit starts to crosslink and polycondensate, and along with the pyrolysis, a plurality of small molecular byproducts are released, the structure of the polymer in the fiber is gradually changed into the structure of polycrystalline carbon, so that non-carbon elements such as oxygen, nitrogen and the like are gradually expelled, and finally the carbon fiber with the lamellar graphite structure is generated. If the carbonization temperature is too high, nitrogen element is largely removed in the form of N ₂, so that the carbon fiber pores are increased, and the performance of the prepared porous carbon fiber-carbon nano tube three-dimensional network skeleton film is reduced.

The pyrolysis temperature is 800-1200 ℃, preferably 900-1000 ℃, more preferably 1000 ℃, the pyrolysis time is 1-5 h, preferably 2-4 h, more preferably 2h, and the pyrolysis heating rate is 0.5-3 ℃, preferably 1-2 ℃ per minute, more preferably 2 ℃.

Further, when the pyrolysis temperature is low, the grown carbon nanotubes are short and sparse, and the too fast or too slow temperature rising rate directly determines whether the carbon nanotubes are generated in the pyrolysis process. In the above parameter range, the prepared porous carbon fiber-carbon nano tube three-dimensional network skeleton film has excellent physical properties.

In a second aspect, the invention provides the porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared by the preparation method according to the first aspect, wherein the thickness of the film is 400-900 μm, the specific surface area is 450-520 m ²/g, the diameter of the carbon nanotube is about 24-35 nm, and the specific charge capacity reaches 240-290 mAh g ^-1 after 100 cycles under the current of 2-A g ^-1.

In a third aspect, a flexible electrode material comprises the porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared by the method of the first aspect.

Examples

The invention is further described below by means of specific examples, which are however only exemplary and do not constitute any limitation on the scope of protection of the invention.

Example 1

(1) Adding 0.5g of zinc acetate and 1g of polyacrylonitrile with the average molecular weight of 130000 into 10mL of N, N-dimethylformamide, heating and stirring to dissolve the zinc acetate and the polyacrylonitrile, wherein the stirring time is 2h, and the stirring temperature is 70 ℃ to obtain a spinning precursor;

Transferring the spinning precursor into a syringe with a stainless steel needle for electrostatic spinning, wherein the voltage of the electrostatic spinning is 11kV, the distance between the needle and a collecting plate is 12cm, and the spinning is finished to obtain the pretreated polyacrylonitrile nanofiber film;

Then, collecting the pretreated polyacrylonitrile nanofiber membrane on an aluminum foil, and preserving heat for 1h at 250 ℃ for pre-oxidation treatment, wherein the temperature rising rate during pre-oxidation is 5 ℃ per minute, so that the polyacrylonitrile nanofiber membrane is prepared, the SEM of the polyacrylonitrile nanofiber membrane is shown as a figure 1 (a), and the prepared polyacrylonitrile nanofiber membrane consists of a large number of nanofibers, and the diameter of the polyacrylonitrile nanofiber membrane is 300-400 nm;

(2) Immersing the polyacrylonitrile nanofiber membrane in 0.05mol/L cobalt acetate aqueous solution for 24 hours, and then drying at 50 ℃ for 24 hours to obtain a modified polyacrylonitrile nanofiber membrane, wherein SEM (scanning electron microscope) characterization is shown as in figure 2, and cobalt ions are adhered to the surface of the polyacrylonitrile nanofiber membrane;

(3) A piece of modified polyacrylonitrile nanofiber membrane (2.3 g) was cut, and placed in a quartz boat together with 100mg of melamine, and pyrolyzed under Ar protection. The pyrolysis temperature is 1000 ℃, the time is 2h, the heating rate is 2 ℃ per minute, the porous carbon fiber-carbon nano tube three-dimensional network skeleton film is obtained and is marked as CFs@CNT-1, and the thickness of the prepared CFs@CNT-1 is 500 mu m.

The SEM image of CFs@CNT-1 is shown in FIG. 1 (b), and the final step3 is shown in FIG. 1 (a) and FIG. 1 (b), wherein the carbon nanotubes uniformly grow on the surface of the fiber to form the porous carbon fiber-carbon nanotube three-dimensional network skeleton film.

Fig. 3 shows a TEM image of carbon nanotubes on the surface of cfs@cnt-1 carbon nanofibers, and it can be seen that most of the carbon nanotubes are multi-walled carbon tubes, and the diameter of the carbon nanotubes is 24-35 nm.

FIG. 4 shows a BET-isothermal adsorption/desorption graph of CFs@CNT-1, in which curve 1 represents an adsorption curve and curve 2 represents a desorption curve, and it is apparent from FIG. 3 that CFs@CNT-1 exhibits a typical type IV adsorption/desorption isotherm, a type H4 hysteresis loop, and the surface area of CFs@CNT-1 reaches 485.15m ² g^-1.

When CFs@CNT-1 is subjected to 100 cycles under the current of 2A g ^-1, the charge-discharge curve is shown in FIG. 5, and it can be seen that the initial specific discharge capacity of CFs@CNT-1 is 491.3mAh g ^-1, the specific charge capacity is 372.2mAh g ^-1, the corresponding initial coulomb efficiency is 75%, after 100 cycles, the specific discharge capacity is 276.7mAh g ^-1, the specific charge capacity is 274.7mAh g ^-1, and compared with the initial specific charge capacity, the capacity retention rate is about 74%.

Example 2

A porous carbon fiber-carbon nanotube three-dimensional network skeletal film was prepared in a similar manner to example 1, except that in step (3), melamine was 200mg.

Finally, the prepared porous carbon fiber-carbon nano tube three-dimensional network skeleton film is marked as CFs@CNT-2.

The CFs@CNT-2 prepared by the method is subjected to 100 cycles under the current of 2A g ^-1, and the result shows that the initial discharge specific capacity of the CFs@CNT-2 is 501.7mAh g ^-1, the specific charge capacity is 371.3mAh g ^-1 and the corresponding initial coulomb efficiency is 74%, after 100 cycles, the discharge specific capacity is 259.5mAh g ^-1, the specific charge capacity is 250.1mAh g ^-1, and compared with the initial charge specific capacity, the capacity retention rate is about 67%.

Comparative example

Comparative example 1

A porous carbon fiber-carbon nanotube three-dimensional network skeleton film was prepared in a similar manner to example 1 except that the polyacrylonitrile nanofiber film was not immersed in the aqueous cobalt acetate solution, and as a result, it was found that no carbon nanotubes were grown on the surface of the final porous carbon fiber.

It is shown by example 1 and comparative example 1 that transition metals such as cobalt are catalysts for carbon nanotube growth on the surface of carbon nanofibers.

The invention has been described in detail with reference to preferred embodiments and illustrative examples. It should be noted, however, that these embodiments are merely illustrative of the present invention and do not limit the scope of the present invention in any way. Various improvements, equivalent substitutions or modifications can be made to the technical content of the present invention and its embodiments without departing from the spirit and scope of the present invention, which all fall within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims

1. A method for preparing a porous carbon fiber-carbon nanotube three-dimensional network skeleton film, which is characterized by comprising the following steps:

Step 1, preparing a polyacrylonitrile nanofiber film;

step 3, pyrolyzing the modified polyacrylonitrile nanofiber membrane to obtain the porous carbon fiber-carbon nanotube three-dimensional network skeleton membrane;

said step 1 comprises the sub-steps of:

Step 1-3, performing pre-oxidation treatment on the pre-treated polyacrylonitrile nanofiber membrane to obtain the polyacrylonitrile nanofiber membrane;

Wherein,

The metal ions are transition metal ions, and the transition metal ions are one or more selected from cobalt ions, iron ions and nickel ions;

one or more of melamine, glucose and polystyrene are also added during pyrolysis.

2. The method according to claim 1, wherein in step 1-1, the polar solvent is any one or more of dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide, sodium thiocyanate, and sulfolane.

3. The method according to claim 2, wherein the polar solvent is dimethyl sulfoxide, N-dimethylformamide or N, N-dimethylacetamide.

4. The method according to claim 2, wherein in step 1-3, the pre-oxidation is performed at a temperature of 200-300 ℃ for a time of 0.5-3 hours.

5. The method according to claim 1, wherein in step 3, the pyrolysis temperature is 800 to 1200 ℃ and the pyrolysis time is 1 to 5 hours.

6. A porous carbon fiber-carbon nanotube three-dimensional network skeletal film made by the method of any one of claims 1 to 5.

7. The three-dimensional network skeleton membrane of porous carbon fiber-carbon nanotube according to claim 6, wherein the thickness of the membrane is 400-900 μm, the specific surface area is 450-520 m ²/g, and the diameter of the carbon nanotube in the membrane is 24-35 nm.

8. A flexible electrode material comprising the porous carbon fiber-carbon nanotube three-dimensional network skeletal film produced by the method of any one of claims 1 to 5.