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

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

Technical Field

[0001] The invention belongs to the technical field of nano composite material preparation, and relates to a porous carbon fiber-carbon nanotube three-dimensional network skeleton film and a preparation method thereof. Background Art

[0002] Light weight, thin thickness and bendability are the development trends of portable electronic products. In order to meet the energy storage needs of portable electronic products, it is urgent to develop flexible electrode materials with high rate performance, high energy density, lightness, thinness and bendability.

[0003] Among them, the most typical flexible electrode material is carbon nanofiber. Carbon nanofiber has many advantages such as large specific surface area, simple preparation method, good mechanical properties, low production cost, etc. It is widely used in electrode materials, sensors, fiber composite reinforced materials, catalyst carriers, hydrogen storage and other fields. The three-dimensional network structure interwoven by carbon nanofibers improves the flexibility of the electrode and can be directly used as the negative electrode of lithium-ion batteries without adding binders, which is beneficial to improve the quality of active materials. In addition, carbon nanofibers have low crystallinity and many defects and functional groups, which can provide sufficient reactive sites for the adsorption of lithium ions. However, the presence of defects will inevitably reduce the initial Coulomb efficiency and conductivity of carbon nanofibers.

[0004] Compared with carbon nanofibers, carbon nanotubes have a high degree of graphitization, high conductivity and structural stability, and can accelerate the transmission of electrons. In addition, the large specific surface area of ​​carbon nanotubes is also conducive to the diffusion and penetration of electrolytes. Therefore, if the characteristics of carbon nanofibers with sufficient reactive active sites and the high conductivity of carbon nanotubes are combined, it will be expected to obtain flexible carbon negative electrode materials with excellent lithium ion storage performance. At present, concentrated acid is often used to treat the surface of carbon fibers to increase the specific surface area in order to deposit catalysts for the growth of carbon nanotubes. This method is cumbersome and has poor safety. In addition, when carbon nanotubes are grown in situ on the surface of carbon fibers, toxic liquid carbon sources and catalyst precursor solutions are generally used, which poses a health hazard. Therefore, it is particularly important to develop a simple method for growing carbon nanotubes in situ on the surface of carbon fibers. Summary of the invention

[0005] In order to overcome the above problems, the inventors have conducted intensive research and developed a porous carbon fiber-carbon nanotube three-dimensional network skeleton film and a preparation method thereof, wherein a polyacrylonitrile nanofiber film is prepared by electrospinning, 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 uses electrospinning combined with pyrolysis to prepare a porous carbon nanofiber film with multi-walled carbon nanotubes uniformly grown on the surface, especially the treatment with a metal salt solution, so that the prepared porous carbon fiber-carbon nanotube three-dimensional network skeleton film has a larger specific surface area and excellent electrical properties; the method,

[0006] The method has the advantages of simple operation, high safety and low cost and has good application prospects, thus completing the present invention.

[0007] Specifically, the purpose of the present invention is to provide the following aspects:

[0008] In a first aspect, a method for preparing a porous carbon fiber-carbon nanotube three-dimensional network skeleton film is provided, the method comprising:

[0009] Step 1, preparing a polyacrylonitrile nanofiber film;

[0010] Step 2, modifying the polyacrylonitrile nanofiber film using metal ions to obtain a modified polyacrylonitrile nanofiber film;

[0011] Step 3: pyrolyze the modified polyacrylonitrile nanofiber film to obtain the porous carbon fiber-carbon nanotube three-dimensional network skeleton film.

[0012] Wherein, in step 1, the polyacrylonitrile nanofiber film contains zinc salt.

[0013] Wherein, the step 1 includes the following sub-steps:

[0014] Step 1-1, adding zinc salt and polyacrylonitrile to a polar solution and stirring to obtain a spinning precursor;

[0015] Step 1-2, electrospinning the spinning precursor to obtain a pretreated polyacrylonitrile nanofiber film;

[0016] Step 1-3, pre-oxidation treatment is performed on the pretreated polyacrylonitrile nanofiber membrane to obtain the polyacrylonitrile nanofiber membrane.

[0017] Wherein, in step 1-1, the polar solvent is any one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, sodium thiocyanate, and sulfolane, preferably dimethyl sulfoxide, N,N-dimethylformamide or N,N-dimethylacetamide.

[0018] Wherein, in step 1-3, the pre-oxidation temperature is 200-300° C., and the pre-oxidation time is 0.5-3 h.

[0019] Wherein, in step 2, the metal ion is a transition metal ion, preferably one or more selected from cobalt ion, iron ion and nickel ion.

[0020] Wherein, in step 3, the pyrolysis temperature is 800-1200° C., and the pyrolysis time is 1-5 hours.

[0021] In a second aspect, a porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared according to the method described in the first aspect is provided.

[0022] The film has a thickness of 400 to 900 μm and a specific surface area of ​​450 to 520 m 2 / g, and the diameter of the carbon nanotubes in the film is 24-35nm.

[0023] In a third aspect, a flexible electrode material is provided, comprising a porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared by the method described in the first aspect.

[0024] The beneficial effects of the present invention include:

[0025] (1) The preparation method of the porous carbon fiber-carbon nanotube three-dimensional network skeleton film provided by the present invention is simple and highly safe. By pyrolyzing melamine and modified polyacrylonitrile nanofiber film, porous carbon nanofibers with multi-walled carbon nanotubes uniformly grown on the surface are obtained, which have a larger specific surface area and better specific capacity.

[0026] (2) The preparation method of the porous carbon fiber-carbon nanotube three-dimensional network skeleton film provided by the present invention significantly improves the lithium ion storage performance at 2A g -1 After 100 cycles under current, the charge capacity reaches 240~290mAh g -1 .

[0027] (3) The porous carbon fiber-carbon nanotube three-dimensional network skeleton film provided by the present invention has high reliability, strong repeatability, good application prospects and is green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only used for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work.

[0029] In the attached picture:

[0030] Figure 1 (a) shows a SEM image of the polyacrylonitrile nanofiber film prepared in Example 1;

[0031] Figure 1 (b) shows the SEM image of CFs@CNT-1 in Example 1;

[0032] Figure 2The SEM image of the modified polyacrylonitrile nanofiber film in Example 1 is shown;

[0033] Figure 3 The carbon nanotube TEM image of the surface of CFs@CNT-1 in Example 1 is shown;

[0034] Figure 4 The BET-isothermal adsorption-desorption curve of CFs@CNT-1 in Example 1 is shown;

[0035] Figure 5 The specific capacity graph of CFs@CNT-1 after 100 cycles in Example 1 is shown. DETAILED DESCRIPTION

[0036] The following will refer to the attached Figure 1 (a) to Figure 5 Specific embodiments of the present invention are described in more detail. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0037] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0038] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0039] 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:

[0040] Step 1, preparing polyacrylonitrile nanofiber film.

[0041] According to a preferred embodiment, the polyacrylonitrile nanofiber film contains zinc salt, and further, the step 1 includes the following sub-steps:

[0042] Step 1-1, adding zinc salt and polyacrylonitrile to a polar solution and stirring to obtain a spinning precursor;

[0043] Step 1-2, electrospinning the spinning precursor to obtain a pretreated polyacrylonitrile nanofiber film;

[0044] Step 1-3, pre-oxidation treatment is performed on the pretreated polyacrylonitrile nanofiber membrane to obtain the polyacrylonitrile nanofiber membrane.

[0045] Wherein, in step 1-1, the zinc salt is preferably selected from zinc acetate and / or zinc nitrate, and more preferably zinc acetate. When the zinc acetate and zinc nitrate react at a certain temperature, no other ions that affect the reaction are generated.

[0046] In the present invention, the microscopic size of the polyacrylonitrile nanofiber film prepared by zinc salt is more uniform, and the size is easy to control. The inventors found that zinc salt has a greater effect on the diameter of the polyacrylonitrile nanofiber film. As the amount of zinc salt increases, the diameter of the obtained polyacrylonitrile nanofiber film decreases. Without being bound by any theory, the inventors believe that this may be because the added zinc salt, such as zinc acetate, increases the conductivity of the solution, which increases the electrostatic repulsion acting on the solution; as the amount of zinc salt continues to increase, the addition of zinc salt increases the viscosity of the spinning precursor, and the increase in viscosity leads to an increase in surface tension, which reduces the instability of the jet, resulting in an increase in the diameter of the obtained polyacrylonitrile nanofiber film.

[0047] Preferably, the amount of the zinc salt added is 0.1-0.4 mol / L, more preferably, the amount of the zinc salt added is 0.2-0.3 mol / L, for example, the amount of the zinc salt added is 0.23 mol / L.

[0048] In the present invention, if the concentration of polyacrylonitrile is too high, the viscosity of the solution will be too high, which will easily cause the spinneret hole to be blocked in the later electrospinning process, interrupting the electrospinning process; if the concentration of polyacrylonitrile is too low, the ejected spinning stream will be easily interrupted or adhered, resulting in poor density of the generated polyacrylonitrile nanofiber film. Using a suitable concentration of polyacrylonitrile can not only increase the viscosity of the spinning precursor, but also make the original silk bear greater tensile strength and improve crystallinity, and the resulting polyacrylonitrile nanofiber film has better performance.

[0049] The concentration of the polyacrylonitrile is 8wt% to 15wt%, preferably 9wt% to 12wt%, such as 10wt%; the average molecular weight of the polyacrylonitrile is 90,000 to 150,000, such as 130,000.

[0050] In step 1-1, the polar solvent is any one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, sodium thiocyanate, and sulfolane, preferably dimethyl sulfoxide, N,N-dimethylformamide or N,N-dimethylacetamide, and more preferably N,N-dimethylformamide.

[0051] In step 1-1, polyacrylonitrile is dissolved in a polar solvent to obtain a uniform solution, which is conducive to obtaining a thin polyacrylonitrile nanofiber with uniform spinning. The polar solvent content needs to be relatively low, and its volatilization speed is relatively fast during the electrospinning process, which is conducive to accelerating the subsequent coagulation and filamentation speed. The effect is better when polyacrylonitrile is dissolved in a polar solvent in the above concentration range.

[0052] In step 1-1, stirring is performed at a certain temperature, which can shorten the stirring time and obtain a uniform solution. The stirring temperature is 50 to 80° C., preferably 60 to 75° C., such as 70° C.; the stirring time is 1 to 3 hours, preferably 1.5 to 2.5 hours, such as 2 hours.

[0053] In the present invention, electrospinning has become one of the main ways to effectively prepare nanofiber materials due to its advantages of simple manufacturing equipment, low spinning cost, a wide variety of spinnable materials, and controllable process. The parameters of electrospinning have a certain influence on the diameter, morphology and structure of the pretreated polyacrylonitrile nanofiber film, and the preparation of a pretreated polyacrylonitrile nanofiber film with good morphology becomes one of the factors for the subsequent preparation of a porous carbon fiber-carbon nanotube three-dimensional network skeleton film.

[0054] In step 1-2, the electrospinning process conditions are: voltage is 9-15 kV, preferably 11 kV; receiving distance (the distance between the needle and the collecting plate) is 10-15 cm, preferably 12 cm.

[0055] In steps 1-3, during the pre-oxidation process, the polyacrylonitrile molecular chain undergoes a series of reactions such as cyclization, oxidation and dehydrogenation to form a cyclized structure, so that the linear macromolecular chain of thermoplastic polyacrylonitrile is converted into a pre-oxidized fiber of polyacrylonitrile-based carbon fiber with a non-plastic heat-resistant trapezoidal structure. The non-plastic heat-resistant trapezoidal structure makes the obtained pre-oxidized fiber not only non-melting and non-flammable during the subsequent high-temperature carbonization, but also maintains the fiber morphology and is thermodynamically stable; it also plays the role of fixing oxygen and carbon in the carbonization process, which is beneficial to improving the mechanical properties of carbon fiber. Pre-oxidation is a process that determines the performance of polyacrylonitrile nanofiber film, and is also an important step in evaluating the quality of polyacrylonitrile nanofiber film, so it is crucial.

[0056] When the oxidation temperature is low, the oxidation degree of the fibers of the obtained polyacrylonitrile nanofiber film is low, which may easily cause the fiber bundles to break and affect the strength of the carbon fibers; when the oxidation temperature is high, the oxidation degree of the fibers of the obtained polyacrylonitrile nanofiber film is high, which may easily cause the skin-core structure of the fibers of the polyacrylonitrile nanofiber film to form defects, thereby reducing the strength of the carbon fibers.

[0057] Wherein, the pre-oxidation temperature is 200-300°C, preferably 230-280°C, for example 250°C; the pre-oxidation time is 0.5-3h, preferably 1-2.5h, for example 2h; the pre-oxidation heating rate is 2-10°C / min, preferably 3-7°C / min, for example 5°C / min.

[0058] Step 2: using metal ions to modify the polyacrylonitrile nanofiber film to obtain a modified polyacrylonitrile nanofiber film.

[0059] In step 2, metal ions are adsorbed onto the surface of the polyacrylonitrile nanofiber film to obtain a modified polyacrylonitrile nanofiber film. The metal ions are transition metal ions, preferably one or more selected from cobalt ions, iron ions, and nickel ions, more preferably cobalt ions and / or iron ions, such as cobalt ions.

[0060] In step 2, a metal salt is dissolved in a solution to obtain a metal salt solution, and the metal ions in the metal salt solution are then adsorbed onto the surface of the polyacrylonitrile nanofiber film. The metal salt is a transition metal salt, preferably selected from one or more of cobalt salts such as cobalt acetate and cobalt nitrate, iron salts such as iron nitrate and iron acetate, and nickel salts such as nickel nitrate and nickel acetate, more preferably cobalt salts or iron salts, and most preferably cobalt salts such as cobalt acetate. The concentration of the metal salt in the metal salt solution is 0.04 to 2 mol / L, preferably 0.05 to 1.5 mol / L, and more preferably 0.05 mol / L.

[0061] According to the present invention, when the concentration of metal salt in the metal salt solution is too high, the metal ions and / or metal salts attached to the surface will cause excessive growth of carbon nanotubes, thereby destroying the original three-dimensional network structure inside the polyacrylonitrile nanofibers; when the concentration is too low, the internal fibers of the polyacrylonitrile nanofibers cannot be connected by nanotubes, or the finally generated carbon nanotubes are relatively sparse, affecting the density of the final porous carbon fiber-carbon nanotube three-dimensional network skeleton film.

[0062] In the present invention, the inventors have found that after the polyacrylonitrile nanofiber film is modified by a metal salt solution, metal ions such as iron ions, cobalt ions, etc. are uniformly attached to the surface of the polyacrylonitrile nanofiber film, and the metal ions form metal nanoparticles, such as iron nanoparticles, cobalt nanoparticles, etc. in the later pyrolysis process, which not only act as catalysts such as accelerating the reaction, but more particularly promote the growth of carbon nanotubes, thereby giving the porous carbon fiber-carbon nanotube three-dimensional network skeleton film excellent electrical properties; if the polyacrylonitrile nanofiber film is not modified as described above, carbon nanotubes will not be formed on the surface of the polyacrylonitrile nanofiber film, and naturally it will not have electrical properties, or it is not suitable as a negative electrode material for lithium ion storage.

[0063] Furthermore, the solvent used to dissolve the metal salt may be water which is cheap and readily available.

[0064] In step 2, the modification treatment includes soaking. The longer the soaking time, the more metal ions adsorbed on the polyacrylonitrile nanofiber film. However, too long soaking time has little effect on the amount of metal ions adsorbed on the polyacrylonitrile nanofiber film. The soaking time is 12 to 48 hours, preferably 18 to 36 hours, and more preferably 24 hours.

[0065] In step 2, according to a preferred embodiment, the soaked polyacrylonitrile nanofiber film is further dried to facilitate the carbonization of the modified polyacrylonitrile nanofiber film in the later stage. The film may be dried at 50-100° C. for 12-24 hours, for example, at 50° C. for 24 hours.

[0066] Step 3: pyrolyze the modified polyacrylonitrile nanofiber film to obtain the porous carbon fiber-carbon nanotube three-dimensional network skeleton film.

[0067] In step 3, one or more of melamine, glucose and polystyrene are added during pyrolysis, preferably melamine.

[0068] In step 3, pyrolysis or carbonization, the internal structure of the modified polyacrylonitrile nanofiber film will be drastically rearranged to form a layered graphite-like structure, which will cause the fiber to shrink significantly. The melt decomposition of melamine causes the nanocarbon fibers to shrink and collapse, causing the nanofibers to flatten, stick and cross-link, forming a three-dimensional network structure, and producing mesopores and macropores of various sizes; at the same time, since metal ions form metal nanoparticles during this pyrolysis process, carbon nanotubes are promoted to grow, and the overlap area of ​​nanofibers in the network is further increased, reducing contact resistance and increasing contact paths, providing a good continuous conductive network structure, and enhancing the conduction capacity of electrons. Finally, the resistance of the porous carbon fiber-carbon nanotube three-dimensional network skeleton film is greatly reduced, thereby improving its electrode electrochemical properties.

[0069] In step 3, pyrolysis is performed under the protection of an inert gas such as argon atmosphere, the melamine is placed upstream of the inert atmosphere, and the modified polyacrylonitrile nanofiber membrane is placed downstream.

[0070] In step 3, in the initial stage of carbonization, the polymer that has not been cyclized during the pre-oxidation process continues to cyclize, or pyrolyzes to release small molecule gas products such as HCN, NH3, H2, H2O, CH4, and CO2; as the temperature rises, the structural units begin to crosslink and polycondense, accompanied by pyrolysis, while releasing many small molecule by-products, and the structure of the polymer in the fiber gradually changes to the structure of polycrystalline carbon, so that non-carbon elements such as oxygen and nitrogen are gradually driven away, and finally a carbon fiber with a layered graphite structure is generated. If the carbonization temperature is too high, the nitrogen element is released in large quantities in the form of N2, which increases the porosity of the carbon fiber, resulting in a decrease in the performance of the porous carbon fiber-carbon nanotube three-dimensional network skeleton film.

[0071] Among them, the pyrolysis temperature is 800-1200°C, preferably 900-1000°C, and more preferably 1000°C; the pyrolysis time is 1-5h, preferably 2-4h, and more preferably 2h; the pyrolysis heating rate is 0.5-3°C, preferably 1-2°C / min, and more preferably 2°C.

[0072] Furthermore, when the pyrolysis temperature is low, the grown carbon nanotubes are shorter and more sparse, while a too fast or too slow heating rate will directly determine whether carbon nanotubes are generated during the pyrolysis process. Within the above parameter range, the prepared porous carbon fiber-carbon nanotube three-dimensional network skeleton film has excellent physical properties.

[0073] In a second aspect, the present invention provides a porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared by the preparation method described in the first aspect, wherein the thickness of the film is 400 to 900 μm and the specific surface area is 450 to 520 m 2 / g, the diameter of carbon nanotubes is about 24-35nm; at 2A g -1 After 100 cycles under current, the charge capacity reaches 240~290mAh g -1 .

[0074] In a third aspect, a flexible electrode material comprises a porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared by the method described in the first aspect.

[0075] Example

[0076] The present invention is further described below through specific examples, but these examples are merely exemplary and do not constitute any limitation to the scope of protection of the present invention.

[0077] Example 1

[0078] (1) adding 0.5 g of zinc acetate and 1 g of polyacrylonitrile with an average molecular weight of 130,000 to 10 mL of N,N-dimethylformamide, heating and stirring to dissolve them, the stirring time is 2 h, and the stirring temperature is 70° C. to obtain a spinning precursor;

[0079] Afterwards, the spinning precursor was transferred to a syringe equipped with a stainless steel needle for electrospinning. The voltage of electrospinning was 11 kV, and the distance between the needle and the collecting plate was 12 cm. After the spinning was completed, a pretreated polyacrylonitrile nanofiber film was obtained.

[0080] Next, the pretreated polyacrylonitrile nanofiber film was collected on aluminum foil and pre-oxidized at 250°C for 1 h. The heating rate during pre-oxidation was 5°C / min to obtain a polyacrylonitrile nanofiber film. Figure 1 As shown in (a), it can be seen that the prepared polyacrylonitrile nanofiber film is composed of a large number of nanofibers with a diameter ranging from 300 to 400 nm;

[0081] (2) The polyacrylonitrile nanofiber film was immersed in a 0.05 mol / L aqueous solution of cobalt acetate for 24 h, and then dried at 50 °C for 24 h to obtain a modified polyacrylonitrile nanofiber film. The SEM characterization of the film is as follows: Figure 2 As shown, it can be seen that cobalt ions are attached to the surface of the polyacrylonitrile nanofiber film;

[0082] (3) Cut a piece of modified polyacrylonitrile nanofiber film (2.3 g), place it and 100 mg of melamine in a quartz boat, and perform pyrolysis under Ar protection. The pyrolysis temperature is 1000 ° C, the time is 2 h, and the heating rate is 2 ° C / min to obtain a porous carbon fiber-carbon nanotube three-dimensional network skeleton film, denoted as CFs @ CNT-1, and the thickness of the obtained CFs @ CNT-1 is 500 μm.

[0083] Figure 1 (b) shows the SEM image of CFs@CNT-1; Figure 1 (a) Figure 1 (b) It can be seen that after the final step 3, carbon nanotubes grow evenly on the fiber surface, forming a porous carbon fiber-carbon nanotube three-dimensional network skeleton film.

[0084] Figure 3 The TEM image of carbon nanotubes on the surface of CFs@CNT-1 carbon nanofibers shows that the carbon nanotubes are mostly multi-walled carbon tubes with a diameter of 24 to 35 nm.

[0085] Figure 4The BET-isothermal adsorption-desorption curve of CFs@CNT-1 is shown, where curve 1 represents the adsorption curve and curve 2 represents the desorption curve. Figure 3 It is obvious that CFs@CNT-1 exhibits a typical IV-type adsorption-desorption isotherm and an H4-type hysteresis loop, and the surface area of ​​CFs@CNT-1 reaches 485.15 m 2 g -1 .

[0086] CFs@CNT-1 was heated to 2A g -1 After 100 cycles under current, the charge and discharge curve is as follows Figure 5 As shown in the figure, it can be seen that the initial discharge capacity of CFs@CNT-1 is 491.3 mAh g -1 , the charge capacity is 372.2mAh g -1 , the corresponding initial coulombic efficiency is 75%; after 100 cycles, the discharge capacity is 276.7 mAh g -1 , the charge capacity is 274.7mAh g -1 , compared with the initial charge specific capacity, the capacity retention rate is about 74%.

[0087] Example 2

[0088] A porous carbon fiber-carbon nanotube three-dimensional network skeleton film was prepared in a manner similar to Example 1, except that the amount of melamine in step (3) was 200 mg.

[0089] Finally, the prepared porous carbon fiber-carbon nanotube three-dimensional network skeleton film was recorded as CFs@CNT-2.

[0090] The prepared CFs@CNT-2 was heated to 2A g -1 After 100 cycles under current, the results showed that the initial discharge capacity of CFs@CNT-2 was 501.7 mAh g -1 , the charging capacity is 371.3mAh g -1 , the corresponding initial coulombic efficiency is 74%; after 100 cycles, the discharge capacity is 259.5 mAh g -1 , the charge capacity is 250.1mAh g -1 , compared with the initial charge specific capacity, the capacity retention rate is about 67%.

[0091] Comparative Example

[0092] Comparative Example 1

[0093] A porous carbon fiber-carbon nanotube three-dimensional network skeleton film was prepared in a manner similar to Example 1, except that the polyacrylonitrile nanofiber film was not immersed in a cobalt acetate aqueous solution. It was found that no carbon nanotubes grew on the surface of the final porous carbon fiber.

[0094] Example 1 and Comparative Example 1 show that transition metals such as cobalt are catalysts for the growth of carbon nanotubes on the surface of carbon nanofibers.

[0095] The present invention is described in detail above in combination with preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are only illustrative explanations of the present invention and do not constitute any limitation on the protection scope of the present invention. Without exceeding the spirit and protection scope of the present invention, various improvements, equivalent substitutions or modifications may be made to the technical content of the present invention and its embodiments, which all fall within the protection scope of the present invention. The protection scope of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a porous carbon fiber-carbon nanotube three-dimensional network skeleton film, characterized in that: The method comprises: Step 1, preparing a polyacrylonitrile nanofiber film; Step 2, modifying the polyacrylonitrile nanofiber film using metal ions to obtain a modified polyacrylonitrile nanofiber film; Step 3, pyrolyzing the modified polyacrylonitrile nanofiber film to obtain the porous carbon fiber-carbon nanotube three-dimensional network skeleton film; The step 1 comprises the following sub-steps: Step 1-1, adding zinc salt and polyacrylonitrile to a polar solution and stirring to obtain a spinning precursor; Step 1-2, electrospinning the spinning precursor to obtain a pretreated polyacrylonitrile nanofiber film; Step 1-3, pre-oxidizing the pretreated polyacrylonitrile nanofiber film to obtain the polyacrylonitrile nanofiber film; in, The metal ion is a transition metal ion, and the transition metal ion is selected from one or more of cobalt ions, iron ions, and nickel ions; During the pyrolysis, one or more of melamine, glucose and polystyrene are added.

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

3. The method according to claim 2, characterized in that The polar solvent is dimethyl sulfoxide, N,N-dimethylformamide or N,N-dimethylacetamide.

4. The method according to claim 2, characterized in that: In step 1-3, the pre-oxidation temperature is 200-300° C., and the pre-oxidation time is 0.5-3 h.

5. The method according to claim 1, characterized in that In step 3, the pyrolysis temperature is 800-1200° C., and the pyrolysis time is 1-5 hours.

6. A porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared according to the method of any one of claims 1 to 5.

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

8. A flexible electrode material, comprising a porous carbon fiber-carbon nanotube three-dimensional network skeleton film prepared by the method according to any one of claims 1 to 5.

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