Method for preparing spiral carbon nanofibers based on flame method

Abstract

The invention discloses a method for preparing spiral carbon nanofibers based on a flame method. The method specifically comprises the following steps: step 1, preparing a SnCl4 solution; wherein according to the mass percent, the concentration of the SnCl4 solution is 40 to 80 weight percent; 2, after foam nickel is cleaned, the foam nickel makes contact with the SnCl4 solution prepared in the step 1; 3, the foamed nickel treated in the step 2 is placed above flame to be fired, a black substance is generated on the foamed nickel, and the black substance is spiral carbon nanofibers; wherein the combustion time is 3 to 15 minutes.

Description

Technical Field

[0001] The present application relates to the technical field of electrode materials, and in particular to a method for preparing spiral carbon nanofibers based on a flame method. Background Art

[0002] Helical carbon nanofibers (HCNFs), as a special nanomaterial, not only inherit many advantages of ordinary carbon nanofibers, such as excellent electrical conductivity, thermal stability and chemical stability, but also exhibit unique superelasticity and chiral characteristics. These characteristics make HCNFs have broad application prospects in the fields of electromagnetic wave absorption, energy materials, sensors, supercapacitors, etc. For example, in terms of electromagnetic wave absorption, HCNFs can effectively scatter and absorb electromagnetic waves due to their special chiral structure, showing good wave absorption performance; in the field of energy materials, HCNFs can be used as efficient electrode materials in lithium-ion batteries and supercapacitors to improve the energy density and power density of energy storage devices.

[0003] At present, the main preparation methods of HCNFs include arc discharge, laser ablation, plasma, chemical vapor deposition (CVD), etc. Among them, the ethanol flame method is mainly used for laboratory-scale research to explore its possibility as a preparation of HCNFs and other nanomaterials. Studies have shown that EFM can successfully synthesize high-quality HCNFs, and by adjusting experimental parameters (such as catalyst type and concentration, flame temperature, firing time, etc.), the morphology and properties of the product can be effectively controlled. However, although EFM has shown initial success, it is still in the research and development stage. Although the ethanol flame method (EFM) has the advantages of short reaction time and relatively simple equipment, the yield of HCNFs prepared by it is relatively low, which is difficult to meet the needs of large-scale industrial production. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of this application is to provide a method for preparing spiral carbon nanofibers based on a flame method, so as to solve the problem that the flame method in the prior art cannot prepare high-quality spiral carbon nanofibers in large quantities.

[0005] In order to solve the above technical problems, this application adopts the following technical solutions:

[0006] A method for preparing spiral carbon nanofibers based on a flame method comprises the following steps:

[0007] Step 1: Prepare a SnCl4 solution; wherein, calculated by mass percentage, the concentration of the SnCl4 solution is 40wt% to 80wt%; in the present invention, the SnCl4 solution can be prepared using water or anhydrous ethanol as a solvent.

[0008] Step 2: After washing the nickel foam with a hydrochloric acid solution, the foam is placed in contact with the SnCl4 solution prepared in step 1 for at least 5 minutes and then dried for later use; wherein the concentration of HCl in the hydrochloric acid solution is 2-4 mol / L;

[0009] Step 3: The nickel foam processed in step 2 is placed above a flame and burned to generate a black substance on the nickel foam, wherein the black substance is spiral carbon nanofibers; wherein the burning time is 3 to 15 minutes.

[0010] Preferably, in step 3, the distance between the nickel foam and the bottom of the flame is 1 to 2.5 cm.

[0011] Preferably, in step 2, after the nickel foam is cleaned, the SnCl4 solution is dripped onto the surface of the nickel foam.

[0012] Preferably, in step 2, the nickel foam is immersed in a SnCl4 solution for 30 to 120 minutes.

[0013] Preferably, in step 2, the nickel foam treated with the hydrochloric acid solution is placed in the SnCl4 solution, which is then heated to be in a distillation reflux state; wherein the solution is kept slightly boiling for 5 to 15 minutes.

[0014] Preferably, the nickel foam treated in step 3 is ultrasonically treated, and the black matter is collected. The collected black matter is washed with concentrated nitric acid and then rinsed with deionized water to obtain spiral carbon nanofibers.

[0015] The present invention provides an electrode material, wherein the spiral carbon nanofiber processed by the above method is used as the electrode material.

[0016] Preferably, the spiral carbon nanofibers prepared by the above method are used to prepare battery electrode materials; or, the nickel foam obtained after treatment by the above method is directly used as an electrode material.

[0017] Preferably, the electrode material is used in the fields of electromagnetic wave absorption, electrochemical energy storage, and sensitive sensing.

[0018] Compared with the prior art, this application has the following beneficial effects:

[0019] 1. The present application improves the flame method by utilizing the three-dimensional structure of nickel foam as a skeleton. Since the three-dimensional structure of nickel foam has an interconnected porous structure, spiral carbon nanofibers can be formed on its surface in large quantities. Thus, while ensuring the quality requirements of spiral carbon nanofibers, a large amount of spiral carbon nanofibers can be prepared, thereby effectively improving production efficiency.

[0020] 2. After in-depth research on the flame method, the present applicant found that immersing the nickel foam in a hydrochloric acid solution of a certain concentration can remove the oxides on the surface of the nickel foam, exposing a fresh metal nickel matrix. After immersing it in a SnCl4 solution, a layer of metal tin will be generated on the surface of the nickel foam through a replacement reaction. Burning the nickel foam with metal tin on the surface over a flame can not only form spiral carbon nanofibers, but also enhance the connection strength between the spiral carbon nanofibers and the nickel foam. At the same time, the present applicant also found that heating the SnCl4 solution soaked with nickel foam can further enhance the connection strength between the spiral carbon nanofibers and the nickel foam, so that a layer of spiral carbon nanofibers firmly connected to the nickel foam is formed on the surface of the nickel foam, so that the treated nickel foam can be directly used as an electrode material with excellent electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the process for preparing spiral carbon nanofibers according to Example 4 of the present application.

[0022] Figure 2 These are scanning electron microscope images of spiral carbon nanofibers prepared in Example 1; wherein, A is an image of nickel foam at low magnification, B is an image of spiral carbon nanofibers grown on nickel foam at low magnification, and C is an image of spiral carbon nanofibers grown on nickel foam at high magnification.

[0023] Figure 3 This is a comparison diagram of the nickel foam used in Example 4 and the nickel sheet used in Comparative Example 2 before and after firing.

[0024] Figure 4 This is a scanning electron microscope image of the spiral carbon nanofibers repeatedly fired with nickel foam in Example 1.

[0025] Figure 5 These are microscopic morphologies of nickel foam obtained after treatment in Example 7; wherein, A is a morphology of spiral carbon nanofibers grown on nickel foam at a low magnification; and B is a morphology of spiral carbon nanofibers grown on nickel foam at a high magnification.

[0026] Figure 6 The performance comparison chart of the electrode material prepared in Example 1, the nickel foam treated in Example 7 directly as an electrode material, and commercial activated carbon as an electrode; wherein A is the cyclic voltammetry curve, B is the constant current charge and discharge curve, and C is the desalination amount. DETAILED DESCRIPTION

[0027] This application will provide a clear and complete description of the technical solutions in the embodiments of this application in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on this application are within the scope of protection of this application.

[0028] Unless otherwise indicated in specific cases in this application, the numerical ranges listed herein include the upper and lower limits, as well as all integers and fractions within the range, and are not limited to the specific values listed when defining the range.

[0029] 1. A method for preparing spiral carbon nanofibers based on flame method

[0030] Step 1: Prepare a SnCl4 solution; wherein, calculated by mass percentage, the concentration of the SnCl4 solution is 40wt% to 80wt%; in the present invention, the SnCl4 solution can be prepared using water or anhydrous ethanol as a solvent.

[0031] Step 2: After washing the nickel foam with a hydrochloric acid solution, the foam is placed in contact with the SnCl4 solution prepared in step 1 for at least 5 minutes and then dried for later use; wherein the concentration of HCl in the hydrochloric acid solution is 2-4 mol / L;

[0032] Step 3: The nickel foam processed in step 2 is placed above a flame and burned to generate a black substance on the nickel foam, wherein the black substance is spiral carbon nanofibers; wherein the burning time is 3 to 15 minutes.

[0033] After an in-depth study of the existing flame method for preparing spiral carbon nanofibers, the present application found that the prior art generally uses nickel sheets as a substrate, which makes the amount of spiral carbon nanofibers prepared very small. For this reason, the present application considers whether it is possible to improve the yield of spiral carbon nanofibers by changing the morphology of the substrate. The present application uses nickel foam to replace the nickel sheet in the prior art as a substrate, and SnCl4 solution is added dropwise to the surface of the nickel foam. The nickel foam has a three-dimensional network structure, which provides a large specific surface area, which is not only conducive to the uniform dispersion of the catalyst, but also increases the growth site of the carbon nanofibers. At the same time, the good thermal conductivity of the nickel foam can ensure that heat is quickly transferred to the entire substrate, making the reaction temperature more uniform, thereby promoting more stable growth of HCNFs. The prepared spiral carbon nanofibers can then be peeled off from the nickel foam by ultrasonic treatment, and the quality of the spiral carbon nanofibers can be guaranteed while improving the yield of the spiral carbon nanofibers. The nickel foam after use can be reused after cleaning, which reduces production costs, which is an important economic advantage for large-scale industrial production.

[0034] In some embodiments of the present application, in step 3, the distance between the nickel foam and the bottom of the flame is 1 to 2.5 cm. In the laboratory, the flame is mainly provided by burning an alcohol lamp, and the distance between the nickel foam and the bottom of the alcohol lamp flame can be controlled between 1 to 2.5 cm. In actual production, the distance between the nickel foam and the bottom of the flame is regulated and controlled to be between 1 to 2.5 cm, which can ensure that the heat of the flame is evenly transferred to the surface of the nickel foam, avoids damage to the substrate or deactivation of the catalyst due to excessively high temperatures, and also avoids reaction without supplementation due to excessively low temperatures, and cannot form spiral carbon nanofibers. Therefore, the distance between the nickel foam and the bottom of the flame can be 1 cm, 1.5 cm, 2.0 cm, 2.5 cm, etc., as well as all ranges and sub-ranges between the above numerical values. It should be understood that, in an embodiment, any of the above ranges can be combined with any other ranges.

[0035] In some embodiments of the present application, while improving the yield of spiral carbon nanomaterials prepared by the flame method, the present application also notes that the spiral carbon nanofiber material exhibits excellent electron transport and ion diffusion capabilities in the field of energy storage due to its unique spiral morphology and continuous conductive network. However, when it is mixed with an insulating binder (such as PVDF) and a conductive agent to form a slurry and coated into an electrode, its intrinsic structural advantage is often significantly weakened. This is because the binder wrapping will cover the active sites on the surface of the spiral carbon nanofiber, and its insulating properties will hinder direct contact between the spiral structures, resulting in the three-dimensional conductive network being divided by inactive ingredients, and the electron transmission path is forced to bypass the binder interface, significantly increasing the interface resistance; at the same time, the shear force and drying shrinkage effect of the slurry during the coating process can easily cause the spiral fibers to deform or even partially break, destroying their internal multi-level pore structure. This process not only reduces the specific surface area of the electrode, but also shortens the continuity of the ion diffusion channel, resulting in ion migration being blocked during charge and discharge, and polarization phenomenon being aggravated. This series of problems together lead to a reduction in the proportion of active materials in the electrode (usually <80%), and the "structure-function synergistic effect" of spiral carbon nanofibers is difficult to give full play to, ultimately limiting the realization of its theoretical capacity and the improvement of rate performance. Therefore, the application considers whether it can be possible to, when preparing spiral carbon nanofiber materials, enable them to grow in large quantities and firmly on matrix materials, so that the matrix materials grown with spiral carbon nanofiber materials can be directly made into electrode materials for use, without the need to prepare slurry and apply, improve the content of active materials and electrochemical performance, thereby giving full play to the advantages of spiral carbon nanofiber materials in electrochemical applications. Based on this, in step 2, the application changes the contact mode of nickel foam and SnCl4 solution, and nickel foam is put into hydrochloric acid solution for soaking, cleaning, drying, and then put into SnCl4 solution for soaking. After in-depth study, it was found that nickel foam and SnCl4 the contact form of solution can affect the connection strength between spiral carbon nanofiber and nickel foam, and nickel foam is soaked in SnCl4 The connection strength of the nickel foam surface spiral carbon nanofiber and matrix obtained by solution post-treatment is significantly better than the mode of dropping. This is because the nickel foam is first immersed in a hydrochloric acid solution of a certain concentration to remove the oxide layer on the surface of the nickel foam and expose the fresh nickel matrix. Then, after immersing it in a SnCl4 solution, a replacement reaction occurs on the surface of the nickel foam, generating a layer of metallic tin covering the nickel matrix. 4+It has strong oxidizing properties, and metallic nickel (Ni) can act as a reducing agent to produce a replacement reaction: SnCl4+Ni→NiCl2+SnCl2+Sn. Burning this nickel foam with metallic tin on its surface over a flame not only forms spiral carbon nanofibers, but also enhances the connection strength between the spiral carbon nanofibers and the nickel foam, forming a layer of spiral carbon nanofibers firmly connected to the nickel foam surface. This allows the treated nickel foam to be directly used as an electrode material and exhibits excellent electrochemical properties. The concentration of HCl in the hydrochloric acid solution is 2-4 mol / L, and the immersion time is 10-20 minutes. A hydrochloric acid concentration that is too low will not be sufficient to effectively remove oxides and other impurities on the surface of the nickel foam, thereby affecting its performance in subsequent applications. A concentration that is too high will damage the nickel matrix, causing it to dissolve. A too short immersion time will result in insufficient surface treatment of the nickel foam, making it insufficient for effective etching. A too long immersion time will dissolve the nickel matrix. Therefore, the concentration of HCl in the hydrochloric acid solution can be 2 mol / L, 3 mol / L, 4 mol / L, etc., and all ranges and sub-ranges between the above values; the soaking time can be 10 min, 15 min, 20 min, etc., and all ranges and sub-ranges between the above values; it should be understood that, in the embodiment, any of the above ranges can be combined with any other ranges.

[0036] In some embodiments of the present application, in step 2, the nickel foam treated with hydrochloric acid is placed in a SnCl₄ solution and then heated to a distillation reflux state; the solution is maintained at a slight boil for 5 to 15 minutes. This distillation reflux treatment can further enhance the effectiveness of the displacement reaction and strengthen the bond between the helical carbon nanofibers and the nickel foam, making them less likely to fall off the nickel foam. Slight boiling means that the boiling level is not too intense; by controlling the temperature, the solution is kept at a slight boiling level with slight bubbling. This bond strength is particularly important when the nickel foam is used directly as an electrode material. Sufficient bond strength allows the helical carbon nanofibers to be attached to the substrate without the aid of an adhesive, ensuring that the surface of the treated nickel foam is completely and firmly covered with the active material, the helical carbon nanofibers. Therefore, the solution can be maintained at a boil for 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, and the like, as well as all ranges and subranges between the aforementioned values. It should be understood that in embodiments, any of the above ranges can be combined with any other range.

[0037] In some embodiments of the present application, the nickel foam treated in step 3 is ultrasonically treated, and the black matter is collected. The collected black matter is washed with concentrated nitric acid and then rinsed with deionized water to obtain spiral carbon nanofibers.

[0038] 2. An electrode material

[0039] The method is used to prepare the nickel foam. Specifically, when a SnCl4 solution is added dropwise onto nickel foam and used to directly prepare spiral carbon nanofibers, a large amount of spiral carbon nanofibers can be prepared, and these spiral carbon nanofibers can be used as an electrode material. The nickel foam is immersed in a SnCl4 solution, and the method described in this application can grow a large amount of spiral carbon nanofibers on its surface. The resulting nickel foam material can be used directly as an electrode material without the need for further coating.

[0040] In some embodiments of the present application, the electrode material is used in the fields of electromagnetic wave absorption, electrochemical energy storage, sensitive sensing, etc.

[0041] 3. Examples and Comparative Examples

[0042] 1. Add SnCl4 solution

[0043] Example 1

[0044] Step 1: Prepare a SnCl4 solution; wherein the solvent is anhydrous ethanol; the concentration of the SnCl4 solution is 70wt%;

[0045] Step 2: After cleaning a 2cm×2cm nickel foam with a hydrochloric acid solution, the SnCl4 solution prepared in step 1 is dripped onto the surface of the nickel foam and dried for later use; the concentration of the hydrochloric acid solution is 3 mol / L.

[0046] Step 3: The nickel foam processed in step 2 is placed above a flame and burned to generate a black substance on the nickel foam, which is spiral carbon nanofibers; wherein the burning time is 9 minutes.

[0047] Step 4: ultrasonically treat the nickel foam treated in step 3, collect the black matter, wash the collected black matter with concentrated nitric acid, and then rinse with deionized water to obtain spiral carbon nanofibers.

[0048] Example 2

[0049] The method was modified based on Example 1, except that the concentration of the SnCl4 solution was 60 wt %. The other steps were identical to those in Example 1.

[0050] Example 3

[0051] The method was modified based on Example 1, except that the concentration of the SnCl4 solution was 80 wt %. The other steps were identical to those in Example 1.

[0052] 2. Soak in SnCl4 solution

[0053] Example 4

[0054] Step 1: preparing a SnCl4 solution; wherein the solvent is water; the concentration of the SnCl4 solution is 70wt%;

[0055] Step 2: Use 2cm×2cm nickel foam to place in 3mol / L hydrochloric acid solution for pretreatment for 15min, clean and dry, and then place in the SnCl4 aqueous solution prepared in step 1 and soak for 120min;

[0056] Step 3: Place the nickel foam treated in step 2 above the flame and burn it to generate a black substance on the nickel foam, which is spiral carbon nanofibers, to prepare nickel foam with spiral carbon nanofibers grown on the surface; wherein the burning time is 9 minutes.

[0057] Example 5

[0058] The improvement was made based on Example 4, except that the sample was immersed in the SnCl4 solution for 60 min. The other steps were exactly the same as those in Example 4.

[0059] Example 6

[0060] The improvement is made on the basis of Example 4, except that the step of soaking in the SnCl4 solution for 30 minutes is performed. The other steps are exactly the same as those in Example 4.

[0061] Example 7

[0062] Step 1: Prepare a SnCl4 solution; wherein the solvent is anhydrous ethanol; the concentration of the SnCl4 solution is 40wt%;

[0063] Step 2: The nickel foam was placed in a 3 mol / L hydrochloric acid solution for pretreatment for 15 min. After cleaning and drying, it was placed in the SnCl4 solution prepared in step 1 and distilled and refluxed in a round-bottom flask to keep the solution slightly boiling for about 10 min.

[0064] Step 3: The nickel foam processed in step 2 is placed above a flame and burned to generate a black substance on the nickel foam, which is spiral carbon nanofibers; wherein the burning time is 9 minutes.

[0065] Comparative Example 1

[0066] The method was modified based on Example 1, except that a nickel sheet with the same size as that of Example 1 was used as the substrate. The other steps were identical to those of Example 1.

[0067] Comparative Example 2

[0068] The method was modified based on Example 4, except that a nickel sheet with the same size as that of Example 4 was used as the substrate. The other steps were identical to those of Example 4.

[0069] Comparative Example 3

[0070] The method was modified based on Example 7, except that a nickel sheet with the same size as that of Example 7 was used as the substrate. The other steps were identical to those of Example 7.

[0071] 4. Performance Comparison

[0072] 1. Preparation of spiral carbon nanofibers

[0073] Taking Example 1 as an example, the surface of nickel foam before ultrasonic treatment was observed. Figure 2 As shown, a large number of spiral carbon nanofibers grow on the surface of nickel foam, and from the microscopic morphology it can be seen that they are all spiral.

[0074] The yields of the spiral carbon nanofibers prepared in Examples 1 to 3 are all above 0.4g, while the yield of Comparative Example 1 generated on the nickel sheet is only 0.28g, which is much lower than that of the embodiment. The size of the nickel foam and the nickel sheet are both 2cm×2cm. The mass of the spiral carbon nanofibers generated on the nickel foam is 0.1 times the mass of the nickel foam, and the mass of the spiral carbon nanofibers generated on the nickel sheet is 0.01 times the mass of the nickel sheet. This shows that the spiral carbon nanofibers are prepared by the ethanol flame method using the nickel foam 3D skeleton. Since the three-dimensional structure of the nickel foam has an interconnected porous structure, the spiral carbon nanofibers can be formed on its surface in large quantities. Therefore, under the premise of ensuring the quality requirements of the spiral carbon nanofibers, a large amount of spiral carbon nanofibers can be prepared, thereby effectively improving the production efficiency.

[0075] Figure 2 This is a microscopic morphology of the spiral carbon nanofiber material prepared after the nickel foam in Example 1 was reused twice. It can be seen that multiple reuses did not affect the formation and microscopic morphology of the spiral carbon nanofiber material, and the prepared yield can still be stably maintained at more than 0.4g.

[0076] This proves that the spiral carbon nanofibers grown on the surface of nickel foam using the method described in this application can be separated from the nickel foam, and the prepared spiral carbon nanofibers can be peeled off from the nickel foam by ultrasonic treatment. The nickel foam can then be reused after cleaning, reducing production costs, which is an important economic advantage for large-scale industrial production.

[0077] 2. The nickel foam obtained after treatment is used as an electrode material

[0078] The surface of the nickel foam obtained by the treatment of Examples 4 to 7 was observed. Figure 5 As shown, a layer of spiral carbon nanofibers firmly connected to the nickel foam is formed on the surface of the nickel foam, and these carbon nanofibers all show a very obvious spiral shape. The products prepared in Examples 4 to 7 were subjected to ultrasonic treatment for 40 minutes, and the connection strength between the spiral carbon nanofibers and the nickel foam was judged by the degree of change in the mass of the nickel foam before and after the ultrasonic treatment. The mass of Examples 4 to 6 decreased by 45% after ultrasonic treatment, which shows that the nickel foam is firmly connected to the spiral carbon nanofibers on its surface, but the remaining mass on the nickel sheet prepared in Comparative Example 2 after ultrasonic treatment is 0; and the mass of the nickel foam in Example 7 after ultrasonic treatment, which has been treated with distillation and reflux, remains at 79%, indicating that the distillation and reflux treatment can further enhance the connection strength between the spiral carbon nanofibers and the nickel foam.

[0079] The helical carbon nanofibers prepared in Example 1 were treated with NaOH+HNO₃. Then, a slurry of helical carbon nanofibers, conductive carbon black, and PVDF was mixed at a mass ratio of 6:3:1. This slurry was then applied to form an electrode sheet. The nickel foam obtained in Example 7 was used directly as an electrode sheet. The electrochemical performance of the electrode sheet was compared with that of commercial activated carbon.

[0080] Electrochemical measurements of the electrodes were performed using a three-electrode configuration method with spiral carbon nanofibers and nickel foam sheets as working electrodes, a calomel electrode as a reference electrode, and a platinum electrode as an auxiliary electrode. The experiment used an electrochemical workstation and 1.0M NaCl solution as the electrolyte, and cyclic voltammetry (CV) and constant current charge-discharge (GCD) were performed at room temperature. Cyclic voltammetry tests were performed at -0.90 to -0.10 V at different scan rates (10, 20, 30, 50, 70, and 100 mV / s). The lowest potential limit of the constant current charge-discharge measurement is -0.90 V, and the current density is from 0.5 A g -1 to 10Ag -1 The symmetrical electrode device in the traditional CDI was used to evaluate the desalination performance of the electrode in the CDI system. The initial conductivity of 60 ml was 105.80 μS cm -1 The NaCl solution (50 mg / L) was pumped into the CDI cell at a flow rate of 10 mL / min, and the electrostatic field voltage applied during the desalination process was 1.2 V.

[0081] Figure 6The cyclic voltammetry curve shown in A shows the current response of the material at different potentials, reflecting the electrochemical activity and reversibility of the material. Among them, the spiral carbon nanofibers prepared in Example 1 show relatively symmetrical cyclic voltammetry curves in the forward and reverse scans, indicating that they have good electrochemical reversibility, which means that in the process of capacitive deionization, the spiral carbon nanofibers can effectively adsorb and release ions, thereby achieving efficient desalination. The nickel foam sheet obtained by the treatment in Example 7 has a large current response, especially in the negative potential region, showing a high electrochemical activity, which indicates that the nickel foam sheet has a strong ion adsorption capacity in the process of capacitive deionization. The current response of commercial activated carbon is relatively small, indicating that its electrochemical activity is low and its ability to adsorb ions in the process of capacitive deionization is weak.

[0082] Figure 6 The constant current charge and discharge curve shown in B shows the potential change of the material under constant current, reflecting the specific capacitance and electrochemical stability of the material. Among them, the spiral carbon nanofiber prepared in Example 1 has a specific capacitance of 173F / g, showing a relatively high capacitance performance; the foam nickel sheet obtained by the treatment in Example 7 has a specific capacitance of 197F / g, which is slightly higher than the spiral carbon nanofiber. This shows that the foam nickel sheet obtained by the treatment in Example 7 can store more charge per unit mass, thereby adsorbing more ions in the process of capacitive deionization. Both have better electrochemical stability than commercial activated carbon. The specific capacitance of commercial activated carbon is 65F / g, which is significantly lower than the first two, indicating that its capacitance performance is poor and its ability to adsorb ions in the process of capacitive deionization is weak.

[0083] Figure 6 The desalination capacity shown in C directly reflects the actual desalination effect of the material in the capacitive deionization process. The desalination capacity of the spiral carbon nanofibers prepared in Example 1 is 44.06 mg / g, indicating that under the same conditions, each gram of spiral carbon nanofibers can remove 44.06 mg of salt from the solution. Figure 6 A and Figure 6 The good electrochemical performance and high specific capacitance of the helical carbon nanofibers in B are consistent. However, the desalination capacity of commercial activated carbon is 32.45 mg / g, indicating that its desalination effect in the capacitive deionization process is poor. Figure 6 A and Figure 6 The lower electrochemical activity and low specific capacitance of commercial activated carbon in B are consistent.

[0084] It can be seen that both the spiral carbon nanofibers prepared by the method described in this application and the nickel foam obtained by the treatment described in this application have excellent electrochemical properties compared with commercial activated carbon and have good prospects in electrochemical applications.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the technical solutions. Those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present application that do not depart from the purpose and scope of the technical solutions of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for preparing spiral carbon nanofibers based on a flame method, characterized in that: The specific steps include: Step 1: preparing a SnCl4 solution; wherein, calculated by mass percentage, the concentration of the SnCl4 solution is 40wt% to 80wt%; Step 2: After washing the nickel foam with a hydrochloric acid solution, the foam is placed in contact with the SnCl4 solution prepared in step 1 for at least 5 minutes and then dried for later use; wherein the concentration of HCl in the hydrochloric acid solution is 2-4 mol / L; Step 3: The nickel foam processed in step 2 is placed above a flame and burned to generate a black substance on the nickel foam, wherein the black substance is spiral carbon nanofibers; wherein the burning time is 3 to 15 minutes.

2. The method according to claim 1, characterized in that In step 3, the distance between the nickel foam and the bottom of the flame is 1 to 2.5 cm.

3. The method according to claim 2, characterized in that In step 2, the SnCl4 solution is dropped onto the surface of the nickel foam and allowed to remain in contact therewith.

4. The method according to claim 2, characterized in that In step 2, the nickel foam is immersed in a SnCl4 solution for 30 to 120 minutes.

5. The method according to claim 2, characterized in that: In step 2, the nickel foam is immersed in a SnCl4 solution and then heated to put the SnCl4 solution into a distillation reflux state; wherein the solution is kept slightly boiling for 5 to 15 minutes.

6. The method according to claim 3, characterized in that: The nickel foam treated in step 3 is ultrasonically treated, and the black matter is collected. The collected black matter is washed with concentrated nitric acid and then rinsed with deionized water to obtain spiral carbon nanofibers.

7. An electrode material, characterized in that The nickel foam treated by any method according to claims 1 to 6 is used as an electrode material.

8. The electrode material according to claim 7, characterized in that The spiral carbon nanofibers prepared by the method of claim 6 are used to prepare battery electrode materials; or the nickel foam obtained by the method of any of claims 4 to 5 is directly used as an electrode material.

9. The electrode material according to claim 7, characterized in that The electrode material is used in the fields of electromagnetic wave absorption, electrochemical energy storage, and sensitive sensing.

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