Preparation method of nitrogen-doped carbon nanotube loaded nano-iron and application thereof in lithium battery negative electrode

Abstract

The application relates to a preparation method of nitrogen-doped carbon nanotube loaded nanometer iron and application of the nitrogen-doped carbon nanotube loaded nanometer iron in a lithium battery negative electrode, and belongs to the technical field of nitrogen-doped carbon nanotubes and lithium ion battery negative electrode materials. The preparation method of the nitrogen-doped carbon nanotube comprises the following steps: (1) dispersing treatment of a catalyst; (2) high-temperature preparation of nitrogen-doped carbon nanotube loaded nanometer iron; and (3) collection and treatment of the nitrogen-doped carbon nanotube loaded nanometer iron. The nitrogen-doped carbon nanotube loaded nanometer iron provided by the application is used as a conductive agent, the lithium battery prepared by using the nitrogen-doped carbon nanotube loaded nanometer iron has low internal resistance and good electrochemical performance, the carbon nanotube is combined with the nanometer iron, the agglomeration and volume expansion of the nanometer iron can be prevented, the excellent conductivity of the nanometer iron and the carbon nanotube is utilized, and the specific capacity and capacity retention rate of the lithium battery are improved.

Description

Technical Field

[0001] This invention belongs to the technical field of nitrogen-doped carbon nanotubes and lithium-ion battery anode materials, specifically relating to a method for preparing nitrogen-doped carbon nanotubes loaded with iron nanoparticles and their application in lithium-ion battery anode materials. Background Technology

[0002] With the rapid development of modern technology, lithium batteries, as an important energy storage device, have always been a research hotspot in the field of science and technology, with their performance improvement and application expansion being particularly important. The anode material of a lithium battery is one of the key factors affecting its overall performance; therefore, finding anode materials with high specific capacity and excellent cycle stability is of great significance for improving lithium battery performance.

[0003] Carbon nanotubes, with their excellent electrical conductivity, high specific surface area, and good chemical stability, are considered promising conductive agents. In recent years, research on modifying carbon nanotubes by doping them with different elements to improve their electrochemical performance has increased. Nitrogen doping is an effective modification method; the introduction of nitrogen can alter the electronic structure of carbon nanotubes, improving their electrochemical activity and thus enhancing the performance of lithium-ion batteries. Additionally, nano-iron, a metallic material with high specific capacity, has also attracted considerable attention. However, nano-iron is prone to agglomeration and volume expansion during charge and discharge, leading to a decline in battery performance. Therefore, combining nano-iron with carbon nanotubes, using carbon nanotubes as a carrier, can not only prevent the agglomeration and volume expansion of nano-iron but also leverage the excellent electrical conductivity of carbon nanotubes to improve the charge and discharge efficiency of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of low specific capacity and poor cycle stability of lithium battery anode materials. It provides a method for preparing nitrogen-doped carbon nanotube-supported iron nanoparticles and their application in lithium battery anodes. This method can not only prevent the agglomeration and volume expansion of iron nanoparticles, but also improve the capacity retention of lithium batteries by utilizing the excellent conductivity of carbon nanotubes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing nitrogen-doped carbon nanotubes loaded with iron nanoparticles, the method comprising:

[0007] (1) Dissolve the catalyst in anhydrous ethanol and disperse it by ultrasonication to obtain a catalyst solution with a concentration of 0.2-0.6 g / L; add the catalyst solution evenly to the designated position on the substrate, and place the substrate with the added catalyst solution in a vacuum drying oven to remove the solvent and obtain catalyst particles;

[0008] (2) Place the substrate of the supported catalyst particles prepared in step (1) into a tube furnace and place it at the gas inlet of the heating zone of the tube furnace; evacuate the tube furnace, introduce a hydrogen-argon mixture, carbon source and nitrogen source, turn on the heating device of the tube furnace, and raise the furnace temperature to the reaction temperature at a heating rate of 10℃ / min to prepare nitrogen-doped carbon nanotube supported nano-iron.

[0009] Furthermore, the method also includes step (3), in which the cooled substrate is removed from the tube furnace and immersed in anhydrous ethanol. The substrate is then ultrasonically treated by an ultrasonic disperser to separate the nitrogen-doped carbon nanotube-loaded iron nanoparticles. The ultrasonically treated solution is then centrifuged to collect the nitrogen-doped carbon nanotube-loaded iron nanoparticles precipitated at the bottom and dried.

[0010] Further, in step (1), the catalyst is one or more of iron oxide, γ-iron oxide, ferric nitrate nonahydrate, and ferrocene.

[0011] Further, in step (1), the substrate is one or more of silicon wafers, nickel foam, and quartz wafers.

[0012] Furthermore, in step (2), the flow rate of the hydrogen-argon mixed gas is controlled at 80-350 sccm.

[0013] Further, in step (2), the carbon source is one or more of ethylene, acetylene, polyethylene and polypropylene.

[0014] Furthermore, in step (2), the nitrogen source is one or more of urea, melamine, xylene, and aniline.

[0015] Furthermore, in step (2), the reaction temperature is 700–950°C and the reaction time is 15–45 min.

[0016] Furthermore, in step (3), the drying process is vacuum drying or freeze drying, which can ensure the dryness and stability of nitrogen-doped carbon nanotube-loaded iron nanoparticles.

[0017] An application of nitrogen-doped carbon nanotube-loaded iron nanoparticles prepared by the above preparation method is described, wherein the nitrogen-doped carbon nanotube-loaded iron nanoparticles are used as a negative electrode conductive agent in a lithium-ion battery; in the negative electrode slurry, the proportions of graphite, SBR, carbon black, CMC, and nitrogen-doped carbon nanotube-loaded iron nanoparticles are 94%:1.8%:2.2%:0.5%~1%:1%~1.5%.

[0018] The advantages of this invention over the prior art are as follows:

[0019] 1. This invention proposes a novel lithium battery negative electrode conductive agent of nitrogen-doped carbon nanotubes loaded with nano-iron. Through a specific preparation process, nano-iron is loaded onto nitrogen-doped carbon nanotubes.

[0020] 2. The lithium battery prepared using the conductive agent provided by this invention has lower internal resistance. The introduction of nitrogen element improves the electrochemical activity of the conductive agent, enabling the conductive network composed of carbon nanotubes to transport electrons faster, thereby reducing the internal resistance of the lithium battery.

[0021] 3. The lithium battery prepared using the conductive agent provided by this invention has higher specific capacity and capacity retention rate. Combining carbon nanotubes with nano-iron not only prevents the agglomeration and volume expansion of nano-iron, but also utilizes the excellent conductivity of carbon nanotubes and nano-iron to improve the specific capacity and capacity retention rate of the lithium battery.

[0022] 4. This invention provides a method for preparing nitrogen-doped carbon nanotubes based on nano-iron. By precisely controlling each step of the preparation process, efficient and stable preparation of carbon nanotubes is achieved. This method has the advantages of simple operation and stable product quality, and is suitable for large-scale production applications. Attached Figure Description

[0023] Figure 1 This is a SEM image of nitrogen-doped carbon nanotubes supporting iron nanoparticles;

[0024] Figure 2 This is the EDS curve of nitrogen-doped carbon nanotubes supporting iron nanoparticles.

[0025] Figure 3 This is a comparison graph of the cycle curves of Example 1 and Comparative Example 2. Detailed Implementation

[0026] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the invention, not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] This invention utilizes a specific preparation process to load nano-iron onto nitrogen-doped carbon nanotubes, combining the advantages of both to improve the performance of lithium-ion battery anode materials. Specifically, this invention achieves nitrogen doping and nano-iron loading onto carbon nanotubes through chemical vapor deposition. Simultaneously, the conductive agent of this invention, when used to fabricate lithium-ion coin cells, shows a certain improvement in capacity retention. The nitrogen-doped carbon nanotube-loaded nano-iron lithium-ion battery anode material proposed in this invention is expected to provide a new solution for improving the performance and expanding the application fields of lithium-ion batteries.

[0028] Example 1

[0029] 1. Catalyst dispersion treatment:

[0030] 2 mg of γ-iron oxide powder was added to 10 ml of anhydrous ethanol and stirred with a magnetic stirrer to fully disperse the γ-iron oxide powder in the ethanol to form a homogeneous mixture. The mixture was then transferred to an ultrasonic disperser and dispersed at a frequency of 40 kHz for 30 minutes. The dispersed mixture was then added dropwise to a silicon wafer and placed in an 80°C oven to dry for 30 minutes until the anhydrous ethanol was completely evaporated.

[0031] 2. Preparation of nitrogen-doped carbon nanotubes supporting iron nanoparticles:

[0032] The dried silicon wafer was placed in the center of the heating zone of a tube furnace. Polypropylene and melamine were placed at the furnace inlet as carbon and nitrogen sources, respectively. The furnace was then evacuated, followed by the introduction of a hydrogen-argon mixture to atmospheric pressure. This process was repeated three times to ensure the purity of the furnace atmosphere. The furnace temperature was increased to 900°C at a rate of 10°C / min. Once the temperature reached 900°C, it was maintained for 45 minutes to allow the polypropylene and melamine to vaporize and contact the γ-iron oxide catalyst on the silicon wafer, thereby triggering the growth of carbon nanotubes.

[0033] 3. Collection and processing of nitrogen-doped carbon nanotube-supported iron nanoparticles

[0034] After the furnace temperature cooled to room temperature, the silicon wafer was removed from the tube furnace. The silicon wafer was immersed in a beaker containing anhydrous ethanol and ultrasonically treated for 10 minutes using an ultrasonic disperser. Finally, the ultrasonically treated solution was centrifuged, and the carbon nanotubes precipitated at the bottom were collected. The washed carbon nanotubes were placed in a vacuum drying oven and dried at 60°C to obtain a dried carbon nanotube sample.

[0035] Finally, a negative electrode slurry was prepared by mixing graphite, SBR, carbon black, CMC, and the sample in a ratio of 94%:1.8%:2.2%:0.5%:1.5%. This slurry was then coated onto copper foil to form the negative electrode sheet. For the positive electrode, a slurry was prepared by mixing lithium iron phosphate, a conductive agent, and PVDF in a specific ratio and coated onto aluminum foil to form the positive electrode sheet. A button cell was then fabricated by combining the positive and negative electrode shells, the positive and negative electrode sheets, a separator, gaskets, springs, and electrolyte, and its electrochemical performance was tested.

[0036] Through the above steps, this embodiment successfully prepared nitrogen-doped carbon nanotubes loaded with iron nanoparticles (such as...). Figure 1 , Figure 2 (As shown in the figure). This method has the advantages of simple operation and stable product quality, and is suitable for large-scale production applications.

[0037] Example 2

[0038] 1. Catalyst dispersion treatment:

[0039] 2 mg of γ-iron oxide powder was added to 10 ml of anhydrous ethanol and stirred using a high-speed stirrer to fully disperse the γ-iron oxide powder in the ethanol to form a homogeneous mixture. The mixture was then transferred to an ultrasonic disperser and dispersed at a frequency of 40 kHz for 30 minutes. The dispersed mixture was then added dropwise to a silicon wafer and placed in an 80°C oven to dry for 30 minutes until the anhydrous ethanol was completely evaporated.

[0040] 2. Preparation of nitrogen-doped carbon nanotubes supporting iron nanoparticles:

[0041] The dried silicon wafer was placed in the center of the heating zone of a tube furnace. Polypropylene and urea were placed at the furnace inlet as carbon and nitrogen sources, respectively. The tube furnace was then evacuated, followed by the introduction of a hydrogen-argon mixture to atmospheric pressure. This process was repeated three times to ensure the purity of the furnace atmosphere. The furnace temperature was increased to 900°C at a rate of 10°C / min. Once the furnace temperature reached 900°C, it was maintained for 45 minutes to allow the polypropylene and melamine to vaporize and contact the γ-iron oxide catalyst on the silicon wafer, thereby triggering the growth of carbon nanotubes.

[0042] 3. Collection and processing of nitrogen-doped carbon nanotube-supported iron nanoparticles

[0043] After the furnace temperature cooled to room temperature, the silicon wafer was removed from the tube furnace. The silicon wafer was immersed in a beaker containing anhydrous ethanol and ultrasonically treated for 10 minutes using an ultrasonic disperser. Finally, the ultrasonically treated solution was centrifuged, and the carbon nanotubes precipitated at the bottom were collected. The washed carbon nanotubes were placed in a vacuum drying oven and dried at 60°C to obtain a dried carbon nanotube sample.

[0044] Finally, a negative electrode slurry was prepared by mixing graphite, SBR, carbon black, CMC, and the sample in a ratio of 94%:1.8%:2.2%:0.5%:1.5%. This slurry was then coated onto copper foil to form the negative electrode sheet. For the positive electrode, a slurry was prepared by mixing lithium iron phosphate, a conductive agent, and PVDF in a specific ratio and coated onto aluminum foil to form the positive electrode sheet. A button cell was then fabricated by combining the positive and negative electrode shells, the positive and negative electrode sheets, a separator, gaskets, springs, and electrolyte, and its electrochemical performance was tested.

[0045] Comparative Example 1

[0046] The conductive agent was replaced with commercially available SUPER-P. Finally, a negative electrode slurry was prepared by mixing graphite, SBR, carbon black, CMC, and the sample in a ratio of 94%:1.8%:2.2%:0.5%:1.5%. This slurry was then coated onto copper foil to form the negative electrode sheet. For the positive electrode, a slurry was prepared by mixing lithium iron phosphate, a conductive agent, and PVDF in a specific ratio and coated onto aluminum foil to form the positive electrode sheet. A button cell was then fabricated by combining the positive and negative electrode shells, positive and negative electrode sheets, separator, gasket, spring, and electrolyte, and its electrochemical performance was tested.

[0047] Comparative Example 2

[0048] The commercially available acetylene black was replaced with a conductive agent. Finally, a negative electrode slurry was prepared by mixing graphite, SBR, carbon black, CMC, and the sample in a ratio of 94%:1.8%:2.2%:0.5%:1.5%. This negative electrode slurry was then coated onto copper foil to form a negative electrode sheet. For the positive electrode, a slurry was prepared by mixing lithium iron phosphate, a conductive agent, and PVDF in a specific ratio and coated onto aluminum foil to form a positive electrode sheet. A button cell was then fabricated by combining the positive and negative electrode shells, positive and negative electrode sheets, separator, gasket, spring, and electrolyte, and its electrochemical performance was tested.

[0049] Comparative Example 3

[0050] Commercially available graphene was used as the conductive agent. Finally, a negative electrode slurry was prepared by mixing graphite, SBR, carbon black, CMC, and the sample in a ratio of 94%:1.8%:2.2%:0.5%:1.5%. This slurry was then coated onto copper foil to form the negative electrode sheet. For the positive electrode, a slurry was prepared by mixing lithium iron phosphate, a conductive agent, and PVDF in a specific ratio and coated onto aluminum foil to form the positive electrode sheet. A button cell was fabricated by combining the positive and negative electrode shells, positive and negative electrode sheets, separator, gasket, spring, and electrolyte, and its electrochemical performance was tested.

[0051] Comparative Example 4

[0052] Commercially available carbon nanotubes were used as the conductive agent. Finally, a negative electrode slurry was prepared by mixing graphite, SBR, carbon black, CMC, and the sample in a ratio of 94%:1.8%:2.2%:0.5%:1.5%. This slurry was then coated onto copper foil to form the negative electrode sheet. For the positive electrode, a slurry was prepared by mixing lithium iron phosphate, a conductive agent, and PVDF in a specific ratio and coated onto aluminum foil to form the positive electrode sheet. A button cell was fabricated by combining the positive and negative electrode shells, positive and negative electrode sheets, separator, gasket, spring, and electrolyte, and its electrochemical performance was tested.

[0053] Depend on Figure 1 , Figure 2 It can be seen that the method used in this invention has successfully prepared carbon nanotubes and doped them with nitrogen and nano-iron.

[0054] The performance of the lithium-ion button batteries used in Examples 1, 2, and Comparative Examples 1-4 were tested respectively, and the test results are as follows:

[0055] Table 1. Electrochemical performance of lithium-ion coin cells prepared in Examples 1, 2 and Comparative Examples 1-4

[0056]

[0057]

[0058] According to the data in Table 1:

[0059] (1) Under the same conditions of conductive agent content, the lithium battery prepared by using the conductive agent provided by the present invention has lower internal resistance, indicating that the conductive agent provided by the present invention has better effect. The introduction of nitrogen element improves the electrochemical activity of the conductive agent, making the conductive network composed of carbon nanotubes transport electrons faster, thereby improving the performance of lithium battery.

[0060] (2) Under the same conditions of conductive agent content, the lithium battery prepared by using the conductive agent provided by the present invention has higher specific capacity and capacity retention rate, indicating that the addition of nano iron improves the specific capacity of the lithium battery. Combining carbon nanotubes with nano iron can not only prevent the agglomeration and volume expansion of nano iron, but also improve the specific capacity and capacity retention rate of the lithium battery by utilizing the excellent conductivity of carbon nanotubes.

Claims

1. A method for preparing nitrogen-doped carbon nanotube supported nanoscale iron, characterized in that: The method is: (1) dissolve the catalyst in anhydrous ethanol, and treat by ultrasonic dispersion to obtain a catalyst solution with a concentration of 0.2-0.6 g / L; uniformly drop the catalyst solution onto the designated position of the substrate, and vacuum dry the substrate with the dropped catalyst solution to remove the solvent, to obtain catalyst particles; the catalyst is one or more of iron oxide, gamma-iron oxide, iron nitrate nonahydrate, and ferrocene; (2) place the substrate with the supported catalyst particles prepared in step (1) in the center position of the heating zone of a tube furnace, and place a carbon source and a nitrogen source at the gas inlet position of the tube furnace; then, perform vacuum treatment on the tube furnace, and then introduce hydrogen-argon mixed gas to normal pressure, and repeat this process three times to ensure the purity of the atmosphere in the furnace; increase the furnace temperature to 900℃ at a temperature increasing rate of 10℃ / min, and when the furnace temperature reaches 900℃, maintain this temperature for 45 minutes of reaction; the carbon source is polypropylene; and the nitrogen source is urea or melamine; (3) take out the cooled substrate from the tube furnace, and immerse it in anhydrous ethanol, and perform ultrasonic treatment on the substrate by an ultrasonic disperser to separate the nitrogen-doped carbon nanotube supported nanometer iron, and perform centrifugal separation on the ultrasonic treated solution by a centrifuge, collect the nitrogen-doped carbon nanotube supported nanometer iron precipitated at the bottom, and perform drying treatment.

2. The production method according to claim 1, characterized by: In step (1), the substrate is one or more of a silicon wafer, a nickel foam, and a quartz wafer.

3. The production method according to claim 1, wherein: In step (2), the hydrogen-argon mixed gas flow is controlled at 80-350 sccm.

4. The production method according to claim 1, wherein: In step (3), the drying treatment is vacuum drying or freeze drying.

5. The use of the nitrogen-doped carbon nanotube supported nanoscale iron prepared by the method of any one of claims 1-4. The nitrogen-doped carbon nanotube supported nanometer iron is used as a negative electrode conductive agent in a lithium ion battery; in the negative electrode slurry, the ratio of graphite, SBR, carbon black, CMC, nitrogen-doped carbon nanotube supported nanometer iron is 94%:1.8%:2.2%:0.5%-1%:1%-1.5%.

Images