Carbon nanofiber and carbonaceous honeycomb framework composite conductive agent material and preparation method thereof

Abstract

The invention discloses a carbon nanofiber and carbonaceous honeycomb framework composite conductive agent material and a preparation method thereof, and belongs to the field of carbon materials. The method comprises the following steps: blending ferric nitrate and nickel nitrate with citric acid according to a molar ratio of 3: 1 to prepare an impregnation precursor solution; dipping an organic colloidal crystal template and drying to obtain a catalyst precursor; in a double-temperature-zone tubular furnace, a carbon source and a catalyst precursor are synchronously heated in a specific atmosphere, and the composite material with a fishbone-shaped structure is obtained through one-step roasting. The material is a composite system of carbon nanofibers and a carbonaceous honeycomb structure, the electronic conductivity reaches 40-140 S / cm, the structure and thermal stability are good, and the rate capability and cycle life of an electrochemical energy storage system such as a lithium ion battery can be remarkably improved and prolonged as a conductive agent. The method is simple in process and mild in condition, and has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon material synthesis and electrochemical energy storage material preparation, and specifically relates to a method for preparing a carbon nanofiber and carbon honeycomb structure composite conductive agent material and its application in electrochemical energy storage systems such as lithium-ion batteries. Background Art

[0002] Carbon nanofibers (CNFs) have high specific surface area (50-300m 2 g -1 ), good electrical conductivity, and excellent structural stability have made them a highly promising conductive additive in electrochemical energy storage systems. Introducing CNFs into electrode materials can construct a three-dimensional conductive network, significantly improving electron transfer efficiency and mitigating the volume expansion of active materials during cycling, thereby enhancing the rate performance and cycle life of the battery.

[0003] Currently, the main methods for preparing CNFs include arc discharge (generating high-temperature plasma through a DC arc), laser ablation (irradiating a graphite target with a pulsed laser), and chemical vapor deposition (CVD). For example, patent CN117699782A uses the arc method to prepare CNFs by adjusting its discharge parameters, patent CN104862696A uses laser power and scanning speed to control material morphology, and patent CN117446786A uses floating CVD technology to achieve CNF synthesis under mild conditions. However, the above methods still have obvious shortcomings in terms of process complexity, energy consumption, and product structure diversity. In particular, the materials produced by the CVD method are mostly straight cylindrical structures (also known as carbon nanotubes (CNTs)), which are difficult to disperse and difficult to adapt to the structural changes of the electrode material during the charging and discharging process, limiting their application in high-performance energy storage devices. The inventors' team previously developed a highly dispersed three-dimensional carbon nanotube aggregate material (Patent No.: CN202210230520.6) based on a nickel salt-impregnated polymethyl methacrylate (PMMA) microsphere template. The simple and efficient preparation process provides a new approach for preparing carbon nanofibers using CVD technology.

[0004] On the other hand, in recent years, carbon honeycomb architectures (CHAs) have attracted widespread attention due to their unique three-dimensional porous structure and good structural stability. CHAs are usually synthesized by template method (see the inventor team’s authorized patent: ZL201610565108.4), with a relatively ordered pore system, uniform pore size distribution, and high specific surface area (up to 100-300m 2 / g), showing potential applications in adsorption, catalysis, energy storage, and other fields. Research has shown that CHAs retain their structure strongly during high-temperature processing, maintaining their original honeycomb skeleton during carbonization, thereby providing excellent support and conductive pathways for the directional growth of carbon nanostructures. Furthermore, their porous nature effectively mitigates volume changes during charge and discharge, improving the material's cycling stability.

[0005] However, although CNFs and CHAs each perform well in terms of electrical conductivity and structural adaptability, they still have certain limitations when used alone. For example, CNFs are prone to agglomeration and their structure is easily destroyed at high temperatures; although CHAs have good structural stability, their electrical conductivity is relatively low, making it difficult to meet the requirements of high-power energy storage devices for electron transport performance. Therefore, how to organically combine CNFs and CHAs to form a composite conductive agent material that simultaneously takes into account high conductivity and structural stability is of great research significance. The present invention proposes a composite material of carbon nanofibers and carbon honeycomb structure with a fishbone-shaped microstructure based on a mixed salt precursor with a molar ratio of ferric nitrate to nickel nitrate of 3:1, and a one-step calcination process using a hard template method. This material shows significant advantages in electrical conductivity, structural stability and electrochemical applications, and has good prospects for industrial application. Summary of the Invention

[0006] The present invention aims to provide a method for preparing a composite conductive agent material of carbon nanofibers and carbon honeycomb structures. The core of the method is to use a mixed salt of ferric nitrate and nickel nitrate in a specific proportion as a catalyst precursor, combined with a hard template method one-step roasting process, to form a composite carbon-based conductive agent material with excellent conductive properties and structural characteristics at a lower temperature and catalyst dosage.

[0007] The method comprises the following steps:

[0008] (1) dissolving ferric nitrate, nickel nitrate and citric acid in water in a specific molar ratio to prepare an impregnation precursor solution;

[0009] (2) immersing the organic polymer colloidal crystal microsphere template in the precursor solution of step (1), and obtaining a metal salt-loaded precursor after filtration and drying;

[0010] (3) placing the organic liquid in the low temperature zone of a dual-temperature zone tubular furnace and placing the catalyst precursor obtained in step (2) in the high temperature zone;

[0011] (4) Under a specific carrier gas atmosphere, the temperature is simultaneously raised and a one-step calcination process is completed to finally obtain a composite material of carbon nanofibers and carbon honeycomb structure.

[0012] In step (1), the molar ratio of ferric nitrate to nickel nitrate is 3:1, and the total concentration of the nitrate solution is 0.5-3 mol / L.

[0013] In step (1), the concentration of citric acid is 0.5-3 mol / L, preferably 1.5 mol / L.

[0014] In step (2), the organic polymer colloidal crystal microsphere template is polymethyl methacrylate (PMMA) colloidal crystal.

[0015] In step (2), the impregnation process is carried out at room temperature, and the impregnation time is 3-24 hours, preferably 4 hours.

[0016] In step (3), the organic liquid includes but is not limited to one or a mixture of ethyl acetate, methyl methacrylate (MMA), pentanol, pentane or cyclohexane, preferably MMA.

[0017] In step (4), the carrier gas is argon (Ar) or a mixture of hydrogen and argon (H2-Ar), with a gas flow rate of 1-300 sccm, preferably 5 sccm. The gas flows from the low temperature zone to the high temperature zone.

[0018] In step (4), the heating program is a staged heating program, specifically: the heating rate in the low temperature zone is 1-50°C / min, and the final roasting temperature is not lower than the boiling point of the organic liquid; the heating rate in the high temperature zone is 1-50°C / min, the final roasting temperature is 700-1200°C, and the holding time is 0-60min and is not 0; preferably, the low temperature zone is heated to 106°C at 2°C / min and kept at a constant temperature, the high temperature zone is heated to 390°C at 10°C / min, and then heated to 750-1000°C (more preferably 1000°C) at 12°C / min, and kept warm for 20min.

[0019] The obtained composite material is a composite material of carbon nanofibers with a fishbone-shaped microstructure and a carbon honeycomb structure; the electronic conductivity of the prepared carbon nanofiber and carbon honeycomb structure composite material is 40-140S / cm, and the angle between the graphene layer of the carbon nanofiber tube wall and the fiber axis is 7-16°.

[0020] After the metal catalyst is etched away (for example, by acid removal), the material can be used as a conductive agent in an electrochemical energy storage system.

[0021] Compared with the prior art, the present invention has the following significant advantages:

[0022] (1) Composite material structure: The prepared material is a composite of carbon nanofibers and a carbon honeycomb structure, wherein the carbon nanofibers exhibit a fishbone-shaped crystal structure, and the angle between the graphene layer on the tube wall and the fiber axis is between 7-16°, which can significantly improve the material's electron transmission efficiency and structural adaptability;

[0023] (2) Excellent electrical conductivity: Composite conductive materials with electrical conductivity as high as 40-140S / cm can be prepared at relatively low calcination temperatures (700-1000°C) and low gas velocity (5 sccm);

[0024] (3) The process is simple and controllable: the one-step roasting process simplifies the operation process and improves the controllability and repeatability of the process;

[0025] (4) Low catalyst dosage: The metal content in the conductive agent material obtained is less than 3 at%, that is, the preparation process can achieve high metal catalyst utilization and material purity, which helps to reduce production costs;

[0026] (5) Outstanding electrochemical performance: After the metal catalyst is etched away, the composite material can be used as a positive electrode conductive agent for lithium-ion batteries to effectively improve the battery's rate performance and cycle stability;

[0027] (6) Strong structural stability: The synergistic effect of fishbone-shaped carbon nanofibers and honeycomb-shaped carbon skeleton makes the material show good stability in thermal and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the structural features and implementation methods of the present invention, the following drawings are provided:

[0029] Figure 1 These are scanning electron microscope (SEM) images of the composite conductive agent material obtained by using MMA at different calcination temperatures in Example 1: (ab) : 750°C; (cd) 1000°C.

[0030] Figure 2 These are SEM images of the materials obtained in Example 2 when other liquid organic matter was used as the carbon source at a calcination temperature of 850° C.: (a) cyclohexane; (b) cyclopentane.

[0031] Figure 3 These are transmission electron microscope (TEM) images of the composite conductive agent material obtained by using MMA at different calcination temperatures in Example 1: (ab) 750°C; (cd) 1000°C.

[0032] Figure 4 This is the electronic conductivity test result of the composite material obtained in Example 1-2.

[0033] Figure 5This is a schematic diagram of the application of the composite material prepared in Example 1 as a conductive agent in the positive electrode of a lithium-ion battery (named LFP-Fe3Ni1-1000), wherein the active material is LiFePO4, the binder is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP). DETAILED DESCRIPTION

[0034] The following examples illustrate the preparation methods of the present invention and are not intended to limit the scope of protection of the present invention. Materials prepared using other metal salt ratios (e.g., Fe:Ni ratios of 1:3, 2:2, and 4:0) are provided as comparative materials, intended only to illustrate the advantages of the present materials in terms of conductivity and structural properties.

[0035] Example 1

[0036] First, a mixed salt solution of ferric nitrate and nickel nitrate was prepared in a molar ratio of 3:1, with a citric acid concentration of 1.5 mol / L and a total salt concentration of 1.5 mol / L. After thorough stirring, an impregnation precursor solution was formed. A PMMA colloidal crystal template was then immersed in the precursor solution for 4 hours, filtered, and dried to obtain a catalyst composite precursor. MMA was then placed in the low-temperature zone of a dual-zone tubular furnace as a carbon source. The resulting precursor was then placed in the high-temperature zone of a calcination furnace. An H₂-Ar gas mixture with a flow rate of 5 sccm flowed from the low-temperature zone to the high-temperature zone. Finally, the low-temperature zone was heated at a rate of 2°C / min to 106°C and held constant. The high-temperature zone was then heated at a rate of 10°C / min to 390°C, then at a rate of 12°C / min to 750°C (or 1000°C) and held there for 20 minutes. After calcination, the mixture was cooled to obtain a composite conductive material with a fishbone-shaped carbon nanofiber structure and a carbon honeycomb structure. Among them, the electrical conductivity of the material obtained by calcining at 750°C (measured after compaction at 200 MPa) and the average diameter and angle of its CNFs component were 45.4 S / cm, 38.6 nm and 11.2°, respectively; the electrical conductivity of the material obtained by calcining at 1000°C (measured after compaction at 200 MPa) and the average diameter and angle of its CNFs component were 140.1 S / cm, 41.1 nm and 9.3°, respectively.

[0037] Example 2

[0038] First, ferric nitrate and nickel nitrate are still prepared in a 3:1 molar ratio, the citric acid concentration is 1.5 mol / L, the total salt concentration is 3 mol / L, and the precursor solution is formed after stirring evenly: secondly, the PMMA colloidal crystal template is immersed in the precursor solution for 4 hours, filtered and dried to obtain a catalyst composite precursor; thirdly, cyclohexane (or cyclopentane) is placed in a low-temperature zone as a carbon source, and the precursor obtained in step 2 is placed in a high-temperature zone. The calcination atmosphere is a H2-Ar mixed gas with a gas flow rate of 5 sccm; finally, the low-temperature zone is heated to 106°C at a rate of 2°C / min and kept at a constant temperature; the high-temperature zone is first heated to 390°C at a rate of 10°C / min, and then heated to 850°C at a rate of 12°C / min, and kept warm for 20 minutes. After calcination is completed and cooled, a carbon nanofiber and carbon honeycomb structure composite material is obtained. When cyclohexane was used as the carbon source, the electrical conductivity of the obtained composite material (compression at 20 MPa) and the average diameter and angle of its CNFs were 82.9 S / cm, 117.7 nm and 13.5°, respectively; when cyclopentane was used as the carbon source, the electrical conductivity of the obtained composite material (compression at 20 MPa) and the average diameter and angle of its CNFs component were 87.8 S / cm, 26.2 nm and 15.3°, respectively.

[0039] Test Example 1

[0040] The microstructure of the material was characterized by a Regulus 4800 scanning electron microscope (SEM) and a JEM F200 high-resolution transmission electron microscope (TEM). The conductivity was measured by a PCRD3100 powder conductivity and compaction density meter. The electrochemical performance of the material in lithium-ion batteries was evaluated by a CT2001A blue battery test system. Figure 5 The performance results show that when the molar ratio of iron nitrate to nickel nitrate is 3:1, the conductive agent performance of the material is better than that of other ratios (2:2 and 4:0). That is, the rate performance and cycle stability of the lithium iron phosphate positive electrode based on this conductive agent are both optimal. For example, at a rate of 5C (current density of 170mA / g at 1C), its specific capacity reaches a maximum of 52.5mAh / g ( Figure 5 (a), and after 35 cycles at 1C, its specific capacity is also the largest among the three (91.5 mAh / g; Figure 5 (b)

Claims

1. A carbon nanofiber and carbon honeycomb structure composite conductive material, characterized in that: Composite materials of carbon nanofibers and carbon honeycomb structure with fishbone-shaped microstructure.

2. A method for preparing a carbon nanofiber and carbon honeycomb structure composite conductive material according to claim 1, characterized in that: The following steps are involved: (1) dissolving ferric nitrate, nickel nitrate and citric acid in water in a specific molar ratio to prepare an impregnation precursor solution; (2) immersing the organic polymer colloidal crystal microsphere template in the precursor solution of step (1), and obtaining a metal salt-loaded precursor after filtration and drying; (3) placing the organic liquid in the low temperature zone of a dual-temperature zone tubular furnace and placing the catalyst precursor obtained in step (2) in the high temperature zone; (4) Under a specific carrier gas atmosphere, the temperature is simultaneously raised and a one-step calcination process is completed to finally obtain a composite material of carbon nanofibers and carbon honeycomb structure.

3. The method according to claim 2, characterized in that In step (1), the molar ratio of ferric nitrate to nickel nitrate is 3:1, and the total concentration of the nitrate solution is 0.5-3 mol / L.

4. The method according to claim 2, characterized in that In step (1), the concentration of citric acid is 0.5-3 mol / L, preferably 1.5 mol / L.

5. The method according to claim 2, characterized in that In step (2), the organic polymer colloidal crystal microsphere template is polymethyl methacrylate (PMMA) colloidal crystal; in step (2), the impregnation process is carried out at room temperature, and the impregnation time is 3-24 hours, preferably 4 hours.

6. The method according to claim 2, characterized in that In step (3), the organic liquid includes but is not limited to one or a mixture of ethyl acetate, methyl methacrylate (MMA), pentanol, pentane or cyclohexane, preferably MMA.

7. The method according to claim 2, characterized in that In step (4), the carrier gas is argon (Ar) or a mixture of hydrogen and argon (H2-Ar), with a gas flow rate of 1-300 sccm, preferably 5 sccm. The gas flows from the low temperature zone to the high temperature zone.

8. The method according to claim 2, characterized in that In step (4), the heating program is a staged heating program, specifically: the heating rate in the low temperature zone is 1-50°C / min, and the final roasting temperature is not lower than the boiling point of the organic liquid; the heating rate in the high temperature zone is 1-50°C / min, the final roasting temperature is 700-1200°C, and the holding time is 0-60min and is not 0; preferably, the low temperature zone is heated to 106°C at 2°C / min and kept at a constant temperature, the high temperature zone is heated to 390°C at 10°C / min, and then heated to 750-1000°C (more preferably 1000°C) at 12°C / min, and kept warm for 20min.

9. The method according to claim 2, characterized in that The electronic conductivity of the prepared carbon nanofiber and carbon honeycomb structure composite material is 40-140S / cm, and the angle between the graphene layer on the tube wall of the carbon nanofiber and the fiber axis is 7-16 degrees.

10. The method according to any one of claims 2 to 9, characterized in that: After the metal catalyst is etched away, the material is used as a conductive agent in an electrochemical energy storage system, such as a lithium-ion battery.

Images