Preparation method and application of high nitrogen-doped porous graphite

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a method for preparing highly nitrogen-doped porous graphite and its application. The present invention addresses the problem that the nitrogen content in the nitrogen-doped porous graphite obtained in the prior art is low, and the improvement in the performance of the graphite material is less than expected. A method for preparing highly nitrogen-doped porous graphite and its application are provided, comprising placing porous graphite powder, a nitrogen source, and a zinc-containing activator into a container, adding water to mix the three evenly, drying, heat-treating in a nitrogen atmosphere in a tubular furnace, washing with hydrochloric acid and water in sequence, and drying to obtain highly nitrogen-doped porous graphite. The present invention adds a zinc-containing activator, which can serve as a nitrogen-constrained reactor to preserve nitrogen-containing intermediates during the thermal conversion process. Compared with the prior art, the nitrogen-containing intermediates are easily decomposed into volatile substances (usually in the form of ammonia), which can effectively increase the nitrogen doping content in the porous graphite.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a preparation method of high-nitrogen-doped porous graphite and application thereof. Background Art

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and mature technology, are widely used in various energy storage devices, demonstrating excellent application prospects. Currently, graphite is the most commonly used anode material due to its low price, low potential, and extremely stable cycling performance. However, graphite's low theoretical specific capacity no longer meets the demand for advanced high-energy-density energy storage devices. Therefore, developing a carbon anode material with a higher capacity is an urgent challenge for lithium-ion batteries.

[0003] Heteroatom doping of graphite materials is an effective way to improve electrochemical performance. Heteroatom doping mainly includes nitrogen, phosphorus, boron and sulfur doping methods, among which nitrogen doping is the most commonly used. In energy storage devices such as lithium-ion batteries and supercapacitors, nitrogen doping can increase the specific surface area of ​​the material, improve the contact between the electrode and the electrolyte, and improve the charge transfer efficiency and ion diffusion rate, thereby improving the energy density, power density and cycle stability of the battery.

[0004] Currently, there are two main methods for preparing highly nitrogen-doped carbon materials: direct carbonization of nitrogen-containing precursors or carbon sources rich in nitrogen molecules. Nitrogen-doped carbon materials are generated by pyrolysis of nitrogen-containing organic precursors (such as melamine, urea, polypyrrole, and imidazole) at high temperatures. This method can be used to prepare nitrogen-doped carbon fibers, carbon nanotubes, graphite, and graphene.

[0005] Nitrogen-doped graphite is a modified material obtained by introducing nitrogen into graphite. This modification can significantly change the physical, chemical and electrical properties of graphite:

[0006] (1) Improve electrical conductivity: Nitrogen doping can change the band structure of graphite materials and improve their electrical conductivity, which is particularly important for applications such as electronic devices and electrode materials;

[0007] (2) Enhanced catalytic activity: Nitrogen doping can provide active sites for graphite materials, improving their catalytic performance in electrocatalysis (such as oxygen reduction reaction, water decomposition, etc.);

[0008] (3) Improved hydrophilicity: The introduction of nitrogen functional groups can increase the hydrophilicity of the material surface, which is beneficial for its application in biomedicine, environmental protection and other fields;

[0009] (4) Improve mechanical strength: Appropriate amount of nitrogen doping can enhance the mechanical strength and stability of graphite materials.

[0010] However, the nitrogen-doping synthesis process in the existing technology often requires more complicated synthesis steps, which will lead to increased production costs and face challenges in large-scale production. At the same time, the nitrogen content in the obtained nitrogen-doped porous graphite is low, and the improvement in the performance of the graphite material is less than expected. Summary of the Invention

[0011] The object of the present invention is to provide a method for preparing highly nitrogen-doped porous graphite in response to the above problems.

[0012] Another object of the present invention is to address the above-mentioned problem and provide a lithium battery electrode plate made of high-nitrogen-doped porous graphite prepared by a preparation method of high-nitrogen-doped porous graphite.

[0013] In order to achieve the above object, the present invention adopts the following technical solutions:

[0014] A method for preparing highly nitrogen-doped porous graphite comprises the following steps:

[0015] Step 1: Place porous graphite powder, nitrogen source and zinc-containing activator into a container, add water to mix the three evenly, and obtain a mixed solution;

[0016] Step 2: drying the mixed solution obtained in step 1 to obtain a dry mixture;

[0017] Step 3: heat-treating the dry mixture obtained in step 2 in a tube furnace under a nitrogen atmosphere to obtain a crude product;

[0018] Step 4: Wash the crude product obtained in step 3 with hydrochloric acid and water in sequence, and then dry to obtain highly nitrogen-doped porous graphite.

[0019] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in step 1 is 1:1-1.5:0.5-1.

[0020] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in step 1 is 1:1-1.1:0.5-0.6.

[0021] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in step 1 is 1:1.1-1.2:0.6-0.7.

[0022] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in step 1 is 1:1.2-1.3:0.7-0.8.

[0023] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in step 1 is 1:1.3-1.4:0.8-0.9.

[0024] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in step 1 is 1:1.4-1.5:0.9-1.

[0025] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the nitrogen source in step 1 is melamine.

[0026] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the zinc-containing activator in step 1 is zinc phosphate.

[0027] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the drying methods in step 2 and step 4 are freeze drying or thermal drying.

[0028] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the heat treatment method in step three is: heating to 380-420°C at 5°C / min and maintaining at this temperature for 0.5-1.5h, then heating to 600-700°C at 5°C / min and maintaining at this temperature for 0.5-1.5h.

[0029] In the above-mentioned method for preparing highly nitrogen-doped porous graphite, the concentration of hydrochloric acid in step 4 is 1 mol / L.

[0030] An application of high nitrogen doped porous graphite, using the high nitrogen doped porous graphite prepared by the above-mentioned preparation method of high nitrogen doped porous graphite as a preparation raw material.

[0031] In the above-mentioned application of high nitrogen-doped porous graphite, lithium battery electrode plates are prepared using high nitrogen-doped porous graphite, and the preparation method is as follows: high nitrogen-doped porous graphite and conductive carbon black are mixed and ground, and PVDF is added after being evenly ground, and the materials are mixed and degassed with a degassing machine to obtain a slurry-like liquid, and the slurry is evenly coated on aluminum foil using a coating machine, and placed in a vacuum oven and heated at 60-80°C for 12-24 hours for drying, and the dried aluminum foil is cut into 14mm discs to obtain lithium battery electrode plates.

[0032] In the application of the above-mentioned high nitrogen doped porous graphite, the mass ratio of the high nitrogen doped porous graphite, conductive carbon black and PVDF is 75-80:15-10:10.

[0033] Compared with the existing technology, the advantages of the present invention are:

[0034] 1. The present invention adds a zinc-containing activator, which can act as a nitrogen-constrained reactor to preserve nitrogen-containing intermediates during the thermal conversion process. Compared with the prior art, nitrogen-containing intermediates are easily decomposed into volatile substances (usually in the form of ammonia), which can effectively increase the nitrogen doping content in porous graphite.

[0035] 2. Under the same conditions, graphitic nitrogen is inactive in electrochemical processes, and an increase in its content leads to a decrease in electrochemical performance. Pyridinic and pyrrolic nitrogen have relatively good chemical activity, which helps improve the battery's ion transport capacity. Therefore, the present invention introduces zinc ions, which can combine with amine compounds to promote the formation of specific nitrides, namely pyridinic and pyrrolic nitrogen.

[0036] 3. The presence of macropores in carbon materials facilitates electrolyte penetration and reduces diffusion distance, while the presence of mesopores provides diffusion channels for ions. Excessive micropores hinder electrolyte penetration and lithium ion transport. The zinc oxide formed by the zinc phosphate at high temperatures acts as an in-situ template, facilitating the formation of macroporous and mesoporous structures, thereby further improving the electrical performance of the resulting electrode sheet.

[0037] 4. The synthesis method provided by the present invention is simple, easy to operate, has low production cost, and is suitable for large-scale promotion and use.

[0038] 5. The present invention found that during the heat treatment process, the performance is optimal when the treatment temperature is 700°C. When the temperature reaches above 800°C, the proportion of graphitic nitrogen formed will increase significantly. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The lithium battery electrode plates prepared in Example 1 and Comparative Example 1 were -1 Performance graph after 100 cycles. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0041] Example 1

[0042] This embodiment provides a lithium battery electrode plate, including the following steps:

[0043] Step 1: placing porous graphite powder, melamine and zinc phosphate into a container, adding water to mix the three evenly to obtain a mixed solution, wherein the mass ratio of porous graphite powder, melamine and zinc phosphate is 1:1.25:0.75;

[0044] Step 2: drying the mixed solution obtained in step 1 under vacuum at 60° C. to obtain a dry mixture;

[0045] Step 3: The dried mixture obtained in step 2 is heat-treated in a tube furnace under a nitrogen atmosphere. The heat treatment method is: heating to 400°C at 5°C / min and maintaining at this temperature for 1 hour, then heating to 700°C at 5°C / min and maintaining at this temperature for 1 hour to obtain a crude product;

[0046] Step 4: The crude product obtained in step 3 is washed with 1 mol / L hydrochloric acid and water in sequence, and vacuum dried at 60°C to obtain highly nitrogen-doped porous graphite;

[0047] Step 5: Mix the high nitrogen-doped porous graphite and conductive carbon black prepared in step 4 and grind them. After grinding evenly, add PVDF. The mass ratio of high nitrogen-doped porous graphite, conductive carbon black and PVDF is 78:12:10. Use a degassing machine to mix and degas the materials to obtain a slurry-like liquid. Use a coating machine to evenly coat the slurry on aluminum foil. Place it in a vacuum oven and heat it at 70°C for 18 hours to dry. Cut the dried aluminum foil into 14mm discs to form lithium battery electrode sheets.

[0048] Among them, the porous graphite powder in this embodiment adopts the porous graphite powder produced by Dongguan Ruitu New Material Technology Co., Ltd., and the other embodiments and comparative examples in the present invention are the same.

[0049] Example 2

[0050] This embodiment provides a lithium battery electrode plate, including the following steps:

[0051] Step 1: placing porous graphite powder, melamine and zinc phosphate into a container, adding water to mix the three evenly to obtain a mixed solution, wherein the mass ratio of porous graphite powder, melamine and zinc phosphate is 1:1:0.5;

[0052] Step 2: drying the mixed solution obtained in step 1 at 80° C. to obtain a dry mixture;

[0053] Step 3: The dried mixture obtained in step 2 is heat-treated in a tube furnace under a nitrogen atmosphere. The heat treatment method is as follows: heating to 380°C at 5°C / min and maintaining at this temperature for 0.5h, then heating to 600°C at 5°C / min and maintaining at this temperature for 0.5h to obtain a crude product;

[0054] Step 4: washing the crude product obtained in step 3 with 1 mol / L hydrochloric acid and water in sequence, and drying at 80°C to obtain highly nitrogen-doped porous graphite;

[0055] Step 5: Mix the high nitrogen-doped porous graphite and conductive carbon black prepared in step 4 and grind them. After grinding evenly, add PVDF. The mass ratio of high nitrogen-doped porous graphite, conductive carbon black and PVDF is 75:10:10. Use a degassing machine to mix and degas the materials to obtain a slurry-like liquid. Use a coating machine to evenly coat the slurry on aluminum foil. Place it in a vacuum oven and heat it at 60°C for 12 hours to dry. Cut the dried aluminum foil into 14mm discs to form lithium battery electrode sheets.

[0056] Example 3

[0057] This embodiment provides a lithium battery electrode plate, including the following steps:

[0058] Step 1: placing porous graphite powder, melamine and zinc phosphate into a container, adding water to mix the three evenly to obtain a mixed solution, wherein the mass ratio of porous graphite powder, melamine and zinc phosphate is 1:1.5:1;

[0059] Step 2: freeze-drying the mixed solution prepared in step 1 to obtain a dry mixture;

[0060] Step 3: The dried mixture obtained in step 2 is heat-treated in a tube furnace under a nitrogen atmosphere. The heat treatment method is as follows: heating to 420°C at 5°C / min and maintaining at this temperature for 1.5 hours, then heating to 650°C at 5°C / min and maintaining at this temperature for 1.5 hours to obtain a crude product;

[0061] Step 4: The crude product obtained in step 3 is washed with 1 mol / L hydrochloric acid and water in sequence, and freeze-dried to obtain highly nitrogen-doped porous graphite;

[0062] Step 5: Mix the high nitrogen-doped porous graphite and conductive carbon black prepared in step 4 and grind them. After grinding evenly, add PVDF. The mass ratio of high nitrogen-doped porous graphite, conductive carbon black and PVDF is 80:15:10. Use a degassing machine to mix and degas the materials to obtain a slurry-like liquid. Use a coating machine to evenly coat the slurry on aluminum foil. Place it in a vacuum oven and heat it at 80°C for 24 hours to dry. Cut the dried aluminum foil into 14mm discs to form lithium battery electrode sheets.

[0063] Comparative Example 1

[0064] This comparative example provides a lithium battery electrode plate, comprising the following steps:

[0065] Step 1: placing porous graphite powder and melamine into a container, adding water and mixing evenly to obtain a mixed solution, wherein the mass ratio of porous graphite powder to melamine is 1:1.25;

[0066] Step 2: drying the mixed solution obtained in step 1 under vacuum at 60° C. to obtain a dry mixture;

[0067] Step 3: The dried mixture obtained in step 2 is heat-treated in a tube furnace under a nitrogen atmosphere. The heat treatment method is: heating to 400°C at 5°C / min and maintaining at this temperature for 1 hour, then heating to 700°C at 5°C / min and maintaining at this temperature for 1 hour to obtain a crude product;

[0068] Step 4: The crude product obtained in step 3 is washed with 1 mol / L hydrochloric acid and water in sequence, and vacuum dried at 60°C to obtain highly nitrogen-doped porous graphite;

[0069] Step 5: Mix the high nitrogen-doped porous graphite and conductive carbon black prepared in step 4 and grind them. After grinding evenly, add PVDF. The mass ratio of high nitrogen-doped porous graphite, conductive carbon black and PVDF is 78:12:10. Use a degassing machine to mix and degas the materials to obtain a slurry-like liquid. Use a coating machine to evenly coat the slurry on aluminum foil. Place it in a vacuum oven and heat it at 70°C for 18 hours to dry. Cut the dried aluminum foil into 14mm discs to form lithium battery electrode sheets.

[0070] Comparative Example 2

[0071] This comparative example provides a lithium battery electrode plate, comprising the following steps:

[0072] Step 1: placing porous graphite powder, melamine and zinc phosphate into a container, adding water to mix the three evenly to obtain a mixed solution, wherein the mass ratio of porous graphite powder, melamine and zinc phosphate is 1:1.25:0.75;

[0073] Step 2: drying the mixed solution obtained in step 1 under vacuum at 60° C. to obtain a dry mixture;

[0074] Step 3: The dried mixture obtained in step 2 is heat-treated in a tube furnace under a nitrogen atmosphere. The heat treatment method is: heating to 400°C at 5°C / min and maintaining at this temperature for 1 hour, then heating to 800°C at 5°C / min and maintaining at this temperature for 1 hour to obtain a crude product;

[0075] Step 4: The crude product obtained in step 3 is washed with 1 mol / L hydrochloric acid and water in sequence, and vacuum dried at 60°C to obtain highly nitrogen-doped porous graphite;

[0076] Step 5: Mix the high nitrogen-doped porous graphite and conductive carbon black prepared in step 4 and grind them. After grinding evenly, add PVDF. The mass ratio of high nitrogen-doped porous graphite, conductive carbon black and PVDF is 78:12:10. Use a degassing machine to mix and degas the materials to obtain a slurry-like liquid. Use a coating machine to evenly coat the slurry on aluminum foil. Place it in a vacuum oven and heat it at 70°C for 18 hours to dry. Cut the dried aluminum foil into 14mm discs to form lithium battery electrode sheets.

[0077] Application Example 1

[0078] The element contents of the lithium battery electrode sheets prepared in Example 1 and the lithium battery electrode sheets prepared in Comparative Example 1 were measured, and the results are shown in the following table:

[0079]

[0080] Result analysis: Comparing the above experimental results, it can be seen that the nitrogen content in the lithium battery electrode plates prepared after adding zinc phosphate is significantly increased.

[0081] Application Example 2

[0082] The contents of pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen and pyridinic oxygen nitrogen in the lithium battery electrode sheets prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were measured by XPS fitting. The results are shown in the following table:

[0083]

[0084] Results Analysis: Comparing the above experimental results, it can be seen that after the introduction of zinc ions, zinc ions can combine with amine compounds, thereby promoting the formation of specific nitrides, namely pyridinic nitrogen and pyrrolic nitrogen, while inhibiting the formation of graphitic nitrogen. After the temperature reaches 800℃, the proportion of graphitic nitrogen increases significantly.

[0085] Application Example 3

[0086] The lithium battery electrode plates prepared in Example 1 and Comparative Example 1 were measured at 200 mAg -1 The performance graph of the next cycle 100 times is as follows Figure 1 shown.

[0087] from Figure 1 As can be seen, both materials show relatively stable cycle performance, and the reversible specific capacities after 100 cycles are 592.3 and 307.1 mAg respectively. -1 The electrochemical performance of the nitrogen-doped carbon material prepared with the addition of zinc phosphate is much higher than that without the addition of zinc phosphate, which is due to the higher nitrogen doping level.

[0088] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A method for preparing highly nitrogen-doped porous graphite, characterized in that: The following steps are involved: Step 1: Place porous graphite powder, nitrogen source and zinc-containing activator into a container, add water to mix the three evenly, and obtain a mixed solution; Step 2: drying the mixed solution obtained in step 1 to obtain a dry mixture; Step 3: heat-treating the dry mixture obtained in step 2 in a tube furnace under a nitrogen atmosphere to obtain a crude product; Step 4: washing the crude product obtained in step 3 with hydrochloric acid and water in sequence, and drying to obtain highly nitrogen-doped porous graphite; The zinc-containing activator in the step 1 is zinc phosphate; The heat treatment method in step 3 is as follows: heating to 380-420°C at 5°C / min and maintaining at this temperature for 0.5-1.5h, then heating to 600-700°C at 5°C / min and maintaining at this temperature for 0.5-1.5h; The nitrogen source in the step 1 is melamine.

2. The method for preparing highly nitrogen-doped porous graphite according to claim 1, wherein: The mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in the step 1 is 1:1-1.5:0.5-1.

3. The method for preparing highly nitrogen-doped porous graphite according to claim 2, wherein: The mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in the step 1 is 1:1-1.1:0.5-0.

6.

4. The method for preparing highly nitrogen-doped porous graphite according to claim 2, wherein: The mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in the step 1 is 1:1.1-1.2:0.6-0.

7.

5. The method for preparing highly nitrogen-doped porous graphite according to claim 2, wherein: The mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in the step 1 is 1:1.2-1.3:0.7-0.

8.

6. The method for preparing highly nitrogen-doped porous graphite according to claim 2, wherein: The mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in the step 1 is 1:1.3-1.4:0.8-0.

9.

7. The method for preparing highly nitrogen-doped porous graphite according to claim 2, wherein: The mass ratio of the porous graphite powder, the nitrogen source and the zinc-containing activator in the step 1 is 1:1.4-1.5:0.9-1.

8. The method for preparing highly nitrogen-doped porous graphite according to claim 1, wherein: The drying methods in step 2 and step 4 are freeze drying or heat drying.

9. The method for preparing highly nitrogen-doped porous graphite according to claim 1, wherein: The concentration of hydrochloric acid in the step 4 is 1 mol / L.

10. An application of highly nitrogen-doped porous graphite, characterized in that: The high nitrogen-doped porous graphite prepared by the method for preparing high nitrogen-doped porous graphite according to any one of claims 1 to 9 is used as the preparation raw material.

11. The use of the highly nitrogen-doped porous graphite according to claim 10, characterized in that: Lithium battery electrode plates are prepared using high-nitrogen-doped porous graphite, and the preparation method is as follows: high-nitrogen-doped porous graphite and conductive carbon black are mixed and ground, and PVDF is added after being evenly ground. The materials are mixed and degassed using a degassing machine to obtain a slurry-like liquid, and the slurry is evenly coated on aluminum foil using a coating machine. The slurry is placed in a vacuum oven and heated at 60-80°C for 12-24 hours for drying. The dried aluminum foil is cut into 14mm discs to obtain lithium battery electrode plates.

12. The use of the highly nitrogen-doped porous graphite according to claim 11, characterized in that: The mass ratio of the highly nitrogen-doped porous graphite, the conductive carbon black and the PVDF is 75-80:15-10:10.

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