Nitrogen-doped phenolic resin-based porous carbon microspheres, preparation method and application thereof

Abstract

This invention provides nitrogen-doped phenolic resin-based porous carbon microspheres, their preparation method, and applications. The preparation method of the nitrogen-doped phenolic resin-based porous carbon microspheres includes the following steps: 1) dissolving polyethyleneimine in a solvent and stirring to obtain a first solution; 2) adding resorcinol and stirring to obtain a second solution; 3) adding melamine to obtain a third solution; 4) adding formaldehyde solution and stirring to obtain a fourth solution; 5) stirring and heating the fourth solution, then adding potassium hydroxide and continuing to stir and heat to obtain a fifth solution; 6) filtering, drying, ball milling, and carbonizing the fifth solution to obtain the final product. This method incorporates small-molecule polyethyleneimine into a phenolic resin carbon microsphere precursor formed from resorcinol and formaldehyde. During the subsequent carbonization process, the small-molecule branched polyethyleneimine decomposes thermally, leaving a porous structure inside the carbon microspheres. Simultaneously, potassium hydroxide etches a porous structure on the surface, and the combination of melamine nitrogen doping imparts superior electrical conductivity to the carbon material.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a nitrogen-doped phenolic resin-based porous carbon microsphere, its preparation method, and its application. Background Technology

[0002] With the increasing consumption of traditional energy sources such as oil, natural gas, and coal, environmental issues have become increasingly prominent in recent years. New energy sources such as hydropower, wind power, and solar energy are being developed vigorously, placing higher demands on mobile energy storage systems in everything from power tools to electric vehicles. Lithium-ion batteries, with their stable capacity and safe and reliable electrical performance, are widely used in various mobile tools. However, with the rapid development of science and technology, people have increasingly higher requirements for the battery life of lithium-ion batteries. Currently, lithium-ion batteries mainly use lithium iron phosphate (LiFePO4) and ternary materials (Li(Ni)... x Co y Mn 1－x－y O2 is the main positive electrode material, while graphite is the main negative electrode material, with an energy density of 200-300 Wh·kg. -1 .

[0003] Porous carbon spheres, as a type of carbon material, possess advantages such as good chemical stability, excellent electrical conductivity, large specific surface area, and low density. Their regular spherical structure further enhances their promising application prospects. Phenolic resins, as carbon source precursors, are widely used in lithium-ion battery anodes due to their good plasticity and controllable synthesis.

[0004] However, the existing synthesis of phenolic resin-based porous carbon microspheres mainly relies on template methods. The templates are mainly metal oxide templates such as PS spheres (polystyrene), zinc oxide, and tin oxide. The raw material cost of templates is relatively high, and the template material needs to be removed later to obtain porous carbon materials. This increases the raw material cost and preparation cost, and also prolongs the process time. In addition, the specific surface area of ​​the prepared porous carbon materials is not high, and the pore size distribution is uneven and not concentrated, with most of them being macropores.

[0005] Various doping methods are often used in lithium battery materials to improve the conductivity of the materials, such as phosphorus doping, nitrogen doping, and metal oxide doping. However, the doping process is relatively complex. For example, hydrothermal method and in-situ synthesis method are complex and require high synthesis conditions, making it difficult to achieve large-scale industrial production.

[0006] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0007] To address the problems of complex processes and uneven pore size distribution in existing technologies, the present invention aims to provide a nitrogen-doped phenolic resin-based porous carbon microsphere, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention relates to a method for preparing nitrogen-doped phenolic resin-based porous carbon microspheres, comprising the following steps:

[0010] (1) Dissolve polyethyleneimine in a solvent and stir to obtain the first solution;

[0011] The mass ratio of the polyethyleneimine to the volume ratio of the solvent is 1 g: (100-300) mL;

[0012] (2) Dissolve resorcinol in the first solution and stir to obtain the second solution;

[0013] The mass ratio of resorcinol to polyethyleneimine is 10:(1-3);

[0014] (3) Dissolve melamine in water, disperse it by ultrasonication, and add it to the second solution to obtain the third solution;

[0015] The mass of the melamine is 2%-5% of the mass of resorcinol;

[0016] (4) Add formaldehyde solution to the third solution and stir to obtain the fourth solution;

[0017] (5) Stir and heat the fourth solution, then add potassium hydroxide, and continue stirring and heating to obtain the fifth solution;

[0018] (6) The fifth solution is filtered, dried, ball-milled and carbonized to obtain the final product.

[0019] Preferably, the solvent is deionized water; the polyethyleneimine is branched polyethyleneimine with a molecular weight of 200-600.

[0020] Preferably, the mass ratio of polyethyleneimine to solvent is 1 g: 100 mL; the mass ratio of resorcinol to polyethyleneimine is 10: 3; and the mass of melamine is 3% of the mass of resorcinol.

[0021] Preferably, the formaldehyde solution has a mass concentration of 20%-50%.

[0022] Preferably, the formaldehyde solution has a mass concentration of 30%; and the mass ratio of resorcinol to the volume of the formaldehyde solution is 1g:2mL.

[0023] Preferably, the concentration of potassium hydroxide is 1 mol / L, and the volume ratio of potassium hydroxide to resorcinol is 1 mL: 1 g.

[0024] Preferably, the stirring time in step (1) is 20-40 min; the stirring time in step (2) is 20-40 min; the ultrasonic time in step (3) is 5-10 min; and the stirring time in step (4) is 20-40 min.

[0025] Preferably, step (5) stirring and heating are carried out in a closed reaction vessel, and the stirring is carried out at a constant temperature while stirring. The stirring speed is 150-400 r / min and the heating temperature is 60-90℃. Before adding potassium hydroxide, the stirring is carried out for 12-30 hours while heating. After adding potassium hydroxide, the stirring is carried out for 20-40 minutes while heating.

[0026] Preferably, in step (5), the stirring speed is 300 r / min, the heating temperature is 85℃, and the stirring is carried out for 24 hours while heating before adding potassium hydroxide; after adding potassium hydroxide, the stirring is carried out for 30 minutes while heating.

[0027] Preferably, the drying temperature in step (6) is 70°C and the drying time is 8-12h; the ball milling speed is 300r / min and the ball milling time is 20min; the carbonization temperature is 600-900°C and the carbonization time is 1-3h.

[0028] This invention provides nitrogen-doped phenolic resin-based porous carbon microspheres, which are prepared by the aforementioned preparation method;

[0029] Preferably, the nitrogen-doped phenolic resin-based porous carbon microspheres have an internal pore structure.

[0030] This invention provides an application of nitrogen-doped phenolic resin-based porous carbon microspheres, specifically the application of the nitrogen-doped phenolic resin-based porous carbon microspheres prepared by the aforementioned method in lithium-ion batteries.

[0031] Beneficial effects:

[0032] This invention involves incorporating small-molecule polyethyleneimine into a phenolic resin carbon sphere precursor formed from resorcinol and formaldehyde. During subsequent carbonization, the small-molecule branched polyethyleneimine decomposes thermally, leaving a porous structure inside the carbon spheres. Simultaneously, potassium hydroxide etches a porous structure onto the surface. This invention also incorporates melamine nitrogen doping, which imparts superior electrical conductivity to the carbon material.

[0033] The preparation process of this invention is simple, green and environmentally friendly, and can be mass-produced. The resulting nitrogen-doped phenolic resin-based porous carbon microspheres can be widely used in energy fields such as supercapacitors and lithium-ion batteries. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0035] Figure 1 The images show scanning electron microscope (SEM) and partial transmission electron microscope (TEM) images of the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1.

[0036] Figure 2 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1 of this invention.

[0037] Figure 3 The adsorption-desorption curves are shown for the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1 of this invention.

[0038] Figure 4 The pore size distribution diagram is shown for the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1 of this invention.

[0039] Figure 5 The image shows the XRD pattern of the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1 of this invention.

[0040] Figure 6 The impedance comparison diagrams are of the carbon microspheres prepared in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0042] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0043] This invention addresses the problems existing in current phenolic resin-based porous carbon microspheres by providing a method for preparing nitrogen-doped phenolic resin-based porous carbon microspheres, comprising the following steps:

[0044] (1) Dissolve polyethyleneimine in a solvent and stir to obtain the first solution;

[0045] The mass ratio of the polyethyleneimine to the volume ratio of the solvent is 1g:100mL-300mL (e.g., 1g:100mL, 1g:150mL, 1g:200mL, 1g:250mL or 1g:300mL).

[0046] (2) Dissolve resorcinol in the first solution and stir to obtain the second solution;

[0047] The mass ratio of resorcinol to polyethyleneimine is 10:(1-3) (e.g., 10:1, 10:2 or 10:3);

[0048] (3) Dissolve melamine in water, disperse it by ultrasonication, and add it to the second solution to obtain the third solution;

[0049] The mass of the melamine is 2%-5% (e.g., 2%, 3%, 4% or 5%) of the mass of resorcinol;

[0050] (4) Add formaldehyde solution to the third solution and stir to obtain the fourth solution;

[0051] (5) Stir and heat the fourth solution, then add potassium hydroxide, and continue stirring and heating to obtain the fifth solution;

[0052] (6) The fifth solution is filtered, dried, ball-milled and carbonized to obtain the final product.

[0053] In a preferred embodiment of the present invention, the solvent is deionized water; the polyethyleneimine is branched polyethyleneimine with a weight-average molecular weight Mw of 200-600.

[0054] In a preferred embodiment of the present invention, the weight-average molecular weight (Mw) of the branched polyethyleneimine is 400-600 Mw.

[0055] This invention uses phenolic resin formed from resorcinol and formaldehyde as the carbon source, melamine as the nitrogen source, and small-molecule polyethyleneimine as the internal pore-forming agent to prepare nitrogen-doped phenolic resin-based porous carbon microspheres via a liquid-phase method. This invention selects low-molecular-weight branched polyethyleneimine because high-molecular-weight polyethyleneimine particles are larger and have an interlaced three-dimensional disordered structure, making it impossible to control the pore size structure of the material. After carbonization heat treatment, the small-molecule branched polymer polyethyleneimine decomposes thermally, leaving a pore structure inside the carbon spheres. Combined with alkaline etching pore-forming treatment during carbonization, porous carbon microspheres with a particle size of 3-5 μm and uniform particle size distribution are obtained.

[0056] In a preferred embodiment of the present invention, the mass ratio of polyethyleneimine to solvent is 1g:100mL; the mass ratio of resorcinol to polyethyleneimine is 10:3; and the mass of melamine is 3% of the mass of resorcinol.

[0057] This invention uses melamine as a nitrogen source. Nitrogen doping can improve the conductivity of the material, and melamine is low in cost and readily available, making it suitable for loading into phenolic resin polymers. However, excessive melamine doping can clog pores and negatively impact the specific surface area of ​​the material, leading to a reduction in the specific surface area. Therefore, in this invention, the melamine doping mass is 3% of the resorcinol mass.

[0058] In a preferred embodiment of the present invention, the mass concentration of the formaldehyde solution is 20%-50%.

[0059] In a preferred embodiment of the present invention, the formaldehyde solution has a mass concentration of 30%; the mass ratio of resorcinol to the volume of the formaldehyde solution is 1g:2mL.

[0060] In a preferred embodiment of the present invention, the concentration of potassium hydroxide is 1 mol / L, and the volume ratio of potassium hydroxide to resorcinol is 1 mL: 1 g.

[0061] In the carbonization process, potassium hydroxide is used for etching and pore-forming treatment to obtain porous carbon microspheres.

[0062] In a preferred embodiment of the present invention, the stirring time in step (1) is 20-40 min (e.g., 20 min, 30 min, or 40 min); the stirring time in step (2) is 20-40 min (e.g., 20 min, 30 min, or 40 min); the ultrasonication time in step (3) is 5-10 min (e.g., 5 min, 6 min, 8 min, or 10 min); the stirring time in step (4) is 20-40 min (e.g., 20 min, 30 min, or 40 min); and the stirring and heating in step (5) are carried out in a sealed reaction vessel. The process involves stirring while maintaining a constant temperature. The stirring speed is 150-400 r / min (e.g., 150 r / min, 200 r / min, 250 r / min, 300 r / min, or 400 r / min), and the heating temperature is 60-90℃ (e.g., 60℃, 75℃, 85℃, or 90℃). Before adding potassium hydroxide, the mixture is heated and stirred for 12-30 h (e.g., 12 h, 24 h, or 30 h). After adding potassium hydroxide, the mixture is heated and stirred for another 20-40 min (e.g., 20 min, 30 min, or 40 min).

[0063] In a preferred embodiment of the present invention, the stirring speed in step (5) is 300 r / min, the heating temperature is 85°C, and the stirring is carried out for 24 hours while heating before adding potassium hydroxide; after adding potassium hydroxide, the stirring is carried out for 30 minutes while heating.

[0064] In a preferred embodiment of the present invention, the drying temperature in step (6) is 70°C and the drying time is 8-12h (e.g., 8h, 10h or 12h); the ball milling speed is 300r / min and the ball milling time is 20min; the carbonization temperature is 600-900°C (e.g., 600°C, 700°C, 800°C or 900°C) and the carbonization time is 1-3h (e.g., 1h, 2h or 3h).

[0065] The present invention also proposes a nitrogen-doped phenolic resin-based porous carbon microsphere, which is prepared by the aforementioned preparation method; the nitrogen-doped phenolic resin-based porous carbon microsphere has an internal pore structure.

[0066] This invention also proposes the application of nitrogen-doped phenolic resin-based porous carbon microspheres, specifically the application of the nitrogen-doped phenolic resin-based porous carbon microspheres prepared by the aforementioned method in lithium-ion batteries.

[0067] The following detailed description of the nitrogen-doped phenolic resin-based porous carbon microspheres, their preparation method, and applications, through specific embodiments, illustrates the present invention.

[0068] In the examples below, the polyethyleneimine used is a commercially available branched polyethyleneimine with a weight-average molecular weight (Mw) of 400-600.

[0069] Example 1

[0070] This embodiment provides a method for preparing nitrogen-doped phenolic resin-based porous carbon microspheres, including the following steps:

[0071] (1) Dissolve 3g of branched polyethyleneimine in 300mL of deionized water and stir for 30min. The solution becomes transparent, and the first solution is obtained.

[0072] (2) Dissolve 10g of resorcinol in the first solution and stir for 30 minutes. The solution is clear and transparent without particles, thus obtaining the second solution.

[0073] (3) Dissolve 0.3g of melamine in 10mL of water, disperse by ultrasonication for 8min until the solution is clear, and add it to the second solution above to obtain the third solution;

[0074] (4) Add 20 mL of 30% formaldehyde solution to the third solution and stir to disperse for 30 min to obtain the fourth solution;

[0075] (5) The fourth solution was transferred to a closed reaction vessel and stirred and heated. The stirring was kept constant at a stirring speed of 300 r / min and a heating temperature of 85℃ for 24 h. A reddish-brown suspension was obtained. Then 10 mL of 1 mol / L potassium hydroxide solution was added. The stirring speed and heating temperature were kept constant. The mixture was stirred for 30 min while heating to obtain the fifth solution.

[0076] (6) The fifth solution is filtered, dried, ball-milled and carbonized to obtain the final product.

[0077] The drying process includes a drying temperature of 70℃ and a drying time of 12 hours; a ball mill speed of 300 r / min and a ball milling time of 4 minutes; and carbonization in a tube furnace under nitrogen gas at a carbonization temperature of 700℃ for 2 hours. After carbonization, washing and drying are also performed.

[0078] Scanning electron microscope (SEM) images (1 μm) and partial transmission electron microscope (TEM) images (20 nm) of the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1 are shown below. Figure 1 As shown. From Figure 1 The scanning electron microscope images show that the prepared porous carbon microspheres are spherical or near-spherical, with individual particle sizes of 3-5 μm; from Figure 1 The partial transmission electron microscope image (attached in the upper right corner) shows that the prepared porous carbon microspheres exhibit internal pore structure and some surface etched pores, with a pore size of about 2 nm.

[0079] X-ray photoelectron spectroscopy (XPS) was performed on the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1. The structure is as follows: Figure 2 As shown. By Figure 2 It can be seen that the nitrogen doping in the obtained nitrogen-doped phenolic resin-based porous carbon microspheres includes both graphitic nitrogen peaks (402.1 eV) and amorphous nitrogen peaks (398.3 eV). This indicates that nitrogen is present in the synthesized material, with both graphitic and amorphous nitrogen present. Graphitic nitrogen contributes to the conductivity of the material.

[0080] The specific surface area was determined using the BET method, and the results are as follows: Figure 3 As shown. By Figure 3 It can be seen that the specific surface area of ​​the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1 of the present invention is 843 m². 2 / g.

[0081] Figure 4 This is a pore size distribution diagram of the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1 of the present invention. Figure 4 It can be seen that the pore size of the obtained nitrogen-doped phenolic resin-based porous carbon microspheres is concentrated in mesopores of about 2 nm, and the pore size is relatively concentrated.

[0082] Figure 5 The image shows the XRD pattern of the nitrogen-doped phenolic resin-based porous carbon microspheres prepared in Example 1 of this invention. XRD analysis of the obtained nitrogen-doped phenolic resin-based porous carbon microspheres shows that the characteristic peaks of graphitic carbon are around 26.6° and 44.66°. This indicates that the synthesized carbonized material is a carbon material.

[0083] Example 2

[0084] This embodiment provides a method for preparing nitrogen-doped phenolic resin-based porous carbon microspheres, including the following steps:

[0085] (1) Dissolve 2g of small molecule polyethyleneimine in 300mL of deionized water and stir for 25min until the solution becomes transparent to obtain the first solution;

[0086] (2) Dissolve 10g of resorcinol in the first solution and stir for 25 minutes. The solution is clear and transparent without particles, thus obtaining the second solution.

[0087] (3) Dissolve 0.4g of melamine in 10mL of water, disperse by ultrasonication for 6min until the solution is clear, add it to the second solution above to obtain the third solution;

[0088] (4) Add 20 mL of 30% formaldehyde solution to the third solution and stir to disperse for 25 min to obtain the fourth solution;

[0089] (5) The fourth solution was transferred to a closed reaction vessel and stirred and heated. The stirring was kept constant at a stirring speed of 250 r / min and a heating temperature of 85℃ for 24 h. A reddish-brown suspension was obtained. Then 10 mL of 1 mol / L potassium hydroxide solution was added. The stirring speed and heating temperature were kept constant. The mixture was stirred for 30 min while heating to obtain the fifth solution.

[0090] (6) The fifth solution is filtered, dried, ball-milled and carbonized to obtain the final product.

[0091] The drying process includes a drying temperature of 70℃ and a drying time of 8 hours; a ball mill speed of 300 r / min and a ball milling time of 20 minutes; and carbonization in a tube furnace under nitrogen gas at a carbonization temperature of 800℃ for 2 hours. After carbonization, washing and drying are also performed.

[0092] Example 3

[0093] This embodiment provides a method for preparing nitrogen-doped phenolic resin-based porous carbon microspheres, including the following steps:

[0094] (1) Dissolve 1g of small molecule polyethyleneimine in 300mL of deionized water and stir for 40min. The solution becomes transparent, and the first solution is obtained.

[0095] (2) Dissolve 10g of resorcinol in the first solution and stir for 40min. The solution is clear and transparent without particles, thus obtaining the second solution.

[0096] (3) Dissolve 0.5g of melamine in 10mL of water, disperse it by ultrasonication for 10min until the solution is clear, and add it to the second solution above to obtain the third solution;

[0097] (4) Add 20 mL of 30% formaldehyde solution to the third solution and stir to disperse for 40 min to obtain the fourth solution;

[0098] (5) The fourth solution was transferred to a closed reaction vessel and stirred and heated. The stirring was kept constant at a stirring speed of 400 r / min and a heating temperature of 85℃ for 24 h. A reddish-brown suspension was obtained. Then 10 mL of 1 mol / L potassium hydroxide solution was added. The stirring speed and heating temperature were kept constant. The mixture was stirred for 30 min while heating to obtain the fifth solution.

[0099] (6) The fifth solution is filtered, dried, ball-milled and carbonized to obtain the final product.

[0100] The drying process includes a drying temperature of 70℃ and a drying time of 12 hours; a ball mill speed of 300 r / min and a ball milling time of 20 minutes; and carbonization in a tube furnace under nitrogen gas at a carbonization temperature of 900℃ for 3 hours. After carbonization, washing and drying are also performed.

[0101] Comparative Example 1

[0102] The difference between this comparative example and Example 1 is that step (3) of adding melamine is not involved; the other steps are the same as in Example 1.

[0103] Comparative Example 2

[0104] The difference between this comparative example and Example 1 is that the addition of small molecule polyethyleneimine in step (1) is not involved; the other steps are the same as in Example 1.

[0105] Comparative Example 3

[0106] The difference between this comparative example and Example 1 is that the mass of melamine in step (3) is 10% of the mass of resorcinol (i.e., 1g of melamine), while the other steps are the same as in Example 1.

[0107] Application Example 1

[0108] The specific surface area and pore size distribution of the materials obtained in Examples 1-3 and Comparative Examples 1-3 were tested, and the results are shown in Table 1 below.

[0109] Using the materials obtained in Examples 1-3 and Comparative Examples 1-3 as negative electrode materials, coin cells were assembled and tested: 1.6g of the synthesized material, 0.2g of conductive graphite, and 0.4g of CMC solution with a solid content of 50% were ball-milled in a planetary ball mill at 300r / min for 1h. After mixing, a coating with a thickness of 100μm was applied, dried, and cut into 12mm small discs for coin cell assembly. The counter electrode was a lithium sheet. Impedance tests were performed, and the results are shown in Table 1 below.

[0110] Figure 6 This is a comparison diagram of the impedance of the materials obtained in Embodiment 1 and Comparative Example 1 of the present invention. Figure 6 It can be seen that the impedance of the coin cell assembled from the material obtained in Example 1 (nitrogen doping) of the present invention is 0.1Ω, and the impedance of the coin cell assembled from the material obtained in Comparative Example 1 (without nitrogen doping) is 0.17Ω.

[0111] Table 1

[0112] Serial Number <![CDATA[Specific surface area (m 2 / g)]]> Aperture distribution (nm) Impedance (Ω) Example 1 843 2 0.1 Example 2 680 4 0.11 Example 3 600 5 0.1 Comparative Example 1 980 1.5 0.17 Comparative Example 2 28 54 0.2 Comparative Example 3 26 58 0.2

[0113] As shown in Table 1, the increasing melamine content in Examples 1 to 3 leads to a certain degree of pore blockage on the material surface due to the increased nitrogen doping. Simultaneously, the decreasing polyethyleneimine content in Examples 1 to 3 results in a gradual reduction in internal pore formation. Therefore, the pore size distribution in Examples 1 to 3 becomes increasingly larger, while the specific surface area gradually decreases, with the specific surface area reaching 843 m². 2 / g, pore size distribution is 2-5nm; in addition, due to the doping of melamine, the conductivity of the material is improved, so the impedance of Examples 1-3 is basically the same at 0.1Ω.

[0114] Comparative Example 1, which did not involve nitrogen doping compared to Example 1, has a larger specific surface area of ​​980 m². 2 / g, with a pore size distribution of 1.5nm, but its impedance increases to 0.17Ω, indicating that nitrogen doping reduces the specific surface area and increases the pore size of the material while reducing the impedance.

[0115] Compared to Example 1, which did not incorporate branched polyethyleneimine for pore formation, Comparative Example 2, due to nitrogen doping causing some blockage of the pores on the material surface and the absence of pore-forming effects from branched polyethyleneimine, resulted in a material with a larger pore size of 54 nm and a smaller specific surface area of ​​only 28 m². 2 / g. Meanwhile, Comparative Example 2 has a relatively high impedance of 0.2Ω because it lacks internal pore structures and ion transport channels, hence the higher impedance.

[0116] Comparative Example 3 has a higher nitrogen doping ratio than Example 1, with melamine doping accounting for 10% of the resorcinol mass, which has a significant impact on the material's pore size, reducing the material's specific surface area to 28 m².2 The pore size is relatively large, at 54 nm. Meanwhile, Comparative Example 3 has a higher nitrogen doping content, which clogs the pore structure and results in a higher impedance of 0.2 Ω. Therefore, when using melamine for nitrogen doping, the doping amount cannot be too high. In this invention, the appropriate range is 2%-5% of the mass of resorcinol.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing nitrogen-doped phenolic resin-based porous carbon microspheres, characterized in that, The method comprises the following steps: (1) dissolving polyethyleneimine in a solvent, stirring to obtain a first solution; The mass of the polyethyleneimine to the volume of the solvent is 1g:(100-300)mL, the polyethyleneimine is branched polyethyleneimine, and the molecular weight is 200-600; (2) dissolving resorcinol in the first solution, stirring to obtain a second solution; The mass of the resorcinol to the mass of the polyethyleneimine is 10:(1-3); (3) dissolving melamine in water, ultrasonic dispersion, and then adding the second solution to obtain a third solution; The mass of the melamine is 2%-5% of the mass of the resorcinol; (4) adding a formaldehyde solution to the third solution, stirring to obtain a fourth solution; (5) stirring and heating the fourth solution, then adding potassium hydroxide, and continuing to stir and heat to obtain a fifth solution; (6) performing suction filtration, drying, ball milling, and carbonization on the fifth solution to obtain the product; The stirring and heating in step (5) are performed in a closed reaction kettle, the stirring is performed while constant-temperature heating, the stirring speed is 150-400r / min, the heating temperature is 60-90℃, the stirring is performed for 12-30h while heating before adding the potassium hydroxide, and the stirring is continued for 20-40min while heating after adding the potassium hydroxide; In step (6), the carbonization temperature is 600-900℃, and the carbonization time is 1-3h.

2. The production method according to claim 1, wherein The mass of the polyethyleneimine to the volume of the solvent is 1g:100mL; the mass of the resorcinol to the mass of the polyethyleneimine is 10:3; and the mass of the melamine is 3% of the mass of the resorcinol.

3. The production method according to claim 1, wherein The mass concentration of the formaldehyde solution is 20%-50%.

4. The production method according to claim 1, wherein The mass concentration of the formaldehyde solution is 30%; and the mass of the resorcinol to the volume of the formaldehyde solution is 1g:2mL.

5. The production method according to claim 1, wherein The concentration of the potassium hydroxide is 1mol / L, and the volume of the potassium hydroxide to the mass of the resorcinol is 1mL:1g.

6. The production method according to claim 1, wherein The stirring time in step (1) is 20-40min; the stirring time in step (2) is 20-40min; the ultrasonic time in step (3) is 5-10min; and the stirring time in step (4) is 20-40min.

7. The production method according to claim 6, wherein The stirring speed in step (5) is 300r / min, the heating temperature is 85℃, the stirring is performed for 24h while heating before adding the potassium hydroxide, and the stirring is continued for 30min while heating after adding the potassium hydroxide; The drying temperature in step (6) is 70℃, the drying time is 8-12h; the ball milling speed is 300r / min, and the ball milling time is 20min.

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