Preparation method of highly graphitized coated carbon material based on phenolic resin

Abstract

The invention relates to the technical field of lithium / sodium ion batteries, in particular to a preparation method of a highly graphitized coated carbon material based on phenolic resin, which comprises the following steps: uniformly mixing formaldehyde, resorcinol and a basic catalyst, and then catalyzing and curing; carrying out carbonization treatment on the uncarbonized phenolic resin based on a gradient heating method; mixing ethidene diamine, dichloromethane and carbonized phenolic resin, and heating in an oil bath; and placing the cured and coated graphitized phenolic resin in a tubular furnace for highly graphitizing. According to the preparation method of the highly-graphitized coated carbon material based on the phenolic resin, high ordering of a carbon layer is achieved through gradient heating graphitization, a carbon six-membered ring plane is promoted to expand, an ABAB stacked graphite structure is formed, the conductivity is effectively improved, a CVD coating and nitrogen doping synergistic technology is combined, a CVD reaction is formed through ethanediamine and dichloromethane, and the high-graphitization coated carbon material based on the phenolic resin is obtained. Functional groups such as pyridine-N and graphite-N are introduced to the surface of the carbon layer, so that the interface bonding force between the carbon layer and the matrix is enhanced, and the conductivity of the carbon layer is further improved.

Description

Technical Field

[0001] This invention relates to the field of lithium / sodium-ion battery technology, specifically to a method for preparing highly graphitized carbon-coated materials based on phenolic resin. Background Technology

[0002] Highly graphitized coated carbon materials are composite materials in which a nano- to micron-scale coating layer with a highly ordered graphite crystal structure is formed on the surface of a carbon matrix (such as graphite, carbon fiber, nanowire, etc.) through a special process. The core of this technology lies in using high-temperature treatment or catalytic graphitization to give the coating layer an order close to that of single-crystal graphite, thereby giving the material a breakthrough improvement in its comprehensive performance, especially in terms of electrical conductivity, thermal conductivity, and electrochemical performance. Therefore, it has good application prospects in the lithium / sodium-ion battery industry.

[0003] A search revealed a method for preparing hollow carbon-coated nano-silicon composite graphite material, disclosed in Chinese Patent Publication No. CN108336320A. This method involves encapsulating lithium-intercalated nano-silicon particles within hollow carbon spheres, then combining them with highly graphitized artificial graphite. The resulting hollow carbon microsphere-coated nano-silicon particle composite material is used as a negative electrode active material in lithium-ion batteries. It possesses high lithium intercalation capacity, enabling the lithium-ion battery to exhibit excellent cycle performance and achieve stable reversible lithium intercalation / deintercalation, thereby improving the energy density of the lithium-ion battery.

[0004] However, the preparation method of hollow carbon-coated nano-silicon composite graphite material did not involve high-temperature graphitization treatment, resulting in the carbon coating layer being mainly amorphous carbon or low-graphitized carbon. The carbon layer has low order, large interlayer spacing, and poor conductivity. Furthermore, the carbon precursor is formed only through a simple polymerization reaction, resulting in low stability of the carbon source molecular structure. After carbonization, it is easy to form a porous and loose carbon layer with poor coating uniformity, which can easily affect the structural stability of the material. Therefore, a method for preparing highly graphitized coated carbon materials based on phenolic resin is proposed. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing highly graphitized coated carbon materials based on phenolic resin. This method has the advantages of significantly improving conductivity and structural stability due to the highly graphitized process, and solves the problem that existing methods for preparing hollow carbon-coated nano-silicon composite graphite materials in the background art require further improvement in high-temperature carbonization and coating processes.

[0007] (II) Technical Solution

[0008] To achieve the aforementioned objective of significantly improving conductivity and structural stability based on a highly graphitized process, this invention provides the following technical solution: a method for preparing highly graphitized carbon-coated materials based on phenolic resin, comprising the following steps:

[0009] S1. Formaldehyde, resorcinol and alkaline catalyst are mixed evenly and then catalytically cured at 70-80℃ for 1-2 days. After cooling and drying, uncarbonized phenolic resin is obtained.

[0010] S2. The uncarbonized phenolic resin is placed in a tube furnace and carbonized under nitrogen protection using a gradient heating method. After cooling and drying, the primary carbonized phenolic resin is obtained.

[0011] S3. Ethylenediamine, dichloromethane and carbonized phenolic resin are mixed and stirred continuously in an oil bath at a temperature of 90-105°C while being refluxed for 12 hours. After cooling, primary coated graphitized phenolic resin is obtained.

[0012] S4. The primary graphitized phenolic resin is dried in a vacuum drying oven at 100-120°C under negative pressure for 6-8 hours, and then cooled to obtain the dried and cured graphitized phenolic resin.

[0013] S5. The cured graphitized phenolic resin is placed in a tube furnace and carbonized at high temperature for 2 hours under the protection of high-purity argon. After cooling, a highly graphitized graphitized phenolic resin is obtained.

[0014] Preferably, the alkaline catalyst is selected from ammonia, sodium carbonate, or sodium hydroxide, and is used to prepare the raw material by reacting formaldehyde and resorcinol at a molar ratio of resorcinol:formaldehyde = 1:(1.5-2). The amount of alkaline catalyst used is 1-5% of the mass or molar ratio of resorcinol, and the catalytic curing reaction process includes:

[0015] 1) Initial mixing: Add resorcinol and catalyst to a three-necked flask, slowly add formaldehyde solution while turning on the magnetic stirrer at 200-400 rpm to mix evenly, and observe the system in the three-necked flask gradually turn into a transparent light yellow solution, forming the initial prepolymer;

[0016] 2) Thermal catalytic curing: Place the three-necked flask in a constant temperature water bath, connect the reflux condenser to the flask and heat it to 75°C. Start a vigorous stirrer at 300-500 rpm to maintain a constant reaction temperature for 18-24 hours.

[0017] 3) Monitoring of the heat curing process, including:

[0018] In the initial period of 0–4 hours, the viscosity of the solution in the bottle gradually increases and the color deepens to reddish-brown;

[0019] During the middle of 4 to 12 hours, a viscous gel gradually forms inside the bottle;

[0020] In the later stages of 12–36 hours, the gel material inside the bottle gradually solidifies and hardens to form a non-flowing, dark red, blocky solid, completing the cross-linking process.

[0021] Turn off the heating, keep stirring until the temperature gradually drops below 60°C, and allow the three-necked flask and the product inside to cool naturally to room temperature.

[0022] 4) Remove the cured resin and rinse the surface with deionized water to remove any residual catalyst. Place it in a petri dish and put it in a forced-air drying oven. Pre-dry at 60-80℃ for 6-12 hours to remove free water and trace amounts of formaldehyde.

[0023] 5) Crush and grind the dried resin blocks, and sieve them through an 80-100 mesh sieve to obtain uniformly sized uncarbonized phenolic resin matrix powder.

[0024] Preferably, in step S2, the obtained uncarbonized phenolic resin matrix powder is evenly spread on a graphite crucible, with a loading thickness ≤5mm. After placing the graphite crucible in the center of the constant temperature zone of a tube furnace, the furnace tube is sealed, and then high-purity nitrogen (N2) is introduced and the furnace tube is purged at a flow rate of 200–300 mL / min for 30–40 min to remove air. The gradient heating carbonization procedure includes the following steps:

[0025] 1) During the low-temperature pyrolysis stage, the temperature is gradually increased from room temperature to 700℃ at a rate of 2-3℃ / min, held at 700℃ for 60min, and N2 is continuously introduced.

[0026] 2) During the transition heating stage, the temperature is gradually increased to the target carbonization temperature at a rate of 5-8℃ / min;

[0027] 3) During the high-temperature carbonization stage, the temperature is kept at 1500℃ for 2 hours to promote carbon structure rearrangement;

[0028] 4) After carbonization and heat preservation, stop heating and maintain the N2 flow rate ≥100mL / min to allow the furnace to cool naturally to below 300℃. When the furnace temperature is ≤300℃, open the furnace door to accelerate cooling to room temperature, then stop the N2 flow and remove the crucible.

[0029] 5) Grind the carbonized black solid product in the crucible, and remove the sintered agglomerates by sieving with a 200-mesh sieve to obtain black powdered carbonized phenolic resin, which is then stored in a desiccator for later use.

[0030] Preferably, in step S3, carbonized phenolic resin is added to ethanol solvent and ultrasonically treated in an ultrasonic disperser for 30 minutes to form a uniform suspension. Ethylenediamine is added as a nitrogen source and the mixture is premixed by magnetic stirring for 10 minutes.

[0031] The premixed solution was transferred to a three-necked round-bottom flask equipped with a reflux condenser and a dropping funnel. The flask was placed in a magnetically stirred oil bath, and the CVD coating reaction was carried out with continuous vigorous stirring at an oil bath temperature of 90–105°C. The reaction process included:

[0032] 1) Start the magnetic stirrer at 500 rpm and control the oil bath temperature to 105℃. When the temperature inside the flask reaches 90℃, add chloroform CHCl3 dropwise at a uniform rate through the dropping funnel as a catalyst and maintain the current reaction conditions for 8 hours. At this time, the solution gradually changes from blackish-gray to bright black, indicating the growth of the coating layer.

[0033] 2) Take a 0.5 mL sample of the solution every 2 hours, centrifuge, collect the supernatant, and use a UV spectrophotometer to detect chloroform residue and confirm the reaction progress;

[0034] 3) Turn off the oil bath heating, stop adding chloroform, maintain stirring until the temperature is ≤60℃, pour the reaction solution into a centrifuge cup, centrifuge at 8000rpm for 10min and remove the supernatant;

[0035] 4) Add 100 mL of anhydrous ethanol to the remaining solid, sonicate for 10 min, repeat centrifugation 3 times until the pH of the supernatant is neutral, then add 100 mL of deionized water, repeat ultrasonic centrifugation and washing 2-3 times, filter to obtain the surface-modified primary graphitized phenolic resin.

[0036] Preferably, in step S4, the moist solid surface-modified primary coated graphitized phenolic resin is evenly spread in a vacuum drying tray, with the spread thickness controlled to be ≤10mm, and a high-temperature resistant non-woven fabric layer is covered on its surface. The drying step in the vacuum drying oven includes:

[0037] 1) Turn on the vacuum pump to slowly evacuate the chamber to -0.08MPa, and gradually raise the temperature to 60℃ during the low-temperature dehydration stage and maintain it for 2 hours;

[0038] 2) During the drying stage, gradually increase the temperature to 105℃ while simultaneously increasing the vacuum to -0.1MPa and maintaining it for 4 hours;

[0039] 3) Turn off the heating, maintain the vacuum state during the constant weight stage and allow it to cool naturally to below 60°C, then slowly introduce N2 into the chamber until it reaches atmospheric pressure;

[0040] 4) Take 1g of sample from the box and test the moisture content with a rapid moisture analyzer. If the moisture content is >0.5wt%, repeat steps 2) and 3) until constant weight is achieved.

[0041] Preferably, in step S5, the prepared primary coated graphitized phenolic resin is immersed in a 0.05M ferric nitrate-ethanol solution, ultrasonically treated for 30 min, concentrated to near dryness in a rotary evaporator, and then transferred to a vacuum drying oven to dry for 2 h to obtain the catalyst-modified precursor.

[0042] The precursor was loaded into a high-purity graphite crucible and placed in the isothermal zone of an ultra-high temperature graphitization furnace. After sealing, high-purity argon gas was continuously purged at a flow rate of 500 mL / min for 1–2 hours. Subsequently, the flow rate was reduced to 200 mL / min and positive pressure was maintained to initiate the gradient temperature graphitization program, which specifically included:

[0043] 1) During the dehydration and degassing stage, the temperature is gradually increased to 600℃ at a rate of 5℃ / min and maintained for 30min to remove adsorbed water and residual gas.

[0044] 2) During the carbon structure recombination stage, the temperature is gradually increased to 2000℃ at a rate of 8℃ / min to achieve the transformation of amorphous carbon into a disordered layered structure;

[0045] 3) Maintain the temperature at 2000℃ for 60 minutes during the catalytic activation stage to promote catalyst melting and penetration;

[0046] 4) During the core graphitization stage, the temperature is gradually increased to 2800℃ at a rate of 5℃ / min and held for 120min to promote the growth of three-dimensional ordered graphite.

[0047] 5) Maintain the temperature at 2800℃ for 30 minutes in the final stable state to eliminate lattice stress.

[0048] Preferably, after the gradient heating graphitization treatment is completed, argon gas is introduced at a flow rate of ≥100mL / min, and the furnace temperature is gradually cooled to 1800℃ at a rate of 3℃ / min, and then naturally cooled to below 300℃. The obtained graphitized product is lightly ground in a planetary ball mill for 10min and filtered through a 325-mesh sieve to obtain a silver-gray highly graphitized coated carbon material.

[0049] (III) Beneficial Effects

[0050] Compared with the prior art, the present invention provides a method for preparing highly graphitized coated carbon materials based on phenolic resin, which has the following beneficial effects:

[0051] 1. This method for preparing highly graphitized carbon materials based on phenolic resin achieves high ordering of carbon layers through gradient heating graphitization, promoting the planar expansion of carbon six-membered rings and forming an ABAB stacked graphite structure, effectively improving conductivity, while avoiding defects in the carbon layers caused by rapid heating.

[0052] 2. This method for preparing highly graphitized coated carbon materials based on phenolic resin uses phenolic resin as a precursor, which easily forms a dense carbon layer after carbonization. By regulating the degree of crosslinking through an alkaline catalyst, the porosity of the carbon layer can be precisely controlled. Combining CVD coating and nitrogen doping synergistic technology, ethylenediamine and dichloromethane form a CVD reaction, introducing functional groups such as pyridine-N and graphitic-N on the surface of the carbon layer, enhancing the interfacial bonding force between the carbon layer and the matrix, and further improving its conductivity. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the 10nm structure of the highly graphitized coated carbon material of the present invention;

[0054] Figure 2 This is a schematic diagram of the 20nm structure of the highly graphitized coated carbon material of the present invention;

[0055] Figure 3 The X-ray diffraction (XRD) pattern of the highly graphitized carbon-coated material of this invention;

[0056] Figure 4 This is a schematic diagram of the gradient heating process of the present invention;

[0057] Figure 5 This is a schematic diagram of the chemical vapor deposition (CVD) coating process of the present invention;

[0058] Figure 6 This is a schematic diagram of the vacuum drying process of the present invention;

[0059] Figure 7 This is a schematic diagram of the catalytic high-temperature graphitization process of the present invention. Detailed Implementation

[0060] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] Example 1

[0062] In this embodiment, the main device modules in step S1 include:

[0063] 1) Reaction vessel: three-necked flask, matching stopper and flange;

[0064] 2) Mixing and stirring system: magnetic stirrer and stainless steel stirring paddle, constant speed control module;

[0065] 3) Heating and temperature control system: constant temperature water bath, precision temperature controller;

[0066] 4) Reflux and safety devices: spherical condenser tubes, fume hood;

[0067] 5) Post-processing equipment: blower drying oven, high-speed pulverizer, standard sample sieve and electronic balance.

[0068] The purpose of introducing a catalytic curing stage into the preparation of phenolic resin matrix is ​​to efficiently synthesize a uniformly cross-linked phenolic resin matrix through an alkaline catalyst, providing a high-quality precursor for subsequent carbonization, effectively shortening the curing time, improving curing efficiency, and controlling the amount of alkaline catalyst relative to resorcinol by mass ratio or molar ratio to avoid excessive cross-linking and embrittlement.

[0069] Controlling the reaction temperature at 75℃ is the optimal point to balance the reaction rate and the side reaction (formaldehyde disproportionation), and to avoid the problem of uneven pore size in the phenolic resin matrix caused by local overheating of the flask.

[0070] Example 2

[0071] In this embodiment, the main device modules in step S2 include:

[0072] 1) High-temperature heat treatment system: horizontal tube furnace, dual-temperature zone controller and matching graphite support;

[0073] 2) Atmosphere control system: high-purity nitrogen cylinder (equipped with pressure reducing valve), mass flow controller, and tail gas treatment device (alkali absorption);

[0074] 3) Crucibles and support containers: high-purity alumina crucibles, graphite crucibles;

[0075] 4) Temperature monitoring equipment: Type B thermocouples, infrared thermometers

[0076] 5) Post-processing equipment: mortar and pestle, standard sieve and vacuum dryer.

[0077] A gradient heating method is introduced for carbonization to prepare a carbon matrix. The high-temperature preparation process of the carbon matrix is ​​divided into several sub-stages, which facilitates strict control of the reaction conditions, such as the temperature, required in each stage, including:

[0078] The phenolic resin matrix undergoes a cracking reaction at 600-800℃. The cracking temperature is set at 700℃. At the same time, a large amount of combustible gas (including CH4, H2, etc.) will be generated during the cracking stage. It is necessary to ensure inert gas protection throughout the process and to carry out combustion or absorption treatment during the exhaust gas discharge stage.

[0079] The target carbonization stage is 1300-1600℃, and the temperature of this stage is set at 1500℃ to promote the initial formation of graphitized microcrystals. At the same time, the holding time can be finely adjusted according to the target degree of graphitization.

[0080] Using low temperature and slow rise can avoid bubbling and splashing caused by rapid pyrolysis of resin. At the same time, the 700℃ heat treatment can maximize the removal of oxygen- or hydrogen-containing groups (reduce disordered carbon generation in the high temperature section) and promote condensation aromatization.

[0081] Shortening the total time spent at high temperatures during the rapid rise phase reduces energy consumption, and heat treatment at 1500℃ can promote the planar expansion of the six-membered carbon ring.

[0082] Example 3

[0083] In this embodiment, the main device modules in step S3 include:

[0084] 1) Reaction system: three-necked round-bottom flask, constant pressure dropping funnel, high-efficiency spherical condenser;

[0085] 2) Heating and stirring: Precision constant temperature oil bath, mechanical stirrer and stirring paddle;

[0086] 3) Dispersion and separation: ultrasonic cleaner, high-speed centrifuge;

[0087] 4) Monitoring and Safety: pH meter, ultraviolet spectrophotometer, exhaust gas absorption system, fume hood.

[0088] Ethylenediamine is introduced as a nitrogen source and bonds to the defect sites on the carbon matrix surface to form -NH2 or -NH- functional groups to enhance nucleophilicity, ultimately generating pyridine-N or graphitic-N and improving conductivity;

[0089] Chloroform pyrolysis kinetics: The pyrolysis rate constant at 105℃ is effectively increased compared to 90℃, shortening the deposition time and controlling the droplet acceleration rate to avoid homogeneous nucleation (particle agglomeration) caused by carbene concentration saturation.

[0090] Example 4

[0091] In this embodiment, the main device modules in step S4 include:

[0092] 1) Drying system: vacuum drying oven, high-temperature resistant silicone sealing ring, double-layer tempered glass observation window, rotary vane vacuum pump, cold trap and vacuum pressure gauge;

[0093] 2) Monitoring equipment: rapid moisture analyzer, temperature monitoring instrument;

[0094] 3) Crushing system: jaw crusher, air jet mill

[0095] 4) Protective gas system: high-purity nitrogen cylinder, pressure reducing valve and flow meter.

[0096] The ethanol-water azeotropic point is broken at 105℃, completely removing residual solvent. Under a vacuum of -0.1MPa, the boiling point of water drops to 45℃, significantly accelerating the diffusion of internal moisture. The dried material has a high specific surface area and will quickly absorb moisture when exposed to air. Airflow pulverization is carried out under N2 protection throughout to maintain stable moisture content.

[0097] Example 5

[0098] In this embodiment, the main device modules in step S5 include:

[0099] 1) Ultra-high temperature processing system: The induction graphitization furnace is equipped with a water-cooled copper coil and a high-frequency power supply, and the matching graphite heating element is equipped with an isostatic graphite cylinder and a multi-layer graphite felt insulation layer.

[0100] 2) Atmosphere and Cooling System: The high-purity argon supply system includes a liquid Ar storage tank, a vaporizer and micro-oxygen analyzer, and a forced water cooling unit;

[0101] 3) Temperature measurement and control system: Type B thermocouple, infrared pyrometer, multi-segment programmable temperature controller;

[0102] 4) Post-processing equipment: argon-filled glove box, planetary ball mill and laser particle size analyzer.

[0103] Heating to 2800℃ can provide more than 5eV of energy to overcome the van der Waals forces between carbon layers, causing the interlayer spacing to shrink to ≤0.336nm and eliminating twisted boundaries to make the crystallite size La>100nm;

[0104] The iron catalytic mechanism includes: molten iron dissolves carbon—carbon atoms diffuse in iron—an ordered carbon layer precipitates on the surface of a graphite substrate; when the temperature drops from 2800℃ to 1800℃, a cooling rate >5℃ / min will lead to interlayer stress cracking in the graphite (i.e., an increase in the ID / IG value).

[0105] The beneficial effects of this invention are as follows: This method for preparing highly graphitized coated carbon materials based on phenolic resin achieves high ordering of the carbon layer through gradient heating graphitization, promoting the planar expansion of the six-membered carbon rings and forming an ABAB stacked graphite structure, effectively improving conductivity, while avoiding defects in the carbon layer caused by rapid heating. Using phenolic resin as a precursor, a dense carbon layer is easily formed after carbonization. By regulating the degree of crosslinking through an alkaline catalyst, the porosity of the carbon layer can be precisely controlled. Combined with CVD coating and nitrogen doping synergistic technology, ethylenediamine and dichloromethane form a CVD reaction, introducing functional groups such as pyridine-N and graphitic-N on the surface of the carbon layer, enhancing the interfacial bonding force between the carbon layer and the matrix, and further improving its conductivity.

[0106] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing highly graphitized carbon-coated materials based on phenolic resin, characterized in that, Includes the following steps: S1. Formaldehyde, resorcinol and alkaline catalyst are mixed evenly and then catalytically cured at 70-80℃ for 1-2 days. After cooling and drying, uncarbonized phenolic resin is obtained. S2. The uncarbonized phenolic resin is placed in a tube furnace and carbonized under nitrogen protection using a gradient heating method. After cooling and drying, the primary carbonized phenolic resin is obtained. S3. Ethylenediamine, dichloromethane and carbonized phenolic resin are mixed and stirred continuously in an oil bath at a temperature of 90-105°C while being refluxed for 12 hours. After cooling, primary coated graphitized phenolic resin is obtained. S4. The primary graphitized phenolic resin is dried in a vacuum drying oven at 100-120°C under negative pressure for 6-8 hours, and then cooled to obtain the dried and cured graphitized phenolic resin. S5. The cured graphitized phenolic resin is placed in a tube furnace and carbonized at high temperature for 2 hours under the protection of high-purity argon. After cooling, a highly graphitized graphitized phenolic resin is obtained.

2. The method for preparing highly graphitized coated carbon materials based on phenolic resin according to claim 1, characterized in that, The alkaline catalyst is selected from ammonia, sodium carbonate, or sodium hydroxide. It is used to prepare the raw materials from formaldehyde and resorcinol at a molar ratio of resorcinol:formaldehyde = 1:(1.5-2). The amount of alkaline catalyst used is 1-5% of the mass or molar ratio of resorcinol. The catalytic curing reaction process includes: 1) Initial mixing: Add resorcinol and catalyst to a three-necked flask, slowly add formaldehyde solution while turning on the magnetic stirrer at 200-400 rpm to mix evenly, and observe the system in the three-necked flask gradually turn into a transparent light yellow solution, forming the initial prepolymer; 2) Thermal catalytic curing: Place the three-necked flask in a constant temperature water bath, connect the reflux condenser to the flask and heat it to 75°C. Start a vigorous stirrer at 300-500 rpm to maintain a constant reaction temperature for 18-24 hours. 3) Monitoring of the heat curing process, including: In the initial period of 0–4 hours, the viscosity of the solution in the bottle gradually increases and the color deepens to reddish-brown; During the middle of 4 to 12 hours, a viscous gel gradually forms inside the bottle; In the later stages of 12–36 hours, the gel material inside the bottle gradually solidifies and hardens to form a non-flowing, dark red, blocky solid, completing the cross-linking process. Turn off the heating, keep stirring until the temperature gradually drops below 60°C, and allow the three-necked flask and the product inside to cool naturally to room temperature. 4) Remove the cured resin and rinse the surface with deionized water to remove any residual catalyst. Place it in a petri dish and put it in a forced-air drying oven. Pre-dry at 60-80℃ for 6-12 hours to remove free water and trace amounts of formaldehyde. 5) Crush and grind the dried resin blocks, and sieve them through an 80-100 mesh sieve to obtain uniformly sized uncarbonized phenolic resin matrix powder.

3. The method for preparing highly graphitized coated carbon materials based on phenolic resin according to claim 1, characterized in that, In step S2, the obtained uncarbonized phenolic resin matrix powder is evenly spread on a graphite crucible, with a loading thickness ≤5mm. The graphite crucible is placed in the center of the constant temperature zone of a tube furnace, and the furnace tube is sealed. Then, high-purity nitrogen (N2) is introduced and the furnace tube is purged at a flow rate of 200–300 mL / min for 30–40 minutes to remove air. The gradient heating carbonization procedure includes the following steps: 1) During the low-temperature pyrolysis stage, the temperature is gradually increased from room temperature to 700℃ at a rate of 2-3℃ / min, held at 700℃ for 60min, and N2 is continuously introduced. 2) During the transition heating stage, the temperature is gradually increased to the target carbonization temperature at a rate of 5-8℃ / min; 3) During the high-temperature carbonization stage, the temperature is kept at 1500℃ for 2 hours to promote carbon structure rearrangement; 4) After carbonization and heat preservation, stop heating and maintain the N2 flow rate ≥100mL / min to allow the furnace to cool naturally to below 300℃. When the furnace temperature is ≤300℃, open the furnace door to accelerate cooling to room temperature, then stop the N2 flow and remove the crucible. 5) Grind the carbonized black solid product in the crucible, and remove the sintered agglomerates by sieving with a 200-mesh sieve to obtain black powdered carbonized phenolic resin, which is then stored in a desiccator for later use.

4. The method for preparing highly graphitized coated carbon materials based on phenolic resin according to claim 1, characterized in that, In step S3, carbonized phenolic resin is added to ethanol solvent and ultrasonically treated in an ultrasonic disperser for 30 minutes to form a uniform suspension. Ethylenediamine is added as a nitrogen source and the mixture is premixed by magnetic stirring for 10 minutes. The premixed solution was transferred to a three-necked round-bottom flask equipped with a reflux condenser and a dropping funnel. The flask was placed in a magnetically stirred oil bath, and the CVD coating reaction was carried out with continuous vigorous stirring at an oil bath temperature of 90–105°C. The reaction process included: 1) Start the magnetic stirrer at 500 rpm and control the oil bath temperature to 105℃. When the temperature inside the flask reaches 90℃, add chloroform CHCl3 dropwise at a uniform rate through the dropping funnel as a catalyst and maintain the current reaction conditions for 8 hours. At this time, the solution gradually changes from blackish-gray to bright black, indicating the growth of the coating layer. 2) Take a 0.5 mL sample of the solution every 2 hours, centrifuge, collect the supernatant, and use a UV spectrophotometer to detect chloroform residue and confirm the reaction progress; 3) Turn off the oil bath heating, stop adding chloroform, maintain stirring until the temperature is ≤60℃, pour the reaction solution into a centrifuge cup, centrifuge at 8000rpm for 10min and remove the supernatant; 4) Add 100 mL of anhydrous ethanol to the remaining solid, sonicate for 10 min, repeat centrifugation 3 times until the pH of the supernatant is neutral, then add 100 mL of deionized water, repeat ultrasonic centrifugation and washing 2-3 times, filter to obtain the surface-modified primary graphitized phenolic resin.

5. The method for preparing highly graphitized coated carbon materials based on phenolic resin according to claim 1, characterized in that, In step S4, the moist solid surface-modified primary coated graphitized phenolic resin is evenly spread in a vacuum drying tray, with the thickness of the spread material controlled to be ≤10mm, and a high-temperature resistant non-woven fabric layer is covered on its surface. The drying steps in the vacuum drying oven include: 1) Turn on the vacuum pump to slowly evacuate the chamber to -0.08MPa, and gradually raise the temperature to 60℃ during the low-temperature dehydration stage and maintain it for 2 hours; 2) During the drying stage, gradually increase the temperature to 105℃ while simultaneously increasing the vacuum to -0.1MPa and maintaining it for 4 hours; 3) Turn off the heating, maintain the vacuum state during the constant weight stage and allow it to cool naturally to below 60°C, then slowly introduce N2 into the chamber until it reaches atmospheric pressure; 4) Take 1g of sample from the box and test the moisture content with a rapid moisture analyzer. If the moisture content is >0.5wt%, repeat steps 2) and 3) until constant weight is achieved.

6. The method for preparing highly graphitized coated carbon materials based on phenolic resin according to claim 1, characterized in that, In step S5, the prepared primary coated graphitized phenolic resin is immersed in a 0.05M ferric nitrate-ethanol solution, ultrasonically treated for 30 min, concentrated to near dryness in a rotary evaporator, and then transferred to a vacuum drying oven to dry for 2 h to obtain the catalyst-modified precursor. The precursor was loaded into a high-purity graphite crucible and placed in the isothermal zone of an ultra-high temperature graphitization furnace. After sealing, high-purity argon gas was continuously purged at a flow rate of 500 mL / min for 1–2 hours. Subsequently, the flow rate was reduced to 200 mL / min and positive pressure was maintained to initiate the gradient temperature graphitization program, which specifically included: 1) During the dehydration and degassing stage, the temperature is gradually increased to 600℃ at a rate of 5℃ / min and maintained for 30min to remove adsorbed water and residual gas; 2) During the carbon structure recombination stage, the temperature is gradually increased to 2000℃ at a rate of 8℃ / min to achieve the transformation of amorphous carbon into a disordered layered structure; 3) Maintain the temperature at 2000℃ for 60 minutes during the catalytic activation stage to promote catalyst melting and penetration; 4) During the core graphitization stage, the temperature is gradually increased to 2800℃ at a rate of 5℃ / min and held for 120min to promote the growth of three-dimensional ordered graphite. 5) Maintain the temperature at 2800℃ for 30 minutes in the final stable state to eliminate lattice stress.

7. The method for preparing highly graphitized coated carbon materials based on phenolic resin according to claim 6, characterized in that, After the gradient heating graphitization process is completed, argon gas is introduced at a flow rate of ≥100mL / min, and the furnace temperature is gradually cooled to 1800℃ at a rate of 3℃ / min, and then naturally cooled to below 300℃. The obtained graphitized product is lightly ground in a planetary ball mill for 10min and filtered through a 325-mesh sieve to obtain a silver-gray highly graphitized coated carbon material.

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