Process for the preparation of carbon materials from fats and oils and their use as battery anodes

Abstract

The application discloses a method for preparing carbon materials from oil and fat and application of the carbon materials to battery negative electrodes, and comprises the following steps: step 1, purification of oil and fat in raw materials; step 2, ester decomposition reaction of the oil and fat to form higher fatty acid salt; step 3, addition of a nitrogen-rich agent to the higher fatty acid salt; step 4, high-temperature carbonization; step 5, removal of impurities by washing and drying to obtain carbon materials; and step 6, application of the carbon materials to lithium / sodium / potassium ion batteries as negative electrodes. The application discloses a novel method for preparing carbon negative electrode materials, uses oil and fat as raw materials, and through the above process steps, obtains nitrogen-rich porous carbon nanosheets, the nanosheet structure of which can improve ion transmission efficiency, the porous structure can improve lithium / sodium / potassium storage capacity, and the nitrogen-rich structure can introduce different types of defects to provide anchoring sites for lithium / sodium / potassium adsorption. The carbon negative electrode materials prepared from oil and fat greatly improve the specific capacity, rate performance and cycle life of lithium / sodium / potassium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of oil and fat application technology, specifically to a method for preparing carbon materials from oils and fats and their application as battery anodes. Background Technology

[0002] The widespread application of renewable energy necessitates the development of efficient and low-cost green energy storage systems. Compared to the widely available lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) also possess numerous advantages, including abundant and inexpensive sodium (2.3 wt%) and potassium (1.5 wt%) resources, and lower redox potentials. Their working principles and battery devices are similar to lithium-ion batteries, making them ideal candidates for high-performance batteries in large-scale storage devices. However, traditional graphite anodes from lithium-ion batteries are unsuitable for SIBs and PIBs, exhibiting severe volume expansion (graphite structure collapse) during charge and discharge, resulting in poor cycle stability. Therefore, breakthroughs in the performance of lithium, sodium, and potassium-ion batteries are crucial for the development of anode materials. Biomass-based hard carbon, with its abundant raw material resources, low cost, and environmental friendliness, is considered the most promising anode material for lithium, sodium, and potassium batteries.

[0003] The electrode preparation raw material used in this invention is biomass oil, generally derived from vegetable oil, animal oil, and used industrial waste oil and kitchen waste oil. Currently, oils are widely used in many fields, primarily for food, but also extensively in the manufacture of soap, paint, biodiesel, emulsifiers, lubricants, etc. However, the waste gas, waste liquid, and waste residue generated after the use of these secondary products made from oils, such as carbon dioxide, will be released back into nature, exacerbating the greenhouse effect and contradicting the new development concepts of low-carbon living and green environmental protection. Therefore, how to efficiently utilize oils as resources is crucial, especially in reducing the pollution of the environment by waste oils (such as industrial waste oil and kitchen waste oil), maintaining the carbon balance of the ecosystem, and achieving good environmental and economic benefits. Research has found that the main component of oils is unsaturated fatty acid glycerides, and their abundant long-chain hydrocarbon molecules contain a large amount of carbon. At the same time, waste oils also contain abundant trace elements, such as N, B, S, and P. Unlike other carbon sources, oils, after high-temperature calcination, readily decompose their long-chain hydrocarbon molecules into short-chain hydrocarbon molecules within the C5-C8 range, thus forming carbon nanosheets with diverse structures. Simultaneously, heteroatoms on carbon materials can be modified with functional groups on their surface, enhancing the reactivity of the carbon materials and providing Li-2O4 for batteries. + Na + K + This provides additional storage sites, thereby significantly improving the electrochemical performance of carbon materials. This makes it possible to convert them into carbon materials and apply them to battery anode materials, demonstrating excellent potential.

[0004] This invention upgrades and transforms grease into a negative electrode material and applies it to the field of new energy battery technology. This not only achieves excellent battery performance, but also enables the reuse of waste grease, reducing environmental pollution and resource waste, and realizing the added value and efficient utilization of grease. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing carbon materials from oils and fats and their application as battery negative electrodes, thereby expanding the application directions of oils and fats and solving the problems of recycling and reusing waste oils and the high cost of raw materials for making battery electrode carbon materials.

[0006] The technical solution adopted by this invention to solve the technical problem is a method for preparing carbon materials from grease and its application as a battery negative electrode, comprising the following steps:

[0007] Step 1: Oil purification. The raw oil contains various types of impurities. First, the oil is filtered through a vacuum filter to remove larger particles and improve the purity of the oil. Finally, small particles of impurities are adsorbed by an adsorbent and the oil is allowed to stand to purify it, resulting in high-purity higher fatty acid glycerides.

[0008] Step 2: Oil solidification. Add an appropriate amount of alkaline substance to the high-purity higher fatty acid glycerides purified in Step 1, and add anhydrous ethanol for stirring to accelerate the reaction. Glycerol and the main component, higher fatty acid salts, can be obtained through ester decomposition reaction. Extract the higher fatty acid salts from the mixture.

[0009] Step 3: Nitrogen doping modification: Add nitrogen-enriching agent to the higher fatty acid salts obtained in Step 2 and mix evenly;

[0010] Step 4: High-temperature calcination. The mixture of higher fatty acid salts and melamine obtained in Step 3 is placed in a high-temperature calcination device for calcination until the mixture of higher fatty acid salts and nitrogen-enriching agent is completely carbonized.

[0011] Step 5: Washing and drying. The calcined product is subjected to multiple acid washing and ethanol washing to remove inorganic salt impurities and organic impurities, and then dried.

[0012] Step 6: Use the carbon material obtained in Step 5 as the negative electrode material for lithium, sodium, and potassium ion batteries, and apply it to lithium, sodium, and potassium ion batteries.

[0013] Preferably, in step 1, an appropriate amount of adsorbent is added and stirred before being allowed to stand to remove impurities from the oil, followed by filtration and purification.

[0014] Preferably, the mass ratio of higher fatty acid glycerides and alkaline substances in the ester decomposition reaction of step 2 is 1:(1-3).

[0015] Preferably, the catalytic conditions for the ester decomposition reaction in step 2 are water bath heating, with the heating temperature controlled within the range of 50℃-100℃.

[0016] Preferably, the mass ratio of the nitrogen-enriching agent to the oil in step 3 is 1:(3-5) to enhance the electrochemical performance of the material by nitrogen doping.

[0017] Preferably, step 4, the high-temperature calcination, includes the following steps:

[0018] (1) Initial calcination: The mixture of higher fatty acid salts and melamine is placed in a calcination device and the temperature is raised to 150-500℃;

[0019] (2) Secondary calcination: After the first calcination, the obtained material is heated to 600-2500℃ and then kept at the same temperature for 0.5-5 hours.

[0020] During the initial calcination process, the temperature is gradually increased in stages to a lower temperature of 150-500℃, and after calcination at 150℃ and 350℃ respectively, the temperature is further increased (5℃ / min) until a higher temperature of 600-2500℃ is reached, which then enters the second calcination process. The second calcination temperature lasts for 0.5-5 hours.

[0021] Preferably, the drying temperature in step 5 is controlled between 50℃ and 200℃, and a vacuum oven is used for auxiliary drying.

[0022] Compared with the carbon negative electrode material of existing batteries, the beneficial effects of this invention are:

[0023] This invention utilizes oils to prepare high-quality electrode carbon materials suitable for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs), thereby producing clean energy and improving the comprehensive utilization value of oils. It broadens the application fields of waste oil recycling, reduces urban pollution caused by waste oils, and can significantly reduce the production cost of electrode carbon materials, thus promoting the development of the new energy battery industry.

[0024] (1) By studying the structure and properties of the carbon materials in the final product, the refining steps of oils (including waste oils) can be simplified, the process links with less impact can be removed, and a simple and efficient oil refining path can be optimized to save production time, reduce production costs, and provide possibilities for industrial production.

[0025] (2) Improve the production efficiency of ester decomposition reaction to efficiently convert oils and fats into higher fatty acid salts, thereby ensuring a high yield of final carbon materials. Through optimization of ester decomposition and carbonization reactions, the yield of oils and fats converted into carbon materials is increased to 80%.

[0026] (3) The preparation process uses alkaline substances (such as potassium hydroxide KOH) and nitrogen-rich agents (such as melamine C3N3(NH2)3) as dual pore-forming agents, which can provide abundant pore sizes for carbon materials. By controlling the amount of pore-forming agent and optimizing the pore-forming conditions, the specific surface area of ​​carbon materials can be increased to 1500 m². 2 g -1 The pore volume reaches 1cm. 3 g -1 above.

[0027] (4) Using nitrogen-enriching agents (such as melamine C3N3(NH2)3) as a nitrogen source to increase the nitrogen content in carbon materials, the nitrogen content of carbon materials can be increased by optimizing the C3N3(NH2)3 doping amount, doping reaction temperature, and time. Because the N atoms in carbon materials are highly electronegative and possess lone pairs of electrons, the N atoms have a strong electronegativity towards Li... + Na + and K + Its adsorption capacity is far stronger than that of carbon materials themselves, thereby improving the electrochemical storage capacity of lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs).

[0028] (5) The nitrogen-rich porous carbon material prepared by this invention has many structural advantages and can achieve excellent electrochemical performance in lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs). Among them, the specific capacity for LIBs reaches 1331 mAh g⁻¹. -1 The above results show that the first-cycle coulombic efficiency reaches over 85%, and the cycle stability exceeds 1000 cycles; the specific capacity of SIBs reaches 489 mAhg. -1 The above results show that the first-cycle coulombic efficiency reaches over 60%, and the cycle stability exceeds 1000 cycles; the specific capacity of PIBs reaches 388 mAh g. -1 The first-cycle coulombic efficiency reached over 50%, and the cycle stability exceeded 1000 cycles. This stable and excellent electrochemical performance lays the foundation for the further industrial production of anode materials prepared from oils and fats. Attached Figure Description

[0029] Figure 1 X-ray diffraction pattern of carbon materials;

[0030] Figure 2 A graph showing the nitrogen adsorption-desorption test of carbon materials;

[0031] Figure 3 A pore size distribution diagram of carbon materials;

[0032] Figure 4 Scanning electron microscope image of carbon material;

[0033] Figure 5 Transmission electron microscope image of carbon material;

[0034] Figure 6 Graphs showing the cyclic charge-discharge test results of lithium-ion batteries (LIBs);

[0035] Figure 7 The diagram shows the cyclic charge-discharge test results for sodium-ion batteries (SIBs).

[0036] Figure 8 This is a diagram showing the cyclic charge-discharge test results of potassium-ion batteries (PIBs). Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the data.

[0038] A method for preparing anode materials from grease includes the following steps:

[0039] Step 1: Oil purification. Oils, especially waste oils, contain a large number of particulate impurities. First, the oil is filtered through a vacuum filter; then, small particulate impurities are adsorbed by an adsorbent and the mixture is allowed to stand to purify the oil, which is a high-purity higher fatty acid glyceride.

[0040] Step 2: Oil solidification. Add an appropriate amount of alkaline substance to the high-purity higher fatty acid glycerides purified in Step 1, and add anhydrous ethanol for stirring to accelerate the reaction. Glycerol and the main component, higher fatty acid salts, can be obtained through ester decomposition reaction. Extract the higher fatty acid salts from the mixture.

[0041] Step 3: Nitrogen doping modification: Add nitrogen-enriching agent to the higher fatty acid salts obtained in Step 2 and mix evenly;

[0042] Step 4: High-temperature calcination. The mixture of higher fatty acid salts and melamine obtained in Step 3 is placed in a high-temperature calcination device for calcination until the mixture of higher fatty acid salts and melamine is completely carbonized.

[0043] Step 5: Washing and drying. The calcined product is subjected to multiple acid washing and ethanol washing to remove inorganic salt impurities and organic impurities. Then it is dried to obtain electrode carbon material that can be used as lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs).

[0044] Step 6: Use the carbon material obtained in Step 5 as the negative electrode material for lithium, sodium, and potassium ion batteries, and apply it to lithium, sodium, and potassium ion batteries.

[0045] Further: After adding an appropriate amount of adsorbent and stirring in step 1, the mixture is allowed to stand, then filtered and purified. The addition of adsorbent can aggregate small particles in the liquid into large particles, which can remove impurities in the mixed liquid more quickly and effectively, resulting in purer grease and preventing the produced electrode carbon material from being affected by impurities in the grease.

[0046] Furthermore: In step 2, the mass ratio of higher fatty acid glycerides to basic substances in the ester decomposition reaction is 1:(1-3).

[0047] Furthermore, in step 2, the ester decomposition reaction is catalyzed using a water bath with the heating temperature controlled between 50℃ and 100℃. Water bath heating can better meet the temperature requirements of the experimental chemical reaction, and the heating process is more stable and is not affected by the temperature of the heat source.

[0048] Furthermore, in step 3, the mass ratio of the nitrogen-enriching agent to the oil is 1:(3-5) to enhance the electrochemical performance of the material through nitrogen doping. Additionally, potassium hydroxide and the nitrogen-enriching agent (such as melamine), while fulfilling their respective functions, can synergistically achieve a pore-forming effect.

[0049] Furthermore: Step 4, the high-temperature calcination, includes the following steps:

[0050] (1) Initial calcination: The mixture of higher fatty acid salts and melamine is placed in a calcination device and the temperature is raised to 150-500℃;

[0051] (2) Secondary calcination: After the first calcination, the obtained material is heated to 600-2500℃ and then kept at the same temperature for 0.5-5 hours.

[0052] Furthermore, during the initial calcination process, the temperature is gradually increased in stages to a lower temperature of 150-500℃, and then calcined at 150℃ and 350℃ respectively before being further increased (5℃ / min) to finally reach a higher temperature of 600-2500℃, thus entering the second calcination, which lasts for 0.5-5 hours. Each calcination gradient is carried out for a certain period of time to ensure sufficient calcination and more thorough carbonization.

[0053] Furthermore, the drying temperature in step 5 is controlled between 50℃ and 200℃, and a vacuum oven is used for auxiliary drying.

[0054] Furthermore, the carbon anode material in step 6 serves as the working electrode of lithium, sodium, and potassium ion batteries, while lithium, sodium, and potassium metals are used as the counter electrode.

[0055] Example 1:

[0056] This embodiment describes a method for preparing a negative electrode material (NWCOC650) using grease. The specific steps are as follows:

[0057] Step 1: Oil purification. The raw oil contains various types of impurities. First, the oil is filtered through a vacuum filter to remove larger particles and improve the purity of the oil. Finally, small particles of impurities are adsorbed by the adsorbent activated clay and allowed to stand to purify the oil, which is a high-purity higher fatty acid glyceride.

[0058] Step 2: The oil is solidified. An appropriate amount of alkaline potassium hydroxide (oil to potassium hydroxide mass ratio of 1:3) is added to the high-purity higher fatty acid glycerides purified in Step 1, and anhydrous ethanol is added and stirred. A water bath is used to catalyze the esterification reaction, with the heating temperature controlled at 90℃. Glycerol and the main component, higher fatty acid salts, can be obtained through the esterification reaction. The higher fatty acid salts are extracted from the mixture.

[0059] Step 3: Nitrogen doping modification. Add nitrogen-rich agent melamine (mass ratio of oil to melamine is 3:1) to the higher fatty acid salt obtained in Step 2 and mix evenly.

[0060] Step 4: High-temperature calcination. The mixture of higher fatty acid salts and melamine obtained in Step 3 is placed in a high-temperature calcination device for segmented calcination. The temperature is raised to 150℃ and 350℃ respectively and calcined continuously, and then the temperature is raised again (5℃ / min) until the highest temperature of 650℃ is reached. Then, a second calcination is carried out. The second calcination temperature is maintained for 0.5-5 hours until the mixture of higher fatty acid salts and melamine is completely carbonized.

[0061] Step 5: Washing and drying. The calcined product is subjected to multiple acid washing and ethanol washing to remove inorganic salt impurities and organic impurities. Then, it is dried in a vacuum drying oven for 12 hours to obtain the carbon anode material, which is named NWCOC650.

[0062] Step 6: Use the carbon material obtained in Step 5 as the working electrode of the lithium, sodium, and potassium ion battery, and the lithium, sodium, and potassium metal sheets as the counter electrode, and assemble the lithium, sodium, and potassium ion battery.

[0063] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, this embodiment discloses the structural characterization of the negative electrode material (NWC0C650) prepared from grease:

[0064] like Figure 1The material composition was analyzed using X-ray diffraction. Two broad characteristic peaks were observed at approximately 2θ = 23.6° and 2θ = 43.6°, corresponding to the (002) and (101) crystal planes of amorphous carbon. Compared to the standard 26° graphite peak (002), the (002) peak of the NWCOC650 sample was at a lower angle, indicating that the carbon material prepared from grease has a larger lattice spacing. This can promote the growth of Li + / Na + / K + The reaction kinetics are maintained while structural stability is preserved.

[0065] like Figure 2 As shown in the nitrogen adsorption-desorption test, NWCOC650 exhibits a mixed shape of type I / IV isotherms and H3 hysteresis loops, indicating the presence of abundant microporous / mesoporous structures within it. Its Brunauer-Emmett-Teller specific surface area is 805.81 m². 2 g -1 It can be Li + / Na + / K + Ions and electrons provide sufficient electrode / electrolyte interface.

[0066] like Figure 3 As shown in the pore size distribution diagram, the pore size of NWCOC650 is concentrated in the range of 1nm-6nm, with an incremental pore volume of 0.037cm³. 3 g -1 Numerous tiny mesopores appear at approximately 3.7 nm, which facilitates the growth of larger Na+ pores. + / K + It improves storage, enhances electrolyte permeability, and more defects / edges can ensure more active sites, thereby improving the electrochemical performance of the anode material.

[0067] like Figure 4 (Scanning electron microscope image) and Figure 5 The surface morphology and microstructure shown in the transmission electron microscope (TEM) images reveal that NWCOC650 is a three-dimensional framework composed of irregular carbon nanosheets. High-magnification TEM images show that the turbine layer structure consists of locally distorted graphite-like domains and pores of uneven size; the diffraction ring type can be attributed to amorphous carbon. Compared to the interlayer spacing of graphite (0.34 nm), NWCOC650 exhibits a larger interlayer spacing (0.4192 nm). This is beneficial for structural stability, a shorter diffusion path, and a longer cycle life, promoting the growth of Li... + / Na + / K + Surface adsorption storage and rapid charge / discharge.

[0068] Example 2:

[0069] This embodiment describes the application of grease-based negative electrode material (NWCOC650) in lithium-ion batteries. The specific steps are as follows:

[0070] In this embodiment, the counter electrode is a lithium sheet, the separator is a Celgard 2500 microporous membrane, and the electrolyte is LiPF6 (1 mol), which includes ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio of 3:7) and 2.0% ethylene carbonate (VC).

[0071] The binder polyvinylidene fluoride, conductive agent acetylene black, and electrode carbon material NWCOC650 are mixed evenly in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone is added, and the mixture is dispersed evenly and then coated onto the current collector copper foil. After drying, the mixture is rolled and punched into round discs (14 mm in diameter) using a punching machine before being assembled into lithium-ion batteries (CR2032 type).

[0072] Figure 6 To illustrate the NWCOC650 in Case 1, consider the 1000-cycle charge-discharge diagram (current density 100 mAh g). -1 The NWCOC650 exhibits excellent charge-discharge cycle stability. During cycling, the specific capacity increases slightly, which can be attributed to electrolyte decomposition and activation processes. In the second cycle, the discharge capacity rapidly decreases to 1219.9 mAh g⁻¹. -1 Significant capacity loss (2996.2 mAh g). -1 ) is formed by the SEI film and Li + Permanent trapping within the pores causes this. From the second cycle onwards, reversible capacity decay is very slow, indicating that NWCOC650 exhibits stable lithium storage behavior. After 1000 cycles, the capacity stabilizes at 887.4 mAh g⁻¹. -1 Furthermore, the coulombic efficiency improved and remained around 100%, indicating that the NWCOC650 electrode performed stably in subsequent cycles.

[0073] Example 3:

[0074] This embodiment describes the application of grease-based negative electrode material (NWCOC650) in sodium-ion batteries. The specific steps are as follows:

[0075] In this embodiment, the counter electrode is a sodium sheet, the diaphragm is Whatman GF / D glass fiber, and the electrolyte is NaClO4 (1 mol), which includes ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) (volume ratio of 1:1:1) and 2.0% fluoroethylene carbonate (FEC).

[0076] The binder polyvinylidene fluoride, conductive agent acetylene black, and electrode carbon material NWCOC650 are mixed evenly in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone is added, and the mixture is dispersed evenly and then coated onto the current collector copper foil. After drying, the mixture is rolled and punched into round discs (14 mm in diameter) using a punching machine before being assembled into lithium-ion batteries (CR2032 type).

[0077] Figure 7 To illustrate the NWCOC650 in Case 2, consider its performance in 1000 charge-discharge cycles (current density of 100 mAh g). -1 The NWCOC650 exhibits excellent cycling stability. The slight increase in specific capacity during cycling can be attributed to electrolyte decomposition and activation processes; however, the discharge capacity rapidly decreases to 508.2 mAh g⁻¹ in the second cycle. -1 Significant capacity loss (1387.3 mAh g). -1 ) is caused by the formation of the SEI layer and Na in the pores + This is caused by permanent capture. From the second cycle onwards, the reversible capacity decay is very slow, indicating that NWCOC650 has stable sodium storage behavior. After 1000 cycles, the capacity remains stable at 312.8 mAh g. -1 Furthermore, the coulombic efficiency increases and remains around 100%, indicating that the NWCOC650 electrode has good cycling performance.

[0078] Example 4:

[0079] This embodiment describes the application of grease-based negative electrode material (NWCOC650) in potassium-ion batteries. The specific steps are as follows:

[0080] In this embodiment, the counter electrode is a potassium sheet, the diaphragm is a double-layer Whatman GF / D glass fiber and Celgard 2500 microporous membrane, and the electrolyte is KPF6 (1 mol), which includes ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) (volume ratio of 1:1:1) and 0.5% fluoroethylene carbonate (FEC).

[0081] The binder polyvinylidene fluoride, conductive agent acetylene black, and electrode carbon material NWCOC650 are mixed evenly in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone is added, and the mixture is dispersed evenly and then coated onto the current collector copper foil. After drying, the mixture is rolled and punched into round discs (14 mm in diameter) using a punching machine before being assembled into lithium-ion batteries (CR2032 type).

[0082] Figure 8 To illustrate the NWCOC650 in Case 3, here is a diagram showing 1000 charge-discharge cycles (current density of 100 mAh g). -1After 1000 cycles, the capacity slowly decreased and then returned to 226.8 mAh g. -1 The coulombic efficiency increased to approximately 100%. The high rate performance and cycle stability of the NWCOC650 confirm the importance of nitrogen-containing functional groups in the grease as anodes in potassium-ion batteries (PIBs). The NWCOC650 electrode exhibits similar Na... + and K + Storage capacity. The high reversible capacity and excellent rate performance of NWCOC650 are attributed to the synergistic effect of high nitrogen doping level, thin carbon nanosheets, large lattice spacing and defect-rich turbine layer structure.

[0083] 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 limited by the appended claims and their equivalents.

Claims

1. A method for preparing carbon materials from oils and fats, characterized in that, Includes the following steps: Step 1: Oil purification. The raw oil contains various types of impurities. First, the oil is filtered through a vacuum filter to remove larger particles and improve the purity of the oil. Finally, small particles of impurities are adsorbed by an adsorbent and the oil is allowed to stand to purify it, which is high-purity higher fatty acid glycerides. Step 2: Oil solidification. Add an appropriate amount of alkaline substance to the high-purity higher fatty acid glycerides purified in Step 1, and add anhydrous ethanol for stirring to accelerate the reaction. Glycerol and the main component, higher fatty acid salts, are obtained through ester decomposition reaction. The higher fatty acid salts in the mixture are extracted. The mass ratio of higher fatty acid glycerides to alkaline substance in the ester decomposition reaction is 1:(1-3). Step 3: Nitrogen doping modification. Add a nitrogen-enriching agent to the higher fatty acid salts obtained in Step 2 and mix them evenly. The nitrogen-enriching agent is melamine. Step 4: High-temperature calcination. The mixture of higher fatty acid salts and nitrogen-enriching agent obtained in Step 3 is placed in a high-temperature calcination device for calcination until the mixture of higher fatty acid salts and nitrogen-enriching agent is completely carbonized. Step 5: Washing and drying. The product after calcination in step 4 is subjected to multiple acid washing and ethanol washing to remove inorganic salt impurities and organic impurities. Then it is dried to obtain carbon material.

2. The method for preparing carbon materials from oils and fats according to claim 1, characterized in that: The raw material oil in step 1 is animal oil, vegetable oil, or waste oil.

3. The method for preparing carbon materials from oils and fats according to claim 1, characterized in that: The adsorbent used in step 1 is activated clay, diatomaceous earth, activated carbon, silica gel, activated alumina, synthetic zeolite, or synthetic resin.

4. The method for preparing carbon materials from oils and fats according to claim 1, characterized in that: The alkaline substance required for the ester decomposition reaction in step 2 is sodium hydroxide, potassium hydroxide, or ammonia.

5. The method for preparing carbon materials from oils and fats according to claim 1, characterized in that: In step 2, the ester decomposition reaction is catalyzed by water bath heating, and the heating temperature is controlled within the range of 50℃-150℃.

6. The method for preparing carbon materials from oils and fats according to claim 1, characterized in that: The mass ratio of nitrogen-enriching agent to oil is 1:(3-5).

7. The method for preparing carbon materials from oils and fats according to claim 1, characterized in that: The high-temperature calcination in step 4 includes the following steps: (1) Initial calcination: The mixture of higher fatty acid salts and melamine is placed in a calcination device and the temperature is raised to 150-500℃; (2) Secondary calcination: After the first calcination, the obtained material is heated to 600-2500℃ and then kept at the same temperature for 0.5-5 hours. During the initial calcination process, the temperature is gradually increased in stages to a lower temperature of 150-500℃. After calcination at 150℃ and 350℃ respectively, the temperature is increased again at 5℃ / min until a higher temperature of 600-2500℃ is reached, which then enters the second calcination process. The second calcination temperature is maintained for 0.5-5 hours.

8. The method for preparing carbon materials from oils and fats according to claim 1, characterized in that: In step 5, the drying temperature is controlled between 50℃ and 200℃, and a vacuum oven is used for auxiliary drying.

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