Carbon material, method for preparing the same, and use thereof

Abstract

The application discloses a kind of carbon materials and its preparation method and application, wherein, the method includes the process that the flame-retardant polyurethane material is pretreated and carbonization treatment;The processing temperature of the pretreatment is 300-950 DEG C;The flame-retardant polyurethane material includes flame retardant, and the flame retardant includes at least one element in N, P, S, B.The preparation method of carbon material provided by the application can realize the technical effect that the specific capacity and the significant improvement of first coulomb efficiency are improved while ensuring high efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a carbon material, its preparation method, and its application. Background Technology

[0002] In recent years, my country's new energy industry has flourished, and the lithium-ion battery industry has become relatively mature. Simultaneously, the demand for sodium-ion batteries due to large-scale energy storage, crucial to my country's energy security, is also increasing. Carbon materials include both solid carbon materials and porous carbon materials. Sodium-ion batteries require carbon materials as the negative electrode, while lithium-ion batteries, characterized by high energy density and fast charging, use porous carbon materials made from solid carbon materials to prepare silicon-carbon negative electrodes. Therefore, the key to the large-scale development of the battery industry lies in achieving improvements in the specific capacity and initial coulombic efficiency of carbon materials, as well as large-scale mass production.

[0003] Currently, carbon materials can be prepared based on biomass precursors. However, due to the differences in morphological characteristics between different batches of biomass precursors, the resulting carbon materials suffer from poor consistency and stability. Carbon materials with poor consistency and stability will exhibit defects such as a decrease in specific capacity and initial coulombic efficiency.

[0004] To address the aforementioned performance issues, researchers have proposed a method for preparing carbon materials using polymers. For example, patent CN 115535998 A describes a method of preparing phenolic resin microspheres by adding phenolic resin prepolymer and a catalyst to a specific solvent for gelation, followed by carbonization of the microspheres to obtain phenolic resin-based spherical carbon materials. However, although the carbon materials prepared by this method show significantly improved performance compared to those prepared using biomass precursors, the solid content of the phenolic resin microspheres obtained by this method is only 5%-10%, resulting in extremely low carbon material preparation efficiency and hindering its commercial application prospects.

[0005] To further address the aforementioned preparation efficiency issues, Chinese patent CN114899520A discloses a method for preparing carbon materials using polyvinyl chloride resin, phenolic resin, or polystyrene resin as raw materials. This method involves using a strong acid or a compound containing metal elements to activate the material, introducing sulfonic acid groups, phosphoric acid groups, nitro groups, carboxyl groups (partially branched oxidation products), and carbon-oxygen bonds (partially branched oxidation products), followed by carbonization treatment. This method has high preparation efficiency, but the use of strong acids for activation treatment results in strong corrosion of equipment and a low safety factor. Furthermore, while using compounds containing metal elements for activation treatment eliminates the risk of equipment corrosion, the method leaves residual metal ions, leading to lower specific capacity and initial coulombic efficiency in the prepared carbon materials.

[0006] Therefore, developing a method that can significantly improve the specific capacity and first coulombic efficiency of carbon materials while ensuring high efficiency has become a research direction for those skilled in the art. Summary of the Invention

[0007] This invention provides a method for preparing carbon materials, which, while ensuring high efficiency, also achieves significant improvements in the specific capacity and initial coulombic efficiency of carbon materials.

[0008] The present invention also provides a carbon material that achieves high specific capacity and high initial coulombic efficiency.

[0009] The present invention also provides a negative electrode active material that achieves high specific capacity and high initial coulombic efficiency.

[0010] The present invention also provides a negative electrode sheet that achieves high specific capacity and high initial coulombic efficiency.

[0011] The present invention also provides a secondary battery that achieves high specific capacity and high initial coulombic efficiency.

[0012] This invention provides a method for preparing carbon materials, which includes a pretreatment and carbonization process for flame-retardant polyurethane materials; the pretreatment temperature is 300-950℃.

[0013] The flame-retardant polyurethane material contains a flame retardant, which contains at least one element selected from N, P, S, and B.

[0014] In the carbon material preparation method described above, the flame retardant is selected from at least one of ammonium polyphosphate, melamine phosphine, and triphenyl phosphate.

[0015] In the carbon material preparation method described above, the flame-retardant polyurethane material is a recycled flame-retardant polyurethane material.

[0016] The method for preparing carbon materials as described above, wherein the pretreatment heating rate is 3-10℃ / min and the holding time is 1-5h; and / or,

[0017] The carbonization process is carried out at a temperature of 1000-1600℃ and a heating rate of 1-10℃ / min.

[0018] In the carbon material preparation method described above, the particle size of the flame-retardant polyurethane material is 2-10 mm; and / or,

[0019] The product obtained from the pretreatment is pulverized to a D50 of 5-15 μm and then subjected to the carbonization treatment.

[0020] The method for preparing carbon materials as described above further includes a step of contacting the product obtained by the carbonization treatment with a pore-forming agent at 650-900°C to perform a pore-forming treatment.

[0021] The pore-forming agent is selected from at least one of water, carbon dioxide, and alkali metal hydroxides.

[0022] The present invention also provides a carbon material, wherein the material is prepared using any of the above-described methods for preparing carbon materials.

[0023] The present invention also provides a negative electrode active material, wherein the material comprises the above-mentioned carbon material.

[0024] The present invention also provides a negative electrode, wherein the negative electrode comprises the above-mentioned carbon material; and / or,

[0025] This includes the aforementioned negative electrode active materials.

[0026] The present invention also provides a secondary battery comprising a carbon material; and / or,

[0027] Including the aforementioned negative electrode active materials; and / or,

[0028] This includes the aforementioned negative electrode sheet.

[0029] The preparation method provided by this invention uses flame-retardant polyurethane material as raw material, and carbon material can be obtained through pretreatment and carbonization without the use of additives, which has a high efficiency effect. At the same time, during the preparation process, the flame retardant contained in the flame-retardant polyurethane material decomposes, causing atoms of at least one element among N, P, S and B to be doped into the carbon lattice, which causes changes in the charge distribution and electronic properties of the carbon structure and induces additional defects. As a result, the carbon material obtained also has the characteristics of high specific capacity and good initial coulombic efficiency. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. 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.

[0031] Currently, carbon materials can be prepared by using polyvinyl chloride resin, phenolic resin, or polystyrene resin as raw materials, and by introducing sulfonic acid groups, phosphoric acid groups, nitro groups, carboxyl groups (partially branched oxidation products), and carbon-oxygen bonds (partially branched oxidation products) through activation treatment with strong acids or compounds containing metal elements, followed by carbonization treatment. However, the inventors have found that although this method is highly efficient, the carbon materials prepared by this method suffer from low specific capacity and low initial coulombic efficiency. Based on the above phenomenon, the inventors speculate that the above defects are due to defects in the lattice structure arrangement of the carbon materials prepared by this method, resulting in fewer active sites that can accept active metal ions (such as sodium ions and lithium ions), thus leading to the defects of low specific capacity and low initial coulombic efficiency in the carbon materials prepared by this method. Therefore, if a method for preparing carbon materials can be developed that can ensure high efficiency while also obtaining carbon materials with suitable crystal structures, the problems existing in the above-mentioned prior art can be solved.

[0032] Based on this, the first aspect of the present invention provides a method for preparing carbon materials, the method comprising pretreating and carbonizing flame-retardant polyurethane materials sequentially to obtain carbon materials; the pretreating temperature is 300-950℃.

[0033] Flame-retardant polyurethane materials include flame retardants, which include at least one element selected from N, P, S, and B.

[0034] Polyurethane materials are widely used in construction, home appliances, and other fields due to their high strength, low density, and low thermal conductivity. Among them, flame-retardant polyurethane materials offer unique safety advantages in areas such as building insulation, pipe insulation, and low-temperature transportation. Flame-retardant polyurethane materials are generally produced by adding flame retardants during the manufacturing process. These flame retardants can be classified into additive, reactive, and intrinsic types based on their mechanism of action.

[0035] Commonly used additive flame retardants include ammonium polyphosphate (APP), expandable graphite, and melamine. The addition of nitrogen (N) and phosphorus (P) elements can effectively improve the limiting oxygen index (LOI) of polyurethane combustion, thus giving polyurethane materials flame-retardant properties.

[0036] Reactive polymerization inhibitors are molecules that participate in the reaction during polymerization and bind to the main chain or branches of the polymer to play a flame-retardant role. They have the characteristics of low migration and excellent long-term effect, but the disadvantage is that the addition of reactive units will affect the mechanical properties of rigid foam.

[0037] The improvement strategy for intrinsic flame-retardant polyurethane is to modify the isocyanate design by adding flame-retardant units to generate functionalized monoisocyanates, thus obtaining intrinsic flame-retardant polyurethane foam.

[0038] The aforementioned additive flame retardants, reactive flame retardants, and intrinsic flame retardants all contain at least one of the doping elements (N, P, S, B). This invention selects flame-retardant polyurethane materials, particularly polymers containing N and P elements as effective flame-retardant components, with a heteroatom content (mass fraction wt%) reaching over 10%.

[0039] Pretreatment of flame-retardant polyurethane materials yields pretreated materials. The pretreatment temperature is 300-950℃. Under these conditions, a carbon lattice is initially formed, and the dopants in the flame-retardant polyurethane material undergo their first migration within the carbon lattice. Pretreatment allows these dopants to migrate to suitable positions, thereby initially improving the specific capacity and initial coulombic efficiency of the prepared carbon material.

[0040] Carbonization further carbonizes the pretreated material while simultaneously enabling the secondary migration of dopant elements within the carbon lattice, placing them in suitable positions to ultimately obtain the carbon material. Carbonization allows for thorough carbonization of the pretreated material at high temperatures, while simultaneously migrating dopant elements to appropriate positions within the lattice. This results in a carbon material with more active sites, thus highlighting its higher specific capacity and initial coulombic efficiency. This invention does not limit the specific processing conditions for carbonization; conditions commonly used in the art can be employed.

[0041] The present invention does not limit the specific processing equipment for carbonization. In one embodiment, a roller kiln can be used for carbonization.

[0042] The inventors discovered that the carbon materials prepared using the above method exhibit high specific capacity and initial coulombic efficiency. The inventors speculate that this is due to several factors: First, introducing dopant atoms into the carbon lattice causes changes in the charge distribution and electronic properties of the carbon structure, inducing additional defects and thus promoting the energy storage conduction rate and specific capacity of the carbon electrode, resulting in high specific capacity and initial coulombic efficiency. Second, the pretreatment and carbonization processes allow the dopant atoms contained in the flame-retardant polyurethane material to complete two migrations within the carbon lattice, resulting in more active sites and further enhancing specific capacity and initial coulombic efficiency. Finally, during the pretreatment and carbonization processes, the escape of heteroatoms affects the reconstruction of the carbon material's microcrystalline structure, forming abundant metal ion binding sites and improving ion diffusion performance, further highlighting the high specific capacity and initial coulombic efficiency of the carbon material. The above preparation method does not require activation treatment; it can be completed using sequential pretreatment and carbonization processes, resulting in high efficiency. Therefore, the carbon material preparation method provided by the present invention has the effect of producing carbon materials with both high specific capacity and high initial coulombic efficiency, while also achieving high efficiency.

[0043] To achieve higher specific capacity and initial coulombic efficiency in the carbon material prepared by the method provided in this invention, the flame retardant included in the flame-retardant polyurethane material can be selected from at least one of ammonium polyphosphate, melamine phosphine, and triphenyl phosphate. Because the aforementioned flame retardants contain higher levels of N and P elements, they can form more abundant metal ion binding sites during pretreatment and carbonization. Therefore, the carbon material prepared using the flame-retardant polyurethane material containing the aforementioned flame retardants exhibits even higher specific capacity and initial coulombic efficiency.

[0044] To further enhance the cost-effectiveness of the carbon material preparation method provided by this invention, in one specific embodiment, the flame-retardant polyurethane material is recycled flame-retardant polyurethane material. Recycled flame-retardant polyurethane material possesses flame-retardant properties while also having a lower raw material price. The price characteristic of recycled materials significantly reduces the preparation cost of carbon materials using polymers as precursors, giving it a greater competitive advantage over other precursor-based carbon materials, thereby contributing to a reduction in the production cost of the carbon material preparation method provided by this invention.

[0045] To further reduce the production cost of the carbon material preparation method provided by this invention, in one specific embodiment, the flame-retardant polyurethane material is selected from wall insulation materials, pipe insulation materials, and door panel filling materials. These materials contain flame retardants, can provide dopant element atoms, and are widely available and inexpensive, thus further reducing the production cost of the carbon material preparation method provided by this invention.

[0046] To further improve the specific capacity and initial coulombic efficiency of carbon materials, in one specific embodiment, the pretreatment heating rate can be controlled at 3-10℃ / min, and the holding time at that temperature can be controlled at 1-5h. The holding time refers to the time spent at the pretreatment temperature after reaching the treatment temperature. These treatment conditions allow the dopant atoms in the flame retardant to move to more suitable positions within the carbon lattice, forming more sites that can bind with active ions, thereby resulting in carbon materials with higher specific capacity and initial coulombic efficiency.

[0047] More specifically, in the above process, the carbonization temperature can be further controlled to 1000-1600℃, and the heating rate to 1-10℃ / min. These processing conditions allow the dopant atoms to move to more suitable positions in the carbon material lattice, further highlighting the high specific capacity and initial coulombic efficiency of the resulting carbon material.

[0048] In a preferred embodiment, the pretreatment temperature can be further controlled at 450-750℃, and the heating rate at 3-6℃ / min; more specifically, the carbonization temperature can be controlled at 1000-1400℃, the heating rate at 1-3℃ / min, and the treatment time at 2-4 hours; in another preferred embodiment, the carbonization temperature can be controlled at 1000-1400℃, the heating rate at 1-10℃ / min, and the temperature can be maintained for 2-4 hours upon reaching the treatment temperature. These conditions further enhance the high specific capacity and initial coulombic efficiency of the resulting carbon material.

[0049] Understandably, to improve the purity of the obtained carbon material, in one embodiment, the carbon material preparation method provided by this invention can select flame-retardant rigid polyurethane foam particles with a particle size of 1-20 mm, preferably 2-10 mm, as raw materials. Magnetic foreign matter is removed using a magnet, and large particle impurities are removed using a large-pore screen. The raw materials are then pretreated by washing with a washing liquid and clean water, followed by drying to remove dust and other inorganic impurities. More specifically, the pretreated product can be pulverized to a D50 of 2-30 μm, preferably 4-15 μm, before carbonization. Pulverizing the pretreated product ensures uniform heating during carbonization, resulting in a more homogeneous carbon material with higher specific capacity and initial coulombic efficiency.

[0050] In a more specific embodiment, the method for preparing carbon materials provided by the present invention further includes a step of contacting the product obtained by carbonization treatment with a pore-forming agent at a temperature of 650-900°C to perform pore-forming treatment.

[0051] The pore-forming agent is selected from at least one of water, carbon dioxide, and alkali metal hydroxides.

[0052] The carbon material prepared by the above process has a high specific surface area and total pore volume, making it suitable as a porous carbon material for use as a silicon-carbon anode in lithium-ion batteries. Specifically, the specific surface area of ​​this porous carbon material is greater than or equal to 1700 m². 2 / g, total pore volume greater than or equal to 0.8cm³ 3 / g. In the above process, under the reaction conditions, the pore-forming agent reacts with the product obtained from the carbonization treatment to generate gas, thereby forming pores and obtaining porous carbon materials.

[0053] The present invention does not limit the reaction equipment used for the above reaction. In one embodiment, the above reaction can be carried out in a fixed bed or fluidized bed reactor.

[0054] A second aspect of this invention provides a carbon material prepared using the method for preparing the carbon material provided in the first aspect of this invention. The carbon material provided by this invention has a specific surface area of ​​5-10 m² / g and further comprises a doping element selected from at least one of N, P, S, and B; the doping element accounts for 0.15-1 wt% of the mass of the carbon material.

[0055] The present invention does not limit the form in which the doping element exists in the carbon material, as long as at least one of the above-mentioned doping elements is present in the carbon material and the mass percentage range is satisfied.

[0056] The inventors have discovered that the carbon material provided by this invention exhibits both high specific capacity and high initial coulombic efficiency. More specifically, the specific capacity of the carbon material is greater than or equal to 323 mAh / g, and the initial coulombic efficiency is greater than or equal to 90%. Based on these phenomena, the inventors speculate that the reason may be that, due to the size difference between the dopant atoms and carbon atoms, and the electronegativity of the dopant atoms, the introduction of dopant atoms into the carbon lattice can cause changes in the charge distribution and electronic properties of the carbon structure, and induce additional defects, thus promoting the increase in the energy storage conduction rate and specific capacity of the carbon electrode. Therefore, the carbon material prepared exhibits both high specific capacity and high initial coulombic efficiency.

[0057] In some specific embodiments, contacting the carbon material provided by this invention (i.e., the product obtained through carbonization) with a pore-forming agent can produce another carbon material. This carbon material has a high specific surface area and total pore volume, and can be used as a porous carbon material in the carbon-silicon anode of lithium-ion batteries. Specifically, the specific surface area of ​​this porous carbon material is greater than or equal to 1700 m². 2 / g, total pore volume greater than or equal to 0.8cm³ 3 / g.

[0058] A third aspect of this invention provides a negative electrode active material, comprising the hard carbon material provided in the second aspect of this invention. The negative electrode active material provided in the third aspect of this invention can be used in the preparation of sodium-ion batteries.

[0059] A fourth aspect of the present invention provides a negative electrode sheet comprising the hard carbon material provided in the second aspect of the present invention; and / or comprising the negative electrode active material provided in the third aspect of the present invention.

[0060] This invention does not limit the specific preparation method of the negative electrode sheet; it can be prepared using conventional methods in the art. In one embodiment, the negative electrode sheet can be prepared by the following method:

[0061] 1) Slurry preparation

[0062] The prepared carbon material is mixed with other components to form a slurry, which typically includes:

[0063] Carbon materials (active substances): the main materials that provide sodium ion storage.

[0064] Conductive agents (such as carbon black, acetylene black, Super P, single-walled carbon nanotubes, etc.) are used to enhance electronic conductivity.

[0065] Adhesives (such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), or polyacrylic acid (PAA)) are used to ensure good bonding between the electrode material and the current collector.

[0066] Stabilizers (such as carboxymethyl cellulose (CMC)) are used to ensure that the slurry is dispersed stably in the solvent.

[0067] Typical slurry proportions (by weight):

[0068] Carbon materials: 92%

[0069] Conductive agent: 4%

[0070] Adhesive: 1.5%

[0071] Stabilizer: 2.5%

[0072] These materials are typically mixed with solvents (such as N-methylpyrrolidone (NMP) or water) to achieve a solid content of 40%, and then stirred to form a homogeneous slurry.

[0073] 2) Coating the current collector

[0074] The prepared slurry is uniformly coated onto the current collector (usually copper foil). Specific steps include:

[0075] Scraping: The slurry is evenly coated onto the copper foil using a scraping process, and the gap between the scrapers is controlled to make the wet film thickness 100 micrometers.

[0076] Drying: Dry at a certain temperature (e.g., 80-120℃) to remove solvent (e.g., NMP), leaving a solid hard carbon electrode material with an areal density of 3.3-3.8 mg / cm³. 2 .

[0077] 3) Compaction and shearing

[0078] Compaction: After drying, the negative electrode sheet usually needs to undergo a rolling process to increase the material's density and mechanical strength, thereby improving conductivity and charge / discharge performance. The compaction density of the electrode sheet is ≥0.92 g / cm3 by adjusting the roller gap.

[0079] Shearing: The compacted electrode sheet is punched into 12mm blanks for easy battery assembly. A fifth aspect of this invention provides a secondary battery comprising the carbon material provided in the second aspect of this invention; and / or, the negative electrode active material provided in the third aspect of this invention; and / or, the negative electrode sheet provided in the fourth aspect of this invention. The secondary battery provided by this invention comprises a carbon material with high specific capacity and high initial coulombic efficiency, thus possessing the characteristics of high specific capacity and high initial coulombic efficiency.

[0080] This invention does not limit the specific preparation method of the secondary battery; conventional methods in the art can be used. In one embodiment, when the secondary battery is a sodium-ion battery, it can be prepared by the following method:

[0081] A coin cell sodium-ion battery is assembled by combining the electrode, separator, sodium metal sheet (which serves as the negative electrode), and electrolyte (such as an ester solution containing NaPF6) under an inert atmosphere (such as dry argon or nitrogen protection).

[0082] The carbon materials, their preparation methods, and applications provided by the present invention will be further illustrated below through specific embodiments:

[0083] The examples and comparative examples use recycled flame-retardant polyurethane materials with the following characteristics:

[0084] Material A: Wall insulation material, flame retardant is ammonium polyphosphate (APP), content 5% wt;

[0085] Material B: Pipe insulation material, flame retardant is melamine phosphine (MHPA), content 2% wt;

[0086] Material C: Door panel filler, flame retardant is triphenyl phosphate (TPP), content 8.5% wt;

[0087] Material D: Refrigerator insulation layer, without flame retardants.

[0088] Material E: Pipe insulation material, with zinc borate (ZnB) as the flame retardant, at a content of 5% wt.

[0089] Material F: Door panel filler, flame retardant new sulfur-nitrogen type flame retardant (SNFR), content 0.2% wt.

[0090] Example 1

[0091] Material B is used as the raw material in this embodiment.

[0092] Material B was crushed into particles with a diameter of 5mm ± 2mm using a rotary vane crusher. It was then cleaned with a 2% sodium dodecylbenzenesulfonate (SDBS) solution to remove oil and inorganic impurities, rinsed with clean water, and dried.

[0093] 0.5 kg of dried material B was placed in a N2 atmosphere box furnace for pretreatment. The temperature was set at 750℃, the heating rate was 5℃ / min, and the temperature was maintained for 1 hour after heating to obtain the pretreated material. The weight of the pretreated material was 160 g, and the calculated pre-carbonization yield was 32%.

[0094] The pretreated material was pulverized a second time using an air jet mill, with the pressure in the pulverizing chamber controlled at 5 barg and the output particle size D50 being 4 μm. The pulverized pre-carbonized material was then transferred to a tube furnace under N2 atmosphere for carbonization treatment. The temperature was set at 1400℃, the heating rate was 3℃ / min, and the temperature was maintained for 1 hour after the heating was completed to obtain carbon material A1.

[0095] Example 2

[0096] The difference between this embodiment and Embodiment 1 is that 0.5 kg of dried material B is replaced with 0.5 kg of dried material A. The pretreatment temperature is 950℃, the heating rate is 5℃ / min, and the temperature is maintained for 1 hour after heating. The pretreated material is then pulverized a second time using an air jet mill and then carbonized. The temperature is set at 1200℃, the heating rate is 4℃ / min, and the temperature is maintained for 2 hours after heating.

[0097] Carbon material A2 was obtained.

[0098] Example 3

[0099] The difference between this embodiment and Embodiment 1 is that 0.5 kg of dried material B is replaced with 0.5 kg of dried material C. The pretreatment temperature is 300℃, the heating rate is 3℃ / min, and the temperature is maintained for 5 hours after heating. The pretreated material is then pulverized a second time using an air jet mill and then carbonized. The temperature is set at 1600℃, the heating rate is 5℃ / min, and the temperature is maintained for 1 hour after heating.

[0100] Carbon material A3 was obtained.

[0101] Example 4

[0102] This embodiment uses carbon material A1 to prepare porous carbon materials:

[0103] Carbon material A1 was loaded into a fixed-bed reactor with an inner diameter of 50 mm. Preheated steam (450°C) was introduced at a rate of 5 g / h. The temperature in the fixed-bed reaction section was 900°C. After 4 hours, the reaction was completed, and the solid was removed from the reaction tube to obtain carbon material M1. Its specific surface area was measured to be 1640 m². 2 / g, pore volume 0.85m 3 / g.

[0104] Example 5

[0105] This embodiment is basically the same as Embodiment 4, except that carbon material A1 is replaced with carbon material A2, CO2 is used as the pore-forming agent, and the pore-forming temperature is 650℃, resulting in carbon material M2. The specific surface area of ​​carbon material M2 was measured to be 1375 m² using a specific surface area analyzer. 2 / g, pore volume is 0.72m 3 / g.

[0106] Example 6

[0107] The difference between this embodiment and Embodiment 1 is that 0.5 kg of dried material B is replaced with 0.5 kg of dried material E. The pretreatment temperature is 500℃, the heating rate is 10℃ / min, and the temperature is maintained for 3 hours after heating. The pretreated material is then pulverized a second time using an air jet mill and then carbonized. The temperature is set at 1200℃, the heating rate is 1℃ / min, and the temperature is maintained for 2 hours after heating.

[0108] Carbon material A4 was obtained.

[0109] Example 7

[0110] The difference between this embodiment and Embodiment 1 is that 0.5 kg of dried material B is replaced with 0.5 kg of dried material F. The pretreatment temperature is 600℃, the heating rate is 7℃ / min, and the temperature is maintained for 2 hours after heating. The pretreated material is then pulverized a second time using an air jet mill and then carbonized. The temperature is set at 1000℃, the heating rate is 10℃ / min, and the temperature is maintained for 1 hour after heating.

[0111] Carbon material A5 was obtained.

[0112] Comparative Example 1

[0113] This comparative example is basically the same as Example 1, except that 0.5 kg of dried material A is replaced with 0.5 kg of dried material D.

[0114] Carbon material B1 was obtained.

[0115] Comparative Example 2

[0116] In this comparative example, the pretreated material obtained in Example 1 was used as carbon material B2.

[0117] Comparative Example 3

[0118] This comparative example is basically the same as Example 1, except that 0.5 kg of dried material B is directly carbonized to obtain carbon material B3.

[0119] Test case

[0120] 1. Doping element content test

[0121] The content of doped elements in the carbon materials obtained in each embodiment and comparative example was tested using an elemental analyzer; the specific surface area of ​​the carbon materials was tested using a specific surface area meter, and the results are shown in Table 1.

[0122] Table 1. Statistics on dopant element content and specific surface area

[0123]

[0124] 2. Electrical performance testing

[0125] Using sodium metal sheets as the negative electrode and carbon materials obtained in Examples 1, 2, 3, 6, 7 and Comparative Examples 1-3 as the positive electrode, and sodium hexafluorophosphate (0.1M) ester electrolyte (mass ratio EC:DMC:PC = 3:3:4), coin cells were assembled in an argon-protected glove box. The initial discharge specific capacity, reversible capacity and initial coulombic efficiency of the materials were measured, and the data are shown in Table 2.

[0126] The test methods for initial discharge specific capacity, reversible capacity, and initial coulombic efficiency are as follows: discharge at a constant current of 0.1C to 5mV, let stand for 10 minutes, then discharge at a constant voltage to 0.01mA (cutoff); after standing for 30 minutes, charge at a constant current of 0.1C to 1.5V (cutoff). Record the initial discharge and charge capacities respectively, and the percentage of charge to discharge capacity is the initial coulombic efficiency.

[0127] Table 2 Electrical performance test data

[0128]

[0129]

[0130] As shown in Table 2, compared to the embodiments, the carbon materials prepared in each comparative example exhibited lower initial discharge specific capacity, reversible capacity, and initial coulombic efficiency when applied to coin cells. This may be because material D used in Comparative Example 1 does not contain flame retardants, thus failing to introduce dopant atoms into the carbon lattice to alter the charge distribution and electronic properties of the carbon structure, thereby inducing additional defects and promoting an increase in the energy conduction rate and specific capacity of the carbon electrode. Furthermore, the carbon material prepared in Comparative Example 2 underwent only pretreatment without carbonization, and the carbon material prepared in Comparative Example 3 was directly carbonized without pretreatment. This prevented the dopant atoms contained in the flame-retardant polyurethane material from completing two migrations within the carbon lattice, resulting in fewer active sites in the carbon material and consequently lower specific capacity and initial coulombic efficiency.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a carbon material, characterized in that, This includes a process of pretreatment and carbonization of flame-retardant polyurethane materials; the pretreatment temperature is 450-750℃. The flame-retardant polyurethane material contains a flame retardant, and the flame retardant contains at least one element selected from N, P, S, and B. The flame retardant is selected from at least one of ammonium polyphosphate, melamine phosphinate, and triphenyl phosphate; The flame-retardant polyurethane material is recycled flame-retardant polyurethane material; The flame-retardant polyurethane material has a particle size of 2-10 mm; and the pretreated product is pulverized to a D50 of 5-15 μm and then subjected to the carbonization treatment. The pretreatment heating rate is 3-10℃ / min, and the holding time is 1-5h; The carbonization process is carried out at a temperature of 1000-1600℃ and a heating rate of 1-10℃ / min. The pretreatment causes the dopant element to migrate for the first time in the carbon lattice, and the carbonization treatment completes the second migration of the dopant element in the carbon lattice, forming metal ion binding sites. The carbon material prepared by the method has a specific surface area of ​​5-10 m² / g; the doping element accounts for 0.15-1wt% of the mass of the carbon material; the specific capacity of the carbon material is greater than or equal to 323 mAh / g, and the initial coulombic efficiency is greater than or equal to 90%.

2. The method according to claim 1, characterized in that, It also includes a step of contacting the product obtained by the carbonization treatment with a pore-forming agent at 650-900°C to perform a pore-forming treatment. The pore-forming agent is selected from at least one of water, carbon dioxide, and alkali metal hydroxides.

3. A carbon material, characterized in that, Prepared using the preparation method described in claim 1 or 2.

4. A negative electrode active material, characterized in that, Including the carbon material as described in claim 3.

5. A negative electrode sheet, characterized in that, Includes the carbon material as described in claim 3; and / or includes the negative electrode active material as described in claim 4.

6. A secondary battery, characterized in that, Including the carbon material as described in claim 3; and / or, Including the negative electrode active material as described in claim 4; and / or, Includes the negative electrode sheet as described in claim 5.

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