Porous carbon, preparation method and application thereof

Abstract

This invention provides a porous carbon, its preparation method, and its application, belonging to the field of materials preparation. The preparation method includes sequentially placing molten asphalt in an organohydrazine gas environment and a heteroatom gas environment to obtain doped modified asphalt; subjecting the doped modified asphalt to a thermal polycondensation reaction to obtain mesophase carbon microspheres; uniformly mixing the mesophase carbon microspheres, an organic activator, a fluorinated lithium salt, and a conductive agent, followed by a hydrothermal reaction to obtain a hydrothermal product; and sequentially activating and reducing the hydrothermal product to obtain porous carbon. This invention, through the prior cross-linking and network building with organohydrazine gas, followed by in-situ doping with heteroatom gas, combined with the synergistic introduction of fluorinated lithium salt and a conductive agent, and the gentle pore-forming effect of the organic activator, prepares a porous carbon that possesses high specific surface area, high pore volume, low resistivity, and high tap density, while also exhibiting excellent isotropic structure. As a lithium-ion battery anode material, it demonstrates excellent rate performance and cycle stability.

Description

Technical Field

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

[0002] Currently, porous carbon is mainly prepared from raw materials such as coconut shells, resins, and anthracite through activation, which results in defects such as poor isotropy and high impedance. Although some studies have attempted to improve its power performance by doping and coating porous carbon with heteroatoms and conductive agents, the improvement is limited and significantly increases production costs.

[0003] Mesophase carbon microspheres, as a high-power anode material, possess advantages such as high isotropy, good power performance, and low expansion, and have been widely used in lithium batteries and other fields. However, the following technical challenges exist in the preparation of porous carbon using mesophase carbon microspheres: (1) Difficulty in creating pores: The mesophase carbon microspheres have a dense structure and a high degree of graphitization. It is difficult to effectively create pores using traditional inorganic base activators, resulting in low pore volume of the obtained porous carbon, which cannot meet the high pore volume requirements of high energy density anode materials.

[0004] (2) Low initial coulombic efficiency: The mesophase carbon microspheres themselves have many structural defects. When they are used directly as a negative electrode material, the initial coulombic efficiency is low, which seriously restricts their commercial application.

[0005] (3) Insufficient conductivity: Although the mesophase carbon microspheres have good isotropy, their electronic conductivity and ion diffusion coefficient still need to be further improved, especially under high current charging and discharging conditions, their power performance is poor.

[0006] (4) Poor resistance to expansion: The volume of the mesophase carbon microsphere-based porous carbon expands significantly during charge and discharge cycles, which leads to a decrease in cycle stability and affects the long-term service life of the battery.

[0007] To address the aforementioned issues, existing research has attempted to improve the electrochemical performance of mesophase carbon microspheres by doping with heteroatoms or coating with conductive agents. However, current technologies mostly employ liquid-phase impregnation or post-doping methods, which suffer from problems such as uneven doping, complex processes, and difficulty in precisely controlling the distribution of doping elements. Furthermore, they have failed to fundamentally solve the problem of pore formation in mesophase carbon microspheres.

[0008] In addition, the inorganic alkaline activators commonly used in existing activation processes have drawbacks such as high levels of residual impurities, severe equipment corrosion, and harsh activation conditions. There is an urgent need to develop a new activation process with mild activation conditions and no residual impurities.

[0009] Therefore, there is an urgent need to develop a method for preparing porous carbon that can simultaneously solve the problems of difficult pore formation, low initial coulombic efficiency, insufficient electrical conductivity, and poor resistance to expansion. Summary of the Invention

[0010] To address the above problems, this invention provides a porous carbon, its preparation method, and its application.

[0011] One objective of this invention is to provide a method for preparing porous carbon, comprising the following steps: Molten asphalt was sequentially treated in an organic hydrazine gas atmosphere and a heteroatom gas atmosphere to obtain doped modified asphalt; The doped and modified asphalt was subjected to a thermal polycondensation reaction to obtain mesophase carbon microspheres; The mesophase carbon microspheres, organic activator, fluorine-containing lithium salt and conductive agent are mixed evenly and then subjected to hydrothermal reaction to obtain hydrothermal product; The hydrothermal products were activated to obtain porous carbon.

[0012] Preferably, the asphalt comprises at least one of petroleum asphalt, coal tar pitch, or mesophase asphalt; and / or, The organohydrazine gas includes at least one of alkylhydrazine, acylhydrazine, or aromatic hydrazine; and / or, Heteroatom gases include phosphorus-containing heteroatom gases or nitrogen-containing heteroatom gases; and / or, Organic activators include organic carboxylates; and / or, The conductive agent includes at least one of graphene, carbon nanotubes, or carbon black.

[0013] Preferably, the volume ratio of the organic hydrazine gas to the heteroatom gas is 2-5:1.

[0014] Preferably, the flow rates of the organic hydrazine gas and the heteroatom gas are each independently 100-500 mL / min; and / or, The residence time of molten asphalt in an organohydrazine gas atmosphere is 30-300 min; and / or, The residence time of molten asphalt in a heteroatom gas atmosphere is 10-60 minutes.

[0015] Preferably, the polycondensation reaction satisfies at least one of the following conditions: (a) Temperature is 400-500℃; and, (b) The time is 1-6 hours.

[0016] Preferably, the fluorinated lithium salt is added in the form of a fluorinated lithium salt solution; in the fluorinated lithium salt solution, the mass concentration of the fluorinated lithium salt is 10-30 wt%; and / or, The conductive agent is added in the form of a conductive agent solution, wherein the mass concentration of the conductive agent in the conductive agent solution is 0.5-5 wt%.

[0017] Preferably, the mass ratio of the mesophase carbon microspheres, the organic activator, the fluorinated lithium salt solution, and the conductive agent solution is 100:100-300:100-300:100-500.

[0018] Preferably, the hydrothermal reaction satisfies at least one of the following conditions: (c) The reaction temperature is 300-500℃; and, (d) The reaction time is 1-6 hours; And / or, The activation treatment must meet at least one of the following conditions: (e) The activation temperature is 900-1100℃; and, (f) Activation time is 1-6 hours; And / or, The activation process is followed by a reduction process, wherein the reduction process satisfies at least one of the following conditions: (g) The temperature is 500-700℃; (h) Reducing gas environment; and, (i) The restoration time is 1-6 hours.

[0019] The second objective of this invention is to provide a porous carbon prepared by the method described above.

[0020] The third objective of this invention is to provide an application of porous carbon as described above in the preparation of silicon-carbon anode materials.

[0021] The beneficial effects of this invention are: In this invention, molten asphalt is sequentially placed in an organic hydrazine gas environment and a heteroatom gas environment for treatment. The organic hydrazine gas first cross-links and forms a network, while the heteroatom gas is then used for in-situ doping. This avoids the two gases consuming each other or competing for reaction sites in the gas phase due to differences in reactivity, achieving in-situ uniform doping of heteroatoms into the cross-linked carbon framework, thus improving the electronic conductivity and kinetic properties of the material. Furthermore, an organic activator is used instead of a traditional inorganic alkali. This achieves gentle pore formation, a high micropore ratio, and no impurity residue. Simultaneously, fluorinated lithium salt and a conductive agent are introduced. After hydrothermal reaction and high-temperature activation, the strong electron-withdrawing effect of fluorine atoms in the fluorinated lithium salt allows lithium ions to efficiently dope into the carbon layer, improving the ion diffusion coefficient. The in-situ composite of the conductive agent further improves the electronic conductivity. Together, these two processes effectively reduce the resistivity of the material powder. The reduction treatment further repairs surface defects and improves the initial coulombic efficiency.

[0022] Through the synergistic effect of the above-mentioned technical means, the porous carbon prepared by this invention has high specific surface area, high pore volume, low resistivity and high tap density, and exhibits excellent first coulombic efficiency and cycle stability when used as a negative electrode material for lithium-ion batteries. Attached Figure Description

[0023] Figure 1 This is a SEM image of the porous carbon prepared in Example 1. Detailed Implementation

[0024] The present application will now be described in further detail with reference to embodiments. In the following description, certain specific details are included to provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented without employing one or more of these specific details, but using other methods, components, materials, etc. Unless otherwise required by the present invention, the terms "comprising" and "including" should be interpreted in an open-ended, inclusive sense, meaning "including but not limited to". Throughout this specification, "an embodiment," "an embodiment," "a preferred embodiment," or "some embodiments" means that at least one embodiment includes a specific reference element, structure, or feature related to that embodiment. Therefore, the phrases "in an embodiment," "in an embodiment," "in a preferred embodiment," or "in some embodiments" appearing in different places throughout the specification do not necessarily all refer to the same embodiment. Furthermore, specific elements, structures, or features may be combined in one or more embodiments in any suitable manner.

[0025] According to a first aspect of the present invention, a method for preparing porous carbon is provided, comprising the following steps: Molten asphalt was sequentially treated in an organic hydrazine gas atmosphere and a heteroatom gas atmosphere to obtain doped modified asphalt; The doped and modified asphalt was subjected to a thermal polycondensation reaction to obtain mesophase carbon microspheres; The mesophase carbon microspheres, organic activator, fluorine-containing lithium salt and conductive agent are mixed evenly and then subjected to hydrothermal reaction to obtain hydrothermal product; The hydrothermal products were activated to obtain porous carbon.

[0026] In this invention, organohydrazine has strong reducing properties. The organohydrazine gas introduced first will preferentially react with the unsaturated bonds in the asphalt, initiating cross-linking. After cross-linking is completed, a heteroatom gas is introduced to avoid the two gases consuming each other or competing for reaction sites in the gas phase due to differences in reactivity. This achieves in-situ uniform doping of heteroatoms in the cross-linked carbon framework, improving electronic conductivity and kinetic performance.

[0027] After cross-linking, the asphalt molecules further condense to form spherical mesophase carbon microspheres with high isotropy and few sharp edges, which improves the compressive strength and expansion resistance of the material.

[0028] Organic activators replace traditional inorganic alkalis, achieving gentle pore formation without residual metal impurities; fluorinated lithium salts utilize the strong electron-withdrawing effect of fluorine atoms to efficiently dope lithium ions into the carbon layer, improving the ion diffusion coefficient; conductive agents are in-situ composited to improve electronic conductivity; the three work synergistically to reduce powder resistivity. Hydrothermal reactions promote uniform dispersion and pre-reaction of the components, activating pore formation and carbonization.

[0029] In a preferred embodiment of the present invention, the asphalt includes at least one of petroleum asphalt, coal tar pitch, or mesophase asphalt, such as petroleum asphalt, coal tar pitch, mesophase asphalt, petroleum asphalt and coal tar pitch, coal tar pitch and mesophase asphalt, petroleum asphalt and mesophase asphalt, or a combination of petroleum asphalt, coal tar pitch, and mesophase asphalt. And / or, The organohydrazine gas includes at least one of alkylhydrazine, acylhydrazine, or aromatic hydrazine, for example, alkylhydrazine, acylhydrazine, aromatic hydrazine, alkylhydrazine and acylhydrazine, alkylhydrazine and aromatic hydrazine, acylhydrazine and aromatic hydrazine, or alkylhydrazine, acylhydrazine and aromatic hydrazine; And / or, Heteroatom gases include phosphorus-containing heteroatom gases or nitrogen-containing heteroatom gases; and / or, Organic activators include organic carboxylates; and / or, The conductive agent includes at least one of graphene, carbon nanotubes or carbon black conductive agents, such as graphene, carbon nanotubes, carbon black conductive agents, graphene and carbon nanotubes, graphene and carbon black conductive agents, carbon nanotubes and carbon black conductive agents, or graphene, carbon nanotubes and carbon black conductive agents.

[0030] In a preferred embodiment of the present invention, the alkylhydrazine includes at least one selected from methylhydrazine, ethylhydrazine, or dimethylhydrazine; and / or, The acylhydrazine includes at least one of acetylhydrazine, benzoylhydrazine, acetylphenylhydrazine, butyrylhydrazine, p-toluenehydrazine, benzylsulfonylhydrazine, or formylhydrazine; and / or, The aromatic hydrazine includes at least one of diphenylhydrazine, phenylhydrazine, toluenehydrazine, nitrophenylhydrazine, or naphthylhydrazine.

[0031] In a preferred embodiment of the present invention, the phosphorus-containing heteroatom gas includes at least one of methamidophos, dibutyl phosphate, tripolyphosphate, triphenyl phosphate, tributyl phosphate, n-butyl phosphate, or monobutyl phosphate. The nitrogen-containing heteroatom gas includes at least one of methylamine, dimethylamine, ethylamine, formamide, dimethylformamide, pyridine, pyrrole, quinoline, carbazole, indole, aniline, acetonitrile, or acrylonitrile.

[0032] In a preferred embodiment of the present invention, the organic carboxylate includes at least one of saturated monocarboxylate, unsaturated carboxylate, polymeric carboxylate, aromatic carboxylate, or polycarboxylate.

[0033] In a preferred embodiment of the present invention, the saturated monocarboxylic acid salt includes potassium laurate, potassium stearate, potassium acetate, potassium propionate, or potassium butyrate; and / or, Unsaturated carboxylates include potassium acrylate or potassium butenoate; and / or, Polycarboxylate salts include potassium polyacrylate or potassium polyitacrylate; and / or, Aromatic carboxylates include at least one of potassium salicylate, potassium benzoate, and potassium terephthalate; and / or, Polycarboxylate salts include at least one of potassium oxalate, potassium citrate, potassium tartrate, potassium malate, potassium maleate, potassium fumarate, and potassium succinate.

[0034] In a preferred embodiment of the present invention, the volume ratio of the organic hydrazine gas to the heteroatom gas is 2-5:1, for example, 2:1, 3:1, 4:1 or 5:1.

[0035] In a preferred embodiment of the present invention, the flow rates of the organohydrazine gas and the heteroatom gas are each independently 100-500 mL / min, for example 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min or 500 mL / min; and / or, the residence time of the molten asphalt in the organohydrazine gas atmosphere is 30-300 min, for example 30 min, 60 min, 120 min, 180 min, 240 min or 300 min; and / or, the residence time of the molten asphalt in the heteroatom gas atmosphere is 10-60 min, for example 10 min, 20 min, 30 min, 40 min, 50 min or 60 min.

[0036] In a preferred embodiment of the present invention, molten asphalt is sequentially placed in an organic hydrazine gas environment and a heteroatom gas environment to obtain doped modified asphalt, comprising: Add asphalt to the reactor and heat to 200-300℃ until it melts; Organic hydrazine gas is first introduced at a flow rate of 100-500 mL / min for 30-300 min, followed by heteroatom gas for 10-60 min, to obtain doped modified asphalt.

[0037] In a preferred embodiment of the present invention, the polycondensation reaction satisfies at least one of the following conditions: (a) Temperatures of 400-500°C, for example 400°C, 420°C, 430°C, 450°C, 480°C, or 500°C; and, (b) The time is 1-6h, for example, 1h, 2h, 3h, 4h, 5h or 6h.

[0038] In a preferred embodiment of the present invention, the doped modified asphalt is subjected to a thermal polycondensation reaction to obtain mesophase carbon microspheres, comprising: The doped modified bitumen was subjected to a polycondensation reaction at 400-500℃ for 1-6 hours. After cooling, it was extracted, filtered, washed and dried to obtain multi-element doped mesophase carbon microspheres.

[0039] Typically, but not limitingly, tetrahydrofuran is used for extraction.

[0040] In a preferred embodiment of the present invention, the fluorinated lithium salt is added in the form of a fluorinated lithium salt solution; in the fluorinated lithium salt solution, the mass concentration of the fluorinated lithium salt is 10-30 wt%, for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt%. And / or, The conductive agent is added in the form of a conductive agent solution, wherein the mass concentration of the conductive agent in the conductive agent solution is 0.5-5.0 wt%, for example, 0.5 wt%, 1 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, or 5.0 wt%. Typically, but not limitingly, the solvent for the fluorinated lithium salt solution is deionized water.

[0041] Typically, but not limitingly, the solvent for the conductive agent solution is N-methylpyrrolidone.

[0042] In a preferred embodiment of the present invention, the mass ratio of the mesophase carbon microspheres, the organic activator, the fluorinated lithium salt solution, and the conductive agent solution is 100:100-300:100-300:100-500.

[0043] In a preferred embodiment of the present invention, the hydrothermal reaction satisfies at least one of the following conditions: (c) 300-500℃, for example, 300℃, 350℃, 400℃, 420℃, 450℃, 480℃, or 500℃; and, (d) The reaction time is 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours; And / or, Activation satisfies at least one of the following conditions: (e) The activation temperature is 900-1100°C, for example, 900°C, 950°C, 980°C, 1000°C, 1020°C, 1050°C, or 1100°C; and, (f) The activation time is 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours; And / or, The activation process is followed by a reduction process, wherein the reduction process satisfies at least one of the following conditions: (g) The temperature is 500-700℃, for example, 500℃, 520℃, 550℃, 580℃, 600℃, 620℃, 650℃, 680℃ or 700℃; (h) Reducing gas environment; and, (i) The restoration time is 1-6h, for example, 1h, 2h, 3h, 4h, 5h or 6h.

[0044] In a preferred embodiment of the present invention, the mesophase carbon microspheres, organic activator, fluorinated lithium salt, and conductive agent are mixed evenly and then subjected to a hydrothermal reaction to obtain a hydrothermal product, comprising: Mesophase carbon microspheres, organic activator, fluorinated lithium salt solution and conductive agent solution were mixed evenly at a mass ratio of 100:100-300:100-300:100-500 and subjected to hydrothermal reaction at a temperature of 300-500℃ for 1-6 hours to obtain hydrothermal product.

[0045] In a preferred embodiment of the present invention, the flow rate of the reducing gas is 100-500 mL / min.

[0046] In a preferred embodiment of the present invention, the hydrothermal products are sequentially activated and reduced to obtain porous carbon, comprising: The hydrothermal product is first heated to 900-1100℃ for 1-6 hours, then cooled to 500-700℃, and reduced by introducing a reducing gas at a flow rate of 100-500 mL / min for 1-6 hours. Finally, the temperature is lowered to 20-30℃ under an inert gas atmosphere to obtain porous carbon.

[0047] Typical, but not limiting, reducing gases include at least one of carbon monoxide, hydrogen, hydrogen sulfide, or sulfur dioxide.

[0048] Typical, but not limiting, inert gases include nitrogen or argon.

[0049] In a preferred embodiment of the present invention, the method for preparing porous carbon specifically includes: Add asphalt to the reactor and heat to 200-300℃ until it melts; Organic hydrazine gas was first introduced at a flow rate of 100-500 mL / min for 30-300 min, followed by heteroatom gas for 10-60 min, to obtain doped modified asphalt. The doped modified asphalt was subjected to a polycondensation reaction at 400-500℃ for 1-6 hours. After cooling, it was extracted, filtered, washed and dried to obtain multi-element doped mesophase carbon microspheres. Mesophase carbon microspheres, an organic activator, a fluorinated lithium salt solution with a mass concentration of 10-30 wt%, and a conductive agent solution with a mass concentration of 0.5-5.0 wt% were mixed evenly at a mass ratio of 100:100-300:100-300:100-500 and subjected to a hydrothermal reaction at a temperature of 300-500℃ for 1-6 hours to obtain a hydrothermal product. The hydrothermal product is first heated to 900-1100℃ for 1-6 hours, then cooled to 500-700℃, and reduced by introducing a reducing gas at a flow rate of 100-500 mL / min for 1-6 hours. Finally, the temperature is lowered to 20-30℃ under an inert gas atmosphere to obtain porous carbon.

[0050] The second objective of this invention is to provide a porous carbon prepared by the method described above.

[0051] The third objective of this invention is to provide an application of porous carbon as described above in the preparation of silicon-carbon anode materials.

[0052] The present application will be further described in detail below with reference to the embodiments. The following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the present application. Unless otherwise specified in the embodiments, the conditions are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products that can be obtained commercially.

[0053] Example 1 A method for preparing porous carbon includes the following steps: 100g of petroleum asphalt was added to a reactor and heated to 250℃ until it reached a molten state. Then, methylhydrazine gas and methyl methamidophos gas were introduced sequentially at a flow rate of 300mL / min. The residence time of the molten asphalt under the organic hydrazine gas atmosphere and the heteroatom gas atmosphere was 150min and 30min, respectively, to obtain doped modified asphalt. The doped modified asphalt was subjected to a thermal polycondensation reaction at 450°C for 3 hours, cooled, extracted with tetrahydrofuran, filtered, washed and dried to obtain mesophase carbon microspheres. 100g of mesophase carbon microspheres, 200g of potassium laurate, 200g of lithium tetrafluoroborate aqueous solution with a mass concentration of 20wt% and 300g of graphene N-methylpyrrolidone solution with a mass concentration of 2wt% were mixed evenly and subjected to hydrothermal reaction at a temperature of 400℃ for 3h. After filtration, the hydrothermal product was obtained. The hydrothermal product was activated at 1000℃ for 3 hours, then cooled to 600℃, and carbon monoxide was introduced at a flow rate of 100-500 mL / min for reduction for 3 hours. Finally, the mixture was cooled to room temperature under inert gas to obtain porous carbon. The SEM image of the porous carbon prepared in Example 1 is shown below. Figure 1 As shown.

[0054] Example 2 The difference from Example 1 is as follows: The asphalt is 100g of coal tar pitch; Heat to 200℃ until molten; The flow rate is 100 mL / min; The organic hydrazine gas was acetylhydrazine gas, and the residence time was 300 min; The heteroatom gas was dibutyl phosphate gas, and the residence time was 60 min; The polycondensation reaction was carried out at a temperature of 400℃ for 6 hours. The organic activator is 100g of potassium acrylate; The lithium salt is 100g of a 30wt% aqueous solution of lithium trifluoromethanesulfonate; The conductive agent is 100g of a 0.5wt% carbon nanotube N-methylpyrrolidone solution; The hydrothermal reaction temperature was 300℃, and the reaction time was 6 hours. The activation temperature was 900℃, and the activation time was 6 hours. The reduction temperature was 500℃, and the time was 6 hours. The reducing gas is hydrogen.

[0055] Example 3 The difference from Example 1 is as follows: The asphalt is 100g of mesophase asphalt; Heat to 300℃ until molten; The flow rate is 500 mL / min; The organic hydrazine gas was diphenylhydrazine gas, and the residence time was 30 min; The heteroatom gas is tripolyphosphate gas, and the residence time is 10 min; The polycondensation reaction was carried out at a temperature of 500℃ for 6 hours. The organic activator is 300g of potassium acetate; The lithium salt is 300g of a 10wt% aqueous solution of lithium trifluoroacetate; The conductive agent is 500g of a 0.5wt% carbon black N-methylpyrrolidone solution; The hydrothermal reaction temperature was 500℃, and the time was 1 hour. The activation temperature was 1100℃, and the activation time was 1 hour. The reduction temperature was 700℃, and the time was 1 hour. The reducing gas is hydrogen sulfide; The inert gas is nitrogen.

[0056] Example 4 The difference from Example 1 is as follows: Heat to 230°C until molten; The flow rate is 200 mL / min; The organic hydrazine gas was butyryl hydrazine gas, and the residence time was 120 min; The heteroatom gas was tributyl phosphate gas, and the residence time was 35 min; The polycondensation reaction temperature was 440℃, and the time was 1 hour. The organic activator is 160g of potassium benzoate; The lithium salt is 160g of a 16wt% aqueous solution of lithium difluorooxalate borate; The conductive agent is 400g of a 5wt% carbon black N-methylpyrrolidone solution; The hydrothermal reaction temperature was 350℃, and the reaction time was 5 hours. The activation temperature was 1050℃, and the activation time was 4 hours. The reduction temperature was 550℃, and the time was 2 hours. The reducing gas is hydrogen sulfide; The inert gas is argon.

[0057] Example 5 The difference from Example 1 is as follows: The asphalt is 100g of coal tar pitch; Heat to 210°C until molten; The flow rate is 150 mL / min; The organic hydrazine gas was dimethylhydrazine, and the residence time was 280 min. The heteroatom gas was trimethyl phosphite gas, and the residence time was 15 min; The polycondensation reaction temperature was 410℃, and the time was 2 hours. The organic activator is 250g of potassium polyacrylate; The lithium salt is 250g of a 14wt% aqueous solution of lithium difluorodioxanol phosphate; The conductive agent is 300g of a carbon nanotube N-methylpyrrolidone solution with a mass concentration of 1.8wt%; The hydrothermal reaction temperature was 370℃, and the reaction time was 3 hours. The activation temperature was 930℃, and the activation time was 2 hours. The reduction temperature was 530℃, and the time was 4 hours. The reducing gas is carbon monoxide.

[0058] Example 6 The difference from Example 1 is as follows: The asphalt is 100g of mesophase asphalt; Heat to 270°C until molten; The flow rate is 400 mL / min; The organic hydrazine gas was p-toluenehydrazine, and the residence time was 50 min. The heteroatom gas was n-butyl phosphate gas, and the residence time was 50 min; The polycondensation reaction temperature was 490℃, and the time was 3 hours. The organic activator is 220g of potassium citrate; The lithium salt is 220g of a 24wt% aqueous solution of lithium perfluorohexanesulfonate; The conductive agent is 450g of a graphene N-methylpyrrolidone solution with a mass concentration of 4.2wt%; The hydrothermal reaction temperature was 430℃, and the reaction time was 4 hours. The activation temperature was 1070℃, and the activation time was 5 hours. The reduction temperature was 670℃, and the time was 5 hours. The reducing gas is sulfur dioxide.

[0059] Example 7 The difference from Example 1 is as follows: Heat to 220°C until molten; The flow rate is 120 mL / min; The organic hydrazine gas was phenylhydrazine gas, and the residence time was 260 min; The heteroatom gas was phosphorus oxychloride, and the residence time was 20 min. The polycondensation reaction temperature was 400℃ and the reaction time was 4 hours. The organic activator is 130g of potassium oxalate; The lithium salt is 130g of a 12wt% aqueous solution of lithium bis(trifluoromethanesulfonyl)imide. The conductive agent is 180g of a 0.8wt% N-methylpyrrolidone solution of graphene and carbon nanotubes (mass ratio 1:1). The hydrothermal reaction temperature was 320℃, and the reaction time was 2.5 hours. The activation temperature was 920℃, and the activation time was 1.5 hours. The reduction temperature was 510℃, and the time was 2.5h. The reducing gas is carbon monoxide; The inert gas is helium.

[0060] Example 8 The difference from Example 1 is as follows: The asphalt is 100g of coal tar pitch; Heat to 240°C until molten; The flow rate is 240 mL / min; The organic hydrazine gas was acetylphenylhydrazine gas, and the residence time was 210 min; The heteroatom gas was triphenyl phosphate gas, and the residence time was 25 min; The polycondensation reaction temperature was 420℃, and the reaction time was 5 hours. The organic activator is 170g of potassium salicylate; The lithium salt is 170g of a 17wt% lithium difluoroacetate aqueous solution; The conductive agent is 350g of a carbon nanotube N-methylpyrrolidone solution with a mass concentration of 3.5wt%; The hydrothermal reaction temperature was 380℃, and the reaction time was 5.5 hours. The activation temperature was 1000℃, and the activation time was 3.5 hours. The reduction temperature was 570℃, and the time was 1.5 hours. The reducing gas is hydrogen.

[0061] Example 9 The difference from Example 1 is as follows: The asphalt is 100g of mesophase asphalt; Heat to 280°C until molten; The flow rate is 450 mL / min; The organic hydrazine gas was naphthalenehydrazine gas, and the residence time was 80 min; The heteroatom gas was triphenylphosphine gas, and the residence time was 45 min; The polycondensation reaction temperature was 500℃, and the time was 2 hours. The organic activator is 280g of potassium stearate; The lithium salt is 280g of a 26wt% lithium trifluoroformate aqueous solution; The conductive agent is 480g of a graphene N-methylpyrrolidone solution with a mass concentration of 4.8wt%; The hydrothermal reaction temperature was 470℃, and the reaction time was 1.5 hours. The activation temperature was 1080℃, and the activation time was 5.5 hours. The reduction temperature was 680℃, and the time was 5.5 hours. The reducing gas is sulfur dioxide; The inert gas is helium.

[0062] Example 10 The difference from Example 1 is as follows: Heat to 260°C until molten; The flow rate is 320 mL / min; The organic hydrazine gas was ethylhydrazine, and the residence time was 100 min. The heteroatom gas was triethylphosphine gas, and the residence time was 40 min; The polycondensation reaction temperature was 460℃, and the reaction time was 2.5h. The organic activator is 190g of potassium terephthalate; The lithium salt is 190g of a 22wt% lithium difluoroacetate aqueous solution; The conductive agent is 420g of a 3.2wt% carbon black N-methylpyrrolidone solution; The hydrothermal reaction temperature was 410℃, and the reaction time was 2 hours. The activation temperature was 950℃, and the activation time was 2.5 hours. The reduction temperature was 500℃, and the time was 3.5 hours. The reducing gas is carbon monoxide.

[0063] Example 11 The difference from Example 1 is as follows: The asphalt is 100g of coal tar pitch; Heat to 290°C until molten; The flow rate is 460 mL / min; The organic hydrazine gas was benzenesulfonyl hydrazine gas, with a residence time of 70 min; The heteroatom gas was phosphine gas, and the residence time was 55 min; The polycondensation reaction temperature was 480℃, and the reaction time was 5.5 hours. The organic activator is 270g of potassium tartrate; The lithium salt is 270g of a 28wt% aqueous solution of lithium perfluorohexanesulfonate; The conductive agent is a 480g N-methylpyrrolidone solution containing a 4.5wt% mixture of graphene and carbon nanotubes (mass ratio 1:1). The hydrothermal reaction temperature was 490℃, and the reaction time was 1.5 hours. The activation temperature was 1090℃, and the activation time was 3.5 hours. The reduction temperature was 700℃, and the time was 2.5 hours. The reducing gas is hydrogen sulfide; The inert gas is helium.

[0064] Example 12 The difference from Example 1 is as follows: The organic activator was 200g of potassium 6-hydroxy-2-naphthalenesulfonate (an organic potassium sulfonate salt, not an organic carboxylic acid salt), and the rest was the same as in Example 1.

[0065] Comparative Example 1 The difference from Example 1 is as follows: Without introducing methylhydrazine gas and methylamine phosphorus gas, the molten asphalt is directly subjected to thermal polycondensation reaction, and the rest is the same as in Example 1.

[0066] Comparative Example 2 The difference from Example 1 is as follows: The aqueous solution of lithium tetrafluoroborate was not added; otherwise, it was the same as in Example 1.

[0067] Comparative Example 3 The difference from Example 1 is as follows: Replace potassium laurate with an equal mass of potassium hydroxide (inorganic base), otherwise the same as in Example 1.

[0068] Comparative Example 4 The difference from Example 1 is as follows: First, methamidophos gas was introduced for 30 minutes, then methylhydrazine gas was introduced for 150 minutes (the order of introduction was reversed), and the rest was the same as in Example 1.

[0069] Comparative Example 5 The difference from Example 1 is as follows: Using commercially available mesophase carbon microspheres (MCMB) as raw material (Xiamen TPT New Energy Technology Co., Ltd., product number: T-MCMB-S), without undergoing the gas phase doping treatment step of molten asphalt; Commercially available mesophase carbon microspheres were mixed with KOH at a mass ratio of 1:5 until homogeneous. The mixture was activated at 900℃ for 30 min, cooled, washed with water, filtered, and dried to obtain porous carbon. It does not involve hydrothermal reaction, fluorine-containing lithium salt doping, conductive agent composite and reduction treatment steps.

[0070] Performance testing (1) Physicochemical property testing The pore volume and pore size of the porous carbons obtained in Examples 1-12 and Comparative Examples 1-5 were tested according to the national standard GB / T-38949-2020 "Determination of Pore Size of Porous Membranes - Standard Particle Method". Their specific surface area and tap density were tested according to the national standard GB / T 38823-2020 "Silicon Carbon". The powder resistivity of each porous carbon was tested using a four-probe tester. The test results are shown in Table 1.

[0071] Table 1. Physicochemical properties of porous carbon in Examples 1-12 and Comparative Examples 1-5

[0072] (2) Compressive strength test The samples were pressed with pressures of 0T, 10T, and 20T respectively, and the change in specific surface area after pressing was tested. The results are shown in Table 2.

[0073] Table 2. Changes in specific surface area (m² / g) under different pressures in Examples 1-12 and Comparative Examples 1-5

[0074] (3) Button cell performance test Using the porous carbon corresponding to Examples 1-12 and Comparative Examples 1-5 as the negative electrode material for lithium-ion batteries, coin cells were prepared according to the following method: The binder LA136D, the conductive agent CNT, and the solvent NMP were added to each porous carbon, stirred and slurryed, coated on copper foil, dried and rolled to obtain the negative electrode sheet; the ratio of porous carbon:CNT:LA136D:NMP was 70g:15g:15g:250mL; the electrolyte was a solution with LiPF6 as the electrolyte and a concentration of 1.1mol / L, and the solvent was a mixture of EC and DEC in a volume ratio of 1:1; the lithium metal sheet was used as the counter electrode, and the separator was a polypropylene (PP) membrane.

[0075] The button cells were assembled in an argon-filled glove box. Electrochemical performance tests were conducted using a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. Discharge specific capacity and initial coulombic efficiency were tested. Simultaneously, the discharge rate-discharge ratio (DCR) at room temperature (50% SOC) was measured. The ion diffusion coefficient of the material was tested using GITT. Cycling performance was tested under the conditions of 0.2C / 0.2C for 100 cycles. The test results are shown in Table 3.

[0076] Table 3. Button cell performance of porous carbon in Examples 1-12 and Comparative Examples 1-5

[0077] Of Examples 1-3, Example 3 exhibits the best overall performance. It utilizes a combination of mesophase pitch, a higher polycondensation temperature, a higher activation temperature, and an upper limit for the mass ratio, which facilitates the formation of a more developed porous structure and more complete heteroatom doping. Examples 1 and 2 also demonstrate excellent performance, verifying the good applicability of the present invention's technical solution to different raw materials and process parameters.

[0078] From the perspective of isotropy, such as Figure 1 As shown, the porous carbon prepared in Example 1 exhibits a spherical morphology. Its specific surface area increase under 10T and 20T pressures is significantly smaller than that of the comparative example, indicating that the spherical isotropic structure allows stress to be uniformly distributed on the surface of the sphere, resulting in strong particle crushing resistance. Meanwhile, the diffusion coefficient and DCR of Examples 1-3 are significantly better than those of the comparative example, which is attributed to the isotropic structure allowing lithium ions to be embedded from the sphere in a 360° direction, resulting in a short diffusion path and low impedance. The improved cycle performance is also partly attributed to the uniform expansion characteristics in all directions brought about by the isotropic structure, which avoids particle cracking caused by stress concentration.

[0079] Examples 4-11 selected different intermediate and endpoint values ​​within various parameter ranges, covering a variety of raw material combinations. Their physicochemical and electrochemical properties were all at an optimal level, further verifying that the technical solution of this invention can achieve excellent performance within a wide process parameter window. Simultaneously, the above examples all exhibited good pressure stability in the compressive strength test, with specific surface area increases comparable to Examples 1-3, indicating that they all maintained a high degree of isotropic spherical structure, and the spherical morphology and isotropic characteristics of the mesophase carbon microspheres were not damaged by parameter adjustments.

[0080] Example 12 used a non-carboxylate organic activator, whose performance was slightly better than that of Comparative Examples 1-3, but slightly lower than that of Example 1. This indicates that although the non-carboxylate organic activator can achieve pore formation and doping, its effect is slightly inferior to that of the carboxylate activator, further verifying the preference of potassium organic carboxylate as an activator.

[0081] Comparative Example 1, without gas-phase doping, exhibited significantly lower specific capacity and initial coulombic efficiency than Example 1, with a marked increase in powder resistivity. This indicates that gas-phase doping plays an irreplaceable role in enhancing the electronic conductivity and electrochemical activity of the material. Furthermore, Comparative Example 1 showed significantly inferior compressive strength compared to Example 1. This is because the organic hydrazine gas-induced cross-linking during gas-phase doping enhances the structural strength of the carbon microspheres. The isotropic structure of the uncross-linked carbon microspheres is unstable and more prone to breakage under pressure.

[0082] Comparative Example 2, without the addition of fluorinated lithium salt, demonstrates that the introduction of fluorinated lithium salt is crucial for improving the ion diffusion coefficient and reducing impedance. However, it should be noted that the compressive strength of Comparative Example 2 did not deteriorate significantly. This is because lithium doping primarily affects electrochemical performance rather than mechanical performance, and the isotropic spherical carbon framework remains intact.

[0083] Comparative Example 3 used inorganic alkali KOH instead of organic activator, demonstrating that organic activator has significant advantages over inorganic alkali in terms of gentle pore formation, absence of impurity residue, and increased compaction density. The compressive strength of Comparative Example 3 deteriorated significantly because the intensive activation conditions of the inorganic alkali caused a certain degree of erosion and damage to the spherical isotropic structure of the carbon microspheres, leading to a decrease in particle mechanical strength.

[0084] Comparative Example 4 reversed the order of introducing the organohydrazine gas and the heteroatom gas, and all performance indicators were lower than those of Example 1, especially the specific capacity and diffusion coefficient, which decreased significantly. This indicates that the order of introducing the two gases cannot be reversed. Introducing the organohydrazine first allows it to preferentially react with the unsaturated bonds in the asphalt to initiate cross-linking. After cross-linking is complete, the phosphorus-containing gas is then introduced, avoiding mutual consumption or competition for reaction sites between the two gases in the gas phase due to differences in reactivity. If the order is reversed, the phosphorus-containing gas will preferentially occupy the active sites, inhibiting the subsequent cross-linking effect of the organohydrazine, resulting in insufficient cross-linking degree, incomplete spherical structure, and decreased isotropy, ultimately causing a comprehensive deterioration in conductivity and electrochemical performance.

[0085] Comparative Example 5, using a conventional process of activating commercially available mesophase carbon microspheres with KOH, exhibited the lowest specific capacity, initial coulombic efficiency, diffusion coefficient, and cycling performance among all samples, while showing the highest powder resistivity and DCR. This indicates that the conventional mesophase carbon microsphere activation process, without synergistic modification through gas-phase doping, organic activators, fluorinated lithium salts, and reduction treatment, cannot achieve efficient doping and gentle pore formation. Furthermore, the drastic activation with KOH severely disrupts the isotropic spherical structure of the carbon microspheres, leading to a comprehensive deterioration in the material's mechanical strength and electrochemical performance.

[0086] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing porous carbon, characterized in that, Includes the following steps: Molten asphalt was sequentially treated in an organic hydrazine gas atmosphere and a heteroatom gas atmosphere to obtain doped modified asphalt; The doped and modified asphalt was subjected to a thermal polycondensation reaction to obtain mesophase carbon microspheres; The mesophase carbon microspheres, organic activator, fluorine-containing lithium salt and conductive agent are mixed evenly and then subjected to hydrothermal reaction to obtain hydrothermal product; The hydrothermal products were activated to obtain porous carbon.

2. The preparation method according to claim 1, characterized in that, The asphalt includes at least one of petroleum asphalt, coal tar pitch, or mesophase asphalt; and / or, The organohydrazine gas includes at least one of alkylhydrazine, acylhydrazine, or aromatic hydrazine; and / or, Heteroatom gases include phosphorus-containing heteroatom gases or nitrogen-containing heteroatom gases; and / or, Organic activators include organic carboxylates; and / or, The conductive agent includes at least one of graphene, carbon nanotubes, or carbon black.

3. The preparation method according to claim 1 or 2, characterized in that, The volume ratio of the organic hydrazine gas to the heteroatom gas is 2-5:

1.

4. The preparation method according to claim 1, characterized in that, The flow rates of the organic hydrazine gas and the heteroatom gas are each independently 100-500 mL / min; and / or, The residence time of molten asphalt in an organohydrazine gas atmosphere is 30-300 min; and / or, The residence time of molten asphalt in a heteroatom gas atmosphere is 10-60 minutes.

5. The preparation method according to claim 1, characterized in that, The thermal polycondensation reaction satisfies at least one of the following conditions: (a) Temperature is 400-500℃; and, (b) The time is 1-6 hours.

6. The preparation method according to claim 1, characterized in that, The fluorinated lithium salt is added in the form of a fluorinated lithium salt solution; in the fluorinated lithium salt solution, the mass concentration of the fluorinated lithium salt is 10-30 wt%; and / or, The conductive agent is added in the form of a conductive agent solution, wherein the mass concentration of the conductive agent in the conductive agent solution is 0.5-5 wt%.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the mesophase carbon microspheres, the organic activator, the fluorinated lithium salt solution, and the conductive agent solution is 100:100-300:100-300:100-500.

8. The preparation method according to claim 1, characterized in that, The hydrothermal reaction satisfies at least one of the following conditions: (c) The reaction temperature is 300-500℃; and, (d) The reaction time is 1-6 hours; And / or, The activation process satisfies at least one of the following conditions: (e) The activation temperature is 900-1100℃; and, (f) Activation time is 1-6 hours; And / or, The activation process is followed by a reduction process, wherein the reduction process satisfies at least one of the following conditions: (g) The temperature is 500-700℃; (h) Reducing gas environment; and, (i) The restoration time is 1-6 hours.

9. A porous carbon prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the porous carbon as described in claim 9 in the preparation of silicon-carbon anode materials.

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