Preparation method of pitch-based porous carbon for high-performance silicon carbon

Abstract

The invention provides a preparation method of pitch-based porous carbon for high-performance silicon carbon. The pitch-based porous carbon is prepared by an integrated process of component separation, structure regulation and surface modification, is dissolved by an alkane solvent, and is filtered to separate an insoluble substance A, and the remainder is a mixture B of oil and wax; dissolving the oil component and the wax mixture B in acetone, freezing to crystallize wax in the mixture B, filtering and separating wax crystals, and distilling filtrate to recover the acetone to obtain the oil component; the insoluble substance A and an organic solvent are mixed, subjected to reflux extraction and filtered and separated, free carbon is obtained, and filtrate is an aromatic and resin mixed solution C; separating aromatic and resin components in the aromatic and resin mixed solution C by adopting column chromatography; heating and uniformly mixing the separated aromatic substances, resin, free carbon, oil and wax in proportion to obtain blended asphalt D; the surface-modified asphalt-based porous carbon material is obtained through carbonization activation treatment and then modification treatment, and the application requirements of batteries in different application scenes can be met.

Description

Technical Field

[0001] This invention relates to the field of porous carbon, and particularly to the field of pitch-based porous carbon for silicon-carbon applications. Background Technology

[0002] CVD silicon-carbon deposition typically involves first depositing silicon nanoparticles onto a porous carbon framework, then using acetylene to pyrolyze them into amorphous carbon, which is then coated onto the silicon nanoparticle surface. Both the amorphous carbon and the porous carbon framework require a porous carbon substrate for the deposition of silicon nanoparticles. Porous carbon accounts for nearly 50% of the cost, and its properties directly affect the specific capacity and cycle performance of silicon-carbon materials. Therefore, porous carbon is crucial to silicon-carbon deposition from both a cost and performance perspective.

[0003] Currently, the main carbon sources for preparing porous carbon include resin-based, biomass-based, petroleum coke-based, coal-based, and pitch-based sources. Resin-based porous carbon is mostly produced by condensing organic monomers into high-molecular-weight polymer resins in a solvent, followed by carbonization and pore-forming with an activator. This method yields the best performance but is also the most expensive, as illustrated by patent CN120081369A. Biomass-based porous carbon mostly uses biomass materials as raw materials, such as coconut shells, bamboo, fruit shells, corn cobs, straw, or lignin. After pretreatment, carbonization, and activation, biomass-based porous carbon is obtained; its yield varies depending on the materials used. The distribution of porous carbon is relatively wide, resulting in a wide range of costs. Its performance is affected by the inherent structure of biomass and individual differences among biomass samples; its electrochemical performance is inferior to that of resin-based porous carbon, and its batch stability is also poor, as shown in patent CN202311566243.7. Petroleum coke-based porous carbon, on the other hand, has a high carbonization activation yield and good conductivity, but its wide pore size distribution makes pore structure adjustment difficult. Furthermore, the carbon skeleton has high rigidity and mechanical strength, making it unable to release the expansion and contraction stress caused by the silicon breathing effect, leading to a tendency for the skeleton to collapse. Short cycle life, as in patent CN202411958058.7; Coal-based porous carbon, although coal costs are lower, requires the addition of ash and impurity removal costs. Even with low-ash anthracite from a certain mine, the output is limited, making it impossible to guarantee batch stability. Furthermore, coal-based porous carbon is more difficult to pore-create, increasing pore-creating costs. The carbon layer has higher mechanical strength and rigidity, leading to more severe stress from silicon expansion and contraction, making the framework prone to collapse and resulting in a short cycle life, as in patent CN202010997901.8; Pitch-based porous carbon... While the material cost is relatively low, the electrochemical performance is also low. Generally, it uses finished asphalt commonly used in the lithium battery industry, which is pre-carbonized to remove volatiles, and then activated with a pore-forming agent to form pores to obtain asphalt-based porous carbon materials, such as patent CN202411929086.6. However, the finished asphalt commonly available on the market, whether in terms of composition or molecular structure, is not the most suitable source of porous carbon. Therefore, it is to be expected that the asphalt-based porous carbon materials obtained cannot meet the first-efficiency and cycle performance requirements of lithium battery silicon carbon. Summary of the Invention

[0004] This invention proposes a method for preparing a pitch-based carbon source for porous carbon used in CVD silicon-carbon silicon production. By controlling the composition and molecular structure of aromatics, resins, free carbon, oils, waxes, and impurities, high-performance pitch-based porous carbon materials can be obtained. Using this method, a high-performance pitch-based porous carbon source can be obtained, meeting the application requirements of batteries in various scenarios.

[0005] The technical solution of this invention is: a method for preparing high-performance silicon-carbon pitch-based porous carbon, which is prepared through an integrated process of component separation, structure regulation, and surface modification. The specific steps are as follows:

[0006] The first step is raw material pretreatment: heating and filtering the raw asphalt to remove large particulate impurities;

[0007] The second step is component separation and preparation: The mixture is then thoroughly mixed with an alkane solvent, heated and stirred until fully dissolved, and filtered to separate insoluble matter A. The filtrate is then distilled under reduced pressure to recover the alkane, leaving a mixture of oil and wax B. This mixture B is dissolved in acetone, frozen to crystallize the wax, and the wax crystals are separated by filtration. The filtrate is then distilled to recover the acetone, yielding the oil. Insoluble matter A is mixed with an organic solvent and refluxed for extraction. Filtration is then performed to separate free carbon, and the filtrate is a mixed solution of aromatics and resin C. Column chromatography is used to separate the aromatic and resin components in the mixed solution C. The separated aromatics, resin, free carbon, oil, and wax are heated and mixed thoroughly in a specific ratio to obtain the prepared asphalt D.

[0008] The third step is carbonization activation treatment: the prepared asphalt D is pre-carbonized under the protection of non-reactive gas to obtain a small amount of pre-carbonized asphalt-based material with micropores and mesopores. After being crushed and mixed with KOH solution, it is carbonized again to obtain asphalt-based porous carbon with a rich three-dimensional pore structure of micropores + mesopores + macropores.

[0009] The fourth step is modification treatment: the obtained three-dimensional pore structure pitch-based porous carbon is pre-oxidized in an air atmosphere to introduce carboxyl and hydroxyl groups for preliminary modification; then it is treated with concentrated nitric acid or concentrated sulfuric acid to obtain surface-modified pitch-based porous carbon material.

[0010] The raw material asphalt includes coal tar pitch, bio-asphalt, or petroleum asphalt, with a sulfur content of 1.0 wt%, a nitrogen content of 0.3 wt%, a softening point of 60℃, and a coking value of 24%.

[0011] The alkane solvent includes any one or more of n-pentane, n-hexane, petroleum ether, n-octane, n-heptane, cyclohexane, and cyclopentane; the mass ratio of the raw material asphalt to the alkane solvent is 1:2 to 10.

[0012] Freeze at -10 to 45°C for 6 to 18 hours.

[0013] The organic solvent includes any one or more of diethyl ether, dipropyl ether, toluene, benzene, p-xylene, chlorobenzene, and o-dichlorobenzene; the mass ratio of insoluble substance A to organic solvent is 1:2 to 10.

[0014] During column chromatography separation, silica gel or alumina is used as the stationary phase. The mobile phase is first eluted with n-hexane to remove aromatics, and then eluted with a mixture of dichloromethane and methanol in a volume ratio of 9:1. The average molecular weight of the resin is 500–2000 g / mol.

[0015] Aromatic compounds, resins, free carbon, oils and waxes are mixed in a mass ratio of 35-55:25-40:10-35:20-40:0-5.

[0016] The pre-carbonization temperature is 380–475℃ for 30 min–2 h; the carbonization temperature is 550–800℃ for 30 min–12 h.

[0017] The mass ratio of asphalt to KOH is 1:0.5 to 6.

[0018] Beneficial effects

[0019] 1. Full-component separation process: Existing technologies only separate asphaltene and soluble substances, failing to achieve complete separation of oils, waxes, aromatics, and resins. Incomplete separation results in a wide component distribution and difficulty in pore size control. For example, a wide pore size distribution means that micropores and mesopores are prone to collapse and breakage when there is a high amount of volatile matter, leading to smaller BET and pore volume, limited silicon loading, and lower energy density. Furthermore, incomplete separation results in a large amount of quinoline insolubles, leading to a low degree of graphitization of aromatic components in the pore wall structure, resulting in brittle mechanical strength and poor high-temperature performance.

[0020] 2. Surface functional group gradient regulation: The dual regulation of functional group type (carboxyl group → sulfonic acid group) and density is achieved through pre-oxidation and secondary acid treatment, breaking through the single oxidation modification of existing technologies.

[0021] 3. Multi-level pore synergistic construction: Combining KOH activation and asphalt component self-activation to form a hierarchical pore structure, the mesoporous rate is increased by 40% compared with the single activation method of the existing technology.

[0022] 4. This invention utilizes an integrated process of component separation, structural regulation, and surface modification to prepare a high-performance silicon-carbon pitch-based porous carbon with low pore-forming difficulty and cost, excellent pore-forming effect, and good performance, meeting the requirements for first-efficiency and cycle performance of lithium-ion battery silicon-carbon. After component separation, the components are carefully selected and mixed to obtain a carbon source for β-resin with controllable volatile matter, low impurity content, low quinoline insoluble matter, and controllable oxygen content. Then, the carbon source is carbonized and activated to create pores, resulting in a multi-level pore structure with a concentrated micro-meso-macro pore size distribution. The specific surface area (BET), pore volume, microporosity, mesoporosity, and average pore size are adjustable, exhibiting good pore connectivity, high tap density, and reversible flexibility and rigidity. The corresponding capacity, first-efficiency, cycle, and rate performance are all controllable. Detailed Implementation

[0023] Product Characterization of the Invention

[0024] Component analysis

[0025] 1. Oil / wax content: determined by n-heptane extraction method (ASTM D4072).

[0026] 2. Aromatic / Resin Content: FTIR analysis of aromatic C=C bonds (1600 cm⁻¹) -1 ) and resin CO bonds (1200cm) -1 )

[0027] 3. Free carbon content: Mass loss measured by thermogravimetric analysis (TGA) at 500-800℃ under nitrogen atmosphere.

[0028] Molecular structure characterization

[0029] 1. X-ray diffraction (XRD): Analysis of graphitization degree (002 peak position)

[0030] 2. Raman spectroscopy: The ID / IG ratio characterizes the disorder of carbon materials.

[0031] 3. Nuclear magnetic resonance (NMR) 13 C-NMR: Analysis of the ratio of aromatic carbons to aliphatic carbons

[0032] Pore ​​structure characterization

[0033] 1. BET Specific Surface Area: Nitrogen Adsorption / Desorption Test (Micromeritics ASAP 2020)

[0034] 2. Pore size distribution: BJH model analysis of mesopores (2-50nm), DFT model analysis of micropores (<2nm)

[0035] 3. SEM / TEM: Observe the microstructure and pore structure of the material.

[0036] I. Raw material pretreatment

[0037] 1. Coarse filtration. 300 g of coal tar pitch, bio-pitch or petroleum pitch with a sulfur content of < 2 wt%, a nitrogen content of 0.5 < wt%, a softening point of 40 - 100 °C, and a coking value of 18 - 30% is heated and stirred at 150 - 200 °C for 1 - 4 hours, and large particulate impurities are removed by filtration;

[0038] II. Component separation and blending

[0039] 2. Pre-separation. 200 - 280 g of the pitch from step 1 is mixed with n-heptane at a mass ratio of 1:2 - 10, and stirred at 50 - 120 °C for 2 - 8 hours. 60 - 220 g of insoluble matter (rich in aromatics, resins and free carbon) is separated by filtration, the filtrate is distilled under reduced pressure to recover n-heptane, and the residue is 60 - 140 g of an oil and wax mixture;

[0040] 3. Separation of oil and wax. The oil-wax mixture is dissolved in acetone and frozen at -10 - 45 °C for 6 - 18 hours to crystallize the wax. 10 - 70 g of wax crystals are separated by filtration. The melting point range is observed by differential scanning calorimetry (DSC melting point 40 - 80 °C), and the wax is characterized by combining the freeze crystallization degree. The filtrate is distilled to recover acetone to obtain 50 - 130 g of oil, and the oil is characterized by infrared spectroscopy (C-H saturated bond absorption peak);

[0041] 4. Separation of free carbon. 50 - 100 g of n-heptane-insoluble matter (the insoluble matter from step 2) is mixed with toluene at a mass ratio of 1:2 - 10, and refluxed and extracted for 2 - 8 hours. 10 - 20 g of insoluble matter (free carbon) is separated by filtration. The carbon material is characterized by XRD graphitization degree and Raman spectrum ID / IG, and the filtrate is a mixed solution of 40 - 90 g of aromatics and resins;

[0042] 5. Separation of resin and aromatics. Column chromatography is used to separate the resin and aromatic components. The stationary phase in the column is silica gel or alumina (100 - 200 mesh), and the mobile phase first elutes the aromatic components (weak polarity) of 25 - 50 g with n-hexane, and the aromatic carbon content is characterized by ultraviolet spectroscopy (characteristic absorption at 250 - 300 nm) or 13 C-NMR analysis > 60%. Then, a mixed solvent of dichloromethane:methanol (9:1) is used to elute the resin components (medium polarity) of 15 - 40 g, and the resin is characterized by gel permeation chromatography (GPC molecular weight distribution, looking at the average molecular weight (500 - 2000 g / mol)). Thus, aromatic and resin components are obtained respectively;

[0043] 6. Component blending. After adding the above aromatic, resin, free carbon, oil and wax components in a mass ratio of 35 - 55:25 - 40:10 - 35:20 - 40:0 - 5, the temperature is raised to 25 - 50 °C above the softening point, and stirred at a speed of 300 rmp for 30 min in a stainless steel container;

[0044] III. Carbonization Activation Treatment

[0045] 7. Pre-carbonization & carbonization. 300g of the prepared asphalt is placed in a square tank boat of a tubular furnace under inert gas protection (N2, Ar or He, etc.) at a flow rate of 100-400mL / min and pre-carbonized at 380-475℃ for 30min-2h from room temperature at a heating rate of 0.5-10℃ / min. After natural cooling, a pre-carbonized asphalt-based material with a small amount of micropores and mesopores is obtained.

[0046] 8. Crushing and premixing. The precarbonized asphalt material that has been naturally cooled is crushed using an air jet mill to obtain carbon material with particles <15μm. Then, it is fully premixed with a KOH solution with a solubility of 50-120wt% at room temperature at a mass ratio of asphalt:KOH = 1:0.5-6 to obtain an asphalt mixture.

[0047] 9. Activation and Pore Formation. The premixed asphalt mixture described above is carbonized in a tubular furnace under inert gas (N2, Ar, or He, etc.) protection at a flow rate of 100-1000 mL / min at 550-800℃ for 30 min-12 h, starting from room temperature and then naturally cooled to room temperature, to obtain asphalt-based porous carbon with a three-dimensional pore structure of rich micropores, mesopores, and macropores.

[0048] IV. Modification Treatment

[0049] 10. Oxidation Modification Treatment. The obtained pitch-based porous carbon is pre-oxidized in air at 150-280℃ for 0.5-6 hours to introduce carboxyl groups (1720cm). -1 ) and hydroxyl groups (3400cm) -1 Preliminary modification was performed using functional groups (FTIR characterization), increasing the surface oxygen content to 0.5-12 at%.

[0050] 11. Modification treatment. Then treat with concentrated nitric acid or concentrated sulfuric acid at 80°C for 1 hour to further increase the surface acidic functional groups (such as sulfonic acid groups or nitro groups), so that the Zeta potential drops to -5 to -80 mV (determined by potentiometric titration) to obtain surface-modified pitch-based porous carbon material.

[0051] Characterization and testing. The obtained porous carbon was subjected to physicochemical property tests including BET (GB / T 19587-2017 "Determination of specific surface area of ​​solid materials by gas adsorption BET method"), tap density (JB / T 10141.2-2013 "Graphite anode materials for lithium-ion batteries - Part 2: Determination of tap density"), crush strength (DL / T 515-2014 "Test methods for activated carbon for power applications"), and electrical conductivity (GB / T24525-2009 "Method for determination of resistivity of carbon materials").

[0052] Example 1

[0053] I. Raw material pretreatment

[0054] 1. Coarse filtration. Heat 300g of coal tar pitch with a sulfur content of 1.0wt%, a nitrogen content of 0.3wt%, a softening point of 60℃, and a coking value of 24% at 150℃ for 2 hours, and then filter to remove large particulate impurities.

[0055] II. Component Separation and Blending

[0056] 2. Pre-separation. Mix 260g of asphalt from step 1 with n-heptane at a mass ratio of 1:4 and stir at 50℃ for 4 hours. Filter to separate 140g of insoluble matter (rich in aromatics, resins, and free carbon). Distill the filtrate under reduced pressure to recover n-heptane, leaving 120g of a mixture of oil and wax.

[0057] 3. Separation of oil and wax. The oil and wax mixture was dissolved in acetone and frozen at -20℃ for 8 hours to crystallize the wax. 40g of wax crystals were separated by filtration. The melting point range was observed by differential scanning calorimetry (DSC melting point 40-80℃), and the degree of crystallinity was combined with the freezing to characterize the wax. The filtrate was distilled to recover acetone and 80g of oil was obtained. The oil was characterized by infrared spectroscopy (CH saturated bond absorption peak).

[0058] 4. Separation of free carbon. 100g of n-heptane insoluble matter (insoluble matter from step 2) was mixed with toluene at a mass ratio of 1:3, refluxed for 4 hours, and filtered to obtain 15g of insoluble matter (free carbon). The carbon material was characterized by XRD graphitization degree and Raman spectroscopy ID / IG. The filtrate was a mixed solution of aromatics and resin, weighing 85g.

[0059] 5. Separation of resin and aromatic components. Column chromatography was used to separate the resin and aromatic components. The stationary phase in the column was silica gel or alumina (100-200 mesh). The mobile phase was first eluted with 45g of n-hexane (weakly polar). Ultraviolet spectroscopy (characteristic absorption at 250-300 nm) or... 13C-NMR analysis showed an aromatic carbon content >60%. Then, 40g of the resin component (moderately polar) was eluted with a dichloromethane:methanol (9:1) mixed solvent. The resin was characterized by gel permeation chromatography (GPC molecular weight distribution, observing the average molecular weight (500-2000 g / mol)), thus obtaining the aromatic and resin components separately.

[0060] 6. Component preparation. Add the aromatic, resin, free carbon, oil and wax components in a mass ratio of 35:30:15:15:5, heat to 25°C above the softening point, and stir at 300 rpm for 30 minutes in a stainless steel container.

[0061] III. Carbonization Activation Treatment

[0062] 7. Pre-carbonization & carbonization. 300g of the well-mixed asphalt was placed in a square tank boat of a tubular furnace under inert N2 gas protection at a flow rate of 100mL / min and pre-carbonized at 450℃ from room temperature for 90min at a heating rate of 0.5℃ / min. The mixture was then allowed to cool naturally to obtain a pre-carbonized asphalt-based material with a small amount of micropores and mesopores.

[0063] 8. Crushing and Premixing. The precarbonized asphalt material that has been naturally cooled is crushed using an air jet mill to obtain carbon material with particles <15μm. Then, it is fully premixed with a KOH solution with a solubility of 80wt% at room temperature at a mass ratio of asphalt:KOH = 1:2.8 to obtain an asphalt mixture.

[0064] 9. Activation and pore formation. The premixed asphalt mixture was pre-carbonized in a tubular furnace under inert N2 gas protection at a flow rate of 300 mL / min, from room temperature to 680℃ at a heating rate of 5℃ / min for 3 hours, and then naturally cooled to room temperature to obtain asphalt-based porous carbon with a three-dimensional pore structure of rich micropores, mesopores and macropores.

[0065] IV. Modification Treatment

[0066] 10. Oxidation Modification Treatment. The obtained pitch-based porous carbon was pre-oxidized in air at 180°C for 2 hours to introduce carboxyl groups (1720 cm⁻¹). -1 ) and hydroxyl groups (3400cm) -1 The functional groups were preliminarily modified (FTIR characterization), and the surface oxygen content was controlled to about 3.0 at%.

[0067] 11. Modification treatment. The material is then treated with concentrated nitric acid at 80°C for 1 hour to further increase the surface acidic functional groups (such as nitro groups), thereby reducing the Zeta potential to -18mV (measured by potentiometric titration) to obtain surface-modified pitch-based porous carbon material.

[0068] 12. Test Characterization. The obtained porous carbon was subjected to physical and chemical property tests including BET (GB / T 19587-2017 Determination of Specific Surface Area of Solid Substances by Gas Adsorption - BET Method), tapped density (JB / T 10141.2-2013 Lithium-Ion Battery Graphite Anode Materials - Part 2: Determination of Tapped Density), crush strength (DL / T 515-2014 Test Methods for Activated Carbon for Electric Power), and conductivity (GB / T 24525-2009 Test Method for Resistivity of Carbon Materials).

[0069] Example 2.

[0070] I. Raw Material Pretreatment

[0071] 1. Coarse filtration. 300 g of petroleum pitch with a sulfur content of 0.3 wt%, a nitrogen content of 0.1 wt%, a softening point of 80 °C, and a coking value of 20% was heated and stirred at 110 °C for 0.5 hours, and large particle impurities were removed by filtration;

[0072] II. Component Separation and Blending

[0073] 2. Pre-separation. 270 g of the pitch from Step 1 was mixed with n-heptane at a mass ratio of 1:4 and stirred at 50 °C for 2 hours. 54 g of insoluble matter (rich in aromatics, resins, and free carbon) was separated by filtration. The filtrate was subjected to vacuum distillation to recover n-heptane, and the residue was a mixture of oil and wax, 216 g;

[0074] 3. Separation of oil and wax. The oil-wax mixture was dissolved in acetone and frozen at -25 °C for 7 hours to crystallize the wax. 32 g of wax crystals were separated by filtration. The wax was characterized by differential scanning calorimetry (DSC melting point 40 - 80 °C) to observe the melting point range and combined with the freeze crystallization degree. The filtrate was distilled to recover acetone to obtain 184 g of oil, and the oil was characterized by infrared spectroscopy (C-H saturated bond absorption peak);

[0075] 4. Separation of free carbon. 54 g of n-heptane-insoluble matter (the insoluble matter from Step 2) was mixed with toluene at a mass ratio of 1:3.5 and refluxed for extraction for 6 hours. 6 g of insoluble matter (free carbon) was separated by filtration. The carbon material was characterized by XRD graphitization degree and Raman spectrum ID / IG, and the filtrate was a mixed solution of aromatics and resins, 48 g; 5. Separation of resin and aromatics. Column chromatography was used to separate the resin and aromatic components. The stationary phase in the column was silica gel or alumina (100 - 200 mesh), and the mobile phase was first used to elute the aromatic components (weak polarity), 22 g, using ultraviolet spectroscopy (characteristic absorption at 250 - 300 nm) or 13C-NMR analysis showed an aromatic carbon content >60%. Then, 26g of the resin component (moderately polar) was eluted with a dichloromethane:methanol (9:1) mixed solvent. The resin was characterized by gel permeation chromatography (GPC molecular weight distribution, observing the average molecular weight (500-2000 g / mol)), thus obtaining the aromatic and resin components separately.

[0076] 6. Component preparation. Add the aromatic, resin, free carbon, oil and wax components in a mass ratio of 40:20:15:20:5, heat to 30°C above the softening point, and stir at 350 rpm for 45 minutes in a stainless steel container.

[0077] III. Carbonization Activation Treatment

[0078] 7. Pre-carbonization & carbonization. 300g of the well-mixed asphalt was placed in a square tank boat of a tubular furnace under inert N2 gas protection at a flow rate of 200mL / min and pre-carbonized at 420℃ for 1h from room temperature at a heating rate of 2℃ / min, and then naturally cooled down to obtain a pre-carbonized asphalt-based material with a small amount of micropores and mesopores.

[0079] 8. Crushing and Premixing. The precarbonized asphalt material that has been naturally cooled is crushed using an air jet mill to obtain carbon material with particles <15μm. Then, it is fully premixed with a KOH solution with a solubility of 90wt% at room temperature at a mass ratio of asphalt:KOH = 1:3.2 to obtain an asphalt mixture.

[0080] 9. Activation and pore formation. The premixed asphalt mixture was pre-carbonized in a tubular furnace under inert N2 gas protection at a flow rate of 200 mL / min, starting at room temperature and increasing to 720℃ at a heating rate of 6℃ / min for 4 hours. After natural cooling to room temperature, a three-dimensional pore structure of asphalt-based porous carbon with rich micropores, mesopores, and macropores was obtained.

[0081] IV. Modification Treatment

[0082] 10. Oxidation Modification Treatment. The obtained pitch-based porous carbon was pre-oxidized in air at 210°C for 3 hours to introduce carboxyl groups (1720 cm⁻¹). -1 ) and hydroxyl groups (3400cm) -1 Preliminary modification was performed using functional groups (FTIR characterization), increasing the surface oxygen content to 2.5 at%.

[0083] 11. Sulfonation modification treatment. Then treat with concentrated sulfuric acid at 80℃ for 1 hour to further increase the surface acidic functional groups (such as sulfonic acid groups), so that the Zeta potential drops to -12mV (determined by potentiometric titration), and obtain surface-modified pitch-based porous carbon material.

[0084] 12. Test Characterization. The obtained porous carbon was tested for its physical and chemical properties, including BET (GB / T 19587-2017 "Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method"), tapped density (JB / T 10141.2-2013 "Lithium-Ion Battery Graphite Anode Materials - Part 2: Determination of Tapped Density"), crush strength (DL / T 515-2014 "Test Methods for Activated Carbon for Electric Power"), and electrical conductivity (GB / T 24525-2009 "Determination Method for Resistivity of Carbon Materials").

[0085] Example 3

[0086] I. Raw Material Pretreatment

[0087] 1. Coarse Filtration. 300 g of petroleum pitch with a sulfur content of 0.6 wt%, a nitrogen content of 0.2 wt%, a softening point of 90 °C, and a coking value of 26% was heated and stirred at 110 °C for 1.0 hour, and large particle impurities were removed by filtration;

[0088] II. Component Separation and Blending

[0089] 2. Pre-separation. 220 g of the pitch from Step 1 was mixed with petroleum ether at a mass ratio of 1:6 and stirred at 55 °C for 2.0 hours. 90 g of insoluble matter (rich in aromatics, resins, and free carbon) was separated by filtration, and the petroleum ether was recovered by vacuum distillation of the filtrate. The residue was a mixture of oil and wax, 130 g;

[0090] 3. Separation of Oil and Wax. The oil-wax mixture was dissolved in acetone and frozen at -25 °C for 6 hours to crystallize the wax. 26 g of wax crystals were separated by filtration. The melting point range was observed and the wax was characterized by combining the freezing crystallinity using differential scanning calorimetry (DSC melting point 40-80 °C). The filtrate was distilled to recover acetone to obtain 104 g of oil, and the oil was characterized by infrared spectroscopy (C-H saturated bond absorption peak);

[0091] 4. Separation of Free Carbon. 80 g of petroleum ether-insoluble matter (the insoluble matter from Step 2) was mixed with toluene at a mass ratio of 1:7 and refluxed for 3 hours. 17 g of insoluble matter (free carbon) was separated by filtration. The carbon material was characterized by XRD graphitization degree and Raman spectrum ID / IG, and the filtrate was a mixed solution of aromatics and resins, 63 g;

[0092] 5. Separation of Resins and Aromatics. Column chromatography was used to separate the resin and aromatic components. The stationary phase in the column was silica gel or alumina (100-200 mesh), and the mobile phase was first eluted with n-hexane to obtain 29 g of aromatic components (weak polarity), which were characterized by ultraviolet spectroscopy (characteristic absorption at 250-300 nm) or 13C-NMR analysis showed an aromatic carbon content >60%. Then, 34 g of the resin component (moderately polar) was eluted with a dichloromethane:methanol (9:1) mixed solvent. The resin was characterized by gel permeation chromatography (GPC molecular weight distribution, observing the average molecular weight (500-2000 g / mol)), thus obtaining the aromatic and resin components separately.

[0093] 6. Component preparation. Add the aromatic, resin, free carbon, oil and wax components in a mass ratio of 25:25:35:12:3, heat to 40°C above the softening point, and stir at 400 rpm for 60 minutes in a stainless steel container.

[0094] III. Carbonization Activation Treatment

[0095] 7. Pre-carbonization & carbonization. 300g of the well-mixed asphalt was placed in a square tank boat of a tubular furnace under inert N2 gas protection at a flow rate of 100mL / min and pre-carbonized at 450℃ for 75min from room temperature at a heating rate of 1.5℃ / min. The mixture was then allowed to cool naturally to obtain a pre-carbonized asphalt-based material with a small amount of micropores and mesopores.

[0096] 8. Crushing and Premixing. The precarbonized asphalt material that has been naturally cooled is crushed using an air jet mill to obtain carbon material with particles <15μm. Then, it is fully premixed with a 100wt% KOH solution at room temperature at a mass ratio of asphalt:KOH = 1:3.8 to obtain an asphalt mixture.

[0097] 9. Activation and pore formation. The premixed asphalt mixture was pre-carbonized in a tubular furnace under inert N2 gas protection at a flow rate of 200 mL / min, starting at room temperature and increasing to 750℃ at a heating rate of 7℃ / min for 4 hours. After natural cooling to room temperature, a three-dimensional pore structure of asphalt-based porous carbon with rich micropores, mesopores, and macropores was obtained.

[0098] IV. Modification Treatment

[0099] 10. Oxidation Modification Treatment. The obtained pitch-based porous carbon was pre-oxidized in air at 220°C for 3 hours to introduce carboxyl groups (1720 cm⁻¹). -1 ) and hydroxyl groups (3400cm) -1 Preliminary modification was performed using functional groups (FTIR characterization), increasing the surface oxygen content to 1.5 at%.

[0100] 11. Modification treatment. The material is then treated with concentrated nitric acid at 80°C for 2.0 hours to further increase the surface acidic functional groups (such as nitro groups), thereby reducing the Zeta potential to -8mV (determined by potentiometric titration) to obtain a surface-modified pitch-based porous carbon material.

[0101] 12. Testing and Characterization. The obtained porous carbon was subjected to physicochemical property tests including BET (GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method"), tap density (JB / T 10141.2-2013 "Graphite Anode Materials for Lithium-ion Batteries Part 2: Determination of Tap Density"), crush strength (DL / T 515-2014 "Test Methods for Activated Carbon for Electric Power"), and electrical conductivity (GB / T 24525-2009 "Methods for Determination of Resistivity of Carbon Materials").

[0102] Comparative Example 1

[0103] Asphalt raw materials are used, but without pretreatment and component separation and blending. The subsequent steps are the same as those in Example 1.

[0104] Comparative Example 2

[0105] The steps are the same as in Example 1, except that the modification treatment steps 10 and 11 are omitted.

[0106]

[0107]

[0108] Compared with 1 where no bitumen components were mixed, it can be seen that the BET, pore volume, average pore size and microporosity are not ideal, and it cannot bear a higher load of silicon deposition under the premise of controllable subsequent expansion.

[0109] In comparison 2, the activated pore size microporosity is low and no surface improvement treatment is performed. The porous carbon structure has high strength and conductivity, but the expansion during subsequent cycling is large, the electrode conductive network is prone to collapse, and the active material is prone to deactivation.

Claims

1. A method for preparing pitch-based porous carbon for high-performance silicon-carbon applications, characterized in that, The preparation process utilizes an integrated approach encompassing component separation, structural regulation, and surface modification. The specific steps are as follows: The first step is raw material pretreatment: heating and filtering the raw asphalt to remove large particulate impurities; The second step is component separation and preparation: The mixture is then thoroughly mixed with an alkane solvent, heated and stirred until fully dissolved, and filtered to separate insoluble matter A. The filtrate is then distilled under reduced pressure to recover the alkane, leaving a mixture of oil and wax B. This mixture B is dissolved in acetone, frozen to crystallize the wax, and the wax crystals are separated by filtration. The filtrate is then distilled to recover the acetone, yielding the oil. Insoluble matter A is mixed with an organic solvent and refluxed for extraction. Filtration is then used to separate free carbon, and the filtrate is a mixed solution of aromatics and resin C. Column chromatography is used to separate the aromatic and resin components in the mixed solution C. The separated aromatics, resin, free carbon, oil, and wax are heated and mixed thoroughly in a specific ratio to obtain the prepared asphalt D. The third step is carbonization activation treatment: the prepared asphalt D is pre-carbonized under the protection of non-reactive gas to obtain a small amount of pre-carbonized asphalt-based material with micropores and mesopores. After being crushed and mixed with KOH solution, it is carbonized again to obtain asphalt-based porous carbon with a rich three-dimensional pore structure of micropores + mesopores + macropores. The fourth step is modification treatment: the obtained three-dimensional pore structure pitch-based porous carbon is pre-oxidized in an air atmosphere to introduce carboxyl and hydroxyl groups for preliminary modification; then it is treated with concentrated nitric acid or concentrated sulfuric acid to obtain surface-modified pitch-based porous carbon material.

2. The method for preparing high-performance silicon-carbon pitch-based porous carbon according to claim 1, characterized in that, The raw material asphalt includes coal tar pitch, bio-asphalt, or petroleum asphalt, with a sulfur content of 1.0 wt%, a nitrogen content of 0.3 wt%, a softening point of 60℃, and a coking value of 24%.

3. The method for preparing high-performance silicon-carbon pitch-based porous carbon according to claim 1, characterized in that, The alkane solvent includes any one or more of n-pentane, n-hexane, petroleum ether, n-octane, n-heptane, cyclohexane, and cyclopentane; the mass ratio of the raw material asphalt to the alkane solvent is 1:2 to 10.

4. The method for preparing high-performance silicon-carbon pitch-based porous carbon according to claim 1, characterized in that, Freeze at -10 to 45°C for 6 to 18 hours.

5. The method for preparing high-performance silicon-carbon pitch-based porous carbon according to claim 1, characterized in that, The organic solvent includes any one or more of diethyl ether, dipropyl ether, toluene, benzene, p-xylene, chlorobenzene, and o-dichlorobenzene; the mass ratio of insoluble substance A to organic solvent is 1:2 to 10.

6. The method for preparing high-performance silicon-carbon pitch-based porous carbon according to claim 1, characterized in that, During column chromatography separation, silica gel or alumina is used as the stationary phase. The mobile phase is first eluted with n-hexane to remove aromatics, and then eluted with a mixture of dichloromethane and methanol in a volume ratio of 9:

1. The average molecular weight of the resin is 500–2000 g / mol.

7. The method for preparing high-performance silicon-carbon pitch-based porous carbon according to claim 1, characterized in that, Aromatic compounds, resins, free carbon, oils and waxes are mixed in a mass ratio of 35-55:25-40:10-35:20-40:0-5.

8. The method for preparing high-performance silicon-carbon pitch-based porous carbon according to claim 1, characterized in that, The pre-carbonization temperature is 380–475℃ for 30 min–2 h; the carbonization temperature is 550–800℃ for 30 min–12 h.

9. The method for preparing high-performance silicon-carbon pitch-based porous carbon according to claim 1, characterized in that, The mass ratio of asphalt to KOH is 1:0.5 to 6.

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