High performance pitch-based porous carbon, and preparation method and application thereof

Abstract

The application discloses high-performance asphalt-based porous carbon and a preparation method and application thereof, and the preparation method comprises the following steps: after refined asphalt is heated and stirred, oxygen-containing gas is introduced, and the refined asphalt is subjected to staged temperature increasing and oxidation treatment to obtain oxygen-containing modified pre-oxidized refined asphalt; the pre-oxidized asphalt is subjected to pre-carbonization in an inert atmosphere and is heated to different temperatures in stages; the pre-carbonization product is placed in a hydrogen-containing mixed atmosphere, and the carbonization process is dynamically controlled according to asphalt components; the carbonization product is mixed with a mixed alkali of potassium hydroxide and sodium hydroxide, is subjected to multi-temperature zone step activation, and is washed and dried to obtain asphalt-based porous carbon. The application directly uses refined asphalt as a carbon source raw material, obtains part of oxygen-containing hard carbon structure through pre-oxidation, obtains a carbonization precursor with extremely low volatile matter through low-temperature pre-carbonization, moderately graphitizes the porous carbon through carbonization, improves the skeleton conductivity, further forms pores to the skeleton through activation, and finally obtains high-performance porous carbon material.

Description

Technical Field

[0001] This invention belongs to the field of porous carbon materials technology, and specifically relates to a high-performance pitch-based porous carbon, its preparation method, and its application. Background Technology

[0002] CVD silicon-carbon refers to the process of first depositing nano-silicon on a porous carbon framework, and then using carbon-containing gases such as acetylene to decompose it into amorphous carbon, which is then deposited on the surface of the nano-silicon, forming a porous carbon-nano-silicon-amorphous carbon structure. In this structure, nano-silicon provides the capacity for active materials; porous carbon provides active sites, a conductive framework, and expansion space; and amorphous carbon provides a coating layer and a conductive agent.

[0003] The current process for preparing porous carbon involves first pretreating the carbon source to obtain a precursor, and then processing it according to the process of pretreatment-carbonization-activation-washing-drying. Among these, the quality of the carbon source, the carbonization and activation process are the core links in the preparation of porous carbon, directly determining the size, quantity, development and connectivity of the pores, and further directly determining the electrochemical performance of the subsequent silicon-carbon anode, as well as the cost of porous carbon, as shown in patent CN202510367469.7. The carbonization heating rate, holding time, atmosphere, atmosphere flow rate and temperature directly affect the pore size, structural stability, surface group state of the pores and the connectivity of the multi-level pores of porous carbon, as shown in patent CN118221099B. Pitch-based porous carbon has a lower material cost, but lower first-efficiency and cycle performance, as shown in patent CN202411929086.6. However, the commercially available asphalt is not a carbon source designed for porous carbon, and cannot be customized for porous carbon in terms of both carbon source and process. Therefore, the obtained pitch-based porous carbon materials cannot meet the first-efficiency and cycle performance requirements of lithium-ion battery silicon-carbon materials in terms of both cost and performance.

[0004] The porous carbon obtained by the above methods has the following problems:

[0005] Poor carbon source performance: The composition of the carbon source was not carefully selected, resulting in an inability to balance the porosity, electrical conductivity, and mechanical properties of the carbon material. This leads to either excessively high costs when using mesophase pitch as the carbon source, or unsuitable conventional pitch components. Even if the coking value meets the standard, the mechanical properties do not meet the requirements and cannot meet the expansion cycle requirements of more than 2000 cycles. Alternatively, the aromaticity is insufficient, resulting in poor electrical conductivity, high internal resistance, and serious rate and heat generation issues.

[0006] Poor carbonization effect: Inappropriate temperature and heating will cause the concentrated burst of volatiles in the pitch-based carbon source, resulting in the collapse of micropores and mesopores, resulting in porous carbon materials dominated by macropores, or organic matter remaining in the pores will hinder the subsequent deposition of silicon atoms.

[0007] Poor activation effect: In order to obtain a well-developed microporous structure, most asphalt-based carbon sources adopt alkali activation with more than 3 times the amount of alkali. However, the effective utilization rate of alkali is low, which makes the cost of porous carbon high, the pressure of environmental wastewater high, the cost of equipment corrosion maintenance and sewage treatment high. Summary of the Invention

[0008] The purpose of this invention is to provide a high-performance pitch-based porous carbon, its preparation method, and its application. The invention uses refined pitch as the carbon source, and after pre-oxidation, low-temperature pre-carbonization, medium-temperature carbonization, and medium-high-temperature activation, a high-performance porous carbon material is obtained. Pre-oxidation yields a partially oxygen-containing hard carbon structure, low-temperature pre-carbonization yields a carbonization precursor with very low volatile matter, carbonization moderately graphitizes the porous carbon to improve the conductivity of the framework, and activation further creates pores in the framework, resulting in a high-performance porous carbon material.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing high-performance pitch-based porous carbon.

[0011] A method for preparing high-performance pitch-based porous carbon includes the following steps:

[0012] (1) Pre-oxidized refined asphalt: After heating and stirring the refined asphalt, oxygen-containing gas is introduced and subjected to staged heating oxidation treatment to obtain oxygen-modified pre-oxidized refined asphalt.

[0013] (2) Low-temperature stepped precarbonization: The pre-oxidized asphalt obtained in step (1) is precarbonized in an inert atmosphere by heating it to different temperatures in stages.

[0014] (3) Medium-temperature carbonization: The pre-carbonized product obtained in step (2) is placed in a hydrogen-containing mixed atmosphere, and the carbonization process is dynamically controlled according to the asphalt components.

[0015] (4) Mixed alkali gradient activation: The carbonization product obtained in step (3) is mixed with potassium hydroxide and sodium hydroxide mixed alkali, and after multi-temperature zone step activation, it is washed and dried to obtain asphalt-based porous carbon.

[0016] Preferably, in step (1), the refined asphalt is a refined product of coal tar pitch, petroleum asphalt, natural asphalt and bio-asphalt.

[0017] Preferably, in step (1), the refined asphalt meets the following requirements: QI content 80-8000ppm, ash content 100-600ppm, carbon content ≥90.00wt%, sulfur content ≤1000ppm, volatile matter 30-60wt%, coking value 45.00-85.00%, softening point 100-230℃, and β resin content >22%.

[0018] Preferably, in step (1), the segmented heating oxidation process includes:

[0019] (11) First heat and stir at the softening point +20℃ for 1-4 hours;

[0020] (12) Introduce air or O2 / N2 mixed gas with an O2 volume content of 5% at a flow rate of 600-2000 mL / min, and ensure that the gas is fully in contact with the liquid asphalt by bubbling. Raise the temperature to 220-280℃ at a heating rate of 2-10℃ / min and keep it at a constant temperature for 0.1-4h.

[0021] (13) Finally, raise the temperature to 270-330℃ at a heating rate of 3-12℃ / min and hold it at that temperature for 0.5-5h.

[0022] Preferably, in step (1), the obtained pre-oxidized refined asphalt has an oxygen content of 2-8 at%, a softening point of 100-280℃.

[0023] Preferably, in step (2), the low-temperature stepped pre-carbonization includes:

[0024] (21) In an atmosphere with N2 purity > 99.99% and a flow rate of 150-200 mL / min, the temperature is raised to 300℃ at a heating rate of 1-5℃ / min and held for 30-120 min.

[0025] (22) Then continue to heat to 400℃ and hold for 50-140 min in an atmosphere with N2 purity >99.99% and flow rate of 150-200 mL / min at a heating rate of 2-6℃ / min.

[0026] (23) Finally, in an atmosphere with N2 purity > 99.99% and a flow rate of 150-200 mL / min, the temperature is raised to 500℃ at a heating rate of 2-6℃ / min and held for 50-140 min.

[0027] Preferably, in step (3), the hydrogen-containing mixed atmosphere is an H2 / N2 mixture with a volume percentage of 5-10% and a flow rate of 150-200 mL / min.

[0028] Preferably, in step (3), the carbonization temperature is 600-650℃, the time is 60-240min, and the holding time is 120-150min when the β resin content is 22-25% and 90-120min when the β resin content is >25%.

[0029] Preferably, in step (4), the mixed alkali is a mixture of KOH and NaOH in a mass ratio of 1:1, and the mass ratio of material to alkali is 1:1.0-2.5.

[0030] Preferably, in step (4), the stepwise activation step is as follows: in an inert atmosphere with a purity >99.99% and a flow rate of 200-800 mL / min, the temperature is increased to 700℃ at a heating rate of 2-6℃ / min and held for 30-60 min, then increased to 750℃ at a heating rate of 2-6℃ / min and held for 60-90 min, and finally increased to 900℃ at a heating rate of 2-6℃ / min and held for 60-120 min.

[0031] Preferably, in step (4), the washing step is: after natural cooling, the product is washed three times with acid and water respectively.

[0032] Secondly, the present invention provides a pitch-based porous carbon, which is prepared by the above method.

[0033] A pitch-based porous carbon, wherein the pitch-based porous carbon has a BET specific surface area of ​​1586-2103 m². 2 / g, pore volume 0.67-0.94cm 3 / g, average pore size 1.34-2.82nm, microporosity 75.3-96.4%, mesoporosity 2.1-24.3%.

[0034] Thirdly, the present invention provides the application of the aforementioned pitch-based porous carbon.

[0035] The application of the aforementioned pitch-based porous carbon in silicon-carbon anodes results in a specific capacity of 1477-2076 mAh / g, an initial efficiency of 86.6-94.7%, a capacity retention rate of 81.3-92.3% after 200 cycles at 0.1C, and a rate retention rate of 80.6-88.7% at 6C / 1C.

[0036] Beneficial effects: The core innovation of this invention lies in the significant differentiated characteristics of the process in three dimensions: precise control of pre-oxidation, synergistic carbonization with multiple atmospheres, and stepwise activation with mixed alkalis.

[0037] 1. The uniqueness of the two-stage pre-oxidation

[0038] Process characteristics: 250℃ air oxidation (preliminary crosslinking) — 300℃ 5% O2 / N2 mixed gas oxidation (depth control, pre-oxidation degree 2-8 at%), and is designed for refined asphalt with high β content (>22%) and low QI (<0.2%).

[0039] 2. The innovativeness of stepped pre-carbonization and hydrogen-co-located intermediate-temperature carbonization

[0040] Process characteristics: 300-400-500℃ stepped pre-carbonization (staged removal of light / medium / heavy components) - 600-650℃ H2 / N2 (H2 5-10%) medium-temperature carbonization (temperature-time dynamic correlation with β content).

[0041] Hydrogen atmosphere carbonization: The core function is to inhibit excessive graphitization of the carbon skeleton (protecting the cross-linked structure derived from β resin) while promoting the decomposition of residual QI (<0.2%).

[0042] β content-related regulation: By dynamically adjusting the carbonization time based on the β content (>22%) (e.g., 120 min for holding at β content of 25%, and shortened to 90 min for β content of 30%), a balance between the rigidity and porosity of the carbon skeleton can be achieved.

[0043] 3. Differentiation in mixed-base stepwise activation

[0044] Process characteristics: KOH+NaOH=1:1 mixed alkali (material-alkali ratio 1:1.0-2.5)—700—750—900℃ step activation, utilizing the eutectic characteristics of mixed alkali (melting point reduced to 280℃) and temperature gradient to synergistically create pores.

[0045] Mixed alkali activation: Most existing patents use KOH and NaOH for stepwise activation (NaOH first, then KOH), and the material-alkali ratio is as high as 1:3-6, which is significantly different from the user's "1:1 synchronous mixing + low material-alkali ratio".

[0046] Stepped activation temperature: Existing technologies use a single activation temperature (800℃), while the 700-750-900℃ gradient design of this invention can achieve step-by-step control of "micropore generation → mesopore expansion → pore structure stabilization", which is suitable for the multi-level pore requirements of silicon-carbon anodes (micropore lithium storage + mesopore buffer expansion). Detailed Implementation

[0047] The present invention will be further explained below with reference to the embodiments.

[0048] Example 1

[0049] This embodiment includes the following steps:

[0050] (1) Pre-oxidized refined asphalt: 320g of refined coal tar pitch powder (QI content 100ppm, ash content 200ppm, carbon content C wt% = 92.00, sulfur content 800ppm, volatile matter 42.5wt%, coking value 65.00%, softening point 130℃, β resin content 22wt%) was added to a 500mL three-necked flask. It was heated and stirred at 150℃ for 2 hours. Then, air was introduced into the flask at a flow rate of 800mL / min. The air was bubbled to ensure that the gas was fully in contact with the liquid asphalt. Finally, the flask was heated from room temperature to 250℃ at a rate of 2℃ / min and held at the temperature for 0.5h. Then, the temperature was increased from room temperature to 300℃ at a rate of 3℃ / min and held at the temperature for 2h to obtain pre-oxidized refined asphalt raw material with target oxygen modified oxygen content of 5at% and softening point of 180℃.

[0051] (2) Low-temperature stepped precarbonization: 400g of pre-oxidized refined asphalt raw material accumulated in step 1 was heated to 300℃ for 60min in an inert atmosphere (N2 purity > 99.99% with a flow rate of 150mL / min) at a heating rate of 3℃ / min. Then, it was heated to 400℃ for 70min in an atmosphere (N2 purity > 99.99% with a flow rate of 150mL / min) at a heating rate of 3℃ / min. Finally, it was heated to 500℃ for 90min in an atmosphere (N2 purity > 99.99% with a flow rate of 200mL / min) at a heating rate of 3℃ / min.

[0052] (3) Medium-temperature carbonization: The pre-carbonized material is carbonized at 620°C for 150 min at a flow rate of 150 mL / min in an H2 / N2 mixture with a H2 ratio of 7.5% V:V.

[0053] (4) Stepwise activation with mixed alkali: The above carbonization product is mixed with a mixed alkali of KOH:NaOH = 1:1 at a mass ratio of 1:2.5 in a V-type mixer. Under an inert N2 atmosphere with a purity >99.99% and a flow rate of 600 mL / min, the mixture is activated by stepwise heating at a rate of 2℃ / min through 700℃ (45 min) - 750℃ (75 min) - 900℃ (90 min). After natural cooling, the mixture is washed three times with acid and water respectively, and then dried to obtain asphalt-based porous carbon material.

[0054] Example 2

[0055] This embodiment includes the following steps:

[0056] (1) Pre-oxidized refined asphalt: 300g of refined petroleum asphalt (QI content 80ppm, ash content 100ppm, carbon content Cwt% = 91.00, sulfur content = 600ppm, volatile matter 45wt%, coking value 55.00%, softening point 110℃, β resin content 16%) was added to asphalt powder in a 500mL three-necked flask. The mixture was heated and stirred at 135℃ for 2 hours. Then, 5% O2 / N2 mixed gas was introduced into the flask at a flow rate of 800mL / min. The gas was bubbled to ensure that the gas was fully in contact with the liquid asphalt. Finally, the flask was heated from room temperature to 270℃ at a rate of 2℃ / min and held at that temperature for 0.5h. Then, the temperature was increased from room temperature to 310℃ at a rate of 3℃ / min and held at that temperature for 2h to obtain pre-oxidized refined asphalt raw material with target oxygen modified oxygen content of 6at% and softening point of 180℃.

[0057] (2) Low-temperature stepped precarbonization: 400g of pre-oxidized refined asphalt raw material accumulated in step 1 was heated to 300℃ for 60min in an inert atmosphere (N2 purity > 99.99% flow rate 180mL / min) at a heating rate of 2℃ / min. Then, it was heated to 400℃ for 70min in an atmosphere (N2 purity > 99.99% flow rate 180mL / min) at a heating rate of 2℃ / min. Finally, it was heated to 500℃ for 80min in an atmosphere (N2 purity > 99.99% flow rate 180mL / min) at a heating rate of 2℃ / min.

[0058] (3) Medium-temperature carbonization: The pre-carbonized material is carbonized at 650°C for 150 min in a H2 / N2 mixture with H2 content of 10% at a flow rate of 180 mL / min.

[0059] (4) Stepwise activation with mixed alkali: The above carbonization product is mixed with a mixed alkali of KOH:NaOH = 1:1 at a mass ratio of 1:1.8 in a V-type mixer. Under an inert N2 atmosphere with a purity >99.99% and a flow rate of 200-800 mL / min, the mixture is activated by stepwise heating at a rate of 5℃ / min through 700℃ (45 min) - 750℃ (75 min) - 900℃ (90 min). After natural cooling, the mixture is washed three times with acid and water respectively, and then dried to obtain asphalt-based porous carbon material.

[0060] Example 3

[0061] This embodiment includes the following steps:

[0062] (1) Pre-oxidized refined asphalt: 320g of refined natural asphalt (QI content 200ppm, ash content 500ppm, carbon content Cwt% = 90.00, sulfur content = 1000ppm, volatile matter 60wt%, coking value 45.00%, softening point 110℃, β resin content = 12wt%) was added to asphalt powder in a 500mL three-necked flask. The mixture was heated and stirred at 130℃ for 0.5h. Then, 5% O2 / N2 mixed gas was introduced into the flask at a flow rate of 800mL / min. The gas was bubbled to ensure that the gas was fully in contact with the liquid asphalt. Finally, the flask was heated from room temperature to 240℃ at a rate of 2℃ / min and held at that temperature for 1h. Then, the temperature was increased from room temperature to 300℃ at a rate of 3℃ / min and held at that temperature for 2h to obtain pre-oxidized refined asphalt raw material with target oxygen modified oxygen content of 7at% and softening point of 100-280℃.

[0063] (2) Low-temperature stepped precarbonization: 400g of pre-oxidized refined asphalt raw material accumulated in step 1 was heated to 300℃ for 30min in an inert atmosphere (N2 purity > 99.99% with a flow rate of 200mL / min) at a heating rate of 2℃ / min. Then, it was heated to 400℃ for 50min in an atmosphere (N2 purity > 99.99% with a flow rate of 200mL / min) at a heating rate of 3℃ / min. Finally, it was heated to 500℃ for 70min in an atmosphere (N2 purity > 99.99% with a flow rate of 200mL / min) at a heating rate of 4℃ / min.

[0064] (3) Medium-temperature carbonization: The pre-carbonized material is carbonized at 600℃ for 150 min in a H2 / N2 mixture with H2 content of 10% at a flow rate of 150 mL / min.

[0065] (4) Stepwise activation with mixed alkali: The above carbonization product is mixed with a mixed alkali of KOH:NaOH = 1:1 at a mass ratio of 1:1.0 in a V-type mixer. Under an inert N2 atmosphere with a purity >99.99% and a flow rate of 400 mL / min, the mixture is activated by stepwise heating at a rate of 4℃ / min through 700℃ (30 min) – 750℃ (60 min) – 900℃ (90 min). After natural cooling, the mixture is washed three times with acid and water respectively, and then dried to obtain asphalt-based porous carbon material.

[0066] Example 4

[0067] The steps are the same as in Example 1, except that the content of refined bitumen β resin in step 1 is changed from 22% to 12%.

[0068] Example 5

[0069] The steps are the same as in Example 1, except that the content of refined bitumen β resin in step 1 is changed from 22% to 32%.

[0070] Example 6

[0071] The steps are the same as in Example 1, except that in step 1, a pre-oxidized refined asphalt raw material with an oxygen content of 2 at% and a softening point of 180°C with the target oxygen modification is obtained.

[0072] Example 7

[0073] The steps are the same as in Example 1, except that in step 1, a pre-oxidized refined asphalt raw material with an oxygen content of 8 at% and a softening point of 180°C with the target oxygen modification is obtained.

[0074] Example 8

[0075] The procedure is the same as in Example 1, except that in step 3, the carbonization conditions of H2 / N2 mixture with a H2 ratio of 7.5% V:V, carbonized at 620°C for 150 min at a flow rate of 150 mL / min, under medium-temperature carbonization conditions, are replaced with carbonization conditions of H2 / N2 mixture with a H2 ratio of 7.5% V:V, carbonized at 650°C for 180 min at a flow rate of 150 mL / min.

[0076] Example 9

[0077] The steps are the same as in Example 1, except that in step 4, the step activation program 700℃ (45 min) - 750℃ (75 min) - 900℃ (90 min) is replaced with a step temperature increase activation of 750℃ (60 min) - 800℃ (60 min) - 900℃ (60 min), while other conditions remain unchanged.

[0078] Comparative Example 1

[0079] The steps are the same as in Example 1, except that in step 2, the temperature increase from 300-400-500 degrees Celsius is changed to a constant temperature plateau of 400 degrees Celsius.

[0080] Comparative Example 2

[0081] The steps are the same as in Example 1, except that in step 3, the H2 / N2 mixture is replaced with a 99.99% N2 atmosphere, while other conditions remain unchanged.

[0082] Comparative Example 3

[0083] The steps are consistent with those in Example 1, except that the carbonization time in step 3 is not related to the β content. That is, the carbonization temperature and time remain unchanged regardless of the β content. For example, when the β content in the refined asphalt is 30%, the medium-temperature carbonization platform is still kept at a constant temperature of 620°C for 150 minutes.

[0084] Comparative Example 4

[0085] The steps are the same as in Example 1, except that the activation step in step 4, which follows a stepwise sequence of 700℃ (45 min) - 750℃ (75 min) - 900℃ (90 min), is replaced by a constant temperature of 850℃ for 3 hours.

[0086] The porous carbon obtained in the above embodiments and comparative examples was tested as follows.

[0087] 1. 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 "Lithium-ion Battery Graphite Anode Materials Part 2: Determination of Tap Density"), crush strength (DL / T 515-2014 "Test Method for Activated Carbon for Electric Power"), and electrical conductivity (GB / T 24525-2009 "Method for Determination of Resistivity of Carbon Materials"). SEM / TEM was also used for morphological observation: the microstructure and pore structure of the material were observed, and pore volume, pore size, micropores, and mesopore ratio could all be calculated from the BET test data.

[0088] 2. Silane Deposition: Silicon-deposited silicon-carbon anode material was prepared according to the following steps: 50g of pitch-based porous carbon was weighed and baked at 80℃ under vacuum for 10h. After drying, it was placed in a fluidized bed, and nitrogen gas was introduced at a rate of 300mL / min while the temperature was gradually increased to 300℃. Then, the temperature was increased to 480℃ at a rate of 10℃ / min. Ethylene and silane were started. While continuously introducing nitrogen gas at a rate of 300mL / min, the acetylene flow rate was 2.5mL / min, and the silane flow rate was 10L / min. After maintaining the temperature for 1h, the acetylene and silane gases were turned off. Subsequently, the nitrogen gas rate was increased to 2.5L / min, and the temperature was lowered to room temperature before discharging.

[0089] 3. Electrochemical Testing: A slurry was prepared by mixing silicon-carbon anode material, binder (LA132), and conductive agent (Super P) in a mass ratio of 70:20:10. The slurry was homogenized and coated onto copper foil, then vacuum dried, rolled, and slit to obtain the corresponding anode sheet. Following conventional lithium-ion battery manufacturing methods, the obtained anode sheets were fabricated into lithium-ion CR2032 coin cells. The specific steps are as follows: an electrolyte containing 1.2 mol / L LiPF6 was used (with a volume ratio of ethyl carbonate:dimethyl carbonate:methyl carbonate = 1:1:1 as the mixed solvent); a polypropylene microporous membrane was used as the separator; and a lithium metal sheet was used as the counter electrode. The silicon-carbon anode sheets were assembled into coin cells in an argon-filled inert gas glove box system. At 25°C, the assembled coin cells were subjected to charge-discharge cycle tests using a blue-light testing instrument to obtain their capacity, initial coulombic efficiency (first efficiency), and capacity retention after 200 cycles. The capacity and first-efficiency test conditions are as follows: 0.1C discharge to a voltage less than 0.01V, 0.02C discharge to a voltage less than 0.005V, and 0.1C charge to a voltage greater than 1.5V. The 200-cycle capacity retention test conditions are as follows: constant current charge-discharge testing is performed on the material using a Blue Electric testing system, with a voltage test range of 0.01-1.5V. The first three cycles use a small current of 0.05C for activation, followed by long-cycle testing at 0.1C. The rate test involves constant 1C charging, followed by discharges at 0.5C / 1C / 2C / 3C / 4C / 5C / 6C, with 5 cycles at each discharge rate. The capacity data for the 1C and 6C cycles are recorded, and the 6C / 1C capacity retention rate is calculated.

[0090] The test results are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] Examples 1-5 demonstrate how the pore size distribution, electrical conductivity, and mechanical strength of porous carbon are influenced by controlling the content of asphalt components. Specifically, the contribution of micropores to specific capacity, the contribution ratios of mesopores and macropores, and the cycle life are all determined by the degree of graphitization and the surface functional group molecules.

[0095] Examples 6-9 demonstrate the optimization of carbonization and activation processes by adjusting the parameters. This addresses the differences in pore size distribution, conductivity (β content and carbonization conditions), and mechanical strength (oxygen-hard carbon structure ratio, coking value, carbon content, and carbonization conditions) required for different application scenarios.

[0096] In Comparative Example 1, the three-stage activation system: at 300℃: removes light components (such as C6-C10 aromatics); at 400℃: promotes β resin crosslinking (the time can be shortened when the β content is >22%); at 500℃: fixes the carbon skeleton (crystal size Lc≈1.5nm).

[0097] In Comparative Example 2, an H2 / N2 mixture (H2 content 5-10%) was introduced during the stepped heating stage to suppress tar deposition and improve the conductivity of carbon materials.

[0098] In Comparative Example 3, the intermediate-temperature carbonization temperature (600-650℃) was directly correlated with the β content. By dynamically adjusting the carbonization time through the β content, the balance between the rigidity and porosity of the carbon skeleton can be precisely controlled. If not correlated, over-carbonization may lead to structural rigidity (such as densification, increased brittleness, and reduced active sites).

[0099] In Comparative Example 4, the correlation between temperature gradient and pore distribution is clearly defined: 700℃ dominates the generation of micropores (<2nm) (accounting for 30-35%), 750℃ dominates the expansion of mesopores (2-50nm) (accounting for 50-55%), and 900℃ stabilizes the pore structure (macropores <15%), which increases the pore volume by 20-25% compared to activation at a single temperature. However, if a single temperature is maintained, the pore volume and pore size distribution uniformity will be poor.

[0100] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-performance pitch-based porous carbon for silicon-carbon anodes, characterized in that: Includes the following steps: (1) Pre-oxidized refined asphalt: After heating and stirring the refined asphalt, oxygen-containing gas is introduced and subjected to staged heating oxidation treatment to obtain oxygen-modified pre-oxidized refined asphalt; The segmented heating oxidation process includes: (11) Heat and stir at the softening point +20℃ for 1-4 hours; (12) Introduce air or O2 / N2 mixed gas with an O2 volume content of 5% at a flow rate of 600-2000 mL / min, and ensure that the gas is fully in contact with the liquid asphalt by bubbling. Raise the temperature to 220-280℃ at a heating rate of 2-10℃ / min and keep it at a constant temperature for 0.1-4h. (13) Finally, raise the temperature to 270-330℃ at a rate of 3-12℃ / min and hold for 0.5-5 hours; The resulting pre-oxidized refined asphalt has an oxygen content of 2-8 at%, and a softening point of 100-280℃. (2) Low-temperature stepped precarbonization: The pre-oxidized asphalt obtained in step (1) is precarbonized in an inert atmosphere by heating it to different temperatures in stages. The low-temperature stepped pre-carbonization includes: (21) In an atmosphere with N2 purity > 99.99% and a flow rate of 150-200 mL / min, heat to 300℃ at a heating rate of 1-5℃ / min and hold for 30-120 min; (22) Then continue to heat to 400℃ for 50-140 min in an atmosphere with N2 purity >99.99% and a flow rate of 150-200 mL / min at a heating rate of 2-6℃ / min; (23) Finally, in an atmosphere with N2 purity > 99.99% and a flow rate of 150-200 mL / min, the temperature is raised to 500℃ at a rate of 2-6℃ / min and held for 50-140 min. (3) Medium-temperature carbonization: The pre-carbonized product obtained in step (2) is placed in a hydrogen-containing mixed atmosphere, and the carbonization process is dynamically controlled according to the asphalt components; The hydrogen-containing mixed atmosphere is an H2 / N2 mixture with an H2 volume percentage of 5-10% and a flow rate of 150-200 mL / min; The carbonization temperature is 600-650℃, the time is 60-240min, and when the β resin content is 22-25%, the holding time is 120-150min, and when the β resin content is >25%, the holding time is 90-120min. (4) Mixed alkali gradient activation: The carbonization product obtained in step (3) is mixed with potassium hydroxide and sodium hydroxide mixed alkali, and after multi-temperature zone step activation, it is washed and dried to obtain asphalt-based porous carbon; The mixed alkali is a mixture of KOH and NaOH in a mass ratio of 1:1, and the material-alkali mass ratio is 1:1.0-2.

5. The stepwise activation steps are as follows: In an inert N2 atmosphere with a purity >99.99% and a flow rate of 200-800 mL / min, the temperature is increased to 700℃ at a heating rate of 2-6℃ / min and held for 30-60 min, then increased to 750℃ at a heating rate of 2-6℃ / min and held for 60-90 min, and finally increased to 900℃ at a heating rate of 2-6℃ / min and held for 60-120 min.

2. The preparation method according to claim 1, characterized in that: In step (1), the refined asphalt meets the following requirements: QI content 80-8000ppm, ash content 100-600ppm, carbon content ≥90.00wt%, sulfur content ≤1000ppm, volatile matter 30-60wt%, coking value 45.00-85.00%, softening point 100-230℃, and β resin content >22%.

3. The preparation method according to claim 1, characterized in that: In step (4), the washing steps are: after natural cooling, the product is washed three times with acid and water respectively.

4. A high-performance pitch-based porous carbon for silicon-carbon anodes prepared by the method according to any one of claims 1-3, characterized in that: The bituminous porous carbon has a BET specific surface area of ​​1586-2103 m² / g, a pore volume of 0.67-0.94 cm³ / g, an average pore diameter of 1.34-2.82 nm, a microporosity of 75.3-96.4%, and a mesoporosity of 2.1-24.3%.

5. The application of the pitch-based porous carbon according to claim 4 in silicon-carbon anodes, characterized in that: The specific capacity of silicon-carbon anodes ranges from 1477 to 2076 mAh / g, with an initial efficiency of 86.6% to 94.7%. Capacity retention after 200 cycles at 0.1C is 81.3-92.3%, and rate retention at 6C / 1C is 80.6-88.7%.

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