Porous carbon material, method for preparing the same, and use thereof

Abstract

The present application belongs to the technical field of carbon materials, and particularly relates to a porous carbon material and a preparation method and application thereof. Bitumen is treated with acid, a polar functional group is introduced, a metal salt is added under acidic conditions, ion exchange or coordination anchoring of metal ions occurs, uniform and stable distribution of a metal template in a carbon precursor is realized, and further introduction of a silica template is carried out, coexistence and connection of micropores, mesopores and even macropores in the same carbon skeleton are realized, and a multi-level pore network is obtained. A battery using a silicon-carbon material based on the porous carbon exhibits a longer cycle life.

Description

Technical Field

[0001] This invention belongs to the field of carbon materials technology, specifically relating to porous carbon materials, their preparation methods, and applications. Background Technology

[0002] Porous carbon materials, with their high specific surface area, tunable pore structure, excellent electrochemical stability, and good electrical conductivity, have become star functional materials in the field of energy storage and conversion. Ideal electrode materials need to meet the combined requirements of efficient ion transport, sufficient active sites, and good structural stability, and porous carbon exhibits significant advantages in all these dimensions. In systems such as lithium-ion batteries, lithium-sulfur batteries, supercapacitors, and metal-air batteries, porous carbon is widely used as anode materials, conductive carriers, or separator modification materials, playing a crucial role in improving battery energy density, cycle life, and rate performance. Of particular note is that, with the continuous increase in cell energy density, next-generation battery technologies such as silicon-carbon anodes and sulfur cathodes place even more stringent demands on the pore structure of carbon carriers; single-size pores are no longer sufficient to meet the synergistic requirements of efficient mass transfer and rapid response.

[0003] Template methods are widely recognized as a powerful technique for preparing porous carbon materials due to their high controllability in pore structure regulation. Based on the type of template, template methods are mainly divided into two categories: hard template methods and soft template methods.

[0004] The soft template method utilizes amphiphilic molecules such as surfactants and block copolymers to form ordered micelle structures through self-assembly. The carbon source polymerizes and solidifies the micelle structure simultaneously with the precursor. After carbonization, the soft template thermally decomposes, leaving pores. This method avoids etching damage to the carbon framework. However, firstly, the molecular assembly of the soft template is extremely sensitive to the solvent system, carbon source type, and reaction temperature, resulting in a narrow process window that hinders large-scale preparation. Secondly, during high-temperature carbonization, the soft template gradually decomposes with increasing temperature, and the pore structure is particularly prone to shrinkage, collapse, or partial closure, making precise control of the target pore size a significant challenge and insufficient to meet the practical requirements for synergistic regulation of multi-level pore structures.

[0005] Hard template methods typically use rigid frameworks such as mesoporous silica (e.g., SBA-15, MCM-41), molecular sieves, or metal oxides as templates. The process involves three basic steps: carbon source filling, high-temperature carbonization, and template removal. After carbonization, the template is dissolved and removed using hydrofluoric acid or a strong alkaline solution. Hard templates effectively ensure the order and connectivity of the pores. Silica is the most widely used template material in hard template methods, which is closely related to its advantages such as good controllability of pore structure, strong monodispersity, and relatively low cost.

[0006] However, despite the advantages of silica hard templates in pore ordering, they still exhibit significant limitations in practical applications. First, this method is a typical exogenous post-templating strategy—a silica template must be prefabricated, and then a carbon source is filled into the template pores via impregnation or vapor deposition. This process demands high rheological properties and uniformity of the carbon source, making it highly susceptible to pore structure defects due to insufficient filling. Second, a single silica template system can essentially only construct pores of a specific scale (such as mesopores or macropores) corresponding to its own morphology, making it difficult to integrate multi-level pore structures in situ within the same carbon material. Furthermore, single-scale pores often cannot simultaneously meet the dual requirements of high ion storage capacity and rapid ion transport in battery applications. Summary of the Invention

[0007] Based on the problems existing in the background technology, the present invention pre-constructs a metal template by in-situ doping with metal before using a silicon dioxide hard template, forming a "metal-silicon dioxide" dual template system.

[0008] The first objective of this invention is to provide a method for preparing porous carbon materials; the second objective of this invention is to provide a porous carbon material; and the third objective of this invention is to provide applications of porous carbon materials.

[0009] Based on the first objective, the present invention provides a method for preparing porous carbon materials, comprising the following steps: Step S1, Modified Asphalt: Asphalt is added to an acid for acid modification treatment to obtain a mixture; the acid is at least one of concentrated sulfuric acid and concentrated nitric acid. Adjust the pH value of the mixture to 1-3, then add at least one of magnesium salt, calcium salt, and aluminum salt, react, separate the solid and liquid, and obtain modified asphalt; Step S2, Preparation of precursor: The modified bitumen was dispersed in deionized water, then mixed evenly with silica sol, and dried to obtain the precursor. Step S3, carbonization: The precursor is carbonized to obtain the carbonized product. Step S4, Remove the template: The template in the carbonization product is removed to obtain a porous carbon material.

[0010] Based on the second objective, the present invention provides a porous carbon material, which satisfies the following characteristics: (a) Specific surface area of ​​800-2000 m² / g, total pore volume of 0.8-1.5 cm³ / g; (b) Based on the pore volume ratio The proportion of pores with a pore size distribution of 2-5 nm is 70-90%; The proportion of pores with a pore size distribution of 5-10 nm is 8-25%; The proportion of pores with a pore size distribution of 10-50 nm is 2-20%; Furthermore, the sum of the pore volume ratios of the three pore sizes mentioned above is 100%.

[0011] For the third objective, the present invention provides a silicon-carbon material obtained by depositing silicon in the pores of the aforementioned porous carbon using chemical vapor deposition.

[0012] In addition, the present invention also provides a battery negative electrode comprising the aforementioned silicon-carbon material.

[0013] The present invention also provides a battery comprising the above-described negative electrode.

[0014] The above-described one or more technical solutions of the present invention can achieve at least one of the following beneficial effects: Acid treatment of asphalt chemically modifies the asphalt by introducing polar functional groups, enabling it to undergo ion exchange or coordination anchoring with metal ions under acidic conditions, thereby achieving a uniform and stable distribution of the metal template in the carbon precursor.

[0015] Silica templates typically form mesopores or macropores (pore size 2-50 nm or larger), while in-situ metal templates can generate micropores or small mesopores (<2 nm or 2-5 nm) during carbonization. Combining these two technologies allows for the coexistence and connectivity of micropores, mesopores, and even macropores within the same carbon framework, forming a hierarchical, highly porous network. This structure provides a high specific surface area for loading active sites (such as lithium and sulfur storage) while ensuring rapid ion / electrolyte transport channels, overcoming the contradictions in kinetics and capacity inherent in single-channel systems.

[0016] Metal templates can be gently removed with dilute acids (such as hydrochloric acid or dilute sulfuric acid), without the need for highly corrosive reagents such as hydrofluoric acid or concentrated alkalis. Although silica templates still need to be removed, the pre-constructed auxiliary channels in the metal templates can appropriately reduce the dependence on complete filling of silica templates, thereby reducing the overall chemical etching damage to the carbon framework and improving the structural integrity and mechanical strength of carbon materials.

[0017] In-situ metal doping catalyzes carbon graphitization during the carbonization process, forming a locally ordered conductive network that retains a highly conductive carbon microcrystalline structure even after template removal. Combined with the low diffusion resistance resulting from hierarchical pores, batteries using porous carbon or silicon-carbon materials based on porous carbon exhibit longer cycle life.

[0018] Metal templates can be introduced in one step through in-situ doping of precursors, without the need for separate synthesis and pre-filling. Attached Figure Description

[0019] Figure 1This is an XPS image of the modified asphalt in Example 1.

[0020] Figure 2 The image shows a SEM image of the porous carbon material obtained in Example 1.

[0021] Figure 3 This is a TEM image of the porous carbon material obtained in Example 1.

[0022] Figure 4 The image shows a TEM image of the porous carbon material obtained in Comparative Example 1. Detailed Implementation

[0023] Based on the first objective, this invention provides a method for preparing porous carbon materials, comprising the following steps: Step S1, Modified Asphalt: Asphalt is added to an acid for acid modification treatment to obtain a mixture; the acid is at least one of concentrated sulfuric acid and concentrated nitric acid. Adjust the pH value of the mixture to 1-3, then add at least one of magnesium salt, calcium salt, and aluminum salt, react, separate the solid and liquid, and obtain modified asphalt; Step S2, Preparation of precursor: The modified bitumen was dispersed in deionized water, then mixed evenly with silica sol, and dried to obtain the precursor. Step S3, carbonization: The precursor is carbonized to obtain the carbonized product. Step S4, Remove the template: The template in the carbonization product is removed to obtain a porous carbon material.

[0024] Step S1: Asphalt undergoes acid modification treatment in at least one of concentrated sulfuric acid and concentrated nitric acid, and the following occurs in this system: Sulfonation reaction: Introducing –SO3H (sulfonic acid group) Nitrification reaction: Introduction of –NO2 (nitro group) Oxidation reaction: Introducing oxygen-containing functional groups such as –OH (phenolic hydroxyl group) and –COOH (carboxyl group).

[0025] These polar groups significantly enhance the hydrophilicity and chemical reactivity of asphalt, transforming it from a hydrophobic, blocky substance into a modified asphalt that can be dispersed or partially dissolved in water.

[0026] The dilution process serves two purposes: firstly, it terminates the reaction and removes excess acid; secondly, it adjusts the system to an acidic environment (pH 1–3). Under these pH conditions, the carboxyl groups (–COOH) and sulfonic acid groups (–SO3H) on the modified asphalt primarily exist as –COO groups. - -SO3 -The presence of this form ensures that subsequently added metal salts remain in an ionic state and do not form hydroxide precipitates.

[0027] The cations in the metal salt undergo ion exchange or coordination adsorption with the negatively charged carboxylate and sulfonate groups on the asphalt, and are uniformly "anchored" to the asphalt molecular framework. This achieves in-situ pre-positioning of the metal template inside the carbon precursor, avoiding metal agglomeration caused by traditional mechanical mixing.

[0028] The concentration of the concentrated sulfuric acid is 98%, and the concentration of the concentrated nitric acid is 68%.

[0029] Furthermore, when the acid is a mixture of concentrated sulfuric acid and concentrated nitric acid, the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixture is 1:4 to 4:1.

[0030] Furthermore, the weight-to-volume ratio of asphalt to acid is 1g:3mL to 1g:5mL. Within this range, a slurry-like suspension can be formed.

[0031] Furthermore, the acid modification treatment is carried out at a temperature of 50-80℃ for 2-8 hours.

[0032] Furthermore, the asphalt is at least one of coal tar pitch, petroleum asphalt, and naphthalene pitch.

[0033] Further, the mixture is placed in an ice-water bath, and water is slowly added to dilute the pH of the mixture to 1-3. During the dilution process, the temperature of the mixture is ensured not to exceed 60°C.

[0034] Furthermore, the magnesium salt is at least one of magnesium nitrate, magnesium citrate, and magnesium acetate.

[0035] Furthermore, the calcium salt is at least one of calcium nitrate, calcium chloride, and calcium acetate.

[0036] Furthermore, the aluminum salt is at least one of aluminum nitrate, aluminum chloride, and aluminum acetate.

[0037] Furthermore, the amount of at least one of the magnesium salt, calcium salt, and aluminum salt added is 5-30% of the mass of the asphalt.

[0038] Furthermore, the reaction temperature is 40-60℃, and the time is 3-8 hours. If the temperature is too low, the kinetics of ion exchange and coordination reactions are slow, and the binding rate between metal ions and functional groups is slow and may be weak. Moreover, the viscosity of the diluted asphalt-water system remains considerable, and low temperatures will exacerbate mass transfer difficulties, leading to uneven anchoring. If the temperature is too high, functional groups will detach: newly grafted sulfonic acid and carboxyl groups on the asphalt may undergo desulfonation and decarboxylation reactions in hot acidic water at excessively high temperatures, thus reducing the number of anchoring points. Furthermore, the pH increases after dilution, and aluminum salts, for example, are easily hydrolyzed above 60℃ to form colloidal precipitates, negating the benefits of ion-level doping.

[0039] Step S2: Building upon step S1, the modified bitumen is further mixed with silica sol to create a dual-template system. The silica template typically forms mesopores or macropores (pore size 2-50 nm or larger), while the in-situ metal template can generate micropores or small mesopores (<2 nm or 2-5 nm) during carbonization. The combination of these two systems allows for the coexistence and connectivity of micropores, mesopores, and even macropores within the same carbon framework, forming a hierarchical, highly porous network. This structure provides a high specific surface area for loading active sites (such as lithium and sulfur storage) while ensuring rapid ion / electrolyte transport channels, overcoming the contradictions in kinetics and capacity inherent in single-channel systems.

[0040] Furthermore, the mass ratio of the modified bitumen to silica sol is 1:2 to 2:1. If the amount of silica sol is too large, the pore walls of the resulting porous carbon will be too thin; if the amount of silica sol is too small, the porous carbon will have too few pores.

[0041] Furthermore, the silica sol contains 10-30% silica by mass and has a particle size of 3-50 nm.

[0042] Furthermore, the drying process is evaporative drying.

[0043] Step S3: Furthermore, the carbonization treatment is carried out at a temperature of 800-1200℃, in a nitrogen or argon atmosphere, for a time of 1-6 hours.

[0044] Furthermore, the heating rate of the carbonization treatment is 1-8℃ / min.

[0045] The carbonization process mainly includes one or more of the following reactions: (1) Metal salts adsorbed in asphalt will decompose to generate metal oxides.

[0046] (2) Pyrolysis and condensation of asphalt produce small molecule hydrocarbons, H2, CO, CO2, etc., forming an amorphous carbon skeleton. Oxygen-containing functional groups (–COOH, –SO3H) are destroyed, releasing gases such as CO2 and SO2.

[0047] (3) Metal oxide nanoparticles act as catalysts, promoting the rearrangement of surrounding amorphous carbon into ordered graphite microcrystals.

[0048] Step S4: Remove the template from the carbonization products, preferably by removing the template in stages.

[0049] Furthermore, the first template is removed using a dilute hydrochloric acid solution with a concentration of 0.5-3 mol / L; then the second template is removed using a hydrofluoric acid solution with a concentration of 0.5-3 mol / L.

[0050] Furthermore, the temperature for removing the first template is 60-80℃, and the time is 4-8 hours.

[0051] Furthermore, the temperature for removing the second template is 60-80℃, and the time is 4-8 hours.

[0052] Based on the second objective, the present invention provides a porous carbon material, which satisfies the following characteristics: (a) Specific surface area of ​​800-2000 m² / g, total pore volume of 0.8-1.5 cm³ / g; (b) Based on the pore volume ratio The proportion of pores with a pore size distribution of 2-5 nm is 70-90%; The proportion of pores with a pore size distribution of 5-10 nm is 8-25%; The proportion of pores with a pore size distribution of 10-50 nm is 2-20%; Furthermore, the sum of the pore volume ratios of the three pore sizes mentioned above is 100%.

[0053] Pores with a diameter of 2-5 nm are the dominant pore channels, accounting for 70-90% of the pore volume. During chemical vapor deposition of silicon, silane gas preferentially nucleates and grows within these 2-5 nm pores. These pore sizes effectively limit silicon particle growth to below the critical size (typically <5 nm), preventing the formation of large silicon particles. Sub-5 nm silicon particles themselves are unlikely to break due to volume expansion. After silicon deposition, the pores are not completely filled, leaving tiny gaps. As the silicon expands towards the center of the pore, it does not forcefully break the carbon walls outwards. This directly leads to a fundamental improvement in the cycle life of the battery.

[0054] Pores with a diameter of 5-10 nm can be considered as support / transport channels, connecting micropores and even smaller mesopores. A small number of 5-10 nm channels ensure long-range gas transport, achieving high and uniform silicon loading.

[0055] Pores with a diameter of 10-50 nm can serve as a rapid channel for silane to enter the interior of particles in the initial stage of chemical vapor deposition.

[0056] Furthermore, the porous carbon material is prepared by the above method.

[0057] Based on a third objective, this invention provides a silicon-carbon material obtained by depositing silicon in the pores of the aforementioned porous carbon using chemical vapor deposition.

[0058] In addition, the present invention also provides a battery negative electrode comprising the aforementioned silicon-carbon material.

[0059] The present invention also provides a battery comprising the above-described negative electrode.

[0060] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0061] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0062] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0063] Example 1 (1) Take 10g of medium-temperature coal tar pitch (softening point 85℃) and crush it through a 200-mesh sieve.

[0064] Preparation of mixed acid: Measure 20 mL of concentrated sulfuric acid (98%) and 30 mL of concentrated nitric acid (68%), mix them thoroughly and place them in a three-necked flask.

[0065] In a 60℃ water bath, add 10g of asphalt powder to the mixed acid and react for 3 hours. After the reaction is complete, place the mixture in an ice-water bath, slowly add deionized water, and control the temperature of the mixture to not exceed 60℃. Dilute the acid concentration to a pH of 2±0.1.

[0066] The system was then heated to 50°C, and 0.5g of magnesium nitrate was added to the system. The reaction was continued for 3 hours.

[0067] After the reaction was completed, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solid phase was repeatedly washed with deionized water. The solid phase was then vacuum dried at 80°C for 12 hours to obtain modified asphalt.

[0068] Figure 1 The image shows the XPS spectrum of magnesium-doped modified asphalt. As can be seen from the image, there is a peak at the Mg 1s position in the full XPS spectrum, indicating that magnesium has been successfully incorporated into the modified asphalt.

[0069] (2) Disperse 5g of modified asphalt in 50mL of deionized water and stir at 60℃ for 2h to obtain a uniform dispersion. Add 20g of acidic silica sol (silica content of 30wt%, particle size of 15nm) to the dispersion and continue stirring for 1h. Transfer the mixture to an evaporating dish, evaporate, and dry to obtain precursor powder.

[0070] (3) The precursor powder was placed in a tube furnace and heated to 800°C at 5°C / min under a nitrogen atmosphere and held for 2 hours to obtain the carbonized product.

[0071] (4) Add the carbonization product to a 1 mol / L hydrochloric acid solution and stir at 80°C for 6 h to remove the magnesium template.

[0072] After solid-liquid separation, the solid phase is added to 1 mol / L hydrofluoric acid and stirred at 80°C for 6 hours to remove the silica template.

[0073] After the template is removed, the material is washed and dried under vacuum at 100°C for 12 hours to obtain porous carbon material.

[0074] Figure 2 This is a SEM image of a porous carbon material.

[0075] Figure 3 This is a TEM image of the porous carbon material obtained in Example 1.

[0076] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that magnesium nitrate was not added in step (1).

[0077] Specifically: (1) Take 10g of medium-temperature coal tar pitch (softening point 85℃) and crush it through a 200-sieve.

[0078] Preparation of mixed acid: Measure 20 mL of concentrated sulfuric acid (98%) and 30 mL of concentrated nitric acid (68%), mix them thoroughly and place them in a three-necked flask.

[0079] Add 10g of asphalt powder to the mixed acid in a 60℃ water bath and react for 3 hours.

[0080] After the reaction was completed, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solid phase was repeatedly washed with deionized water. The solid phase was then vacuum dried at 80°C for 12 hours to obtain modified asphalt.

[0081] (2) Disperse 5g of modified asphalt in 50mL of deionized water and stir at 60℃ for 2h to obtain a uniform dispersion. Add 20g of acidic silica sol (silica content of 30wt%, particle size of 15nm) to the dispersion and continue stirring for 1h. Transfer the mixture to an evaporating dish, evaporate, and dry to obtain precursor powder.

[0082] (3) The precursor powder was placed in a tube furnace and heated to 800°C at 5°C / min under a nitrogen atmosphere and held for 2 hours to obtain the carbonized product.

[0083] (4) Add the carbonization product to a 1 mol / L hydrochloric acid solution and stir at 80°C for 6 h to remove the magnesium template.

[0084] After solid-liquid separation, the solid phase is added to 1 mol / L hydrofluoric acid and stirred at 80°C for 6 hours to remove the silica template.

[0085] After the template is removed, the material is washed and dried under vacuum at 100°C for 12 hours to obtain porous carbon material.

[0086] Figure 4 The image shows a TEM image of the porous carbon material obtained in Comparative Example 1. As can be seen from the image, compared with Example 1, the graphite-like streaks in Comparative Example 1 are less obvious.

[0087] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no silica sol was added.

[0088] Specifically: (1) Take 10g of medium-temperature coal tar pitch (softening point 85℃) and crush it through a 200-sieve.

[0089] Preparation of mixed acid: Measure 20 mL of concentrated sulfuric acid (98%) and 30 mL of concentrated nitric acid (68%), mix them thoroughly and place them in a three-necked flask.

[0090] In a 60℃ water bath, add 10g of asphalt powder to the mixed acid and react for 3 hours. After the reaction is complete, place the mixture in an ice-water bath, slowly add deionized water, and control the temperature of the mixture to not exceed 60℃. Dilute the acid concentration to a pH of 2±0.1.

[0091] The system was then heated to 50°C, and 0.5g of magnesium nitrate was added to the system. The reaction was continued for 3 hours.

[0092] After the reaction was completed, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solid phase was repeatedly washed with deionized water. The solid phase was then vacuum dried at 80°C for 12 hours to obtain modified asphalt.

[0093] (2) Place 5g of modified asphalt in a tube furnace and heat it to 800℃ at 5℃ / min under a nitrogen atmosphere. Hold the temperature for 2h to obtain carbonized products.

[0094] (3) Add the carbonized product to a 1 mol / L hydrochloric acid solution and stir at 80°C for 6 h to remove the magnesium template. After solid-liquid separation, add the solid phase to a 1 mol / L hydrofluoric acid solution and stir at 80°C for 6 h to remove the silica template.

[0095] After the template is removed, the material is washed and dried under vacuum at 100°C for 12 hours to obtain porous carbon material.

[0096] Example 2 (1) Take 10g of petroleum asphalt and crush it through a 200-sieve.

[0097] Take 30 mL of 98% concentrated sulfuric acid.

[0098] In a 50℃ water bath, add 10g of asphalt powder to the mixed acid and react for 5 hours. After the reaction is complete, place the mixture in an ice-water bath, slowly add deionized water, and control the temperature of the mixture to not exceed 60℃. Dilute the acid concentration to a pH of 1±0.1.

[0099] The system was then heated to 40°C, and 1g of calcium chloride was added to the system. The reaction was continued for 8 hours.

[0100] After the reaction was completed, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solid phase was repeatedly washed with deionized water. The solid phase was then vacuum dried at 80°C for 12 hours to obtain modified asphalt.

[0101] (2) Disperse 5g of modified asphalt in 100mL of deionized water and stir at 60℃ for 2h to obtain a uniform dispersion. Add 5g of acidic silica sol (silica content of 20wt%, particle size of 20nm) to the dispersion and continue stirring for 2h. Transfer the mixture to an evaporating dish, evaporate, and dry to obtain precursor powder.

[0102] (3) The precursor powder was placed in a tube furnace and heated to 900°C at 5°C / min under a nitrogen atmosphere and held for 2 hours to obtain the carbonized product.

[0103] (4) Add the carbonization product to a 0.5 mol / L hydrochloric acid solution and stir at 60°C for 8 hours to remove the calcium template.

[0104] After solid-liquid separation, the solid phase is added to 1.5 mol / L hydrofluoric acid and stirred at 80°C for 4 hours to remove the silica template.

[0105] After the template is removed, the material is washed and dried under vacuum at 100°C for 12 hours to obtain porous carbon material.

[0106] Example 3 (1) Take 10g of coal tar pitch and crush it through a 200-mesh sieve.

[0107] Take 40 mL of concentrated nitric acid with a concentration of 68%.

[0108] In an 80℃ water bath, add 10g of asphalt powder to the mixed acid and react for 2 hours. After the reaction is complete, place the mixture in an ice-water bath, slowly add deionized water, and control the temperature of the mixture to not exceed 60℃. Dilute the acid concentration to a pH of 2±0.1.

[0109] The system was then heated to 60°C, and 1g of magnesium citrate was added to the system. The reaction was continued for 4 hours.

[0110] After the reaction was completed, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solid phase was repeatedly washed with deionized water. The solid phase was then vacuum dried at 80°C for 12 hours to obtain modified asphalt.

[0111] (2) Disperse 5g of modified asphalt in 50mL of deionized water and stir at 60℃ for 2h to obtain a uniform dispersion. Add 7.5g of acidic silica sol (silica content of 30wt%, particle size of 15nm) to the dispersion and continue stirring for 3h. Transfer the mixture to an evaporating dish, evaporate, and dry to obtain precursor powder.

[0112] (3) The precursor powder was placed in a tube furnace and heated to 1200°C at 5°C / min under an argon atmosphere. The temperature was maintained for 1 hour to obtain the carbonized product.

[0113] (4) Add the carbonization product to a 1 mol / L hydrochloric acid solution and stir at 60°C for 8 hours to remove the magnesium template.

[0114] After solid-liquid separation, the solid phase is added to 2 mol / L hydrofluoric acid and stirred at 60°C for 8 hours to remove the silica template.

[0115] After the template is removed, the material is washed and dried under vacuum at 100°C for 12 hours to obtain porous carbon material.

[0116] Example 4 (1) Take 10g of petroleum asphalt and crush it through a 200-sieve.

[0117] Prepare mixed acid: Measure 10 mL of concentrated sulfuric acid (98%) and 40 mL of concentrated nitric acid (68%), mix them thoroughly and place them in a three-necked flask.

[0118] In a 60℃ water bath, add 10g of asphalt powder to the mixed acid and react for 3 hours. After the reaction is complete, place the mixture in an ice-water bath, slowly add deionized water, and control the temperature of the mixture to not exceed 60℃. Dilute the acid concentration to a pH of 3±0.1.

[0119] The system was then heated to 40°C, and 2g of aluminum chloride was added to the system. The reaction was continued for 8 hours.

[0120] After the reaction was completed, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solid phase was repeatedly washed with deionized water. The solid phase was then vacuum dried at 80°C for 12 hours to obtain modified asphalt.

[0121] (2) Disperse 5g of modified asphalt in 50mL of deionized water and stir at 60℃ for 2h to obtain a uniform dispersion. Add 10g of acidic silica sol (silica content of 10wt%, particle size of 10nm) to the dispersion and continue stirring for 3h. Transfer the mixture to an evaporating dish, evaporate, and dry to obtain precursor powder.

[0122] (3) The precursor powder was placed in a tube furnace and heated to 1000°C at 3°C / min under a nitrogen atmosphere and held for 3 hours to obtain the carbonized product.

[0123] (4) Add the carbonization product to a 3 mol / L hydrochloric acid solution and stir at 70°C for 6 h to remove the magnesium template.

[0124] After solid-liquid separation, the solid phase is added to 1 mol / L hydrofluoric acid and stirred at 70°C for 4 hours to remove the silica template.

[0125] After the template is removed, the material is washed and dried under vacuum at 100°C for 12 hours to obtain porous carbon material.

[0126] Example 5 (1) Take 10g of naphthalene pitch and crush it through a 200-sieve.

[0127] Preparation of mixed acid: Measure 40 mL of concentrated sulfuric acid (98%) and 10 mL of concentrated nitric acid (68%), mix them thoroughly and place them in a three-necked flask.

[0128] In a 60℃ water bath, 10g of asphalt powder was added to the mixed acid and reacted for 8 hours. After the reaction was completed, the mixture was placed in an ice-water bath, and deionized water was slowly added while controlling the temperature of the mixture to not exceed 60℃. The acid concentration was diluted to a pH of 1±0.1.

[0129] The system was then heated to 50°C, and 3g of calcium nitrate was added to the system. The reaction was continued for 6 hours.

[0130] After the reaction was completed, the mixture was cooled to room temperature, and the solid and liquid phases were separated. The solid phase was repeatedly washed with deionized water. The solid phase was then vacuum dried at 80°C for 12 hours to obtain modified asphalt.

[0131] (2) Disperse 5g of modified asphalt in 50mL of deionized water and stir at 60℃ for 2h to obtain a uniform dispersion. Add 10g of acidic silica sol (silica content of 10wt%, particle size of 30nm) to the dispersion and continue stirring for 6h. Transfer the mixture to an evaporating dish, evaporate, and dry to obtain precursor powder.

[0132] (3) The precursor powder was placed in a tube furnace and heated to 900°C at 5°C / min under a nitrogen atmosphere and held for 6 hours to obtain the carbonized product.

[0133] (4) Add the carbonization product to a 1 mol / L hydrochloric acid solution and stir at 80°C for 4 h to remove the magnesium template.

[0134] After solid-liquid separation, the solid phase is added to 1 mol / L hydrofluoric acid and stirred at 80°C for 4 hours to remove the silica template.

[0135] After the template is removed, the material is washed and dried under vacuum at 100°C for 12 hours to obtain porous carbon material.

[0136] The specific surface area, pore volume, etc. of the porous carbon products obtained in Examples 1-5 and Comparative Examples 1-2 were tested using the following methods.

[0137] Reference standard: GB / T 19587-2017 Determination of specific surface area of ​​solid substances by gas adsorption BET method.

[0138] Testing instrument: BSD-PS type BSD specific surface area tester.

[0139] Specific steps: Sample pretreatment: Pass the porous carbon powder through a 200-mesh sieve, weigh about 100-200 mg of sample and place it in a sample tube, and degas it under vacuum at 300℃ for 6-12 h to remove moisture and impurity gases adsorbed on the sample surface.

[0140] Test Procedure: The treated sample tube was installed in the analysis station, and the nitrogen adsorption-desorption isotherm was measured at liquid nitrogen temperature (77K). The relative pressure (P / P0) was measured in the range of 0.005-0.995. The specific surface area was calculated using the multi-point BET method, and adsorption data points within the relative pressure range of 0.05-0.30 were selected for linear fitting. The pore size distribution and pore volume were analyzed using the BJH model. The total pore volume was calculated from the adsorption amount at a relative pressure P / P0≈0.99.

[0141] Main testing parameters: specific surface area, total pore volume, and pore volume of pores in different pore size ranges.

[0142] The test results are shown in Table 1.

[0143] Table 1 As can be seen from the data in Table 1: (1) When there is no in-situ doped metal as a template, the 2-5 nm pores of the obtained porous carbon material are no longer the main pores. The main pores are mainly provided by the silica template, with a pore size of 5-10 nm. Moreover, the specific surface area and total pore volume of the porous carbon are reduced.

[0144] (2) When only in-situ doped metal is used as template, the pores of 2-5 nm in the obtained porous carbon material are the main pores. However, the specific surface area and total pore volume of the porous carbon material are greatly reduced.

[0145] The porous carbon materials obtained in Example 1, Comparative Examples 1-2, and Examples 2-5 were deposited with silicon in the following manner to obtain silicon-carbon materials: 1. Loading and atmosphere replacement: Take 10g of porous carbon material, spread it evenly in a quartz boat, and push it into the constant temperature zone of the tube furnace; after sealing the furnace, evacuate to below 10Pa, introduce high-purity argon gas to atmospheric pressure, repeat 3 times to purge the air, and maintain the basic argon gas flow rate of 50mL / min throughout the process.

[0146] 2. Temperature pre-stabilization: Heat to 520℃ at a rate of 5℃ / min and hold at that temperature for 1 hour to ensure uniform temperature inside the furnace and remove residual adsorbed water from the porous carbon surface.

[0147] 3. Isothermal silicon deposition: Keep the temperature and argon flow rate constant, switch to 10% silane-argon mixture, control the total flow rate of the mixture to 100 mL / min, and deposit at an isothermal temperature for 6 hours; immediately turn off the silane mixture after deposition and restore pure argon purging.

[0148] 4. Annealing and cooling discharge: Maintain pure argon purging, continue annealing at 520℃ for 1 hour, then cool naturally to room temperature at a rate of 5℃ / min. After discharge, the material is sieved through a 200-mesh sieve to obtain silicon-carbon material.

[0149] The silicon-carbon material was used to prepare the negative electrode sheet: N-methylpyrrolidone (NMP) was added according to the mass ratio of silicon-carbon material: conductive agent SP: binder PVDF = 92:3:5, and the mixture was stirred at high speed to make a slurry. The slurry was coated on copper foil, dried under vacuum at 80°C for 4 hours, and then rolled (compacted density 1.5 g / cm³) and cut into sheets (diameter 12 mm) to obtain the negative electrode sheet.

[0150] A CR2032 coin cell was assembled in an argon glove box using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and 1 mol / L LiPF6 / EC+DMC+EMC (volume ratio 1:1:1) as the electrolyte.

[0151] Electrochemical performance testing was performed on the battery. The specific testing method was as follows: A battery testing system was used, with a test voltage range of 0.01-2.0V. First, constant current charge-discharge cycles were performed at a 0.1C rate, and the initial lithium insertion specific capacity (i.e., initial discharge specific capacity) and initial coulombic efficiency were recorded. Subsequently, 400 constant current charge-discharge cycles were performed at a 1C rate, and the discharge capacity retention rate at the 400th cycle was calculated (retention rate = discharge capacity at the 400th cycle / discharge capacity at the first cycle × 100%). All tests were performed with at least three parallel samples, and the average value was taken.

[0152] The test results are shown in Table 2.

[0153] Table 2 The porous carbon provided in Example 1 contains abundant hierarchical pores, and silicon can be deposited along 5-10nm and 10-50nm pores into 2-5nm pores to achieve uniform silicon deposition, thereby effectively suppressing the volume expansion of silicon during charging and discharging and maintaining a high capacity retention rate.

[0154] The porous carbon material provided in Comparative Example 1 has a low content of 2-5nm pores, which causes silicon to agglomerate and deposit in 5-10nm pores. During the charging and discharging process, volume expansion cannot be effectively suppressed, causing the electrode structure to collapse and resulting in a decrease in the battery's capacity retention rate.

[0155] The porous carbon material provided in Comparative Example 2 contains a large number of 2-5nm pores, but lacks 5-10nm pores and 10-50nm pores, which prevents silicon from being effectively deposited in the 2-5nm pores. Most of the silicon is deposited on the outside of the porous carbon, resulting in low first efficiency and low capacity retention.

[0156] When the porous carbon material is provided by Example 5, the proportion of pores of 10-50nm in the porous carbon material is relatively large, and the silicon particles deposited in the macropores are large. During the charging and discharging process, they are prone to pulverization and shedding or failure in contact with the carbon matrix, and the capacity retention rate of the battery is not high.

[0157] 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 porous carbon materials, characterized in that, Includes the following steps: Step S1, Modified Asphalt: Asphalt is added to an acid for acid modification treatment to obtain a mixture; the acid is at least one of concentrated sulfuric acid and concentrated nitric acid. Adjust the pH value of the mixture to 1-3, then add at least one of magnesium salt, calcium salt, and aluminum salt, react, separate the solid and liquid, and obtain modified asphalt; The magnesium salt is at least one of magnesium nitrate, magnesium citrate, and magnesium acetate; The calcium salt is at least one of calcium nitrate, calcium chloride, and calcium acetate; The aluminum salt is at least one of aluminum nitrate, aluminum chloride, and aluminum acetate; The amount of at least one of the magnesium salt, calcium salt, and aluminum salt added is 5-30% of the mass of the asphalt; The reaction is carried out at a temperature of 40-60℃ for 4-8 hours. Step S2, Preparation of precursor: The modified bitumen was dispersed in deionized water, then mixed evenly with silica sol, and dried to obtain the precursor. Step S3, carbonization: The precursor is carbonized to obtain the carbonized product. Step S4, Remove the template: The template in the carbonization product is removed to obtain a porous carbon material.

2. The preparation method according to claim 1, characterized in that, Step S1 also includes at least one of the following features (a)-(d): (a) When the acid is a mixture of concentrated sulfuric acid and concentrated nitric acid, the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixture is 1:4-4:1; (b) The weight-to-volume ratio of asphalt to acid is 1g:3mL-1g:5mL; (c) The acid modification treatment is performed at a temperature of 50-80℃ for 2-8 hours; (d) The asphalt is at least one of coal tar pitch, petroleum asphalt, and naphthalene pitch.

3. The preparation method according to claim 1 or 2, characterized in that, Step S1 also includes: placing the mixture in an ice-water bath, slowly adding water to dilute the pH of the mixture to 1-3, and ensuring that the temperature of the mixture does not exceed 60°C during the dilution process.

4. The preparation method according to claim 1, characterized in that, Step S2 also includes at least one of the following features (j)-(l): (j) The mass ratio of the modified bitumen to silica sol is 1:2-2:1; (k) The silica sol contains 10-30% silica by mass and has a particle size of 3-50 nm. (l) The drying process is evaporative drying.

5. The preparation method according to claim 1, characterized in that, In step S3, The carbonization process is carried out at a temperature of 800-1200℃, in a nitrogen or argon atmosphere, for a time of 1-6 hours. The heating rate of the carbonization process is 1-8℃ / min.

6. A porous carbon material, characterized in that, The porous carbon material satisfies the following characteristics: (a) Specific surface area of ​​800-2000 m² / g, total pore volume of 0.8-1.5 cm³ / g; (b) Based on the pore volume ratio The proportion of pores with a pore size distribution of 2-5 nm is 70-90%; The proportion of pores with a pore size distribution of 5-10 nm is 8-25%; The proportion of pores with a pore size distribution of 10-50 nm is 2-20%; Furthermore, the sum of the pore volume percentages of the three pore sizes mentioned above is 100%; (c) The porous carbon material is prepared by the preparation method according to any one of claims 1-5.

7. A silicon-carbon material, characterized in that, Silicon is obtained by depositing silicon in the pores of the porous carbon material described in claim 6 using chemical vapor deposition.

8. A battery negative electrode, characterized in that, Includes the silicon-carbon material as described in claim 7.

9. A battery, characterized in that, Includes the negative electrode as described in claim 8.

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