A porous carbon material for silicon-carbon negative electrode and its preparation method and application

Abstract

The present invention discloses a porous carbon material for silicon-carbon negative electrode, and its preparation method and application, belonging to the technical field of lithium-ion batteries. Asphalt and mixed acid are uniformly mixed and then heated to fully react to obtain acid-modified asphalt; the acid-modified asphalt is dispersed in deionized water to prepare an asphalt aqueous solution, and then melamine and KOH are added in sequence, dispersed uniformly to obtain a mixed liquid, and dried to obtain a precursor powder; the precursor powder is carbonized under nitrogen protection, and then CO2 or water vapor or a mixture of the two is introduced for activation; the activated product is washed and dried to obtain a porous carbon material. The material obtained by the present invention has excellent conductivity, stability and high loading capacity for silicon, and can be applied to the field of lithium-ion battery negative electrode materials. The silicon-carbon negative electrode prepared with the porous carbon material as a carrier is applied to lithium-ion batteries, which can achieve the technical effects of high capacity density and long cycle.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a porous carbon material for use in silicon-carbon negative electrodes, and a preparation method and application thereof. Background Art

[0002] In recent years, silicon materials have been widely considered to be a strong competitor to replace traditional graphite in lithium-ion batteries due to their abundant resources and high capacity. However, problems such as relatively low initial efficiency, large volume expansion, and weak dynamic performance in applications have limited the rapid application of silicon materials.

[0003] At present, the above problems are expected to be solved by depositing silicon in the pores of porous carbon, but the low-cost acquisition of porous carbon materials has not yet been fully realized, which to a certain extent limits the development of silicon-carbon negative electrodes and high-capacity density lithium-ion batteries using silicon-carbon negative electrodes as raw materials. The route of manufacturing porous carbon using resin as raw material has high raw material cost and low yield. The porous carbon using biomass as raw material has large fluctuations in biomass components and impurity content, resulting in weak performance of the prepared porous carbon and is not widely accepted by the market. The preparation of porous carbon using coal tar or petroleum residue by-product asphalt has the advantages of low cost, fixed components, and high yield, but its development is limited by imperfect preparation technology and product performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a porous carbon material for silicon-carbon negative electrode, its preparation method and application, and to prepare a silicon-carbon negative electrode using the porous carbon material as a carrier and apply it to lithium-ion batteries, which has the characteristics of high capacity density and long cycle stability.

[0005] To solve the above technical problems, according to one aspect of the present invention, a method for preparing a porous carbon material for a silicon-carbon negative electrode is provided, comprising:

[0006] Step 1: Mix asphalt with mixed acid in a mass ratio of 1:1-1:3, wherein the mixed acid is prepared by concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:2-3:1, and fully react at 55°C-65°C. After cooling, filter and wash to neutrality to obtain acid-modified asphalt;

[0007] Step 2: Dispersing the acid-modified asphalt obtained in step 1 in deionized water to prepare an asphalt aqueous solution, then sequentially adding melamine and KOH to the asphalt aqueous solution in a mass ratio of acid-modified asphalt: melamine: KOH = 100:5-20:30-100, stirring and dispersing the mixture to obtain a mixed solution;

[0008] Step 3, drying the mixed solution obtained in step 2 to obtain a precursor powder;

[0009] Step 4: The precursor powder obtained in step 3 is heated to 600-800°C under nitrogen protection for carbonization, and then CO2 or water vapor or a mixture of the two is introduced at 800-1000°C for activation;

[0010] Step 5: Wash the activated product with hydrochloric acid until it becomes neutral, then wash it with deionized water and dry it to obtain a porous carbon material.

[0011] Furthermore, in step 1, the mass concentration of the concentrated sulfuric acid is 98%, and the mass concentration of the concentrated nitric acid is 65-68%.

[0012] Furthermore, in step 1, the asphalt and the mixed acid are stirred and reacted at 60°C.

[0013] Furthermore, in step 2, the mass concentration of the asphalt aqueous solution is 20%.

[0014] Furthermore, in step three, the mixed solution is dried at 80° C. for 12 hours to obtain a precursor powder.

[0015] Furthermore, in step 4, the temperature is raised to 600-800° C. at 5° C. / min and then carbonized at a constant temperature for 3 hours.

[0016] Furthermore, in step 4, the CO2, water vapor or a mixed gas thereof is introduced at a flow rate of 500 mL / min.

[0017] Furthermore, in step 4, the volume ratio of the mixed gas is CO2:water vapor=1:1-3:1.

[0018] According to one aspect of the present invention, provided is a porous carbon material for silicon-carbon negative electrode obtained by the above preparation method.

[0019] According to another aspect of the present invention, provided is the use of the porous carbon material in preparing anode materials for lithium-ion batteries and lithium-ion batteries.

[0020] This invention uses asphalt as raw material and utilizes a carbon-activation integrated process to produce a cost-effective porous carbon material through mixed acid modification, combined with heteroatom introduction and physical and chemical synergistic pore creation. This combined mixed acid modification, heteroatom introduction, and physical and chemical synergistic pore creation significantly enhances the specific surface area and multi-level pore distribution of the porous carbon, increases adsorption functional groups and electrical conductivity, and reduces raw material costs.

[0021] The material obtained by this invention has excellent conductivity, stability, and high silicon loading capacity, and can be used in the field of lithium-ion battery anode materials. Silicon-carbon anodes prepared using this porous carbon material as a carrier for lithium-ion batteries can achieve high capacity density and long cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the first charge and discharge curve of the negative electrode material in Example 4;

[0023] Figure 2 This is a graph showing the rate cycle capacity retention of the negative electrode assembled battery in Example 4. DETAILED DESCRIPTION

[0024] The basic concept of the present invention is to mix low-cost asphalt with concentrated sulfuric acid and concentrated nitric acid for acidification treatment to obtain acid-modified asphalt; dissolve the acid-modified asphalt in water to form an asphalt aqueous solution, add melamine and potassium hydroxide to disperse evenly and then dry; then carbonize and activate the dried product, wash and dry it to obtain a porous carbon material, and deposit silicon based on the porous carbon for application in lithium-ion batteries.

[0025] Based on this, a typical embodiment of the present invention provides a method for preparing a porous carbon material for a silicon-carbon negative electrode, comprising the following steps 1 to 5.

[0026] Step 1: Mix asphalt with mixed acid in a mass ratio of 1:1-1:3, wherein the mixed acid is prepared by concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:2-3:1, and fully react at 55°C-65°C. After cooling, filter and wash to neutrality to obtain acid-modified asphalt.

[0027] In step 1, mixed acid is added to modify the asphalt. The mass ratio of asphalt to mixed acid can be arbitrarily selected within the range of 1:1-1:3, for example, 1:1, 1:1.5, 1:2, 1:2.5, 1:3.

[0028] The mass concentration of concentrated sulfuric acid is 98%, and the mass concentration of concentrated nitric acid is 65-68%, for example, 65%, 66%, 67%, and 68%.

[0029] In step 1, the asphalt and the mixed acid react under heating conditions, for example, at 55° C., 60° C., or 65° C. Preferably, the asphalt and the mixed acid react at 60° C. for 2 hours under stirring.

[0030] Step 2: Disperse the acid-modified asphalt obtained in step 1 in deionized water to prepare an asphalt aqueous solution. Then, add melamine and KOH to the asphalt aqueous solution in sequence at a mass ratio of acid-modified asphalt: melamine: KOH = 100:5-20:30-100, and stir and disperse evenly to obtain a mixed solution.

[0031] In this step, after adding melamine, nitrogen doping is used to improve electronic conductivity and enhance rate performance.

[0032] In step 2, the mass concentration of the asphalt aqueous solution prepared by dispersing the acid-modified asphalt in deionized water is 20%.

[0033] Step three, drying the mixed solution obtained in step two to obtain precursor powder.

[0034] Preferably, the mixed solution is dried at 80° C. for 12 hours to obtain a precursor powder.

[0035] Step 4: The precursor powder obtained in step 3 is heated to 600-800° C. under nitrogen protection for carbonization, and then CO 2 or water vapor or a mixture of the two is introduced at 800-1000° C. for activation.

[0036] In this step, physical-chemical synergistic pore formation occurs during activation. Activation with CO2, water vapor or their mixed gases can significantly increase the specific surface area and optimize the multi-level pore structure, providing sufficient space for silicon deposition while improving the volume expansion of silicon during the cycle.

[0037] In step 4, the precursor powder is subjected to an integrated carbonization and activation process. During carbonization, the temperature is preferably increased to 600-800°C at a rate of 5°C / min, and the carbonization time is preferably 3 hours.

[0038] During activation, the CO2 or water vapor, or a mixed gas of CO2 and water vapor, is preferably introduced at a flow rate of 500 mL / min, wherein the volume ratio of the mixed gas is preferably CO2:water vapor = 1:1-3:1.

[0039] Step 5: Wash the activated product with hydrochloric acid until it becomes neutral, then wash it with deionized water and dry it to obtain a porous carbon material.

[0040] In the above implementation, asphalt is first modified with mixed acid: concentrated sulfuric acid and nitric acid sulfonate and oxidize the asphalt, introducing oxygen-containing functional groups and enhancing its hydrophilicity. Heteroatom doping is then performed: melamine is decomposed at high temperatures to produce a nitrogen-doped carbon skeleton, improving conductivity and stability.

[0041] In the above-mentioned embodiment, chemical and physical methods are used to create pores in a coordinated manner, achieving the preparation of porous carbon with a controlled multi-level porosity from micropores to mesopores. Physical activation simultaneously increases the oxygen-containing functional groups, thereby enhancing the porous carbon's pores' adsorption capacity for silane gas. In step four, the integrated carbonization and activation process simplifies the process and reduces manufacturing costs.

[0042] The technical solutions claimed in the present invention are further illustrated below by means of some examples. However, the examples and comparative examples are intended to illustrate the embodiments of the present invention and do not exceed the scope of the subject matter of the present invention. The scope of protection of the present invention is not limited by the examples. Unless otherwise specified, the materials and reagents used in the present invention can be obtained from commercial products in the art. Example 1

[0043] Asphalt and mixed acid were mixed in a mass ratio of 1:1, wherein the mixed acid was prepared according to concentrated sulfuric acid: concentrated nitric acid = 3:1 (volume ratio), stirred and reacted at 60°C for 2 hours, filtered after cooling, and washed with deionized water until neutral to obtain acid-modified asphalt.

[0044] The acid-modified asphalt was dispersed in deionized water and stirred evenly to prepare an asphalt aqueous solution with a mass concentration of 20%; then, melamine and KOH were added to the asphalt aqueous solution in sequence at a mass ratio of acid-modified asphalt: melamine: KOH = 100:20:100, and the mixture was stirred and dispersed evenly to obtain a mixed solution.

[0045] The mixed solution was vacuum dried at 80° C. for 12 hours to obtain a dry precursor powder.

[0046] The precursor powder was placed in a tubular furnace, heated to 650°C under nitrogen protection, and kept at this temperature for 2 hours; then a mixed gas was introduced at a rate of 500 mL / min, with a carbon dioxide: water vapor ratio of 2:1 (volume ratio) in the mixed gas, and the temperature was raised to 850°C, kept at this temperature for 3 hours, and then cooled with nitrogen.

[0047] The cooled product was washed with 2 mol / L hydrochloric acid until neutral, then washed with deionized water and dried to obtain a porous carbon material.

[0048] The porous carbon material was placed in a fluidized bed reactor at 550°C, with a silane-argon mixture (the volume ratio of silane to argon was 1:9) passing through it at a rate of 30 mL / min for 25 minutes, and then maintained for 3 hours for deposition and cracking. Then, a methane-nitrogen mixture (the volume ratio of methane to nitrogen was 8:2) was introduced and carbon deposition and coating were carried out at 900°C for 30 minutes to produce a silicon-carbon negative electrode that can be used for lithium-ion batteries.

[0049] Example 2-17

[0050] On the basis of Example 1, the acid ratio, asphalt ratio, solution ratio, mixed gas ratio, carbonization temperature and activation temperature were adjusted. The specific parameter differences involved are shown in Table 1.

[0051] Comparative Example 1

[0052] Asphalt and mixed acid are mixed in a mass ratio of 1:2, wherein the mixed acid is prepared in a volume ratio of concentrated sulfuric acid: concentrated nitric acid = 3:1, stirred and reacted at 60°C for 2 hours, filtered after cooling, and washed with deionized water until neutral to obtain acid-modified asphalt.

[0053] The acid-modified asphalt was dispersed in deionized water and stirred evenly to prepare an asphalt aqueous solution with a mass concentration of 20%; KOH was added at a mass ratio of acid-modified asphalt: KOH = 100:100, and the mixture was stirred and dispersed evenly to obtain a mixed solution.

[0054] The mixed solution was vacuum dried at 80° C. for 12 hours to obtain a dry precursor powder.

[0055] The precursor powder was placed in a tubular furnace, heated to 650°C under nitrogen protection, and kept at this temperature for 2 hours; then a mixed gas was introduced at a rate of 500 mL / min, with a carbon dioxide: water vapor ratio of 2:1 (volume ratio) in the mixed gas, and the temperature was raised to 850°C, kept at this temperature for 3 hours, and then cooled with nitrogen.

[0056] The cooled product was washed with 2 mol / L hydrochloric acid until neutral, then washed with deionized water and dried to obtain a porous carbon material.

[0057] The porous carbon material was placed in a fluidized bed reactor at 550°C, with a silane-argon mixture (the volume ratio of silane to argon was 1:9) passing through it at a rate of 30 mL / min for 25 minutes, and then maintained for 3 hours for deposition and cracking. Then, a methane-nitrogen mixture (the volume ratio of methane to nitrogen was 8:2) was introduced and carbon deposition and coating were carried out at 900°C for 30 minutes to produce a silicon-carbon negative electrode that can be used for lithium-ion batteries.

[0058] Comparative Example 2

[0059] Asphalt and mixed acid are mixed in a mass ratio of 1:2, wherein the mixed acid is prepared in a volume ratio of concentrated sulfuric acid: concentrated nitric acid = 3:1, stirred and reacted at 60°C for 2 hours, filtered after cooling, and washed with deionized water until neutral to obtain acid-modified asphalt.

[0060] The acid-modified asphalt was dispersed in deionized water and stirred evenly to prepare an asphalt aqueous solution with a mass concentration of 20%; melamine and KOH were added in sequence with a mass ratio of acid-modified asphalt: melamine: KOH = 100:20:100, and the mixture was stirred and dispersed evenly to obtain a mixed solution.

[0061] The uniformly dispersed mixed solution was vacuum dried at 80°C for 12 hours to obtain dry powder.

[0062] The dried powder was placed in a tube furnace, heated to 650°C under nitrogen protection, and kept at this temperature for 2 hours; then the temperature was continued to be raised to 850°C under N2 atmosphere, kept at this temperature for 3 hours, and then cooled.

[0063] The cooled product was washed with 2 mol / L hydrochloric acid until neutral, then washed with deionized water and dried to obtain a porous carbon material.

[0064] The porous carbon material was placed in a fluidized bed reactor at 550°C, with a silane-argon mixture (the volume ratio of silane to argon was 1:9) passing through it at a rate of 30 mL / min for 25 minutes, and then maintained for 3 hours for deposition and cracking. Then, a methane-nitrogen mixture (the volume ratio of methane to nitrogen was 8:2) was introduced and carbon deposition and coating were carried out at 900°C for 30 minutes to produce a silicon-carbon negative electrode that can be used for lithium-ion batteries.

[0065] Table 1 Main preparation conditions of each embodiment and comparative example

[0066]

[0067] Note: In Table 1, the acid ratio refers to the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid; the asphalt ratio refers to the mass ratio of asphalt to the mixed acid. Except for Comparative Example 1, the solution ratio refers to the mass ratio of acid-modified asphalt, melamine, and KOH. In Comparative Example 1, the solution ratio refers to the mass ratio of acid-modified asphalt to KOH. Except for Examples 10, 13, and 2, the activation atmosphere refers to the volume ratio of carbon dioxide to water vapor.

[0068] The yield of the porous carbon materials in the above examples and comparative examples was calculated, and their specific surface area and pore characteristics were tested. Lithium-ion batteries were prepared using the silicon-carbon anodes in the above examples and comparative examples, and their performance was tested. The flow rate for depositing silicon on the porous carbon was designed to achieve a 10% loading, resulting in a theoretical initial discharge capacity of 600 mAh / g.

[0069] Test conditions:

[0070] The yield of the porous carbon material prepared in the comparative example and the example = the mass of the porous carbon obtained / the mass of the input asphalt × 100%.

[0071] The specific surface area of the porous carbon materials prepared in the comparative examples and the examples was tested by nitrogen adsorption according to the BET method, and the void characteristics were tested by mercury intrusion porosimetry.

[0072] The silicon-carbon material prepared in the comparative example and the embodiment was used as the negative electrode material, mixed with a binder polyvinylidene fluoride (PVDF) and a conductive agent (Super-P) in a mass ratio of 80:10:10, and an appropriate amount of N-methylpyrrolidone (NMP) was added as a solvent to form a slurry, which was coated on a copper foil and prepared into a negative electrode sheet by vacuum drying and roller pressing; a metallic lithium sheet was used as the counter electrode, and a 1 mol / L LiPF6 three-component mixed solvent was used as an electrolyte mixed in the ratio of EC:DMC:EMC=1:1:1 (v / v). A polypropylene microporous membrane was used as a diaphragm, and the cells were assembled into a CR2032 button cell in a glove box filled with inert gas.

[0073] The charge and discharge test of button batteries was carried out on the battery testing system of Wuhan Blue Electric Electronics Co., Ltd. at room temperature, with a constant current of 0.1C and a charge and discharge voltage limited to 0.005-1.5V, to test the first discharge capacity and first discharge efficiency of the silicon-carbon negative electrode.

[0074] The following method is used to test and calculate the fast charging performance of the material: the prepared negative electrode material is charged and discharged at 0.1C, and its discharge capacity is marked as 0.1C / 0.1C capacity; 0.3C charge / 0.3C discharge, and its discharge capacity is marked as 0.3C / 0.3C capacity; 0.5C charge / 0.5C discharge, and its discharge capacity is marked as 0.5C / 0.5C capacity; respectively, compared with the 0.1C / 0.1C capacity to evaluate the rate performance, 1Rate%=0.1C / 0.1C capacity ÷ 0.1C / 0.1C capacity × 100%, 3Rate%=0.3C / 0.3C capacity ÷ 0.1C / 0.1C capacity × 100%, 5Rate%=0.5C / 0.5C capacity ÷ 0.1C / 0.1C capacity × 100%.

[0075] The following method was used to test and calculate the fast charge cycle performance of the material: the prepared negative electrode material was charged and discharged at 0.3C, and the capacity retention rate after 30 cycles was evaluated. The capacity retention rate = capacity after 30 cycles of 0.3C charge and discharge / 0.1C charge and discharge capacity in the first week × 100%.

[0076] Table 2. Physical and electrochemical properties of materials in various examples and comparative examples

[0077]

[0078] Comparative Example 1: Compared to Example 4, in which no melamine was added and other conditions were the same as in Example 4, the 30-cycle capacity retention in Comparative Example 1 was 86.3%, significantly lower than the 96.9% in Example 4. This indicates that the absence of the nitrogen-doped carbon layer weakened the conductive network, resulting in reduced lithium-ion transport efficiency. This indicates that nitrogen doping with melamine significantly improves initial efficiency and cycling stability, while its absence leads to a significant decline in material performance.

[0079] Comparative Example 2 Compared with Example 4, Comparative Example 2 does not use a mixed gas of CO2 and water vapor for activation (only N2 is introduced), and other conditions are the same. The mesopore ratio of the porous carbon material obtained in Comparative Example 2 is 17.2%, which is much lower than the mesopore ratio of 27.5% of the porous carbon material obtained in Example 4, indicating that physical activation is crucial to improving the mesopore ratio of porous carbon. The mesopore ratio has a significant effect on the cycle stability. The fast charge cycle retention rate of Comparative Example 2 is 84.5%, which is significantly lower than 96.9% of Example 4. This shows that mixed gas activation is a key step in increasing the mesopore ratio, optimizing the pore structure and reducing the volume expansion of silicon. Although its absence significantly affects the first efficiency and rate cycle performance.

[0080] In summary, the comparison between the comparative examples and the exemplary embodiments fully demonstrates that the synergistic effect of nitrogen doping of melamine and physical and chemical activation significantly increases the specific surface area of porous carbon, optimizes the pore distribution, and improves the electronic conductivity, thereby achieving high initial efficiency, excellent fast charging performance and long cycle stability of the silicon-carbon negative electrode.

Claims

1. A method for preparing a porous carbon material for a silicon-carbon negative electrode, characterized in that: include: Step 1: Mix asphalt with mixed acid in a mass ratio of 1:1-1:3, wherein the mixed acid is prepared by concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:2-3:1, and fully react at 55°C-65°C. After cooling, filter and wash to neutrality to obtain acid-modified asphalt; the mass concentration of the concentrated sulfuric acid is 98%, and the mass concentration of the concentrated nitric acid is 65-68%; Step 2: Dispersing the acid-modified asphalt obtained in step 1 in deionized water to prepare an asphalt aqueous solution, then sequentially adding melamine and KOH to the asphalt aqueous solution in a mass ratio of acid-modified asphalt: melamine: KOH = 100:5-20:30-100, stirring and dispersing the mixture to obtain a mixed solution; Step 3, drying the mixed solution obtained in step 2 to obtain a precursor powder; Step 4: The precursor powder obtained in step 3 is heated to 600-800°C under nitrogen protection for carbonization, and then CO2 or water vapor or a mixture of the two is introduced at a temperature of 800-1000°C for activation; Step 5: Wash the activated product with hydrochloric acid until it becomes neutral, then wash it with deionized water and dry it to obtain a porous carbon material.

2. The method for preparing a porous carbon material for a silicon-carbon negative electrode according to claim 1, wherein: In step 1, the asphalt and the mixed acid are stirred and reacted at 60°C.

3. The method for preparing a porous carbon material for a silicon-carbon negative electrode according to claim 2, wherein: In step 2, the mass concentration of the asphalt aqueous solution is 20%.

4. The method for preparing a porous carbon material for a silicon-carbon negative electrode according to claim 1 or 3, characterized in that: In step 3, the mixed solution is dried at 80° C. for 12 hours to obtain a precursor powder.

5. The method for preparing a porous carbon material for a silicon-carbon negative electrode according to claim 4, wherein: In step 4, the temperature is raised to 600-800°C at 5°C / min and then carbonized at a constant temperature for 3 hours.

6. The method for preparing a porous carbon material for a silicon-carbon negative electrode according to claim 5, wherein: In step 4, the CO2, water vapor or a mixture thereof is introduced at a flow rate of 500 mL / min.

7. The method for preparing a porous carbon material for a silicon-carbon negative electrode according to claim 6, wherein: In step 4, the volume ratio of the mixed gas is CO2: water vapor = 1:1-3:

1.

8. The porous carbon material for silicon-carbon negative electrode obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the porous carbon material for silicon-carbon negative electrode according to claim 8 in preparing negative electrode materials for lithium-ion batteries.

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