Porous carbon material applied to silicon-carbon negative electrode as well as preparation method and application of porous carbon material

Abstract

The invention discloses a porous carbon material applied to a silicon-carbon negative electrode as well as a preparation method and application of the porous carbon material, and belongs to the technical field of lithium ion batteries. Uniformly mixing asphalt and mixed acid, heating and fully reacting to obtain acid modified asphalt; dispersing the acid modified asphalt in deionized water to prepare an asphalt aqueous solution, sequentially adding melamine and KOH, uniformly dispersing to obtain a mixed solution, and drying to obtain precursor powder; carbonizing the precursor powder under the protection of nitrogen, and then introducing CO2 or water vapor or mixed gas of the CO2 and the water vapor for activation; and washing and drying the activated product to obtain the porous carbon material. The obtained material has excellent conductivity, stability and high silicon loading performance, and can be applied to the field of lithium ion battery negative electrode materials, a silicon-carbon negative electrode prepared by taking the porous carbon material as a carrier is applied to a lithium ion battery, and the technical effects of high capacity density and long circulation can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries. Specifically, it relates to a porous carbon material applied to a silicon-carbon negative electrode, its preparation method and application. Background Art

[0002] In recent years, due to its rich resources and high capacity, silicon materials are generally regarded as strong competitors to replace traditional graphite in the application of lithium-ion batteries. However, problems such as low initial efficiency, large volume expansion, and weak kinetic performance shown by silicon materials in applications limit the rapid application of silicon materials.

[0003] Currently, depositing silicon in the pores of porous carbon is expected to solve the above problems. However, the low-cost acquisition of porous carbon materials has not been fully realized yet, which to a certain extent restricts 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. For porous carbon made from biomass, the biomass components and impurity content fluctuate greatly, resulting in weak performance of the prepared porous carbon and it not being widely accepted by the market. Preparing porous carbon from coal tar or petroleum residue pitch by-products has advantages such as low cost, fixed components, and high yield, but its development is restricted due to 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 applied to a silicon-carbon negative electrode, its preparation method and application. Using this porous carbon material as a carrier to prepare a silicon-carbon negative electrode and apply it to a lithium-ion battery 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 preparation method of a porous carbon material applied to a silicon-carbon negative electrode is provided, including: Step 1: Mix asphalt with a mixed acid in a mass ratio of 1:1 - 1:3, where the mixed acid is prepared by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:2 - 3:1, fully react at 55°C - 65°C, cool, filter, and wash until neutral to obtain acid-modified asphalt; Step 2: Disperse the acid-modified asphalt obtained in Step 1 in deionized water to prepare an asphalt aqueous solution. Then, by mass ratio, add melamine and KOH to the asphalt aqueous solution in an amount of acid-modified asphalt:melamine:KOH = 100:5 - 20:30 - 100, and stir and disperse evenly to obtain a mixed solution; Step 3: Dry the mixed solution obtained in Step 2 to obtain a precursor powder; Step 4: Heat the precursor powder obtained in Step 3 to 600 - 800 °C for carbonization under nitrogen protection, and then introduce a mixed gas composed of CO2 or water vapor or both at 800 - 1000 °C for activation; Step 5: Wash the activated product with hydrochloric acid until neutral, then wash with deionized water and dry to obtain the porous carbon material.

[0006] Further, 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%.

[0007] Further, in Step 1, the pitch and the mixed acid are stirred and reacted at 60 °C.

[0008] Further, in Step 2, the mass concentration of the pitch aqueous solution is 20%.

[0009] Further, in Step 3, the mixed solution is dried at 80 °C for 12 hours to obtain the precursor powder.

[0010] Further, in Step 4, heat to 600 - 800 °C at a rate of 5 °C / min and then keep the temperature constant for carbonization for 3 hours.

[0011] Further, in Step 4, introduce the CO2, water vapor or their mixed gas at a flow rate of 500 mL / min.

[0012] Further, in Step 4, the volume ratio of the mixed gas is CO2: water vapor = 1:1 - 3:1.

[0013] According to one aspect of the present invention, provided is a porous carbon material for silicon-carbon anodes obtained by the above preparation method.

[0014] According to another aspect of the present invention, provided is the application of the porous carbon material in the preparation of anode materials for lithium-ion batteries and lithium-ion batteries.

[0015] The present invention uses pitch as a raw material and prepares a high-performance and cost-effective porous carbon material through mixed acid modification, combined with heteroatom introduction, and physical and chemical synergistic pore-forming technology, applying a carbon-activation integrated process. Through mixed acid modification combined with heteroatom introduction and physical and chemical synergistic pore-forming technology, the specific surface area and multi-level pore distribution of the porous carbon are significantly improved, the adsorption functional groups and conductivity are increased, and the raw material cost is reduced at the same time.

[0016] The material obtained by the present invention has excellent conductivity, stability and high silicon loading, and can be applied to the field of anode materials for lithium-ion batteries. Using this porous carbon material as a carrier to prepare a silicon-carbon anode for lithium-ion batteries can achieve the technical effects of high capacity density and long cycle life. Description of the Drawings

[0017] Figure 1 It is the first charge-discharge curve graph of the negative electrode material in Example 4; Figure 2 It is the graph of the rate cycling capacity retention rate of the battery assembled with the negative electrode in Example 4. Detailed implementation manners

[0018] 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, disperse evenly and then dry; then perform carbonization and activation treatment on the dried product, and obtain a porous carbon material after washing and drying. Based on this porous carbon, silicon deposition is carried out and applied to lithium-ion batteries.

[0019] Based on this, a preparation method of a porous carbon material applied to a silicon-carbon negative electrode provided by a typical implementation manner of the present invention includes the following steps one to five.

[0020] Step one, mix asphalt with mixed acid according to a mass ratio of 1:1 - 1:3, wherein the mixed acid is prepared from concentrated sulfuric acid and concentrated nitric acid according to a volume ratio of 1:2 - 3:1, fully react at 55°C - 65°C, filter and wash to neutrality after cooling to obtain acid-modified asphalt.

[0021] In step one, when adding mixed acid to modify asphalt, the mass ratio of asphalt to mixed acid can be arbitrarily selected within the range of 1:1 - 1:3, such as 1:1, 1:1.5, 1:2, 1:2.5, 1:3.

[0022] The mass concentration of concentrated sulfuric acid is 98%, and the mass concentration of concentrated nitric acid is 65 - 68%, such as 65%, 66%, 67%, 68%.

[0023] In step one, asphalt reacts with mixed acid under heating conditions, such as reacting at 55°C, 60°C, 65°C. Preferably, asphalt stirs and reacts with mixed acid at 60°C for 2 hours.

[0024] Step two, disperse the acid-modified asphalt obtained in step one in deionized water to prepare an asphalt aqueous solution, and then, by mass ratio, add melamine and KOH to the asphalt aqueous solution in sequence according to the mass ratio of acid-modified asphalt: melamine: KOH = 100:5 - 20:30 - 100, and stir and disperse evenly to obtain a mixed solution.

[0025] In this step, after adding melamine, the electronic conductivity is improved through nitrogen doping to enhance the rate performance.

[0026] In step two, the mass concentration of the asphalt aqueous solution prepared by dispersing the acid-modified asphalt in deionized water is 20%.

[0027] Step 3: Dry the mixture obtained in Step 2 to obtain a precursor powder.

[0028] Preferably, the mixture is dried at 80 °C for 12 hours to obtain a precursor powder.

[0029] Step 4: Heat the precursor powder obtained in Step 3 to 600 - 800 °C for carbonization under nitrogen protection, and then introduce a mixed gas composed of CO2 or water vapor or both at 800 - 1000 °C for activation.

[0030] In this step, physical - chemical synergistic pore - forming occurs during activation. Activation with CO2, water vapor or their mixed gas can significantly increase the specific surface area and optimize the hierarchical pore structure, provide sufficient space for silicon deposition, and at the same time improve the silicon volume expansion during the cycling process.

[0031] In Step 4, the precursor powder is subjected to integrated carbonization and activation treatment. During carbonization, it is preferably heated to 600 - 800 °C at a rate of 5 °C / min, and the carbonization time is preferably 3 hours.

[0032] During activation, the CO2 or water vapor, or the mixed gas composed of CO2 and water vapor is preferably introduced at a flow rate of 500 mL / min. Among them, the volume ratio of the mixed gas is preferably CO2: water vapor = 1:1 - 3:1.

[0033] Step 5: Wash the activated product with hydrochloric acid until neutral, then wash with deionized water and dry to obtain a porous carbon material.

[0034] In the above - mentioned embodiments, first, the asphalt is modified with a mixed acid. Concentrated sulfuric acid and concentrated nitric acid are used to sulfonate and oxidize the asphalt, introducing oxygen - containing functional groups to enhance hydrophilicity. Then, heteroatom doping is carried out. Melamine decomposes at high temperature to form a nitrogen - doped carbon skeleton, improving conductivity and stability.

[0035] In the above - mentioned embodiments, through the synergistic pore - forming of chemical and physical methods, the preparation of hierarchical - pore porous carbon with controlled pores from micropores to mesopores is realized. At the same time, physical activation increases the oxygen - containing functional groups and improves the adsorption capacity of the porous carbon pores for silane gas. In Step 4, the integrated carbonization and activation treatment simplifies the treatment process and reduces the manufacturing cost.

[0036] The following further illustrates the technical solutions claimed in the present invention through some embodiments. However, the embodiments and comparative examples are used to explain the implementation schemes of the present invention and do not exceed the scope of the present invention's theme. The protection scope of the present invention is not limited by the described embodiments. Unless otherwise specifically stated, the materials and reagents used in the present invention can be obtained from commercial products in the art. Example 1

[0037] Mix asphalt with mixed acid in a mass ratio of 1:1, where the mixed acid is prepared according to concentrated sulfuric acid: concentrated nitric acid = 3:1 (volume ratio). Stir and react at 60°C for 2 hours, filter after cooling, and wash with deionized water until neutral to obtain acid-modified asphalt.

[0038] Disperse the acid-modified asphalt in deionized water and stir evenly to prepare an asphalt aqueous solution with a mass concentration of 20%. Then, add melamine and KOH to the asphalt aqueous solution in a mass ratio of acid-modified asphalt: melamine: KOH = 100:20:100, and stir and disperse evenly to obtain a mixed solution.

[0039] Vacuum dry the mixed solution at 80°C for 12 hours to obtain a dry precursor powder.

[0040] Place the precursor powder in a tube furnace, heat it to 650°C under nitrogen protection, and keep it at a constant temperature for 2 hours. Then, introduce a mixed gas at a speed of 500 mL / min. The volume ratio of carbon dioxide to water vapor in the mixed gas is 2:1. Heat it to 850°C, keep it at a constant temperature for 3 hours, and then cool it with nitrogen.

[0041] Wash the cooled product with 2 mol / L hydrochloric acid until neutral, then wash it with deionized water and dry it to obtain a porous carbon material.

[0042] In a fluidized bed reactor, pass a mixed gas of silane and argon (volume ratio of silane to argon is 1:9) at a speed of 30 mL / min for 25 minutes at 550°C for the porous carbon material, keep it for 3 hours for deposition and cracking, and then introduce a mixed gas of methane and nitrogen (volume ratio of methane to nitrogen is 8:2), and carry out carbon deposition coating at 900°C for 30 minutes to obtain a silicon-carbon negative electrode for lithium-ion batteries.

[0043] Examples 2 - 17 On the basis of Example 1, adjust the acid ratio, asphalt ratio, solution ratio, mixed gas ratio, carbonization temperature, and activation temperature. The specific parameter differences involved are shown in Table 1.

[0044] Comparative Example 1 Mix asphalt with mixed acid in a mass ratio of 1:2, where the mixed acid is prepared according to a volume ratio of concentrated sulfuric acid: concentrated nitric acid = 3:1. Stir and react at 60°C for 2 hours, filter after cooling, and wash with deionized water until neutral to obtain acid-modified asphalt.

[0045] Disperse the acid-modified asphalt in deionized water, stir evenly, and prepare an asphalt aqueous solution with a mass concentration of 20%. Add KOH, and the mass ratio of acid-modified asphalt: KOH = 100:100. Stir and disperse evenly to obtain a mixed solution.

[0046] Vacuum dry the mixed solution at 80°C for 12 hours to obtain a dry precursor powder.

[0047] Place the precursor powder in a tube furnace, heat it to 650 °C under nitrogen protection, and keep it at a constant temperature for 2 h; then introduce a mixed gas at a rate of 500 mL / min. In the mixed gas, carbon dioxide: water vapor = 2:1 (volume ratio). Heat it to 850 °C, keep it at a constant temperature for 3 h, and then cool it by introducing nitrogen.

[0048] Wash the cooled product with 2 mol / L hydrochloric acid until neutral, then wash it with deionized water and dry it to obtain a porous carbon material.

[0049] Place this porous carbon material in a fluidized bed reactor at 550 °C, introduce a silane-argon mixed gas (volume ratio of silane to argon is 1:9) at a rate of 30 mL / min for 25 min, keep it for 3 hours for deposition and cracking, and then introduce a methane-nitrogen mixed gas (volume ratio of methane to nitrogen is 8:2), and carry out carbon deposition coating at 900 °C for 30 minutes to prepare a silicon-carbon negative electrode for lithium-ion batteries.

[0050] Comparative Example 2 Mix pitch and mixed acid in a mass ratio of 1:2. Among them, the mixed acid is prepared according to a volume ratio of concentrated sulfuric acid: concentrated nitric acid = 3:1. Stir and react at 60 °C for 2 h, filter after cooling, and wash with deionized water until neutral to obtain acid-modified pitch.

[0051] Disperse the acid-modified pitch in deionized water and stir evenly to prepare an aqueous pitch solution with a mass concentration of 20%; add melamine and KOH in turn, and the mass ratio is acid-modified pitch: melamine: KOH = 100:20:100, and stir and disperse evenly to obtain a mixed solution.

[0052] Vacuum dry the evenly dispersed mixed solution at 80 °C for 12 h to obtain a dry powder.

[0053] Place the dry powder in a tube furnace, heat it to 650 °C under nitrogen protection, and keep it at a constant temperature for 2 h; then continue to heat it to 850 °C under N2 atmosphere, keep it at a constant temperature for 3 h, and then cool it.

[0054] Wash the cooled product with 2 mol / L hydrochloric acid until neutral, then wash it with deionized water and dry it to obtain a porous carbon material.

[0055] Place this porous carbon material in a fluidized bed reactor at 550 °C, introduce a silane-argon mixed gas (volume ratio of silane to argon is 1:9) at a rate of 30 mL / min for 25 min, keep it for 3 hours for deposition and cracking, and then introduce a methane-nitrogen mixed gas (volume ratio of methane to nitrogen is 8:2), and carry out carbon deposition coating at 900 °C for 30 minutes to prepare a silicon-carbon negative electrode for lithium-ion batteries.

[0056] Table 1 Main preparation conditions of each example and comparative example

[0057] 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 Example 10, Example 13, and Comparative Example 2, the activation atmosphere refers to the volume ratio of carbon dioxide to water vapor.

[0058] The yield of the porous carbon materials in the above examples and comparative examples was calculated, and the 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 of porous carbon deposited silicon was designed according to a loading of 10%, and the theoretical initial discharge capacity was 600 mAh / g.

[0059] Test conditions: Yield of the porous carbon materials prepared in the comparative examples and examples = mass of the obtained porous carbon / mass of the input asphalt × 100%.

[0060] The specific surface area of the porous carbon materials prepared in the comparative examples and examples was tested by nitrogen adsorption using the BET method, and the pore characteristics were tested by mercury intrusion porosimetry.

[0061] The silicon-carbon materials prepared in the comparative examples and examples were used as anode materials, mixed with the binder polyvinylidene fluoride (PVDF) and the 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 make a slurry, which was coated on a copper foil and prepared into a negative electrode sheet through vacuum drying and rolling; a metallic lithium sheet was used as the counter electrode, an electrolyte of 1 mol / L LiPF6 ternary mixed solvent mixed according to EC:DMC:EMC = 1:1:1 (v / v) was used, and a polypropylene microporous membrane was used as the separator, and a CR2032 type button cell was assembled in a glove box filled with inert gas.

[0062] The charge-discharge test of the button cell was carried out on the battery test system of Wuhan Blue Electronic Co., Ltd. Under normal temperature conditions, with a constant current charge-discharge of 0.1C, the charge-discharge voltage was limited to 0.005 - 1.5V, and the initial discharge capacity and initial discharge efficiency of the silicon-carbon anode were tested.

[0063] The fast charging performance of the material was tested and calculated by the following method: the prepared anode material was charged at 0.1C / discharged at 0.1C, and its discharge capacity was marked as the 0.1C / 0.1C capacity; charged at 0.3C / discharged at 0.3C, and its discharge capacity was marked as the 0.3C / 0.3C capacity; charged at 0.5C / discharged at 0.5C, and its discharge capacity was marked as the 0.5C / 0.5C capacity; and compared with the 0.1C / 0.1C capacity respectively 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%.

[0064] The fast charging cycle performance of the material was tested and calculated by the following method: the prepared anode material was charged at 0.3C / 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 / capacity of the first week of 0.1C charge and discharge × 100%.

[0065] Table 2. Physical and Electrochemical Property Characterization of Materials in Each Example and Comparative Example

[0066] Comparative Example 1 compared with Example 4, in Comparative Example 1, melamine was not added, and other conditions were the same as those in Example 4. The capacity retention rate of Comparative Example 1 after 30 cycles was 86.3%, which was much lower than 96.9% of Example 4, indicating that the absence of the nitrogen-doped carbon layer weakened the conductive network, resulting in a decrease in the lithium-ion transport efficiency. It can be seen that the nitrogen doping of melamine has an obvious effect on improving the first efficiency and cycle stability, and its absence leads to a significant decline in the material performance.

[0067] Comparative Example 2 compared with Example 4, in Comparative Example 2, the activation with a mixed gas of CO2 and water vapor was not used (only N2 was introduced), and other conditions were the same. The mesopore ratio of the porous carbon material obtained in Comparative Example 2 was 17.2%, which was much lower than the mesopore ratio of 27.5% of the porous carbon material obtained in Example 4, indicating that physical activation is crucial for improving the mesopore ratio of porous carbon. The mesopore ratio has a significant impact on the cycle stability. The fast charging cycle retention rate of Comparative Example 2 was 84.5%, which was significantly lower than 96.9% of Example 4. It can be seen that the activation with a mixed gas is a key step in improving the mesopore ratio, optimizing the pore structure, and reducing the silicon volume expansion, and its absence significantly affects the first efficiency and rate cycle performance.

[0068] In summary, the comparison between the comparative examples and the examples fully demonstrates that the synergistic effect of nitrogen doping of melamine with physical and chemical activation significantly increases the specific surface area of the porous carbon, optimizes the pore distribution, and enhances the electronic conductivity, thereby achieving a high first efficiency, excellent fast charging performance, and long cycle stability of the silicon-carbon negative electrode.

Claims

1. A preparation method of a porous carbon material applied to a silicon-carbon negative electrode, characterized in that, Comprising: Step 1: Mix asphalt and mixed acid in a mass ratio of 1:1 - 1:3, where the mixed acid is prepared by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:2 - 3:

1. React fully at 55°C - 65°C, cool, filter, and wash until neutral to obtain acid-modified asphalt; Step 2: Disperse the acid-modified asphalt obtained in Step 1 in deionized water to prepare an asphalt aqueous solution. Then, in terms of mass ratio, add melamine and KOH to the asphalt aqueous solution in a mass ratio of acid-modified asphalt:melamine:KOH = 100:5 - 20:30 - 100, and stir to disperse evenly to obtain a mixed solution; Step 3: Dry the mixed solution obtained in Step 2 to obtain a precursor powder; Step 4: Heat the precursor powder obtained in Step 3 to 600 - 800°C for carbonization under nitrogen protection, and then introduce CO2 or water vapor or a mixed gas composed of both at a temperature of 800 - 1000°C for activation; Step 5: Wash the activated product with hydrochloric acid until neutral, then wash with deionized water and dry to obtain a porous carbon material.

2. The preparation method of the porous carbon material applied to the silicon-carbon negative electrode according to claim 1, wherein, 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%.

3. The preparation method of the porous carbon material applied to the silicon-carbon negative electrode according to claim 1 or 2, characterized in that, In Step 1, asphalt and the mixed acid are stirred and reacted at 60°C.

4. The preparation method of the porous carbon material applied to the silicon-carbon negative electrode according to claim 3, wherein, In Step 2, the mass concentration of the asphalt aqueous solution is 20%.

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

6. The preparation method of the porous carbon material applied to the silicon-carbon negative electrode according to claim 5, characterized in that, In Step 4, heat to 600 - 800°C at a rate of 5°C / min and keep the temperature constant for carbonization for 3 hours.

7. The preparation method of the porous carbon material applied to the silicon-carbon negative electrode according to claim 6, characterized in that, In Step 4, introduce the CO2, water vapor or their mixed gas at a flow rate of 500 mL / min.

8. The preparation method of the porous carbon material applied to the silicon-carbon negative electrode according to claim 7, characterized in that, In Step 4, the volume ratio of the mixed gas is CO2:water vapor = 1:1 - 3:

1.

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

10. The application of the porous carbon material applied to the silicon-carbon negative electrode according to claim 9 in the preparation of a negative electrode material for a lithium-ion battery.

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