A porous carbon and a preparation method and application thereof

Abstract

The application discloses a kind of porous carbon and its preparation method and application, its preparation method includes: resin is added in organic solvent A, after being dissolved sufficiently, pitch is added and is dispersed treatment, and composite slurry is obtained;Activation agent is dissolved in organic solvent B, and activation agent solution is obtained;Composite slurry and activation agent solution are mixed uniformly, heated to remove organic solvent A and organic solvent B, and composite precursor is obtained;Under inert atmosphere, the composite precursor is heat treated, then after pickling, washing, drying, crushing and sieving, the porous carbon material is obtained, the preparation method of the application is simple, can accurately control pore structure, so that the prepared porous carbon has good mechanical strength, structural stability and high specific surface area, so as to effectively improve the electrochemical performance of silicon-carbon composite material.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials and carbon material preparation technology, specifically relating to a porous carbon, its preparation method and application. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and high operating voltage, have been widely used in consumer electronics, electric vehicles, and energy storage systems. With the increasing demand for high-energy-density batteries, higher requirements are being placed on anode materials. Silicon-based anodes have attracted widespread attention due to their high theoretical specific capacity; however, they suffer from problems such as large volume expansion, low intrinsic electronic conductivity, and poor interface stability during lithium insertion / extraction, which easily lead to particle pulverization, conductive network failure, and rapid capacity decay, limiting their industrial application.

[0003] To address the aforementioned issues, existing technologies typically involve depositing or uniformly loading nano-active silicon components onto the surface, pores, matrix channels, or interparticle voids of a porous carbon framework, and further constructing a carbon coating layer on the composite material surface. The porous carbon provides both an electron transport network and a buffer for silicon volume expansion; its inherent framework strength and structural toughness also help disperse stress generated by repeated silicon expansion and contraction, reducing the risk of particle pulverization and electrode structure damage. The outer carbon coating layer helps stabilize the solid electrolyte interface film and improves the cycling stability of the silicon-carbon anode.

[0004] Currently, the main methods for preparing porous carbon materials include physical activation, chemical activation, and template methods. While physical and chemical activation methods can produce porous carbon with high specific surface areas, they result in a wide pore size distribution, making precise control of the pore structure difficult. Although template methods can better control the pore size distribution, they suffer from complex template preparation processes and cumbersome template removal steps. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a porous carbon and its preparation method. The preparation method of this invention is simple and can precisely control the pore structure, so that the prepared porous carbon has good mechanical strength, structural stability and high specific surface area, thereby effectively improving the electrochemical performance of silicon-carbon composite materials.

[0006] The technical solution of this invention is implemented as follows:

[0007] A method for preparing porous carbon specifically includes the following steps:

[0008] S1: Add the resin to organic solvent A, dissolve it completely, then add asphalt and disperse it to obtain a composite slurry;

[0009] S2: Dissolve the activator in organic solvent B to obtain an activator solution;

[0010] S3: Mix the composite slurry and activator solution evenly, and heat to remove organic solvent A and organic solvent B to obtain the composite precursor;

[0011] S4: The composite precursor is heat-treated under an inert atmosphere, and then subjected to acid washing, water washing, drying, crushing and sieving to obtain the porous carbon material.

[0012] Further, the resin is one or more of epoxy resin, phenolic resin, polyimide resin and furan resin; the mass ratio of the resin to organic solvent A is 1:(1-20).

[0013] Furthermore, both organic solvent A and organic solvent B are one or more of methanol, ethanol, methyl acetal, and acetone.

[0014] Further, in step S2, the mass ratio of organic solvent B to activator is (1-20):1.

[0015] Furthermore, the softening point of the asphalt is 180-220℃; and the mass ratio of asphalt to resin is (9-11):(9-11).

[0016] Furthermore, the activator is one of potassium hydroxide, sodium hydroxide, zinc chloride and phosphoric acid, and the mass ratio of the activator to the total mass of asphalt and resin is (5-7):2.

[0017] Furthermore, the heat treatment process specifically involves heating to 750-850℃ at a heating rate of 2-10℃ / min, and then holding at that temperature for 30-300min.

[0018] The present invention also provides a porous carbon, which is prepared by the porous carbon preparation method described above.

[0019] The present invention also provides a silicon-carbon composite material, which is prepared by the following method: using a porous carbon as a matrix, nano-silicon is deposited on its surface using silane, and then a carbon layer is deposited on the surface; the silicon content in the silicon-carbon composite material is 15-60% by mass.

[0020] The aforementioned silicon-carbon composite material is used in lithium-ion battery anode materials.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. This invention utilizes soluble resins such as phenolic resins dissolved in organic solvents with asphalt, which has a high softening point (180-220℃). A characteristic phase system is constructed within the precursor system, consisting of a continuous resin phase, a dispersed asphalt phase, and an activator evenly distributed. By controlling the ratio of resin to asphalt, the amount of KOH used, and the heat treatment temperature, precise control of the specific surface area and hierarchical pore structure of porous carbon is achieved. The resin possesses excellent cross-linking and curing capabilities and pore structure stability, forming a continuous and stable skeletal carbon phase after carbonization, providing a supporting framework and mechanical strength for the porous carbon. During heat treatment, the asphalt exhibits softening flow, aromatic carbon structure rearrangement, and pore structure evolution capabilities, facilitating the formation of a hierarchical pore structure where micropores, mesopores, and pore openings coexist. It also acts as a soft carbon regulating phase, improving interparticle connectivity and pore hierarchy. Thus, the resin and asphalt complement each other, while the activator performs in-situ etching along the interface and contact area between the two phases, achieving a comprehensive balance in terms of conductive continuity, structural stability, and pore hierarchy in the porous carbon.

[0023] 2. This invention employs a solvent-induced synergistic dispersion method to achieve uniform contact and synergistic distribution of the resin phase, asphalt phase, and activator phase in the precursor stage. Compared with traditional dry mixing, the solvent method allows the resin to be fully dissolved or wetted to form a continuous liquid phase, and further coats and connects the asphalt particles and activator particles, reducing the problems of local agglomeration, local over-activation, and uneven component distribution in dry mixing. In the subsequent controlled volatilization and heat treatment processes, the resin phase preferentially solidifies to form a continuous supporting skeleton, the asphalt phase is distributed between the skeleton and participates in the evolution of pore structure, and the activator etches pores along the relatively uniform contact area in the precursor, ultimately forming a composite structure of a continuous resin skeleton phase, an asphalt-derived carbon dispersed phase, and activated pore-forming hierarchical pores.

[0024] 3. The process of this invention is simple and efficient, requiring only three steps: organic solvent mixing and dispersion, solvent removal, and heat treatment. It eliminates the need for complex template removal or prolonged hydrothermal treatment. Raw materials are widely available, parameters are clearly controllable, and it has good potential for scale-up preparation. The porous carbon prepared by this invention has a compressive strength of up to 276.7 MPa. In silicon-carbon anode applications, the initial discharge specific capacity of the prepared silicon-carbon anode material reaches 968.4 mAh / g, and the specific capacity remains stable during 100 charge-discharge cycles, with an average coulombic efficiency as high as 99.6%. After 100 cycles, it still has a specific capacity of 837.6 mAh / g, with a capacity retention rate of 86.5%, demonstrating good cycle stability. Attached Figure Description

[0025] Figure 1 -Porous carbon and nitrogen adsorption-desorption curves obtained in Example 1.

[0026] Figure 2 - Pore size distribution curve of porous carbon obtained in Example 1.

[0027] Figure 3 - Scanning electron microscope image of porous carbon prepared in Example 1.

[0028] Figure 4 - Scanning electron microscope image of the silicon-carbon anode material prepared in Example 1.

[0029] Figure 5 - X-ray diffraction pattern of silicon-carbon anode material prepared in Example 1.

[0030] Figure 6 -Chart of charge-discharge cycle test of silicon-carbon anode material prepared in Example 1. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0032] Example 1

[0033] A method for preparing porous carbon materials includes the following steps:

[0034] (1) Take 20g of phenolic resin and dissolve it completely in 40g of anhydrous ethanol. Then add it to 20g of asphalt with a softening point of 200℃ and disperse it by ultrasonic stirring to obtain an asphalt / resin solution. At the same time, take 120g of KOH and dissolve it completely in 350g of anhydrous ethanol to obtain a KOH solution.

[0035] (2) Mix the asphalt / resin solution obtained in step (1) with KOH solution, heat and stir at 70°C to remove anhydrous ethanol, then place the mixture in a tube furnace, heat it to 800°C at a heating rate of 5°C / min under an inert atmosphere, hold it at 800°C for 2 hours, and then cool it to room temperature naturally.

[0036] (3) The sample obtained in (3) was washed with 0.5 mol / L HCl, then washed with ultrapure water until neutral, dried at 100℃, and then crushed to about 7 μm by an air jet mill to obtain porous carbon, denoted as PC.

[0037] (4) Place PC in a tube furnace, evacuate, and deposit at 500°C with 160 sccm of silane-argon mixture (5% silane, 95% argon) for 30 min. Then raise the temperature to 800°C and deposit at 100 sccm of acetylene for 2 h to obtain silicon-carbon anode material, denoted as PC@Si.

[0038] Example 2

[0039] This embodiment is the same as embodiment 1, except that in step (1) of this embodiment, the amount of phenolic resin is 18 g and the amount of asphalt is 22 g.

[0040] Example 3

[0041] This embodiment is the same as embodiment 1, except that in step (1) of this embodiment, the amount of phenolic resin is 22 g and the amount of asphalt is 18 g.

[0042] Example 4

[0043] This embodiment is the same as embodiment 1, except that the temperature is raised to 750°C in step (2).

[0044] Example 5

[0045] This embodiment is the same as embodiment 1, except that the temperature is raised to 850°C in step (2).

[0046] Example 6

[0047] This embodiment is the same as embodiment 1, except that the softening point of the asphalt in step (1) is 180℃.

[0048] Example 7

[0049] This embodiment is the same as embodiment 1, except that the mass of KOH in step (1) of this embodiment is 100 g.

[0050] Example 8

[0051] This embodiment is the same as embodiment 1, except that the mass of KOH in step (1) of this embodiment is 140 g.

[0052] Comparative Example 1

[0053] This embodiment is the same as embodiment 1, except that in step (1) of this embodiment, the amount of phenolic resin is 10 g and the amount of asphalt is 30 g.

[0054] Comparative Example 2

[0055] This embodiment is the same as embodiment 1, except that in step (1) of this embodiment, the amount of phenolic resin is 30 g and the amount of asphalt is 10 g.

[0056] Comparative Example 3

[0057] This embodiment is the same as embodiment 1, except that the mass of KOH in step (1) of this embodiment is 80 g.

[0058] Comparative Example 4

[0059] This embodiment is the same as embodiment 1, except that step (1) in this embodiment is as follows: Take 40 g of asphalt with a softening point of 200℃, add 40 g of anhydrous ethanol and stir ultrasonically to disperse it. At the same time, take 120 g of KOH and completely dissolve the KOH in 350 g of anhydrous ethanol.

[0060] Comparative Example 5

[0061] This embodiment is the same as Embodiment 1, except that step (1) in this embodiment is as follows: Take 40 g of phenolic resin and completely dissolve the phenolic resin in 40 g of anhydrous ethanol. At the same time, take 120 g of KOH and completely dissolve the KOH in 350 g of anhydrous ethanol.

[0062] Comparative Example 6

[0063] This embodiment is the same as embodiment 1, except that the softening point of the asphalt in step (1) of this embodiment is 120℃.

[0064] Comparative Example 7

[0065] This embodiment is the same as embodiment 1, except that step (2) in this embodiment is as follows: the asphalt / resin solution obtained in step (1) and KOH solution are mixed and heated and stirred at 70°C to remove anhydrous ethanol. Then, the mixture is placed in a forced-air drying oven at 150°C for 5 h to cure. The mixture is then placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min under an inert atmosphere and kept at that temperature for 2 h before naturally cooling to room temperature.

[0066] Comparative Example 8

[0067] This embodiment is the same as embodiment 1, except that in step (2) of this embodiment, the temperature is raised to 900°C.

[0068] 1. Figure 1 and Figure 2 The figures are the adsorption-desorption curves and pore size distribution curves of the porous carbon and nitrogen gas prepared in Example 1, respectively.

[0069] Depend on Figure 1 It is evident that the porous carbon and nitrogen adsorption-desorption curves exhibit characteristics of both Type I and Type IV curves. In the low relative pressure region (P / P0 < 0.1), the adsorption capacity increases sharply, indicating the presence of abundant micropores. Meanwhile, in the medium-to-high relative pressure region (0.4 < P / P0 < 0.9), a distinct H4-type hysteresis loop is observed, indicating the simultaneous presence of mesopores in the material. Figure 1 It can also be seen that the synthesized porous carbon material has a high specific surface area and pore volume (1959 m). 2 / g and 1.15 cm 3 / g).

[0070] Depend on Figure 2 It can be seen that the porous carbon is mainly composed of micropores and mesopores. The micropores are mainly around 1 nm in diameter, with a small number of pores larger than 50 nm. The mesopore size distribution is within a controllable range of 2-50 nm, indicating that the porous carbon prepared by this invention has excellent uniformity in pore size distribution. During silicon deposition, the mesopores provide a fast channel for the entry of silane gas, reducing the formation of surface floating silicon, while the smaller micropores not only provide silicon loading sites but also inhibit excessive growth of silicon particles to a certain extent. For subsequent charge-discharge cycles, this hierarchical pore structure, due to the relatively concentrated micropore size, ensures uniform distribution of silicon nanoparticles, reduces silicon agglomeration, and inhibits excessive volume expansion during lithium intercalation. An appropriate proportion of mesopores is beneficial for electrolyte wetting and lithium-ion transport, improving electrode reaction kinetics. At the same time, the remaining mesopores, macropores, and interparticle voids after silicon deposition provide a certain buffer space for volume changes during silicon lithium intercalation, reducing the risk of particle pulverization and carbon skeleton damage, and improving the overall electrochemical performance of silicon-carbon anode materials.

[0071] 2. Figure 3 and Figure 4 The images are scanning electron microscope (SEM) images of the porous carbon and silicon-carbon anode materials prepared in Example 1 at 100,000x magnification.

[0072] Depend on Figure 3 It is evident that the surface of porous carbon particles is relatively rough, and a certain number of holes, pits, or open pore structures can be observed, indicating that the material formed a relatively developed surface pore structure after activation treatment.

[0073] Depend on Figure 4 It can be seen that after introducing silicon and further carbon coating, the resulting silicon-carbon anode material still maintains a granular morphology. The surface of the particles is smoother and denser than that of porous carbon, indicating that the silicon deposition / loading and subsequent carbon coating process fill or cover the pores on the surface of porous carbon to a certain extent.

[0074] 3. The X-ray diffraction pattern of the silicon-carbon anode material prepared in Example 1 is shown below. Figure 5 As shown in the figure, the silicon-carbon anode material exhibits a broad diffuse diffraction peak at 2θ = 20°-30°, and a weaker peak packet exists in the 40°-50° region. Overall, there are no sharp crystalline diffraction peaks, indicating that it is a typical amorphous carbon structure with long-range disorder and short-range order. This structure is beneficial for providing buffer space for silicon volume expansion and increasing lithium storage active sites.

[0075] 4. Using the silicon-carbon anode material and silicon powder with a particle size of 300 nm prepared in the above examples and comparative examples as anode materials, coin cells were assembled, and then electrochemical performance was tested. Specifically, the anode material, conductive carbon black (Super P), and lithium-ionized polyacrylic acid (PAALi) were mixed in a mass ratio of 6:2:2 to form a slurry. The slurry was uniformly coated onto a copper foil current collector, dried in a vacuum drying oven at 80 °C for 12 h, and then cut into 12 mm diameter discs as the working electrode. Lithium foil was used as the counter electrode. The separator was made of PP material with a diameter of 19 mm. A 1 mol / L LiPF6 electrolyte (solvent being a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate) was used as the electrolyte, with 1% VC and 5% fluoroethylene carbonate added by volume. The coin cells were assembled in an argon-atmosphere Shanghai Micron glove box.

[0076] The coin cells assembled using the silicon-carbon anode materials prepared in the examples and comparative examples as anode materials underwent 100 charge-discharge cycle tests in a voltage range of 0.01-1.5 V and a discharge rate of 0.3 C. The test results are shown in Table 1. The charge-discharge cycle test curve of the coin cell assembled using the silicon-carbon anode material prepared in Example 1 in a voltage range of 0.01-1.5 V and a discharge rate of 0.3 C is shown below. Figure 6 As shown.

[0077]

[0078] As can be seen from the table above: (1) Although the silicon-based anode prepared from pure nano-silicon has a high initial discharge specific capacity, its initial coulombic efficiency is low and its capacity decays rapidly during cycling. As can be seen from Examples 1-8, the porous carbon prepared by this invention has good framework stability, suitable specific surface area and pore structure, which makes the silicon-carbon anode material have excellent initial discharge specific capacity, initial coulombic efficiency and cycling stability.

[0079] (2) As can be seen from Examples 1-3, Comparative Examples 1-2 and Comparative Examples 4-5, the compounding of asphalt and resin within a reasonable ratio range can produce a synergistic effect, which can improve the stability of the porous carbon skeleton structure while maintaining a high specific surface area and a reasonable hierarchical pore structure, thereby enabling the silicon-carbon anode material to have excellent electrochemical performance.

[0080] (3) As can be seen from Examples 1, 4-5 and Comparative Example 8, the heat treatment temperature has a significant impact on the performance of porous carbon. At a suitable temperature, sufficient activation and pore formation and carbon layer ordering can be ensured, while avoiding micropore expansion and framework strength reduction. This provides sufficient micropore loading sites for subsequent silicon deposition and also inhibits silicon particle growth and limits silicon volume expansion, thereby enabling silicon-carbon anode materials to have high initial discharge specific capacity and cycle stability.

[0081] (4) As can be seen from Examples 1, 6 and Comparative Example 6, the softening point of asphalt also has a certain influence on the performance of porous carbon and silicon-carbon anode materials. The softening point of the asphalt used in this invention is 180-220℃, which makes the asphalt have certain fluidity and volatile matter, and at the same time has high thermal stability, which is conducive to constructing a stable and porous porous carbon skeleton.

[0082] (5) As can be seen from Examples 1, 7-8 and Comparative Example 3, insufficient KOH dosage results in insufficient activation, limited silicon deposition sites, and low initial discharge specific capacity; excessive KOH will damage the carbon skeleton and reduce cycle stability. Therefore, only within a moderate dosage range can the synergy of high specific capacity and high cycle stability be guaranteed.

[0083] (6) As can be seen from Example 1 and Comparative Example 7, the additional curing treatment after removing the organic solvent can easily lead to excessive cross-linking of the resin, while introducing too many oxygen-containing functional groups, increasing surface defects and irreversible reaction sites, promoting electrolyte decomposition and SEI film formation, thereby reducing the first coulombic efficiency and capacity utilization.

[0084] Finally, it should be noted that the above embodiments of the present invention are merely illustrative examples and not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing porous carbon, characterized in that, Specifically, the following steps are included: S1: Add the resin to organic solvent A, dissolve it completely, then add asphalt and disperse it to obtain a composite slurry; S2: Dissolve the activator in organic solvent B to obtain an activator solution; S3: Mix the composite slurry and activator solution evenly, and heat to remove organic solvent A and organic solvent B to obtain the composite precursor; S4: The composite precursor is heat-treated under an inert atmosphere, and then subjected to acid washing, water washing, drying, crushing and sieving to obtain the porous carbon material.

2. The method for preparing porous carbon according to claim 1, characterized in that, The resin is one or more of epoxy resin, phenolic resin, polyimide resin and furan resin; the mass ratio of the resin to organic solvent A is 1:(1-20).

3. A method for preparing porous carbon according to claim 1 or 2, characterized in that, Both organic solvent A and organic solvent B are one or more of methanol, ethanol, methyl acetal, and acetone.

4. A method for preparing porous carbon according to claim 1 or 3, characterized in that, In step S2, the mass ratio of organic solvent B to activator is (1-20):

1.

5. The method for preparing porous carbon according to claim 1, characterized in that, The softening point of the asphalt is 180-220℃; and the mass ratio of asphalt to resin is (9-11):(9-11).

6. The method for preparing porous carbon according to claim 1, characterized in that, The activator is one of potassium hydroxide, sodium hydroxide, zinc chloride and phosphoric acid, and the mass ratio of the activator to the total mass of asphalt and resin is (5-7):

2.

7. The method for preparing porous carbon according to claim 1, characterized in that, The heat treatment process specifically involves heating to 750-850℃ at a heating rate of 2-10℃ / min, and then holding at that temperature for 30-300min.

8. A porous carbon, characterized in that, It is prepared by the method for preparing porous carbon according to any one of claims 1-7.

9. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material is prepared by the following method: using a porous carbon as described in claim 8 as a matrix, nano-silicon is deposited on its surface using silane, and then a carbon layer is deposited on the surface; the silicon content in the silicon-carbon composite material is 15-60% by mass.

10. The application of the silicon-carbon composite material according to claim 9 in the negative electrode material of lithium-ion batteries.

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