Preparation method of copper-doped double-crosslinked pitch-based porous carbon, product and application thereof

Abstract

The application discloses a preparation method of copper-doped double-crosslinked asphalt-based porous carbon and a product thereof and application of the porous carbon to preparation of a silicon-carbon negative electrode material, and the preparation method of the porous carbon comprises the following steps: S1, dissolving cellulose in a copper ammonia solution to obtain a uniform solution, adding asphalt, and fully mixing and then drying through heating to obtain a copper ammonia cellulose@asphalt composite material; S2, pre-oxidizing and crosslinking the copper ammonia cellulose@asphalt composite material through heating, and then performing pre-carbonization treatment under a protective atmosphere to obtain carbonized material; and S3, performing activation treatment on the carbonized material to obtain the copper-doped double-crosslinked asphalt-based porous carbon. The asphalt-based porous carbon prepared by the method disclosed by the application has high conductivity and excellent mechanical properties, and the silicon-carbon negative electrode material prepared by taking the asphalt-based porous carbon as a substrate has excellent cycle stability and rate performance.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion batteries, specifically relating to a method for preparing copper-doped double-crosslinked pitch-based porous carbon, its products, and applications. Background Technology

[0002] Silicon is currently the anode material with the highest theoretical capacity, boasting a specific capacity of up to 4200 mAh / g, far exceeding the theoretical capacity of graphite (which has a theoretical capacity of only 372 mAh / g). Furthermore, silicon offers advantages such as low lithium intercalation potential and low cost, making it a promising candidate to replace graphite as the next-generation anode material for lithium-ion batteries. However, as an anode material, silicon experiences significant volume expansion and contraction during lithium intercalation and deintercalation, leading to easy pulverization and detachment from the current collector, resulting in the loss of electrochemical performance.

[0003] Due to the structural stability of carbon materials, their volume change during charge and discharge is relatively small, resulting in good cycle stability. Furthermore, carbon's chemical properties are similar to those of silicon, making it a common composite material for silicon and carbon to mitigate the volume expansion effect of silicon and improve its electrochemical stability. Porous carbon has been widely used in the preparation of novel vapor-deposited silicon-carbon composite materials. However, the high cost of porous carbon preparation processes has limited the industrialization of novel silicon-carbon anodes. Developing high-economic-efficiency porous carbon products holds significant appeal for existing research fields and enterprises.

[0004] Asphalt has a high carbon content, making it an ideal precursor for porous carbon preparation. However, asphalt contains a large number of conjugated benzene ring structures, which easily form graphite-like structures, resulting in low strength of the porous carbon framework and limited tolerance to silicon anode expansion. Furthermore, asphalt-based porous carbon preparation offers limited improvement in conductivity.

[0005] To address the aforementioned issues, most researchers have introduced pre-oxidation processes and modifiers to improve the carbon skeleton strength and conductivity of pitch-based porous carbon. For example, Chinese patent document CN118206115A discloses a high-performance pitch-based porous carbon material and its preparation method. The method includes: step one, mixing coal tar pitch and carbon nanotubes to prepare a precursor; step two, pre-treating and pulverizing the precursor; step three, adding graphene and drying; step four, pre-oxidation treatment; and step five, carbonization and activation treatment. This technical solution introduces various carbon materials, such as graphene and carbon nanotubes, for filling and modification, constructing a multidimensional enriched network, effectively improving the carbon skeleton strength and conductivity of pitch-based porous carbon. The finished porous carbon achieves a conductivity of 25 S cm⁻¹ at 130 MPa. -1The particle strength reaches over 3.0 GPa. However, graphene and carbon nanotubes are expensive to prepare and difficult to mass-produce. Furthermore, the preparation process involves multiple uneven physical mixing processes, which may lead to poor local conductivity and inconsistent distribution of skeletal strength in porous carbon, which is detrimental to the final production of silicon-carbon anodes. Summary of the Invention

[0006] To address the aforementioned problems, this invention discloses a method for preparing copper-doped double-crosslinked pitch-based porous carbon. The prepared pitch-based porous carbon exhibits high conductivity and excellent mechanical properties, and silicon-carbon anode materials prepared using it as a substrate possess both excellent cycle stability and rate performance.

[0007] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing copper-doped double-crosslinked pitch-based porous carbon, comprising:

[0009] S1: Dissolve cellulose in a copper ammonia solution to obtain a homogeneous solution, then add asphalt, mix thoroughly, and then heat and dry to obtain a copper ammonia cellulose@asphalt composite material;

[0010] S2: The cuprammonium cellulose@asphalt composite material is heated for pre-oxidative crosslinking, and then pre-carbonized under a protective atmosphere to obtain carbonized material;

[0011] S3: The carbonized material is activated to obtain copper-doped double-crosslinked pitch-based porous carbon.

[0012] This invention first prepares a homogeneous solution by completely dissolving sparingly soluble cellulose in a copper ammonia solution. This process not only provides a prerequisite for the subsequent full cross-linking between cellulose molecules and pitch molecules, but also introduces copper into the porous carbon to reduce its powder resistance. Subsequent pre-oxidative cross-linking forms a double-cross-linked structure (cross-linking between pitch molecules and additional cross-linking between cellulose and pitch molecules through bridging oxygen), which together improves the overall hardness of the material. Hard carbon nanowires with a cellulose molecular framework are distributed throughout the three-dimensional pitch matrix space, limiting the excessive expansion of nano-silicon particles inside the porous carbon. Finally, pitch-based porous carbon is prepared after pre-carbonization and activation treatment. During the pre-carbonization and activation process, the introduced copper element, high-valence copper, is reduced to elemental copper or low-valence copper, reducing the powder resistance of the porous carbon substrate and thus increasing the conductivity of the silicon-carbon anode. Furthermore, it was found that the introduction of copper and cellulose has a synergistic effect, further improving the particle strength of the pitch-based porous carbon and more effectively mitigating the volume expansion of silicon particles.

[0013] In an optional implementation, step S1 includes at least one of the following features (1) to (7):

[0014] (1) The cellulose includes, but is not limited to, one or more of α-cellulose, β-cellulose, microcrystalline cellulose, and carboxymethyl cellulose, with a number average molecular weight of 2000 to 15000;

[0015] Optionally, the cellulose is selected from one or more of α-cellulose, β-cellulose, and microcrystalline cellulose; more preferably, the cellulose is selected from α-cellulose.

[0016] Optionally, the number-average molecular weight of the cellulose is 5,000 to 15,000.

[0017] (2) The preparation method of the copper ammonia solution includes: reacting 10-20 wt% copper salt solution with 5-15 wt% alkaline solution to generate copper hydroxide precipitate, separating and washing the precipitate, and then adding 15-25 wt% ammonia water until the precipitate dissolves.

[0018] Optionally, the copper salt solution is selected from aqueous solutions soluble in copper, specifically from conventional types in the art, such as copper nitrate, copper sulfate, and copper chloride.

[0019] Optionally, the alkaline solution is selected from aqueous solutions of alkalis, specifically from conventional types in the art; alternatively, the alkali is selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.

[0020] (3) The preparation of the homogeneous solution is carried out at a low temperature of -15 to -5℃;

[0021] (4) The mass ratio of cellulose to copper ammonia solution is 1:(4-16);

[0022] Optionally, the mass ratio of cellulose to copper ammonia solution is 1:(4-8); further optionally, the mass ratio of cellulose to copper ammonia solution is 1:8.

[0023] (5) The asphalt is in powder form with a particle size D. 50 3–9 μm, D max ≤50μm;

[0024] Optionally, the asphalt is selected from conventional types in the art, such as petroleum asphalt, coal tar pitch, mesophase asphalt, naphthalene pitch, etc.; further optionally, the asphalt is selected from petroleum asphalt or coal tar pitch.

[0025] (6) The mass ratio of cellulose to pitch is 1:(25-100);

[0026] Optionally, the mass ratio of cellulose to bitumen is 1:(25-50); further optionally, the mass ratio of cellulose to bitumen is 1:50.

[0027] (7) The heating and drying process is carried out at a temperature of 60-90℃.

[0028] The purpose of drying is to remove the solvent from the system to obtain a fully mixed composite solid.

[0029] In an optional implementation, in step S2:

[0030] Optionally, the pre-oxidative crosslinking is performed at a temperature of 250–350°C.

[0031] Optionally, the pre-oxidative crosslinking time is 1 to 5 hours.

[0032] Optionally, the pre-oxidative crosslinking is carried out at a heating rate of 0.5–5 °C / min.

[0033] Optionally, the pre-oxidative crosslinking is carried out in a rotary kiln, with the air flow rate controlled at 0.5 to 10 L / min and the rotary kiln speed controlled at 5 to 10 rpm.

[0034] Optionally, the pre-carbonization treatment is carried out under a protective atmosphere, which includes one or more of nitrogen, argon, and helium.

[0035] Optionally, the pre-carbonization treatment is carried out at a temperature of 600–800°C.

[0036] Optionally, the pre-carbonization treatment takes 4 to 10 hours.

[0037] Optionally, the pre-carbonization treatment has a heating rate of 0.5–20 °C / min.

[0038] In an optional implementation, step S3, the activation process includes at least one of the following features (1) to (4):

[0039] (1) The activation treatment is selected from physical activation, and the activator is selected from one or more of CO, CO2, water vapor, and oxygen;

[0040] Optionally, the activator is selected from one or more of CO, CO2, and water vapor.

[0041] (2) The activation treatment is performed at a temperature of 700 to 1000°C; optionally, the temperature is 800 to 900°C.

[0042] (3) The activation treatment lasts for 2 to 15 hours;

[0043] (4) The activation process is carried out at a flow rate of 0.01 to 5 kg / h.

[0044] Optionally, in the activation treatment, the flow rate of the activator is 0.1 to 2.5 kg / h.

[0045] Optionally, the activation treatment involves a heating rate of 0.5–20 °C / min.

[0046] Optionally, the activation treatment is carried out in a rotary kiln, and the rotation speed of the rotary kiln is controlled to be 0.5 to 10 rpm.

[0047] Secondly, the present invention also provides a copper-doped double-crosslinked pitch-based porous carbon prepared according to the above method, which has a particle strength of not less than 4.1 GPa and a powder resistance of not more than 0.17 Ω·cm at 20 MPa; it has both high strength and high conductivity.

[0048] Thirdly, the present invention also provides a method for preparing a silicon-carbon anode material, which is prepared by sequentially performing silicon deposition and carbon coating on copper-doped double-crosslinked pitch-based porous carbon as a substrate.

[0049] In an optional embodiment, the silicon deposition includes at least one of the following features (1) to (7):

[0050] (1) The silicon deposition process uses a silicon source gas as the raw material gas.

[0051] Optionally, the silicon source gas is selected from conventional types in the art, including one or more of silane, disilane, dichlorosilane, and trichlorosilane.

[0052] (2) The flow rate of the raw material gas is 1-50 L / h;

[0053] (3) The silicon deposition temperature is 300-800℃;

[0054] (4) The silicon deposition time is 1 to 40 hours;

[0055] (5) The raw material gas also includes carrier gas;

[0056] (6) The carrier gas is selected from nitrogen and / or argon;

[0057] (7) The volume ratio of the carrier gas is 1 to 30% based on the total volume of the raw material gas as 100%.

[0058] In an optional embodiment, the carbon coating includes at least one of the following features (1) to (6):

[0059] (1) The carbon coating uses carbon-containing gas as the raw material.

[0060] (2) The carbon-containing gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes; optionally, the C1-C4 alkanes are selected from methane, ethane, propane, and butane; optionally, the C2-C4 alkenes are selected from ethylene, propylene, butene, and 1,3-butadiene; optionally, the C2-C4 alkynes are selected from acetylene, propyne, and butyne.

[0061] (3) The flow rate of the carbon-coated raw material gas is 1 to 10 L / h;

[0062] (4) The carbon coating is carried out at a temperature of 400–1200°C;

[0063] (5) The carbon coating time is 1 to 10 hours;

[0064] (6) The carbon-coated raw material gas also includes an inert gas.

[0065] Optionally, the inert gas is selected from conventional types in the art, such as nitrogen, argon, etc.

[0066] Fourthly, the present invention also provides a silicon-carbon anode material prepared according to the above method.

[0067] Fifthly, the present invention also provides a lithium-ion battery comprising the aforementioned silicon-carbon anode material.

[0068] Compared with the prior art, the present invention has the following advantages:

[0069] This invention discloses a method for preparing pitch-based porous carbon. Initial pre-oxidation induces cross-linking between pitch molecules, and cellulose molecules and pitch generate additional cross-linking through bridging oxygen. This double-cross-linked structure collectively improves the overall hardness of the material. Hard carbon nanowires with a cellulose molecular framework are distributed throughout the three-dimensional pitch matrix space, limiting the excessive expansion of nano-silicon particles within the porous carbon. Furthermore, copper possesses good ductility and conductivity. The copper element remaining in the raw material solution is incorporated into the pitch matrix during the pre-carbonization step. In the subsequent activation process, high-valence copper is reduced to elemental copper and / or low-valence copper, which not only synergizes with the introduction of cellulose to further improve the particle strength of the pitch-based porous carbon but also helps to mitigate the volume expansion of silicon particles. Moreover, it reduces the powder resistance of the porous carbon substrate, thereby increasing the conductivity of the silicon-carbon anode. In addition, since the substances contained in the precursor preparation are all required for subsequent reactions, acid washing is not required, simplifying the production steps and reducing processing costs. Attached Figure Description

[0070] Figure 1 This is a flowchart of the method for preparing copper-doped double-crosslinked pitch-based porous carbon disclosed in this invention;

[0071] Figure 2 This is a structural diagram of α-cellulose used in Example 1 of the present invention;

[0072] Figure 3 The scanning electron microscope mapping range (a) and the copper element distribution within the selected area (b) of the pitch-based porous carbon in Example 1 of the present invention are shown. Detailed Implementation

[0073] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0074] In the description of this invention, it should be noted that those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. The embodiments of this invention are described below based on its overall structure. Unless otherwise specified, the raw materials used in the embodiments of this invention were all purchased commercially.

[0075] In a first aspect, the present invention provides a method for preparing copper-doped double-crosslinked pitch-based porous carbon, comprising:

[0076] S1: Dissolve cellulose in a copper ammonia solution to obtain a homogeneous solution, then add asphalt, mix thoroughly, and then heat and dry to obtain a copper ammonia cellulose@asphalt composite material;

[0077] S2: The cuprammonium cellulose@asphalt composite material is heated for pre-oxidative crosslinking, and then pre-carbonized under a protective atmosphere to obtain carbonized material;

[0078] S3: The carbonized material is activated to obtain copper-doped double-crosslinked pitch-based porous carbon.

[0079] This invention first prepares a homogeneous solution by completely dissolving sparingly soluble cellulose in a copper ammonia solution. This process not only provides a prerequisite for the subsequent full cross-linking between cellulose molecules and pitch molecules, but also introduces copper into the porous carbon to reduce its powder resistance. Subsequent pre-oxidative cross-linking forms a double-cross-linked structure (cross-linking between pitch molecules and additional cross-linking between cellulose and pitch molecules through bridging oxygen), which together improves the overall hardness of the material. Hard carbon nanowires with a cellulose molecular framework are distributed throughout the three-dimensional pitch matrix space, limiting the excessive expansion of nano-silicon particles inside the porous carbon. Finally, pitch-based porous carbon is prepared after pre-carbonization and activation treatment. During the pre-carbonization and activation process, the introduced copper element, high-valence copper, is reduced to elemental copper or low-valence copper, reducing the powder resistance of the porous carbon substrate and thus increasing the conductivity of the silicon-carbon anode. Furthermore, it was found that the introduction of copper and cellulose has a synergistic effect, further improving the particle strength of the pitch-based porous carbon and more effectively mitigating the volume expansion of silicon particles.

[0080] In an optional implementation, step S1 includes at least one of the following features (1) to (7):

[0081] (1) The cellulose includes, but is not limited to, one or more of α-cellulose, β-cellulose, microcrystalline cellulose, and carboxymethyl cellulose, with a number average molecular weight of 2000 to 15000;

[0082] Optionally, the cellulose is selected from α-cellulose, β-cellulose, and microcrystalline cellulose.

[0083] Experiments revealed that, compared to α-cellulose, β-cellulose, and microcrystalline cellulose, carboxymethyl cellulose had a higher solution viscosity, lower uniformity of liquid-phase mixing, and a slight decrease in the particle strength of the prepared pitch-based porous carbon.

[0084] Alternatively, the cellulose may be selected from α-cellulose.

[0085] The number-average molecular weight of the cellulose can specifically be 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, or any value within the above range. Optionally, the number-average molecular weight of the cellulose is 5000 to 15000.

[0086] Experiments have shown that the particle strength of the prepared pitch-based porous carbon is related to the number-average molecular weight of the cellulose used.

[0087] (2) The preparation method of the copper ammonia solution includes: reacting 10-20 wt% copper salt solution with 5-15 wt% alkaline solution to generate copper hydroxide precipitate, separating and washing the precipitate, and then adding 15-25 wt% ammonia water until the precipitate dissolves.

[0088] Optionally, the copper salt solution is selected from aqueous solutions soluble in copper, specifically from conventional types in the art, such as copper nitrate, copper sulfate, and copper chloride. The concentration of the copper salt solution can specifically be 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, or any value within the above range.

[0089] Optionally, the alkaline solution is selected from aqueous solutions of alkalis, specifically from conventional types in the art; alternatively, the alkali is selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. The concentration of the alkaline solution can specifically be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, or any value within the above range.

[0090] Optionally, the concentration of the ammonia water can be 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, or any value within the above range.

[0091] (3) The preparation of the homogeneous solution is carried out at a low temperature of -15 to -5℃; specifically, it can be -15℃, -14℃, -13℃, -12℃, -11℃, -10℃, -9℃, -8℃, -7℃, -6℃, -5℃ or any value within the above range.

[0092] (4) The mass ratio of cellulose to cuprammonium solution is 1:(4-16); specifically, it can be 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16 or any ratio within the above range. Optionally, the mass ratio of cellulose to cuprammonium solution is 1:(4-8); more preferably, the mass ratio of cellulose to cuprammonium solution is 1:8.

[0093] Experiments have shown that optimizing the mass ratio of cellulose to copper ammonia solution results in more superior particle strength and electrical conductivity of the prepared pitch-based porous carbon.

[0094] (5) The asphalt is in powder form with a particle size D. 50 The value is 3–9 μm, specifically 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or any value within the above range; D max ≤50μm, specifically can be 0.1μm, 0.5μm, 1μm, 2μm, 4μm, 3μm, 4μm, 5μm, 10μm, 20μm, 30μm, 40μm, 50μm or any value within the above range.

[0095] Optionally, the asphalt is selected from conventional types in the art, such as petroleum asphalt, coal tar pitch, mesophase asphalt, naphthalene pitch, etc.; further optionally, the asphalt is selected from petroleum asphalt or coal tar pitch.

[0096] (6) The mass ratio of cellulose to pitch is 1:(25-100); specifically, it can be 1:25, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:100, 1:16 or any ratio within the above range.

[0097] Optionally, the mass ratio of cellulose to bitumen is 1:(25-50); further optionally, the mass ratio of cellulose to bitumen is 1:50.

[0098] Experiments have shown that by optimizing the mass ratio of cellulose to asphalt, the prepared asphalt-based porous carbon exhibits superior particle strength and electrical conductivity.

[0099] (7) The heating and drying temperature is 60 to 90°C, specifically 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or any value within the above range.

[0100] The purpose of drying is to remove the solvent from the system to obtain a fully mixed composite solid.

[0101] In an optional implementation, in step S2:

[0102] Optionally, the pre-oxidative crosslinking temperature is 250–350°C, specifically 250°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, or any value within the above range.

[0103] Optionally, the pre-oxidative crosslinking time is 1 to 5 hours, specifically 1 hour, 1.5 hours, 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours or any value within the above range.

[0104] Optionally, the pre-oxidative crosslinking is carried out at a heating rate of 0.5 to 5 °C / min, specifically 0.5 °C / min, 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min, 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min, 5 °C / min or any value within the above range.

[0105] Optionally, the pre-oxidation crosslinking is carried out in a rotary kiln, with the air flow rate controlled at 0.5 to 10 L / min, specifically 0.5 L / min, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min or any value within the above range; and the rotation speed of the rotary kiln controlled at 5 to 10 rpm, specifically 5 rpm, 6 rpm, 7 rpm, 8 rpm, 9 rpm, 10 rpm or any value within the above range.

[0106] Optionally, the pre-carbonization treatment is carried out under a protective atmosphere, which includes one or more of nitrogen, argon, and helium.

[0107] Optionally, the pre-carbonization treatment is carried out at a temperature of 600 to 800°C, specifically at 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C or any value within the above range.

[0108] Optionally, the pre-carbonization treatment time is 4 to 10 hours, specifically 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, 6.0 hours, 6.5 hours, 7.0 hours, 7.5 hours, 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours, 10 hours or any value within the above range.

[0109] Optionally, the pre-carbonization treatment has a heating rate of 0.5 to 20 °C / min, specifically 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, 15 °C / min, 20 °C / min or any value within the above range.

[0110] In an optional implementation, step S3, the activation process includes at least one of the following features (1) to (4):

[0111] (1) The activation treatment is selected from physical activation, and the activator is selected from one or more of CO, CO2, water vapor, and oxygen;

[0112] Optionally, the activator is selected from one or more of CO, CO2, and water vapor.

[0113] (2) The activation treatment is performed at a temperature of 700 to 1000°C, specifically at 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 950°C, 1000°C or any value within the above range; optionally, the temperature is 800 to 900°C.

[0114] (3) The activation treatment time is 2 to 15 hours, specifically 2 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or any value within the above range.

[0115] (4) In the activation treatment, the flow rate of the activator is 0.01 to 5 kg / h, specifically 0.01 kg / h, 0.05 kg / h, 0.1 kg / h, 0.5 kg / h, 1 kg / h, 1.5 kg / h, 2 kg / h, 2.5 kg / h, 3 kg / h, 3.5 kg / h, 4 kg / h, 4.5 kg / h, 5 kg / h or any value within the above range; optionally, in the activation treatment, the flow rate of the activator is 0.1 to 2.5 kg / h.

[0116] Optionally, the activation treatment involves a heating rate of 0.5–20 °C / min, specifically 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, 15 °C / min, 16 °C / min, 17 °C / min, 18 °C / min, 19 °C / min, 20 °C / min, or any value within the above range.

[0117] Optionally, the activation treatment is carried out in a rotary kiln, and the rotation speed of the rotary kiln is controlled to be 0.5 to 10 rpm, specifically 0.5 rpm, 1 rpm, 2 rpm, 3 rpm, 4 rpm, 5 rpm, 6 rpm, 7 rpm, 8 rpm, 9 rpm, 10 rpm or any value within the above range.

[0118] Secondly, the present invention also provides a copper-doped double-crosslinked pitch-based porous carbon prepared according to the above method, which has a particle strength of not less than 4.1 GPa and a powder resistance of not more than 0.17 Ω·cm at 20 MPa; it has both high strength and high conductivity.

[0119] Thirdly, the present invention also provides a method for preparing a silicon-carbon anode material, which is prepared by sequentially performing silicon deposition and carbon coating on copper-doped double-crosslinked pitch-based porous carbon as a substrate.

[0120] In an optional embodiment, the silicon deposition includes at least one of the following features (1) to (7):

[0121] (1) The silicon deposition process uses a silicon source gas as the raw material gas.

[0122] Optionally, the silicon source gas is selected from conventional types in the art, including one or more of silane, disilane, dichlorosilane, and trichlorosilane.

[0123] (2) The flow rate of the raw material gas is 1 to 50 L / h, specifically 1 L / h, 2 L / h, 3 L / h, 5 L / h, 10 L / h, 15 L / h, 20 L / h, 25 L / h, 30 L / h, 35 L / h, 40 L / h, 45 L / h, 50 L / h or any value within the above range.

[0124] (3) The silicon deposition temperature is 300 to 800°C, specifically 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C or any value within the above range.

[0125] (4) The silicon deposition time is 1 to 40 hours, specifically 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours or any value within the above range.

[0126] (5) The raw material gas also includes carrier gas;

[0127] (6) The carrier gas is selected from nitrogen and / or argon;

[0128] (7) With the total volume of the raw material gas as 100%, the volume ratio of the carrier gas is 1 to 30%, specifically 1%, 5%, 8%, 10%, 15%, 18%, 20%, 25%, 28%, 30% or any value within the above range.

[0129] In an optional embodiment, the carbon coating includes at least one of the following features (1) to (6):

[0130] (1) The carbon coating uses carbon-containing gas as the raw material.

[0131] (2) The carbon-containing gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes; optionally, the C1-C4 alkanes are selected from methane, ethane, propane, and butane; optionally, the C2-C4 alkenes are selected from ethylene, propylene, butene, and 1,3-butadiene; optionally, the C2-C4 alkynes are selected from acetylene, propyne, and butyne.

[0132] (3) The flow rate of the carbon-coated raw material gas is 1 to 10 L / h, specifically 1 L / h, 2 L / h, 3 L / h, 4 L / h, 5 L / h, 6 L / h, 7 L / h, 8 L / h, 9 L / h, 10 L / h or any value within the above range.

[0133] (4) The carbon coating temperature is 400 to 1200℃, specifically 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ or any value within the above range.

[0134] (5) The carbon coating time is 1 to 10 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or any value within the above range.

[0135] (6) The carbon-coated raw material gas also includes an inert gas.

[0136] Optionally, the inert gas is selected from conventional types in the art, such as nitrogen, argon, etc.

[0137] Fourthly, the present invention also provides a silicon-carbon anode material prepared according to the above method.

[0138] Fifthly, the present invention also provides a lithium-ion battery comprising the aforementioned silicon-carbon anode material.

[0139] Example 1

[0140] S1, 15wt% copper nitrate aqueous solution and 10wt% sodium hydroxide aqueous solution react chemically to form copper hydroxide precipitate. The precipitate is separated, washed, and 20wt% ammonia solution is added dropwise until the precipitate dissolves to prepare a copper ammonia solution. At -10℃, α-cellulose (number average molecular weight 12000) and the copper ammonia solution are dissolved at a mass ratio of (1kg:8kg) to obtain a homogeneous solution. Under vigorous stirring, the particle size D... 50 5μm, D max 50 kg of 30 μm powdered petroleum asphalt was added to the above homogeneous solution, and after stirring and mixing for 10 h, it was dried at 80 °C to obtain a cuprammonium cellulose@asphalt composite material.

[0141] S2. Place 50 kg of the composite material in a tube furnace, introduce air at a flow rate of 5 L / min, raise the temperature to 300℃ at 5℃ / min and hold for 4 hours to achieve pre-oxidation of the asphalt. Then switch to nitrogen. When the oxygen content drops below 30 ppm, raise the temperature to 700℃ at 5℃ / min to achieve pre-carbonization of the composite material. The carbonization time is 6 hours.

[0142] S3. Place 30 kg of the above pre-carbonized material in a rotary kiln, set the rotation speed to 5 r / min, and heat to 850℃ at 10℃ / min for steam activation to obtain asphalt-based porous carbon. The steam flow rate is 0.5 kg / h, and the activation time is 12 h.

[0143] The distribution of copper doping on the material surface was observed using scanning electron microscopy and energy dispersive spectroscopy. Figure 3 The image shows the copper element on the surface of the pitch-based porous carbon prepared in step S3 of this embodiment. It is observed that the copper element is relatively uniformly distributed on the porous carbon.

[0144] Example 2

[0145] The preparation process is basically the same as in Example 1, except that in step S1, the mass of the added α-cellulose is replaced with 2 kg.

[0146] Example 3

[0147] The preparation process is basically the same as in Example 1, except that in step S1, the mass of the added α-cellulose is replaced with 0.5 kg.

[0148] Example 4

[0149] The preparation process is basically the same as in Example 1, except that in step S1, the mass of the added copper ammonia solution is replaced with 4 kg.

[0150] Example 5

[0151] The preparation process is basically the same as in Example 1, except that in step S1, the mass of the added copper ammonia solution is replaced with 16 kg.

[0152] Example 6

[0153] The preparation process is basically the same as in Example 1, except that in step S1, α-cellulose is replaced with an equal mass of β-cellulose (number average molecular weight of 5000).

[0154] Example 7

[0155] The preparation process is basically the same as in Example 1, except that in step S1, α-cellulose is replaced with an equal mass of microcrystalline cellulose (number average molecular weight of 3000).

[0156] Example 8

[0157] The preparation process is basically the same as in Example 1, except that in step S1, α-cellulose is replaced with an equal mass of carboxymethyl cellulose (number average molecular weight of 2200).

[0158] Comparative Example 1

[0159] The preparation process is basically the same as in Example 1, except that in step S1, α-cellulose is not added. Instead, 50 kg of powdered petroleum asphalt is directly added to 8 kg of copper ammonia solution, stirred and mixed for 10 h, and then dried at 80 °C to obtain the composite material.

[0160] Comparative Example 2

[0161] The preparation process is basically the same as in Example 1, except that in step S1, the copper ammonia solution is replaced with an equal mass of deionized water, that is, 50 kg of powdered petroleum asphalt is directly added to 8 kg of deionized water, stirred and mixed for 10 h, and then dried at 80 °C to obtain the composite material.

[0162] Comparative Example 3

[0163] The preparation process is basically the same as in Example 1, except that in step S1, α-cellulose is replaced with an equal mass of epoxy resin (Shanghai Guangyan Chemical Technology Co., Ltd., brand: 618, model: ZZZF04031) as a reinforcing agent.

[0164] Comparative Example 4

[0165] The preparation process is basically the same as in Example 1, except that in step S1, the mass of the added copper ammonia solution is replaced with 32 kg.

[0166] Comparative Example 5

[0167] S1. Disperse 1 kg of α-cellulose in 8 kg of 10 wt% sodium hydroxide aqueous solution. Under vigorous stirring, the particle size D... 50 5μm, D max 50 kg of 30 μm powdered petroleum asphalt was added to the above solution, and then 1.5 kg of copper nitrate powder was added. After stirring and mixing for 10 h, the mixture was dried at 80 °C to obtain copper nitrate modified cellulose@asphalt composite material.

[0168] Steps S2 to S3 are exactly the same as in Example 1.

[0169] The performance data of the pitch-based porous carbon prepared in each embodiment and comparative example are listed in Table 1 below. The elemental content was obtained by ICP-MS testing, the specific surface area and pore distribution were obtained by the Precision High-Precision Nitrogen Gas Adsorption-Desorption Testing System, the powder resistivity was obtained by ST2722B four-terminal powder resistivity tester, and the strength of the particles was measured by a strength tester when the particles were tested.

[0170] Table 1

[0171]

[0172]

[0173] Comparing Examples 1 to 3 in Table 1, the porous carbon prepared in Example 1 has better overall physical properties and excellent overall electrochemical performance; while the porous carbon powder prepared in Example 2 has slightly increased resistance and slightly decreased particle strength, which may be due to the increased amount of cellulose, increased oxygen content, and overlapping behavior of cellulose chains; the porous carbon prepared in Example 3 has decreased particle strength, which may be due to the decreased amount of cellulose.

[0174] Comparing Examples 1, 4-5 and Comparative Example 4, the porous carbon prepared in Example 4 showed increased electrical resistance and slightly decreased particle strength, possibly due to a decrease in the amount of copper ammonia solution and a reduction in copper content. The particle strength of the porous carbon prepared in Example 5 also decreased, possibly because the amount of copper ammonia solution increased, and the interface between the pitch and cellulose carbon was separated by copper during carbonization, resulting in a slight decrease in strength. The particle strength of the porous carbon prepared in Comparative Example 4 decreased significantly due to a large excess of copper ammonia solution.

[0175] Compared with Examples 1 and 6-8, the particle strength of porous carbon prepared in Examples 6 and 7 is slightly lower than that in Example 1. This may be because the number-average molecular weight of cellulose used in Examples 6 and 7 is lower than that in Example 1. The particle strength of porous carbon prepared in Example 8 is the lowest, which may be due to the high viscosity of the carboxymethyl cellulose solution and the low uniformity of liquid phase mixing, resulting in a decrease in the particle strength of pitch-based porous carbon.

[0176] Comparing Example 1 with Comparative Example 1 and Comparative Example 3, Comparative Example 1 did not add cellulose, and the resulting porous carbon particles had extremely low strength; Comparative Example 3 used epoxy resin, another common reinforcing agent, instead of cellulose, and the reinforcing effect was not ideal.

[0177] Comparing Example 1 with Comparative Examples 2 and 5, Comparative Example 2, which did not include a copper ammonia solution (i.e., did not introduce copper), not only significantly increased the powder resistivity of the porous carbon, but also unexpectedly showed a significantly lower particle strength compared to Example 1. This indicates that the addition of copper can synergistically enhance the particle strength of the porous carbon with cellulose. In Comparative Example 5, the method of first dissolving cellulose in an alkaline solution and then adding copper salt resulted in a significant decrease in the particle strength and a significant increase in the powder resistivity of the prepared porous carbon. This may be due to the uneven dispersion of cellulose.

[0178] Application examples

[0179] Ten kg of pitch-based porous carbon prepared in each embodiment and comparative example was placed in a rotary kiln as a substrate. A raw material gas consisting of silane and nitrogen was introduced at 500°C at a flow rate of 9 L / h, and the deposition time was 25 h. The carbon coating process involved feeding the aforementioned silicon-carbon material into the rotary kiln, introducing acetylene gas, and conducting the process under nitrogen protection and a high temperature of 700°C at a flow rate of 4 L / h for 8 h.

[0180] The products prepared in each embodiment and each comparative example were used as negative electrode materials to assemble batteries.

[0181] (1) Preparation of positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (NCM811), conductive agent SuperP, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97:1:0.5:1.5 to prepare a positive electrode slurry (solid content of 70wt%). The slurry is coated on both sides of the current collector aluminum foil, dried at 100℃, and then cold-pressed at room temperature at 4MPa. The slurry is then trimmed, cut into strips, and slit, and the tabs are welded to form the positive electrode sheet.

[0182] (2) Preparation of negative electrode sheet: Under a nitrogen protective atmosphere, the solvent N-methylpyrrolidone (NMP) and binder PVDF are stirred and mixed, then the conductive agent SuperP is added and stirred and mixed, and then the final products prepared in each example and each comparative example are added as negative electrode active materials and stirred and mixed thoroughly to prepare negative electrode slurry (solid content is 50wt%).

[0183] The above-mentioned negative electrode slurry is coated on both sides of the current collector copper foil, dried at 100°C, and then cold-pressed at 4MPa at room temperature. After that, the edges are cut, the foil is cut into strips, and the tabs are welded to form the negative electrode sheet.

[0184] (3) Assembly of lithium-ion batteries

[0185] Using a porous PE polymer film as a separator, the prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes, and then wound to obtain a bare battery cell. The bare battery cell is placed in an aluminum-plastic shell package and subjected to a relative vacuum pressure of -0.95 × 10⁻⁶. 5 At Pa, the cells were dried at 100℃ until the moisture content was below 100ppm. The electrolyte, composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) (EC:EMC:DEC volume ratio = 1:1:1) and LiPF6 (1.0M), was injected into the dried bare cells. The cells were then encapsulated, allowed to stand, formed (0.02C constant current charging for 2 hours, 0.1C constant current charging for 2 hours), shaped, and capacity tested (capacity grading) to produce soft-pack liquid lithium-ion batteries. During battery assembly, five batteries were prepared for each test group, and five sets of data were tested. The final performance was the average of the five sets of data.

[0186] Battery cycle performance was tested on Blue Electric equipment, specifically as follows: at 25℃, the battery was first discharged at 0.1C to 0.005V, then discharged at 0.08C to 0.001V, then at 0.05C to 0.001V, and finally at 0.02C to 0.001V, and then left to stand for 10 minutes; next, it was charged at 0.1C to 1.5V, left to stand for 10 minutes, and the charge-discharge capacity after the first cycle was recorded, and the initial coulombic efficiency was calculated; the battery was cycled 100 times in the same manner, and the charge-discharge capacity after 100 cycles was recorded, and the capacity retention rate after 100 cycles was calculated. The expansion test was performed after the battery was cycled, by disassembling the battery and comparing the thickness of the electrode plates with that before the cycle. The rate performance test was conducted by increasing the charge-discharge rate to 2C based on the cycle test. The specific test / calculation results are shown in Table 2 below.

[0187] Table 2

[0188]

[0189]

[0190] Comparing Examples 1 to 8 in Table 2, the silicon-carbon anode materials prepared in each example all have excellent cycle stability and high rate performance. However, the product prepared in Example 1 has the best electrochemical performance. Due to the slight difference in powder resistance and particle strength of the porous carbon substrate itself, the cycle retention rate, expansion rate and rate performance of the silicon-carbon anode materials prepared in other examples are slightly different.

[0191] Compared with Comparative Examples 1, 3, and 5, the silicon-carbon anode materials prepared in Comparative Examples 1, 3, and 5 all exhibit poor cycle stability and large expansion rates, which is related to the low particle strength of the porous carbon substrate itself.

[0192] Comparative Examples 1 and 2 and 4: The rate performance of the silicon-carbon anode materials prepared in Comparative Examples 2 and 4 decreased significantly, which is related to the high powder resistivity of the porous carbon substrate itself.

[0193] The above-described embodiments are preferred embodiments, but the scope of protection of the present invention is not limited thereto. Those skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, The material was prepared by sequentially performing silicon deposition and carbon coating on copper-doped double-crosslinked pitch-based porous carbon as a substrate. The copper-doped double-crosslinked pitch-based porous carbon has a particle strength of not less than 4.1 GPa and a powder resistivity of not more than 0.17 Ω·cm at 20 MPa. The method for preparing the copper-doped double-crosslinked pitch-based porous carbon includes: S1: Dissolve cellulose in a copper ammonia solution to obtain a homogeneous solution, then add asphalt, mix thoroughly, and then heat and dry to obtain a copper ammonia cellulose@asphalt composite material; The mass ratio of cellulose to copper ammonia solution is 1:(4~16). S2: The cuprammonium cellulose@asphalt composite material is heated for pre-oxidative crosslinking, and then pre-carbonized under a protective atmosphere to obtain carbonized material; S3: The carbonized material is activated to obtain copper-doped double-crosslinked pitch-based porous carbon.

2. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, Step S1 includes at least one of the following features (1) to (6): (1) The cellulose includes, but is not limited to, one or more of α-cellulose, β-cellulose, microcrystalline cellulose, and carboxymethyl cellulose, with a number average molecular weight of 2000 to 15000; (2) The copper ammonia solution is prepared by: reacting 10-20 wt% copper salt solution with 5-15 wt% alkaline solution to generate copper hydroxide precipitate, separating and washing the precipitate, and then adding 15-25 wt% ammonia water until the precipitate dissolves; (3) The preparation of the homogeneous solution is carried out at a low temperature of -15~-5℃; (4) The asphalt is in powder form with a particle size D. 50 3~9μm, D max ≤50μm; (5) The mass ratio of cellulose to asphalt is 1:(25~100); (6) The heating and drying temperature is 60~90℃.

3. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In step S2: The pre-oxidative crosslinking is carried out at a temperature of 250~350℃ for 1~5 hours. The pre-carbonization treatment uses a protective atmosphere including one or more of nitrogen, argon, and helium, at a temperature of 600~800℃, for a time of 4~10h.

4. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In step S3, the activation treatment includes at least one of the following features (1) to (4): (1) The activation treatment is selected from physical activation, and the activator is selected from one or more of CO, CO2, water vapor, and oxygen; (2) The activation treatment is performed at a temperature of 700~1000℃; (3) The activation treatment lasts for 2 to 15 hours; (4) The activation process involves an activator flow rate of 0.01~5 kg / h.

5. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The silicon deposition includes at least one of the following features (1) to (5): (1) The silicon deposition process uses a raw material gas including a silicon source gas; (2) The flow rate of the raw gas is 1~50 L / h; (3) The silicon deposition temperature is 300~800℃; (4) The silicon deposition time is 1~40h; (5) The raw material gas also includes a carrier gas, which is selected from nitrogen and / or argon. The volume ratio of the carrier gas is 1 to 30% based on the total volume of the raw material gas as 100%.

6. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The carbon coating comprises at least one of the following features (1) to (6): (1) The carbon coating uses a carbon-containing gas as the raw material; the carbon-containing gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes. (2) The flow rate of the carbon-coated raw material gas is 1~10 L / h; (3) The carbon coating temperature is 400~1200℃; (4) The carbon coating time is 1~10h; (5) The carbon-coated raw material gas also includes inert gas.

7. A silicon-carbon anode material prepared by the method according to any one of claims 1 to 6.

8. A lithium-ion battery, characterized in that, Including the silicon-carbon anode material as described in claim 7.

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