Preparation method of spherical silicon-carbon composite negative electrode material

Abstract

The invention relates to the technical field of lithium ion battery negative electrode materials, in particular to a preparation method of a spherical silicon-carbon composite negative electrode material. According to the preparation method, salicylic acid adsorption modification treatment and epoxy silane coupling agent treatment are sequentially performed on the carbon nanotubes, when the carbon nanotubes are matched with subsequent phenolic resin synthesis, the catalyst contains a certain amount of 2, 2-bis (hydroxymethyl)-2, 2 ', 2' '-nitrile triethanol, so that the carbon nanotubes can be uniformly dispersed in the phenolic resin, and after the phenolic resin is subjected to subsequent carbonization, the carbon nanotubes can be uniformly dispersed in the phenolic resin; and good dispersibility is still maintained in the activation pore-forming process. The low electronic conductivity of the product silicon-carbon composite negative electrode material is obviously improved, and the high-rate performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a method for preparing a spherical silicon-carbon composite anode material. Background Technology

[0002] In the field of lithium-ion batteries, the demand for high-energy-density batteries is increasingly urgent; however, existing graphite-based anode materials face numerous challenges. Their theoretical specific capacity of 372 mAh / g is insufficient to meet the higher capacity requirements of high-energy-density batteries. Furthermore, this material suffers from problems such as electrode pulverization, SEI film rupture, and insufficient conductivity due to repeated cycling during use. It is also prone to polarization during high-rate charge-discharge cycles, leading to capacity decay and severely impacting battery performance and lifespan. Simultaneously, traditional carbon electrodes also exhibit significant defects in high-compaction processes; their structure is prone to collapse, resulting in poor contact of the active material and ultimately severe capacity decay, limiting their application in scenarios requiring high electrode structural stability.

[0003] Spherical carbon possesses a unique three-dimensional, closely packed spherical morphology, a structural feature that allows it to uniformly distribute stress. During battery charging and discharging, this ability to uniformly distribute stress effectively suppresses particle breakage, thereby improving the stability of the electrode structure and reducing capacity decay caused by particle breakage. Carbon nanotubes are characterized by high strength and lightweight, while also exhibiting near-metallic conductivity. Their high strength provides support in the electrode structure, enhancing the electrode's mechanical properties; their lightweight nature helps reduce the overall battery weight and increase energy density; and their excellent conductivity improves electrode conductivity, reduces resistance, and increases battery charging and discharging efficiency. Silicon materials possess a significantly high theoretical specific capacity, reaching 4200 mAh / g, a value far exceeding that of graphite-based anode materials, making it an ideal candidate material for improving battery energy density.

[0004] Considering the advantages of spherical carbon and carbon nanotubes in terms of structure and conductivity, as well as the high specific capacity of silicon-based materials, developing spherical porous carbon / carbon nanotube silicon-carbon composite materials has become a highly promising direction for solving the above problems.

[0005] CN119480981A discloses a method for preparing a silicon-carbon anode material, comprising the following steps: S1, mixing nano-silicon and resin prepolymer with a conductive agent, then performing cross-linking curing and carbonization to obtain a silicon-carbon precursor, wherein the conductive agent is selected from carbon nanotubes and conductive carbon black; S2, coating the silicon-carbon precursor with carbon to obtain the silicon-carbon anode material.

[0006] CN121076116A discloses a low-expansion spherical silicon-carbon composite anode material for charge and discharge, with spherical porous carbon as the core, and an amorphous carbon layer and a fast plasma layer sequentially coated on the outside of the spherical porous carbon. The average particle size of the spherical silicon-carbon composite anode material is 5-10 μm, the thickness of the amorphous carbon layer is 10-20 nm, and the thickness of the fast plasma layer is 1-5 nm. The spherical porous carbon contains a conductive agent, which is selected from carbon nanotubes or graphene.

[0007] To address the low electronic conductivity of silicon-carbon composite anode materials, existing technologies have involved mixing them with nano-conductive materials such as carbon nanotubes and graphene. However, carbon nanotubes exhibit significant π-π stacking effects, making them prone to spontaneous aggregation and entanglement, forming large agglomerates. This leads to reduced utilization of carbon nanotubes, discontinuous conductive networks, and limited improvement in overall electronic conductivity. The agglomeration phenomenon is severe, especially under high-rate conditions, which may cause localized areas of silicon particles to undergo excessively rapid lithium insertion / extraction, resulting in defects and rapid capacity decay. Summary of the Invention

[0008] The purpose of this invention is to solve the problems of poor battery electrical performance caused by low electronic conductivity and poor structural stability of existing silicon-carbon anode materials, as well as poor cycle stability caused by large volume expansion during charge and discharge. A spherical silicon-carbon composite material is proposed to improve the electrical performance and stability of lithium-ion battery anode materials. This invention improves the dispersion of carbon nanotubes in the spherical resin synthesis process by adding modified carbon nanotubes, which are co-modified with salicylic acid and epoxy silane coupling agents. In the synthesis of phenolic resin, a combination of polyamine and 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol is used as a catalyst to improve the dispersion of carbon nanotubes in the material. Through this invention's preparation process, adding a small amount of carbon nanotubes can significantly improve the electronic conductivity of the silicon-carbon composite anode material, without adversely affecting its electrochemical performance at high rates. The phenolic resin prepared by this invention is carbonized to form a spherical carbon / carbon nanotube composite material. Using this composite material as a substrate, silicon deposition forms a spherical porous carbon / carbon nanotube silicon-carbon composite material. The carbon nanotubes enable the material to achieve rapid and efficient electron transport, greatly improving the material's conductivity and reducing the volume expansion caused by silicon-based materials during charge and discharge. The presence of spherical carbon ensures the stability of the material, and the combination with nano-silicon further improves the rate performance and cycle stability of the composite anode material. Specifically, this invention provides the following technical solutions:

[0009] A method for preparing a spherical silicon-carbon composite anode material includes the following steps:

[0010] (S1) Carbon nanotubes were subjected to boiling water treatment under high pressure, then restored to normal pressure and cooled. After that, salicylic acid was added, stirred and then solid-liquid separation was performed. The mixture was washed and dried to obtain salicylic acid-treated carbon nanotubes.

[0011] (S2) Salicylic acid-treated carbon nanotubes were dispersed in water, and an alcohol solution containing an epoxy silane coupling agent was added. The mixture was heated to react, and the solid and liquid were separated. The mixture was washed and dried to obtain modified carbon nanotubes.

[0012] (S3) Phenolic monomers, formaldehyde monomers, aromatic aldehyde monomers, emulsifiers, catalysts and modified carbon nanotubes are added to an alcohol solvent and reacted under stirring and heating conditions. After the reaction is completed, the solid and liquid are separated. The obtained solid is dried and then crushed, carbonized and activated to form porous carbon. The porous carbon is then subjected to silane deposition and carbon coating to obtain a spherical porous carbon / carbon nanotube silicon-carbon composite material. The catalyst contains 20-30 wt% of 2,2-bis(hydroxymethyl)-2,2',2"-nitrile ethanol and polyamines.

[0013] Further, in step (S1), the high-pressure condition is 10-100 MPa, and the treatment time in boiling water is 1-10 h; preferably, the high-pressure condition is 20-30 MPa, and the treatment time in boiling water is 3-5 h. The purpose of boiling water treatment under high pressure is to moderately oxidize the carbon nanotubes. The oxidized carbon nanotubes will introduce oxygen-containing functional groups (hydroxyl, carboxyl, carbonyl, etc.), increasing the hydrophilicity of the carbon nanotubes, and the oxygen-containing functional groups facilitate subsequent modification treatment. However, the degree of oxidation cannot be too high, otherwise the conductivity will decrease. Therefore, conventional strong oxidation methods such as mixed acids or hydrogen peroxide are not suitable. Under high pressure and high temperature conditions (such as 20-30 MPa), the ion product of water increases, which can provide an environment similar to weak acid / weak oxidation, which is conducive to introducing oxygen-containing functional groups on the surface of carbon nanotubes without severely damaging their sp² conjugated structure. Thus, while improving hydrophilicity and reactivity, the intrinsic conductivity of carbon nanotubes is preserved to the maximum extent.

[0014] Preferably, the carbon nanotubes are single-walled carbon nanotubes, more preferably rod-shaped single-walled carbon nanotubes with a diameter of 1-5 nm and a length of 5-50 μm; more preferably, the rod-shaped single-walled carbon nanotubes have a diameter of 1-2 nm and a length of 10-30 μm. After boiling water treatment, the mass concentration of carbon nanotubes in the cooled aqueous solution containing the dispersed carbon nanotubes is 1-2 wt%.

[0015] Further, in step (S1), the amount of salicylic acid added is such that the concentration of salicylic acid in the system is 3-5 wt%, the stirring speed is 100-200 rpm, and the stirring time is 20-30 h, for example, 24 h; solid-liquid separation is performed by vacuum filtration or centrifugation, washing is done with ethanol, and drying is done by vacuum drying. Salicylic acid is adsorbed onto carbon nanotubes through π-π stacking interactions and hydrogen bonding, completing the initial modification of carbon nanotubes.

[0016] Further, in step (S2), the ratio of salicylic acid-treated carbon nanotubes to water is 0.1 g: 10-20 mL; the epoxy silane coupling agent is selected from at least one of 3-glycidyl etheroxypropyltrimethoxysilane, 3-(2,3-epoxypropoxy)propyltriethoxysilane, and 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane; the concentration of silane coupling agent in the alcohol solution of the epoxy silane coupling agent is 20-30 wt%, and the alcohol is ethanol; the amount of alcohol solution containing the epoxy silane coupling agent added is such that the mass ratio of silane coupling agent to salicylic acid-treated carbon nanotubes is 0.2-0.3:1; the heating reaction is carried out at 50-70℃ for 3-5 h; solid-liquid separation is by vacuum filtration or centrifugation, washing is by ethanol washing, and drying is by vacuum drying.

[0017] Further, in step (S3), the phenolic monomer is selected from at least one of phenol, resorcinol, catechol, hydroquinone, phloroglucinol, and methylphenol; the aromatic aldehyde monomer is selected from at least one of benzaldehyde, hydroxybenzaldehyde, methoxybenzaldehyde, and naphthaldehyde; the emulsifier is selected from at least one of polyoxypropylene-polyoxyethylene block copolymer, lauroyl diethanolamine, cocamidopropyl betaine, sorbitan monooleate, polysorbate, sucrose fatty acid ester, fatty alcohol polyoxyethylene ether (AEO), alkylphenol polyoxyethylene ether (APEO), and fatty acid polyoxyethylene ester (FAE); and the alcohol solvent is selected from at least one of ethanol, butanol, n-butanol, and isopropanol. Furthermore, the molar ratio of phenolic monomers, formaldehyde monomers, and aromatic aldehyde monomers is 1:1.8-2.5:0.1-0.4; preferably 1:1.8-2.2:0.2-0.3; more preferably 1:1.9-2.0:0.2-0.3.

[0018] Further, in step (S3), the polyamine is selected from at least one of ethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine, and p-phenylenediamine; and the mass percentage of 2,2-bis(hydroxymethyl)-2,2',2"-nitriol in the catalyst is 20-30 wt%.

[0019] The inventors discovered that the catalyst 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol, as a tertiary amine, can not only catalyze the preparation of phenolic resin, but also react with epoxy groups to anchor modified carbon nanotubes in the phenolic resin and ensure uniform dispersion during the synthesis process. Furthermore, this uniform dispersion is stable and does not change during subsequent carbonization and pore-forming processes. This enables the preparation of uniformly doped silicon-carbon composite anode materials with carbon nanotubes, improving the electrochemical performance of the anode material, especially its high-rate performance.

[0020] Further, in step (S3), the mass ratio of the total monomer mass, emulsifier, catalyst, and modified carbon nanotubes is 100:1-5:3-5:0.4-0.6. There is no particular limitation on the amount of alcohol solvent added, as long as the system can complete the reaction smoothly. Considering the utilization efficiency of carbon nanotubes, the mass of the alcohol solvent should be 2-4 times the total monomer mass, for example, 3 times. The total monomer mass is the sum of the masses of phenolic monomers, formaldehyde monomers, and aromatic aldehyde monomers.

[0021] Further, in step (S3), the reaction under stirring and ultrasonic conditions is carried out at a stirring speed of 300-500 rpm and a reaction temperature of 60-80℃ for 10-15 hours; crushing is performed to reduce the particle size of the material to below 100 μm; the carbonization temperature is 600-800℃; carbonization is carried out under an inert atmosphere, which is nitrogen and / or argon; pore-forming activation is performed using potassium hydroxide at an activation temperature of 700-800℃ for 2-5 hours; specifically, the activation method involves mixing the carbonized material and potassium hydroxide at a mass ratio of 1:2-3, and holding the mixture at the activation temperature for 10-20 hours; silane deposition... The process involves pyrolyzing activated porous carbon to deposit nano-silicon under silane gas, resulting in a silicon content of 50-55 wt% in the silicon-carbon composite material. The silane gas is selected from at least one of silane and disilane. Nitrogen and / or argon are used as carrier gases for silane deposition, with a flow ratio of 3-5:1 between the carrier gas and the silane gas. The pyrolysis temperature for silane deposition is 400-600℃. Carbon coating is achieved by pyrolyzing a carbon source gas at 500-600℃. The carbon source gas is selected from at least one of methane, ethane, propane, butane, ethylene, and acetylene. The carbon coating thickness is 3-15 nm, preferably 5-10 nm.

[0022] The present invention has the following advantages over the prior art:

[0023] This invention modifies carbon nanotubes sequentially through salicylic acid adsorption and then through epoxy silane coupling agent treatment. When used in the subsequent synthesis of phenolic resin, the catalyst contains a certain amount of 2,2-bis(hydroxymethyl)-2,2',2"-nitriethanol, which allows the carbon nanotubes to be uniformly dispersed in the phenolic resin. Even after subsequent carbonization and activation pore-forming processes, the phenolic resin maintains excellent dispersibility. This significantly improves the low electronic conductivity of the silicon-carbon composite anode material, enhancing the high-rate performance of the battery.

[0024] This invention involves uniformly mixing modified carbon nanotubes with phenols, aromatic aldehydes, a catalyst, and an emulsifier, followed by a heated reaction to synthesize a resin with both spherical and carbon nanotube morphologies, thereby improving the structural strength of the material. The mixture is then pyrolyzed; after pyrolysis, the material continues to maintain its spherical and carbon nanotube morphologies, forming a stable spherical carbon / carbon nanotube composite material. This composite material exhibits stronger structural strength, better thermal stability, and improved electrical conductivity, resulting in a lithium-ion battery anode composite material with high energy density and excellent cycle performance. Attached Figure Description

[0025] Figure 1 The image shown is an electron microscope image of the spherical silicon-carbon composite material prepared in Example 1.

[0026] Figure 2 This is a magnified electron microscope image of a spherical silicon-carbon composite material prepared in Example 1.

[0027] Figure 3 The X-ray diffraction pattern is shown for the spherical silicon-carbon composite material prepared in Example 1.

[0028] Figure 4 This is a TEM image of the spherical silicon-carbon composite material prepared in Example 1.

[0029] Figure 5 The electrical performance curves of the battery prepared using the spherical silicon-carbon composite material of Example 1 as the active material of the negative electrode are shown. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0031] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0032] The carbon nanotubes are single-walled carbon nanotubes, purchased from Ningbo Xiwo New Material Technology Co., Ltd., with a length of 10-30μm and a diameter of 1-2nm.

[0033] Example 1

[0034] (S1) 1 kg of single-walled carbon nanotubes were added to a high-pressure hydrothermal reactor and boiled for 5 h at 20 MPa. After restoring to normal pressure and cooling, a dispersion with a carbon nanotube mass concentration of 1 wt% and a salicylic acid concentration of 3 wt% was obtained by adding salicylic acid. The mixture was stirred at 150 rpm for 24 h and then centrifuged to obtain a solid. The solid was washed with ethanol and dried under vacuum to obtain salicylic acid-treated carbon nanotubes.

[0035] (S2) 0.1 kg of salicylic acid-treated carbon nanotubes were dispersed in 10 L of water, and 0.1 kg of 30 wt% KH-560 ethanol solution was added (the mass ratio of silane coupling agent to salicylic acid-treated carbon nanotubes was 0.3:1). The mixture was heated to 60 °C and reacted for 5 h. After centrifugation, the solid obtained was washed with ethanol and dried under vacuum to obtain modified carbon nanotubes.

[0036] (S3) Phenol, formaldehyde, and benzaldehyde (the total mass of phenol, formaldehyde, and benzaldehyde is 10 kg) are added to the reactor in a molar ratio of 1:2:0.2. 30 kg of ethanol, 0.5 kg of emulsifier alkylphenol polyoxyethylene ether (APEO), 0.5 kg of catalyst (ethylenediamine and 2,2-bis(hydroxymethyl)-2,2',2"-nitrile triethanolol in a mass ratio of 8:2), and 0.04 kg of the modified carbon nanotubes prepared in step (S2) are added. The system is heated to 60 °C and reacted for 12 h with stirring at 300 rpm, resulting in precipitation. Solid-liquid separation is performed, and the alcohol solvent is recovered from the liquid phase. Carbon nanotubes were dried and crushed to a particle size of less than 100 μm. They were then transferred to a muffle furnace and carbonized at 800 °C for 4 hours under a nitrogen atmosphere to obtain carbonized material. Subsequently, the carbonized material and potassium hydroxide were mixed uniformly by ball milling at a mass ratio of 1:2 and activated at 700 °C for 15 hours to obtain porous carbon. The porous carbon was then subjected to silicon deposition (silane and nitrogen flow ratio of 3:1, silicon deposition temperature of 450 °C) and carbon coating (methane as carbon source gas, carbon coating process temperature of 550 °C) to obtain a silicon-carbon composite material with a silicon content of 52.4 wt% and a carbon coating layer thickness of 5-10 nm.

[0037] Figure 1 The image shown is an electron microscope image of the spherical silicon-carbon composite material prepared in Example 1. Figure 2 This is a magnified electron microscope image of a spherical silicon-carbon composite material prepared in Example 1. Figure 3 The X-ray diffraction pattern is shown for the spherical silicon-carbon composite material prepared in Example 1. Figure 4 This is a TEM image of the spherical silicon-carbon composite material prepared in Example 1.

[0038] Example 2

[0039] (S1) 1 kg of single-walled carbon nanotubes were added to a high-pressure hydrothermal reactor and boiled in water at 30 MPa for 4 h. After restoring to normal pressure and cooling, a dispersion with a carbon nanotube mass concentration of 1 wt% and a salicylic acid concentration of 3 wt% was obtained by adding salicylic acid. The mixture was stirred at 150 rpm for 24 h and then centrifuged to obtain a solid. The solid was washed with ethanol and dried under vacuum to obtain salicylic acid-treated carbon nanotubes.

[0040] (S2) 0.1 kg of salicylic acid-treated carbon nanotubes were dispersed in 10 L of water, and 0.1 kg of 20 wt% KH-560 ethanol solution was added (the mass ratio of silane coupling agent to salicylic acid-treated carbon nanotubes was 0.2:1). The mixture was heated to 60 °C and reacted for 5 h. After centrifugation, the solid obtained was washed with ethanol and dried under vacuum to obtain modified carbon nanotubes.

[0041] (S3) Resorcinol, formaldehyde, and benzaldehyde (the total mass of resorcinol, formaldehyde, and benzaldehyde is 10 kg) are added to the reactor in a molar ratio of 1:1.9:0.3. 30 kg of ethanol, 0.3 kg of emulsifier (fatty alcohol polyoxyethylene ether (AEO), 0.3 kg of catalyst (ethylenediamine and 2,2-bis(hydroxymethyl)-2,2',2"-nitrile triethanolol in a mass ratio of 7:3), and 0.06 kg of the modified carbon nanotubes prepared in step (S2) are added. The system is heated to 60 °C and reacted for 12 h with stirring at 300 rpm, resulting in precipitation. Solid-liquid separation is performed, and the alcohol solution is recovered from the liquid phase. The agent and carbon nanotubes were dried and crushed to a particle size of less than 100 μm. The solid was then transferred to a muffle furnace and carbonized at 800℃ for 4 hours under a nitrogen atmosphere to obtain carbonized material. The carbonized material and potassium hydroxide were then mixed uniformly by ball milling at a mass ratio of 1:2 and activated at 700℃ for 15 hours to obtain porous carbon. The porous carbon was then subjected to silicon deposition (silane and nitrogen flow ratio of 3:1, silicon deposition temperature of 450℃) and carbon coating (methane as carbon source gas, carbon coating process temperature of 550℃) to obtain silicon-carbon composite material with a silicon content of 51.9 wt% and a carbon coating layer thickness of 5-10 nm.

[0042] Example 3

[0043] The other conditions and operations are the same as in Example 1, except that in step (S2), the 30wt% KH-560 ethanol solution is replaced with a 30wt% KH-561 ethanol solution.

[0044] Example 4

[0045] The other conditions and operations are the same as in Example 1, except that the molar ratio of phenol, formaldehyde, and benzaldehyde is 1:1.8:0.4.

[0046] Example 5

[0047] The other conditions and operations are the same as in Example 1, except that the molar ratio of phenol, formaldehyde, and benzaldehyde is 1:2.1:0.1.

[0048] Comparative Example 1

[0049] Commercial graphite / silicon anode material from a certain manufacturer is used, with a silicon content of approximately 50%.

[0050] Comparative Example 2

[0051] The other conditions and operations are the same as in Example 1, except that step (S1) is omitted and carbon nanotubes are used instead of salicylic acid to treat carbon nanotubes in step (S2).

[0052] Comparative Example 3

[0053] The other conditions and operations are the same as in Example 1, except that step (S2) is omitted and in step (S3), the carbon nanotubes treated with salicylic acid in step (S1) are used instead of the modified carbon nanotubes.

[0054] Comparative Example 4

[0055] The other conditions and operations are the same as in Example 1, except that in step (S3), the catalyst is ethylenediamine and 2,2-bis(hydroxymethyl)-2,2',2"-nitriol is not added.

[0056] Comparative Example 5

[0057] The other conditions and operations are the same as in Example 1, except that in step (S3), the catalyst is a mixture of ethylenediamine and tris(hydroxymethyl)aminomethane in a mass ratio of 8:2.

[0058] Application examples

[0059] Performance testing of composite materials as lithium battery anode materials

[0060] The electrochemical performance of the silicon-carbon composite anode materials of the above examples and comparative examples was tested as follows: Silicon-carbon composite material, Super P, and carboxymethyl cellulose / styrene-butadiene rubber composite binder were mixed at a mass ratio of 80:10:10 to form a slurry (CMC and SBR mass ratio was 1:1). This slurry was coated onto copper foil using a 150 μm thick wet film preparation device, allowed to stand and dry for 30-40 minutes, and then vacuum dried for 10 hours to prepare the anode composite electrode sheet. Then, lithium metal was used as the counter electrode, PP+alumina coating was used as the separator, and 1 mol / L LiPF6 (a mixture of ethylene carbonate, ethyl methyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:2:1) was used as the electrolyte. 2% FEC was added to the electrolyte. The cells were assembled into coin cells in an inert gas glove box under an argon atmosphere. The assembled cells were then tested on a LAND charge-discharge testing system within a charge-discharge range of 0.005V-1.5V.

[0061] Figure 5 The image shows the electrical performance curve of the battery made using the spherical silicon-carbon composite material of Example 1 as the active material of the negative electrode.

[0062] Following the same method, the silicon-carbon composite materials obtained in the embodiments and comparative examples of the present invention were assembled into coin-type lithium batteries as negative electrode materials, and the electrochemical test results are listed in Table 1.

[0063] Table 1 Electrochemical performance test of silicon-carbon composite anode materials

[0064]

[0065] As shown in Table 1, the negative electrode composite material provided by this invention exhibits excellent performance in lithium battery testing. The material preparation method of this invention is simple and efficient, and the resulting composite material possesses higher density, better thermal stability and conductivity, as well as effective diffusion channels and a shorter diffusion distance. This material demonstrates extremely low expansion rate in lithium-ion battery performance testing, while also exhibiting high specific capacity, initial coulombic efficiency, and excellent rate performance.

Claims

1. A method for preparing a spherical silicon-carbon composite anode material, characterized in that, Includes the following steps: (S1) Carbon nanotubes were subjected to boiling water treatment under high pressure, then restored to normal pressure and cooled. After that, salicylic acid was added, stirred and then solid-liquid separation was performed. The mixture was washed and dried to obtain salicylic acid-treated carbon nanotubes. (S2) Salicylic acid-treated carbon nanotubes were dispersed in water, and an alcohol solution containing an epoxy silane coupling agent was added. The mixture was heated to react, and the solid and liquid were separated. The mixture was washed and dried to obtain modified carbon nanotubes. (S3) Phenolic monomers, formaldehyde monomers, aromatic aldehyde monomers, emulsifiers, catalysts and modified carbon nanotubes are added to an alcohol solvent and reacted under stirring and heating conditions. After the reaction is completed, the solid and liquid are separated. The obtained solid is dried and then crushed, carbonized and activated to form porous carbon. The porous carbon is then subjected to silane deposition and carbon coating to obtain a spherical porous carbon / carbon nanotube silicon-carbon composite material. The catalyst contains 20-30 wt% of 2,2-bis(hydroxymethyl)-2,2',2"-nitriol and polyamines.

2. The preparation method according to claim 1, characterized in that, In step (S1), the high pressure condition is 10-100 MPa, and the treatment time in boiling water is 1-10 h; preferably, the high pressure condition is 20-30 MPa, and the treatment time in boiling water is 3-5 h. Preferably, the carbon nanotubes are single-walled carbon nanotubes, more preferably rod-shaped single-walled carbon nanotubes with a diameter of 1-5 nm and a length of 5-50 μm; more preferably, the rod-shaped single-walled carbon nanotubes have a diameter of 1-2 nm and a length of 10-30 μm; more preferably, after the carbon nanotubes are treated with boiling water, the mass concentration of carbon nanotubes in the cooled aqueous solution containing the carbon nanotubes is 1-2 wt%.

3. The preparation method according to claim 1, characterized in that, In step (S1), the amount of salicylic acid added is such that the concentration of salicylic acid in the system is 3-5 wt%, the stirring speed is 100-200 rpm, and the stirring time is 20-30 h.

4. The preparation method according to claim 1, characterized in that, In step (S2), the ratio of salicylic acid to water for treating carbon nanotubes is 0.1 g: 10-20 mL; Furthermore, the epoxy silane coupling agent is selected from at least one of 3-glycidyl etheroxypropyltrimethoxysilane, 3-(2,3-epoxypropoxy)propyltriethoxysilane, and 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane; Furthermore, the concentration of silane coupling agent in the alcohol solution of epoxy silane coupling agent is 20-30 wt%, and the amount of alcohol solution containing epoxy silane coupling agent added makes the mass ratio of silane coupling agent to salicylic acid treated carbon nanotubes 0.2-0.3:

1. Furthermore, the heating reaction is carried out at 50-70℃ for 3-5 hours.

5. The preparation method according to claim 1, characterized in that, In step (S3), the phenolic monomer is selected from at least one of phenol, resorcinol, catechol, hydroquinone, phloroglucinol, and methylphenol; the aromatic aldehyde monomer is selected from at least one of benzaldehyde, hydroxybenzaldehyde, methoxybenzaldehyde, and naphthaldehyde. Furthermore, the molar ratio of phenolic monomers, formaldehyde monomers, and aromatic aldehyde monomers is 1:1.8-2.5:0.1-0.4; preferably 1:1.8-2.2:0.2-0.3; more preferably 1:1.9-2.0:0.2-0.

3.

6. The preparation method according to claim 1, characterized in that, In step (S3), the emulsifier is selected from at least one of polyoxypropylene-polyoxyethylene block copolymer, lauroyl diethanolamine, cocamidopropyl betaine, sorbitan monooleate, polysorbate, sucrose fatty acid ester, fatty alcohol polyoxyethylene ether (AEO), alkylphenol polyoxyethylene ether (APEO), and fatty acid polyoxyethylene ester (FAE); the alcohol solvent is selected from at least one of ethanol, butanol, n-butanol, and isopropanol.

7. The preparation method according to claim 1, characterized in that, In step (S3), the polyamine is selected from at least one of ethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine, and p-phenylenediamine; and the mass percentage of 2,2-bis(hydroxymethyl)-2,2',2"-nitriol in the catalyst is 20-30 wt%.

8. The preparation method according to claim 1, characterized in that, In step (S3), the mass ratio of the total mass of monomers, emulsifier, catalyst, and modified carbon nanotubes is 100:1-5:3-5:0.4-0.

6. Furthermore, the amount of alcohol solvent added is 2-4 times the total mass of the monomers.

9. The preparation method according to claim 1, characterized in that, In step (S3), the reaction under stirring and ultrasonic conditions is carried out at a stirring speed of 300-500 rpm and at 60-80℃ for 10-15 h; and / or, Crushing reduces the material particle size to below 100 μm; carbonization temperature is 600-800℃; carbonization is carried out under an inert atmosphere, which is nitrogen and / or argon; and / or... Pore ​​formation activation is performed using potassium hydroxide at a temperature of 700-800℃ for 2-5 hours; and / or, Silane deposition results in a silicon content of 50-55 wt% in silicon-carbon composites; and / or, Carbon coating results in a carbon coating layer thickness of 3-15 nm, preferably 5-10 nm, in silicon-carbon composite materials.

10. A spherical silicon-carbon composite anode material, characterized in that, It is prepared by the method described in any one of claims 1-9.

Images