Preparation method of silicon-carbon composite negative electrode material with improved safety

Abstract

The invention relates to the technical field of lithium ion battery negative electrode materials, in particular to a preparation method of a silicon-carbon composite negative electrode material with improved safety, which comprises the following steps: (S1) reacting a first phenol monomer, a second phenol monomer and an aldehyde monomer, sequentially curing twice to obtain a phenolic resin block, and sequentially crushing, pre-oxidizing, pyrolyzing and carbonizing to obtain a silicon-carbon composite negative electrode material; pyrolytic carbon is obtained; the second phenol monomer is cardiac phenol; (S2) carrying out activated pore-forming on the pyrolytic carbon, and carrying out high-temperature treatment in an inert atmosphere to obtain porous carbon; and (S3) sequentially performing vapor phase silicon deposition and carbon coating on the porous carbon to obtain the silicon-carbon composite negative electrode material. By adjusting a monomer formula and a secondary curing process in resin synthesis, regulation and control on the hybridization degree of SP3 and SP2 are realized, the crosslinking degree and mechanical strength of the resin are improved, the defects of a porous carbon substrate are reduced, and a silicon-carbon negative electrode material with a certain grain size can be prepared during later-stage deposition; the high performance of the silicon-carbon negative electrode material is maintained, and the silicon-carbon negative electrode material also has higher safety.

Description

Technical Field

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

[0002] In the current field of lithium-ion battery technology, replacing traditional graphite anodes with high-specific-capacity anode materials is a highly effective approach to achieve higher energy density. Silicon-based anode materials achieve lithium storage through alloying reactions with lithium, boasting a theoretical specific capacity as high as 4200 mAh / g, and are considered the most promising alternative to graphite anodes. However, silicon-based anode materials face severe challenges in practical applications. During lithium insertion and extraction, silicon-based anode materials undergo significant volume changes, leading to particle breakage and pulverization, resulting in severe degradation of the silicon particle structure and the formation of an unstable solid electrolyte interface layer, ultimately reducing battery cycle stability. To overcome the challenges faced by silicon-based anode materials, numerous pioneering studies have demonstrated that shrinking the characteristic size of silicon materials to the nanometer scale enables silicon particles to withstand enormous volumetric strain without fracturing, exhibiting excellent electrochemical performance. For example, the volumetric strain generated by sub-nanometer-sized silicon particles is far less than that of larger silicon particles. For this reason, sub-nanometer silicon materials exhibit excellent performance in terms of kinetic properties and cycle performance, meeting the standards for the practical application of silicon-based anode materials.

[0003] Currently, methods for preparing sub-nanometer-sized silicon materials are relatively scarce, with research mainly focusing on the nanometer or several-nanometer scale, such as silicon nanosheets, silicon nanowires, and silicon nanotubes. The macroscopic dimensions of these materials are typically several nanometers or even tens of nanometers, making it difficult to effectively improve their electrochemical performance. Although methods such as alloying, redox methods, sol-gel methods, chemical vapor deposition, and mechanical polishing can significantly reduce the size of silicon materials, they all have limitations in achieving uniform sub-nanometer-scale preparation. Introducing a gaseous silicon source into a carbon framework with a microporous structure is a relatively effective method for preparing sub-nanometer-sized silicon materials. For example, introducing gaseous silane into a microporous carbon framework via chemical vapor infiltration, and then decomposing the gaseous silane under suitable conditions to form sub-nanometer-sized silicon, can significantly improve the cycle stability of silicon-based materials. However, sub-nanometer silicon formed by vapor deposition has extremely high surface energy, which, when combined with a porous carbon substrate at high temperatures, forms silicon carbide, leading to violent exothermic reactions and affecting the safety of material applications, creating numerous safety hazards during battery use. Summary of the Invention

[0004] To address the safety concerns of existing silicon-carbon composite materials used in the preparation of sub-nanometer silicon, where the high reactivity of nano-silicon makes it easily ignited and safety needs improvement, this invention aims to provide a method for enhancing the safety of sub-nanometer silicon particles in vapor-deposited silicon-carbon materials. Its core innovations include: I. Porous Carbon Substrate Design: Select a substrate pore volume of 0.8-1.2 cm³. 3 / g, micropores (<2 nm) account for 80-90%, mesopores (2-50 nm) account for 10-20%, and macropores (>50 nm) account for no more than 2%. This pore structure buffers the volume expansion of silicon through physical confinement effect, while providing a uniform silicon deposition space, so that the silicon deposited is mainly 2.5-10 nm sub-nanometer level silicon, improving safety.

[0005] II. Regarding the carbon source, cross-linked phenolic resin polymers are used (high-temperature pyrolysis and carbonization to form a high SP³ hybrid carbon skeleton, enhancing mechanical strength, conductivity, and safety). Traditional phenol-formaldehyde carbon precursors contain less SP... 2 High degree of hybridization, SP 2 Graphitized carbon frameworks readily react with highly reactive sub-nanometer-sized silicon at high temperatures to form silicon carbide, which is violently exothermic and may ignite, posing a safety hazard. This invention addresses this by adding a second phenolic monomer, cardiac glycoside, to obtain a phenolic resin carbon precursor with a suitable degree of crosslinking, thereby improving the spline properties of the resulting pyrolytic carbon. 3 Hybridization level, SP 3 Hybridized carbon has higher bond energies, suppressing reactions between silicon and carbon at high temperatures and improving safety. However, increasing SP... 3 An excessive hybrid carbon ratio can lead to an overabundance of amorphous regions, reducing the initial coulombic efficiency. Therefore, strict control of the sp(s) ratio is necessary. 3 Only a certain degree of hybridization can balance the electrochemical performance and safety of the resulting silicon-carbon composite material.

[0006] III. Precise control of silicon grain crystallinity: By adjusting silicon deposition conditions (temperature, gas flow rate) through chemical vapor deposition (CVD), the silicon grain size is made to be 2.5-10 nm (calculated based on the Scherrer formula of XRD), balancing the risks of expansion suppression and safety.

[0007] The present invention achieves the above objectives through the following technical solutions: A method for preparing a silicon-carbon composite anode material with improved safety includes the following steps: (S1) The first phenol monomer, the second phenol monomer, and an aldehyde monomer are reacted, and an alkaline catalyst is added for the first curing. After drying the obtained polymer, a curing agent is added for the second curing to obtain a phenolic resin block. Then, the block is crushed, pre-oxidized, and pyrolyzed to obtain pyrolytic carbon. The first phenol monomer is selected from at least one of resorcinol, phenol, p-chlorophenol, and p-cresol, and the second phenol monomer is cardiotonic phenol. The molar ratio of the first phenol monomer to the second phenol monomer is 6-10:1. (S2) Pyrolytic carbon is activated to form pores, and then treated at high temperature under an inert atmosphere to obtain porous carbon; (S3) Porous carbon is sequentially subjected to vapor-phase silicon deposition and carbon coating to obtain silicon-carbon composite anode material.

[0008] The safety of the present invention is achieved by controlling the preparation of porous carbon in the front end, thereby regulating the crystallization form of silicon particles formed by chemical vapor deposition in the silicon-carbon composite material. The crystallization form of the silicon particles in the present invention can be obtained by Scherrer formula based on the full width at half maximum (FWHM) of the diffraction peak (2θ=28.4°) attributable to Si(111) in X-ray diffraction, and the silicon grain size range that meets the high safety requirement is 2.5-10 nm. The porous carbon substrate is formed by high-temperature pyrolysis and carbonization of polymer compounds, and can form a well-developed pore structure through pore-forming methods.

[0009] Further, in step (S1), the aldehyde monomer is selected from at least one of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde, preferably an aqueous formaldehyde solution; the molar ratio of the phenolic monomer to the aldehyde monomer is 1:2.2-2.7. The phenolic resin obtained by polycondensation of the above monomers in a certain proportion can have a moderately cross-linked structure, forming SP after carbonization. 3 A carbon precursor with a high hybridization ratio and suitable crosslinking degree. Phenolic and aldehyde monomers are added to water to prepare a 30-50 wt% solution for reaction. An alkaline catalyst is used in the reaction process, including but not limited to sodium hydroxide, potassium hydroxide, triethylamine, and ammonia, preferably 0.1-1 M ammonia, with the amount of ammonia being 1-5% of the total mass of the first and second phenolic monomers. This invention creatively introduces a small amount of cardiotonic phenol as the second phenolic monomer. On the one hand, its long-chain alkyl group introduces steric hindrance, preventing the ordered arrangement of carbon atoms into a graphite structure and promoting SP... 3 Hybridization; on the other hand, cardiac phenol can appropriately enhance the cross-linking structure, but the proportion of cardiac phenol in the phenol monomer needs to be controlled. If the cross-linking ratio is too high, it will not be conducive to the electrochemical performance of the final silicon-carbon composite material.

[0010] Further, in step (S1), the reaction is carried out at 80-100℃ for 2-4 hours, the first curing is carried out at 130-150℃ for 1-3 hours, followed by curing at 160-170℃ for 1-2 hours. After the cured material is dried, it is cured a second time at 180-190℃ for 0.5-1 hours. This secondary curing method can improve the crosslinking degree of the resin material and reduce carbon defects. The curing agent is selected from at least one of hexamethylenetetramine, N,N'-methylenebisacrylamide, paraformaldehyde, and epoxy silane coupling agent. The amount of curing agent is 3-5 wt% of the mass of the polymer material after drying. Further, the epoxy silane coupling agent is selected from at least one of KH-560, KH-561, and KH-563.

[0011] Preferably, during the second curing, the curing agent is a mixture of hexamethylenetetramine and an epoxy-based silane coupling agent in a mass ratio of 3-5:1. The inventors unexpectedly discovered that using the above-mentioned compounded curing agent for the second curing effectively improves the electrochemical performance and safety of the silicon-carbon composite material. A possible reason is that hexamethylenetetramine is a conventional phenolic resin curing agent; after curing, it provides a rigid framework, and the residual phenolic hydroxyl groups react with the epoxy groups in the epoxy-based silane coupling agent, increasing the crosslinking density. Furthermore, the epoxy-based silane coupling agent condenses at high temperatures into a three-dimensional Si-O-Si network, compensating for the localized weak crosslinking areas caused by the long-chain alkyl groups of the cardiotonic phenol.

[0012] Further, in step (S1), crushing is performed by crushing the solidified block to a particle size of <2mm using a jaw crusher or ball mill and passing it through a 100-200 mesh sieve; pre-oxidation is performed by holding the temperature at 230-300℃ for 1-2 hours in an oxygen-containing atmosphere, the purpose of which is to improve the degree of resin cross-linking; pyrolysis carbonization is performed by heating to 600-800℃ and holding the temperature for 2-5 hours in an inert atmosphere, the inert atmosphere being nitrogen and / or argon.

[0013] This invention obtains phenolic resin from specific monomers in a certain proportion, and then obtains SP after pre-oxidation and pyrolysis carbonization. 3 In Raman spectra, carbon substrates with high hybridization ratios show I... D / I G >1.1, and located between 1060-1200cm -1 T peak and 1500-1700cm -1 The G peak area ratio, i.e., S T / S G >0.5, in the C spectrum of XPS SP 3 / SP 2With a peak area >2, it is suitable as a carbon substrate for silane vapor deposition, enabling the deposited silicon to be deposited in porous carbon at the sub-nanometer scale. It has good electrochemical activity, and due to the larger silicon grain size, it has higher stability and significantly improved safety. In laser ignition experiments, it shows safety by not being able to ignite or having a long laser ignition time.

[0014] Further, in step (S2), the activation pore formation is high-temperature steam activation pore formation, the activation pore formation temperature is 800-1000℃, and the pore formation time is 5-10h; the high-temperature treatment is to keep warm at 1400-1600℃ for 1-3h, and the inert atmosphere is nitrogen and / or argon.

[0015] The porous carbon obtained in step (S2) has a pore volume of 0.8–1.2 cm³. 3 / g, micropores (<2 nm) account for 80-90%, mesopores (2-50 nm) account for 10-20%, and macropores (>50 nm) account for no more than 2%.

[0016] Further, in step (S3), the silicon source gas for vapor-phase silicon deposition is selected from at least one of silane and disilane. The silicon source gas is decomposed and deposited in the porous carbon substrate by chemical vapor deposition. The process conditions for vapor-phase silicon deposition are as follows: the silicon source gas is introduced at 450-550°C, and the flow rate of the silicon source gas is such that the silicon mass percentage in the silicon-carbon composite anode material is 40-60%, preferably 45-55%, such as 47%, 48%, 49%, 50%, 51%, 52%, 53%, and 54%.

[0017] Further, in step (S3), carbon coating is performed by introducing a carbon-containing gas at 600-700°C, and the thickness of the carbon layer after carbon coating is 3-10 nm, preferably 4-7 nm, such as 5 nm or 6 nm; the carbon-containing gas is selected from at least one of methane, ethane, propane, ethylene, and acetylene.

[0018] This invention achieves SP by adjusting the monomer formulation and secondary curing process in resin synthesis. 3 and SP 2 By controlling the degree of hybridization, the crosslinking degree and mechanical strength of the resin can be improved, and the defects of the porous carbon substrate can be reduced. During the later stage of deposition, silicon-carbon anode materials with a certain grain size can be prepared, which not only maintains the high performance of silicon-carbon anode materials, but also has higher safety. Attached Figure Description

[0019] Figure 1 The image shown is a scanning electron microscope (SEM) image of the silicon-carbon composite material prepared in Example 1. Figure 2 The Raman spectrum of the silicon-carbon composite material obtained in Example 1; Figure 3 The XPS C1s peak spectrum of the silicon-carbon composite material obtained in Example 1; Figure 4 The XRD diffraction pattern of the silicon-carbon composite material obtained in Example 1; Figure 5 The electrochemical performance of the silicon-carbon composite material prepared in Example 1 was tested. Figure 6 The curves show the comparison of the dQ / dV electrochemical differential capacitance of the silicon-carbon composite materials prepared in Example 1 and Comparative Example 3. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0021] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0022] The scanning electron microscope (SEM) used was a JEOL-6701F, and the transmission electron microscope (TEM) used was a JEM-2100F.

[0023] Example 1 (S1) A mixture of resorcinol and cardiotonic phenol at a molar ratio of 6:1 was used as the phenol monomer, and a 35wt% formaldehyde aqueous solution was used as the aldehyde monomer. The phenol monomer and aldehyde monomer were added to a reaction vessel at a molar ratio of 1:2.2. An appropriate amount of deionized water was added to prepare a 30wt% solution. Then, 0.2 M ammonia was added as a catalyst, with the amount of ammonia added ensuring that the mass of NH3·H2O was 5% of the mass of the phenol monomer. After the phenol monomer and aldehyde monomer were mixed evenly, the reaction vessel was heated to 90 ℃ and reacted for 2 h to obtain a semi-solid resin with a viscosity of 800 mPa·s. This resin was then transferred to a curing reactor and cured at 140 ℃ for 2 h, followed by a slow increase to 165 ℃ for another 2 h. After curing, the material was dried, and 3wt% of a curing agent (a mixture of hexamethylenetetramine and KH-560 at a mass ratio of 3:1) was added to the dried material. The temperature was then raised to 180 ℃ and maintained for 4 hours. h, a second curing process is performed to obtain phenolic resin blocks; the blocks are crushed to a particle size of <2 mm using a jaw crusher and a roller crusher, passed through a 100~200 mesh sieve, and then pre-oxidized at 280 ℃ for 2 h in an air atmosphere to further enhance the structural stability of the carbon material after carbonization; subsequently, the pre-oxidized material is heated to 800 ℃ at a heating rate of 5 ℃ / min and held for 2 h in a nitrogen atmosphere to obtain pyrolytic carbon with a high SP3 hybridization ratio; (S2) The above-mentioned pyrolytic carbon was subjected to steam activation at 900 °C for 20 h to create pores, resulting in a pore volume of 0.92 cm³.3 A porous carbon substrate with a micropore content of 86.3% and a mesopore content of 12.5% ​​was obtained by heating it to 1600 °C for 2 h under a nitrogen atmosphere. (S3) The porous carbon is pulverized to a suitable particle size of Dv50 = about 7 μm, put into a reactor and silane is introduced. The silane is introduced at 500 °C and penetrates into the pores of the porous carbon substrate to cause pyrolysis, resulting in a silicon-carbon composite material with a silicon mass ratio of 52.7%. Then, acetylene is introduced at 600 °C to perform chemical vapor deposition carbon coating, resulting in a silicon-carbon composite material with a carbon coating layer of 4-7 nm thickness.

[0024] Figure 1 The image shown is a scanning electron microscope (SEM) image of the silicon-carbon composite material prepared in Example 1, with a particle size of approximately 7 µm.

[0025] Figure 2 The Raman spectrum of the silicon-carbon composite material obtained in Example 1 is shown in Figure I. D / I G =1.2, and located between 1060-1200cm -1 T peak and 1500-1700cm -1 The G peak area ratio, i.e., S T / S G =0.91.

[0026] Figure 3 The XPS C1s peak spectrum of the silicon-carbon composite material obtained in Example 1 is shown below. 3 / SP 2 Peak area > 2.

[0027] Figure 4 The XRD diffraction pattern of the silicon-carbon composite material obtained in Example 1 was analyzed using an X-ray diffraction analyzer (XRD, Rigaku D / max 2500, Cu Kα), and the internal silicon crystals were found to be 3.5 nm in size.

[0028] The safety of the material powder was verified by observing the ignition process under laser irradiation and recording the ignition time. This invention prepares materials with larger silicon grain sizes. Because the internal silicon particles are no longer in a sub-nanometer state, they are difficult to be excited by the heat of the laser and therefore difficult to ignite. In contrast, materials with smaller silicon grains, where the internal silicon particles are in a sub-nanometer state, will undergo a reaction between silicon and carbon after laser irradiation to form silicon carbide, releasing a large amount of heat and causing the material to burn. The safety of the material can be determined by the ignition time after laser irradiation.

[0029] Example 2 The other conditions are the same as in Example 1, except that in step (S1), the molar ratio of phenol monomer to aldehyde monomer is changed from 1:2.2 to 1:2.7; during the second curing, the curing agent is a mixture of hexamethylenetetramine and KH-561 in a mass ratio of 5:1.

[0030] Example 3 The other conditions are the same as in Example 1, except that in step (S1), m-diphenol and cardiotonic phenol are compounded in a molar ratio of 10:1 as phenol monomers; during the second curing, the amount of curing agent added is 5 wt% of the dried material.

[0031] Example 4 The other conditions are the same as in Example 1, except that in step (S1), the pre-oxidation is replaced by keeping the temperature at 330 °C for 2 h in an air atmosphere.

[0032] Example 5 The other conditions are the same as in Example 1, except that in step (S1), the pre-oxidation is replaced by keeping the temperature at 240 °C for 2 h in an air atmosphere.

[0033] Example 6 The other conditions are the same as in Example 1, except that in step (S1), the curing agent is hexamethylenetetramine.

[0034] Example 7 The other conditions are the same as in Example 1, except that in step (S1), the curing agent is KH-560.

[0035] Example 8 The other conditions are the same as in Example 1, except that in step (S1), the curing agent is a mixture of paraformaldehyde and KH-560 in a mass ratio of 3:1.

[0036] Comparative Example 1 The other conditions are the same as in Example 1, except that in step (S1), the phenol monomer is m-diphenol, that is, no cardiac phenol is added.

[0037] Comparative Example 2 The other conditions are the same as in Example 1, except that in step (S1), the phenol monomers are a mixture of m-diphenol and cardiotonic phenol in a molar ratio of 4.8:1.

[0038] Comparative Example 3 The other conditions are the same as in Example 1, except that in step (S1), the phenol monomers are a mixture of m-diphenol and cardiotonic phenol in a molar ratio of 12.6:1.

[0039] Figure 6 The curves showing the comparison of the dQ / dV electrochemical differential capacitance of the silicon-carbon composite materials prepared in Example 1 and Comparative Example 3 indicate that the weakening of the 0.7V peak in Example 1 indicates a reduction in side reactions.

[0040] Comparative Example 4 The other conditions are the same as in Example 1, except that no curing agent is added during the second curing in step (S1).

[0041] Application examples The electrochemical performance of the silicon-based anode materials prepared in the examples and comparative examples was tested according to the following method: The prepared silicon-carbon composite material, carbon black, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) composite binder were mixed in a mass ratio of 80:10:10 to form a slurry (where the mass ratio of CMC and SBR was 1:1). The slurry was uniformly coated onto a copper foil current collector and dried under vacuum for 12 h to form a working electrode. A lithium sheet was used as the counter electrode, a glass fiber membrane (purchased from Whatman, UK) was used as the separator, and 1 mol / L LiPF6 (the solvent was a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) was used as the electrolyte. 1% VC and 5% FEC were added to the electrolyte. The cells were assembled into coin cells in an argon-atmosphere inert gas glove box from Braun, Germany.

[0042] The electrochemical performance of the silicon-carbon composite material prepared in Example 1 was tested, and the results are as follows: Figure 5 As shown, the charge / discharge range is 0-1.5 V. When charged and discharged at a current density of 0.2C, the material capacity can reach 1858.9 mAh / g, and the first-cycle coulombic efficiency is 93.9%.

[0043] The safety of a silicon-carbon composite material during application is measured by the ratio of the maximum value of dQ / dV in the 0.4-0.5 V range of the electrochemical differential capacitance curve to the specific capacitance of the composite material. A larger ratio indicates more silicon particles deposited on the outer surface of the particles, resulting in more interfacial side reactions, thus leading to poorer safety and lower cycle capacity retention. Figure 4 The battery cycle curve of the material prepared in Example 1 after 100 cycles at a 0.1C rate shows a capacity retention rate of up to 98.4%, proving that the silicon-carbon composite material obtained in this invention has high capacity, high safety and excellent cycle performance.

[0044] Laser ignition test of silicon-carbon materials: 1. Laser source preparation: The laser linear size is 30*1mm. The light source is perpendicular to the material layer, the distance between the light source and the material layer surface is 260mm, and the light source power is 30w.

[0045] 2. Experimental preparation: Fix a 300mm long * 200mm wide * 3mm thick polytetrafluoroethylene (PTFE) liner directly below the laser source. Prepare a ceramic boat with dimensions of 60mm long * 30mm wide * 20mm high. Evenly fill the ceramic boat with 12g of experimental material. After filling the ceramic boat with the material, place it on the PTFE liner.

[0046] 3. Operation Verification Process: Turn on the laser and slowly push the ceramic boat in, ensuring that the 30mm wide edge of the ceramic boat is parallel to the laser irradiation line. After the laser irradiates the surface of the material, stop pushing the ceramic boat and observe the ignition of the experimental material. If the material is ignited, stop pushing the ceramic boat until the material stops burning. Continue pushing the ceramic boat to the edge of the unignited part of the experimental material and observe the ignition of the material after laser irradiation. Repeat the above operation until the entire 60mm material layer is irradiated by the laser.

[0047] 4. End: Turn off the laser, pull the ceramic boat out of the laser equipment, and take samples for testing after the material has cooled down.

[0048] The negative electrode materials of the examples and comparative examples were tested according to the above method, and the results are shown in Table 1 below: Table 1 Performance Tests of Anode Materials .

[0049] In summary, the test results show that the composition and ratio of raw materials affect the degree of cross-linking, which in turn affects the degree of silicon crystallization, the laser ignition time (i.e., safety), and capacity retention. Furthermore, a slight increase in the pre-oxidation temperature of the raw materials results in larger deposited silicon grains, while a slight decrease results in smaller deposited silicon grains, with similar electrochemical performance. Therefore, the preparation method of the raw materials, pre-oxidation treatment, high-temperature treatment, and silane deposition temperature have a significant impact on the material's safety, capacity retention, capacity, and first-cycle efficiency. The preparation method of this invention is simple and efficient, and the resulting silicon-carbon composite material, when used as a negative electrode material for lithium-ion batteries, exhibits high first-cycle efficiency, excellent structural stability and cycle performance, and superior electrochemical performance.

Claims

1. A method for preparing a silicon-carbon composite anode material with improved safety, characterized in that, The following steps are involved: (S1) The first phenol monomer, the second phenol monomer, and an aldehyde monomer are reacted, and an alkaline catalyst is added for the first curing. After drying the obtained polymer, a curing agent is added for the second curing to obtain a phenolic resin block. Then, the block is crushed, pre-oxidized, and pyrolyzed to obtain pyrolytic carbon. The first phenol monomer is selected from at least one of resorcinol, phenol, p-chlorophenol, and p-cresol, and the second phenol monomer is cardiotonic phenol. The molar ratio of the first phenol monomer to the second phenol monomer is 6-10:

1. (S2) Pyrolytic carbon is activated to form pores, and then treated at high temperature under an inert atmosphere to obtain porous carbon; (S3) Porous carbon is sequentially subjected to vapor-phase silicon deposition and carbon coating to obtain silicon-carbon composite anode material.

2. The preparation method according to claim 1, characterized in that, In step (S1), the aldehyde monomer is selected from at least one of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde, and the molar ratio of phenol monomer to aldehyde monomer is 1:2.2-2.

7.

3. The preparation method according to claim 1, characterized in that, The phenol monomer and aldehyde monomer are added to water to prepare a 30-50 wt% solution for reaction; the reaction process uses an alkaline catalyst, including but not limited to sodium hydroxide, potassium hydroxide, triethylamine, and ammonia.

4. The preparation method according to claim 1, characterized in that, In step (S1), the reaction is carried out at 80-100℃ for 2-4 hours. The first curing is carried out at 130-150℃ for 1-3 hours, and then the temperature is raised to 160-170℃ for 1-2 hours. After the cured material is dried, it is cured a second time at 180-190℃ for 0.5-1 hours.

5. The preparation method according to claim 1, characterized in that, In step (S1), the curing agent is selected from at least one of hexamethylenetetramine, N,N'-methylenebisacrylamide, paraformaldehyde, and epoxy silane coupling agent, and the amount of curing agent used is 3-5 wt% of the mass of the material after the polymer is dried.

6. The preparation method according to claim 5, characterized in that, In step (S1), the epoxy silane coupling agent is selected from at least one of KH-560, KH-561, and KH-563.

7. The preparation method according to claim 5, characterized in that, During the second curing process, the curing agent is a mixture of hexamethylenetetramine and epoxy silane coupling agent in a mass ratio of 3-5:

1.

8. The preparation method according to claim 1, characterized in that, In step (S1), crushing involves using a jaw crusher or ball mill to crush the solidified block to a particle size of <2mm and passing it through a 100-200 mesh sieve; pre-oxidation involves holding the material at 230-300℃ for 1-2 hours in an oxygen-containing atmosphere, the purpose of which is to improve the degree of resin cross-linking; pyrolysis carbonization involves heating the material to 600-800℃ and holding it for 2-5 hours in an inert atmosphere, the inert atmosphere being nitrogen and / or argon.

9. The preparation method according to claim 1, characterized in that, In step (S2), the activation pore-forming is performed using high-temperature steam activation at a temperature of 800-1000℃ for 5-10 hours; the high-temperature treatment involves holding at 1400-1600℃ for 1-3 hours under an inert atmosphere of nitrogen and / or argon; and / or, The porous carbon obtained in step (S2) has a pore volume of 0.8–1.2 cm³. 3 / g, micropores (<2 nm) account for 80-90%, mesopores account for 10-20%, and macropores account for no more than 2%.

10. The preparation method according to claim 1, characterized in that, In step (S3), the silicon source gas for vapor-phase silicon deposition is selected from at least one of silane and disilane; the process conditions for vapor-phase silicon deposition are that the silicon source gas is introduced at 450-550°C, and the flow rate of the silicon source gas is such that the silicon mass ratio in the silicon-carbon composite anode material is 40-60%; and / or Carbon coating is performed by introducing a carbon-containing gas at 600-700℃, resulting in a carbon layer thickness of 3-10 nm. The carbon-containing gas is selected from at least one of methane, ethane, propane, ethylene, and acetylene.

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