Preparation method of silicon-carbon composite negative electrode material for improving safety

Abstract

The application 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 phenolic monomer, a second phenolic monomer and an aldehyde monomer, carrying out twice solidification in sequence, obtaining a phenolic aldehyde resin block, and then carrying out crushing, pre-oxidation and pyrolytic carbonization in sequence to obtain pyrolytic carbon; the second phenolic monomer is a cardiac phenol; (S2) carrying out activation and pore making on the pyrolytic carbon, carrying out high-temperature treatment in an inert atmosphere to obtain porous carbon; (S3) carrying out gas phase silicon deposition and carbon coating on the porous carbon in sequence to obtain the silicon-carbon composite negative electrode material. By adjusting the monomer formula in resin synthesis and the secondary solidification process, the application realizes the regulation of the SP 3 and SP 2 hybridization degree, improves the crosslinking degree and mechanical strength of the resin, reduces the defects of the porous carbon base, and can prepare the silicon-carbon negative electrode material with certain grain size in the deposition in the later stage, so that the silicon-carbon negative electrode material has higher safety in addition to the high performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion battery negative electrode materials, and particularly relates to a preparation method of a silicon-carbon composite negative electrode material with improved safety. BACKGROUND

[0002] In the current lithium ion battery technology field, to achieve higher energy density, using high specific capacity negative electrode materials to replace traditional graphite negative electrodes is a very effective way. Silicon-based negative electrode materials realize lithium storage by alloying with lithium, and have a theoretical specific capacity of 4200 mAh / g, and are regarded as the most potential graphite negative electrode replacement material. However, silicon-based negative electrode materials encounter severe challenges in practical application. In the process of lithium intercalation and deintercalation, silicon-based negative electrode materials will undergo significant volume change, which causes particle breakage and pulverization, and further causes serious degradation of the structure of silicon material particles, and also forms an unstable solid electrolyte interface layer, and finally leads to reduced battery cycle stability. To overcome the problems faced by silicon-based negative electrode materials, many pioneering researches have confirmed that reducing the characteristic size of silicon materials to the nanometer level can make silicon particles not break when they bear a large volume strain, and exhibit excellent electrochemical performance. For example, the volume strain generated by sub-nanometer silicon particles is much smaller than that of larger size silicon particles. Therefore, sub-nanometer silicon materials perform excellently in terms of kinetic characteristics and cycle performance, and reach the practical standard of silicon-based negative electrode materials.

[0003] At present, there are few methods for preparing sub-nanometer silicon materials, and the main research direction still focuses on nanometer or sub-nanometer, such as silicon nanosheets, silicon nanowires, silicon nanotubes and the like. The macroscopic size of these materials is usually several nanometers or even tens of nanometers, and it is difficult to effectively improve the electrochemical performance of the materials. Although alloying, redox method, sol-gel method, chemical vapor deposition method and mechanical grinding method can further significantly reduce the size of silicon materials, there are limitations in realizing uniform sub-nanometer preparation. Introducing gaseous silicon source into a carbon skeleton with a microporous structure is a relatively effective method for preparing sub-nanometer silicon materials. For example, gaseous silane is introduced into a microporous carbon skeleton by chemical vapor infiltration, and sub-nanometer silicon is formed by cracking the gaseous silane under suitable conditions, which can significantly improve the cycle stability of silicon-based materials. However, the sub-nanometer silicon formed by the gas deposition method itself has extremely high surface energy, and will form silicon carbide with the porous carbon substrate under high temperature conditions, causing severe heat release, affecting the safety of material application, and causing a large number of safety hazards in the application process of the battery. SUMMARY

[0004] To solve the safety problem of the silicon-carbon composite material prepared by the prior art, since the nano-silicon has high activity and is easy to be ignited, the safety needs to be improved, the purpose of the present application is to provide a method for improving the safety of sub-nanometer silicon particles in vapor deposition silicon-carbon material, and the core innovation points include:

[0005] I. Porous carbon substrate design: the substrate pore volume is selected to be 0.8-1.2 cm 3 / g, the micropore (<2 nm) accounts for 80-90%, the mesopore (2-50 nm) accounts for 10-20%, and the macropore (>50 nm) accounts for not more than 2%. This pore structure buffers the volume expansion of silicon through physical confinement effect, and at the same time provides uniform silicon deposition space, so that mainly sub-nanometer silicon of 2.5-10 nm is obtained after silicon deposition, and the safety is improved.

[0006] II. Cross-linked phenolic resin macromolecule is used as carbon source (high-temperature pyrolysis carbonization, forming high SP 2 hybrid carbon skeleton, enhancing mechanical strength, electrical conductivity and safety. The SP 2 hybrid degree of traditional phenol-formaldehyde carbon precursor is higher, and the SP 3 hybrid carbon skeleton of graphitized carbon is easy to react with high-activity sub-nanometer silicon at high temperature to generate silicon carbide, which releases heat violently and may cause ignition, which has safety hazards. The second phenolic monomer strong acid is added to obtain a phenolic resin carbon precursor with appropriate cross-linking degree, and the SP 3 hybrid degree of the obtained pyrolytic carbon is improved, and the SP 3 hybrid carbon has higher bond energy, which inhibits the reaction between silicon and carbon at high temperature, and improves the safety. However, increasing the proportion of SP 3 hybrid carbon will cause too much amorphous region and reduce the first coulomb efficiency. Therefore, the SP

[0007] III. Precise control of silicon particle crystallinity: adjust the silicon deposition conditions (temperature, gas flow rate) by chemical vapor deposition (CVD) to balance the risk of expansion inhibition and safety.

[0008] The present application realizes the above-mentioned purpose by the following technical solutions:

[0009] A preparation method of a silicon-carbon composite negative electrode material with improved safety, comprising the following steps:

[0010] (S1) reacting a first phenolic monomer, a second phenolic monomer and an aldehyde monomer, adding an alkali catalyst for the first solidification, drying the obtained polymer, and then adding a curing agent for the second solidification to obtain a phenolic resin block, and then sequentially performing crushing, pre-oxidation and pyrolytic carbonization to obtain pyrolytic carbon; the first phenolic monomer is selected from at least one of resorcinol, phenol, p-chlorophenol and p-cresol, and the second phenolic monomer is ephedrine; the molar ratio of the first phenolic monomer to the second phenolic monomer is 6-10:1;

[0011] (S2) activating and forming pores in the pyrolytic carbon, and high-temperature treatment in an inert atmosphere to obtain porous carbon;

[0012] (S3) sequentially performing gas-phase silicon deposition and carbon coating on the porous carbon to obtain a silicon-carbon composite negative electrode material.

[0013] The safety is achieved by regulating the crystalline form of the silicon particles formed by chemical vapor deposition in the silicon-carbon composite material prepared by the porous carbon; the crystalline form of the silicon particles can be calculated by the half-peak width of the diffraction peak (2θ=28.4°) attributed to Si(111) in X-ray diffraction, and the silicon grain size range meeting the high safety is 2.5-10 nm;

[0014] The porous carbon substrate is formed by high-temperature pyrolytic carbonization of a high molecular compound, and a developed pore structure can be formed by pore forming.

[0015] Further, in step (S1), the aldehyde monomer is selected from at least one of formaldehyde, acetaldehyde, propyl aldehyde, butyl aldehyde and benzaldehyde, and preferably formaldehyde aqueous solution; the molar ratio of the phenolic monomer to the aldehyde monomer is 1:2.2-2.7. The phenolic aldehyde resin obtained by condensation of the above monomers in a certain proportion can have a moderate crosslinking structure, and form SP 3 carbon after carbonization. The phenolic monomer and the aldehyde monomer are configured into a 30-50wt% solution in water for reaction; an alkali catalyst is used in the reaction process, including but not limited to sodium hydroxide, potassium hydroxide, triethylamine and ammonia water, and preferably 0.1-1M ammonia water, and the amount of ammonia water is 1-5% of the total mass of the first phenolic monomer and the second phenolic monomer. A small amount of ephedrine is creatively introduced as the second phenolic monomer, which on the one hand introduces steric hindrance of long-chain alkyl to hinder the ordered arrangement of carbon atoms into a graphite structure, and on the other hand promotes SP 3 hybridization; on the other hand, ephedrine can appropriately strengthen the crosslinking structure, but the proportion of ephedrine in the phenolic monomer needs to be controlled, and a too high crosslinking ratio is also not conducive to the electrochemical performance of the final silicon-carbon composite material.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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%.

[0022] 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%.

[0023] 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.

[0024] 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

[0025] Figure 1 The image shown is a scanning electron microscope (SEM) image of the silicon-carbon composite material prepared in Example 1.

[0026] Figure 2 The Raman spectrum of the silicon-carbon composite material obtained in Example 1;

[0027] Figure 3 The XPS C1s peak spectrum of the silicon-carbon composite material obtained in Example 1;

[0028] Figure 4 The XRD diffraction pattern of the silicon-carbon composite material obtained in Example 1;

[0029] Figure 5 The electrochemical performance of the silicon-carbon composite material prepared in Example 1 was tested.

[0030] 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

[0031] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0033] The scanning electron microscope (SEM) used was a JEOL-6701F, and the transmission electron microscope (TEM) used was a JEM-2100F.

[0034] Example 1

[0035] (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;

[0036] (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.

[0037] (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.

[0038] 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.

[0039] 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 -1The G peak area ratio, i.e., S T / S G =0.91.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Example 2

[0044] 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.

[0045] Example 3

[0046] 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.

[0047] Example 4

[0048] 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.

[0049] Example 5

[0050] 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.

[0051] Example 6

[0052] The other conditions are the same as in Example 1, except that in step (S1), the curing agent is hexamethylenetetramine.

[0053] Example 7

[0054] The other conditions are the same as in Example 1, except that in step (S1), the curing agent is KH-560.

[0055] Example 8

[0056] 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.

[0057] Comparative Example 1

[0058] 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.

[0059] Comparative Example 2

[0060] 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.

[0061] Comparative Example 3

[0062] 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.

[0063] 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.

[0064] Comparative Example 4

[0065] The other conditions are the same as in Example 1, except that no curing agent is added during the second curing in step (S1).

[0066] Application examples

[0067] 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.

[0068] 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%.

[0069] 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.

[0070] Laser ignition test of silicon-carbon materials:

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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:

[0076] Table 1 Performance Tests of Anode Materials

[0077] .

[0078] 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 producing a silicon-carbon composite negative electrode material for improving safety, characterized by, Comprising the following steps: (S1) reacting a first phenolic monomer, a second phenolic monomer and an aldehyde monomer, adding an alkali catalyst for the first curing, drying the obtained polymer, then adding a curing agent for the second curing to obtain a phenolic resin block, and then sequentially crushing, pre-oxidizing and pyrolyzing carbonizing to obtain pyrolytic carbon; the first phenolic monomer is selected from at least one of resorcinol, phenol, p-chlorophenol and p-cresol, and the second phenolic monomer is oleoresin; the molar ratio of the first phenolic monomer to the second phenolic monomer is 6-10:1; the curing agent is a compound of hexamethylenetetramine and epoxy silane coupling agent in a mass ratio of 3-5:1; (S2) activating and pore-forming the pyrolytic carbon, and high-temperature treatment in an inert atmosphere to obtain porous carbon; (S3) sequentially depositing silicon gas and coating carbon on the porous carbon to obtain a silicon-carbon composite negative electrode material.

2. The production method according to claim 1, characterized by, In step (S1), the aldehyde monomer is selected from at least one of formaldehyde, acetaldehyde, propyl aldehyde, butyl aldehyde and benzaldehyde, and the molar ratio of the phenolic monomer to the aldehyde monomer is 1:2.2-2.

7.

3. The preparation method according to claim 1, characterized in that, The phenolic monomer and the aldehyde monomer are configured into a 30-50wt% solution in water for reaction; an alkali catalyst is used in the reaction process, including but not limited to sodium hydroxide, potassium hydroxide, triethylamine and ammonia.

4. The production method according to claim 1, characterized by, In step (S1), the reaction is carried out at 80-100℃ for 2-4h, the first curing is carried out at 130-150℃ for 1-3h, then the temperature is raised to 160-170℃ for 1-2h, and after the cured material is dried, the second curing is carried out at 180-190℃ for 0.5-1h.

5. The preparation method according to claim 1, 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.

6. The method of claim 1, wherein, In step (S1), the crushing is carried out by a jaw crusher or a ball mill to break the cured block to a particle size of <2mm and pass through a 100-200 mesh screen; the pre-oxidation is carried out at 230-300℃ for 1-2h in an oxygen-containing atmosphere, and the purpose of pre-oxidation is to increase the cross-linking degree of the resin; the pyrolytic carbonization is carried out in an inert atmosphere by raising the temperature to 600-800℃ for 2-5h, and the inert atmosphere is nitrogen and / or argon.

7. The preparation method according to claim 1, characterized in that, In step (S2), the activating and pore-forming is high-temperature steam activating and pore-forming, the activating and pore-forming temperature is 800-1000℃, and the pore-forming time is 5-10h; the high-temperature treatment is carried out at 1400-1600℃ for 1-3h in an inert atmosphere of nitrogen and / or argon; and / or The pore volume of the porous carbon obtained in step (S2) is 0.8-1.2 cm³ / g, the micropore ratio is 80-90%, the mesopore ratio is 10-20%, and the macropore ratio is not higher than 2%.

8. The method of claim 1, wherein, In step (S3), the silicon source gas for the silicon deposition is selected from at least one of monosilane and disilane; the process conditions for the silicon deposition are that the silicon source gas is introduced at 450-550℃, and the flow rate of the silicon source gas is such that the silicon mass ratio in the silicon-carbon composite negative electrode material is 40-60%; and / or The carbon coating is carried out by introducing a carbon-containing gas at 600-700℃, and the thickness of the carbon layer after the carbon coating is 3-10nm; the carbon-containing gas is selected from at least one of methane, ethane, propane, ethylene and acetylene.

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