Silicon-carbon composite material, preparation method thereof and lithium ion battery negative electrode

Abstract

This invention provides a silicon-carbon composite material, its preparation method, and a lithium-ion battery anode, belonging to the field of lithium-ion battery technology. The invention employs vapor deposition to coat an organic layer onto the surface of porous carbon, forming a selective coating structure of "outer sealed, inner hollow" through size effect. The formed organic layer is stable at lower temperatures and chemically inert, preventing silicon deposition on its surface during the first silicon deposition. By selecting silicon source deposition parameters, small-molecule silicon sources can penetrate the organic coating layer and enter the pores of the porous carbon for deposition. Then, by heating to remove the organic coating layer, the pores of the porous carbon reopen, inducing silicon to continue depositing within the pores during the second silicon deposition, avoiding pore blockage and improving the pore utilization rate of the porous carbon. The open pores provide space for silicon expansion, improving cycle stability. Finally, the deposited carbon coating layer protects the silicon, enhancing the stability of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a silicon-carbon composite material, its preparation method, and a lithium-ion battery negative electrode. Background Technology

[0002] In the field of lithium-ion batteries, the pursuit of high energy density, high rate capability, and high safety has become the core direction of technological development. Traditional graphite anodes, with a theoretical specific capacity of only 372 mAh / g, are gradually failing to meet the stringent battery performance requirements of industries such as laptops, drones, electric vehicles, and robots.

[0003] Silicon-based materials, with their ultra-high theoretical specific capacity of 4200 mAh / g and abundant resource reserves, are considered the most promising next-generation anode materials. However, the practical application of silicon-based materials faces two major bottlenecks: first, the dramatic volume expansion (over 300%) during charge and discharge easily leads to electrode material pulverization and structural damage, severely impairing cycle stability; second, the poor intrinsic conductivity of pure silicon limits its rate performance. These problems have constrained the commercialization of silicon-based anodes.

[0004] To overcome these bottlenecks, current research mainly focuses on structural design, composite methods, and materials. Chemical vapor deposition (CVD) is one of the mainstream technologies for silicon-based anodes. It involves introducing a silicon source precursor into a porous carbon framework, causing it to decompose and deposit nano-silicon particles in situ, thus constructing a structurally stable silicon-carbon composite material. This significantly alleviates the volume expansion problem. While CVD improves the performance of silicon-carbon composites to some extent, it lacks effective means to control the silicon deposition location. At high temperatures, silane gas deposits not only inside the carbon channels but also on the surface of the carbon particles. As deposition progresses, it clogs the pore openings, resulting in low utilization of the internal channels and hindering the full utilization of the specific surface area advantage of porous carbon. Furthermore, after the pore openings of the porous carbon are clogged, the silicon deposited on the carbon particle surface lacks space to support the volume expansion during charging and discharging, leading to repeated rupture and regeneration of the SEI film and accelerating capacity decay. Summary of the Invention

[0005] The purpose of this invention is to provide a silicon-carbon composite material, its preparation method, and a lithium-ion battery anode. The preparation method provided by this invention allows for the directional deposition of silicon within the pores of porous carbon, resulting in high pore utilization. The lithium-ion battery assembled from the prepared silicon-carbon composite material exhibits high specific capacity and high cycle stability.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a silicon-carbon composite material, comprising the following steps: Organic coating layers are deposited on porous carbon using vapor deposition to obtain organically coated porous carbon. The deposition temperature of the organic coating layer is 80~200℃. The organic layer material in the organically coated porous carbon includes one or more of oligomeric polyethylene glycol, camphor, paraffinic hydrocarbons, and naphthalene. The average molecular weight of the oligomeric polyethylene glycol is 1000~2000. The pore size distribution of the porous carbon is 2~50nm. The organic layer coated with porous carbon is subjected to a first silicon deposition to obtain a first silicon-carbon intermediate; the silicon source for the first silicon deposition includes cyclopentylsilane, cyclohexylsilane, neopentylsilane or propane; the temperature of the first silicon deposition is 80~200℃; The first silicon-carbon intermediate is pyrolyzed to obtain the second silicon-carbon intermediate; the pyrolysis temperature is 350~500℃. The second silicon-carbon intermediate is subjected to a second silicon deposition to obtain a third silicon-carbon intermediate; the temperature of the second silicon deposition is 350~600℃, the silicon source flow rate is 15~25L / min, the carrier gas flow rate is 15~25L / min, and the deposition time is 60~240min. Carbon coating layer deposition is performed on the third silicon-carbon intermediate to obtain silicon-carbon composite material; the carbon coating layer deposition temperature is 350~600℃, the carbon source flow rate is 10~20L / min, the carrier gas flow rate is 30~40L / min, and the deposition time is 60~180min.

[0007] Preferably, the carrier gas flow rate for the organic coating layer deposition is 1~3L / min, and the deposition time is 40~80min.

[0008] Preferably, the parameters for the first silicon deposition include: silicon source flow rate of 10~20L / min, carrier gas flow rate of 20~30L / min, and deposition time of 30~180min.

[0009] Preferably, the pyrolysis time is 30-60 minutes.

[0010] Preferably, the silicon source for the second silicon deposition is silane or ethyl silane.

[0011] Preferably, the carbon source for the carbon coating layer deposition is acetylene.

[0012] Preferably, the specific surface area of ​​the porous carbon is not less than 2000 m². 2 / g.

[0013] Preferably, the porous carbon includes MOF-derived porous carbon, biomass-derived porous carbon, or resin-derived porous carbon.

[0014] The present invention also provides a silicon-carbon composite material prepared by the preparation method described in the above technical solution.

[0015] The present invention also provides a lithium-ion battery anode, wherein the active material of the lithium-ion battery anode is the silicon-carbon composite material described in the above technical solution.

[0016] This invention provides a method for preparing silicon-carbon composite materials. The method employs vapor deposition to coat an organic layer onto the surface of porous carbon. During vapor deposition, the molecules of the organic layer material preferentially adsorb onto the abundant oxygen-containing functional groups on the porous carbon surface. Upon entering the nanopores, diffusion is significantly restricted, forming a selective coating structure of "outer sealed, inner hollow." The formed organic layer is stable at lower temperatures and chemically inert, preventing silicon deposition on its surface during the first silicon deposition. By performing the first silicon deposition at a lower temperature, the silicon source gas decomposes more slowly, allowing sufficient time for diffusion. Small-molecule silicon sources can penetrate the organic coating layer and enter the pores of the porous carbon, where abundant defects within the pores... The presence of functional groups provides thermodynamic and kinetic advantages for preferential nucleation and growth. After silicon deposition within the porous carbon channels, the organic coating layer is removed by heating, reopening the pores of the porous carbon. During the second silicon deposition, the silicon already deposited within the channels can induce further silicon deposition within the channels, reducing silicon deposition at the pore openings. By limiting the parameters of the second silicon deposition, the amount of silicon deposition is increased while avoiding pore blockage, thus improving the pore utilization rate of the porous carbon. The open channels provide space for silicon expansion, which can improve cycle stability when used as a lithium-ion battery anode. Finally, the deposited carbon coating layer protects the silicon and improves the stability of the composite material. The results of the embodiments show that the silicon-carbon composite material prepared by the method provided by the present invention can achieve a pore utilization rate of 90%, the specific capacity of the assembled battery reaches 2220 mAh / g, the first-cycle efficiency is higher than 92%, and the capacity retention rate after 100 cycles at 0.1C is higher than 91%. Attached Figure Description

[0017] Figure 1 This is a SEM image of the silicon-carbon composite material prepared in Example 1 of the present invention. Detailed Implementation

[0018] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0019] The purity of all raw materials used in this invention is not particularly limited. However, this invention preferably uses raw materials with high purity or conventional purity in the field of lithium-ion batteries. In the embodiments of this invention, the purity of the silane is required to be greater than 99.99%, and the porous carbon ash content is less than 0.5%.

[0020] This invention provides a method for preparing a silicon-carbon composite material, comprising the following steps: Organic coating layers are deposited on porous carbon using vapor deposition to obtain organically coated porous carbon. The deposition temperature of the organic coating layer is 80~200℃. The organic layer material in the organically coated porous carbon includes one or more of oligomeric polyethylene glycol, camphor, paraffinic hydrocarbons, and naphthalene. The average molecular weight of the oligomeric polyethylene glycol is 1000~2000. The pore size distribution of the porous carbon is 2~50nm. The organic layer coated with porous carbon is subjected to a first silicon deposition to obtain a first silicon-carbon intermediate; the silicon source for the first silicon deposition includes cyclopentylsilane, cyclohexylsilane, neopentylsilane or propane; the temperature of the first silicon deposition is 80~200℃; The first silicon-carbon intermediate is pyrolyzed to obtain the second silicon-carbon intermediate; the pyrolysis temperature is 350~500℃. The second silicon-carbon intermediate is subjected to a second silicon deposition to obtain a third silicon-carbon intermediate; the temperature of the second silicon deposition is 350~600℃. A carbon coating layer is deposited on the third silicon-carbon intermediate to obtain a silicon-carbon composite material; the carbon coating layer deposition temperature is 350~600℃.

[0021] This invention employs vapor phase deposition to deposit an organic coating layer on porous carbon, thereby obtaining porous carbon coated with an organic layer.

[0022] In this invention, the porous carbon has a pore size distribution of 2-50 nm, preferably 2-20 nm. A pore size distribution within this range restricts the entry of organic layer material molecules into the pores of the porous carbon, forming a selective coating layer that is "sealed on the outside and hollow on the inside".

[0023] In this invention, the specific surface area of ​​the porous carbon is preferably not less than 2000 m². 2 / g. The specific surface area of ​​porous carbon is within the above range, which can provide space for the expansion of silicon, and can further improve cycle stability when used as a negative electrode in lithium-ion batteries.

[0024] In this invention, the porous carbon preferably includes MOF-derived porous carbon, biomass-derived porous carbon, or resin-derived porous carbon. These porous carbons are common types, and their use is beneficial for improving the stability of silicon-carbon composite materials.

[0025] As one embodiment of the present invention, the porous carbon can be dried before use; the drying process can be as follows: the porous carbon is placed in the raw material tank of the vapor deposition device, and nitrogen is introduced at 120°C for 1 hour for purging, and the nitrogen flow rate can be 50 L / min.

[0026] In this invention, the organic layer material coating the porous carbon comprises one or more of oligomeric polyethylene glycol, camphor, paraffinic hydrocarbons, and naphthalene, wherein the average molecular weight of the oligomeric polyethylene glycol is 1000-2000. These materials can be deposited at relatively low temperatures and can undergo residue-free pyrolysis at higher temperatures.

[0027] In this invention, the temperature for depositing the organic coating layer is 80~200℃, preferably 100~150℃; as one embodiment of this invention, the temperature for depositing the organic coating layer can be 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 160℃, 180℃, or 190℃. Depositing the organic coating layer within the above temperature range allows for the coating of an organic layer onto the porous carbon surface, preventing pyrolysis of the material.

[0028] In this invention, the carrier gas flow rate for the organic coating layer deposition is preferably 1~3 L / min, more preferably 2 L / min; the deposition time for the organic coating layer deposition is preferably 40~80 min, more preferably 60 min. With the parameters for organic coating layer deposition within the above ranges, an organic layer with a thickness of 5~20 nm can be obtained, which facilitates the passage of small molecule silanes and the deposition of silicon within the pores of porous carbon.

[0029] In one embodiment of the present invention, the organic layer material coated in the porous carbon can be heated to the boiling point first, and then carried into the reaction chamber of vapor deposition using a carrier gas; the carrier gas can be nitrogen.

[0030] After obtaining the porous carbon coated with an organic layer, the present invention performs a first silicon deposition on the porous carbon coated with the organic layer to obtain a first silicon-carbon intermediate.

[0031] In this invention, the silicon source for the first silicon deposition includes cyclopentylsilane, cyclohexylsilane, neopentylsilane, or propane. These silicon sources have relatively weak Si-Si bond energies, allowing for silicon deposition through decomposition at lower temperatures.

[0032] In this invention, the temperature for the first silicon deposition is 80~200℃, preferably 120~150℃; as one embodiment of this invention, the temperature for the first silicon deposition can be 100℃, 120℃, 140℃, 160℃, 180℃, or 190℃. When the temperature for the first silicon deposition is within the above range, the decomposition of the organic coating layer can be avoided during silicon deposition.

[0033] In this invention, the silicon source flow rate for the first silicon deposition is preferably 10-20 L / min, more preferably 15 L / min; the carrier gas flow rate is preferably 20-30 L / min, more preferably 25 L / min; and the deposition time is preferably 30-180 min, more preferably 60-120 min. Parameters for the first silicon deposition within the above ranges facilitate the deposition of the silicon source through the organic coating layer within the pores of the porous carbon.

[0034] In one embodiment of the present invention, the carrier gas for the first silicon deposition can be nitrogen.

[0035] After obtaining the first silicon-carbon intermediate, the present invention pyrolyzes the first silicon-carbon intermediate to obtain the second silicon-carbon intermediate.

[0036] In this invention, the pyrolysis temperature is 350~500℃, preferably 400~450℃; as one embodiment of this invention, the pyrolysis temperature can be 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, 480℃, or 500℃. Within the above temperature range, the organic coating layer can be fully pyrolyzed.

[0037] In this invention, the pyrolysis time is preferably 30-60 minutes. A pyrolysis time within this range is beneficial for the complete pyrolysis of the organic coating layer.

[0038] In one embodiment of the present invention, the pyrolysis can be carried out in a vapor deposition reaction chamber, and the pyrolysis product gas is carried out by a carrier gas; the heating rate of the vapor deposition reaction chamber can be 2~10℃ / min or 5℃ / min.

[0039] After obtaining the second silicon-carbon intermediate, the present invention performs a second silicon deposition on the second silicon-carbon intermediate to obtain the third silicon-carbon intermediate.

[0040] In this invention, the temperature for the second silicon deposition is 350~600℃, preferably 400~500℃; as one embodiment of this invention, the temperature for the second silicon deposition can be 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, or 550℃. Within the above temperature range, silicon deposition can be efficiently performed within the pores and on the surface of porous carbon; the deposition kinetics cause the silicon source to preferentially diffuse into the interior of the pores for reaction, while the deposition rate at the pore openings is slow.

[0041] In this invention, the silicon source for the second silicon deposition is preferably silane or silane; the flow rate of the silicon source is 15-25 L / min, preferably 20 L / min; the carrier gas flow rate for the second silicon deposition is 15-25 L / min, preferably 20 L / min; and the deposition time for the second silicon deposition is 60-240 min, preferably 120-180 min. Parameters for the second silicon deposition within the above ranges are beneficial for silicon deposition and can also prevent excessive deposition from clogging the orifices.

[0042] In one embodiment of the present invention, the carrier gas for the second silicon deposition can be nitrogen.

[0043] After obtaining the third silicon-carbon intermediate, the present invention performs carbon coating layer deposition on the third silicon-carbon intermediate to obtain a silicon-carbon composite material.

[0044] In this invention, the carbon coating layer is deposited at a temperature of 350~600℃, preferably 400~550℃; as one embodiment of this invention, the carbon coating layer deposition temperature can be 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, or 550℃. Within the above temperature range, carbon deposition can be performed efficiently on the surface of the material.

[0045] In this invention, the carbon source for the carbon coating deposition is preferably acetylene; the carbon source flow rate is 10-20 L / min, preferably 15 L / min; the carrier gas flow rate for the carbon coating deposition is 30-40 L / min, preferably 35 L / min; and the deposition time for the carbon coating deposition is 60-180 min, preferably 120 min. Parameters for carbon coating deposition within the above ranges are beneficial for carbon coating deposition and prevent excessive deposition that could clog the pores.

[0046] In one embodiment of the present invention, the carrier gas for the carbon coating layer deposition can be nitrogen.

[0047] In one embodiment of the present invention, after the carbon coating layer is deposited, heating can be stopped, acetylene supply can be stopped, and the mixture can be cooled to room temperature in a nitrogen atmosphere.

[0048] This invention employs vapor deposition to coat an organic layer onto the surface of porous carbon. During vapor deposition, the molecules of the organic layer material preferentially adsorb onto the abundant oxygen-containing functional groups on the porous carbon surface. Upon entering the nanopores, diffusion is significantly restricted, forming a selective coating structure that is "outer-sealed and inner-hollow." The resulting organic layer is stable at lower temperatures and chemically inert, preventing silicon deposition on its surface during the first silicon deposition. By performing the first silicon deposition at a lower temperature, the silicon source gas decomposes more slowly, allowing sufficient time for diffusion. Small-molecule silicon sources can penetrate the organic coating layer and enter the pores of the porous carbon, where abundant defects within the pores... The presence of functional groups provides thermodynamic and kinetic advantages for preferential nucleation and growth. After silicon deposition within the porous carbon channels, the organic coating layer is removed by heating, reopening the pores of the porous carbon. During the second silicon deposition, the silicon already deposited within the channels can induce further silicon deposition within the channels, reducing silicon deposition at the pore openings. By limiting the parameters of the second silicon deposition, the amount of silicon deposition is increased while avoiding pore blockage, thus improving the utilization rate of the porous carbon channels. The open channels provide space for silicon expansion, which can improve cycle stability when used as a negative electrode in lithium-ion batteries. Finally, the deposited carbon coating layer protects the silicon and improves the stability of the composite material.

[0049] The present invention also provides a silicon-carbon composite material prepared by the preparation method described in the above technical solution.

[0050] The present invention also provides a lithium-ion battery anode, wherein the active material of the lithium-ion battery anode is the silicon-carbon composite material described in the above technical solution.

[0051] This invention does not impose any particular limitations on other materials and preparation methods for the lithium-ion battery anode; conventional materials and preparation methods in the art can be used.

[0052] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0053] Example 1 A method for preparing a silicon-carbon composite material, comprising the following steps: Porous carbon derived from MOF has a specific surface area of ​​2100 m². 2 / g, with a pore size distribution of 2~20nm, is placed in the raw material tank of the vapor deposition apparatus and fed into the reaction chamber through a conveying device; the reaction chamber is heated to 120℃ and kept at a stable temperature, high-purity nitrogen is turned on at a flow rate of 50L / min, and the tail gas valve group is opened for 1 hour. Oligomeric polyethylene glycol (average molecular weight 1500) was heated to 150°C to volatilize. Using nitrogen as the carrier gas, the oligomeric polyethylene glycol vapor was introduced into the vapor deposition reaction chamber at a flow rate of 2L / min. Deposition was carried out at 120°C for 60min to form an organic coating layer on the outer surface of porous carbon, thus obtaining organic layer coated porous carbon. The reaction gas was switched to cyclopentylsilane at a flow rate of 15 L / min, nitrogen at a flow rate of 25 L / min, and the temperature of the vapor deposition reaction chamber was 130 °C. The organic layer coated with porous carbon was subjected to first silicon deposition for 120 min to obtain the first silicon-carbon intermediate. After the first silicon deposition is completed, the reaction gas is cut off, the nitrogen flow rate is 5L / min, and the temperature of the vapor deposition reaction chamber is raised to 380℃ at a rate of 5℃ / min. The temperature is held for 60min for pyrolysis to obtain the second silicon-carbon intermediate. After pyrolysis, the temperature of the vapor deposition reaction chamber is raised to 500°C at a rate of 2°C / min. Silane is introduced at a flow rate of 20 L / min, and nitrogen is introduced at a flow rate of 20 L / min. The second silicon-carbon intermediate is subjected to second silicon deposition for 180 min to obtain the third silicon-carbon intermediate. After the second silicon deposition is completed, the reaction gas is cut off, the temperature of the vapor deposition reaction chamber is raised to 550°C at a rate of 2°C / min, acetylene is introduced at a flow rate of 15L / min, nitrogen at a flow rate of 35L / min, and carbon coating layer is deposited on the third silicon-carbon intermediate for 120min. After the carbon coating layer is deposited, the reaction gas is cut off, heating is stopped, and the mixture is cooled to room temperature in a nitrogen atmosphere. The reactants are then removed to obtain the silicon-carbon composite material.

[0054] The silicon-carbon composite material was observed using a scanning electron microscope, and the SEM image is shown below. Figure 1 As shown. From Figure 1 As can be seen, the surface of the silicon-carbon composite material is smooth and intact.

[0055] Example 2 A method for preparing a silicon-carbon composite material, comprising the following steps: Porous carbon derived from MOF has a specific surface area of ​​2100 m². 2 / g, with a pore size distribution of 2~20nm, is placed in the raw material tank of the vapor deposition apparatus and fed into the reaction chamber through a conveying device; the reaction chamber is heated to 120℃ and kept at a stable temperature, high-purity nitrogen is turned on at a flow rate of 50L / min, and the tail gas valve group is opened for 1 hour. Camphor was heated to 160°C to volatilize. Using nitrogen as the carrier gas, the camphor vapor was introduced into the vapor deposition reaction chamber at a flow rate of 2L / min. The vapor was deposited at 120°C for 60min to form an organic coating layer on the outer surface of the porous carbon, thus obtaining organic-coated porous carbon. The reaction gas was switched to cyclopentylsilane at a flow rate of 15 L / min, nitrogen at a flow rate of 25 L / min, and the temperature of the vapor deposition reaction chamber was 130 °C. The organic layer coated with porous carbon was subjected to first silicon deposition for 120 min to obtain the first silicon-carbon intermediate. After the first silicon deposition is completed, the reaction gas is cut off, the nitrogen flow rate is 5L / min, and the temperature of the vapor deposition reaction chamber is raised to 380℃ at a rate of 5℃ / min. The temperature is held for 60min for pyrolysis to obtain the second silicon-carbon intermediate. After pyrolysis, the temperature of the vapor deposition reaction chamber is raised to 500°C at a rate of 2°C / min. Silane is introduced at a flow rate of 20 L / min, and nitrogen is introduced at a flow rate of 20 L / min. The second silicon-carbon intermediate is subjected to second silicon deposition for 180 min to obtain the third silicon-carbon intermediate. After the second silicon deposition is completed, the reaction gas is cut off, the temperature of the vapor deposition reaction chamber is raised to 550°C at a rate of 2°C / min, acetylene is introduced at a flow rate of 15L / min, nitrogen at a flow rate of 35L / min, and carbon coating layer is deposited on the third silicon-carbon intermediate for 120min. After the carbon coating layer is deposited, the reaction gas is cut off, heating is stopped, and the mixture is cooled to room temperature in a nitrogen atmosphere. The reactants are then removed to obtain the silicon-carbon composite material.

[0056] Comparative Example 1 A method for preparing a silicon-carbon composite material, the steps of which are the same as in Example 1, except that the organic coating layer deposition and pyrolysis are omitted.

[0057] Comparative Example 2 A method for preparing a silicon-carbon composite material, comprising the following steps: Porous carbon derived from MOF has a specific surface area of ​​2100 m². 2 / g, with a pore size distribution of 2~20nm, is placed in the raw material tank of the vapor deposition apparatus and fed into the reaction chamber through a conveying device; the reaction chamber is heated to 120℃ and kept at a stable temperature, high-purity nitrogen is turned on at a flow rate of 50L / min, and the tail gas valve group is opened for 1 hour. Propylene was introduced into the vapor deposition reaction chamber at a flow rate of 20 L / min, nitrogen flow rate was 20 L / min, and deposition was carried out at 120 °C for 30 min to form a carbon coating layer on the outer surface of porous carbon, thus obtaining carbon-coated porous carbon. The reaction gas was switched to cyclopentylsilane at a flow rate of 15 L / min, nitrogen at a flow rate of 25 L / min, and the temperature of the vapor deposition reaction chamber was 130 °C. The carbon-coated porous carbon was subjected to first silicon deposition for 120 min to obtain the first silicon-carbon intermediate. After the first silicon deposition is completed, the reaction gas is cut off, the nitrogen flow rate is 5L / min, and the temperature of the vapor deposition reaction chamber is raised to 380℃ at a rate of 5℃ / min. The temperature is held for 60min for pyrolysis to obtain the second silicon-carbon intermediate. After pyrolysis, the temperature of the vapor deposition reaction chamber is raised to 500°C at a rate of 2°C / min. Silane is introduced at a flow rate of 20 L / min, and nitrogen is introduced at a flow rate of 20 L / min. The second silicon-carbon intermediate is subjected to second silicon deposition for 180 min to obtain the third silicon-carbon intermediate. After the second silicon deposition is completed, the reaction gas is cut off, the temperature of the vapor deposition reaction chamber is raised to 550°C at a rate of 2°C / min, acetylene is introduced at a flow rate of 15L / min, nitrogen at a flow rate of 35L / min, and carbon coating layer is deposited on the third silicon-carbon intermediate for 120min. After the carbon coating layer is deposited, the reaction gas is cut off, heating is stopped, and the mixture is cooled to room temperature in a nitrogen atmosphere. The reactants are then removed to obtain the silicon-carbon composite material.

[0058] Comparative Example 3 A method for preparing a silicon-carbon composite material, the steps of which are the same as in Example 1, except that the pyrolysis of the organic coating layer is omitted.

[0059] Test Example 1 Electrochemical tests were conducted on the silicon-carbon composite materials prepared in Examples 1-2, Comparative Example 1, and Comparative Example 3 (Comparative Example 2 was not tested due to poor silicon deposition, severe product heating, and powder agglomeration): The silicon-carbon composite material was pressed into electrode sheets (15.6 mm diameter discs), with lithium metal sheets as counter electrodes, LiPF6 solution as electrolyte, Sone as binder, and Super P as conductive agent, and CR2032 button half-cells were assembled; the first charge-discharge efficiency was tested at 0.1C, and constant current charge-discharge cycles were performed at 0.1C rate to test the capacity retention rate after 100 cycles. The test results are recorded in Table 1.

[0060] Test Example 2 The silicon content of the silicon-carbon composite materials prepared in Examples 1-2, Comparative Example 1 and Comparative Example 3 was tested: Thermogravimetric analysis was used. The sample was placed in a thermogravimetric analyzer and heated to 1000℃ at 4℃ / min in an air atmosphere. The carbon component was completely oxidized to CO2 and escaped, and the remainder was SiO2. Based on the initial mass and the mass of the remaining SiO2, the content of elemental silicon in the silicon-carbon composite material was calculated by converting the atomic weight of silicon. The results are recorded in Table 1.

[0061] The pore utilization rate of the silicon-carbon composite materials prepared in Examples 1-2, Comparative Examples 1 and 3 was tested: A nitrogen physical adsorption method was used. Samples were placed in a surface area and pore size analyzer and degassed under vacuum at 200℃ for 2 hours. The nitrogen adsorption-desorption isotherm was measured at liquid nitrogen temperature of 77K to obtain the total pore volume of the samples. The pore utilization rate was calculated using the following formula: Pore ​​utilization rate = (V porous carbon - V post-deposited silicon carbon) ÷ V porous carbon.

[0062] Table 1 Electrochemical Test Records of Different Silicon-Carbon Composite Materials

[0063] As shown in Table 1, the samples prepared in Examples 1 and 2 exhibit excellent electrochemical performance, with high discharge capacity, high initial coulombic efficiency, and good cycle stability. This is attributed to the use of organic materials as dynamically removable templates, which enables precise confined deposition of silicon within the pores, avoiding surface deposition and pore blockage, and resulting in high utilization of the porous carbon channels.

[0064] The sample in Comparative Example 1 had no organic coating layer. During the silicon deposition process, the deposition occurred simultaneously inside and outside the pores. When the external deposition layer reached a certain thickness, the pore openings were blocked, and the internal pores could not be fully utilized. At the same time, the silicon content was reduced, resulting in relatively low capacity and poor cycle stability.

[0065] Comparative Example 2 sample underwent permanent carbon sealing, resulting in silicon deposition only near the pore openings. This limited pore utilization and made subsequent unblocking impossible, thus limiting performance improvement. After preparation, the sample exhibited high activity of the nano-silicon, leading to phenomena such as heating and agglomeration.

[0066] In Comparative Example 3, the organic layer was not removed by heating after the first silicon deposition, and the pores were still blocked by the organic layer. During the second silicon deposition, silicon could not enter the pores and could only be deposited on the surface of the organic layer, forming free silicon particles. The pore utilization and silicon content were both low, resulting in poor capacity and cycle performance.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that, The steps include the following: Organic coating layers are deposited on porous carbon using vapor deposition to obtain organically coated porous carbon. The deposition temperature of the organic coating layer is 80~200℃. The organic layer material in the organically coated porous carbon includes one or more of oligomeric polyethylene glycol, camphor, paraffinic hydrocarbons, and naphthalene. The average molecular weight of the oligomeric polyethylene glycol is 1000~2000. The pore size distribution of the porous carbon is 2~50nm. The carrier gas flow rate for the organic coating layer deposition is 1~3L / min, and the deposition time is 40~80min. The organic layer coated with porous carbon is subjected to a first silicon deposition to obtain a first silicon-carbon intermediate; the silicon source for the first silicon deposition includes cyclopentylsilane, cyclohexylsilane, neopentylsilane or propane. The temperature of the first silicon deposition is 80~200℃; The parameters for the first silicon deposition include: silicon source flow rate of 10~20L / min, carrier gas flow rate of 20~30L / min, and deposition time of 30~180min; The first silicon-carbon intermediate is pyrolyzed to obtain the second silicon-carbon intermediate; the pyrolysis temperature is 350~500℃. The second silicon-carbon intermediate is subjected to a second silicon deposition to obtain a third silicon-carbon intermediate; the temperature of the second silicon deposition is 350~600℃, the silicon source flow rate is 15~25L / min, the carrier gas flow rate is 15~25L / min, and the deposition time is 60~240min. Carbon coating layer deposition is performed on the third silicon-carbon intermediate to obtain silicon-carbon composite material; the carbon coating layer deposition temperature is 350~600℃, the carbon source flow rate is 10~20L / min, the carrier gas flow rate is 30~40L / min, and the deposition time is 60~180min.

2. The preparation method according to claim 1, characterized in that, The pyrolysis time is 30-60 minutes.

3. The preparation method according to claim 1, characterized in that, The silicon source for the second silicon deposition is silane or ethyl silane.

4. The preparation method according to claim 1, characterized in that, The carbon source for the carbon coating layer deposition is acetylene.

5. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the porous carbon is not less than 2000 m². 2 / g.

6. The preparation method according to claim 5, characterized in that, The porous carbon includes MOF-derived porous carbon, biomass-derived porous carbon, or resin-derived porous carbon.

7. The silicon-carbon composite material prepared by the preparation method according to any one of claims 1 to 6.

8. A lithium-ion battery negative electrode, characterized in that, The active material of the lithium-ion battery negative electrode is the silicon-carbon composite material as described in claim 7.

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