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

Abstract

This invention discloses a silicon-carbon composite material, its preparation method, and a lithium-ion battery, belonging to the field of lithium-ion battery material technology. The silicon-carbon composite material includes a core comprising a modified graphite carbon matrix and silicon material formed in the pores and surface of the modified graphite carbon matrix; and a coating layer formed on the surface of the core, the coating layer being a carbon layer. This invention uses modified graphite as the carbon matrix, with silicon material embedded in the pores and surface of the graphite. A first-phase carbon source and a second-phase carbon source synergistically coat the core to form a double-layer carbon coating structure, effectively improving the conductivity of the silicon-carbon composite material, suppressing the volume expansion of silicon material during the charging and discharging process of the lithium-ion battery, and improving the structural stability of the silicon-carbon composite material. When applied to lithium-ion batteries, the silicon-carbon composite material of this invention can effectively reduce expansion and improve rate performance and cycle stability.

Description

Technical Field

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

[0002] Currently, graphite is the primary anode material for lithium-ion batteries, with a theoretical specific capacity of 372 mAh / g and limited potential for energy density improvement. Silicon-based materials, on the other hand, boast a theoretical specific capacity as high as 4200 mAh / g, far exceeding that of graphite, making them one of the most promising anode materials. However, silicon materials undergo significant volume expansion during charge and discharge, leading to cracking and pulverization of the silicon anode material, resulting in irreversible capacity loss and low initial coulombic efficiency. Furthermore, it causes capacity decay and poor cycle stability.

[0003] To suppress the volume expansion of silicon materials, the mainstream method in the industry is to prepare silicon-carbon composite materials by combining silicon materials with carbon materials. That is, using porous carbon as the matrix, silicon is embedded in the carbon matrix. The pores of the porous carbon are used to alleviate the volume expansion, while the high stability of the carbon material is used to coat or embed the silicon material to suppress the volume change of the silicon material and improve the cycle performance.

[0004] However, the porous carbon matrix used in the aforementioned silicon-carbon materials is mostly amorphous carbon, resulting in poor matrix strength. During the rolling process of the negative electrode sheet, the particles are easily broken, leading to unresolved expansion issues and poor rate performance. The cycle stability of silicon-carbon materials in batteries still needs further improvement. Therefore, how to enhance the structural stability of silicon-carbon materials and improve their expansion, rate performance, and cycle stability remains a pressing technical problem to be solved in this field. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a silicon-carbon composite material, its preparation method and lithium-ion battery, wherein the silicon-carbon composite material has good structural stability, can effectively alleviate the volume expansion of the material and improve the cycle stability of the material in lithium-ion battery.

[0006] To achieve the above objectives, the present invention provides a silicon-carbon composite material, comprising a core, the core comprising a modified graphite-carbon matrix and silicon material formed in the pores and on the surface of the modified graphite-carbon matrix; and a coating layer formed on the surface of the core, the coating layer being a carbon layer.

[0007] This invention uses modified graphite as the carbon matrix. The sp² hybridization of graphite forms a stable two-dimensional carbon framework, giving the carbon matrix good structural stability and conductivity. This provides stronger support for silicon materials and inhibits particle breakage under high pressure. At the same time, silicon materials are embedded in the pores and surface of graphite, and the first-phase carbon source and the second-phase carbon source work together to form a composite carbon layer, which can effectively improve the conductivity of silicon-carbon composite materials, inhibit the volume expansion of silicon materials during charging and discharging, and improve the structural stability of silicon-carbon composite materials.

[0008] Furthermore, the carbon layer has a double-layer carbon coating structure.

[0009] Furthermore, the specific surface area of ​​the modified graphite carbon matrix is ​​2~1000 m². 2 / g, pore volume 0.01~0.8cm 3 / g, with an average pore size of 0.3~30nm.

[0010] Furthermore, the silicon-carbon composite material has a particle size Dv50 of 0.5~50 μm and a specific surface area of ​​0.3~100 m². 2 / g; In the silicon-carbon composite material, the carbon content is 45-95wt% and the silicon content is 0.5-40wt%.

[0011] Furthermore, the silicon material is one or more of amorphous silicon and crystalline silicon.

[0012] The aforementioned particle size and specific surface area ranges are beneficial for slurry dispersion and electrode processing; within this range, silicon content can control expansion while ensuring capacity; and within this range, graphite carbon content can ensure matrix strength. By controlling the total content of the composite carbon layer and the ratio of the two phases, conductivity can be ensured while avoiding increased ion transport resistance caused by over-coating, thus achieving a balance between conductivity and rate performance.

[0013] This invention also provides a method for preparing a silicon-carbon composite material, comprising the following steps: S1. Activate and pore-forming graphite raw materials in an oxygen-containing atmosphere to obtain a modified graphite carbon matrix with a porous structure. S2. In a protective atmosphere, at a deposition temperature of 350~650℃, silicon source gas is introduced, and silicon material is deposited in the pores and on the surface of the modified graphite carbon matrix by vapor deposition to obtain a silicon-carbon composite precursor. S3. In a protective atmosphere, at a coating temperature of 450~900℃, a first-phase carbon source and a second-phase carbon source are sequentially used to perform carbon coating treatment on the surface of the silicon-carbon composite precursor by vapor deposition to obtain the silicon-carbon composite material.

[0014] Furthermore, the graphite raw material includes at least one of natural graphite and artificial graphite; Furthermore, the oxygen-containing atmosphere includes at least one of oxygen, air, carbon dioxide, carbon monoxide, and water vapor; Furthermore, the silicon source gas includes at least one of the group consisting of silane, silane, propane, butane, chlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0015] Furthermore, the carbon source of the first phase is a hydrocarbon, selected from at least one of acetylene, methane, ethane, propane, butane, ethylene, propylene, butene, and benzene.

[0016] Furthermore, the second phase carbon source is an oxygen-containing carbon source, selected from at least one of methanol, ethanol, propanol, acetone, acetic acid, ethylene oxide, and dimethyl ether. By selectively optimizing the specific types of the first and second phase carbon sources, the vapor deposition reaction rate and the microstructure of the carbon layer can be controlled. The first phase carbon source decomposes to form the carbon layer framework, while the active oxygen species generated during the decomposition of the second phase carbon source can selectively etch amorphous carbon, promoting the formation of a composite carbon layer with higher crystallinity and fewer defects, thereby further improving the conductivity and structural stability of the material.

[0017] Furthermore, in step S1, the temperature of the activation and pore-forming treatment is 300~800℃, the treatment time is 0.5~20h, and the flow rate of the oxygen-containing atmosphere is 0.1~100L / min. This range of temperature, time, and gas flow rate can form an appropriate amount of pore structure without damaging the main graphite structure; if the temperature is too low or the time is too short, the pore formation will be insufficient, and if the temperature is too high or the time is too long, it may lead to excessive damage to the graphite structure.

[0018] Furthermore, in step S2, the flow rate of the silicon source gas is 0.1~100 L / min, and the deposition time is 0.5~20 h. This deposition temperature range ensures that the silane gas is fully decomposed and uniformly deposited within the graphite pores; if the temperature is too low, the deposition efficiency is low, and if the temperature is too high, it may cause silicon particles to agglomerate or form crystalline silicon, affecting the cycle performance.

[0019] Furthermore, the ratio of the first-phase carbon source to the second-phase carbon source is (10~1):(0.5~5); the coating treatment time is 0.2~10h, and the flow rates of the first-phase carbon source and the second-phase carbon source are 0.1~100L / min, respectively. This coating temperature range allows the carbon source to fully decompose and form a dense carbon layer; controlling the ratio of the first-phase carbon source to the second-phase carbon source within the above range allows the two-phase carbon layers to work synergistically to form a composite carbon layer with fewer defects and higher crystallinity.

[0020] Furthermore, the protective gas is selected from one or more of nitrogen, argon, helium, neon, and krypton. Using this inert protective atmosphere effectively avoids the oxidation and ablation of the graphite carbon matrix and the oxidation failure of the silicon material during high-temperature processing, ensuring the purity of each reaction step and the integrity of the material structure, thereby improving the purity of the final product and the consistency of its electrochemical performance.

[0021] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery contains the silicon-carbon composite material or the silicon-carbon composite material prepared by the preparation method.

[0022] Compared with the prior art, the beneficial technical effects of this invention are reflected in: (1) Using modified graphite as the carbon matrix, the stable two-dimensional carbon skeleton formed by the sp² hybridization of graphite is utilized to give the carbon matrix good structural stability and conductivity, which can provide effective support for silicon materials. (2) The porous structure formed after graphite modification provides embedding space and volume expansion buffer space for silicon materials, effectively alleviating the volume expansion of silicon materials; (3) The carbon layer formed by the first phase carbon source avoids direct contact between silicon material and electrolyte, thus improving the conductivity of the material; the second phase carbon source is an oxygen-containing carbon source. On the one hand, the carbon layer formed by it selectively etches away the sp³ hybrid amorphous carbon formed in the reaction of the first carbon layer, forming sp² hybrid graphite carbon with high crystallinity, and forming a coating carbon layer with fewer defects. On the other hand, some oxygen atoms in the carbon source molecules may be doped into the lattice of the final carbon material, which will have a synergistic effect with the first carbon source coating layer, forming a composite carbon layer with fewer defects and higher crystallinity, thus improving the electronic and ionic conductivity of the material. (4) The above-mentioned silicon-carbon composite material is used as a negative electrode material in lithium-ion batteries, which can effectively reduce expansion and improve the rate performance and cycle stability of lithium-ion batteries. Attached Figure Description

[0023] Figure 1 A schematic diagram of the silicon-carbon composite material structure provided by the present invention.

[0024] Figure 2 This is a scanning electron microscope image of the silicon-carbon composite material in Example 1.

[0025] Figure 3 The graph shows the cycling performance of the silicon-carbon composite material in Example 1.

[0026] In the figure: 1-Modified graphite carbon matrix; 2-Silicon material; 3-First carbon layer; 4-Second carbon layer. Detailed Implementation

[0027] The present invention will be further described in detail below. The described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The first aspect of the present invention provides a silicon-carbon composite material, comprising a modified graphite carbon matrix, a silicon material, and a carbon coating layer; wherein the graphite has a porous structure, the silicon material exists in the pores and on the surface of the graphite, and the carbon coating layer is a double-layer carbon coating structure, coating the silicon material and the modified graphite matrix.

[0029] In some embodiments, the specific surface area of ​​the porous graphite carbon matrix is ​​2~1000 m². 2 / g, for example, could be 5m 2 / g, 10m 2 / g, 50m 2 / g, 100m 2 / g or 500m 2 / g; the pore volume of the porous graphite carbon matrix is ​​0.01~0.8cm³. 3 / g, for example, could be 0.05cm 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.2cm 3 / g, 0.3cm 3 / g, 0.5cm 3 / g; the average pore size of the porous graphite carbon matrix is ​​0.3~30nm, for example, it can be 1nm, 1.2nm, 1.5nm, 1.8nm, 2nm, 2.5nm, 5nm, or 10nm.

[0030] In some embodiments, the Dv of the silicon-carbon composite material 50 The value can range from 0.5 to 50 μm, for example, it can be 3 μm, 5 μm, 6 μm, 8 μm or 10 μm.

[0031] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.3~100 m². 2 / g, for example, could be 0.5m 2 / g, 0.8m 2 / g, 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g、2m 2 / g or 80m 2 / g.

[0032] In some embodiments, the silicon material is one or more of amorphous silicon and crystalline silicon, for example, it can be amorphous silicon, it can be crystalline silicon, or it can contain both amorphous silicon and crystalline silicon.

[0033] In some embodiments, the carbon content in the silicon-carbon composite material is 45-95 wt%, for example, it can be 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%.

[0034] In some embodiments, the silicon content in the silicon-carbon composite material is 0.5 to 40 wt%, for example, it can be 1 wt%, 3 wt%, 5 wt%, 10 wt%, 20 wt%, or 30 wt%.

[0035] A second aspect of the present invention also provides a method for preparing a silicon-carbon composite material, comprising the following steps: S1. Activate and pore-forming graphite raw materials in an oxygen-containing atmosphere to obtain a modified graphite carbon matrix with a porous structure. S2. In a protective atmosphere, at a deposition temperature of 350~650℃, silicon source gas is introduced, and silicon material is deposited in the pores and on the surface of the modified graphite carbon matrix by vapor deposition to obtain a silicon-carbon composite precursor. S3. In a protective atmosphere, at a coating temperature of 450~900℃, a first-phase carbon source and a second-phase carbon source are sequentially used to perform carbon coating treatment on the surface of the silicon-carbon composite precursor by vapor deposition to obtain the silicon-carbon composite material.

[0036] In some embodiments, the graphite raw material includes at least one of natural graphite and artificial graphite.

[0037] In some embodiments, the oxygen-containing atmosphere includes at least one of oxygen, air, carbon dioxide, carbon monoxide, and water vapor.

[0038] In some embodiments, the silicon source gas includes at least one of silane, silane, propane, butane, chlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0039] In some embodiments, the carbon source of the first phase is a hydrocarbon selected from at least one of acetylene, methane, ethane, propane, butane, ethylene, propylene, butene, and benzene.

[0040] Furthermore, the carbon source of the second phase is an oxygen-containing carbon source selected from at least one of methanol, ethanol, propanol, acetone, acetic acid, ethylene oxide, and dimethyl ether.

[0041] In some embodiments, in step S1, the temperature of the activation pore-forming treatment is 300~800℃, for example, 350℃, 400℃, 450℃, 500℃ or 600℃; the treatment time is 0.5~20h, for example, 0.5h, 1h, 2h, 3h, 5h or 6h; the flow rate of the oxygen-containing gas is 0.1~100L / min, for example, 1L / min, 2L / min, 3L / min, 5L / min, 10L / min or 20L / min.

[0042] In some embodiments, in step S2, the deposition temperature of the silicon material is 350~650℃, for example, it can be 400℃, 450℃, 500℃, 550℃ or 600℃; the deposition time is 0.5~20h, for example, it can be 0.5h, 1h, 2h, 3h, 5h or 6h; the flow rate of the silicon source gas is 0.1~100L / min, for example, it can be 1L / min, 2L / min, 3L / min, 5L / min, 10L / min or 20L / min.

[0043] The deposition temperature of the first and second phase carbon source coating is 450~900℃, for example, it can be 500℃, 530℃, 550℃, 580℃, 600℃ or 650℃; the time is 0.2~10h, for example, it can be 0.5h, 1h, 2h, 3h, 5h or 6h; the flow rate of the carbon source gas is 0.1~100L / min, for example, it can be 1L / min, 2L / min, 3L / min, 5L / min, 10L / min or 20L / min.

[0044] In some embodiments, the protective atmosphere gas is selected from one or more of nitrogen, argon, helium, neon, and krypton.

[0045] A third aspect of the present invention also provides a lithium-ion battery, wherein the lithium-ion battery contains the silicon-carbon composite material or the silicon-carbon composite material prepared by the preparation method.

[0046] The present invention will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention.

[0047] Example 1 A method for preparing a silicon-carbon composite material specifically includes the following steps: Step S1: Place 1 kg of artificial graphite material in a fluidized bed device, use nitrogen as the carrier gas at a flow rate of 15 L / min, heat to 500℃, start introducing oxygen for 3 hours at a flow rate of 3 L / min, and discharge the material after cooling to obtain modified graphite carbon matrix. Step S2: Place 1 kg of the modified graphite carbon matrix in a fluidized bed, introduce nitrogen as a protective gas and carrier gas at a flow rate of 15 L / min, heat to 510 °C, and introduce silane to perform silane deposition treatment on the modified graphite carbon matrix. The silane introduction time is 1 h and the flow rate is 3 L / min. Silicon material is formed in the pores and on the surface of the modified graphite to obtain a silicon-carbon composite precursor. Step S3: The silicon-carbon composite precursor is kept in a fluidized bed without being discharged. Under a nitrogen atmosphere, the temperature is raised to 570°C, and acetylene, the first-phase carbon source, is introduced for vapor deposition carbon coating. The temperature is maintained for 1 hour at a flow rate of 3 L / min. After the first-phase carbon source is stopped, ethanol, the second-phase carbon source, is introduced for vapor deposition carbon coating. The temperature is maintained for 1 hour at a flow rate of 3 L / min, thus obtaining the silicon-carbon composite material.

[0048] The structure of the silicon-carbon composite material prepared in this embodiment was observed, such as... Figure 1 As shown, the composite material has a core-shell structure, in which a modified graphite carbon matrix 1 serves as a framework support, and silicon material 2 is uniformly distributed within its pores and on its surface; a first phase carbon source is deposited to form a first carbon layer 3, and a second phase carbon source is deposited to form a second carbon layer 4. The first carbon layer 3 and the second carbon layer 4 together constitute a composite carbon layer, continuously coating the outermost layer of the core to form a complete protective structure. A scanning electron microscope image of the silicon-carbon composite material prepared in Example 1 is shown below. Figure 2 As shown in the figure, the cycle performance graph is as follows: Figure 3 As shown. By Figure 2 It can be seen that the carbon matrix of this silicon-carbon composite material is graphite, and the surface of the silicon-carbon composite material particles is smooth; Figure 3 It can be seen that the silicon-carbon composite material retains 91.7% of its capacity after 1000 cycles.

[0049] Example 2 The difference from Example 1 is that in step S1, the temperature is raised to 600°C, while the remaining steps are the same as in Example 1.

[0050] Example 3 The difference from Example 1 is that in step S1, the oxygen introduction time is 2 hours, and the rest of the steps are the same as in Example 1.

[0051] Example 4 The difference from Example 1 is that in step S2, the silane is introduced for 1.5 hours, while the other steps are the same as in Example 1.

[0052] Example 5 The difference from Example 1 is that in step S3, the first phase carbon source acetylene is introduced and kept at a constant temperature for 2 hours; the second phase carbon source ethanol is introduced and kept at a constant temperature for 0.5 hours; the remaining steps are the same as in Example 1.

[0053] Comparative Example 1 The difference from Example 1 is that 1 kg of artificial graphite material is used without step S1, and steps S2 and S3 are performed directly, while the remaining steps are the same as in Example 1.

[0054] Comparative Example 2 The difference from Example 1 is that in step S3, only the first phase carbon source acetylene is introduced. After the first phase carbon source is stopped being introduced, the second phase carbon source is not introduced. The remaining steps are the same as in Example 1.

[0055] Performance testing The silicon-carbon composite materials prepared in the above embodiments and comparative examples were subjected to performance tests, and the specific test methods are as follows: (1) The pore volume and specific surface area of ​​the modified graphite carbon matrix and the specific surface area of ​​the silicon carbon composite material were measured by using a fully automatic specific surface area and pore size analyzer and by fitting analysis through DFT model. The average pore size was calculated as 4 × pore volume / specific surface area.

[0056] (2) The particle size Dv50 of the carbon skeleton and silicon anode material was measured using a Malvern laser particle size analyzer.

[0057] (3) The microstructure of the material was observed using a scanning electron microscope (SEM).

[0058] (4) The carbon content in the silicon-carbon composite material was determined using a carbon-sulfur analyzer; The silicon content was tested using a thermogravimetric method, by heating the sample to 1100℃ in air and then applying the formula... Si (wt%) = 100 * [M] 1100 M is calculated using *[28 / (28+(16*2)] / M0]. 1100 M0 is the mass at 1100℃, and M0 is the initial mass.

[0059] (5) Electrochemical testing: Negative electrode preparation: Silicon-carbon composite material, conductive agent, and binder were mixed in a ratio of 92.5:2 (SP:CNTs=1.9:0.1):5.5 (PAA:SBR=4.4:1.1) to form a slurry, which was then uniformly coated onto copper foil. After drying, the slurry was rolled to a thickness of 1.6 g / cm³. 3 Compact the material to prepare a negative electrode sheet; Initial reversible capacity and first-efficiency tests: The prepared negative electrode sheet was assembled with the counter lithium sheet, separator, and electrolyte into a coin cell, and its electrochemical performance was tested on the Xinwei Battery test cabinet. The charge-discharge regime was as follows: the battery was left to stand for 10 hours, and then the initial coulombic efficiency was tested at a current density of 0.1C, with a discharge cutoff voltage of 0.005V and a charge cutoff voltage of 1.5V.

[0060] Capacity retention after 1000 cycles: The prepared negative electrode sheet was assembled with the positive NCM88 electrode sheet, separator, and electrolyte into a pouch cell. After stacking and assembly, it was sealed in an aluminum-plastic film shell, baked, and injected with electrolyte, followed by formation and capacity grading. The cells were then placed in a battery holder at 25°C, with a test voltage range of 2.5~4.25V, and cycled 1000 times under a 1C / 1C charge / discharge regime.

[0061] Tables 1 and 2 list the structural parameters and electrochemical performance test results of the silicon-carbon composite materials prepared in each example and comparative example, respectively.

[0062] Table 1. Structural parameters of materials prepared in different embodiments and comparative examples

[0063] Table 2 Electrochemical performance tests of materials prepared in different embodiments and comparative examples

[0064] The test results in Tables 1 and 2 show that the graphite in Comparative Example 1 was not activated, had almost no pores, and a very small pore volume. Compared to Comparative Example 1, the modified graphite prepared in Examples 1-5 had a significantly higher specific surface area and pore volume than the unmodified graphite, which is beneficial for subsequent silicon deposition, allowing the silicon material to embed into the pores and alleviating the volume expansion of silicon. Electrochemical test results show that Examples 1-5 had higher initial coulombic efficiency, significantly lower full-charge expansion rate, and higher 1000-cycle retention rate, indicating that the silicon material present in the pores can effectively alleviate material expansion and improve the cycling performance of the material.

[0065] Compared to Comparative Example 2, the samples coated with a double-layer carbon coating structure in Examples 1-5 showed lower full-charge expansion rates and better cycling performance. This indicates that the double-layer carbon coating structure formed by the synergistic coating of the first and second phase carbon sources is beneficial to improving the structural stability of the material, further alleviating expansion, and improving cycling stability.

[0066] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

[0067] It should be particularly noted that the various embodiments listed in this specification and accompanying drawings are intended to illustrate the technical solutions and advantages of the present invention, and not to limit the scope of protection of the present invention. Without departing from the core ideas and technical effects of the present invention, those skilled in the art can make any form of improvement, substitution, combination, or modification to the structural arrangement, process parameters, material selection, control logic, etc., of the described embodiments; any obvious changes based on the same concept should be considered equivalent solutions of the present invention and should be included within the scope of protection defined by the claims of the present invention. The actual scope of protection of the present invention is determined by the appended claims and should be correctly understood in conjunction with the specification and accompanying drawings.

Claims

1. A silicon-carbon composite material, characterized in that, include: The core comprises a modified graphite carbon matrix and silicon material formed within the pores and on the surface of the modified graphite carbon matrix. And a coating layer formed on the surface of the core, the coating layer being a carbon layer.

2. The silicon-carbon composite material according to claim 1, characterized in that, The carbon layer has a double-layer carbon coating structure.

3. A method for preparing the silicon-carbon composite material as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Activate and pore-forming graphite raw materials in an oxygen-containing atmosphere to obtain a modified graphite carbon matrix with a porous structure. S2. In a protective atmosphere, a silicon source gas is introduced, and silicon material is deposited in the pores and on the surface of the modified graphite carbon matrix by vapor deposition to obtain a silicon-carbon composite precursor. S3. In a protective atmosphere, a first-phase carbon source and a second-phase carbon source are used sequentially to perform carbon coating treatment on the surface of the silicon-carbon composite precursor by vapor deposition, thereby obtaining the silicon-carbon composite material.

4. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, In step S2, the deposition temperature of the silicon material is 350~650℃, the flow rate of the silicon source gas is 0.1~100L / min, and the deposition time is 0.5~20h.

5. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, In step S3, the carbon coating treatment time is 0.2~10h, the temperature is 450~900℃, and the flow rates of the first phase carbon source and the second phase carbon source are 0.1~100L / min, respectively.

6. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, In step S1, the graphite raw material is selected from at least one of natural graphite and artificial graphite; In step S1, the oxygen-containing atmosphere is selected from at least one of oxygen, air, carbon dioxide, carbon monoxide, and water vapor; In step S2, the silicon source gas is selected from at least one of silane, silane, propane, butane, chlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane; In step S3, the carbon source of the first phase is selected from hydrocarbons, specifically from at least one of acetylene, methane, ethane, propane, butane, ethylene, propylene, butene, and benzene. In step S3, the second phase carbon source is selected from oxygen-containing carbon sources, specifically from at least one of methanol, ethanol, propanol, acetone, acetic acid, ethylene oxide, and dimethyl ether.

7. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, In step S1, the temperature of the activation pore-forming treatment is 300~800℃, the treatment time is 0.5~20h, and the flow rate of the oxygen-containing atmosphere is 0.1~100L / min.

8. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, In step S3, the mass ratio of the first phase carbon source to the second phase carbon source is (10~1):(0.5~5).

9. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, The protective atmosphere described in step S2 or S3 is selected from at least one of nitrogen, argon, helium, neon, and krypton.

10. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the silicon-carbon composite material according to any one of claims 1 to 4, or the silicon-carbon composite material prepared by any one of claims 3 to 9.

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