A spherical multi-layer carbon-based material and a negative electrode and a preparation method thereof

Abstract

The application discloses a kind of spherical multilayer carbon-based materials and its negative electrode, preparation method, belong to battery material preparation technical field.Spherical multilayer carbon-based material includes porous silicon carbon matrix from inside to outside, modification layer, carbon coating layer.Porous silicon carbon matrix includes porous carbon skeleton and nanometer silicon, and nanometer silicon is deposited to porous carbon skeleton surface and inside hole, wherein the pore size of porous carbon skeleton is 0.5~5nm, sphericity is greater than or equal to 0.9.Modification layer is the carbon layer of doped N or B.This spherical multilayer carbon-based material stress distribution is uniform, can effectively inhibit volume expansion, avoid structural collapse, simultaneously, porous carbon skeleton structure provides abundant active site for silicon deposition, increases the specific capacity of material.Modification layer is the carbon layer of doped N or B, not only can improve the conductivity of material and expand lithium ion transmission channel, improve rate performance, simultaneously play buffering and gradual change effect, reduce the direct contact between silicon particles, thereby reduce the stress brought by volume expansion, prolong the cycle life of material.

Description

Technical Field

[0001] This invention belongs to the field of battery material preparation technology, specifically relating to a spherical multilayer carbon-based material and its negative electrode, and a preparation method thereof. Background Technology

[0002] With the increasing demand for high-performance batteries in numerous fields such as new energy vehicles, low-altitude aircraft, and mobile electronic devices, silicon-carbon anode materials have become a research hotspot due to their extremely high theoretical specific capacity (4200 mAh / g). However, the current development of silicon-carbon anodes faces many bottlenecks. On the one hand, traditional carbon-based supports, such as artificial graphite and natural graphite, suffer from insufficient interaction between silicon and carbon, resulting in low silicon deposition efficiency and failing to fully realize the potential of silicon. On the other hand, traditional carbon-based supports lack sufficient mechanical strength to effectively cope with the volume expansion of silicon during charging / discharging, easily leading to structural damage. Furthermore, the limited electronic conductivity of traditional carbon-based supports restricts the fast-charging capability of silicon-carbon anodes. Traditional carbon-based supports, such as artificial graphite and natural graphite, have high surface chemical inertness and weak bonding with silicon. Existing technologies often use graphene to coat silicon particles, which improves conductivity, but the silicon and carbon layers are only bonded through physical contact, making them prone to interfacial delamination under cyclic stress. Experiments show that after 50 cycles, the silicon particle shedding rate of this type of structure exceeds 30%, and the capacity retention rate is less than 80%. Although porous carbon supports can provide silicon deposition space, their pore size distribution is wide and the mechanical strength of the pore walls is insufficient. When silicon is deposited in the pores, the stress concentrates at the weak points of the pore walls when the large-sized channels expand in volume, causing the support framework to collapse. Scanning electron microscopy observations show that the pore size distortion rate of this type of material is as high as 40% after cycling, leading to blockage of ion transport channels. Related researchers have also proposed carbon nanotube / silicon composite structures, but direct contact between carbon nanotubes and silicon will form local high current density regions, accelerating electrolyte decomposition. At the same time, the lack of effective electron transition media between silicon particles limits rate performance. Existing technologies mostly use a single coating layer, such as amorphous carbon or graphene, whose modulus abrupt changes lead to interfacial stress concentration. Finite element simulations show that the stress peak at the silicon / carbon interface during expansion can reach 2.5 GPa, far exceeding the yield strength of the carbon layer, which is the fundamental cause of coating layer rupture. To overcome the above challenges, it is urgent to develop a spherical multilayer carbon-based material, its anode, and its preparation method. Summary of the Invention

[0003] Addressing the shortcomings of existing silicon-carbon anode materials and at least some of the aforementioned problems, this invention proposes a spherical multilayer carbon-based material. The high conductivity of the outer carbon coating layer ensures efficient electron conduction, the middle modification layer regulates stress distribution, and the high specific surface area of ​​the inner porous silicon-carbon matrix provides abundant silicon deposition sites. Its multilayer gradient structure design can meet various requirements in the silicon deposition process, effectively alleviating the difficulties faced by silicon-carbon anodes in practical applications and providing new possibilities for improving the performance of silicon-carbon anode materials.

[0004] A first aspect of the present invention relates to a spherical multilayer carbon-based material, comprising, from the inside out, a porous silicon-carbon matrix, a modification layer, and a carbon coating layer. The porous silicon-carbon matrix comprises a porous carbon framework and nano-silicon, wherein the nano-silicon is deposited on the surface and interior of the porous carbon framework. The porous carbon framework has a pore size of 0.5–5 nm and a sphericity ≥0.9. The modification layer is a carbon layer doped with N or B.

[0005] In some embodiments of the present invention, the specific surface area of ​​the porous silicon-carbon matrix is ​​1000-2000 m2 / g, and the particle size of the porous silicon-carbon matrix is ​​4-18 μm.

[0006] In some embodiments of the present invention, the thickness of the modification layer is 200-800 nm, and the thickness of the carbon coating layer is 20-100 nm.

[0007] In some embodiments of the present invention, the particle size D50 of the spherical multilayer carbon-based material is 4–20 μm; the silicon content by weight is 30–60%.

[0008] In some embodiments of the present invention, the raw material for preparing the carbon coating layer is at least one of carbon nanotubes and graphene;

[0009] And / or, the raw materials for preparing the modified layer include a carbon source, a dopant gas, and a carrier gas;

[0010] And / or, the raw materials for preparing the porous silicon-carbon matrix are at least one of sucrose, glucose, cellulose, citric acid and polysaccharides.

[0011] The second aspect of the present invention discloses a method for preparing the spherical multilayer carbon-based material described in the first aspect, comprising the following steps:

[0012] S01, Preparation of porous silicon-carbon matrix;

[0013] SO2, preparation of the modification layer;

[0014] SO3, preparation of carbon coating layer.

[0015] In some embodiments of the present invention, in S01, the raw materials are carbonized under inert gas protection, activated and pore-forming, washed, dried and pulverized to obtain a high specific surface area porous carbon skeleton, followed by surface deposition of silicon, and after cleaning, drying and calcination, a porous silicon-carbon matrix is ​​obtained.

[0016] Preferably, the inert gas is at least one of nitrogen, argon, and helium;

[0017] Preferably, the carbonization treatment has a heating rate of 2-10℃ / min, a final temperature of 600-800℃, and a holding time of 2-3h.

[0018] Preferably, the method for activating pore formation is at least one of chemical activation, physical activation, microwave-assisted activation, and molten salt-assisted activation.

[0019] Preferably, the chemical activation method uses at least one of KOH, NaOH, and H3PO4;

[0020] Preferably, the physical activation method is steam activation or carbon dioxide activation;

[0021] Preferably, NaCl / K2CO3 is used in the molten salt-assisted activation method;

[0022] Preferably, the method for depositing silicon is electroless plating or chemical vapor deposition;

[0023] Preferably, the plating solution of the chemical plating method includes a silicon source and a reducing agent, the reaction temperature is 60-90°C, and the reaction time is 3-6 hours; the silicon source is a silicate or a halosilane; the reducing agent is hydrazine hydrate or sodium borohydride.

[0024] Preferably, the silicon source used in the vapor deposition method is SiH4, SiH2Cl2, etc., the carrier gas is an inert gas, the reaction temperature is 800-1200℃, and the deposition time is 1-6h.

[0025] In some embodiments of the present invention, in S02, the surface of the porous silicon-carbon matrix obtained in step S01 is coated with carbon material doped with heteroatoms by chemical vapor deposition to form a modification layer.

[0026] Preferably, a hydrocarbon gas is used as the carbon source, and ammonia or borane is used as the dopant gas to react and form a modified layer.

[0027] Preferably, the carbon source is a hydrocarbon gas, and more preferably at least one of methane, ethane, propane, ethylene, propylene, and acetylene;

[0028] Preferably, the doping amount by weight is controlled between 1% and 5%, the reaction temperature is 800 to 1000°C, and the reaction time is 2 to 4 hours.

[0029] In some embodiments of the present invention, in S03, a highly conductive material is selected as the raw material, and a precursor with an outer highly conductive carbon layer (i.e., a carbon coating layer) is obtained through high-temperature graphitization treatment.

[0030] Preferably, the highly conductive material is carbon nanotubes or graphene; more preferably, the graphene has a particle size of 0.01–10 μm, the carbon nanotubes have a particle size of 1–20 nm, and a length of 1–100 μm.

[0031] Preferably, the high-temperature graphitization temperature is 2500-3000℃, the atmosphere is a vacuum or inert atmosphere, and the holding time is 1-2 hours;

[0032] Preferably, the inert atmosphere is at least one of nitrogen, argon, and neon.

[0033] In some embodiments of the present invention, in S03, the precursor is composited on the outside of the modified layer, and after cleaning and drying, the spherical multilayer carbon-based material is finally prepared.

[0034] Preferably, the precursor accounts for 5-20% of the weight of the spherical or near-spherical particles with a modified layer obtained in step S02;

[0035] Preferably, the composite method is a solvothermal method;

[0036] Preferably, the solvothermal method uses one of the following solvents: deionized water, disodium ethylenediaminetetraacetate, ethylenediamine, ethanol, and N,N-dimethylformamide, with a reaction temperature of 150–200°C and a reaction time of 12–24 h.

[0037] Preferably, the cleaning process is physical cleaning, chemical cleaning, or a combination of cleaning methods.

[0038] Preferably, the physical cleaning is ultrasonic cleaning or plasma cleaning;

[0039] Preferably, the chemical cleaning is acid washing, alkaline washing, or surface oxidation;

[0040] Preferably, the composite cleaning is a sol-gel cleaning;

[0041] Preferably, the drying atmosphere is a vacuum or inert atmosphere, and the temperature is 80–130°C;

[0042] Preferably, the inert atmosphere is at least one of nitrogen, argon, and neon.

[0043] A third aspect of the present invention discloses a negative electrode for an energy storage device, the raw materials for which include the spherical multilayer carbon-based material described in the first aspect. The energy storage device may be a battery or other device.

[0044] In some embodiments of the present invention, the spherical multilayer carbon-based material described in the first aspect can be used to prepare carbon-based anode materials, such as silicon-carbon anode materials.

[0045] Beneficial effects:

[0046] The spherical multilayer carbon-based material proposed in this invention exhibits a multilayer structure, consisting of a highly conductive carbon layer (carbon coating layer), a modification layer, and a high-surface-area silicon-carbon layer (porous silicon-carbon matrix) from the outside in. The outer highly conductive carbon layer utilizes highly graphitized carbon material, exhibiting excellent electronic conductivity and reducing electrode polarization. The modification layer is a carbon layer doped with a small number of heteroatoms (such as nitrogen and boron), which acts as a buffer and gradient between the inner and outer layers to regulate stress distribution during silicon deposition, preventing structural collapse due to stress concentration. The inner high-surface-area silicon-carbon layer uses nanoporous carbon material with abundant pores, providing numerous active sites and ample space for silicon deposition. The layers of the gradient carbon-based material are tightly bonded through chemical bonding and physical nesting, forming a synergistic overall structure that enhances the material's stability and mechanical properties.

[0047] The gradient carbon-based material and its method for preparing silicon-carbon anode materials proposed in this invention achieve efficient silicon loading and deposition through a unique structural design, significantly improving the performance of silicon-carbon anode materials and providing new ideas and technical solutions for the research and development of high-performance battery anode materials.

[0048] This invention proposes a spherical multilayer carbon-based material with a novel structure, unlike traditional single-structure carbon-based carriers or silicon-oxygen anode structures with an outer carbon coating. The proposed spherical multilayer consists of three layers from the inside out. The outer layer is a carbon coating made of a highly conductive material, ensuring rapid electron transport and reducing battery polarization. The middle modification layer is a carbon layer doped with N or B atoms, which acts as a buffer and gradient, regulating the stress generated by silicon expansion during the charging / discharging process of the inner porous silicon-carbon material and preventing structural collapse. The high specific surface area and porous structure of the silicon-carbon matrix provide abundant active sites for silicon deposition, increasing the material's specific capacity. Therefore, this invention provides a novel structural basis for the high performance of silicon-carbon anode materials. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of a spherical multilayer carbon-based material according to one embodiment of the present invention, wherein 1 is a carbon coating layer, 2 is a modification layer, 3 is a porous silicon-carbon matrix, 4 is a porous channel, 5 is nano-silicon, and 6 is N or B.

[0050] Figure 2 This invention provides a method for preparing spherical multilayer carbon-based materials according to one embodiment. Detailed Implementation

[0051] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0052] In the following embodiments, the silicon-carbon matrix comprises a porous carbon framework and nano-silicon, with the nano-silicon deposited on the surface and inside the pores of the porous carbon framework. The pore size of the porous carbon framework is 0.5–5 nm, and the sphericity is ≥0.9. Unless otherwise specified, the embodiments and comparative examples are parallel experiments with the same composition, component content, preparation steps, preparation parameters, dimensions, and other parameters.

[0053] Example 1

[0054] A spherical multilayer carbon-based material, such as Figure 1 As shown, the preparation method is as follows: Figure 2 As shown, it includes the following steps:

[0055] 1. Glucose was heated to 800℃ under an inert gas atmosphere at a heating rate of 2℃ / min and held for 2 hours. Then, pores were created using KOH activation, with a mass ratio of MkOH:M carbonized product = 3:1, and held at 900℃ under N2 (purity ≥99.99%, flow rate 100 sccm) for 2 hours. After thorough washing with deionized water, the material was dried, ground, and sieved to obtain a high specific surface area porous carbon framework with a particle size of 4–18 μm. Subsequently, silicon was deposited using chemical vapor deposition: SiH4 flow rate 20 sccm, Ar as carrier gas 100 sccm, temperature 1000℃, duration 6 hours (ensuring a silicon deposition rate of 30–60%). A porous silicon-carbon matrix was obtained after deposition.

[0056] 2. Using methane (purity ≥99.99%, flow rate 20 sccm) as the carbon source, ammonia (purity ≥99.99%, flow rate 5 sccm) as the dopant gas, and Ar (purity ≥99.99%, flow rate 50 sccm) as the carrier gas, chemical vapor deposition was carried out in a tube furnace at a set temperature of 1000℃ for 4 hours to form a modification layer on the surface of a porous silicon-carbon substrate. The deposition thickness was controlled to be between 200 and 800 nm.

[0057] 3. Using 0.01–10 μm graphene as raw material, graphitization was performed at an inert high temperature of 3000℃ for 1 h to obtain a precursor with a highly conductive carbon layer. Subsequently, a solvothermal method was used to composite the modified layer surface with a highly conductive material: using disodium ethylenediaminetetraacetate as solvent, a polytetrafluoroethylene-lined reactor was filled to 60% capacity. 2 g of the highly conductive precursor and 10 g of the porous silicon-carbon matrix containing the modified layer were added. The reaction temperature was 180℃, the reaction time was 24 h, and the composite thickness was controlled to be 20–100 nm. After the reaction, the mixture was filtered and washed, and then vacuum dried at 120℃ to obtain spherical multilayer carbon-based materials.

[0058] Example 2

[0059] A spherical multilayer carbon-based material, such as Figure 1 As shown, the preparation method is as follows: Figure 2 As shown, the following adjustments were made compared to Example 1 (all other steps and parameters remained the same):

[0060] In step 3, graphene was replaced with carbon nanotubes with a particle size of 1–20 nm and a length of 1–100 μm. The carbonization temperature was 2500℃, and the process was carried out for 2 hours to obtain a precursor with a highly conductive carbon layer. Subsequently, a solvothermal method was used to composite the modified layer surface with a highly conductive material: N,N-dimethylformamide was used as the solvent in the solvothermal method, and the mixture was placed in a polytetrafluoroethylene-lined reactor, occupying 60% of the volume. 2 g of the highly conductive precursor and 10 g of the porous silicon-carbon matrix containing the modified layer were added. The reaction temperature was 200℃, the reaction time was 18 hours, and the composite thickness was controlled to be 20–100 nm. After the reaction was complete, the mixture was filtered and washed, and then vacuum dried at 120℃ to obtain spherical multilayer carbon-based materials.

[0061] Example 3

[0062] A spherical multilayer carbon-based material, such as Figure 1 As shown, the preparation method is as follows: Figure 2 As shown, the following adjustments were made compared to Example 1 (all other steps and parameters remained the same):

[0063] In step 2, methane (purity ≥99.99%, flow rate 20 sccm) was used as the carbon source, borane (purity ≥99.99%, flow rate 5 sccm) was used as the dopant gas, and Ar (purity ≥99.99%, flow rate 50 sccm) was used as the carrier gas. Chemical vapor deposition was carried out in a tube furnace at a set temperature of 1000℃ for 4 hours to form a modification layer on the surface of the porous silicon-carbon substrate. The deposition thickness was controlled to be between 200 and 800 nm.

[0064] Example 4

[0065] A spherical multilayer carbon-based material, such as Figure 1As shown, the preparation method is as follows: Figure 2 As shown, the following adjustments were made compared to Example 1 (all other steps and parameters remained the same):

[0066] In step 1, a mixture of sucrose, glucose, cellulose, citric acid, and polysaccharides (mass ratio 1:1:1:1:1) is heated to 800℃ at a heating rate of 2℃ / min under an inert gas atmosphere and held for 2 hours. Then, microwave-assisted activation and pore formation are performed, with a mass ratio of MkOH:M 碳化产物 The ratio of silicon content to carbon was 3:1, the microwave reactor frequency was 1 GHz, and the irradiation time was 5 min. After thorough cleaning with deionized water, the carbon was dried, ground, and sieved to obtain a high specific surface area porous carbon framework with a particle size of 4–18 μm. Subsequently, silicon was deposited using a chemical plating method: the porous carbon framework was immersed in a plating solution of silicate (1 M) and hydrazine hydrate (0.2 M) at a reaction temperature of 80 °C for 4 h. After deposition, a porous silicon-carbon matrix was obtained, with the silicon content controlled at a weight ratio of 30–60%.

[0067] Example 5

[0068] A spherical multilayer carbon-based material, such as Figure 1 As shown, the preparation method is as follows: Figure 2 As shown, the following adjustments were made compared to Example 1 (all other steps and parameters remained the same):

[0069] In step 1, glucose was heated to 800℃ under an inert gas at a heating rate of 8℃ / min and held for 2 hours. Then, pores were created using KOH activation, with a mass ratio of MkOH:M carbonized product = 3:1, and held at 900℃ under N2 (purity ≥99.99%, flow rate 100 sccm) for 2 hours. After thorough washing with deionized water, the material was dried, ground, and sieved to obtain a high specific surface area porous carbon framework with a particle size of 4–18 μm. Subsequently, silicon was deposited using chemical vapor deposition: SiH4 flow rate 10 sccm, Ar as carrier gas 100 sccm, temperature 1000℃, duration 4 hours (ensuring a silicon deposition rate of 30–60%). After deposition, a porous silicon-carbon matrix was obtained.

[0070] Example 6

[0071] A spherical multilayer carbon-based material, such as Figure 1 As shown, the preparation method is as follows: Figure 2 As shown, the following adjustments were made compared to Example 1 (all other steps and parameters remained the same):

[0072] In step 1, a mixture of sucrose, glucose, cellulose, citric acid, and polysaccharides (mass ratio 1:1:1:1:1) is heated to 800℃ at a heating rate of 2℃ / min under an inert gas atmosphere and held for 2 hours. Then, microwave-assisted activation and pore formation are performed, with a mass ratio of MkOH:M 碳化产物The ratio was 3:1, the microwave reactor frequency was 1 GHz, and the irradiation time was 5 min. After thorough washing with deionized water, the material was dried, ground, and sieved to obtain a high specific surface area porous carbon framework with a particle size of 4–18 μm.

[0073] In step 3, 0.01–10 μm graphene and carbon nanotubes (1–20 nm in diameter and 1–100 μm in length) were selected as raw materials in a mass ratio of 2:1. Graphitization was performed at an inert high temperature of 3000℃ for 1 hour to obtain a precursor with a highly conductive carbon layer. Subsequently, a solvothermal method was used to composite the modified layer surface with a highly conductive material: disodium ethylenediaminetetraacetate was used as the solvent, and the mixture was placed in a polytetrafluoroethylene-lined reactor, occupying 60% of the volume. 2 g of the highly conductive precursor and 10 g of the porous silicon-carbon matrix containing the modified layer were added. The reaction temperature was 180℃, the reaction time was 24 hours, and the composite thickness was controlled to be 20–100 nm. After the reaction was complete, the mixture was filtered and washed, and then vacuum dried at 120℃ to obtain spherical multilayer carbon-based materials.

[0074] Comparative Example 1

[0075] Compared to Example 1: without a modification layer and a highly conductive carbon layer, carbon is directly coated onto the surface of a porous silicon-carbon substrate. The specific steps are as follows:

[0076] 1. Glucose was heated to 800℃ under an inert gas atmosphere at a heating rate of 2℃ / min and held for 2 hours. Then, pores were created using KOH activation, with a mass ratio of MkOH:M carbonized product = 3:1, and held at 900℃ under N2 (purity ≥99.99%, flow rate 100 sccm) for 2 hours. After thorough washing with deionized water, the material was dried, ground, and sieved to obtain a high specific surface area porous carbon framework with a particle size of 4–18 μm. Subsequently, silicon was deposited using chemical vapor deposition: SiH4 flow rate 20 sccm, Ar as carrier gas 100 sccm, temperature 1000℃, duration 6 hours (ensuring a silicon deposition rate of 30–60%). A porous silicon-carbon matrix was obtained after deposition.

[0077] 2. Using methane (purity ≥99.99%, flow rate 20 sccm) as the carbon source and Ar as the carrier gas (purity ≥99.99%, flow rate 50 sccm), chemical vapor deposition was performed in a tube furnace at a set temperature of 1000℃ for 2 hours to form a carbon layer on the surface of a porous silicon-carbon matrix. The deposition thickness was controlled to be between 20 and 100 nm. The final product was a silicon-carbon material with carbon coating.

[0078] Comparative Example 2

[0079] Compared to Example 1: the outer highly conductive carbon layer and the porous silicon-carbon with the transition layer were not surface-composite, but only simply physically mixed at a mass ratio of 1:20; the specific steps are as follows (consistent with steps 1 and 2 in Example 1):

[0080] Graphene with a thickness of 0.01–10 μm was selected as the raw material and graphitized at an inert high temperature of 3000℃ for 1 hour. After washing with deionized water, it was vacuum dried (120℃) to obtain a precursor with a highly conductive carbon layer. Subsequently, the highly conductive carbon layer and a porous silicon-carbon matrix with a transition layer were physically blended at a mass ratio of 1:20 at 1000 rpm for 2 hours to obtain a silicon-carbon material containing high conductivity.

[0081] The testing methods for porous carbon framework pore size, sphericity, specific surface area of ​​porous silicon-carbon matrix, particle size of porous silicon-carbon matrix, modification layer thickness, carbon coating layer thickness, D50, and silicon content are described below:

[0082] Pore ​​size: Nitrogen adsorption-desorption isotherm

[0083] Sphericity: Analysis using scanning electron microscopy and ImageJ

[0084] Porous carbon specific surface area: BET method - nitrogen adsorption

[0085] Matrix particle size mean + D50: Laser diffraction particle size analysis

[0086] Modification layer + carbon coating: Transmission electron microscopy (TEM) cross-sectional measurement

[0087] Silicon content: Inductively coupled plasma optical emission spectroscopy (ICP-OES)

[0088] The above materials were assembled into a coin cell, and the specific capacity, initial efficiency, capacity retention after 100 cycles, and electrode expansion rate before / after cycling were measured.

[0089] Table 1 Test Results

[0090]

[0091] Based on the above test data, considering experimental errors, the spherical multilayer carbon-based materials prepared in Examples 1-6 of this invention exhibit an initial capacity between 1940 and 2070 mAh / g, with an initial efficiency maintained above 88%, demonstrating high overall performance. The capacity retention rate after 100 cycles also remains above 94%, indicating the feasibility of the experimental conditions mentioned in this invention. Example 5 shows a significant decrease in initial capacity due to the low SiH4 flow rate and short silicon deposition time during the vapor deposition process, resulting in low silicon content, but its expansion rate is clearly the lowest. Compared to the porous silicon-carbon material with carbon coating in Comparative Example 1, this material has a clear advantage. Comparative Example 1 lacks a modification layer, yet its expansion rate after 100 cycles reaches 25.7%, indirectly reflecting that the modification layer can regulate the stress generated by the volume expansion of the silicon-carbon anode material during charging / discharging, verifying the effectiveness of the structure proposed in this invention. Comparative Example 2 exhibits poor initial efficiency, capacity retention rate, and expansion rate, indicating that the silicon-carbon material obtained without solvothermal composite method has an unstable structure, leading to structural collapse during battery cycling and affecting overall performance. The results of the above embodiments show that the spherical multilayer carbon-based material proposed in this invention has excellent electrical properties and is expected to be applied in batches or on a large scale in the future.

[0092] The preferred embodiments and examples of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments and examples. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the concept of the present invention.

Claims

1. A spherical multilayer carbon-based material, characterized in that, The invention comprises a porous silicon-carbon matrix, a modification layer, and a carbon coating layer, from the inside out. The porous silicon-carbon matrix includes a porous carbon framework and nano-silicon, and the nano-silicon is deposited on the surface and inside of the porous carbon framework. The porous carbon framework has a pore size of 0.5~5 nm and a sphericity ≥0.

9. The modification layer is a carbon layer doped with N or B. The specific surface area of ​​the porous silicon-carbon matrix is ​​1000~2000 m². 2 / g, wherein the particle size of the porous silicon-carbon matrix is ​​4-18μm; The carbon coating layer is a precursor obtained by high-conductivity material through high-temperature graphitization treatment. The precursor of the carbon coating layer is then composited onto the outside of the modification layer by a solvothermal method to form a carbon layer. The highly conductive material is carbon nanotubes or graphene; the high-temperature graphitization temperature is 2500~3000 ℃, the atmosphere is vacuum or inert atmosphere, and the holding time is 1~2h; the solvothermal method uses one of deionized water, disodium ethylenediaminetetraacetate, ethylenediamine, ethanol and N,N-dimethylformamide as solvent, the reaction temperature is 150~200 ℃, and the reaction time is 12~24h; The thickness of the modified layer is 200~800 nm, and the thickness of the carbon coating layer is 20-100 nm.

2. The spherical multilayer carbon-based material according to claim 1, characterized in that, The spherical multilayer carbon-based material has a particle size D50 of 4~20 μm and a silicon content of 30~60% by weight.

3. The spherical multilayer carbon-based material according to claim 1, characterized in that, The raw materials for preparing the modified layer include a carbon source, a doping gas, and a carrier gas; And / or, the raw materials for preparing the porous carbon framework are at least one of sucrose, glucose, cellulose, citric acid and polysaccharides.

4. A method for preparing a spherical multilayer carbon-based material according to any one of claims 1-3, characterized in that, Includes the following steps: S01, Preparation of porous silicon-carbon matrix; SO2, preparation of the modification layer; SO3, preparation of carbon coating layer.

5. The method for preparing spherical multilayer carbon-based materials according to claim 4, characterized in that, In S01, the raw materials are carbonized under inert gas protection, activated and pore-forming, washed, dried and pulverized to obtain a porous carbon framework with high specific surface area. Then, silicon is deposited on the surface, and after cleaning, drying and calcination, a porous silicon-carbon matrix is ​​obtained. The inert gas is at least one of nitrogen, argon, and helium; The carbonization process involves a heating rate of 2-10 °C / min, a final temperature of 600-800 °C, and a holding time of 2-3 h. The method for activating pore formation is at least one of chemical activation, physical activation, microwave-assisted activation, and molten salt-assisted activation. The chemical activation method uses at least one of KOH, NaOH, and H3PO4; The physical activation method is either steam activation or carbon dioxide activation; NaCl / K2CO3 is used in the molten salt-assisted activation method; The method for depositing silicon is either chemical plating or vapor deposition. The electroless plating solution includes a silicon source and a reducing agent, the reaction temperature is 60~90 ℃, and the reaction time is 3~6 h; the silicon source is a silicate or a halosilane; the reducing agent is hydrazine hydrate or sodium borohydride; The silicon source used in the vapor deposition method is SiH4 or SiH2Cl2, the carrier gas is an inert gas, the reaction temperature is 800~1200 ℃, and the deposition time is 1~6h.

6. The method for preparing spherical multilayer carbon-based materials according to claim 4, characterized in that, In S02, the surface of the porous silicon-carbon matrix obtained in step S01 is coated with carbon material doped with heteroatoms by chemical vapor deposition to form a modification layer. Hydrocarbon gas is used as the carbon source, and ammonia or borane is used as the dopant gas. The reaction forms a modified layer. The carbon source is a hydrocarbon gas, specifically at least one of methane, ethane, propane, ethylene, propylene, and acetylene; The doping weight ratio is controlled between 1% and 5%, the reaction temperature is 800-1000 ℃, and the reaction time is 2-4 h.

7. The method for preparing spherical multilayer carbon-based materials according to claim 4, characterized in that, In S03, a precursor with an outer carbon coating layer is obtained by using a highly conductive material as raw material and through high-temperature graphitization treatment. The highly conductive material is carbon nanotubes or graphene; the graphene particle size is 0.01~10 μm. The high-temperature graphitization temperature is 2500~3000 ℃, the atmosphere is vacuum or inert atmosphere, and the holding time is 1~2 hours; The inert atmosphere is at least one of nitrogen, argon, and neon.

8. The method for preparing spherical multilayer carbon-based materials according to claim 7, characterized in that, In S03, the precursor is composited on the outside of the modified layer, and after cleaning and drying, the spherical multilayer carbon-based material is finally prepared. The precursor accounts for 5-20% of the weight of the spherical or near-spherical particles with a modified layer obtained in step S02; The composite method is a solvothermal method; The solvothermal method uses one of the following solvents: deionized water, disodium ethylenediaminetetraacetate, ethylenediamine, ethanol, and N,N-dimethylformamide. The reaction temperature is 150~200 ℃, and the reaction time is 12~24 h. The cleaning process can be physical cleaning, chemical cleaning, or a combination of cleaning methods. The physical cleaning is ultrasonic cleaning or plasma cleaning. The chemical cleaning is acid washing, alkaline washing, or surface oxidation; The composite cleaning is a sol-gel cleaning; The drying atmosphere is a vacuum or inert atmosphere, and the temperature is 80~130 ℃; The inert atmosphere is at least one of nitrogen, argon, and neon.

9. A negative electrode for an energy storage device, characterized in that, The raw materials for preparation include the spherical multilayer carbon-based materials described in any one of 1-3.

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