Silicon-carbon negative electrode material, preparation method and application thereof

Abstract

The application belongs to the technical field of batteries, and particularly relates to a silicon-carbon negative electrode material and a preparation method and application thereof. The method comprises the following steps: preparing a porous carbon fiber membrane loaded with a metal catalyst; preparing a dispersion solution of a nano-silicon-based material, and distributing the nano-silicon-based material into the porous carbon fiber membrane to obtain a composite porous carbon fiber membrane; and performing thermal chemical vapor deposition on the composite porous carbon fiber membrane in an inert atmosphere containing a carbon source, growing carbon nanofibers and vertical graphene on the surface of the composite porous carbon fiber membrane, and obtaining a silicon-carbon negative electrode material. Through a synthesis route of thermal chemical vapor deposition (T-CVD), the synthesis process is optimized, and a multi-level three-dimensional network structure of carbon nanofibers and vertical graphene is constructed to enhance the electrical conductivity of the silicon-carbon negative electrode material, accelerate carrier transmission, improve the interface contact performance between the silicon-based material and the carbon material, improve the loading capacity of the nano-silicon-based material, inhibit the volume expansion of the nano-silicon-based material, and improve the structure and cycle stability of the nano-silicon-based material.

Description

Technical Field

[0001] This application belongs to the field of battery technology, and in particular relates to a silicon-carbon anode material, its preparation method and application. Background Technology

[0002] With the rise of electric vehicles and portable electronic devices, the market demand for efficient and safe lithium-ion batteries (LIBs) has surged. Advanced anode materials play a crucial role in improving their performance, particularly in terms of capacity, cycle life, and energy density. However, graphite anodes have a limited theoretical capacity (372 mAh g / L). -1 The limited rate performance of lithium metal and its poor capacitance restrict their application in next-generation energy storage devices. To overcome this obstacle, extensive research has been conducted to develop novel anode materials, including lithium metal, SnO2, TiO2, and Li4Ti5O. 12 And Fe2N. However, these novel anode materials face challenges such as lithium metal dendrite formation, short cycle life of tin-based materials, poor conductivity of titanium-containing compounds, and complex and costly manufacturing processes for transition metal nitrides.

[0003] Among various anode materials, silicon (Si) stands out due to its high theoretical specific capacity (3579 mAh g⁻¹). -1 Low lithium insertion / deintercalation electrochemical potential (<0.5V versus Li / Li). + Silicon, with its low price and abundant natural resources, has become a promising competitor for next-generation lithium-ion batteries. However, the nearly 300% volume expansion of silicon during lithiation and delithiation generates significant mechanical stress. After multiple cycles, silicon particles fracture and pulverize, leading to the formation of an unstable solid electrolyte interface phase and loss of electrical contact, ultimately resulting in rapid capacity decay and anode failure. To address these challenges, various strategies have been explored to rationally design and manufacture novel silicon-based anode materials, and various advanced silicon-carbon composite materials have been developed, such as silicon-amorphous carbon, silicon-graphene, silicon-carbon nanotubes, silicon-graphite, and silicon-carbon nanofibers.

[0004] However, silicon-carbon composite materials still face some key challenges, such as: the volume expansion of nano-silicon particles during cycling, which causes silicon particle breakage and pulverization, affecting the stability of the solid electrolyte membrane (SEI); the difficulty in obtaining uniformly distributed high-load silicon-carbon composite materials in traditional processes; and the poor interface contact between silicon and carbon materials, which limits electron and ion transport in silicon-carbon composite materials. Summary of the Invention

[0005] The purpose of this application is to provide a silicon-carbon anode material, its preparation method, and its application, aiming to solve to some extent the problems of poor interface contact between silicon and carbon materials, large volume expansion of silicon particles, poor stability of the solid electrolyte interface, and poor carrier transport efficiency in silicon-carbon anode materials prepared by existing processes.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application provides a method for preparing a silicon-carbon anode material, comprising the following steps:

[0008] Preparation of porous carbon fiber membranes supported on metal catalysts;

[0009] A dispersion of nano-silicon-based material is prepared, and the nano-silicon-based material is distributed in the porous carbon fiber membrane to obtain a composite porous carbon fiber membrane.

[0010] In an inert atmosphere containing a carbon source, the composite porous carbon fiber membrane is subjected to thermochemical vapor deposition to grow carbon nanofibers and vertical graphene on the surface of the composite porous carbon fiber membrane, thereby obtaining a silicon-carbon anode material.

[0011] In some possible implementations, the step of preparing a porous carbon fiber membrane loaded with a metal catalyst includes: preparing a solution of the metal catalyst, immersing a porous carbon fiber substrate in the solution of the metal catalyst, and drying to obtain the porous carbon fiber membrane loaded with the metal catalyst.

[0012] In some possible implementations, the metal catalyst includes at least one of a cobalt catalyst, a nickel catalyst, a copper catalyst, and a platinum catalyst.

[0013] In some possible implementations, the metal catalyst includes at least one cobalt catalyst selected from cobalt acetylacetonate, cobalt acetate, and cobalt chloride.

[0014] In some possible implementations, the porous carbon fiber substrate includes at least one of carbon felt, graphite paper, graphite plate, and carbon fiber cloth.

[0015] In some possible implementations, the concentration of the metal catalyst solution is 40 mg / mL to 60 mg / mL.

[0016] In some possible implementations, the fiber diameter in the porous carbon fiber substrate is 5 μm to 15 μm.

[0017] In some possible implementations, the thickness of the porous carbon fiber membrane is 0.5 mm to 1.5 mm.

[0018] In some possible implementations, the solvent in the solution of the metal catalyst includes at least one of methanol, ethanol, acetone, benzene, isopropanol, and n-hexane.

[0019] In some possible implementations, the preparation of the composite porous carbon fiber membrane includes the steps of: preparing a dispersion of the nano-silicon-based material, and distributing the nano-silicon-based material in the dispersion into the porous carbon fiber membrane by filtration to obtain the composite porous carbon fiber membrane.

[0020] In some possible implementations, the solvent in the dispersion of the nano-silicon-based material includes at least one of methanol, ethanol, acetone, benzene, isopropanol, and n-hexane.

[0021] In some possible implementations, the mass percentage of the nano-silicon-based material in the dispersion is 5% to 50%.

[0022] In some possible implementations, the nano-silicon-based material includes at least one of elemental silicon, silicon oxide, and silicon carbide.

[0023] In some possible implementations, the particle size D50 of the nano-silicon-based material is 30 nm to 200 nm.

[0024] In some possible implementations, the loading of the nano-silicon-based material in the composite porous carbon fiber membrane is 1 mg / cm³. 2 ~40mg / cm 2 .

[0025] In some possible implementations, the carbon source in the inert atmosphere includes at least one of ethanol, acetone, benzene, methanol, isopropanol, and n-hexane.

[0026] In some possible implementations, the inert atmosphere includes at least one inert gas selected from argon, nitrogen, and helium.

[0027] In some possible implementations, the inert atmosphere also contains an etching gas.

[0028] In some possible implementations, the etching gas includes at least one of hydrogen, oxygen, and hydrogen fluoride.

[0029] In some possible implementations, the inert gas in the inert atmosphere has a flow rate of 100 mL / min to 180 mL / min; the carbon source gas has a flow rate of 100 mL / min to 180 mL / min; and the etching gas has a flow rate of 100 mL / min to 150 mL / min.

[0030] In some possible implementations, the heating rate of the thermochemical vapor deposition is 5℃ / min to 10℃ / min, the holding temperature is 1000℃ to 1200℃, and the holding time is 6h to 12h.

[0031] In some possible implementations, the steps include: after growing the carbon nanofibers and the vertical graphene, naturally cooling them to 600℃~900℃, and then performing a nitrogen doping reaction using a nitrogen source gas to obtain a nitrogen-doped silicon-carbon anode material.

[0032] In some possible implementations, the nitrogen source gas includes at least one of ammonia, nitric oxide, and urea.

[0033] In some possible implementations, the flow rate of the nitrogen source gas is 15 mL / min to 25 mL / min.

[0034] In some possible implementations, the nitrogen doping reaction lasts for 20 to 40 minutes.

[0035] In some possible implementations, the thermochemical vapor deposition step includes: heating to 1000℃ to 1200℃ at a heating rate of 5℃ / min to 10℃ / min under the condition that the inert gas flow rate is 100mL / min to 180mL / min, then introducing the carbon source and the etching gas and holding at this temperature for 6h to 12h to grow the carbon nanofibers and the vertical graphene; naturally cooling to 600℃ to 900℃, then introducing the nitrogen source gas at a flow rate of 15mL / min to 25mL / min and reacting for 20min to 40min to obtain the nitrogen-doped silicon-carbon anode material.

[0036] Secondly, this application provides a silicon-carbon anode material, comprising a porous carbon fiber substrate and a nano-silicon-based material loaded in the porous carbon fiber substrate, wherein carbon nanofibers and vertical graphene are coated on the surface of the nano-silicon-based material.

[0037] Thirdly, this application provides a negative electrode sheet, which includes a silicon-carbon negative electrode material prepared by the above method, or the silicon-carbon negative electrode material described above.

[0038] Fourthly, this application provides a secondary battery that includes the aforementioned negative electrode.

[0039] The method for preparing silicon-carbon anode materials provided in the first aspect of this application involves preparing a porous carbon fiber membrane loaded with a metal catalyst, and then distributing nano-silicon-based materials into the porous carbon fiber membrane to form a composite porous carbon fiber membrane with a bilayer loading of metal catalyst and nano-silicon-based materials. Then, in an inert atmosphere containing a carbon source, thermochemical vapor deposition is performed on the composite porous carbon fiber membrane to grow carbon nanofibers (CNFs) and vertical graphene (VGs) on the surface of the composite porous carbon fiber membrane. By using a thermochemical vapor deposition (T-CVD) synthesis route, the synthesis process is optimized and a multi-level three-dimensional network structure of carbon nanofibers and vertical graphene is constructed to enhance the conductivity of the silicon-carbon anode material and accelerate carrier transport. On the one hand, the grown carbon nanofibers and vertical graphene form a multi-layered integrated three-dimensional network structure on the surface of silicon-based materials. This not only tightly coats the silicon nanofibers, effectively mitigating the volume expansion of the silicon during lithium intercalation, but also firmly anchors the silicon nanofibers within the porous carbon fiber substrate. This not only improves the loading capacity of the silicon nanofibers but also enhances the interfacial contact performance between the silicon and carbon materials, thereby improving carrier transport and the structural and cycle stability of the silicon-carbon anode material. Furthermore, vertical graphene (VGs) and carbon nanofibers (CNFs) possess significant mechanical strength, excellent chemical stability, and high electrical conductivity, offering significant advantages in mitigating the volume expansion of silicon nanofibers, promoting the stable formation of the solid electrolyte interfacial phase, and improving the electrical conductivity of silicon-carbon anode materials.

[0040] This application discloses a silicon-carbon anode material comprising a porous carbon fiber substrate and a nano-silicon-based material loaded within the porous carbon fiber substrate. The surface of the nano-silicon-based material is coated with carbon nanofibers and vertical graphene. Vertical graphene (VGs) and carbon nanofibers (CNFs) possess significant mechanical strength, excellent chemical stability, and high electrical conductivity, exhibiting significant advantages in mitigating the volume expansion of the nano-silicon-based material, promoting the stable formation of the solid electrolyte interface phase, and improving the electrical conductivity of the silicon-carbon anode material. Furthermore, the carbon nanofibers and vertical graphene construct a multi-layered three-dimensional network structure on the surface of the silicon-based material, tightly encapsulating the nano-silicon-based material and suppressing volume changes during charge and discharge. Simultaneously, this three-dimensional network structure firmly anchors the nano-silicon-based material within the porous carbon fiber substrate, increasing the areal capacity of the nano-silicon-based material and improving the electrochemical performance of the silicon-carbon anode material, including structural and cycle stability, conductivity, and SEI film stability.

[0041] The negative electrode sheet of this application includes the aforementioned silicon-carbon negative electrode material. This silicon-carbon negative electrode material has characteristics such as small volume change during charging and discharging, high structural stability, high conductivity, and is conducive to promoting the stable formation of the solid electrolyte interface phase. Therefore, the negative electrode sheet has high electronic conductivity and specific surface area, high capacity, promotes rapid electron and lithium ion transport, high cycle stability, and is beneficial to improving the stability of the solid electrolyte interface.

[0042] The secondary battery of this application includes the aforementioned negative electrode sheet with high capacity, high conductivity, and good cycle stability, thus giving the secondary battery characteristics such as high energy density, rate performance, and cycle life. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic flowchart of the preparation method of the silicon-carbon anode material provided in the embodiments of this application;

[0045] Figure 2 This is a schematic flowchart of the preparation method of the silicon-carbon anode material provided in Embodiment 1 of this application;

[0046] Figure 3 This is an overall SEM image of the silicon-carbon anode material provided in Embodiment 1 of this application;

[0047] Figure 4 This is a SEM image of the cross-section of the fiber in the silicon-carbon anode material provided in Example 1 of this application;

[0048] Figure 5 This is a TEM image of the silicon-carbon anode material provided in Example 1 of this application;

[0049] Figure 6 This is the XRD pattern of the silicon-carbon anode material provided in Example 1 of this application;

[0050] Figure 7 This is the Raman spectrum of the silicon-carbon anode material provided in Example 1 of this application;

[0051] Figure 8 This is the full-cell cycle stability curve of the silicon-carbon anode material provided in Example 1 of this application. Detailed Implementation

[0052] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0053] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0054] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0055] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0056] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0057] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass mentioned in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0058] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0059] The first aspect of this application provides a method for preparing a silicon-carbon anode material, as shown in the attached figure. Figure 1 As shown, it includes the following steps:

[0060] S10. Preparation of porous carbon fiber membranes supported on metal catalysts;

[0061] S20. Prepare a dispersion of nano-silicon-based material, and distribute the nano-silicon-based material into a porous carbon fiber membrane to obtain a composite porous carbon fiber membrane;

[0062] S30. In an inert atmosphere containing a carbon source, a composite porous carbon fiber membrane is subjected to thermochemical vapor deposition to grow carbon nanofibers and vertical graphene on the surface of the composite porous carbon fiber membrane, thereby obtaining a silicon-carbon anode material.

[0063] The method for preparing silicon-carbon anode materials provided in the first aspect of this application involves preparing a porous carbon fiber membrane loaded with a metal catalyst, and then distributing nano-silicon-based materials into the porous carbon fiber membrane to form a composite porous carbon fiber membrane with a double layer of metal catalyst and nano-silicon-based materials. Then, in an inert atmosphere containing a carbon source, thermochemical vapor deposition is performed on the composite porous carbon fiber membrane to grow carbon nanofibers (CNFs) and vertical graphene (VGs) on its surface. By using a thermochemical vapor deposition (T-CVD) synthesis route, the synthesis process is optimized, and a multi-level three-dimensional network structure of carbon nanofibers and vertical graphene is constructed to enhance the conductivity of the silicon-carbon anode material and accelerate carrier transport. On the one hand, the grown carbon nanofibers and vertical graphene form a multi-layered integrated three-dimensional network structure on the surface of silicon-based materials. This not only tightly coats the silicon nanofibers, effectively mitigating the volume expansion of the silicon during lithium intercalation, but also firmly anchors the silicon nanofibers within the porous carbon fiber substrate. This not only improves the loading capacity of the silicon nanofibers but also enhances the interfacial contact performance between the silicon and carbon materials, thereby improving carrier transport and the structural and cycle stability of the silicon-carbon anode material. Furthermore, vertical graphene (VGs) and carbon nanofibers (CNFs) possess significant mechanical strength, excellent chemical stability, and high electrical conductivity, offering significant advantages in mitigating the volume expansion of silicon nanofibers, promoting the stable formation of the solid electrolyte interfacial phase, and improving the electrical conductivity of silicon-carbon anode materials.

[0064] In step S10 above:

[0065] In some possible implementations, the steps for preparing a porous carbon fiber membrane loaded with a metal catalyst include: preparing a solution of the metal catalyst, immersing a porous carbon fiber substrate in the solution of the metal catalyst, and drying to obtain a porous carbon fiber membrane loaded with the metal catalyst. In this case, after preparing the metal catalyst into a solution, the porous carbon fiber substrate can be uniformly loaded with the metal catalyst by impregnating it, resulting in a porous carbon fiber membrane uniformly loaded with the metal catalyst.

[0066] In some possible implementations, the metal catalyst includes at least one of cobalt, nickel, copper, and platinum catalysts. These metal catalysts can all catalyze the growth of carbon nanofibers and vertical graphene during subsequent thermochemical vapor deposition.

[0067] In some possible implementations, the metal catalyst includes at least one cobalt catalyst selected from cobalt acetylacetonate, cobalt acetate, and cobalt chloride. In this case, cobalt is used as the metal catalyst because, on the one hand, cobalt has good catalytic activity, effectively promoting graphene growth; on the other hand, cobalt has good thermal stability, making it suitable for T-CVD vertical graphene growth under high-temperature conditions; and cobalt catalysts are also relatively inexpensive, offering a cost advantage.

[0068] In some possible implementations, the concentration of the metal catalyst solution is 40 mg / mL to 60 mg / mL, specifically, it can be any typical but non-limiting point value or a range between any two points, such as 40 mg / mL, 45 mg / mL, 50 mg / mL, 55 mg / mL, and 60 mg / mL. In other embodiments, the mass percentage of the metal catalyst in the solution is 5% to 20%, specifically, it can be any typical but non-limiting point value or a range between any two points, such as 5%, 10%, 15%, and 20%. The concentration of the metal catalyst solution in the above embodiments of this application sufficiently ensures the loading of the metal catalyst in the porous carbon fiber substrate, ensuring that there is sufficient metal catalyst in the porous carbon fiber membrane to catalyze the growth of carbon nanofibers and vertical graphene in the subsequent T-CVD process.

[0069] In some possible implementations, the solvent in the metal catalyst solution includes at least one of methanol, ethanol, acetone, benzene, isopropanol, and n-hexane. These solvents all have good dissolving and dispersing effects on the metal catalyst, ensuring the stability of the metal catalyst solution and facilitating the uniform and high-load loading of the metal catalyst onto the porous carbon fiber substrate through impregnation treatment.

[0070] In some possible implementations, the porous carbon fiber substrate includes at least one of carbon felt, graphite paper, graphite plate, and carbon fiber cloth; these carbon substrates all have a porous structure, which is beneficial for the loading of metal catalysts and nano-silicon-based materials. In some specific embodiments, the porous carbon fiber substrate is selected from carbon felt, which has a rich 3D network structure, further facilitating the loading of metal catalysts and nano-silicon-based materials.

[0071] In some possible implementations, the fiber diameter in the porous carbon fiber substrate is 5 μm to 15 μm. This facilitates the formation of appropriately sized and abundant pore structures in the porous carbon fiber substrate, ensuring that the carbon substrate possesses a rich three-dimensional porous structure. This is beneficial for the preparation of silicon-carbon anode materials by loading metal catalysts and nano-silicon-based materials. For example, the fiber diameter in the porous carbon fiber substrate can be any typical but non-limiting point value or a range between any two points, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm.

[0072] In some embodiments, the porous carbon fiber substrate is selected from carbon felt, and the fiber diameter in the carbon felt is 5μm to 15μm.

[0073] In some possible implementations, the thickness of the porous carbon fiber membrane is 0.5 mm to 1.5 mm. In this case, the thickness of the porous carbon fiber membrane provides a suitable conductive carrier for the high load of the nano-silicon-based material, while also ensuring the thickness of the silicon-carbon anode material. This ensures the thickness of the silicon-carbon anode material when used as an anode sheet, giving the electrode sheet a suitable application thickness. For example, the thickness of the porous carbon fiber membrane can be any typical but non-limiting point value or a range between any two points, such as 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, and 1.5 mm.

[0074] In step S20 above:

[0075] In some possible implementations, the preparation of the composite porous carbon fiber membrane includes the following steps: preparing a dispersion of nano-silicon-based material, and distributing the nano-silicon-based material in the dispersion into the porous carbon fiber membrane by filtration to obtain the composite porous carbon fiber membrane. In this case, using filtration to distribute the nano-silicon-based material in the dispersion into the porous carbon fiber membrane can improve the uniformity of the nano-silicon-based material loading and also allows for flexible control of the loading amount, thereby improving the loading efficiency.

[0076] In some embodiments, the preparation of the composite porous carbon fiber membrane includes the following steps: preparing a dispersion of nano-silicon-based material; loading the nano-silicon-based material in the dispersion onto a porous carbon fiber membrane by vacuum filtration; repeatedly filtering both sides of the porous carbon fiber membrane to ensure that the nano-silicon-based material is fully and uniformly loaded onto the porous carbon fiber membrane; and drying the membrane in a vacuum oven at a temperature of 60°C to 90°C after filtration to obtain the composite porous carbon fiber membrane.

[0077] In some possible implementations, the solvent in the dispersion of the nano-silicon-based material includes methanol (CH3OH), ethanol (C2H5OH), acetone (C3H6O), benzene (C6H6), isopropanol (C3H7OH), and n-hexane (C6H6OH). 14 At least one of the following solvents; these solvents all have high dispersibility for nano-silicon-based materials. In some specific embodiments, ethanol is used as the solvent, which has good dispersibility for nano-silicon-based materials, is safe and inexpensive, and facilitates subsequent drying.

[0078] In some possible implementations, the mass percentage of the nano-silicon-based material in the dispersion is 5% to 50%. This ensures both the dispersion stability of the nano-silicon-based material in the dispersion and facilitates its loading onto the porous carbon fiber membrane via filtration. Exemplarily, the mass percentage of the nano-silicon-based material in the dispersion can be any typical but non-limiting point value or a range between any two points, such as 5%, 10%, 20%, 30%, 40%, or 50%.

[0079] In some possible implementations, the nano-silicon-based material includes at least one of elemental silicon, silicon oxide, and silicon carbide; these silicon-based materials all have high capacity.

[0080] In some possible implementations, the particle size D50 of the nano-silicon-based material is 30 nm to 200 nm. The particle size of the nano-silicon-based material in the embodiments of this application directly affects its surface area and availability in electrochemical reactions. Smaller particle sizes of silicon-based materials result in a larger specific surface area, providing more active reaction sites, which is beneficial for rapid ion transport and efficient reactions during lithium-ion insertion / extraction. Furthermore, smaller particle sizes of silicon-based materials help reduce stress and cracks between materials during expansion, thereby improving the cycle stability and long-term lifespan of the material. Simultaneously, smaller particle sizes of silicon-based materials contribute to the formation of a more uniform and continuous electron conduction network, reducing resistance loss and improving the conductivity and power performance of the electrode. Therefore, silicon-based materials with a particle size D50 of 30 nm to 200 nm have relatively uniform particle sizes, which is beneficial for forming a uniform electrode layer and improving the consistency and stability of the electrode. Moreover, silicon-based materials within this particle size range exhibit a higher reaction rate during lithium-ion insertion / extraction, enabling a faster electrochemical reaction kinetic response, thereby improving the charge-discharge performance of the battery. Compared to silicon-based materials with larger particle sizes, silicon-based materials with a particle size of 30-200nm can more effectively alleviate the stress caused by volume expansion and improve the cycle stability and cycle life of electrode materials.

[0081] For example, the particle size D50 of the nano-silicon-based material can be any typical but non-limiting point value or an interval between any two point values, such as 30nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm.

[0082] In some possible implementations, the loading of nano-silicon-based materials in the composite porous carbon fiber membrane is 1 mg / cm³. 2 ~40mg / cm 2 In this context, the loading of nano-silicon-based materials in the composite porous carbon fiber membrane can be flexibly adjusted from low to high loading. In some embodiments, the loading of nano-silicon-based materials in the composite porous carbon fiber membrane can reach 30 mg / cm³. 2 ~40mg / cm 2 The ultra-high silicon loading significantly increases the silicon loading of silicon-carbon anode materials, thereby improving the capacity of silicon-carbon anodes.

[0083] For example, in a composite porous carbon fiber membrane, the loading of nano-silicon-based material can be 1 mg / cm³. 2 5mg / cm 2 10mg / cm 2 15mg / cm 2 20mg / cm 2 25mg / cm 2 30mg / cm 235mg / cm 2 40mg / cm 2 Typical but unrestricted arbitrary point values ​​or interval values ​​between any two point values.

[0084] In step S30 above:

[0085] In some possible implementations, the carbon source in an inert atmosphere includes at least one of ethanol, acetone, benzene, methanol, isopropanol, and n-hexane; all of these carbon sources can induce the growth of vertical graphene and carbon nanofibers.

[0086] In some possible implementations, the inert atmosphere includes at least one inert gas selected from argon, nitrogen, and helium. These inert gases can both remove non-reactive gaseous components from the reaction system, improving reaction purity, and regulate the content of carbon source and etching gas, thereby increasing the efficiency of carbon nanofiber and vertical graphene growth.

[0087] In some possible implementations, the inert atmosphere also includes an etching gas. In some possible implementations, the etching gas includes at least one of hydrogen, oxygen, and hydrogen fluoride. In this case, the etching gas can control the number of carbon atoms deposited, thereby achieving a vertically oriented growth structure of graphene nanosheets. Flexible vertical graphene nanosheets form a high-strength conductive network with oriented channels within the silicon-carbon composite particles, creating a highly mechanically strong, structurally stable, and robust conductive network. This improves the conductivity of the silicon-carbon anode and suppresses the volume expansion effect of silicon-based materials.

[0088] In some possible implementations, the inert gas flow rate is 100 mL / min to 180 mL / min in an inert atmosphere; the carbon source gas flow rate is 100 mL / min to 180 mL / min; and the etching gas flow rate is 100 mL / min to 150 mL / min. In this case, the inert gas flow rate can better improve reaction purity, control the content of carbon source gas and etching atmosphere, and improve the growth efficiency of carbon nanofibers and vertical graphene. The carbon source gas flow rate can better initiate the growth of carbon nanofibers and vertical graphene. The etching gas flow rate is beneficial for enhancing the growth of vertical graphene while avoiding the formation of byproducts and improving product purity.

[0089] For example, in an inert atmosphere, the flow rate of the inert gas can be any typical but non-limiting point value or a range between any two points, such as 100 mL / min, 110 mL / min, 120 mL / min, 130 mL / min, 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min; the flow rate of the carbon source gas can be any typical but non-limiting point value or a range between any two points, such as 100 mL / min, 110 mL / min, 120 mL / min, 130 mL / min, 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min; and the flow rate of the etching gas can be any typical but non-limiting point value or a range between any two points, such as 100 mL / min, 110 mL / min, 120 mL / min, 130 mL / min, 140 mL / min, 150 mL / min.

[0090] In some possible implementations, the heating rate of thermochemical vapor deposition is 5℃ / min to 10℃ / min, the holding temperature is 1000℃ to 1200℃, and the holding time is 6h to 12h. Under these conditions, the carbon source gas can be stably decomposed, initiating the growth of carbon nanofibers and vertical graphene, and ensuring that carbon nanofibers and vertical graphene grow sufficiently on the surface of silicon-based materials to form a 3D hierarchical network structure.

[0091] For example, the heating rate of thermochemical vapor deposition can be any typical but non-limiting point value or a range between any two points, such as 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min; the holding temperature can be any typical but non-limiting point value or a range between any two points, such as 1000℃, 1050℃, 1100℃, 1150℃, 1200℃; and the reaction time can be any typical but non-limiting point value or a range between any two points, such as 6h, 7h, 8h, 9h, 10h, 11h, 12h.

[0092] In some possible implementations, the steps include: after growing carbon nanofibers and vertical graphene, naturally cooling to 600℃~900℃, and then performing a nitrogen doping reaction using a nitrogen source gas to obtain a nitrogen-doped silicon-carbon anode material. In this case, by introducing a nitrogen source gas to dope the silicon-carbon anode material, the wettability of the electrolyte to the silicon-carbon anode material is enhanced, further improving the conductivity of the silicon-carbon anode material. Exemplarily, the temperature conditions for the nitrogen doping reaction can be typical but not limiting arbitrary point values ​​such as 600℃, 700℃, 800℃, and 900℃, or a range between any two point values.

[0093] In some possible implementations, the nitrogen source gas includes at least one of ammonia, nitric oxide, and urea; these nitrogen source gases can all be doped into silicon-carbon anode materials at high temperatures of 600°C to 900°C.

[0094] In some possible implementations, the flow rate of the nitrogen source gas is 15 mL / min to 25 mL / min. In this case, the flow rate of the nitrogen source gas is sufficient to ensure the nitrogen doping effect on the silicon-carbon anode material. For example, the flow rate of the nitrogen source gas can be any typical but non-limiting point value or a range between any two points, such as 15 mL / min, 18 mL / min, 20 mL / min, 22 mL / min, or 25 mL / min.

[0095] In some possible implementations, the nitrogen doping reaction duration is 20 min to 40 min; under this reaction duration, sufficient doping modification of the silicon-carbon anode material can be ensured. For example, the doping reaction duration can be any typical but non-limiting point value or a range between any two points, such as 20 min, 25 min, 30 min, 35 min, or 40 min.

[0096] In some possible implementations, the thermochemical vapor deposition steps include: heating to 1000℃ to 1200℃ at a heating rate of 5℃ / min to 10℃ / min under an inert gas flow rate of 100 mL / min to 180 mL / min, then introducing a carbon source and etching gas and holding at that temperature for 6h to 12h to grow carbon nanofibers and vertical graphene; naturally cooling to 600℃ to 900℃, then introducing a nitrogen source gas at a flow rate of 15 mL / min to 25 mL / min and reacting for 20min to 40min to obtain nitrogen-doped silicon-carbon anode material.

[0097] Secondly, embodiments of this application provide a silicon-carbon anode material, comprising a porous carbon fiber substrate and a nano-silicon-based material loaded in the porous carbon fiber substrate, wherein carbon nanofibers and vertical graphene are coated on the surface of the nano-silicon-based material.

[0098] This application describes a silicon-carbon anode material comprising a porous carbon fiber substrate and a nano-silicon-based material supported on the porous carbon fiber substrate. Carbon nanofibers and vertical graphene are coated on the surface of the nano-silicon-based material. The vertical graphene (VGs) and carbon nanofibers (CNFs) possess significant mechanical strength, excellent chemical stability, and high electrical conductivity, offering significant advantages in mitigating the volume expansion of the nano-silicon-based material, promoting the stable formation of the solid electrolyte interface phase, and improving the electrical conductivity of the silicon-carbon anode material. Furthermore, the carbon nanofibers and vertical graphene construct a multi-layered three-dimensional network structure on the surface of the silicon-based material, which not only gives the silicon-carbon anode material high electronic conductivity and specific surface area but also promotes electron and Li bonding.+ This allows for rapid transport and tightly encapsulates the nano-silicon-based material, suppressing volume changes during charging and discharging. Simultaneously, this three-dimensional network structure firmly anchors the nano-silicon-based material within the porous carbon fiber substrate, enhancing its areal capacity and improving the electrochemical properties of the silicon-carbon anode material, including structural and cycle stability, conductivity, and SEI film stability.

[0099] The silicon-carbon anode material of this application embodiment can be prepared by the method described in the above embodiments.

[0100] In some embodiments, silicon-carbon anode materials have self-supporting properties and characteristics such as good structural stability, good cycle stability, and high conductivity. They can be directly used as anode sheets in batteries without the need for additional auxiliary materials such as binders and conductive agents, or additional current collectors.

[0101] In some possible implementations, the particle size D50 of the silicon-based nanomaterial in the silicon-carbon anode material is 30 nm to 200 nm.

[0102] In some possible implementations, the fiber diameter in silicon-carbon anode materials ranges from 5 μm to 15 μm.

[0103] In some possible implementations, the thickness of the silicon-carbon anode material is 0.5 mm to 1.5 mm.

[0104] In some possible implementations, the nano-silicon-based material includes at least one of elemental silicon, silicon oxide, and silicon carbide; these silicon-based materials all have high capacity.

[0105] In some possible implementations, the loading of nano-silicon-based materials in silicon-carbon anode materials is 1 mg / cm³. 2 ~40mg / cm 2 .

[0106] In some possible implementations, the porous carbon fiber substrate in the silicon-carbon anode material has a mass percentage of 60%–70%; the total mass percentage of carbon nanofibers and vertical graphene has a mass percentage of 10%–20%.

[0107] The beneficial effects of the above embodiments of this application have been discussed above and will not be repeated here.

[0108] Thirdly, embodiments of this application provide a negative electrode sheet, which includes a silicon-carbon negative electrode material prepared by the above method, or the silicon-carbon negative electrode material described above.

[0109] The negative electrode sheet in this application embodiment includes the aforementioned silicon-carbon negative electrode material. This silicon-carbon negative electrode material has characteristics such as small volume change during charging and discharging, high structural stability, high conductivity, and is conducive to promoting the stable formation of the solid electrolyte interface phase. Therefore, the negative electrode sheet has high electronic conductivity and specific surface area, high capacity, promotes rapid electron and lithium ion transport, high cycle stability, and is beneficial to improving the stability of the solid electrolyte interface.

[0110] Fourthly, embodiments of this application provide a secondary battery that includes the aforementioned negative electrode sheet.

[0111] The secondary battery in this application embodiment includes the aforementioned negative electrode sheet with high capacity, high conductivity, and good cycle stability, thus enabling the secondary battery to have high energy density, rate performance, cycle life, and other characteristics.

[0112] This application does not specifically limit the positive electrode, electrolyte, separator, etc. in the secondary battery of the embodiments, and can be applied to any battery system.

[0113] In some possible implementations, the positive electrode includes a current collector and a positive electrode active layer formed on the surface of the current collector.

[0114] In some possible implementations, the preparation of the positive electrode sheet includes the following steps: mixing the positive electrode material, conductive agent and binder to form an electrode slurry, coating the electrode slurry onto the current collector, and then preparing the positive electrode sheet through steps such as drying, rolling and die cutting.

[0115] In some possible implementations, the mass percentage of the positive electrode material in the positive electrode active layer of the positive electrode sheet is 90% to 95%.

[0116] In some possible implementations, the current collector of the positive electrode includes, but is not limited to, any one of copper foil or aluminum foil.

[0117] In some possible implementations, the binder content in the positive electrode active material layer is 2wt% to 5wt%.

[0118] In some possible implementations, the binder includes one or more of the following: polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0119] In some possible implementations, the conductive agent content in the positive electrode active material layer is 1 wt% to 5 wt%.

[0120] In some possible implementations, the conductive agent includes graphite, carbon black, acetylene black, graphene, carbon fiber, and C. 60And one or more of carbon nanotubes.

[0121] In some possible implementations, the membrane is capable of blocking electrons while allowing ions to pass through. Exemplary membranes include, but are not limited to, at least one material selected from polypropylene fibers, polyacrylonitrile fibers, polyvinyl formal fibers, poly(ethylene glycol terephthalate), polyethylene terephthalate, polyamide fibers, and poly(p-phenylene terephthalamide).

[0122] In some possible implementations, the electrolyte comprises at least one soluble metal salt. In some specific embodiments, the metal salt includes LiClO4, LiBF4, LiPF6, LiAsF6, LiCF3SO3, LiTDI, Li[(CF3SO2)2N], Li[(FSO2)2N], Li[(C m F 2m+1 SO2)(C n F 2n+1 At least one of SO2(N)[m, n], where m and n are natural numbers. These electrolytic salts can ensure high ionic conductivity of the electrolyte and do not undergo harmful side reactions with electrode materials, electrolyte, diaphragm, etc., and have good chemical stability.

[0123] In some possible implementations, the secondary battery includes at least one of a battery cell, a battery module, and a battery pack.

[0124] In some possible implementations, the battery cell types include lithium-ion batteries, as well as novel batteries such as lithium-air batteries and lithium metal batteries.

[0125] In some possible implementations, the battery cells of this application embodiment can be assembled into a battery module. The number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Furthermore, the battery module may also include a housing with a receiving space, in which multiple battery cells are received.

[0126] In one possible implementation, battery cells and / or battery modules can also be assembled into a battery pack, and the number of battery cells or battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0127] To enable those skilled in the art to clearly understand the above-described implementation details and operations of this application, and to demonstrate the significant advancements in the performance of the silicon-carbon anode material, its preparation method, and its application in the embodiments of this application, the following examples illustrate the above technical solutions.

[0128] Example 1

[0129] A silicon-carbon anode material, as shown in the attached... Figure 2As shown, its preparation includes the following steps:

[0130] 1. Preparation of porous carbon fiber membrane loaded with metal catalyst: Prepare a 50 mg / mL cobalt acetylacetonate (Co(C5H7O2)2) ethanol solution, and immerse carbon felt CF with a thickness of 1 mm, a fiber diameter of 10 μm, and a porosity of 50% in the solution for 2 h to ensure uniform catalyst loading. Then remove the CF and place it in an 80℃ oven to air dry for later use to obtain a porous carbon fiber membrane.

[0131] 2. Loading of silicon nanoparticles: Prepare an ethanol dispersion of 40% Si nanoparticles (SiNPs) by mass. Introduce the Si nanoparticles into a porous carbon fiber membrane by vacuum filtration. Control the loading by controlling the vacuum filtration time to 30 min and the volume of the Si nanoparticle ethanol dispersion to 100 ml. Repeat filtration on both sides to ensure uniform loading of Si nanoparticles. Dry in a vacuum oven at 80℃ and cut into fixed sizes for later use to obtain a composite porous carbon fiber membrane, labeled CF / Si.

[0132] 3. T-CVD Process: The composite porous carbon fiber membrane prepared in the previous steps is placed in the central area of ​​the furnace. The furnace tubes are then purged with argon (Ar) at a flow rate of 180 mL / min to remove air. The temperature is raised to 1000 °C under ambient pressure in an Ar atmosphere and maintained at a constant temperature of 5 °C / min. The argon flow rate is maintained at 100 mL / min. Subsequently, an Ar / C₂H₅OH mixed gas is added at the same flow rate to grow carbon nanofibers (VGs) / vertical graphene (CNFs) on the CF / Si surface. The growth process includes introducing H₂ / Ar at a flow rate of 125 ± 5 mL / min. The CF / Si composite material is held at the desired temperature for 12 hours to promote the growth of VGs and CNFs. As the VGs and CNFs grow, the furnace is naturally cooled to 900 °C. Then, ammonia gas was introduced at a flow rate of 20 mL / min for 30 min to dope N into the silicon-carbon anode material, labeled as CF@Si@CNFs@VGs electrode, wherein the silicon loading was 40 mg / cm³. 2 .

[0133] Example 2

[0134] A silicon-carbon anode material differs from Example 1 in that the prepared electrode nanoparticles have a lower loading of Si, approximately 50% of that in Example 1, and a silicon loading of 20 mg / cm³. 2 The other steps remain unchanged.

[0135] Example 3

[0136] A silicon-carbon anode material differs from Example 1 in that the prepared electrode nanoparticles have a lower loading of Si, approximately 25% of that in Example 1, and a silicon loading of 10 mg / cm³. 2 The other steps remain unchanged.

[0137] Example 4

[0138] A silicon-carbon anode material differs from Example 1 in that the prepared electrode has a lower loading of nano-Si, approximately 13% of that in Example 1, and a silicon loading of 5 mg / cm³. 2 The other steps remain unchanged.

[0139] Example 5

[0140] A silicon-carbon anode material differs from Example 1 in that the type of metal catalyst used is different, and cobalt acetylacetonate in step 1 is replaced with nickel chloride, while other steps remain unchanged.

[0141] Example 6

[0142] A silicon-carbon anode material differs from Example 1 in that the type of metal catalyst used is different, and cobalt acetylacetonate in step 1 is replaced with copper chloride, while other steps remain unchanged.

[0143] Example 7

[0144] A silicon-carbon anode material differs from Example 1 in that the type of metal catalyst used is different, and cobalt acetylacetonate in step 1 is replaced with platinum chloride, while other steps remain unchanged.

[0145] Example 8

[0146] A silicon-carbon anode material differs from Example 1 in that the type of silicon-based material used is different, and the Si nanoparticles in step 2 are replaced with silicon oxide, while other steps remain unchanged.

[0147] Example 9

[0148] A silicon-carbon anode material differs from Example 1 in that the type of silicon-based material used is different, and the Si nanoparticles in step 2 are replaced with silicon carbide, while other steps remain unchanged.

[0149] Example 10

[0150] A silicon-carbon anode material differs from Example 1 in that the heat preservation temperature of T-CVD is different, and the heat preservation temperature in step 3 is replaced by 950℃ instead of 1000℃, while other steps remain unchanged.

[0151] Example 11

[0152] A silicon-carbon anode material differs from Example 1 in that the heat preservation temperature of T-CVD is different, and the heat preservation temperature in step 3 is replaced by 1200℃ instead of 1000℃, while other steps remain unchanged.

[0153] Example 12

[0154] A silicon-carbon anode material differs from Example 1 in that the heat preservation temperature of T-CVD is different, and the heat preservation temperature in step 3 is replaced by 1250℃ instead of 1000℃, while other steps remain unchanged.

[0155] Example 13

[0156] A silicon-carbon anode material, which differs from Example 1 in that it does not undergo nitrogen doping, but other steps remain unchanged.

[0157] Comparative Example 1

[0158] A silicon-carbon anode material, differing from Example 1 in that: the SiNPs were not treated in any way; instead, a slurry composed of SiNPs, carbon black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) was directly coated onto copper foil to prepare the working electrode, followed by vacuum drying at 100°C for 12 hours. The weights of various electrodes ranged from 0.8 to 1.5 mg / cm³. -2 The remaining test steps remain unchanged.

[0159] Comparative Example 2

[0160] A silicon-carbon anode material differs from Example 1 in that it does not undergo T-CVD process to grow VGs and CNFs, while other steps remain unchanged.

[0161] Comparative Example 3

[0162] A silicon-carbon anode material differs from Example 1 in that step 3 does not involve in-situ growth of VGs and CNFs, but instead directly mixes the composite porous carbon fiber membrane with VGs and CNFs, while other steps remain unchanged.

[0163] Comparative Example 4

[0164] A silicon-carbon anode material differs from Example 1 in that: in step 1, the porous carbon fiber membrane is not loaded with a metal catalyst; in step 3, since no metal catalyst is used, only vertical graphene is grown, and no carbon nanofibers are generated; the other steps remain unchanged.

[0165] Furthermore, to verify the progressiveness of the embodiments of this application, the silicon-carbon anode materials prepared in the above embodiments and comparative examples were subjected to the following performance tests:

[0166] 1. The morphology of the silicon-carbon anode material prepared in Example 1 was observed, and the test results are attached. Figure 3 and 4 The scanning electron microscope image shows that, among other things, the attached... Figure 3 Here is the overall SEM image of CF@Si@CNFs@VGs, attached. Figure 4 SEM images of the cross-section of CF@Si@CNFs@VGs fibers are shown. (Attached) Figure 4 In the image, 'a' represents the overall SEM image of the cross-section of the CF@Si@CNFs@VGs fiber, attached. Figure 4 In this context, 'b' represents the cross-section of a single fiber. Figure 4 The c-section image shows a magnified SEM image of the vertical graphene. Figure 4 In the figure, d represents a magnified SEM image of the CNFs@VGs network in the cross-sectional view. In the silicon-carbon anode material prepared in this application, the CNFs and VGs grown are interconnected with the carbon felt fibers to form a multi-layered three-dimensional network structure.

[0167] 2. The silicon-carbon anode material prepared in Example 1 was subjected to transmission electron microscopy (TEM) testing. The test results are shown in the attached figure. Figure 5 The TEM image of CF@Si@CNFs@VGs shows that abundant carbon materials are grown on the Si particles, and these carbon materials have obvious characteristics of multilayer vertical graphene.

[0168] 3. X-ray diffraction tests were performed on the silicon-carbon anode material prepared in Example 1. The test results are shown in the attached figure. Figure 6 As shown in the XRD pattern, the silicon-carbon anode material prepared in the embodiments of this application contains characteristic peaks of both carbon and silicon.

[0169] 4. Raman diffraction tests were performed on the silicon-carbon anode material prepared in Example 1. The test results are shown in the attached figure. Figure 7 As shown in the Raman diagram, Raman spectroscopy confirms the successful synthesis of graphene, which can be observed from 1340 cm⁻¹. -1 (D belt), 1581cm -1 (G-band) and 2680cm -1 This is proven in the characteristic signals of (2D band).

[0170] 5. The lithium-ion battery anode performance of the above examples and comparative examples was tested: The prepared silicon-carbon anode material was cut into small circular pieces with a diameter of 12 mm using a slicer, weighed and recorded. The weighed electrode pieces were dried in a vacuum drying oven at 85°C for 12 h to remove moisture. Battery assembly was carried out in a glove box filled with argon atmosphere, using 2032 coin half-cells. The anode material was the 12 mm circular pieces cut in the above steps, the separator was Celgard 2400, the lithium sheet was used as the counter electrode and reference electrode, and the electrolyte was 1 M lithium hexafluorophosphate (LiPF6) dissolved in a mixed solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and dimethyl carbonate (DEC) with a volume ratio of 1:1:1. Electrochemical performance was evaluated using a Neware battery testing system at 30°C, within a voltage range of 0.005-2.0 V (relative to Li / Li+) and at different current densities. The electrochemical performance was assessed using an electrochemical workstation (CHI760D) at 10... 5 ~10 -2 Cyclic voltammetry (CV) curves and electrochemical impedance spectroscopy (EIS) curves were obtained at different scan rates within the Hz range, with an amplitude of 5 mV.

[0171] The electrochemical performance test results are shown in Table 1 below:

[0172] Table 1

[0173]

[0174] In Example 1, the silicon loading in the silicon-carbon anode material CF@Si@CNFs@VGs can reach 40 mg / cm³. 2 The cycle stability curves of the prepared full cells are shown in the attached figure. Figure 8 As shown, the battery still exhibits high capacity and good cycle stability after 500 cycles.

[0175] The test results above show that the multi-level 3D network structure formed by introducing Co-based catalyst and growing CNFs and VGs by T-CVD process effectively slows down the volume expansion of Si during charge-discharge cycles, while enhancing the electronic conductivity and ion transport efficiency of the electrode. N doping effectively improves the wettability of the electrolyte. Therefore, the silicon-carbon anode material CF@Si@CNFs@VGs exhibits high capacity and better cycle stability.

[0176] Comparative studies of Examples 1-4 show that the loading of silicon material ranges from 1 to 40 mg / cm³. 2 Both silicon-carbon anode materials exhibit high cycle stability.

[0177] By comparing Examples 1 and Examples 6-8, it can be seen that when a cobalt catalyst is used as the metal catalyst, the catalytic effect is better, and the capacity and cycle stability of the silicon-carbon anode material can be improved more effectively.

[0178] By comparing Examples 1 and Examples 8-9, it can be seen that the silicon-based material in the embodiments of this application can be nano-silicon, or silicon carbide, silicon oxide, etc.

[0179] By comparing Examples 1 and Examples 10-12, it can be seen that T-CVD has a better sintering effect when the holding temperature is between 1000℃ and 1200℃, which can better improve the capacity and cycle stability of silicon-carbon anode materials.

[0180] By comparing Example 1 and Example 13, it can be seen that nitrogen doping can better improve the capacity and cycle stability of silicon-carbon anode materials.

[0181] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized by, The method comprises the following steps: preparing a porous carbon fiber membrane loaded with a metal catalyst; dispersing a nano-silicon-based material in a solution to distribute the nano-silicon-based material into the porous carbon fiber membrane to obtain a composite porous carbon fiber membrane; carrying out a thermal chemical vapor deposition on the composite porous carbon fiber membrane in an inert atmosphere containing a carbon source to grow carbon nanofibers and vertical graphene on the surface of the composite porous carbon fiber membrane to obtain a silicon-carbon negative electrode material.

2. The method for preparing a silicon-carbon negative material according to claim 1, characterized in that, The step of preparing the porous carbon fiber membrane loaded with the metal catalyst comprises: preparing a solution of the metal catalyst, immersing a porous carbon fiber substrate into the solution of the metal catalyst, and drying to obtain the porous carbon fiber membrane loaded with the metal catalyst; The metal catalyst comprises at least one of a cobalt catalyst, a nickel catalyst, a copper catalyst, and a platinum catalyst.

3. The method for preparing a silicon-carbon negative material according to claim 2, characterized in that, The metal catalyst comprises at least one of cobalt acetylacetonate, cobalt acetate, and cobalt chloride. The porous carbon fiber substrate comprises at least one of carbon felt, graphite paper, graphite plate, and carbon fiber cloth. The concentration of the solution of the metal catalyst is 40 mg / mL to 60 mg / mL. The diameter of the fibers in the porous carbon fiber substrate is 5 μm to 15 μm. The thickness of the porous carbon fiber membrane is 0.5 mm to 1.5 mm. The solvent in the solution of the metal catalyst comprises at least one of methanol, ethanol, acetone, benzene, isopropyl alcohol, and n-hexane.

4. The method for preparing a silicon-carbon negative material according to any one of claims 1 to 3, characterized in that, The preparation of the composite porous carbon fiber membrane comprises the following steps: preparing a dispersion of the nano-silicon-based material, and distributing the nano-silicon-based material in the dispersion into the porous carbon fiber membrane by filtration to obtain the composite porous carbon fiber membrane. The solvent in the dispersion of the nano-silicon-based material comprises at least one of methanol, ethanol, acetone, benzene, isopropyl alcohol, and n-hexane. The mass percentage of the nano-silicon-based material in the dispersion of the nano-silicon-based material is 5% to 50%. The nano-silicon-based material comprises at least one of elemental silicon, silicon oxide, and silicon carbide. The particle size D50 of the nano-silicon-based material is 30 nm to 200 nm. and / or, the loading amount of the nanosilicon-based material in the composite porous carbon fiber membrane is 1 mg / cm 2 ~ 40 mg / cm 2 .

5. The method for preparing a silicon-carbon negative material according to claim 4, characterized in that, The carbon source in the inert atmosphere comprises at least one of ethanol, acetone, benzene, methanol, isopropyl alcohol, and n-hexane. The inert gas in the inert atmosphere comprises at least one of argon, nitrogen, and helium. The inert atmosphere further comprises an etching gas.

6. The method for preparing a silicon-carbon negative material according to claim 5, characterized in that, The etching gas comprises at least one of hydrogen, oxygen, and hydrogen fluoride. The flow rate of the inert gas in the inert atmosphere is 100 mL / min to 180 mL / min, the flow rate of the carbon source is 100 mL / min to 180 mL / min, and the flow rate of the etching gas is 100 mL / min to 150 mL / min. The heating rate of the thermal chemical vapor deposition is 5 ℃ / min to 10 ℃ / min, the holding temperature is 1000 ℃ to 1200 ℃, and the holding time is 6 h to 12 h. And / or, further comprising the steps of: after growing the carbon nanofiber and the vertical graphene, naturally cooling to 600-900 DEG C, carrying out nitrogen doping reaction through nitrogen source gas, to obtain the nitrogen-doped silicon-carbon negative electrode material.

7. The method for preparing a silicon-carbon negative material according to claim 6, characterized in that, The nitrogen source gas comprises at least one of ammonia, nitric oxide and urea; And / or, the flow rate of the nitrogen source gas is 15-25 mL / min; And / or, the nitrogen doping reaction lasts for 20-40 min; And / or, the step of thermal chemical vapor deposition comprises: under the condition that the flow rate of the inert gas is 100-180 mL / min, heating to 1000-1200 DEG C at a heating rate of 5-10 DEG C / min, then passing in the carbon source and the etching gas to grow the carbon nanofiber and the vertical graphene for 6-12 h; naturally cooling to 600-900 DEG C, passing in the nitrogen source gas at a flow rate of 15-25 mL / min to react for 20-40 min, to obtain the nitrogen-doped silicon-carbon negative electrode material.

8. The silicon-carbon anode material prepared according to the method of any one of claims 1 to 7, characterized in that, The porous carbon fiber substrate and the nanosilicon-based material loaded in the porous carbon fiber substrate, and the surface of the nanosilicon-based material is coated with carbon nanofiber and vertical graphene.

9. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises the silicon-carbon negative electrode material prepared by the method of any one of claims 1-7, or the silicon-carbon negative electrode material of claim 8.

10. A secondary battery characterized by comprising: The secondary battery comprises the negative electrode sheet of claim 9. The secondary battery comprises the negative electrode sheet of claim 9.

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