Silicon-based composite negative electrode material, preparation method thereof, negative electrode sheet, and secondary battery

Abstract

Embodiments of the present application provide a silicon-based composite negative electrode material, a preparation method thereof, a negative electrode sheet and a secondary battery. The preparation method comprises: preparing a precursor fiber by electrospinning a precursor dispersion liquid containing a first silicon source, a second silicon source, a first carbon source and a second carbon source; and obtaining the silicon-based composite negative electrode material by heat treatment of the precursor fiber; the first silicon source is silicon particles; the second silicon source carries one or more of a silicon halogen bond, a silicon oxygen bond and a silicon hydrogen bond in a molecular structure; the first carbon source is a high molecular compound; and the second carbon source is an oxygen-containing small molecule organic compound. The present application adds two silicon sources and oxygen-containing group organic compounds to the spinning precursor dispersion liquid, so as to improve the structural stability and electrochemical performance of the silicon-based negative electrode material, thereby achieving the technical effects of inhibiting volume expansion while ensuring high capacity, significantly improving the cycle stability and safety, and simplifying the preparation process and reducing the cost.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a silicon-based composite negative electrode material, its preparation method, a negative electrode sheet, and a secondary battery. Background Technology

[0002] The rapid development of electric vehicles (EVs) is driven by advancements in lithium-ion batteries (LIBs), particularly in anode materials. Graphite electrodes are widely used due to their high porosity, good conductivity, light weight, and cost-effectiveness. Silicon anodes offer higher capacity and energy density and are safer due to their non-flammability. However, the tendency of silicon to expand and contract during cycling presents challenges. Nanoscale materials offer significant progress for lithium-ion batteries by reducing the diffusion path of lithium ions, a key limitation currently held by batteries using micron-sized particles with minimal surface area. This reduction improves charge and discharge rates. The transition to nanoscale particles significantly enhances lithium storage capacity. Nanostructured electrodes possess a hierarchical chemical nanoscale structure, which can shorten diffusion lengths and improve electrode kinetics. Furthermore, they introduce novel lithium storage mechanisms at the electrode surface, improving capacity, flexibility, and cycle stability. Challenges include the expansion and contraction issues of silicon anodes during cycling, the long diffusion paths and low capacity of micron-sized lithium-ion batteries, and the large-scale fabrication, cost control, long-term stability, and compatibility with existing processes for nanostructured electrodes.

[0003] With the increasing demand for high-performance materials driven by technological advancements, electrospinning technology has emerged as a necessary advancement. Its advantages are significant: the prepared materials possess nano- or micron-scale fiber structures, large specific surface area, high porosity, providing more active sites and exhibiting good air permeability. Furthermore, it is multifunctional, allowing for the preparation of materials with different properties to meet diverse needs by adjusting parameters. It also boasts excellent mechanical properties, a simple preparation process, low environmental requirements due to its operation at room temperature and pressure, strong adaptability, and low cost, making it suitable for large-scale production and laboratory research. Despite these advantages, electrospinning currently faces challenges such as the difficulty in controlling fiber structure, the need to improve production efficiency, and the need to further enhance the stability of material properties.

[0004] The existing electrospinning methods for preparing silicon anode materials mainly include the following two forms. One is as shown in CN113417069A, which uses deionized water and anhydrous ethanol as solvents, and mixes organosilicon sources and organic carbon sources as solutes. The pH value of the solution is adjusted to form a transparent sol. The spinning solution is mixed evenly with the prepared transparent sol, and a fiber membrane is obtained by electrospinning. The fiber membrane is placed in a drying oven for drying. The dried fiber membrane is then heat-treated under argon protection to obtain the silicon anode material. Secondly, as in CN111952577A, a method first uses electrospinning to prepare a PAN / Si / Fe composite nanofiber membrane. Based on this, carbon nanotubes (CNTs) are grown on the Fe active sites using chemical vapor deposition (CVD). Then, through high-temperature carbonization, a C / Si / CNTs composite carbon nanofiber membrane is prepared. The CNTs grown on the PAN base effectively alleviate the volume expansion of the silicon anode. Using the C / Si / CNTs composite carbon nanofiber membrane as the anode of a lithium-ion battery significantly reduces the capacity decay of the lithium-ion battery and improves the cycle stability. The aforementioned patent applications respectively involve fusing silicon and carbon sources to form a transparent sol, electrospinning followed by carbonization to form a silicon anode material, and CVD growth of carbon nanotubes from the electrospinned nanofiber membrane to form a silicon anode material. However, these methods often suffer from complex processes and incomplete removal of the substrate material, leading to potential safety and cycle performance issues.

[0005] In other words, while existing technologies have proposed some effective strategies, these often come with complex synthesis processes and high costs, and may also introduce potential safety hazards. In particular, how to simplify the production process, reduce costs, and improve the feasibility of large-scale production while ensuring the integrity of the fiber structure and material properties is a key issue that urgently needs to be addressed in the current research and development of silicon-based anode materials.

[0006] There is currently no good solution to the above problems. Summary of the Invention

[0007] This application provides a silicon-based composite anode material, its preparation method, anode electrode sheet, and a secondary battery, so as to at least solve the technical problem that it is difficult to prepare silicon-based composite anode materials with excellent electrochemical performance and low volume expansion in the prior art.

[0008] According to a first aspect of the embodiments of this application, a method for preparing a silicon-based composite anode material is provided, comprising: step S1, preparing a precursor fiber by electrospinning a precursor dispersion containing a first silicon source, a second silicon source, a first carbon source, and a second carbon source; step S2, subjecting the precursor fiber to heat treatment to obtain the silicon-based composite anode material; wherein the first silicon source is silicon particles; the molecular structure of the second silicon source carries one or more of silicon halide bonds, silicon oxygen bonds, and silicon hydrogen bonds; the first carbon source is a polymer compound; and the second carbon source is an oxygen-containing small molecule organic compound.

[0009] Further, the weight ratio of the first silicon source, the second silicon source, and the first carbon source is (0.8~1.2):(1.5~2.5):(2~3); and / or, based on the total weight of the precursor dispersion as 100%, the content of the second carbon source is 0.1%~1.0%.

[0010] Furthermore, the preparation method of the silicon-based composite anode material further includes sequentially ball milling and sieving the first silicon source to make the D50 of the first silicon source 6μm~10μm; and / or, the second silicon source is selected from one or more of tetraethyl orthosilicate, phenyltrichlorosilane, trichloromethylsilane and phenylsilane, preferably tetraethyl orthosilicate; and / or, the first carbon source is selected from one or more of polyvinylpyrrolidone, polyvinyl alcohol and polyacrylonitrile, preferably polyvinylpyrrolidone; and / or, the second carbon source is selected from one or more of citric acid, glucose and sucrose, preferably citric acid; preferably, the ball milling speed is 500rpm~700rpm and the time is 5min~15min; and / or, the sieving process uses a 30μm~50μm sieve.

[0011] Furthermore, the precursor dispersion also includes a silane coupling agent, and the content of the silane coupling agent is 0.5% to 2.0% based on the total weight of the precursor dispersion (100%). Preferably, the silane coupling agent is selected from one or more of KH-550, KH-560, KH-570, and KH-792.

[0012] Further, the preparation process of the precursor solution includes: step R1, preparing a first carbon source and a first solvent into a first solution; preparing a second silicon source, an acid solution, and a second solvent into a second solution; step R2, mixing the first solution, the second solution, the first silicon source, the second carbon source, and the coupling agent to obtain a precursor dispersion; in the first solution, the mass concentration of the first carbon source is 15wt%~25wt%; the volume ratio of the second silicon source, the acid solution, and the second solvent is 1:(0.3~0.8):2; the first solvent is selected from one or more of ethanol, N,N-dimethylformamide, dimethyl sulfoxide, and acetone; the second solvent is selected from one or more of water, ethanol, methanol, and isopropanol; the acid solution is selected from one or more of hydrochloric acid, nitric acid, and acetic acid, and the molar concentration of the acid solution is 0.1M~0.5M.

[0013] Furthermore, prior to electrospinning, the preparation method of the silicon-based composite anode material also includes aging the precursor dispersion; the aging time is 1 to 3 months, and the aging is carried out at 0℃ to 10℃; after aging, the viscosity of the precursor dispersion is 0.12 Pa·s to 0.16 Pa·s.

[0014] Furthermore, during the electrospinning process, the spinning voltage is 18kV~22kV, the receiving distance is 12cm~18cm; and / or, the heating rate of the heat treatment is 5℃ / min~15℃ / min, the holding temperature is 600℃~700℃, and the holding time is 0.5h~2h; preferably, the size of the precursor fiber is 8cm~12cm×8cm~12cm.

[0015] According to a second aspect of the embodiments of this application, a silicon-based composite anode material is also provided. The silicon-based composite anode material is prepared by the above-described method for preparing silicon-based composite anode materials, and the silicon-based composite anode material includes silicon dioxide fibers coated with a carbon layer and elemental silicon dispersed in the silicon dioxide fibers; preferably, the D50 of the elemental silicon is 6 μm to 10 μm; and / or, the diameter of the silicon dioxide fibers is 0.2 μm to 3.5 μm; and / or, the thickness of the carbon layer is 8 nm to 40 nm; and / or, the oxygen content of the carbon layer is 4 at% to 12 at%.

[0016] According to a third aspect of the embodiments of this application, a negative electrode sheet is also provided, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on at least one surface of the current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material being the aforementioned silicon-based composite negative electrode material; or, the negative electrode active material being prepared by the aforementioned method for preparing silicon-based composite negative electrode material; preferably, the silicon-based composite negative electrode material is sequentially pulverized and slurried to obtain a slurry; the slurry is coated on at least one surface of the current collector to form a negative electrode active layer; or, the silicon-based composite negative electrode material is used as a self-supporting active layer and bonded to at least one surface of the current collector, and after a lamination treatment, a negative electrode sheet is obtained; more preferably, the lamination treatment time is 5 min to 10 min, and the lamination treatment is carried out under conditions of a pressure of 10 MPa to 20 MPa and a temperature of 100°C to 150°C.

[0017] According to a fourth aspect of the embodiments of this application, a secondary battery is also provided, including a negative electrode sheet, which is the aforementioned negative electrode sheet.

[0018] In this embodiment, electrospinning technology is used to improve the structural stability and electrochemical performance of silicon-based anode materials by introducing two silicon sources and oxygen-containing organic compounds into the spinning precursor dispersion. This achieves the technical effects of suppressing volume expansion while ensuring high capacity, thereby significantly improving cycle stability and safety, as well as simplifying the preparation process and reducing costs. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0020] As described in the background section, it is difficult to prepare silicon-based composite anode materials with excellent electrochemical performance and low volume expansion using existing technologies. To address the aforementioned technical problems, according to embodiments of this application, a method for preparing a silicon-based composite anode material is provided, comprising: step S1, preparing a precursor fiber from a precursor dispersion containing a first silicon source, a second silicon source, a first carbon source, and a second carbon source by electrospinning; step S2, subjecting the precursor fiber to heat treatment to obtain the silicon-based composite anode material; wherein the first silicon source is silicon particles; the second silicon source carries one or more of silicon halide bonds, silicon-oxygen bonds, and silicon-hydrogen bonds in its molecular structure; the first carbon source is a polymer compound; and the second carbon source is an oxygen-containing small molecule organic compound.

[0021] This application forms a silicon-based composite material with a unique microstructure and excellent electrochemical properties through a specific combination and treatment of a first silicon source (silicon particles), a second silicon source (silicon-containing compounds carrying silicon halide bonds, silicon oxygen bonds, and silicon hydrogen bonds), a first carbon source (polymer compound), and a second carbon source (oxygen-containing small molecule organic matter), based on two key steps: electrospinning and heat treatment.

[0022] In particular, the second silicon source can gradually condense in the precursor dispersion to form a SiO2 precursor, thereby forming a three-dimensional network structure on the surface of silicon particles and inside the fibers, providing a basis for pore formation and carbon layer formation in subsequent heat treatment. During this process, the second carbon source, an oxygen-containing small-molecule organic compound, provides more active sites for the hydrolysis of the second silicon source, enabling a more uniform distribution of silicon particles in the resulting silica fibers. Specifically, in the above preparation process: First, in the electrospinning stage, the precursor dispersion containing the first silicon source, the hydrolysis product of the second silicon source, the first carbon source, and the second carbon source is stretched into nano- to micron-sized fibers through the stretching effect of a high-voltage electric field. The spun fibers accumulate to form two-dimensional fiber sheets, initially constructing a physical framework. Then, in the heat treatment stage, the first carbon source decomposes at high temperature, releasing carbon to form a continuous amorphous carbon layer. This carbon layer not only improves the electronic conductivity of the material but also acts as a buffer layer to mitigate the volume change of silicon during lithium-ion intercalation / deintercalation, protecting the integrity of the fiber structure. Furthermore, the second silicon source after hydrolysis can generate SiO gas during heat treatment, thereby inducing a pore-forming effect, increasing the porosity and specific surface area of ​​the resulting anode material. The resulting structure can reduce lithium-ion diffusion resistance and improve rate performance. Meanwhile, the synergistic effect of the two carbon sources is equally important. The first carbon source forms a macroscopic carbon layer framework during heat treatment, while the second carbon source can begin carbonization at lower temperatures, forming uniform amorphous carbon on the fiber surface. The combination of the two carbon layers not only significantly enhances the conductivity of the resulting composite anode material but also further optimizes its pore structure, improving the cycle stability and rate performance of the final secondary battery.

[0023] In summary, through careful design and treatment of the precursor dispersion, the preparation method of this invention successfully constructed a unique microstructure of silicon-based composite anode material, including a stable carbon layer surrounding SiO2 fibers and uniformly distributed silicon particles within the fibers. The nanoscale distribution and fibrous structure of the silicon particles provide numerous active sites and lithium-ion transport pathways, enabling the anode material to maintain a high capacity retention even after multiple charge-discharge cycles. Furthermore, the pore-forming and carbonization effects of the second silicon source during heat treatment, along with the carbon framework formed by the first carbon source, collectively promote the optimization of the internal pore structure of the resulting anode material, thereby improving its cycle life.

[0024] Furthermore, the weight ratio of the first silicon source, the second silicon source, and the first carbon source is (0.8~1.2):(1.5~2.5):(2~3). The optimal amount of silicon particles, as the active material, directly affects the capacity of the resulting anode material. The polymer compound acts as a fiber-forming agent during electrospinning; increasing its amount helps fiber formation, but excessive amounts inhibit the activity of silicon particles, leading to a decrease in electrochemical performance. The second silicon source hydrolyzes and polymerizes in the precursor dispersion to produce a SiO2 precursor. This precursor reacts with silicon particles during heat treatment, forming pores and refining the silicon particles. Regarding its amount, excessive amounts result in an overly porous structure, while insufficient amounts lead to insufficient porosity, affecting the lithium-ion insertion and extraction efficiency. Based on this, the optimal ratio of the three components as described above promotes a more uniform reaction within the material, allowing the fibers to maintain a high specific surface area while also promoting more effective distribution of silicon particles. This results in a more uniformly distributed pore structure and carbon layer, which not only improves the conductivity of the anode material but also significantly buffers the volume change of silicon during charging and discharging, reducing stress in the electrochemical reaction. Consequently, it significantly improves the initial coulombic efficiency and cycle capacity retention of the obtained silicon-based composite anode material.

[0025] Furthermore, based on the total weight of the precursor dispersion (100%), the content of the second carbon source is preferably 0.1% to 1.0%. Throughout the preparation process, the second carbon source first provides more active sites for the hydrolysis of the second silicon source, and then undergoes carbonization at the heat treatment temperature, synergistically forming a carbon layer with the first carbon source. To further optimize the above effects, the amount of the second carbon source is preferably as described above, thereby further stabilizing the material structure and, while improving conductivity, more effectively optimizing the structural stability and cycle performance of the resulting silicon-based anode material.

[0026] Furthermore, the preparation method of the silicon-based composite anode material also includes sequentially ball-milling and sieving the first silicon source to achieve a D50 of 6 μm to 10 μm. Through ball milling and sieving, the size of the silicon particles is reduced, the particle size distribution is optimized, and the specific surface area is increased. After the anode material is prepared, it facilitates faster diffusion and intercalation of lithium ions, thereby further improving the electrochemical performance of the obtained silicon-based composite anode material. Simultaneously, the optimized particle size also enables the formation of a more stable pore structure during the preparation process, thus more effectively accommodating the volume expansion of silicon during lithium intercalation, ultimately significantly improving the cycle stability of the obtained silicon-based composite anode material.

[0027] In several typical embodiments, the second silicon source is preferably selected from one or more of tetraethyl orthosilicate, phenyltrichlorosilane, trichloromethylsilane, and phenylsilane, more preferably tetraethyl orthosilicate; and / or, the first carbon source is preferably selected from one or more of polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylonitrile, more preferably polyvinylpyrrolidone; and / or, the second carbon source is preferably selected from one or more of citric acid, glucose, and sucrose, more preferably citric acid. In particular, when the second silicon source is tetraethyl orthosilicate, the first carbon source is polyvinylpyrrolidone, and the second carbon source is citric acid, based on their special chemical properties and coordination, they have a more significant technical effect on the formation of the material's microstructure and the optimization of its electrochemical performance. Specifically, tetraethyl orthosilicate (TEOS) can more effectively hydrolyze to generate a precursor of SiO2 under acidic conditions. The resulting SiO2 reacts with silicon particles during heat treatment to generate SiO gas, creating pores and refining the silicon particles. The resulting SiO2 network can provide more stable support for the silicon particles, contributing to the formation of a porous microstructure with a high specific surface area. Meanwhile, the SiO2 interface formed on the silicon particle surface by TEOS can further enhance the interfacial bonding between silicon particles and the carbon layer through the interaction between the silane coupling agent and the polyvinylpyrrolidone (PVP) network. Citric acid, containing multiple carboxyl groups, can further react with the SiO2 hydrolysis products, providing more active sites for TEOS hydrolysis. This results in a more uniform distribution of SiO2 on the silicon particle surface, further optimizing the interfacial chemical properties, improving the bonding between silicon particles and the carbon layer, and ultimately significantly enhancing the overall stability and electrochemical performance of the resulting silicon-based composite anode material.

[0028] During the ball milling process of the first silicon source, in order to reduce its agglomeration, optimize its specific surface area, and activate its surface, the ball milling speed is preferably 500 rpm to 700 rpm and the time is 5 min to 15 min. Furthermore, in order to obtain silicon particles with a more suitable median particle size (i.e., D50), a sieve with a mesh size of 30 μm to 50 μm is preferably used for the sieving process.

[0029] Furthermore, the precursor dispersion also includes a silane coupling agent, and the content of the silane coupling agent is 0.5%~2.0% based on 100% of the total weight of the precursor dispersion. The silane coupling agent can act as a molecular bridge, connecting silicon particles, silicon dioxide obtained from the hydrolysis of the second silicon source, and the carbon source. Adding it to the precursor dispersion in a preferred amount can further form a more stable three-dimensional structure and enhance interfacial bonding, ultimately resulting in a silicon-based composite anode material with more stable structure and cycle performance after spinning and heat treatment. In practical applications, the silane coupling agent can be selected from one or more of KH-550, KH-560, KH-570, and KH-792.

[0030] In the preparation of the precursor solution, it preferably includes: step R1, preparing a first solution by mixing a first carbon source and a first solvent; preparing a second solution by mixing a second silicon source, an acid, and a second solvent; and step R2, mixing the first solution, the second solution, the first silicon source, the second carbon source, and the coupling agent to obtain a precursor dispersion. In this preferred embodiment, the first solution prepared by the first carbon source and the first solvent, and the second solution prepared by the second silicon source and the acid and the second solvent are processed separately, thereby controlling the dissolution state of the first carbon source and the degree of hydrolysis of the second silicon source respectively. This ensures that the two main components are in a better state before final mixing, which is beneficial to further improving the structural consistency and performance stability of the final material.

[0031] In the above preparation process: preferably, the mass concentration of the first carbon source in the first solution is 15wt%~25wt%, which facilitates the full dissolution of the first carbon source while optimizing the solution viscosity. This improves the continuity and uniformity of the fibers during electrospinning, and ultimately optimizes the specific surface area and pore structure of the resulting silicon-based composite anode material. To more effectively control the hydrolysis reaction of the second silicon source under acidic conditions, reducing premature gel formation due to excessively rapid hydrolysis and its impact on the spinning performance of the solution, and also reducing uneven SiO2 distribution within the fibers due to excessively slow hydrolysis, the preferred volume ratio of the second silicon source, acid, and second solvent in the second solution is 1:(0.3~0.8):2. This preferred volume ratio helps form more uniform and stable SiO2 hydrolysis products, providing a better precursor basis for pore formation and fiber structure optimization in the subsequent heat treatment process, ultimately resulting in a silicon-based composite anode material with superior electrochemical and cycle performance.

[0032] In several typical embodiments, the first solvent is selected from one or more of ethanol, N,N-dimethylformamide, dimethyl sulfoxide and acetone; the second solvent is selected from one or more of water, ethanol, methanol and isopropanol; the acid is selected from one or more of hydrochloric acid, nitric acid and acetic acid, and the molar concentration of the acid is 0.1M to 0.5M.

[0033] Furthermore, prior to electrospinning, to promote more complete polymerization of the second silicon source and minimize stratification of the precursor dispersion sol system during spinning, the preferred preparation method for the silicon-based composite anode material also includes aging the precursor dispersion; the aging time is 1 to 3 months, and the aging process is carried out at 0°C to 10°C. After aging, the viscosity of the precursor dispersion is 0.12 Pa·s to 0.16 Pa·s, which can more effectively maintain the stability of the spinning process, reduce the generation of broken fibers or bead-like structures, and form a slender and unbroken fiber structure. This results in a more stable and uniform precursor fiber structure, which, after heat treatment, ultimately yields a silicon-based composite anode material with more stable structure and cycle performance.

[0034] In the electrospinning process, the preferred spinning voltage is 18kV~22kV, and the preferred receiving distance is 12cm~18cm. The preferred voltage more effectively overcomes the surface tension of the solution to form nanoscale fibers, optimizing the diameter and morphology of the resulting precursor fibers; while the preferred receiving distance better controls the solvent evaporation rate, thereby further improving fiber orientation and pore structure. By optimizing the electrospinning parameters as described above, fibers with more stable structures and high porosity can be formed, ultimately yielding silicon-based composite anode materials with better electrochemical performance and cycle stability.

[0035] To promote a more ordered transformation of the material's internal structure during heat treatment, the preferred heating rate is 5°C / min to 15°C / min. This allows for the gradual evaporation of solvents and organic matter, reducing uneven decomposition and fiber structure damage caused by excessively rapid heating. The preferred holding temperature is 600°C to 700°C, and the holding time is 0.5h to 2h. Under these conditions, the first carbon source can be more fully decomposed and carbonized, forming a continuous carbon coating layer. Simultaneously, these conditions also promote the carbonization of the second carbon source, leaving a uniform thin layer on the fiber surface, and working synergistically with the first carbon source to significantly improve the conductivity and cycle stability of the resulting composite anode material. Furthermore, to minimize edge effects and improve temperature uniformity during heat treatment, thereby forming a more uniform carbon layer and porous network, the preferred size of the precursor fibers obtained from spinning is 8cm to 12cm × 8cm to 12cm.

[0036] In practical applications, in order to promote incomplete carbonization and thus more effectively form a defect-rich conductive carbon layer, heat treatment is preferably carried out in an air atmosphere.

[0037] According to a second aspect of the embodiments of this application, a silicon-based composite anode material is also provided. This silicon-based composite anode material is prepared by the aforementioned method for preparing silicon-based composite anode materials, and includes silicon dioxide fibers coated with a carbon layer and elemental silicon dispersed within the silicon dioxide fibers. The silicon-based composite anode material prepared according to the above method has the following structure, inferred from the reaction process: a silicon dioxide fiber network serves as the matrix, with elemental silicon particles uniformly dispersed therein as the active material, and the surface of the fiber network is also coated with a layer of amorphous carbon. This composite structure can significantly improve its electronic conductivity and mechanical stability. In particular, the porous structure formed by the synergistic effect between the elemental silicon particles and the silicon dioxide fibers can further suppress the volume change of the material when used as an anode active material, thereby significantly enhancing its cycle stability.

[0038] It should be noted that due to the complex structural formation and compositional changes during the preparation process, and the limitations of the material field and existing testing and characterization methods, it is difficult to perform a comprehensive quantitative characterization of the complex microstructure of the obtained silicon-based composite anode material. However, performance test results show that the anode material obtained in this invention exhibits particularly superior specific capacity and cycle stability in application.

[0039] Regarding the obtained microstructure, in several preferred embodiments: the D50 of elemental silicon is preferably 6 μm to 10 μm, so as to promote higher activity and capacity of the obtained silicon-based composite anode material in electrochemical reactions. In conjunction with the above-mentioned particle size characteristics of elemental silicon, the diameter of the silica fibers is preferably 0.2 μm to 3.5 μm (preferably 0.5 μm to 2.0 μm), thereby further optimizing the pore structure of the obtained silicon-based composite anode material, resulting in smaller volume changes and higher cycle stability during charge and discharge. To more significantly improve the conductivity and structural stability of the obtained silicon-based composite anode material, the thickness of the carbon layer is preferably 8 nm to 40 nm (preferably 10 nm to 30 nm); and / or, the oxygen content of the carbon layer is 4 at% to 12 at% (preferably 4 at% to 8 at%).

[0040] According to a third aspect of the embodiments of this application, a negative electrode sheet is also provided. The negative electrode sheet includes a current collector and a negative electrode active layer disposed on at least one surface of the current collector. The negative electrode active layer includes a negative electrode active material, which is the aforementioned silicon-based composite negative electrode material; or, the negative electrode active material is prepared by the aforementioned method for preparing silicon-based composite negative electrode materials. Because the composite negative electrode material (or the prepared composite negative electrode material) provided by this invention has a special structure and superior stability, it can enable the negative electrode sheet to suppress volume expansion and exhibit excellent electrochemical performance during cycling, thus demonstrating higher cycle stability during battery operation.

[0041] In practical applications, the obtained silicon-based composite anode material can be prepared into a negative electrode sheet in the following manner: the silicon-based composite anode material is sequentially pulverized and slurried to obtain a slurry; the slurry is coated on at least one surface of the current collector to form a negative electrode active layer; or, the silicon-based composite anode material is used as a self-supporting active layer and bonded to at least one surface of the current collector, and after a lamination process, a negative electrode sheet is obtained. Specifically, the lamination process takes 5 to 10 minutes and is carried out under conditions of a pressure of 10 MPa to 20 MPa and a temperature of 100°C to 150°C.

[0042] According to a fourth aspect of the embodiments of this application, a secondary battery is also provided, including a negative electrode sheet, which is the aforementioned negative electrode sheet. By assembling and integrating the negative electrode sheet containing the aforementioned silicon-based composite negative electrode material into a secondary battery (especially a lithium-ion battery), the resulting secondary battery achieves a dual improvement in electrical performance and lifespan. In particular, the silicon-based composite negative electrode material significantly improves the overall performance of the secondary battery and extends its cycle life by suppressing volume expansion and improving electrochemical stability.

[0043] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0044] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0045] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0046] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0047] Example 1

[0048] A method for preparing a silicon-based composite anode material:

[0049] Raw material pretreatment: Single-crystal silicon particles were subjected to planetary ball milling (600 rpm, 10 min), dried, and passed through a 40 μm sieve to obtain silicon particles with a median particle size of 7.17 μm. XRD showed that it was a pure silicon crystalline phase (ICDD 04-006-2527), with an XRF silicon content of 99.64%. XRD analysis was performed using a PANalytical X'Pert Pro diffractometer (Co target, 40 kV / 40 mA), with a scanning range of 2θ = 10°-90° and a step size of 0.02°, to determine the crystalline phase structure of the silicon particles. XRF detection was performed using a WD-XRF Axios spectrometer in vacuum mode to determine the elemental composition, and the results were normalized.

[0050] Preparation of precursor dispersion:

[0051] (R1) Polyvinylpyrrolidone (PVP, the first carbon source) was dissolved in ethanol to prepare a solution with a mass concentration of 20 wt%. Tetraethoxysilane (TEOS, the second silicon source) was mixed with hydrochloric acid (0.3 M molar concentration) and deionized water at a volume ratio of 1:0.5:2 and hydrolyzed to obtain a solution.

[0052] (R2) After that, the two solutions above were mixed with the silicon particles obtained by ball milling according to the mass ratio of silicon particles: TEOS: PVP = 1:2:2.5. At the same time, silane coupling agent (KH-550, accounting for 1.5% of the total mass of the obtained dispersion) and citric acid (oxygen-containing organic matter, accounting for 0.5% of the total mass of the obtained dispersion) were added to obtain the precursor dispersion.

[0053] Electrospinning and heat treatment:

[0054] (S1) The obtained precursor dispersion was aged at 5°C for 2 months to form a stable sol system with a viscosity of 0.14 Pa·s. Then, electrospinning was performed under the conditions of spinning voltage of 20 kV and receiving distance of 15 cm to obtain a 10 cm × 10 cm precursor fiber film.

[0055] (S2) The obtained precursor fiber membrane is placed in a tube furnace and heated to 650°C at 10°C / min in an air atmosphere. The temperature is maintained for 1 hour to remove the PVP matrix and form a silicon fiber structure with an amorphous carbon layer on the surface, thus obtaining the silicon-based composite anode material.

[0056] The resulting composite material includes silica fibers coated with a carbon layer and elemental silicon dispersed in the silica fibers.

[0057] Example 2

[0058] A method for preparing a silicon-based composite anode material:

[0059] Raw material pretreatment: Single crystal silicon particles were subjected to planetary ball milling (500 rpm for 15 min), dried, and then passed through a 30 μm sieve to obtain silicon particles with a median particle size of 6.20 μm.

[0060] Preparation of precursor dispersion:

[0061] (R1) Polyvinylpyrrolidone (PVP, the first carbon source) was dissolved in ethanol to prepare a solution with a mass concentration of 18 wt%. Tetraethoxysilane (TEOS, the second silicon source) was mixed with hydrochloric acid (0.2 M molar concentration) and deionized water at a volume ratio of 1:0.5:2 and hydrolyzed to obtain a solution.

[0062] (R2) After that, the two solutions above were mixed with the silicon particles obtained by ball milling according to the mass ratio of silicon particles: TEOS: PVP = 0.8: 1.5: 2. At the same time, silane coupling agent (KH-550, accounting for 0.8% of the total mass of the obtained dispersion) and citric acid (oxygen-containing organic matter, accounting for 0.2% of the total mass of the obtained dispersion) were added to obtain the precursor dispersion.

[0063] Electrospinning and heat treatment:

[0064] (S1) The obtained precursor dispersion was aged at 0℃ for 3 months to form a stable sol system with a viscosity of 0.12 Pa·s. Then, electrospinning was performed under the conditions of spinning voltage of 18 kV and receiving distance of 12 cm to obtain a 9 cm × 9 cm precursor fiber film.

[0065] (S2) The obtained precursor fiber membrane is placed in a tube furnace and heated to 600°C at 5°C / min in an air atmosphere. The temperature is maintained for 2 hours to remove the PVP matrix and form a silicon fiber structure with an amorphous carbon layer on the surface, thus obtaining the silicon-based composite anode material.

[0066] The resulting composite material includes silica fibers coated with a carbon layer and elemental silicon dispersed in the silica fibers.

[0067] Example 3

[0068] A method for preparing a silicon-based composite anode material:

[0069] Raw material pretreatment: Single crystal silicon particles were subjected to planetary ball milling (700 rpm for 5 min), dried, and then passed through a 50 μm sieve to obtain silicon particles with a median particle size of 8.90 μm.

[0070] Preparation of precursor dispersion:

[0071] (R1) Polyvinylpyrrolidone (PVP, the first carbon source) was dissolved in ethanol to prepare a solution with a mass concentration of 22 wt%. Tetraethoxysilane (TEOS, the second silicon source) was mixed with hydrochloric acid (0.4 M molar concentration) and deionized water at a volume ratio of 1:0.5:2 and hydrolyzed to obtain a solution.

[0072] (R2) After that, the two solutions above were mixed with the silicon particles obtained by ball milling according to the mass ratio of silicon particles: TEOS: PVP = 1.2: 2.5: 3. At the same time, silane coupling agent (KH-550, accounting for 2% of the total mass of the obtained dispersion) and citric acid (oxygen-containing organic matter, accounting for 1% of the total mass of the obtained dispersion) were added to obtain the precursor dispersion.

[0073] Electrospinning and heat treatment:

[0074] (S1) The obtained precursor dispersion was aged at 10°C for 1 month to form a stable sol system with a viscosity of 0.16 Pa·s. Then, electrospinning was performed under the conditions of spinning voltage of 22 kV and receiving distance of 18 cm to obtain a 10 cm × 10 cm precursor fiber film.

[0075] (S2) The obtained precursor fiber membrane is placed in a tube furnace and heated to 700°C at 15°C / min in an air atmosphere. The temperature is maintained for 0.5h to remove the PVP matrix and form a silicon fiber structure with an amorphous carbon layer on the surface, thus obtaining the silicon-based composite anode material.

[0076] The resulting composite material includes silica fibers coated with a carbon layer and elemental silicon dispersed in the silica fibers.

[0077] Example 4

[0078] A method for preparing a silicon-based composite anode material:

[0079] Raw material pretreatment: Single crystal silicon particles were subjected to planetary ball milling (650 rpm for 8 min), dried, and then passed through a 45 μm sieve to obtain silicon particles with a median particle size of 7.50 μm.

[0080] Preparation of precursor dispersion:

[0081] (R1) Polyvinylpyrrolidone (PVP, the first carbon source) was dissolved in ethanol to prepare a solution with a mass concentration of 19 wt%. Tetraethoxysilane (TEOS, the second silicon source) was mixed with hydrochloric acid (0.25 M molar concentration) and deionized water at a volume ratio of 1:0.5:2 and hydrolyzed to obtain a solution.

[0082] (R2) After that, the two solutions above were mixed with the silicon particles obtained by ball milling according to the mass ratio of silicon particles: TEOS: PVP = 1:2:2.2. At the same time, silane coupling agent (KH-550, accounting for 1.2% of the total mass of the obtained dispersion) and citric acid (oxygen-containing organic matter, accounting for 0.6% of the total mass of the obtained dispersion) were added to obtain the precursor dispersion.

[0083] Electrospinning and heat treatment:

[0084] (S1) The precursor dispersion obtained was aged at 3°C ​​for 2.5 months to form a stable sol system with a viscosity of 0.14 Pa·s. Then, electrospinning was performed under the conditions of spinning voltage of 19 kV and receiving distance of 14 cm to obtain a 10 cm × 10 cm precursor fiber film.

[0085] (S2) The obtained precursor fiber membrane is placed in a tube furnace and heated to 620°C at 8°C / min in an air atmosphere. The temperature is maintained for 1.5h to remove the PVP matrix and form a silicon fiber structure with an amorphous carbon layer on the surface, thus obtaining the silicon-based composite anode material.

[0086] The resulting composite material includes silica fibers coated with a carbon layer and elemental silicon dispersed in the silica fibers.

[0087] Example 5

[0088] A method for preparing a silicon-based composite anode material:

[0089] Raw material pretreatment: Single crystal silicon particles were subjected to planetary ball milling (550 rpm for 12 min), dried, and passed through a 35 μm sieve to obtain silicon particles with a median particle size of 7.80 μm.

[0090] Preparation of precursor dispersion:

[0091] (R1) Polyvinylpyrrolidone (PVP, the first carbon source) was dissolved in ethanol to prepare a solution with a mass concentration of 21 wt%. Tetraethoxysilane (TEOS, the second silicon source) was mixed with hydrochloric acid (0.35 M molar concentration) and deionized water at a volume ratio of 1:0.5:2 and hydrolyzed to obtain a solution.

[0092] (R2) After that, the two solutions above were mixed with the silicon particles obtained by ball milling according to the mass ratio of silicon particles: TEOS: PVP = 0.9: 1.8: 2.8. At the same time, silane coupling agent (KH-550, accounting for 1.8% of the total mass of the obtained dispersion) and citric acid (oxygen-containing organic matter, accounting for 0.8% of the total mass of the obtained dispersion) were added to obtain the precursor dispersion.

[0093] Electrospinning and heat treatment:

[0094] (S1) The precursor dispersion obtained was aged at 8°C for 1.5 months to form a stable sol system with a viscosity of 0.15 Pa·s. Then, electrospinning was performed under the conditions of spinning voltage of 21 kV and receiving distance of 16 cm to obtain a 9 m × 9 cm precursor fiber film.

[0095] (S2) The obtained precursor fiber membrane is placed in a tube furnace and heated to 680°C at 12°C / min in an air atmosphere. The temperature is maintained for 1 hour to remove the PVP matrix and form a silicon fiber structure with an amorphous carbon layer on the surface, thus obtaining the silicon-based composite anode material.

[0096] The resulting composite material includes silica fibers coated with a carbon layer and elemental silicon dispersed in the silica fibers.

[0097] Example 6

[0098] A method for preparing a silicon-based composite anode material:

[0099] The only difference between this embodiment and Embodiment 1 is that: in the raw material pretreatment process, a 15μm sieve is selected, and silicon particles with a median particle size of 3μm~5μm are obtained as the first silicon source.

[0100] Example 7

[0101] A method for preparing a silicon-based composite anode material:

[0102] The only difference between this embodiment and Embodiment 1 is that: during the raw material pretreatment process, an 80μm sieve is selected, and silicon particles with a median particle size of 12μm~15μm are obtained as the first silicon source.

[0103] Example 8

[0104] A method for preparing a silicon-based composite anode material:

[0105] The only difference between this embodiment and Example 1 is that hydrochloric acid was not added to the solution containing TEOS in step (R1) of preparing the precursor dispersion.

[0106] Example 9

[0107] A method for preparing a silicon-based composite anode material:

[0108] The only difference between this embodiment and Embodiment 1 is that in the step (R2) of preparing the precursor dispersion, the solutions containing PVP and TEOS were not prepared separately, but all raw materials were directly added together and mixed to obtain the dispersion.

[0109] Example 10

[0110] A method for preparing a silicon-based composite anode material:

[0111] The only difference between this embodiment and Embodiment 1 is that in step (R2) of preparing the precursor dispersion, the mass ratio of silicon particles:TEOS:PVP is changed to 0.5:3:1.

[0112] Example 11

[0113] A method for preparing a silicon-based composite anode material:

[0114] The only difference between this embodiment and Embodiment 1 is that in step (R2) of preparing the precursor dispersion, the mass ratio of silicon particles:TEOS:PVP is changed to 1.5:1:4.

[0115] Example 12

[0116] A method for preparing a silicon-based composite anode material:

[0117] The only difference between this embodiment and Example 1 is that no silane coupling agent was added in step (R2) of preparing the precursor dispersion.

[0118] Example 13

[0119] A method for preparing a silicon-based composite anode material:

[0120] The only difference between this embodiment and Embodiment 1 is that the spinning voltage is changed to 25V and the receiving distance is changed to 20cm during the electrospinning process.

[0121] Example 14

[0122] A method for preparing a silicon-based composite anode material:

[0123] The only difference between this embodiment and Embodiment 1 is that, during the heat treatment process, the heating rate is changed to 3℃ / min, the holding time is changed to 500℃, and the holding time is changed to 3h.

[0124] Example 15

[0125] A method for preparing a silicon-based composite anode material:

[0126] The only difference between this embodiment and Embodiment 1 is that, during the heat treatment process, the heating rate is changed to 20℃ / min, the holding time is changed to 800℃, and the holding time is changed to 0.1h.

[0127] Comparative Example 1

[0128] A method for preparing a composite anode material:

[0129] The only difference between this comparative example and Example 1 is that no silicon particles were added in step (R2) of preparing the precursor dispersion.

[0130] Comparative Example 2

[0131] A method for preparing a composite anode material:

[0132] The only difference between this comparative example and Example 1 is that, in step (R2) of preparing the precursor dispersion, SiO2 particles of equal weight and median particle size are used instead of silicon particles.

[0133] Comparative Example 3

[0134] A method for preparing a composite anode material:

[0135] The only difference between this comparative example and Example 1 is that citric acid, the second carbon source, was not added in step (R2) of preparing the precursor dispersion.

[0136] Performance testing of negative electrode material samples:

[0137] The diameter of silica fibers and the D50 particle size of silicon particles within them: fiber morphology and particle distribution were observed using a TESCAN VEGA 3 LMU microscope (15kV accelerating voltage) in secondary electron mode.

[0138] Carbon layer thickness: obtained from HRTEM (high-resolution transmission microscopy) measurements.

[0139] Oxygen content in the carbon layer: obtained from XPS testing.

[0140] Specific surface area (BET): Micromeritics ASAP 2020 instrument, nitrogen adsorption method for determining specific surface area.

[0141] Preparation and performance testing of lithium-ion battery samples:

[0142] Following conventional lithium-ion battery electrode preparation methods, the negative electrode material samples obtained in each embodiment and comparative example were used as negative electrode active materials. A slurry was prepared with an active material: conductive agent (Super P): binder (polyvinylidene fluoride, PVDF) ratio of 8:1:1. A 10 μm thick copper foil was used as the negative electrode current collector. The resulting slurry was prepared at approximately 2.0 mg / cm³. 2 The areal density is coated to form a film to obtain the negative electrode sheet. Of course, the film-like composite negative electrode material obtained based on the above embodiments can also be directly composited with the negative electrode current collector by hot pressing to directly obtain the negative electrode sheet. Then, lithium cobalt oxide (LiCoO2) is used as the positive electrode active material, and a positive electrode sheet is prepared by a similar coating process; using Celgard 2400 polypropylene porous membrane as the separator and 1M LiPF6 EC / DEC (volume ratio 1:1) solution as the electrolyte, a coin cell sample with a capacity of about 100~150 mAh (corresponding to the CR2032 type coin cell standard) is assembled in an argon-protected glove box.

[0143] Electrical performance testing: (1) Cyclic voltammetry (CV): Three-electrode system (Li sheet as counter / reference electrode), scan rate 0.1 mV / s, voltage range 0.01-1.5 V vs. Li / Li + ; The reversible capacity of the coin cell samples was obtained. (2) Constant current charge and discharge: LAND CT2001A tester, current density 0.1C, voltage window 0.01~1.5V, calculate the initial coulombic efficiency and cycle stability (i.e. capacity retention rate after 50 cycles) of each battery sample. (3) AC impedance (EIS): CHI660E workstation, frequency range 10mHz-100kHz, amplitude 5mV, fit the equivalent circuit, and obtain the charge transfer resistance of the coin cell samples.

[0144] The above tests were performed on the negative electrode material samples and battery samples obtained from each embodiment and comparative example, and the results are shown in Table 1 and Table 2.

[0145] Table 1

[0146]

[0147] Table 2

[0148]

[0149] As can be seen from the above description, compared with the comparative examples, the embodiments of the present invention have achieved the preparation of silicon-based composite anode materials with unique microstructure and excellent electrochemical performance. The obtained silicon-based composite anode material uses a silica fiber network as the matrix, with elemental silicon particles uniformly dispersed therein as the active material, and the surface of the fiber network is also coated with a layer of amorphous carbon. The pore structure formed by the synergistic effect between the elemental silicon particles and the silica fibers can suppress the volume change of the material when used as an anode active material, thereby significantly enhancing its cycle stability.

[0150] Specifically, in each embodiment:

[0151] Comparing Examples 6 and 7 with Example 1, it can be seen that by optimizing the median particle size D50 of the silicon particles, the diffusion and intercalation of lithium ions are facilitated after the anode material is prepared, thereby further improving the electrochemical performance of the obtained silicon-based composite anode material. Simultaneously, a more stable pore structure is formed during the preparation process, which more effectively accommodates the volume expansion of silicon during lithium intercalation, ultimately significantly improving the cycle stability of the obtained silicon-based composite anode material.

[0152] Comparing Example 8 with Example 1, it can be seen that by preferably adding acid to the solution containing the second silicon source, it is possible to form more uniform and stable SiO2 hydrolysis products, which provides a better precursor basis for pore formation and fiber structure optimization in the next heat treatment process, and finally obtains a silicon-based composite anode material with better electrochemical performance and cycle performance.

[0153] Comparing Example 9 with Example 1, it can be seen that by optimizing the order of adding the two carbon sources and the two silicon sources, the dissolution state of the first carbon source and the degree of hydrolysis of the second silicon source can be optimized, so that the two main components are in a better state before final mixing, which is beneficial to further improve the structural consistency and performance stability of the final material.

[0154] Comparing Examples 10 and 11 with Example 1, it can be seen that by optimizing the weight ratio of the first silicon source, the second silicon source, and the first carbon source, a more uniformly distributed pore structure and carbon layer can be formed. This not only improves the conductivity of the anode material but also significantly buffers the volume change of silicon during charging and discharging, reducing stress in the electrochemical reaction. Consequently, the initial coulombic efficiency and cycle capacity retention of the obtained silicon-based composite anode material are significantly improved.

[0155] Comparing Example 12 with Example 1, it can be seen that by using a silane coupling agent, it can be promoted to act as a molecular bridge to connect silicon particles, silicon dioxide obtained by hydrolysis of the second silicon source, and carbon source, thereby forming a more stable three-dimensional structure and enhancing the interfacial bonding force. Finally, after spinning and heat treatment, a silicon-based composite anode material with more stable structure and cycle performance is obtained.

[0156] Comparing Example 13 with Example 1, it can be seen that by optimizing the parameters of electrospinning, fibers with more stable structure and high porosity can be formed, and ultimately silicon-based composite anode materials with better electrochemical performance and cycle stability can be obtained.

[0157] Comparing Examples 14 and 15 with Example 1, it can be seen that by optimizing the heat treatment conditions, a more ordered transformation of the internal structure of the material can be promoted during the heat treatment process, which can significantly improve the conductivity and cycle stability of the obtained composite anode material.

[0158] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0159] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a silicon-based composite anode material, characterized in that, include: Step S1: The precursor dispersion containing the first silicon source, the second silicon source, the first carbon source and the second carbon source is prepared into precursor fibers by electrospinning. Step S2: The precursor fiber is heat-treated to obtain the silicon-based composite anode material; The first silicon source is silicon particles; The molecular structure of the second silicon source carries one or more of the following: silicon halide bonds, silicon oxygen bonds, and silicon hydrogen bonds; The first carbon source is a high molecular weight compound; the second carbon source is an oxygen-containing small molecule organic compound.

2. The method for preparing the silicon-based composite anode material according to claim 1, characterized in that, The weight ratio of the first silicon source, the second silicon source, and the first carbon source is (0.8~1.2):(1.5~2.5):(2~3); and / or, Based on the total weight of the precursor dispersion as 100%, the content of the second carbon source is 0.1% to 1.0%.

3. The method for preparing the silicon-based composite anode material according to claim 1 or 2, characterized in that, The method for preparing the silicon-based composite anode material further includes sequentially ball-milling and sieving the first silicon source to achieve a D50 of 6 μm to 10 μm; and / or, The second silicon source is selected from one or more of tetraethyl orthosilicate, phenyltrichlorosilane, trichloromethylsilane, and phenylsilane, preferably tetraethyl orthosilicate; and / or, The first carbon source is selected from one or more of polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylonitrile, preferably polyvinylpyrrolidone; and / or, The second carbon source is selected from one or more of citric acid, glucose, and sucrose, preferably citric acid; Preferably, the ball milling speed is 500 rpm to 700 rpm and the time is 5 min to 15 min; and / or, the sieving process uses a 30 μm to 50 μm sieve.

4. The method for preparing the silicon-based composite anode material according to any one of claims 1 to 3, characterized in that, The precursor dispersion also includes a silane coupling agent, and the content of the silane coupling agent is 0.5% to 2.0% based on the total weight of the precursor dispersion (100%). Preferably, the silane coupling agent is selected from one or more of KH-550, KH-560, KH-570 and KH-792.

5. The method for preparing the silicon-based composite anode material according to claim 4, characterized in that, The preparation process of the precursor solution includes: Step R1: Prepare a first solution by mixing the first carbon source and the first solvent; prepare a second solution by mixing the second silicon source, the acid solution, and the second solvent. Step R2: The first solution, the second solution, the first silicon source, the second carbon source, and the coupling agent are mixed to obtain the precursor dispersion. In the first solution, the mass concentration of the first carbon source is 15wt%~25wt%; The volume ratio of the second silicon source, the acid solution, and the second solvent is 1:(0.3~0.8):2; The first solvent is selected from one or more of ethanol, N,N-dimethylformamide, dimethyl sulfoxide, and acetone; The second solvent is selected from one or more of water, ethanol, methanol, and isopropanol; The acid solution is selected from one or more of hydrochloric acid, nitric acid, and acetic acid, and the molar concentration of the acid solution is 0.1M to 0.5M.

6. The method for preparing the silicon-based composite anode material according to any one of claims 1 to 5, characterized in that, Prior to electrospinning, the preparation method of the silicon-based composite anode material further includes aging the precursor dispersion. The aging process takes 1 to 3 months and is carried out at 0°C to 10°C. After the aging treatment, the viscosity of the precursor dispersion is 0.12 Pa·s to 0.16 Pa·s.

7. The method for preparing the silicon-based composite anode material according to any one of claims 1 to 6, characterized in that, During the electrospinning process, the spinning voltage is 18kV~22kV, and the receiving distance is 12cm~18cm; and / or, The heating rate of the heat treatment is 5℃ / min~15℃ / min, the holding temperature is 600℃~700℃, and the holding time is 0.5h~2h. Preferably, the precursor fiber has a size of 8cm~12cm × 8cm~12cm.

8. A silicon-based composite anode material, characterized in that, The silicon-based composite anode material is prepared by the method for preparing silicon-based composite anode material according to any one of claims 1 to 7, and the silicon-based composite anode material includes silicon dioxide fibers coated with a carbon layer and elemental silicon dispersed in the silicon dioxide fibers; Preferably, the D50 of the elemental silicon is 6μm to 10μm; and / or, the diameter of the silicon dioxide fiber is 0.2μm to 3.5μm; and / or, the thickness of the carbon layer is 5nm to 40nm; and / or, the oxygen content of the carbon layer is 4at% to 12at.

9. A negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on at least one surface of the current collector, the negative electrode active layer comprising a negative electrode active material, characterized in that, The negative electrode active material is the silicon-based composite negative electrode material according to claim 8; or, the negative electrode active material is prepared by the preparation method of the silicon-based composite negative electrode material according to any one of claims 1 to 7. Preferably, the silicon-based composite negative electrode material is sequentially crushed and slurried to obtain a slurry; the slurry is coated on at least one side surface of the current collector to form the negative electrode active layer; or, the silicon-based composite negative electrode material is used as a self-supporting active layer and bonded to at least one side surface of the current collector, and after a bonding process, the negative electrode sheet is obtained. More preferably, the lamination process takes 5 to 10 minutes and is carried out under conditions of 10 MPa to 20 MPa pressure and 100°C to 150°C temperature.

10. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet is the negative electrode sheet as described in claim 9.

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