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

Abstract

The application provides a preparation method of a silicon-carbon composite negative electrode material, comprising the following steps: nanocrystallizing silicon material under a protective environment to obtain nanosilicon; self-assembling the nanosilicon with a first carbon source and a high polymer, and then adding a second carbon source to perform self-assembly, to obtain layered nanosilicon; granulating the layered nanosilicon to obtain a precursor; and sintering the precursor at a sintering temperature of 800 DEG C to 1200 DEG C to obtain the silicon-carbon composite negative electrode material. The application also provides a silicon-carbon composite negative electrode material and a battery comprising the same. The preparation method is simple in process, easy to control the process, and suitable for industrial production, and the prepared silicon-carbon composite negative electrode material can inhibit expansion and has improved conductivity and capacity.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a silicon-carbon composite anode material, a method for preparing the same, and a battery including the silicon-carbon composite anode material. Background Technology

[0002] In recent years, silicon has gained popularity due to its low cost, environmental friendliness, and high specific capacity (4200 mAh·g). -1 Silicon is considered a promising next-generation anode material to replace graphite anodes due to its advantages such as a slightly higher voltage plateau than graphite and the absence of lithium metal deposition on the surface during charging. However, silicon exhibits a dramatic volume expansion (~300%) during lithium insertion and a dramatic contraction during delithiation. This repeated and drastic volume change (known as the volume effect) can cause silicon to crack and pulverize, leading to structural collapse. This results in the active material losing electrical contact with the current collector, reducing battery cycle stability. Furthermore, due to this volume effect, silicon struggles to form a stable solid-state electrolyte interface (SEI) in the electrolyte. As the structure deteriorates, new silicon is exposed on the surface, continuously forming an SEI film, exacerbating silicon corrosion and capacity decay.

[0003] To alleviate the aforementioned problems and improve the electrochemical performance of silicon materials, current techniques typically involve oxidizing the silicon material to form a silicon oxide shell. However, silicon has an electrical conductivity of 10⁻⁶. 3 Ω·m, while the oxidized material (SiO) x The electrical conductivity is even lower, which severely affects charge transfer. Furthermore, SiO₂... x To suppress expansion, the increased consumption of lithium ions due to electrochemical side reactions will affect the long-cycle performance. Summary of the Invention

[0004] In view of this, this application proposes a method for preparing a silicon-carbon composite anode material, which can suppress expansion and has improved conductivity and capacity.

[0005] Furthermore, it is necessary to propose a battery that includes this silicon-carbon composite anode material.

[0006] One embodiment of this application provides a method for preparing a silicon-carbon composite anode material, comprising the following steps:

[0007] Silicon material is nano-sized in a protective environment to obtain nano-silicon; wherein the protective environment is a vacuum environment, or the protective environment is obtained by introducing an inert atmosphere or adding a solvent;

[0008] Under the aforementioned protective environment, the nano-silicon is self-assembled with a first carbon source and a polymer, and then a second carbon source is added for self-assembly to obtain layered nano-silicon.

[0009] Under the aforementioned protective environment, the layered nano-silicon is granulated to obtain a spherical precursor;

[0010] The precursor is sintered in a reducing atmosphere or vacuum environment at a sintering temperature of 800℃~1200℃ to obtain the silicon-carbon composite anode material.

[0011] Silicon material is nano-sized under a protective environment, then ground with a first carbon source and a polymer. Utilizing the hydrophilic and hydrophobic properties of the polymer at both ends, the nano-silicon, the first carbon source, and the polymer undergo ordered stacking and self-assembly, resulting in nano-silicon coated with a carbon buffer layer (composed of the first carbon source). This carbon buffer layer inhibits expansion. A second carbon source is then added to coat the carbon buffer layer, and the carbon conductive layer formed by the second carbon source provides charge transfer, thereby increasing the capacitance. After the self-assembled stacking layer is completed, granulation and sintering steps yield an oxygen-free silicon-carbon composite anode material. This silicon-carbon composite anode material exhibits a high specific capacity (>1600 mAh·g). -1 ).

[0012] The oxygen-free silicon-carbon composite anode material described in this application refers to a silicon-carbon composite anode material that is completely free of oxides or almost free of oxides (especially silicon oxide), for example, containing oxides of no more than 0.1 wt% of the mass of the silicon-carbon composite anode material.

[0013] In one embodiment, the first carbon source includes at least one of pitch, graphite, and graphene. The first carbon source is layered, and the carbon buffer layer formed by the first carbon source encapsulates the nano-silicon inside, which can suppress volume expansion and reduce volume effects.

[0014] In one embodiment, the second carbon source includes at least one of carbon black, carbon nanotubes, and carbon nanofibers. The carbon conductive layer formed by the second carbon source can coat the carbon buffer layer. The second carbon source has a higher conductivity than the first carbon source, and the carbon conductive layer can provide charge transfer, thereby increasing the capacitance.

[0015] In one embodiment, the inert atmosphere includes at least one of argon, nitrogen, and helium. The inert atmosphere provides an oxygen-free environment, preventing the oxidation of nano-silicon and ensuring that the prepared silicon-carbon composite anode material is free of SiO₂. x This is beneficial for improving the electrochemical performance of the silicon-carbon composite anode material and reducing the volume effect.

[0016] In one embodiment, the solvent includes at least one selected from diethylene glycol, polyethylene glycol, propylene glycol, and dimethyl sulfoxide. This solvent prevents the oxidation of nano-silicon, resulting in a silicon-carbon composite anode material free of SiO₂. xThis is beneficial for improving the electrochemical performance of the silicon-carbon composite anode material and reducing the volume effect.

[0017] In one embodiment, the polymer is an amphoteric polymer, possessing both hydrophobic and hydrophilic groups.

[0018] In one embodiment, the polymer comprises at least one of N-allyl-(2-ethylxananoyl)propionamide and dimethylformamide. Utilizing the characteristic that the polymer has hydrophilic and hydrophobic groups at both ends, the difference in hydrophilicity and hydrophobicity between nano-silicon and the first and second carbon sources (the first and second carbon sources can be collectively referred to as carbon substrates) can be improved, enabling the carbon substrate, polymer, and nano-silicon to undergo homogenized self-assembly coating to form a layered structure.

[0019] In one embodiment, the reducing atmosphere comprises a nitrogen-hydrogen mixture. Sintering under a reducing atmosphere can remove excessive functional groups on the surface, increase the density and integrity of the carbon substrate coating, and the reducing atmosphere can also prevent the nano-silicon cores from being oxidized (no oxides).

[0020] In one embodiment, the particle size of the nano-silicon grains is 10 nm to 50 nm. This facilitates subsequent self-assembly and coating, and the preparation of silicon-carbon composite anode materials with suitable particle sizes, making them suitable for current secondary battery slurry preparation processes.

[0021] In one embodiment, the precursor has a particle size of 5 μm to 10 μm. This is suitable for current secondary battery slurry preparation processes and also avoids agglomeration during the sintering process.

[0022] This application also provides a silicon-carbon composite anode material, which is prepared by the above-described preparation method. The prepared silicon-carbon composite anode material includes a nano-silicon core, a carbon buffer layer covering the nano-silicon core, and a carbon conductive layer covering the carbon buffer layer. The nano-silicon core improves the diffusion rate of lithium ions, and the carbon buffer layer and carbon conductive layer covering the nano-silicon core prevent direct contact with the electrolyte, thus forming a stable SEI film on the surface of the silicon-carbon composite anode material, thereby significantly improving the cycle performance of the material. Furthermore, this silicon-carbon composite anode material is oxygen-free and has a carbon buffer layer composed of a first carbon source, which effectively reduces the volume effect. The carbon conductive layer provides charge transfer, thereby increasing the capacity.

[0023] This application also provides a battery, including a positive electrode, a negative electrode, and a separator, wherein the negative electrode includes the silicon-carbon composite negative electrode material.

[0024] This application presents an oxide-free silicon-carbon composite anode material (meaning the silicon-carbon composite anode material is completely free of oxides or almost free of oxides, especially free of silicon oxide, for example, containing no more than 0.1 wt% oxides by mass). During charge-discharge cycles, no irreversible oxides increase lithium-ion consumption, thereby improving efficiency. This silicon-carbon composite anode material comprises a nano-silicon core, a carbon buffer layer coating the nano-silicon core, and a carbon conductive layer coating the carbon buffer layer. The carbon buffer layer inhibits expansion, and the carbon conductive layer provides charge transfer, thereby increasing capacity and improving the electrochemical performance of the silicon-carbon composite anode material. The method for preparing the silicon-carbon composite anode material in this application is simple, easy to control, and suitable for industrial production. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the homogenization and self-assembly of a carbon substrate, a polymer, and nano-silicon provided in one embodiment of this application.

[0026] Figure 2 This is a schematic diagram of the structure of a silicon-carbon composite anode material provided in one embodiment of this application.

[0027] Figure 3 The images show the XRD (X-Ray Diffraction) patterns of the silicon-carbon composite anode materials prepared in Example 1 and Comparative Example 1.

[0028] Figure 4 The image shows an SEM (scanning electron microscope) image of the silicon-carbon composite anode material prepared in Example 1.

[0029] Explanation of main component symbols

[0030] Nano Silicon 11

[0031] Polymer 12

[0032] Carbon substrate 13

[0033] Silicon-carbon composite anode material 100

[0034] Nano-silicon core 10

[0035] Carbon buffer layer 30

[0036] Carbon conductive layer 50

[0037] The following detailed description, in conjunction with the accompanying drawings, further illustrates the embodiments of this application. Detailed Implementation

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of this application belong. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application.

[0039] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0040] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0041] One embodiment of this application provides a method for preparing a silicon-carbon composite anode material, comprising the following steps:

[0042] S1: Silicon material is nano-sized under a protective environment to obtain nano-silicon; wherein the protective environment is a vacuum environment, or the protective environment is obtained by introducing an inert atmosphere or adding a solvent.

[0043] In some embodiments, the silicon material can be semiconductor-grade silicon (≥10 μm). Nanoscale formation can be achieved through methods including, but not limited to, machining and mechanical ball milling, which can be dry or wet milling. Nanoscale silicon can also be prepared by chemical or physical vapor deposition methods, simultaneously introducing an alkane atmosphere such as CH4 during the deposition process to act as a precursor for carbon coating, followed by sintering to form surface carbonization. However, this method is costly and not suitable for large-scale industrial production.

[0044] In some embodiments, the inert atmosphere includes at least one of argon (Ar), nitrogen (N2), and helium (He). The inert atmosphere provides an oxygen-free environment, preventing the oxidation of nano-silicon and ensuring that the prepared silicon-carbon composite anode material is free of SiO2. x This is beneficial for improving the electrochemical performance of silicon-carbon composite anode materials and reducing the volume effect.

[0045] In some embodiments, the solvent may be diethylene glycol (DEG), polyethylene glycol (PEG), propylene glycol (PG), dimethyl sulfoxide (DMSO), or a combination thereof. These solvents prevent the oxidation of nano-silicon, resulting in a silicon-carbon composite anode material free of SiO₂. x This is beneficial for improving the electrochemical performance of the silicon-carbon composite anode material and reducing the volume effect.

[0046] In some embodiments, the particle size of the nano-silicon grains is 10 nm to 50 nm. This facilitates subsequent self-assembly and coating, and allows for the preparation of silicon-carbon composite anode materials with suitable particle sizes, making them suitable for current secondary battery slurry preparation processes.

[0047] S2: Under a protective environment, nano-silicon is self-assembled with a first carbon source and a polymer, and then a second carbon source is added for self-assembly to obtain layered nano-silicon.

[0048] In some embodiments, the polymer is an amphoteric polymer, possessing both hydrophobic and hydrophilic groups. Further, the polymer may be N-allyl-(2-ethylxananoyl)propionamide (NAPA), dimethylformamide (DMF), or a combination thereof. The polymer is a medium containing, for example, amino and hydroxyl groups. Utilizing the property of the polymer having a hydrophilic group at one end and a hydrophobic group at the other, the difference in hydrophilicity and hydrophobicity between nano-silicon and the first carbon source and the second carbon source (the first and second carbon sources can be collectively referred to as carbon substrates) can be improved.

[0049] For details, please refer to Figure 1 The hydrophilic groups on the polymer 12 can bond with the nano-silicon 11, while the hydrophobic groups on the other end can bond with the carbon substrate 13, allowing the nano-silicon 11 to be firmly coated on the carbon substrate 13 and preventing it from easily agglomerating with other nano-silicon 11. The carbon substrate 13, polymer 12, and nano-silicon 11 can thus undergo homogenized self-assembly coating to form a layered structure.

[0050] Furthermore, the homogenization self-assembly process can be, but is not limited to, machining, electrical discharge machining, or mechanical ball milling. Among these, mechanical ball milling can be dry milling or wet milling.

[0051] In some embodiments, the first carbon source includes at least one of pitch, graphite, and graphene. The first carbon source is layered, and the carbon buffer layer formed by the first carbon source encapsulates the nano-silicon, which can suppress volume expansion and reduce volume effects. Furthermore, during self-assembly, particle escape can trigger an exothermic reaction, and the first carbon source can undergo thermal diffusion to prevent agglomeration and to prevent the nano-silicon from being oxidized due to the exothermic phenomenon.

[0052] In some embodiments, the second carbon source includes at least one of carbon black, carbon nanotubes, and carbon nanofibers. The carbon conductive layer formed by the second carbon source can coat the carbon buffer layer. The second carbon source has higher conductivity than the first carbon source, and the carbon conductive layer can provide charge transfer, thereby increasing capacitance. Furthermore, during self-assembly, particle escape can trigger an exothermic reaction; the second carbon source can undergo thermal diffusion, preventing agglomeration and preventing the nano-silicon from being oxidized due to the exothermic reaction.

[0053] S3: In a protective environment, layered nano-silicon is granulated to obtain spherical precursors.

[0054] Furthermore, the particle size of the spherical precursor after granulation is 5μm to 10μm. This is suitable for the current slurry preparation process of secondary batteries, while also avoiding agglomeration during the sintering process. The specific granulation process is a commonly used technique in this field, and this application does not limit it.

[0055] S4: The precursor is sintered in a reducing atmosphere or vacuum environment at a sintering temperature of 800℃~1200℃ to obtain silicon-carbon composite anode material.

[0056] In some embodiments, the reducing atmosphere includes a nitrogen-hydrogen mixture. Sintering under a reducing atmosphere can remove excess functional groups from the surface, increase the density and integrity of the carbon substrate coating, and prevent the nano-silicon cores from being oxidized (oxide-free).

[0057] It is understandable that labeling the steps is intended to clearly describe the specific preparation method, not to restrict the order of the steps.

[0058] This application also provides a silicon-carbon composite anode material, which is prepared by the above-described preparation method. Please refer to [link / reference]. Figure 2 The silicon-carbon composite anode material 100 includes a nano-silicon core 10, a carbon buffer layer 30 covering the nano-silicon core 10, and a carbon conductive layer 50 covering the carbon buffer layer 30. The nano-silicon core 10 improves the diffusion rate of lithium ions, and the carbon buffer layer 30 and carbon conductive layer 50 covering the nano-silicon core 10 prevent direct contact between it and the electrolyte, thus forming a stable SEI film on the surface of the silicon-carbon composite anode material 100, thereby significantly improving the cycle performance of the material. Furthermore, this silicon-carbon composite anode material 100 is an oxygen-free material and has a carbon buffer layer 30 composed of a first carbon source, which effectively reduces the volume effect. The carbon conductive layer 50 provides charge transfer, thereby increasing the capacity.

[0059] The silicon-carbon composite anode material described in this application is completely free of oxides or almost free of oxides (especially silicon oxide), for example, it contains no more than 0.1 wt% of oxides as a percentage of the mass of the silicon-carbon composite anode material.

[0060] This application also provides a battery, including a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises the silicon-carbon composite negative electrode material. The battery may be a secondary battery, such as a lithium-ion secondary battery or a sodium-ion battery, but is not limited thereto.

[0061] This application involves nano-sizing silicon material under a protective environment, followed by grinding with a first carbon source and a polymer. Utilizing the hydrophilic and hydrophobic properties of the polymer at both ends, the nano-silicon, the first carbon source, and the polymer undergo ordered stacking and self-assembly, resulting in nano-silicon coated with a carbon buffer layer (composed of the first carbon source). This carbon buffer layer inhibits expansion. A second carbon source is then added to coat the carbon buffer layer, and this second carbon source forms a conductive carbon layer that provides charge transfer, thereby increasing the capacitance. After the self-assembled stacking layer is completed, granulation and sintering steps yield an oxygen-free silicon-carbon composite anode material. This silicon-carbon composite anode material exhibits a high specific capacity (>1600 mAh·g). -1 ).

[0062] The present application will be further described below with reference to specific embodiments.

[0063] Example 1

[0064] S1: Semiconductor-grade silicon (≥10μm) and solvent diethylene glycol are added to a grinding mill with a rotation speed of 2400rpm~300rpm for mechanical processing to obtain nano-silicon with a particle size of 10nm~50nm.

[0065] S2: Add N-allyl-(2-ethylxanthanoyl)propionamide (NAPA), a polymer (5% of the mass of silicon), and graphite (5-10% of the mass of silicon) to nano-silicon and grind them to make them stacked and self-assembled in an orderly manner. Then add carbon nanotubes (1-5% of the mass of silicon) and grind them to obtain layered nano-silicon.

[0066] In the grinding mill, the temperature difference between the core grinding temperature and the slurry outlet temperature must not exceed 5°C. This prevents excess heat from oxidizing the nano-silicon.

[0067] S3: Spray granulation of layered nano-silicon yields a precursor with a particle size of 5μm to 10μm.

[0068] S4: The precursor is placed in a sintering furnace containing a nitrogen-hydrogen mixture (hydrogen volume percentage of 3%), with a gas flow rate of 2L / min, and heat-treated at 800℃~1200℃ for 12h to obtain silicon-carbon composite anode material.

[0069] Comparative Example 1

[0070] The only difference between Comparative Example 1 and Example 1 is that in step S4, the reducing atmosphere is pure nitrogen. Everything else is the same as in Example 1 and will not be repeated here.

[0071] The XRD (X-ray Diffraction) patterns of the silicon-carbon composite anode materials prepared in Example 1 and Comparative Example 1 are shown below. Figure 3 .Depend on Figure 3 It can be seen that the silicon-carbon composite anode material prepared in Example 1 only shows characteristic peaks of Si (Cubic,Fd-3m(227)) and C (Hexagonal,p63 / mmc(194)), and does not have characteristic peaks of silicon oxide, indicating that the silicon-carbon composite anode material prepared in Example 1 does not contain silicon oxide SiO. x The silicon-carbon composite anode material prepared in Comparative Example 1 showed characteristic peaks of SiO in its XRD pattern, indicating that a small amount of nano-silicon was oxidized. This demonstrates that the protective effect of the nitrogen-hydrogen mixture is superior to that of pure nitrogen.

[0072] Please see the SEM (scanning electron microscope) image of the silicon-carbon composite anode material prepared in Example 1. Figure 4 .Depend on Figure 4 It can be seen that the silicon-carbon composite anode material prepared in Example 1 has a smooth particle surface, indicating that an effective carbon layer protection has been formed.

[0073] Three samples of the silicon-carbon composite anode material prepared in Example 1 were extracted and designated as Sample 1, Sample 2, and Sample 3, respectively. Each of the three samples was dissolved in water with a conductive agent (Super P conductive carbon black) and a binder (SBR styrene-butadiene rubber) at a mass ratio of 88:1:11 to obtain a mixture, which was then prepared into a slurry with a solid content of 50%. The slurry was coated onto a copper foil current collector and vacuum dried to obtain the anode sheet. Then, using conventional production processes, ternary cathode sheets, an electrolyte with a lithium salt concentration of 1 mol / L (composed of LiPF6 / EC+DMC+EMC), and a Celgard 2400 separator were assembled for pouch cell stacking and 5Ah assembly. The battery assembled from Sample 1 was designated as Battery 1, the battery assembled from Sample 2 was designated as Battery 2, and the battery assembled from Sample 3 was designated as Battery 3. Battery 1, Battery 2, and Battery 3 were subjected to the following performance tests.

[0074] Positive electrode de-lithiation capacity test: Current density 0.1C, voltage rise to 4.2V, and then the negative electrode specific capacity is converted according to the following formula to obtain the de-lithiation capacity.

[0075]

[0076] Lithiation capacity test of positive electrode: current density 0.1C, voltage drop to 2.0V, and then the specific capacity of negative electrode is converted to obtain the lithium intercalation capacity.

[0077] Efficiency = (Lithium delithiation capacity / Lithium insertion capacity) × 100%

[0078] The performance test results are shown in Table 1.

[0079] Table 1

[0080] <![CDATA[Delithiation capacity (mAh·g -1 )]]> <![CDATA[Intercalation lithium capacity (mAh·g -1 )]]> efficiency(%) Battery 1 1580 1790 88.3 Battery 2 1587 1800 88.2 Battery 3 1536 1780 86.3

[0081] As shown in Table 1, the batteries assembled from the silicon-carbon composite anode material prepared by the method of this application have high capacity and efficiency, indicating that the silicon-carbon composite anode material prepared by this application can suppress volume expansion and improve conductivity and capacity.

[0082] This application presents an oxide-free silicon-carbon composite anode material. During charge-discharge cycling, no irreversible oxides are generated to increase lithium-ion consumption, thereby improving efficiency. The silicon-carbon composite anode material comprises a nano-silicon core, a carbon buffer layer coating the nano-silicon core, and a carbon conductive layer coating the carbon buffer layer. The carbon buffer layer suppresses expansion, and the carbon conductive layer provides charge transfer, thereby increasing capacity and improving the electrochemical performance of the silicon-carbon composite anode material. The method for preparing the silicon-carbon composite anode material in this application is simple, easy to control, and suitable for industrial production.

[0083] The above description describes some specific embodiments of this application, but in actual applications, the application should not be limited to these embodiments. For those skilled in the art, other modifications and alterations made based on the technical concept of this application should fall within the protection scope of this application.

Claims

1. A method for preparing a silicon-carbon composite anode material, characterized in that, The preparation method includes the following steps: Silicon material is nano-sized in a protective environment to obtain nano-silicon; wherein the protective environment is a vacuum environment, or the protective environment is obtained by introducing an inert atmosphere or adding a solvent. Under the aforementioned protective environment, the nano-silicon is self-assembled with a first carbon source and N-allyl-(2-ethylxanthoxy)propionamide, and then a second carbon source is added for self-assembly to obtain layered nano-silicon. The first carbon source is layered and includes at least one of pitch, graphite and graphene. The second carbon source includes at least one of carbon black, carbon nanotubes and carbon nanofibers. Under the aforementioned protective environment, the layered nano-silicon is granulated to obtain a spherical precursor; The precursor is sintered in a reducing atmosphere or vacuum environment at a sintering temperature of 800℃~1200℃ to obtain the silicon-carbon composite anode material. The silicon-carbon composite anode material contains no oxides, or contains oxides accounting for no more than 0.1 wt% of the mass of the silicon-carbon composite anode material.

2. The method for preparing the silicon-carbon composite anode material as described in claim 1, characterized in that, The inert atmosphere includes at least one of argon, nitrogen, and helium, and the solvent includes at least one of diethylene glycol, polyethylene glycol, propylene glycol, and dimethyl sulfoxide.

3. The method for preparing the silicon-carbon composite anode material as described in claim 1, characterized in that, The reducing atmosphere comprises a nitrogen-hydrogen mixture.

4. The method for preparing the silicon-carbon composite anode material as described in claim 1, characterized in that, The particle size of the nano-silicon is 10nm~50nm.

5. The method for preparing the silicon-carbon composite anode material as described in claim 1, characterized in that, The precursor has a particle size of 5μm to 10μm.

6. A silicon-carbon composite anode material, characterized in that, The silicon-carbon composite anode material is prepared by the preparation method according to any one of claims 1-5, and the silicon-carbon composite anode material includes a nano-silicon core, a carbon buffer layer covering the nano-silicon core, and a carbon conductive layer covering the carbon buffer layer.

7. A battery comprising a positive electrode, a negative electrode, and a separator, characterized in that, The negative electrode sheet comprises the silicon-carbon composite negative electrode material as described in claim 6.

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