Silicon-carbon composite negative electrode material, preparation method thereof and secondary battery
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HON HAI PRECISION INDUSTRY CO LTD
- Filing Date
- 2025-01-21
- Publication Date
- 2026-07-21
Smart Images
Figure CN122436478A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, and in particular to a silicon-carbon composite anode material and its preparation method, as well as a secondary battery using the silicon-carbon composite anode material. Background Technology
[0002] In recent years, lithium-ion batteries have been widely used in electric vehicles, consumer electronics, and other products. The cost, energy density, rate performance, cycle life, and safety of lithium-ion batteries largely depend on the electrode materials used in them.
[0003] Silicon is widely available, low in cost, environmentally friendly, and has a high specific capacity (4200 mAh·g). -1 Silicon, with its advantages such as a slightly higher voltage plateau than graphite and the absence of lithium metal deposition on its surface during charging, is considered a promising next-generation anode material to replace graphite. However, as a semiconductor material, silicon has a conductivity of only 10³ Ω·m, resulting in an initial charge-discharge Faraday efficiency (ICE%) of less than 80%. Furthermore, silicon exhibits a large volume change rate during charge and discharge, which can cause cracking and pulverization, leading to short circuits due to the active material losing contact with the current collector. Therefore, it is urgent to address the issues of poor conductivity and volume expansion during charge and discharge of silicon. Summary of the Invention
[0004] In view of this, it is indeed necessary to provide a silicon-carbon composite anode material and its preparation method that can solve the problems of poor conductivity and volume expansion during charging and discharging of silicon materials, as well as a secondary battery using the silicon-carbon composite anode material.
[0005] A silicon-carbon composite anode material, wherein the silicon-carbon composite anode material has a core-shell structure, comprising a nano-silicon core layer and an outer shell layer that at least partially or completely covers the nano-silicon, wherein the outer shell layer is a nitrogen-containing graphite layer, and the nano-silicon is bonded to the nitrogen-containing graphite layer by non-covalent bonds.
[0006] A method for preparing a silicon-carbon composite anode material includes the following steps: introducing a nitrogen-containing substance into a two-dimensional graphite layer to form a nitrogen-containing graphite layer; nano-sizing silicon material under a protective environment to form nano-silicon; homogenizing and self-assembling the nitrogen-containing graphite layer, the nano-silicon, and a polymer compound under the protective environment to form a composite; granulating the composite under the protective environment to obtain a spherical precursor; and sintering the spherical precursor under a reducing atmosphere or vacuum environment to obtain the silicon-carbon composite anode material.
[0007] A secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises a silicon-carbon composite negative electrode material as described above.
[0008] Compared with existing technologies, the silicon-carbon composite anode material provided by this invention includes a nano-silicon core layer and a nitrogen-containing graphite outer shell layer covering the nano-silicon. The nano-silicon and the nitrogen-containing graphite layer are bonded by non-covalent bonds, so the nano-silicon and the nitrogen-containing graphite layer are firmly bonded, and the nitrogen-containing graphite layer is not easily detached or peeled off from the nano-silicon. The nitrogen-containing graphite layer can suppress the volume expansion of the nano-silicon and improve the poor conductivity of the nano-silicon. Furthermore, the preparation method of the silicon-carbon composite anode material is simple, easy to control, and suitable for industrial production. Attached Figure Description
[0009] Figure 1 The process flow diagram is shown for the preparation method of the silicon-carbon composite anode material provided by the present invention.
[0010] Figure 2 Scanning electron microscope image of nitrogen-containing graphite layer provided for this invention.
[0011] Figure 3 Raman spectra of nitrogen-containing graphite layers and graphene provided for this invention.
[0012] Explanation of main component symbols
[0013] none
[0014] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation
[0015] The silicon-carbon composite anode material, its preparation method, and the secondary battery of the present invention will be further described in detail below with reference to the accompanying drawings.
[0016] 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.
[0017] Furthermore, the terminology used herein is for describing particular embodiments only and is not intended to limit the embodiments. Expressions used in the singular include plural expressions unless they have a clearly different meaning in the context. In this specification, the terms “comprising,” “having,” indicate the presence of the listed features, integrals, steps, operations, components, and / or constructions, and do not exclude the presence or addition of one or more features, integrals, steps, operations, components, constructions, and / or sets thereof.
[0018] Furthermore, the numerical values stated herein are within the permissible deviation range for a specific value, determined by those skilled in the art taking into account errors related to the specific quantity being measured (e.g., limitations of the measurement system). For example, this may mean within one or more standard deviations relative to the stated value, or within ±20%, 10%, or 5%.
[0019] The technical solution of the present invention will be further described in detail below with reference to the specification, drawings and specific embodiments.
[0020] Please see Figure 1 The first embodiment of the present invention provides a method for preparing a silicon-carbon composite anode material, comprising the following steps:
[0021] S1. Provide a two-dimensional graphite layer, and introduce a nitrogen-containing substance (introduced by intercalation) into the two-dimensional graphite layer to form a nitrogen-containing graphite layer;
[0022] S2. Under a protective environment, silicon material is nano-sized to form nano-silicon;
[0023] S3. Under the protective environment, the nitrogen-containing graphite layer, the nano-silicon, and a polymer compound are homogenized and self-assembled to form a composite.
[0024] S4. Under the protective environment, the complex is granulated to obtain a spherical precursor;
[0025] S5. The spherical precursor is sintered in a reducing atmosphere or vacuum environment.
[0026] In step S1, blocky natural graphite, artificial graphite, mesophase spherical graphite, etc., can be exfoliated into the two-dimensional graphite layer. The two-dimensional graphite layer is a two-dimensional layered graphite material. The size of the two-dimensional graphite layer is related to the size of the particles formed by subsequent granulation. In a specific embodiment, the size of the two-dimensional graphite layer is between 1 micrometer and 3 micrometers. Preferably, the size of the two-dimensional graphite layer is approximately 2 micrometers.
[0027] Nitrogen-containing substances (such as hydrazine, ethylenediamine, ammonia, urea, melamine, etc.) are introduced into the two-dimensional graphite layer via intercalation using physical methods to further improve the thickness of the two-dimensional graphite layer. The two-dimensional graphite layer has a layered structure, comprising multiple layers of graphite, the number of which is represented by n. <3. Specifically, the two-dimensional graphite layer is placed in a dispersion of a nitrogen-containing substance and stirred. The dispersion includes water, ethanol, ethylene glycol, etc. In one specific embodiment, the nitrogen-containing substance is melamine, the dispersion is ethanol, and the dispersion of the nitrogen-containing substance is an ethanol solution containing melamine. Because the number of graphite layers in the two-dimensional graphite layer is less than or equal to three, the two-dimensional graphite layer has strong structural mechanical properties, and stirring will not destroy its structure. The nitrogen-containing substance will penetrate or be introduced into the interlayer of the two-dimensional graphite layer to form the nitrogen-containing graphite layer, and the interlayer of the nitrogen-containing graphite layer is bonded by non-covalent bonds. In one specific embodiment, the two-dimensional graphite layer is graphene, and the nitrogen-containing graphite layer is nitrogen-containing graphene. The nitrogen content of the nitrogen-containing graphite layer is 0.1% to 10%, for example, 1% to 10%, 5% to 10%, or 2% to 5%. The optimal nitrogen content of the nitrogen-containing graphite layer is 3%.
[0028] The surface of the nitrogen-containing graphite layer has a positive charge, which originates from nitrogen. Since nitrogen itself carries a positive charge, this facilitates the deposition of nano-silicon particles with a size of less than 100 nm onto the nitrogen-containing graphite layer. That is, the nitrogen-containing graphite layer (e.g., a nitrogen-containing graphite layer with a size of 2 micrometers) supports the nano-silicon particles and provides support during silicon expansion.
[0029] In step S2, the silicon material can be semiconductor-grade silicon (≥10μm). Nanoscale formation can be achieved through methods including, but not limited to, machining and mechanical ball milling, where the mechanical ball milling 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, these methods are costly and not suitable for large-scale industrial production.
[0030] The protective environment is a vacuum environment, or it can be obtained by introducing an inert atmosphere or adding a solvent. 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 silicon oxide (SiO2). x This is beneficial for improving the electrochemical performance of silicon-carbon composite anode materials and reducing the volume effect.
[0031] The solvent can be diethylene glycol (DEG), polyethylene glycol (PEG), propylene glycol (PG), dimethyl sulfoxide (DMSO), or a combination thereof. The solvent prevents the oxidation of nano-silicon, ensuring that the prepared silicon-carbon composite anode material is free of silicon oxide (SiO₂). x This is beneficial for improving the electrochemical performance of the silicon-carbon composite anode material and reducing the volume effect.
[0032] In one specific embodiment, the particle size of the nano-silicon is 50 to 100 nanometers. 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.
[0033] In step S3, the composite has a layered structure. The polymer is an amphoteric polymer, possessing both hydrophobic and hydrophilic groups. Further, the polymer can be polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyphthalamide resin (PPA), polyacrylic acid (PAA), 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 that the polymer has a hydrophilic group (at least one hydrophilic side chain) at one end and a hydrophobic group (at least one hydrophobic side chain) at the other end, the difference in hydrophilicity and hydrophobicity between the nano-silicon and the nitrogen-containing graphite layer can be improved.
[0034] Specifically, the hydrophilic group at one end of the polymer compound bonds to the nano-silicon, while the hydrophobic group at the other end bonds to the nitrogen-containing graphite layer. This ensures that the nano-silicon is firmly located on the nitrogen-containing graphite layer and is less prone to agglomeration with other nano-silicon. The nitrogen-containing graphite layer, the polymer compound, and the nano-silicon can thus undergo homogenized self-assembly to form a layered structure.
[0035] That is, a polymer compound is first used to coat the surface of nano-silicon. Then, taking advantage of the hydrophilic and hydrophobic properties of the polymer compound's two ends, the hydrophobic polymer chains can combine with the subsequently added nitrogen-containing graphite layer, thereby completing the ordered stack self-assembly of silicon / polymer compound / nitrogen-containing graphite layer. Therefore, in a specific embodiment, during the process of homogenizing the nitrogen-containing graphite layer, the nano-silicon, and a polymer compound to form a composite, the nano-silicon and the polymer compound are mixed first, and then the nitrogen-containing graphite layer is added.
[0036] Furthermore, the homogenization self-assembly process can be, but is not limited to, machining, electrical discharge machining, or mechanical ball milling. Mechanical ball milling can be dry or wet milling. After the homogenization self-assembly process, the nitrogen-containing graphite layer and the nano-silicon are bonded by non-covalent bonds.
[0037] A two-dimensional layered nitrogen-containing graphite layer covers the nano-silicon, and the layers of the nitrogen-containing graphite are bonded by non-covalent bonds. Therefore, the nitrogen-containing graphite layer is relatively strong and can suppress the volume expansion of the nano-silicon, reducing the volume effect. Furthermore, during the self-assembly process, the escape of nano-silicon particles triggers an exothermic reaction. The nitrogen-containing graphite layer can diffuse heat, preventing the nano-silicon from agglomerating and from being oxidized due to the exothermic reaction.
[0038] In one specific embodiment, silicon nanostructuring is performed first in a container under the same solvent, followed by self-assembly of the nitrogen-containing graphite layer. That is, the solvent used for self-assembly is the same solvent used during silicon nanostructuring.
[0039] In step S4, the composite is granulated under a protective environment to obtain a spherical precursor. The particle size of the granulated precursor is 5 to 10 micrometers. This size is suitable for the secondary battery slurry preparation process and also avoids agglomeration during the sintering process. The specific granulation process is a commonly used technique in the art, and this application does not limit it.
[0040] In step S5, the spherical precursor is sintered in a reducing atmosphere or vacuum environment at a sintering temperature of 800℃~1100℃ to obtain a silicon-carbon composite anode material.
[0041] The reducing atmosphere is a nitrogen-hydrogen mixture or an argon-hydrogen mixture, etc. Sintering under a reducing atmosphere can remove excessive functional groups on the surface, increase the density and integrity of the nitrogen-containing graphite layer, and prevent the oxidation of nano-silicon, thus avoiding the formation of oxides. In a specific embodiment, the spherical precursor is placed in a sintering furnace containing a nitrogen-hydrogen mixture at a gas flow rate of 2 L / min, and heat-treated at 950°C for 8 hours to obtain the silicon-carbon composite anode material.
[0042] A spherical precursor with a size of 5 to 10 micrometers is sintered under a protective atmosphere at a temperature of 800°C to 1100°C. This process not only removes functional groups (such as hydrogen groups H-) from the surface of the spherical precursor that could easily trap lithium, leaving carbon functional groups C- and nitrogen functional groups N-, but also allows nitrogen atoms (N) to enter the C-C lattice of the graphite material, forming CN bonds. Therefore, the electron adsorption force between nano-silicon and the nitrogen-containing graphite layer supporting the nano-silicon can be effectively improved, resulting in the silicon-carbon composite anode material, which can be used as an anode material for (lithium, sodium) secondary batteries.
[0043] The low-temperature drying stage in step S4 of the granulation process and the sintering stage in step S5 result in solid spheres rather than hollow spheres. That is, the spherical precursor is a solid sphere rather than a hollow sphere, avoiding any impact on the preparation of the battery electrode. The reducing atmosphere prevents the nano-silicon from being oxidized (i.e., oxide-free), thereby increasing the density of the silicon-carbon composite anode material.
[0044] The silicon-carbon composite anode material is composed of silicon and nitrogen-intercalated graphite. The polymer compounds added during self-assembly are carbonized and removed in the sintering step of step S5.
[0045] After the sintering process in step 5, the non-covalent bond between the nitrogen-containing graphite layer and the nano-silicon is further strengthened.
[0046] It is understood that the numbering of steps S1 to S5 is intended to clearly describe the specific preparation method, and is not a limitation on the order of the steps. Please refer to [link / reference]. Figure 2 The second embodiment of the present invention provides a silicon-carbon composite anode material prepared by the method for preparing the silicon-carbon composite anode material. The silicon-carbon composite anode material has an approximately spherical core-shell structure, mainly comprising the nano-silicon (core layer) and the nitrogen-containing graphite layer (outer shell layer) partially or completely covering the nano-silicon. The nano-silicon and the nitrogen-containing graphite layer are bonded by non-covalent bonds, and the layers within the nitrogen-containing graphite layer are bonded by non-covalent bonds.
[0047] The silicon-carbon composite anode material has a Si:C:N ratio of 1.0:0.05-0.5:0.01-0.05. In one specific embodiment, the silicon-carbon composite anode material is composed of nano-silicon and a nitrogen-containing graphite layer coating the nano-silicon.
[0048] The nano-silicon is made of silicon, and the nitrogen-containing graphite layer is nitrogen-intercalated graphite. Nano-silicon improves the diffusion rate of lithium ions, and the nitrogen-containing graphite layer coating the nano-silicon prevents direct contact between silicon and the electrolyte, forming a stable SEI film on the surface of the silicon-carbon composite anode material, thereby significantly improving the material's cycle performance. Furthermore, the silicon-carbon composite anode material is oxygen-free, effectively reducing the volume effect.
[0049] The silicon-carbon composite anode material is completely free of oxides or almost free of oxides (especially silicon oxide), for example, containing no more than 0.1 wt% oxides by mass of the silicon-carbon composite anode material. In one specific embodiment, the silicon-carbon composite anode material is completely free of oxides. In another specific embodiment, the silicon-carbon composite anode material contains a small amount of oxides (such as silicon oxide), the percentage of which is less than 0.1 wt% by mass.
[0050] A third embodiment of the present invention provides a secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises the silicon-carbon composite negative electrode material. The secondary battery may be a metal-ion secondary battery, such as a lithium-ion secondary battery or a sodium-ion battery, but is not limited thereto. In a specific embodiment, the silicon-carbon composite negative electrode material, a conductive agent, and a binder in a mass percentage ratio of 88:1:11 are dissolved in a solvent to obtain a mixture, with the solid content controlled at 50%. The resulting mixture is coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet. The types of the conductive agent and binder are not limited and can be commonly used conductive agents and binders in the battery field.
[0051] The following will further illustrate the silicon-carbon composite anode material and its preparation method, as well as the secondary battery using the silicon-carbon composite anode material, with reference to specific embodiments. Specific Implementation Example 1
[0053] The first step involves processing graphite particles (such as natural graphite, artificial graphite, mesophase spherical graphite, graphene, etc.) into a two-dimensional layered graphite material with a size of 2 to 3 micrometers. Then, nitrogen-containing substances (such as hydrazine, ethylenediamine, ammonia, urea, melamine, etc.) are introduced into the interlayer of the layered graphite material via intercalation to obtain the nitrogen-containing graphite layer. Figure 2 This is a scanning electron microscope image of a nitrogen-containing graphite layer.
[0054] The second step involves placing semiconductor-grade silicon (≥10μm) and diethylene glycol as solvent into a mill with a rotation speed of 2400rpm to 3000rpm for mechanical processing to obtain nano-silicon with a particle size of 50nm to 100nm.
[0055] The third step involves adding a polymer compound (comprising 5 wt% of the total silicon-carbon composite anode material) and a nitrogen-containing graphite layer (comprising 10 wt% of the total silicon-carbon composite anode material) to the nano-silicon and grinding them to allow for ordered stacking and self-assembly, resulting in a layered composite. 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.
[0056] Step 4: Spray granulation of the layered composite to obtain spherical precursors with a particle size of 5μm to 10μm.
[0057] Step 5: Place the spherical precursor into a sintering furnace containing a nitrogen-hydrogen (or argon-hydrogen) mixture at a gas flow rate of 2 L / min and heat-treat at 950°C for 8 hours to obtain the silicon-carbon composite anode material.
[0058] Comparative Example 1
[0059] The only difference between Comparative Example 1 and Specific Example 1 is that the graphite layer in Specific Example 1 contains nitrogen, while the graphite layer in Comparative Example 1 does not have nitrogen intercalation; that is, Comparative Example 1 is pure two-dimensional graphene. Everything else is the same as Specific Example 1, and will not be repeated here.
[0060] Figure 3 The images show the Raman spectra of the nitrogen-containing graphite layer in Specific Example 1 and the graphene in Comparative Example 1. Figure 3 In this context, GP represents graphene, and 2D Layered Carbon-N represents the nitrogen-containing graphene layer, where the number of graphene layers n=1, therefore 2DLayered Carbon-N represents nitrogen-containing graphene. Figure 3 It can be seen that peak G is 1529.6 cm. -1 It becomes 1537.3cm-1 and 1563.7cm. -1 It became 1564.1cm -1 1597.7cm -1 It became 1592.8cm -1 The overall G peak shape became narrower (from 68 to 55), indicating that the nitrogen atoms in nitrogen-containing graphene caused the sp-value of graphene. 2 Things have changed. Figure 3 It is evident that nitrogen-containing graphene has a diameter of 1328.2 cm⁻¹ compared to graphene. -1 and 1353.3cm -1 The two D peaks indicate that the nitrogen atoms intercalated in the nitrogen-containing graphene layers cause changes between the graphene layers, increasing the disordered structure. Because doping causes structural distortion, even though carbon and nitrogen have similar atomic numbers, it still causes changes in the carbon lattice. Therefore, nitrogen is more readily doped into sp... 2 The hybrid orbitals cause structural distortion, and the outermost electron orbital of nitrogen is 2p. 3 The outermost electron orbital of carbon is 2p. 2 Therefore, it can provide the carrier orbital domain needed to improve charge transport.
[0061] Raman analysis was performed to determine the D peak (1200–1400 cm⁻¹). -1 ) and G peak (1500-1600cm) -1 The half-width at half-height (WHH) calculation shows that the number of layers is less than 3, which is considered a few layers. At the same time, ID1 / G<1, ID2 / G<0.1, ID3 / G<0.1, and ID4 / G<0.1 also indicate that the graphite material was not severely crushed during the processing and the edges of the graphite material remained intact.
[0062] Meanwhile, the X-ray diffraction spectrum of the composite phase clearly shows that only characteristic peaks of Si(Cubic,Fd-3m(227)) and C(Hexagonal,P63 / mmc(194)) appear. Specific Implementation Example 2
[0064] The silicon-carbon composite anode material prepared in Specific Example 1 was dissolved in water with a conductive agent (conductive carbon black) and a binder (styrene-butadiene rubber SBR) at a ratio of "silicon-carbon composite anode material: conductive agent: binder (mass ratio) = 88:1:11" to obtain a mixture, which was then prepared into a slurry with a solid content of 50%. The resulting slurry was coated onto a copper foil current collector and vacuum dried to obtain the anode sheet.
[0065] Then, using conventional manufacturing 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. Following the same method, the anode material prepared in Comparative Example 1 was assembled into a battery.
[0066] The silicon-carbon composite anode material prepared in Specific Example 1 is designated as Sample 1, and the anode material prepared in Comparative Example 1 is designated as Sample 2. The battery assembled from Sample 1 is designated as Battery 1, and the battery assembled from Sample 2 is designated as Battery 2. Battery 1 and Battery 2 were subjected to the following performance tests.
[0067] Negative electrode lithium-ion extraction (de-lithiation) capacity test: Current density 0.1C, voltage drop to 3.0V, then the specific capacity of the negative electrode is converted according to the following formula to obtain the extraction capacity (de-lithiation capacity):
[0068]
[0069] The performance test results are shown in Table 1.
[0070] Table 1 Battery performance test results
[0071]
[0072] In Table 1, "Faraday first efficiency" refers to the first charge-discharge efficiency, and "retention rate" refers to the capacity retention rate. As shown in Table 1, the battery assembled using the silicon-carbon composite anode material prepared with a nitrogen-doped graphite layer has a higher retention rate, indicating that the silicon-carbon composite anode material prepared in this invention can suppress volume expansion and improve the battery's retention rate.
[0073] The silicon-carbon composite anode material and its preparation method, as well as the secondary battery using the silicon-carbon composite anode material, have the following advantages: First, the silicon-carbon composite anode material is oxide-free, and during charge-discharge cycles, there are no irreversible oxides to increase lithium-ion consumption, thereby improving efficiency; Second, the silicon-carbon composite anode material comprises nano-silicon and a nitrogen-containing graphite layer coating the nano-silicon, wherein the nitrogen-containing graphite layer is composed of carbon atoms sp. 2 The silicon-carbon composite anode material exhibits several advantages: First, it possesses a large specific surface area, high conductivity, and excellent chemical stability, which can suppress volume expansion and improve the electrochemical performance of the material. Second, the nano-silicon and the nitrogen-containing graphite layer are bonded by non-covalent bonds, resulting in a strong bond between the nano-silicon and the nitrogen-containing graphite layer, making it difficult for the nitrogen-containing graphite layer to detach or peel off. Third, the nitrogen-containing graphite layer coating the nano-silicon improves its relatively poor conductivity. Fourth, the preparation method of the silicon-carbon composite anode material is simple, easy to control, and suitable for industrial production.
[0074] Furthermore, those skilled in the art may make other changes within the spirit of this invention, and of course, all such changes made in accordance with the spirit of this invention should be included within the scope of protection claimed by this invention.
Claims
1. A silicon-carbon composite anode material, characterized in that, The silicon-carbon composite anode material has a core-shell structure, comprising a nano-silicon core layer and an outer shell layer that at least partially or completely covers the nano-silicon. The outer shell layer is a nitrogen-containing graphite layer, and the nano-silicon is bonded to the nitrogen-containing graphite layer by non-covalent bonds.
2. The silicon-carbon composite anode material as described in claim 1, characterized in that, The nitrogen-containing graphite layers are bonded to each other by non-covalent bonds.
3. The silicon-carbon composite anode material as described in claim 1, characterized in that, The nitrogen-containing graphite layer is composed of carbon atoms sp. 2 form.
4. The silicon-carbon composite anode material as described in claim 1, characterized in that, The nitrogen content of the nitrogen-containing graphite layer is less than 10%.
5. The silicon-carbon composite anode material as described in claim 4, characterized in that, The nitrogen content of the nitrogen-containing graphite layer is between 2% and 5%.
6. The silicon-carbon composite anode material as described in claim 1, characterized in that, The particle size of nano-silicon is between 50 nanometers and 100 nanometers.
7. The silicon-carbon composite anode material as described in claim 6, characterized in that, The core-shell structure has a size between 5 micrometers and 10 micrometers.
8. A method for preparing a silicon-carbon composite anode material, characterized in that, Includes the following steps: Nitrogen-containing substances are introduced into a two-dimensional graphite layer to form a nitrogen-containing graphite layer; In a protective environment, silicon material is nano-sized to form nano-silicon; Under the aforementioned protective environment, the nitrogen-containing graphite layer, the nano-silicon, and the polymer compound are homogenized and self-assembled to form a composite. Under the aforementioned protective environment, the complex is granulated to obtain a spherical precursor; and The spherical precursor is sintered in a reducing atmosphere or vacuum environment to obtain a silicon-carbon composite anode material.
9. The method for preparing the silicon-carbon composite anode material as described in claim 8, characterized in that, The nitrogen-containing substance is introduced into the two-dimensional graphite layer by intercalation. The nitrogen-containing substance is hydrazine, ethylenediamine, ammonia, urea, or melamine.
10. The method for preparing the silicon-carbon composite anode material as described in claim 8, characterized in that, The two-dimensional graphite layer has a layered structure, which includes multiple layers of graphite, and the number of the multiple layers of graphite is less than or equal to 3.
11. The method for preparing the silicon-carbon composite anode material as described in claim 8, characterized in that, The size of the nitrogen-containing graphite layer is between 1 micrometer and 3 micrometers.
12. The method for preparing the silicon-carbon composite anode material as described in claim 8, characterized in that, The polymeric compound may be polyvinylpyrrolidone, polyvinyl alcohol, resin polyphthalamide, polyacrylic acid, N-allyl-(2-ethylxanthoxy)propionamide, dimethylformamide, or a combination thereof.
13. A secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The negative electrode comprises the silicon-carbon composite negative electrode material as described in any one of claims 1 to 7.