Nitrogen-doped carbon-coated silicon nanocomposites, green synthesis method and application thereof

Abstract

The application relates to a nitrogen-doped carbon-coated silicon nanocomposite material and a green synthesis method and application thereof, and comprises the following steps: under a protective atmosphere, mixing silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine and a non-ionic surfactant according to a mass ratio of (1-14):(28-42):(7-14):(70-105), performing grinding to obtain a uniform powder mixture; performing heat curing treatment on the powder mixture to obtain a resin-based precursor; performing high-temperature annealing on the resin-based precursor under the protective atmosphere to carbonize and form a nitrogen-doped carbon layer, so as to obtain the nitrogen-doped carbon-coated silicon nanocomposite material. The application does not need organic solvents and flammable gases in the whole process, the method steps are simple, the equipment requirement is low, the prepared composite material has excellent electronic conductivity, structural stability and electrochemical performance, and is suitable for high-energy-density lithium ion battery negative electrodes.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery materials technology, specifically relating to a nitrogen-doped carbon-coated silicon nanocomposite material and its green synthesis method and application. Background Technology

[0002] Lithium-ion batteries have become an important power source for electric vehicles and energy storage systems due to their high energy density and long cycle life. Traditional graphite anodes have a limited theoretical capacity (approximately 372 mAh / g), making it difficult to meet the demands of high energy density and fast charging. Silicon, with its extremely high theoretical specific capacity (approximately 4200 mAh / g) and low redox potential, is considered an ideal anode material for next-generation high-energy-density lithium-ion batteries. However, silicon undergoes a volume expansion of over 300% during lithium-ion insertion / extraction, leading to electrode pulverization, SEI film instability, and capacity decay, severely limiting its practical application.

[0003] To mitigate these issues, carbon coating and composite strategies are commonly employed to improve the conductivity and structural stability of silicon. Existing methods, such as chemical vapor deposition (CVD) and wet chemical methods, suffer from problems such as the use of flammable gases, the generation of hazardous waste liquids, and complex processes, which are not conducive to large-scale production and environmental protection. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a nitrogen-doped carbon-coated silicon nanocomposite material and its green synthesis method and application, solving the technical problems that silicon is prone to volume expansion when used as a negative electrode material for lithium-ion batteries, and that conventional preparation methods require the use of flammable gases and generate harmful waste liquids.

[0005] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0006] In a first aspect, the present invention provides a green synthesis method for nitrogen-doped carbon-coated silicon nanocomposite materials, comprising the following steps: S1, under a protective atmosphere, mixing silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine and a nonionic surfactant in a mass ratio of (1-14):(28-42):(7-14):(70-105), and grinding to obtain a uniform powder mixture; S2, subjecting the powder mixture to thermosetting treatment to obtain a resin-based precursor; S3, subjecting the resin-based precursor to high-temperature annealing under a protective atmosphere to carbonization to form a nitrogen-doped carbon layer, thereby obtaining a nitrogen-doped carbon-coated silicon nanocomposite material.

[0007] Secondly, the present invention provides a nitrogen-doped carbon-coated silicon nanocomposite material prepared by the above method.

[0008] Thirdly, the present invention provides a lithium-ion battery negative electrode sheet, which includes the above-mentioned nitrogen-doped carbon-coated silicon nanocomposite material as an active material.

[0009] Fourthly, the present invention provides a lithium-ion battery comprising the aforementioned negative electrode sheet.

[0010] Compared with the prior art, the beneficial effects of the present invention include: (1) Green, environmentally friendly and safe: The entire process of this invention does not require organic solvents or flammable gases, thus avoiding the safety hazards and environmental pollution problems of traditional CVD and wet processes, which is in line with the concept of green chemistry; (2) Simple process and low cost: The method and steps are simple, the equipment requirements are low, and there is no need for a complex gas transportation and waste liquid treatment system, which significantly reduces the production cost and makes it easy to achieve large-scale production.

[0011] (3) Excellent material structure: The prepared Si@NC material has a uniform core-shell structure. The nitrogen-doped carbon layer not only provides high electronic conductivity, but also effectively buffers the volume expansion of silicon during cycling and maintains the integrity of the electrode structure. (4) Excellent electrochemical performance: This nitrogen-doped carbon-coated silicon nanocomposite material has excellent electronic conductivity, structural stability and electrochemical performance. As a lithium-ion battery anode, it exhibits high specific capacity, excellent rate performance and long cycle stability, and is suitable for high energy density lithium-ion battery anodes. Attached Figure Description

[0012] Figure 1 The image shows the TEM morphology of the Si@NC-800 composite material prepared in Example 1. Figure 2 The images show the XRD patterns of the Si@NC composite materials obtained in Examples 1-4. Figure 3 The Raman spectrum of the Si@NC-800 composite material prepared in Example 1; Figure 4 XPS spectrum of Si@NC-800 composite material prepared in Example 1; Figure 5 Electrochemical cycling test results of batteries made from the Si@NC composite materials obtained in Examples 1-4; Figure 6 Electrochemical rate test results for batteries made from the Si@NC composite materials obtained in Examples 1-4; Figure 7 The constant current intermittent titration curve of the battery made based on the Si@NC-800 composite material obtained in Example 1; Figure 8 The constant current intermittent titration curve is shown for the battery prepared based on nano Si in Comparative Example 1. Figure 9EIS analysis diagrams of batteries made from the Si@NC-800 composite material obtained in Example 1 and the nano Si of Comparative Example 1 are shown. Figure 10 The graph shows a comparison of electrochemical cycling tests of batteries made from Si@NC-800 obtained in Example 1, Si@NC-H obtained in Example 5, and Si@NC-L obtained in Example 6. Figure 11 The image shows a TEM image of the Si@NC-CTAB material prepared in Comparative Example 2. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0014] 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 this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0015] To address the shortcomings of current methods for preparing silicon as a negative electrode material in lithium-ion batteries, which suffer from volume expansion and require the use of flammable gases and generate harmful waste liquids, this invention provides a nitrogen-doped carbon-coated silicon nanocomposite material, its green synthesis method, and its application. This invention prepares nitrogen-doped carbon-coated silicon nanocomposite material through a simple process that is solvent-free and free of flammable gases, featuring green synthesis characteristics. The resulting nitrogen-doped carbon-coated silicon nanocomposite material exhibits excellent electrochemical performance and can be used as a silicon-based negative electrode material.

[0016] In a first aspect, the present invention provides a green synthesis method for nitrogen-doped carbon-coated silicon nanocomposites, comprising the following steps: S1, under a protective atmosphere and solvent-free conditions, silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine and nonionic surfactant are mixed in a mass ratio of (1-14):(28-42):(7-14):(70-105) and then ground without solvent to obtain a uniform powder mixture. S2, The powdered mixture is subjected to thermosetting treatment to obtain a resin-based precursor; S3, the resin-based precursor is subjected to high-temperature annealing under a protective atmosphere to carbonize and form a nitrogen-doped carbon layer, thereby obtaining a nitrogen-doped carbon-coated silicon nanocomposite material.

[0017] This invention employs a completely solvent-free mechanochemical mixing and thermosetting synergistic process, specifically: (1) Solid silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine and nonionic surfactant are ground and mixed in a certain proportion under a protective atmosphere to form a uniform solid precursor. The solvent-free grinding step creates a solid reaction microenvironment in which the components are uniformly mixed and pre-assembled at the nanoscale. This invention creatively replaces the functions of solvent in the traditional method of "dispersion", "mixing" and "mass transfer" through the innovative step of "mechanical chemical grinding". Thus, high-performance nanocomposite materials are successfully prepared under the premise of completely eliminating the use of solvent. This invention has overcome a series of problems in the traditional solvent method in terms of production cost, environmental friendliness, operational safety and process complexity. At the same time, through ingenious formulation design (especially the use of nonionic surfactant), the nanostructure and performance of the product are not damaged, or even better. (2) The subsequent thermosetting process uses hexamethylenetetramine (HMTA) as a high-temperature nitrogen / carbon source, which functions to decompose and participate in polymerization to construct a nitrogen-doped precursor; (3) The specific ratio of raw material combination in this invention is the key to ensuring that effective polymerization and carbonization can occur under the solvent-free conditions and ultimately form a high-performance coating structure.

[0018] The method of this invention avoids the use of solvents, simplifies the process, reduces costs and environmental risks, and the resulting product has excellent electrochemical performance.

[0019] In some embodiments, in step S1, the nonionic surfactant includes pluronic F127.

[0020] In this embodiment, the nonionic surfactant used is poloxamer F127 as a key structure directing agent, dispersant and reaction medium: (1) Structure directing: F127 is a triblock copolymer (PEO-PPO-PEO). During heating, its hydrophobic PPO segments have an affinity for the polymer / carbon precursor that is being formed, while the hydrophilic PEO segments tend to repel each other. This microphase separation behavior can guide the carbon source to be uniformly and orderly coated on the surface of silicon particles, and may even form a porous carbon structure; (2) Dispersion and isolation: During grinding, F127 can help silicon nanoparticles and organic monomers to mix uniformly and prevent silicon particles from agglomerating; in the early stage of pyrolysis, the "soft template" formed by its decomposition can prevent the sintering of silicon particles at high temperature and the excessive densification of carbon layers; (3) Reaction medium: When heated to a certain temperature, F127 will melt, providing a uniform "liquid microenvironment" for the polymerization reaction of m-phenylenediamine and hexamethylenetetramine (HMTA). This is the key to the successful reaction of the solventless method, otherwise the solid phase reaction is difficult to proceed uniformly.

[0021] In some embodiments, in step S1, the silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine and nonionic surfactant are in a mass ratio of (1-14):33:10:83, more preferably (5-7):33:10:83.

[0022] In some embodiments, in step S2, the temperature of the thermosetting treatment is 150–180°C and the time is 20–28 h.

[0023] In this embodiment, formaldehyde and m-phenylenediamine produced by the decomposition of HMTA are polymerized under ammonia catalysis through thermosetting treatment, and silicon particles are encapsulated under the guidance of nonionic surfactants (especially F127) to form a resin-based precursor.

[0024] In this invention, thermosetting treatment (especially temperature) is a key step in achieving efficient and controllable nitrogen doping. The thermosetting treatment at 150℃~180℃ for 20~28 hours is not a simple heating process, but a necessary and crucial step in achieving in-situ polymerization and efficient nitrogen predoping. Its importance is reflected in the following two aspects: (I) Regulating the chemical reaction pathway to construct a nitrogen-doped precursor structure: The core design of this invention lies in utilizing the thermal decomposition behavior of hexamethylenetetramine (HMTA) within a specific temperature range. HMTA begins to decompose above 150°C, continuously and controllably releasing formaldehyde gas. The released formaldehyde and m-phenylenediamine undergo in-situ polymerization under the catalysis of ammonia gas generated within the reaction system, generating a nitrogen-rich phenolic resin polymer (resin-based precursor). This polymerization process is guided by surfactant F127, ensuring that the generated resin uniformly coats the silicon particles. Therefore, nitrogen is firmly introduced into the polymer backbone through chemical bonding before carbonization, laying the chemical structural foundation for the subsequent formation of a stable and uniform nitrogen-doped carbon matrix. (II) Temperature is the decisive factor in realizing the transformation from "curing agent" to "nitrogen source": Temperature is key to controlling the decomposition rate of HMTA and the formaldehyde release kinetics. If the temperature is too low (<150℃), HMTA decomposition is incomplete, resulting in insufficient formaldehyde release, inadequate polymerization, low crosslinking degree of the precursor resin, and ultimately unsatisfactory nitrogen fixation rate and doping amount. If the temperature is too high (>180℃), HMTA decomposition may be too rapid, leading to explosive formaldehyde release, causing localized overpolymerization or the generation of byproducts. Simultaneously, it may cause the decomposition or volatilization of some amine components, thus reducing nitrogen utilization and doping uniformity. Therefore, 150℃~180℃ is the optimal temperature window for this invention to realize the transformation of HMTA from a traditional "curing agent" to a controllable "nitrogen source," ensuring efficient and stable nitrogen introduction and achieving chemical synthesis and nitrogen pre-doping.

[0025] Therefore, through systematic process design, this invention can achieve active, efficient and stable nitrogen doping, thereby significantly improving the conductivity and electrochemical performance (such as first-time efficiency and cycle stability) of the material.

[0026] In some embodiments, in step S2, the thermosetting process is carried out in a closed reaction vessel (such as a high-pressure reactor).

[0027] In some embodiments, in step S3, the high-temperature annealing is performed by holding at 600–1200°C for 2–6 hours.

[0028] In some embodiments, in step S3, the heating rate of high-temperature annealing is 1 to 10 °C / min.

[0029] In some embodiments, the protective atmosphere includes nitrogen or argon.

[0030] Secondly, the present invention provides a nitrogen-doped carbon-coated silicon nanocomposite material prepared by the above method.

[0031] In some embodiments, the nitrogen-doped carbon-coated silicon nanocomposite material of the present invention has a core-shell structure with silicon nanoparticles as the core and a nitrogen-doped carbon layer as the shell; the thickness of the carbon layer is 200 nm to 300 nm; the nitrogen element exists in the form of pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen.

[0032] The nitrogen-doped carbon-coated silicon nanocomposite material of the present invention has a clear core-shell structure. The silicon nanoparticles are uniformly coated with a nitrogen-doped amorphous carbon layer. The nitrogen element exists in multiple forms such as pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen, which effectively improves the conductivity and electrochemical activity of the material.

[0033] Thirdly, the present invention provides a lithium-ion battery negative electrode sheet, which includes the above-mentioned nitrogen-doped carbon-coated silicon nanocomposite material as an active material.

[0034] In some embodiments, the negative electrode sheet of a lithium-ion battery may also include a conductive agent (such as acetylene black) and a binder (such as polyacrylic acid PAA).

[0035] Furthermore, the mass ratio of the active material, conductive agent and binder is (65-75):(10-20):(10-20), more preferably 70:15:15.

[0036] Fourthly, the present invention provides a lithium-ion battery comprising the aforementioned negative electrode sheet.

[0037] The present invention will be further described in detail below through specific embodiments. The silicon nanoparticles used are commercially available silicon nanoparticles with an average particle size of approximately 100 nm.

[0038] Example 1 A green synthesis method for nitrogen-doped carbon-coated silicon nanocomposite material (Si@NC-800) includes the following steps: S1, Weigh 0.035 g silicon nanoparticles, 0.33 g m-phenylenediamine, 0.1 g hexamethylenetetramine and 0.83 g Pluronic F127, grind and mix the above materials for 30 minutes in an argon-filled glove box using an agate mortar and pestle to obtain a uniform powder mixture; S2, the powdered mixture was transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor, sealed and placed in an oven, and heat-cured at 160°C for 24 hours to obtain a dark brown blocky resin-based precursor. S3. The resin-based precursor was crushed and placed in a ceramic boat, which was then placed in a tube furnace. Under an argon atmosphere (flow rate 200 mL / min), the temperature was increased to 800℃ at a rate of 5℃ / min and held at this temperature for 4 hours. Then, it was naturally cooled to room temperature to obtain a black powdery nitrogen-doped carbon-coated silicon nanocomposite material, denoted as Si@NC-800.

[0039] Example 2 Compared with Example 1, the only difference is that the heat preservation temperature in step S3 is adjusted to 600°C, while the other steps and conditions are the same as in Example 1. The resulting nitrogen-doped carbon-coated silicon nanocomposite material is denoted as Si@NC-600.

[0040] Example 3 Compared with Example 1, the only difference is that the heat preservation temperature in step S3 is adjusted to 1000℃, while the other steps and conditions are the same as in Example 1. The resulting nitrogen-doped carbon-coated silicon nanocomposite material is denoted as Si@NC-1000.

[0041] Example 4 Compared with Example 1, the only difference is that the heat preservation temperature in step S3 is adjusted to 1200℃, while the other steps and conditions are the same as in Example 1. The resulting nitrogen-doped carbon-coated silicon nanocomposite material is denoted as Si@NC-1200.

[0042] Example 5 Compared with Example 1, the only difference is that the mass ratio of silicon nanoparticles, m-phenylenediamine, HMTA and F127 in step S1 is adjusted to 14:33:10:83. Other steps and conditions are the same as in Example 1. The resulting nitrogen-doped carbon-coated silicon nanocomposite material is denoted as Si@NC-H.

[0043] Example 6 Compared with Example 1, the only difference is that the mass ratio of silicon nanoparticles, m-phenylenediamine, HMTA and F127 in step S1 is adjusted to 1:33:10:83. Other steps and conditions are the same as in Example 1. The resulting nitrogen-doped carbon-coated silicon nanocomposite material is denoted as Si@NC-L.

[0044] Comparative Example 1 Uncoated commercial silicon nanoparticles (denoted as nano Si) are used as the active material.

[0045] Comparative Example 2 Compared with Example 1, the only difference is that F127 in step S1 is replaced with the ionic surfactant hexadecyltrimethylammonium bromide (CTAB), and the other steps and conditions are the same as in Example 1. The resulting nitrogen-doped carbon-coated silicon nanocomposite material is denoted as Si@NC-CTAB.

[0046] Comparative Example 3 The traditional sol-gel method was employed (Reference: Qin, G.; Jia, Z.; Sun, S.; Wu, H.; Hu, K.; Liu, D.; Gao, Y.; Chen, J. Carbon-Coated Si Nanosheets as Anode Materials for High-Performance Lithium-Ion Batteries). ACS Appl. Nano Mater. 2024, 7 (7),7595–7604.) Synthesize carbon-coated silicon materials.

[0047] The properties of the obtained material are similar to those of Example 1 of the present invention, but its preparation process involves the use of a large amount of ethanol and water, which is complicated and generates chemical waste liquid.

[0048] Application Example 1 Negative electrode preparation and battery assembly: The Si@NC-800 composite material obtained in Example 1 was used as the active material and mixed with conductive agent acetylene black and binder polyacrylic acid (PAA) at a mass ratio of 70:15:15. Deionized water was added and stirred to form a slurry. The slurry was coated onto copper foil, vacuum dried at 120°C for 12 hours, and then cut into electrodes with a diameter of 10 mm (active material loading of approximately 1.2 mg / cm²). In an argon glove box, using this electrode as the working electrode, a lithium metal sheet as the counter / reference electrode, a Whatman GF / A glass fiber membrane as the separator, and a 1M LiPF6 in EC / DMC electrolyte (volume ratio 1:1) containing 5% FEC, a CR2016 coin cell was assembled.

[0049] Performance testing (1) Morphology and structure: The morphology and structure of the Si@NC composite material obtained in the above examples were characterized, and the results are as follows: Figures 1-4 As shown.

[0050] Figure 1 The image shows a transmission electron microscope (TEM) image of Si@NC-800 obtained in Example 1. It can be seen that it is a spherical particle with a diameter of about 1 μm, with a clear core-shell structure and a uniform carbon layer thickness (about 250 nm).

[0051] Figure 2 The images are XRD patterns of the Si@NC composite materials obtained in Examples 1-4, showing only the characteristic peaks of crystalline silicon, indicating that the carbon layer is amorphous.

[0052] Figure 3 This is the Raman spectrum of Si@NC-800 obtained in Example 1, where I D / I G A value of 1.22 indicates that the carbon layer has a moderate degree of graphitization and defects.

[0053] Figure 4 The image shows the N 1s X-ray photoelectron spectrum (XPS) of Si@NC-800 obtained in Example 1, confirming the successful nitrogen doping, which exists in the form of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen.

[0054] (2) Using the method of Application Example 1, the Si@NC composite materials obtained in Examples 1-6 were used as active materials to assemble CR2016 coin cells, and their electrochemical performance was tested. The results are as follows: Figures 5-9 And as shown in Tables 1 and 2.

[0055] Table 1. Electrochemical performance test results (current density 200 mA / g)

[0056] Depend on Figure 5 (The cycling performance of battery A assembled with Si@NC-600, Si@NC-800, Si@NC-1000, and Si@NC-1200 as active materials in Examples 1-4 at 200 mA / g) and the results in Table 1 show that, within the range of 600-1200℃, different heat preservation temperatures have a relatively small impact on the performance of the obtained materials. Among them, Si@NC-800 has relatively superior electrochemical performance, especially discharge capacity and capacity retention.

[0057] Table 2. Rate performance test results at different current densities

[0058] Depend on Figure 6(The rate performance of battery B assembled with Si@NC-600, Si@NC-800, Si@NC-1000, and Si@NC-1200 as active materials in Examples 1-4 at 200 mAh / g, 500 mAh / g, 1000 mAh / g, 2000 mAh / g, and 5000 mAh / g) and the results in Table 2 show that different heat preservation temperatures have a certain impact on the rate performance of the obtained materials in the range of 600-1200℃.

[0059] Meanwhile, the test results of batteries A and B at 200 mA / g show that their data are quite similar, indicating that the material prepared by this invention has good stability and is beneficial for industrial production.

[0060] Figure 7 and Figure 8 The galvanostatic intermittent titration (GITT) curves of the batteries prepared from Si@NC-800 in Example 1 and nano Si in Comparative Example 1 are used to analyze the lithium-ion diffusion kinetics. Figure 9 The electrochemical impedance spectroscopy (EIS) of the batteries prepared from Si@NC-800 in Example 1 and nano Si in Comparative Example 1 is shown. GITT and EIS tests show that Si@NC-800 has a higher lithium-ion diffusion coefficient and a lower charge transfer resistance than pure silicon nanoparticles, indicating that it has faster reaction kinetics.

[0061] Meanwhile, after 50 cycles, the Si@NC-800 electrode structure remained intact, with a thickness expansion of only about 11.5%; while the pure silicon electrode showed severe cracking and pulverization, with a thickness expansion rate of 95.4%, demonstrating that the nitrogen-doped carbon layer has an effective volume buffering effect. Furthermore, the electrochemical performance of nano Si was far inferior to that of Si@NC-800, exhibiting rapid capacity decay.

[0062] Figure 10 The graph shows the cycle performance of batteries made from Si@NC-800, Si@NC-H, and Si@NC-L at 200 mAh / g. The performance of the materials varies significantly under different raw material ratios. Among them, the overall capacity and capacity retention of the battery with Si@NC-H as the active material are higher than those of Si@NC-800, but the stability is poor and the capacity decays more rapidly. The cycle stability of the battery with Si@NC-L as the active material is similar to that of Si@NC-800, but the capacity is not as good as that of Si@NC-800. Therefore, the present invention prefers a mass ratio of silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine and nonionic surfactant of (5-7):33:10:83, and the performance of the resulting material is close to that of Si@NC-800.

[0063] Figure 11The image shows a TEM image of the Si@NC-CTAB material obtained in Comparative Example 2. The results show that the silicon particles in the obtained material are severely agglomerated, the carbon coating is uneven, and the material exhibits an irregular morphology.

[0064] In summary, this invention involves grinding and mixing silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine, and surfactant F127 under solvent-free conditions, followed by thermosetting to form a precursor, and then high-temperature annealing under a protective atmosphere to obtain the Si@NC composite material. The solvent-free synthesis method provided by this invention is green, safe, and efficient, avoiding the problems of using flammable gases or generating large amounts of waste liquid in traditional chemical vapor deposition and wet chemical methods. The process is simple, environmentally friendly, and suitable for large-scale production. The prepared nitrogen-doped carbon-coated silicon nanocomposite material (Si@NC) exhibits excellent comprehensive electrochemical performance. As a lithium-ion battery anode, this material demonstrates high specific capacity (reversible capacity >900 mAh / g at 0.2C), excellent rate performance, and long-term cycle stability (good capacity retention after 100 cycles at 0.2A / g). Its overall performance is significantly superior to that of uncoated silicon nanoparticles, showing broad application prospects in the field of high-energy-density lithium-ion batteries.

[0065] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A green synthesis method for nitrogen-doped carbon-coated silicon nanocomposite materials, characterized in that, Includes the following steps: S1, Under a protective atmosphere, silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine and nonionic surfactant are mixed in a mass ratio of (1-14):(28-42):(7-14):(70-105) and ground to obtain a uniform powder mixture; S2, The powdered mixture is subjected to thermosetting treatment to obtain a resin-based precursor; S3, the resin-based precursor is subjected to high-temperature annealing under a protective atmosphere to carbonize and form a nitrogen-doped carbon layer, thereby obtaining a nitrogen-doped carbon-coated silicon nanocomposite material.

2. The green synthesis method for nitrogen-doped carbon-coated silicon nanocomposite materials according to claim 1, characterized in that, In step S1, the nonionic surfactant includes poloxamer F127.

3. The green synthesis method for nitrogen-doped carbon-coated silicon nanocomposite materials according to claim 1, characterized in that, In step S1, the silicon nanoparticles, m-phenylenediamine, hexamethylenetetramine and nonionic surfactant are in a mass ratio of (1-14):33:10:

83.

4. The green synthesis method for nitrogen-doped carbon-coated silicon nanocomposite materials according to claim 1, characterized in that, In step S2, the temperature of the thermosetting treatment is 150-180°C, and the time is 20-28 hours. The thermosetting process is carried out in a closed reaction vessel.

5. The green synthesis method for nitrogen-doped carbon-coated silicon nanocomposite materials according to claim 1, characterized in that, In step S3, the high-temperature annealing is performed by holding at 600–1200°C for 2–6 hours.

6. The green synthesis method for nitrogen-doped carbon-coated silicon nanocomposite materials according to claim 1, characterized in that, In step S3, the heating rate of the high-temperature annealing is 1 to 10 °C / min.

7. The nitrogen-doped carbon-coated silicon nanocomposite material prepared by the method according to any one of claims 1-6.

8. The nitrogen-doped carbon-coated silicon nanocomposite material according to claim 7, characterized in that, The nitrogen-doped carbon-coated silicon nanocomposite material has a core-shell structure with silicon nanoparticles as the core and nitrogen-doped carbon layers as the shell; the carbon layer thickness is 200 nm to 300 nm; the nitrogen element exists in the forms of pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen.

9. A negative electrode sheet for a lithium-ion battery, characterized in that, The active material includes the nitrogen-doped carbon-coated silicon nanocomposite material as described in any one of claims 7-8.

10. A lithium-ion battery, characterized in that, It includes the negative electrode sheet as described in claim 9.

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