Silicon confined one-dimensional tubular carbon network composite material, and preparation method and application thereof

Abstract

The application relates to a silicon confined one-dimensional tubular carbon network composite material and a preparation method and application thereof. The composite material is formed by interweaving nitrogen-doped one-dimensional hollow carbon nanotubes to form a three-dimensional conductive network, and nano silicon particles are contained in the hollow inner cavity of the carbon nanotube to form a core-shell-tube integrated structure of silicon embedded in the cavity of the carbon tube. The carbon tube has a diameter of 80-200 nm, the embedded silicon particles have a particle size of 50-100 nm, and pyridine nitrogen accounts for 40-47% of the total nitrogen. During preparation, the nano silicon is first anchored into a methyl orange rubber band to construct a composite template, then an iron trichloride oxidant is added, and finally pyrrole is added dropwise for in-situ polymerization, and the product is obtained after carbonization. When the obtained composite material is used as a negative electrode of a lithium ion battery, the capacity retention rate can reach 96% under a current density of 1 A g ‑1 for 100 cycles, and the capacity can still be maintained at about 250 mAh g ‑1 for 1000 cycles under a current density of 5 A g ‑1 The application realizes in-situ integration and confinement of silicon and carbon tubes, and has simple process and stable structure.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a silicon / nitrogen-doped one-dimensional carbon nanotube network composite material prepared based on a methyl orange soft template-assisted in-situ confined polymerization strategy, its preparation method, and its application in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, have become dominant in portable electronic devices, electric vehicles, and renewable energy storage systems. However, as the market demands for higher energy density, faster charge / discharge rates, and longer cycle life continue to increase, traditional graphite anode materials are limited by their 372 mAh g⁻¹ capacity. -1 The theoretical specific capacity of current lithium-ion batteries is gradually becoming insufficient to meet the development needs of next-generation high-energy storage systems. Therefore, developing novel anode materials with higher specific capacity has become an important research topic in the field of lithium-ion batteries.

[0003] Against the backdrop described above, silicon, due to its high 4200mAh g⁻¹, -1 Theoretical specific capacity, low lithium intercalation potential (approximately 0.4 V vs Li / Li) + Silicon, with its abundant reserves in nature, is widely recognized as one of the most promising next-generation lithium-ion battery anode materials. However, the commercial application of silicon-based anodes faces a series of severe technical challenges. During charging and discharging, silicon undergoes an alloying reaction with lithium to form Li₂. x The Si alloy phase undergoes a process accompanied by a massive volume expansion of nearly 300%. This drastic volume change causes silicon particles to expand, fragment, and pulverize during cycling, thereby disrupting the overall structure of the electrode material and causing the active material to detach from the current collector. Volume expansion also leads to repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, continuously consuming electrolyte and lithium ions, resulting in a sustained increase in interfacial impedance, fluctuations in coulombic efficiency, and rapid capacity decay. Furthermore, the inherently poor conductivity of silicon severely restricts the electron transport efficiency within the electrode, limiting the battery's rate performance and rapid charge / discharge capabilities.

[0004] To address these issues, researchers have developed various technical strategies, among which constructing silicon-carbon composite materials is considered one of the most effective approaches. Carbon materials not only possess excellent electrical conductivity, enhancing the electron transport capability of composite electrodes, but their good mechanical flexibility can also buffer the volume expansion of silicon during lithium insertion / extraction to some extent. Among numerous carbon-based materials, one-dimensional carbon nanotubes (CNTs) have attracted significant attention due to their high conductivity, high aspect ratio, and excellent mechanical strength. They can construct a three-dimensional conductive network spanning the entire electrode, demonstrating advantages in improving the rate performance and cycle stability of silicon-based anodes. For example, Chinese invention patent CN107658452A discloses a silicon / carbon nanotube composite anode material, which constructs a conductive network by loading nano-silicon particles onto a carbon nanotube network. Chinese invention patent CN106169564A further proposes a method for preparing silicon-carbon composite materials, forming a composite structure through the physical mixing of carbon nanotubes and silicon particles. The above schemes all belong to physical mixing or simple loading routes. The combination of silicon particles and carbon nanotubes mainly relies on weak physical adsorption, resulting in poor interfacial contact. During cycling, silicon particles are very easy to detach from the surface of carbon nanotubes, leading to failure of the conductive network and rapid capacity decay.

[0005] In recent years, various technical solutions have emerged around the carbonization derivation route of conductive polymers. Polypyrrole (PPy), a typical conductive polymer, can be transformed into nitrogen-doped amorphous carbon materials after carbonization. This not only provides localized coating and volume expansion buffering but also introduces nitrogen heteroatoms to enhance interfacial reactivity and electronic conductivity. Chinese invention patent CN104157875A discloses a composite material of polypyrrole-coated silicon nanoparticles and its preparation method. A polypyrrole coating layer is formed on the surface of silicon particles through in-situ polymerization, resulting in a silicon / conductive polymer composite material with a core-shell structure. Chinese invention patent CN108149343A discloses a method for preparing a nitrogen-doped carbon-coated silicon composite material. A silicon-containing nanofiber membrane is obtained through electrospinning, followed by in-situ polymerization to coat polypyrrole, finally yielding a nitrogen-doped carbon-coated silicon composite nanomaterial. In the above solutions, the polypyrrole coating layer exists only on the particle surface, making it difficult to precisely control the coating layer thickness. When the silicon particles expand in volume, there is a risk that the carbon coating layer is prone to cracking and the interface may de-adhede. Chinese invention patent CN111675208A discloses a method for preparing sulfur-nitrogen-doped hollow carbon nanotubes. Using methyl orange as a template and FeCl3 as an oxidant, polypyrrole hollow nanotubes are synthesized, and after carbonization, they are used as a sulfur carrier in the cathode of lithium-sulfur batteries. While this method achieves nitrogen doping of the hollow carbon nanotubes, it only uses them as a sulfur carrier material and does not involve the composite with silicon particles, nor does it achieve an integrated confined structure of silicon and carbon nanotubes.

[0006] In existing silicon-carbon nanotube composite technologies, most schemes follow the technical route of "first preparing carbon nanotubes or carbon shells, and then physically combining them with silicon." For example, a paper published in the Journal of Power Sources in 2024 (Novelsilicon nanoparticles-based carbonized polypyrrole nanotube composites asanode materials for Li-ion batteries, Feb.15(2024):593.) reported a scheme for constructing silicon-based anodes based on the physical mixing of carbonized polypyrrole nanotubes and silicon nanoparticles. This involves carbonizing pre-synthesized polypyrrole nanotubes and then physically combining them with silicon particles. Although this method achieves the combination of silicon particles and one-dimensional nitrogen-doped carbon fillers, it is essentially a two-step method, where the carbon nanotube preparation and silicon composite are performed independently. The silicon particles are distributed on the outside of the carbon nanotubes, and the interfacial bonding relies solely on the physical contact between the outer wall of the carbon nanotubes and the silicon particles. The lack of strong chemical anchoring leads to the easy detachment of silicon particles from the surface of the carbon nanotubes and the breakage of the conductive network during cycling, thus limiting long-term cycling stability. Furthermore, in existing technologies using the methyl orange template method to prepare polypyrrole tubes, ammonium persulfate (APS) is typically used as the oxidant. However, the carbon nanotubes obtained using the APS system have a relatively low specific surface area (generally below 40 μm). 2 g -1 The nitrogen doping type is mainly graphitic nitrogen, while the proportion of highly active pyridine nitrogen is relatively low, making it difficult to meet the surface active site requirements of rapid electrochemical reactions. Furthermore, the APS system is prone to excessive oxidation of the silicon particle surface during carbonization, resulting in irreversible loss of active silicon.

[0007] Further searches revealed that although existing patent documents (such as CN108063056A) disclose methyl orange template binding Fe 3+ While there are existing technologies for preparing polypyrrole tubes, their applications are limited to supercapacitors or adsorbent materials, and none have addressed the in-situ confined composite of this system with silicon particles. There are no reports in the current technology of "pre-anchoring silicon particles within methyl orange micelles before the polymerization reaction, thereby achieving in-situ encapsulation of silicon within the tubes simultaneously with the formation of polypyrrole tubes." This technological gap prevents silicon-carbon composite materials from achieving the ideal structure of "silicon confined within carbon tubes," and the interfacial bonding strength and buffering capacity are far from optimal.

[0008] In summary, the existing methods for preparing silicon-carbon composite materials have the following technical defects: (1) In the physical mixing and sequential coating strategies, the interfacial bonding force between silicon particles and carbon components is weak, and silicon is easily detached from the carbon matrix during the cycle, resulting in rapid capacity decay; (2) Chemical vapor deposition or electrospinning methods are complex, require high-end equipment, and are expensive, making it difficult to achieve large-scale production; (3) In the scheme of pre-synthesized carbon nanotubes and then physically composited with silicon, silicon particles can only be loaded on the outer surface of the carbon nanotubes and cannot be effectively confined inside the carbon nanotubes, thus limiting the ability to buffer volume expansion; (4) In the existing technology, the type and content of nitrogen doping in the carbon matrix are difficult to precisely control, and the proportion of active nitrogen species such as pyridine nitrogen is low, which limits the surface reaction kinetics of the material; (5) In the technical route of preparing carbon nanotubes using the template method, there is no scheme that integrates the three steps of template self-assembly, in-situ polymerization and silicon confinement, especially lacking reports on using the steric hindrance effect of micelles in the methyl orange soft template to pre-anchor silicon particles inside the template, thereby achieving in-situ encapsulation of silicon inside the tube during the polymerization process. Therefore, developing a silicon-carbon composite material that can achieve simultaneous in-situ generation of carbon nanotubes and silicon confinement, with strong interfacial bonding, stable structure, and excellent electrochemical performance, and its simple preparation method, is of great research significance and application value. Summary of the Invention

[0009] To address the problems of weak silicon-carbon interface bonding, ineffective internal confinement, and insufficient buffering capacity in existing technologies, this invention provides an integrated "silicon-embedded" composite material and its preparation method. The core innovation of this invention lies in: pre-anchoring silicon particles using a methyl orange soft template within Fe... 3+ During the in-situ polymerization of pyrrole, silicon is simultaneously encapsulated within polypyrrole tubes, and after carbonization, a composite material in which silicon is confined within nitrogen-doped carbon nanotubes is obtained. 3+ The system also synergistically regulates the high pyridine nitrogen content (40%~47%), high specific surface area, and inhibits the high-temperature oxidation of silicon, enabling the material to exhibit stable and efficient electrochemical performance.

[0010] Technical solution

[0011] A silicon-confined one-dimensional tubular carbon network composite material is formed by interweaving nitrogen-doped one-dimensional hollow carbon nanotubes to form a three-dimensional continuous conductive network. Nanoscale silicon particles are in-situ confined and encapsulated inside the hollow cavity of the carbon nanotubes, forming an integrated core-shell-tube embedded structure with silicon particles as the core, the inner wall of the carbon nanotubes as the shell, and the hollow carbon nanotubes as the outer channel. The nitrogen-doped one-dimensional hollow carbon nanotubes are derived from polypyrrole by high-temperature carbonization in an inert atmosphere. The wall of a single carbon nanotube completely and continuously encapsulates the silicon particles inside it, and a direct contact interface without binder is formed between the silicon particles and the carbon nanotube wall.

[0012] The composite material simultaneously meets the following structural, compositional, and physical property requirements:

[0013] 1) Morphology and size: The diameter of the carbon nanotubes is 80-200 nm, and the particle size of the embedded nano-silicon particles is 50-100 nm;

[0014] (2) Nitrogen doping configuration: X-ray photoelectron spectroscopy was used to determine the configuration. Charge correction was performed using the C1s characteristic peak at 284.8 eV. Peak fitting calculations were performed on the N1s spectrum to determine that the pyridine nitrogen in the carbon nanotube framework accounted for 40% to 47% of the total nitrogen mass.

[0015] (3) Pore structure: The specific surface area of ​​the composite material was 30–60 m², as determined by the BET method with nitrogen adsorption at 77 K. 2 g -1 The pore size is concentrated in the mesoporous range of 2–10 nm;

[0016] (4) Silicon loading: thermogravimetric analysis in air (heating rate 10℃ min) -1 (At room temperature to 800℃), the total silicon element mass fraction is 25-35 wt%.

[0017] The preparation method of the above-mentioned composite material specifically includes:

[0018] (1) At room temperature, methyl orange template agent was dissolved in deionized water, the pH of the solution was adjusted to 3.0-4.5, nano-silicon particles were added, ultrasonically dispersed and stirred for 6-24 h to form a Si@MO composite template system;

[0019] (2) Add Fe to the above system 3+ The oxidizing agent solution was stirred for 6-24 hours.

[0020] (3) After stirring in step (2), the aqueous solution of pyrrole monomer purified by vacuum distillation is slowly added dropwise. After the addition is complete, the reaction continues for 6 to 24 hours to allow pyrrole to polymerize along the template and encapsulate silicon in the tube to obtain Si@PPy precursor.

[0021] (4) Carbonize in argon or nitrogen at 500-700℃ for 2-5 h to obtain the product.

[0022] Preferably, the mass ratio of methyl orange to nano-silicon is (2~5):1, and the mass ratio of pyrrole to nano-silicon is (5~20):1. The oxidant is ferric chloride hexahydrate, with a molar ratio of (1~2):1 to pyrrole. The preferred carbonization conditions are 600℃ for 3 hours. During carbonization, the methyl orange soft template decomposes into CO2 and NO at high temperature. x The gaseous products were carried away by an inert gas stream. XPS and TGA analyses confirmed that no methyl orange residual phase was detected in the final product, and it had no adverse effect on the electrochemical performance of the negative electrode.

[0023] The present invention also provides a lithium-ion battery negative electrode comprising the composite material.

[0024] Beneficial effects:

[0025] Compared with the prior art, the present invention has the following outstanding advantages:

[0026] (1) The core innovation of this invention lies in the first realization of an integrated strategy of "template in-situ polymerization - simultaneous confinement of silicon". Unlike the traditional approach of first synthesizing carbon nanotubes and then physically mixing or sequentially coating them with silicon, this invention, before the polymerization reaction, uses the spatial confinement effect of a methyl orange soft template to pre-anchor silicon particles within methyl orange micelles to form a Si@MO composite template system, followed by Fe... 3+ During the oxidative polymerization of pyrrole, polypyrrole forms tubular structures along the template surface, while silicon particles already anchored inside the template are in situ encapsulated within the tubular cavity. This one-step method yields a composite precursor in which silicon particles are confined within polypyrrole tubes. After carbonization, the individual carbon nanotubes of the resulting product completely and continuously encapsulate the silicon particles inside, forming a direct, binder-free interface between the silicon particles and the carbon nanotube walls. This unique "silicon-embedded in tube" structure fundamentally solves the problem of poor interfacial contact between silicon and carbon components in existing technologies.

[0027] (2) The Fe used in this invention 3+ The oxidant and the methyl orange template have a unique synergistic regulatory effect. Experiments have shown that Fe... 3+ In the reaction system, it not only acts as an oxidant for pyrrole polymerization but also forms a stable micelle template with methyl orange, guiding the ordered polymerization of polypyrrole to form carbon nanotube structures with uniform diameter and continuous walls. Compared with the ammonium persulfate oxidant system, Fe... 3+ The composite material prepared by the system has a higher specific surface area (54.2 m²). 2 g -1 vs 37.8m 2 g -1 It has better thermal stability (30% vs 14.44% of the remaining mass at 800℃) and a higher pyridine nitrogen content (44.06% vs 23.15%), and effectively inhibits the excessive oxidation of silicon, retaining more active silicon components (Si-Si bond content 18.88% vs 1.77%).

[0028] (3) The “silicon-embedded in a tube” structure constructed in this invention not only achieves effective confinement of silicon particles, but the hollow cavity inside the carbon tube also provides sufficient buffer space for the volume expansion of silicon during electrochemical cycling, allowing the silicon particles to fully release stress during lithium insertion and extraction, thus avoiding particle pulverization and cracking. Combined with the good mechanical strength and continuous three-dimensional conductive network of the carbon tube itself, the electrode maintains structural integrity and continuity of conductive path throughout the charging and discharging process.

[0029] (4) The composite material prepared by this invention exhibits stable and efficient electrochemical performance. The half-cell at 1 A g... -1 After 100 cycles at current density, the capacity retention rate reached 96%, at 5 A g. -1 It can still maintain approximately 250 mAh g after 1000 cycles at high current density. -1 The reversible capacitance. Its pseudocapacitance contributes 1.6 mV / s. -1 The scanning rate reaches 95%, and the lithium-ion diffusion coefficient reaches 10. -9 ~10 -11 cm 2 s -1 .

[0030] (5) The preparation method of the present invention is simple, mild, and requires little equipment. It does not require expensive precursors or complex equipment and is suitable for large-scale production. Methyl orange is used as a soft template and FeCl3 is used as an oxidant. The raw materials are cheap and readily available. The reaction is carried out in the aqueous phase, which is environmentally friendly and cost-controllable. Attached Figure Description

[0031] Figure 1 SEM images of the APS oxidant system: (a) PPy-CNTs precursor (APS, without MO template), (b) PPy-CNTs (APS, without MO template), (c) PPy-CNTs (APS, 0.1 g MO), (d) PPy-CNTs (APS, 0.2 g MO), (e) PPy-CNTs (APS, 0.3 g MO), (f) Si@PPy-CNTs (APS, 0.3 g MO, 0.05 g Si), (g) Si@PPy-CNTs (APS, 0.3 g MO, 0.1 g Si), (h) Si@PPy-CNTs (APS, 0.15 g MO, 0.15 g Si), (i) Si@PPy-CNTs (APS, 0.3 g MO, 0.2 g Si).

[0032] Figure 2SEM images of the FeCl3 oxidant system: (a) PPy-CNTs precursor (FeCl3, without MO template), (b) PPy-CNTs (FeCl3, 0.3 g MO), (c) Si@PPy-CNTs (FeCl3, 0.05 g Si), (df) Si@PPy-CNTs (FeCl3, 0.3 g MO, 0.1 g Si), (g) Si@PPy-CNTs (FeCl3, 0.3 g MO, 0.05 g Si), (h) Si@PPy-CNTs (FeCl3, 0.3 g MO, 0.15 g Si), (i) Si@PPy-CNTs (FeCl3, 0.3 g MO, 0.2 g Si).

[0033] Figure 3 The TEM image of Embodiment 1 of the present invention shows that silicon particles are confined inside the hollow cavity of carbon nanotubes, forming a silicon-embedded structure within the tube (abstract figure).

[0034] Figure 4 The images shown are STEM image (a) and EDS element distribution diagram (be) of Embodiment 1 of the present invention.

[0035] Figure 5 The XRD patterns are those of Example 1 and Comparative Examples 1, 3 and 4 of the present invention.

[0036] Figure 6 The Raman spectra of Example 1 and Comparative Examples 1-3 of this invention are shown.

[0037] Figure 7 These are the fine XPS spectra of Embodiment 1 and Comparative Examples 1-3 of the present invention.

[0038] Figure 8 The nitrogen adsorption-desorption isotherms are those of Example 1 and Comparative Examples 1-2 of this invention.

[0039] Figure 9 The thermogravimetric curves are those of Embodiment 1 and Comparative Examples 1-3 of the present invention.

[0040] Figure 10 The rate performance of Embodiment 1 and Comparative Examples 1-2 of the present invention is shown.

[0041] Figure 11 For the samples of Examples 1-3 of this invention, in 1A g -1 The loop performance is as follows.

[0042] Figure 12 Example 1 and Comparative Example 1 of the present invention were prepared at 5A g. -1 The loop performance is as follows.

[0043] Figure 13The images show the EIS spectra of different electrodes in this invention.

[0044] Figure 14 For each sample of the present invention at 0.4 mV s -1 CV curve at sweep speed.

[0045] Figure 15 This is a GITT analysis chart of sample example 1 of the present invention.

[0046] Figure 16 The image shows the SEM cross-sections of the electrode before and after cycling in Example 1 of the present invention (a: before cycling; b: after 100 cycles).

[0047] Figure 17 The diagram shows the cycle performance (a) and rate performance (b) of the full cell matched with the positive electrode in Example 1 of the present invention.

[0048] Figure 18 The diagram shows the long-cycle performance (a) and Ragone diagram (b) of the full cell of Sample Example 1 of the present invention matched with the positive electrode.

[0049] Figure 19 The images shown are TEM images (a) of Embodiment 2 and TEM images (b) of Embodiment 4 of the present invention.

[0050] Figure 20 This is a TEM image of Comparative Example 6 of the present invention. Detailed Implementation

[0051] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the present invention is not limited thereto.

[0052] Raw materials used in the examples and comparative examples: nano-silicon particles (average particle size of about 80 nm, purity >99%, purchased from Shanghai Chaowei Nanotechnology Co., Ltd.), methyl orange (analytical grade), pyrrole (purity >98%, distilled under reduced pressure before use), ferric chloride hexahydrate (analytical grade), and ammonium persulfate (analytical grade).

[0053] Electrode preparation and battery assembly: The composite material, Super P conductive agent, and polyacrylic acid binder were mixed at a mass ratio of 70:15:15, and water was added to form a slurry. This slurry was coated onto copper foil, vacuum dried, and then cut into sheets to form the working electrodes. The half-cell used a lithium sheet as the counter electrode, a 1M LiPF6 EC / DMC (volume ratio 1:1) solution as the electrolyte, and Celgard 2400 as the separator. The full-cell cathode was layered lithium-rich manganese oxide (LRMO, prepared according to existing technology), with an N / P ratio controlled at 1.1. Charge-discharge tests were performed on a Blue Electric testing system, and cyclic voltammetry and impedance were measured on an electrochemical workstation. All electrochemical data are based on the average of three parallel tests; error bars represent standard deviation.

[0054] Example 1 (Optimal solution, MO:Si=3:1, FeCl3 system)

[0055] Step 1: Formation of the Si@MO composite template system. At room temperature, 0.3 g of methyl orange was dissolved in 100 mL of deionized water, and the pH of the solution was adjusted to the range of 3.0–4.5. 0.1 g of nano-silicon particles were added, and the mixture was sonicated for 10 minutes to ensure uniform dispersion. Subsequently, the mixture was continuously stirred under magnetic stirring for 12 hours to ensure sufficient contact between the silicon particles and the methyl orange self-assembled structure, resulting in a Si@MO composite template system in which silicon particles are anchored within methyl orange micelles.

[0056] Step 2: Introduction of oxidizing agent. Dissolve 2.0 g of ferric chloride hexahydrate in 50 mL of deionized water, and then sonicate to ensure complete dissolution, yielding Fe. 3+ Oxidant solution. The oxidant solution was added to the Si@MO composite template system obtained in step one, and the mixture was stirred for 12 hours to ensure that the oxidant was evenly distributed in the composite template system.

[0057] Step 3: In-situ oxidative polymerization of pyrrole. Add 1 mL of pyrrole monomer purified by vacuum distillation to 50 mL of deionized water and sonicate for 10 minutes to form a pyrrole dispersion. Slowly add this pyrrole dispersion dropwise to the reaction system from Step 2, under Fe... 3+ Under the oxidative initiation of Fe, pyrrole monomers undergo in-situ oxidative polymerization along the surface of methyl orange micelles to form polypyrrole tubular structures. Simultaneously, silicon particles anchored within the methyl orange micelles are in-situ encapsulated within the generated polypyrrole tubes, resulting in a Si@PPy composite precursor where silicon particles are confined within the polypyrrole tubes. The polymerization reaction time is 12 hours. Although pyrrole has limited solubility in water, it is effective under the template of methyl orange micelles and Fe... 3+ In an aqueous system where oxidants coexist, pyrrole monomers can achieve uniform dispersion and ordered polymerization through hydrophobic interactions with the micelle surface and the traction of the oxidant.

[0058] Step 4: Carbonization Treatment. After the polymerization reaction, the product was separated by filtration and repeatedly washed with ultrapure water and anhydrous ethanol until the filtrate was colorless. It was then dried overnight under vacuum at 70°C to obtain black Si@PPy composite precursor powder. The precursor was placed in a tube furnace and heated at 5°C for 5 minutes under an argon atmosphere. -1 The heating rate was increased to 600℃, and calcination was carried out for 3 hours to convert polypyrrole into nitrogen-doped conductive carbon nanotubes, while maintaining the confinement of silicon particles within the carbon nanotubes. After furnace cooling to room temperature, a Si@PPy-CNTs composite material with black powdery silicon particles confined within nitrogen-doped one-dimensional carbon nanotubes was obtained. During carbonization, the methyl orange soft template decomposed into CO2 and NO at high temperature. xThe gaseous products were carried away by the argon gas flow. XPS full-spectrum scanning and TGA residual analysis confirmed that there was no methyl orange residual phase in the final product, and it had no adverse effect on the electrochemical performance of the negative electrode.

[0059] Thermogravimetric analysis (air atmosphere, heating rate 10℃ / min) was performed. -1 Measurements were taken at temperatures ranging from room temperature to 800°C, and the mass fraction of silicon in the Si@PPy-CNTs composite material prepared in this example was approximately 30.03%. BET specific surface area testing (77 K nitrogen adsorption) showed a specific surface area of ​​54.2 m². 2 g -1 XPS analysis (with charge correction at the C1s peak of 284.8 eV, and peak fitting of the N1s spectrum) showed that pyridine nitrogen accounted for 44.06% of the total nitrogen. In this example, the mass ratio of methyl orange to nano-silicon particles was 3:1 (falling within the range of 2 to 5:1 in claim 6), and the pyrrole monomer (density approximately 0.97 g / mL) was... -1 The mass ratio of FeCl3·6H2O (2.0 g, about 7.4 mmol) to nano-silicon particles is about 9.7:1 (falling within the range of 5 to 20:1 of claim 7), and the molar ratio of FeCl3·6H2O (2.0 g, about 7.4 mmol) to pyrrole monomer (1 mL, about 14.4 mmol) is about 1.2:1 (falling within the range of 1 to 2:1 of claim 8).

[0060] Example 2 (Verification of the lower limit boundary of MO:Si, MO:Si=2:1)

[0061] The difference from Example 1 is that the amount of silicon nanoparticles was adjusted to 0.15 g, so that the mass ratio of methyl orange (0.3 g) to silicon nanoparticles (0.15 g) was 2:1 (the lower limit of claim 6). The amount of pyrrole monomer was kept at 1 mL, and the amount of FeCl3·6H2O was kept at 2.0 g. The remaining steps were exactly the same as in Example 1.

[0062] SEM characterization ( Figure 2 h) shows that when MO:Si=2:1, a one-dimensional tubular structure can still be formed, with carbon nanotube diameters of approximately 80~100 nm. The continuity of the three-dimensional network structure is better than that of Example 1 ( Figure 2 The df (dt) decreased slightly but still maintained a tubular network morphology, without particle accumulation or irregular morphology. TEM characterization ( Figure 19 a) This indicates that the silicon particles are still effectively confined within the lumen, and the embedded silicon structure remains intact. Electrochemical performance tests show that at 1 A g... -1After 100 cycles at the current density, the capacity retention rate is approximately 89%, which is still significantly better than Comparative Example 1 (79%) and the pure silicon electrode (3%). This result indicates that the basic structure of "silicon embedded in the tube" can still be achieved and good electrochemical performance can be maintained even when the mass ratio of methyl orange to silicon is at the lower limit, verifying the rationality of the lower limit of the MO:Si=(2~5):1 range in claim 6.

[0063] Example 3 (Verification of the lower limit boundary of Pyr:Si, Pyr:Si=5:1)

[0064] The difference from Example 1 is that the amount of pyrrole monomer was adjusted to 0.52 mL (approximately 0.5 g), so that the mass ratio of pyrrole to nano-silicon particles (0.1 g) was 5:1 (the lower limit of claim 7). The amount of methyl orange was maintained at 0.3 g, and the amount of FeCl3·6H2O was maintained at 2.0 g. The remaining steps were exactly the same as in Example 1.

[0065] SEM characterization showed that when Pyr:Si = 5:1, a carbon nanotube interwoven network structure could still be formed, with carbon nanotube diameters of approximately 90–110 nm. The carbon nanotube walls were thinner than in Example 1, approximately 15–25 nm. A few areas showed discontinuities in the tube walls, but the overall tubular network structure remained intact, and no large areas of exposed silicon particles were observed. Electrochemical performance testing showed that at 1 A g… -1 After 100 cycles at the current density, the capacity retention rate is approximately 86%, significantly better than Comparative Example 1 and the pure silicon electrode. This result indicates that the material retains usable cycling performance even when the pyrrole dosage is at the lower limit, verifying the rationality of the lower limit of the Pyr:Si=(5~20):1 range in claim 7.

[0066] Example 4 (Verification of the upper limit boundary of Pyr:Si, Pyr:Si≈19:1)

[0067] The difference from Example 1 is that the amount of pyrrole monomer was adjusted to 1.94 mL (approximately 1.88 g), so that the mass ratio of pyrrole to nano-silicon particles (0.1 g) was approximately 19:1 (near the upper limit boundary of claim 7). The amount of methyl orange was maintained at 0.3 g, and the amount of FeCl3·6H2O was maintained at 2.0 g. The remaining steps were exactly the same as in Example 1.

[0068] SEM characterization showed that when Pyr:Si≈19:1, the carbon nanotube diameter increased significantly, to approximately 150~200 nm, the tube wall thickened considerably, and localized accumulation and adhesion occurred between the carbon nanotubes. TEM characterization ( Figure 19 (b) This indicates that the silicon particles remain effectively confined within the lumen, with no exposed or detached particles. Electrochemical performance testing shows that at 1 A g... -1After 100 cycles at the current density, the capacity retention rate was approximately 83%, mainly due to the excessively thick carbon layer leading to an extended lithium-ion diffusion path and insufficient cavity space limiting the buffering of silicon volume expansion. This result indicates that the material maintains usable performance even when the pyrrole content is at its upper limit, although there is a performance degradation trend, validating the rationality of setting the Pyr:Si upper limit to 20:1 in claim 7.

[0069] Comparative Example 1 (Preparation of Si@PPy-CNTs (APS))

[0070] This comparative example provides a control sample prepared using ammonium persulfate as the oxidant instead of FeCl3. Details are as follows:

[0071] Step 1: Same as Step 1 in Example 1.

[0072] Step 2: Dissolve 2.0 g of ammonium persulfate in 50 mL of deionized water and sonicate to ensure complete dissolution, obtaining an APS oxidant solution. Add this oxidant solution to the Si@MO composite template system obtained in Step 1 and continue stirring for 12 hours to ensure uniform distribution of the oxidant in the composite template system.

[0073] Steps three and four are the same as in Example 1.

[0074] XPS analysis showed that pyridine nitrogen accounted for only 23.15% of the total nitrogen in this comparative example, while graphitic nitrogen accounted for as high as 48.72%; the Si-Si bond ratio in the Si 2p spectrum was only 1.77%, indicating that silicon was severely oxidized during carbonization. Its specific surface area was 37.8 m². 2 g -1 This is lower than in Example 1. SEM characterization corresponds to Figure 1 g.

[0075] Comparative Example 2 (Preparation of silicon-free PPy-CNTs (FeCl3))

[0076] Except for the absence of silicon, the remaining steps are exactly the same as in Example 1. SEM characterization corresponds to... Figure 2 b. This comparative example is used to illustrate the effect of silicon introduction on the morphology and electrochemical performance of carbon nanotubes.

[0077] Comparative Example 3 (Preparation of Silicon-Free PPy-CNTs (APS))

[0078] Except for the absence of silicon, the remaining steps are exactly the same as in Comparative Example 1. SEM characterization corresponds to... Figure 1 e. XPS analysis showed that its pyridine nitrogen content was 25.41% and graphitic nitrogen content was 45.33%, confirming that the nitrogen doping characteristics of the APS system, which is dominated by graphitic nitrogen, are not affected by the presence or absence of silicon.

[0079] Comparative Example 4 (Preparation of a methyl orange-free template Si@PPy(FeCl3))

[0080] Except for the absence of a methyl orange template, the remaining steps are exactly the same as in Example 1. SEM characterization corresponds to... Figure 2 a) Precursor and subsequent carbonization morphology. The results show that without the methyl orange template, the product is in a particle-stacking state and cannot form a one-dimensional tubular structure. The silicon particles are agglomerated in large quantities, which verifies the necessity of the methyl orange template for constructing an integrated silicon-embedded structure within the tube.

[0081] Comparative Example 5 (verifying that MO:Si exceeds the upper limit, MO:Si=6:1)

[0082] The difference from Example 1 is that the amount of silicon nanoparticles was adjusted to 0.05 g, so that the mass ratio of methyl orange (0.3 g) to silicon nanoparticles (0.05 g) was 6:1, which exceeds the upper limit of 5:1 in claim 6. The remaining steps are exactly the same as in Example 1.

[0083] SEM characterization ( Figure 2 g) shows that when MO:Si=6:1, although the carbon nanotube structure forms, it exhibits excessive porosity and localized collapse, resulting in uneven tube diameter. Electrochemical performance tests show that at 1 A g -1 After 100 cycles at current density, the capacity retention rate was only about 68%, which verifies the rationality of setting the upper limit of MO:Si in claim 6 to 5:1.

[0084] Comparative Example 6 (verifying that MO:Si is below the lower limit, MO:Si = 1.5:1)

[0085] The difference from Example 1 is that the amount of silicon nanoparticles was adjusted to 0.2 g, so that the mass ratio of methyl orange (0.3 g) to silicon nanoparticles (0.2 g) was 1.5:1, which is lower than the lower limit of 2:1 in claim 6. The remaining steps are exactly the same as in Example 1.

[0086] SEM characterization ( Figure 2 i) shows that when MO:Si = 1.5:1, the carbon nanotube network is incomplete, with numerous broken and missing regions, and silicon particles are clearly exposed and aggregated, failing to form an effective three-dimensional conductive network. TEM characterization ( Figure 20 The results showed that the carbon nanotube wall was ruptured, with a large amount of silicon particles exposed on the outside of the carbon nanotube, and the internal confinement structure completely failed. Electrochemical performance tests showed that at 1 Ag... -1 After 100 cycles at current density, the capacity retention rate was only about 42%, far lower than that of Example 2 (89%), proving that once the lower limit of MO:Si=2:1 is crossed, the structure undergoes a qualitative change and the performance drops sharply, verifying the criticality and necessity of setting the lower limit of MO:Si to 2:1 in claim 6.

[0087] Material characterization

[0088] SEM analysis: Figure 1 The morphological evolution of the APS oxidant system under different conditions is shown. Figure 1 ab is the precursor and carbonized product without a MO template, both of which are granular aggregates without tubular structures. Figure 1 ce represents the carbon nanotube morphology under different MO dosages (0.1 g, 0.2 g, 0.3 g) in silicon-free conditions. The tubular structure tends to become more regular with increasing MO dosage. Figure 1 fi represents the morphology of the APS system under silicon-containing conditions with different MO / Si ratios: Figure 1 g (MO:Si=3:1, Comparative Example 1) has a relatively complete tubular structure, but the tube wall is thick and the tube diameter is uneven in some areas; Figure 1 The tubular structure of h (MO:Si=1:1) has clearly degraded, and silicon particle agglomeration has occurred; Figure 1 The tubular structure of i (MO:Si=1.5:1) is severely damaged, and a large number of silicon particles are exposed.

[0089] Figure 2 The morphology of the FeCl3 oxidant system under different conditions is shown. Figure 2 a represents the particle packing morphology of the precursor without a MO template. Figure 2 b represents a regular one-dimensional tubular structure formed under silicon-free conditions (MO=0.3g, Comparative Example 2). Figure 2 df shows the morphology of Example 1 (MO:Si=3:1) at different magnifications, exhibiting a high-density, continuous one-dimensional tubular interwoven network with carbon nanotube diameters of approximately 100~130 nm, continuous tube walls, and a dense and complete three-dimensional conductive network. Figure 2 h represents Example 2 (MO:Si=2:1), with carbon nanotubes having a diameter of approximately 80~100 nm. The network continuity is slightly lower than that of Example 1, but the tubular network structure is still maintained. Figure 2 g represents Comparative Example 5 (MO:Si=6:1, exceeding the upper limit), where the carbon nanotube structure is excessively porous and exhibits localized collapse. Figure 2 i is Comparative Example 6 (MO:Si=1.5:1, below the lower limit), where the carbon nanotube network is incomplete, with numerous fractured and missing areas, and silicon particles are clearly exposed and aggregated.

[0090] TEM analysis: TEM of Example 1 ( Figure 3 , Figure 4 The TEM (exposure propagation) of Example 2 shows that silicon nanoparticles are tightly encapsulated inside carbon nanotubes, exhibiting a typical hollow tubular structure. The clearly visible lattice fringes (interplanar spacing of 0.31 nm) of the silicon particles correspond to the Si (111) crystal planes. Figure 19 a) and TEM of Example 4 Figure 19b) Both indicate that under their respective preparation conditions, the silicon particles remain inside the cavity, and the confined structure is maintained. Comparative Example 6 TEM ( Figure 20 The results showed that when MO:Si = 1.5:1 (below the lower limit), the carbon nanotube wall cracked, and a large number of silicon particles were exposed on the outside of the carbon nanotube, completely destroying the confined structure inside the tube. STEM-EDS elemental surface scan analysis ( Figure 4 The results show that C, N, and Si elements are highly uniformly overlapped in the composite structure of Example 1, and no obvious phase separation phenomenon is observed, indicating that carbon nanotubes have achieved complete and uniform coating of silicon particles.

[0091] XRD patterns ( Figure 5 The results show that the composite material retains both the characteristic diffraction peaks of Si and the broadened, diffuse peaks of amorphous carbon. Compared to pure Si, the diffraction peak intensity of Si in the composite material is significantly reduced, which is due to the shielding effect of the carbon layer. The peak intensity of Si in Example 1 is significantly weaker than that in Comparative Example 1, indicating that the FeCl3 system has a better confinement effect on silicon particles and a stronger carbon shielding effect.

[0092] Raman spectroscopy ( Figure 6 The data shows that all samples were at approximately 1350 cm. -1 and 1580 cm -1 D and G peaks appeared at the point. The I_D / I_G value of Example 1 was 0.90, which was higher than that of Comparative Example 1 (0.69), indicating that the carbon material prepared by the FeCl3 system had a higher degree of defect and more disordered structure, which is beneficial for providing abundant electrochemical reaction active sites.

[0093] XPS analysis ( Figure 7 The results (ad) show that in Example 1, pyridine nitrogen accounted for 44.06% of the total nitrogen content, graphitic nitrogen accounted for 17.86%, and pyrrole nitrogen accounted for 38.08%. In Comparative Example 1 (APS system), pyridine nitrogen accounted for only 23.15%, graphitic nitrogen accounted for as high as 48.72%, and pyrrole nitrogen accounted for 28.13%. Pyridine nitrogen has higher electrochemical activity, which is beneficial for improving interfacial reaction kinetics. In Comparative Example 3, pyridine nitrogen accounted for 25.41% and graphitic nitrogen accounted for 45.33%, further confirming that the nitrogen doping type of the APS system, which is dominated by graphitic nitrogen, is not affected by the presence or absence of silicon. The Si 2p spectrum shows that in Example 1, the Si-Si bond ratio was 18.88% and the Si-O bond ratio was 81.12%, while in Comparative Example 1, the Si-Si bond ratio was only 1.77% and the Si-O bond ratio was as high as 98.23%, indicating that the FeCl3 system effectively suppressed the excessive oxidation of silicon and retained more active silicon components.

[0094] Nitrogen adsorption-desorption test ( Figure 8 This indicates that the specific surface area of ​​Example 1 is 54.20 m². 2 g-1 This is significantly higher than the 37.83 m in Comparative Example 1. 2 g -1 The pore size is mainly concentrated in the mesoporous range of 2~10 nm, forming a hierarchical pore structure, which is beneficial for electrolyte wetting, ion transport and volume expansion buffering.

[0095] TGA analysis ( Figure 9 The results show that the remaining mass of Example 1 at 800°C was 30.03%, which is much higher than that of Comparative Example 1 (14.44%), indicating that the FeCl3 oxidation system is more conducive to achieving high loading of silicon in a carbon matrix.

[0096] Electrochemical performance testing

[0097] The composite materials obtained in Examples 1-4 and Comparative Examples 1-6 were assembled into half-cells for electrochemical performance testing.

[0098] In 1 A g -1 Cyclic performance test at current density ( Figure 11 The results show that the initial discharge specific capacity of Example 1 is 901 mAh g. -1 After 100 cycles, the capacity retention rate reached 96%, far exceeding the 79% of Comparative Example 1. Example 2 (MO:Si = 2:1 lower limit) achieved a retention rate of approximately 89% after 100 cycles, Example 3 (Pyr:Si = 5:1 lower limit) achieved approximately 86%, and Example 4 (Pyr:Si ≈ 19:1 upper limit) achieved approximately 83%, all superior to Comparative Example 1. Comparative Example 5 (MO:Si = 6:1, exceeding the upper limit) achieved a capacity retention rate of only approximately 68% after 100 cycles, and Comparative Example 6 (MO:Si = 1.5:1, below the lower limit) achieved a capacity retention rate of only approximately 42%, demonstrating a precipitous drop in performance beyond the scope of the claims. Although the pure silicon electrode had an initial capacity as high as 2486 mAh g⁻¹, it still exhibited a significant performance degradation. -1 However, after 100 cycles, only 3% of the capacity remains.

[0099] In 5 A g -1 Long-cycle performance testing at high current density ( Figure 12 The results show that Example 1 can maintain approximately 250 mAh g after 1000 cycles. -1 The reversible capacity of the first example is maintained at a coulomb efficiency close to 100%, while the capacity of the second example rapidly decays to close to 0 after about 500 cycles.

[0100] Ratio performance test ( Figure 10 As shown, in Example 1, the current density was increased from 0.2 A g. -1 Increase to 15 Ag -1 Then restore to 0.2 A g -1During the process, the capacity can recover to approximately 1100 mAh g. -1 In 15 A g -1 Even at ultra-high current densities, this electrode can still output approximately 210 mAh g⁻¹. -1 Reversible capacity.

[0101] CV ( Figure 14 ) and GITT analysis ( Figure 15 This indicates that in Example 1, the pseudocapacitance contributes as much as 95% (1.6 mV s) during the lithium insertion / extraction process. -1 The lithium-ion diffusion coefficient remains stable at 10. -9 ~10 -11 cm 2 s -1 The range is better than that of Comparative Example 1. EIS fit analysis ( Figure 13 The results showed that the R_SEI, R_ct, and Warburg impedance of the FeCl3 system electrode were significantly lower than those of Comparative Example 1, indicating that it has advantages in terms of interface stability and reaction kinetics.

[0102] Example 1: Before cycling, the cross-sectional carbon coating layer was intact, and the three-dimensional network structure formed by carbon nanotubes was clear. Figure 16 a). After 100 cycles, the cross-sectional thickness expansion was significantly reduced, and the surface maintained a continuous and uniform microporous structure, with no obvious cracks or pulverization observed. Figure 16 (b) indicates that the electrode material has good structural integrity during long-term cycling.

[0103] Full battery performance test

[0104] Example 1 was assembled with a layered lithium-rich manganese oxide (LRMO) cathode to form a coin cell for performance testing. At 1 A g -1 After 100 cycles at current density, the capacity retention rate is as high as 94%. Figure 17 a) The coulombic efficiency stabilizes at close to 100%. At 3A g -1 At high current densities, the capacity retention rate still reaches 90% after 300 cycles. Figure 18 a). Ragone diagram ( Figure 18 b) shows that the energy density and power density of the material of the present invention are superior to those of similar systems reported at the full-cell level.

[0105] Overall Conclusion

[0106] This invention utilizes a "methyl orange soft template-assisted Fe" 3+An integrated strategy of "in-situ confinement of silicon by oxidative polymerization" has been successfully employed to construct a composite anode material in which silicon particles are in-situ confined within nitrogen-doped one-dimensional hollow carbon nanotubes. This method anchors silicon particles within methyl orange micelles before polymerization, allowing polypyrrole to simultaneously encapsulate silicon within the tubes during template polymerization. This achieves a strong interfacial bond between silicon and carbon nanotubes, as well as efficient intratube confinement.

[0107] Through systematic comparative experiments (Examples 1-4 and Comparative Examples 1-6), this invention fully verified the effective working window of key parameters: MO:Si=(2~5):1, Pyr:Si=(5~20):1. Within this range, the "silicon embedded in the tube" structure remains intact, and the electrochemical performance is excellent; once it exceeds this range—MO:Si=6:1 (Comparative Example 5) leads to a loose structure and a decrease in performance, MO:Si=1.5:1 (Comparative Example 6) leads to carbon nanotube rupture, exposed silicon particles, and complete failure of the confined structure in the tube—resulting in a precipitous drop in performance.

[0108] Compared with existing technologies, the "silicon-embedded in-tube" structure of this invention not only provides a continuous conductive network and sufficient volume buffer space, but also utilizes Fe... 3+ The system achieved a nitrogen-doped configuration dominated by pyridine nitrogen, which synergistically improved the rate performance and cycle stability of the material at multiple scales. The preparation method of this invention is simple, uses inexpensive raw materials, and is highly adaptable, making it valuable for applications in the next generation of high-energy-density lithium-ion batteries.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-confined one-dimensional tubular carbon network composite material, characterized in that: A three-dimensional continuous conductive network is formed by the interweaving of nitrogen-doped one-dimensional hollow carbon nanotubes. Nanoscale silicon particles are in-situ confined and encapsulated within the hollow cavities of the carbon nanotubes, forming an integrated core-shell-tube embedded structure with silicon particles as the core, the inner wall of the carbon nanotubes as the shell, and the hollow carbon nanotubes as the outer channel. The nitrogen-doped one-dimensional hollow carbon nanotubes are derived from polypyrrole through high-temperature carbonization in an inert atmosphere. The walls of individual carbon nanotubes completely and continuously encapsulate the silicon particles inside, forming a direct, binder-free contact interface between the silicon particles and the carbon nanotube walls. The composite material simultaneously meets the following structural, compositional, and physical property requirements: (1) Morphology and size: The diameter of the carbon nanotubes is 80-200 nm, and the diameter of the embedded nano-silicon particles is 50-100 nm. (2) Nitrogen doping configuration: X-ray photoelectron spectroscopy was used to determine the configuration. Charge correction was performed using the C1s characteristic peak at 284.8 eV. Peak fitting calculations were performed on the N1s spectrum to determine that the pyridine nitrogen in the carbon nanotube framework accounted for 40% to 47% of the total nitrogen mass. (3) Pore structure: The specific surface area of ​​the composite material was 30–60 m², as determined by the BET method with nitrogen adsorption at 77 K. 2 g -1 The pore size is concentrated in the mesoporous range of 2–10 nm; (4) Silicon loading: thermogravimetric analysis in air (heating rate 10℃ min) -1 (at room temperature to 800℃), with a total silicon element mass fraction of 25–35 wt%.

2. The silicon-confined one-dimensional tubular carbon network composite material according to claim 1, characterized in that: The composite material has a pore structure dominated by mesopores of 2–10 nm.

3. A method for preparing the silicon-confined one-dimensional tubular carbon network composite material according to any one of claims 1 to 2, characterized in that, The process involves a four-step sequential preparation: room temperature template self-assembly, oxidant dispersion, in-situ oxidative polymerization, and high-temperature carbonization under an inert atmosphere. The core raw material ratios and operating conditions for each step are essential technical features, and the process includes the following steps: (1) Template self-assembly: At room temperature (20-30℃), methyl orange was dissolved in deionized water, the pH of the solution was adjusted to 3.0-4.5, nano-silicon particles were added, and after ultrasonic dispersion, the mixture was stirred continuously for 6-24 h to achieve self-assembly, resulting in a Si@MO composite template system in which silicon particles were anchored inside methyl orange rod micelles; the mass ratio of methyl orange to nano-silicon particles was 2-5:

1. (2) Oxidant dispersion: Add ferric chloride hexahydrate aqueous solution to the Si@MO composite template system obtained in step (1) and stir continuously for 6 to 24 h to make the oxidant uniformly dispersed in the micelle template system; (3) In-situ polymerization: Under stirring, the aqueous dispersion of pyrrole monomer purified by vacuum distillation is slowly added dropwise to the system of step (2), and the reaction is kept at a constant temperature for 6-24 h after the addition is complete; the mass ratio of pyrrole monomer to nano-silicon particles in step (1) is 5-20:1, and the molar ratio of ferric chloride hexahydrate to pyrrole monomer is 1-2:1; in Fe 3+ Under the action of oxidation initiation, pyrrole polymerizes in an orderly manner along the outer wall of methyl orange micelles to form tubular polypyrrole, and simultaneously encapsulates the internal silicon particles in the inner lumen of the polypyrrole tubes to obtain the Si@PPy composite precursor. (4) High-temperature carbonization: The Si@PPy composite precursor was filtered, washed sequentially with deionized water and anhydrous ethanol, and then vacuum dried. It was then placed in a tube furnace under an argon inert atmosphere and carbonized at 5°C for 1 minute. -1 The heating rate was increased to 500–700℃, and the carbonization was carried out for 2–5 hours. The polypyrrole was carbonized into nitrogen-doped hollow carbon nanotubes, and the target composite material with silicon confined in the inner cavity of the carbon nanotubes was finally obtained.

4. The preparation method according to claim 3, characterized in that: Step (4) The carbonization process is further optimized with an argon atmosphere and calcination at 600℃ for 3 hours.

5. The preparation method according to claim 3, characterized in that: The pyrrole monomer used in step (3) is purified by vacuum distillation before use to remove monomer impurities.

6. The preparation method according to claim 3, characterized in that: Step (1) Adjust the pH of the methyl orange aqueous solution to 3.0-4.5 to stabilize the preparation of rod-shaped methyl orange micelle templates.

7. A lithium-ion battery negative electrode, characterized in that: The negative electrode active material is the silicon-confined one-dimensional tubular carbon network composite material as described in any one of claims 1 to 2. The negative electrode slurry is prepared by mixing the active material, Super P conductive agent, and polyacrylic acid binder with water at a mass ratio of 70:15:

15. The slurry is coated on a copper foil current collector and then vacuum dried, rolled, and cut to obtain the negative electrode sheet.

8. A lithium-ion battery, characterized in that: It comprises the lithium-ion battery negative electrode, positive electrode, electrolyte, and Celgard 2400 separator as described in claim 7; the electrolyte is 1 mol / L. -1 The lithium-ion battery is a 1:1 mixture of LiPF6 EC / DMC volume ratio; the N / P ratio of the positive and negative electrodes is controlled at 1.1; the positive electrode is further preferably a layered lithium-rich manganese oxide LRMO; the lithium-ion battery is a consumer electronics battery, a power battery or an energy storage battery.

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