Single-walled carbon nanotube silicon-carbon composite material as well as preparation method and application thereof

Abstract

The invention discloses a single-walled carbon nanotube silicon-carbon composite material and a preparation method and application thereof, and belongs to the technical field of new energy, the single-walled carbon nanotube composite material comprises silicon particles, a carbon shell layer and a single-walled carbon nanotube wrapping layer; the microstructure unit of the single-walled carbon nanotube composite material has the following structural general formula: Si (at) C (at) SWCNT, wherein Si represents a silicon particle, C represents a carbon shell layer wrapping the outer surface of the silicon particle, and SWCNT represents a single-walled carbon nanotube wrapping layer tightly wrapping the outer surface of the carbon shell layer; the single-walled carbon nanotube wrapping layer is of a two-dimensional net bag-shaped layer structure which is formed by assembling a non-tube-bundle type single dispersed oxidized single-walled carbon nanotube as an assembling element. The composite material has excellent electrochemical performance.

Description

Technical Field

[0001] The present application relates to a single-walled carbon nanotube silicon-carbon composite material and a preparation method and application thereof, belonging to the technical field of new energy. Background Art

[0002] Lithium-ion batteries (LIBs) have become the primary power source for new energy vehicles and portable electronic devices due to their high energy density, long cycle life, and excellent safety. Currently, the most widely used anode material in commercial LIBs is graphite, whose reversible specific capacity approaches the theoretical specific capacity of 372 mAh / g. Therefore, to increase the energy density of LIBs, anode materials with higher specific capacities are needed. Silicon, with its high theoretical capacity (≈4200 mAh g⁻¹), has attracted attention in the development of high-energy-density LIBs. However, silicon suffers from volume expansion (≈400%) and poor conductivity during charge and discharge, hindering its commercialization. A common strategy to address these issues is to construct silicon-carbon composites, leveraging the advantages of carbon materials, such as conductivity or structural stability, by combining them with silicon to complement each other and improve the electrochemical performance of silicon anode materials. For example, silicon-carbon anode materials can be obtained by uniformly physically mixing silicon particles with a conductive carbon material, or silicon-carbon composites can be obtained by coating silicon particles with a carbon shell. These strategies are effective in alleviating silicon's poor electrical conductivity and inhibiting particle volume expansion. To further improve the electrochemical performance of silicon-carbon electrode materials, single-walled carbon nanotubes (SWCNTs), with their superior electrical conductivity, are often added to the aforementioned silicon-carbon composites to further enhance the overall conductivity of the electrode and the stability of the electrode material during charge and discharge cycles. However, the application of single-walled carbon nanotubes in silicon-carbon lithium-ion batteries still faces many problems: 1. Low purity, which affects the electrochemical properties of electrode materials: the purity of the currently prepared single-walled carbon nanotubes is generally low, and they contain a considerable amount of amorphous carbon, crystalline carbon particles and fullerene spheres, metal catalyst particles, and carbon spheres coated with metal catalyst particles, and purification is very difficult; 2. Poor dispersibility: They are insoluble in many solvents and difficult to disperse, which affects their use in the production of silicon-carbon electrodes; 3. Bundle-type single-walled carbon nanotubes: The single-walled carbon nanotubes prepared by the currently widely used preparation methods are all bundle-type, not single discrete ones (single tube diameter is about 1-2nm), but large bundles formed by densely stacking multiple tubes (bundle diameter is about 10-50nm). The mechanical flexibility and aspect ratio are weakened, and it is difficult to exert the intrinsic advantages. Not only does it invisibly waste the amount of single-walled carbon nanotubes, but it also increases the cost. 4. When bundled single-walled carbon nanotubes are used as conductive additives in silicon-carbon materials, the single-walled carbon nanotube bundles usually shuttle between the silicon-carbon particles, and have point-to-line physical contact with the silicon-carbon particles. Although this can improve the network conductivity to a certain extent, it has limited effect in suppressing the volume expansion of the silicon-carbon anode during the charge and discharge process and maintaining the stability of the electrode structure. Summary of the Invention

[0003] In order to solve the above-mentioned technical problems existing in the application of single-walled carbon nanotubes in silicon-carbon anode materials, the present application provides a single-walled carbon nanotube silicon-carbon composite material and its preparation method and application, using non-tube-bundled single dispersed single-walled carbon nanotubes as assembly units to tightly wrap the outer surface of silicon-carbon particles in a net-bag-like manner to construct a multi-level carbon-coated silicon-carbon composite material and use it as an anode material in lithium-ion batteries.

[0004] This application adopts the following technical solutions:

[0005] A single-walled carbon nanotube silicon-carbon composite material, comprising silicon particles, a carbon shell layer, and a single-walled carbon nanotube wrapping layer;

[0006] The microstructure unit of the single-walled carbon nanotube composite material has the following general structural formula: Si@C@SWCNT;

[0007] Wherein, Si represents silicon particles, C represents the carbon shell layer wrapped around the outer surface of the silicon particles, and SWCNT represents the single-walled carbon nanotube wrapping layer tightly wrapped around the outer surface of the carbon shell layer;

[0008] The single-walled carbon nanotube wrapping layer is a two-dimensional net-bag-like layer structure formed by assembling non-bundled single dispersed oxidized single-walled carbon nanotubes as assembly units.

[0009] In the present application, the silicon particles are the innermost core, the carbon shell layer is coated on the outer surface of the silicon particles, and the single-walled carbon nanotube coating layer is a two-dimensional net-bag-shaped coating layer tightly wrapped on the outer surface of the carbon shell layer C. The two-dimensional net-bag-shaped coating layer is assembled with non-tube-bundled single dispersed oxidized single-walled carbon nanotubes as assembly units.

[0010] Optionally, the silicon particles are nanoparticles.

[0011] Optionally, the silicon particles have a particle size of 10 to 500 nm.

[0012] Optionally, the carbon shell layer consists of porous carbon.

[0013] Optionally, the thickness of the carbon shell layer is 5 to 60 nm.

[0014] Optionally, the content of the single-walled carbon nanotube wrapping layer in the single-walled carbon nanotube-silicon-carbon composite material is 0.2-10 wt %.

[0015] Optionally, the content of the single-walled carbon nanotube wrapping layer in the single-walled carbon nanotube silicon-carbon composite material is selected from any value among 0.2wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.1wt%, 1.3wt%, 1.5wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% or any range value between two of them.

[0016] Optionally, the content of the single-walled carbon nanotube wrapping layer in the single-walled carbon nanotube-silicon-carbon composite material is 1.5-5 wt %.

[0017] Optionally, the content of the single-walled carbon nanotube wrapping layer in the single-walled carbon nanotube-silicon-carbon composite material is 3.4 wt %.

[0018] Optionally, the content of the silicon particles in the single-walled carbon nanotube silicon-carbon composite material is 30 to 90 wt%.

[0019] Optionally, the content of the silicon particles in the single-walled carbon nanotube silicon-carbon composite material is selected from any value among 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt% or any range value between two of them.

[0020] Optionally, the content of the silicon particles in the single-walled carbon nanotube silicon-carbon composite material is 60-80 wt%.

[0021] Optionally, the content of the silicon particles in the single-walled carbon nanotube silicon-carbon composite material is 70-75 wt %.

[0022] According to a second aspect of the present application, there is provided a method for preparing the above-mentioned single-walled carbon nanotube silicon-carbon composite material, comprising the following steps:

[0023] a1) modifying the outer surface of the Si@C composite material with polyquaternary ammonium salt (PQAS) to obtain Si@C-PQAS;

[0024] b1) wrapping a single-walled carbon nanotube wrapping layer tightly around the outer surface of Si@C-PQAS, and annealing under an inert atmosphere or under vacuum to obtain a single-walled carbon nanotube silicon-carbon composite material;

[0025] The Si@C composite material refers to a composite material formed by a carbon shell coating the outer surface of silicon particles.

[0026] The single-walled carbon nanotube wrapping layer described in step b1) is a two-dimensional net-bag-shaped coating layer tightly wrapped around the outer surface of the carbon shell layer C. The two-dimensional net-bag-shaped coating layer is assembled with non-bundled single dispersed oxidized single-walled carbon nanotubes as assembly units.

[0027] Optionally, the step a1) of modifying the polyquaternary ammonium salt on the Si@C-PQAS is adsorbing and / or bonding the polyquaternary ammonium salt on the Si@C surface.

[0028] Optionally, step a1) comprises: adding a polyquaternium salt to a Si@C dispersion, and ultrasonically treating to obtain Si@C-PQAS.

[0029] Optionally, the ultrasonic treatment time is 0.1 to 1 hour.

[0030] Optionally, step b1) includes: adding a solution containing non-tubular single dispersed oxidized single-walled carbon nanotubes to the dispersion of Si@C-PQAS, so that the non-tubular single dispersed oxidized single-walled carbon nanotubes are tightly wrapped along the outer surface of Si@C-PQAS and wrapped on the surface of Si@C-PQAS, and annealing at 300-1000°C in an inert atmosphere or vacuum for 0.5-12h to obtain the single-walled carbon nanotube silicon-carbon composite material.

[0031] Optionally, the polyquaternary ammonium salt in step a1) is at least one selected from polydiallyldimethylammonium chloride (PDDA), polydimethyldiallylammonium chloride, polymethacrylamidepropyltrimethylammonium chloride, and polymethacrylamidepropyldodecyldimethylammonium chloride.

[0032] Optionally, in step b1), the solution containing the non-bundled single dispersed oxidized single-walled carbon nanotubes is added to the Si@C-PQAS dispersion by dropwise addition and sufficient stirring.

[0033] Optionally, the inert atmosphere is selected from at least one of nitrogen and rare gases.

[0034] Optionally, the concentration of Si@C-PQAS in the Si@C-PQAS dispersion in step b1) is 0.05-1 g / L.

[0035] Optionally, the concentration of Si@C-PQAS in the Si@C-PQAS dispersion in step b1) is selected from any value selected from 0.05 g / L, 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.04 g / L, 0.05 g / L, 0.1 g / L, 0.3 g / L, 0.5 g / L, 0.8 g / L, 1 g / L, or any range therebetween.

[0036] The concentration of the non-bundled single dispersed oxidized single-walled carbon nanotubes in the solution containing the non-bundled single dispersed oxidized single-walled carbon nanotubes is 0.001-0.05 g / L.

[0037] The concentration of non-tubular single dispersed oxidized single-walled carbon nanotubes in the solution containing non-tubular single dispersed oxidized single-walled carbon nanotubes is selected from any value among 0.001 g / L, 0.002 g / L, 0.003 g / L, 0.004 g / L, 0.005 g / L, 0.01 g / L, 0.02 g / L, 0.03 g / L, 0.04 g / L, 0.05 g / L, or any range between two values.

[0038] Optionally, the annealing temperature in step b1) is selected from any value of 300°C, 350°C, 400°C, 450°C, 550°C, 650°C, 750°C, 850°C, 950°C, 1000°C or any range therebetween.

[0039] Optionally, the annealing time in step b1) is 0.5 to 12 hours.

[0040] Optionally, the annealing time in step b1) is selected from any value of 0.5 hours, 1 hour, 2 hours, 5 hours, 8 hours, 10 hours, 12 hours, or any range therebetween.

[0041] Optionally, the preparation method of the single-walled carbon nanotube silicon-carbon composite material comprises the following steps:

[0042] (1) Preparation of a dispersed aqueous solution of non-bundled single dispersed oxidized single-walled carbon nanotubes:

[0043] Potassium permanganate solid is first added to an excess of concentrated sulfuric acid solution for complete reaction, and then the original single-walled carbon nanotube ash is added to the above solution and stirred evenly. The resulting reaction mixture is stirred and reacted at a temperature of 50-60° C. for 2-3 hours. The reaction mixture is then diluted with deionized water, and then an excess of hydrogen peroxide solution is added to reduce and remove the manganese dioxide solid generated during the reaction. After filtering through a microporous filter membrane and washing with a hydrochloric acid solution, the resulting solid is washed with water to remove some impurity ions in the solution. When the pH of the single-walled carbon nanotube mixed aqueous solution is 4-5, the solution is centrifuged at 5000-14000 rpm for 30 minutes, and then the upper homogeneous solution is taken out. The homogeneous solution is then filtered and washed with water to collect the black solid, which is then dissolved in water before drying to obtain the dispersed aqueous solution of the non-bundled single dispersed single-walled carbon nanotubes.

[0044] Optionally, the non-bundled single dispersed single-walled carbon nanotubes refer to single-walled carbon nanotubes that do not exist in a bundle form, but each single-walled carbon nanotube is independently peeled off from the single-walled carbon nanotube bundle and exists in a discrete form.

[0045] Optionally, the purity of the single-walled carbon nanotubes in the original single-walled carbon nanotube ash is 60-95 wt%.

[0046] (2) Preparation of Si@C composite materials:

[0047] Silicon powder is dispersed in a mixed solution of water and anhydrous ethanol, and dopamine hydrochloride and ammonia water are added in sequence. Stirring is continued until the discrete silicon particles are completely coated with polydopamine (PDA). Si@PDA core-shell structure particles are obtained by washing and centrifugation. The Si@PDA core-shell structure particles are then placed in an inert atmosphere and heated at 600-1000°C for 1-12 hours to carbonize the polydopamine and generate the Si@C composite material.

[0048] (3) Modify the outer surface of Si@C with polyquaternary ammonium salt to prepare Si@C-PQAS:

[0049] Polyquaternium salt is added to the Si@C dispersion, and ultrasonic treatment is carried out for 0.1 to 1 hour with continuous stirring until a good colloidal dispersion is obtained. The dispersion is then centrifuged and washed to remove free polyquaternium salt that is not modified on the Si@C surface, thereby obtaining Si@C surface-modified with polyquaternium salt, namely, the Si@C-PQAS.

[0050] (4) Preparation of Si@C@SWCNT composite materials:

[0051] The Si@C-PQAS is dispersed in water to form a dispersion with a concentration of 0.05 to 1 g / L, and then added dropwise to a dispersion aqueous solution of non-tubular single dispersed oxidized single-walled carbon nanotubes with a concentration of 0.001 to 0.05 g / L, and stirred continuously until the Si@C-PQAS and the non-tubular single dispersed oxidized single-walled carbon nanotubes are completely electrostatically assembled. The obtained product is filtered, washed, and dried, and then annealed at 300 to 1000° C. in an inert atmosphere or vacuum for 0.5 to 12 hours to obtain a Si@C@SWCNT composite material, that is, the single-walled carbon nanotube silicon-carbon composite material.

[0052] Optionally, in step (1), the impurities in the original single-walled carbon nanotube ash include at least one of crystalline carbon sphere particles, multi-walled carbon nanotubes, graphite sheets, graphene sheets, fullerene spheres, metal nanoparticles, and metal crystalline carbon particles.

[0053] Optionally, the metallic crystalline carbon particles are crystalline carbon sphere particles coated with metal nanoparticles.

[0054] Optionally, the purity of the single-walled carbon nanotubes in the non-bundled single dispersed oxidized single-walled carbon nanotubes is 99.5-100 wt %.

[0055] Optionally, the surfaces of the single-walled carbon nanotubes in the dispersed aqueous solution of the non-bundled single dispersed single-walled carbon nanotubes contain oxygen-containing functional groups.

[0056] The oxygen-containing functional groups include hydroxyl, carboxyl and epoxy groups.

[0057] Optionally, the polyquaternary ammonium salt described in step (3) is selected from at least one of polydiallyldimethylammonium chloride (PDDA), polydimethyldiallylammonium chloride, polymethacrylamidepropyltrimethylammonium chloride, and polymethacrylamidepropyldodecyldimethylammonium chloride.

[0058] Optionally, the modification of the polyquaternary ammonium salt on the Si@C-PQAS is adsorption and / or bonding of the polyquaternary ammonium salt on the Si@C surface.

[0059] Optionally, the Si@C-PQAS is dispersed in water, has a positive Zeta potential, and has a positive charge on the surface of the particles.

[0060] Optionally, the Si@C@SWCNT composite material described in step (4) comprises silicon particles, a carbon shell layer and a single-walled carbon nanotube wrapping layer, and its microstructure unit has the following general structural formula: Si@C@SWCNT, wherein Si represents silicon particles, C represents a carbon shell layer wrapped around the outer surface of the silicon particles, and SWCNT represents a single-walled carbon nanotube wrapping layer; the silicon particles are the innermost core, the carbon shell layer is coated on the outer surface of the silicon particles, and the single-walled carbon nanotube wrapping layer is a two-dimensional net-bag-shaped coating layer tightly wrapped around the outer surface of the carbon shell layer C, and the two-dimensional net-bag-shaped coating layer is assembled with a non-tube-bundled single dispersed oxidized single-walled carbon nanotube as the assembly unit.

[0061] Optionally, the inert atmosphere is at least one of nitrogen or a rare gas.

[0062] According to a third aspect of the present application, there is provided an application of the above-mentioned single-walled carbon nanotube silicon-carbon composite material or the single-walled carbon nanotube silicon-carbon composite material prepared according to the above-mentioned preparation method in an electrode material.

[0063] Optionally, the electrode material is selected from the electrode material of a primary electrochemical generator, a secondary electrochemical generator, and a high-energy generator.

[0064] According to a fourth aspect of the present application, a secondary battery is provided, wherein the anode material of the secondary battery contains the above-mentioned single-walled carbon nanotube silicon-carbon composite material or the single-walled carbon nanotube silicon-carbon composite material prepared according to the above-mentioned preparation method;

[0065] Optionally, the secondary battery is a lithium-ion battery.

[0066] Optionally, the secondary battery includes a cathode, an anode and an electrolyte.

[0067] The anode comprises: a current collector and an anode material supported on the current collector; wherein the anode material contains the above-mentioned single-walled carbon nanotube silicon-carbon composite material.

[0068] The beneficial effects of this application include:

[0069] (1) The preparation method of the single-walled carbon nanotube silicon-carbon composite material provided in this application directly uses original single-walled carbon nanotube ash containing a large number of complex impurities as the initial raw material, and through the action of potassium permanganate and concentrated sulfuric acid, combined with specific washing, separation and purification parameters, the pH is controlled at 4-5, so that the original single-walled carbon nanotube ash containing a large number of complex system impurities is converted into ultra-high-purity non-bundled single dispersed oxidized single-walled carbon nanotubes. The ultra-high-purity non-bundled single dispersed oxidized single-walled carbon nanotubes have three characteristics at the same time: first, the purity of the single-walled carbon nanotubes is as high as 99.5% or more; second, the obtained single-walled carbon nanotubes are non-bundled and have a higher aspect ratio; and third, they are soluble in a variety of aqueous and organic solvents. The above preparation method solves the three difficult problems of single-walled carbon nanotubes in the application of silicon-carbon electrodes. In addition, this method controls the order of adding raw materials, which can retain the length of the original single-walled carbon nanotubes as much as possible, effectively reducing the excessive shortening of single-walled carbon nanotubes caused by premature oxidation of single-walled carbon nanotube raw materials by concentrated sulfuric acid, thereby obtaining single-walled carbon nanotubes that are longer than those in the existing technology, and is expected to achieve better mechanical and mechanical properties.

[0070] (2) The preparation method of the single-walled carbon nanotube silicon-carbon composite material provided by the present application is an electrostatic orderly assembly under a uniform liquid phase, and the non-tube-type single dispersed oxidized single-walled carbon nanotube can form a uniform and independent coating on each microscopic silicon-carbon particle. Under liquid phase conditions, the surface of the silicon-carbon particles is positively charged, and the surface of the non-tube-type single dispersed oxidized single-walled carbon nanotube is negatively charged. Under the orderly driving of the electrostatic effect, the silicon-carbon particles and the non-tube-type single dispersed oxidized single-walled carbon nanotube complete orderly electrostatic adsorption, so that the single-walled carbon nanotube can be orderly and tightly wrapped on the outer surface of the silicon-carbon particles. Then, after annealing, the surface groups of the single-walled carbon nanotubes and the surface groups of the silicon-carbon particles are bonded to form a stable covalent or hydrogen bond force. At the same time, the cross-links between each single-walled carbon nanotube will also form a stable covalent or hydrogen bond force, so that the entire composite material forms a stable cross-linking system. The overall structure has strong mechanical strength and flexibility, which is beneficial to the stress release of the electrode material during the charge and discharge process and the stability of the overall structure.

[0071] (3) The preparation method of the single-walled carbon nanotube silicon-carbon composite material provided in this application, the order and method of adding the solution containing non-bundled single dispersed oxidized single-walled carbon nanotubes to the Si@C-PQAS dispersion (dropwise addition and sufficient stirring), and the very dilute concentration of the single-walled carbon nanotubes are to prevent the rapid agglomeration of the single-walled carbon nanotubes before coating, so as to ensure the uniformity and effectiveness of the coating process.

[0072] (4) The single-walled carbon nanotube silicon-carbon composite material prepared in the present application has a structure in which a two-dimensional net-like wrapping layer formed by single-walled carbon nanotubes is tightly wrapped on the outer surface of the carbon shell to form a wrapping layer, which makes the best use of the excellent aspect ratio and flexibility of non-tube-bundled single-walled carbon nanotubes. Each single-walled carbon nanotube is tightly attached to the outer surface of the carbon shell, realizing the line-surface contact between the two-dimensional linear single-walled carbon nanotube and the carbon shell, effectively improving the electronic and ion conductivity of the electrode active material; at the same time, each single-walled carbon nanotube is cross-linked with each other to form a stable two-dimensional spherical network wrapped on the outer surface of the carbon shell. This wrapping mechanism and structure effectively suppresses the stress generated by the expansion and contraction of the silicon-carbon electrode material during the charge and discharge process, and effectively maintains the mechanical stability of the overall structure of the electrode material and the effectiveness of the conductive network. In the existing technology, single-walled carbon nanotubes are directly added to silicon-carbon materials. Since traditional single-walled carbon nanotubes are bundle-type, and the cross-sectional diameter of the bundle is usually 10-50nm, when they are directly compounded and applied to silicon-carbon materials, they usually do not form a coating structure for the silicon-carbon particles, but instead shuttle between the silicon-carbon particles to form a conductive network of point-line contact. The conductive mechanism of this conductive network is weaker than the line-surface conductive mechanism, and no stable coating network is formed, so the effect of inhibiting the expansion of the electrode material is limited.

[0073] (5) The single-walled carbon nanotube silicon-carbon composite material prepared in this application has a net-shaped single-walled carbon nanotube in the outermost layer, and a single single-walled carbon nanotube has high conductivity. They can provide a more reliable electron transmission path, increase the conductivity of the negative electrode material, reduce resistance, and improve the rate performance of the battery; secondly, the two-dimensional net-shaped wrapping layer formed by a single single-walled carbon nanotube has good mechanical strength and can effectively relieve the stress caused by the expansion of silicon particles, thereby reducing its structural damage and powder aggregation, and improving the cycle stability of the negative electrode; in addition, the net-shaped single single-walled carbon nanotube formed on the periphery can also stabilize the contact between silicon and carbon particles and reduce the interface reaction between silicon and carbon particles and the electrolyte. Such a structure is conducive to rapid ion diffusion and buffering volume changes while maintaining structural stability and high cycle stability. As a lithium ion anode material, it exhibits high specific capacity, excellent rate performance and outstanding cycle stability. At 8A g -1 The current density was 834 mAh g -1 High specific capacity at 1Ag -1After 500 cycles, it still maintains 1267mAh g -1 The specific capacity of the battery is very high, and it has a long-life cycle performance. In addition, the first coulombic efficiency is as high as 88.7%, which has the advantage of high first efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 (a) is a schematic diagram of the process for preparing Si@C@SWCNT composite materials. The first step is to coat the surface of the silicon particles with a carbon shell layer, and the second step is to self-assemble a single-walled carbon nanotube coating layer on the coated carbon layer; (b), (c), and (d) are scanning electron microscope photos of Si, Si@C, and Si@C@SWCNT during the preparation of Si@C@SWCNT composite materials, respectively.

[0075] Figure 2 (a), (b), and (c) are the XRD, RAMAN, and TG spectra of Si, Si@C, and Si@C@SWCNT in the examples; (d) is the BET specific surface area and pore size distribution test curve of Si@C@SWCNT.

[0076] Figure 3 This is a charge and discharge cycle performance diagram when Si, Si@C, and Si@C@SWCNT are used as anode materials for ion batteries in the examples.

[0077] Figure 4 This is a rate performance diagram when Si, Si@C, and Si@C@SWCNT are used as anode materials for ion batteries in the examples.

[0078] Figure 5 These are scanning electron microscope photos of the volume expansion and surface microstructure changes of Si, Si@C, and Si@C@SWCNT electrode materials during the charge and discharge process in the examples, where (a), (b), and (c) are the original cross-section, cross-section after charge and discharge cycles, and top view of the surface after charge and discharge cycles of the Si electrode material during the charge and discharge process; (d), (e), and (f) are the original cross-section, cross-section after charge and discharge cycles, and top view of the surface after charge and discharge cycles of the Si@C electrode material during the charge and discharge process; (h), (i), and (j) are the original cross-section, cross-section after charge and discharge cycles, and top view of the surface after charge and discharge cycles of the Si@C electrode material during the charge and discharge process.

[0079] Figure 6 This is a transmission electron microscope photo of Si@C@SWCNT prepared in Example.

[0080] Figure 7 This is a transmission electron microscope photograph of the original single-walled carbon nanotube ash in Example.

[0081] Figure 8This is a transmission electron microscope photograph of a non-bundled single dispersed oxidized single-walled carbon nanotube in the example.

[0082] Figure 9 The charge-discharge cycle performance diagram of Si@C-SWCNT and Si@C@RGO prepared in the comparative example is a lithium-ion battery assembled in the same way as in Example 1 and tested using the same test method.

[0083] Figure 10 This is a scanning electron microscope image of Si@C-SWCNT.

[0084] Figure 11 This is a scanning electron microscope image of Si@C@RGO. DETAILED DESCRIPTION

[0085] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0086] Unless otherwise specified, the raw materials in the examples of this application were purchased from commercial sources, wherein graphene oxide GO was prepared by the inventors according to the literature (J. Mater. Chem., 2011, 21, 7376–7380).

[0087] Unless otherwise specified, conventional methods were used for testing, and the instrument settings were all those recommended by the manufacturers. Transmission electron microscopy (TEM, FEI, Tecnai F20) was used for transmission electron microscopy analysis; X-ray powder diffractometer (XRD, Rigaku, Miniflex600) was used for phase analysis of the compounds; an automatic gas physical adsorption instrument (Autosorb-iQ2-XR, Quantachrome Instruments, USA) was used to test the specific surface area and perform pore structure analysis; an X-ray photoelectron spectrometer (XPS, Thermo Fisher, ESCALAB) was used to analyze the surface area and pore structure of the compounds. 250Xi) for X-ray photoelectron spectroscopy analysis; an electrochemical workstation (Shanghai Chenhua, CHI660D) for cyclic voltammetry and electrochemical impedance spectroscopy; a field emission scanning electron microscope (FESEM, SU-8010, Hitachi, Japan) for scanning electron microscopy analysis; a synchronous thermal analyzer (TG / DTA, STA449F3, Netzsch) for thermogravimetric analysis; a battery testing system (Wuhan Landian, CT3001A) for battery performance testing; and a laser Raman spectrometer (RAMAN, LabRam HR Evo) for testing.

[0088] Example 1

[0089] (1) Preparation of a dispersed aqueous solution of non-bundled single-dispersed oxidized single-walled carbon nanotubes:

[0090] 0.4 g of potassium permanganate solid was added to a beaker containing 15 ml of concentrated sulfuric acid (98 wt%). After stirring for complete reaction, 0.2 g of single-walled carbon nanotube ash was poured into the above solution and stirred thoroughly. The mixture was then placed in a constant temperature oil bath at 50°C and stirred for 2 hours. During this period, a glass cover was placed to prevent the concentrated sulfuric acid from absorbing water. After cooling to room temperature, the mixture was diluted with about 100 ml of deionized water while stirring continuously. About 10 ml of 30% hydrogen peroxide solution was then added. After stirring for 15 minutes, the mixture was filtered through a microporous filter membrane. The obtained black solid is directly poured into 100 ml of 4% dilute hydrochloric acid, stirred and washed, then filtered through a microporous filter membrane, and filtered and washed with deionized water. The obtained black solid is then poured into 200 ml of deionized water and fully stirred. It is then centrifuged at 14,000 rpm for 30 minutes. After stratification, the supernatant is discarded, and 200 ml of deionized water is continued to be added to the centrifuge tube, stirred and washed, and then centrifuged again. The layers are separated and the supernatant is discarded. The centrifugation and washing are repeated 2-3 times until the pH value of the mixed solution is 4 when deionized water is added to the centrifuge tube. The mixture is centrifuged again at 10,000 rpm for 30 minutes, the supernatant is extracted, and the dispersed solution is collected and filtered and washed with a microporous filter membrane to remove residual impurity ions. The collected black solid is dissolved in deionized water to obtain a dispersed aqueous solution of non-tubular single dispersed oxidized single-walled carbon nanotubes.

[0091] The purity of the non-bundled, single-piece, dispersed oxidized single-walled carbon nanotubes is over 99.5 wt%. Elemental analysis using an X-ray energy spectrometer reveals no residual metal impurities. Transmission electron microscopy and scanning electron microscopy reveal no other impurities, such as graphene, multi-walled carbon nanotubes, carbon particles, or metal particles.

[0092] The bundle diameter of the non-bundled single dispersed oxidized single-walled carbon nanotube is significantly smaller than that of the original single-walled carbon nanotube. Figure 8 ).

[0093] The surface of the ultra-high-purity single-walled carbon nanotube is connected with oxygen-containing groups, which include hydroxyl groups, epoxy groups, carboxyl groups and carbonyl groups.

[0094] The purity of the single-walled carbon nanotube raw ash is 75wt%; the impurities in the single-walled carbon nanotube raw ash include crystalline carbon sphere particles, graphene sheets, fullerene spheres, metal crystalline carbon particles and multi-walled carbon nanotubes, wherein the content of metal impurities is 8wt%.

[0095] The particle size of the metal particles in the metal crystal carbon particles is 1-50 nm; the particle size of the metal particles in the metal crystal carbon particles is 2-10 nm;

[0096] The single-walled carbon nanotubes in the raw ash are aggregated in the form of tube bundles ( Figure 7 ), the tube bundles are intertwined and randomly entangled with each other, and the metallic crystalline carbon particles are embedded in the interlaced grids of the single-walled carbon nanotubes. Some of them adhere to the surface of the single-walled carbon nanotubes, and some are bonded to the surface of the single-walled carbon nanotubes.

[0097] Multi-walled carbon nanotubes were detected in the centrifugal sediment after being oxidized and peeled off into long graphene sheets, indicating that multi-walled carbon nanotubes can also be removed by this method.

[0098] According to one embodiment of the present application, the purity of the raw ash of single-walled carbon nanotubes in the method of step (1) of this embodiment can be adjusted to 60-95wt% and then

[0099] According to one embodiment of the present application, the temperature of the constant temperature oil bath in the method of step (1) of this embodiment can be selected from 50-60°C.

[0100] According to one embodiment of the present application, the pH value of the mixed solution before the last centrifugation in the method of step (1) of this embodiment can be selected from 4-5.

[0101] According to one embodiment of the present application, the last centrifugal revolution in the method of step (1) of this embodiment can be selected from 5000-14000 revolutions per minute.

[0102] (2) Preparation of Si@C composite materials:

[0103] 0.1g silicon powder (Si) was dispersed in a beaker containing 100ml water and anhydrous ethanol (v / v=1:4), and then ultrasonicated for 60min. The beaker was then placed in a 50°C water bath, and 0.1g dopamine hydrochloride and 1mL ammonia water (28wt%) were added to the above beaker in sequence to form a homogeneous mixture, which was then stirred continuously at 50°C for 24h to achieve a polydopamine (PDA) coating. Si@PDA core-shell nanoparticles were repeatedly washed with water and ethanol (v / v=1:1) and collected by centrifugation and vacuum freeze drying. The prepared Si@PDA particles were placed in a tube furnace and spun at 5°C min under an argon atmosphere. -1 The temperature is raised to 700° C. at a rate of 0.05° C. and maintained for 3 hours to carbonize and convert the carbonized silicon into Si@C material. The silicon powder (Si) is a nanoparticle with a particle size of 10-500 nm.

[0104] (3) Preparation of Si@C@SWCNT composites:

[0105] First, Si@C was modified using polydiallyldimethylammonium chloride (PDDA) (20 wt%). The specific steps included: 50 mg of Si@C was dispersed in a mixed solution of 100 mL of deionized water and sonicated for 30 minutes. Then, 4 mL of PDDA was added to the suspension, followed by sonication for 60 minutes and magnetic stirring for 4 hours to obtain a well-dispersed colloidal solution. Subsequently, excess PDDA was removed from the solution by centrifugation at 13,000 rpm for 15 minutes, and the Si@C sediment was redispersed in deionized water. The above two steps were repeated twice to ensure that no excess PDDA remained in the aqueous dispersion, ultimately obtaining surface-modified Si@C-PDDA. Furthermore, 50 mg of Si@C-PDDA was dispersed in 100 mL of deionized water to a nominal concentration of 0.5 mg / mL, and then added dropwise to 400 mL of a dispersion of non-bundled, individually dispersed oxidized single-walled carbon nanotubes (0.00625 mg / mL) and stirred for 12 hours. The obtained samples were centrifuged and freeze-dried, and then heated in an Ar atmosphere at 5 °C min -1 The Si@C@SWCNT composite material was obtained by heating at 350 °C for 1 h.

[0106] According to one embodiment of the present application, the PDDA in the method of step (3) of this example can be replaced with other polyquaternary ammonium salts, which can be selected from polydimethyldiallylammonium chloride, polymethacrylamidopropyltrimethylammonium chloride, and polymethacrylamidopropyldodecyldimethylammonium chloride. The argon atmosphere is selected from other inert gases or a vacuum atmosphere.

[0107] According to one embodiment of the present application, the concentration of Si@C-PDDA in the method of step (3) of this example can be selected from 0.05 to 1 g / L.

[0108] According to one embodiment of the present application, in the method of step (3) of this embodiment, the dispersion of non-bundled single dispersed oxidized single-walled carbon nanotubes can be selected from 0.001 to 0.05 g / L.

[0109] According to one embodiment of the present application, in the method of step (3) of this embodiment, the annealing temperature in an inert atmosphere or vacuum can be selected from 300 to 1000° C. for 0.5 to 12 hours.

[0110] (4) Lithium-ion battery assembly and performance testing:

[0111] The above-mentioned electrode active materials (Si, Si@C and Si@C@SWCNT) (70wt%), conductive carbon black (Super P) (15wt%) and carboxymethyl cellulose (CMC 15wt%) were placed in an agate mortar and ground simultaneously, with deionized water as a dispersant and copper foil as a current collector. The ground slurry was evenly coated on the copper foil with a coater and dried under vacuum at 80°C for 12 hours. The copper foil was cut into 10mm electrode sheets and weighed. The mass difference before and after the copper foil coating was used to obtain the load mass of the slurry on each electrode sheet. Finally, the electrode sheet was quickly transferred to the glove box for assembly of button batteries.

[0112] The button cells were assembled in an argon-filled glove box. For the assembly of lithium-ion battery (LIB) half-cells, the counter electrode and separator were lithium sheets and celgard 2500 membranes, respectively. The electrolyte was 1MLiPF6 in ethylene carbonate (EC): diethyl carbonate (DEC) (volume ratio 1:1), containing 10wt% fluoroethylene (FEC). The cells were designated B-1-Li and B-1-Na. The constant current charge and discharge test mainly examined the charge and discharge specific capacity, cycle performance, and rate performance of the lithium-ion half-cell at different current densities. The cyclic voltammetry test was performed on an electrochemical workstation (CHI660C) at 0.1mV s -1 The scan rate is performed. Figure 1 a is a schematic diagram of the process for preparing Si@C@SWCNT composite materials. The first step is to coat the surface of silicon particles with a carbon shell layer, and the second step is to self-assemble a single-walled carbon nanotube coating layer on the coated carbon layer; Figure 1 Figures 1b, 1c, and 1d show scanning electron micrographs of Si, Si@C, and Si@C@SWCNT, respectively, during the preparation of the Si@C@SWCNT composite. Observations show that the silicon particles range in size from 10 to 500 nm, with a Si@C carbon shell coating the outer surface. The thickness of the carbon shell can be adjusted between 5 and 60 nm. This thickness can be controlled by controlling the amount of PDA and reaction conditions. In theory, increasing the amount of PDA and reaction time can increase the thickness of the carbon layer. The outermost surface of the Si@C@SWCNT is coated with a single-walled carbon nanotube (SWCNT) layer. Individual SWCNTs adhere closely to the carbon shell surface, forming a thin, cross-linked network of SWCNTs.

[0113] Figure 2 a, 2b, and 2c are the XRD, RAMAN, and TG spectra of Si, Si@C, and Si@C@SWCNT in the examples; Figure 2Figure d shows the BET surface area and pore size distribution of Si@C@SWCNT. The test results show that the silicon contents of Si@C and Si@C@SWCNT are 72.5 wt.% and 69.1 wt.%, respectively, while the single-walled carbon nanotube content is 3.4 wt.%. The silicon content can be adjusted experimentally, ranging from 60-80 wt.%, and the single-walled carbon nanotube content can be adjusted from 0.2-10 wt.%. Figure 3 、 4 The charge and discharge cycle performance and rate performance diagrams of Si, Si@C, and Si@C@SWCNT as ion battery anode materials are shown in Table 1. The electrochemical impedance fitting data of Si, Si@C, and Si@C@SWCNT electrodes before and after charge and discharge cycles are shown in Table 1. When Si, Si@C, and Si@C@SWCNT are used as ion battery anode materials, the first reversible capacities are 3416.8, 2443.4, and 2337.1 mAh g-1, respectively; when Si@C@SWCNT is used as ion battery anode material, the first reversible capacity is 3416.8, 2443.4, and 2337.1 mAh g-1, respectively. -1 The current density was 834 mA hg -1 High specific capacity at 1A g -1 After 500 cycles, it still maintains 1267mAh g -1 The specific capacity of Si@C is 1A g, which has a long life cycle performance. In addition, the first coulombic efficiency is as high as 88.7%, which has the advantage of high first efficiency. -1 After 500 cycles, the current remains at 554 mA hg -1 The specific capacity of 8Ag -1 The current density was 120mA hg -1 High specific capacity of Si at 1A g -1 After 150 cycles, it maintains 266 mAh g -1 The first coulombic efficiency of Si and Si@C are 82.2% and 84.5% respectively. In addition, when Si@C@SWCNT is used as the anode material of ion battery, the -1 The current density was 100 cycles and the capacity was 1637 mAh g -1 high specific capacity.

[0114] Table 1 Electrochemical impedance spectroscopy fitting data of Si, Si@C, and Si@C@SWCNT electrodes before and after charge and discharge cycles

[0115]

[0116]

[0117] Figure 5Scanning electron micrographs (SEM) show the volume expansion and surface microstructural changes of the Si, Si@C, and Si@C@SWCNT electrode materials during charge and discharge in the examples. The thickness changes and surface morphologies of the Si, Si@C, and Si@C@SWCNT electrodes were analyzed before and after 150 cycles. The initial thicknesses of the Si, Si@C, and Si@C@SWCNT electrodes were 15μm, 14μm, and 14μm, respectively. After 150 cycles, their thicknesses increased to 32μm, 25μm, and 20μm, respectively. The pure Si electrode exhibited an exceptionally high expansion rate, reaching 113.3%. Repeated fractures of the silicon resulted in separation of the active material from the copper substrate. This reaction caused some electrodes to fail, and irreversible capacity decay continued, consistent with their cycling performance. The expansion rates of the Si@C and Si@C@SWCNT electrodes were 78.6% and 42.9%, respectively, which were not as high as those of the Si electrode. Importantly, the Si@C@SWCNT electrode exhibits the lowest expansion rate, which can be attributed to the excellent mechanical properties provided by the SWCNT outer layer, which enhances the stability of the entire electrode. Figure 5 c and 5f show that Si and Si@C electrodes have obvious cracks, with crack widths of 12μm and 7μm, respectively, while the Si@C@SWCNT electrode is only 3μm. Figure 5 These results are consistent with the variation of electrode thickness, indicating that the wrapping SWCNT plays a crucial role in stabilizing the electrode structure.

[0118] Figure 6 This is a transmission electron micrograph of the Si@C@SWCNT prepared in this example. The image shows a single-walled carbon nanotube coating on the outermost surface. Individual single-walled carbon nanotubes are tightly wrapped along the surface of the carbon shell, forming a thin, cross-linked network of single-walled carbon nanotubes that coats the outer surface of the carbon shell. This coating can be a single layer of single-walled carbon nanotubes. Therefore, the single-walled carbon nanotubes described can be a single-layer or multi-layered single-walled carbon nanotube coating.

[0119] According to one embodiment of the present application, the purity of the raw ash of single-walled carbon nanotubes in step 1) in Example 1 can be selected from 60-95 wt %.

[0120] According to one embodiment of the present application, the temperature of the constant temperature oil bath in step 1) of Example 1 can be selected from 50-60°C.

[0121] According to one embodiment of the present application, the pH value of the mixed solution before the last centrifugation in step 1) of Example 1 can be selected from 4-5.

[0122] According to one embodiment of the present application, the number of revolutions of the last centrifugation in step 1) of Example 1 can be selected from 5000-14000 revolutions per minute.

[0123] According to one embodiment of the present application, the PDDA in step (3) in Example 1 can be replaced by other polyquaternary ammonium salts, which can be selected from any one of polydimethyldiallyl ammonium chloride, polymethacrylamidepropyltrimethylammonium chloride, and polymethacrylamidepropyldodecyldimethylammonium chloride.

[0124] According to one embodiment of the present application, the argon atmosphere in step (3) in Example 1 can be replaced by other inert gases or a vacuum atmosphere.

[0125] According to one embodiment of the present application, the concentration of Si@C-PDDA in step (3) in Example 1 can be adjusted to be selected from 0.05 to 1 g / L.

[0126] According to one embodiment of the present application, the non-bundled single dispersed oxidized single-walled carbon nanotube dispersion in step (3) of Example 1 can be adjusted to be selected from 0.001 to 0.05 g / L.

[0127] Comparative Example 1

[0128] 0.4 g of potassium permanganate solid was added to a beaker containing 15 ml of concentrated sulfuric acid (98%). After stirring and the reaction was complete, 0.2 g of single-walled carbon nanotube ash ( Figure 2) is poured into the above solution, stirred thoroughly, and placed in a constant temperature oil bath at 50°C and stirred for 2 hours. During this period, a glass cover is added to prevent the concentrated sulfuric acid from absorbing water. After cooling to room temperature, it is diluted with about 100 ml of deionized water and stirred continuously. Then, about 10 ml of 30% hydrogen peroxide solution is added, and the reaction is stirred for 15 minutes, and then filtered with a microporous filter membrane. The obtained black solid was directly poured into 100 ml of 4% dilute hydrochloric acid, stirred and washed, then filtered through a microporous filter membrane and filtered and washed with deionized water. The obtained black solid was poured into 200 ml of deionized water and stirred thoroughly. It was centrifuged at 14,000 rpm for 30 minutes. After separation, the supernatant was discarded, and an appropriate amount of deionized water was added to the centrifuge tube, stirred and washed thoroughly, and then centrifuged again. Separation and the supernatant was discarded. Centrifugation and washing were repeated until the supernatant was neutral (pH = 6-7). Finally, the centrifugal sediment was collected and about 200 ml of deionized water was added. After stirring for 30 minutes, the obtained dispersion was divided into two parts. After centrifugation at 5,000 rpm and 14,000 rpm for 30 minutes, the upper dispersed solution was carefully extracted and collected. The components in the two solutions were monitored by transmission electron microscopy. It was found that in addition to single carbon nanotubes, both solutions contained a considerable amount of graphene oxide sheets and multi-walled carbon nanotubes. This indicates that the ions in the solution must be completely washed away until the pH of the dispersion reaches 6-7. At this point, neither the graphene oxide sheets nor the single-walled carbon nanotubes are easily aggregated, and the dispersion environment does not meet the conditions for separating and purifying the graphene oxide sheets and single-walled carbon nanotubes. We found that the solubility stability of the oxidized and exfoliated single-walled carbon nanotubes in weak acid solutions is better than that of the graphene oxide sheets, and the graphene oxide sheets are more likely to aggregate in weak acid solutions. Similarly, in the initial centrifugal washing step, because the pH is below 4, both the oxidized carbon nanotubes and the graphene oxide are easily aggregated, and they will settle together during centrifugation, preventing separation and purification.

[0129] The SWNT ash in this comparative example is the same as that in Example 1. The SWNT ash refers to impure SWNTs, i.e., SWNTs containing some non-SWNT impurities, including metal particle impurities and carbon impurities.

[0130] Comparative Example 2

[0131] (1) Preparation of Si@C-SWCNT composite material: 50 mg of Si@C-PDDA was dissolved in 100 mL of deionized water, ultrasonicated for 60 min, 2.5 g of tubular single-walled carbon nanotubes was added, and then magnetically stirred for 4 h. Finally, the sample Si@C-SWCNT was obtained by centrifugation and freeze-drying.

[0132] (2) Preparation of Si@C@RGO composite material: 50 mg of Si@C-PDDA was dispersed in 100 mL of deionized water to a nominal concentration of 0.5 mg / ml, and then added dropwise to 400 mL of redox graphene dispersion (0.00625 mg / ml) and stirred for 12 h. The obtained sample was centrifuged and freeze-dried, and then heated in an Ar atmosphere at 5 °C min -1 The Si@C@RGO composite material was obtained by heating at 350 °C for 1 h.

[0133] The samples prepared above were made into button batteries using the same method as in Example 1, and the battery performance was tested using the same testing method.

[0134] Figure 9 The charge-discharge cycle performance of Si@C-SWCNT and Si@C@RGO prepared in the comparative example is shown in the figure. -1 The specific capacity after 400 and 300 cycles at a current density of 966.7 mAh g -1 and 933.5mAh g -1 , which are lower than those of Si@C@SWCNT.

[0135] Figure 10 This is a scanning electron microscope image of Si@C-SWCNT. As can be seen from the image, the bundled single-walled carbon nanotubes do not form a coating structure on the silicon-carbon particles, but rather the bundles shuttle between the silicon-carbon particles.

[0136] Figure 11 This is a scanning electron microscope image of Si@C@RGO. The image shows graphene sheets attached to the surface of silicon-carbon particles.

[0137] Comparative Example 3

[0138] Preparation of Si@SWCNT composite material: The difference between this embodiment and embodiment 1 is that Si@C in step (3) is replaced by silicon powder. The samples prepared above are made into button batteries using the same method as in embodiment 1, and the battery performance is tested using the same test method. The test results show that the Si@SWCNT composite material has a good thermal conductivity at 1Ag. -1 After 200 cycles at a current density of 1.5 GHz, the specific capacity is 341 mA h g -1 , its cycle stability, rate performance and first coulombic efficiency are all worse than those of Si@C@SWCNT composite materials.

[0139] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A single-walled carbon nanotube silicon-carbon composite material, characterized in that: The single-walled carbon nanotube composite material comprises silicon particles, a carbon shell layer, and a single-walled carbon nanotube wrapping layer; The microstructure unit of the single-walled carbon nanotube composite material has the following general structural formula: Si@C@SWCNT; Wherein, Si represents silicon particles, C represents the carbon shell layer wrapped around the outer surface of the silicon particles, and SWCNT represents the single-walled carbon nanotube wrapping layer tightly wrapped around the outer surface of the carbon shell layer; The single-walled carbon nanotube wrapping layer is a two-dimensional net-bag-like layer structure formed by assembling non-bundled single dispersed oxidized single-walled carbon nanotubes as assembly units.

2. The single-walled carbon nanotube silicon-carbon composite material according to claim 1, characterized in that: The silicon particles are nanoparticles; Preferably, the particle size of the silicon particles is 10 to 500 nm; Preferably, the carbon shell layer is composed of porous carbon; Preferably, the thickness of the carbon shell is 5 to 60 nm; Preferably, the content of the single-walled carbon nanotube wrapping layer in the single-walled carbon nanotube-silicon-carbon composite material is 0.2 to 10 wt %; Preferably, the content of the silicon particles in the single-walled carbon nanotube silicon-carbon composite material is 30 to 90 wt%.

3. The method for preparing the single-walled carbon nanotube silicon-carbon composite material according to claim 1 or 2, characterized in that: The steps include: a1) modifying the outer surface of the Si@C composite material with a polyquaternary ammonium salt to obtain Si@C-PQAS; b1) wrapping a single-walled carbon nanotube wrapping layer tightly around the outer surface of Si@C-PQAS, and annealing under an inert atmosphere or under vacuum to obtain a single-walled carbon nanotube silicon-carbon composite material; The Si@C composite material refers to a composite material formed by a carbon shell coating the outer surface of silicon particles.

4. The preparation method according to claim 3, characterized in that Step a1) comprises: adding a polyquaternium salt to a Si@C dispersion, and ultrasonically treating the dispersion to obtain Si@C-PQAS; Preferably, step b1) comprises: adding a solution containing non-bundled single dispersed oxidized single-walled carbon nanotubes to a dispersion of Si@C-PQAS, so that the non-bundled single dispersed oxidized single-walled carbon nanotubes are tightly wrapped along the outer surface of Si@C-PQAS on the surface of Si@C-PQAS, and annealing at 300-1000° C. for 0.5-12 h in an inert atmosphere or vacuum to obtain the single-walled carbon nanotube silicon-carbon composite material; Preferably, the polyquaternary ammonium salt in step a1) is at least one selected from polydiallyldimethylammonium chloride, polydimethyldiallylammonium chloride, polymethacrylamidepropyltrimethylammonium chloride, and polymethacrylamidepropyldodecyldimethylammonium chloride; Preferably, in step b1), the solution containing the non-bundled single dispersed oxidized single-walled carbon nanotubes is added to the Si@C-PQAS dispersion by dropwise addition and sufficient stirring.

5. The preparation method according to claim 4, characterized in that The concentration of Si@C-PQAS in the Si@C-PQAS dispersion in step b1) is 0.05 to 1 g / L; The concentration of the non-bundled single dispersed oxidized single-walled carbon nanotubes in the solution containing the non-bundled single dispersed oxidized single-walled carbon nanotubes is 0.001-0.05 g / L.

6. The preparation method according to claim 4, characterized in that The preparation method of the single-walled carbon nanotube silicon-carbon composite material comprises the following steps: (1) Preparation of a dispersed aqueous solution of non-bundled single dispersed oxidized single-walled carbon nanotubes: First, potassium permanganate solid is added to an excess of concentrated sulfuric acid solution for complete reaction, and then the original single-walled carbon nanotube ash is added to the above solution, and after stirring evenly, the resulting reaction mixture is stirred and reacted at a temperature of 50-60° C. for 2-3 hours, and then the reaction mixture is diluted with deionized water, and then an excess of hydrogen peroxide solution is added to reduce and remove the manganese dioxide solid generated during the reaction process. After filtering through a microporous filter membrane and washing with a hydrochloric acid solution, the obtained solid is washed with water to remove some impurity ions in the solution, and washed with water until the pH of the single-walled carbon nanotube mixed aqueous solution is 4-5. The solution is centrifuged at 5000-14000 rpm for 30 minutes, and then the upper homogeneous solution is taken out, and the homogeneous solution is filtered, washed with water, and the collected black solid is dissolved in water before it is dried to obtain the dispersed aqueous solution of the non-bundled single dispersed single-walled carbon nanotubes; Preferably, the non-bundled single dispersed single-walled carbon nanotubes refer to single-walled carbon nanotubes that are not in the form of bundles, but each single-walled carbon nanotube is independently peeled off from the single-walled carbon nanotube bundle and exists in a discrete form; Preferably, the purity of the single-walled carbon nanotubes in the original single-walled carbon nanotube ash is 60 to 95 wt%; (2) Preparation of Si@C composite materials: Silicon powder is dispersed in a mixed solution of water and anhydrous ethanol, dopamine hydrochloride and ammonia water are added in sequence, and stirring is continued until the discrete silicon particles are completely coated with polydopamine. Si@PDA core-shell structure particles are obtained by washing and centrifugation. The Si@PDA core-shell structure particles are then heated at 600-1000° C. for 1-12 hours under an inert atmosphere to carbonize the polydopamine and generate the Si@C composite material. (3) Modify the outer surface of Si@C with polyquaternary ammonium salt to prepare Si@C-PQAS: Adding polyquaternium salt to the Si@C dispersion, ultrasonically treating for 0.1 to 1 hour with continuous stirring until a good colloidal dispersion is obtained, and centrifuging and washing to remove free polyquaternium salt not modified on the Si@C surface to obtain Si@C surface-modified with polyquaternium salt, i.e., the Si@C-PQAS; (4) Preparation of Si@C@SWCNT composite materials: The Si@C-PQAS is dispersed in water to form a dispersion with a concentration of 0.05 to 1 g / L, and then added dropwise to a dispersion aqueous solution of non-tubular single dispersed oxidized single-walled carbon nanotubes with a concentration of 0.001 to 0.05 g / L, and stirred continuously until the Si@C-PQAS and the non-tubular single dispersed oxidized single-walled carbon nanotubes are completely electrostatically assembled. The obtained product is filtered, washed, and dried, and then annealed at 300 to 1000° C. in an inert atmosphere or vacuum for 0.5 to 12 hours to obtain a Si@C@SWCNT composite material, that is, the single-walled carbon nanotube silicon-carbon composite material.

7. The preparation method according to claim 6, characterized in that In step (1), the impurities in the original single-walled carbon nanotube ash include at least one of crystalline carbon sphere particles, multi-walled carbon nanotubes, graphite sheets, graphene sheets, fullerene spheres, metal nanoparticles, and metal crystalline carbon particles; Preferably, the metallic crystalline carbon particles are crystalline carbon sphere particles coated with metal nanoparticles; Preferably, the purity of the single-walled carbon nanotubes in the non-bundled single dispersed oxidized single-walled carbon nanotubes is 99.5-100 wt%; Preferably, the surface of the single-walled carbon nanotubes in the dispersed aqueous solution of the non-bundled single dispersed single-walled carbon nanotubes contains oxygen-containing functional groups; The oxygen-containing functional groups include hydroxyl, carboxyl and epoxy groups; Preferably, the polyquaternary ammonium salt described in step (3) is at least one selected from polydiallyldimethylammonium chloride, polydimethyldiallylammonium chloride, polymethacrylamidepropyltrimethylammonium chloride, and polymethacrylamidepropyldodecyldimethylammonium chloride; Preferably, the modification of the polyquaternary ammonium salt on the Si@C-PQAS is adsorption and / or bonding of the polyquaternary ammonium salt on the Si@C surface; Preferably, the Si@C-PQAS is dispersed in water, has a positive Zeta potential, and has a positive charge on the surface of the particles; Preferably, the Si@C@SWCNT composite material described in step (4) comprises silicon particles, a carbon shell layer and a single-walled carbon nanotube wrapping layer, and its microstructure unit has the following general structural formula: Si@C@SWCNT, wherein Si represents silicon particles, C represents a carbon shell layer wrapped around the outer surface of the silicon particles, and SWCNT represents a single-walled carbon nanotube wrapping layer; the silicon particles are the innermost core, the carbon shell layer is coated on the outer surface of the silicon particles, and the single-walled carbon nanotube wrapping layer is a two-dimensional net-bag-shaped coating layer tightly wrapped around the outer surface of the carbon shell layer C, and the two-dimensional net-bag-shaped coating layer is assembled with a non-tube-bundled single dispersed oxidized single-walled carbon nanotube as the assembly unit.

8. Use of the single-walled carbon nanotube-silicon-carbon composite material according to claim 1 or 2, or the single-walled carbon nanotube-silicon-carbon composite material prepared by the method according to any one of claims 3 to 7, in electrode materials.

9. The preparation method according to claim 8, characterized in that The electrode material is selected from the electrode material of a primary electrochemical generator, a secondary electrochemical generator, and a high-energy generator.

10. A secondary battery, characterized in that: The anode material of the secondary battery contains the single-walled carbon nanotube silicon-carbon composite material according to claim 1 or 2 or the single-walled carbon nanotube silicon-carbon composite material prepared by the method according to any one of claims 3 to 7; Preferably, the secondary battery is a lithium-ion battery.

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