Silicon-carbon composite material as well as preparation method and application thereof

Abstract

The invention discloses a silicon-carbon composite material as well as a preparation method and application thereof, and belongs to the field of lithium ion batteries. The silicon-carbon composite material comprises carbon fibers and a composite material formed by coating silicon with single-walled carbon nanotubes. The composite material of the single-walled carbon nanotube coated silicon is embedded in the carbon fiber; the single-walled carbon nanotube-coated silicon composite material comprises silicon particles and a single-walled carbon nanotube net-shaped coating layer, the single-walled carbon nanotube net-shaped wrapping layer is tightly wrapped on the outer surfaces of the silicon particles; the single-walled carbon nanotube net-shaped wrapping layer is of a two-dimensional net bag type structure formed by assembling non-tube-bundle type single dispersed oxidized single-walled carbon nanotubes serving as assembling elements. The composite material has excellent electrochemical performance.

Description

Technical Field

[0001] The present application relates to a silicon-carbon composite material, a preparation method thereof, and an application thereof, belonging to the field of lithium-ion batteries. Background Art

[0002] Lithium-ion batteries (LIBs) have become the most widely used electrochemical energy storage devices today due to their high energy density, long cycle life, and good safety. Currently, the most common anode material for commercial lithium-ion batteries is graphite, and its reversible specific capacity has approached the theoretical specific capacity of 372 mAh / g. Therefore, to improve the energy density of lithium batteries, anode materials with higher specific capacity need to be developed. Silicon has a high theoretical capacity (≈4200 mAh / g), abundant crustal reserves, and a suitable lithium intercalation potential (~0.4 V vs Li), and is widely regarded as the most promising next-generation anode material for lithium-ion batteries. However, silicon materials have problems of volume expansion (≈400%) and poor electrical conductivity during charge and discharge, which hinder their commercial promotion.

[0003] Usually, the common strategy to solve the above problems is to construct a silicon-carbon composite material, and use the advantages of carbon materials such as electrical conductivity or structural stability to be compounded with silicon to achieve complementary advantages and improve the electrochemical performance of the silicon anode material. For example, a silicon-carbon composite material of carbon-coated silicon particles is obtained with a silicon particle core and a carbon shell layer coated on the outside. Electrospinning technology is one of the common means to prepare such a silicon-carbon composite material of carbon-coated silicon particles. However, usually, pure silicon is directly used for electrospinning, and pure silicon is easily exposed outside and agglomerates on the surface of carbon fibers, making it difficult to form a uniform core-shell structure, resulting in silicon being directly exposed to the electrolyte and difficult to maintain good electrochemical performance. Summary of the Invention

[0004] To solve the above technical problems existing in the process of preparing a silicon-carbon composite anode material by electrospinning and to achieve better electrochemical performance of the carbon fiber silicon-carbon composite anode material prepared by electrospinning, the present application provides a silicon-carbon composite material, a preparation method thereof, and an application thereof.

[0005] According to the first aspect of the present application, a silicon-carbon composite material is provided. The silicon-carbon composite material comprises a composite material of carbon fiber and single-walled carbon nanotube-coated silicon; the composite material of single-walled carbon nanotube-coated silicon comprises silicon particles and a single-walled carbon nanotube mesh wrapping layer; the microstructure unit of the composite material of single-walled carbon nanotube-coated silicon has the following general structural formula: Si-SWCNT, wherein Si represents silicon particles, SWCNT represents a single-walled carbon nanotube mesh wrapping layer tightly wrapped on the outer surface of silicon particles; the single-walled carbon nanotube mesh wrapping layer is a wrapping layer of a two-dimensional net bag structure formed by assembling non-bundle-type single dispersed oxidized single-walled carbon nanotubes as assembly elements; the microstructure unit of the silicon-carbon composite material has the following general structural formula: Si-SWCNT@CNF; wherein CNF represents carbon fiber, and the composite material of single-walled carbon nanotube-coated silicon is embedded in the carbon fiber.

[0006] A silicon-carbon composite material, comprising a composite material of carbon fiber and single-walled carbon nanotube-coated silicon;

[0007] The composite material of single-walled carbon nanotubes coated with silicon is embedded inside the carbon fiber;

[0008] The composite material of single-walled carbon nanotube-coated silicon comprises silicon particles and a single-walled carbon nanotube mesh wrapping layer;

[0009] The single-walled carbon nanotube mesh wrapping layer is tightly wrapped around the outer surface of the silicon particle;

[0010] The single-walled carbon nanotube mesh wrapping layer is a two-dimensional net bag structure formed by assembling non-tube-bundled single dispersed oxidized single-walled carbon nanotubes as assembly primitives.

[0011] Optionally, the surface of the non-bundled single dispersed oxidized single-walled carbon nanotube contains oxygen-containing functional groups;

[0012] The oxygen-containing functional groups include hydroxyl, carboxyl and epoxy groups.

[0013] Optionally, the silicon particles are selected from one or both of pure silicon particles and silicon monoxide particles.

[0014] Optionally, in the composite material of single-walled carbon nanotube-coated silicon, the content of the single-walled carbon nanotube network wrapping layer relative to the silicon particles is 1 to 15 wt.%.

[0015] Optionally, in the composite material of single-walled carbon nanotube-coated silicon, the content of the single-walled carbon nanotube network wrapping layer relative to the silicon particles is 5-10 wt.%.

[0016] Optionally, in the composite material of single-walled carbon nanotube-coated silicon, the content of the single-walled carbon nanotube network wrapping layer relative to the silicon particles is 10 wt.%.

[0017] Optionally, in the composite material of single-walled carbon nanotube-coated silicon, the content of the single-walled carbon nanotube network wrapping layer relative to the silicon is selected from any value or the range value between any two of 1 wt.%, 3 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 13 wt.%, 15 wt.%.

[0018] Optionally, in the silicon-carbon composite material, the content of the silicon particles is 30-60 wt.%.

[0019] Optionally, in the silicon-carbon composite material, the content of the silicon particles is 35-50 wt.%.

[0020] Optionally, in the silicon-carbon composite material, the content of the silicon particles is selected from any value or the range value between any two of 30 wt.%, 35 wt.%, 40 wt.%, 45 wt.%, 50 wt.%, 55 wt.%, 60 wt.%.

[0021] According to the second aspect of the present application, a preparation method of the above-mentioned silicon-carbon composite material is provided.

[0022] The preparation method of the above-mentioned silicon-carbon composite material includes the following steps:

[0023] (a1) Modify polyquaternary ammonium salt on the outer surface of silicon particles to obtain Si-PQAS;

[0024] (b1) Tightly wrap a single-walled carbon nanotube network wrapping layer on the outer surface of Si-PQAS, and anneal in an inert atmosphere or under vacuum to obtain a composite material of single-walled carbon nanotube-coated silicon, Si-SWCNT;

[0025] (c1) Dissolve Si-SWCNT in a solvent, and add polyacrylonitrile to obtain a homogeneous and stable dispersion precursor;

[0026] (d1) Electrospinning the dispersion precursor to obtain a nanofiber cloth;

[0027] (e1) After pre-oxidation treatment of the nanofiber cloth in air, high-temperature annealing and carbonization are carried out to obtain the above-mentioned silicon-carbon composite material.

[0028] Optionally, the step (a1) includes: adding polyquaternary ammonium salt to the dispersion of silicon, and performing ultrasonic treatment to obtain Si-PQAS;

[0029] The polyquaternary ammonium salt is selected from at least one of poly(diallyldimethylammonium chloride), poly(dimethyldiallylammonium chloride), poly(methacrylamidopropyltrimethylammonium chloride), and poly(methacrylamidopropyldodecyldimethylammonium chloride).

[0030] Optionally, in step (a1), modifying the polyquaternary ammonium salt on Si-PQAS is adsorbing and / or bonding the polyquaternary ammonium salt on the Si surface.

[0031] Optionally, the time of the ultrasonic treatment is 0.1 to 1 hour.

[0032] Optionally, step (b1) includes: adding a solution containing non-bundled single-dispersed oxidized single-walled carbon nanotubes to the dispersion of Si-PQAS, and annealing at 300 to 1000 °C for 0.1 to 12 h in an inert atmosphere or under air isolation to obtain the composite material Si-SWCNT with silicon coated by single-walled carbon nanotubes.

[0033] Optionally, step (b1) includes: adding a solution containing non-bundled single-dispersed oxidized single-walled carbon nanotubes to the dispersion of Si-PQAS, such that the non-bundled single-dispersed oxidized single-walled carbon nanotubes closely wrap around the outer surface of Si-PQAS along the surface of Si-PQAS, and annealing at 300 to 1000 °C for 0.1 to 12 h in an inert atmosphere or under air isolation to obtain the composite material (Si-SWCNT) with silicon coated by single-walled carbon nanotubes.

[0034] Optionally, the inert atmosphere is selected from at least one of nitrogen and noble gases.

[0035] Optionally, in step (b1), the method of adding the solution containing non-bundled single-dispersed oxidized single-walled carbon nanotubes to the dispersion of Si-PQAS includes dropwise addition and sufficient stirring.

[0036] Optionally, in the dispersion of Si-PQAS, the concentration of Si-PQAS is 0.05 to 1 g / L.

[0037] Optionally, the concentration of Si-PQAS is selected from any value of 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 the range value between any two of them.

[0038] Optionally, in the solution containing non-bundled single-dispersed oxidized single-walled carbon nanotubes, the concentration of non-bundled single-dispersed oxidized single-walled carbon nanotubes is 0.001 to 0.05 g / L.

[0039] Optionally, the concentration of the non-bundled single-root 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 the range value between any two of them.

[0040] Optionally, in step (b1), the annealing temperature is selected from any value among 300 °C, 350 °C, 400 °C, 450 °C, 550 °C, 650 °C, 750 °C, 850 °C, 950 °C, 1000 °C or the range value between any two of them.

[0041] Optionally, in step (b1), the annealing time is 0.1 to 12 hours.

[0042] Optionally, in step (b1), the annealing time is selected from any value among 0.1 hour, 0.5 hour, 1 hour, 2 hours, 5 hours, 8 hours, 10 hours, 12 hours or the range value between any two of them.

[0043] Optionally, in step (b1), the content of the single-walled carbon nanotube network-like coating layer relative to silicon in the composite material of single-walled carbon nanotube-coated silicon is 1 to 15 wt.%.

[0044] Optionally, in step (b1), the content of the single-walled carbon nanotube network-like coating layer relative to silicon in the composite material of single-walled carbon nanotube-coated silicon is 5 to 10 wt.%.

[0045] Optionally, in step (b1), the content of the single-walled carbon nanotube network-like coating layer relative to silicon in the composite material of single-walled carbon nanotube-coated silicon is 10 wt.%.

[0046] Optionally, in step (b1), the surface of the non-bundled single-root dispersed oxidized single-walled carbon nanotubes contains oxygen-containing functional groups.

[0047] Optionally, the oxygen-containing functional groups include hydroxyl groups, carboxyl groups and epoxy groups.

[0048] Optionally, the preparation method of the solution containing non-bundled single-root dispersed oxidized single-walled carbon nanotubes includes:

[0049] First, add potassium permanganate to an excessive amount of concentrated sulfuric acid solution until the reaction is complete. Then, add the original ash of single-walled carbon nanotubes to the above solution and stir evenly. The resulting reaction mixture is continuously stirred at a temperature of 50 - 60 °C for 2 - 3 h. Then, dilute the reacted mixture with water, add an excessive amount of hydrogen peroxide solution to reduce and remove the manganese dioxide solid generated during the reaction. After filtration and washing with an acid solution, the obtained solid is further washed with water to remove some impurity ions in the solution. When the pH of the aqueous solution of the single-walled carbon nanotube mixture is 4 - 5, centrifuge at 5000 - 14000 revolutions per minute. Then, take out the upper homogeneous solution, filter the homogeneous solution, wash and collect the obtained black solid, and dissolve it in water before it is dried to obtain the dispersion aqueous solution of the non-bundled single-root dispersed single-walled carbon nanotubes.

[0050] Optionally, the non-bundled single-root dispersed single-walled carbon nanotubes refer to that the single-walled carbon nanotubes do not exist 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 single discrete form.

[0051] Optionally, in the original ash of single-walled carbon nanotubes, the purity of the single-walled carbon nanotubes is 60 - 95 wt%.

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

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

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

[0055] Optionally, the surface of the single-walled carbon nanotubes in the dispersion aqueous solution of the non-bundled single-root dispersed single-walled carbon nanotubes contains oxygen-containing functional groups;

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

[0057] The single-walled carbon nanotube network-like wrapping layer is a two-dimensional net-like wrapping layer that tightly wraps around the outer surface of the silicon particles. The two-dimensional net-like wrapping layer is assembled with non-bundled single-root dispersed oxidized single-walled carbon nanotubes as the assembly units.

[0058] Optionally, the step (c1) includes: uniformly dispersing Si-SWCNT in N,N-dimethylformamide solvent, and then adding polyacrylonitrile to completely dissolve it in the dispersion to obtain a homogeneous and stable dispersion precursor.

[0059] Optionally, the mass ratio of the Si-SWCNT to the polyacrylonitrile is 0.3 to 1:1;

[0060] Optionally, the mass ratio of the Si-SWCNT to the polyacrylonitrile is selected from any value or the range value between any two of 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1.

[0061] Optionally, the concentration of the polyacrylonitrile relative to N,N-dimethylformamide is 10 to 15 wt.%.

[0062] Optionally, step (c1) includes: uniformly dispersing the Si-SWCNT in an N,N-dimethylformamide (DMF) solvent by ultrasonic means, then adding polyacrylonitrile, and heating and stirring to completely dissolve it in the dispersion to obtain a homogeneous and stable dispersion precursor; the heating and stirring temperature is 50 to 70 °C.

[0063] Optionally, in the step (d1), the electrospinning is uniaxial electrospinning, and its injection speed is 1 to 1.5 mL·h -1 , and the applied voltage is 12 to 15 kV.

[0064] Optionally, in the step (d1), the electrospinning is uniaxial electrospinning, and its injection speed is 1 mL·h -1 , and the applied voltage is 13.5 kV.

[0065] Optionally, in the step (e1), the pre-oxidation treatment is to keep the temperature constant at 260 to 300 °C for 3 to 5 h.

[0066] Optionally, in the step (e1), the pre-oxidation treatment is to keep the temperature constant at 260 °C for 3 h.

[0067] Optionally, in the step (e1), the high-temperature annealing and carbonization include: annealing at 600 to 1000 °C for 0.5 to 12 h in an inert atmosphere or under air isolation.

[0068] Optionally, the preparation method of the silicon-carbon composite material includes the following steps:

[0069] (a11) Modifying the outer surface of Si with polyquaternary ammonium salt to prepare Si-PQAS:

[0070] Adding polyquaternary ammonium salt to the dispersion of Si, performing ultrasonic treatment for 0.1 to 1 h and continuously stirring until a good colloidal dispersion is obtained, centrifuging and washing to remove the free polyquaternary ammonium salt that has not been modified to the surface of Si, and obtaining Si with a surface-modified polyquaternary ammonium salt, that is, obtaining the Si-PQAS;

[0071] (b11) Preparation of Si-SWCNT composite material:

[0072] Disperse Si-PQAS in water to form a dispersion with a concentration of 0.05 - 1 g / L, and then dropwise add it to an aqueous dispersion of non-bundled single-walled carbon nanotubes with a concentration of 0.001 - 0.05 g / L. Continuously stir until the electrostatic assembly of Si-PQAS and non-bundled single-walled carbon nanotubes is complete. Filter, wash, and dry the obtained product, and then anneal it at 300 - 1000 °C for 0.1 - 12 h in an inert atmosphere or vacuum to obtain the Si-SWCNT composite material, that is, the composite material of single-walled carbon nanotube-coated silicon.

[0073] Optionally, the Si-PQAS is dispersed in water with a positive Zeta potential and the particle surface is positively charged;

[0074] Optionally, in step (b11), the composite material of single-walled carbon nanotube-coated silicon includes silicon particles and a single-walled carbon nanotube network-like wrapping layer; the microstructure unit of the composite material of single-walled carbon nanotube-coated silicon has the following structural general formula: Si-SWCNT, where Si represents silicon particles and SWCNT represents the single-walled carbon nanotube network-like wrapping layer tightly wrapped on the outer surface of the silicon particles; the single-walled carbon nanotube network-like wrapping layer is a wrapping layer with a two-dimensional net-bag structure assembled from non-bundled single-walled carbon nanotubes as assembly units;

[0075] (c11) Ultrasonically treat Si-SWCNT to uniformly disperse it in N,N-dimethylformamide (DMF) solvent, and then add polyacrylonitrile and heat and stir to completely dissolve it in the dispersion to obtain a homogeneous and stable dispersion precursor;

[0076] (d11) Electrospun the above dispersion precursor to obtain a nanofiber cloth;

[0077] Optionally, step (d11) includes: electrospinning the above dispersion precursor to obtain a nanofiber cloth; the electrospinning is single-axis electrospinning with an injection speed of 1 - 1.5 ml·h -1 , and the applied voltage is 12 - 15 kV;

[0078] (e11) After pre-oxidation treatment of the above nanofiber cloth in air, perform high-temperature annealing and carbonization to obtain the silicon-carbon composite material (Si-SWCNT@CNF).

[0079] According to the third aspect of the present application, there is provided an application of the above silicon-carbon composite material or the silicon-carbon composite material prepared by the above preparation method in electrode materials.

[0080] Use of the silicon-carbon composite material described above or the silicon-carbon composite material prepared according to the preparation method described above in an electrode material.

[0081] Optionally, the electrode material is selected from the electrode materials of a primary electrochemical generator, a secondary electrochemical generator, and a high-energy generator.

[0082] According to the fourth aspect of the present application, a secondary battery is provided.

[0083] A secondary battery, wherein the negative electrode material of the secondary battery contains the silicon-carbon composite material described above or the silicon-carbon composite material prepared according to the preparation method described above.

[0084] Optionally, the secondary battery is a lithium-ion battery.

[0085] Optionally, the secondary battery includes a positive electrode, a negative electrode, and an electrolyte.

[0086] The negative electrode includes: a current collector and a negative electrode material loaded on the current collector; wherein, the negative electrode material contains the above-mentioned silicon-carbon composite material.

[0087] The beneficial effects that can be produced by the present application include:

[0088] (1) In the preparation method of the silicon-carbon composite material provided by the present application, electrostatic ordered assembly is carried out under a homogeneous liquid phase. The non-bundled single-dispersed oxidized single-walled carbon nanotubes can form a uniform coating on each microscopic silicon-carbon particle. Under liquid phase conditions, the surface of the silicon particles is positively charged, and the surface of the non-bundled single-dispersed oxidized single-walled carbon nanotubes is negatively charged. Driven by the ordered electrostatic interaction, the silicon particles and the non-bundled single-dispersed oxidized single-walled carbon nanotubes complete ordered electrostatic adsorption, so that the single-walled carbon nanotubes can be tightly and orderly wrapped on the surface of the silicon particles. Then, after annealing, the surface groups of the single-walled carbon nanotubes and the surface groups of the silicon-carbon particles bond to form a stable covalent or hydrogen bond force, forming a new silicon composite Si-SWCNT. The surface chemical properties of this composite are beneficial for its better dispersion in DMF, and are also beneficial for the spontaneous formation of an ordered interaction between it and PAN, ensuring that the silicon particles always remain inside the fiber during subsequent electrospinning and carbonization processes.

[0089] (2) In the preparation method of the silicon-carbon composite material provided by the present application, the addition sequence and addition method (dropwise addition and sufficient stirring) of adding a solution containing non-bundled single-dispersed oxidized single-walled carbon nanotubes to the dispersion of Si@C-PQAS, and the very low concentration of the single-walled carbon nanotubes are to prevent the rapid agglomeration of the single-walled carbon nanotubes before coating, and to ensure the uniformity and effectiveness of the coating process.

[0090] (3) The preparation method of the silicon-carbon composite material provided by this application uses the methods of electrostatic self-assembly and electrospinning to prepare a novel fibrous core-shell structure Si-SWCNT@CNF as the anode material for lithium-ion batteries. By introducing single-walled carbon nanotubes on the surface of Si particles, it not only provides a conductive network for Si nanoparticles, but also provides sufficient active sites, increases the compatibility between Si-SWCNT particles and the spinning solution, and obtains a continuous and uniform core-shell structure. Such a hierarchical structure, with single-walled carbon nanotubes inside further maintaining electrical contact between silicon particles, and the external carbon fiber shell blocking direct contact with the electrolyte, ensures the stability of the material. And the fibrous structure, interlaced with each other, further stabilizes the structure of the electrode and ensures the rapid transmission of electrons. This multi-composite structure can synergistically function in buffering volume expansion, stabilizing the SEI film, and improving conductivity. It has obvious differences from the Si@CNF sample obtained by electrospinning pure Si alone. In the Si@CNF sample, serious Si particle agglomeration occurs, while no Si particle agglomeration, shedding, or exposure occurs in Si-SWCNT@CNF. At the same time, we further explored the effects of different Si contents on Si-SWCNT@CNF and Si@CNF materials. The results show that the Si@CNF electrodes with contents of 42%, 41%, and 54% have reversible capacities of 597.6, 689.2, and 352 mAh g -1 respectively at a high current density of 4 A g -1 , while the Si-SWCNT@CNF electrodes with contents of 38%, 41%, and 50% have reversible capacities of 675, 720.8, and 728.4 mAh g -1 respectively at a high current density of 4 A g -1 . And when the current density of Si-SWCNT@CNF-2 returns to 0.2 A g -1 , the capacity recovers to 1313.6 mA h g -1 , proving that the electrode structure is relatively intact. We carried out long-cycle performance tests on Si@CNF-2 and Si-SWCNT@CNF-2 electrodes. At a current density of 0.5 A g -1 , the Si@CNF-2 was charged and discharged for 200 cycles, and the specific capacity remained 713.9 mAh g -1 , and the specific capacity retention rate was 38.49%. While the Si-SWCNT@CNF-2 electrode was charged and discharged for 200 cycles at the same current density, and the specific capacity remained 966.1 mAh g -1 , and the specific capacity retention rate was 62.17%, proving the performance improvement brought by the addition of single-walled carbon nanotubes. At the same time, the Si-SWCNT@CNF-2 electrode was charged and discharged for 220 cycles at a current density of 1 A g -1 , and still had a specific capacity of 727.8 mAh g-1 The reversible specific capacity. Description of the Drawings

[0091] Figure 1 It is a schematic diagram of the preparation process of Si-SWCNT@CNF.

[0092] Figure 2 For Example 1, (a) SEM image of pure Si; (b) SEM image of Si-SWCNT, (c) TEM image and (d) TEM-EDS mapping image.

[0093] Figure 3 Among them, (a-c) are SEM images of Si@CNF-1, Si@CNF-2 and Si@CNF-3; (d-f) are SEM images of Si-SWCNT@CNF-1, Si-SWCNT@CNF-2 and Si-SWCNT@CNF-3; (g-h) TEM image and TEM-EDS mapping image of Si-SWCNT@CNF-2.

[0094] Figure 4 It is the lithium storage performance of the composite material Si-SWCNT@CNF. (a) CV curve at 0.1 mV s -1 The initial three cycles of the Si-SWCNT@CNF electrode at 0.2 A g -1 Among (c and e), the rate performance between 0.2 and 4.0 A g of the (c) Si@CNF and (e) Si-SWCNT@CNF electrodes with different Si contents -1 The cycle performance of the Si-SWCNT, Si@CNF-2 and Si-SWCNT@CNF-2 electrodes at 0.5 A g -1 The cycle stability of the Si-SWCNT@CNF-2 at 1 A g -1

[0095] Figure 5 It is the transmission electron microscope photograph of non-bundled single-dispersed oxidized single-walled carbon nanotubes in the examples.

[0096] Figure 6 It is the transmission electron microscope photograph of the original ash of the original single-walled carbon nanotubes in the examples. Detailed Description of the Invention

[0097] The present application will be described in detail below with reference to the examples, but the present application is not limited to these examples.

[0098] Unless otherwise specified, the raw materials in the examples of the present application are all purchased through commercial channels.

[0099] Among them, the non-bundled single-root dispersed oxidized single-walled carbon nanotube dispersion aqueous solution described in this embodiment is prepared according to the steps of Example 1 in the Chinese invention patent (application number: 2024102122774) previously applied by the inventor. The specific steps are as follows:

[0100] 0.4 g of potassium permanganate solid is added to a beaker containing 15 mL of concentrated sulfuric acid (98 wt%). After the stirring reaction is complete, 0.2 g of raw single-walled carbon nanotube ash is poured into the above solution. After stirring evenly, it is placed in a constant-temperature oil bath at 50 °C and stirred for 2 hours. During this period, a glass cover is covered 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 continuously stirred. Then about 10 mL of 30% hydrogen peroxide solution is added. After stirring and reacting for 15 minutes, it is 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, stirred well, and centrifuged at 14,000 rpm for 30 minutes. After stratification, the upper clear liquid is poured off, and 200 mL of deionized water is continuously added to the centrifuge tube, stirred well, washed, and then centrifuged again. After stratification, the upper clear liquid is poured off. This centrifugation and washing process is repeated 3 times until the pH value of the mixed solution is 4 when deionized water is added to the centrifuge tube. Then it is centrifuged at 10,000 rpm for 30 minutes, the upper clear liquid is extracted, and the collected dispersion solution is filtered and washed through a microporous filter membrane to remove residual impurity ions. The black solid collected is dissolved in deionized water to obtain the non-bundled single-root dispersed oxidized single-walled carbon nanotube dispersion aqueous solution.

[0101] The purity of the non-bundled single-root dispersed oxidized single-walled carbon nanotubes reaches over 99.5 wt%. The elemental analysis results of the X-ray energy spectrometer show that no residual metal impurities are detected. No other impurity components such as graphene, multi-walled carbon nanotubes, carbon particles, or metal particles are detected by transmission electron microscopy and scanning electron microscopy.

[0102] The bundle diameter of the non-bundled single-root dispersed oxidized single-walled carbon nanotubes is significantly smaller than that of the original single-walled carbon nanotubes, and it is a non-bundled single-root dispersed single-walled carbon nanotube ( Figure 5 ).

[0103] The surface of the ultra-high purity single-walled carbon nanotubes is connected with oxygen-containing groups, and the oxygen-containing groups include hydroxyl groups, epoxy groups, carboxyl groups, and carbonyl groups.

[0104] The purity of the ashed single-walled carbon nanotubes is 75 wt%; the impurities in the ashed single-walled carbon nanotubes include crystalline carbon sphere particles, graphene sheets, fullerene spheres, metal crystalline carbon particles, and multi-walled carbon nanotubes, and the content of metal impurities is 8 wt%. The particle size of the metal particles in the metal crystalline carbon particles is 1 - 50 nm; the particle size of the metal particles in the metal crystalline carbon particles is 2 - 10 nm. The single-walled carbon nanotubes in the ashed single-walled carbon nanotubes exist in bundles ([ Figure 6 ), and the bundles are staggered with each other and intertwined irregularly. The metal crystalline carbon particles are embedded between the staggered grids of the single-walled carbon nanotubes, and some are adhered to the surface of the single-walled carbon nanotubes, and some are bonded to the surface of the single-walled carbon nanotubes together.

[0105] Multi-walled carbon nanotubes were monitored to be oxidized and peeled into long graphene sheets in the centrifugal sediment, indicating that multi-walled carbon nanotubes can also be removed by this method.

[0106] Unless otherwise specified, the test methods are all conventional methods, and the instrument settings are all the settings recommended by the manufacturer.

[0107] Among them, transmission electron microscopy (TEM, FEI Company, USA, Tecnai F20) was used for transmission electron microscopy analysis; X-ray powder diffractometer (XRD, Rigaku, Miniflex600) was used for phase analysis of compounds; a fully automatic gas physical adsorption instrument (Quantachrome Instruments, USA, Autosorb-iQ2-XR) was used to test the specific surface area and perform pore structure analysis; X-ray photoelectron spectrometer (XPS, Thermo Fisher, ESCALAB 250Xi) was used for X-ray photoelectron spectroscopy analysis; an electrochemical workstation (Chenhua, Shanghai, CHI660D) was used for cyclic voltammetry testing and electrochemical impedance testing; a field emission scanning electron microscope (FESEM, SU-8010, Hitachi, Japan) was used for scanning electron microscopy analysis; a synchronous thermal analyzer (TG / DTA, STA449F3, Netzsch) was used for thermogravimetric analysis; a battery test system (Wuhan Blue Electric, CT3001A) was used for battery performance testing; a laser Raman spectrometer (RAMAN, LabRam HR Evo) was used for testing.

[0108] Example 1

[0109] (1) Preparation of Si-SWCNT

[0110] First, modify Si with poly(diallyldimethylammonium chloride) (PDDA) (20 wt.%). Specifically, disperse 300 mg of Si in a mixed solution of 300 mL of deionized water and ultrasonicate for 30 min. Then, add 9 mL of PDDA to the suspension, ultrasonicate for 60 min, and stir for 8 h to obtain a well-dispersed colloidal solution. Subsequently, remove the excess PDDA in the solution by centrifugation at 13,000 rpm for 15 min, and redisperse the Si sediment in deionized water successively. Repeat the above two steps twice to ensure that there is no residual excess PDDA in the aqueous dispersion, and finally obtain surface-modified Si-PDDA. In addition, dilute Si-PDDA with deionized water to 300 mL to make its nominal concentration 1 mg / mL, and then drop it into an aqueous dispersion of 800 mL of non-bundled single-dispersed oxidized single-walled carbon nanotubes (concentration 0.0375 mg / mL) and stir for 12 h. After the obtained sample is centrifuged and the sediment is freeze-dried, heat it in an argon atmosphere at 350 °C for 1 h to obtain the Si-SWCNT composite material, which is the composite material of single-walled carbon nanotube-coated silicon. The content of the single-walled carbon nanotube network wrapping layer relative to silicon is 10 wt.%.

[0111] (2) Preparation of Si-SWCNT@CNF

[0112] First, uniformly disperse 180 mg of Si-SWCNT in 3.2 mL of N,N-dimethylformamide (DMF) solvent and ultrasonically disperse it evenly; then add 460.8 mg of polyacrylonitrile (PAN, Mw = 150,000) with a concentration of 12.5 wt.% under stirring. Continue to stir at 60 °C for 8 h. Subsequently, electrospinning is carried out under specific conditions (voltage of 13.5 kV and flow rate of 1 mL / h), and the collected fibrous cloth is named Si-SWCNT@PAN. Then, place Si-SWCNT@PAN in an air muffle furnace and heat it to 260 °C at a rate of 2 °C / min. After pre-oxidation at this temperature for 3 h, obtain a black fibrous cloth and cut it into electrode sheets. Finally, heat the cut electrode sheets in an argon atmosphere to 800 °C at a rate of 5 °C / min and then keep the temperature constant for carbonization for 3 h to obtain the sample, which is the silicon-carbon composite material (Si-SWCNT@CNF). Denote the obtained silicon-carbon composite material of this Example 1 as Si-SWCNT@CNF-1, and the content of its silicon particles is 38 wt.%.

[0113] (3) Lithium-ion battery assembly and performance testing

[0114] The above-mentioned electrode active material (Si-SWCNT@CNF-1) (70 wt%), conductive carbon black (Super P) (15 wt%), and carboxymethyl cellulose (CMC 15 wt%) were simultaneously placed in an agate mortar for grinding, with deionized water as the dispersant and copper foil as the current collector. The ground slurry was evenly coated on the copper foil using a coater. After drying in a vacuum at 80 °C for 12 h, the copper foil was cut into 10-mm electrode sheets and weighed. The loading mass of the slurry on each electrode sheet was obtained based on the mass difference of the copper foil before and after coating. Finally, the electrode sheet was quickly transferred to a glove box for assembling a coin cell.

[0115] The coin cell was assembled in a glove box filled with argon. For the assembly of the lithium-ion battery (LIB) half-cell, the counter electrode and separator were a lithium sheet and a Celgard 2500 membrane, respectively, and the electrolyte was 1 M LiPF6 in ethylene carbonate (EC): diethyl carbonate (DEC) (volume ratio 1:1), containing 10 wt% fluoroethylene (FEC). The constant current charge-discharge test mainly examined the charge-discharge specific capacity, cycling 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 a scanning rate of 0.1 mV s -1 .

[0116] Example 2

[0117] The difference between this example and Example 1 was that the mass of the Si-SWCNT input was 240 mg. The obtained silicon-carbon composite material was denoted as Si-SWCNT@CNF-2.

[0118] Example 3

[0119] The difference between this example and Example 1 was that the mass of the Si-SWCNT input was 300 mg. The obtained silicon-carbon composite material was denoted as Si-SWCNT@CNF-3.

[0120] Example 4

[0121] The differences between this example and Example 1 are as follows: the mass of the input Si-SWCNT is 150 mg; in the method of step (1), the concentration of Si-PDDA can be selected from 0.5 g / L, the dispersion of non-bundled single-walled carbon nanotubes can be selected from 0.05 g / L, and the annealing temperature in an inert atmosphere or vacuum can be selected from 300 °C for 12 hours; in the method of step (1), the content of the single-walled carbon nanotube network wrapping layer relative to silicon in the silicon-coated single-walled carbon nanotube composite is adjusted to 15 wt.%; in the method of step (2), the concentration of polyacrylonitrile relative to DMF is 10 wt.%; in the method of step (2), the high-temperature annealing and carbonization conditions are 600 °C for 12 h in a nitrogen atmosphere; the finally obtained silicon-carbon composite is denoted as Si-SWCNT@CNF-4, and the content of its silicon particles is 30 wt.%. Although the silicon content in the fibers of Si-SWCNT@CNF-4 is low, slight agglomeration of silicon particles still appears on the outer shell of the fibers.

[0122] Example 5

[0123] The differences between this example and Example 1 are as follows: the mass of the input Si-SWCNT is 400 mg; in the method of step (1), the concentration of Si-PDDA can be selected from 0.05 g / L, the dispersion of non-bundled single-walled carbon nanotubes can be selected from 0.001 g / L, and the annealing temperature in an inert atmosphere or vacuum can be selected from 1000 °C for 0.1 hour; in the method of step (2), the concentration of polyacrylonitrile relative to DMF is 15 wt.%; in the method of step (1), the content of the single-walled carbon nanotube network wrapping layer relative to silicon in the silicon-coated single-walled carbon nanotube composite is adjusted to 5 wt.%; in the method of step (2), the high-temperature annealing and carbonization conditions are 1000 °C for 0.5 h in a nitrogen atmosphere; the finally obtained silicon-carbon composite is denoted as Si-SWCNT@CNF-5, and the content of its silicon particles is 60 wt.%. There is too much Si-SWCNT in the fibers of Si-SWCNT@CNF-5, and more silicon particles agglomerate on the outer shell of the fibers.

[0124] Comparative Example 1

[0125] The difference between this Comparative Example 1 and the examples is that step (1) is not performed, and silicon particles are directly used to replace Si-SWCNT in step (2). The dosages of silicon are 180 mg, 240 mg, and 300 mg respectively, and three samples are obtained, denoted as Si@CNF-1, Si@CNF-2, and Si@CNF-3.

[0126] Comparative Example 2

[0127] The difference between this embodiment and Embodiment 1 is that the non-bundled single-root dispersed oxidized single-walled carbon nanotubes in step (1) are replaced with the original bundled single-walled carbon nanotubes. Due to the surface chemical inertness of the original bundled single-walled carbon nanotubes, it is difficult to form a uniform coating with silicon particles. And the single-walled carbon nanotubes in the electrospinning precursor solution prepared in step (2) significantly settle at the bottom, failing to form a uniform precursor solution and unable to smoothly carry out the expected electrospinning.

[0128] Taking Examples 1-3 and Comparative Example 1 as typical examples for characterization tests:

[0129] The preparation process of Si-SWCNT@CNF is as Figure 1 shown. First, the original Si particles are electrostatically self-assembled to achieve a network-like coating layer of single-walled carbon nanotubes wrapped on the surface of the silicon particles, obtaining Si-SWCNT. Then, Si-SWCNT is encapsulated in the core of the core-shell nanofibers by electrospinning. Finally, Si-SWCNT@CNF is obtained through pre-oxidation and subsequent high-temperature carbonization, where Si-SWCNT particles are uniformly encapsulated in the hierarchical porous carbon framework. Figure 2 SEM pictures were observed to show the coating process of the SWCNT layer on the surface of Si nanoparticles. Figure 2 (a) shows that the original nano-Si has a spherical shape with an average diameter of about 100 nm. Figure 2 (b) shows the Si nanoparticles anchored with single-walled carbon nanotubes, namely Si-SWCNT, demonstrating a well-dispersed network-like coating covering the silicon particles. Figure 2 (c) and Figure 2 (d) show the TEM images and Mapping element distribution maps of Si-SWCNT, further verifying that a thin layer of network-like coating of single-walled carbon nanotubes is anchored on the surface of silicon.

[0130] Figure 3 It shows the morphological observation of the final samples with different silicon contents during the electrospinning process. Different groups of samples are obtained by controlling the amounts of Si and Si-SWCNT. The influence of different silicon precursor contents on the morphology. Figure 3 (a-c) show the Si@CNF samples corresponding to different Si contents. It can be seen that among the three samples, pure Si undergoes severe agglomeration, and the severity of agglomeration becomes more and more obvious with the increase of Si content, indicating that it is difficult for pure Si precursors to infiltrate with the spinning solution to obtain a good fiber core-shell structure. Pure Si will directly contact the electrolyte in the subsequent electrochemical tests, resulting in the failure of electrochemical performance, which is reflected in the subsequent electrochemical tests. In Figure 3(d-f) show the morphological observations of Si-SWCNT@CNF samples obtained with different contents of Si-SWCNT. Agglomeration is greatly alleviated, indicating that a single-walled carbon nanotube network coating layer is anchored on the Si particles to form Si-SWCNT, and the surface is rich in oxygen-containing groups. The formation of these bonds not only reduces the agglomeration between nano-Si, but also provides sufficient hydrogen bonds and active sites between Si-SWCNT and the precursor (PAN). At the same time, we observe the morphology of the Si-SWCNT@CNF-2 sample, which is relatively continuous and uniform in the shape of a fiber core-shell. The content of Si-SWCNT in the fibers of Si-SWCNT@CNF-1 is less, showing discontinuity; the content of Si-SWCNT in the fibers of Si-SWCNT@CNF-3 is excessive, showing slight agglomeration in the outer shell of the fiber. As Figure 3 (g) and 3(h) show, the microstructure of Si-SWCNT@CNF-2 was observed by TEM ( Figure 3 (g)). It can be seen that Si-SWCNT nanoparticles are uniformly embedded in the core layer of the hierarchical porous CNF. The TEM-EDS mapping of Si-SWCNT@CNF-2 further confirms that Si-SWCNT nanoparticles are uniformly embedded in the porous CNF ( Figure 3 (h)).

[0131] The nitrogen physical adsorption properties of Si, Si-SWCNT, Si@CNF-2 and Si-SWCNT@CNF-2 were tested respectively, and specific surface area analysis and pore size distribution analysis were carried out. The results show that their specific surface areas are 17, 75.2, 201.1, 209.5 m 2 g -1 . Si@CNF-2 and Si-SWCNT@CNF-2 have a rapid increase in adsorption at low pressure and an obvious hysteresis loop at medium pressure, indicating the presence of micropores and mesopores in the samples. The presence of mesopores not only helps the rapid penetration of the electrolyte, thus promoting the transport of lithium ions and electrons in the composite material, but also provides sufficient space for the expansion of silicon during cycling. And Si-SWCNT@CNF-2 has a larger specific surface area, which is more conducive to the transport of ions. At the same time, there are a large number of mesopores centered at 3-15 nm in Si-SWCNT@CNF-2, which may be due to the shrinkage of polyacrylonitrile at high temperature during the carbonization process, releasing a large amount of water and hydrogen, thus generating a porous carbon layer. Table 1 lists the specific surface area, total pore volume and average pore diameter of the four samples. Si-SWCNT@CNF-2 has the largest total pore volume. The addition of single-walled carbon nanotubes makes Si-SWCN form a uniform core-shell structure inside the carbon fiber, thus generating more voids inside. Si, Si-SWCNT, Si@CNF and Si-SWCNT@CNF were tested in air atmosphere at 5 °C min-1 Thermogravimetric tests (TGA) were conducted on the heating rate from 30 °C to 800 °C. The results showed that the Si contents in Si@CNF-1, Si@CNF-2, and Si@CNF-3 were 42%, 48%, and 54% respectively. Similarly, the Si contents of Si-SWCNT@CNF-1, Si-SWCNT@CNF-2, and Si-SWCNT@CNF-3 were 38%, 41%, and 50% respectively.

[0132] As Figure 4 (a) shows, cyclic voltammetry (CV) tests were carried out on the initial three cycles in the potential range of 0.05 - 2.0 V at a scan rate of 0.1 mV s -1 to study the lithiation / delithiation process of the Si-SWCNT@CNF-2 anode. A broad cathodic peak at 0.41 V was observed at 0.3 - 0.7 V, but it disappeared in subsequent cycles. This phenomenon corresponded to the formation of the SEI film on the electrode surface. The anodic peaks at 0.31 V and 0.50 V were attributed to the delithiation process of amorphous Li x Si. The cathodic peak at 0.2 V and the anodic peaks at 0.31 V and 0.50 V for each cycle curve remained almost unchanged, which could be attributed to the good reversibility during the insertion and extraction of Li in the Si particles. It can be clearly seen that as the number of cycles increased, the intensities of the two oxidation peaks gradually increased, which was a sign of the gradual activation of the anode. Figure 4 (b) shows the galvanostatic charge-discharge curves of Si-SWCNT@CNF-2 for the initial three cycles at 0.2 A g -1 . During the initial discharge process, an extended discharge plateau was observed, which was related to the formation of the amorphous LixSi alloy. There was a relatively flat and extended charge plateau below 0.5 V, which was due to the formation of single-crystalline silicon. The initial discharge / charge capacities were 1554 / 1335.7 mAh g -1 , and the initial Coulombic efficiency (ICE) was 86.0%. The irreversible capacity loss was attributed to the generation of the SEI film and electrolyte loss during the initial cycle. Figure 4 (c) and 4(e) depict the charge-discharge curves of the first two cycles of Si@CNF-2 and Si-SWCNT respectively. Their first charge-discharge capacities were 1854.4 / 1569.5 and 3213 / 2873.7 mAh g -1 , and the initial ICEs were 84.5% and 89.4% respectively. It was found that the first Coulombic efficiency of Si-SWCNT was higher, probably due to the addition of single-walled carbon nanotubes to form a conductive network, and more Si participated in the reaction. To evaluate the electrochemical performance of Si@CNF and Si-SWCNT@CNF with different Si contents, the rate performance tests of samples with different Si contents were carried out at different current densities. AsFigure 4 As shown in (c), among the Si@CNF samples with different Si contents, Si@CNF-2 exhibits the best rate performance. At 200, 500, 1000, 2000, and 4000 mA g -1 the specific capacities are 1807.4, 1272.6, 1097.7, 882, and 689.2 mAh g -1 respectively. Since Si@CNF-1 has a lower Si content, its capacity at different current densities is smaller than that of Si@CNF-2. It is worth noting that Si@CNF-3 shows the worst rate performance. This is because the increase in Si content leads to more serious agglomeration during the electrospinning process, further decreasing the overall stability of the electrode structure, which corresponds to the situation observed by SEM. In Figure 4 (e), it can be seen that among the Si-SWCNT@CNF electrodes with different Si contents, the Si-SWCNT@CNF-2 electrode has the best rate performance. At 200, 500, 1000, 2000, and 4000 mA g -1 the specific capacities are 1567.6, 1157.3, 994.4, 838.9, and 720.8 mAh g -1 respectively. In addition, when the current density returns to 0.2 A g -1 , the charging capacity quickly rebounds to 1313.6 mA h g -1 , showing excellent capacity retention. However, in the Si-SWCNT@CNF-3 electrode, the recovery is not as good, indicating that as the Si content in the material increases, the electrode structure becomes unstable and damaged after charge-discharge cycling at high current densities, resulting in capacity loss. Si-SWCNT@CNF-2 has an appropriate Si content, ensuring the structural uniformity and thus generating good electrochemical performance. The capacity of Si-SWCNT decays rapidly, indicating that simply anchoring a single-walled carbon nanotube coating layer around nano-Si cannot effectively improve the cycling stability of the anode material.

[0133] Figure 4 (d) further compares the cycling stabilities of Si-SWCNT, Si@CNF-2, and Si-SWCNT@CNF-2. Si-SWCNT@CNF-2 at 0.5 A g -1After 200 cycles, the charging capacity remains at 966.1 mAh g. Even after 500 cycles, the specific capacity remains at 1017.9 mA h g-1, and the capacity retention rate reaches 87.7% (relative to the initial specific capacity of 0.5 A g-1). In contrast, both Si@CNF-2 and Si-SWCNT show rapid capacity decay, and the capacity retention rates are only 38.49% and 12.52% after 200 cycles. The better capacity retention rate of Si-SWCNT@CNF-2 is attributed to its continuous and uniform core-shell structure. The addition of single-walled carbon nanotubes can well fix the Si-SWCNT particles in the carbon fiber tube, avoiding direct contact with the electrolyte. At the same time, the multi-level core-shell structure can further alleviate the volume expansion of Si. As shown in Figure 4 (f), even at a current density of 1.0 A g -1 , after 220 cycles, Si-SWCNT@CNF-2 still maintains a high charging specific capacity of 727.8 mAh g -1 .

[0134] Table 1 Specific surface area, pore volume and average pore diameter of Si-SWCNT@CNF-2, Si@CNF-2, Si-SWCNT and Si composites

[0135]

[0136] As mentioned above, the above are only several embodiments of the present application, and do not impose any form of limitation on the present application. Although the present application is disclosed as above with preferred embodiments, it is not used to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the technical content disclosed above is equivalent to equivalent implementation cases, and all belong to the scope of the technical solution.

Claims

1. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material includes a composite material of carbon fiber and single-walled carbon nanotube coated silicon; The composite material of single-walled carbon nanotubes coated with silicon is embedded inside the carbon fiber; The composite material of single-walled carbon nanotube-coated silicon comprises silicon particles and a single-walled carbon nanotube mesh wrapping layer; The single-walled carbon nanotube mesh wrapping layer is tightly wrapped around the outer surface of the silicon particle; The single-walled carbon nanotube mesh wrapping layer is a two-dimensional net bag structure formed by assembling non-tube-bundled single dispersed oxidized single-walled carbon nanotubes as assembly primitives.

2. The silicon-carbon composite material according to claim 1, characterized in that: The surface of the non-bundled single dispersed oxidized single-walled carbon nanotube contains oxygen-containing functional groups; The oxygen-containing functional groups include hydroxyl, carboxyl and epoxy groups; Preferably, the silicon particles are selected from one or both of pure silicon particles or silicon dioxide particles; Preferably, in the composite material of single-walled carbon nanotube-coated silicon, the content of the single-walled carbon nanotube network wrapping layer relative to the silicon particles is 1 to 15 wt.%; Preferably, in the silicon-carbon composite material, the content of the silicon particles is 30-60 wt.%.

3. The method for preparing the silicon-carbon composite material according to any one of claims 1 to 2, characterized in that: The steps include: (a1) Modifying the outer surface of silicon particles with polyquaternary ammonium salt to obtain Si-PQAS; (b1) wrapping a single-walled carbon nanotube mesh wrapping layer tightly on the outer surface of Si-PQAS, and annealing in an inert atmosphere or under vacuum to obtain a single-walled carbon nanotube-coated silicon composite material Si-SWCNT; (c1) dissolving Si-SWCNT in a solvent and adding polyacrylonitrile to obtain a uniform and stable dispersion precursor; (d1) electrospinning the dispersion precursor to obtain a nanofiber cloth; (e1) Pre-oxidizing the nanofiber cloth in air and then annealing and carbonizing it at high temperature to obtain the silicon-carbon composite material.

4. The preparation method according to claim 3, characterized in that: The step (a1) comprises: adding polyquaternary ammonium salt to a silicon dispersion, and ultrasonically treating the mixture to obtain Si-PQAS; The polyquaternary ammonium salt is selected from at least one of polydiallyldimethylammonium chloride, polydimethyldiallylammonium chloride, polymethacrylamidepropyltrimethylammonium chloride, and polymethacrylamidepropyldodecyldimethylammonium chloride.

5. The preparation method according to claim 3, characterized in that: The step (b1) comprises: adding a solution containing non-bundled single dispersed oxidized single-walled carbon nanotubes to a dispersion of Si-PQAS, and annealing at 300 to 1000° C. for 0.1 to 12 hours in an inert atmosphere or in an airtight state to obtain the single-walled carbon nanotube-coated silicon composite material Si-SWCNT; Preferably, in the Si-PQAS dispersion, the concentration of Si-PQAS is 0.05 to 1 g / L; Preferably, in the solution containing non-tube-bundled single dispersed oxidized single-walled carbon nanotubes, the concentration of the non-tube-bundled single dispersed oxidized single-walled carbon nanotubes is 0.001-0.05 g / L.

6. The preparation method according to claim 5, characterized in that: The method for preparing the solution containing non-bundled single dispersed oxidized single-walled carbon nanotubes comprises: Potassium permanganate 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 after being stirred evenly, the obtained reaction mixture is continuously stirred and reacted at a temperature of 50-60°C for 2-3 hours, and then the reaction mixture is diluted with water, and then an excess of hydrogen peroxide solution is added to reduce and remove the manganese dioxide solid generated in the reaction process, and after filtering and washing with an 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, centrifuged at 5000-14000 rpm, and then the upper uniform solution is taken out, and then the uniform solution is filtered, washed with water to collect the black solid, and then dissolved in water before it is dried to obtain the dispersed aqueous solution of the non-tube-bundled single dispersed single-walled carbon nanotube.

7. The preparation method according to claim 3, characterized in that: The step (c1) comprises: uniformly dispersing Si-SWCNT in N,N-dimethylformamide solvent, and then adding polyacrylonitrile to completely dissolve it in the dispersion to obtain a uniform and stable dispersion precursor; Preferably, the mass ratio of Si-SWCNT to polyacrylonitrile is 0.3 to 1:1; Preferably, the concentration of polyacrylonitrile relative to N,N-dimethylformamide is 10-15 wt.%.

8. The preparation method according to claim 3, characterized in that: In the step (d1), the electrospinning is uniaxial electrospinning, and the injection speed is 1 to 1.5 mL·h -1 , the applied voltage is 12-15 kV; Preferably, in the step (e1), the pre-oxidation treatment is carried out at a constant temperature of 260 to 300° C. for 3 to 5 hours; Preferably, in the step (e1), the high temperature annealing and carbonization comprises: annealing at 600-1000° C. for 0.5-12 h in an inert atmosphere or in an airtight state.

9. Use of the silicon-carbon composite material according to any one of claims 1 to 2 or the silicon-carbon composite material prepared by the preparation method according to any one of claims 3 to 8 in electrode materials; Preferably, 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 negative electrode material of the secondary battery contains the silicon-carbon composite material according to any one of claims 1 to 2 or the silicon-carbon composite material prepared by the preparation method according to any one of claims 3 to 8; Preferably, the secondary battery is a lithium-ion battery.

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