Preparation method for constructing topological defects of silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes

Abstract

The invention discloses a preparation method for constructing topological defects of a silicon-carbon negative electrode and growing a composite multi-walled carbon nanotube, which comprises the following steps of: performing plasma treatment on the surface of a silicon-carbon negative electrode material in a plasma environment by adopting plasma treatment equipment to obtain the silicon-carbon negative electrode material with the topological defects; the preparation method comprises the following steps: putting a silicon-carbon negative electrode material with topological defects into a tubular furnace of chemical vapor deposition equipment, introducing inert gas to remove air, heating to a preset temperature, then introducing a mixed atmosphere composed of the inert gas and carbon source gas, and carrying out autocatalytic growth of a multi-walled carbon nanotube on the surface of the silicon-carbon negative electrode material to obtain the multi-walled carbon nanotube. And preparing the silicon-carbon negative electrode composite multi-walled carbon nanotube material. According to the method disclosed by the invention, the intrinsic conductivity of the silicon-carbon negative electrode material is fundamentally improved, the problem that a physical mixing interface of the conductive agent and the active substance is unstable is avoided, meanwhile, the constructed three-dimensional conductive network can further relieve stress caused by expansion of the silicon negative electrode, and the electrode preparation process is simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-carbon negative electrode material preparation, and in particular to a method for constructing silicon-carbon negative electrode topological defects and growing composite multi-walled carbon nanotubes. Background Art

[0002] Among the many lithium-ion battery negative electrode materials, silicon negative electrode has a high capacity of up to 4200mAhg -1 The theoretical capacity of silicon is about 0.4V, and the lithium insertion potential is about 0.4V. It is less likely to precipitate lithium than graphite. In addition, the content of silicon in the earth's crust is second only to oxygen, and its reserves are abundant and its sources are wide. Therefore, silicon negative electrode is considered to be the best substitute for graphite negative electrode. However, the volume expansion of silicon negative electrode during lithium storage is as high as 300% and its extremely low electrical conductivity has brought great obstacles to its practical application. The more mature solution strategy at present is to prepare silicon-carbon negative electrode by compounding nano-silicon with porous carbon. The void structure of porous carbon can effectively inhibit the volume change of nano-silicon. However, porous carbon materials are basically amorphous carbon matrices. Therefore, the conductivity of silicon-carbon negative electrode is very limited. Its application in lithium-ion batteries requires the addition of a large amount of conductive agent, which not only increases the application cost, but also has an unsatisfactory effect on improving the conductivity of silicon-carbon negative electrode.

[0003] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for constructing topological defects in a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes, aiming to solve the problem of low conductivity of existing silicon-carbon negative electrode materials.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for constructing topological defects in a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes, comprising the steps of:

[0007] Provide silicon-carbon anode materials;

[0008] Using a plasma treatment device to perform plasma treatment on the surface of the silicon-carbon negative electrode material in a plasma environment, so that topological defects are generated on the surface of the silicon-carbon negative electrode material, thereby obtaining a silicon-carbon negative electrode material with topological defects;

[0009] The silicon-carbon negative electrode material with topological defects is placed in a tubular furnace of a chemical vapor deposition device, an inert gas is introduced to remove the air, and the temperature is raised to a predetermined temperature. Then, a mixed atmosphere consisting of an inert gas and a carbon source gas is introduced to perform autocatalytic growth of multi-walled carbon nanotubes on the surface of the silicon-carbon negative electrode material to obtain a silicon-carbon negative electrode composite multi-walled carbon nanotube material.

[0010] The method for preparing the silicon-carbon negative electrode topological defect construction and growth of composite multi-walled carbon nanotubes, wherein, in the step of using plasma treatment equipment to perform plasma treatment on the surface of the silicon-carbon negative electrode material in a plasma environment, argon is used as the plasma gas source, the gas flow rate is 5-50sccm, the chamber pressure during treatment is 0.2-1.0MPa, the treatment power is 100-300W, and the treatment time is 10-120s.

[0011] The method for constructing topological defects of the silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes, wherein the topological defects refer to one or more of five-membered ring defects, seven-membered ring defects and eight-membered ring defects in the carbon matrix of the silicon-carbon negative electrode material.

[0012] In the method for constructing topological defects of a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes, the inert gas is one of argon and helium.

[0013] In the method for constructing topological defects of a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes, the carbon source gas is one of acetylene, ethylene and methane.

[0014] In the method for constructing topological defects of a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes, the flow rate ratio of the inert gas to the carbon source gas is 9:1-5:5.

[0015] The method for preparing the silicon-carbon negative electrode topological defect construction and growth of composite multi-walled carbon nanotubes, wherein, in the step of heating to a predetermined temperature after introducing an inert gas to remove air, the temperature is kept at 5-10°C / min. -1 The heating rate is increased to 400-600℃.

[0016] In the method for preparing silicon-carbon negative electrode topological defect construction and growth of composite multi-walled carbon nanotubes, the autocatalytic growth time is 0.5h-5h in the step of performing autocatalytic growth of multi-walled carbon nanotubes on the surface of the silicon-carbon negative electrode material.

[0017] A silicon-carbon negative electrode composite multi-walled carbon nanotube material is prepared by the method for constructing silicon-carbon negative electrode topological defects and growing composite multi-walled carbon nanotubes according to the present invention.

[0018] An application of a silicon-carbon negative electrode composite multi-walled carbon nanotube material, wherein the silicon-carbon negative electrode composite multi-walled carbon nanotube material of the present invention is used to prepare a lithium ion battery negative electrode.

[0019] Beneficial effects: The method proposed in the present invention for constructing topological defects on the surface of silicon-carbon negative electrode materials using plasma can not only realize the efficient construction of topological defects in the carbon matrix on the surface of silicon-carbon negative electrode materials, but also avoid the problem that other construction methods will have adverse effects on the structure, chemical composition and performance of silicon-carbon negative electrode materials; the strategy proposed in the present invention for self-catalytic growth of multi-walled carbon nanotubes on the surface of silicon-carbon negative electrode materials not only fundamentally improves the intrinsic conductivity of silicon-carbon negative electrode materials, but also avoids the problem of unstable interface between the physical mixing of conductive agent and active material. At the same time, the constructed three-dimensional conductive network can further alleviate the stress caused by the expansion of silicon negative electrode and simplify the electrode preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a method for constructing topological defects in a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes according to the present invention.

[0021] Figure 2 This is an electron microscope image of the topological defect construction and growth of composite multi-walled carbon nanotubes in the silicon-carbon negative electrode prepared in Example 1 of the present invention.

[0022] Figure 3 This is an electron microscope image of the topological defect construction and growth of composite multi-walled carbon nanotubes in the silicon-carbon negative electrode prepared in Example 2 of the present invention.

[0023] Figure 4 This is a TEM characterization image of the multi-walled carbon nanotubes produced in Example 2 of the present invention.

[0024] Figure 5 This is an electron microscope image of the topological defect construction and growth of composite multi-walled carbon nanotubes in the silicon-carbon negative electrode prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0025] The present invention provides a method for constructing topological defects in a silicon-carbon anode and growing composite multi-walled carbon nanotubes. To make the objectives, technical solutions, and effects of the present invention more clear and explicit, the present invention is further described below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0026] The current silicon-carbon negative electrode is used in lithium-ion batteries. The process of improving the conductivity of the electrode by adding a conductive agent has the following main problems: 1) Interface instability of physical mixing. The conductive agent and the silicon-carbon negative electrode material are physically mixed and lack chemical bonding. When the volume of the silicon matrix expands, the contact interface between the conductive agent and the active particles is prone to peeling, resulting in interruption of electron transmission and increased internal resistance; 2) The conductive agent is unevenly dispersed. The addition of a large amount of conductive agent requires prolonged homogenization time, but local "dead zones" may still be formed due to particle agglomeration. In these areas, electron transmission is too strong and ion conduction is hindered, which can easily cause polarization; 3) The proportion of active material is reduced. The conductive agent itself has extremely low lithium storage capacity. Its addition will cause the overall specific capacity of the electrode to decrease; 4) The first efficiency of the silicon negative electrode is already low (75-85%). The conductive agent increases the surface area of ​​the electrode, prompting the electrolyte to decompose to form a thicker SEI film, consuming more active lithium, and causing the first efficiency to further decrease; 5) The high conductive agent content increases the slurry viscosity, requiring additional solvent dilution, which not only increases the cost but also introduces residual risks.

[0027] Based on this, the present invention provides a method for constructing silicon-carbon anode topological defects and growing composite multi-walled carbon nanotubes, such as Figure 1 As shown, it includes the steps of:

[0028] S10, providing silicon-carbon negative electrode material;

[0029] S20, using a plasma treatment device to perform plasma treatment on the surface of the silicon-carbon negative electrode material in a plasma environment, so that topological defects are generated on the surface of the silicon-carbon negative electrode material, thereby obtaining a silicon-carbon negative electrode material with topological defects;

[0030] S30. Place the silicon-carbon negative electrode material with topological defects in a tubular furnace of a chemical vapor deposition device, introduce an inert gas to remove the air and then heat it to a predetermined temperature, then introduce a mixed atmosphere consisting of an inert gas and a carbon source gas to perform autocatalytic growth of multi-walled carbon nanotubes on the surface of the silicon-carbon negative electrode material to obtain a silicon-carbon negative electrode composite multi-walled carbon nanotube material.

[0031] Specifically, topological defects in the carbon matrix refer to non-hexagonal defects such as five-membered rings, seven-membered rings, and eight-membered rings in the carbon matrix. These defects can induce local charge rearrangement of the carbon substrate, thereby having excellent catalytic activity. In theory, they can serve as excellent catalytic active sites for promoting the growth of carbon nanotubes. If a large number of topological defects are constructed on the surface of the silicon-carbon negative electrode, and the growth of carbon nanotubes by the silicon-carbon negative electrode is achieved, it is expected to greatly improve the intrinsic conductivity of the silicon-carbon negative electrode, and fundamentally solve the problem of low electrical conductivity of the silicon-carbon negative electrode. Based on this idea, the present invention first needs to construct a large number of topological defects on the surface of the silicon-carbon negative electrode material, and then achieve the growth of carbon nanotubes by the silicon-carbon negative electrode to improve its intrinsic conductivity, and fundamentally solve the problem of poor electrical conductivity of the silicon-carbon negative electrode. However, current methods for constructing topological defects in carbon matrices, such as chemical in-situ etching (usually in a strong alkaline environment) and high-temperature heteroatom removal (usually at temperatures ≥1100°C), are unable to ensure the efficient construction of topological defects without affecting the structure and chemical composition of the silicon-carbon negative electrode material itself.

[0032] Therefore, in order to address the problem that the existing carbon matrix topological defect construction method is not suitable for silicon-carbon negative electrode materials, the present invention proposes a method of using plasma treatment to construct topological defects on the surface of silicon-carbon negative electrode materials. The advantages of plasma treatment are: 1) low-temperature treatment and environmental friendliness. Plasma treatment mainly occurs in the gas phase and on the surface of the material. The overall substrate temperature can be kept very low or even at room temperature, which will not affect the structure and chemical composition of the silicon-carbon negative electrode material itself; 2) high energy density and selective activity. Plasma is composed of high-energy electrons, ions, excited atoms / molecules and free radicals. The energy range is usually from a few electron volts to tens of electron volts, which is much higher than the carbon-carbon bond energy (-3.6 eV). These high-energy particles can selectively "knock out" carbon atoms in specific positions or cause them to shift / rotate, thereby generating topological defects; 3) precise controllability and adjustability. The parameters of plasma treatment (such as power, gas type, gas pressure, treatment time, etc.) provide extremely rich controllable dimensions; 4) surface selectivity and non-destructiveness. The depth of plasma treatment is usually limited to a few nanometers to tens of nanometers on the surface of the material, thus avoiding affecting the main structure and performance of the silicon-carbon negative electrode material; 5) high efficiency and rapid processing. Plasma treatment is usually completed in seconds to minutes, which is much more efficient than other physical / chemical methods.

[0033] After obtaining a silicon-carbon negative electrode material with topological defects, a CVD method is used to induce a carbon source gas to undergo a self-catalytic reaction on the surface of the silicon-carbon negative electrode material to generate multi-walled carbon nanotubes, thereby obtaining a silicon-carbon negative electrode topological defect construction and growth composite multi-walled carbon nanotubes. Compared with the process of improving the conductivity of the silicon-carbon negative electrode by adding a conductive agent, the advantages of the method of the present invention are: 1) Atomic-level interface bonding solves the contact failure problem. The carbon nanotubes grow directly from the surface carbon layer of the silicon-carbon negative electrode material in the form of covalent bonds to form an atomic-level interface bonding, avoiding the problem of surface interface instability of physical mixing; 2) The precise construction of a three-dimensional continuous conductive network structure. This strategy can regulate the arrangement direction and density of carbon nanotubes, and construct a long-range continuous three-dimensional conductive path between the silicon-carbon negative electrode particles. This structure can simultaneously replace the functions of traditional conductive agents, adhesives and even part of the current collector, realizing the "conductivity-mechanical enhancement-bonding" multifunctional integration; wherein, the density of carbon nanotubes is mainly adjusted by the pre-treatment of the silicon-carbon negative electrode, that is, plasma treatment, and the carbon surface is adjusted by different degrees of treatment. The defect density of the surface determines the density of the carbon tubes; the arrangement direction of the carbon tubes. Since the carrier of silicon in the silicon-carbon negative electrode is three-dimensional porous carbon, defects are constructed on the porous carbon surface and carbon tubes are grown in situ. The arrangement of carbon tubes is also basically three-dimensional. The silicon-carbon negative electrode particles and particles can realize the construction of a three-dimensional conductive network through the entanglement of a large number of carbon tubes grown in situ on the surface; 3) Active buffering mechanism of dynamic volume expansion. The in-situ growth of carbon nanotubes forms a "root-like" coating structure, which absorbs deformation stress through radial flexible support and evenly transfers local stress to the entire electrode through axial stress dispersion; 4) Ion / electron dual channel optimization. The in-situ grown carbon nanotubes not only make up for the intrinsic low conductivity of the silicon-carbon negative electrode material, but also the nanoscale pores formed between the carbon nanotubes shorten the Li + Diffusion path; 5) Subversively simplify the electrode preparation process. The self-catalytic growth of carbon nanotubes advances the construction of the conductive network to the material synthesis stage. Electrode preparation only requires simple coating, which will greatly shorten the homogenization time and avoid processing defects caused by high-viscosity slurry; 6) Compatible with high-silicon content systems, promoting a leap in energy density. This technology makes high-capacity negative electrodes with silicon content >30% possible.

[0034] In summary, the method proposed in the present invention for constructing topological defects on the surface of silicon-carbon negative electrode materials using plasma can not only realize the efficient construction of topological defects in the carbon matrix on the surface of silicon-carbon negative electrode materials, but also avoid the problem that other construction methods will have adverse effects on the structure, chemical composition and performance of silicon-carbon negative electrode materials; the strategy proposed in the present invention for self-catalytic growth of multi-walled carbon nanotubes on the surface of silicon-carbon negative electrode materials not only fundamentally improves the intrinsic conductivity of silicon-carbon negative electrode materials, but also avoids the problem of unstable interface between the physical mixing of conductive agent and active material. At the same time, the constructed three-dimensional conductive network can further alleviate the stress caused by the expansion of silicon negative electrode and simplify the electrode preparation process.

[0035] In some embodiments, in the step of plasma treating the surface of the silicon-carbon negative electrode material in a plasma environment using a plasma treatment device, argon is used as the plasma gas source, the gas flow rate is 5-50sccm, the chamber pressure during treatment is 0.2-1.0MPa, the processing power is 100-300W, and the processing time is 10-120s, but not limited thereto. As an example, the gas flow rate can be 5sccm, 10sccm, 15sccm, 20sccm, 25sccm, 30sccm, 35sccm, 40sccm, 45sccm, 50sccm, etc.; the chamber pressure during processing can be 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1.0MPa, etc.; the processing power can be 100W, 120W, 150W, 180W, 200W, 220W, 250W, 280W, 300W, etc.; the processing time can be 10s, 20s, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, etc.

[0036] In some embodiments, the topological defects are one or more of five-membered ring defects, seven-membered ring defects, and eight-membered ring defects in the carbon matrix of the silicon-carbon anode material, but are not limited thereto. Specifically, in ideal graphene, carbon atoms are connected by sp 2Hybridization forms a perfect six-membered ring honeycomb structure, while the topological defects in this embodiment describe the atomic-level structural defects present in the carbon matrix in the silicon-carbon negative electrode material. Its essence is that the arrangement of carbon atoms deviates from the hexagonal grid structure of ideal graphene. That is, topological defects refer to non-six-membered ring structures that appear in the carbon matrix, including five-membered ring defects, seven-membered ring defects, and eight-membered ring defects. These defects can cause the curvature of the carbon layer to change: for example, the five-membered ring causes the plane to bulge upward, while the seven- and eight-membered rings cause the plane to concave downward. For example, when five-membered rings / seven-membered rings appear in the carbon matrix, their local electron distribution is distorted: the five-membered ring: the carbon atom electron cloud density increases (electron-rich region); the seven-membered ring: the carbon atom electron cloud density decreases (electron-deficient region). This charge rearrangement forms highly active sites that can catalyze the decomposition of carbon source gases (such as acetylene) and trigger the growth of carbon nanotubes. Traditional methods require the addition of metal catalysts (such as Fe, Co), while the present invention utilizes the topological defects of the carbon matrix itself to achieve self-catalysis, avoiding the negative impact of metal impurities on battery performance.

[0037] In some embodiments, in the step of using a CVD method to induce a carbon source gas to undergo an autocatalytic reaction on the surface of the silicon-carbon anode material to form multi-walled carbon nanotubes, the inert gas is one of, but not limited to, argon and helium; the carbon source gas is one of, but not limited to, acetylene, ethylene, and methane; and the flow rate ratio of the inert gas to the carbon source gas is 9:1-5:5. Taking a total mixed atmosphere flow rate of 100 sccm as an example, the corresponding flow rates of the inert gas and the carbon source gas can be 90 sccm and 10 sccm, 80 sccm and 20 sccm, 70 sccm and 30 sccm, 60 sccm and 40 sccm, 50 sccm and 50 sccm, etc.

[0038] In some embodiments, in the step of heating to a predetermined temperature after the inert gas is introduced to remove air, the temperature is increased at 5-10°C / min. -1 The temperature is raised to 400-600° C. at a heating rate of 0.05° C. For example, the predetermined temperature may be 400° C., 420° C., 450° C., 480° C., 500° C., 520° C., 550° C., 580° C., 600° C., etc.

[0039] In some embodiments, in the step of autocatalytically growing multi-walled carbon nanotubes on the surface of the silicon-carbon negative electrode material, the autocatalytic growth time is 0.5 h to 5 h. For example, the autocatalytic growth time can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, etc.

[0040] In some embodiments, the silicon-carbon negative electrode material may be a commercial silicon-carbon negative electrode material, and the silicon-carbon negative electrode material may also be prepared by the following process:

[0041] Pretreatment of nano-silicon powder: Take nano-silicon powder with a particle size of 50-200nm, add it to anhydrous ethanol, ultrasonically disperse it for 30 minutes, add a 5% volume fraction of hydrofluoric acid solution, stir at room temperature for 10 minutes to remove the surface oxide layer (SiO2), then centrifuge and wash it with deionized water until it is neutral, vacuum dry it at 60℃ for 12 hours, and set aside.

[0042] Porous carbon selection and pretreatment: pore size of 50-200nm and specific surface area of ​​500-1500m 2 / g porous carbon (such as activated carbon, carbon aerogel or mesoporous carbon) was ground through a 200-mesh sieve and annealed at 300°C for 2h in an argon atmosphere to remove surface adsorbed impurities and set aside.

[0043] Preparation of composite slurry: Weigh the pretreated nano-silicon powder and porous carbon in a mass ratio of 1:3-1:5 (nano-silicon: porous carbon), add them to N-methylpyrrolidone (NMP) solvent, and add a dispersant (such as polyethylene glycol) accounting for 1%-3% of the total mass; use a planetary ball mill to mix, with a ball-to-material ratio of 10:1, a rotation speed of 300-500r / min, and a ball milling time of 4-6h to form a uniform nano-silicon-porous carbon mixed slurry.

[0044] Molding and curing: The mixed slurry is coated on the copper foil current collector with a coating thickness of 50-100 μm, and air-dried at 60°C for 2 h to initially remove the solvent; the mixture is transferred to a vacuum drying oven and vacuum-dried at 120°C for 12 h to completely remove the residual solvent to obtain a silicon-carbon composite electrode precursor.

[0045] Carbon coating and heat treatment: The precursor was placed in a tube furnace and heated at 5°C / min to 700-900°C under an argon atmosphere (flow rate 50 sccm). The temperature was maintained for 2 hours to stabilize the porous carbon and nano-silicon interface and reduce the surface activity of the nano-silicon. The precursor was then naturally cooled to room temperature to obtain the silicon-carbon anode material.

[0046] In some embodiments, the present invention further provides a silicon-carbon negative electrode composite multi-walled carbon nanotube material, which is prepared using the method for constructing silicon-carbon negative electrode topological defects and growing composite multi-walled carbon nanotubes described in the present invention.

[0047] In some embodiments, the present invention further provides an application of a silicon-carbon negative electrode composite multi-walled carbon nanotube material, which uses the silicon-carbon negative electrode composite multi-walled carbon nanotube material of the present invention to prepare a lithium-ion battery negative electrode.

[0048] The present invention will be further explained below by means of specific embodiments:

[0049] Example 1

[0050] A method for constructing topological defects in a silicon-carbon cathode and growing composite multi-walled carbon nanotubes comprises the following steps:

[0051] Preparation of silicon-carbon negative electrode material: Take nano-silicon powder with a particle size of 100nm, add it to anhydrous ethanol, ultrasonically disperse it for 30min, add 5% hydrofluoric acid solution by volume, stir it at room temperature for 10min to remove the surface oxide layer (SiO2), then centrifuge and wash it with deionized water until it is neutral, vacuum dry it at 60℃ for 12h, and set aside; select nano-silicon powder with a pore size of 100nm and a specific surface area of ​​1000m 2 / g of porous carbon (such as activated carbon) is ground through a 200-mesh sieve, annealed at 300°C for 2h in an argon atmosphere to remove surface adsorbed impurities, and set aside; the pretreated nano-silicon powder and porous carbon are weighed in a mass ratio of 1:4 (nano-silicon:porous carbon), added to an N-methylpyrrolidone (NMP) solvent, and a dispersant (such as polyethylene glycol) accounting for 2% of the total mass is added; and the mixture is ball-milled in a planetary ball mill with a ball-to-material ratio of 10:1, a rotation speed of 400 r / min, and a ball-milling time of 5h to form a uniform nano-silicon-porous carbon mixed slurry; The mixed slurry was coated on a copper foil current collector with a coating thickness of 80 μm, and dried at 60°C for 2 h to preliminarily remove the solvent; the mixture was transferred to a vacuum drying oven and vacuum dried at 120°C for 12 h to completely remove the residual solvent to obtain a silicon-carbon composite electrode precursor; the precursor was placed in a tubular furnace, and in an argon atmosphere (flow rate of 50 sccm), the temperature was raised to 800°C at 5°C / min and kept warm for 2 h to form a stable bond between the porous carbon and the nano-silicon interface, while reducing the surface activity of the nano-silicon; the mixture was naturally cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0052] Plasma treatment: placing the silicon-carbon negative electrode material in a chamber of a plasma treatment instrument, performing plasma treatment with argon as a plasma gas source, a gas flow rate of 10 sccm, a chamber pressure of 0.5 MPa, a processing power of 200 W, and a processing time of 30 s, so that topological defects are generated on the surface of the silicon-carbon negative electrode material, thereby obtaining a silicon-carbon negative electrode material with topological defects;

[0053] The silicon-carbon anode material was used to self-catalyze the growth of multi-walled carbon nanotubes: the plasma-treated silicon-carbon anode material was placed in a CVD tube furnace and purged with argon gas for 1 h at room temperature (the argon flow rate was 100 sccm); then, the temperature was set at 8 °C min -1 The temperature was raised to 500°C, and catalytic growth was carried out for 2 hours at 500°C in a mixed atmosphere of argon and acetylene (total gas flow rate was 100 sccm, and the flow rate ratio of argon to acetylene was 7:3) to carry out autocatalytic growth of carbon nanotubes on the surface of the silicon-carbon negative electrode material, thereby preparing a silicon-carbon negative electrode composite multi-walled carbon nanotube material.

[0054] The electron microscope image of the silicon-carbon negative electrode composite multi-walled carbon nanotube material prepared in Example 1 at a scale of 5 μm is as follows: Figure 2 As shown, from Figure 2 It can be seen that a large number of multi-walled carbon nanotubes are generated on the surface of the silicon-carbon negative electrode material through an autocatalytic reaction. These carbon nanotubes are arranged in a three-dimensional network, with uniform diameter and moderate length, and can form continuous connections between the silicon-carbon particles. The advantages of this structure are: the three-dimensional network can replace traditional conductive agents, directly constructing long-range electron transport channels, significantly improving the conductivity of the material; the entanglement between the carbon nanotubes can buffer the stress generated by the volume expansion of the silicon particles, and combined with their covalent bonding with the silicon-carbon matrix, it avoids the interfacial delamination problem of physically mixed conductive agents, providing support for cycle stability.

[0055] Example 2

[0056] A method for constructing topological defects in a silicon-carbon cathode and growing composite multi-walled carbon nanotubes comprises the following steps:

[0057] The preparation of silicon-carbon negative electrode material is the same as that in Example 1;

[0058] Plasma treatment: placing the silicon-carbon negative electrode material in a chamber of a plasma treatment instrument, performing plasma treatment with argon as the plasma gas source, a gas flow rate of 5 sccm, a chamber pressure of 0.2 MPa during treatment, a treatment power of 100 W, and a treatment time of 60 s, so that topological defects are generated on the surface of the silicon-carbon negative electrode material, thereby obtaining a silicon-carbon negative electrode material with topological defects;

[0059] The silicon-carbon anode material was used to autocatalyze the growth of multi-walled carbon nanotubes: the plasma-treated silicon-carbon anode material was placed in a CVD tube furnace and purged with argon gas for 1 h at room temperature (the argon flow rate was 100 sccm); then, the temperature was set at 5 °C min -1 The temperature was raised to 600°C, and at 600°C, in a mixed atmosphere of argon and acetylene (total gas flow rate was 100 sccm, and the flow rate ratio of argon to acetylene was 9:1), catalytic growth was carried out for 0.5 h to carry out autocatalytic growth of carbon nanotubes on the surface of the silicon-carbon negative electrode material, thereby preparing a silicon-carbon negative electrode composite multi-walled carbon nanotube material.

[0060] The electron microscope image of the silicon-carbon negative electrode composite multi-walled carbon nanotube material prepared in Example 2 at a scale of 5 μm is as follows: Figure 3 As shown, from Figure 3It can be seen that the multi-walled carbon nanotubes grown on the surface of the silicon-carbon negative electrode have a higher density and are more evenly distributed. The carbon nanotubes extend outward with the silicon-carbon particles as the base, and some tubes overlap each other to form a bridging structure, building a dense conductive path between the particles. The core advantages of this state are reflected in: high-density carbon nanotubes further reduce the electron transmission resistance, making the conductivity reach 25.8S / m; uniformly distributed carbon nanotubes can more evenly disperse the silicon expansion stress, combined with the stable crystal structure formed at a growth temperature of 600°C, the material cycle performance is greatly improved; the orderly growth state reduces the problem of excessive electrolyte contact area caused by disordered agglomeration, and the coulombic efficiency is improved for the first time.

[0061] Figure 4 for Figure 3 The TEM characterization of the carbon nanotubes clearly shows the microstructure of the multi-walled carbon nanotubes: the tube body exhibits a clear multi-layered tubular structure, the wall layers are regularly arranged and free of obvious defects, and the tube diameter is uniform, approximately 10-20nm. The advantages of this structure include: the regular multi-layer structure ensures rapid electron transmission within the tube, further improving the material's intrinsic conductivity; the defect-free tube wall structure enhances the mechanical strength of the carbon nanotubes, making them less likely to break during silicon expansion and maintaining the stability of the conductive network; the uniform tube diameter avoids local current concentration, reduces the uneven growth of the SEI film, and indirectly improves the battery cycle life.

[0062] Example 3

[0063] A method for constructing topological defects in a silicon-carbon cathode and growing composite multi-walled carbon nanotubes comprises the following steps:

[0064] The preparation of silicon-carbon negative electrode material is the same as that in Example 1;

[0065] Plasma treatment: placing the silicon-carbon negative electrode material in a chamber of a plasma treatment instrument, performing plasma treatment with argon as a plasma gas source, a gas flow rate of 50 sccm, a chamber pressure of 1.0 MPa, a processing power of 300 W, and a processing time of 10 s, so that topological defects are generated on the surface of the silicon-carbon negative electrode material, thereby obtaining a silicon-carbon negative electrode material with topological defects;

[0066] The silicon-carbon anode material was used to autocatalyze the growth of multi-walled carbon nanotubes: the plasma-treated silicon-carbon anode material was placed in a CVD tube furnace and purged with argon gas for 1 h at room temperature (the argon flow rate was 100 sccm); then, the temperature was set at 10 °C min -1 The temperature was raised to 400°C, and catalytic growth was carried out for 3 hours at 400°C in a mixed atmosphere of argon and ethylene (total gas flow rate was 100 sccm, and the flow rate ratio of argon to ethylene was 5:5) to carry out autocatalytic growth of carbon nanotubes on the surface of the silicon-carbon negative electrode material, thereby preparing a silicon-carbon negative electrode composite multi-walled carbon nanotube material.

[0067] The electron microscope image of the silicon-carbon negative electrode composite multi-walled carbon nanotube material prepared in Example 3 at a scale of 5 μm is as follows: Figure 5 As shown, from Figure 5 It can be seen that the multi-walled carbon nanotubes grown on the surface of the silicon-carbon anode material exhibit a relatively loose three-dimensional distribution. The carbon nanotubes extend outward from the silicon-carbon particles, and some tubes are entangled with each other, but the overall density is lower than that of Example 2. This phenomenon is directly related to the preparation process of Example 3, which uses a relatively low growth temperature of 400°C, a high carbon source ratio of argon to ethylene of 5:5, and a plasma treatment time of only 10 seconds (low defect density), resulting in certain limitations on the carbon nanotube growth rate and density. The multi-walled carbon nanotubes in this state can still play a corresponding role: despite the low density, the carbon nanotubes form discontinuous but effective conductive paths between the silicon and carbon particles by entanglement, so that the material conductivity reaches 18.3S / m, which is higher than the comparative example 1 (10.2S / m) with the traditional addition of conductive agents, indicating that it can still improve the intrinsic conductivity; the loose structure reserves a certain amount of space for the volume expansion of the silicon particles, and the flexible characteristics of the carbon nanotubes can relieve the expansion stress, so the 100-cycle capacity retention rate (66.2%) is still higher than the comparative example; the relatively small number of carbon nanotubes reduces the contact area with the electrolyte, which reduces the consumption of active lithium to a certain extent, and the first coulombic efficiency (80.1%) is better than the comparative example. However, due to the low density of carbon nanotubes and slightly poor growth uniformity, the continuity and stress dispersion ability of their conductive network are weaker than those of Example 2, so the conductivity, cycle retention and other indicators are slightly lower. However, compared with the traditional method, it still reflects the advantages of self-catalytic growth of carbon nanotubes in improving the performance of silicon-carbon negative electrodes.

[0068] Comparative Example 1

[0069] The preparation of the traditional silicon-carbon negative electrode with the addition of a conductive agent includes the following steps:

[0070] The preparation of silicon-carbon negative electrode material is the same as that in Example 1;

[0071] Silicon-carbon negative electrode material, conductive carbon black (Super P), and binder (PVDF) were mixed in a mass ratio of 90:5:5, and NMP was added to homogenize for 2 hours. The mixture was coated on copper foil and dried to obtain an electrode.

[0072] Comparative Example 2

[0073] The steps of constructing defects by high-temperature heteroatom removal to prepare silicon-carbon negative electrode composite materials include:

[0074] The silicon-carbon negative electrode material was prepared according to the method of Example 1 and pre-doped with 5% nitrogen atoms (urea was used as the nitrogen source;

[0075] High-temperature heteroatom removal: Under argon atmosphere, only nitrogen-doped silicon-carbon anode material was calcined at 1200°C for 1 hour to obtain activated silicon-carbon anode material;

[0076] Silicon-carbon negative electrode material self-catalyzes the growth of multi-walled carbon nanotubes: the activated silicon-carbon negative electrode material prepared in the above steps is used to replace the silicon-carbon negative electrode material in Example 1, and the same method as in Example 1 is used to grow multi-walled carbon nanotubes to prepare a silicon-carbon negative electrode composite material.

[0077] The conductivity of the materials prepared in Examples 1-3 and Comparative Examples 1-2 was tested by a four-probe method. The materials prepared in Examples 1-3 and Comparative Examples 1-2 were used as working electrodes, lithium metal sheets as counter electrodes and reference electrodes, Celgard 2400 as a separator, and 1 mol / L LiPF (EC:DMC:EMC=1:1:1, volume ratio) as an electrolyte. CR2032 button cells were assembled and their initial coulombic efficiency, 100-cycle capacity retention, and volume expansion rate were tested. The results are shown in Table 1.

[0078] Table 1 Test results

[0079]

[0080] As can be seen from the data in Table 1, the electrical conductivity of the silicon-carbon negative electrode composite multi-walled carbon nanotube material prepared in Examples 1-3 (18.3-25.8S / m) is much higher than that of Comparative Example 1 (10.2S / m), and better than that of Comparative Example 2 (11.6S / m). Comparative Example 1 forms a conductive path by physical mixing of conductive carbon black (Super P). The particles are only bound by van der Waals forces, which are easy to peel off when the volume expands, and the electron transmission path is broken, so the electrical conductivity is low (10.2S / m). In the embodiment, the carbon nanotubes grow self-catalytically through the topological defects on the surface of the silicon-carbon negative electrode, forming covalent bonds with the matrix. The constructed three-dimensional continuous network can resist volume expansion and has low electron transmission resistance (conductivity ≥ 18.3S / m). Compared with Comparative Example 2 (high temperature treatment), it is shown that high temperature (1200°C) causes silicon particles to agglomerate (particle size increases by 20%), reduces the uniformity of defect sites, and reduces the growth density of carbon nanotubes. Therefore, the electrical conductivity (11.6 S / m) is also significantly lower than that of Example 1 (25.8 S / m).

[0081] From the data in Table 1, it can be seen that the first coulombic efficiency in Examples 1-3 (80.1-86.7%) is higher than that in Comparative Examples 1-2 (77.3-81.2%). This is because in Comparative Example 1, due to the addition of conductive carbon black (large specific surface area), the contact area between the electrode and the electrolyte is increased, resulting in more electrolyte decomposition to form SEI film, consuming active lithium, and the first coulombic efficiency is low (78.5%); while in the embodiment, although the carbon nanotubes increase the surface area, due to their orderly arrangement (rather than disordered agglomeration), the SEI film is more uniform and thin, consumes less active lithium, and has a higher first efficiency. The high temperature treatment in Comparative Example 2 partially oxidizes the surface of the silicon particles (SiO x The oxide layer consumes lithium (SiO x +2xLi + +2xe-=Si+xLi2O), resulting in a first efficiency (77.3%) slightly lower than that of Example 1.

[0082] As can be seen from the data in Table 1, the 100-cycle capacity retention rate in Examples 1-3 (66.2%-82.3%) is much higher than that in Comparative Example 1 (56.3%) and Comparative Example 2 (56.5%). This is because the conductive agent in Comparative Example 1 is physically mixed with the active particles, and the interface peels off when the silicon volume expands (200%), the electron transmission is interrupted, and the capacity decays rapidly (retention rate 56.3%). In this embodiment, the "root-like" structure of the carbon nanotubes controls the volume expansion rate to 120%-135% through radial flexible support (absorbing deformation) and axial stress dispersion, and the conductive network is stable and the cycle retention rate is high. The high temperature of Comparative Example 2 causes the silicon particles to agglomerate, the volume expansion is more uneven (local expansion reaches 180%), the carbon nanotubes are easily broken, and the cycle retention rate (56.5%) is lower than that of Example 1.

[0083] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for constructing topological defects in a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes, characterized in that: Including steps: Based on silicon-carbon anode materials; Using a plasma treatment device to perform plasma treatment on the surface of the silicon-carbon negative electrode material in a plasma environment, so that topological defects are generated on the surface of the silicon-carbon negative electrode material, thereby obtaining a silicon-carbon negative electrode material with topological defects; The silicon-carbon negative electrode material with topological defects is placed in a tubular furnace of a chemical vapor deposition device, an inert gas is introduced to remove the air, and the temperature is raised to a predetermined temperature. Then, a mixed atmosphere consisting of an inert gas and a carbon source gas is introduced to perform autocatalytic growth of multi-walled carbon nanotubes on the surface of the silicon-carbon negative electrode material to obtain a silicon-carbon negative electrode composite multi-walled carbon nanotube material.

2. The method for preparing silicon-carbon negative electrode topological defect construction and growth of composite multi-walled carbon nanotubes according to claim 1, characterized in that: In the step of plasma treating the surface of the silicon-carbon negative electrode material in a plasma environment using plasma treatment equipment, argon is used as the plasma gas source, the gas flow rate is 5-50sccm, the chamber pressure during treatment is 0.2-1.0MPa, the treatment power is 100-300W, and the treatment time is 10-120s.

3. The method for constructing topological defects of a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes according to claim 1, characterized in that: The topological defects refer to one or more of five-membered ring defects, seven-membered ring defects and eight-membered ring defects in the carbon matrix of the silicon-carbon negative electrode material.

4. The method for preparing silicon-carbon anode topological defect construction and growth of composite multi-walled carbon nanotubes according to claim 1, characterized in that: The inert gas is one of argon and helium.

5. The method for constructing topological defects of a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes according to claim 1, characterized in that: The carbon source gas is one of acetylene, ethylene and methane.

6. The method for constructing topological defects of a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes according to claim 1, characterized in that: The flow rate ratio of the inert gas to the carbon source gas is 9:1-5:

5.

7. The method for constructing topological defects in a silicon-carbon cathode and growing composite multi-walled carbon nanotubes according to claim 1, characterized in that: In the step of heating to a predetermined temperature after the inert gas is introduced to remove the air, the temperature is kept at 5-10℃min. -1 The heating rate is increased to 400-600℃.

8. The method for constructing topological defects in a silicon-carbon cathode and growing composite multi-walled carbon nanotubes according to claim 1, characterized in that: In the step of performing autocatalytic growth of multi-walled carbon nanotubes on the surface of the silicon-carbon negative electrode material, the autocatalytic growth time is 0.5h-5h.

9. A silicon-carbon negative electrode composite multi-walled carbon nanotube material, characterized in that: The method for constructing topological defects of a silicon-carbon negative electrode and growing composite multi-walled carbon nanotubes is used to prepare the carbon nanotubes.

10. An application of a silicon-carbon negative electrode composite multi-walled carbon nanotube material, characterized in that: The silicon-carbon negative electrode composite multi-walled carbon nanotube material according to claim 9 is used to prepare a negative electrode for a lithium-ion battery.

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