Carbon nanotube reinforced silicon-carbon core-shell negative electrode material and preparation method thereof

Abstract

The application relates to a carbon nanotube reinforced silicon-carbon core-shell negative electrode material and a preparation method thereof, which comprises the following steps: mixing and stirring carbon nanotubes, water and a silane coupling agent to obtain a dispersion liquid; adding a compound dispersant, silicon powder, graphite, a carbon source, water and an alcohol solvent into the dispersion liquid to uniformly mix to obtain a precursor solution; granulating the precursor solution to obtain precursor microspheres; and calcining the precursor microspheres to obtain the carbon nanotube reinforced silicon-carbon core-shell negative electrode material. The negative electrode material comprises a static carbon shell layer and a silicon core layer, and carbon nanotubes are distributed between the carbon shell layer and the silicon core layer. The static carbon shell layer provides an initial expansion space, and the dynamic carbon nanotube network provides continuous restoring force. The two synergistically improve the cycle performance and reduce the volume expansion rate.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a carbon nanotube-reinforced silicon-carbon core-shell anode material and its preparation method. Background Technology

[0002] Energy density and cycle life of lithium-ion batteries are key constraints on the development of electric vehicles and advanced consumer electronics. Among anode materials, silicon-based materials are considered the most promising direction due to their extremely high theoretical specific capacity (approximately 4200 mAh / g, about 10 times that of traditional graphite), which is expected to push battery energy density beyond 300 Wh / kg. However, silicon undergoes a volume expansion of up to 300% during charge and discharge. This fundamental defect triggers a series of chain problems: the rupture and pulverization of active particles, repeated rupture and uncontrolled thickening of the solid electrolyte interphase (SEI) film, and the collapse of the conductive network inside the electrode. The direct consequence is rapid capacity decay (e.g., retention rate is often less than 80% after 100 cycles), severely hindering the commercialization of silicon-carbon anodes.

[0003] To address these challenges, existing technologies mainly seek breakthroughs in three areas: material structure design, composite process optimization, and interface engineering. However, various solutions still have significant limitations in terms of buffering efficiency, process complexity, or cost control.

[0004] I. Material and structural design schemes Core-shell structure: This method buffers expansion stress by constructing a carbon coating layer on the surface of silicon particles. For example, the core-shell structure silicon-based material from Hefei Guoxuan High-Tech Power Energy Co., Ltd. (CN120809799A) consists of a silicon core and a SiOC shell covering the surface of the silicon core. The free carbon component in the SiOC shell has good electronic conductivity, which helps to promote charge transport within the electrode material, thereby helping to improve the conductivity of the core-shell structure silicon-based material. Although this approach increases the cycle life to over 200 cycles, SiO itself affects the energy density of the material.

[0005] Three-dimensional carbon network structure: Pre-designed pores within silicon accommodate expansion. For example, Shaanxi Saineng Ruike Technology Co., Ltd. (CN120300167A) uses gradient carbon layers to coat porous silicon, with a hard carbon inner layer providing mechanical support and a soft carbon outer layer enhancing flexibility. While this method improves cycle performance, the porosity depends on the porosity of the silicon material, making the process complex and difficult to scale up.

[0006] II. Composite Process Optimization Solutions Pore ​​control and pyrolysis process optimization: For example, the patent of Pu'er University (CN120998697A) involves crushing and pretreating silicon-containing agricultural residues, mixing them with tetraethyl orthosilicate, and then pyrolyzing them at high temperature under a nitrogen atmosphere to generate SiO2 nanotemplates to control the pore structure, partially reducing them to SiO nanoparticles, thus forming an in-situ SiO@C core-shell structure material with hierarchical pores of micropores and mesopores. This method effectively overcomes the limitations of traditional technologies in terms of pore control and environmental friendliness, but its final capacity is limited.

[0007] III. Interface Engineering Optimization Scheme Nitrogen-doped carbon interface coating: Shandong Solide New Material Technology Co., Ltd. (CN120383310B) forms sulfur-nitrogen-doped conductive hollow carbon spheres after sulfur and nitrogen doping. Sulfur doping can participate in the formation of the SEI film, generating a stable interface layer to reduce electrolyte decomposition and irreversible consumption of active lithium. However, this interface is gradually depleted during subsequent cycles, and the SEI film will regenerate, reducing the later cycle performance.

[0008] In summary, there is an urgent need to develop a simple, environmentally friendly, and efficient preparation method that can precisely control the pore structure and thus significantly improve the cycle stability of silicon-carbon anode materials, in order to meet the development needs of high-energy-density lithium-ion batteries. Summary of the Invention

[0009] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a carbon nanotube-reinforced silicon-carbon core-shell anode material and its preparation method, thereby solving the technical problem that silicon-carbon anode materials have poor cycle stability due to volume expansion in the prior art.

[0010] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a method for preparing a carbon nanotube-reinforced silicon-carbon core-shell anode material, comprising the following steps: S1, mixing and stirring carbon nanotubes, water, and a silane coupling agent to obtain a dispersion; adding a compound dispersant, silicon powder, graphite, carbon source, water, and alcohol solvent to the dispersion, and mixing evenly to obtain a precursor solution; S2, granulating the precursor solution to obtain precursor microspheres; S3, calcining the precursor microspheres to obtain the carbon nanotube-reinforced silicon-carbon core-shell anode material.

[0011] Secondly, the present invention provides a carbon nanotube-reinforced silicon-carbon core-shell anode material prepared by the above-mentioned preparation method.

[0012] Compared with the prior art, the beneficial effects of the present invention include: This invention involves first uniformly mixing and dispersing a silane coupling agent with carbon nanotubes (S-CNTs), allowing the amino groups of the silane coupling agent to react with the hydroxyl groups on the surface of the S-CNTs, thereby improving compatibility with silicon powder. Water and alcohol are used as the main solvents to facilitate uniform mixing of the solid raw materials. The resulting precursor solution is granulated to obtain precursor microspheres, initially forming a framework structure. The precursor microspheres are then calcined to enhance the silicon-S-CNTs-amorphous carbon interface bonding, resulting in a carbon nanotube-reinforced silicon-carbon core-shell anode material. The anode material of this invention comprises a static carbon shell layer and a silicon core layer, with carbon nanotubes distributed between the carbon shell and silicon core layers. The static carbon shell layer provides initial expansion space, while the dynamic carbon nanotube network provides continuous recovery force. The synergistic effect of these two elements improves cycle performance and reduces volume expansion rate. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the carbon nanotube-reinforced silicon-carbon core-shell anode material of the present invention. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0016] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0017] To address the current bottlenecks in the industrial application of silicon-carbon anode materials, such as cycle failure caused by volume expansion and the contradiction between process environmental protection and cost, this invention provides a carbon nanotube-reinforced silicon-carbon core-shell anode material and its preparation method. Through the innovative design of carbon nanotube-reinforced silicon-carbon core-shell spheres, the following core objectives are achieved: (1) Introducing carbon nanotubes (instead of graphite) prepared by a specific method into the silicon-carbon spray granulation system, utilizing its "elastic structure + three-dimensional conductive channel" characteristics—elastic deformation buffers silicon expansion (50% more elastic than graphite), and one-dimensional tube bundles form a continuous three-dimensional conductive network (conductivity is an order of magnitude higher than graphite). (2) Developing a process of "catalyst-supported template method for preparing S-CNTs + compound dispersant for anti-agglomeration + silane coupling agent for interface modification" to solve the core pain points of S-CNTs agglomeration and weak bonding with the silicon / amorphous carbon interface.

[0018] In a first aspect, the present invention provides a method for preparing a carbon nanotube-reinforced silicon-carbon core-shell anode material, comprising the following steps: S1, carbon nanotubes, water and silane coupling agent are mixed and stirred to obtain a dispersion; a compound dispersant, silicon powder, graphite, carbon source, water and alcohol solvent are added to the dispersion and mixed evenly to obtain a precursor solution; S2, the precursor solution is granulated to obtain precursor microspheres; S3, precursor microspheres are calcined to obtain carbon nanotube-reinforced silicon-carbon core-shell anode material.

[0019] In this invention, a silane coupling agent is first mixed and dispersed uniformly with carbon nanotubes (S-CNTs) to allow the amino groups of the silane coupling agent to react with the hydroxyl groups on the surface of the S-CNTs, thereby improving the compatibility with silicon powder. Water and alcohol are used as the main solvents to facilitate the dispersion of the S-CNTs modified with the silane coupling agent and to ensure uniform mixing with other solid raw materials. The addition of graphite prevents the agglomeration of pure nano-silicon powder, which would affect subsequent granulation. The resulting precursor solution is granulated to obtain precursor microspheres, which initially form a framework structure. The precursor microspheres are then calcined to enhance the interfacial bonding between silicon, S-CNTs, and amorphous carbon, resulting in a carbon nanotube-reinforced silicon-carbon core-shell anode material.

[0020] like Figure 1 As shown, the carbon nanotube-reinforced silicon-carbon core-shell anode material obtained in this invention includes a static carbon shell layer and a silicon core layer, with carbon nanotubes distributed between the carbon shell layer and the silicon core layer. The main advantages of this structure include: (1) Improved cycle stability: The static carbon shell layer provides initial expansion space, and the dynamic carbon nanotube network provides continuous recovery force. The two work together to improve cycle performance. The capacity retention rate after 100 cycles is >83% (1C, 25℃), which is 20% higher than that of traditional silicon-carbon anodes. (2) Enhanced robustness of conductive network: The three-dimensional continuous conductive pathway formed by the carbon nanotubes ensures that even if local silicon particles fail, the overall electron transport remains unimpeded.

[0021] In some embodiments, step S1, the preparation step of carbon nanotubes includes: The template with pores is immersed in a catalyst precursor solution, so that the catalyst precursor is uniformly adsorbed on the inner wall of the pores. Then, after drying and calcination oxidation, the template loaded with metal catalyst is obtained. Carbon nanotubes are grown along the pores of a template by CVD under the induction of a metal catalyst; subsequently, the template and metal catalyst are removed to obtain carbon nanotubes.

[0022] Furthermore, the template is a pretreated anodized aluminum template, which is ultrasonically cleaned with 4-6% HF solution for 5-15 minutes, followed by rinsing with deionized water and drying.

[0023] Furthermore, the catalyst precursor includes ferric nitrate or cobalt nitrate.

[0024] Furthermore, the concentration of the catalyst precursor solution is 0.1–0.5 mol / L, and the pH value is 6–7.

[0025] Furthermore, the conditions for immersing the template in the catalyst precursor solution include: a temperature of 40–80°C and a time of 1.5–2.5 h.

[0026] Furthermore, drying is performed under vacuum at 50–70°C for 2–8 hours; calcination oxidation is carried out in air at 400–600°C for 0.5–1.5 hours. In this invention, calcination transforms the catalyst precursor into Fe2O3 / Co3O4 nanoparticles with a particle size of approximately 20–50 nm.

[0027] Furthermore, the specific steps of growing carbon nanotubes along the pores of the template by CVD under the induction of a metal catalyst include: placing the template loaded with the metal catalyst into a CVD furnace, introducing Ar gas and heating it to 700-800℃ and holding it at that temperature for 2-4 hours, and then switching the Ar gas to a mixture of acetylene and Ar gas and holding it at that temperature for 1-3 hours.

[0028] Furthermore, the Ar gas flow rate is 60–100 sccm; the heating rate is 4–6 °C / min; the volume ratio of acetylene to Ar gas in the mixed gas is 1:(7–20); and the total flow rate of the mixed gas is 110–130 sccm.

[0029] Further, the steps for removing the template and metal catalyst to obtain carbon nanotubes specifically include: immersing the template on which carbon nanotubes are grown in a 20-45% HF solution for etching for 2-4 hours, then immersing it in a hydrochloric acid solution for ultrasonic cleaning, and after ultrasonic cleaning, washing and drying with deionized water to obtain carbon nanotubes. This invention removes the template by hydrofluoric acid etching and removes the metal catalyst by hydrochloric acid ultrasonic cleaning.

[0030] In some embodiments, in step S1, the carbon nanotubes (S-CNTs) have a diameter of 200–800 nm, a length of 3–8 μm, and an aspect ratio ≥100.

[0031] In some embodiments, in step S1, both the silicon powder and graphite particles are submicron in size (D90 < 5 μm).

[0032] In some embodiments, in step S1, the solid raw materials include 3-15% carbon nanotubes, 40-60% silicon powder, 5-20% graphite and 10-30% carbon source by mass percentage.

[0033] Furthermore, the silane coupling agent includes KH550 coupling agent; the amount of silane coupling agent used is 0.3 to 0.8 wt% of the total mass of the solid raw materials.

[0034] Furthermore, the compound dispersant is a mixture of polyvinylpyrrolidone (PVP) and sodium dodecylbenzenesulfonate (SDBS); the amount of compound dispersant used is 1 to 2 wt% of the total mass of the solid raw materials. More preferably, PVP:SDBS = 1:1.

[0035] In some embodiments, in step S1, the carbon source includes sucrose.

[0036] In some embodiments, in step S1, the stirring reaction is carried out at 40–60°C for 0.5–1.5 h.

[0037] In some embodiments, in step S1, the alcohol solvent includes isopropanol; the total amount of water used to the volume ratio of the alcohol solvent is (3-5.5):1.

[0038] It should be noted that the water and alcohol solvent added to the dispersion account for the majority of the total solvent, and the volume ratio of this water to alcohol solvent is preferably 5:1, which is more suitable for the dispersion of modified S-CNTs.

[0039] In some embodiments, in step S1, after adding a compound dispersant, silicon powder, graphite, carbon source, water and alcohol solvent to the dispersion, the mixture is stirred for more than 12 hours to obtain a precursor solution.

[0040] In some embodiments, in step S2, the granulation method is spray drying granulation; the precursor microspheres have a particle size of 20-50 μm and a moisture content of <2 wt%. Specifically, the present invention can obtain precursor microspheres with corresponding target requirements by controlling conditions such as inlet temperature, outlet temperature, atomization pressure, and feed rate.

[0041] In some embodiments, the calcination conditions in step S3 include: being carried out under a protective atmosphere, a calcination temperature of 650–950°C, and a calcination time of 1.5–2.5 h.

[0042] The main reaction mechanism of calcination in this invention includes sucrose carbonization and carbon layer graphitization (ID / IG value reduced to 0.75-0.80), wherein the sucrose carbonization reaction is as follows:

[0043] Secondly, the present invention provides a carbon nanotube-reinforced silicon-carbon core-shell anode material prepared by the above-mentioned preparation method.

[0044] The main mechanism of action and advantages of this invention are as follows: (1) The core innovation of this invention lies in constructing a carbon nanotube framework with a unique “three-dimensional continuous ripple” inside the silicon-carbon composite spherical particles. This framework is not a simple additive, but a carefully designed integrated structure that plays the key roles of “mechanical elastic element”, “electronic highway network” and “stress redistributor”, thus fundamentally solving the dynamic failure problem caused by silicon volume expansion.

[0045] (2) Buffering advantage of elastic structure: The morphology of S-CNTs (diameter 200-800nm) endows them with excellent deformation recovery ability, and the elastic modulus is ≥1TPa. When the silicon powder expands in volume during charging and discharging, the nanotube support structure can absorb the expansion stress through "stretching-contraction" deformation, avoid the composite sphere from cracking, improve the buffering efficiency by more than 50%, and reduce the volume expansion rate from 300% in the traditional solution to ≤80%.

[0046] (3) Advantages of one-dimensional tube bundle conductive network: S-CNTs have an aspect ratio ≥80, far exceeding that of traditional graphite (aspect ratio ≤10). Its structure forms a continuous "three-dimensional conductive path" in the sphere rather than the "discrete conductive path" of sheet graphite, with a conductivity ≥10. 4 S / m (an order of magnitude higher than graphite) reduces the resistivity of the composite spheres to ≤30Ω. cm (traditional solution ≈ 100Ω) cm), which solved the problem of poor conductivity of silicon powder (resistivity ≥10). 6 Ω The problem of insufficient rate performance caused by (cm).

[0047] (4) Synergistic effect of low addition amount: Through structural optimization, the addition amount of S-CNTs is only 3-15wt% (graphite requires 5-20wt%), which can simultaneously achieve the functions of "buffering expansion" and "enhancing conductivity". Compared with the existing technology, the carbon phase ratio is reduced by 2-5wt%, the effective ratio of silicon powder is increased, and the first discharge capacity exceeds 2000mAh / g (traditional solution ≈1500mAh / g).

[0048] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0049] The template material is γ-phase alumina, purchased from Beijing Deco Island Gold Technology Co., Ltd. The silicon powder and graphite were ground to submicron level (D90 < 5 μm) using a ball milling method.

[0050] The preparation steps of the carbon nanotubes used in this invention include: (1) Weigh one piece of anodic aluminum oxide template with channels (0.2g), immerse it in 200 mL of 5% HF solution and ultrasonically clean it for 10 min (power 300W, frequency 40kHz), rinse it with deionized water 3 times, vacuum dry it at 60℃ for 2 h and then cool it to room temperature to obtain the pretreated template for use. (2) Weigh 0.808 g of ferric nitrate nonahydrate and add it to 100 mL of deionized water to obtain a 0.2 mol / L ferric nitrate solution. Adjust the pH to 6-7 with ammonia water. The solution is a yellowish-brown colloid. Immerse the pretreated template in this solution and keep it in a water bath at 60℃ for 2 hours to allow the Fe... 3+ The Fe2O3 nanocatalyst was uniformly adsorbed onto the inner wall of the template pores and then vacuum dried at 60℃ for 4 hours. The dried template was then transferred to a tube furnace and calcined at 500℃ for 1 hour in air atmosphere (heating rate 5℃ / min) to obtain the Fe2O3 nanocatalyst. (3) The template containing the Fe2O3 nanocatalyst was placed in a quartz boat in a CVD furnace, and Ar gas (flow rate 80 sccm) was introduced and heated to 750℃ (the optimal growth temperature of S-CNTs, lower than the graphitization temperature) and held for 3 h at a heating rate of 5℃ / min to reduce the catalyst particles to Fe nanoparticles; then the mixture of acetylene (C2H2) and Ar gas (volume ratio 1:15, total flow rate 120 sccm) was switched and held for 2 h (to control the length of S-CNTs) to allow CNTs to grow along the template channels under the induction of the catalyst; the product was immersed in 40% HF solution for etching for 4 h (to remove the template), then immersed in 1 mol / L hydrochloric acid solution for ultrasonic cleaning for 30 min (to remove the metal catalyst), centrifuged and washed 3 times with deionized water (10000 rpm, 10 min each time), and vacuum dried at 60℃ for 12 h to obtain S-CNTs (key parameters: diameter 200-800 nm, length 3-8 μm, aspect ratio ≥100).

[0051] Example 1 A method for preparing a carbon nanotube-reinforced silicon-carbon core-shell anode material includes the following steps: S1, Preparation of precursor solution: Take 0.12g of S-CNTs and put them into a 20mL centrifuge tube. Add 2mL of deionized water and sonicate for 20min (power 300W, frequency 40kHz) to obtain the first dispersion. Use a micropipette to add 0.0075g of KH550 (density 0.94g / mL, volume about 8μL) to the above dispersion. Place the centrifuge tube in a water bath at 50℃ for 1h. During this period, stir for 1min every 15min (speed 500rpm) to allow KH550 to fully react with the hydroxyl groups on the surface of S-CNTs to obtain the second dispersion. Accurately weigh 0.01125g of PVP, 0.01125g of SDBS, 0.8g of silicon powder, 0.2g of graphite, 0.4g of sucrose, 100mL of deionized water, and 20mL of isopropanol. Place them together with the above second dispersion into a 200mL beaker and stir for 12h to obtain the precursor solution. S2, Spray drying: Adjust the equipment parameters: inlet temperature 180±5℃, outlet temperature 95±5℃; atomization pressure 0.3MPa, feed rate 1 mL / min, and pass the precursor solution into the spray drying equipment for granulation to obtain precursor microspheres. S3, High-temperature calcination: The precursor microspheres were placed in a rotating tube furnace for calcination at a heating rate of 5℃ / min and a holding temperature of 850℃ for 2 h under an argon atmosphere (flow rate of 100 mL / min). The furnace was then cooled to obtain a carbon nanotube-reinforced silicon-carbon core-shell anode material.

[0052] Example 2 (Low S-CNTs group) Compared to Example 1, the only difference is that the proportion of solid raw materials in the precursor solution is adjusted to form a low S-CNTs group; all other steps and conditions are the same as in Example 1. The difference lies in: S1, Precursor Solution Preparation: 0.045 g of S-CNTs were placed in a 20 mL centrifuge tube, and 2 mL of deionized water was added. The mixture was ultrasonically dispersed for 20 min (300 W, 40 kHz) to obtain the first dispersion. 0.0075 g of KH550 (density 0.94 g / mL, volume approximately 8 μL) was added dropwise to the above dispersion using a micropipette. The centrifuge tube was placed in a water bath at 50 °C for 1 h, with stirring every 15 min for 1 min (500 rpm) to ensure sufficient reaction between KH550 and the hydroxyl groups on the surface of S-CNTs, resulting in the second dispersion. 0.01125 g of PVP and 0.01125 g of... SDBS (sodium dodecylbenzenesulfonate), 0.825g silica powder, 0.225g graphite, 0.4g sucrose, 100mL deionized water, 20mL isopropanol, and the above second dispersion were placed together in a 200mL beaker and stirred for 12h to obtain the precursor solution.

[0053] Example 3 (High S-CNTs Group) Compared to Example 1, the only difference is that the proportion of solid raw materials in the precursor solution is adjusted to form a high S-CNTs group; all other steps and conditions are the same as in Example 1. The difference lies in: S1, Precursor Solution Preparation: 0.24 g of S-CNTs were placed in a 20 mL centrifuge tube, and 2 mL of deionized water was added. The mixture was ultrasonically dispersed for 20 min (300 W, 40 kHz) to obtain the first dispersion. 0.0075 g of KH550 (density 0.94 g / mL, volume approximately 8 μL) was added dropwise to the above dispersion using a micropipette. The centrifuge tube was placed in a water bath at 50 °C for 1 h, with stirring every 15 min for 1 min (500 rpm) to ensure sufficient reaction between KH550 and the hydroxyl groups on the surface of S-CNTs, resulting in the second dispersion. 0.01125 g of PVP and 0.01125 g of... SDBS (sodium dodecylbenzenesulfonate), 0.825g silica powder, 0.225g graphite, 0.4g sucrose, 100mL deionized water, 20mL isopropanol, and the above second dispersion were placed together in a 200mL beaker and stirred for 12h to obtain the precursor solution.

[0054] Comparative Example 1 Compared with Example 1, the only difference is that S-CNTs in step 1 are not added, while the other steps and conditions are the same as in Example 1.

[0055] Comparative Example 2 Compared with Example 1, the only difference is that the S-CNTs in step 1 are replaced with straight-walled carbon nanotubes, while the other steps and conditions are the same as in Example 1.

[0056] Comparative Example 3 Compared with Example 1, the only difference is that KH550 coupling agent is not added in step S1, while the other steps and conditions are the same as in Example 1.

[0057] Electrochemical testing methods 1. Method for testing coulomb efficiency in the first week: Test setup: CR2032 coin cell (negative electrode: carbon nanotube-reinforced silicon-carbon core-shell negative electrode material to be tested; positive electrode: lithium metal sheet; electrolyte: 1M LiPF6 in EC / DEC=1:1).

[0058] Test procedure: ① Discharge at a constant current of 0.1C (1C=2000 mA / g) to 0.01V (vs. Li + / Li), switch to constant voltage until current ≤0.005C; ② after standing for 5 min, charge at a constant current of 0.1C to 1.5V; ③ first week coulombic efficiency = (discharge capacity / charge capacity) × 100%.

[0059] Standard: GB / T 37201-2018 "Test Methods for Electrochemical Performance of Anode Materials for Lithium-ion Batteries".

[0060] 2. Capacity retention rate test method: The capacity retention rate is tested using a coin cell half-cell under the condition of 1C cycling 100 times.

[0061] (1) Battery assembly Negative electrode preparation: A slurry was prepared by mixing the active material (carbon nanotube-reinforced silicon-carbon core-shell negative electrode material to be tested): conductive agent (Super P): binder (PAA) in a ratio of 8:1:1, and coated onto copper foil (area density ≈ 2.5 mg / cm²). The slurry was then vacuum dried at 120℃ for 12 h. Counter electrode: 16 mm diameter lithium metal sheet (0.6 mm thickness). Electrolyte: 1 M LiPF6 in EC / DEC + 10 wt% FEC. Separator: Celgard 2400. Battery model: CR2032 (assembled in a glove box with a dew point ≤ -40℃).

[0062] (2) Testing process Activation cycle (0.1C, 1C=2000 mA / g): Discharge: 0.1C constant current (100 mA / g) → 0.01 V → constant voltage until current ≤0.005C; Charge: 0.1C constant current → 1.5 V; Repeat 5 times (to eliminate the irreversible effect of the initial SEI formation).

[0063] Cyclic testing: 1C rate cycling (2000 mA / g), constant current charge and discharge: discharge to 0.01V → charge to 1.5V (no constant voltage stage); 300 cycles, temperature 25±1℃.

[0064] Capacity retention calculation: Capacity retention rate = (Discharge capacity at 100th cycle / Discharge capacity at 6th cycle) × 100%.

[0065] The electrochemical performance of the carbon nanotube-reinforced silicon-carbon core-shell anode materials obtained in Examples 1-3 and Comparative Examples 1-3 was tested, and the results are shown in Table 1 below.

[0066] Table 1. Electrochemical performance test results of Examples 1-3 and Comparative Examples 1-3

[0067] As shown in Table 1, the carbon nanotube-reinforced silicon-carbon core-shell anode material obtained in the embodiments of the present invention exhibits superior electrochemical performance. The initial discharge capacity of the materials obtained in this invention all exceed 2000 mAh / g. Due to certain weighing errors during battery preparation, the performance of the assembled batteries fluctuates slightly. Based on this, it can be considered that the initial discharge capacity of the embodiments of the present invention and the comparative examples are basically the same. However, cycle stability is a direct comparison of the same battery before and after cycling, eliminating the interference of weighing errors. Therefore, the capacity retention rate after 100 cycles better demonstrates the advantage. A comparison of Example 1 and Comparative Examples 1-3 shows that the present invention, after adding the prepared S-CNTs, along with other solid raw materials and a silane coupling agent, results in better cycle stability of the material.

[0068] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a carbon nanotube-reinforced silicon-carbon core-shell negative electrode material, characterized in that, Includes the following steps: S1, carbon nanotubes, water and silane coupling agent are mixed and stirred to obtain a dispersion; a compound dispersant, silicon powder, graphite, carbon source, water and alcohol solvent are added to the dispersion and mixed evenly to obtain a precursor solution; S2, the precursor solution is granulated to obtain precursor microspheres; S3, precursor microspheres are calcined to obtain carbon nanotube-reinforced silicon-carbon core-shell anode material.

2. The method for preparing carbon nanotube-reinforced silicon-carbon core-shell anode material according to claim 1, characterized in that, In step S1, the preparation steps of the carbon nanotubes include: The template with pores is immersed in a catalyst precursor solution, so that the catalyst precursor is uniformly adsorbed on the inner wall of the pores. Then, after drying and calcination oxidation, the template loaded with metal catalyst is obtained. Carbon nanotubes are grown along the pores of a template by CVD under the induction of a metal catalyst; subsequently, the template and metal catalyst are removed to obtain carbon nanotubes.

3. The method for preparing carbon nanotube-reinforced silicon-carbon core-shell anode material according to claim 2, characterized in that, The template is a pretreated anodized aluminum template, which involves ultrasonic cleaning with a 4-6% HF solution for 5-15 minutes, followed by rinsing with deionized water and drying; and / or, The catalyst precursor includes ferric nitrate or cobalt nitrate; and / or, The concentration of the catalyst precursor solution is 0.1–0.5 mol / L, and the pH value is 6–7; and / or, The conditions under which the template is immersed in the catalyst precursor solution include: a temperature of 40–80°C and a time of 1.5–2.5 h; and / or, The calcination oxidation is carried out in an air atmosphere at 400–600°C for 0.5–1.5 hours; and / or, The step of growing carbon nanotubes along the pores of a template via CVD under the induction of a metal catalyst specifically includes: placing the template loaded with the metal catalyst into a CVD furnace, introducing Ar gas and heating to 700–800°C and holding for 2–4 hours; subsequently, switching the Ar gas to a mixture of acetylene and Ar gas and holding for 1–3 hours; and / or, The removal of the template and metal catalyst involves immersing the template with grown carbon nanotubes in a 20-45% HF solution for etching for 2-4 hours, followed by ultrasonic cleaning in a hydrochloric acid solution.

4. The method for preparing carbon nanotube-reinforced silicon-carbon core-shell anode material according to claim 1, characterized in that, In step S1, the carbon nanotubes have a diameter of 200–800 nm, a length of 3–8 μm, and an aspect ratio ≥100; and / or, Both the silicon powder and the graphite have submicron particles.

5. The method for preparing carbon nanotube-reinforced silicon-carbon core-shell anode material according to claim 1, characterized in that, In step S1, the solid raw materials, by mass percentage, include 3–15% carbon nanotubes, 40–60% silicon powder, 5–20% graphite, and 10–30% carbon source; and / or, The carbon source includes sucrose; and / or, The alcohol solvent includes isopropanol; the total amount of water used to the volume ratio of the alcohol solvent is (3-5.5):

1.

6. The method for preparing the carbon nanotube-reinforced silicon-carbon core-shell anode material according to claim 5, characterized in that, The silane coupling agent includes KH550 coupling agent; and / or, The amount of the silane coupling agent is 0.3 to 0.8 wt% of the total mass of the solid raw materials; the compound dispersant is a mixture of polyvinylpyrrolidone and sodium dodecylbenzenesulfonate; the amount of the compound dispersant is 1 to 2 wt% of the total mass of the solid raw materials.

7. The method for preparing carbon nanotube-reinforced silicon-carbon core-shell anode material according to claim 1, characterized in that, In step S1, the stirring reaction is carried out at 40-60°C for 0.5-1.5 hours.

8. The method for preparing the carbon nanotube-reinforced silicon-carbon core-shell anode material according to claim 1, characterized in that, In step S2, the granulation method is spray drying granulation; and / or, The precursor microspheres have a particle size of 20–50 μm and a water content of <2 wt%.

9. The method for preparing carbon nanotube-reinforced silicon-carbon core-shell anode material according to claim 1, characterized in that, In step S3, the calcination conditions include: being carried out under a protective atmosphere, a calcination temperature of 650–950°C, and a calcination time of 1.5–2.5 h.

10. The carbon nanotube-reinforced silicon-carbon core-shell anode material prepared by the preparation method according to any one of claims 1-9.

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