Silicon-carbon nanocomposite material, preparation method and application thereof

Abstract

The application discloses a silicon-carbon nanometer composite material and a preparation method and application thereof, and belongs to the technical field of lithium battery materials. The method comprises the following steps: preparing a graphene-isolated and dispersed nanometer silicon suspension; preparing graphene-isolated and dispersed nanometer silicon powder; preparing polymer-blended and modified nanometer silicon particles; obtaining Si / GNP@1C through primary carbonization; coating pitch by adopting a solvent method, and obtaining Si / GNP@2C through secondary carbonization after drying; and obtaining a silicon-carbon nanometer composite material finished product through screening after airflow vortex micronizer crushing. The preparation process has the characteristics of greenness, energy saving and environmental protection, and the ternary nanometer composite microstructure well solves the problems of poor conductivity and battery performance deterioration due to expansion of silicon as a lithium ion negative electrode material.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a silicon-carbon nanocomposite material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) are essential power sources for portable electronics, power tools, and electric vehicles. The negative electrode material is a crucial component of lithium-ion batteries, determining their overall performance. Most commercially available lithium-ion batteries use graphite as the negative electrode material. However, graphite's theoretical capacity is only 372 mAh / g. -1 It has an ultra-high theoretical capacity (4200mAh·g) -1 Silicon, an active material, is abundant in natural resources and is a promising next-generation LIB anode material. However, during lithiation and delithiation, silicon undergoes large volume changes (>300%), generating mechanical strain, leading to electrode pulverization, increased electron transfer resistance, and deterioration of electrochemical stability, which greatly limits its application.

[0003] To address the aforementioned issues, silicon-carbon composite methods are considered the most promising approach. Chinese patent application CN111063890A discloses a method for preparing micron-sized silicon-carbon composite materials using spray drying, effectively improving the tap density of nano-silicon anode materials. By combining highly conductive reduced graphene oxide with silicon and carbon (sucrose, citric acid, and glucose precursors), high-rate-capacity silicon-carbon composite materials were obtained. With the increasing demand for fast charging, superior rate performance will enhance battery safety and fast-charging capabilities. Chinese patent application CN111092204A discloses a method of electrospinning hollow carbon fibers (polymer spinning solution to obtain a nanofiber precursor), carbonizing the nanofiber precursor to obtain hollow carbon fibers (outer diameter 50nm-500nm), and introducing them into silicon-carbon anode materials (carbon precursors include pitch, sucrose, glucose, soluble starch, citric acid, phenolic resin, sodium hydroxymethyl cellulose, and polyvinylpyrrolidone). This effectively buffers the structural damage to the silicon-carbon anode material caused by volume expansion during lithiation / delithiation, resulting in improved cycle stability while achieving high capacity. However, solution mixing and spray drying methods make it difficult to precisely control the microstructure morphology, particle size, and distribution of silicon-carbon composite materials, leading to… Improvements in battery electrochemical performance are limited. Chinese patent application CN101710617A discloses a method using a semi-liquid 30-50 nm mesophase pitch, employing a nano-jetting device to uniformly coat micron- or submicron-sized silicon, resulting in a high-energy silicon-carbon composite anode material with a specific capacity of 1050 mAh / g, retaining over 80% of its capacity after 500 cycles. However, this high-temperature coating process makes it difficult to achieve complete coating of nano-silicon. Patent application WO2022 / 067030A1 discloses the preparation of impregnated amorphous nano-silicon through chemical vapor infiltration on a porous carbon scaffold. While this method produces silicon-carbon composites with improved electrochemical performance, it requires expensive raw materials such as silanes, hindering industrial application. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a method for preparing silicon-carbon nanocomposite materials. By improving the conductivity of nano-silicon and effectively suppressing expansion, this method solves the problems of low initial efficiency, poor cycle stability, and inadequate rate performance in existing silicon-carbon composite materials. Another technical problem this invention aims to solve is to provide a silicon-carbon nanocomposite material prepared by the above method. A further technical problem this invention aims to solve is to provide applications of the above-described silicon-carbon nanocomposite material.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a silicon-carbon nanocomposite material includes the following steps:

[0007] 1) The nano-silicon and dispersant are uniformly mixed with graphene in a solvent to obtain a graphene-isolated and dispersed nano-silicon suspension;

[0008] 2) The graphene-isolated dispersed nano-silicon suspension was concentrated by filtration through a ceramic membrane, and then vacuum dried after pressure filtration to obtain graphene-isolated dispersed nano-silicon powder.

[0009] 3) Graphene-isolated dispersed nano-silicon powder and polymer carbon source are vacuum melt-extruded and blended to obtain polymer-modified nano-silicon particles.

[0010] 4) Polymer-modified nano-silicon particles are carbonized to obtain a primary silicon carbide carbon nanocomposite material (Si / GNP@1C);

[0011] 5) After crushing Si / GNP@1C, it is further coated with asphalt by solution spraying, dried and then carbonized twice to obtain secondary carbonized silicon-carbon nanocomposite material (Si / GNP@2C);

[0012] 6) The silicon-carbon nanocomposite material is obtained by crushing and sieving with an airflow vortex micro powder mill.

[0013] The preparation method of the silicon-carbon nanocomposite material uses ethanol and isopropanol as solvents. The silicon source is silicon nanosheets or silicon nanospheres. The dispersant is a comb-shaped superdispersant (SMA-g-PEG) prepared by reacting a copolymer of styrene and maleic anhydride with polyetheramine.

[0014] The preparation method of the silicon-carbon nanocomposite material uses a 100-nanometer ceramic membrane concentration process.

[0015] The method for preparing the silicon-carbon nanocomposite material, wherein the carbon source includes one or more of polyacrylonitrile, pitch, and phenolic resin.

[0016] The preparation method of the silicon-carbon nanocomposite material, wherein the blending is a vacuum melt blending.

[0017] In the preparation method of the silicon-carbon nanocomposite material, step 4) involves carbonization, which includes gradually heating to the carbonization temperature and carbonizing for 1 hour, with a gradual heating rate of 5°C / min; the carbonization temperature is 600-800°C. The inert gas is argon or nitrogen.

[0018] In the preparation method of the silicon-carbon nanocomposite material, in step 4), the solution method is used to spray and coat asphalt, and the amount of asphalt used is 3% of the mass of the primary carbonized material.

[0019] In the preparation method of the silicon-carbon nanocomposite material, the drying is vacuum drying.

[0020] In the preparation method of the silicon-carbon nanocomposite material, step 5) involves a gradual heating rate of 5°C / min and a carbonization temperature of 1000°C. The carbonization process lasts for 1 hour. The inert gas is nitrogen.

[0021] The method for preparing the silicon-carbon nanocomposite material involves pulverizing the material using an airflow vortex micronizer and then sieving it to obtain the finished silicon-carbon nanocomposite material.

[0022] The silicon-carbon nanocomposite material obtained by the aforementioned preparation method.

[0023] The application of the silicon-carbon nanocomposite material in the preparation of lithium-ion battery anode materials, or lithium-ion half-cells, or lithium-ion full-cells.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0025] 1) An ideal silicon / carbon / graphene ternary microstructure was constructed. First, nano-silicon was uniformly dispersed by graphene nanosheets, which not only effectively solved the problem of aggregation of nano-silicon due to its large specific surface area, but also endowed the nano-silicon with a conductive network. Second, a vacuum melt extrusion blending process was used to achieve uniform dispersion of silicon, graphene, and polymer carbon source. During the primary carbonization process, the melting of pitch can effectively coat the silicon / graphene nanocomposite. Third, by controlling the particle size, distribution, and specific surface area of ​​the silicon-carbon nanocomposite by adjusting the rotation speed and grinding time of a planetary ball mill, the tap density of the silicon-carbon composite material can be improved. Fourth, through secondary carbonization, the small amount of nano-silicon exposed during the pulverization process of the primary carbonized composite material is completely coated, avoiding direct contact between the nano-silicon and the electrolyte.

[0026] 2) In silicon-carbon nanocomposites, graphene and carbon form a three-dimensional conductive network structure on the nano-silicon, which makes the prepared silicon-carbon nanocomposites not only have high initial efficiency, but also excellent rate capability and cycle stability.

[0027] 3) The solvent used in the solution mixing method for preparing graphene-isolated and dispersed nano-silicon is recycled through filtrate and condensation during drying. Therefore, the entire preparation process is green, energy-saving and environmentally friendly. Attached Figure Description

[0028] Figure 1 The image shows the TEM morphology of the raw materials used in Product 1; in the image, a is silicon nanosheets, b is graphene-isolated dispersed silicon nanosheets, and c is graphene nanosheets.

[0029] Figure 2 The images show the SEM morphology of the silicon-carbon nanocomposites prepared from products 1-4; in the images, a is product 1, b is product 2, c is product 3, and d is product 4.

[0030] Figure 3 The image shows the Malvern particle size distribution of the silicon-carbon nanocomposites prepared from products 1-4.

[0031] Figure 4 The image shows the SEM morphology of the polymer / silicon composite material of product 7 before carbonization. In the image, a is before carbonization, b is after the first carbonization, and c is after the second carbonization.

[0032] Figure 5 This is the Malvern particle size distribution diagram of the silicon-carbon nanocomposite material prepared by product 7;

[0033] Figure 6 This is a comparison chart of the cycle stability of button batteries using silicon-carbon composite material of Product 1 and Comparison Product 1 applied to modified graphite anodes.

[0034] Figure 7 The impedance comparison diagram of the composite material prepared by Product 1 and Comparison Product 1 after 500 cycles of button cell is shown.

[0035] Figure 8 The graph shows the rate curve of a 18650 full cell assembled from silicon-carbon nanocomposite material prepared by product 7, which is applied to a modified graphite anode. Detailed Implementation

[0036] To better understand the purpose, technical solution, and advantages of this invention, the following detailed description, in conjunction with the accompanying drawings, provides a method for preparing silicon-carbon nanocomposite materials and its applications.

[0037] Example 1

[0038] A method for preparing a silicon-carbon nanocomposite material includes the following steps:

[0039] Step 1: Nano-silicon, dispersant, and graphene nanosheets are uniformly mixed in a solvent to obtain a graphene-isolated dispersed nano-silicon suspension. In the graphene-isolated dispersed nano-silicon solution, the mass ratio of nano-silicon, graphene, dispersant, and solvent is 10-15:2-5:0.03-0.05:80-85. The silicon source is at least one of nanosheet silicon and nanosphere silicon. The dispersant is a superdispersant containing benzene rings or fused rings and carboxyl groups, such as a comb-like superdispersant prepared by reacting a copolymer of styrene and maleic anhydride with polyetheramine. The solvent is at least one of ethanol and isopropanol.

[0040] Step 2: The graphene-isolated dispersed nano-silicon suspension is concentrated by filtration through a ceramic membrane, and then vacuum dried after pressure filtration to obtain graphene-isolated dispersed nano-silicon powder; the concentration process adopts a 100-nanometer ceramic membrane filtration process.

[0041] Step 3: Vacuum melt extrusion blending and granulation of graphene-isolated dispersed nano-silicon powder and polymer carbon source to obtain polymer-modified nano-silicon particles; the carbon source includes at least one of polyacrylonitrile, asphalt and phenolic resin.

[0042] Step 4: The obtained polymer / silicon nanoparticle / graphene composite is carbonized to obtain a primary silicon carbide carbon nanocomposite material (Si / GNP@1C). Carbonization is carried out in a rotary kiln, with gradual heating to the carbonization temperature for 1.0-2.5 hours. The gradual heating rate is 5-10℃ / min, the carbonization temperature is 600-800℃, and the carbonization atmosphere is at least one of nitrogen or argon.

[0043] Step 5: After pulverizing Si / GNP@1C, the asphalt is further coated onto the primary silicon carbide carbon nanocomposite material using a solution spray method. After drying, a secondary carbonization is performed to obtain the secondary silicon carbide carbon nanocomposite material (Si / GNP@2C). The pulverization is carried out using a planetary ball mill. The asphalt coating is performed using a solution spray method, with the amount of asphalt being 3-5% of the mass of the primary carbonized material. The drying is performed using vacuum drying. The carbonization is carried out by gradually increasing the temperature to the carbonization temperature, wherein the gradual heating rate is 5℃ / min, the carbonization temperature is 1000℃, the carbonization time is 1-1.5h, and the carbonization atmosphere is at least one of nitrogen or argon.

[0044] Step 6: After pulverizing and sieving using an airflow vortex micro powder mill, the finished silicon-carbon nanocomposite material is obtained.

[0045] Example 2

[0046] The series of products were prepared using the method described in Example 1, as follows:

[0047] Product 1: Si / GNP@1C (asphalt)

[0048] 3.5 kg of silicon nanosheets, 29.94 kg of isopropanol, 0.5 kg of graphene nanosheets, and 6.25 g of dispersant (TEGO-760W) were dispersed at 1500 r / min for 20 min, followed by sand milling for 4 h. The resulting powder was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene-isolated dispersion (Si / GNP) nanocomposite powder. The Si / GNP nanocomposite powder was then melt-extruded and granulated with 4.29 kg of asphalt at 360 °C under vacuum. A second carbonization was performed in a rotary kiln, followed by heating to 800 °C at 5 °C / min under a nitrogen atmosphere and holding for 1 h to obtain Si / GNP@1C silicon-carbon nanocomposite material. This material was then micronized and classified using an airflow vortex milling process for 3 minutes, achieving a silicon / carbon ratio of 1:1.

[0049] Figure 1The images show the TEM morphology of nanosheet silicon (a), graphene-isolated dispersed nanosilicon (b), and graphene nanosheets (c) used in Product 1. Figure 1 It can be seen that the size of silicon nanosheets is between 80-150 nm, while the average size of graphene nanosheets is 500 nm. Figure 1 c) Under the action of a dispersant, through liquid-phase stirring and milling, the final morphology of graphene-isolated and dispersed nano-silicon structures was obtained. Figure 1 b).

[0050] Product 2: Si / GNP@1C (Phenolic Resin 1)

[0051] 3.5 kg of silicon nanosheets, 29.94 kg of isopropanol, 0.5 kg of graphene nanosheets, and 6.25 g of dispersant (TEGO-760W) were dispersed at 1500 r / min for 20 min, followed by sand milling for 4 h. The resulting powder was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene-isolated dispersion (Si / GNP) nanocomposite powder. The Si / GNP nanocomposite powder was then melt-extruded and granulated with 2.39 kg of phenolic resin at 150 °C under vacuum. This granulation was followed by a single carbonization process in a rotary kiln, with the temperature increased to 800 °C at 5 °C / min and held for 1 h under a nitrogen atmosphere to obtain Si / GNP@1C silicon-carbon nanocomposite material. This material was then micronized and classified using an airflow vortex milling process for 3 minutes, achieving a silicon / carbon ratio of 1:1.

[0052] Product 3: Si / GNP@1C (Phenolic Resin 2)

[0053] 3.5 kg of silicon nanosheets, 29.94 kg of isopropanol, 0.5 kg of graphene nanosheets, and 6.25 g of dispersant (TEGO-760W) were dispersed at a high speed of 1500 r / min for 20 min, followed by sand milling for 4 h. The resulting powder was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene-isolated dispersion (Si / GNP) nanocomposite powder. The Si / GNP nanocomposite powder was then melt-extruded and granulated with 11 kg of phenolic resin at 150 °C under vacuum. A second carbonization was performed in a rotary kiln, followed by heating to 800 °C at a rate of 5 °C / min under a nitrogen atmosphere and holding for 1 h to obtain Si / GNP@1C silicon-carbon nanocomposite material. This material was then micronized and classified using an airflow vortex milling process for 3 minutes, resulting in a silicon / carbon ratio of 1:1.456.

[0054] Product 4: Si / GNP@1C (Polyacrylonitrile)

[0055] 3.5 kg of silicon nanosheets, 29.94 kg of isopropanol, 0.5 kg of graphene nanosheets, and 6.25 g of dispersant (TEGO-760W) were dispersed at 1500 r / min for 20 min, followed by sand milling for 4 h. The resulting powder was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene-isolated dispersion (Si / GNP) nanocomposite powder. The Si / GNP nanocomposite powder was then melt-extruded and granulated with 5.76 kg of polyacrylonitrile at 180 °C under vacuum. This granulation was followed by a single carbonization process in a rotary kiln, with the temperature increased to 800 °C at 5 °C / min and held for 1 h under a nitrogen atmosphere to obtain Si / GNP@1C silicon-carbon nanocomposite material. This material was then micronized and classified using an airflow vortex milling process for 3 minutes, achieving a silicon / carbon ratio of 1:0.92.

[0056] Figure 2 The image shows the SEM morphology of the silicon-carbon nanocomposites prepared from products 1-4. Figure 2 The results show that different carbon sources and silicon-carbon ratios directly affect the morphology and size of the prepared silicon-carbon nanocomposites. Silicon-carbon nanocomposites prepared using pitch as a carbon source have a wide particle size distribution and form many carbon fragments; while silicon-carbon nanocomposites prepared using phenolic resin as a carbon source have larger particles and relatively smooth surfaces. Increasing the relative content of phenolic resin results in silicon-carbon nanocomposites with relatively lower phenolic resin content, which not only have larger particle sizes but also adsorb more small particles on the surface; while silicon-carbon nanocomposites prepared using polyacrylonitrile as a carbon source have many small filamentous structures adsorbed on their large particles.

[0057] Figure 3 The image shows the Malvern particle size distribution of the silicon-carbon nanocomposites prepared from products 1-4. Figure 3 The Malvern particle size distributions of silicon-carbon nanocomposites prepared by products 1-4 are shown. Although the peak values ​​of the particle size distributions of silicon-carbon nanocomposites prepared by asphalt and polyacrylonitrile are the same, the silicon-carbon nanocomposites prepared by polyacrylonitrile carbon source have a wider distribution of larger particles. The peak values ​​of the particle size distributions of silicon-carbon nanocomposites prepared by phenolic carbon source are 37.67 μm and 62.76 μm, respectively. Increasing the proportion of phenolic carbon source is beneficial to obtaining silicon-carbon nanocomposites with larger particle sizes.

[0058] Product 5: Si / GNP@1C (asphalt) mill

[0059] 3.5 kg of silicon nanosheets, 29.94 kg of isopropanol, 0.5 kg of graphene nanosheets, and 6.25 g of dispersant (TEGO-760W) were dispersed at 1500 r / min for 20 min, followed by sand milling for 4 h. The resulting powder was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene-isolated dispersion (Si / GNP) nanocomposite powder. The Si / GNP nanocomposite powder was then melt-extruded and granulated with 6.78 kg of asphalt at 360 °C under vacuum. A subsequent carbonization process was performed in a rotary kiln, followed by heating to 800 °C at 5 °C / min under a nitrogen atmosphere and holding for 1 h to obtain Si / GNP@1C silicon-carbon nanocomposite material. This material was then milled using a planetary ball mill at 600 r / min for 20 min, with a silicon / carbon ratio of 1:1.5.

[0060] Product 6: Spheres Si / GNP@2C (asphalt)

[0061] 3.5 kg of silicon nanospheres, 29.94 kg of isopropanol, 0.5 kg of graphene nanosheets, and 6.25 g of dispersant (TEGO-760W) were dispersed at a high speed of 1500 r / min for 20 min, then milled for 4 h, and concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene isolated dispersion (Si / GNP) nanocomposite powder. Si / GNP nanocomposite powder was vacuum melt-extruded and granulated with 5.76 kg of asphalt at 360 °C, followed by a first carbonization in a rotary kiln. The temperature was increased to 600 °C at 5 °C / min under a nitrogen atmosphere and held for 1 h to obtain Si / GNP@1C silicon-carbon nanocomposite material. Then, 0.21 kg of asphalt was dissolved in 2 kg of tetrahydrofuran, and the surface of Si / GNP@1C was modified by spraying. After vacuum drying, a second carbonization was carried out in a rotary kiln. The temperature was increased to 1000 °C at 5 °C / min under a nitrogen atmosphere and held for 1 h. The material was then micronized and classified by airflow vortex grinding for 3 minutes, with a silicon / carbon ratio of 1:1.

[0062] Product 7: Si / GNP@2C (asphalt)

[0063] 3.5 kg of silicon nanosheets, 29.94 kg of isopropanol, 0.5 kg of graphene nanosheets, and 6.25 g of dispersant (TEGO-760W) were dispersed at a high speed of 1500 r / min for 20 min, followed by sand milling for 4 h. The mixture was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene isolated dispersion (Si / GNP) nanocomposite powder. Si / GNP nanocomposite powder was vacuum melt-extruded and granulated with 5.76 kg of asphalt at 360 °C, followed by a first carbonization in a rotary kiln. The temperature was increased to 800 °C at 5 °C / min under a nitrogen atmosphere and held for 1 h to obtain Si / GNP@1C silicon-carbon nanocomposite material. A planetary ball mill was used at 300 r / min for 1 h. Then, 0.21 kg of asphalt was dissolved in 2 kg of tetrahydrofuran, and the surface of Si / GNP@1C was modified by spraying. After vacuum drying, a second carbonization was carried out in a rotary kiln. The temperature was increased to 1000 °C at 5 °C / min under a nitrogen atmosphere and held for 1 h. The powder was then micronized and classified by airflow vortex grinding for 3 min, with a silicon / carbon ratio of 1:1.

[0064] Figure 4 The image shows the SEM morphology of the polymer / silicon composite material of product 7 before carbonization. In the image, a is before carbonization, b is after the first carbonization, and c is after the second carbonization. Figure 4 The image shows the morphology of the polymer / silicon composite material of product 7 before carbonization. The morphology changed significantly after one carbonization. Figure 4 (b) This is the process where the polymer melts during carbonization and encapsulates the graphene-dispersed silicon nanoparticles. Further carbonization forms carbon-coated Si / GNP, i.e., Si / GNP@1C. After grinding in a planetary ball mill, a small amount of silicon nanoparticles are exposed. These are then surface-modified with 3% by mass of Si / i / GNP@1C asphalt. During the secondary carbonization process, the melting of the asphalt effectively encapsulates the exposed silicon nanoparticles, ultimately forming a secondary silicon-carbon nanocomposite material (Si / GNP@2C). The particle surface is smoother than that of Si / GNP@1C. Figure 4 c).

[0065] Figure 5 This is the Malvern particle size distribution diagram of the silicon-carbon nanocomposite material prepared by product 7; Figure 5 The Malvern particle size distribution of the silicon-carbon nanocomposite material prepared by product 7 is shown. It exhibits a normal distribution with a peak particle size of 11.9 micrometers. It has good gradation with the graphite anode material, indicating that the particle size and distribution of silicon-carbon nanocomposite materials can be controlled by adjusting the rotation speed and time of the planetary ball mill.

[0066] Product 8: Change the proportion

[0067] 2.5 kg of silicon nanosheets, 16.67 kg of isopropanol, 1.0 kg of graphene nanosheets, and 10.0 g of dispersant (TEGO-760W) were dispersed at 1500 r / min for 20 min, followed by sand milling for 4 h. The resulting powder was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene-isolated dispersion (Si / GNP) nanocomposite powder. The Si / GNP nanocomposite powder was then melt-extruded and granulated with 2.14 kg of asphalt at 360 °C under vacuum. A subsequent carbonization process was performed in a rotary kiln, followed by heating to 800 °C at 5 °C / min under a nitrogen atmosphere and holding for 1 h to obtain Si / GNP@1C silicon-carbon nanocomposite material. This material was then micronized and classified using an airflow vortex milling process for 3 minutes, achieving a silicon / carbon ratio of 1:1.

[0068] Product 9: Change Solvent

[0069] 3.5 kg of silicon nanosheets, 29.94 kg of ethanol, 0.5 kg of graphene nanosheets, and 6.25 g of dispersant (TEGO-760W) were dispersed at 1500 r / min for 20 min, followed by sand milling for 4 h. The resulting powder was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 4 kg of graphene-isolated dispersion (Si / GNP) nanocomposite powder. The Si / GNP nanocomposite powder was then melt-extruded and granulated with 4.29 kg of asphalt at 360 °C under vacuum. A second carbonization was performed in a rotary kiln, followed by heating to 800 °C at 5 °C / min under a nitrogen atmosphere and holding for 1 h to obtain Si / GNP@1C silicon-carbon nanocomposite material. This material was then micronized and classified using an airflow vortex milling process for 3 minutes, achieving a silicon / carbon ratio of 1:1.

[0070] Comparison Product 1

[0071] 3.5 kg of silicon nanosheets, 29.94 kg of isopropanol, and 6.25 g of dispersant (TEGO-760W) were dispersed at 1500 r / min for 20 min, followed by sand milling for 4 h. The resulting powder was then concentrated by filtration through a 100 nm ceramic membrane and vacuum dried to obtain 3.5 kg of graphene-isolated dispersion (Si@GNP) nanocomposite powder. The silicon nanocomposite powder was then melt-extruded and granulated with 5 kg of asphalt at 360 °C under vacuum. A second carbonization was performed in a rotary kiln, followed by heating to 800 °C at 5 °C / min under a nitrogen atmosphere and holding for 1 h to obtain Si / @1C silicon-carbon nanocomposite material. This material was then micronized and classified using an airflow vortex milling process for 3 minutes, achieving a silicon / carbon ratio of 1:1.

[0072] Example 3

[0073] Products 1-9 prepared in Example 2 and Comparative Product 1 were assembled into a half-cell, and the performance of the half-cell was tested.

[0074] The assembly method for the half-cell is as follows: a standard CR2032-type button cell is assembled in an argon-filled glove box (H2O and O2 < 0.5ppm). The electrolyte used is the Shanshan SS-SDTK005 silicon-carbon anode battery. A copper foil circular electrode sheet coated with a self-made silicon-carbon anode material serves as the anode, and metallic lithium serves as the cathode, separated by a Celgard 2325 polypropylene film to form a button cell (CR2032).

[0075] Determination of the integrity of silicon carbon coating: Weigh 200 mg of silicon carbon into a 50 mL pear-shaped flask with a rubber stopper. Add 5 mL of 1 M KOH using a syringe. After mixing at room temperature, place the flask in a 60 °C water bath and react for 5 min, 15 min, and 25 min. Determine the molar fraction of hydrogen generated in the system using gas chromatography, assuming the molar concentration of nitrogen in the test system remains constant. The concentration of H2 generated can be determined according to the following standard: A (peak area) = 2163.9 x (mol / mol standard gas in the flask) + 57.912.

[0076] Table 1 shows the test results for the carbon coating integrity of half-cells of products 1-9 and comparison product 1.

[0077]

[0078]

[0079] The results of the carbon coating integrity determination of silicon are shown in Table 1. Comparing Products 1, 2, 3, and 4, the silicon-carbon nanocomposite prepared with pitch carbon source exhibits the best silicon-carbon nanocomposite coating integrity, while the silicon-carbon nanocomposite prepared with polyacrylonitrile carbon source has the worst silicon-carbon nanocomposite coating integrity. Comparing Products 2 and 3, it is not the case that a higher proportion of carbon source polymer leads to more complete coating of nano-silicon, but rather it is closely related to the uniformity of the mixing of polymer and Si / GNP. Comparing Products 1 and 5, it can be seen that the silicon-carbon nanoparticles pulverized at high grinding speed expose more uncoated nano-silicon, thus generating more and more hydrogen gas as the reaction time increases. Compared to Product 1, Product 6 only uses nanosphere silicon, and its nano-silicon coating integrity is slightly worse than that of Product 1, which uses nanosheet silicon. This is due to the difference in the gradation between particles with different morphologies. In contrast, the hydrogen peak area in Product 7 does not increase with the extension of reaction time, indicating that the surface of the nano-silicon is completely coated with carbon under these conditions. In step 5, product 7 uses a planetary ball mill to pulverize the primary carbide (300 r / min, 1 hour) to expose as much uncoated nano-silicon as possible. Then, 0.21 kg of asphalt is dissolved in 2 kg of tetrahydrofuran, and the Si / GNP@1C surface is modified using a spray method. After vacuum drying, a second carbonization is performed in a rotary kiln. During the second carbonization process, all uncoated nano-silicon is repaired. This is one of the reasons why the product exhibits excellent cycle stability and rate performance in full-cell testing.

[0080] The assembly of the ternary 18650-2000mAh / 15C includes the following processes: positive and negative electrode material preparation; positive and negative electrode coating; positive and negative electrode rolling, slitting, and sheet forming; winding; casing, spot welding, and laser welding; electrolyte injection and sealing; formation and capacity testing. The electrolyte used is Shanshan SS-SDTK005 silicon-carbon negative electrode-specific electrolyte.

[0081] The standard CR2032-type button cell was assembled in an argon-filled glove box (H2O and O2 < 0.5 ppm). The electrolyte used was Shanshan SS-SDTK005 silicon-carbon anode-specific electrolyte. A self-made silicon-carbon anode material coated with copper foil was used as the anode, and metallic lithium as the cathode, separated by a Celgard 2325 polypropylene film to form the button cell (CR2032).

[0082] Testing was conducted using a Neware battery testing system (CT-4008, Neware, China) under the following conditions: a voltage window of 0.01-3.0V (vs. Li+ / Li), and constant current charge-discharge (GCD) tests were performed at different current densities. Cyclic voltammetry (CV, 0.1mV s) was performed at the Shanghai Chenhua CHI660 A electrochemical station. -1Measurements were performed using electrochemical impedance spectroscopy (EIS, 0.01 Hz - 100 kHz), ranging from 0.01 to 3.0 V.

[0083] The results of the cycle stability comparison of button batteries are as follows: Figure 6 As shown, the specific capacity changes over the first 200 cycles. The specific capacity of Product 1 decreases at a very slow rate over the first 200 cycles, while the specific capacity of the silicon-carbon composite material of Comparative Product 1 decreases significantly over the first 200 cycles. This result fully demonstrates that graphene-isolated and dispersed nano-silicon not only improves the conductivity of nano-silicon, but also plays a positive role in suppressing the expansion of nano-silicon.

[0084] The composite material prepared from Product 1 and Comparison Product 1 was applied to the modified graphite anode. The impedance comparison results of the button cell after 500 cycles are as follows: Figure 7 As shown, even after 500 cycles, the charge transfer resistance of Product 1 does not exceed 100Ω, and the ion diffusion channel remains well maintained. In contrast, after 500 cycles, the charge transfer resistance of Product 1 increases to over 100,000Ω, and the ion diffusion channel disappears. Therefore, the battery performance shows a significant deterioration.

[0085] The silicon-carbon nanocomposite material prepared by Product 7 was applied to a modified graphite anode and assembled into an 18650 full cell, with the rate curve shown below. Figure 8 As shown, from Figure 8 It can be seen that the capacity retention rates of 1C, 2.5C, 5C, 10C and 15C are 98.56%, 98.78%, 95.89% and 87.42% respectively, showing good rate performance.

[0086] Table 2 Electrochemical performance test results

[0087]

[0088]

[0089] Table 2 shows that the specific capacity of the first-cycle battery depends not only on the silicon content in the negative electrode material, but also on the specific capacity of the first-cycle full cell, which, with the addition of 4% silicon-carbon prepared from product 7, achieves a specific capacity of 390.1 mAh g⁻¹. The other eight coin cells assembled, through the addition of different silicon-carbon nanocomposites, achieve a silicon mass fraction of 3% in the negative electrode material. The specific capacity of the first cycle varies depending on the type of carbon source and the silicon-carbon ratio, and is also affected by the morphology of the nano-silicon. The highest initial efficiency was achieved by product number 8 (a silicon-carbon composite material prepared by adding 4% by mass of product 7 to a full 18650 cell, 0.5C charge, 10C discharge) at 90.5%, which is related to the fact that the actual amount of silicon added was only 2% (by mass). The highest initial efficiency was achieved by product number 6 (a coin cell) at 88.8%, which is related to the small size of the spherical silicon and the fact that double carbon coating can effectively improve the integrity of the nano-silicon coating. Product number 7's initial efficiency of 88.6% was close to that of product number 6, indicating that double carbonization can effectively improve the initial efficiency of the coin cell by increasing the integrity of the carbon coating. In contrast, product number 1 had the lowest initial efficiency, which is closely related to the poor conductivity of its electrodes. In terms of capacity retention after 500 cycles, cells 1-7, regardless of their carbon source and silicon-to-carbon ratio, exhibited excellent cycle stability under 0.1C charge-discharge conditions. In the 18650 full-cell cycle stability test, even with 0.5C charge and 10C discharge, the capacity retention after 500 cycles was 85.11%, while product 1's capacity retention dropped to 22.1% after 500 cycles. Regarding rate performance, cell 3 showed the best rate performance, achieving a 62.6% capacity retention at 1C discharge compared to 0.1C, while product 1 only retained 8.9% under the same conditions. Furthermore, the carbon source, silicon-to-carbon ratio, and the size and morphology of nano-silicon can all affect the rate performance of cell batteries.

[0090] Compared to adding Product 1, adding Product 8 resulted in a decrease in specific capacity and initial efficiency in the first cycle, but an improvement in cycle stability and rate performance. This is because Product 8 has a higher graphene content than Product 1, which increases the specific surface area of ​​the composite material. This allows the battery to form more SEI film, thus reducing the specific capacity and initial efficiency in the first cycle. The increased graphene content is beneficial for electron transport in the battery, thereby improving cycle stability and rate performance.

[0091] Compared to adding product 1, adding product 9 resulted in a more similar specific capacity and first-cycle efficiency in the first cycle, but reduced cycle stability and rate performance. This is because product 9 uses ethanol as a solvent, which increases the size of silicon in the composite material compared to isopropanol. Therefore, during repeated expansion in the battery, the charge transfer resistance tends to increase, resulting in a decrease in cycle stability and rate performance.

Claims

1. A method for preparing a silicon-carbon nanocomposite material, characterized in that, Includes the following steps: 1) Nano-silicon, graphene, and dispersant are uniformly mixed in a solvent to obtain a graphene-isolated and dispersed nano-silicon suspension; wherein, the mass ratio of nano-silicon, graphene, dispersant, and solvent is 10-15∶2-5∶0.03-0.05∶80-85, the nano-silicon is nanosheet silicon, and the solvent is isopropanol. 2) The graphene-isolated dispersed nano-silicon suspension was concentrated by filtration through a ceramic membrane, and then vacuum dried after pressure filtration to obtain graphene-isolated dispersed nano-silicon powder. 3) Graphene-isolated dispersed nano-silicon powder and a polymer carbon source are vacuum melt-extruded and blended into granules to obtain polymer-modified nano-silicon particles; the polymer carbon source is asphalt. 4) The polymer-modified nano-silicon particles are carbonized to obtain a primary silicon-carbon nanocomposite material; the gradual heating rate of carbonization is 5℃-10℃ / min, the carbonization temperature is 600-800℃, and the carbonization atmosphere is at least one of nitrogen or argon. 5) After pulverizing the primary silicon carbide carbon nanocomposite material, it is further coated with asphalt using a solution spray method, dried, and then carbonized a second time to obtain a secondary silicon carbide carbon nanocomposite material. Among them, the pulverization is carried out using a planetary ball mill with a speed of 300 r / min and a grinding time of 1 h; the asphalt is coated by solution method, and the amount of asphalt is 3-5% of the mass of the primary carbonized material; the carbonization is carried out by gradually increasing the temperature to the carbonization temperature at a rate of 5℃ / min, the carbonization temperature is 1000℃, the carbonization time is 1-1.5 h, and the carbonization atmosphere is at least one of nitrogen or argon. 6) The silicon-carbon nanocomposite material is obtained by crushing and sieving with an airflow vortex micro powder mill.

2. The method for preparing silicon-carbon nanocomposite materials according to claim 1, characterized in that, The concentration process uses a 100-nanometer ceramic membrane filtration process, the blending process is vacuum melt extrusion blending, and the drying process is vacuum drying.

3. The silicon-carbon nanocomposite material obtained by the preparation method of the silicon-carbon nanocomposite material according to any one of claims 1-2.

4. The application of the silicon-carbon nanocomposite material according to claim 3 in the preparation of lithium-ion battery anode materials, or lithium-ion half-cells, or lithium-ion full-cells.

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