Preparation method of silicon-carbon negative electrode material of lithium ion battery and silicon-carbon negative electrode material

Abstract

The invention provides a preparation method of a silicon-carbon negative electrode material of a lithium ion battery and the silicon-carbon negative electrode material. The preparation method comprises the following steps: S1, adding silicon powder, titanium nitride, stearic acid, N-methyl pyrrolidone, carbon nanotubes and low-temperature asphalt into absolute ethyl alcohol, and stirring and dispersing; s2, adding the obtained mixture into a sand mill for grinding, and discharging; s3, performing spray drying to obtain powder; s4, the powder is placed in a nitrogen atmosphere sintering furnace, and a sintered material is obtained; s5, firstly adding the sintered material, high-temperature asphalt, graphite and nickel powder into a high-temperature coating reaction kettle, then completing a secondary coating process under the protection of nitrogen, and discharging; s6, transferring into a nitrogen and ammonia gas mixed atmosphere furnace for sintering; and step S7, crushing to obtain the silicon-carbon negative electrode material. According to the invention, the technical problems of volume expansion, insufficient conductivity, uneven carbon layer coating and the like of the existing silicon-carbon negative electrode material can be effectively solved, and the comprehensive performance is remarkably improved.

Description

Technical Field

[0001] This invention relates to a method for preparing battery materials, particularly to a method for preparing silicon-carbon anode materials for lithium-ion batteries, and further to silicon-carbon anode materials using the method for preparing silicon-carbon anode materials for lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries have been commercialized on a large scale due to their high energy density and long cycle life. However, the capacity of graphite anodes has been developed to its theoretical limit, restricting further improvements in battery energy density. Silicon anode materials have a theoretical capacity of up to 4200 mAh / g, making them the preferred choice for next-generation high-capacity anodes. However, silicon anode materials suffer from several problems: insufficient conductivity and severe volume expansion during lithiation, which can lead to material breakage and failure. To address these issues, the main optimization methods are nano-sizing and carbon coating to obtain silicon-carbon anode materials, thereby extending their actual lifespan. Among these methods, the sand-milling spray process is simple, low-cost, and has high production capacity, making it suitable for large-scale production of silicon-carbon anode materials. However, silicon-carbon anode materials prepared by the sand-milling spray process still have a high expansion rate, resulting in poor cycle performance, and the uneven carbon layer coating thickness also degrades the conductivity of the silicon-carbon anode material. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a method for preparing silicon-carbon anode materials for lithium-ion batteries, aiming to solve the technical problems of existing silicon-carbon anode materials such as volume expansion, insufficient conductivity, and uneven carbon layer coating, thereby improving the overall performance of silicon-carbon anode materials. Furthermore, this invention provides silicon-carbon anode materials prepared using this method for preparing silicon-carbon anode materials for lithium-ion batteries.

[0004] To address this issue, the present invention provides a method for preparing a silicon-carbon anode material for lithium-ion batteries, comprising the following steps:

[0005] Step S1: Add silica powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt to anhydrous ethanol and stir to disperse until the mixture is homogeneous; wherein the total mass of silica powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt accounts for 10-20% of the mass of anhydrous ethanol; the mass percentages of silica powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt are 62-67%, 6-9%, 2-4%, 1-3%, 0.1-0.3%, and 19.8-24.8%, respectively.

[0006] Step S2: Add the mixture obtained in step S1 to a sand mill for grinding until the particle size distribution of the material meets the requirement of D50<0.1μm and then discharge the material.

[0007] Step S3: Powder is obtained by spray drying using a spray dryer, wherein the inlet air temperature of the spray dryer is 165~175℃ and the outlet air temperature is 85~95℃.

[0008] Step S4: Place the powder in a nitrogen atmosphere sintering furnace and treat it at a temperature range of 480~510 ℃ for 3.8~4.1 h to obtain the sintered material;

[0009] In step S5, the calcined material, high-temperature pitch, graphite, and nickel powder are added to the high-temperature coating reactor in the following proportions by mass: 58-62%, 24-26%, 13.95-15.95%, and 0.04-0.06%, respectively. Then, under nitrogen protection, the reactor is heated to 490-510°C and stirred at 190-210 rpm for 3.9-4.1 hours to complete the secondary coating process, and the material is then discharged.

[0010] Step S6: The product obtained in step S5 is transferred to a furnace with a mixed atmosphere of nitrogen and ammonia, and sintered at a temperature of 790~810℃ for 1.9~2.1h, wherein the volume content of ammonia is 4.5~5.5%.

[0011] Step S7: After sintering, the product is mechanically crushed to obtain silicon-carbon anode material.

[0012] A further improvement of the present invention is that, in step S1, the purity of the silicon powder is greater than 99.99%.

[0013] A further improvement of the present invention is that, in step S1, the particle size distribution of the silicon powder satisfies D50≤3μm, and the particle size distribution of the titanium nitride satisfies D50≤0.1μm; and in step S5, the particle size distribution of the nickel powder satisfies D50≤0.5μm.

[0014] A further improvement of the present invention is that, in step S1, the low-temperature asphalt refers to asphalt with a softening point below 150°C; and in step S5, the high-temperature asphalt refers to asphalt with a softening point above 270°C.

[0015] A further improvement of the present invention is that, in step S1, the mass percentages of the silicon powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes and low-temperature asphalt are 65%, 8%, 3%, 2%, 0.2% and 21.8%, respectively.

[0016] A further improvement of the present invention is that, in step S1, the total mass of the silicon powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes and low-temperature pitch accounts for 15% of the mass of anhydrous ethanol; and in step S2, the material is discharged when the particle size distribution of the material meets the requirement of D50 < 0.09 μm.

[0017] A further improvement of the present invention is that, in step S3, the inlet air temperature of the spray dryer is 170°C and the outlet air temperature is 90°C; in step S4, the sintering temperature of the nitrogen atmosphere sintering furnace is 500°C and the sintering time is 4 hours.

[0018] A further improvement of the present invention is that, in step S5, the mass percentages of the sintered material, high-temperature pitch, graphite and nickel powder are 60%, 25%, 14.95% and 0.05%, respectively; and in the secondary coating process, the reactor is heated to 500°C and stirred at 200 rpm for 4 hours.

[0019] A further improvement of the present invention is that, in step S6, the volume percentages of nitrogen and ammonia in the mixed atmosphere furnace are 95% and 5%, respectively, and sintering is carried out at a temperature of 800°C for 2 hours; in step S7, the structure of the silicon-carbon anode material obtained is Si@TiN@C@NC.

[0020] The present invention also provides a silicon-carbon anode material, wherein the preparation process of the silicon-carbon anode material adopts the preparation method of the silicon-carbon anode material for lithium-ion batteries as described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: Silicon-carbon anode materials for lithium-ion batteries are prepared through the synergistic operation of steps S1 to S7. First, in step S1, a reasonable mass percentage of titanium nitride is introduced to form an expansion buffer layer between silicon powder and carbon nanotubes, uniformly releasing silicon expansion stress and reducing its volume expansion rate. Simultaneously, a loose carbon layer is formed by low-temperature asphalt carbonization with a suitable mass percentage to improve the lithium-ion diffusion rate. Based on this, after grinding in step S2, spray drying in step S3, and sintering in step S4, in step S5, a dense carbon layer is formed by secondary coating with high-temperature asphalt, forming a loose inner and tight outer carbon layer together with the layer formed in step S1. This ensures the lithium-ion diffusion rate while effectively reducing direct contact between silicon and the electrolyte, further improving the material's stability and cycle performance. Furthermore, in step S6, nickel powder catalyzes the decomposition of a mixed atmosphere of nitrogen and ammonia to form an in-situ nitrogen-doped structure in the outer carbon layer, which, in synergy with the internal titanium nitride, further enhances the conductivity of the silicon-carbon anode material. Therefore, the present invention can effectively solve the technical problems of existing silicon-carbon anode materials, such as volume expansion, insufficient conductivity and uneven carbon layer coating, and significantly improve the overall performance of silicon-carbon anode materials. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the workflow of one embodiment of the present invention;

[0023] Figure 2 This is a graph showing the electrical performance test results of one embodiment of the present invention.

[0024] Figure 3 This is a comparative electrical performance test curve diagram of one embodiment of the present invention;

[0025] Figure 4 This is a scanning electron microscope (SEM) characterization image of an embodiment of the present invention. Detailed Implementation

[0026] In the description of this invention, the term "several" means one or more; the term "multiple" means two or more; the terms "greater than," "less than," and "exceeding" are all understood to exclude the stated number; and the terms "above," "below," and "within" are all understood to include the stated number. The terms "first," "second," etc., are understood to be used only to distinguish identical or similar technical feature names, and should not be construed as implying / indicating the relative importance of the technical features, the number of technical features, or the sequential relationship between the technical features.

[0027] The preferred embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0028] like Figure 1 As shown, this embodiment provides a method for preparing a silicon-carbon anode material for lithium-ion batteries, including the following steps:

[0029] Step S1: Add silicon powder (Si), titanium nitride (TiN), stearic acid, N-methylpyrrolidone (NMP), carbon nanotubes (CNTs), and low-temperature asphalt to anhydrous ethanol and stir to disperse until the mixture is homogeneous; wherein the total mass of silicon powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt accounts for 10-20% of the mass of anhydrous ethanol; the mass percentages of silicon powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt are 62-67%, 6-9%, 2-4%, 1-3%, 0.1-0.3%, and 19.8-24.8%, respectively;

[0030] Step S2: Add the mixture obtained in step S1 to a sand mill for grinding until the particle size distribution of the material meets the requirement of D50<0.1μm and then discharge the material.

[0031] Step S3: Powder is obtained by spray drying using a spray dryer, wherein the inlet air temperature of the spray dryer is 165~175℃ and the outlet air temperature is 85~95℃.

[0032] Step S4: Place the powder in a nitrogen atmosphere sintering furnace and treat it at a temperature range of 480~510 ℃ for 3.8~4.1 h to obtain the sintered material;

[0033] In step S5, the calcined material, high-temperature pitch, graphite, and nickel powder (Ni) are added to a high-temperature coating reactor in the following proportions by mass: 58-62%, 24-26%, 13.95-15.95%, and 0.04-0.06%, respectively. Then, under nitrogen protection, the reactor is heated to 490-510°C and stirred at 190-210 rpm for 3.9-4.1 hours to complete the secondary coating process, and the material is then discharged.

[0034] Step S6: The product obtained in step S5 is transferred to a furnace with a mixed atmosphere of nitrogen and ammonia, and sintered at a temperature of 790~810℃ for 1.9~2.1h, wherein the volume content of ammonia is 4.5~5.5%.

[0035] Step S7: After sintering, the product is mechanically crushed to obtain silicon-carbon anode material.

[0036] In step S1 of this embodiment, the silicon powder used is high-purity silicon powder, preferably with a purity greater than 99.99%; the titanium nitride, with the chemical formula TiN, is used as an additive; the N-methylpyrrolidone, also known as NMP, is used as a dispersant; and the low-temperature asphalt is used as a carbon source to form a loose carbon layer. In step S5, the nickel powder is preferably micro-nano-sized Ni powder (i.e., micro-nano-sized nickel powder); unlike step S1, this step uses high-temperature asphalt and other materials for secondary coating. In step S6, the in-situ nitrogen-doped structure is formed on the external carbon layer by catalytic decomposition of a nitrogen-ammonia mixed atmosphere using Ni powder (i.e., nickel powder).

[0037] It should be noted that in this embodiment, silicon-carbon anode material for lithium-ion batteries is prepared through steps S1 to S7 working in synergy. First, in step S1, a reasonable mass percentage of titanium nitride (TiN) is introduced to form an expansion buffer layer between silicon powder and carbon nanotubes, uniformly releasing silicon expansion stress and effectively reducing its volume expansion rate. At the same time, a loose carbon layer is formed by low-temperature pitch carbonization with a suitable mass percentage to improve the lithium-ion diffusion rate. Based on this, after grinding in step S2, spray drying in step S3, and sintering in step S4, in step S5, a dense carbon layer is formed by secondary coating with high-temperature pitch. Together with step S1, it forms a carbon layer that is loose inside and tight outside. While ensuring the lithium-ion diffusion rate, it can also effectively reduce the direct contact between silicon and electrolyte, further improving the stability and cycle performance of silicon-carbon anode material.

[0038] In addition, in step S6 of this embodiment, an in-situ nitrogen-doped structure is formed on the outer carbon layer by decomposing a mixture of nitrogen and ammonia gas with nickel powder. The in-situ nitrogen-doped structure and the internal titanium nitride (TiN) can further improve the conductivity of the silicon-carbon anode material under synergistic effect.

[0039] Therefore, this embodiment can effectively solve the technical problems of existing silicon-carbon anode materials, such as volume expansion, insufficient conductivity, and uneven carbon layer coating, and significantly improve the overall performance of silicon-carbon anode materials.

[0040] It should also be noted that the different component ratios and preparation conditions / processes of each component have a non-linear effect on silicon-carbon anode materials. Therefore, how to select a more reasonable component ratio and its preparation conditions / processes is also one of the difficulties in this embodiment.

[0041] In this embodiment, the technical effects of various preferred solutions are tested and demonstrated through three different embodiments and four different comparative examples. Specifically, they are shown in Tables 1 and 2 below.

[0042] Table 1 Performance Test Data

[0043] Si TiN stearic acid NMP CNT Low-temperature asphalt Burning material High-temperature asphalt graphite Ni Example 1 65% 8% 3% 2% 0.2% 21.8% 60% 25% 14.95% 0.05% Example 2 65% 10% 3% 2% 0.2% 19.8% 60% 25% 14.95% 0.05% Example 3 65% 5% 3% 2% 0.2% 24.8% 60% 25% 14.95% 0.05% Comparative Example 1 65% 0 3% 2% 0.2% 29.8% 60% 25% 15% 0 Comparative Example 2 65% 8% 3% 0 0 24% 60% 25% 14.95% 0.05% Comparative Example 3 65% 8% 3% 2% 0.2% 21.8% 60% 39.95% 0 0.05% Comparative Example 4 65% 8% 3% 2% 0.2% 21.8% 60% 25% 15% 0 Comparative Example 5 83% 10% 4% 2.8% 0.2% 0 60% 25% 14.95% 0.05% Comparative Example 6 65% 8% 3% 2% 0.2% 21.8% 0 0 0 0

[0044] Table 2 Electrical Performance Data

[0045] 0.1C first-cycle capacity First effect 50-cycle retention rate 6060110 battery cell full charge thickness Example 1 1866.9mAh / g 89.9% 87.6% 6.07mm Example 2 1760.3mAh / g 85.3% 81.3% 6.11mm Example 3 1804.1mAh / g 87.1% 82.2% 6.19mm Comparative Example 1 1620.8mAh / g 81.5% 70.5% 7.13mm Comparative Example 2 1821.7mAh / g 85.4% 85.1% 6.15mm Comparative Example 3 1716.2mAh / g 82.2% 78.5% 6.48mm Comparative Example 4 1794.6mAh / g 86.7% 82.1% 6.28mm Comparative Example 5 1922.8 mAh / g 78.8% 64.2% 7.18mm Comparative Example 6 1931.7 mAh / g 76.9% 55.8% 7.21mm

[0046] From the test data in Tables 1 and 2, the following conclusions can be drawn.

[0047] First, the addition of a reasonable mass percentage of titanium nitride (TiN) has a significant effect on improving the material properties.

[0048] Examples 1 to 3 contain the same silicon powder (Si), stearic acid, N-methylpyrrolidone (NMP), and carbon nanotubes (CNT), but differ in the mass percentage of titanium nitride (TiN) and low-temperature asphalt.

[0049] In Example 1, with the addition of 8% titanium nitride (TiN), the initial capacity at 0.1C was 1866.9 mAh / g, the initial efficiency was 89.9%, the 50-cycle retention rate was 87.6%, and the cell thickness at full charge was 6.07 mm. The electrical performance curves for Example 1 are shown below. Figure 2 As shown, the scanning electron microscope (SEM) characterization image is as follows: Figure 4 As shown.

[0050] In Example 2, with the addition of 10% titanium nitride (TiN), the first-cycle capacity at 0.1C was 1760.3 mAh / g, the first-cycle efficiency was 85.3%, the 50-cycle retention rate was 81.3%, and the cell thickness at full charge was 6.11 mm.

[0051] In Example 3, with the addition of 5% titanium nitride (TiN), the first-cycle capacity at 0.1C was 1804.1 mAh / g, the first-cycle efficiency was 87.1%, the 50-cycle retention rate was 82.2%, and the cell thickness at full charge was 6.19 mm.

[0052] In Comparative Example 1, without the addition of titanium nitride (TiN), the initial capacity at 0.1C was 1620.8 mAh / g, the initial efficiency was 81.5%, the 50-cycle retention rate was 70.5%, and the cell thickness at full charge was 7.13 mm. The electrical performance curves for Comparative Example 1 are shown below. Figure 3 As shown.

[0053] Therefore, it can be seen that adding titanium nitride (TiN) can significantly improve the first-cycle efficiency and cycle retention of silicon-carbon anode materials, while reducing the full-charge thickness of the cell. This is because introducing a reasonable mass percentage of titanium nitride (TiN) can form an expansion buffer layer between silicon powder and carbon nanotubes, uniformly releasing silicon expansion stress and effectively reducing its volume expansion rate. Moreover, among Examples 1 to 3, Example 1 (with 8% TiN added) performed the best, exhibiting the highest first-cycle capacity and cycle retention.

[0054] Second, regarding the effects of adding N-methylpyrrolidone (NMP) and carbon nanotubes (CNTs) on the performance of silicon-carbon anode materials.

[0055] In Example 1, 2% N-methylpyrrolidone (NMP) and 0.2% carbon nanotubes (CNT) were added. The first-cycle capacity at 0.1C was 1866.9 mAh / g, the first-cycle efficiency was 89.9%, the 50-cycle retention rate was 87.6%, and the cell thickness at full charge was 6.07 mm.

[0056] In Comparative Example 2, without the addition of N-methylpyrrolidone (NMP) and carbon nanotubes (CNT), the first-cycle capacity at 0.1C was 1821.7 mAh / g, the first-cycle efficiency was 85.4%, the 50-cycle retention rate was 85.1%, and the cell thickness at full charge was 6.15 mm.

[0057] Although both Example 1 and Comparative Example 2 contain 65% silicon powder (Si), 8% titanium nitride (TiN), 3% stearic acid, 19.8-24.8% low-temperature pitch, 60% sintered material, 25% high-temperature pitch, 14.95% graphite, and 0.05% nickel powder (Ni), Example 1 performs better than Comparative Example 2.

[0058] It is evident that adding appropriate mass percentages of N-methylpyrrolidone (NMP) and carbon nanotubes (CNTs) can improve the first-cycle efficiency and cycle retention of silicon-carbon anode materials, while reducing the full-charge thickness of the cell.

[0059] Third, regarding the impact of adding high-temperature asphalt and graphite on performance.

[0060] In Example 1, 25% high-temperature asphalt and 14.95% graphite were added. The first-cycle capacity at 0.1C was 1866.9 mAh / g, the first-cycle efficiency was 89.9%, the 50-cycle retention rate was 87.6%, and the cell thickness at full charge was 6.07 mm.

[0061] In Comparative Example 3, no graphite was added, but the proportion of high-temperature asphalt was increased, raising the mass percentage of high-temperature asphalt to 39.95%. The first-cycle capacity at 0.1C was 1716.2 mAh / g, the first-cycle efficiency was 82.2%, the 50-cycle retention rate was 78.5%, and the cell thickness at full charge was 6.48 mm.

[0062] In Comparative Example 4, no nickel powder (Ni) was added, but 25% high-temperature asphalt and 15% graphite were added. The first-cycle capacity at 0.1C was 1794.6 mAh / g, the first-cycle efficiency was 86.7%, the 50-cycle retention rate was 82.1%, and the cell thickness at full charge was 6.28 mm. The performance was not as good as Example 1, but better than Comparative Example 3.

[0063] Therefore, adding graphite can significantly improve the initial efficiency and cycle retention of silicon-carbon anode materials, while reducing the full-charge thickness of the cell. Furthermore, an inappropriate proportion of high-temperature asphalt can also significantly impact performance, as shown in Comparative Example 3.

[0064] Fourth, regarding the effect of adding nickel powder (Ni) on performance.

[0065] Example 1: With the addition of 0.05% nickel powder (Ni), the first-cycle capacity at 0.1C is 1866.9 mAh / g, the first-cycle efficiency is 89.9%, the 50-cycle retention rate is 87.6%, and the cell thickness at full charge is 6.07 mm.

[0066] Comparative Example 1, without added nickel powder (Ni), has a first-cycle capacity of 1620.8 mAh / g at 0.1C, an initial efficiency of 81.5%, a 50-cycle retention rate of 70.5%, and a full-charge cell thickness of 7.13 mm.

[0067] Comparative Example 4 differs slightly from Example 1 in graphite content, with the most significant difference being the absence of nickel powder (Ni). Its initial capacity at 0.1C is 1794.6 mAh / g, initial efficiency is 86.7%, 50-cycle retention is 82.1%, and the cell thickness at full charge is 6.28 mm. Its performance is superior to Comparative Example 1 but inferior to Example 1.

[0068] It is evident that adding nickel powder (Ni) can significantly improve the first-cycle efficiency and cycle retention of silicon-carbon anode materials, while reducing the full-charge thickness of the cell. This is because the nickel powder (Ni) catalyzes the decomposition of nitrogen and ammonia in a mixed atmosphere to form an in-situ nitrogen-doped structure on the outer carbon layer. This in-situ nitrogen-doped structure, in synergy with the internal titanium nitride (TiN), can further enhance the conductivity of silicon-carbon anode materials.

[0069] Fifth, regarding the impact of stepwise coating of low-temperature asphalt and high-temperature asphalt.

[0070] Example 1: With the addition of 21.8% low-temperature asphalt and 25% high-temperature asphalt, the first-cycle capacity at 0.1C is 1866.9 mAh / g, the first-cycle efficiency is 89.9%, the 50-cycle retention rate is 87.6%, and the cell thickness at full charge is 6.07 mm.

[0071] Comparative Example 5, compared to Example 1, did not add low-temperature asphalt but added 25% high-temperature asphalt. Its first-cycle capacity at 0.1C was 1922.8 mAh / g, its first-cycle efficiency was 78.8%, its 50-cycle retention rate was 64.2%, and its fully charged cell thickness was 7.18 mm. The stability and cycle performance of Comparative Example 5 were significantly lower than those of Example 1, and the fully charged cell thickness was increased.

[0072] Comparative Example 6, compared to Example 1, added 21.8% low-temperature asphalt but did not add high-temperature asphalt, graphite, or nickel powder. Its initial capacity at 0.1C was 1931.7 mAh / g, with an initial efficiency of 76.9%, a 50-cycle retention rate of 55.8%, and a fully charged cell thickness of 7.21 mm. Similarly, the stability and cycle performance of Comparative Example 6 were significantly lower than those of Example 1, and the fully charged cell thickness was further increased.

[0073] It is evident that stepwise coating with low-temperature and high-temperature asphalt can jointly form a carbon layer that is loose inside and tight outside. While ensuring the lithium-ion diffusion rate, it can also effectively reduce the direct contact between silicon and electrolyte, further improving the stability and cycle performance of silicon-carbon anode materials.

[0074] In summary, steps S1 to S7 of this embodiment constitute a complete and synergistic preparation method, including: introducing a reasonable mass percentage of titanium nitride (TiN) to form an expansion buffer layer between silicon powder and carbon nanotubes, uniformly releasing silicon expansion stress and effectively reducing its volume expansion rate; forming a loose carbon layer by low-temperature asphalt carbonization with a suitable mass percentage to improve the lithium-ion diffusion rate; forming a dense carbon layer by secondary coating with high-temperature asphalt, which together with the low-temperature asphalt forms a carbon layer that is loose inside and tight outside, ensuring the lithium-ion diffusion rate while effectively reducing direct contact between silicon and electrolyte, further improving the stability and cycle performance of silicon-carbon anode material; and forming an in-situ nitrogen-doped structure in the outer carbon layer by decomposing a mixed atmosphere of nitrogen and ammonia gas catalyzed by nickel powder (Ni), which, under the synergistic effect of the internal titanium nitride (TiN), can further improve the conductivity of silicon-carbon anode material.

[0075] Therefore, in order to achieve better electrical performance while solving the technical problems to be solved in this application, the preferred technical solution adopted in this embodiment is as follows.

[0076] Preferably, in step S1 of this embodiment, the particle size distribution of the silicon powder satisfies D50≤3μm, and the particle size distribution of the titanium nitride satisfies D50≤0.1μm; in step S5, the particle size distribution of the nickel powder satisfies D50≤0.5μm, thereby better achieving the uniformity of the mixture and the reliability of the secondary coating.

[0077] In step S1 of this embodiment, the low-temperature asphalt refers to asphalt with a softening point below 150°C; in step S5, the high-temperature asphalt refers to asphalt with a softening point above 270°C. Thus, through the combination of low-temperature asphalt and high-temperature asphalt, a stable and reliable carbon layer with a loose inner layer and a tight outer layer is formed.

[0078] In step S1 of this embodiment, the mass percentages of silicon powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt are 65%, 8%, 3%, 2%, 0.2%, and 21.8%, respectively. This fixed optimized ratio can well guarantee the various high-performance requirements of silicon-carbon anode materials, including 0.1C first-cycle capacity, first-cycle efficiency, 50-cycle retention rate, and cell thickness when fully charged.

[0079] In step S1 of this embodiment, the total mass of silicon powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature pitch accounts for 15% of the mass of anhydrous ethanol; in step S2, the material is discharged when the particle size distribution meets D50<0.09μm, so as to achieve better dispersion and provide a basis for subsequent spray drying.

[0080] In step S3 of this embodiment, the inlet air temperature of the spray dryer is 170°C and the outlet air temperature is 90°C; in step S4, the sintering temperature of the nitrogen atmosphere sintering furnace is 500°C and the sintering time is 4 hours, so as to more reasonably control the spray drying temperature and sintering process, and provide a basis for subsequent steps.

[0081] In step S5 of this embodiment, the mass percentages of the sintered material, high-temperature pitch, graphite, and nickel powder are 60%, 25%, 14.95%, and 0.05%, respectively. During the secondary coating process, the reactor is heated to 500°C and stirred at 200 rpm for 4 hours. This fixed optimized ratio and preparation process / technique can further ensure the various high-performance requirements of the silicon-carbon anode material.

[0082] A scanning electron microscope (SEM) image is an image obtained using a scanning electron microscope (SEM). SEM is a high-resolution microscope that can provide information about the morphology and structure of a sample surface. Figure 4 The image shown is a scanning electron microscope (SEM) characterization image of Example 1, illustrating the surface morphology of the silicon-carbon anode material prepared in Example 1. Figure 4 The image shows the particle distribution, particle size, and possible surface features of the material. For example, this figure shows silicon particles encapsulated by a carbon layer, which helps in understanding the material's stability and cycling performance. Furthermore, uniform particle distribution and appropriate particle size are crucial for improving the material's electrochemical performance. Therefore, Figure 4 The characterization information shown can help to understand the relationship between the microstructure and performance of the silicon-carbon anode material in this embodiment.

[0083] Figure 4In the image specifications, Dwt ETD-SE indicates the SEM model / configuration used; ETD stands for Everhart-Thornley detector; SE indicates Secondary Electron mode, used to acquire surface topography information. MAG x500 indicates the image magnification is 500x. HV 15kV indicates the accelerating electron beam voltage is 15 kilovolts (kV), sufficient to generate sufficient electron beam energy to penetrate the sample and generate a signal. Gear 30um indicates the working distance, i.e., the distance from the electron gun to the sample surface is 30 micrometers (um). WD 10.36mm indicates the actual working distance is 10.36 millimeters (mm). Res 1536x1024 indicates the image resolution is 1536 pixels wide by 1024 pixels high. SEM5000 indicates the SEM equipment model used. Scale bar = 20μm indicates the scale bar in the image, which is a 20-micrometer (μm) long scale bar displayed in the image to help observers understand the actual size of the structures in the image.

[0084] In step S6 of this embodiment, the volume percentages of nitrogen and ammonia in the mixed atmosphere furnace are 95% and 5%, respectively, i.e., the ammonia content is 5%, and sintering is carried out at a temperature of 800°C for 2 hours; in step S7, the structure of the silicon-carbon anode material is Si@TiN@C@NC, and the silicon content in the finished silicon-carbon anode material is 40~60%.

[0085] This embodiment also provides a silicon-carbon anode material, the preparation process of which adopts the preparation method of silicon-carbon anode material for lithium-ion batteries as described above.

[0086] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material for lithium-ion batteries, characterized in that, Includes the following steps: Step S1: Add silica powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt to anhydrous ethanol and stir to disperse until the mixture is homogeneous; wherein the total mass of silica powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt accounts for 10-20% of the mass of anhydrous ethanol; the mass percentages of silica powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt are 62-67%, 6-9%, 2-4%, 1-3%, 0.1-0.3%, and 19.8-24.8%, respectively. Step S2: Add the mixture obtained in step S1 to a sand mill for grinding until the particle size distribution of the material meets the requirement of D50<0.1μm and then discharge the material. Step S3: Powder is obtained by spray drying using a spray dryer, wherein the inlet air temperature of the spray dryer is 165~175℃ and the outlet air temperature is 85~95℃. Step S4: Place the powder in a nitrogen atmosphere sintering furnace and treat it at a temperature range of 480~510 ℃ for 3.8~4.1 h to obtain the sintered material; In step S5, the calcined material, high-temperature pitch, graphite, and nickel powder are added to the high-temperature coating reactor in the following proportions by mass: 58-62%, 24-26%, 13.95-15.95%, and 0.04-0.06%, respectively. Then, under nitrogen protection, the reactor is heated to 490-510°C and stirred at 190-210 rpm for 3.9-4.1 hours to complete the secondary coating process, and the material is then discharged. Step S6: The product obtained in step S5 is transferred to a furnace with a mixed atmosphere of nitrogen and ammonia, and sintered at a temperature of 790~810℃ for 1.9~2.1h, wherein the volume content of ammonia is 4.5~5.5%. Step S7: After sintering, the product is mechanically crushed to obtain silicon-carbon anode material.

2. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, In step S1, the purity of the silicon powder is greater than 99.99%.

3. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, In step S1, the particle size distribution of the silicon powder satisfies D50≤3μm, and the particle size distribution of the titanium nitride satisfies D50≤0.1μm; in step S5, the particle size distribution of the nickel powder satisfies D50≤0.5μm.

4. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, In step S1, the low-temperature asphalt refers to asphalt with a softening point below 150°C; in step S5, the high-temperature asphalt refers to asphalt with a softening point above 270°C.

5. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that, In step S1, the mass percentages of silicon powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature asphalt are 65%, 8%, 3%, 2%, 0.2%, and 21.8%, respectively.

6. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to any one of claims 1 to 5, characterized in that, In step S1, the total mass of silicon powder, titanium nitride, stearic acid, N-methylpyrrolidone, carbon nanotubes, and low-temperature pitch accounts for 15% of the mass of anhydrous ethanol; in step S2, the material is discharged when the particle size distribution meets the requirement of D50 < 0.09 μm.

7. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to any one of claims 1 to 5, characterized in that, In step S3, the inlet air temperature of the spray dryer is 170°C and the outlet air temperature is 90°C; in step S4, the sintering temperature of the nitrogen atmosphere sintering furnace is 500°C and the sintering time is 4 hours.

8. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to any one of claims 1 to 5, characterized in that, In step S5, the mass percentages of the sintered material, high-temperature asphalt, graphite, and nickel powder are 60%, 25%, 14.95%, and 0.05%, respectively; during the secondary coating process, the reactor is heated to 500°C and stirred at 200 rpm for 4 hours.

9. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to any one of claims 1 to 5, characterized in that, In step S6, the volume percentages of nitrogen and ammonia in the mixed atmosphere furnace are 95% and 5%, respectively, and sintering is carried out at a temperature of 800°C for 2 hours; in step S7, the structure of the silicon-carbon anode material obtained is Si@TiN@C@NC.

10. A silicon-carbon anode material, characterized in that, The preparation process of the silicon-carbon anode material adopts the preparation method of lithium-ion battery silicon-carbon anode material as described in any one of claims 1 to 9.

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