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

Abstract

The application provides a preparation method of a silicon-carbon negative electrode material of a lithium ion battery and the silicon-carbon negative electrode material, and comprises the following steps: S1, silicon powder, titanium nitride, stearic acid, N-methyl pyrrolidone, carbon nanotubes and low-temperature pitch are added into anhydrous ethanol for stirring and dispersing; S2, the obtained mixture is added into a sand mill for grinding and discharging; S3, spray drying is performed to obtain a powder; S4, the powder is placed in a nitrogen atmosphere sintering furnace to obtain a sintered material; S5, the sintered material, high-temperature pitch, graphite and nickel powder are added into a high-temperature coating reaction kettle, then a secondary coating process is completed under the protection of nitrogen, and the material is discharged; S6, the material is transferred into a nitrogen and ammonia mixed atmosphere furnace for sintering; and S7, the material is broken to obtain the silicon-carbon negative electrode material. The application can effectively solve the technical problems of volume expansion, insufficient conductivity and uneven carbon layer coating of the existing silicon-carbon negative electrode material, and significantly improve the comprehensive performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a battery material, in particular to a preparation method of a silicon-carbon negative electrode material of a lithium ion battery, and further relates to a silicon-carbon negative electrode material adopting the preparation method of the silicon-carbon negative electrode material of the lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have been widely commercialized due to their high energy density and long cycle life, but the current graphite negative electrode capacity has been developed to the theoretical limit, which limits the further improvement of the battery energy density. The theoretical capacity of silicon negative electrode material can reach 4200 mAh / g, which is the preferred solution for the next generation of high-capacity negative electrode. However, the silicon negative electrode material has the following problems: the conductivity of the silicon negative electrode is insufficient and the volume expansion during lithiation is serious, which may cause the material to be easily broken and failed. In view of the above problems, the main optimization means at present is nanocrystallization and carbon coating, and then the silicon-carbon negative electrode material is obtained, so as to prolong the actual service life. Among them, the sand mill spray method is simple in process, low in cost and high in production capacity, and is suitable for large-scale production of silicon-carbon negative electrode material. However, the expansion rate of the silicon-carbon negative electrode material prepared by the sand mill spray process is still high, which leads to poor cycle performance, and the thickness of the carbon layer is not uniform, which also makes the conductivity of the silicon-carbon negative electrode material worse. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a preparation method of a silicon-carbon negative electrode material of a lithium ion battery, which aims to solve the technical problems of volume expansion, insufficient conductivity and uneven carbon layer coating of the existing silicon-carbon negative electrode material, and further improve the comprehensive performance of the silicon-carbon negative electrode material. On this basis, a silicon-carbon negative electrode material adopting the preparation method of the silicon-carbon negative electrode material of the lithium ion battery is further provided.

[0004] To this end, the present application provides a preparation method of a silicon-carbon negative electrode material of a lithium ion battery, comprising the following steps:

[0005] Step S1, silicon powder, titanium nitride, stearic acid, N-methyl pyrrolidone, carbon nanotubes and low temperature pitch are added to anhydrous ethanol for stirring and dispersing until the mixture is uniform; wherein the total mass of the silicon powder, titanium nitride, stearic acid, N-methyl pyrrolidone, carbon nanotubes and low temperature pitch accounts for 10-20% of the mass of the anhydrous ethanol; the mass percentage between the silicon powder, titanium nitride, stearic acid, N-methyl pyrrolidone, carbon nanotubes and low temperature pitch is 62-67%, 6-9%, 2-4%, 1-3%, 0.1-0.3% and 19.8-24.8% respectively;

[0006] Step S2, the mixture obtained in step S1 is added to a sand mill for grinding until the particle size distribution of the material meets D50<0.1μm, and then the material is discharged;

[0007] Step S3, spray drying is carried out by using a spray dryer to obtain powder, wherein the inlet air temperature of the spray dryer is 165-175 DEG C, and the outlet air temperature is 85-95 DEG C;

[0008] Step S4, the powder is placed in a nitrogen atmosphere sintering furnace and treated at a temperature of 480-510 DEG C for 3.8-4.1 h to obtain a sintered material;

[0009] Step S5, the sintered material, high-temperature pitch, graphite and nickel powder are added into a high-temperature coating reaction kettle in proportions of 58-62%, 24-26%, 13.95-15.95% and 0.04-0.06% respectively, then the reaction kettle is heated to 490 DEG C-510 DEG C under nitrogen protection, and stirred at a speed of 190-210 rpm for 3.9-4.1 h to complete the secondary coating process, and the material is discharged;

[0010] Step S6, the product obtained in step S5 is transferred into a nitrogen and ammonia mixed atmosphere furnace, sintered at a temperature of 790-810 DEG C, and the sintering time is 1.9-2.1 h, wherein the volume content of ammonia is 4.5-5.5%;

[0011] Step S7, after sintering, the product is mechanically crushed to obtain a silicon-carbon negative electrode material.

[0012] Further improvement of the application is that in step S1, the purity of the silicon powder is greater than 99.99%.

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

[0014] Further improvement of the application is that in step S1, the low-temperature pitch refers to pitch with a softening point lower than 150 DEG C; in step S5, the high-temperature pitch refers to pitch with a softening point higher than 270 DEG C.

[0015] Further improvement of the application is that in step S1, the mass percentages of the silicon powder, titanium nitride, stearic acid, N-methyl pyrrolidone, carbon nanotube and low-temperature pitch are 65%, 8%, 3%, 2%, 0.2% and 21.8% respectively.

[0016] The further improvement of the present application is that in the step S1, the total mass of the silicon powder, titanium nitride, stearic acid, N-methyl pyrrolidone, carbon nanotube and low temperature pitch accounts for 15% of the mass of the anhydrous ethanol; in the step S2, the grinding is performed until the particle size distribution of the material meets D50 < 0.09 μm.

[0017] The further improvement of the present application is that in the step S3, the inlet air temperature of the spray dryer is 170℃, and the outlet air temperature is 90℃; in the step S4, the sintering temperature of the nitrogen atmosphere sintering furnace is 500℃, and the sintering time is 4h.

[0018] The further improvement of the present application is that in the step S5, the mass percentage of the burned material, high temperature pitch, graphite and nickel powder is 60%, 25%, 14.95% and 0.05% respectively; in the secondary coating process, the reaction kettle is heated to 500℃, and the stirring speed is 200 rpm for 4h.

[0019] The further improvement of the present application is that in the step S6, the volume percentage of the nitrogen and ammonia in the mixed atmosphere furnace is 95% and 5% respectively, and the sintering is performed at a temperature of 800℃ for 2h; in the step S7, the structure of the obtained silicon-carbon negative electrode material is Si@TiN@C@NC.

[0020] The present application also provides a silicon-carbon negative electrode material, and the preparation process of the silicon-carbon negative electrode material adopts the preparation method of the lithium ion battery silicon-carbon negative electrode material.

[0021] Compared with the prior art, the present application has the beneficial effects that: the silicon-carbon negative electrode material of the lithium ion battery is prepared through the steps S1 to S7 working in cooperation, first, in the step S1, the titanium nitride with reasonable mass percentage is introduced to form an expansion buffer layer between the silicon powder and the carbon nanotube, uniformly release the silicon expansion stress and reduce the volume expansion rate; at the same time, the loose carbon layer is formed through the carbonization of the low temperature pitch with appropriate mass percentage to improve the lithium ion diffusion rate; on this basis, after the grinding of the step S2, the spray drying of the step S3 and the sintering of the step S4, in the step S5, the carbon layer formed by the secondary coating of the high temperature pitch is dense, and together with the step S1, forms the carbon layer with loose inside and tight outside, which can not only ensure the lithium ion diffusion rate, but also effectively reduce the direct contact of the silicon and the electrolyte, further improve the stability and cycle performance of the material; in addition, in the step S6, the nickel powder catalyzes the decomposition of the mixed atmosphere of nitrogen and ammonia to form the in-situ nitrogen doped structure in the external carbon layer, which further improves the conductivity of the silicon-carbon negative electrode material in cooperation with the titanium nitride inside. Therefore, the present application can effectively solve the technical problems of the existing silicon-carbon negative electrode material, such as volume expansion, insufficient conductivity and uneven carbon layer coating, and significantly improve the comprehensive performance of the silicon-carbon negative electrode material. 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, spray drying is performed by 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, the powder is placed in a nitrogen atmosphere sintering furnace and treated at a temperature of 480-510℃ for 3.8-4.1h to obtain a sintered material;

[0033] Step S5, the sintered material, high-temperature pitch, graphite and nickel powder (Ni) are added into a high-temperature coating reaction kettle in a mass percentage of 58-62%, 24-26%, 13.95-15.95% and 0.04-0.06% respectively, then the reaction kettle is heated to 490-510℃ under nitrogen protection, and stirred at a speed of 190-210 rpm for 3.9-4.1h to complete the secondary coating process, and the product is discharged;

[0034] Step S6, the product obtained in step S5 is transferred into a nitrogen and ammonia mixed atmosphere furnace, 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 a silicon-carbon negative electrode material.

[0036] In step S1 of the embodiment, the silicon powder used is high-purity silicon powder, and the purity of the silicon powder is preferably greater than 99.99%; the chemical formula of titanium nitride is TiN, which is used as an additive; N-methyl pyrrolidone, also known as NMP, is used as a dispersing agent; low-temperature pitch is used as a carbon source to form a loose carbon layer. In step S5, the nickel powder is preferably a trace of nano-level Ni powder (i.e. trace of nano-level nickel powder); unlike step S1, this step uses high-temperature pitch and other materials for secondary coating. In step S6, the Ni powder (i.e. nickel powder) catalyzes the decomposition of the nitrogen and ammonia mixed atmosphere to form an in-situ nitrogen-doped structure in the external carbon layer.

[0037] It should be noted that the silicon-carbon negative electrode material of the lithium ion battery is prepared by the steps S1 to S7 of the embodiment. First, in step S1, a reasonable mass percentage of titanium nitride (TiN) is introduced to form an expansion buffer layer between the silicon powder and the carbon nanotube, uniformly release the silicon expansion stress, and effectively reduce the volume expansion rate. At the same time, a loose carbon layer is formed by carbonization of a suitable mass percentage of low-temperature pitch to improve the lithium ion diffusion rate. On this basis, after grinding in step S2, spray drying in step S3, and sintering in step S4, in step S5, a carbon layer is formed by secondary coating of high-temperature pitch, which is dense and forms an inner loose and outer tight carbon layer with step S1, which can effectively reduce the direct contact of silicon and electrolyte while ensuring the lithium ion diffusion rate, and further improve the stability and cycle performance of the silicon-carbon negative electrode material.

[0038] In addition, in step S6, the embodiment also forms an in-situ nitrogen-doped structure by decomposing a mixed atmosphere of nitrogen and ammonia gas with nickel powder catalysis in the outer carbon layer. The in-situ nitrogen-doped structure and the titanium nitride (TiN) inside can further improve the conductivity of the silicon-carbon negative electrode material in a synergistic manner.

[0039] Therefore, the embodiment can effectively solve the technical problems of volume expansion, insufficient conductivity, and uneven carbon layer coating of existing silicon-carbon negative electrode materials, and significantly improve the comprehensive performance of the silicon-carbon negative electrode material.

[0040] Similarly, it should be noted that the different component ratios and preparation conditions / processes of each component do not belong to linear changes, therefore, how to select more reasonable component ratios and preparation conditions / processes is also one of the difficulties of the embodiment.

[0041] In the embodiment, three different examples and four different comparative examples are used to test and prove the technical effects of the preferred schemes of the embodiment. Specifically, as shown in Table 1 and Table 2 below.

[0042] Table 1 Performance test data table

[0043] Si TiN Stearic acid NMP CNT Low temperature pitch Burnt material High temperature pitch 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 table

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

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

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

[0048] The silicon powder (Si), stearic acid, N-methyl pyrrolidone (NMP) and carbon nanotubes (CNT) in Example 1 to Example 3 are consistent, and the difference lies in the mass percentage of titanium nitride (TiN) and low-temperature pitch.

[0049] In Example 1, 8% titanium nitride (TiN) is added, the 0.1C first circle capacity is 1866.9 mAh / g, the first efficiency is 89.9%, the 50 cycle retention rate is 87.6%, and the full charge thickness of the battery cell is 6.07 mm. The electrical performance curve of Example 1 is shown in Figure 2 , and the scanning electron microscope (SEM) characterization diagram is shown in Figure 4 .

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

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

[0052] In Comparative Example 1, no titanium nitride (TiN) is added, the 0.1C first circle capacity is 1620.8 mAh / g, the first efficiency is 81.5%, the 50 cycle retention rate is 70.5%, and the full charge thickness of the battery cell is 7.13 mm. The electrical performance curve of Comparative Example 1 is shown in Figure 3 .

[0053] Therefore, the addition of titanium nitride (TiN) can significantly improve the first efficiency and cycle retention rate of the silicon-carbon negative electrode material, and reduce the full charge thickness of the battery cell; the reason is that the introduction of a reasonable mass percentage of titanium nitride (TiN) can form an expansion buffer layer between the silicon powder and the carbon nanotubes, uniformly release the silicon expansion stress, and effectively reduce the volume expansion rate. Moreover, among Example 1 to Example 3, Example 1 (adding 8% TiN) performs best, with the highest first circle capacity and cycle retention rate.

[0054] Second, the effect of the addition of N-methyl pyrrolidone (NMP) and carbon nanotubes (CNT) on the performance of the silicon-carbon negative electrode material.

[0055] In Example 1, 2% N-methyl pyrrolidone (NMP) and 0.2% carbon nanotubes (CNT) are added, the 0.1C first circle capacity is 1866.9 mAh / g, the first efficiency is 89.9%, the 50 cycle retention rate is 87.6%, and the full charge thickness of the battery cell is 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, adding 0.05% of nickel powder (Ni), the 0.1C first circle capacity is 1866.9 mAh / g, the first efficiency is 89.9%, the 50 circle cycle retention rate is 87.6%, and the full charge thickness of the battery cell is 6.07 mm.

[0066] Comparative Example 1, without adding nickel powder (Ni), the 0.1C first circle capacity is 1620.8 mAh / g, the first efficiency is 81.5%, the 50 circle cycle retention rate is 70.5%, and the full charge thickness of the battery cell is 7.13 mm.

[0067] Comparative Example 4, compared with Example 1, there is a slight difference in the content of graphite, the biggest difference is that no nickel powder (Ni) is added, the 0.1C first circle capacity is 1794.6 mAh / g, the first efficiency is 86.7%, the 50 circle cycle retention rate is 82.1%, and the full charge thickness of the battery cell is 6.28 mm. The performance is better than that of Comparative Example 1, but lower than that of Example 1.

[0068] As can be seen, adding nickel powder (Ni) can significantly improve the first efficiency and cycle retention rate of the silicon-carbon negative electrode material, and at the same time reduce the full charge thickness of the battery cell, the reason is that the nickel powder (Ni) catalyzes the decomposition of the mixed nitrogen and ammonia atmosphere in the external carbon layer to form an in-situ nitrogen-doped structure, which, in cooperation with the internal titanium nitride (TiN), can further improve the conductivity of the silicon-carbon negative electrode material.

[0069] Fifth, the influence of step-by-step coating of low-temperature pitch and high-temperature pitch.

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

[0071] Comparative Example 5, compared with Example 1, no low-temperature pitch is added, and 25% of high-temperature pitch is added, the 0.1C first circle capacity is 1922.8 mAh / g, the first efficiency is 78.8%, the 50 circle cycle retention rate is 64.2%, and the full charge thickness of the battery cell is 7.18 mm. The stability and cycle performance of this Comparative Example 5 are significantly lower than those of Example 1, and the full charge thickness of the battery cell increases.

[0072] Comparative Example 6, compared with Example 1, 21.8% of low-temperature pitch is added, and no high-temperature pitch, graphite, or nickel powder is added, the 0.1C first circle capacity is 1931.7 mAh / g, the first efficiency is 76.9%, the 50 circle cycle retention rate is 55.8%, and the full charge thickness of the battery cell is 7.21 mm. Similarly, the stability and cycle performance of this Comparative Example 6 are also significantly lower than those of Example 1, and the full charge thickness of the battery cell further increases.

[0073] Therefore, by the step-by-step coating of low-temperature pitch and high-temperature pitch, the inner loose and outer tight carbon layer can be formed, the lithium ion diffusion rate can be ensured, the direct contact between silicon and electrolyte can be effectively reduced, and the stability and cycle performance of the silicon-carbon negative electrode material can be further improved.

[0074] In summary, the steps S1 to S7 constitute a complete and synergistic preparation method, which includes: forming an expansion buffer layer between the silicon powder and the carbon nanotube by introducing a reasonable mass percentage of titanium nitride (TiN), uniformly releasing the silicon expansion stress, and effectively reducing the volume expansion rate; forming a loose carbon layer by carbonizing a suitable mass percentage of low-temperature pitch to improve the lithium ion diffusion rate; forming a dense carbon layer by the secondary coating of high-temperature pitch, and forming an inner loose and outer tight carbon layer together with the low-temperature pitch, which can ensure the lithium ion diffusion rate, effectively reduce the direct contact between silicon and electrolyte, and further improve the stability and cycle performance of the silicon-carbon negative electrode material; and forming an in-situ nitrogen-doped structure by decomposing the mixed nitrogen and ammonia atmosphere outside the carbon layer catalyzed by the nickel powder (Ni), which can further improve the conductivity of the silicon-carbon negative electrode material in cooperation with the titanium nitride (TiN) inside.

[0075] Therefore, in order to achieve better electrical performance on the basis of solving the technical problems addressed in this application, the preferred technical solutions adopted in this embodiment are as follows.

[0076] Preferably, in the 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 the step S5, the particle size distribution of the nickel powder satisfies D50≤0.5μm, thereby better realizing the uniformity of the mixture and the reliability of the secondary coating.

[0077] In the step S1, the low-temperature pitch refers to pitch with a softening point lower than 150℃; in the step S5, the high-temperature pitch refers to pitch with a softening point higher than 270℃, thereby forming a stable and reliable inner loose and outer tight carbon layer by the cooperation of low-temperature pitch and high-temperature pitch.

[0078] In the step S1, the mass percentages of the silicon powder, titanium nitride, stearic acid, N-methyl pyrrolidone, carbon nanotube, and low-temperature pitch are 65%, 8%, 3%, 2%, 0.2%, and 21.8%, respectively. With the fixed optimal ratio, various high-performance requirements of the silicon-carbon negative electrode material can be well guaranteed, including 0.1C first circle capacity, first efficiency, 50 cycle retention rate, and full charge thickness of the battery cell, etc.

[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 above, Dwt ETD-SE indicates the SEM model / configuration used; ETD indicates Everhart-Thornley detector; SE indicates Secondary Electron mode, which is used to acquire surface topography information. MAG x500 indicates the magnification of the image is 500x. HV 15kV indicates the high voltage of the accelerating electron beam is 15 kilovolts (kV), which is used to generate sufficient electron beam energy to penetrate the sample and generate signals. Gear 30um indicates the working distance (WD), 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 resolution of the image is 1536 pixels wide by 1024 pixels high. SEM5000 indicates the SEM device model used. Scale bar = 20um indicates the scale in the image, i.e. a ruler of 20 micrometers (um) length shown in the image, which is used to help the observer understand the actual size of the structure in the image.

[0084] In step S6, the volume percentage of nitrogen and ammonia in the mixed atmosphere furnace is 95% and 5% respectively, i.e. the ammonia content is 5%, and sintering is carried out at a temperature of 800°C, and the sintering time is 2h; in step S7, the structure of the silicon-carbon negative electrode material obtained is Si@TiN@C@NC, at this time, the silicon content in the finished product of the silicon-carbon negative electrode material is 40-60%.

[0085] The embodiment also provides a silicon-carbon negative electrode material, and the preparation process of the silicon-carbon negative electrode material adopts the preparation method of the lithium ion battery silicon-carbon negative electrode material as described above.

[0086] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be considered as falling within the protection scope of the present application.

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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