A method for preparing nano silicon by graded steps

Abstract

The invention discloses a hierarchical preparation method of nano silicon, the preparation method comprising preparing a mixed slurry with a solvent, silicon powder, a dispersant and a wetting agent, then subjecting the mixed slurry to primary grinding, adding graphene oxide nanosheets and then continuing secondary grinding to obtain nano silicon; in terms of mass, the silicon powder accounts for 18%-30% of the total mass of the mixed slurry. The preparation method of nano silicon of the invention avoids the process of using pickling, and through the coordination between various substances, ensures the stability of silicon powder in the preparation process of nano silicon, in addition, in the secondary grinding, graphene oxide nanosheets are added and coated on the surface of silicon powder, which is not only conducive to overcoming the primary grinding limit, but also can reduce the specific surface area of ​​silicon powder, thereby obtaining silicon powder particles with small particle size; in addition, it can also prevent silicon from being directly exposed to the electrolyte, which helps to form a stable SEI film, and greatly improves the cycle performance of the negative electrode material.

Description

Technical Field

[0001] The invention relates to the technical field of negative electrode materials, and in particular to a method for preparing nano silicon, a negative electrode material for lithium ion batteries. Background Art

[0002] Nano silicon powder is a new generation of optoelectronic semiconductor material. It is also a high-power light source material because of its wide gap energy semiconductor. It can also replace nano carbon powder or graphite as a negative electrode material for lithium batteries. Due to the high absorption rate of nano silicon to lithium batteries, the use of nano silicon in lithium batteries can greatly increase the capacity of lithium batteries (theoretically up to 4000mA / h).

[0003] At present, the common methods for preparing nano silicon powder include mechanical grinding, plasma evaporation condensation and chemical vapor deposition. Although mechanical grinding can reduce costs and prepare nano silicon efficiently, a large amount of acid is required for cleaning during the preparation process, which is not conducive to equipment maintenance and also causes environmental pollution. In addition, during the preparation process, due to the increase in the specific surface area of ​​silicon, agglomeration is prone to occur, so a large amount of dispersant is added for dispersion. However, a large amount of dispersant will not only increase the cost, but also reduce the performance of nano silicon powder materials. In addition, the nano-based silicon powder finally obtained is easy to be oxidized and corroded due to its high surface reactivity, and is extremely unstable. Summary of the invention

[0004] In view of the problems in the prior art, the present invention discloses a method for preparing nano silicon by grading, which simplifies the process flow and the dosage of the dispersant, thereby obtaining nano silicon with a fineness (D90) less than 200nm, a high concentration of particle size distribution and stability.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention provides a graded preparation method for nano silicon, which comprises preparing a mixed slurry with a solvent, silicon powder, a dispersant and a wetting agent, then subjecting the mixed slurry to primary grinding, adding graphene oxide nanosheets and then continuing secondary grinding to obtain nano silicon; in terms of mass, the silicon powder accounts for 18%-30% of the total mass of the mixed slurry.

[0007] The above-mentioned design of the present invention and the preparation process of the present invention adopt a two-stage grinding method. During the secondary grinding, graphene oxide nanosheets are added, which is not only beneficial to reducing the specific surface area of ​​silicon powder, but also beneficial to overcoming the grinding limit of the primary grinding. We also further limit the mass of silicon powder in the mixed slurry, and the silicon powder accounts for 18%-30% of the total mass of the mixed slurry. We found that the addition amount of silicon powder within this range is firstly more conducive to obtaining a smaller particle size and promoting stable dispersion of particles in the two-stage grinding, and secondly, it can cooperate with the graphene oxide nanosheets in the secondary grinding to interact more easily, breaking through the grinding limit of the primary grinding, and finally conducive to obtaining silicon powder with a small particle size and concentrated particle size dispersion. In addition, the present invention not only simplifies the process flow of nano-scale silicon particles, but also reduces the amount of dispersant used. By using the mutual cooperation between the dispersant, wetting agent and solvent, the dispersant and wetting agent are adsorbed on the surface of the silicon particles to form a mechanical barrier, so that the wetting speed of the solvent to the silicon powder matches the speed of increase of the silicon specific surface area during the grinding process, thereby reducing the agglomeration between the silicon powders. On this basis, the dispersant is added to reduce the interaction force between the silicon powders, which is beneficial to the secondary grinding dispersion and enhances the stability of the silicon during the grinding process.

[0008] As a further solution, the mass ratio of the solvent, silicon powder, dispersant, wetting agent and graphene oxide nanosheets is (70-80 parts): (20-30 parts): (0.1-0.5 parts): (0.1-0.5 parts): (3-10 parts). The appropriate ratio between the substances makes the obtained nano-silicon have a small particle size.

[0009] As a further solution, the particle size of the graphene oxide nanosheets is D97=50 nm.

[0010] As a further solution, the silicon powder is obtained by a pulse discharge method. The silicon powder obtained by this method has a smoother surface morphology, which is conducive to being coated in secondary grinding, thereby obtaining a smaller particle size.

[0011] As a further embodiment, the solvent includes one or more of isopropanol, ethanol, water, ethylene glycol, triethanolamine, and polymeric alcohol amine.

[0012] As a further embodiment, the dispersant includes one or more of sodium deoxycholate, ammonium citrate, sodium silicate, polymethyl methacrylate ammonium, polyethylene glycol 20000 (PEG20000), dodecylbenzenesulfonic acid, sodium fatty acid methyl ester sulfonate, polymethacrylic acid, polyacrylic acid, polyvinyl alcohol, BYK dispersant (BYK-ET 3002), BYK dispersant (BYK-ET 3001) and ethylene bisstearamide.

[0013] As a further embodiment, the wetting agent includes one or more of silicone wetting agent LS-7, OP-10, sodium dodecyl sulfate, SOPA-270 (wetting dispersant-270), T-1004, Igebal BC / 10, wetting agent HY-6086, alkylphenol polyoxyethylene ether, succinate sulfonate, sodium dodecylbenzene sulfonate, and wetting agent WA (WA-8401).

[0014] As a further solution, the step of preparing the mixed slurry includes stirring the solvent, silicon powder, dispersant and wetting agent, the stirring time is 60min-90min, and the stirring speed is 2000r / min-3000r / min.

[0015] As a further solution, the primary grinding step includes adding a primary grinding medium, setting the material pressure to 0.4 bar-0.8 bar, the cooling water temperature is lower than 10 ° C, the cooling water flow rate is 100 kg / h-200 kg / h, the rotor speed is 1000 r / min-1500 r / min, and the size of the primary grinding medium includes One or more of the following; the secondary grinding step includes adding secondary grinding media, setting the material pressure to 0.4 bar-0.8 bar, the cooling water temperature to be lower than 10 ° C, the cold water flow rate to be 100 kg / h-200 kg / h, the rotor speed to be 1000 r / min-1500 r / min, and the size of the secondary grinding media to include One or more of the above. Cooling water helps to reduce the temperature rise caused by the mechanical energy generated by grinding. Controlling the temperature and flow of cooling water with appropriate rotation speed and material pressure can control the heat generated during grinding and prevent the silicon surface from being heated and oxidized. Selecting the size of the grinding medium that matches the particle size is conducive to the porosity between the silicon powder and the grinding medium within a certain range, thereby increasing the force of the grinding medium on the powder surface and reducing the particle size of the silicon powder.

[0016] As a further solution, the termination conditions of the primary grinding and the secondary grinding are that the particle size of the obtained silicon powder is detected for more than 2 times in a row, and the interval between each detection is more than 10 minutes, and the grinding is terminated when the average particle size of the silicon powder is within 5%. When grinding to a certain fineness, the grinding limit will appear. This may be because the void ratio between the grinding medium and the silicon powder particle size is too large at this time, resulting in the inability of mechanical force to act on the silicon powder surface. Therefore, the grinding medium continues to grind, but cannot reduce the particle size of the silicon powder. In fact, the silicon powder may be in an extremely unstable state because it absorbs this part of the mechanical energy, causing the silicon powder to agglomerate and increase the particle size. Therefore, the particle size of the silicon powder after the first-level grinding is between 0.3μm and 0.5μm. In the secondary grinding process, a grinding medium with a particle size similar to that after the first-level grinding is used, and with the cooperation of graphene oxide nanosheets, the graphene oxide nanosheets are coated on the surface of the silicon powder, which not only reduces the porosity between the grinding medium and the silicon powder, but also reduces the specific surface area of ​​the silicon powder, thereby overcoming the primary grinding limit and making the silicon powder smaller in particle size and more concentrated in particle size dispersion.

[0017] As a further solution, the method for preparing nano-silicon further includes drying the obtained nano-silicon.

[0018] As a further solution, the drying temperature is between 20° C. and 110° C., the drying time is between 4 h and 18 h, and the drying environment is an inert gas.

[0019] As a further solution, the mixed slurry includes isopropanol, silicon powder, polymethacrylic acid, and alkylphenol polyoxyethylene ether; by mass, the ratio of the isopropanol, silicon powder, polymethacrylic acid, alkylphenol polyoxyethylene ether and graphene oxide nanosheet is (70-75 parts): (20-30 parts): (0.2-0.3 parts): (0.2-0.3 parts): (5-6 parts). Polymethacrylic acid and alkylphenol polyoxyethylene ether can be well adsorbed on the silicon surface, so that the dispersibility of silicon is enhanced, and the use of organic reagent isopropanol can be well matched with alkylphenol polyoxyethylene ether, so that the surface tension of silicon is reduced, and the particle size dispersion degree finally obtained by nano-silicon is concentrated, and it is conducive to reducing the oxidation of silicon during the grinding process. In the secondary grinding process, adding a suitable amount of graphene oxide nanosheets to the optimized grinding system is conducive to matching with a dispersant, reducing the specific surface area of ​​silicon powder, and in the secondary grinding process, reducing the agglomeration of particles caused by mechanical properties or thermal energy, and improving the dispersibility between silicon powder particles.

[0020] The characteristics and beneficial effects of the present invention are:

[0021] (1) The method for preparing nano-silicon of the present invention avoids the use of an acid-washing process and ensures the stability of silicon powder during the preparation of nano-silicon through the coordination of various substances, so that the silicon element accounts for no less than 95% of the nano-silicon finally obtained; in addition, the particle size of the silicon powder is reduced, and nano-silicon with good dispersibility and stability is finally obtained.

[0022] (2) In the secondary grinding, graphene oxide nanosheets are added and coated on the surface of silicon powder, which not only helps to overcome the primary grinding limit, but also reduces the specific surface area of ​​silicon powder, thereby obtaining silicon powder particles with small particle size; in addition, it can also prevent silicon from being directly exposed to the electrolyte, which helps to form a stable SEI film and greatly improves the cycle performance of the negative electrode material.

[0023] (3) The production efficiency of nano-scale silicon particles is improved.

[0024] (4) It breaks the grinding limit of traditional mechanical methods and obtains silicon powder products with nano-silicon fineness (D90) less than 200nm, or even less than 50nm, while the particle dispersion concentration is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A molecular schematic diagram of the primary ground large-particle silicon powder provided in an embodiment of the present invention.

[0027] Figure 2 A molecular schematic diagram of the secondary ground small-particle silicon powder provided in an embodiment of the present invention.

[0028] Figure 3 This is a SEM photo of the nano-scale silicon powder of 300nm-500nm obtained after primary grinding provided in an embodiment of the present invention.

[0029] Figure 4 This is a SEM photo of nano-scale silicon powder of 50nm-100nm obtained after secondary grinding provided in an embodiment of the present invention.

[0030] Figure 5 This is a diagram of element contents of nano-scale silicon powder obtained after primary grinding provided in an embodiment of the present invention.

[0031] Figure 6This is an XPS photo of the nano-scale silicon powder obtained after primary grinding provided in an embodiment of the present invention.

[0032] Figure 7 A schematic diagram of a process for preparing nano-silicon provided in an embodiment of the present invention.

[0033] Figure 8 This is a particle size distribution diagram after secondary grinding provided in Example 1 of the present invention.

[0034] Fig. 9 This is a particle size distribution diagram after secondary grinding provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0035] In order to facilitate understanding of the hierarchical preparation method of nano-silicon of the present invention, the preparation method of the present invention will be described more comprehensively below, and embodiments of the present invention are given, but the scope of the present invention is not limited thereby.

[0036] The preparation method of nano silicon includes (such as Figure 7 shown):

[0037] S1: The mass ratio of the solvent, silicon powder, dispersant and wetting agent is (70-80 parts): (20-30 parts): (0.1-0.5 parts): (0.1-0.5 parts), respectively, and the solvent, silicon powder, dispersant and wetting agent are prepared into a mixed slurry. The mixture is stirred by a disperser to be evenly dispersed, the stirring time is 60min-90min, and the stirring speed is 2000r / min-3000r / min.

[0038] S2: Perform primary grinding, add primary grinding media, set the material pressure to 0.4bar-0.8bar, the cooling water temperature is lower than 10℃, the cooling water flow rate is 100kg / h-200kg / h, the rotor speed is 1000r / min-1500r / min, and the primary grinding is terminated when the average value of the particle size change of nano-silicon is within 5% after four consecutive tests. Figure 1 and Figure 3 The middle is the SEM photo of large-particle silicon powder in the slurry after primary grinding.

[0039] S3: Perform secondary grinding, add 3-10 parts of graphene oxide nanosheets and secondary grinding media, then set the material pressure to 0.4bar-0.8bar, the cooling water temperature to below 10°C, the cooling water flow rate to 100kg / h-200kg / h, the rotor speed to 1000r / min-1500r / min, and end the secondary grinding when the average value of the particle size change of the nano-silicon is within 5% after four consecutive tests. Figure 2 and Figure 4Middle is the SEM photo of small particle silicon powder in the slurry after secondary grinding.

[0040] The size of the primary grinding media is Secondary grinding media size One or more of .

[0041] S4: Drying: The drying temperature is 20°C-110°C, the drying time is 4h-18h, and the drying environment is inert gas.

[0042] The silicon powder includes one or more of Japan Shin-Etsu, Dow Corning, Admatechs, Tatsumori, Admatechs, Denka, Micro, Zhejiang Zhongcheng, Henan Xinguang, Chengdu Jinchun Metal, and Guangzhou Sino Biotechnology.

[0043] The bead mill for mixing the slurry includes one or more combinations of Wuxi Buhler, Chongqing Sanmo Haida, Jiangxi Haoxin. The bead mill separator includes one or more of a screen-type bead separator, a slit-type bead separator, and a centrifugal bead separator. The mechanical sealing fluid includes ethylene glycol and water.

[0044] The grinding media include one or more of zirconium oxide, corundum balls (alumina balls), quartz sand, carbon steel balls, chrome steel balls, stainless steel balls, high chromium cast iron balls, glass balls, agate balls, and natural sand; the shape of the grinding media includes one or more of spherical, columnar, and irregular shapes.

[0045] The particle size analyzer includes one or more of a laser particle size analyzer, a spray particle size analyzer, a nano particle size analyzer, a single particle light obstruction particle size analyzer, and an image particle size analyzer.

[0046] Verification results analysis

[0047] We successfully obtained nano-silicon through this method. We tested the nano-silicon prepared by the present invention. The test results are as follows: Figure 5-Figure 6 shown.

[0048] Figure 5 The element content diagram of the nano-scale silicon powder obtained after the first-level grinding provided in the embodiment of the present invention shows that the Si element content accounts for 97%, indicating that the silicon powder is basically not oxidized and corroded during the grinding process. This shows that the combination of the solvent and the wetting agent in the present method reduces the tension on the silicon surface and reduces the oxidation of the silicon during the grinding process, thereby effectively improving the stability of the silicon powder during the grinding process. Figure 6 In the XPS photograph of the nano-scale silicon powder obtained after the primary grinding provided in the embodiment of the present invention, the main peak of Si single substance is the highest, indicating that the purity of silicon is high, which can also verify our conjecture.

[0049] We also further studied the particle size distribution of the final obtained nano-silicon, such as Figure 8 and Fig. 9 As shown. Among them, Figure 8 The particle size distribution diagram of nano-silicon obtained in Example 1 is as follows: Figure 8 It can be seen that the particle size D90 of the nano-silicon obtained in Example 1 is 0.157 μm, D50 is 0.102 μm, and the particle size of the particles is concentrated in the range of 0.050 μm-0.157 μm, and the particles in this particle size range account for 89.81%; Fig. 9 The particle size distribution diagram of the nano silicon obtained in Example 2 is shown in FIG. 1 , wherein the particle size of the nano silicon obtained in Example 2 is D90=0.030 μm, D50 is 0.023 μm, and the particle size of the particles is concentrated in the range of 0.020 μm-0.050 μm, and the particles in this particle size range account for 100%. It can be seen that the nano silicon obtained by this method has a finer particle size, and the distribution of the particle size is very concentrated.

[0050] Table 1 Particle size changes of silicon powder during primary and secondary grinding

[0051]

[0052] This method adopts a preparation method of secondary grinding. During the secondary grinding, graphene oxide nanosheets are added to in-situ coat silicon particles, so that the obtained nano-scale silicon particles can be more stable. Since the graphene oxide nanosheets are uniformly coated on the silicon powder particles, the specific surface area of ​​the silicon powder particles is reduced, and the porosity between the grinding medium and the silicon powder is reduced, thereby overcoming the grinding limit of the primary grinding, and promoting the silicon powder particles to obtain a smaller particle size in the secondary grinding, as shown in Table 1. We found that with the increase of grinding time, the degree of particle size reduction is decreasing, and it can be seen that the force of the grinding medium on the particle size is weakening, mainly because there is a grinding limit. If the porosity between the grinding medium and the silicon powder particle size is too large, it may cause the mechanical force to be unable to act on the silicon powder surface, so that the force of the grinding medium on the silicon powder is weakened. Therefore, with the increase of grinding time, the porosity between the grinding medium and the silicon powder particle size increases, and even if the grinding continues, the particle size of the particles cannot be reduced; Therefore, by adding graphene oxide nanosheets in the secondary grinding process, not only can the grinding limit of the primary grinding be overcome, the particle size is reduced, but also it is beneficial to shorten the grinding time.

[0053] We further found from Table 1 that the silicon powder of Japan Yuexin and Zhejiang Zhongcheng silicon powder use the same method, and the particle size of the nano silicon obtained is very different. We believe that it may be due to the different methods used by manufacturers to prepare silicon powder, which makes the obtained silicon powders different. The method used by Japan Yuexin is the pulse discharge method, which converts kinetic energy into thermal energy and finally obtains silicon powder by condensation. The particle size distribution of silicon powder obtained by this method is more uniform, and the surface characteristics of silicon powder are smoother. More wetting agents and dispersion systems are adsorbed through the electron-withdrawing effect, thereby promoting better coating of graphene oxide nanosheets, reducing the specific surface area, and obtaining a smaller particle size during the secondary grinding of silicon powder. The domestic silicon powder obtained by the method of the present invention has a minimum nano silicon fineness (D90) of 156nm, while the fineness (D90) obtained by the pulse discharge method is only about 1 / 5 of the domestic silicon powder obtained by the general preparation method. The fineness (D90) of Example 2 is 34nm. We further prefer that the silicon powder is obtained by the pulse discharge method.

[0054] Table 2 Nano-silicon prepared by the method of the present invention

[0055]

[0056] We obtained nano silicon with different particle sizes by the preparation method of the present invention, as shown in Table 2. As shown in Examples 1 to 15 and 17 to 20, the fineness (D90) of the nano silicon particles obtained by the present invention is less than 200 nm, which shows that nano silicon can be successfully obtained by the method of the present invention, and the preparation method does not limit the source of silicon powder.

[0057] First, different reagents have certain differences in the particle size of the generated nano-silicon, as shown in Examples 1 and 3 to 7. In the process of preparing nano-silicon, the specific surface area of ​​silicon particles increases during the grinding of silicon powder, and agglomeration occurs during the grinding process, thereby affecting the grinding. Dispersants need to be adsorbed on the surface of solid particles to reduce the interfacial tension between solid and liquid. Dispersants and silicon form an electron-withdrawing effect, which promotes the formation of a flocculent structure on the surface of silicon, so that the outer layer of the structure can have a strong affinity with the solvent, while the particles are kept away from each other due to electrostatic repulsion. On this basis, we chose polymethacrylic acid, which has a carboxyl group that can form a strong electron-withdrawing effect with silicon powder, and the methyl group in polymethacrylic acid can induce the lone pair of electrons of silicon to move toward the carboxyl group, thereby enhancing the connection between polymethacrylic acid and silicon. Wetting agents can reduce the tension on the silicon surface, so that the solvent can wet the silicon. For this reason, we chose a wetting agent, alkylphenol polyoxyethylene ether, which can connect with the silicon surface and is similar to the dispersant. The choice of solvent needs to consider the solubility of the dispersant and the wetting agent. For this reason, we chose the organic solvent isopropanol. The intermolecular force between isopropanol molecules with branches is small, which can promote the dissolution of polymethacrylic acid and alkylphenol polyoxyethylene ether and stably adsorb on the silicon surface, which is beneficial to reduce the oxidation of silicon during the grinding process. Generally speaking, the amount of dispersant used in the prior art is mostly more than 1%, but in the secondary grinding process of the present invention, we add graphene oxide nanosheets, so that the graphene oxide nanosheets can be grown in situ on the silicon surface, which can not only stabilize the dispersibility of nano-silicon and help reduce the amount of dispersant, but also prevent silicon from being directly exposed to the electrolyte, which helps to form the SEI film and is beneficial to improve the cycle performance of the negative electrode material. For this reason, we further select the optimal preparation system of the present invention, including silicon powder, polymethacrylic acid, alkylphenol polyoxyethylene ether, isopropyl alcohol, and graphene oxide nanosheets.

[0058] On this basis, we further optimized the difference between the particle sizes of nano silicon obtained by different addition amounts under the optimal preparation system, as compared with Example 1 and Example 8-Example 17. First, the amount of dispersant added, as shown in Example 1 and Example 8-Example 9, can be found from Table 1 that the less amount of dispersant added, the smaller the particle size of nano silicon obtained. In the traditional mechanical grinding method, a large amount of dispersant is required to improve the dispersibility between silicon powders. Excessive dispersants may bridge each other to form a network structure, increase the viscosity of the medium, and lead to poor fluidity of the mixed slurry, which may affect the dispersion of the particle size, thereby affecting the grinding; while in the method of the present invention, less dispersant addition is more conducive to obtaining nano silicon with smaller particle size, and the amount of dispersant added is further selected to be 0.2g-0.3g.

[0059] We also studied the effect of the amount of wetting agent added on the particle size. As found by comparing Example 1 and Example 10, when the amount of wetting agent added is smaller, the particle size of the obtained silicon powder is smaller. We believe that this may be because the amount of wetting agent added is larger, which makes the wetting speed of the silicon powder unable to match the speed of increase of the silicon specific surface area during the grinding process, causing the dispersion of the silicon powder particles to decrease, and finally affecting the particle size of the silicon powder. We further selected the amount of wetting agent added to be 0.2g-0.3g.

[0060] We also studied the effect of the amount of solvent added on reducing the particle size. As shown in the comparison between Example 1 and Example 11-Example 12, when the amount of solvent added is large, it is beneficial to reduce the particle size of the final nano-silicon obtained. When the amount of solvent added is less, it is not conducive to the dispersion of other substances in the solvent. We further selected the amount of solvent added to be 70g-75g.

[0061] During the secondary grinding, graphene oxide nanosheets are added to in-situ coat the silicon particles, so that the obtained nano-scale silicon particles can be more stable. Since the graphene oxide nanosheets are uniformly coated on the silicon powder particles, the specific surface area of ​​the silicon powder particles is reduced and the primary grinding limit is overcome, so that the silicon powder particles are prompted to obtain a smaller particle size in the secondary grinding, as shown in Examples 1 and 14-17. When the amount of graphene oxide nanosheets added is more, it is conducive to obtaining nano-silicon with a smaller particle size. It may be because the amount added is not enough and cannot be fully coated on the silicon powder particles, which may cause the agglomeration of silicon powder, as shown in Example 16. We further selected the addition amount of graphene oxide nanosheets to be 5g-6g.

[0062] In summary, the preparation method of the present invention can not only improve the work efficiency of the preparation and reduce the process flow, but also obtain stably dispersed nano-scale silicon particles.

[0063] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing nano-silicon by graded steps, characterized in that: The preparation method comprises preparing a mixed slurry of isopropyl alcohol, silicon powder, polymethacrylic acid and alkylphenol polyoxyethylene ether, and then performing primary grinding, wherein the primary grinding step comprises adding primary grinding media, setting the material pressure to 0.4 bar-0.8 bar, the temperature of cooling water to be lower than 10° C., the flow rate of cooling water to be 100 kg / h-200 kg / h, the rotor speed to be 1000 r / min-1500 r / min, and the size of the primary grinding media to be one or more of φ0.5 mm-φ0.3 mm; Then, secondary grinding is performed, wherein the secondary grinding step includes adding secondary grinding media and graphene oxide nanosheets, setting the material pressure to 0.4 bar-0.8 bar, the cooling water temperature to be lower than 10° C., the cold water flow rate to be 100 kg / h-200 kg / h, the rotor speed to be 1000 r / min-1500 r / min, and the size of the secondary grinding media to be one or more of φ0.1 mm-φ0.3 mm; After grinding, nano silicon is obtained; In terms of mass, the ratio of isopropanol, silicon powder, polymethacrylic acid, alkylphenol polyoxyethylene ether and graphene oxide nanosheets is (70-75 parts): (20-30 parts): (0.2-0.3 parts): (0.2-0.3 parts): (5-6 parts).

2. The method for preparing nano-silicon by graded steps according to claim 1, characterized in that: The particle size of the graphene oxide nanosheets is D97=50 nm.

3. The method for preparing nano-silicon by graded steps according to claim 1, characterized in that: The silicon powder is obtained by a pulse discharge method.

4. The method for preparing nano-silicon by graded steps according to claim 1, characterized in that: The step of preparing the mixed slurry comprises stirring isopropyl alcohol, silicon powder, polymethacrylic acid and alkylphenol polyoxyethylene ether for 60-90 minutes and at a stirring speed of 2000-3000 r / min.

5. The method for preparing nano-silicon by graded method according to claim 1, characterized in that: The termination conditions of the primary grinding and the secondary grinding are that the particle size of the obtained silicon powder is detected for more than 2 times in succession, and the interval between each detection is more than 10 minutes, and the grinding is terminated when the average particle size of the silicon powder is within 5%.

6. The method for preparing nano-silicon by graded steps according to claim 1, characterized in that: The method for preparing nano-silicon further comprises drying the obtained nano-silicon.

7. The method for preparing nano-silicon by graded steps according to claim 6, characterized in that The drying temperature is between 20° C. and 110° C., the drying time is between 4 h and 18 h, and the drying environment is an inert gas.

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