Method for preparing nano silicon by utilizing silicon dioxide

Abstract

The invention belongs to the technical field of silicon-based material synthesis, and particularly discloses a method for preparing nano silicon by using silicon dioxide, which comprises the following steps: S1, mixing silicon dioxide with a reducing agent, loading into a ball mill, and grinding in an inert atmosphere; s2, passivating a product in the step S1 with an alcoholic solution, and adding an acid solution to remove impurities while stirring; and S3, separating a water phase and an organic phase in the product in the step S2, washing the organic phase with deionized water, and evaporating alcohol in the organic phase in a vacuum or inert atmosphere to obtain the nano silicon. The nano silicon prepared by the method has the advantages of no agglomeration and growth, small particles, uniform distribution, good dispersity and the like.

Description

Technical Field

[0001] The invention relates to the technical field of silicon-based material synthesis, and in particular to a method for preparing nano-silicon by using silicon dioxide. Background Art

[0002] In recent years, graphite has been the mainstream negative electrode material for commercial lithium-ion batteries. However, its specific capacity has reached its limit (372mAh / g), and its lithium insertion potential platform is close to the deposition potential of metallic lithium. It is easy to cause safety hazards during fast charging or low-temperature charging, which limits the application of graphite in the field of large-capacity batteries. Silicon has a theoretical specific capacity 10 times higher than graphite (4200mAh / g), a moderate lithium desorption potential (<0.5V vs Li + / Li) and abundant reserves (27.6%) have attracted close attention from researchers of lithium-ion battery anodes.

[0003] Large-sized silicon particles will produce a large volume expansion during the lithiation process, causing them to be easily broken and pulverized, which in turn causes a rapid decline in capacity. By optimizing the electrolyte and SEI film, its cycle stability can be improved, but there is still a long way to go before commercial applications. Nano silicon particles have a small particle size, which shortens the diffusion distance of lithium ions and can better adapt to volume expansion and contraction during charging and discharging, so they usually show higher reversible capacity and better cycle stability.

[0004] At present, the preparation methods for nano silicon mainly include carbon thermal reduction, chemical vapor deposition (CVD), ball milling, sol-gel method, etc. In patent CN110040734A, silicon dioxide and graphene powder are used as raw materials, and nano silicon particles are obtained after two high temperature sinterings and pickling and crushing. Although the final product has high purity and uniform particle size distribution, the heat treatment temperature is high and the time is long in its preparation process, which is large for energy consumption and increases the preparation cost. In patent CN115571881A, commercial silicon oxide-containing materials are first subjected to high temperature calcination and pickling to obtain silicon oxide, and silicon oxide is subjected to metal thermal reduction reaction to obtain porous nano silicon. In the preparation process, it is inevitable to be oxidized when pickling impurities after obtaining nano silicon, resulting in an increase in oxygen content, thereby affecting the electrochemical properties of nano silicon.

[0005] Therefore, it is particularly important to develop a new preparation method to address the problems of high energy consumption and easy oxidation in the preparation process of nano-silicon. Summary of the invention

[0006] In view of the above-mentioned shortcomings, the present invention provides a method for preparing nano-silicon using silicon dioxide. The nano-silicon prepared by the present invention has the advantages of no agglomeration and growth, small particles, uniform distribution and good dispersibility.

[0007] In order to achieve the above object, in a first aspect, the present invention provides a method for preparing nano-silicon by using silicon dioxide, comprising the following steps:

[0008] S1, mixing silicon dioxide and a reducing agent, loading into a ball mill, and grinding under an inert atmosphere;

[0009] S2, passivating the product of step S1 with an alcohol solution, and then adding an acid solution to remove impurities while stirring;

[0010] S3, separating the aqueous phase and the organic phase in the product of step S2, washing the organic phase with deionized water, and evaporating the alcohol therein under vacuum or inert atmosphere to obtain nano-silicon.

[0011] According to one aspect of the present invention, in step S1, the particle size of the silicon dioxide is 20 nm-2 μm; the particle size of the reducing agent is 100 nm-3 μm; and the mass ratio of the reducing agent to silicon dioxide is 1:1-10:1.

[0012] According to one aspect of the present invention, in step S1, the reducing agent includes at least one of magnesium and aluminum.

[0013] According to one aspect of the present invention, in step S1, the grinding speed is 200 rpm-1200 rpm, the grinding time is 10 min-1200 min, and the grinding temperature is 20°C-800°C.

[0014] According to one aspect of the present invention, in step S2, the alcohol is at least one of 1-pentanol, n-butanol, and n-hexanol; the acid is a mixed acid, the mixed acid includes HF, and the mixed acid also includes at least one of HCl, H2SO4, HNO3, HClO, HClO4, CH3COOH and H2CO3.

[0015] According to one aspect of the present invention, in step S3, the evaporation temperature is 80°C-500°C.

[0016] According to one aspect of the present invention, the inert atmosphere includes at least one of nitrogen, argon and helium.

[0017] In a second aspect, the present invention also provides nano-silicon prepared by any of the above methods.

[0018] According to one aspect of the present invention, the particle size of the nano-silicon is 20nm-150nm, and the specific surface area is 5m 2 / g-30m 2 / g, and the oxygen content is 1%-10%; the nano-silicon is at least one of nano-spheres, nano-wires, nano-sheets, and porous nano-silicon.

[0019] In a third aspect, the present invention also provides the use of nano-silicon prepared by any of the above methods in negative electrode materials for lithium-ion batteries.

[0020] According to one aspect of the present invention, the lithium-ion battery obtained by using nano-silicon prepared by any of the above methods as the negative electrode material has an initial discharge capacity of 2500mAh / g-3700mAh / g, an initial charge capacity of 1900mAh / g-3500mAh / g, and an initial coulombic efficiency of 75%-95%.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention uses metal powder to reduce silicon dioxide by high-energy ball milling. Different from the traditional magnesium / aluminum thermite reaction with strong exothermicity, the present invention can control the reaction temperature at a lower level. The prepared nano-silicon particles will not agglomerate or grow due to high-temperature melting. The particles are small in size and evenly distributed with good dispersibility, which can effectively alleviate the volume effect in the cycle process and improve the cycle performance.

[0023] (2) The present invention passivates the silicon surface by using an alcohol solution. During the subsequent pickling process, the surface passivation layer effectively prevents oxygen from entering the interior of the nano-silicon particles, preventing the nano-silicon particles from further oxidation, thereby reducing the oxygen content, thereby significantly improving the capacity and cycle performance of the nano-silicon. At the same time, it can also reduce the loss of silicon in the preparation process and improve the nano-silicon yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a preparation flow chart of the method for preparing nano-silicon using silicon dioxide according to Example 1 of the present invention;

[0025] Figure 2 This is a scanning electron microscope image of nano-silicon prepared in Example 1 of the present invention;

[0026] Figure 3 This is the X-ray diffraction pattern of nano-silicon prepared in Example 1 of the present invention;

[0027] Figure 4 This is a comparison chart of the cycle performance of lithium-ion batteries prepared with nano-silicon prepared in Example 1 of the present invention and in Comparative Example 1. DETAILED DESCRIPTION

[0028] To make the present invention easier to understand, the present invention is further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professional and technical personnel in the field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0029] Example 1

[0030] A method for preparing nano-silicon using silicon dioxide, the preparation flow chart is as follows Figure 1 As shown, the following steps are included:

[0031] (1) 6 g of silica nanoparticles, 10 g of magnesium nanoparticles, and 40 g of zirconium beads were placed in a ball mill, and the mixture was ground in a planetary ball mill at 250 rpm for 20 min at room temperature and in a nitrogen atmosphere. The particle size of the silica was 20 nm-2 μm; the particle size of the magnesium nanoparticles was 100 nm-3 μm;

[0032] (2) Before the powder is exposed to air, 100 mL of 1-pentanol is injected into the container to passivate the powder. 200 mL of 18 wt% HCl solution is added to the mixture under stirring. The mixture is allowed to settle to form a clear phase boundary.

[0033] (3) Remove the lower aqueous phase containing MgCl2 and excess HCl. Wash the organic phase thoroughly with deionized water for more than three times to completely remove the inorganic salts. The final washing step uses 100 mL of a 5 wt% HF solution in a polytetrafluoroethylene beaker to remove the surface oxide layer. Evaporate 1-pentanol in a vacuum at 80°C to obtain a product in the form of a dark brown powder. The prepared solid nanosilicon is subjected to scanning electron microscopy and X-ray analysis, and the results are as follows: Figures 2-3 As shown. Figures 2-3 It can be seen that the above product is nano-silicon, and the nano-silicon has no agglomeration and growth, the particles are small and evenly distributed, and the dispersion is good. The above-prepared nano-silicon was subjected to oxygen content and half-cell tests, and charge and discharge tests were performed between 0.01 and 1.5 V. The electrochemical properties are shown in Table 1.

[0034] Example 2

[0035] A method for preparing nano-silicon using silicon dioxide comprises the following steps:

[0036] (1) 6 g of silica nanoparticles, 13 g of aluminum powder, and 100 g of zirconium beads were placed in a ball mill, and the mixture was ground in a planetary ball mill at 300 rpm for 40 min at room temperature under nitrogen atmosphere.

[0037] (2) Before the powder is exposed to air, 100 mL of 1-pentanol is injected into the container to passivate the powder. 500 mL of 18 wt% HCl solution is added to the mixture under stirring. The mixture is allowed to settle to form a clear phase boundary.

[0038] (3) Remove the lower aqueous phase containing AlCl3 and excess HCl. Wash the organic phase thoroughly with deionized water for more than three times to completely remove the inorganic salts. The final washing step uses 100mL, 5wt% HF solution in a polytetrafluoroethylene beaker to remove the surface oxide layer. Evaporate 1-pentanol in a vacuum at 80°C to obtain solid nanosilicon in the form of a dark brown powder. The solid nanosilicon prepared above was subjected to oxygen content and half-cell tests, and charge and discharge tests were performed between 0.01 and 1.5V. The electrochemical properties are shown in Table 2.

[0039] Example 3

[0040] A method for preparing nano-silicon using silicon dioxide comprises the following steps:

[0041] (1) 6 g of silica nanoparticles, 10 g of magnesium nanoparticles, and 40 g of zirconium beads were placed in a ball mill, and the mixture was ground in a planetary ball mill at 250 rpm for 20 min at room temperature under nitrogen atmosphere.

[0042] (2) Before the powder is exposed to air, 100 mL of n-butanol is injected into the container to passivate the powder. 200 mL of 18 wt% HCl solution is added to the mixture under stirring. The mixture is allowed to settle to form a clear phase boundary.

[0043] (3) Remove the lower aqueous phase containing MgCl2 and excess HCl. Wash the organic phase thoroughly with deionized water for more than three times to completely remove the inorganic salts. The final washing step uses 100mL, 5wt% HF solution in a polytetrafluoroethylene beaker to remove the surface oxide layer. Evaporate n-butanol in a vacuum at 120°C to obtain solid nanosilicon in the form of a dark brown powder. The solid nanosilicon prepared above was subjected to oxygen content and half-cell tests, and charge and discharge tests were performed between 0.01 and 1.5V. The electrochemical properties are shown in Table 3.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 1 is that step (2) in Example 1 is changed, and 1-pentanol is not used to passivate the particles before using the HCl solution, and other experimental conditions are controlled to be the same. Oxygen content and half-cell tests are carried out, and charge and discharge tests are carried out between 0.01 and 1.5 V. The electrochemical properties are shown in Table 1, and the cycle performance is shown in Table 1. Figure 4 shown.

[0046] Table 1 Comparison of performance parameters of nano-silicon after magnesium reduction with 1-pentanol passivation and non-passivation

[0047]

[0048] From Table 1 and Figure 4 It can be seen that after passivation, the impurities are acid-dissolved, and the passivation layer plays a good protective role on the inside of the nano-silicon, preventing it from being further oxidized. Therefore, the oxygen content of the nano-silicon is significantly lower than that of the unpassivated one, so the electrochemical performance of the nano-silicon is better.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 1 is that step (2) in Example 2 is changed, 1-pentanol is not used to passivate the particles before using the HCl solution, and other experimental conditions are controlled to be the same. Oxygen content and half-cell tests are performed, and charge and discharge tests are performed between 0.01 and 1.5 V. The electrochemical properties are shown in Table 2.

[0051] Table 2 Comparison of performance parameters of nano-silicon after aluminum reduction with 1-pentanol passivation and non-passivation

[0052]

[0053] It can be seen from Table 2 that after the aluminum-reduced nano-silicon is passivated with 1-pentanol, the oxygen content introduced by pickling to remove impurities is significantly lower than that of the nano-silicon that has not been passivated, so its capacity and cycle performance are significantly better.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that step (2) in Example 3 is changed, n-butanol is not used to passivate the particles before using the HCl solution, and other experimental conditions are controlled to be the same. Oxygen content and half-cell tests are carried out, and charge and discharge tests are carried out between 0.01 and 1.5 V. The electrochemical properties are shown in Table 3.

[0056] Table 3 Comparison of performance parameters of nano-silicon after magnesium reduction with n-butanol passivation and non-passivation

[0057]

[0058] It can be seen from Table 3 that after the nano-silicon after magnesium reduction is passivated with n-butanol, the oxygen content introduced by acid washing to remove impurities is significantly lower than that of the nano-silicon without passivation treatment. The effect of n-butanol is close to that of 1-pentanol, so its capacity and cycle performance are significantly better.

[0059] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the art within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing nano-silicon using silicon dioxide, characterized in that: The following steps are involved: S1, mixing silicon dioxide and a reducing agent, loading into a ball mill, and grinding under an inert atmosphere; S2, passivating the product of step S1 with an alcohol solution, and then adding an acid solution to remove impurities while stirring; S3, separating the aqueous phase and the organic phase in the product of step S2, washing the organic phase with deionized water, and evaporating the alcohol therein under vacuum or inert atmosphere to obtain nano-silicon.

2. The method for preparing nano-silicon using silicon dioxide according to claim 1, characterized in that: In step S1, the particle size of the silicon dioxide is 20 nm-2 μm; the particle size of the reducing agent is 100 nm-3 μm; and the mass ratio of the reducing agent to silicon dioxide is 1:1-10:

1.

3. The method for preparing nano-silicon using silicon dioxide according to claim 1, characterized in that: In step S1, the reducing agent includes at least one of magnesium and aluminum.

4. The method for preparing nano-silicon by using silicon dioxide according to claim 1, characterized in that: In step S1, the grinding speed is 200 rpm-1200 rpm, the grinding time is 10 min-1200 min, and the grinding temperature is 20°C-800°C.

5. The method for preparing nano-silicon by using silicon dioxide according to claim 1, characterized in that: In step S2, the alcohol includes at least one of 1-pentanol, n-butanol, and n-hexanol; the acid includes HF, and the mixed acid also includes at least one of HCl, H2SO4, HNO3, HClO, HClO4, CH3COOH, and H2CO3.

6. The method for preparing nano-silicon by using silicon dioxide according to claim 1, characterized in that: In step S3, the evaporation temperature is 80°C-500°C.

7. The method for preparing nano-silicon by using silicon dioxide according to claim 1, characterized in that: The inert atmosphere includes at least one of nitrogen, argon and helium.

8. Nano-silicon prepared by the method according to any one of claims 1 to 7.

9. The nano-silicon according to claim 8, characterized in that: The particle size of the nano-silicon is 20nm-150nm, and the specific surface area is 5m 2 / g-30m 2 / g, and the oxygen content is 1%-10%; the nano-silicon is at least one of nano-spheres, nano-wires, nano-sheets, and porous nano-silicon.

10. Use of the nano-silicon prepared by the method according to any one of claims 1 to 7 or the nano-silicon according to any one of claims 8 to 9 in negative electrode materials for lithium-ion batteries.

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