Method for preparing nano silicon by using sodium silicate

Abstract

The invention belongs to the technical field of silicon-based material synthesis, and particularly discloses a method for preparing nano silicon by using sodium silicate, which comprises the following steps: reacting sodium silicate with excessive acid, filtering and drying to obtain silicic acid solid; mixing the silicic acid solid with a heat scavenger and a reducing agent, and heating in an inert atmosphere to obtain a mixture; and adding excessive acid into the mixture, stirring byproducts in the solvent, filtering, washing, and drying in an inert atmosphere to obtain the nano silicon. The nanometer silicon prepared through the method has the advantages of being small in particle size, uniform in distribution, good in dispersity and the like, by adding the fused salt, the fused salt can be good in wettability at the high temperature, has certain corrosivity and can serve as a pore forming agent, porous nanometer silicon is obtained, and therefore the fused salt can effectively adapt to volume expansion in the circulation process, and the performance of the nanometer silicon is improved. And capacity fading is delayed, and better cycle performance is achieved.

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 utilizing sodium silicate. Background Art

[0002] In recent years, graphite, as the mainstream choice of negative electrode materials for lithium-ion batteries, has reached a specific capacity limit of 372mAh / g. In addition, due to the similarity between the potential platform of lithium insertion and the potential of metal lithium deposition, there are safety risks under fast or low-temperature charging conditions, which limits the further development of graphite in the field of large-capacity batteries. In contrast, silicon has become a hot spot in the research of negative electrodes for lithium-ion batteries due to its excellent theoretical specific capacity (up to 10 times that of graphite, i.e. 4200mAh / g), suitable lithium desorption potential (<0.5V vs Li+ / Li) and abundant natural resources (accounting for 27.6%).

[0003] However, large-sized silicon anodes face severe volume expansion problems during the lithiation process, which makes them extremely easy to break and pulverize, resulting in a sharp drop in capacity. In order to improve this situation, researchers have tried to improve their cycle stability by optimizing the electrolyte and solid electrolyte interface (SEI) film, but even so, their performance is still somewhat behind that of nano-silicon anodes. Nano-silicon anodes, with their tiny particle size, not only significantly shorten the diffusion path of lithium ions, but also more effectively alleviate the volume expansion effect of silicon, so they can usually show higher reversible capacity and better cycle stability.

[0004] Patent CN110040734A uses silicon dioxide and graphene to sinter twice to obtain nano silicon particles, but they need to be crushed in the middle process; Patent CN116216722A directly uses larger silicon particles for secondary grinding to obtain nano silicon particles, which has the problems of high production cost and complicated grinding process; Patent CN115571881A uses silicon dioxide to prepare nano silicon, but it is necessary to prepare nano-scale silicon dioxide powder first, and there may be problems such as high temperature causing silicon particles to agglomerate, increase in size and uneven particle size distribution during the reduction process.

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

[0006] In view of the above-mentioned shortcomings that currently exist, the present invention provides a method for preparing nano-silicon using sodium silicate. The nano-silicon prepared by the method of the present invention has the advantages of small particle size, uniform distribution, good dispersibility, etc. The method of the present invention adds molten salt, which has good wettability at high temperature and certain corrosiveness, and can be used as a pore-forming agent to obtain porous nano-silicon. Therefore, it can effectively adapt to the volume expansion during the cycle process, delay capacity attenuation, and have better cycle performance.

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

[0008] S1, reacting sodium silicate with excess acid, filtering and drying to obtain silicic acid solid;

[0009] S2, mixing the silicic acid solid with a heat scavenger and a reducing agent, and heating under an inert atmosphere to obtain a mixture;

[0010] S3, adding an excess amount of acid to the mixture and stirring to dissolve the byproducts therein, and then filtering, washing, and drying in an inert atmosphere to obtain nano-silicon.

[0011] It should be noted that the above-mentioned heat scavenger is a salt heat scavenger, and a common characteristic of salt heat scavengers is that they can become a melt at a relatively low temperature.

[0012] According to one aspect of the present invention, in step S1, the acid includes at least one of HCl, H2SO4, CH3COOH and H2CO3, HNO3, H2C2O4; and the drying temperature is 60-200°C.

[0013] According to one aspect of the present invention, in step S2, the heat scavenger includes at least one of sodium chloride and potassium chloride; and the mixing mass ratio of the heat scavenger to the silicic acid solid is 3:1-10:1.

[0014] According to one aspect of the present invention, in step S2, the reducing agent includes at least one of magnesium and aluminum; and the mass ratio of the silicate solid to the reducing agent is 1:10-1:1.

[0015] It should be noted that the above-mentioned reducing agent is metal powder, such as magnesium powder, aluminum powder and the like.

[0016] According to one aspect of the present invention, in step S2, the inert atmosphere is one or more of nitrogen, argon, and helium.

[0017] According to one aspect of the present invention, in step S2, the heating temperature is 300-1800° C. and the heating time is 4-20 hours.

[0018] According to one aspect of the present invention, in step S3, the by-products include magnesium silicide, magnesium, silicon dioxide, magnesium oxide, and magnesium hydroxide; the acid includes at least one of hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, and carbonic acid.

[0019] According to one aspect of the present invention, in step S3, the reagent used for washing includes at least one of deionized water, ethanol, and ether; the inert atmosphere is at least one of vacuum, nitrogen, argon, and helium; and the drying temperature is 80 to 300°C.

[0020] In a second aspect, the present invention also provides nano-silicon prepared by any of the above methods, wherein the nano-silicon is at least one of nano-spheres, nano-wires, nano-sheets, and porous nano-silicon; the particle size of the nano-silicon is 10 to 500 nm; the specific surface area is 20 to 10000 m 2 / g.

[0021] 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.

[0022] According to one aspect of the present invention, the lithium ion battery has an initial discharge specific capacity of 2200-4000 mAh / g, an initial charge specific capacity of 1600-3800 mAh / g, an initial coulombic efficiency of 73%-96%, and an oxygen content of 1%-15%.

[0023] Beneficial effects of the present invention:

[0024] The present invention adds a heat scavenger before the metal thermal reduction, which can absorb a large amount of heat generated by the metal thermal reduction reaction during the reduction process, and can effectively prevent silicon nanoparticles from agglomerating due to high-temperature melting; and the heat scavenger becomes a melt at high temperature, can be evenly dispersed around the newly generated nano-silicon, and covers the silicon surface to inhibit its growth, so that the prepared nano-silicon particles have the advantages of small particle size, uniform distribution, good dispersibility, etc.; the molten salt has good wettability at high temperature and has certain corrosiveness, and can be used as a pore-forming agent to obtain porous nano-silicon; the nano-silicon prepared by the present invention can effectively adapt to the volume expansion in the cycle process, delay capacity decay, and have better cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the preparation of nano-silicon according to Example 1 of the present invention;

[0026] Figure 2 is a SEM image of the nano-silicon prepared in Example 1;

[0027] Figure 3 is the XRD pattern of nano-silicon prepared in Example 1;

[0028] Figure 4 The solid nano-silicon prepared in Example 1 and Comparative Example 1 is used in the cycle performance of negative electrode materials of lithium-ion batteries. DETAILED DESCRIPTION

[0029] 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.

[0030] Example 1

[0031] A method for preparing nano-silicon using sodium silicate comprises the following steps, and its preparation flow chart is as follows: Figure 1 As shown:

[0032] (1) Add 160 mL of 18 wt % hydrochloric acid solution to 12.2 g of sodium silicate solid, stir to obtain silicic acid precipitate, and evaporate the solution at 75° C. to obtain silicic acid solid.

[0033] (2) The above-mentioned silicic acid solid was mixed with 10 g of magnesium powder and 30 g of sodium chloride, and heated under argon gas at 800° C. for 7 h to obtain a mixture.

[0034] (3) 160 mL of 18 wt % hydrochloric acid and 100 mL of 5 wt % hydrofluoric acid solution were added to the mixture, stirred for 4 h, and the solution was filtered. The solid was washed three times with deionized water and dried at 80 ° C. under vacuum for 12 h to obtain solid particles, which were analyzed by scanning electron microscopy and X-ray. The results are as follows: Figures 2-3 As shown. Figures 2-3 It can be seen that the solid particles prepared in Example 1 of the present application are nano silicon particles, and the nano silicon particles have a small particle size, uniform distribution and good dispersibility. The above solid nano particles were subjected to table 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.

[0035] Example 2

[0036] A method for preparing nano-silicon using sodium silicate comprises the following steps:

[0037] (1) Add 160 mL of 18 wt % hydrochloric acid solution to 12.2 g of sodium silicate solid, stir to obtain silicic acid precipitate, and evaporate the solution at 75° C. to obtain silicic acid solid.

[0038] (2) The above-mentioned silicic acid solid was mixed with 10 g of magnesium powder and 24 g of potassium chloride, and heated under argon gas at 800° C. for 7 h to obtain a mixture.

[0039] (3) Add 160 mL of 18 wt% hydrochloric acid and 100 mL of 5 wt% hydrofluoric acid solution to the mixture, stir for 4 h, filter the solution, wash the solid three times with deionized water, and dry at 80 ° C in a vacuum environment for 12 h to obtain solid nano silicon particles. Perform a table and half-cell test, and perform a charge and discharge test between 0.01 and 1.5 V. The electrochemical properties are shown in Table 2.

[0040] Example 3

[0041] A method for preparing nano-silicon using sodium silicate comprises the following steps:

[0042] (1) Add 160 mL of 18 wt % hydrochloric acid solution to 12.2 g of sodium silicate solid, stir to obtain silicic acid precipitate, and evaporate the solution at 75° C. to obtain silicic acid solid.

[0043] (2) The above-mentioned silicate solid was mixed with 17 g of aluminum powder and 24 g of potassium chloride, and heated under argon gas at 800° C. for 7 h to obtain a mixture.

[0044] (3) Add 160 mL of 18 wt% hydrochloric acid and 100 mL of 5 wt% hydrofluoric acid solution to the mixture, stir for 4 h, filter the solution, wash the solid three times with deionized water, and dry at 80 ° C in a vacuum environment for 12 h to obtain solid nano silicon particles. Perform a specific table and half-cell test, and perform a charge and discharge test between 0.01 and 1.5 V. The electrochemical properties are shown in Table 3.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that step (2) in Example 1 is changed, and sodium chloride powder is not added before heating. The other steps and parameters are the same as Example 1. The prepared solid silicon particles are subjected to table and half-cell tests, 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.

[0047] Table 1 Comparison of nano-silicon performance parameters with and without sodium chloride when magnesium is used as a reducing agent

[0048]

[0049] From Table 1 and Figure 4It can be seen that the particle size of nano-silicon reduced by adding sodium chloride is significantly smaller than that of nano-silicon reduced without adding sodium chloride, because the addition of heat scavenger reduces the phenomenon of nano-silicon melting and agglomeration due to large amount of heat, so that the nano-silicon remains in a smaller size. The volume effect of small-sized nano-silicon particles is weaker than that of large-sized particles during the cycle, which leads to better cycle performance of small-sized silicon particles.

[0050] Comparative Example 2

[0051] The difference between this comparative example and Example 2 is that step (2) in Example 2 is changed, and potassium chloride powder is not added before heating. The other steps and parameters are the same as Example 2. The prepared solid silicon particles are subjected to table and half-cell tests, and charge and discharge tests are carried out between 0.01 and 1.5 V. The electrochemical properties are shown in Table 2.

[0052] Table 2 Comparison of nano-silicon performance parameters with and without potassium chloride when magnesium is used as a reducing agent

[0053]

[0054]

[0055] It can be seen from Table 2 that the addition of potassium chloride has a similar effect to that of sodium chloride. This is because the addition of the heat scavenger reduces the phenomenon of nano-silicon melting and agglomeration due to a large amount of heat, keeps the nano-silicon in a smaller size, buffers the volume expansion during the cycle, and optimizes the cycle performance of nano-silicon.

[0056] Comparative Example 3

[0057] The difference between this comparative example and Example 3 is that step (2) in Example 3 is changed, and potassium chloride powder is not added before heating. The other steps and parameters are the same as those in Example 3. The prepared solid silicon particles are subjected to a specific table and a half-cell test, and a charge and discharge test is performed between 0.01 and 1.5 V. The electrochemical properties are shown in Table 3.

[0058] Table 3 Comparison of nano-silicon performance parameters with and without potassium chloride when aluminum is used as a reducing agent

[0059]

[0060] It can be seen from Table 3 that when aluminum is used as a reducing agent, potassium chloride can still play the role of a heat scavenger. The prepared nano-silicon particles have a small particle size, a high cycle retention rate, and the electrochemical performance is significantly improved compared to when no potassium chloride is added.

[0061] 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 sodium silicate, characterized in that: The following steps are involved: S1, reacting sodium silicate with excess acid, filtering and drying to obtain silicic acid solid; S2, mixing the silicic acid solid with a heat scavenger and a reducing agent, and heating under an inert atmosphere to obtain a mixture; S3, adding an excess amount of acid to the mixture and stirring to dissolve the byproducts therein, and then filtering, washing, and drying in an inert atmosphere to obtain nano-silicon.

2. The method for preparing nano-silicon using sodium silicate according to claim 1, characterized in that: In step S1, the acid includes at least one of HCl, H2SO4, CH3COOH and H2CO3, HNO3, H2C2O4; and the drying temperature is 60-200°C.

3. The method for preparing nano-silicon using sodium silicate according to claim 1, characterized in that: In step S2, the heat scavenger includes at least one of sodium chloride and potassium chloride; and the mixing mass ratio of the heat scavenger to the silicate solid is 3:1-10:

1.

4. The method for preparing nano-silicon using sodium silicate according to claim 1, characterized in that: In step S2, the reducing agent includes at least one of magnesium and aluminum; and the mass ratio of the silicic acid solid to the reducing agent is 1:10-1:

1.

5. The method for preparing nano-silicon by using sodium silicate according to claim 1, characterized in that: In step S2, the inert atmosphere is one or more of nitrogen, argon, and helium.

6. The method for preparing nano-silicon using sodium silicate according to claim 1, characterized in that: In step S2, the heating temperature is 300-1800°C and the heating time is 4-20h.

7. The method for preparing nano-silicon using sodium silicate according to claim 1, characterized in that: In step S3, the by-products include magnesium silicide, magnesium, silicon dioxide, magnesium oxide, and magnesium hydroxide; the acid includes at least one of hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, and carbonic acid.

8. The method for preparing nano-silicon using sodium silicate according to claim 1, characterized in that: In step S3, the reagent used for washing includes at least one of deionized water, ethanol, and ether; the inert atmosphere is at least one of vacuum, nitrogen, argon, and helium; and the drying temperature is 80 to 300°C.

9. Nano-silicon prepared by the method according to any one of claims 1 to 8, characterized in that: The nano silicon is at least one of nano spheres, nano wires, nano sheets, and porous nano silicon; the particle size of the nano silicon is 10 to 500 nm; the specific surface area is 20 to 10000 m 2 / g.

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

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