CN106241812A - The method preparing silicon nano material - Google Patents

Abstract

The invention provides a method for preparing silicon nanomaterials, which is characterized in that the method comprises the following steps: a) grinding and mixing silicon-containing raw materials with excess metal; b) heating the mixture obtained in a) to 300 to 700 ℃ to react, the silicon in the silicon-containing raw material is reduced to the form of metal silicide; c) the reaction product in b) is heated to 450 to 700 ℃ under the flow of oxygen-containing gas to react, and the metal silicide therein core-shell silicon nanomaterials oxidized to elemental silicon core-silica shells. The method of the invention has the advantages of simple process operation, low cost, easy expansion of production, wide range of silicon sources, friendly environment, excellent product properties and the like.

Description

Method for preparing silicon nanomaterials

technical field

The invention relates to the field of silicon nanometer materials, in particular to a method for preparing silicon nanometer materials.

Background technique

Based on the continuous improvement of the demand for lithium-ion batteries, the development of high-performance lithium-ion battery electrode materials has also received further attention. Due to its high theoretical lithium storage capacity (-4200mAh/g, the lithium storage capacity is more than ten times that of commercial graphite anode materials) and low discharge potential (<0.5V, Li/Li ⁺ ), silicon nanomaterials are considered to be the next best choice. The key anode material for a generation of high-performance lithium-ion batteries. Currently, the preparation of silicon nanomaterials for lithium-ion batteries has been extensively studied.

A method for preparing silicon nanomaterials by reducing silicon dioxide by magnesia thermal reduction has been proposed (for example, Bao Z, Weatherspoon MR, Shian S et al., Nature, 446: 172-175 (2007)). The magnesium thermal reduction method is to use an appropriate amount of magnesium to reduce silicon dioxide to silicon and generate magnesium oxide at the same time. In this method, hydrofluoric acid is used to dissolve the residual silica. Hydrofluoric acid is known to be corrosive and particularly harmful to health.

There is still a need for a method of obtaining silicon nanomaterials with good electrode material properties in a more convenient, environmentally friendly, wide-ranging raw material source, and low cost.

Contents of the invention

In order to solve the above problems, the present invention provides the following technical solutions.

[1] A method for preparing silicon nanomaterials, characterized in that the method comprises the following steps:

a) milling and mixing silicon-containing raw materials with excess metal;

b) heating the mixture obtained in a) to 300 to 700°C for reaction, reducing the silicon in the silicon-containing raw material to the form of metal silicide;

c) heating the reaction product in b) to 450 to 700° C. for reaction under an oxygen-containing gas flow, and oxidizing the metal silicide therein into a core-shell silicon nanomaterial of elemental silicon core-silica shell.

[2] The method according to [1], wherein the metal is selected from the group consisting of lithium, sodium, calcium, magnesium, zinc, iron as a single substance or alloy, and combinations thereof.

[3] The method according to [1] or [2], wherein the molar ratio of silicon in the silicon-containing raw material to the metal is 1:3 to 1:20.

[4] The method according to any one of [1] to [3], characterized in that, in step b), the reaction temperature is 450-650°C, and the reaction time is 1-20h.

[5] The method according to any one of [1] to [4], characterized in that, in step c), the reaction temperature is 500-650°C, and the reaction time is 1-20h.

[6] The method according to any one of [1] to [5], characterized in that, in step c), the oxygen-containing gas is air or oxygen nitrogen with an oxygen content of 1% to 40%. , Oxygen-argon gas mixture.

[7] The method according to any one of [1] to [6], wherein the silicon-containing raw material is silicon dioxide, silicic acid, silicate, silicon-containing minerals or simple silicon powder.

[8] The method according to [7], wherein the silica can be silica in the following forms: silica sand, industrial silica waste, silica molecular sieve, white carbon black, glass fiber , microsilica, and combinations thereof.

[9] The method according to [7], wherein the silicon-containing mineral is selected from the group consisting of diatomaceous earth, albite, potassium feldspar, sepiolite, attapulgite, and their combination.

[10] The method according to [7], wherein the silicon-containing mineral is pre-treated, and the pre-treatment includes grinding and/or washing with water and/or pickling.

The technical scheme of the invention has the advantages of simple process operation, low cost, easy expansion of production and the like. Moreover, the present invention expands the scope of silicon sources, can directly use industrial silicon dioxide waste as raw material, effectively solve the problems of accumulation and pollution of industrial waste; and can directly use silicon-containing minerals as initial raw materials, providing a It is an effective way to directly prepare nano-silicon materials from minerals; and there is no need to use specially synthesized raw materials such as silicon tetrachloride as silicon sources, which reduces the cost of silicon sources. In the synthesis process, the use of high-polluting substances such as hydrofluoric acid and toxic organic solvents is avoided, and the method is environmentally friendly and easy for industrial production. The synthesized silicon nanopowder can be directly used in lithium-ion battery anode materials, and has the characteristics of excellent electrochemical performance, which provides the possibility to realize the macro preparation of high-performance nano-silicon anode materials.

Description of drawings

Fig. 1 is the X-ray diffractogram of process product in embodiment 1. From top to bottom: the XRD pattern of industrial silica raw materials; the XRD pattern after reaction in a high-temperature kettle; the XRD pattern after aerated calcination; the XRD pattern of the final product after cleaning.

Fig. 2 is the X-ray fluorescence spectrogram of the final product obtained in Example 1.

3 is a scanning electron microscope image of the final product obtained in Example 1.

4 is a transmission electron microscope image of the final product obtained in Example 1.

FIG. 5 is a high-resolution transmission electron microscope image of the final product obtained in Example 1.

FIG. 6 is an X-ray diffraction pattern of the product obtained in Example 2.

7 is a scanning electron microscope and a transmission electron microscope image of the final product obtained in Example 2.

Fig. 8 is the schematic diagram and physical photo of the 5L stainless steel reactor used in embodiment 3.

9 is an X-ray diffraction diagram of the product obtained in Example 3.

FIG. 10 is a scanning electron micrograph of the final product obtained in Example 3.

FIG. 11 is a transmission electron microscope image of the final product obtained in Example 3.

FIG. 12 is a high-resolution transmission electron microscope image of the final product obtained in Example 3.

FIG. 13 is an X-ray diffraction pattern obtained in Example 4. FIG.

FIG. 14 is a charge-discharge curve diagram of the characteristics of the silicon nanopowder obtained in Application Example 1. FIG.

FIG. 15 is an electrochemical cycle stability graph of the silicon nanopowder obtained in Application Example 1. FIG.

Fig. 16 is a diagram of the electrochemical rate performance of the silicon nanopowder obtained in Application Example 2, 1C=3600mA/g.

Fig. 17 is the electrochemical cycle stability diagram of the silicon nanopowder obtained in application example 2, 1C=3600mA/g.

detailed description

The invention provides a method for preparing silicon nanomaterials, which is characterized in that the method comprises the following steps: a) grinding and mixing silicon-containing raw materials with excess metal; b) heating the mixture obtained in a) to 300 to react at 700°C, and reduce the silicon in the silicon-containing raw material to the form of metal silicide; c) heat the reaction product in b) to 450 to 700°C under the flow of oxygen-containing gas to react, and the metal therein Silicide oxidation to elemental silicon core-silica shell core-shell silicon nanomaterials.

The "excess metal" referred to in step a) of the present invention means that the amount of metal is sufficient so that after the reaction in step b), there is still metal remaining. For example, when the silicon-containing raw material is silicon dioxide, an excessive amount of metal, such as magnesium, is used in step a), so that after the reaction under the conditions in step b), the silicon in the silicon dioxide and magnesium form magnesium silicide, and the two Oxygen in silicon oxide forms magnesium oxide with magnesium, and unreacted magnesium also remains. This is different from prior art such as magnesium thermal reaction. In a typical magnesothermic reaction, magnesium is not "in excess", and silica reacts with magnesium to directly form elemental silicon, but no unreacted magnesium remains.

Therefore, in the method of the present invention, the silicon in the silicon-containing raw material is first fully reduced into the form of metal silicide in step b), and then the metal silicide is oxidized into the form of elemental silicon in step c). Through this first reduction and then oxidation process, nano-scale silicon materials are naturally formed.

The grinding and mixing can be ground into a uniform powder by using a mortar or a ball mill. There are no particular requirements for the particle size of the powder. Although the raw material powder is not a nanometer powder, the silicon powder prepared by the method of the present invention is a nanometer powder.

The method of the invention is not carried out in solvents. In step b), the reaction can be carried out in a sealed reactor; of course, the reaction can also be carried out under the protection of an inert gas. The sealed reactor can be a sealed stainless steel autoclave. Typically, the autoclave used in the method of the present invention has a volume of 20 mL-50 L.

The final product obtained in step c) of the method of the present invention is a core-shell silicon nanomaterial of elemental silicon core-silica shell. Under the condition of passing oxygen-containing gas with heating, when all metal silicides are oxidized to elemental silicon, a silicon dioxide film will be formed on the surface of elemental silicon nanomaterials. Research has found that in certain applications, particularly as a negative electrode for lithium-ion batteries, it is advantageous to coat silicon particles with a layer of silicon dioxide. In this regard, the preparation method of the present invention can naturally form a layer of silicon dioxide on the surface of silicon nanoparticles without separate steps, which is very advantageous. Moreover, by adopting the method of the present invention, the properties of the silica shell can be conveniently influenced in step c) by adjusting specific conditions such as oxygen-containing gas, reaction time, and temperature.

Although the presence of a silica shell is advantageous in negative electrode material applications, it is understood that it is much less abundant than the elemental silicon core. The thickness of the silica shell is usually about several nm, such as less than 5 nm, and may be about 2-3 nm, while the particle size of the silicon nanomaterial is usually about tens to hundreds of nm.

Of course, according to actual needs, the product obtained by the method of the present invention can also be further processed.

The method of the present invention does not need to use highly polluting substances such as hydrofluoric acid and toxic organic solvents commonly used in the preparation of existing nano-silicon materials, and is environmentally friendly, easy to industrial production, and the electrochemical performance of the synthesized silicon nano-powder Excellent, can be directly used in lithium-ion battery negative electrode materials.

The metal mentioned in the method of the present invention is a metal capable of reducing silicon to a metal silicide. Preferably, the metal is selected from the group consisting of lithium, sodium, calcium, magnesium, zinc, iron or alloys thereof, and combinations thereof. The aforementioned metals are common, sufficiently reactive and economically viable metals.

In the method of the present invention, the metal may be in excess. Preferably, the molar ratio of silicon in the silicon-containing raw material to the metal is 1:3 to 1:20. Within this range, it can be ensured that the metal meets the excess requirement of the method of the present invention, and the excess metal will not cause waste.

In step b) of the present invention, the reaction time is generally 1-36h; the preferred reaction temperature is 450-650°C; the preferred reaction time is 1-20h, such as about 10h. If the temperature is too low, the reaction rate will be slow; if the temperature is too high, the energy consumption will be large. If the time is too short, the response will be insufficient; if the time is too long, the efficiency will be low, resulting in waste of time and energy.

In step c) of the present invention, the reaction time is usually 1-72h; the preferred reaction temperature is 500-650°C; the preferred reaction time is 1-20h, more preferably 5-10h. If the temperature is too low, the reaction rate will be slow; if the temperature is too high, the energy consumption will be large. If the time is too short, the response will be insufficient; if the time is too long, the efficiency will be low, resulting in waste of time and energy. The preferred reaction time is also conducive to the formation of silica shells that are beneficial to the performance of the negative electrode of lithium-ion batteries.

The oxygen-containing gas in step c) refers to a gas containing oxygen, such as pure oxygen. Preferably, the oxygen-containing gas may be air or a mixed gas of oxygen-nitrogen and oxygen-argon with an oxygen content of 1%-40%. As mentioned above, under the conditions of oxygen-containing atmosphere and temperature in step c), the finally formed silicon nanomaterial has a layer of silicon dioxide shell (film) on its surface. When used in lithium battery negative electrodes, the silicon dioxide film can improve the performance of the battery.

The silicon-containing raw materials of the present invention include common silicon-containing materials. Preferably, the silicon-containing raw material is silicon dioxide, silicic acid, silicate, silicon-containing minerals or simple silicon powder.

Preferably, the silica may be silica in the form of silica sand, industrial silica waste, silica molecular sieve, white carbon, glass fiber, microsilica, and combinations thereof. The direct use of industrial silicon dioxide waste as a raw material can especially effectively solve the problems of accumulation and pollution of industrial waste, and provides useful uses of industrial silicon dioxide waste.

The silicon-containing minerals with abundant reserves can be used as raw materials to directly prepare nano-silicon powder, the process is simple, the cost is low, and the production is easy to expand. The silicon-containing mineral is preferably selected from the group consisting of diatomaceous earth, albite, potassium feldspar, sepiolite, attapulgite, and combinations thereof.

It is also possible to directly use elemental silicon powder as the silicon-containing raw material. The method of the invention provides a simple and efficient way to prepare nano silicon powder material from elemental silicon powder.

The invention does not need to use specially synthesized raw materials such as silicon tetrachloride as the silicon source, expands the scope of the silicon source, and reduces the cost of the silicon source.

In the method of the present invention, part of the silicon-containing minerals is firstly pretreated to remove impurities such as grinding, water washing and/or pickling. More specifically, the pretreatment process is as follows: the silicon-containing raw ore is mechanically ground or crushed into a uniform powder with a hammer mill, and then mixed with water at a mass ratio of 1:1 to 100, more preferably 1: 4-50 mix and soak for a sufficient time for cleaning, such as 0.5-4 hours. Then, after pouring the supernatant, add a mineral acid solution such as 0.5M hydrochloric acid solution, stir at room temperature for 1-20 hours, preferably 5-10 hours, and then let stand for 1-50 hours, preferably 2-24 hours. Finally, after washing and drying, the cleaned silicon-containing minerals are obtained. It should be noted that in the method of the present invention, the silicon-containing minerals used as raw materials may not be pretreated, especially when diatomaceous earth, activated clay, etc. are used as raw materials, the above pretreatment process may not be required at all.

The product after step c) of the present invention obviously also includes metal oxides and the like. However, as those skilled in the art can imagine, the product of the present invention can be subjected to subsequent steps of pickling, separation, washing, drying, etc. to separate silicon nanoparticle powder. For example, the product of step c) can be washed with dilute hydrochloric acid, the metal oxides (such as magnesium oxide) etc. can be dissolved therein, and the solid silicon nanomaterials can be separated by centrifugation, etc., followed by washing with water and drying to obtain silicon nanoparticles.

The silicon nanomaterial prepared by the method of the present invention can be used in various applications of the silicon nanomaterial. In particular, the silicon nanoparticles obtained in the present invention have excellent electrical properties and can be used as negative electrode materials for lithium-ion batteries.

The present invention will be further described in detail through specific examples below, but it should be understood that these examples are only for the purpose of illustration, and are not intended to limit the scope of the present invention.

Example 1: Preparation of silicon nanomaterials using industrial silica waste as raw material.

Take 5 grams of industrial silica (China Tianxin Group Co., Ltd.) and 10 grams of magnesium powder, grind and mix evenly, put it into a 50mL stainless steel high-temperature kettle, seal it and place it in a muffle furnace for 10 hours at 500°C, and then cool it naturally After reaching room temperature, the reaction product was poured into a crucible and placed in a muffle furnace, and reacted at 600°C for 5 hours. The obtained product was washed with 1M dilute hydrochloric acid, washed with water and centrifuged at a speed of 4000 rpm for 5 minutes with a high-speed centrifuge, poured off the supernatant and washed with water for centrifugation, and circulated three times until the pH of the supernatant was 7. The washed sample Placed in a vacuum oven and dried at 80° C. overnight to obtain 2.2 grams of silicon nanopowder with a yield of 94%.

Adopt X-ray powder diffractometer (Philips X'Pert) to carry out X-ray diffraction analysis to the product of different reaction stage, Fig. 1 is the X-ray diffraction spectrum of this embodiment gained process product. Wherein from top to bottom: (1) the X-ray diffraction spectrogram of industrial silicon dioxide waste material, as seen from the figure, this industrial silicon dioxide waste material is amorphous phase silicon dioxide; (2) use excessive magnesium powder in high temperature kettle The X-ray diffraction spectrum of the product obtained after internal reduction, it can be seen from the figure that this product is mainly composed of magnesium silicide, magnesium oxide and unreacted magnesium; (3) The X-ray diffraction spectrum of the product calcined in air , it can be seen from the figure that the product is mainly composed of magnesium oxide and silicon, without the peak of magnesium silicide, which proves that the process is mainly that magnesium silicide is oxidized in oxygen to generate magnesium oxide and elemental silicon; (4) X-ray of the product after cleaning Diffraction spectrum, as can be seen from the figure, in the X-ray diffraction spectrum, 2θ has clearly visible diffraction peaks in the range of 10-80°, and all diffraction peaks can be indexed as cubic Si (JPCDS 77-2111). Combined with X-ray fluorescence spectrum (XPS, FIG. 2 ) analysis, it is shown that the product after cleaning is a silicon nanopowder, and a small amount of amorphous silicon dioxide is distributed on the surface.

The scanning electron micrographs (Fig. 3) and transmission electron micrographs (Fig. 4) of the final product show that the silicon powder prepared under this condition has a nanoporous structure, and the pores are evenly distributed in the range of several nanometers. A high-resolution transmission electron microscope image (FIG. 5) shows that the surface of the obtained material is coated with an amorphous silicon dioxide film with a thickness of about 3 nm.

Example 2: Preparation of silicon nanomaterials using diatomite raw ore as raw material.

As in implementing the scheme described in 1, take 1 gram of diatomite (with a silicon dioxide content of about 90%, Linjiang Hengtai Filter Aid Co., Ltd.) and 2 grams of magnesium powder, grind and mix them evenly, and put them into 20 mL of stainless steel high temperature In the kettle, seal it and place it in a muffle furnace for 10 hours at 500°C, and then cool it down to room temperature naturally. After opening the kettle, pour the reaction product into a crucible and place it in a muffle furnace, and react at 600°C for 10 hours. The obtained product was washed with 1M dilute hydrochloric acid, washed with water and centrifuged at a speed of 4000 rpm for 5 minutes with a high-speed centrifuge, poured off the supernatant and washed with water for centrifugation, and circulated three times until the pH of the supernatant was 7. The washed sample Place it in a vacuum oven and dry overnight at 80° C. to obtain >0.37 g of silicon nanopowder, with a yield of more than 88%.

X-ray diffraction ( FIG. 6 ), scanning electron microscope and transmission electron microscope ( FIG. 7 ) analysis were performed on the obtained silicon nanopowder, and results similar to those in Example 1 were obtained.

Embodiment 3: As described in Embodiment 1, the difference is that silicon nanopowder is prepared by using elemental silicon powder as the silicon source.

As in implementing the scheme described in 1, take 11.2 grams of industrial silicon powder (200 mesh, silicon content of 99%, Sinopharm Group) and 20.2 grams of magnesium powder, grind and mix evenly, put it into a 50mL stainless steel high-temperature kettle, seal it and place it in a horse React in a furnace at 500°C for 10h, then cool naturally to room temperature, pour the reaction product into a stainless steel pan and place it in a 5L reactor, and react at 600°C for 10h under air flow (the reactor is shown in Figure 8, 101 :Temperature Sensor). The obtained product was washed with 1M dilute hydrochloric acid, washed with water and centrifuged at a speed of 4000 rpm for 5 minutes with a high-speed centrifuge, poured off the supernatant and washed with water for centrifugation, and circulated three times until the pH of the supernatant was 7. The washed sample Place in a vacuum drying oven at 80° C. and dry overnight to obtain >10 grams of silicon nanopowder with a yield of more than 90%.

X-ray diffraction ( FIG. 9 ), scanning electron microscope ( FIG. 10 ) and transmission electron microscope ( FIG. 11 ) analysis were performed on the obtained silicon nanopowder, and results similar to those in Example 1 were obtained. A high-resolution transmission electron microscope image (FIG. 12) shows that the surface of the obtained material is coated with an amorphous silicon dioxide film with a thickness of about 2-3 nm.

Embodiment 4: The scheme as described in Embodiment 1, the difference is that silicic acid is used as the silicon source to prepare silicon nanopowder.

As in the implementation of the scheme described in 1, take 1.04 grams of silicic acid (the content of silicon dioxide is about 77%, Sinopharm Group) and 2.1 grams of magnesium powder, grind and mix evenly, put it into a 20mL stainless steel high-temperature kettle, seal it and place it in a muffle React in the furnace at 500°C for 10h, then cool down to room temperature naturally, pour the reaction product into a crucible and place it in a muffle furnace, and react at 600°C for 5h. The obtained product was washed with 1M dilute hydrochloric acid, washed with water and centrifuged at a speed of 4000 rpm for 5 minutes with a high-speed centrifuge, poured off the supernatant and washed with water for centrifugation, and circulated three times until the pH of the supernatant was 7. The washed sample Placed in a vacuum oven and dried overnight at 80° C. to obtain 0.35 g of silicon nanopowder with a yield of 94%.

The obtained silicon nanopowder was analyzed by X-ray diffraction ( FIG. 13 ), and a result similar to that of Example 1 was obtained. It is shown that the method described in the present invention can be further extended to use silicic acid and silicate as silicon source.

Application example 1: The obtained silicon nanopowder is used as the negative electrode material of lithium ion battery.

Add the silicon nanopowder obtained in the above-mentioned Example 1, sodium alginate adhesive, and conductive carbon black at a mass ratio of 6:2:2 (60mg:20mg:20mg) and put an appropriate amount of water into a ball mill jar for mixing, 250 RPM ball milled for 2 hours to form a uniform slurry, which was coated on a copper foil current collector, dried in vacuum at 80°C for 12 hours, and then pressed into a negative electrode sheet. The negative electrode sheet is used as the test electrode, the lithium sheet is the counter electrode, and the polyolefin porous membrane (Celgard2400) is used as the diaphragm, with ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 1) of 1M LiPF6 and a mixed solution of 10% fluoroethylene carbonate (FEC) additive as the electrolyte (Zhuhai Saiwei), and assembled into a CR2016 button battery, and the assembly of the CR2016 battery was completed in a glove box with an argon atmosphere. The assembled CR2016 button battery was tested for lithium-ion battery lithium storage performance at room temperature. The charge and discharge cut-off voltage is 0.005-1.5V. Fig. 14 is a charge-discharge curve diagram of the characteristics of the silicon nanopowder; Fig. 15 is a graph of the electrochemical cycle stability of the silicon nanopowder. It can be seen from the figure that under the current density of 3.6A/g, the internal capacity of 1000 cycles is stably maintained above 1000mAh/g. It can be known that the silicon nanopowder prepared by the embodiment 1 of the method of the present invention can be used as a high-performance lithium-ion battery negative electrode material.

Application example 2: the silicon nanopowder obtained in Example 3 is used as the negative electrode material of lithium ion battery.

Add the silicon nanopowder obtained in the above-mentioned Example 3, sodium alginate adhesive, and conductive carbon black at a mass ratio of 6:2:2 (60mg:20mg:20mg) and put an appropriate amount of water into a ball mill jar for mixing, 250 RPM ball milled for 2 hours to form a uniform slurry, which was coated on a copper foil current collector, dried in vacuum at 80°C for 12 hours, and then pressed into a negative electrode sheet. The negative electrode sheet was used as a test electrode, the lithium sheet was used as a counter electrode, and the polyolefin porous membrane (Celgard 2400) was used as a diaphragm, and ethylene carbonate (EC) and dimethyl carbonate (DMC) of 1M LiPF6 (volume ratio 1:1 ) and 10% fluoroethylene carbonate (FEC) additive as the electrolyte (Zhuhai Saiwei), assembled into a CR2016 button battery, and the assembly of the CR2016 battery was completed in an argon atmosphere glove box. The assembled CR2016 button battery was tested for lithium-ion battery lithium storage performance at room temperature. The charge and discharge cut-off voltage is 0.005-1.5V. FIG. 16 is a rate performance diagram of the silicon nanopowder; FIG. 17 is an electrochemical cycle stability diagram of the silicon nanopowder. It can be seen from the figure that at a current density of 36A/g, the capacity is above 1000mAh/g; at a current density of 1.8A/g, the capacity within 400 cycles is stably maintained above 1200mAh/g. It can be seen that the silicon nanopowder prepared by the embodiment 3 of the method of the present invention can be used as a high-performance lithium-ion battery negative electrode material.

The results of the examples show that the method of the present invention uses cheap raw materials to realize the preparation of silicon nanopowder, and the yield is higher than 90%. Appropriate scale-up experiments prove that this method has the possibility of easy scale-up production. When the obtained silicon nanopowder is used as a negative electrode material for lithium-ion batteries, it shows a much higher lithium storage capacity and better cycle stability than graphite negative electrodes, and can be used as a potential next-generation high-performance lithium-ion battery negative electrode material.

Claims (10)

1. A method for preparing silicon nanomaterials, characterized in that the method may further comprise the steps: a) milling and mixing silicon-containing raw materials with excess metal; b) heating the mixture obtained in a) to 300 to 700°C for reaction, reducing the silicon in the silicon-containing raw material to the form of metal silicide; c) heating the reaction product in b) to 450 to 700° C. for reaction under an oxygen-containing gas flow, and oxidizing the metal silicide therein into a core-shell silicon nanomaterial of elemental silicon core-silica shell. 2 . The method according to claim 1 , wherein the metal is selected from the group consisting of lithium, sodium, calcium, magnesium, zinc, iron, or alloys thereof, and combinations thereof. 3. The method according to claim 1, characterized in that the molar ratio of silicon in the silicon-containing raw material to the metal is 1:3 to 1:20. 4. The method according to claim 1, characterized in that, in step b), the reaction temperature is 450-650°C, and the reaction time is 1-20h. 5. The method according to claim 1, characterized in that, in step c), the reaction temperature is 500-650°C, and the reaction time is 1-20h. 6. The method according to claim 1, characterized in that, in step c), the oxygen-containing gas is air or a mixed gas of oxygen-nitrogen and oxygen-argon with an oxygen content of 1%-40%. 7. The method according to claim 1, wherein the silicon-containing raw material is silicon dioxide, silicic acid, silicate, silicon-containing minerals or elemental silicon powder. 8. The method according to claim 7, characterized in that the silica may be silica in the form of silica sand, industrial silica waste, silica molecular sieves, white carbon black, glass fibers, Silica fume, and their combinations. 9. The method according to claim 7, wherein the silicon-containing mineral is selected from the group consisting of diatomaceous earth, albite, potassium feldspar, sepiolite, attapulgite, and their The combination. 10. The method according to claim 7, characterized in that the silicon-containing mineral is pre-treated in advance, and the pre-treatment includes grinding and/or washing with water and/or pickling.