Silicon nanowire and preparation method and application thereof

Abstract

The application provides a silicon nanowire and a preparation method and application thereof, a silicon source is evaporated once to obtain silicon vapor; an aluminum source is evaporated twice to obtain aluminum vapor; the silicon vapor is passed into the aluminum vapor at a speed of 2-5 g / min to react, and a silicon nanowire is obtained; the preparation method of the silicon nanowire uses aluminum with a lower melting point and a reducing property as a silicon nanowire control agent, and the cost is controllable; and the preparation method is simple and reliable in process, and is convenient for large-scale mass production.

Description

Technical Field

[0001] This invention belongs to the field of lithium batteries, specifically relating to a silicon nanowire, its preparation method, and its application. Background Technology

[0002] Nanoscale materials exhibit a series of physical effects, such as quantum size effect, macroscopic quantum tunneling effect, Coulomb blocking effect, small size effect, and volume effect. Silicon nanowires possess all the physical effects of nanomaterials and are the primary representative of semiconductor nanomaterials. They have unique properties in the semiconductor field and physical properties that differ from bulk silicon materials, such as field emission, visible light luminescence, and thermal conductivity. They have a promising market for applications in sensors, field-effect transistors, photocatalysis, and batteries.

[0003] Compared to traditional graphite anode materials, silicon exhibits an extremely high specific capacity of 4200 mAh / g. Compared to lithium metal, silicon also possesses a high volumetric capacity due to its similar packing density in alloy materials. Furthermore, silicon nanowires, compared to silicon nanoparticles, show less lateral volumetric effect during lithium insertion / extraction and do not pulverize and lose electrical contact like silicon nanoparticles, resulting in better cycle stability.

[0004] Currently, there are many methods for preparing silicon nanowires, including chemical vapor deposition (CVD), molecular beam epitaxy (MEB), laser ablation (LA), oxide-assisted ablation (OGA), solution methods, and etching methods. According to the growth mode of silicon nanowires, their preparation methods can be divided into two categories: "top-down" and "bottom-up" techniques.

[0005] "Bottom-up" growth refers to the process of continuously depositing and growing nanostructures from the atomic level through self-assembly. This mainly includes chemical vapor deposition (CVD), molecular beam epitaxy (MBE), laser ablation, oxide-assisted etching (OE), and solution etching. "Top-down" growth begins with etching the template to shape the sample into nanostructures of the desired size; it can be likened to carving in stone, where the substrate is gradually eroded to achieve the desired shape. Methods include electron beam lithography (EBL), nanoimprint lithography, and metal-assisted chemical etching (MAC).

[0006] CN110950323A discloses a carbon nanotube-silicon carbide nanowire composite material, which is a one-dimensional nanostructure in which silicon carbide nanowires grow along the length of the carbon nanotubes. The preparation method involves placing a pretreated substrate in a tube furnace and depositing carbon nanotubes on the substrate using chemical vapor deposition (CVD); then, silicon carbide nanowires are deposited on the carbon nanotubes using CVD to obtain the carbon nanotube-silicon carbide nanowire composite material. This method fully utilizes the VLS growth mechanism followed by both carbon nanotubes and silicon carbide nanowires during CVD preparation, thus producing a novel one-dimensional nanostructure material.

[0007] CN107445167A discloses a method for preparing ultralong silicon carbide nanowires, comprising the following steps: dispersing silicon suboxide and organic carbon in anhydrous ethanol at a weight ratio of 1:2-2:1; evaporating and drying the anhydrous ethanol; mixing reduced iron powder and silicon suboxide at a weight ratio of 1:5-20; placing the mixture in a ceramic boat and then in a tube furnace under an argon atmosphere; sintering at 1000-1400℃ for 1-4 hours; finally, soaking in hydrofluoric acid for 2 hours; washing, centrifuging, and drying to obtain silicon carbide nanowires. This method utilizes SiO2 as a reactant and template, a series of materials providing carbon sources as reducing agents and structural supports, and iron as a catalyst to prepare silicon carbide nanowires through a co-reduction method with iron.

[0008] CN1590599A A method for preparing silicon nanowires, comprising: (1) Preparation of silicon source for evaporation: silicon (Si) powder with a purity of 99.99% and silicon dioxide (SiO2) powder with a purity of 99.99% are mixed in a weight ratio of 1:1, and then the Si+SiO2 powder is pressed into a sheet by a tablet press and placed in the source crucible of an ultra-high vacuum electron beam system for vacuuming and preparation; (2) Preparation of silicon nanowire growth substrate: SiO2 / Si(111) or SiO2 with a purity of 100-600nm is selected as the growth substrate of silicon nanowires, and silicon nanowires are grown in vacuum.

[0009] However, existing technologies have certain drawbacks, such as high requirements for raw materials, often requiring a purity of 99.99%; complex processes, requiring the mixing and pressing of silicon powder and silica powder; the need for expensive equipment such as high vacuum and electron beam; and low growth efficiency.

[0010] Therefore, there is a need for a method to produce silicon nanowires that has low requirements for raw materials, controllable costs, simple and reliable processes, and is easy to mass-produce. Summary of the Invention

[0011] The purpose of this invention is to provide a silicon nanowire, its preparation method, and its application. The method involves first evaporating a silicon source to obtain silicon vapor; then second evaporating an aluminum source to obtain aluminum vapor; and finally, passing the silicon vapor into the aluminum vapor at a rate of 2-5 g / min to react and obtain silicon nanowires. The silicon nanowire preparation method of this invention uses aluminum, which has a low melting point and reducing properties, as a silicon nanowire control agent, resulting in controllable costs. Furthermore, the preparation method is simple, reliable, and suitable for large-scale mass production.

[0012] To achieve this objective, the present invention adopts the following technical solution:

[0013] One objective of this invention is to provide a method for preparing silicon nanowires, the method comprising the following steps:

[0014] (1) Silicon vapor is obtained by evaporating the silicon source once;

[0015] (2) Aluminum source is subjected to secondary evaporation to obtain aluminum vapor;

[0016] (3) The silicon vapor is passed into aluminum vapor at a rate of 2-5 g / min to carry out the reaction and obtain silicon nanowires.

[0017] It is worth noting that in this invention, aluminum, which has a low melting point and reducing properties, is used as a control agent for the growth of silicon nanowires and also plays a catalytic role. Silicon nanowires begin to grow when silicon vapor and aluminum vapor meet. The requirements for the purity of raw materials are not high, and the cost is controllable. Moreover, the preparation method is simple and reliable, which is convenient for large-scale mass production.

[0018] It is worth noting that in step (3), the rate at which silicon vapor is introduced into aluminum vapor is 2-5 g / min, for example, it can be 2 g / min, 2.2 g / min, 2.4 g / min, 2.6 g / min, 2.8 g / min, 3 g / min, 3.2 g / min, 3.4 g / min, 3.6 g / min, 3.8 g / min, 4 g / min, 4.2 g / min, 4.4 g / min, 4.6 g / min, 4.8 g / min, 5 g / min, etc. In this invention, the rate at which silicon vapor is introduced into aluminum vapor is 2-5 g / min. If it is higher than 5 g / min, it will result in a thicker diameter and shorter length of silicon nanowires; if it is lower than 2 g / min, it will result in thinner and shorter length of silicon nanowires.

[0019] As a preferred technical solution of the present invention, the purity of the silicon source in step (1) is ≥95%, for example, it can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 99.9%, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0020] Preferably, the silicon source in step (1) includes any one or a combination of at least two of silicon powder, silicon ingot, silicon dioxide or silicon suboxide. Typical but non-limiting examples of such combinations include combinations of silicon powder and silicon ingot, combinations of silicon powder and silicon dioxide, combinations of silicon powder and silicon suboxide, combinations of silicon ingot and silicon dioxide, combinations of silicon ingot and silicon suboxide, and combinations of silicon dioxide and silicon suboxide.

[0021] As a preferred technical solution of the present invention, the temperature of the first evaporation in step (1) is 1600-2000℃, for example, it can be 1600℃, 1650℃, 1700℃, 1750℃, 1800℃, 1850℃, 1900℃, 2000℃, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0022] As a preferred technical solution of the present invention, the aluminum source in step (2) includes any one or at least two of aluminum plates, aluminum powder or aluminum wire. Typical but non-limiting examples of the combination include the combination of aluminum plates and aluminum powder, the combination of aluminum plates and aluminum wire, and the combination of aluminum powder and aluminum wire.

[0023] Preferably, the surface of the aluminum source in step (2) contains a coating.

[0024] Preferably, the material of the coating includes gold and / or silver.

[0025] As a preferred technical solution of the present invention, the temperature of the secondary evaporation in step (2) is 500-800℃, for example, it can be 500℃, 520℃, 550℃, 580℃, 600℃, 630℃, 650℃, 670℃, 700℃, 730℃, 50℃, 780℃, 800℃, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0026] Preferably, the secondary evaporation in step (2) is carried out in an argon atmosphere.

[0027] As a preferred technical solution of the present invention, the reaction temperature in step (3) is 500-800℃, for example, it can be 500℃, 520℃, 550℃, 580℃, 600℃, 630℃, 650℃, 670℃, 700℃, 730℃, 50℃, 780℃, 800℃, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0028] Preferably, the reaction time in step (3) is 1-5 hours, for example, it can be 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.3 hours, 2.5 hours, 2.7 hours, 3 hours, 3.2 hours, 3.5 hours, 3.8 hours, 4 hours, 4.2 hours, 4.5 hours, 4.7 hours, 5 hours, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0029] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0030] (1) Silicon vapor is obtained by heating a silicon source with a purity of ≥95% to 1600-2000℃ and evaporating it once;

[0031] The silicon source includes any one or a combination of at least two of silicon powder, silicon ingot, silicon dioxide, or silicon suboxide;

[0032] (2) The aluminum source is heated to 500-800℃ and subjected to secondary evaporation under an argon atmosphere to obtain aluminum vapor;

[0033] The aluminum source includes any one or a combination of at least two of aluminum plates, aluminum powder, or aluminum wire; the surface of the aluminum source contains a gold and / or silver plating layer.

[0034] (3) Silicon vapor is introduced into aluminum vapor at a rate of 2-5 g / min and reacted at 500-800℃ for 1-5 h to obtain silicon nanowires.

[0035] A second objective of this invention is to provide a silicon nanowire obtained by the preparation method described in the first objective, wherein the silicon nanowire has a diameter of <200 nm and a length of >100 μm.

[0036] A third objective of this invention is to provide an application of the silicon nanowires described in the second objective, wherein the silicon nanowires are used to prepare the negative electrode sheet of a lithium battery.

[0037] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The method for preparing silicon nanowires described in this invention does not require high purity of raw materials. It uses aluminum, which has a low melting point and is reducing, as a silicon nanowire control agent, and the cost is controllable.

[0040] (2) The preparation method of silicon nanowires described in this invention is simple and reliable, and is easy to mass-produce. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the evaporation reaction apparatus described in this invention;

[0042] Among them, 1-evaporation chamber; 2-reaction chamber; 3-pipeline; 4-silicon source; 5-aluminum source;

[0043] Figure 2 This is a scanning electron microscope image of the silicon nanowire described in Example 1 of the present invention, magnified at 20000.

[0044] Figure 3 This is a scanning electron microscope image of the silicon nanowire described in Example 1 of the present invention, magnified to 1000. Detailed Implementation

[0045] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0046] It is worth noting that in all the specific embodiments described in this invention, the following methods are employed: Figure 1 The evaporation reaction apparatus shown is completed. The apparatus includes an evaporation chamber 1 and a reaction chamber 2, which are connected by a pipe 3. Silicon source 4 is evaporated once to obtain silicon vapor; aluminum source 5 is evaporated a second time to obtain aluminum vapor; the silicon vapor is then introduced into reaction chamber 2 through pipe 3 to react with the aluminum vapor, resulting in silicon nanowires. Figure 1 The direction of the middle arrow indicates the flow direction of silicon vapor.

[0047] Example 1

[0048] This embodiment provides a silicon nanowire and its preparation method, the preparation method comprising the following steps:

[0049] (1) Heat 3 kg of 98% pure silicon dioxide to 1800℃ and evaporate it once to obtain silicon dioxide vapor;

[0050] (2) Aluminum vapor is obtained by heating an aluminum plate with a silver coating to 700°C and evaporating it under an argon atmosphere.

[0051] (3) Silica vapor was introduced into aluminum vapor at a rate of 2 g / min and reacted at 750 °C for 3 h to obtain silicon nanowires.

[0052] The scanning electron microscope image of the silicon nanowires obtained in this embodiment, with a magnification of 20000, is shown below. Figure 2 As shown, by Figure 2 It can be seen that the diameter of the silicon nanowires obtained in this embodiment is approximately 100-200 nm; Figure 3 This is a scanning electron microscope (SEM) image of the silicon nanowires obtained in this embodiment, magnified to 1000. Figure 3 It can be seen that the silicon nanowires produced in this embodiment are relatively uniform.

[0053] Example 2

[0054] This embodiment provides a silicon nanowire and its preparation method, the preparation method comprising the following steps:

[0055] (1) 2 kg of 95% pure silicon powder was heated to 2000℃ and evaporated once to obtain silicon vapor;

[0056] (2) Aluminum vapor is obtained by heating an aluminum block with a gold plating layer on its surface to 800°C and evaporating it under an argon atmosphere.

[0057] (3) Silicon vapor was introduced into aluminum vapor at a rate of 5 g / min and reacted at 800 °C for 1 h to obtain silicon nanowires.

[0058] Example 3

[0059] This embodiment provides a silicon nanowire and its preparation method, the preparation method comprising the following steps:

[0060] (1) 1 kg of 96% pure silicon powder and 2 kg of 96% pure silicon dioxide are heated to 1700℃ and evaporated once to obtain silicon vapor;

[0061] (2) Aluminum vapor is obtained by heating an aluminum plate with a silver coating to 600°C and evaporating it under an argon atmosphere.

[0062] (3) Silicon vapor was introduced into aluminum vapor at a rate of 3 g / min and reacted at 600 °C for 2 h to obtain silicon nanowires.

[0063] Example 4

[0064] This embodiment provides a silicon nanowire and its preparation method, the preparation method comprising the following steps:

[0065] (1) 2.1 kg of silicon block with a purity of 97.2% was heated to 1600℃ and evaporated once to obtain silicon vapor;

[0066] (2) Aluminum vapor is obtained by heating an aluminum plate with a gold coating to 500°C and evaporating it under an argon atmosphere.

[0067] (3) Silicon vapor was introduced into aluminum vapor at a rate of 3 g / min and reacted at 500 °C for 5 h to obtain silicon nanowires.

[0068] Example 5

[0069] This embodiment provides a silicon nanowire and its preparation method, the preparation method comprising the following steps:

[0070] (1) 1.5 kg of silicon powder with a purity of 98.1% and 1 kg of silicon dioxide with a purity of 98% are heated to 1850℃ and evaporated once to obtain silicon vapor;

[0071] (2) Aluminum vapor is obtained by heating an aluminum plate with a gold coating to 650°C and evaporating it under an argon atmosphere.

[0072] (3) Silicon vapor was introduced into aluminum vapor at a rate of 4 g / min and reacted at 650 °C for 2.5 h to obtain silicon nanowires.

[0073] Comparative Example 1

[0074] This comparative example provides a silicon nanowire and its preparation method, which is the same as the preparation method described in Example 1, except that the rate at which silicon vapor is introduced into aluminum vapor is changed from 2 g / min to 1 g / min.

[0075] Comparative Example 2

[0076] This comparative example provides a silicon nanowire and its preparation method, which is the same as the preparation method described in Example 1, except that the rate at which silicon vapor is introduced into aluminum vapor is changed from 2 g / min to 6 g / min.

[0077] The size and yield of the silicon nanowires obtained in the above embodiments and comparative examples were tested using the following methods:

[0078] Dimensions: Average diameter of silicon nanowires was measured using scanning electron microscopy (SEM); average length of silicon nanowires was measured using Image Pro Plus 6.0.

[0079] Yield: The ratio of the mass M of the obtained silicon nanowires to the mass M0 of the initial silicon source is the yield, i.e., yield = M / M0 × 100%.

[0080] The test results of the silicon nanowires obtained in the above embodiments and comparative examples are listed in Table 1.

[0081] Table 1

[0082] project Average diameter / nm Average length / μm Theoretical yield / % Yield / % Example 1 146 178.3 53.3 48.3 Example 2 152.3 187.1 100 98.5 Example 3 147.3 177.2 68.9 65.2 Example 4 158.3 195.3 100 98.1 Example 5 149.6 182.1 81.3 77.6 Comparative Example 1 136.5 149.4 100 97.0 Comparative Example 2 164.1 136.3 100 92.2

[0083] It is worth noting that the theoretical yield is the mass percentage of silicon in the raw material.

[0084] The following points can be drawn from Table 1:

[0085] (1) As can be seen from Examples 1-5, the silicon nanowires obtained by the silicon nanowire preparation method of the present invention have an average diameter of about 150 nm and an average length of about 180 μm.

[0086] (2) Comparing Example 1 with Comparative Examples 1 and 2, it can be found that, since the rate at which silicon vapor is introduced into aluminum vapor in Comparative Example 1 is 1 g / min, which is lower than the preferred rate of 2-5 g / min of the present invention, the average diameter of silicon nanowires becomes smaller and the average length becomes shorter; since the rate at which silicon vapor is introduced into aluminum vapor in Comparative Example 2 is 6 g / min, which exceeds the preferred rate of 2-5 g / min of the present invention, the average diameter of silicon nanowires increases and the average length becomes shorter.

[0087] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing silicon nanowires, characterized in that, The preparation method includes the following steps: (1) Silicon vapor is obtained by evaporating the silicon source once; (2) Aluminum vapor is obtained by secondary evaporation of the aluminum source; (3) The silicon vapor is introduced into aluminum vapor at a rate of 2-5 g / min to carry out the reaction and obtain silicon nanowires.

2. The method for preparing silicon nanowires according to claim 1, characterized in that, The purity of the silicon source in step (1) is ≥95%.

3. The method for preparing silicon nanowires according to claim 1, characterized in that, The silicon source in step (1) includes any one or a combination of at least two of silicon powder, silicon ingot, silicon dioxide or silicon suboxide.

4. The method for preparing silicon nanowires according to claim 1, characterized in that, The temperature of the first evaporation in step (1) is 1600-2000℃.

5. The method for preparing silicon nanowires according to claim 1, characterized in that, The aluminum source in step (2) includes any one or a combination of at least two of aluminum plates, aluminum powder or aluminum wire.

6. The method for preparing silicon nanowires according to claim 1, wherein the surface of the aluminum source in step (2) contains a coating.

7. The method for preparing silicon nanowires according to claim 6, wherein the material of the coating includes gold and / or silver.

8. The method for preparing silicon nanowires according to claim 1, characterized in that, The temperature of the secondary evaporation in step (2) is 500-800℃.

9. The method for preparing silicon nanowires according to claim 1, wherein the secondary evaporation in step (2) is carried out in an argon atmosphere.

10. The method for preparing silicon nanowires according to claim 1, characterized in that, The reaction temperature in step (3) is 500-800℃.

11. The method for preparing silicon nanowires according to claim 1, characterized in that, The reaction time in step (3) is 1-5 hours.

12. The method for preparing silicon nanowires according to claim 1, characterized in that, The preparation method includes the following steps: (1) Silicon vapor is obtained by heating a silicon source with a purity of ≥95% to 1600-2000℃ and evaporating it once; The silicon source includes any one or a combination of at least two of silicon powder, silicon ingot, silicon dioxide, or silicon suboxide; (2) The aluminum source is heated to 500-800℃ and subjected to secondary evaporation under an argon atmosphere to obtain aluminum vapor; The aluminum source includes any one or a combination of at least two of aluminum plates, aluminum powder, or aluminum wire; the surface of the aluminum source contains a gold and / or silver plating layer. (3) Silicon vapor is introduced into aluminum vapor at a rate of 2-5 g / min and reacted at 500-800℃ for 1-5 h to obtain silicon nanowires.

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