Method for preparing silicon nanowire by using metal halide, prepared silicon nanowire and application

Abstract

The invention belongs to the technical field of nano material preparation. The invention provides a method for preparing a silicon nanowire by using a metal halide, the prepared silicon nanowire and application, and the method comprises the following steps: uniformly mixing a metal reducing agent, a silicon source and the metal halide, and carrying out heating reaction to obtain the silicon nanowire. According to the invention, the metal halide is used as the catalyst to replace a pure metal simple substance catalyst used in the prior art, so that the temperature of a reaction system can be greatly reduced, the problems of reaction uniformity and high energy consumption are effectively solved, and a relatively low-temperature preparation environment enables the silicon nanowire to be more strictly controllable.

Description

Technical Field

[0001] The invention belongs to the field of nano material preparation, and relates to a method for preparing silicon nanowires by utilizing metal halides, the prepared silicon nanowires and uses thereof. Background Art

[0002] Compared with traditional graphite negative electrode materials, silicon has an extremely high mass specific capacity of 4200mAh / g. Compared with metallic lithium, silicon also has a high volume specific capacity because its stacking density in alloy materials is similar to that of lithium. However, silicon materials face the following problems in actual use: when lithium ions are fully embedded in the silicon matrix, the silicon matrix will produce severe volume expansion (>300%), which will cause the silicon negative electrode to pulverize after multiple charge and discharge cycles, and then cause the silicon to lose electrical contact with the current collector, and the battery capacity will decay rapidly; the volume effect generated by the silicon negative electrode during the cycle process will cause the SEI film to rupture and regenerate repeatedly, which will lead to a decrease in the coulomb efficiency of the battery and an increase in the ion transfer resistance.

[0003] In order to alleviate the volume effect, the preparation and application of silicon nanowires have become an important development trend. Compared with nano-silicon particles, silicon nanowires do not have obvious lateral volume effects during the lithium insertion and extraction process, and they will not be crushed and lose electrical contact like nano-silicon particles, so the cycle stability is better. When the material scale reaches the nanoscale, a series of physical effects will appear, such as quantum size effect, macroscopic quantum tunneling effect, Coulomb blockade effect, small size effect and volume effect. Silicon nanowires have all the above physical effects of nanomaterials and are the primary representative of semiconductor nanomaterials. They have special properties in the semiconductor field. They are not only applied in the negative electrode field, but also have physical properties different from bulk silicon materials in field emission, visible photoluminescence and thermal conductivity, and have great development potential.

[0004] At present, there are many methods for preparing silicon nanowires, mainly including: chemical vapor deposition (CVD), molecular beam epitaxy (MEB), laser ablation (LA), oxide-assisted (OGA), solution method and etching method. According to the growth mode, it can be divided into two categories, namely "top-down" and "bottom-up" technology. "Bottom-up" is a mode in which nanostructures are continuously deposited and grown from the atomic level through self-assembly, mainly including chemical vapor deposition, molecular beam epitaxy, laser ablation, oxide-assisted method and solution method. "Top-down" is first to etch the template for pretreatment, and etch the sample into a growth mode of nanostructures of the desired size. It can be likened to carving with stone, the substrate is gradually corroded, and finally reaches the desired shape. Its methods mainly include electron beam lithography (EBL), nanoimprint lithography and metal-assisted chemical etching technology.

[0005] Among them, when growing silicon nanowires by vapor deposition (CVD), metal catalysts are usually required, such as gold (boiling point 2500℃), silver (boiling point 1955℃), copper (boiling point 2360℃) and titanium (boiling point 3287℃). The metal catalyst is deposited on a substrate or carrier with a thickness of several nanometers by electron beam evaporation, thermal evaporation or magnetron sputtering. Then the metal film is heated to form metal liquid beads (i.e., seeds) with a diameter of tens of nanometers, which are evenly distributed on the substrate. When the silicon source in the gas phase is dissolved into the seeds in an atomic state and exceeds the saturated solubility of silicon in the seeds, silicon precipitates from the seeds in the form of silicon wires, and the diameter of the silicon wires is usually smaller than the diameter of the metal liquid beads. This process is called the VLS mechanism for growing silicon nanowires, where VLS refers to the silicon source in the gas phase (V), the metal catalyst in the liquid phase (L) and the silicon nanowire in the solid phase (S). This VLS mechanism requires that the growth temperature of the silicon wire be controlled above the eutectic point of silicon-metal. For example, when copper is used as a catalyst, the temperature must be above the eutectic point of copper-silicon alloy (803°C); when titanium is used as a catalyst, the temperature must be controlled above the eutectic point of titanium-silicon alloy (1318°C). The preparation process is relatively complicated, and the gasification temperature required for these metal catalysts is very high, resulting in high energy consumption and high cost of the entire process. In addition, there will be problems with uneven distribution of the catalyst, which reduces the uniformity of the reaction and production efficiency.

[0006] Therefore, there is still a need to develop a new technical solution for producing silicon nanowires to achieve controllable growth of silicon nanowires with lower energy consumption and cost. Summary of the invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing silicon nanowires using metal halides, the prepared silicon nanowires and their uses, the method comprising uniformly mixing a metal reducing agent, a silicon source and a metal halide, heating the mixture for reaction, and obtaining silicon nanowires. The present invention uses metal halides as catalysts to replace the pure metal catalysts used in the prior art, which can significantly reduce the temperature of the reaction system, effectively solve the problems of reaction uniformity and high energy consumption, and the relatively low temperature preparation environment makes the silicon nanowires more strictly controllable.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing silicon nanowires using metal halides, the method comprising the following steps:

[0010] The metal reducing agent, silicon source and catalyst are uniformly mixed, wherein the catalyst comprises metal halide, and heated to react to obtain silicon nanowires.

[0011] The present invention uses metal halides instead of monomer metals (metallic elements) as catalysts, and utilizes the gas phase reduction reaction between metal reducing agents and metal halides to generate monomer metal catalysts in situ. Due to the in-situ generation, the uniformity in the system is better, and the boiling point of metal halides is significantly lower than that of monomer metals. Therefore, using metal halides instead of monomer metals can significantly reduce the system temperature, effectively reduce energy consumption and costs, and the relatively low temperature reaction environment is conducive to the controllable synthesis of silicon nanowires.

[0012] Specifically, the metal reducing agent (such as zinc or aluminum) reduces the silicon source (such as silicon tetrachloride) to generate silicon atoms in the gas phase, and at the same time reduces the metal halide (such as copper chloride or titanium chloride, etc.) to generate copper or titanium atoms in the gas phase in situ. The temperature required for this gas phase reduction reaction is much lower than the boiling point of directly evaporating the monomer metal.

[0013] Subsequently, during the catalyst nucleation process, metal atoms such as copper (or titanium) acting as catalysts self-condense, and zinc atoms acting as reducing agents self-condense to form a single catalyst nucleus, or metal catalyst copper atoms (or titanium atoms) and zinc are combined in situ to form alloy nucleus droplets (or titanium and aluminum are combined in situ to form titanium-aluminum alloy droplets). As the nuclei continue to grow, the nuclei floating in the gas phase are implanted on the substrate or on the inner wall of the cavity to form semicircular droplets (i.e., seeds). During the nucleation process, gaseous silicon atoms continuously dissolve into metal seeds to form binary silicon alloys or ternary silicon alloys. When the concentration of silicon in the seeds exceeds its saturated solubility, silicon atoms precipitate from the seeds and grow into silicon nanowires.

[0014] Compared with the metal halide used in the present invention, when a single metal (such as zinc or copper) is used directly as a catalyst, the surface tension of zinc is small and close to the critical surface tension, and the droplets are easy to spread, resulting in instability of the seed crystal, and it is easy to generate silicon wires with a thicker diameter or irregular shape, or even silicon rods with a diameter of micrometers. Compared with the copper single metal catalyst, the melting and boiling points of the copper chloride used in the present invention are very low and it is easy to vaporize. The present invention effectively reduces the temperature of the reaction system by using the in-situ generated copper-zinc alloy catalyst and the low liquid phase limit temperature of the copper-zinc-silicon ternary alloy system. For example, when the molar fractions of the Cu-Zn-Si ternary alloy are 17.4% Cu, 1.4% Si and 81.2% Zn respectively, the liquid phase limit temperature (i.e., the ternary eutectic temperature) is 665°C. In comparison, the eutectic temperature of the copper-silicon binary alloy system is 803°C, which is 138°C higher than the ternary alloy. In other words, the ternary system requires lower temperatures to grow silicon nanowires through the VLS mechanism, has a wider process temperature window, and is easier to control the growth of silicon wires. Similarly, when titanium tetrachloride is used as a catalyst, metallic aluminum is used as a reducing agent to reduce the silicon source (silicon tetrachloride) and titanium tetrachloride in the gas phase to generate silicon and titanium atoms. Titanium, aluminum, and silicon combine in situ to form ternary alloy seeds. The liquid phase limit temperature of the Ti-Al-Si ternary alloy can be as low as 573°C. In comparison, the eutectic temperatures of the Ti-Si and Al-Si binary systems are 1318°C and 577.1°C, respectively. The process temperature window of the ternary system is wider and easier to control.

[0015] It should also be noted that the prior art is based on the synthesis of a monomeric metal catalyst on a carrier or substrate by spraying, spin coating, electroplating, or vapor deposition, and then forming a metal liquid bead (i.e., seed crystal) through heat treatment. The gaseous silicon source dissolves into the seed crystal and precipitates therefrom to grow into silicon nanowires. Unlike the commonly used methods in the prior art, the present invention does not require the catalyst to be additionally prepared into a layer on the carrier or substrate.

[0016] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0017] As a preferred technical solution of the present invention, the metal halide is denoted as MX y ;

[0018] Wherein, M comprises any one of zinc, iron, cobalt, nickel, tin, lead, copper, silver, gold or titanium, or a combination of at least two thereof, and typical but non-limiting examples of the combination include a combination of zinc and iron, a combination of zinc and cobalt, a combination of zinc and nickel, a combination of zinc and tin, a combination of zinc and lead, a combination of zinc and copper, a combination of zinc and silver, a combination of zinc and gold, a combination of zinc and titanium, a combination of iron and cobalt, a combination of nickel and tin, a combination of lead and copper, a combination of copper and silver, a combination of silver and gold, a combination of copper and gold, or a combination of titanium and copper.

[0019] X includes any one of Cl, Br or I, or a combination of at least two of them. Typical but non-limiting examples of the combination include a combination of Cl and Br, a combination of Cl and I, or a combination of Br and I.

[0020] 1≤y≤4, for example, 1, 2, 3 or 4.

[0021] Preferably, the metal halide comprises any one of zinc chloride, lead chloride, silver chloride, cupric chloride, cuprous chloride, ferric chloride, ferrous chloride, gold chloride, titanium chloride, zinc bromide, lead bromide, silver bromide, copper bromide, ferric bromide, gold bromide or titanium bromide, or a combination of at least two thereof. Typical but non-limiting examples of the combination include a combination of zinc chloride and lead chloride, a combination of silver chloride and cupric chloride, a combination of cuprous chloride and cupric chloride, a combination of ferric chloride and ferrous chloride, a combination of gold chloride and titanium chloride, a combination of titanium chloride and cupric chloride, a combination of titanium chloride and zinc chloride, a combination of zinc chloride and cupric chloride, a combination of zinc bromide and zinc chloride, a combination of lead bromide and silver bromide, a combination of copper bromide and ferric bromide, a combination of copper bromide and zinc chloride, a combination of gold bromide and titanium bromide, a combination of titanium bromide and zinc bromide, or a combination of zinc bromide and copper bromide.

[0022] As a preferred technical solution of the present invention, the molar ratio of the metal reducing agent to the silicon source is (2-3):1, for example 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3:1, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0023] Preferably, the molar ratio of the metal reducing agent to the metal halide is (2-50):1, for example 2:1, 4:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, 22:1, 24:1, 26:1, 28:1, 30:1, 32:1, 34:1, 36:1, 38:1, 40:1, 42:1, 44:1, 46:1, 48:1 or 50:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0024] The primary effect of the amount of metal halide used is that the more metal halide is used, the more nuclei are formed, and the thinner the diameter of the resulting silicon nanowires is. However, the secondary effect is more complicated, which may change the composition and melting point of the seed crystals, as well as the solubility of silicon in the seed crystals, thereby affecting the growth of silicon wires.

[0025] As a preferred technical solution of the present invention, the metal reducing agent includes a metal element, and the metal activity of the metal element is stronger than the metal activity of the metal element in the metal halide.

[0026] As a preferred technical solution of the present invention, the metal element includes any one of sodium, potassium, lithium, calcium, magnesium, aluminum or zinc, or a combination of at least two of them. Typical but non-limiting examples of the combination include a combination of sodium and potassium, a combination of sodium and lithium, a combination of calcium and magnesium, a combination of calcium and zinc, a combination of potassium and lithium, a combination of lithium and magnesium, a combination of lithium and aluminum, a combination of zinc and magnesium, a combination of zinc and aluminum, or a combination of aluminum and magnesium.

[0027] Preferably, the metal element is metal powder.

[0028] Preferably, the silicon source comprises any one of silicon tetrachloride, trichlorosilane, dichlorosilane, oligomeric silane or elemental silicon, or a combination of at least two thereof. Typical but non-limiting examples of the combination include a combination of silicon tetrachloride and trichloromethane, a combination of silicon tetrachloride and dichloromethane, a combination of silicon tetrachloride and oligomeric silane, a combination of oligomeric silane and elemental silicon, a combination of elemental silicon and dichlorosilane, a combination of elemental silicon and trichlorosilane, or a combination of trichlorosilane and oligomeric silane.

[0029] Preferably, the silicon tetrachloride is in liquid state.

[0030] As a preferred technical solution of the present invention, the temperature of the heating reaction is 400-1000°C, for example, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 550°C, 580°C, 600°C, 640°C, 670°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are equally applicable.

[0031] Preferably, the insulation time of the heating reaction is 5 to 10 hours, for example 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0032] Preferably, the heating rate of the heating reaction is 1 to 8°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min or 8°C / min, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0033] As a preferred technical solution of the present invention, the method further comprises cleaning and drying the obtained silicon nanowires.

[0034] Preferably, the cleaning agent comprises hydrochloric acid and / or water.

[0035] Preferably, the drying temperature is 40-80°C, such as 40°C, 50°C, 60°C, 70°C or 80°C, but is not limited to the listed values, and other values ​​not listed within the above range are also applicable.

[0036] As a preferred technical solution of the present invention, the method comprises:

[0037] Mixing powdered sodium, potassium, lithium, calcium, magnesium, aluminum or zinc metal elements or a combination of at least two of them as a metal reducing agent, with a liquid silicon source, such as silicon tetrachloride, trichlorosilane, dichlorosilane, oligomeric silane or elemental silicon or a combination of at least two of them, and a metal halide as a catalyst, and controlling the molar ratio of the metal reducing agent to the silicon source to be (2-3):1, and the molar ratio of the metal reducing agent to the metal halide to be (2-50):1, and the metal activity of the metal element is stronger than the metal activity of the metal element in the metal halide; the metal halide includes zinc chloride, lead chloride, silver chloride, cupric chloride, cuprous chloride, ferric chloride, ferrous chloride, gold chloride, titanium chloride, zinc bromide, lead bromide, silver bromide, copper bromide, ferric bromide, gold bromide or titanium bromide or a combination of at least two of them;

[0038] Then, the temperature is raised to a heating temperature of 400-1000° C. at a heating rate of 1-8° C. / min and kept for 5-10 hours. The obtained sample is washed with hydrochloric acid and water and dried at 40-80° C. to obtain silicon nanowires.

[0039] In a second aspect, the present invention provides a silicon nanowire, which is prepared by the method described in the first aspect.

[0040] In a third aspect, the present invention provides a battery negative electrode, wherein the battery negative electrode contains the silicon nanowires described in the second aspect.

[0041] As a preferred technical solution of the present invention, compared with the prior art solution, the present invention has at least the following beneficial effects:

[0042] The present invention uses metal halides instead of monomer metals (metallic elements) as catalysts, and utilizes the gas phase reduction reaction between metal reducing agents and metal halides to generate monomer metal catalysts in situ. Due to the in-situ generation, the uniformity in the system is better, and the boiling point of metal halides is significantly lower than that of monomer metals. Therefore, in the process of preparing silicon nanowires, metal halides are used instead of monomer metals directly, which can significantly reduce the system temperature, effectively reduce energy consumption and costs, and the silicon nanowires prepared in a relatively low temperature reaction environment are strictly controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 and Figure 2 3 is a scanning electron microscope image of the silicon nanowires obtained in Example 1. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0045] Example 1

[0046] This embodiment provides a method for preparing silicon nanowires using metal halides, the method comprising the following steps:

[0047] The metal reducing agent zinc powder is evenly mixed with the silicon source liquid silicon tetrachloride and the metal halide copper chloride, and the molar ratio of the metal reducing agent to the silicon source is controlled to be 2.1:1, and the molar ratio of the metal reducing agent to the metal halide is controlled to be 10:1. Then, the temperature is increased to a heating temperature of 700°C at a heating rate of 5°C / min and kept warm for 8 hours. The obtained sample is washed with hydrochloric acid and water and then dried at 60°C to obtain silicon nanowires.

[0048] Figure 1 and Figure 2 This is a scanning electron microscope image of the silicon nanowires obtained in Example 1. The main features are that the silicon nanowires have uniform morphology, uniform thickness, and an average diameter of 130 nm. From the figure, it can be inferred that the aspect ratio of the silicon nanowires is not less than 1000. Such ultra-high aspect ratio silicon nanowires have monodisperse morphological characteristics, and the silicon wires are not entangled with each other, knotted, or agglomerated, which is convenient for the dispersion, coating, granulation, pulping, coating and other process steps in the process of making lithium battery negative electrodes.

[0049] Example 2

[0050] This embodiment provides a method for preparing silicon nanowires using metal halides, the method comprising the following steps:

[0051] The metal reducing agent aluminum powder is evenly mixed with the silicon source liquid silicon tetrachloride and the metal halide titanium chloride, and the molar ratio of the metal reducing agent to the silicon source is controlled to be 3:1, and the molar ratio of the metal reducing agent to the metal halide is controlled to be 20:1. Then, the temperature is increased to 950°C at a heating rate of 8°C / min and kept warm for 10 hours. The obtained sample is washed with hydrochloric acid and water and then dried at 80°C to obtain silicon nanowires.

[0052] Example 3

[0053] This embodiment provides a method for preparing silicon nanowires using metal halides, the method comprising the following steps:

[0054] The metal reducing agent magnesium powder and zinc powder are evenly mixed with the silicon source liquid silicon tetrachloride and the metal halide copper chloride and titanium bromide, and the molar ratio of the metal reducing agent to the silicon source is controlled to be 2.6:1, and the molar ratio of the metal reducing agent to the metal halide is controlled to be 50:1. Then, the temperature is increased to a heating temperature of 700°C at a heating rate of 1°C / min and kept warm for 5 hours. The obtained sample is washed with hydrochloric acid and water and then dried at 40°C to obtain silicon nanowires.

[0055] Comparative Example 1

[0056] As a comparison with Example 1, Comparative Example 1 provides a method for preparing silicon nanowires using metal copper powder as a catalyst, the method comprising the following steps:

[0057] The metal reducing agent zinc powder is evenly mixed with the silicon source liquid silicon tetrachloride and the metal catalyst copper powder, and the molar ratio of the metal reducing agent to the silicon source is controlled to be 2.1:1, and the molar ratio of the metal reducing agent to the metal catalyst powder is controlled to be 10:1. Then, the temperature is increased to a heating temperature of 950°C at a heating rate of 5°C / min and kept warm for 8 hours. The obtained sample is washed with hydrochloric acid and water and then dried at 60°C to obtain silicon nanowires.

[0058] Based on the method for preparing silicon nanowires from metal halides provided in Example 1, the parameters were changed and adjusted according to Table 1 to prepare Examples 4-21. Based on the method for preparing silicon nanowires from metal halides provided in Comparative Example 1, the parameters were changed and adjusted according to Table 1 to prepare Comparative Examples 2-6, and the corresponding silicon nanowires were obtained.

[0059] Table 1

[0060]

[0061]

[0062] The silicon nanowires obtained in each embodiment and comparative example were subjected to the following tests: the color and uniformity of the samples were visually inspected and the average diameter of the silicon nanowires was measured by scanning electron microscopy. The test results are recorded in Table 2.

[0063] Table 2

[0064]

[0065]

[0066] Application Example 1

[0067] The silicon nanowires obtained in Example 1 were used as the negative electrode material, and an aqueous slurry was made according to the ratio of silicon nanowire: conductive agent: binder = (70-90): (5-15): (5-15), with a solid content of 1% to 30%. The slurry was then coated on a copper current collector in a conventional manner to form a pole piece, which was then rolled and punched to form a Φ12 pole piece. After vacuum drying, the pole piece was assembled with a lithium sheet in a glove box to form a 2032 button battery. The electrical properties of the silicon nanowire negative electrode were tested, and the results are shown in Table 3.

[0068] Table 3

[0069]

[0070] From Table 2 and Table 3, we can see that:

[0071] Comparing Examples 1 and 4-8, under the same conditions of other parameters, the ratio of copper chloride to zinc powder increases in sequence, and the average diameter and output of silicon nanowires decrease in sequence. This is because as the ratio of copper chloride increases, the number of catalyst nuclei increases, the diameter of the nucleation seeds decreases, and the diameter of the silicon nanowires grown from the seeds decreases accordingly. On the other hand, as the ratio of zinc powder decreases, the concentration of silicon atoms produced decreases, and the output of silicon nanowires decreases accordingly. Following the general rules for preparing nanomaterials, as the nanometer size decreases, the output usually decreases. Considering the factors such as the diameter, monodispersity, uniformity, and output of silicon nanowires, Example 1 has the best effect. In short, metal halides, except for lead halides, have generally better effects. Comparing Example 2 with Comparative Example 6, the former uses titanium chloride as a catalyst, and the latter uses elemental titanium as a catalyst, and the other experimental conditions are the same. The silicon nanowires prepared by the former are yellow in color, uniform, and have an average diameter of 127nm. The latter has poor uniformity and a larger diameter. This is because titanium has a high melting point (1660°C) and boiling point (3287°C). At a reaction temperature of 950°C, the saturated vapor pressure of titanium is less than 10 -13atm, the gas phase titanium atoms are extremely thin and insufficient to catalyze the growth of silicon nanowires. Therefore, the morphology of the silicon product is mainly determined by the chemical reaction process of zinc reducing silicon tetrachloride. In comparison, the use of titanium chloride as a catalyst has effectively solved the problem of the difficulty in vaporizing elemental titanium. Since titanium chloride has a very low melting and boiling point, it vaporizes rapidly under reaction conditions, is reduced to form titanium atoms in an atmosphere at the reduction reaction temperature, and combines in situ to form a ternary alloy. Therefore, silicon undergoes the process of nucleation-droplet-seed, and continuously precipitates from the bottom of the seed according to the VLS mechanism and grows into silicon wires.

[0072] For comparison, comparative examples 1-6 use metal elements as catalysts. The overall effect is not very good. The main reason is that the reaction temperature is much lower than the boiling point of the metal element due to the limitation of zinc reduction of silicon tetrachloride. The concentration of metal atoms in the gas phase is too low to catalyze the growth of silicon nanowires. The saturated vapor pressure of metals such as titanium, iron and gold is less than 10 at a temperature of 950°C. -10 atm, it has almost no effect. The saturated vapor pressure of copper is slightly higher, and the effect is better. It can be seen from Table 3:

[0073] The button cell made by using silicon nanowires as negative electrode according to the method described in Example 1 has an initial charge and discharge efficiency of 92.17%, and the gram capacity is close to the theoretical value of silicon.

[0074] Therefore, the present invention uses metal halides instead of monomer metals (metallic elements) as catalysts, and utilizes the gas phase reduction reaction between metal reducing agents and metal halides to generate monomer metal catalysts in situ. Due to the in-situ generation, the uniformity in the system is better, and the boiling point of metal halides is significantly lower than that of monomer metals. Therefore, in the process of preparing silicon nanowires, metal halides are used instead of monomer metals directly, which can significantly reduce the system temperature, effectively reduce energy consumption and costs, and the silicon nanowires prepared in a relatively low temperature reaction environment are strictly controllable.

[0075] The present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0076] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0077] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0078] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing silicon nanowires using metal halides, It is characterized in that The method comprises the following steps: The metal reducing agent, silicon source and catalyst are uniformly mixed, wherein the catalyst comprises metal halide, and heated to react to obtain silicon nanowires.

2. The method according to claim 1, It is characterized in that The metal halide is denoted as MX y , wherein M includes any one of zinc, iron, cobalt, nickel, tin, lead, copper, silver, gold or titanium or a combination of at least two thereof; X includes any one of Cl, Br or I or a combination of at least two thereof; 1≤y≤4; Preferably, the metal halide includes any one of zinc chloride, lead chloride, silver chloride, cupric chloride, cuprous chloride, ferric chloride, ferrous chloride, gold chloride, titanium chloride, zinc bromide, lead bromide, silver bromide, copper bromide, ferric bromide, gold bromide or titanium bromide, or a combination of at least two thereof.

3. The method according to claim 1 or 2, It is characterized in that The molar ratio of the metal reducing agent to the silicon source is (2-3):1; Preferably, the molar ratio of the metal reducing agent to the metal halide is (2-50):

1.

4. The method according to any one of claims 1 to 3, It is characterized in that The metal reducing agent includes a metal element having a metal activity stronger than that of the metal element in the metal halide.

5. The method according to claim 4, It is characterized in that The metal element includes any one of sodium, potassium, lithium, calcium, magnesium, aluminum or zinc, or a combination of at least two thereof; Preferably, the metal element is metal powder; Preferably, the silicon source comprises any one of silicon tetrachloride, trichlorosilane, dichlorosilane, oligomeric silane or elemental silicon, or a combination of at least two thereof; Preferably, the silicon tetrachloride is in liquid state.

6. The method according to any one of claims 1 to 5, It is characterized in that The temperature of the heating reaction is 400-1000°C; Preferably, the insulation time of the heating reaction is 5 to 10 hours; Preferably, the heating rate of the heating reaction is 1 to 8°C / min.

7. The method according to any one of claims 1 to 6, It is characterized in that The method further comprises cleaning and drying the obtained silicon nanowires; Preferably, the cleaning agent comprises hydrochloric acid and / or water; Preferably, the drying temperature is 40-80°C.

8. The method according to any one of claims 1 to 7, It is characterized in that The method comprises: Mixing powdered metal single substances of sodium, potassium, lithium, calcium, magnesium, aluminum or zinc, or a combination of at least two of them, as a metal reducing agent, with a liquid silicon source, such as silicon tetrachloride, trichlorosilane, dichlorosilane, oligomeric silane or single silicon, or a combination of at least two of them, and a metal halide as a catalyst, and controlling the molar ratio of the metal reducing agent to the silicon source to be (2-3):1, and the molar ratio of the metal reducing agent to the metal halide to be (2-50):1, and the metal activity of the metal single substance is stronger than the metal activity of the metal element in the metal halide; the metal halide includes zinc chloride, lead chloride, silver chloride, cupric chloride, cuprous chloride, ferric chloride, ferrous chloride, gold chloride, titanium chloride, zinc bromide, lead bromide, silver bromide, copper bromide, ferric bromide, gold bromide or titanium bromide, or a combination of at least two of them; Then, the temperature is raised to a heating temperature of 400-1000° C. at a heating rate of 1-8° C. / min and kept for 5-10 hours. The obtained sample is washed with hydrochloric acid and water and dried at 40-80° C. to obtain silicon nanowires.

9. A silicon nanowire, It is characterized in that Prepared by the method described in any one of claims 1 to 8.

10. A negative electrode of a battery, It is characterized in that Containing the silicon nanowire according to claim 9.

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