Method for producing silicon microparticles with surface pores and / or microprotrusions

Abstract

To provide a surface processing method for silicon fine particles that is easy to scale up while maintaining simple operation and the use of inexpensive materials.SOLUTION: A surface processing method of silicon fine particles according to the present invention comprises a first etching step in which transition metal particles are deposited on surfaces of the silicon fine particles by immersing the silicon fine particles in a solution containing hydrofluoric acid and transition metal ions and, along with the deposition, surfaces of the silicon fine particles with a portion contacting the transition metal particles having been oxidized are etched with hydrofluoric acid, and a second etching step in which an oxidizing agent is added to the mixture liquid that has passed through the first etching step and these are reacted with each other while being mixed. In the first etching step, the transition metal ions are added so that the concentration in the solution is between 0.7 mmol / L and 40 mmol / L.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing silicon microparticles having surface pores and / or microprotrusions. [Background technology]

[0002] In recent years, nano-level processing has been performed on components constituting various devices, including those in the field of energy-related products such as solar cells and storage batteries, in order to improve the functionality of the products. Among these, silicon materials in particular have been used to prepare various structures with microstructures by applying microfabrication techniques accumulated over many years in the semiconductor field. As an example of a structure using such microfabrication techniques, Patent Document 1 proposes forming microgrooves with specific taper angles and depths in a single-crystal silicon substrate by grinding, and then etching the grooves to obtain an ordered array of needle-like structures with sharp tips. Patent Document 2 also proposes forming nano-level microstructures consisting of needle-like crystal protrusions and dendrites on a silicon substrate by irradiating a nanosecond laser, and claims that silicon materials with such microstructures are useful for mechanical and electronic components.

[0003] Silicon is also used as a power generating element in solar cells, and in this field, various fine surface processing techniques are being carried out to improve power generation efficiency. As an example, Patent Document 3 proposes etching the surface of a silicon wafer to form a surface texture such as nanopores on the surface.

[0004] Silicon is also expected to be used as a high-capacity negative electrode material in lithium-ion secondary batteries. However, silicon undergoes large volume changes as lithium ions are inserted and extracted, which poses a problem of secondary battery capacity reduction due to negative electrode degradation over repeated charge and discharge. As one means of solving this problem, for example, Patent Document 4 proposes reducing a mixture of SiO2 powder and sodium chloride and etching the silicon obtained by reduction to obtain porous silicon with a microstructure, which can be used as an electrode material. Furthermore, Patent Document 5 proposes preparing porous silicon particles from a porous silicon wafer and using them as the negative electrode of a lithium-ion secondary battery.

[0005] Under these circumstances, the present inventors have proposed a method for forming fine holes and protrusions on the surface of silicon particles by applying a metal-assisted chemical etching method (see Patent Documents 6 and 7). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-114345 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-231376 [Patent Document 3] Special Publication No. 2017-504179 [Patent Document 4] Special Publication No. 2017-520089 [Patent Document 5] Japanese Patent Application Publication No. 2016-051622 [Patent Document 6] Japanese Patent Publication No. 2020-059631 [Patent Document 7] Japanese Patent Publication No. 2020-059632 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, various means for forming microstructures by surface processing of silicon have been proposed. However, many of these types of processing methods are costly and laborious, and it is true that there are many issues with their industrial use. On the other hand, the methods proposed by the present inventors and shown in Patent Documents 6 and 7 are superior to previous methods in that they can form micropores and protrusions on the surface of silicon microparticles using simple operations and inexpensive materials. However, the methods shown in Patent Documents 6 and 7 are difficult to scale up for mass production, and in this respect there is room for improvement.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for surface processing of silicon microparticles that is easy to scale up while retaining the advantages of simple operation and the use of inexpensive materials. [Means for solving the problem]

[0009] The inventors conducted extensive research to solve the above problems and discovered that controlling the addition method of transition metal salts and the etching reaction time in metal-assisted chemical etching methods can solve the above problems. Etching processes for surface processing of silicon microparticles are inherently problematic because the target particles are microparticles. In other words, increasing the etching reaction rate or extending the reaction time in an attempt to improve the degree of surface processing increases the risk of dissolving the silicon microparticles and reducing yield. For this reason, the surface processing methods described in Patent Documents 6 and 7 involve maintaining low concentrations of components in the etching solution to suppress particle dissolution, while instead using techniques such as doping the silicon microparticles with impurities to control electron density. Due to this background, the surface processing methods described in Patent Documents 6 and 7 have been difficult to scale up.

[0010] Subsequently, the inventors of the present invention sought a method for surface processing using metal-assisted chemical etching that could be scaled up, and discovered that by adjusting the concentration of the transition metal salt used in the metal-assisted chemical etching method to a predetermined range, it is possible to scale up the surface processing while suppressing the dissolution of silicon microparticles. The present invention was made based on this finding and provides the following.

[0011] (1) The present invention provides a method for producing silicon particles by immersing the silicon particles in a solution containing hydrofluoric acid and transition metal ions, thereby precipitating transition metal particles on the surfaces of the silicon particles, and etching the surfaces of the silicon particles with hydrofluoric acid, the surfaces of which have been oxidized at the contact points with the transition metal particles as a result of the precipitating process; and a method for producing silicon particles by adding an oxidizing agent to the mixed solution obtained in the first etching process and mixing the mixed solution. 10 to 30 minutes and a second etching step of reacting the transition metal ions with the solution, wherein the transition metal ions are added in the first etching step so that the concentration in the solution is 0.7 mmol / L to 40 mmol / L. The oxidizing agent is hydrogen peroxide, which is added in the second etching step so that the amount is 0.3% by volume to 1.0% by volume in terms of 30% by mass hydrogen peroxide solution. The present invention is a method for producing silicon microparticles having surface pores and / or microprotrusions, characterized by:

[0013] (2) The present invention is also characterized in that the hydrofluoric acid added in the first etching step is added to the solution so as to have a concentration of 10% by volume to 15% by volume in terms of 46% by mass hydrofluoric acid. Section (1) This is a method for producing silicon microparticles having the surface pores and / or microprotrusions described above.

[0014] (3) The present invention also provides the method (1), characterized in that the transition metal is silver. or paragraph (2) This is a method for producing silicon microparticles having the surface pores and / or microprotrusions described above. [Effects of the Invention]

[0016] According to the present invention, a method for processing the surface of silicon microparticles is provided which is easy to operate and uses inexpensive materials, and can also be easily scaled up. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an SEM image of the surface-pore silicon microparticles of Examples 1 and 2. [Figure 2] FIG. 2 is an SEM image of the micro-projection silicon particles of Examples 3 and 4. [Figure 3] FIG. 3 is an SEM image of the hybrid silicon microparticles of Examples 5 and 6. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, one embodiment of the method for producing silicon microparticles having surface pores and / or microprotrusions according to the present invention (hereinafter also referred to as silicon microparticles of the present invention) will be described. Note that the present invention is not limited to the following embodiment, and can be practiced with appropriate modifications within the scope of the present invention.

[0019] The method for producing silicon microparticles having surface pores and / or microprotrusions of the present invention comprises a first etching step in which silicon microparticles are immersed in a solution containing hydrofluoric acid and transition metal ions to precipitate transition metal particles on the surface of the silicon microparticles, and the surfaces of the silicon microparticles, whose contact areas with the transition metal particles have been oxidized as a result of the precipitation, are etched with hydrofluoric acid; and a second etching step in which an oxidizing agent is added to the mixed solution that has undergone the first etching step and the two are reacted while being mixed.

[0020] In the method for producing silicon microparticles of the present invention, surface pores and / or microprotrusions are formed on the surface of the silicon microparticles. "Forming surface pores and / or microprotrusions" means forming only surface pores, only microprotrusions, or both surface pores and microprotrusions on the surface of the silicon microparticles. Silicon microparticles with surface pores have multiple pores formed on the surface of the silicon microparticles, and are in a state that can be called porous particles. Silicon microparticles with microprotrusions have multiple protrusions formed on the silicon surface, and are shaped like confetti.

[0021] In the method for producing silicon microparticles of the present invention, surface pores and fine protrusions are formed on the surface of silicon microparticles by etching them in a solution. It is preferable to use powdered silicon microparticles with particle sizes ranging from 10 nm to submicrons as the raw material. Any silicon powder can be used as the silicon microparticles, and they may be silicon wafer cuttings (including silicon sludge, which is an industrial waste) generated during the production of semiconductor devices or pulverized silicon obtained by reducing silica. Particularly preferred are waste silicon obtained by reducing a silane compound in the gas phase using plasma or cuttings, and these may be commercially available products. The silicon microparticles may be undoped or doped silicon, but undoped silicon is preferred.

[0022] In the method for producing silicon microparticles of the present invention, a metal-assisted chemical etching method is used as the etching method for forming surface pores and microprotrusions on the surface of the microparticles. This method involves etching silicon microparticles in an etching solution containing both transition metal ions and hydrofluoric acid, thereby forming structures such as surface pores and microprotrusions on the surface of the silicon microparticles through the following process.

[0023] First, silicon microparticles are immersed in a solution containing transition metal ions and hydrofluoric acid. The hydrofluoric acid dissolves and removes the oxide film (SiO2) covering the surface of the silicon microparticles. This exposes silicon (Si) on the surface of the silicon microparticles, which then come into contact with the transition metal ions in the solution. The electrons contained in the silicon are then transferred to the transition metal ions, which then become transition metal particle nuclei and attach to the silicon surface. Meanwhile, at the contact points between the transition metal particle nuclei and the silicon, the silicon loses electrons and is locally oxidized. The locally oxidized silicon is then removed by the hydrofluoric acid contained in the solution, and is then further oxidized by the transition metal ions at those points, growing the transition metal particle nuclei. This reaction is repeated, and the transition metal particles penetrate the silicon microparticles, as if digging through the silicon surface, forming holes at those points. If such pores are formed sparsely on the silicon surface, the resulting silicon microparticles will have multiple surface pores, whereas if they are formed densely, the silicon remaining between the pores will remain in the form of protrusions, resulting in silicon microparticles with multiple microprotrusions on the surface. The density of such pore formation depends on the concentration of transition metal ions in the etching solution, so by adjusting the concentration of transition metal ions contained in the etching solution, it is possible to produce silicon microparticles with surface pores or silicon microparticles with microprotrusions. Note that if etching is performed under conditions intermediate between the two, it is also possible to form silicon microparticles with both surface pores and microprotrusions.

[0024] In this embodiment, a crushing step for crushing silicon particles contained in the silicon powder is carried out before the first etching step, and a removal step for removing transition metal particle nuclei from the surfaces of the silicon particles is carried out after the second etching step. These crushing and removal steps are optional steps. Each step will be described below.

[0025] [Crushing process] First, the crushing step will be described. In this step, silicon powder as a raw material is dispersed in water, and an appropriate external force is applied to the mixture to crush the silicon powder in the mixture. Preferred devices for applying such an external force include a general stirring device and a commercially available ultrasonic homogenizer.

[0026] When processing with an ultrasonic homogenizer, silicon powder is dispersed in water and placed in a suitable container, and the dispersion is crushed by contacting the crushing horn of a commercially available ultrasonic homogenizer with the dispersion. The mixing ratio of silicon microparticles to water in this case can be approximately 300 mg of silicon microparticles per 44 mL of water, and the crushing conditions for the ultrasonic homogenizer can be an oscillation frequency of 20 kHz, an output of 400 W, a maximum amplitude of 30%, an oscillation time (ON / OFF) of 10 seconds / 5 seconds, and a processing time of approximately 5 minutes, although these conditions can be set appropriately.

[0027] In the dispersion, a hydrophilic solvent such as alcohol may be used in place of or in addition to water. As for the silicon powder, as already explained, commercially available silicon powder may be used.

[0028] Through this crushing step, the silicon powder dispersed in the mixed solution is crushed into silicon fine particles. The mixed solution containing the silicon fine particles is then subjected to a first etching step.

[0029] [First etching process] The first etching step is a step in which silicon microparticles are immersed in a solution containing hydrofluoric acid and transition metal ions to precipitate transition metal particles on the surface of the silicon microparticles, and the surface of the silicon microparticles, whose contact points with the transition metal particles have been oxidized as a result of the precipitation, is etched with hydrofluoric acid.

[0030] In this embodiment, hydrofluoric acid and transition metal ions are added to the mixed solution that has undergone the disintegration step, thereby achieving the state of "soaking silicon microparticles in a solution containing hydrofluoric acid and transition metal ions." If the disintegration step is not performed, silicon microparticles can be added to an appropriate amount of water to form a mixed solution, and hydrofluoric acid and transition metal ions can be added to this mixed solution. As already explained, the amount of water in this case can be approximately 44 mL per 300 mg of silicon microparticles. The order in which hydrofluoric acid and transition metal ions are added is not particularly limited and does not matter.

[0031] Examples of the transition metal include copper, silver, gold, and iron, with silver being preferred. These transition metals are added to the mixed solution in the form of transition metal salts, which become transition metal ions. Examples of such transition metal salts include hydrochlorides, nitrates, and sulfates, with nitrates being preferred.

[0032] The concentration of transition metal ions in the solution is 0.7 mmol / L to 40 mmol / L. As mentioned above, the concentration of transition metal ions in the solution determines whether the shape formed on the surface of the silicon microparticles is surface pores, microprotrusions, or both. Generally, the transition metal ion concentration is approximately 10 mmol / L, with lower concentrations forming surface pores and higher concentrations forming microprotrusions. At the boundary of approximately 10 mmol / L, a hybrid type having both of these features is formed. Even at a high transition metal ion concentration of approximately 30 mmol / L, a hybrid type can be obtained by shortening the reaction time in the second etching step described below. Thus, depending on the concentration of transition metal ions in the first etching step and the reaction time in the second etching step, the surface state of the silicon microparticles can be changed from surface pores (low etching level) to hybrid (intermediate etching level) to microprotrusions (high etching level). By setting the concentration of the transition metal ions in the solution within the above range, surface pores or microprotrusions are favorably formed on the surfaces of the silicon microparticles while the dissolution of the silicon microparticles is suppressed. The concentration of the transition metal ions in the solution is more preferably 1 mmol / L to 30 mmol / L.

[0033] The hydrofluoric acid to be added to the solution is preferably added so that the concentration in the solution is 10% by volume to 15% by volume, calculated as 46% by mass hydrofluoric acid, which is a commercially available hydrofluoric acid solution.

[0034] The mixed solution containing the transition metal ions and hydrofluoric acid is stirred appropriately at room temperature (approximately 15°C to 30°C) to allow the etching reaction to proceed. The stirring time is, for example, approximately 1 minute, but is not particularly limited. The resulting mixed solution is subjected to the second etching step.

[0035] [Second etching process] The second etching step involves adding an oxidizing agent to the mixed solution obtained in the first etching step and allowing the two to react while mixing. As previously mentioned, in the first etching step, the silicon particles are locally oxidized by the exchange of electrons between the transition metal ions and the silicon particles, and then the oxidized silicon is dissolved in hydrofluoric acid, resulting in local etching. However, as transition metal particles are generated on the surface of the silicon particles, the supply of electrons gradually saturates, making it difficult to locally etch the silicon particles, and making it impossible to increase the pore depth required for forming pores or fine protrusions. Therefore, in the second etching step, an additional oxidizing agent is added to the mixed solution. This allows the hydrogen peroxide to steal electrons from the transition metal particles, promoting local etching in the depth direction inside the silicon particles.

[0036] The oxidizing agent is not particularly limited, but a preferred example is aqueous hydrogen peroxide. When aqueous hydrogen peroxide is used as the oxidizing agent, it is preferably added so that the concentration in the mixed solution is 0.3% by volume to 1.0% by volume, calculated as 30% by mass aqueous hydrogen peroxide, which is commercially available aqueous hydrogen peroxide. By adding an amount of aqueous hydrogen peroxide within this range, it is possible to favorably form surface pores or fine protrusions on the surfaces of the silicon microparticles while preventing the silicon microparticles from being completely dissolved. More preferably, about 0.3 mL of aqueous 30% by mass aqueous hydrogen peroxide is added per 50 mL of the mixed solution, but this amount is not particularly limited.

[0037] The mixture containing the hydrogen peroxide solution is stirred at room temperature (approximately 15°C to 30°C). During this time, surface pores and microprotrusions are formed on the surface of the silicon microparticles by etching. As mentioned above, microprotrusions are formed by the formation of numerous adjacent surface pores, and therefore, to form these, the silicon microparticles must be highly etched. For this reason, when forming microprotrusions on a silicon surface, a longer reaction time is required than when forming surface pores. To form surface pores on a silicon surface, it is desirable to ensure this reaction time is approximately 10 minutes. Furthermore, when forming microprotrusions on a silicon surface or when forming both microprotrusions and surface pores, it is desirable to allow the reaction to take place for approximately 10 to 30 minutes. Note that this reaction time is an example, and can be adjusted as appropriate depending on the progress of etching so that the desired surface structure is formed on the silicon surface.

[0038] After the above reaction, an appropriate amount of water is added to the mixture to reduce the concentration of hydrofluoric acid and hydrogen peroxide, thereby stopping the etching reaction.The silicon particles contained in the mixture are then subjected to a removal process.

[0039] [Removal process] The removal step is a step of removing the transition metal particles from the silicon microparticles that have been subjected to the second etching step.

[0040] In this process, the silicon particles that have undergone the second etching process are subjected to an acid treatment to remove the transition metal particles. Specifically, the silicon particles contained in the mixed solution are introduced into an acid aqueous solution, either as the mixed solution or after being filtered out from the mixed solution, and immersed therein. This causes the transition metal particles to migrate from the silicon particles into the acid aqueous solution. A dilute nitric acid aqueous solution is preferably used as the acid aqueous solution, and the treatment method used here involves immersing the filtered silicon particles in the acid aqueous solution for about 10 minutes.

[0041] The silicon particles that have been subjected to the acid treatment in this step are filtered out. The silicon particles that have been filtered out have surface pores and / or fine protrusions formed on their surfaces.

[0042] As already mentioned, the present invention is not limited to the above-described embodiments, and can be practiced with appropriate modifications within the scope of the present invention.

[0043] For example, in the above embodiment, the treatment was performed on 300 mg of silicon microparticles, but according to the present invention, it is also possible to scale up the treatment as desired by setting the ratio of the reaction solution volume to 300 mg of silicon microparticles at approximately 50 mL.

[0044] The silicon microparticles prepared by the production method of the present invention have surface pores and / or microprotrusions formed on their surfaces, and are therefore suitable for applications requiring a large surface area as a semiconductor, such as the active layer in a solar cell, or for applications requiring repeated expansion and contraction, such as the negative electrode active material in a lithium ion secondary battery. [Example]

[0045] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples in any way.

[0046] [Example 1] Preparation of surface-porous silicon microparticles 1 300 mg of commercially available silicon powder was added to 44 mL of pure water and subjected to ultrasonic homogenization. The ultrasonic homogenization conditions were: oscillation frequency 20 kHz, output power 400 W, maximum amplitude 30%, oscillation time (ON / OFF) 10 seconds / 5 seconds, and treatment time 5 minutes. 5.7 mL of commercially available 46% by mass hydrofluoric acid and 8.5 mg of silver nitrate were added to the resulting dispersion and stirred at 50 rpm for 1 minute at room temperature. At this time, the silver ion concentration in the mixture was approximately 1 mmol / L. Then, 0.3 mL of commercially available 30% by mass hydrogen peroxide solution was added to the mixture and stirred for 10 minutes. After the reaction was complete, the solid was filtered off and washed with 100 mL of pure water. The filtered silicon microparticles were added to 10 mL of dilute nitric acid (1 mol / L) and left for 10 minutes. Then, pure water was added and ultrasonically crushed for several tens of seconds to obtain surface-pore silicon microparticles.

[0047] [Example 2] Preparation of surface-porous silicon microparticles 2 300 mg of commercially available silicon powder was added to 44 mL of pure water and subjected to ultrasonic homogenization. The ultrasonic homogenization conditions were: oscillation frequency 20 kHz, output power 400 W, maximum amplitude 30%, oscillation time (ON / OFF) 10 seconds / 5 seconds, and treatment time 5 minutes. 5.7 mL of commercially available 46% by mass hydrofluoric acid and 84.9 mg of silver nitrate were added to the resulting dispersion and stirred at 50 rpm for 1 minute at room temperature. At this time, the silver ion concentration in the mixture was approximately 10 mmol / L. Then, 0.3 mL of commercially available 30% by mass hydrogen peroxide solution was added to the mixture and stirred for 10 minutes. After the reaction was completed, the solid was filtered off and washed with 100 mL of pure water. The filtered silicon microparticles were added to 10 mL of dilute nitric acid (1 mol / L) and left for 10 minutes. After adding pure water, the mixture was ultrasonically crushed for several tens of seconds to obtain surface-pore silicon microparticles.

[0048] [Example 3] Preparation of fine protrusion silicon particles 1 300 mg of commercially available silicon powder was added to 44 mL of pure water and subjected to ultrasonic homogenization. The ultrasonic homogenization conditions were an oscillation frequency of 20 kHz, an output of 400 W, a maximum amplitude of 30%, an oscillation time (ON / OFF) of 10 seconds / 5 seconds, and a processing time of 5 minutes. 5.7 mL of commercially available 46% by mass hydrofluoric acid and 169 mg of silver nitrate were added to the resulting dispersion and stirred at room temperature for 1 minute at a stirring speed of 50 rpm. At this time, the silver ion concentration in the mixture was approximately 20 mmol / L. Then, 0.3 mL of commercially available 30% by mass hydrogen peroxide solution was added to the mixture and stirred for 10 minutes. After the reaction was completed, the solid was filtered off and washed with 100 mL of pure water. The filtered silicon microparticles were added to 10 mL of dilute nitric acid (1 mol / L) and left for 10 minutes. Then, pure water was added and the mixture was ultrasonically crushed for several tens of seconds to obtain fine-projection silicon microparticles.

[0049] [Example 4] Preparation of fine protrusion silicon particles 2 300 mg of commercially available silicon powder was added to 44 mL of pure water and subjected to ultrasonic homogenization. The ultrasonic homogenization conditions were an oscillation frequency of 20 kHz, an output of 400 W, a maximum amplitude of 30%, an oscillation time (ON / OFF) of 10 seconds / 5 seconds, and a processing time of 5 minutes. 5.7 mL of commercially available 46% by mass hydrofluoric acid and 84.9 mg of silver nitrate were added to the resulting dispersion and stirred at room temperature for 1 minute at a stirring speed of 50 rpm. At this time, the silver ion concentration in the mixture was approximately 10 mmol / L. Then, 0.3 mL of commercially available 30% by mass hydrogen peroxide solution was added to the mixture and stirred for 30 minutes. After the reaction was completed, the solid was filtered off and washed with 100 mL of pure water. The filtered silicon microparticles were added to 10 mL of dilute nitric acid (1 mol / L) and left for 10 minutes. Then, pure water was added and ultrasonically crushed for several tens of seconds to obtain fine-projection silicon microparticles.

[0050] [Example 5] Preparation of hybrid silicon microparticles 1 300 mg of commercially available silicon powder was added to 44 mL of pure water and subjected to ultrasonic homogenization. The ultrasonic homogenization conditions were an oscillation frequency of 20 kHz, output power of 400 W, maximum amplitude of 30%, oscillation time (ON / OFF) of 10 seconds / 5 seconds, and treatment time of 5 minutes. 5.7 mL of commercially available 46% by mass hydrofluoric acid and 84.9 mg of silver nitrate were added to the resulting dispersion and stirred at room temperature for 1 minute at a stirring speed of 50 rpm. At this time, the silver ion concentration in the mixture was approximately 10 mmol / L. Then, 0.3 mL of commercially available 30% by mass hydrogen peroxide solution was added to the mixture and stirred for 20 minutes. After the reaction was completed, the solid was filtered off and washed with 100 mL of pure water. The filtered silicon microparticles were added to 10 mL of dilute nitric acid (1 mol / L) and left for 10 minutes. After adding pure water and ultrasonically crushing for several tens of seconds, hybrid silicon microparticles with surface pores and microprotrusions were obtained.

[0051] [Example 6] Preparation of hybrid silicon microparticles 2 300 mg of commercially available silicon powder was added to 44 mL of pure water and subjected to ultrasonic homogenization. The ultrasonic homogenization conditions were an oscillation frequency of 20 kHz, output power of 400 W, maximum amplitude of 30%, oscillation time (ON / OFF) of 10 seconds / 5 seconds, and processing time of 5 minutes. 5.7 mL of commercially available 46% by mass hydrofluoric acid and 254.8 mg of silver nitrate were added to the resulting dispersion and stirred at room temperature for 1 minute at a stirring speed of 50 rpm. At this time, the silver ion concentration in the mixture was approximately 30 mmol / L. Then, 0.3 mL of commercially available 30% by mass hydrogen peroxide solution was added to the mixture and stirred for 10 minutes. After the reaction was completed, the solid was filtered off and washed with 100 mL of pure water. The filtered silicon microparticles were added to 10 mL of dilute nitric acid (1 mol / L) and left for 10 minutes. After that, pure water was added and ultrasonically crushed for several tens of seconds to obtain hybrid silicon microparticles with surface pores and microprotrusions.

[0052] The surface conditions of the surface-pore silicon microparticles of Examples 1 and 2, the micro-protrusion silicon microparticles of Examples 3 and 4, and the hybrid silicon microparticles of Examples 5 and 6 were observed using a scanning electron microscope (SEM). The images are shown in Figures 1 to 3, respectively. Figure 1 is an SEM image of the surface-pore silicon microparticles of Examples 1 and 2, Figure 2 is an SEM image of the micro-protrusion silicon microparticles of Examples 3 and 4, and Figure 3 is an SEM image of the hybrid silicon microparticles of Examples 5 and 6.

[0053] As shown in FIGS. 1 to 3, it can be seen that according to the present invention, a surface pore structure and a fine protrusion structure can be formed on the surface of silicon microparticles by a simple procedure.

Claims

1. a first etching step of immersing silicon microparticles in a solution containing hydrofluoric acid and transition metal ions to precipitate transition metal particles on the surfaces of the silicon microparticles, and etching the surfaces of the silicon microparticles, the contact portions with the transition metal particles being oxidized as a result of the precipitation, with hydrofluoric acid; a second etching step in which an oxidizing agent is added to the mixed solution that has been subjected to the first etching step, and the two are reacted for 10 to 30 minutes while being mixed; In the first etching step, the transition metal ions are added so that their concentration in the solution is 0.7 mmol / L to 40 mmol / L; A method for producing silicon microparticles with surface pores and / or fine protrusions, characterized in that the oxidizing agent is hydrogen peroxide, which is added in the second etching step so as to be 0.3 volume % to 1.0 volume % in terms of 30 mass % hydrogen peroxide solution.

2. 2. The method for producing silicon microparticles having surface pores and / or microprotrusions according to claim 1, wherein the hydrofluoric acid added in the first etching step is added to the solution so as to be 10% by volume to 15% by volume in terms of 46% by mass hydrofluoric acid.

3. 3. The method for producing silicon microparticles having surface pores and / or microprojections according to claim 1, wherein the transition metal is silver.

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