Methods for producing silicon using gas-phase electrical reduction

Abstract

Silicon manufacturing process using gas-phase electrical reduction, wherein the silicon manufacturing process comprises: a first step in applying an electrical voltage to a surface of a base material, arranged in a reactor; a second step to introduce a silicon-based compound in the gas phase to the base material with the applied electrical voltage; and a third step in which the silicon-based compound, which reaches the surface of the base material in the gas phase, is reduced from the surface of the base material to form a silicon coating layer on the surface of the base material, wherein in the second step electrons are supplied to the silicon-based compound which reaches the surface of the base material in the reactor when an electrical voltage is applied to the surface of the base material, in the third step the silicon-based compound is reduced from the surface of the base material by the electrons in order to coat the surface of the base material with silicon; where the silicon-based compound is a chlorosilane compound and, in the step of supplying the silicon-based compound in the gas phase, the chlorosilane compound is supplied in a gaseous state without being dissolved in a liquid medium; wherein the chlorosilane compound is supplied continuously or in pulses without the use of a catalyst or reducing agent; wherein the chlorosilane compound is added to the base material in a reactor and The reactor temperature range is 150 °C to 250 °C; where the current density per unit area is 1 to 200 mA / cm² 2 amounts; where the applied electrical voltage is 1 to 100 V.

Description

Technical area

[0001] The present invention relates to a method for producing silicon using gas-phase electroreduction, and more particularly to a method for supplying a silicon-based compound in the gas phase to the surface of a base material with an electric voltage applied thereto without using a liquid medium to form a reduction layer of silicon on the surface of the base material. State of the art

[0002] A lithium secondary battery, which is a battery charged and discharged using a redox reaction of lithium ions, comprises a positive electrode and a negative electrode formed in the state where an ion exchange membrane is interposed therebetween, and an electrolyte solution.

[0003] In order to use the lithium secondary battery in a system requiring a higher capacity battery, including an electric vehicle, there is a need to increase the capacity of a negative electrode active material and improve the output and cycle life characteristics.

[0004] A conventional carbon-based negative electrode active material has a theoretical capacity of only 372 mAh / g, and its output characteristics are significantly reduced, especially during high-speed charging, due to the mechanism of interlayer insertion and removal of lithium ions into and from carbon during charging and discharging.

[0005] Accordingly, active research has been carried out on the application of silicon, whose lithium capacity is ten times higher than that of currently used carbon-based materials, to the negative electrode of the lithium battery.

[0006] However, the higher the silicon content, the lower the performance, such as volume expansion during charging and discharging and a reduced service life.

[0007] Conventional technology for reducing chlorosilane molecules to silicon involves dissolving molecules in a liquid medium, such as a liquid electrolyte or molten metal salts, and reducing molecules to silicon by electrochemical deposition; however, there is the problem that precise control of the coating is difficult and application to a porous material is impossible. State-of-the-art documents

[0008] Korean registered patent KR 10 1 929 413 B1. DE 1 135 667 A

[0009] DE 1 135 667 A discloses a process for producing a metal with a high degree of purity, in which a vaporous halide of the metal to be obtained or a gas mixture consisting of a halide and a reducing gas is passed into a device in which a negative electrode is located, and that an electric field is generated between this and a further positive electrode and the gas is introduced into the space in which the electric field is located, characterized in that the negative electrode is heated to a temperature at which the halide or mixture decomposes. KR 10 2008 0 099 616 A

[0010] KR 10 2008 0 099 616 A discloses, inter alia, a method comprising the following steps: placing a substrate in a chamber and introducing a reaction gas; dissociating the reaction gas using a heating element; forming charged nanoparticles while nucleated nanoparticles grow; and applying an electric field to the substrate using an electric field applying part to deposit the charged nanoparticles on the substrate. RevelationTechnical Problem

[0011] It is an object of the present invention to provide a silicon coating method having good precision and controllability on a porous material without using a liquid medium. Technical solution

[0012] To achieve the above object, the present invention provides a silicon manufacturing method using gas phase electroreduction, the silicon manufacturing method comprising: a first step of applying an electrical voltage to a surface of a base material arranged in a reactor; a second step of supplying a silicon-based compound in the gas phase to the base material with the electrical voltage applied thereto; and a third step in which the silicon-based compound reaching the surface of the base material in the gas phase is reduced from the surface of the base material to form a silicon coating layer on the surface of the base material, wherein in the second step, electrons are supplied to the silicon-based compound reaching the surface of the base material in the reactor when an electric voltage is applied to the surface of the base material, in the third step, the silicon-based compound is reduced from the surface of the base material by the electrons to coat the surface of the base material with silicon; wherein the silicon-based compound is a chlorosilane compound and, in the step of supplying the silicon-based compound in the gas phase, the chlorosilane compound is supplied in a gaseous state without being dissolved in a liquid medium; wherein the chlorosilane compound is fed continuously or in pulses without using a catalyst or a reducing agent; wherein the chlorosilane compound is added to the base material in a reactor and the reactor temperature range is 150°C to 250°C; where the current density per unit area is 1 to 200 mA / cm 2 amounts; where the applied electrical voltage is 1 to 100 V. Beneficial effects

[0013] According to the present invention, a silicon-based precursor compound is supplied in the gas phase without using a liquid medium such as a liquid electrolyte or molten metal salts, thereby enabling application to a porous material and achieving excellent precision.

[0014] Furthermore, a coating layer prepared by a method according to the present invention is applicable to a silicon-based compound in a negative electrode active material of a lithium ion battery, and high capacity characteristics are developed even when charging and discharging are repeated, whereby excellent cycle life characteristics and stability can be achieved. Description of the drawings Fig. 1 is a view of a chemical reaction of a method according to the present invention. Fig. 2 is a view showing a process of supplying a silicon-based precursor in the gas phase according to an embodiment of the present invention. Best mode

[0015] The present invention will be described in more detail below.

[0016] The present invention relates to a silicon production process using gas phase electroreduction, the silicon production process comprising: a first step of applying an electrical voltage to a surface of a base material arranged in a reactor; a second step of supplying a silicon-based compound in the gas phase to the base material with the electrical voltage applied thereto; and a third step in which the silicon-based compound reaching the surface of the base material in the gas phase is reduced from the surface of the base material to form a silicon coating layer on the surface of the base material, wherein in the second step, electrons are supplied to the silicon-based compound reaching the surface of the base material in the reactor when an electric voltage is applied to the surface of the base material, in the third step, the silicon-based compound is reduced from the surface of the base material by the electrons to coat the surface of the base material with silicon; wherein the silicon-based compound is a chlorosilane compound and, in the step of supplying the silicon-based compound in the gas phase, the chlorosilane compound is supplied in a gaseous state without being dissolved in a liquid medium; wherein the chlorosilane compound is fed continuously or in pulses without using a catalyst or a reducing agent; wherein the chlorosilane compound is added to the base material in a reactor and the reactor temperature range is 150°C to 250°C; where the current density per unit area is 1 to 200 mA / cm 2 amounts; where the applied electrical voltage is 1 to 100 V.

[0017] In the method of the present invention, a silicon coating is formed directly on the surface of the base material using an electrochemical or chemical process without using a liquid medium. Specifically, a silicon-based compound, wherein the silicon-based compound is a chlorosilane compound, is supplied in the gas phase to the surface of the base material, and an electrical voltage is applied thereto to form a reduction layer of silicon on the surface of the base material.

[0018] In the embodiment of the present invention, the silicon-based precursor compound in the gas phase, which is a chlorosilane compound, may be supplied in a gaseous state without being dissolved in a liquid medium, and the silicon coating layer may be formed on the surface of the base material arranged in a reactor using a chemical deposition method (particularly, a field chemical deposition method).

[0019] The formation process of the silicon coating layer on the surface of the base material is preferably carried out in a temperature range of 150°C to 250°C (i.e., the temperature range of the reactor) for 0.1 to 5 hours, while the silicon-based precursor compound is continuously fed into the reactor. The temperature range of the reactor (i.e., the temperature range within the reactor) is 150°C to 250°C, in which case, decomposition of the base material can be minimized or inhibited. Gas such as argon (Ar) or nitrogen (N2) can flow into the reactor at a constant flow rate.

[0020] In the embodiment of the invention, the silicon-based compound may be supplied using a separate storage vessel for the stainless steel precursor, and the storage vessel may be heated to a temperature range of room temperature to 350°C to evaporate the silicon-based compound.

[0021] According to the present invention, the chlorosilane compound is supplied in a gaseous state without being dissolved in a liquid medium and is supplied continuously or in pulses without using a catalyst or a reducing agent.

[0022] In the embodiment of the present invention, the silicon coating layer may consist of a plurality of silicon nanoparticles dispersed in the form of islands, films, or a combination thereof.

[0023] In particular, when gas-phase electroreduction is used, the silicon coating layer begins to be formed in the shape of islands, and the islands are formed only in cavities in the preformed negative electrode active material, which makes the islands suitable for responding to the volume expansion of the silicon nanoparticles contained in the silicon coating.

[0024] However, as the deposition amount increases, the silicon coating layer is formed in the form of films, and eventually, the silicon coating layer is formed in the state where the films and islands are intermingled. In this case, the capacity per weight of silicon particles can be improved, and the formation efficiency can be improved.

[0025] In contrast, using a physical manufacturing process such as ball milling, it is almost impossible to control the distribution of silicon nanoparticles to be uniform and achieve attachment without electrical resistance.

[0026] The silicon nanoparticles formed in the carbon-based negative electrode active material by gas-phase electroreduction are already electrically bonded to the carbon-based material at the interface between them, thus minimizing irreversible capacity loss. In contrast, in an electrode consisting of a mixture of presynthesized silicon nanoparticles and carbon-based negative electrode active material, the surface of each individual silicon nanoparticle is exposed, which acts as a source of irreversible capacity loss.

[0027] The silicon nanoparticles formed by gas-phase electroreduction can be spherical particles with a diameter of 5 to 100 µm and can be amorphous. Furthermore, carbon, oxygen, or nitrogen in the precursor can participate in the reduction of the silicon-based compound, making it possible to synthesize not only pure silicon nanoparticles but also nanoparticles of a silicon-based compound. The amorphous silicon nanoparticles have a large capacity per particle weight, and the stress due to volume expansion during charging (i.e., alloying with lithium) is significantly lower than that of crystalline silicon nanoparticles. The rate of alloying with and dealloying of lithium is fast, which is beneficial for the charging and discharging rates.

[0028] In the embodiment of the present invention, the silicon coating layer may have a thickness of 5 to 100 µm.

[0029] In the embodiment of the invention, a hydrochlorosilane compound such as silicon tetrachloride (SiCl4), hexachlorodisilane (Si2Cl6), or dichlorosilane (SiH2Cl2), a methylchlorosilane compound such as methylsilane (CH3SiH3), tetrakis(trichlorosilyl)silane, or silicon tetrafluoride (SiF4) can be used as the silicon-based compound; however, the present invention is not limited thereto.

[0030] According to the present invention, the silicon-based compound is a chlorosilane compound.

[0031] According to the present invention, current or voltage is applied to the base material continuously or in pulses to apply an electrical voltage to the surface of the base material, allowing electrons to be supplied thereto. The applied electrical voltage can be applied to the base material in the form of direct current, alternating current, or an artificially generated pulse.

[0032] A conductor such as graphite, copper, lithium, aluminum, stainless steel, or a battery material (NMC / NCA / LFP) can be used as the base material; however, the present invention is not limited to these. Depending on the type of base material, the electrical voltage can be applied in the form of a constant current or a constant voltage, with the current density per unit area being 1 to 200 mA / cm2. The voltage applied to the base material is 1 to 100 V, depending on the type of chlorosilane compound.

[0033] According to the present invention, by using the silicon coating, high capacity characteristics can be stably developed even when charging and discharging are repeated, thereby making it possible to manufacture a lithium ion / metal battery with excellent cycle life characteristics and stability.

Claims

[1] A silicon manufacturing process using gas-phase electroreduction, the silicon manufacturing process comprising: a first step of applying an electrical voltage to a surface of a base material arranged in a reactor; a second step of supplying a silicon-based compound in the gas phase to the base material with the electrical voltage applied thereto; and a third step in which the silicon-based compound reaching the surface of the base material in the gas phase is reduced from the surface of the base material to form a silicon coating layer on the surface of the base material, wherein in the second step, electrons are supplied to the silicon-based compound reaching the surface of the base material in the reactor when an electric voltage is applied to the surface of the base material, in the third step, the silicon-based compound is reduced from the surface of the base material by the electrons to coat the surface of the base material with silicon; wherein the silicon-based compound is a chlorosilane compound and, in the step of supplying the silicon-based compound in the gas phase, the chlorosilane compound is supplied in a gaseous state without being dissolved in a liquid medium; wherein the chlorosilane compound is fed continuously or in pulses without using a catalyst or a reducing agent; wherein the chlorosilane compound is added to the base material in a reactor and the reactor temperature range is 150 °C to 250 °C; where the current density per unit area is 1 to 200 mA / cm 2 amounts; where the applied electrical voltage is 1 to 100 V. [2] The silicon manufacturing method according to claim 1, wherein the silicon-based compound is silicon tetrachloride, SiCl4, hexachlorodisilane, Si2Cl6, dichlorosilane, SiH2Cl2, methylsilane, CH3SiH3, tetrakis(trichlorosilyl)silane or silicon tetrafluoride, SiF4. [3] The silicon manufacturing method according to claim 1, wherein the base material is graphite, copper, lithium, aluminum, stainless steel or a battery material, NMC / NCA / LFP.

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