Process for forming silicon from silica and passivated silicon

Abstract

A process for forming silicon by reducing silica and / or passivated silicon, the process comprising the following steps: - feeding silane to a reactor (2) placed under an inert atmosphere; - feeding silica and / or passivated silicon to the reactor (2) to obtain a mixture formed by the silane and the silica and / or passivated silicon; - applying a carbon dioxide laser beam (6a) to said mixture for the formation of silicon and water in the reactor (2); and - recovering the silicon obtained. Figure for the abstract: Fig 1

Description

Title of the invention: Process for forming silicon from silica and passivated silicon

[0001] The present invention relates, in general, to the formation of silicon and the recycling of silica and passivated silicon waste from various fields such as microelectronics, photovoltaic energy or even batteries.

[0002] More specifically, the invention relates to a method for forming silicon from silica and / or passivated silicon as well as a device for forming silicon from silica and / or passivated silicon.

[0003] Among the new lithium-ion battery electrode materials, silicon, Si, is one of the promising candidates to replace graphite, in particular because of its high theoretical capacity.

[0004] Conventionally, silica, SiO2, is extracted from quartz quarries and then reduced by carbo-reduction to obtain silicon.

[0005] Carbo-reduction is carried out in the presence of carbon, at a very high temperature, around 1700°C, and generates, in addition to silicon, carbon monoxide, CO, or carbon dioxide, CO2.

[0006] Other existing processes make it possible to obtain silicon from silica.

[0007] In particular, a known method is based on the use of a gaseous cloud of aluminum to create a reducing atmosphere intended to reduce silica to silicon.

[0008] However, this process lasts several hours and requires chemical preparation to create the aluminum cloud from aluminum chloride.

[0009] The existing processes for reducing silica are therefore long processes, involving the use of very high temperature furnaces and / or the succession of several synthesis stages, and sometimes even the use of chemical products which are dangerous for the user.

[0010] In addition, these processes need to be carried out in batch form and the homogeneity of the powders obtained is not always guaranteed.

[0011] The invention therefore aims to remedy these drawbacks and to propose a simple and rapid process making it possible to obtain silicon from silica without the formation of polluting compounds, not requiring high temperatures.

[0012] There is therefore provided a method of forming silicon by reduction of silica and / or passivated silicon, the forming method comprising the following steps:

[0013] - conveying silane to a reactor placed under an inert atmosphere;

[0014] - conveying silica and / or passivated silicon to the reactor to obtain a mixture formed by silane and silica and / or passivated silicon;

[0015] - applying a carbon dioxide laser beam to said mixture for the formation of silicon and water in the reactor; and

[0016] - recover the silicon obtained.

[0017] The formation process is carried out in a single step and leads to the production of silicon and water vapor. The reaction takes place under an inert atmosphere and without any other reagent than silane, making it possible to produce silicon powders with high purity levels.

[0018] The silicon obtained can be used in many fields such as microelectronics, photovoltaic energy, or even batteries, such as batteries for electric or hybrid motor vehicles.

[0019] Preferably, the silica and / or passivated silicon are delivered in aerosol form.

[0020] Advantageously, the formation method may comprise varying the flow rate of silica and / or passivated silicon conveyed to the reactor, in particular as a function of at least one parameter chosen from: the residence time of the silica and / or passivated silicon in the reactor or the desired silicon production rate.

[0021] Advantageously, the formation method may comprise varying the flow rate of silane conveyed to the reactor, in particular as a function of at least one parameter chosen from: the residence time of the silane in the reactor, the temperature in the reactor.

[0022] Preferably, the size of the silica and / or passivated silicon particles is between 100 nm and 100 pm.

[0023] Advantageously, the formation process may comprise grinding the silica and / or passivated silicon before being conveyed to the reactor.

[0024] Preferably, the conveyance of the silane and / or silica and / or passivated silicon to the reactor is carried out using an inert gas, preferably argon.

[0025] Preferably, the power of the carbon dioxide laser is between 500 and 2500 W.

[0026] Advantageously, the mixture of silane and silica and / or passivated silicon can be conveyed to the reactor using an inlet of a mixture of silane and silica and / or passivated silicon, the method comprising varying the diameter of the inlet of a mixture of silane and silica and / or passivated silicon, in particular as a function of at least one parameter chosen from: the desired silicon production rate, the size of the particles of silica and / or passivated silicon, or the desired purity of the silicon.

[0027] Advantageously, the silica and / or passivated silicon may be conveyed to the reactor using a silica and / or passivated silicon inlet, the method comprising varying the diameter of the silica and / or passivated silicon inlet, in particular by function of at least one parameter chosen from: the desired silicon production rate, the size of the silica and / or passivated silicon particles, or the desired purity of the silicon.

[0028] Preferably, the silicon obtained is collected by a filter using a pump arranged downstream of the reactor.

[0029] Advantageously, the purity of the silicon obtained can be modulated, preferably from at least one of the following parameters: the temperature of the reaction flame generated during the application of the carbon dioxide laser beam to said mixture, the residence time of the silica and / or the passivated silicon in the reactor, or the silica / silane ratio in the reactor.

[0030] Advantageously, the size of the silicon particles obtained can be modulated, preferably from at least one of the following parameters: the residence time in the flame generated during the application of the carbon dioxide laser beam to said mixture, or the temperature of said flame.

[0031] In one embodiment, the forming method may comprise forming a carbon coating on the surface of the resulting silicon. The silicon compounds thus coated with carbon may advantageously be used in a battery, such as a motor vehicle battery.

[0032] In one embodiment, the silica and / or passivated silicon are derived from silica and / or passivated silicon waste.

[0033] Such recycling makes it possible to limit the environmental impact linked to the extraction of silica from quartz quarries by recycling silica and / or passivated silicon from various sectors such as microelectronics, photovoltaic energy, or even batteries, such as electric or hybrid motor vehicle batteries.

[0034] The invention also relates to a use of silicon capable of being obtained by a formation process as previously described or by a recycling process as previously described in a battery such as a lithium-ion battery.

[0035] The silicon obtained can be used as an active material for lithium-ion cells, for example, in the context of a particularly high-performance battery.

[0036] The invention also relates to a method of forming silicon by reduction of silica and / or passivated silicon, comprising:

[0037] - a reactor under an inert atmosphere;

[0038] - a silane inlet and a silica and / or passivated silicon inlet configured to convey the silane and silica and / or passivated silicon to the reactor;

[0039] - a carbon dioxide laser configured to apply a beam to a mixture formed by silane and silica and / or silicon passivated in the reactor; and

[0040] - an output of the obtained silicon.

[0041] Preferably, the training device comprises an upstream aerosol generator. from the arrival of silica and / or passivated silicon.

[0042] Advantageously, the formation device may comprise a pump arranged downstream of the reactor and a filter capable of collecting the silicon obtained.

[0043] Other aims, advantages and characteristics will emerge from the description which follows, given purely for illustrative purposes and with reference to the attached drawing in which:

[0044] [Fig.l] illustrates a silicon forming device according to one embodiment of the invention.

[0045] In the description of the invention which will be made, the expression "at least one" used must be considered equivalent to the expression "one or more".

[0046] Furthermore, the limits of a domain of values ​​are included in this domain, in particular in the expression “between”.

[0047] [Fig.l] illustrates a device 1 for forming silicon by reduction of silica and / or passivated silicon, according to one embodiment of the invention.

[0048] In the present invention, passivated silicon means a silicon compound comprising an oxidation layer, on all or part of its surface. Indeed, silicon has a tendency to rapidly oxidize on contact with air to form a surface layer of silica. The oxidation layer is commonly called a passivation layer, hence the term "passivated silicon".

[0049] The formation device 1 comprises a reactor 2, placed under an inert atmosphere such as argon, and forming a reaction zone within which the reduction of the silica and / or the passivated silicon to silicon can be carried out.

[0050] An inlet of silica and / or passivated silicon 3 allows the transport of silica and / or passivated silicon to the reactor 2.

[0051] A silane inlet 4 also allows the transport of silane to reactor 2.

[0052] The inlet of silica and / or passivated silicon 3 and the inlet of silane 4 can be formed, respectively, by a first pipe and a second pipe.

[0053] In the example illustrated, the first and second pipes open into a third pipe 5 in fluid connection with the reactor 2.

[0054] Advantageously, the third pipe 5 has an end 5a opening onto the reactor 2.

[0055] The end 5a of the third pipe 5 forms an inlet for a mixture of silane and silica and / or passivated silicon allowing the mixture of silane and silica and / or passivated silicon to enter the reactor 2.

[0056] A carbon dioxide laser 6 is positioned so as to apply a beam 6a to the mixture formed by the silane and the silica and / or the passivated silicon conveyed into the reactor 2.

[0057] Preferably, the silane inlet 4 is positioned downstream of the silica and / or passivated silicon inlet 3, which makes it possible to avoid a flashback, taking into account the reaction between the silane and the carbon dioxide laser 6.

[0058] The presence of the third pipe 5 into which the silane 4 inlet and the silica and / or passivated silicon inlet open, downstream of the reactor 2, makes it possible to separate the silane 4 inlet and the silica and / or passivated silicon inlet and to position the silane 4 inlet downstream of the silica and / or passivated silicon inlet 3.

[0059] The forming device 1 also comprises an output of obtained silicon 7.

[0060] Preferably, the end 5a of the third conduit 5 and the silicon outlet obtained 7 are positioned on a common axis.

[0061] The reaction zone is very localized, which promotes homogeneity of the silicon powder obtained thanks to a reduction reaction which takes place within the flame, on a small quantity of aerosol powder at each moment.

[0062] Advantageously, the carbon dioxide laser 6 can be positioned so that the beam 6a extends along an axis perpendicular to the common axis along which the end 5a of the third pipe 5 and the output of the obtained silicon 7 are positioned.

[0063] Preferably, the forming device 1 further comprises an aerosol generator 8 positioned upstream of the arrival of silica and / or passivated silicon 3. The aerosol generator 8 is capable of forming an aerosol from a silica and / or passivated silicon powder.

[0064] Preferably, the forming device 1 comprises a filter 9 capable of collecting the silicon obtained.

[0065] Advantageously, a pump 10 can be arranged downstream of the reactor 2 so as to force the evacuation of the gaseous phase produced, comprising silicon and water vapor, towards the silicon outlet obtained 7 and in particular to facilitate the recovery of the silicon obtained on the filter 9.

[0066] The invention also relates to a method of forming silicon by reduction of silica and / or passivated silicon.

[0067] The forming process comprises supplying silane to the reactor 2 placed under an inert atmosphere, such as argon.

[0068] The forming method also comprises conveying silica and / or passivated silicon to the reactor 2.

[0069] A mixture formed by silane and silica and / or passivated silicon is obtained. This mixture is conveyed to reactor 2.

[0070] In the example illustrated, the conveyance of silica and / or passivated silicon is carried out by means of the first pipe forming the inlet of silica and / or passivated silicon 3.

[0071] In addition, the silane is conveyed by means of the second pipe forming the silane inlet 4.

[0072] Also, the first and second pipes open into the third pipe 5 in fluid connection with the reactor 2 which allows the transport of the mixture formed by the silane and the silica and / or the passivated silicon to the reactor 2.

[0073] According to one embodiment, only silica can be conveyed to the reactor 2.

[0074] According to an alternative, only passivated silicon can be conveyed to the reactor 2.

[0075] According to another alternative, a mixture of silica and passivated silicon can be transported to reactor 2.

[0076] A beam 6a of carbon dioxide laser 6 is then applied to the mixture of silane and the silica and / or the passivated silicon until the formation of silicon and water in the reactor 2.

[0077] The silicon obtained is recovered.

[0078] The inert atmosphere of reactor 2 makes it possible to avoid the presence of additional oxygen which would promote the oxidation of the silane rather than the reduction of the silica.

[0079] The silane, by absorption of the beam 6a of the carbon dioxide laser 6, decomposes into silicon and dihydrogen, producing a high temperature flame, up to more than 1000°C depending on the power of the laser 6 used and the flow rate of silane conveyed.

[0080] At the intersection between the carbon dioxide laser 6 and the silane, the silica and / or the passivated silicon is therefore found in a highly reducing atmosphere, given the presence of dihydrogen, and at high temperature, causing the reduction of the silica molecules of the silica and / or the passivated silicon. The reduction results in the formation of silicon and water.

[0081] The reduction of silica and / or passivated silicon takes place according to the following reaction:

[0082] SiH4 Si + 2H2

[0083] SiO2 + H2 SiO + H2O

[0084] SiO + H2 Si + H2O

[0085] Let the total reaction be as follows:

[0086] SiO2 + SiH4 = 2Si + 2H2O

[0087] The silane is conveyed to reactor 2 in the gas phase.

[0088] The silica and / or passivated silicon are conveyed to reactor 2 in aerosol form.

[0089] A solid aerosol comprising silica powder and / or passivated silicon suspended in a gaseous medium, such as argon, is generated by the aerosol generator 8 before being conveyed to the reactor 2.

[0090] The reaction zone is very localized which promotes homogeneity of the silicon powder obtained thanks to a reduction reaction which takes place within the flame. generated when applying the carbon dioxide laser beam to the mixture of silane and silica and / or passivated silicon, on a small quantity of aerosol powder at each instant.

[0091] The size of the silica and / or passivated silicon particles is preferably between 100 nm and 100 pm.

[0092] The forming process may advantageously comprise a step of grinding the silica and / or passivated silicon, before being conveyed to the reactor 2 in order to reduce and homogenize the size of the particles.

[0093] Preferably, the conveyance of the silane and / or silica and / or passivated silicon to the reactor 2 is carried out using an inert gas forming a transport fluid, preferably argon.

[0094] Preferably, the laser power is set between 500 W and 2500 W.

[0095] The forming method may comprise varying the diameter of the silica and / or passivated silicon inlet 3.

[0096] Preferably, the diameter of the inlet of the mixture of silane and silica and / or passivated silicon, formed in the example illustrated by the end 5a of the third pipe 5, may be between 5 mm and 12 mm.

[0097] The variation of the diameter of the arrival of the mixture of silane and silica and / or passivated silicon can be carried out as a function of at least one parameter chosen from: the desired silicon production rate, the size of the silica and / or passivated silicon particles, or the desired purity of the silicon.

[0098] Advantageously, the forming method may comprise varying the diameter of the silica and / or passivated silicon inlet 3, in particular as a function of at least one parameter chosen from: the desired silicon production rate, the size of the silica and / or passivated silicon particles, or the desired purity of the silicon.

[0099] The forming method may also include varying the flow rate of silica and / or passivated silicon fed to the reactor 2.

[0100] The variation of the flow rate of silica and / or passivated silicon can be carried out as a function of at least one parameter chosen from: the residence time of the silica and / or passivated silicon in the reactor 2 or the desired silicon production rate.

[0101] The forming method may include varying the flow rate of silane supplied to the reactor 2.

[0102] The variation of the silane flow rate can be carried out as a function of at least one parameter chosen from: the residence time of the silane in the reactor 2 or the temperature in the reactor 2.

[0103] The flame temperature and residence time are dependent on the flow rates of silane and silica and / or passivated silicon fed into reactor 2. A higher concentration of silane arriving in reactor 2 allows greater absorption of carbon dioxide laser energy 6 and a higher reaction temperature, but with a shorter residence time.

[0104] The forming method may also comprise modulating the purity of the silicon obtained, preferably from at least one of the following parameters: the temperature of the reaction flame generated during the application of the beam 6a of carbon dioxide laser 6 to the mixture of silane and silica and / or passivated silicon, the residence time of the silica and / or passivated silicon in the reactor 2, or the silica and / or passivated silicon / silane ratio in the reactor 2.

[0105] The forming method may also comprise modulating the size of the silicon particles, preferably from at least one of the following parameters: the residence time of the silica and / or passivated silicon in the flame generated during the application of the beam 6a of carbon dioxide laser 6 to the mixture of silane and silica and / or passivated silicon, or the temperature of the flame generated during the application of the beam 6a of carbon dioxide laser 6 to the mixture of silane and silica and / or passivated silicon.

[0106] The forming process is therefore flexible. Controlling the incoming flow rates of inert transport gas and silica and / or passivated silicon aerosol as well as controlling the power of the beam 6a of the carbon dioxide laser 6 makes it possible to vary the production flow rates and the size of the particles obtained.

[0107] The forming process allows silicon to be formed continuously. For this, the silane and the silica and / or the passivated silicon can be injected into the reactor 2 continuously.

[0108] The formation process makes it easier to industrialize it and thus facilitate the formation of silicon on a large scale.

[0109] In the example illustrated, the silicon obtained is collected by the filter 9 using the pump 10 arranged downstream of the reactor 2.

[0110] The forming method can be used to form silicon from previously unused silica and / or passivated silicon.

[0111] Alternatively, the forming method may be used to form silicon from silica scrap and / or passivated silicon.

[0112] By silica and / or passivated silicon waste is meant in the present invention a silica material and / or a passivated silicon material which has already been used during at least one first use.

[0113] This makes it possible to recycle silica and / or passivated silicon waste from various sectors.

[0114] The invention also relates to the use of silicon obtained by a formation method as previously described in a battery such as a lithium-ion battery.

Claims

Claims

1. A method of forming silicon by reducing silica and / or passivated silicon, the method comprising the following steps: - supplying silane to a reactor (2) placed under an inert atmosphere; - supplying silica and / or passivated silicon to the reactor (2) to obtain a mixture formed by the silane and the silica and / or the passivated silicon; - applying a beam (6a) of a carbon dioxide laser (6) to said mixture for the formation of silicon and water in the reactor (2); and - recovering the silicon obtained.

2. A forming method according to claim 1, wherein the silica and / or passivated silicon are supplied to the reactor (2) in aerosol form.

3. Forming method according to claim 2, comprising varying the flow rate of silica and / or passivated silicon conveyed to the reactor (2), in particular as a function of at least one parameter chosen from: the residence time of the silica and / or passivated silicon in the reactor (2) or the desired silicon production rate.

4. A forming method according to any one of the preceding claims, wherein the mixture of silane and silica and / or passivated silicon is fed to the reactor (2) using an inlet of mixture of silane and silica and / or passivated silicon, the method comprising varying the diameter of the inlet of mixture of silane and silica and / or passivated silicon, in particular as a function of at least one parameter chosen from: the desired silicon production rate, the size of the particles of silica and / or passivated silicon, or the desired purity of the silicon.

5. A forming method according to any one of the preceding claims, wherein the purity of the silicon obtained is modulated from at least one of the following parameters: the temperature of the reaction flame generated during the application of the beam (6a) of carbon dioxide laser (6) to said mixture, the residence time of the silica and / or passivated silicon in the reactor (2), or the silica / silane ratio in the reactor (2).

6. A method of formation according to any one of the preceding claims, the size of the silicon particles obtained is modulated from at least one of the following parameters: the residence time in the flame generated when applying the beam (6a) of carbon dioxide laser (6) to said mixture, or the temperature of said flame.

7. A forming method according to any preceding claim, wherein the silica and / or passivated silicon are derived from silica and / or passivated silicon waste.

8. Use of silicon obtained by a formation method according to any one of claims 1 to 7 in a battery such as a lithium-ion battery.

9. Device for forming silicon by reduction of silica and / or passivated silicon, comprising: - a reactor (2) under an inert atmosphere; - a silane inlet (4) and a silica and / or passivated silicon inlet (3) configured to convey the silane and the silica and / or the passivated silicon to the reactor (2); - a carbon dioxide laser (6) configured to apply a beam (6a) to a mixture formed by the silane and the silica and / or the passivated silicon in the reactor (2); and - an outlet for the silicon obtained.

10. Device according to claim 9, comprising an aerosol generator (8) upstream of the arrival of silica and / or passivated silicon (3).

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