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WO2012083480A1 - Procédé et appareil pour la production de silicium pur - Google Patents

Procédé et appareil pour la production de silicium pur Download PDF

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Publication number
WO2012083480A1
WO2012083480A1 PCT/CN2010/002087 CN2010002087W WO2012083480A1 WO 2012083480 A1 WO2012083480 A1 WO 2012083480A1 CN 2010002087 W CN2010002087 W CN 2010002087W WO 2012083480 A1 WO2012083480 A1 WO 2012083480A1
Authority
WO
WIPO (PCT)
Prior art keywords
alloy
electrolyte
crucible
pure silicon
electrolysis
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
PCT/CN2010/002087
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English (en)
Inventor
Albert Pui Sang LAU
Lee Cheung LAU
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Epro Development Ltd
Original Assignee
Epro Development Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Epro Development Ltd filed Critical Epro Development Ltd
Priority to PCT/CN2010/002087 priority Critical patent/WO2012083480A1/fr
Priority to JP2013545013A priority patent/JP2014502671A/ja
Priority to TW100147484A priority patent/TW201231391A/zh
Priority to DE112011104441T priority patent/DE112011104441T5/de
Priority to CN2011800616056A priority patent/CN103261095A/zh
Priority to PCT/CN2011/002138 priority patent/WO2012083588A1/fr
Priority to EP11850059.4A priority patent/EP2655252A1/fr
Priority to US13/996,403 priority patent/US20130277227A1/en
Publication of WO2012083480A1 publication Critical patent/WO2012083480A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/33—Silicon
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/02—Process control or regulation
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a method and apparatus for producing silicon, and in particular, silicon of suitable purity for use in solar-cell applications and the like.
  • Siemens the “Siemens Process”
  • Siemens process high-purity silicon rods are exposed to trichlorosilane at 1150°C such that the trichlorosilane gas decomposes and deposits additional silicon onto the rods to enlarge them.
  • the Siemens process is however considered to be both relatively expensive and not environmentally-friendly. In energy terms, it is estimated that the Siemens process expends approximately 200 MW.Hr of electricity in order to produce 1 ton of solar- grade silicon.
  • Carbothermic reduction processes have also been developed as an alternative to the Siemens process. However, these processes do not produce silicon which is of solar-grade quality since impurities such as boron and phosphorous, which are inherently contained in carbon, cannot be removed to suitably low levels (i.e. to levels in the parts-per-million or parts-per-billion).
  • the present invention seeks to alleviate at least one of the above-described problems.
  • the present invention may involve several broad . forms. Embodiments of the present invention may include one or any combination of the different broad forms herein described.
  • the present invention provides a method of producing pure silicon from an electrolyte wherein the method includes the steps of:
  • the stirring of the molten electrolyte during electrolysis may assist in both generating ion-flow within the molten electrolyte, and, increasing the contact between the electrolyte and the molten alloy anode.
  • the pure silicon may thereafter be readily segregated from the alloy using a segregation technique as discussed further below.
  • the electrolyte may include cryolite, calcium oxide particles and quartz particles. More preferably, the electrolyte may comprise approximately between 82-94% cryolite particles by weight of the electrolyte. Also typically, the electrolyte may comprise approximately between 3-15% calcium oxide particles by weight of the electrolyte. Also preferably, the electrolyte may comprise approximately 3% quartz particles by weight of the electrolyte. More preferably, the electrolyte may comprise approximately 87% cryolite particles, 10% calcium oxide particles and 3% quartz particles by weight of the electrolyte. Also preferably, the present invention may include a step of controllably adding quartz particles to the molten electrolyte during electrolysis to substantially maintain approximately 3% quartz particles in the electrolyte by weight of the electrolyte.
  • the first crucible may include at least one of a carbon, silicon nitrate and silicon carbide material.
  • the first crucible material may be adapted to generate heat if placed within an induction furnace, or, to conduct heat in a relatively efficient manner if placed in a direct heating furnace.
  • the first crucible may include a recess defined by an inner peripheral wall and a base for receiving the electrolyte.
  • the recess may include a cylindrical shape.
  • a crucible lining may be arranged inside the first crucible recess between the first crucible and the electrolyte. More preferably, the crucible lining may be contoured to substantially complement the inner peripheral wall of the first crucible.
  • the crucible lining may include a quartz material.
  • the crucible lining may include at least one of a calcium oxide, magnesium fluoride, sodium fluoride and silicon material.
  • the material used as the crucible lining may be temperature resistant above at least approximately 1000°C.
  • the material used as the crucible lining may also be corrosion-resistant when exposed to the electrolyte during the electrolysis process.
  • the crucible lining may assist in preventing electrolyte from being absorbed into the first crucible wall which tends to decrease efficiency in the electrolysis process. Additionally, because the crucible lining assists in blocking absorption of the electrolyte into the first crucible wall, this results in more electrolyte being directed towards the alloy anode to further improve efficiency of the electrolysis process.
  • the crucible lining may be formed from the molten electrolyte itself by generating a temperature gradient within the molten electrolyte wherein a portion of the molten electrolyte may be solidified adjacent the inner peripheral wall of the first crucible.
  • electric arc heating may be used to create the temperature gradient between the cathode and molten electrolyte adjacent the inner peripheral wall of the first crucible.
  • the electrolyte may be heated using at least one of an arc furnace and an induction furnace.
  • the molten electrolyte may be stirred using at least one of an induction furnace to magnetically stir the molten electrolyte, and, a mechanical stirrer.
  • the anode may include at least one of a copper, gold, silver, zinc and a magnesium material.
  • the anode includes a copper material.
  • the anode may comprise an alloy of copper and pure silicon.
  • the pure silicon may comprise approximately 3% by weight of the alloy.
  • the alloy prior to step (i) of the first broad form, the alloy may be positioned in the first crucible adjacent the base of the first crucible and melted in the first crucible whereby said electrolyte may be thereafter deposited into the first crucible on top of the melted alloy in readiness for step (i) of the first broad form to be performed.
  • the alloy may be melted at a temperature of between approximately 950-980°C.
  • step (i) of the first broad form may include heating the electrolyte in the first crucible to a temperature of at least approximately 900°C in order to form the molten electrolyte.
  • the molten electrolyte may be maintained at a temperature whereby the molten electrolyte does not solidify.
  • the temperature may be maintained between approximately 900-1000°C to alleviate solidification of the molten electrolyte.
  • the temperature may be maintained at approximately 980°C to prevent solidification of the molten electrolyte.
  • the molten electrolyte may be exposed to a current density of between approximately 0.1A/cm 2 to 2.
  • the cathode may include at least one of a carbon, copper, tungsten and a platinum material.
  • the cathode may be formed by pressing purified carbon powder into a solid rod. More preferably, the carbon powder may be purified by exposing the carbon powder to an acid wash and chlorine flushing to remove impurities.
  • the cathode may be positioned in the first crucible after the electrolyte has been heated to form the molten electrolyte wherein the cathode is in electrical/ionic communication with the molten electrolyte.
  • the present invention may include a step of segregating the pure silicon from the alloy after step (ii).
  • the step of segregating the pure silicon from the alloy may be performed when pure silicon produced as a result of electrolysis may no longer be soluble with the alloy.
  • the temperature of the alloy is between approximately 950-980°C, the pure silicon may no longer be soluble with the alloy when the pure silicon in the alloy is approximately 25% per weight of the alloy.
  • the step of segregating the pure silicon from the alloy may include adjusting the temperature of the alloy to between approximately 800-850°C whereby pure silicon is able to naturally segregate from the alloy.
  • the alloy may be transferred into a second crucible.
  • the second crucible may include a material which is inert with respect to the alloy and/or molten salts.
  • molten salts may be used to cover the segregated pure silicon to alleviate re-oxidisation of the pure silicon.
  • the alloy in the second crucible may be reintroduced back into the first crucible when a predetermined percentage of pure silicon particles by weight of the alloy has segregated from the alloy. More typically, the predetermined percentage of pure silicon particles by weight of the alloy may include approximately 11% of pure silicon particles by weight of the alloy when the alloy in the second crucible is reintroduced into the first crucible.
  • the following steps may be applied: (i) forming the alloy in the second crucible into at least one of a tape and a powder; and
  • pure silicon particles may be segregated from the alloy in the form of nano-sized pure silicon particles.
  • the tape may be formed by at least one of casting and extruding the alloy.
  • the powder may be formed by mechanically grinding or milling the alloy.
  • the powder may be formed by grinding the alloy in a controlled environment.
  • the powder may include micron to nano sized alloy particles.
  • the step of applying the secondary electrolysis may include submerging the tape or powder in an electrolyte solution.
  • the electrolyte solution may include at least one of hydrochloric acid (HCI), dehydrated acetic acid, iodine solutions (i.e. potassium iodine solution), hydrazoic acid (HN3), acetone, concentrated alcohol and a combination thereof.
  • HCI hydrochloric acid
  • iodine solutions i.e. potassium iodine solution
  • HN3 hydrazoic acid
  • acetone concentrated alcohol and a combination thereof.
  • concentrated alcohol concentrated alcohol
  • the acidity of the electrolyte solution may be replenished.
  • a current of less than 1A may be applied during the secondary electrolysis.
  • the electrolyte solution containing the nano-sized pure silicon particles may be further processed to separate the nano-sized pure silicon particles from the electrolyte solution.
  • the nano-sized pure silicon particles may be centrifugally separated from the electrolyte solution.
  • the separated nano-sized pure silicon particles may thereafter be stored in a substance suitable for alleviating reaction with free oxygen.
  • the substance may include concentrated alcohol.
  • any one of the above steps of segregating pure silicon from the alloy in the second crucible may be performed directly upon the alloy in the first crucible without being removed into a second crucible.
  • the present invention provides an apparatus for producing pure silicon from an electrolyte including:
  • a heat source for heating the electrolyte in the first crucible to form a molten electrolyte
  • an anode and a cathode which are adapted for electrical/ionic communication with the molten electrolyte wherein electrolysis is able to be applied to the molten electrolyte when a potential difference is provide between the anode and the cathode;
  • a stirring device for stirring the molten electrolyte when electrolysis is being applied whereby pure silicon is produced which is soluble with the anode to form an alloy.
  • the electrolyte may include cryolite, calcium oxide particles and quartz particles. More preferably, the electrolyte may comprise approximately between 82-94% cryolite particles by weight of the electrolyte. Also typically, the electrolyte may comprise approximately between 3-15% calcium oxide particles by weight of the electrolyte. Also preferably, the electrolyte may comprises approximately 3% quartz particles by weight of the electrolyte. More preferably, the electrolyte may comprise approximately 87% cryolite particles, 10% calcium oxide particles and 3% quartz particles by weight of the electrolyte.
  • the present invention may include a dispenser for dispensing quartz particles in to the electrolyte during electrolysis to substantially maintain approximately 3% quartz particles in the electrolyte by weight of the electrolyte.
  • the first crucible may include at least one of a carbon, silicon nitrate and silicon carbide material.
  • the first crucible may include a recess defined by an inner peripheral wall and a base for receiving the electrolyte.
  • the recess may include a cylindrical shape.
  • the present invention may include a crucible lining arranged inside of the first crucible recess between the first crucible and the electrolyte.
  • the crucible lining may be contoured to substantially complement the inner peripheral wall of the first crucible.
  • the crucible lining may include at least one of a quartz, calcium oxide, magnesium fluoride, sodium fluoride and silicon material.
  • the first crucible may include a crucible lining formed from solidification of a portion of the molten electrolyte as a result of a temperature gradient being generated within the molten electrolyte.
  • the present invention may include an electric arc heating device for generating the temperature gradient between the cathode and molten electrolyte adjacent the inner peripheral wall of the first crucible.
  • the heat source may include at least one of an arc furnace and an induction furnace.
  • the arc furnace may be a primary source of heat.
  • the molten electrolyte may be stirred using at least one of an induction furnace to magnetically stir the molten electrolyte, and, a mechanical stirrer.
  • an induction furnace may alleviate production costs by providing a dual function as a heat source and as a stirring device.
  • the anode may include at least one of a copper, silver, gold, zinc and a magnesium material.
  • the anode may include a copper material.
  • the anode may include an alloy of copper and pure silicon.
  • the pure silicon may comprise approximately 3% by weight of the alloy.
  • the alloy may be melted in the first crucible adjacent the base of the first crucible and the electrolyte may be positionable on top of the alloy.
  • the heat source may be adapted to melt the alloy at a temperature of between approximately 950-980°C.
  • the heat source may be adapted to heat the electrolyte in the first crucible to a temperature of at least approximately 900 C C in order to form the molten electrolyte.
  • the heat source may be adapted to maintain the molten electrolyte at a temperature whereby the molten electrolyte does not solidify.
  • the heat source may be adapted to maintain the temperature of the molten electrolyte at between approximately 900-1000°C to prevent solidification of the molten electrolyte.
  • the heat source may be adapted to maintain the temperature of the molten electrolyte at approximately 980°C to prevent solidification of the molten electrolyte.
  • the molten electrolyte may be exposed to a current density of between approximately 0.1 A/cm 2 to 2. OA/cm 2 in the first crucible when electrolysis is applied.
  • the cathode may include at least one of a carbon, copper, tungsten and a platinum material.
  • the cathode may include a solid rod formed from pressed purified carbon powder. More preferably, the carbon powder may be purified by exposing the carbon powder to an acid wash and chlorine flushing to remove impurities.
  • the cathode may be adapted for positioning in to the first crucible after the electrolyte has been heated to form the molten electrolyte whereby the cathode is in electrical/ionic communication with the molten electrolyte.
  • the present invention may include an apparatus for segregating the pure silicon from the alloy.
  • the apparatus for segregating the pure silicon from the alloy may be adapted to segregate the pure -silicon from the alloy when the pure silicon produced as a result of electrolysis is no longer soluble with the alloy.
  • the apparatus for segregating the pure silicon from the alloy may be adapted to adjust the temperature of the alloy to between approximately 800- 850°C whereby pure silicon may be able to segregate from the alloy.
  • the apparatus for segregating the pure silicon from the alloy may be adapted to transfer the alloy into a second crucible before adjusting the temperature of the alloy to between approximately 800-850°C.
  • the second crucible may include a material which may be inert with respect to the alloy and/or molten salts.
  • molten salts may be used to cover segregated pure silicon to alleviate re- oxidisation of the pure silicon.
  • the present invention may be adapted for reintroducing the alloy in the second crucible back into the first crucible when a predetermined percentage of pure silicon particles by weight of the alloy has segregated from the alloy. More typically, the predetermined percentage of pure silicon particles by weight of the alloy may include approximately 11% of pure silicon particles by weight of the alloy.
  • the apparatus for segregating the pure silicon from the alloy in the second crucible may include:
  • the apparatus for forming the alloy into a tape may be adapted to cast or extrude the alloy into the tape.
  • the apparatus for forming the powder may be adapted for mechanically grinding or milling the alloy into the powder in a controlled environment.
  • the powder may be formed by grinding the alloy.
  • the powder may include micron to nano sized alloy particles.
  • the apparatus for applying the secondary electrolysis may be adapted for submerging the tape or powder in an electrolyte solution.
  • the electrolyte solution may include at least one of hydrochloric acid (HCI), dehydrated acetic acid, iodine solutions (i.e. potassium iodine solution), hydrazoic acid (HN 3 ), acetone, concentrated alcohol and a combination thereof.
  • HCI hydrochloric acid
  • iodine solutions i.e. potassium iodine solution
  • HN 3 hydrazoic acid
  • acetone concentrated alcohol and a combination thereof.
  • concentrated alcohol concentrated alcohol
  • the acidity of the electrolyte solution may be replenished.
  • the apparatus for applying the secondary electrolysis may be adapted for applying a current of less than 1 A during the secondary electrolysis.
  • the present invention may include an apparatus for separating nano-sized pure silicon particles in the electrolyte solution from the electrolyte solution after the secondary electrolysis has been applied.
  • this may include a centrifuge device for centrifugally separating the nano-sized pure silicon particles from the electrolyte solution.
  • the present invention may include a storage apparatus for storing the separated nano-sized pure silicon particles in a substance suitable for alleviating reaction with free oxygen.
  • the substance may include concentrated alcohol.
  • the apparatus for segregating the pure silicon from the alloy in the second crucible may be adapted to similarly separate pure silicon directly from the alloy in the first crucible without being removed into a second crucible.
  • the present invention provides a method of producing pure silicon from an electrolyte wherein the method includes the steps of:
  • the present invention provides an apparatus for producing pure silicon from an electrolyte including:
  • a heat source for heating the electrolyte in the first crucible to form a molten electrolyte
  • an anode and a cathode which are adapted for electrical/ionic communication with the molten electrolyte wherein electrolysis is able to be applied to the molten electrolyte when a potential difference is provide between the anode and the cathode;
  • a crucible lining arranged inside the first crucible to substantially separate the molten electrolyte from an inner peripheral wall of the first crucible as electrolysis is being applied to the molten electrolyte;
  • the present invention provides a method of segregating pure silicon from an alloy containing at least one of a copper, gold, silver, zinc and a magnesium material alloyed with pure silicon particles, the method including the steps of :
  • pure silicon particles may be segregated from the alloy in the form of nano-sized pure silicon particles.
  • the tape may be formed by at least one of casting and extruding the alloy.
  • the powder may be formed by mechanically grinding or milling the alloy in a controlled environment.
  • the powder is formed by grinding the alloy.
  • the powder may include micron to nano sized alloy particles.
  • the step of performing the electrolysis may include submerging the tape or powder in an electrolyte solution.
  • the electrolyte solution may include at least one of hydrochloric acid (HCI), dehydrated acetic acid, iodine solutions (i.e. potassium iodine solution), hydrazoic acid (HN3), acetone, concentrated alcohol and a combination thereof.
  • HCI hydrochloric acid
  • iodine solutions i.e. potassium iodine solution
  • HN3 hydrazoic acid
  • acetone concentrated alcohol and a combination thereof.
  • concentrated alcohol concentrated alcohol
  • the acidity of the electrolyte solution may be replenished.
  • a current of less than 1 A may be applied during the electrolysis.
  • the electrolyte solution containing the nano-sized pure silicon particles may be further processed to separate the nano-sized pure silicon particles from the electrolyte solution.
  • the nano-sized pure silicon particles may be centrifugally separated from the electrolyte solution.
  • the separated nano-sized pure silicon particles may thereafter be stored in a substance suitable for alleviating reaction with free oxygen.
  • the substance may include concentrated alcohol.
  • the present invention provides an apparatus for segregating pure silicon from an alloy containing at least one of a copper, gold, silver, zinc and a magnesium material alloyed with pure silicon particles, the apparatus including:
  • pure silicon particles may be segregated from the alloy in the form of nano-sized pure silicon particles.
  • the apparatus for forming the alloy into a tape may be adapted to cast or extrude the alloy into the tape.
  • the apparatus for forming the powder may be adapted for mechanically grinding or milling the alloy into the powder.
  • the powder may be formed by grinding the alloy in a controlled environment.
  • the powder may include micron to nano sized alloy particles.
  • the apparatus for performing the electrolysis may be adapted for submerging the tape or powder in an electrolyte solution.
  • the electrolyte solution may include at least one of hydrochloric acid (HCI), dehydrated acetic acid, iodine solutions (i.e. potassium iodine solution), hydrazoic acid (HN3), acetone, concentrated alcohol and a combination thereof.
  • HCI hydrochloric acid
  • iodine solutions i.e. potassium iodine solution
  • HN3 hydrazoic acid
  • acetone concentrated alcohol and a combination thereof.
  • concentrated alcohol concentrated alcohol
  • the acidity of the solution may be replenished.
  • the apparatus for performing the electrolysis may be adapted for applying a current of less than 1A during the electrolysis.
  • the present invention may include an apparatus for separating nano-sized pure silicon particles in the electrolyte solution from the electrolyte solution.
  • this may include a centrifuge device for centrifugally separating the nano-sized pure silicon particles from the electrolyte solution.
  • the present invention may include a storage apparatus for storing the separated nano- sized pure silicon particles in a substance suitable for alleviating reaction with free oxygen.
  • the substance may include concentrated alcohol.
  • the present invention provides a pure silicon produced in accordance with any one of the broad forms of the present invention described herein.
  • the present invention provides a solar cell including pure silicon produced in accordance with any one of the broad forms of the present invention described herein.
  • the present invention provides a battery including pure silicon produced in accordance with any one of the broad forms of the present invention described herein.
  • an anode of the battery is formed from the pure silicon.
  • the present invention provides a crucible liner adapted for use in accordance with any one of the broad forms of the present invention described herein.
  • the present invention provides an electrical-grade silicon material suitable for use in forming an integrated circuit element, said electrical-grade silicon material being produced in accordance with any one of the broad forms of the present invention described herein.
  • Figure 1 shows a flowchart of a method for producing pure silicon from an electrolyte in accordance with an embodiment of the present invention
  • Figure 2 shows a flowchart of an embodiment method for segregating pure silicon from the alloy formed in accordance with the method steps depicted in Fig. 1 ;
  • Figure 3 shows a side cut-away view of an apparatus for producing pure silicon in accordance with an embodiment of the present invention
  • Figures 4(a) and 4(b) show an EDX chart and corresponding SEM image of a first sample taken of an alloy containing pure silicon after the first electrolysis in the first crucible;
  • Figures 5(a) and 5(b) show an EDX chart and corresponding SEM image of a second sample taken of an alloy containing pure silicon after the first electrolysis in the first crucible;
  • Figures 6(a) and 6(b) show an EDX chart and corresponding SEM image of a third sample taken of an alloy containing pure silicon after the first electrolysis in the first crucible;
  • Figures 7(a) and 7(b) show an EDX chart and corresponding SEM image of a fourth sample taken of an alloy containing pure silicon after the first electrolysis in the first crucible;
  • Figure 8 shows EDX data and a corresponding SEM image of a sample of pure silicon which has naturally segregated from the alloy transferred from the first crucible into the second crucible in accordance with embodiments of the present invention
  • Figure 9 shows EDX data and a corresponding SEM image of a sample of nano-sized pure silicon which has segregated from the alloy in the second crucible during a secondary electrolysis involving use of a 10%hydrochloric acid (HCI) electrolyte solution in accordance with embodiments of the present invention
  • Figure 10 shows EDX data and a corresponding SEM image of a sample of nano-sized pure silicon which has segregated from the alloy in the second crucible during a secondary electrolysis involving use of a 20%hydrochloric acid (HCI) electrolyte solution in accordance with embodiments of the present invention
  • Figure 11 shows a further EDX data and a corresponding SEM image of a further sample of nano-sized pure silicon which has segregated from the alloy in the second crucible during a secondary electrolysis in accordance with embodiments of the present invention
  • Figure 12 shows an amorphous tape casted from an alloy remaining in the second crucible after natural segregation of some of the pure silicon particles in the alloy in accordance with embodiments of the present invention.
  • Figure 13 shows testing parameters and test result data observed in producing an alloy containing pure silicon in the first crucible in accordance with embodiments of the present invention described herein when a direct heat furnace and induction furnace are variably used in heating the electrolyte during the first electrolysis.
  • Figures 1 and 2 depict flowcharts of method steps in accordance with embodiments of the for producing pure silicon.
  • the term "pure silicon” refers to solar-grade silicon.
  • An apparatus (1 ) which is used in performing the method steps depicted in Figs. 1 and 2 is shown in Fig.
  • first crucible (2) for receiving an electrolyte
  • crucible lining (3) arranged within the first crucible (2) which separates the electrolyte from an inner peripheral wall (2a) of the first crucible (2)
  • a heat source for heating the first crucible (2)
  • an electrolysis device for applying electrolysis to the electrolyte (4) after the electrolyte (4) has been melted by the heat source
  • a device for stirring the molten electrolyte (4) during electrolysis Pure silicon produced by electrolysis forms an alloy with the anode (5). The pure silicon can thereafter be extracted from the alloy through use of a segregation apparatus and processes as will be described in greater detail below.
  • the electrolyte used in embodiments described herein comprise approximately 87% cryolite particles, 10% calcium oxide particles and 3% quartz particles by weight of the electrolyte (4).
  • the electrolyte (4) Before being deposited into the first crucible (2), the electrolyte (4) is manufactured by melting together the cryolite, calcium oxide and quartz particles at a temperature of 1200°C and then allowing the melted substance to solidify. The resulting density of this electrolyte (4) is approximately 3g/cm 3 .
  • the first crucible (2) is formed from a carbon material and has an internal recess (2c) for receiving the electrolyte (4).
  • the recess (2c) is cylindrically-shaped and is defined by an inner peripheral wall (2a) and a base (2b).
  • the first crucible (2) and internal recess (2c) need not be cylindrically-shaped in alternative embodiments.
  • the first crucible (2) can alternatively be formed from materials such as silicon nitrate or silicon carbide material. Whichever material is used, it is desirable that the first crucible (2) material be able to generate heat if placed within an induction furnace, or, to conduct heat in a relatively efficient manner if placed in a direct heating furnace.
  • the electrolysis device includes an anode (5) and a cathode (7) which are connected to positive and negative terminals of a power supply (not shown).
  • a power supply not shown.
  • the anode (5) includes an alloy of copper and approximately 3% pure silicon particles by weight of the alloy.
  • the alloy is initially formed by melting the copper and combining the approximately 3% pure silicon particles at a temperature of approximately 1200°C.
  • the inclusion of the 3% pure silicon particles in the alloy anode assists in setting the melting temperature of the alloy at a temperature which is applied during electrolysis.
  • this amount is a suitable minimum level in setting a suitable melting point.
  • the cathode (7) includes a carbon rod which is formed by pressed purified carbon powder.
  • the carbon powder is purified before pressing by applying an acid wash and chlorine flushing to remove any impurities in the carbon powder.
  • the carbon rod is controllably positionable and only lowered into the crucible recess into contact with the electrolyte (4) after the electrolyte (4) has been heated to form the molten electrolyte (4).
  • positioning of the carbon cathode (7) would be actuated by any automated mechanical positioning system known to persons skilled in the art. In the course of testing embodiments described herein, the carbon rod was lowered manually into contact with the molten electrolyte.
  • the crucible lining (3) is a cylindrical tube-shaped configuration which fits snugly within the first crucible recess.
  • the crucible lining (3) complements and sits flush against the inner peripheral wall (2a) of the first crucible recess (2c). Accordingly, in use, the crucible lining (3) provides a barrier for separating the electrolyte (4) in the recess (2c) from the inner peripheral wall (2a) of the first crucible recess (2c).
  • the presence of the crucible lining (3) assists in preventing electrolyte (4) from being absorbed into the first crucible wall (2a) which would otherwise decrease efficiency in the electrolysis process.
  • the crucible lining (3) assists in blocking absorption of the electrolyte (4) into the first crucible wall (2a), this results in more electrolyte (4) being directed towards the alloy anode to further improve efficiency of the electrolysis process.
  • the crucible lining (3) is formed from quartz.
  • the quartz lining (3) is gradually corroded by the electrolyte (4) during electrolysis, this creates a time limitation upon the duration at which electrolysis can occur, and hence, the total amount of time which may be utilised in production of pure silicon via electrolysis.
  • other less corrosive materials such as calcium oxide, magnesium fluoride, and sodium fluoride could be used in place of quartz.
  • a quartz material is used as the crucible lining (3), it can conveniently provide a suitable amount of additional quartz particles necessary to maintain the proportion of quartz particles in the molten electrolyte (4) at a predetermined level throughout the duration of electrolysis.
  • pure silicon could be used to form the crucible lining (3) as this material does not tend to melt at temperatures applied in the electrolysis process, and, it does not tend to corrode due to interaction with the electrolyte (4).
  • the selected thickness of the pure silicon crucible lining (3) is a less critical consideration than when a corrodible crucible lining (3) such as a quartz crucible lining (3) is used. Accordingly, in large scale production of pure silicon it is envisaged that the use of a pure silicon crucible lining (3) would be particularly advantageous because it can be reused to save ongoing costs of production.
  • a pure silicon crucible lining (3) would assist in alleviating the practical complexities associated with use of a corrodible crucible lining (3) in which case a new crucible lining (3) would need to be regularly re-inserted into the first crucible (2).
  • a quartz crucible of approximately 9.5 cm diameter was used.
  • this could be implemented by generating a suitable temperature gradient whereby the temperature at the cathode (7) could be set relatively higher than the electrolyte situated adjacent the inner peripheral wall (2a) of the first crucible (2).
  • Electric arc heating would be a particularly well-suited to generating the suitable temperature gradient due to relatively high temperatures arising at the cathode (7) relative to the electrolyte adjacent the inner peripheral wall of the first crucible (2).
  • the temperature of the cathode (7) were for example set at 980°C and the temperature of the electrolyte (4) adjacent the inner peripheral wall (2a) of the first crucible set at 900°C or lower, this would allow solidification of a natural crucible lining (3) adjacent the inner peripheral wall (2a) of the first crucible (2) whilst the remaining electrolyte (4) inwardly of the first crucible (2) would remain in molten form by virtue of the cathode (7) temperature.
  • the creation of a natural crucible lining (3) is advantageous in that it obviates the need to provide a standalone crucible lining (3) thereby alleviating production costs and process implementation complexities.
  • a direct heat furnace was used as the primary heat source for heating the first crucible (2), the electrolyte (4), and, the alloy within the first crucible (2).
  • electric arc heating could be used as an alternative heat source in alternative embodiments whereby electrical resistance in the electrolyte medium between the anode (5) and cathode (7) gives rise to heat being generated. It would be readily understood that the further apart the anode (5) and cathode (7) are positioned, the higher the resistance that will be generated and hence the greater the amount of heat that will be transferred to the electrolyte (4) in the first crucible (2).
  • an induction furnace could be used to provide induction heating.
  • the stirring device is used to constantly stir the molten electrolyte (4) during electrolysis. Stirring of the molten electrolyte (4) assists in both generating ion-flow in the electrolyte (4), and, increasing the contact between the electrolyte (4) and the molten alloy anode (5).
  • the use of an induction furnace would inherently provide a stirring effect within the molten electrolyte during electrolysis. Accordingly, an induction furnace could be utilised both as a secondary heat source for regulating temperature, but also as the mechanism for stirring the molten electrolyte (4) during electrolysis. This would assist in alleviating costs incurred in acquiring a separate specialised stirring equipment.
  • the stirring provided by the induction furnace is due to electromagnetic force rather than direct mechanical interaction with the molten electrolyte (4), the time and cost required to repair a mechanical stirring devices may be alleviated.
  • the induction furnace could be configured to apply current pulsing to stir the molten electrolyte (4).
  • a specialised magnetic stirring device could be used to magnetically stir the alloy in the first crucible (2).
  • the quartz crucible lining (3) is fitted inside of the crucible recess by sliding the lining into the recess.
  • This step is represented by block (100) in Fig. 1.
  • the anode alloy (5) is thereafter deposited inside the crucible recess (2c) such that it sits in contact with the base of the first crucible (2).
  • the first crucible (2) is then heated by the direct heat furnace at a temperature of between approximately 950- 980°C so as to melt the alloy.
  • This step is represented by block (110) in Fig. 1.
  • electrolysis of the molten electrolyte (4) is commenced by lowering the carbon rod into contact with the molten electrolyte (4).
  • This step is represented by block (140) in Fig. 1.
  • the cathode (7) is electrically connected directly to a negative terminal of the power supply, and, the alloy anode is electrically connected to a positive terminal of the power supply via the first crucible (2) (which is itself a conductive material) the potential difference between anode and cathode (7) facilitate electrolysis.
  • YIELD Current (A) x [Electrolysis Constant (0.262g/A h)] x [Hours of Electrolysis (h)]u
  • the molten electrolyte (4) is maintained at a temperature between approximately 900-1000°C to prevent solidification of the molten electrolyte (4) during electrolysis.
  • a temperature between approximately 900-1000°C to prevent solidification of the molten electrolyte (4) during electrolysis.
  • the efficiency of pure silicon production is improved.
  • certain limitations regarding the selected temperature should be noted. Firstly, it has been found that during testing of embodiments herein described, maintaining the temperature of the molten electrolyte (4) at a temperature of approximately 980°C during electrolysis, produces particularly desirable results.
  • Temperatures above 980°C tend to cause an increase in evaporation and viscosity of the molten electrolyte (4) which impedes efficiency of pure silicon production and which may ultimately result in halted of electrolysis. Temperatures at or below 980°C will not tend to cause increases in evaporation and viscosity of the molten electrolyte (4) however the temperature should not drop below 900°C as the molten electrolyte (4) will solidify below this temperature.
  • the molten electrolyte (4) is stirred to increase flux of pure silicon particles produced during the electrolysis, into contact with the alloy anode (5).
  • automated mechanical stirring was employed.
  • an induction furnace could be conveniently used to magnetically stir the molten electrolyte (4) by applying current pulsing to the molten electrolyte (4). This step is represented by block (150) in Fig. 1.
  • the proportion of quartz particles in the electrolyte (4) should be maintained at approximately 3% by weight of the electrolyte (4).
  • a sensor is used to periodically measure the quartz particles in the electrolyte (4) and a dispensing means is used to controllably dispense additional amounts of quartz particles into the molten electrolyte (4) to compensate for any depletion as required.
  • a quartz material is used as the crucible lining (3) it may be feasible to utilise the quartz particles in the lining to compensate for depletion in quartz particles within the molten electrolyte (4) during electrolysis thereby maintaining the proportion of required quartz particles.
  • This step is represented by block (160) in Fig. 1.
  • the pure silicon (6) which forms an alloy with the anode (5) by use of the above embodiment is shown in Figs. 5 and 6.
  • the pure silicon (6) is able to be segregated from the alloy (5) by use of segregation techniques.
  • Electrolysis in the first crucible (2) will cease, after a limited timeframe, when the solubility limit of pure silicon in the alloy is reached.
  • This step is represented by block (170) in Fig. 1. It has been found that during testing of embodiments of the present invention, when the alloy (5) is heated at a temperature between approximately 950-980°C, the pure silicon (6) is no longer soluble with the alloy (5) when the pure silicon (6) in the alloy (5) reaches approximately 25% by weight of the alloy (5).
  • the time taken for the solubility limit to be reached will depend upon several factors including the surface area of the molten electrolyte (4) undergoing electrolysis. However, in testing of embodiment described herein, this solubility limit was found to be reached at around 8 hours. In terms of the yield and degree of purity of pure silicon (6) produced in accordance with the embodiments herein described, this would be understood to represent a considerable improvement in efficiency over existing production methods.
  • segregation of pure silicon from the alloy is thereafter commenced by first transferring the molten alloy (5) into a second crucible (not shown) by use of a suction device or any other suitable mechanical extraction means.
  • the second crucible can be made from any material suitable for exposure to temperatures between approximately 800-1000°C.
  • the material used to form the second crucible should however be inert with respect to the alloy and/or molten salts - that is, it should not chemically react with the alloy or any other molten salts.
  • This step is represented by block (200) in Fig. 2.
  • the molten alloy is maintained at a temperature of between approximately 800-850°C in the second crucible whereby some of the pure silicon (6) within the molten alloy (5) will tend to naturally segregate from the alloy (5) as a result of thermodynamics.
  • the pure silicon (6) which is of lower density than copper, naturally floats to the top of the molten alloy (5).
  • This step is represented by block (210) in Fig. 2.
  • block (210) in Fig. 210) This step is represented by block (210) in Fig. 2.
  • approximately 11% pure silicon (6) particles by weight of the alloy (5) will float to the top of the melt as solid pure silicon (6).
  • the now floating pure silicon (6) is able to be re-melted into ingots.
  • This form of naturally segregated pure silicon (6) has been found during testing to be suitable for solar-cell grade applications and is expected to provide at least around 18% efficiency which is consistent with the performance of conventionally produced solar-cell grade poly-silicon.
  • Molten salts are used to cover the molten alloy (5) in the second crucible to alleviate the now floating solid pure silicon (6) from re-oxidising.
  • Electronic grade silicon may also be produced via this method after several passes of zone refining is applied.
  • the alloy remaining in the second crucible may be reintroduced back into the first crucible when approximately 11 % pure silicon (6) by weight of the molten alloy has naturally segregated from the alloy in the second crucible.
  • the reintroduced molten alloy will sink to the bottom of the first crucible (2) and contribute further to the electrolysis process.
  • the alloy remaining in the second crucible could be cast or extruded into an amorphous tape, or, mechanically grinded or milled into a powder of micron to nano sized alloy particles. It would be appreciated by a person skilled in the art that mechanical milling of the alloy has a greater tendency to introduce significant amount of impurities. Testing of embodiments of the present invention to date have involved mechanical grinding of alloys in the second crucible instead of tape casting. This step is represented by block (220) in Fig. 2.
  • the process and apparatus used in the casting of the amorphous tape can be configured to control the microstructure of the nano-sized pure silicon particles in the tape itself depending upon the rate of cooling during the tape casting.
  • the nano- sized pure silicon particles which are thereafter able to be segregated from the tape in accordance with embodiments described herein could be in a range approximately between 10nm-60nm.
  • Figure 12 shows an amorphous tape -which has been cast from the alloy.
  • a secondary electrolysis is applied to the tape or the powder after submerging the tape or powder in an electrolyte solution.
  • electrolyte solutions having 10% hydrochloric acid (HCI) and 20% hydrochloric acid (HCI) were each used on different occasions with the results of these variations being indicated in Figs. 9 and 10 respectively.
  • the acidity of the electrolyte solution is regularly replenished during the secondary electrolysis by pumping HCI gas into the electrolyte solution to maintain suitable pH and Cl ' levels.
  • the alloy could be submerged in other electrolyte solutions including dehydrated acetic acid, iodine solutions (i.e.
  • a current of less than approximately 1A is applied during the secondary electrolysis to suitably remove the copper from the alloy. After the secondary electrolysis is applied, the electrolyte solution contains Cu/Cu+/Cu++ and nano-sized pure silicon particles. A centrifuge device is then used to separate the nano-sized pure silicon particles from the electrolyte solution by way of centrifugal motion. This step is represented by block (240) in Fig. 2. It is possible in alternative embodiments to apply a current of greater than 1A during the secondary electrolysis however this may result in oxidation of the silicon. If that is the case, then an acid such as HF (hydrofluoric acid) could be used to melt the oxidized layer of silicon (quartz) to obtain nano-silicon.
  • HF hydrofluoric acid
  • the nano-sized pure silicon particles have a greater tendency to react with oxygen
  • the nano-sized pure silicon particles are stored in a substance such as concentrated alcohol to alleviate reaction with free oxygen. This step is represented by block (250) in Fig. 2.
  • copper could be removed from the alloy in the second crucible by flushing the tape or powder with HCI gas or chlorine gas in an enclosed area that is oxygen free to allow the tape or powder to react with the HCI gas or chlorine gas.
  • CuCI 2 will then have to be removed via mechanical methods or rinsing with suitable solutions in which CuCI 2 is soluble in. Nano-sized pure silicon particles can then be removed.
  • CuCI 2 is paramagnetic as a person skilled in the art would readily appreciate. Accordingly, a magnetic field could be applied to the powder that contains CuCI 2 to remove CuCI 2 from the powder whilst alleviating introduction of contaminants if it were to be rinsed by oxygen containing solutions.
  • CuCI 2 which is formed as a result of flushing the tape or powder with HCI gas or chlorine gas would readily dissolve into any concentrated alcohol which is used to alleviate re-oxidation of the nano-sized pure silicon particles.
  • the above process and apparatus for segregating pure silicon from the alloy in the second crucible could be similarly performed directly upon the alloy in the first crucible without first removing the alloy in the first crucible (2) into a second crucible and without first allowing natural segregation of pure silicon from the alloy.
  • the alloy in the first crucible (2) containing 25% pure silicon particle by weight of the alloy could be exposed to the above-described segregation apparatus and process by forming the alloy into a tape or powder and applying electrolysis to the tape or powder before separating formed nano-sized pure silicon particles from the electrolyte solution.
  • Figures 4(a)-4(b), 5(a)-5(b), 6(a)-6(b) and 7(a)-7(b) show EDX data and corresponding SEM images for 4 different sample regions of an alloy produced in the first crucible after the first electrolysis in accordance with embodiments of the present invention described herein. It would be understood by a person skilled in the art that the variation in proportion of pure silicon to copper in the alloy for each analysed sample varies as a result of the location upon the alloy at which the sample reading has been taken. For instance, Figs. 5(a) and 5(b) which indicate a relatively high component of pure silicon (i.e.
  • Figs. 4(a) and 4(b) indicate a relatively lower component of pure silicon in the alloy (i.e. 68.83%) due to the sample reading being taken at or near an interface between silicon and copper in the alloy.
  • Figure 8 shows EDX data and a corresponding SEM image of pure silicon which has naturally segregated from the alloy in the second crucible due to different densities between the pure silicon and the copper in the alloy.
  • the pure silicon shown in Fig. 8 is suitable for melting into ingots.
  • Figures 9, 10 and 11 show EDX data and a corresponding SEM images of nano-sized pure silicon particles which have been produced and segregated from alloys following the secondary electrolysis and processing described herein.
  • the nano-sized pure silicon particles shown in Fig. 9 involved the use of an electrolyte solution having 10% hydrochloric acid (HCI) whilst the nano-sized particles shown in Fig.
  • HCI hydrochloric acid
  • Figure 13 shows data produced during testing of embodiments of the present invention in producing pure silicon. An average efficiency of approximately 71% and 75% is achieved using direct heat furnacing and induction furnacing during the first electrolysis in the first crucible respectively.
  • the fourth columns ("g (before)") in Fig. 13 indicates the amount of pure silicon in the alloy anode before the first electrolysis commences whilst the fifth columns (“g (after)”) indicates the pure silicon in the alloy after the first electrolysis in the first crucible (2) has taken place. The efficiency is able to be determined by the net gain in pure silicon against energy expended in the process.

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Abstract

L'invention porte sur un procédé et un appareil pour la production de silicium pur à partir d'un électrolyte. Le procédé comprend les étapes consistant à : (i) chauffer l'électrolyte dans un premier creuset pour former un électrolyte fondu; et (ii) effectuer une électrolyse sur l'électrolyte fondu par l'application d'une différence de potentiel entre une anode et une cathode qui sont conçues pour être en communication électrique/ionique avec l'électrolyte fondu, l'électrolyte fondu étant agité lorsque l'électrolyse est en train d'être effectuée et le silicium pur produit à cause de l'électrolyse étant soluble avec l'anode pour former un alliage. L'invention porte également sur le silicium pur et le matériau à base de silicium de qualité électrique obtenus par le procédé et sur une photopile et une batterie fabriquées à partir du silicium pur.
PCT/CN2010/002087 2010-12-20 2010-12-20 Procédé et appareil pour la production de silicium pur Ceased WO2012083480A1 (fr)

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PCT/CN2010/002087 WO2012083480A1 (fr) 2010-12-20 2010-12-20 Procédé et appareil pour la production de silicium pur
JP2013545013A JP2014502671A (ja) 2010-12-20 2011-12-20 シリコンの製造方法および器具
TW100147484A TW201231391A (en) 2010-12-20 2011-12-20 A method and apparatus for producing silicon
DE112011104441T DE112011104441T5 (de) 2010-12-20 2011-12-20 Verfahren und Vorrichtung zur Produktion von Silicium
CN2011800616056A CN103261095A (zh) 2010-12-20 2011-12-20 用于制造硅的方法和装置
PCT/CN2011/002138 WO2012083588A1 (fr) 2010-12-20 2011-12-20 Procédé et appareil pour la production de silicium
EP11850059.4A EP2655252A1 (fr) 2010-12-20 2011-12-20 Procédé et appareil pour la production de silicium
US13/996,403 US20130277227A1 (en) 2010-12-20 2011-12-20 Method and apparatus for producing silicon

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WO2014085467A1 (fr) * 2012-11-28 2014-06-05 Trustees Of Boston University Procédé et appareil de production de silicium de qualité solaire au moyen d'un processus d'électrolyse som
TWI628145B (zh) * 2013-01-29 2018-07-01 希利柯爾材料股份有限公司 用於純化矽之覆蓋助熔劑及方法

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EP2655252A1 (fr) 2013-10-30
TW201231391A (en) 2012-08-01

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