Method and apparatus for producing solar grade silicon using a SOM electrolysis process

Patent metadata

Field	Value
Publication number	US-10266951-B2
Application number	US-201314353008-A
Country	US
Kind code	B2
Filing date	Nov 26, 2013
Priority date	Nov 28, 2012
Publication date	Apr 23, 2019
Grant date	Apr 23, 2019

Abstract

A method of manufacturing silicon via a solid oxide membrane electrolysis process, including providing a crucible, providing a flux including silica within the crucible, providing a cathode in the crucible in electrical contact with the flux, and providing an anode disposed in the crucible spaced apart from the cathode and in electrical contact with the flux. The cathode includes a silicon-absorbing portion in fluid communication with the flux. The anode includes a solid oxide membrane around at least a portion of the anode. The method also includes generating an electrical potential between the cathode and anode sufficient to reduce silicon at an operating temperature, and cooling the silicon-absorbing portion to below the operating temperature, and precipitating out the silicon from the silicon-absorbing portion. The silicon-absorbing portion preferentially absorbs silicon, the silicon-absorbing portion is a liquid metal at the operating temperature, and the solid oxide membrane is permeable to oxygen.

First claim

We claim:

1. A method of manufacturing silicon via a solid oxide membrane electrolysis process, comprising:
providing a first crucible defining a cavity;
providing a flux within said cavity of said first crucible, said flux comprising silicon oxide in solution;
providing a cathode disposed in said cavity of said first crucible in electrical contact with said flux, said cathode comprising a silicon-absorbing portion within a second crucible disposed inside said first crucible containing said flux, said silicon-absorbing portion being in fluid communication with said flux, said silicon-absorbing portion comprising a metal;
providing an anode disposed in said cavity of said first crucible and spaced apart from said cathode and being in electrical contact with said flux, said anode comprising a solid oxide membrane around at least a portion of said anode;
heating said flux and said silicon-absorbing portion to an operating temperature of said solid oxide membrane electrolysis process;
generating an electrical potential between said cathode and said anode sufficient to dissociate the silicon oxide and reduce silicon at said operating temperature of said solid oxide membrane electrolysis process, said operating temperature being sufficient to form a liquid solution of said silicon and said metal; and
cooling said silicon-absorbing portion to a precipitation temperature that is below said operating temperature and at which said silicon separates out of said silicon-absorbing portion and precipitates in solid form into said second crucible while the metal of the silicon-absorbing portion remains a liquid,
wherein said silicon-absorbing portion preferentially absorbs silicon relative to a remainder of said flux at said operating temperature, and said silicon-absorbing portion is a liquid at said operating temperature, and
wherein said solid oxide membrane is permeable to oxygen.

2. The method according to claim 1 , further comprising stirring said flux with an inert-gas-bubbling tube.

3. The method according to claim 1 , wherein said generating said electrical potential includes increasing said electrical potential at about 5 mV/s until said electrical potential reaches or exceeds the dissociation potential of silicon oxide.

4. The method according to claim 3 , wherein said dissociation potential is at least 0.8 V.

5. The method according to claim 1 , wherein said operating temperature is 800 to 1500 degrees Celsius.

6. The method according to claim 1 , wherein said anode further comprises a liquid metal anode portion.

7. The method according to claim 1 , wherein said silicon-absorbing portion has a lower melting temperature than silicon.

8. The method according to claim 1 , wherein said cathode further comprises a current collector in contact with said silicon-absorbing portion.

9. The method according to claim 8 , wherein said current collector comprises tungsten.

10. The method according to claim 1 , wherein said solid oxide membrane comprises zirconium oxide.

11. The method according to claim 1 , wherein said solid oxide membrane comprises cerium oxide.

12. The method according to claim 10 , wherein said solid oxide membrane further comprises a stabilizing element, and
wherein said stabilizing element is at least one or more oxides of yttrium, calcium, scandium, and magnesium.

13. The method according to claim 1 , wherein said flux further comprises an oxide of at least one of yttrium, calcium, barium, and magnesium.

14. The method according to claim 13 , wherein said oxide is at least one of CaO, MgO, and Y 2 O 3 .

15. The method according to claim 1 , wherein said silicon-absorbing portion has a higher density than said flux at said operating temperature.

16. The method according to claim 1 , wherein said silicon-absorbing portion is selected from the group consisting of tin, aluminum, and bismuth.

17. The method according to claim 1 , wherein, at said operating temperature, said flux has an ionic conductivity of at least 2 S/cm.

18. The method according to claim 1 , wherein, at said operating temperature, said flux has an oxide solubility of at least 0.5 wt %.

19. The method according to claim 18 , wherein said oxide solubility is about 1 to 10 wt %.

20. The method according to claim 1 , wherein, at said operating temperature, said flux has a viscosity of less than 0.1 Pa·s.

21. The method according to claim 1 , wherein, at said operating temperature, said flux has a volatility of less than 10 −6 g/cm 2 s.

22. The method according to claim 1 , wherein, at said operating temperature, said flux is inert with respect to said solid oxide membrane.

23. The method according to claim 1 , wherein said flux comprises halides having cations with a lower electronegativity than silicon.

24. The method according to claim 23 , wherein said halides include at least one of magnesium, barium, calcium, and lithium.

25. The method according to claim 1 , wherein said flux comprises 10-50 wt % MgF 2 , 2-15 wt % YF 3 , and 1 to 7 wt % SiO 2 , with a balance of said flux comprising BaF 2 .

26. The method according to claim 25 , wherein said flux comprises 76.8 wt % BaF 2 , 15.2 wt % MgF 2 , 5 w % YF 3 , and 3 wt % SiO 2 .

27. The method according to claim 1 , wherein said flux comprises 2 wt % SiO 2 and 15 wt % YF 3 added into an eutectic mix of magnesium fluoride-barium fluoride (MgF 2 —BaF 2 ) powder comprising 16.5 wt % MgF 2 and 83.5 wt % BaF 2 .

28. The method according to claim 1 , wherein said operating temperature is 900 to 1500 degrees Celsius.

Assignees

• Univ Boston

Inventors

• Pal Uday B
• Basu Soumendra N
• Jiang Yihong
• Xu Jiapeng

Classifications

• Y02P70/521

  Cross-Sectional Technologies · mapped topic

• C25B9/08

  Chemistry & Metallurgy · mapped topic

• Y02E10/546

  Polycrystalline silicon PV cells · CPC title

• H01L31/182

  Electricity · mapped topic

• C25C3/00

  Electrolytic production, recovery or refining of metals by electrolysis of melts (C25C5/00 takes precedence) · CPC title