Method of forming silicon

• US 10,090,513 B2
• Filed: 06/03/2013
• Issued: 10/02/2018
• Est. Priority Date: 06/06/2012
• Status: Active Grant

• Current Assignee: Nexeon Limited
• Original Assignee: Nexeon Limited
• Inventors: Canham, Leigh, Friend, Christopher Michael, Macklin, William James, Brown, Scott
• Primary Examiner(s): Mayes, Melvin C.
• Assistant Examiner(s): Forrest, Michael
• Application Number:
  US14/403,478
• Publication Number:
  US 20150104705A1
• Time in Patent Office: 1,947 Days
• Field of Search: 423349
• CPC Class Codes: C01B 33/023 by reduction of silica or free silica-containing material
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 2004/027 Negative electrodes
• CPC Class Codes: H01M 4/134 Electrodes based on metals, Si or alloys
• CPC Class Codes: H01M 4/386 Silicon or alloys based on silicon
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A method of forming a particulate material comprising silicon, the method comprising the step of reducing a particulate starting material comprising silica-containing particles having an aspect ratio of at least 3:1 and a smallest dimension of less than 15 microns, or reducing a particulate starting material comprising silica-containing particles comprising a plurality of elongate structural elements, each elongate structural element having an aspect ratio of at least 3:1 and a smallest dimension of less than 15 microns.

Claims

1. A method of forming a particulate material comprising silicon, the method comprising steps of:

reducing a particulate starting material comprising silica-containing particles having an aspect ratio of at least 3;

1 and a smallest dimension of less than 15 microns to form a particulate material comprising silicon;

or

reducing a particulate starting material comprising silica-containing particles comprising a plurality of elongate structural elements, each elongate structural element having an aspect ratio of at least 3;

1 and a smallest dimension of less than 15 microns to form a particulate material comprising silicon;

wherein the reduction takes place in the presence of a thermal moderator, and

wherein the particulate material comprising silicon has a BET value of less than 100 m²/g after removal of by-products of the reduction.

2. The method according to claim 1, wherein the aspect ratio of the silica-containing particles or of the elongate structural elements is at least 5:

1 and/or wherein the smallest dimension of the silica-containing particles or of the elongate structural elements is less than 10 microns.

3. The method according to claim 2, wherein the smallest dimension of the silica-containing particles or of the elongate structural elements is less than 3 microns.

4. The method according to claim 1, wherein substantially all silica of the starting material is reduced.

5. The method according to claim 1, wherein the geometric surface area of the silicon material is substantially the same as the geometric surface area of the starting material and/or wherein the shape of the particles of the material comprising silicon is substantially the same as the shape of the starting material particles.

6. The method according to claim 1, wherein silica at a surface of the starting material particles is reduced and silica at a core of the starting material particles is not reduced.

7. The method according to claim 6, wherein the silica at the core is selectively removed.

8. The method according to claim 6, wherein the silica at the core is selectively removed by exposure to HF.

9. The method according to claim 6, wherein the particulate material comprising silicon formed following selective removal of silica is a flake having a hollow core, or a tube.

10. The method according to claim 6, wherein the geometric surface area of the material comprising silicon is greater than the geometric surface area of the starting material.

11. The method according to claim 1, wherein the starting material is n- or p-doped or wherein the starting material is undoped.

12. The method according to claim 1, wherein the starting material particles have an open framework structure.

13. The method according to claim 1, wherein the starting material is reduced at a reaction temperature of no more than 750°

C.

14. The method according to claim 1, wherein the starting material is reduced by exposure to liquid metal or metal vapour.

15. The method according to claim 14, wherein the metal is magnesium or calcium.

16. The method according to claim 14, wherein the thermal moderator is a salt, and wherein the thermal moderator is mixed with the starting material and a reducing agent or wherein a layer of thermal moderator is in contact with the starting material.

17. The method according to claim 1, wherein the silica is reduced by exposure to a reducing composition that causes both reduction of the silica and doping of the silicon.

18. The method according to claim 1, comprising a further step of coating at least part of the surface of the material comprising silicon.

19. The method according to claim 1, wherein the starting material is formed by electrospinning silica or wherein the starting material is biogenic silica.

20. The method according to claim 1, wherein the material comprising silicon has a BET value that is the same as or less than a BET value of the starting material.

21. The method according to claim 1, wherein the material comprising silicon has a BET value of less than 50 m²/g.

22. The method according to claim 1, wherein the starting material is no more than 95% silica by weight.

23. The method according to claim 1, wherein the particulate material comprising silicon is treated to remove reaction by-products.

24. The method according to claim 23, wherein the reaction by-products are removed by HCl treatment.

25. The method according to claim 1, wherein the particulate material comprising silicon is etched to form silicon pillars extending from a silicon core of the particulate material.

26. The method according to claim 1, wherein the particulate starting material comprises microcrystalline, nanocrystalline, or amorphous silica and wherein the material comprising silicon comprises microcrystalline or nanocrystalline silicon.

27. The method according to claim 1, wherein the reducing takes place at a reaction temperature at which the starting material is reduced, and wherein the particulate starting material comprises silica with a softening temperature that is lower than the reaction temperature and a melting temperature that is higher than the reaction temperature.

28. The method according to claim 1, wherein the starting material is heated to a reaction temperature of 650-725°

C. at a heating rate of 5-15°

C. per minute, held at the reaction temperature for 30-150 minutes and cooled down to room temperature at a rate of 5-15°

C. per minute.

29. The method according to claim 1, wherein the silica starting material comprises impurities selected from:

(1) carbon in an amount of up to 10 wt %; and

(2) Li, Na, Mg, Zn, Al, Ti, Ca, B or oxides thereof, wherein each metal oxide is present in an amount of no more than 20 wt %, and wherein the total amount of all metal oxides is no more than 45 wt %.

30. The method according to claim 1, wherein the starting material is reduced at a reaction temperature of no more than 650°

C.

31. The method according to claim 1, comprising a further step of coating at least part of the surface of the material comprising silicon with silicon oxide or carbon.

32. The method according to claim 1, wherein the starting material is no more than 90% silica by weight.

33. The method according to claim 1, wherein the particulate material comprising silicon is etched by metal-assisted chemical etching to form silicon pillars extending from a silicon core of the particulate material.