Conductive silicon composite, preparation thereof, and negative electrode material for non-aqueous electrolyte secondary cell

1. A conductive silicon composite in which particles of the structure that crystallites of silicon having a size of 1 to 500 nm are dispersed in silicon dioxide are coated on their surfaces with carbon.

2. The conductive silicon composite of claim 1 wherein the particles of the structure that crystallites of silicon are dispersed in silicon dioxide have an average particle size of 0.01 to 30 μm, a BET specific surface area of 0.5 to 20 m 2 /g, and a carbon coverage of 3 to 70% by weight.

3. The conductive silicon composite of claim 1 wherein the particle surfaces are at least partially fused to carbon.

4. The conductive silicon composite of claim 1 wherein when analyzed by x-ray diffractometry, a diffraction peak attributable to Si(111) is observed, and the silicon crystallites have a size of 1 to 500 nm as determined from the half width of the diffraction peak by Scherrer method, and the carbon coverage is 5 to 70% by weight of the silicon composite.

5. The conductive silicon composite of claim 1 which contains 1 to 35% by weight of zero-valent silicon capable of generating hydrogen gas upon reaction with an alkali hydroxide solution.

6. The conductive silicon composite of claim 1 wherein on Raman spectroscopy, the Raman shift provides a graphite structure-intrinsic spectrum near 1580 cm −1 .

7. A method for preparing the conductive silicon composite of claim 1 , comprising the steps of disproportionating silicon oxide with an organic gas and/or vapor at a temperature of 900 to 1,400° C. and simultaneously effecting chemical vapor deposition.

8. A method for preparing the conductive silicon composite according to claim 7 wherein the silicon oxide represented by the general formula: SiOx wherein 1≦x<1.6 is in the form of particles having an average particle size of 0.01 to 30 μm and a BET specific surface area of 0.1 to 30 m 2 /g.

9. A method for preparing the conductive silicon composite according to claim 7 wherein the method is conducted in a reactor selected from a fluidized bed reactor, rotary furnace, vertical moving bed reactor, tunnel furnace, batch furnace and rotary kiln.

10. A method for preparing the conductive silicon composite of claim 1 , comprising the step of effecting chemical vapor deposition of a component with an organic gas and/or vapor at a temperature of 800 to 1,400° C.,

the component being selected from among a silicon composite obtained by previously heat treating silicon oxide in an inert gas atmosphere at 900 to 1,400° C. for disproportionation, a composite obtained by coating silicon microparticulates with silicon dioxide by the sol-gel method, a composite obtained by coagulating silicon fine powder with the aid of finely divided silica and water and sintering, and a product obtained by heating silicon and partial oxide or nitride thereof in an inert gas stream at 800 to 1,400° C.

11. A negative electrode material for a non-aqueous electrolyte secondary cell, comprising the conductive silicon composite of claim 1 .

12. A negative electrode material for a non-aqueous electrolyte secondary cell, comprising a mixture of the conductive silicon composite of claim 1 and 1 to 60% by weight of a conductive agent, the mixture having a total carbon content of 25 to 90% by weight.

13. The conductive silicon composite of claim 1 wherein the particles have an average particle size of 0.01 to 30 μm.

14. The conductive silicon composite of claim 1 wherein the particles have a BET specific surface area of 0.1 to 30 m 2 /g.

15. The conductive silicon composite of claim 1 wherein the particles have a BET specific surface area of 1 to 10 m 2 /g.

16. The conductive silicon composite of claim 1 having an electrical conductivity of at least 1×10 −6 S/m.

17. The conductive silicon composite of claim 1 having an electrical conductivity of at least 1×10 −4 S/m.

18. A method for preparing a conductive silicon composite in which particles of the structure that crystallites of silicon are dispersed in a silicon compound are coated on their surfaces with carbon

comprising the steps of previously subjecting silicon oxide to chemical vapor deposition with an organic gas and/or vapor at a temperature of 500 to 1,200° C. and heat treating the resulting product in an inert gas atmosphere at 900 to 1,400° C. for disproportionation.