Fibrous carbon aerogels coated with nano-thin silicon as lithium battery anodes

1. A method of preparing a silica-carbon composite material comprising a carbon material of low bulk density, the carbon material comprising a skeletal framework comprising carbon nanofibers, the skeletal framework forming a pore structure comprising an array of interconnected pores, the silica-carbon composite material further comprising a conformal coating layer of amorphous silica on the carbon nanofibers, the method comprising:

providing a fibrous polyimide aerogel;

impregnating the fibrous polyimide aerogel with a silica sol;

allowing the silica sol to gel, spontaneously forming the conformal coating layer of amorphous silica on the fibrous polyimide aerogel;

drying the silica coated fibrous polyimide aerogel under ambient or supercritical conditions to form a silica aerogel coating layer on the polyimide aerogel fibers; and

pyrolyzing the silica aerogel coated fibrous polyimide aerogel to form the silica-carbon composite material.

2. The method of claim 1 , wherein the silica sol comprises tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, pre-hydrolyzed pre-polymers of ethyl polysilicate, methyl polysilicate, methyl triethoxysilane, polydimethylsiloxane, or combinations thereof.

3. The method of claim 1 , wherein the silica sol comprises tetraethyl orthosilicate, tetramethyl orthosilicate, polydimethylsiloxane, or a combination thereof.

4. The method of claim 1 , wherein the silica-carbon composite material comprises silica in an amount by weight from about 30 to about 80%, or from about 40 to about 70%.

5. The method of claim 1 , wherein the conformal coating layer of amorphous silica has a thickness from about 1 to about 20 nm.

6. The method of claim 1 , wherein the silica-carbon composite material is in monolithic form, in a form of thin sheets, or in a form of particles.

7. The method of claim 1 , wherein the silica-carbon composite material is in the form of particles.

8. The method of claim 7 , wherein the particles are spherical, having a diameter from about 100 nm to about 4 mm, or from about 5 μm to about 4 mm.

9. The method of claim 1 , wherein the silica of the silica aerogel coating layer is amorphous.

10. The method of claim 1 , further comprising metallothermically reducing at least a portion of the silica of the silica aerogel coating layer present in the silica-carbon composite material, forming a silicon-carbon composite material.

11. The method of claim 10 , wherein metallothermically reducing comprises contacting the silica-carbon composite material with a metallic reducing agent at an elevated temperature and under an inert atmosphere for a period of time sufficient to reduce a substantial portion of the silica to silicon.

12. The method of claim 11 , wherein the metallic reducing agent comprises magnesium, calcium, combinations thereof, or alloys thereof.

13. The method of claim 11 , wherein the metallic reducing agent is magnesium.

14. The method of claim 13 , wherein the magnesium is in bulk form, in a form of turnings, or in particulate form.

15. The method of claim 13 , wherein the magnesium is in particulate form having a particle size from about 0.3 to about 300 micrometers.

16. The method of claim 11 , wherein the elevated temperature is from about 450 to about 900° C.

17. The method of claim 11 , further comprising washing the silicon-carbon composite material with an acid.

18. The method of claim 17 , wherein the acid is a solution of hydrochloric acid, phosphoric acid, hydrofluoric acid, or combinations thereof.

19. A silicon-carbon composite material prepared by the method of claim 10 .