Structurally controlled deposition of silicon onto nanowires
Provided herein are nanostructures for lithium ion battery electrodes and methods of fabrication. In some embodiments, a nanostructure template coated with a silicon coating is provided. The silicon coating may include a non-conformal, more porous layer and a conformal, denser layer on the non-conformal, more porous layer. In some embodiments, two different deposition processes, e.g., a PECVD layer to deposit the non-conformal layer and a thermal CVD process to deposit the conformal layer, are used. Anodes including the nanostructures have longer cycle lifetimes than anodes made using either a PECVD or thermal CVD method alone.
1. An anode for a lithium battery, comprising:
a) a substrate;
b) a nanowire template rooted to the substrate;
c) a first amorphous silicon layer substantially coating the nanowire template, the first amorphous silicon layer having a first density; and
d) a second amorphous silicon layer over the first amorphous silicon layer and any exposed nanowire template, the second amorphous silicon layer having a density higher than the density of the first amorphous silicon layer.
2. The anode of claim 1 , wherein the first density is less than 2.2 g/cm 3 .
3. The anode of claim 1 , wherein the first density is less than 2.1 g/cm 3 .
4. The anode of claim 1 , wherein the second amorphous silicon layer has a density greater than 2.25 g/cm 3 .
5. The anode of claim 1 , wherein the second amorphous silicon layer has a density at least 0.05 g/cm 3 greater than that of the first amorphous silicon layer.
6. The anode of claim 1 , wherein the second amorphous silicon layer has a density at least 0.15 g/cm 3 greater than that of the first amorphous silicon layer.
7. The anode of claim 1 , wherein the first amorphous silicon layer is non-conformal to the nanowire template.
8. The anode of claim 1 , wherein the second amorphous silicon layer is conformal to the underlying surface of the first amorphous silicon layer.
9. The anode of claim 1 , wherein the hydrogen content of the first amorphous silicon layer is at least 10% atomic.
10. The anode of claim 1 , wherein the hydrogen content of the second amorphous silicon layer is no more than 5% atomic.
11. The anode of claim 1 , wherein the nanowire template comprises silicide nanowires.
12. The anode of claim 1 , wherein the first amorphous silicon layer is between about 5 and 20 microns thick at its maximum diameter.
13. The anode of claim 1 , wherein the second amorphous silicon layer is between about 5 and 500 nanometers thick.
14. The anode of claim 1 , wherein the second amorphous silicon layer is about 5 and 100 nanometers thick.
15. A lithium battery, comprising:
an anode as in claim 1 ;
a lithium-containing cathode;
an electrolyte in ionic communication with both the anode and the cathode.
16. An anode for a lithium battery, comprising:
a substrate;
a nanowire template rooted to the substrate;
a first layer substantially coating the nanowire template, the first layer comprising amorphous silicon and having a first density; and
a second layer over the first layer and any exposed nanowire template, the second layer comprising amorphous silicon and having a density higher than the density of the first layer.
17. An anode for a lithium battery, comprising:
a substrate;
a nanowire template rooted to the substrate;
a first layer over the nanowire template, the first layer comprising silicon and having a first density; and
a second layer over the first layer and any exposed nanowire template, the second layer comprising amorphous silicon and having a density greater than the density of the first layer.
18. The anode of claim 17 , wherein the first density is less than 2.2 g/cm 3 .
19. The anode of claim 17 , wherein the first density is less than 2.1 g/cm 3 .
20. The anode of claim 17 , wherein the second layer has a density greater than 2.25 g/cm 3 .
21. The anode of claim 17 , wherein the second layer has a density at least 0.05 g/cm 3 greater than that of the first layer.
22. The anode of claim 17 , wherein the second layer has a density at least 0.15 g/cm 3 greater than that of the first layer.
23. The anode of claim 17 , wherein the first layer is non-conformal to the nanowire template.
24. The anode of claim 17 , wherein the second layer is conformal to the underlying surface of the first layer.
25. The anode of claim 17 , wherein the hydrogen content of the first layer is at least 10% atomic.
26. The anode of claim 17 , wherein the hydrogen content of the second layer is no more than 5% atomic.
27. The anode of claim 17 , wherein the nanowire template comprises silicide nanowires.
28. The anode of claim 17 , wherein the first layer is between about 5 and 20 microns thick at its maximum diameter.
29. The anode of claim 17 , wherein the second layer is between about 5 and 500 nanometers thick.
30. The anode of claim 17 , wherein the second layer is about 5 and 100 nanometers thick.