Compositionally modified silicon coatings for use in a lithium ion battery anode
Provided herein are nanostructures for lithium ion battery electrodes and methods of fabrication. In some embodiments, a nanostructure template coated with a silicon-based coating is provided. The silicon coating may include a non-conformal, more porous silicon-rich SiE x layer and a conformal, denser SiE x layer on the non-conformal, more porous layer. In some embodiments, two different deposition processes are used: a PECVD layer to deposit the non-conformal, silicon-rich SiE x layer and a thermal CVD process to deposit the conformal layer. The silicon-rich SiE x material prevents silicon crystalline domain growth, limits macroscopic swelling, increases lithium diffusion rate and enhances significantly battery life during lithium ion battery cycle of charge and discharge.
1. An anode for a lithium battery, comprising:
a substrate;
an array of nanowires rooted to the substrate, the nanowires each having a surface;
a first layer coating most or all of the surfaces of the nanowires, the layer comprising a SiE x material; and
a second layer over the first layer, any exposed surfaces of the nanowires, and the substrate, the second layer comprising either silicon or a SiF y material;
wherein x greater than zero and less than 1;
wherein y is greater than zero and less than 1; and
wherein E is selected from the group consisting of nitrogen, carbon, boron, phosphorus, magnesium, aluminum, germanium, tin, nickel, copper, and combinations thereof, and F is each selected from the group consisting of nitrogen, carbon, boron, phosphorus, oxygen, magnesium, aluminum, germanium, tin, nickel, copper, and combinations thereof
and F is selected independently from the group consisting of nitrogen, carbon, boron, phosphorus, oxygen, magnesium, aluminum, germanium, tin, nickel, copper, and combinations thereof.
2. The anode of claim 1 , wherein x is between 0.01 and 0.5.
3. The anode of claim 1 , wherein x between is 0.01 and 0.3.
4. The anode of claim 1 , wherein x is between 0.01 and 0.1.
5. The anode of claim 1 wherein a concentration gradient of E in the SiE x material varies through a thickness direction of the first layer and/or a concentration gradient of F in the SiF y material varies through a thickness direction of the second layer.
6. The anode of claim 1 , wherein the density of the second layer is greater than the density of the first layer.
7. The anode of claim 1 , wherein the average density of the first layer is less than 2.1 g/cm 3 .
8. The anode of claim 1 , wherein the average density of the second layer is greater than 2.0 g/cm 3 .
9. The anode of claim 1 , wherein the density of the first layer varies throughout the first layer.
10. The anode of claim 1 , wherein the density of the second layer varies throughout the second layer.
11. The anode of claim 1 , wherein the first layer is non-conformal to the array of nanowires.
12. The anode of claim 1 , wherein the second layer is conformal to the first layer.
13. The anode of claim 1 , further comprising a third layer over the second layer, the third layer comprising no silicon.
14. The anode of claim 1 , wherein the array of nanowires comprises silicide nanowires.
15. The anode of claim 1 , wherein the first layer is between about 5 and 20 microns thick at its maximum diameter.
16. The anode of claim 1 , wherein the second layer is between 5 and 500 nanometers thick.
17. The anode of claim 1 , wherein the second layer is between 5 and 100 nanometers thick.
18. 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.