Structured silicon anode

1. A method of fabricating an energy storage device comprising the steps of:

forming an anode comprising an array of sub-micron silicon structures supported on a silicon substrate;

forming a cathode comprising lithium; and

arranging the anode and cathode in communication to form a battery.

2. A method of fabricating a device according to claim 1 in which the anode is arranged to tolerate the conditions occasioned by the volume changes caused by charging/discharging of the battery.

3. A method according to claim 1 in which the anode is arranged to maintain structural integrity throughout a cycling of the battery.

4. A method according to claim 1 in which the anode is arranged to withstand repeated volume expansion associated with alloying during use of the battery.

5. A method according to claim 1 wherein the step of forming the array of submicron silicon structures comprises forming an array of sub-micron silicon pillars.

6. A method according to claim 5 wherein the step of forming the pillars comprises forming pillars having a surface area of about 4 FH/d times the substrate area wherein F is the surface fractional coverage, H is the height of the pillar and d is the diameter of the pillar.

7. A method according to claim 5 further comprising the step of arranging the sub-micron pillars to not exceed a fractional coverage of 0.5 of the substrate.

8. A method according to claim 5 wherein the step of forming the pillars comprises forming pillars which are 0.1 to 1.0 microns in diameter and 1 to 10 microns in height.

9. A method according to claim 5 wherein the step of forming the pillars comprises forming pillars which are approximately 0.3 microns in diameter and approximately 6 microns in height.

10. A method according to claim 1 wherein the sub-micron silicon structures are formed on a substrate comprising n-type silicon.

11. A method according to claim 1 comprising forming the energy storage device on a wafer-bonded silicon-on-insulator substrate.

12. A method of operating a battery, including a silicon anode comprising an array of sub-micron silicon pillars on a silicon substrate and a lithium cathode, the method comprising the step of forming a compound film on the silicon pillars during a charging step.

13. A method according to claim 12 wherein the film is a Zintl-Phase Compound.

14. A method according to claim 12 wherein the step of forming the compound film comprises forming a deformable compound film which does not to give rise to significant stress-induced cracking during the volume change in a charging or discharging step of the battery.

15. A method of fabricating an electrode to form a battery with a lithium cathode and a lithium-based electrolyte comprising forming sub-micron silicon pillars on a silicon substrate.

16. A method according to claim 1 further comprising the steps of forming the sub-micron silicon structures on a silicon substrate, the steps comprising:

(a) depositing a thin film of cesium chloride onto a silicon based substrate;

(b) exposing the film to water vapour so that the film reorganizes into a distribution of hemispherical islands on the surface; and

(c) reactive ion etching the coated substrate, with the islands of cesium chloride acting as a resist so that the uncoated silicon is etched away leaving the sub-micron silicon structures on the surface of the substrate.

17. A method according to claim 1 wherein the step of forming the array of sub-micron structures supported on a silicon-based substrate, comprises:

(a) depositing a film of a soluble solid onto the silicon-based substrate;

(b) exposing the film to solvent vapour so that the film reorganises into an array of discrete hemispherical islands on the surface; and

(c) reactively ion etching the silicon-based substrate with the islands of highly soluble solid acting as a resist so that the exposed silicon-based substrate is etched away leaving sub-micron silicon structures corresponding to the islands.