Electrode assembly for an ultracapacitor

1. An electrode assembly for an ultracapacitor that defines a length between opposing first and second longitudinal edges, wherein the electrode assembly comprises:

a first electrode comprising a first current collector electrically coupled to a first carbonaceous coating, wherein at least a portion of the first current collector projects beyond the first longitudinal edge to define a first projecting portion, wherein the offset ratio of the first projecting portion is from 0.05 to about 0.3;

a second electrode comprising a second current collector electrically coupled to a second carbonaceous coating, wherein at least a portion of the second current collector projects beyond the second longitudinal edge to define a second projecting portion, wherein the offset ratio of the second projecting portion is from 0.05 to about 0.3; and

a separator positioned between the first electrode and the second electrode.

2. The electrode assembly of claim 1 , wherein the length of the first projecting portion, the second projecting portion, or both is from about 1 to about 20 millimeters.

3. The electrode assembly of claim 1 , wherein the length of the electrode assembly is from about 5 to about 100 millimeters.

4. The electrode assembly of claim 1 , wherein the electrode assembly has a jellyroll configuration.

5. The electrode assembly of claim 1 , wherein the first current collector and the second current collector each contain a substrate that includes a conductive metal.

6. The electrode assembly of claim 5 , wherein the conductive metal is aluminum or an alloy thereof.

7. The electrode assembly of claim 1 , wherein the first carbonaceous coating, the second carbonaceous coating, or both contain activated carbon particles.

8. The electrode assembly of claim 1 , wherein the separator includes a cellulosic fibrous material.

9. An ultracapacitor that comprises the electrode assembly of claim 1 and a nonaqueous electrolyte that is in ionic contact with the first electrode and the second electrode.

10. The ultracapacitor of claim 9 , wherein the nonaqueous electrolyte contains an ionic liquid that is dissolved in a nonaqueous solvent, wherein the ionic liquid contains a cationic species and a counterion.

11. The ultracapacitor of claim 10 , wherein the nonaqueous solvent includes propylene carbonate, a nitrile, or a combination thereof.

12. The ultracapacitor of claim 10 , wherein the cationic species includes an organoquaternary ammonium compound.

13. The ultracapacitor of claim 12 , wherein the organoquaternary ammonium compound has the following structure:

wherein m and n are independently a number from 3 to 7.

14. The ultracapacitor of claim 10 , wherein the ionic liquid is present at a concentration of about 1.0 M or more.

15. The ultracapacitor of claim 9 , wherein the ultracapacitor exhibits an ESR of about 100 mohms or less as determined at a frequency of 100 kHz and temperature of 25° C.

16. The ultracapacitor of claim 9 , wherein the ultracapacitor exhibits a capacitance value of about 6 Farads per square centimeter or more as determined at a frequency of 120 Hz and temperature of 25° C.

17. The ultracapacitor of claim 9 , wherein the ultracapacitor contains a housing that includes a container having a base and an open end, wherein a lid is disposed adjacent to the open end, and further wherein the electrode assembly is positioned within the housing so that the first projecting portion is placed into electrical contact with the base or the lid.

18. The ultracapacitor of claim 17 , wherein the container is formed from a metal.

19. The ultracapacitor of claim 17 , wherein the container has a cylindrical shape.

20. The ultracapacitor of claim 1 , wherein the offset ratio of the first projecting portion is from 0.05 to about 0.2.

21. The ultracapacitor of claim 1 , wherein the first projecting portion is in electrical contact with the base and the second projection portion is in electrical contact with the lid.