Ultracapacitors with high frequency response
An electric double layer capacitor (EDLC) is disclosed including: a first electrode including a first current collector and first plurality of carbon nanotubes (CNTs) disposed substantially directly upon the first current collector; a second electrode comprising a second current collector and second plurality of CNTs disposed substantially directly upon the second current collector; and an electrolyte disposed between and in contact with (e.g., wetting) the first and second electrodes. In some embodiments, the EDLC is configured to have a capacitive frequency window comprising about 1 Hz to about 50 Hz.
1. An electric double layer capacitor (EDLC) comprising:
a first electrode comprising a first current collector and a first plurality of vertically aligned carbon nanotubes (CNTs) on the first current collector;
a second electrode comprising a second current collector and a second plurality of carbon nanotubes (CNTs) on the second current collector; wherein at least one of the first current collector and the second current collector comprises a layer of aluminum carbide whiskers on an aluminum base layer, and where the vertically aligned carbon nanotubes contact the aluminum carbide whiskers; where the whiskers protrude into the vertically aligned carbon nanotubes; and
an electrolyte contacting the first and second electrodes; wherein the electrolyte comprises a salt of the following formula:
wherein R 1 and R 2 can be the same or different and are each a straight-chain or branched alkyl having 1 to 4 carbon atoms, and X− is an anion that comprises [B(CN)4] − or [BFn(CN)4-n] − , where n=0, 1, 2 or 3; wherein the EDLC has a capacitive frequency window comprising a frequency range of about 1 Hz to an upper boundary of at least 150 Hz, wherein the upper boundary is a cutoff frequency, f 3 db, that is defined by a 3 db reduction in capacitance.
2. The electric double layer capacitor (EDLC) of claim 1 , wherein: the upper boundary is at least 200 Hz.
3. The electric double layer capacitor (EDLC) of claim 1 , wherein: the upper boundary is between 150 Hz and 1000 Hz.
4. The electric double layer capacitor (EDLC) of claim 1 , wherein:
at least one of the first current collector and the second current collector consists essentially of aluminum.
5. The electric double layer capacitor (EDLC) of claim 1 , wherein:
the first current collector and the second current collector comprises a layer of aluminum carbide whiskers disposed on an aluminum base layer.
6. The electric double layer capacitor (EDLC) of claim 1 , wherein:
at least one plurality of carbon nanotubes (CNTs) is disposed on a respective current collector without a binder material.
7. The electric double layer capacitor (EDLC) of claim 1 , wherein:
a layer of catalyst material is disposed between a respective current collector and plurality of carbon nanotubes (CNTs).
8. The electric double layer capacitor (EDLC) of claim 7 , wherein:
the catalyst material comprises at least one of iron and an alloy that is at least one of corrosion resistant and oxidation resistant.
9. The electric double layer capacitor (EDLC) of claim 7 , wherein:
the catalyst material comprises at least one of austenite and an austenic alloy.
10. The electric double layer capacitor (EDLC) of claim 1 , wherein:
at least one of the plurality of carbon nanotubes (CNTs) comprises an average height of less than 50 μm.
11. The electric double layer capacitor (EDLC) of claim 1 , wherein:
lateral spacing between CNTs within at least one of the plurality of carbon nanotubes (CNTs) comprises void spaces having a size that is several times a size of at least one of an anion and a cation in the electrolyte.
12. The electric double layer capacitor (EDLC) of claim 1 , wherein:
lateral spacing between CNTs within at least one of the plurality of carbon nanotubes (CNTs) is between 2 and 100 times a size of at least one of an anion and a cation in the electrolyte.
13. An electric double layer capacitor (EDLC) comprising:
a first electrode comprising a first current collector and a first plurality of vertically aligned carbon nanotubes (CNTs) on the first current collector, wherein the first current collector comprises at least one of roughened aluminum and anodized aluminum;
a second electrode comprising a second current collector and a second plurality of carbon nanotubes (CNTs) on the second current collector, wherein the second current collector comprises at least one of roughened aluminum and anodized aluminum; wherein at least one of the first current collector and the second current collector comprises a layer of aluminum carbide whiskers; and where the vertically aligned carbon nanotubes contact the aluminum carbide whiskers; where the whiskers protrude into the vertically aligned carbon nanotubes; and
an electrolyte contacting the first and second electrodes; wherein the electrolyte comprises a salt of the following formula:
wherein R 1 and R 2 can be the same or different and are each a straight-chain or branched alkyl having 1 to 4 carbon atoms, and X− is an anion that comprises [B(CN) 4 ] − or [BF n (CN) 4-n ] − , where n=0, 1, 2 or 3;
wherein the EDLC has a capacitive frequency window comprising a frequency range of about 1 Hz to an upper boundary of at least 150 Hz, wherein the upper boundary is a cutoff frequency, f 3 db, that is defined by a 3 db reduction in capacitance.
14. An electric double layer capacitor (EDLC) comprising:
a first electrode comprising a first current collector and a first plurality of vertically aligned carbon nanotubes (CNTs) formed on the first current collector;
a second electrode comprising a second current collector and a second plurality of carbon nanotubes (CNTs) formed on the second current collector; wherein the second current collector comprises at least one of roughened aluminum and anodized aluminum; wherein at least one of the first current collector and the second current collector comprises a layer of aluminum carbide whiskers; and where the vertically aligned carbon nanotubes contact the aluminum carbide whiskers; where the whiskers protrude into the vertically aligned carbon nanotubes; and
an electrolyte contacting the first and second electrodes; wherein the electrolyte comprises a salt of the following formula:
wherein R 1 and R 2 can be the same or different and are each a straight-chain or branched alkyl having 1 to 4 carbon atoms, and X− is an anion that comprises [B(CN) 4 ] − or [BF n (CN) 4-n ] − , where n=0, 1, 2 or 3; wherein the EDLC is configured to have a capacitive frequency window comprising a frequency range of about 1 Hz to an upper boundary of 150 Hz, wherein the upper boundary is a phase shift frequency, f 70, where a magnitude of the phase of the capacitor drops below seventy (70) degrees.
15. The electric double layer capacitor (EDLC) of claim 14 , wherein:
at least one plurality of carbon nanotubes (CNTs) is disposed on a respective current collector without a binder material.
16. The electric double layer capacitor (EDLC) of claim 14 , wherein:
at least one of the plurality of carbon nanotubes (CNTs) comprises an average height of less than 50 μm.
17. The electric double layer capacitor (EDLC) of claim 14 , wherein:
lateral spacing between CNTs within at least one of the plurality of carbon nanotubes (CNTs) comprises void spaces having a size that is several times a size of at least one of an anion and a cation in the electrolyte.
18. The electric double layer capacitor (EDLC) of claim 14 , wherein:
lateral spacing between CNTs within at least one of the plurality of carbon nanotubes (CNTs) is between 2 and 100 times a size of at least one of an anion and a cation in the electrolyte.