Ultracapacitors with high frequency response

An electric double layer capacitor (EDLC) comprising:

• a first electrode comprising a first current collector and first plurality of aligned carbon nanotubes (CNTs) formed on the first current collector;
• a second electrode comprising a second current collector and second plurality of carbon nanotubes (CNTs) formed on the second current collector;
• wherein for each of the first and the second current collectors, the first plurality of CNTs and the second plurality of CNT's are separated from the respective current collector by only thin regions of CNT growth catalyst material disposed directly on the respective current collector in a single layer and proximal to bases of the CNTs;
• wherein the catalyst material is configured to self assemble into a plurality of nanodots during CNT formation and regions of the catalyst material include localized islands each proximal to a base of one of the CNTs;
• wherein the first plurality of CNTs and the second plurality of CNTs each have an average CNT height of less than about 20 μm;
• an electrolyte contacting the first and second electrodes and comprising cations and ions;
• wherein the electrolyte comprises a salt of the formula:
• wherein R1 and R2 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 is configured to have a capacitive frequency window comprising a frequency range of about 1 Hz to an upper boundary of at least about 150 Hz, wherein the upper boundary is a cutoff frequency, f3db, that is defined by a 3 db reduction in capacitance.