Carbon surface modification for three-volt ultracapacitor

A method of making an ultracapacitor, comprising:

• providing a first current collector electrically coupled to a positive electrode and a second current collector electrically coupled to a negative electrode, and separated by a separator into a housing;
• and
• adding an electrolyte to the housing, wherein the electrolyte comprises a quaternary ammonium salt in ionic contact with the positive electrode and the negative electrode, wherein the electrolyte comprises less than 1 M salt;
• wherein the capacitor is configured to operate at 3 volts or greater at 65° C. and maintaining greater than 80% of its initial capacitance for over 1500 hours.

A method of making an ultracapacitor, comprising:

• providing a first current collector electrically coupled to a positive electrode and a second current collector electrically coupled to a negative electrode, and separated by a separator into a housing;
• and
• adding an electrolyte to the housing, wherein the electrolyte comprises a quaternary ammonium salt in ionic contact with the positive electrode and the negative electrode, wherein the electrolyte comprises less than 1 M salt;
• wherein the capacitor is configured to operate at 3 volts or greater at 65° C. and maintaining less than 200% of its initial equivalent series resistance for over 1500 hours.