High temperature energy storage device

1. An ultracapacitor comprising:

a positive electrode,

a negative electrode,

a separator, and

an electrolyte within a hermetically sealed housing,

wherein the ultracapacitor has less than 200 ppm of halides and a water content of less than 100 ppm,

wherein the ultracapacitor exhibits an equivalent series resistance (ESR) increase of less than about 300 percent while held at a constant voltage for at least 20 hours while held at a substantially constant temperature within a temperature range of between about 80 degrees Celsius and 210 degrees Celsius, and

wherein:

the ultracapacitor is configured to operate at a temperature between 80 degrees Celsius and 210 degrees Celsius with a volumetric leakage current of less than 1,000 mAmp per Liter, and/or

the ultracapacitor exhibits a volumetric leakage current of less than 10 mA/cc while held at a substantially constant temperature between 100 degrees Celsius and 150 degrees Celsius.

2. The ultracapacitor of claim 1 , wherein the ESR increase is less than about 100 percent.

3. The ultracapacitor of claim 1 , wherein at least one of the positive electrode and the negative electrode comprises a carbonaceous energy storage media comprising at least one of activated carbon, carbon fibers, rayon, graphene, aerogel, carbon cloth, and carbon nanotubes.

4. The ultracapacitor of claim 1 , wherein the electrolyte comprises an ionic liquid comprising:

a cation selected from the group consisting of ammonium cations, imidazolium cations, functionalized imidazolium cations, oxazolium cations, phosphonium cations, piperidinium cations, pyrazinium cations, pyrazolium cations, pyridazinium cations, pyridinium cations, pyrimidinium cations, pyrrolidinium cations, sulfonium cations, thiazolium cations, triazolium cations, guanidium cations, isoquinolinium cations, benzotriazolium cations, and viologen-type cations; and

an anion selected from the group consisting of bis(trifluoromethanesulfonate)imide, tris(trifluoromethanesulfonate)methide, dicyanamide, tetra-fluoroborate, hexafluorophosphate, trifluoromethanesulfonate, bis(pentafluoroethanesulfonate)-imide, thiocyanate, and trifluoro(trifluoromethyl)borate.

5. The ultracapacitor of claim 4 , wherein the electrolyte further comprises a solvent selected from the group consisting of acetonitrile, amides, benzonitrile, butyrolactone, cyclic ether, diethylether, dimethoxyethane, dimethylformamide, dimethylsulfone, dioxane, dioxolane, ethyl formate, ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate, dibutyl carbonate, lactone, methyl formate, methyl propionate, methyltetrahydrofuran, tetrahydrofuran, nitrobenzene, nitromethane, N-methylpyrrolidone, sulfolane, tetramethylene sulfone, thiophene, ethyleneglycol, diethylene glycol, triethylene glycol, polyethylene glycols, carbonic acid ester, γ-butyrolactone, and tricyanohexane.

6. The ultracapacitor of claim 1 , wherein the hermetically sealed housing exhibits a leakage rate of helium that is between about 10 −5 standard He cc/second and about 10 −9 standard He cc/second.

7. The ultracapacitor of claim 1 , wherein the hermetically sealed housing exhibits a leakage rate of helium that is between about 10 −7 standard He cc/second and about 10 −10 standard He cc/second.

8. The ultracapacitor of claim 1 , wherein the temperature range is between about 100 degrees Celsius and about 210 degrees Celsius.

9. The ultracapacitor of claim 1 , wherein the temperature range is between about 150 degrees Celsius and about 210 degrees Celsius.