An ultracapacitor that is capable of exhibiting good properties even after being subjected to high temperatures, such as experienced during solder reflow, is provided. The ultracapacitor contains a housing having sidewalls that extend in a direction generally perpendicular to a base. An interior cavity is defined between an inner surface of the base and the sidewalls within which an electrode assembly can be positioned. To attach the electrode assembly, first and second conductive members are disposed on the inner surface of the base. The electrode assembly likewise contains first and second leads that extend outwardly therefrom and are electrically connected to the first and second conductive members, respectively. The first and second conductive members are, in turn, electrically connected to first and second external terminations, respectively, which are provided on an outer surface of the base.

An electrolytic solution for an electrochemical device a solvent, an ionic substance, and an additive agent, the additive agent containing α-methyl-γ-butyrolactone and δ-valerolactone.

An electrolytic solution for an electrochemical device a solvent, an ionic substance, and an additive agent, the additive agent containing α-methyl-γ-butyrolactone and δ-valerolactone.

An electrochemical device includes a positive electrode, a negative electrode, and an electrolyte having lithium ion conductivity. The positive electrode includes a positive current collector and a positive electrode mixture layer supported on the positive current collector. The positive electrode mixture layer contains a positive electrode active material reversibly doped with an anion. The negative electrode includes a negative current collector and a negative electrode mixture layer supported on the negative current collector. The negative electrode mixture layer contains a negative electrode active material reversibly doped with lithium ions. The negative electrode active material contains non-graphitizable carbon. A ratio Mp/Mn of a mass Mp of the positive electrode active material supported on a unit area of the positive electrode to a mass Mn of the negative electrode active material supported on a unit area of the negative electrode is in a range from 1.1 to 2.5, inclusive.

An electrolytic solution is provided and includes an electrolytic solution for an electrochemical device including a magnesium electrode as a negative electrode and a positive electrode, the electrolytic solution containing: a solvent; and a first magnesium salt having a disilazide structure represented by General Formula (1):

(R.sub.3Si).sub.2N  (1) wherein R is an aliphatic hydrocarbon group having 1 or more and 10 or less carbon atoms, and each R may be the same as or different from each other, the electrolytic solution substantially comprising no halogen.

A flexible energy storage device with a redox-active polymer hydrogel electrolyte is provided. The flexible energy storage device can include a pair of electrodes separated by the redox-active polymer hydrogel electrolyte. The redox-active polymer hydrogel electrolyte can include a polymer hydrogel, charge balancing anions and redox-active transition metal cations at least one selected from the group consisting of vanadium, chromium, manganese, cobalt, and copper. The flexible energy storage device may retain greater than 75% of an unbent specific capacitance when bent at an angle of 100 to 170°.

Provided is an electrochemical device including a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode. In the electrochemical device, the negative electrode is an electrode containing magnesium, and is in contact with a fullerene analogue-containing layer containing a fullerene analogue. The electrolytic solution of the electrochemical device includes a solvent and a magnesium salt contained in the solvent.

A power system adapted for supplying power in a high temperature environment is disclosed. The power system includes a rechargeable energy storage that is operable in a temperature range of between about seventy degrees Celsius and about two hundred and fifty degrees Celsius coupled to a circuit for at least one of supplying power from the energy storage and charging the energy storage; wherein the energy storage is configured to store between about one one hundredth (0.01) of a joule and about one hundred megajoules of energy, and to provide peak power of between about one one hundredth (0.01) of a watt and about one hundred megawatts, for at least two charge-discharge cycles. Methods of use and fabrication are provided. Embodiments of additional features of the power supply are included.

A power system adapted for supplying power in a high temperature environment is disclosed. The power system includes a rechargeable energy storage that is operable in a temperature range of between about seventy degrees Celsius and about two hundred and fifty degrees Celsius coupled to a circuit for at least one of supplying power from the energy storage and charging the energy storage; wherein the energy storage is configured to store between about one one hundredth (0.01) of a joule and about one hundred megajoules of energy, and to provide peak power of between about one one hundredth (0.01) of a watt and about one hundred megawatts, for at least two charge-discharge cycles. Methods of use and fabrication are provided. Embodiments of additional features of the power supply are included.

A downhole power system includes an energy storage adapted to operate at high temperatures, and a modular signal interface device that serves to control the energy storage component as well as offer a means of data logging at high temperatures. The controller is fabricated from pre-assembled components that may be selected for various combinations to provide desired functionality. The energy storage may include at least one ultracapacitor.