An aspect of the present invention is a nonaqueous electrolyte energy storage device including: a positive electrode including a positive active material layer of 5 mAh/cm.sup.2 or more in capacity density per unit area; a negative electrode including metallic lithium; and a nonaqueous electrolyte including an ionic liquid and a fluorinated ether.

In one embodiment, the present invention relates to an electric device, comprising an electrolyte comprising a solvent; a first quaternary ammonium or phosphonium salt; and a second quaternary ammonium or phosphonium salt, containing an ammonium group having a general formula [NR.sup.1R.sup.2R.sup.3R.sup.4].sup.+, or a phosphonium group having a general formula [PR.sup.1R.sup.2R.sup.3R.sup.4].sup.+, wherein R.sup.1═R.sup.2, R.sup.3═R.sup.4, R.sup.2≠R.sup.3, and each R.sup.1, R.sup.2, R.sup.3 and R.sup.4 independently is a branched or unbranched alkyl group containing from 1 to about 20 carbon atoms, and in which each salt comprises an anion, and wherein the first and second ammonium or phosphonium are not the same. In another embodiment, the present invention relates to the electrolyte.

In one embodiment, the present invention relates to an electric device, comprising an electrolyte comprising a solvent; a first quaternary ammonium or phosphonium salt; and a second quaternary ammonium or phosphonium salt, containing an ammonium group having a general formula [NR.sup.1R.sup.2R.sup.3R.sup.4].sup.+, or a phosphonium group having a general formula [PR.sup.1R.sup.2R.sup.3R.sup.4].sup.+, wherein R.sup.1═R.sup.2, R.sup.3═R.sup.4, R.sup.2≠R.sup.3, and each R.sup.1, R.sup.2, R.sup.3 and R.sup.4 independently is a branched or unbranched alkyl group containing from 1 to about 20 carbon atoms, and in which each salt comprises an anion, and wherein the first and second ammonium or phosphonium are not the same. In another embodiment, the present invention relates to the electrolyte.

A secondary battery having good performance especially in a high-temperature environment can be obtained by using an electrolyte solution for secondary batteries, which is characterized by containing an ionic liquid represented by formula (1) and a lithium salt.

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(In the formula, each of R.sup.1 and R.sup.2 independently represents an alkyl group having 1-5 carbon atoms; and n represents 1 or 2.)

An ultracapacitor that contains a first electrode, second electrode, separator, nonaqueous electrolyte, and housing is provided. The first electrode comprises a first current collector electrically coupled to a first carbonaceous coating and the second electrode comprises a second current collector electrically coupled to a second carbonaceous coating. The first current collector and the second current collector each contain a substrate that includes a conductive metal, wherein a plurality of fiber-like whiskers project outwardly from the substrate of the first current collector, the substrate of the second current collector, or both.

The present invention provides a nonaqueous electrolytic solution that provides an electric double layer capacitor having excellent durability. The nonaqueous electrolytic solution of the present invention is a nonaqueous electrolytic solution for electric double layer capacitors prepared by dissolving a quaternary ammonium salt as an electrolyte in a nonaqueous solvent, and the nonaqueous electrolytic solution has an alkali metal cation concentration of 0.1 to 30 ppm.

To provide a power storage device whose charge and discharge characteristics are unlikely to be degraded by heat treatment. To provide a power storage device that is highly safe against heat treatment. The power storage device includes a positive electrode, a negative electrode, a separator, an electrolytic solution, and an exterior body. The separator is located between the positive electrode and the negative electrode. The separator contains polyphenylene sulfide or solvent-spun regenerated cellulosic fiber. The electrolytic solution contains a solute and two or more kinds of solvents. The solute contains LiBETA. One of the solvents is propylene carbonate.

To provide a power storage device whose charge and discharge characteristics are unlikely to be degraded by heat treatment. To provide a power storage device that is highly safe against heat treatment. The power storage device includes a positive electrode, a negative electrode, a separator, an electrolytic solution, and an exterior body. The separator is located between the positive electrode and the negative electrode. The separator contains polyphenylene sulfide or solvent-spun regenerated cellulosic fiber. The electrolytic solution contains a solute and two or more kinds of solvents. The solute contains LiBETA. One of the solvents is propylene carbonate.

To provide a secondary battery that can be mounted on a substrate and can easily select a voltage to be output in manufacture and a manufacturing method thereof. A secondary battery in which small cells with substantially the same form are stacked and whose voltage to be output is easily selected in manufacture by changing the number of stacked layers is manufactured. In the cell, an electrolytic solution including a spacer and a polymer is used to keep at least a certain distance between the positive electrode active material layer and the negative electrode active material layer with the spacer. Furthermore, the electrolytic solution is made to gelate by the polymer to be an electrolytic solution that can be formed in the form of a sheet. Furthermore, the positive electrode active material layer and the negative electrode active material layer are formed using a printing method typified by screen printing.

To provide a secondary battery that can be mounted on a substrate and can easily select a voltage to be output in manufacture and a manufacturing method thereof. A secondary battery in which small cells with substantially the same form are stacked and whose voltage to be output is easily selected in manufacture by changing the number of stacked layers is manufactured. In the cell, an electrolytic solution including a spacer and a polymer is used to keep at least a certain distance between the positive electrode active material layer and the negative electrode active material layer with the spacer. Furthermore, the electrolytic solution is made to gelate by the polymer to be an electrolytic solution that can be formed in the form of a sheet. Furthermore, the positive electrode active material layer and the negative electrode active material layer are formed using a printing method typified by screen printing.