Field of the Invention
The present invention relates to an electric storage device with built-in, chargeable/dischargeable electric storage element.
Description of the Related Art
Known electric storage devices include electric double-layer capacitors, redox capacitors, lithium ion capacitors, lithium ion batteries, etc. In particular, lithium ion capacitors are drawing attention for their high level of energy density and high number of repeatable charge/discharge cycles which are made possible by combining a positive electrode similar to that of an electric double-layer capacitor or redox capacitor, and a negative electrode using a carbon material capable of occluding lithium ions.
At the same time, recently lithium ion capacitors are required to maintain their capacitance in a low-temperature state, while ensuring reliability in a high-temperature state (such as 85° C.).
In the area of improving low-temperature characteristics, Patent Literature 1 below, for example, proposes a lithium ion capacitor offering improved low-temperature characteristics by forming a film on the surface of the negative electrode by means of adding vinylene carbonate, as an additive, to non-aqueous electrolytic solution containing γ-butyrolactone.
In the area of improving high-temperature reliability, on the other hand, Patent Literature 2 below, for example, proposes an electrolytic solution capable of improving the cycle characteristics, as well as characteristics after short-term (24 hours or so) high-temperature holding test, of a lithium ion battery by adding a methylene bis sulfonate derivative to an electrolytic solution that uses a mixed solvent of ethylene carbonate and ethyl methyl carbonate.