Method for preparing electrolytic solution, electrolytic solution and electric double-layer capacitor

An electrolytic solution for an electric double-layer capacitor, which undergoes cyclical charging and discharging within a predetermined operating range of voltage, said capacitor comprising:

• said electrolytic solution;
• electrodes;
• and
• a casing for housing said electrolytic solution and electrodes,
• wherein said electrolytic solution is prepared with a method comprising the step of preparing an ion concentration of said electrolytic solution so that said electrolytic solution turns to a nonconductor at a first predetermined voltage, which is so set as to be equal to or greater than an upper limit of said predetermined operating range of voltage and less than or equal to a maximum allowable voltage of said capacitor.

An electric double-layer capacitor which undergoes cyclical charging and discharging within a predetermined operating range of voltage, said capacitor comprising:

• an electrolytic solution;
• electrodes;
• and
• a casing for housing said electrolytic solution and electrodes,
• wherein said electrolytic solution is prepared by a method comprising the step of preparing an ion concentration of said electrolytic solution so that said electrolytic solution turns to a nonconductor at a first predetermined voltage, which is so set as to be equal to or greater than an upper limit of said predetermined operating range of voltage and less than or equal to a maximum allowable voltage of said capacitor.