Electrochemical energy storing device

An electrochemical energy storing device comprising:

• a positive electrode containing a positive-electrode active material;
• a negative electrode;
• and
• a nonaqueous electrolyte solution which is in contact with the positive electrode and the negative electrode and contains, as a solvent, an ionic liquid including cations having an alkoxyalkyl group as a component, the ionic liquid being a major component of the solvent, wherein:
• in a discharged state, the positive-electrode active material contains at least one selected from the group consisting of (1) an alkali metal chloride, (2) an alkaline-earth metal chloride, and (3) a quaternary alkylammonium chloride,
• the ionic liquid of the nonaqueous electrolyte solution dissolves (1) the alkali metal chloride contained in the positive-electrode active material, (2) the alkaline-earth metal chloride contained in the positive-electrode active material, and/or (3) the quaternary alkylammonium chloride contained in the positive-electrode active material, and
• the nonaqueous electrolyte solution has (1) an alkali metal ion conductivity in the case where the positive-electrode active material contains the alkali metal chloride, (2) an alkaline-earth metal ion conductivity in the case where the positive-electrode active material contains the alkaline-earth metal chloride, and/or a quaternary alkylammonium ion conductivity in the case where the positive-electrode active material contains the quaternary alkylammonium chloride.