Ionic liquid of dimethylethyl(methoxyethyl)ammonium for an electric double layer capacitor and a secondary battery

Electrical storage devices having excellent low-temperature properties can be obtained by using a quaternary salt (or ionic liquid) of general formula (1) below as an electrolyte salt for electrical storage devices or a liquid electrolyte for electrical storage devices. In formula (1), R to R are each independently an alkyl group of 1 to 5 carbons or an alkoxyalkyl group of the formula R'-O-(CH2)n-, with the proviso that at least one group from among R to R is the above alkoxyalkyl group. X is a nitrogen or phosphorus atom, and Y is a monovalent anion.