Nonaqueous electrolyte, capacitor device using same, and carboxylic acid ester compound used in same

A nonaqueous electrolytic solution having an electrolyte salt dissolved in a nonaqueous solvent, the nonaqueous electrolytic solution comprising from 0.001 to 10% by mass of a carboxylic acid ester compound represented by the following general formula (I):

• wherein:
• each of R1 and R2 independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 6 carbon atoms, an aralkyl group having 7 to 13 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a —C(═O)—OR4 group, and when R1 and R2 are each an alkyl group, then R1 and R2 may be bonded to each other to form a ring structure;
• R3 represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms;
• n represents an integer of 1 to 3;
• when n is 1, then L and R4 may be the same as or different from each other and represent an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 6 carbon atoms, an alkoxyalkyl group having 2 to 6 carbon atoms, a cyanoalkyl group having 2 to 6 carbon atoms, an aralkyl group having 7 to 13 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and when n is 2 or 3, then L represents an n-valent connecting group constituted of a carbon atom and a hydrogen atom, which may contain an ether bond, a thioether bond, or an SO2 bond and R4 is the same as described above;
• and
• X is selected from the group consisting of, an —S(═O)—group, an —S(═O)2—group, an —S(═O)2—R5—S(═O)2—group or a CR6R7 group, R5 represents an alkylene group having 1 to 4 carbon atoms, in which at least one hydrogen atom may be substituted with a halogen atom or an alkyl group having 1 to 4 carbon atoms, and each of R6 and R7 independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, in which at least one hydrogen atom may be substituted with a halogen atom,
• wherein at least one hydrogen atom of the alkyl group having 1 to 6 carbon atoms, the cycloalkyl group having 3 to 6 carbon atoms, the alkenyl group having 2 to 6 carbon atoms, the alkynyl group having 3 to 6 carbon atoms, the alkoxyalkyl group having 2 to 6 carbon atoms, the cyanoalkyl group having 2 to 6 carbon atoms, the aralkyl group having 7 to 13 carbon atoms, or the aryl group having 6 to 12 carbon atoms as R1, R2, R4, or L, may be substituted with a halogen atom.