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

The present invention provides a nonaqueous electrolytic solution capable of improving electrochemical characteristics in the case of using an energy storage device at a high temperature and at a high voltage and further capable of inhibiting the gas generation while maintaining a capacity retention rate after storage at a high temperature and at a high voltage and also provides an energy storage device using the same. Disclosed is a nonaqueous electrolytic solution having an electrolyte salt dissolved in a nonaqueous solvent, the nonaqueous electrolytic solution containing a carboxylic acid ester compound represented by the following general formula (I).In the formula, each of R1 and R2 independently represents a hydrogen atom, a -C(═O)-OR4 group, or the like, and R1 and R2 may be bonded to each other to form a ring structure. R3 represents a hydrogen atom or the like, and n represents an integer of 1 to 3. When n is 1, then L and R4 represent an alkyl group having 1 to 6 carbon atoms or the like; and when n is 2 or 3, then L represents an n-valent connecting group, X represents a -C(═O)- group, 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, and each of R6 and R7 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.