Patent ID: 7794876

Claim:
A nonaqueous electrolyte solution, in which an electrolyte salt is dissolved in a nonaqueous solvent, the nonaqueous electrolyte solution comprising a pentafluorophenyloxy compound in an amount of 0.01 to 10% by weight based on the weight of the nonaqueous electrolyte solution, the pentafluorophenyloxy compound being represented by the following formula (II): wherein R 3 represents a —COCO— group, a C═O group, a S═O group or a S(═O) 2 group, R 4 represents a C 1 to C 12 alkyl group, a C 3 to C 12 cycloalkyl group, a C 2 to C 12 alkenyl group, a C 3 to C 12 alkynyl group, a C 6 to C 18 aryl group or a C 7 to C 20 aralkyl group wherein at least one of the hydrogen atoms of R 4 may optionally be substituted with a halogen atom, with the proviso that R 4 represents a C 2 to C 12 alkenyl group or a C 3 to C 12 alkynyl group when R 3 represents a C═O group.