Electrolyte for lithium secondary battery and lithium secondary battery including the same

An electrolyte for a lithium secondary battery comprising:

• a lithium salt;
• an organic solvent;
• and
• an additive including a lactone compound represented by Formula 1 below:
• In Formula 1, X is a substituted or unsubstituted C1-C5 alkylene group,
• wherein the substituted C1-C5 alkylene group is the alkylene group in which at least one hydrogen of the alkylene group is substituted with substituent selected from the group consisting of a halogen, a C1-C6 alkyl group, a C2-C6 alkenyl group, an amino group, a C1-C6 alkoxy group, a C3-C7 cycloalkyl group, and a 5- to 7-membered heterocycloalkyl group.