Lithium Secondary Battery

An electrolyte composite for a lithium secondary battery comprising:

• a lithium salt;
• a non-aqueous organic solvent;
• a conjugated diene compound represented by the following Formula 1;
• and
• an at least one additive selected from the group consisting of an oxalato phosphate-based compound, an oxalato borate-based compound, a fluorine-substituted carbonate-based compound, a vinylidene carbonate-based compound, and a sulfinyl group-containing compound:
• wherein
• R1 is hydrogen or C1-C3alkyl substituted with a C4-C8alkenyl,
• when R1 is hydrogen, R2, R3, R4, and R5 are each independently C1-C3alkyl, and
• when R1 is C1-C3alkyl substituted with a C4-C8alkenyl, R2, R3, R4, and R5 are all hydrogen.