An electrolyte for a secondary battery comprising: a non-aqueous solvent; a lithium salt; and a heterocyclic compound represented by Formula 1: wherein, in Formula 1, R 1 and R 2 are each independently selected from hydrogen, a halogen group, a cyano group, a hydroxy group, a nitro group, -C(=O)R a, -C(=O)OR a, -OCO(OR a), -C=N(R a), a substituted or unsubstituted C 1 -C 20 alkyl group, and a combination thereof, wherein R a is selected from hydrogen and a C 1 -C 10 alkyl group, and R 3, R 4, R 5, and R 6 are each independently selected from hydrogen, a halogen group, a cyano group, a hydroxy group, -C(=O)R b, -C(=O)OR b, -OCO(OR b), -C=N(R b), -SR b, -S(=O)R b, -S(=O) 2 R b, -P(R b) 2, a substituted or unsubstituted C 1 -C 20 alkyl group, a substituted or unsubstituted C 1 -C 20 alkoxy group, a substituted or unsubstituted C 2 -C 20 alkenyl group, a substituted or unsubstituted C 2 -C 20 alkynyl group, a C 2 -C 20 alkylene oxide group, a substituted or unsubstituted C 3 -C 30 cycloalkyl group, a substituted or unsubstituted C 6 -C 30 aryl group, a substituted or unsubstituted C 6 -C 30 aryloxy group, a substituted or unsubstituted C 6 -C 30 heteroaryl group, and a combination thereof, wherein R b is selected from hydrogen, a C 1 -C 10 alkyl group, and a C 6 -C 20 aryl group, provided that at least one selected from R 1 and R 2 is selected from a halogen group, a cyano group, a hydroxy group, a nitro group, -C(=O)R a, -C(=O)OR a, or a C 1 -C 20 alkyl group substituted with at least one halogen atom, hydroxy group, nitro group, or cyano group. a non-aqueous solvent; a lithium salt; and a heterocyclic compound represented by Formula 1: wherein, in Formula 1, R 1 and R 2 are each independently selected from hydrogen, a halogen group, a cyano group, a hydroxy group, a nitro group, -C(=O)R a, -C(=O)OR a, -OCO(OR a), -C=N(R a), a substituted or unsubstituted C 1 -C 20 alkyl group, and a combination thereof, wherein R a is selected from hydrogen and a C 1 -C 10 alkyl group, and R 3, R 4, R 5, and R 6 are each independently selected from hydrogen, a halogen group, a cyano group, a hydroxy group, -C(=O)R b, -C(=O)OR b, -OCO(OR b), -C=N(R b), -SR b, -S(=O)R b, -S(=O) 2 R b, -P(R b) 2, a substituted or unsubstituted C 1 -C 20 alkyl group, a substituted or unsubstituted C 1 -C 20 alkoxy group, a substituted or unsubstituted C 2 -C 20 alkenyl group, a substituted or unsubstituted C 2 -C 20 alkynyl group, a C 2 -C 20 alkylene oxide group, a substituted or unsubstituted C 3 -C 30 cycloalkyl group, a substituted or unsubstituted C 6 -C 30 aryl group, a substituted or unsubstituted C 6 -C 30 aryloxy group, a substituted or unsubstituted C 6 -C 30 heteroaryl group, and a combination thereof, wherein R b is selected from hydrogen, a C 1 -C 10 alkyl group, and a C 6 -C 20 aryl group, provided that at least one selected from R 1 and R 2 is selected from a halogen group, a cyano group, a hydroxy group, a nitro group, -C(=O)R a, -C(=O)OR a, or a C 1 -C 20 alkyl group substituted with at least one halogen atom, hydroxy group, nitro group, or cyano group. R 1 and R 2 are each independently selected from hydrogen, a halogen group, a cyano group, a hydroxy group, a nitro group, -C(=O)R a, -C(=O)OR a, -OCO(OR a), -C=N(R a), a substituted or unsubstituted C 1 -C 20 alkyl group, and a combination thereof, wherein R a is selected from hydrogen and a C 1 -C 10 alkyl group, and R 3, R 4, R 5, and R 6 are each independently selected from hydrogen, a halogen group, a cyano group, a hydroxy group, -C(=O)R b, -C(=O)OR b, -OCO(OR b), -C=N(R b), -SR b, -S(=O)R b, -S(=O) 2 R b, -P(R b) 2, a substituted or unsubstituted C 1 -C 20 alkyl group, a substituted or unsubstituted C 1 -C 20 alkoxy group, a substituted or unsubstituted C 2 -C 20 alkenyl group, a substituted or unsubstituted C 2 -C 20 alkynyl group, a C 2 -C 20 alkylene oxide group, a substituted or unsubstituted C 3 -C 30 cycloalkyl group, a substituted or unsubstituted C 6 -C 30 aryl group, a substituted or unsubstituted C 6 -C 30 aryloxy group, a substituted or unsubstituted C 6 -C 30 heteroaryl group, and a combination thereof, wherein R b is selected from hydrogen, a C 1 -C 10 alkyl group, and a C 6 -C 20 aryl group, provided that at least one selected from R 1 and R 2 is selected from a halogen group, a cyano group, a hydroxy group, a nitro group, -C(=O)R a, -C(=O)OR a, or a C 1 -C 20 alkyl group substituted with at least one halogen atom, hydroxy group, nitro group, or cyano group.