An electrolyte for a rechargeable lithium battery, comprising: a lithium salt; an organic solvent comprising a sulfur-containing compound represented by Chemical Formula 1 and a fluoroalkyl ether; and an additive comprising a phosphazene compound represented by Chemical Formula 3: wherein R 1 to R 8 are each independently a hydrogen atom or a substituted or unsubstituted C1 to C30 alkyl group; wherein: X 1 to X 5 are each independently a halogen or a halogen-containing group and wherein at least one of X 1 to X 5 is a halogen; and Z is NR 9 R 10 or OR 11, wherein: R 9 and R 10 are each independently a substituted or unsubstituted C1 to C30 alkyl group or a substituted or unsubstituted C3 to C30 cycloalkyl group, and R 11 is a substituted or unsubstituted C1 to C30 alkyl group; and wherein the fluoroalkyl ether is represented by Chemical Formula 2: wherein R 12 and R 13 are each independently a C1 to C10 alkyl group substituted with at least one fluorine atom; wherein the phosphazene compound is present in an amount of 1 part by weight to 20 parts by weight based on 100 parts by weight of the organic solvent; and characterized in that the fluoroalkyl ether is present in an amount of 1% by volume to 10% by volume based on the total amount of the organic solvent. a lithium salt; an organic solvent comprising a sulfur-containing compound represented by Chemical Formula 1 and a fluoroalkyl ether; and an additive comprising a phosphazene compound represented by Chemical Formula 3: wherein R 1 to R 8 are each independently a hydrogen atom or a substituted or unsubstituted C1 to C30 alkyl group; wherein: X 1 to X 5 are each independently a halogen or a halogen-containing group and wherein at least one of X 1 to X 5 is a halogen; and Z is NR 9 R 10 or OR 11, wherein: R 9 and R 10 are each independently a substituted or unsubstituted C1 to C30 alkyl group or a substituted or unsubstituted C3 to C30 cycloalkyl group, and R 11 is a substituted or unsubstituted C1 to C30 alkyl group; and wherein the fluoroalkyl ether is represented by Chemical Formula 2: wherein R 12 and R 13 are each independently a C1 to C10 alkyl group substituted with at least one fluorine atom; wherein the phosphazene compound is present in an amount of 1 part by weight to 20 parts by weight based on 100 parts by weight of the organic solvent; and characterized in that the fluoroalkyl ether is present in an amount of 1% by volume to 10% by volume based on the total amount of the organic solvent. X 1 to X 5 are each independently a halogen or a halogen-containing group and wherein at least one of X 1 to X 5 is a halogen; and Z is NR 9 R 10 or OR 11, wherein: R 9 and R 10 are each independently a substituted or unsubstituted C1 to C30 alkyl group or a substituted or unsubstituted C3 to C30 cycloalkyl group, and R 11 is a substituted or unsubstituted C1 to C30 alkyl group; and wherein the fluoroalkyl ether is represented by Chemical Formula 2: wherein R 12 and R 13 are each independently a C1 to C10 alkyl group substituted with at least one fluorine atom; R 9 and R 10 are each independently a substituted or unsubstituted C1 to C30 alkyl group or a substituted or unsubstituted C3 to C30 cycloalkyl group, and R 11 is a substituted or unsubstituted C1 to C30 alkyl group; and wherein the fluoroalkyl ether is represented by Chemical Formula 2: wherein R 12 and R 13 are each independently a C1 to C10 alkyl group substituted with at least one fluorine atom; wherein the phosphazene compound is present in an amount of 1 part by weight to 20 parts by weight based on 100 parts by weight of the organic solvent; and characterized in that the fluoroalkyl ether is present in an amount of 1% by volume to 10% by volume based on the total amount of the organic solvent.