An electrolyte composition comprising: a lithium salt; a non-aqueous organic solvent; a compound represented by Formula 1; and an oligomer represented by formula 2: wherein, in Formula 1, R 1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 3 to 8; wherein, in Formula 2, R is an alkylene group having 1 to 4 carbon atoms which is unsubstituted or substituted with fluorine, R 2 and R 2 ' are each independently an alkylene group having 1 to 5 carbon atoms or -(CF 2) o -O-, wherein o is an integer of 1 to 3, R 3 and R 3 ' are each independently an alkylene group having 1 to 5 carbon atoms or -(R 5) o2 -O-, wherein R 5 is an unsubstituted or substituted alkylene group having 1 to 5 carbon atoms, and o2 is an integer of 1 to 3), R 4 is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group, Ra, Rb, Rc, and Rd are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, n, m, and m' are each independently an integer of 1 to 10, k is an integer of 10 to 1,000, p and p' are each independently an integer of 0 or 1, c and c1 are each independently an integer of 1 to 3, and d and d1 are each independently an integer of 1 or 2. a lithium salt; a non-aqueous organic solvent; a compound represented by Formula 1; and an oligomer represented by formula 2: wherein, in Formula 1, R 1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 3 to 8; wherein, in Formula 2, R is an alkylene group having 1 to 4 carbon atoms which is unsubstituted or substituted with fluorine, R 2 and R 2 ' are each independently an alkylene group having 1 to 5 carbon atoms or -(CF 2) o -O-, wherein o is an integer of 1 to 3, R 3 and R 3 ' are each independently an alkylene group having 1 to 5 carbon atoms or -(R 5) o2 -O-, wherein R 5 is an unsubstituted or substituted alkylene group having 1 to 5 carbon atoms, and o2 is an integer of 1 to 3), R 4 is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group, Ra, Rb, Rc, and Rd are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, n, m, and m' are each independently an integer of 1 to 10, k is an integer of 10 to 1,000, p and p' are each independently an integer of 0 or 1, c and c1 are each independently an integer of 1 to 3, and d and d1 are each independently an integer of 1 or 2. R 1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 3 to 8; wherein, in Formula 2, R is an alkylene group having 1 to 4 carbon atoms which is unsubstituted or substituted with fluorine, R 2 and R 2 ' are each independently an alkylene group having 1 to 5 carbon atoms or -(CF 2) o -O-, wherein o is an integer of 1 to 3, R 3 and R 3 ' are each independently an alkylene group having 1 to 5 carbon atoms or -(R 5) o2 -O-, wherein R 5 is an unsubstituted or substituted alkylene group having 1 to 5 carbon atoms, and o2 is an integer of 1 to 3), R 4 is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group, Ra, Rb, Rc, and Rd are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, n, m, and m' are each independently an integer of 1 to 10, k is an integer of 10 to 1,000, p and p' are each independently an integer of 0 or 1, c and c1 are each independently an integer of 1 to 3, and d and d1 are each independently an integer of 1 or 2. R is an alkylene group having 1 to 4 carbon atoms which is unsubstituted or substituted with fluorine, R 2 and R 2 ' are each independently an alkylene group having 1 to 5 carbon atoms or -(CF 2) o -O-, wherein o is an integer of 1 to 3, R 3 and R 3 ' are each independently an alkylene group having 1 to 5 carbon atoms or -(R 5) o2 -O-, wherein R 5 is an unsubstituted or substituted alkylene group having 1 to 5 carbon atoms, and o2 is an integer of 1 to 3), R 4 is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group, Ra, Rb, Rc, and Rd are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, n, m, and m' are each independently an integer of 1 to 10, k is an integer of 10 to 1,000, p and p' are each independently an integer of 0 or 1, c and c1 are each independently an integer of 1 to 3, and d and d1 are each independently an integer of 1 or 2.