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

1. An electrolyte for a lithium secondary battery, the electrolyte comprising:

a lithium salt;

an organic solvent; and

an oligomer represented by Formula 1:

wherein, in Formula 1,

R is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,

R 1 to R 3 are each independently a fluorine-substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,

R 4 is an alkylene group having 1 to 4 carbon atoms,

R′ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

a is 1 to 3,

n is the number of repeating units, and

n is an integer of 1 to 75.

2. The electrolyte for a lithium secondary battery of claim 1 , wherein, in the oligomer represented by Formula 1,

the aliphatic hydrocarbon group comprises at least one alicyclic hydrocarbon group selected from the group consisting of a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms; a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms which contains an isocyanate group (NCO); a substituted or unsubstituted cycloalkenylene group having 4 to 20 carbon atoms; and a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms, or a linear hydrocarbon group selected from the group consisting of a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms; a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms which contains an isocyanate group (NCO); a substituted or unsubstituted alkoxylene group having 1 to 20 carbon atoms; a substituted or unsubstituted alkenylene group having 2 to 20 carbon atoms; and a substituted or unsubstituted alkynylene group having 2 to 20 carbon atoms, and

the aromatic hydrocarbon group comprises a substituted or unsubstituted arylene group having 6 to 20 carbon atoms; or a substituted or unsubstituted heteroarylene group having 2 to 20 carbon atoms.

3. The electrolyte for a lithium secondary battery of claim 1 , wherein the oligomer represented by Formula 1 comprises an oligomer represented by Formula 1a:

wherein in Formula 1a,

R is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,

R 1 is a fluorine-substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,

n1 is the number of repeating units, and

n1 is an integer of 1 to 75.

4. The electrolyte for a lithium secondary battery of claim 3 , wherein the oligomer represented by Formula 1a comprises an oligomer represented by Formula 1a-1:

wherein in Formula 1a-1,

n2 is the number of repeating units, and

n2 is an integer of 20 to 75.

5. The electrolyte for a lithium secondary battery of claim 1 , wherein the oligomer represented by Formula 1 is included in an amount of 0.5 wt % to 20 wt % based on a total weight of the electrolyte for a lithium secondary battery.

6. The electrolyte for a lithium secondary battery of claim 1 , wherein the oligomer represented by Formula 1 is included in an amount of 0.5 wt % to 15 wt % based on a total weight of the electrolyte for a lithium secondary battery.

7. The electrolyte for a lithium secondary battery of claim 1 , wherein, in a case in which the electrolyte for a lithium secondary battery comprises the oligomer represented by Formula 1, the electrolyte for a lithium secondary battery is a liquid electrolyte.

8. The electrolyte for a lithium secondary battery of claim 1 , wherein, in a case in which the electrolyte for a lithium secondary battery comprises a polymer derived from the oligomer represented by Formula 1, the electrolyte for a lithium secondary battery is a gel polymer electrolyte.

9. The electrolyte for a lithium secondary battery of claim 8 , wherein the polymer derived from the oligomer represented by Formula 1 is a matrix polymer in which the oligomer represented by Formula 1 is polymerized in the presence of a polymerization initiator to have a three-dimensional structure.

10. The electrolyte for a lithium secondary battery of claim 8 , wherein the gel polymer electrolyte further comprises inorganic particles.

11. The electrolyte for a lithium secondary battery of claim 10 , wherein the inorganic particles comprise a single material selected from the group consisting of BaTiO 3 , BaTiO 3 , Pb(Zr x Ti 1-x )O 3 (0≤x≤1) (PZT), Pb 1-b La b Zr 1-c Ti c O 3 (PLZT, where 0<b<1, 0<c<1), Pb(Mg 1/3 Nb 2/3 ) O 3 —PbTiO 3 (PMN-PT), hafnia (HfO 2 ), SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, ZrO 2 , Y 2 O 3 , Al 2 O 3 , TiO 2 , SiC, and a mixture thereof, or a mixture of two or more thereof.

12. The electrolyte for a lithium secondary battery of claim 10 , wherein the inorganic particles are included in an amount of 10 wt % to 25 wt % based on a total weight of the gel polymer electrolyte.

13. A lithium secondary battery comprising a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and

the electrolyte for a lithium secondary battery of claim 1 .

14. The lithium secondary battery of claim 13 , wherein the electrolyte for a lithium secondary battery is a liquid electrolyte.

15. The lithium secondary battery of claim 13 , wherein the electrolyte for a lithium secondary battery is a gel polymer electrolyte.