Polymer electrolyte and lithium secondary battery including the same

1. A polymer electrolyte comprising:

a lithium salt; and

a copolymer represented by Formula 1b or 1c:

wherein, in Formula 1b and 1c,

each of m, n, and o is the number of repeating units,

m is an integer of 1 to 10,

n is an integer of 1 to 10, and

o is an integer of 1 to 500.

2. A polymer electrolyte, comprising:

a lithium salt; and

a copolymer represented by Formula 2:

wherein, in Formula 2,

R′ 1 and R′ 2 are each independently a fluorine-substituted or unsubstituted alkylene group having 1 to 4 carbon atoms,

R 3 is hydrogen, or an alkyl group having 1 to 6 carbon atoms,

R 4 is an alkylene group having 1 to 6 carbon atoms,

R 5 is an alkylene group having 1 to 5 carbon atoms, or —CO—NH—R 6 —NH—CO—O—,

R 6 is an aliphatic, alicyclic, or aromatic hydrocarbon group,

each of m1, n1, and o1 is the number of repeating units,

m1 is an integer of 1 to 10,

n1 is an integer of 1 to 10, and

o1 is an integer of 1 to 500.

3. The polymer electrolyte of claim 2 , wherein a weight ratio of the copolymer represented by Formula 1 to the lithium salt is in a range of 7:3 to 9.5:0.5.

4. The polymer electrolyte of claim 2 , wherein the aliphatic hydrocarbon group comprises an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms which contains an isocyanate group (NCO); an alkoxylene group having 1 to 20 carbon atoms; an alkenylene group having 2 to 20 carbon atoms; or an alkynylene group having 2 to 20 carbon atoms,

the alicyclic hydrocarbon group comprises 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 cycloalkenylene group having 4 to 20 carbon atoms; or a heterocycloalkylene 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 heteroarylene group having 2 to 20 carbon atoms.

5. The polymer electrolyte of claim 2 , wherein the copolymer represented by Formula 2 comprises at least one selected from the group consisting of copolymers represented by Formulae 2a to 2c:

wherein, in Formula 2a,

each of m2, n2, and o2 is the number of repeating units,

m2 is an integer of 1 to 10,

n2 is an integer of 1 to 10, and

o2 is an integer of 1 to 500,

wherein, in Formula 2b,

each of m3, n3, and o3 is the number of repeating units,

m3 is an integer of 1 to 10,

n3 is an integer of 1 to 10, and

o3 is an integer of 1 to 500,

wherein, in Formula 2c,

each of m4, n4, and o4 is the number of repeating units,

m4 is an integer of 1 to 10,

n4 is an integer of 1 to 10, and

o4 is an integer of 1 to 500.

6. The polymer electrolyte of claim 2 , wherein the copolymer represented by Formula 2 has a weight-average molecular weight (Mw) of 200 g/mol to 100,000 g/mol.

7. The polymer electrolyte of claim 2 , further comprising a ceramic electrolyte.

8. The polymer electrolyte of claim 7 , wherein the ceramic electrolyte comprises a single material selected from the group consisting of a phosphate-based electrolyte selected from the group consisting of lithium phosphate, lithium titanium phosphate, lithium aluminum titanium phosphate, and lithium aluminum germanium phosphate; a sulfide-based electrolyte selected from the group consisting of SiS 2 (Li x Si y S z )-based glass, P 2 S 5 (Li x P y S z )-based glass, lithium germanium thiophosphate, and lithium phosphorus sulfide-based glass; lithium lanthanum titanate; lithium nitride; lithium lanthanum zirconate; and tantalum pentoxide, or a mixture of two or more thereof.

9. The polymer electrolyte of claim 2 , further comprising inorganic particles.

10. The polymer electrolyte of claim 9 , wherein the inorganic particles comprise a single material selected from the group consisting of Al 2 O 3 , BaTiO 3 , SnO 2 , CeO 2 , SiO 2 , TiO 2 , Li 3 PO 4 , NiO, ZnO, MgO, Mg(OH) 2 , CaO, ZrO 2 , Y 2 O 3 , Pb(Zr,Ti)O 3 , Pb 1-x La x Zr 1-y Ti y O 3 (where, 0<x<1 and 0<y<1), PB(Mg 3 Nb 2/3 )O 3 —PbTiO 3 , and hafnia, or a mixture of two or more thereof.

11. The polymer electrolyte of claim 2 , further comprising a plasticizer.

12. The polymer electrolyte of claim 11 , wherein the plasticizer comprises at least one compound of a carbonate-based compound, a lactone-based compound, an alkyl ether-based compound, an alkyl acetate-based compound, and an alkyl propionate-based compound.

13. A lithium secondary battery comprising:

a positive electrode;

a negative electrode; and

a polymer electrolyte formed on at least one surface of the positive electrode and the negative electrode,

wherein the polymer electrolyte comprises the polymer electrolyte for a secondary battery of claim 2 .

14. The lithium secondary battery of claim 13 , further selectively comprising a porous olefin-based separator between the positive electrode and the negative electrode.