Polymer electrolyte and lithium secondary battery including the same

1. A polymer electrolyte having a multilayer structure comprising:

a first polymer layer to provide mechanical strength against external force; and

a second polymer layer to secure a conduction path for lithium ions,

wherein the first polymer layer comprises a first polymer matrix and an ionic salt-containing organic electrolyte in an amount ranging from 0 wt % to 60 wt %, based on a weight of the first polymer matrix, and

wherein the second polymer layer comprises a second polymer matrix and an ionic salt-containing organic electrolyte in an amount ranging from 60 wt % to 400 wt %, based on a weight of the second polymer matrix,

wherein the first and second polymer matrix are selected from the group consisting of a linear polymer having affinity with the organic electrolyte, a crosslinked polymer having a three-dimensional network structure, and combinations thereof, and

wherein the linear polymer is a polar non-crosslinked polymer.

2. The polymer electrolyte according to claim 1 , wherein the first polymer layer is disposed on an upper surface and/or a lower surface of the second polymer layer.

3. The polymer electrolyte according to claim 1 , wherein the second polymer layer is disposed on an upper surface and/or a lower surface of the first polymer layer.

4. The polymer electrolyte according to claim 1 , wherein the ionic salt is a lithium salt.

5. The polymer electrolyte according to claim 1 , wherein each of the first and second polymer layers has a tensile strength of 1 MPa to 100 MPa.

6. The polymer electrolyte according to claim 1 , wherein each of the first and second polymer layers has an elongation percentage of 20% to 500%.

7. The polymer electrolyte according to claim 1 , wherein an amount of the ionic salt-containing organic electrolyte in the first polymer layer ranges from 0.1 wt % to 60 wt %, based on the weight of the first polymer matrix.

8. The polymer electrolyte according to claim 1 , wherein each of the first and second polymer layers has an ionic conductivity ranging from 10-5 S/cm to 10-3 S/cm.

9. The polymer electrolyte according to claim 1 , wherein a weight ratio of the linear polymer to the crosslinked polymer is 1:9 to 8:2.

10. The polymer electrolyte according to claim 1 , wherein the first and second polymer matrix comprises both a polyoxide-based non-crosslinked polymer and a polar non-crosslinked polymer.

11. The polymer electrolyte according to claim 1 , wherein the cross-linked polymer is a polymer of monomers having at least two functional groups, or a copolymer of monomers having at least two functional groups and polar monomers having a single functional group.

12. The polymer electrolyte according to claim 1 , wherein each of the first and second polymer layers further comprises a solid phase component providing mechanical strength.

13. The polymer electrolyte according to claim 12 , wherein an amount of the solid phase component in the first polymer layer ranges from 5 wt % to 80 wt %, based on the weight of the first polymer matrix, and

wherein an amount of the solid phase component in the second polymer layer ranges from 5 wt % to 80 wt %, based on the weight of the second polymer matrix.

14. The polymer electrolyte according to claim 12 , wherein the solid phase component is a solid compound having no reactivity with lithium ions, the solid compound comprising solid phase particles having an average particle diameter of 10 nm to 5 μm.

15. The polymer electrolyte according to claim 14 , wherein the solid compound is at least one selected from the group consisting of an oxide, a nitride, and a carbide that have no reactivity with lithium ions.

16. The polymer electrolyte according to claim 1 , wherein a thickness of the first polymer layer arranges from 10% to 100% based on a thickness of the second polymer layer.

17. An electrode assembly including a cathode, an anode, and the polymer electrolyte according to claim 1 disposed between the cathode and the anode.

18. A lithium secondary battery comprising the electrode assembly according to claim 17 .

19. A battery module comprising the lithium secondary battery according to claim 18 as a unit battery.

20. A battery pack comprising the battery module according to claim 19 .

21. A medium or large-scale device comprising the battery pack according to claim 20 as a power source.

22. The medium or large-scale device according to claim 21 , wherein the medium or large-scale device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for storing power.