Flexible battery and flexible electronic device including the same

1. A flexible battery comprising:

a cell stack comprising a plurality of unit cells;

an external casing sealing the cell stack, and

a first electrolyte,

wherein each of the unit cells comprises:

a negative electrode,

a positive electrode,

an electrolyte layer comprising a second electrolyte disposed between the negative electrode and the positive electrode, and

a first polymer film surrounding the negative electrode, the positive electrode, and the electrolyte layer,

wherein the plurality of unit cells are in sliding contact with each other, and

wherein the first electrolyte is contained in a space which is external to the unit cells and in the external casing.

2. The flexible battery of claim 1 , wherein at least one portion of the unit cells facing the external casing is free of the external casing.

3. The flexible battery of claim 1 , wherein the external casing is a moisture-proof multi-layered film comprising a second polymer film and a metal layer.

4. The flexible battery of claim 1 , wherein:

the negative electrode further comprises a negative current collector and a negative active material layer disposed on a surface of the negative current collector, and

the positive electrode further comprises a positive current collector and a positive active material layer disposed on a surface of the positive current collector.

5. The flexible battery of claim 4 , wherein:

the negative current collector is at least one metal selected from the group consisting of copper (Cu), stainless steel, nickel (Ni), aluminum (Al), and titanium (Ti), and

the positive current collector is at lest one metal selected from the group consisting of aluminum (Al), stainless steel, titanium (Ti), copper (Cu), and silver (Ag).

6. The flexible battery of claim 4 , wherein the negative current collector and the positive current collector contact the first polymer film.

7. The flexible battery of claim 4 , further comprising terminal wires electrically connecting the plurality of unit cells in series, wherein the terminal wires extend out of the external casing.

8. The flexible battery of claim 4 , further comprising terminal wires electrically connecting the plurality of unit cells in parallel, wherein the terminal wires extend out of the external casing.

9. The flexible battery of claim 1 , wherein the flexible battery comprises a lithium secondary battery.

10. The flexible battery of claim 1 , wherein:

each of the unit cells is respectively sealed by the first polymer film,

terminal wires contact at least one of the positive electrode and negative electrode of each of the unit cells, and

the terminal wires extend out of the external casing.

11. The flexible battery of claim 1 , wherein the internal pressure of the flexible battery is the same as the surrounding air pressure.

12. The flexible battery of claim 1 , further comprising a separator between the negative electrode and the positive electrode.

13. The flexible battery of claim 12 , wherein the first polymer film is at least partially adhered to the separator.

14. The flexible battery of claim 1 , wherein the first polymer film has a thickness in the range of about 1 to about 50 μm.

15. The flexible battery of claim 1 , wherein the first polymer film comprises a thermoplastic resin having a melting point in the range of about 70 to about 200 ° C.

16. The flexible battery of claim 15 , wherein the first polymer film further comprises an elongated film.

17. The flexible battery of claim 15 , wherein the first polymer film comprises a Polypropylene resin.

18. The flexible battery of claim 1 , wherein the first polymer film is laminated on the surface of at least one of the negative electrode and the positive electrode.

19. A flexible electronic device comprising a flexible battery as a power source according to claim 1 .