Cable-type secondary battery

1. A cable-type secondary battery which comprises:

a cable-type electrode assembly comprising an inner electrode and a separation layer surrounding the outer surface of the inner electrode to prevent a short-circuit between electrodes; and

a sheet-form outer electrode helically surrounding the outer surface of the cable-type electrode assembly, and satisfies the mathematical formula of C>W (wherein C is the circumference of the section perpendicular to the longitudinal direction of the cable-type electrode assembly, and W is the width of the sheet-form outer electrode),

wherein the sheet-form outer electrode comprises an outer current collector and an outer electrode active material layer integrally formed on one surface of the outer current collector, such that the outer current collector and the outer electrode active material layer together helically surround the outer surface of the cable-type electrode assembly.

2. The cable-type secondary battery according to claim 1 , wherein the sheet-form outer electrode has a strip structure extended in one direction.

3. The cable-type secondary battery according to claim 1 , wherein the sheet-form outer electrode further comprises a porous first supporting layer formed on the outer electrode active material layer.

4. The cable-type secondary battery according to claim 3 , which further comprises a porous coating layer comprising a mixture of inorganic particles and a binder polymer, on the first supporting layer.

5. The cable-type secondary battery according to claim 1 , wherein the sheet-form outer electrode further comprises a second supporting layer formed on the other surface of the outer current collector.

6. The cable-type secondary battery according to claim 1 , wherein the inner electrode is provided with at least one inner current collector and an inner electrode active material layer formed on the surface of the inner current collector.

7. The cable-type secondary battery according to claim 6 , wherein the inner current collector further comprises a primer coating layer including a conductive material and a binder.

8. The cable-type secondary battery according to claim 6 , wherein the inner electrode comprises the inner electrode active material layer formed on the whole surface of the inner current collector, or the inner electrode active material layer formed to surround the outer surface of the inner current collector on which it is wound.

9. The cable-type secondary battery according to claim 1 , wherein the inner electrode has a hollow structure having a space therein.

10. The cable-type secondary battery according to claim 9 , wherein the inner electrode comprises at least one helically wound wire-form inner current collector or at least one helically wound sheet-form inner current collector.

11. The cable-type secondary battery according to claim 9 , wherein an inner electrode current collector core portion, a lithium ion supplying core portion including an electrolyte or a filler core portion is formed in the space formed in the inner electrode.

12. The cable-type secondary battery according to claim 1 , wherein the inner electrode is a negative electrode or positive electrode, and the outer electrode is a positive electrode or negative electrode corresponding thereto.

13. The cable-type secondary battery according to claim 1 , which further comprises a protective coating formed to surround the outer surface of the sheet-form outer electrode.

14. The cable-type secondary battery according to claim 1 , wherein the cable-type electrode assembly comprises at least two inner electrodes disposed in parallel with each other, and a separation layer surrounding the outer surfaces of the inner electrodes to prevent a short-circuit between electrodes.