Positive electrode for secondary battery

1. A cathode for a secondary battery, comprising a combination of:

one or more selected from compounds represented by Formula 1; and

one or more selected from compounds represented by Formula 2,

x Li 2 MO 3 *(1 −x )LiM′O 2   (1)

(1 −u )LiFePO 4 *u C  (2)

wherein M is at least one element selected from the group consisting of Mn, Sn and Zr; M′ is at least one element selected from the group consisting of Ni, Mn and Co; 0<x<1 and 0<u<0.1; and u denotes a weight ratio,

wherein the compound represented by Formula 1 and the compound represented by Formula 2 are contained in a relative ratio by wight ranging from 7:3 to 9:1,

wherein phosphouous (P) sites in the compound represented by Formula 2 are doped with a stable material for a tetrahedral structure, and

wherein the stable material for a tetrahedral structure is one, two or more selected from the group consisting of Si, V and Ti.

2. The cathode according to claim 1 , wherein M comprises Mn.

3. The cathode according to claim 1 , wherein the cathode exhibits a potential plateau in the 4.4 to 4.6V region during initial charging.

4. The cathode according to claim 1 , wherein M, M′ and Fe in Formulae 1 and 2 are substituted with metals or non-metallic elements which have a 6-coordinate structure, in a predetermined substitution amount.

5. A secondary battery having the cathode as set forth in claim 1 .

6. A medium and/or large-scale battery pack including the lithium secondary battery according to claim 5 as a unit cell.

7. The cathode according to claim 1 , wherein the compound represented by Formula 1 is a composite having a layered structure or a solid solution.

8. The cathode according to claim 1 , wherein oxygen (O) ions in Formulas 1 and 2 are substituted with anions selected from the group consisting of F, Cl, Br, I, S, chalcogenide compounds and nitrogen in a substitution amount, and

wherein a substitution amount of the anions ranges from a mole ratio of 0.01 to 0.2.