POSITIVE ELECTRODE ACTIVE MATERIAL FOR SECONDARY BATTERY AND SECONDARY BATTERY USING THE SAME

Provided is a lithium ion positive electrode active material for a secondary battery that can realize a high operating voltage and a high capacity while suppressing capacity drop with cycles by using a low-cost material. A positive electrode active material for a secondary battery, which is a lithium manganese composite oxide represented by the following general formula (I) €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒLi a (M x Mn 2-x-y Y y )(O 4-w Z w )€ƒ€ƒ€ƒ€ƒ€ƒ(I) wherein in the formula (I), 0.5 ‰¤ x 1.2, 0 < y ‰¤ 0.3, 0 ‰¤ a ‰¤1.2, and 0 < w ‰¤ 1; M contains at least Fe and may further contain at least one selected from the group consisting of Ni, Cr and Cu other than Fe; Y is at least one selected from the group consisting of Li, Be, B, Na, Mg, Al, K, Ca, Ti and Si; and Z is at least one of F and Cl.