Patent ID: 8551659

Claim:
An active material for a lithium secondary battery comprising: a solid solution of a lithium transition metal composite oxide having an α-NaFeO 2 -type crystal structure, wherein a composition ratio of Li, Co, Ni, and Mn contained in the solid solution satisfies Li 1+(1/3)x Co 1-x-y Ni (1/2)y Mn (2/3)x+(1/2)y where x+y≦1, 0≦y and 1−x−y=z; in an Li[Li 1/3 Mn 2/3 ]O 2 (x)-LiNi 1/2 Mn 1/2 O 2 (y)-LiCoO 2 (z) type ternary phase diagram, (x, y, z) is represented by values in a range present on or within a line of a heptagon (ABCDEFG) defined by vertexes; point A(0.45, 0.55, 0), point B(0.63, 0.37, 0), point C(0.7, 0.25, 0.05), point D(0.67, 0.18, 0.15), point E(0.75, 0, 0.25), point F(0.55, 0, 0.45), and point G(0.45, 0.2, 0.35); and an intensity ratio between diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry before charge-discharge is I (003) /I (104) ≧1.56 and at an end of discharge is I (003) /I (104) >1.