| abstract |
An active material for a lithium secondary battery capable of increasing a discharge capacity in a potential region of 4.3 V or less is provided. 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 the composition ratio of Li, Co, Ni and Mn contained in the solid solution is , Li 1+ (1/3) x Co 1-xy Ni (1/2) y Mn (2/3) x + (1/2) y (x + y ≦ 1, 0 ≦ y, 1-xy = z), Li [Li 1/3 Mn 2/3 ] O 2 (x) -LiNi 1/2 Mn 1/2 O 2 (y) -LiCoO 2 (z) In the triangular phase diagram, (x, y, z) are point H (0.6, 0.4, 0), point I (0.67, 0.13, 0.2), point J (0.7, 0, 0.3) and It is represented by a value in a range existing on or inside a quadrilateral HIJK with the point K (0.55, 0.05, 0.4) as a vertex. [Selection] Figure 1 |