TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The sub crystalline phase: has a crystal structure (which is a tetragonal crystal or an orthorhombic crystal) or a spinel structure, and a crystallinity which is detectable by diffractometry; includes a representative element and manganese (zinc and manganese); has a composition of zinc and manganese at a ratio (Mn/Zn) greater than or equal to 2 and less than 4; and has a thickness of 1-100 nm. In the cathode active material, an intermediate phase is present at an interface between the main crystalline phase and the sub crystalline phase. The intermediate phase includes at least a part of an element of the main crystalline phase and at least a part of an element of the sub crystalline phase. The cathode active material has an overall composition (including the main crystalline phase and the sub crystalline phase) of lithium metal oxide complex of formula (Li1-xM12-2xM2xM32xO4-y). The lithium-containing transition metal oxide: contains only manganese as a transition metal; and has a lattice constant of 8.22-8.25 Angstrom . The sub crystalline phase and the main crystalline phase part are formed in a manner so that a 011 plane of the main crystalline phase part and a 001 plane of the sub crystalline phase are adjacent to each other.x = 0.01-0.1;M1 = Mn and/or at least one transition metal element other than Mn;M2, M3 = at least one representative metal element or at least one transition metal element, where M1, M2, and M3 are different from one another; andy = a value which satisfies electrical neutrality with x. EXAMPLE - Zinc oxide and tin oxide (IV) were weighed at a molar ratio of 2:1, and mixed for 5 hours in an automated mortar. The mixture was then baked at 1000 degrees C for 12 hours in an air atmosphere to obtain a baked product. The baked product was crushed and mixed in an automated mortar for 5 hours to obtain a spinel-type compound. Lithium carbonate and electrolytic manganese dioxide were weighed at a molar ratio of 1:2, and the spinel-type compound was weighed so that the spinel-type compound and the main crystalline phase would achieve x = 0.05 in the lithium metal oxide complex formula (Li1-xM12-2xM2xM32xO4-y). The lithium carbonate, the electrolytic manganese dioxide and the spinel type compound were mixed with one another in an automated mortar for 5 hours, and then pre-baked at 550 degrees C for 12 hours in an air atmosphere (pre-baking step) to obtain a baked product, which was then crushed and mixed in an automated mortar for 5 hours to obtain a powder. The powder was molded into a pellet shape and then baked at 800 degrees C for 12 hours in an air atmosphere (baking step). The resulting baked product was next crushed and mixed in an automated mortar for 5 hours to obtain a cathode active material.