Production process for composite oxide, positive-electrode active material for lithium-ion secondary battery and lithium-ion secondary battery

A production process for composite oxide being characterized in that:

• it is a production process for composite oxide being expressed by a compositional formula:
• LiMn1-xAxO2, where “A” is one or more kinds of metallic elements other than Mn;
• 0≦“x”<1;
• and an averaged oxidation number of Mn falls in a range of from 2.8 to 3.2;
• said composite oxide is obtained via the following:
• a raw-material mixture preparation step of preparing a raw-material mixture by mixing a metallic-compound raw material and a molten-salt raw material with each other,
• the metallic-compound raw material at least including an Mn-containing nitrate that includes one or more kinds of metallic elements in which Mn is essential,
• the molten-salt raw material including lithium hydroxide and lithium nitrate, and exhibiting a proportion of the lithium nitrate with respect to the lithium hydroxide, Lithium Nitrate/Lithium Hydroxide, that falls in a range of from 1.2 to 3 by molar ratio;
• a molten reaction step of reacting said raw-material mixture at 500° C. or less by melting it;
• and
• a recovery step of recovering said composite oxide being generated from said raw-material mixture that has undergone the reaction,
• wherein the molten-salt raw material does not include lithium peroxide;
• and
• said composite oxide has a crystal structure belonging to an orthorhombic-system space group.