Secondary battery, method for manufacturing secondary battery, positive electrode active material, and method for manufacturing positive electrode active material

A method for manufacturing a lithium-ion secondary battery comprising a positive electrode comprising a positive electrode active material and a negative electrode, the method comprising the steps of:

• a first step of heating a first composite oxide comprising lithium and a transition metal;
• a second step of mixing the first composite oxide comprising the lithium and the transition metal with a magnesium source, a nickel source, and an aluminum source to form a first mixed solution;
• and
• a third step of performing heating after drying the first mixed solution to form a second composite oxide,
• wherein the magnesium source comprises an organometallic compound comprising magnesium,
• wherein the nickel source comprises an organometallic compound comprising nickel, and
• wherein the aluminum source comprises an organometallic compound comprising aluminum.

A method for manufacturing a positive electrode active material, comprising:

• forming a lithium composite oxide comprising nickel, cobalt, manganese, and a first additive element source;
• heating the lithium composite oxide;
• and
• adding a second additive element source to the heated lithium composite oxide,
• wherein the first additive element source and the second additive element source each comprise one or more selected from titanium, calcium, aluminum, zirconium, magnesium, and fluorine.