Abstract: Cycle performance is improved without degrading initial efficiency of a non-aqueous electrolyte secondary battery that includes a positive electrode, a negative electrode, a non-aqueous electrolyte containing a solute and a solvent, the positive electrode including a positive electrode active material made of a lithium-containing transition metal oxide that contains lithium and cobalt and has a layered structure. The lithium-containing transition metal oxide is at least partially covered with a surface-treatment layer containing a phosphate compound represented by the chemical formula M1POk, where M1 is at least one element that can have a valency of 3 and k is an integer in a range of 2 to 4, and the lithium-containing transition metal oxide contains a group IVA element M2 and a group IIA element M3 of the periodic table.