| abstract |
The present invention provides a positive electrode active material capable of realizing high thermal stability at low cost. A positive electrode active material for a lithium ion secondary battery, etc., comprising a lithium-nickel composite oxide having a layered structure of a hexagonal crystal system and composed of secondary particles formed by agglomeration of a plurality of primary particles, a lithium-nickel composite oxide It contains lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb) and any element M1, and the ratio of the material amount of each of the above elements is Li:Ni:Mn:M:Ti: Nb=a: (1‑x1‑y1‑b‑c): x1: y1: b: c (wherein, 0.95≤a≤1.25, (1‑x1‑y1‑b‑c)＜0.80, 0.03≤x1≤ 0.35, 0≤y1≤0.35, 0.005≤b≤0.05, 0.001＜c≤0.03) means that, in the ratio of substance mass, satisfying (b+c)≤0.06 and b>c, the lithium dissolved in water when immersed in water The amount is 0.07 mass % or less with respect to the whole positive electrode active material. |