POSITIVE ELECTRODE ACTIVE MATERIAL FOR ALL-SOLID-STATE LITHIUM ION SECONDARY BATTERY AND METHOD FOR MANUFACTURING THE SAME

An object is to provide a positive electrode active material having improved charging and discharging cycle characteristics in an all-solid-state battery. A positive electrode active material for an all-solid-state lithium ion secondary battery, including: lithium-nickel composite oxide particles; and coating layers, wherein the lithium-nickel composite oxide particles have a crystal structure belonging to a space group R-m, and contain Li, Ni, Mn, and an element M, a mole number ratio among elements being represented by Li:Ni:Mn:M=a:(1−x−y):x:y (0.95≤a≤1.10, 0