NOVELTY - A positive electrode active material (31a) comprises: 1) lithium nickel cobalt manganese oxide; and at least one type of a lithium ion acceptance capacity adjustment compound selected from: 2a) lithium vanadium composite oxide, vanadium oxide, lithium vanadium phosphate, and lithium vanadium fluorophosphates; and 2b) e.g. niobium oxide, titanium oxide, tungsten oxide, molybdenum oxide, and iron oxide.    USE - As positive electrode active material used in a lithium ion electric storage device (claimed) such as lithium ion secondary battery and lithium ion capacitor used in electric vehicles and electric devices.    ADVANTAGE - The present positive electrode active material has increased lithium ion acceptance capacity, hence fire and overheating can be suppressed when a short circuit occurs in an electric storage device using the material, and thus provides a superior degree of safety to the device due to the low possibility of fire and overheating. Moreover, the device comprising the material exhibits superior typical electric storage device characteristics such as required power and durability; and the electric storage device obtained using this positive electrode material is highly suitable for installation in means of transportation intended to travel safely using clean energy, such as an electric vehicle or a hybrid vehicle, and other electric devices.    DETAILED DESCRIPTION - A positive electrode active material (31a) comprises: 1) lithium nickel cobalt manganese oxide; and at least one type of a lithium ion acceptance capacity adjustment compound selected from: 2a) lithium vanadium composite oxide, vanadium oxide, lithium vanadium phosphate, and lithium vanadium fluorophosphates; and 2b) niobium oxide (Nb2O5), titanium oxide (TiO2), Li3/4Ti5/3O4, tungsten oxide (WO2), molybdenum oxide (MoO2), and iron oxide (Fe2O3). INDEPENDENT CLAIMS are included for the following:    (1) a lithium ion electric storage device (30) comprising the positive electrode active material (31a); and    (2) manufacturing the lithium ion electric storage device, involving: obtaining a positive electrode composite material by dispersing a mixture containing the positive electrode active material and a binder in a solvent; coating a positive electrode collector (31b) with the positive electrode composite material; and drying the positive electrode composite material.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic sectional view of a lithium ion secondary battery.    Lithium ion secondary battery (30)    Positive electrode (31)    Positive electrode composite material layer (31a)    Positive electrode collector (31b)    Negative electrode (32)    Positive electrode terminal (36)