US Patent 7981546 Non-aqueous electrolyte secondary battery

A lithium-containing composite oxide represented by the formula 1: LixNi1-y-z-v-wCoyAlzM1vM2wO2 is used as a positive electrode active material for a non-aqueous electrolyte secondary battery. The element M1 is at least one selected from the group consisting of Mn, Ti, Y, Nb, Mo, and W. The element M2 includes at least two selected from the group consisting of Mg, Ca, Sr, and Ba, and the element M2 includes at least Mg and Ca. The formula 1 satisfies 0.97≦x≦1.1, 0.05≦y≦0.35, 0.005≦z≦0.1, 0.0001≦v≦0.05, and 0.0001≦w≦0.05. The primary particles have a mean particle size of 0.1 μm or more and 3 μm or less, and the secondary particles have a mean particle size of 8 μm or more and 20 μm or less.