POSITIVE ELECTRODE ACTIVE MATERIAL FOR NONAQUEOUS ELECTROLYTE SECONDARY BATTERY AND NONAQUEOUS ELECTROLYTE SECONDARY BATTERY

A positive electrode active material for a nonaqueous electrolyte secondary battery, the positive electrode active material comprising a Ni-containing lithium composite oxide a, b, wherein the Ni-containing lithium composite oxide a has an average primary particle size of 1 μm or more which is larger than the average primary particle size of the Ni-containing lithium composite oxide b, the Ni-containing lithium composite oxide a has an average secondary particle size of 2 to 6 μm, the Ni-containing lithium composite oxide b has an average primary particle size of 0.05 μm or more and an average secondary particle size of 10 to 20 μm, the Ni-containing lithium composite oxide a contains Mn and at least one of B and Al, the Ni-containing lithium composite oxide b contains Mn, and the ratio of the Ni-containing lithium composite oxide a to the Ni-containing lithium composite oxide b is 5:95 to 55:45.