Active material composite, method for producing same, positive electrode active material for nonaqueous electrolyte secondary batteries, and nonaquoeus electrolyte secondary battery

This positive electrode active material for nonaqueous electrolyte secondary batteries is obtained by bonding active material particles, which are formed of an active material and have an average particle diameter of 100 nm or less, and conductive particles, which are formed of a conductive material and have an average particle diameter of 100 nm or less, with each other. This positive electrode active material for nonaqueous electrolyte secondary batteries has a specific surface area of 150 m 2 /g or more.