The present invention provides a secondary battery-use active material that allows for an improvement in thermal stability after charge and discharge are repeated. The secondary battery-use active material of the present invention includes a cathode active material that includes (A) a main phase and a sub-phase, (B) the main phase containing a first lithium compound represented by LiaNibMcAldOe (where M is an element such as cobalt, and 0.8 0, and (b+c+d)≤1), and (C) the sub-phase containing a second lithium compound that contains lithium, aluminum, and oxygen as constituent elements.