Using a positive electrode active material including spinel type manganese oxide as the main constituent, a novel low cost and high output power flat type nonaqueous secondary cell for HEVs that has increased safety at overcharge, and superior storage properties and cycle life is provided. A flat type nonaqueous secondary cell that has increased safety and is superior in storage and cycle properties even though the cell is a laminate type cell which does not have a blocking mechanism can be obtained by blending the spinel type lithium manganese oxide of the positive electrode and 5 wt % to 40 wt % of layered type lithium manganese oxide, to suppress storage deterioration at a high temperature and to simultaneously achieve safety when overcharged, and further, by adding a Li compound having a structure as shown in Formula (1) structure, to suppress deterioration of a mixed positive electrode active material during a high temperature cycle.