Abstract: A positive electrode active material having a high charge-discharge capacity and high safety and a secondary battery including the positive electrode active material are provided. The positive electrode active material includes lithium, a transition metal M, an additive element, and oxygen. The powder volume resistivity of the positive electrode active material is higher than or equal to 1.0×105 ?·cm at a temperature of higher than or equal to 180° C. and lower than or equal to 200° C. and at a pressure of higher than or equal to 0.3 MPa and lower than or equal to 2 MPa. The median diameter of the positive electrode active material is preferably greater than or equal to 3 ?m and less than or equal to 10 ?m.

Abstract: A positive electrode and a secondary battery with little deterioration due to charge and discharge are provided. A positive electrode and a secondary battery with high electrode density are provided. Alternatively, a positive electrode and a secondary battery with excellent rate characteristics are provided. The positive electrode contains a positive electrode active material and a coating material. The coating material covers at least part of a surface of the positive electrode active material, and the positive electrode active material contains lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel. The lithium cobalt oxide includes a region with the highest concentration of one or more selected from the magnesium, the fluorine, and the aluminum in a surface portion. The coating material is preferably one or more selected from glass, carbon black, graphene, and a graphene compound.

Abstract: A positive electrode active material that is stable in a high potential state or a high temperature state and a highly safe secondary battery are provided. The positive electrode includes a first material and a second material and includes a region where at least part of a surface of the first material is covered with the second material. The first material includes a lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel. The second material includes a composite oxide (containing one or more selected from Fe, Ni, Co, and Mn) having an olivine crystal structure.