SECONDARY BATTERY

A secondary battery that achieves higher conductivity of a positive electrode and has higher capacity is provided. The secondary battery includes a positive electrode that includes a positive electrode active material, a first conductive material, and a second conductive material whose shape is different from that of the first conductive material. The positive electrode active material includes lithium cobalt oxide containing magnesium in its surface portion. The weight of the second conductive material is lower than or equal to the weight of the first conductive material. The second conductive material forms an assembly and has a portion sticking to the positive electrode active material.