The lithium ion secondary battery is a secondary battery in which a positive electrode 30 and a negative electrode 40 are stacked alternatively via a separator 25, wherein the separator 25 is a single layer and is not melted or softened at least 200° C., a thermal shrinkage ratio of the separator being 3% or below, wherein an insulating layer 70 is formed on a surface of the positive electrode 30, the surface facing to the separator 25.