LITHIUM ION SECONDARY BATTERY

摘要

Provided is a lithium ion secondary battery that includes a package housing a positive electrode, a negative electrode, a separator, and an electrolyte solution. In the lithium ion secondary battery: the package including a stack including a metal base material, an acid modified polypropylene layer, and a polypropylene layer stacked sequentially; the polypropylene layer forms an inner surface of the package; the package includes a heat-sealed portion and a non-sealed portion; and the thickness of one acid modified polypropylene layer included in the heat-sealed portion is smaller than a half of the thickness of the polypropylene layer included in the heat-sealed portion.