Packaging material for lithium ion battery

A packaging material for a lithium ion battery, comprising:

• at least a first adhesive layer, a metal foil layer, a corrosion prevention-treated layer, a second adhesive layer, and a sealant layer which are sequentially laminated on one surface of a base material layer, wherein
• a thickness of the base material layer is 15 to 40 mm,
• when performing stretching according to the following stretching method in such a manner that an amount of elongation of a test specimen becomes 5 mm, adhesivity between the base material layer and the metal foil layer is 5 N or less in the following adhesivity test,
• when performing the stretching according to the following stretching method in such a manner that the amount of elongation of the test specimen becomes 10 mm, the adhesivity between the base material layer and the metal foil layer is 2 N or more in the following adhesivity test,
• the stretching method includes:
• cutting the test specimen from the packaging material for a lithium ion battery to have a sample width of 6 mm;
• mounting the test specimen on chucks of a stretching machine with a distance between the chucks set to 10 mm;
• and
• stretching the test specimen at a stretching rate of 300 mm/minute, and
• the adhesivity test includes:
• forming a notch between the base material layer and the metal foil layer of the test specimen stretched by the stretching method;
• gripping the base material layer and a laminated portion from the metal foil layer to the sealant layer, respectively;
• T-type peeling the test specimen, which is stretched in the stretching method, under a condition of a peeling rate of 30 mm/minute;
• and
• measuring adhesivity thereof.