Abstract: According to the present invention, a lithium ion battery outer cover material that has superior resistance to electrolytes without chromate treatment, has superior deep drawing formability and high quality, and can be produced easily is provided. The lithium ion battery outer cover material (1) of a first embodiment of the present invention has a base material layer (11), first adhesive layer (12) containing an adhesive, aluminum foil layer (13), corrosion prevention treated layer (14), second adhesive layer (15) containing an adhesive or adhesive resin, and sealant layer (16) laminated in that order. The base material layer (11) is a film base material in which the difference (?2??1) of the elasticity (?1) to the yield point and the elasticity (?2) to the rupture point as measured according to JIS-K7127 is 100% or greater in at least one of the MD direction and TD direction.