A lithium-ion battery outer package material, provided with: a base layer, and a first adhesive layer, a metallic foil layer, a corrosion prevention treatment layer, a second adhesive layer, and a sealant layer sequentially layered on one of the surfaces of the base layer. When a tensile test (a sample of the substrate layer is stored for 24 hours in a 23° C. and 40% RH environment; a tensile test is subsequently performed in a 23° C. and 40% RH environment with the specimen width being 15 mm, the distance between gauge points being 50 mm, and the tensile speed being 100 mm/min; and the tensile elongation and tensile stress of the specimen are measured) is performed, the tensile elongation in a first direction, which is either the TD direction or the MD direction of the sample, relative to the length of the sample is from about not less than 50% to less than 80%, and the tensile stress in a second direction, which is perpendicular to the first direction, is from about not less than 150 to 230 MPa.