Provided is an exterior material for a
power storage device, the exterior material being formed from a laminate comprising at least a base material layer, a
barrier layer, and a thermally-fusible resin layer in this order from the outside, and the exterior material having a tensile strength at break of 180 MPa or greater as measured by the method below, and having a
creep resistance characteristic of 10 minutes or more as measured by the method below. <Measurement of tensile strength at break> Each tensile strength at break in the
machine direction (MD) of the exterior material for the
power storage device is measured by a method compliant with the provisions of JIS K7127:1999 by using a tensile tester. The measurement conditions are such that a
dumbbell 7 shape is used for a sample shape, the distance between target lines is 10 mm, the tensile speed is 0.5 mm / min, the test environment is set to a temperature of 120ºC, and the average value from three measurements is used. <Measurement of
creep resistance characteristic> The exterior material for a
power storage device is
cut out so as to have a width of 60 mm in the transverse direction (TD) and a length of 150 mm in the MD direction and is then folded in half such that the thermally-fusible resin layer is positioned at the inside. The folded exterior material is then heat sealed using a 7 mm heat seal bar at a position 10 mm from the fold such that the thickness of the thermally-fusible resin layer is in a range of 60-95% the thickness prior to sealing. The resulting heat-sealed exterior material for a power storage device is then
cut to a width of 15 mm to form a sample. Both of the mutually opposing ends of the sample are affixed to respective SUS plates (stainless
steel plates) by using an
adhesive, and a weight of 2 kg is applied to one side. The end on the opposite side is hung from the top of a thermostatic bath and stored in the thermostatic bath at 150ºC. The
creep resistance is evaluated using the time until the sealed part opens. The SUS plates that are used have a thickness of 2 mm, a width of 30 mm, a length of 100 mm, and a weight of 42.5 g, and one side of the SUS plates is S-shaped.