A surface-treated steel sheet for a battery container includes a steel sheet, an iron-nickel diffusion layer formed on the steel sheet, and a nickel layer foamed on the iron-nickel diffusion layer and constituting the outermost layer. When the Fe intensity and the Ni intensity are continuously measured from the surface of the surface-treated steel sheet for a battery container along the depth direction with a high frequency glow discharge optical emission spectrometric analyzer, the thickness of the iron-nickel diffusion layer being the difference (D2−D1) between the depth (D1) at which the Fe intensity exhibits a first predetermined value and the depth (D2) at which the Ni intensity exhibits a second predetermined value is 0.04 to 0.31 μm; and the total amount of the nickel contained in the iron-nickel diffusion layer and the nickel contained in the nickel layer is 10.8 to 26.7 g/m2.

An energy storage apparatus includes a plurality of energy storage devices each including an electrode assembly and a container in which the electrode assembly is accommodated, the energy storage devices being disposed in a predetermined arrangement direction in a laminated manner. The plurality of energy storage devices includes a pair of first energy storage devices located at outermost ends in the arrangement direction and second energy storage devices located between the pair of first energy storage devices. Rigidity of the container of the first energy storage device is higher than rigidity of the container of the second energy storage device.

An energy storage apparatus includes a plurality of energy storage devices each including an electrode assembly and a container in which the electrode assembly is accommodated, the energy storage devices being disposed in a predetermined arrangement direction in a laminated manner. The plurality of energy storage devices includes a pair of first energy storage devices located at outermost ends in the arrangement direction and second energy storage devices located between the pair of first energy storage devices. Rigidity of the container of the first energy storage device is higher than rigidity of the container of the second energy storage device.

A polypropylene composition includes (A) a polypropylene, (B1) a first copolymer of ethylene and -olefin having a density of 0.891 to 0.912 g/cm.sup.3, and (B2) a second copolymer of ethylene and -olefin having a density in the range of 0.859 to 0.881 g/cm.sup.3, wherein the amount of (A) the polypropylene is in the range from 71 to 87 wt % based on the total amount of the polymer composition, and wherein the ratio between the amount of the (B2) second copolymer of ethylene and -olefin and the amount of the (B1) first copolymer of ethylene and -olefin is in the range from 3.8 to 1.0. The polypropylene composition has improved stress whitening resistance. A battery case including the polypropylene composition is also disclosed.

A packaging material for a power storage device includes a laminated material. The laminated material is composed of a metal foil layer, a substrate layer provided on an outer surface side of the metal foil layer, and a heat-fusible resin layer provided on an inner surface side of the metal foil layer. The heat-fusible resin layer is arranged on an inner surface side of the packaging material. The heat-fusible resin layer is formed of a polyolefin-based film. Martens hardness HMs of the heat-fusible resin layer measured with a Berkovich indenter is in a range of 15 N/mm.sup.2 to 25 N/mm.sup.2.

A packaging material for a power storage device includes a laminated material. The laminated material is composed of a metal foil layer, a substrate layer provided on an outer surface side of the metal foil layer, and a heat-fusible resin layer provided on an inner surface side of the metal foil layer. The heat-fusible resin layer is arranged on an inner surface side of the packaging material. The heat-fusible resin layer is formed of a polyolefin-based film. Martens hardness HMs of the heat-fusible resin layer measured with a Berkovich indenter is in a range of 15 N/mm.sup.2 to 25 N/mm.sup.2.

An electrochemical cell, preferably a secondary, rechargeable cell, including a casing comprised of a main body portion having opposed lower and upper open ends closed by respective lower and upper lids is described. The main body portion is composed of titanium Grades 5 or 23 having a relatively high electrical resistivity material while the lower and upper lids are composed of titanium Grades 1 or 2. The lids are preferably joined to the main body portion using laser welding. The combination of these differing titanium alloys provides a cell casing that effectively retards eddy current induced heating during cell recharging.

A surface-treated steel sheet for a battery container, including a steel sheet, an iron-nickel diffusion layer formed on the steel sheet, and a nickel layer formed on the iron-nickel diffusion layer and constituting the outermost layer, wherein when the Fe intensity and the Ni intensity are continuously measured from the surface of the surface-treated steel sheet for a battery container along the depth direction with a high frequency glow discharge optical emission spectrometric analyzer, the thickness of the iron-nickel diffusion layer being the difference between the depth at which the Fe intensity exhibits a first predetermined value and the depth at which the Ni intensity exhibits a second predetermined value is 0.04 to 0.31 m; and the total amount of the nickel contained in the iron-nickel diffusion layer and the nickel contained in the nickel layer is 10.8 to 26.7 g/m.sup.2.

The present invention provides a nickel-plated heat-treated steel sheet for a battery can (1), having a nickel layer with a nickel amount of 4.4 to 26.7 g/m.sup.2 on a steel sheet (11), wherein when the Fe intensity and the Ni intensity are continuously measured along the depth direction from the surface of the nickel-plated heat-treated steel sheet for a battery can, by using a high frequency glow discharge optical emission spectrometric analyzer, the difference (D2-D1) between the depth (D1) at which the Fe intensity exhibits a first predetermined value and the depth (D2) at which the Ni intensity exhibits a second predetermined value is less than 0.04 m.

A nickel-plated heat-treated steel sheet for a battery can, having a nickel layer with a nickel amount of 4.4 to 26.7 g/m.sup.2 on a steel sheet. When the Fe intensity and the Ni intensity are continuously measured along the depth direction from the surface of the nickel-plated heat-treated steel sheet for a battery can, by using a high frequency glow discharge optical emission spectrometric analyzer, the difference between the depth at which the Fe intensity exhibits a first predetermined value and the depth at which the Ni intensity exhibits a second predetermined value is less than 0.04 m.